Page 1

Hippocampal Neurogenesis Forgetting and the Effects of Exercise, Aging, and Stress on Memory - PG77 The impact of

Social Defeat Stress on behavior and the Dopaminergic system PG224

Erasing Fear Memories - Is It Possible? PG178


Table of Contents Yasmine Abdelaal - The Potential Therapeutic Impact of an Enriched Environment on Animal Models of Post-Traumatic Stress Disorder - pg 2

Sonja Ing - A novel pharmacogenetic approach: Transient neuronal activation through TRPV1 and capsaicin - pg 116

Padmesh Ramanujam - Reviewing glutamate mediated excitotoxicity in miR-1000 Drosophila mutants - pg 219

Adeoluwa Adesina - Nanoparticle Drug Delivery and its many Benefits compared to Conventional Methods - pg 8

Sylvia Jennings - Differential Brain Activation in Sommeliers: Effects of expertise on flavour integration - pg 121

Joravir Riar - The impact of Social Defeat Stress on behavior and the Dopaminergic system - pg 224

Ashima Agarwal - Oxytocin enhances social bonding, an effect moderated by baseline individual differences in socio-emotional factors including empathy - pg 11

Nimara Dias - Modeling and Treatment of Familial Parkinson’s Disease Using iPSCs - pg 124

Ariba Alam - Increased Phosphorylation of CREB at Ser133 in the Dentate Gyrus Reverses Depressive Behavior in Rodents - pg 16 Samin Alikhanzadeh - The rate of increase in adult hippocampal neurogenesis and spatial learning in C57BL/6J mice is greater in response to voluntary exercise than in response to sensory stimuli manipulations - pg 21 Mie Andersen - subPCP induced alterations in gut microbiota associated with memory deficit in schizophrenia model - pg 26 Ami Baba - Environmental Enrichment: A Neurorehabiitation Method utilized to treat deficits conferred from Traumatic Brain Injury (TBI) - pg 30 Vanessa C. Bracaglia - Creatine Supplementation on brain performance suggestive of potential therapeutic agent - pg 34 Alana Brown - The Neural Mechanisms of SocioSexual Partner Preference - pg 37 Megan E. Cabral - Impact of KIBRA Polymorphism On The Hippocampus - pg 41 Sammy Cai - α5GABAA Receptors Mediate Inflammation-Induced Memory Deficits in the Hippocampus - pg 44 Qasid Chaudhry - Evaluating syanpto-protection in a three compartmented microfluidic chip model following a chemically induced axotomy. - pg 49 Chun-Chi Chu - Potential link between intestinal microbiota and anxiety - pg 54 Melissa Colaluca - Elevations in the Serum Levels of the Brain Derived Neurotrophic Factor during Aerobic Physical Activity - A Simple, yet Often Disregarded Remedy for Frontotemporal Dementia - pg 57 Erica Confreda - High fat diet intake is related to impaired hippocampal dependent memory in juvenile rats - pg 63 Akua Obeng-Dei - Caffeine prevents memory consolidation impairments associated with sleep deprivation - pg 66 Daniel Derkach - Conflicting or Corroborating Evidence? Interleukin-6 and the JAK-STAT Signaling Pathway in Neural Precursor Self-Renewal - pg 70 Rachel Duncan - Trans-Cranial Direct Stimulation: A device for out of the box thinking - pg 74 Saadia Esat - Hippocampal Neurogenesis, Forgetting and the Effects of Exercise, Aging, and Stress on Memory - pg 77 Vanessa Ferlaino - Deep brain stimulation and Alzheimer’s disease: Benefits, cost-effectiveness and feasibility of deep brain stimulation on Alzheimer’s disease and cognitive dysfunction. - pg 80 Floriana Ferri - The Efficacy of Neurofeedback Training as a Treatment for Attention-Deficit Hyperactivity Disorder - pg 85 Chantel George - Review of Intentional and Incidental forgetting - pg 89 Jessica Gosio - The Novel Role of mTOR-Dependent Macroautophagy in Autism Spectrum Disorder - pg 95 Man Lai Ho - The pivotal role of TNF-α in inducing cognitive dysfunction - pg 100 Patrick Hopper - AKAP150 Underlies Deficits Seen in Spatial Memory Following Short-Term Sleep Deprivation - pg 103 Patrick Hornlimann - Maternal Behavior Hormone Receptor might be a crucial player in the development of social and mood disorders - pg 107 Justin Huang - Consolidation of Memories Following Sleep is the Result of Synaptic Potentiation - pg 111

Xin Yue Kou - To accomplish more or loss less: the story of sleep deprivation and Alzheimer’s disease - pg 128 Alexandra Kubica - Reconsolidation and Extinction Are Dissociable and Mutually Exclusive Processes: Behavioral and Molecular Evidence The Importance of Specificity in Neuroscience - pg 131 Shikha Kuthiala - The Effects Of Kynurenic Acid On The Brain And Its Implications In Schizophrenia - pg 134 Soonji Kwon - Selectively Activating Endogenous A3 Receptors is The New Therapeutic Solution to Chronic Pain - pg 139 Shonali Lakhani - Working memory training is most effective in healthy young adults to improve cognitive skills - pg 142 Dong-Eun Lee - Neural Correlates of Artistic Imagination through the Visual Modality - pg 146 Victor Lee - Overcoming social difficulties with the help of medications - pg 151 Ella Lew - Role of mu-opioid receptors in stress affecting vulnerability to substance abuse - pg 155 Vivian Liu - Seeking Autism-Linked Performance Within the Synaptic World: Effect of Neurexins and Related Proteins - pg 158 Yi Xuan Li - Effects of systems consolidation, optogenetic inhibition, and adult neurogenesis in hippocampal memory traces - pg 163 Ziteng Li - Adult hippocampal neurogenesis and its role in Alzheimer’s disease in transgenic mice models - pg 166 Bernie Longange - Improved cognitive function through the elucidation of alcoholically induced changes in the brain - pg 170 Tong Mai - Down-Regulation of Amyloid-Beta Peptide Binding P75 in Basal Forebrain Cholinergic Neurons Rescued Neurodegeneration and Behavioral Deficits in AD Mouse Models - pg 173 Fazila Malek - Discovering Biomarkers to Detect Early Onset of Stroke - pg 175 Divya Mamootil - Erasing Fear Memories– Is it possible? - pg 178 Catherine B. Matolcsy1 - Bridging the Gap in Traumatic Brain Injury: The promise of the Collagen Matrix - pg 181 Lucy McPhee - The potential for epigenetic treatment of neuropsychological disorders. - pg 185 Amaara Mohammed - Distinguishing the neurobiological features of resilient cognition in Alzheimer’s Disease. - pg 188 Arinda Muntean - Musical experience enhances cognitive performance among the aging population - pg 191 Jena L. Niceforo - Visualizing anxiety through mGlu7 receptor immunocytochemistry - pg 195 Yuki Nishimura - The Next Step in Antidepressant Therapy: BDNF Oscillation Patterns as a Potential Early Predictor for Therapy Response - pg 198 Miranda Nong - Further Insight on Using Mean Diffusivity as a Potential Biomarker to Identify Mild Cognitive Impairment Converters to Alzheimer’s Disease - pg 201 Daria Pacurariu - Don’t Stress About it: 5HTT Genotype and Epigenetics - pg 204 Hyun Park - Chronic Sleep Deprivation is Enough Induce Neuronal Degeneration - pg 207 Hemish Patel - Can Neurogenesis Using Stem Cells Be the Key to Post-Stroke Functional Recovery? A Review of Neurogenesis and Stroke Recovery in Animal Models - pg 211 Maryna Pilkiw - Lateral entorhinal cortex encodes associations of past experience and location - pg 215

Ashkan Salehi - An investigation of the facilitative effects of exercise on learning and memory - pg 227 Husain Shakil - Brain Inflammation, A Link Between Obesity and Cognitive Deficits - pg 231 Arman Shekari - The role of cAMP in mediating hippocampal-dependent spatial memory loss following periods of acute sleep deprivation - pg 235 Jaclin Simonetta - Treating Alzheimer’s Disease with Magnetic Resonance Imaging-Guided Focused Ultrasound - pg 239 Olivia Singh - Novel Metabotropic Function of NMDARs in Alzheimer’s Disease - pg 243 Pranay Siriya - Dopamine D1/D5 Receptor mediated tLTP Pathway in the Dentate Gyrus and Implications in Spatially-Dependent Learning and Memory - pg 247 Stephanie Strug - Suppression of α-syn in Mice Model of Human Lewy Body Disorders Reverses Detrimental Effects of α-syn Accumulation - pg 251 Ola Taji - A reserve pool of glutamate receptors is required for LTP - pg 254 Daniel Takla - Demyelination: Prevention and Restoration - pg 258 Eugene C. Tang - Study Shows How Transcranial Magnetic Stimulation Changes Depressed Brains - pg 261 Lauren Tessier - PPARδ: New Target for Alzheimer’s Pharmacotherapy? - pg 264 Carmen Tu - Temporal-Spatial Disconnect of Tauopathy and Amyloidopathy in Alzheimer’s Disease - pg 268 Madli Vahtra - Neuregulin 1-ErbB4 Signaling and Reduced Activity in NMDA Receptors: A Molecular Pathway for the Development of Schizophrenia and a Potential Target for Future Antipsychotics - pg 272 Chuqi Sandy Wang1 - Amygdala Dependent Retroactive Consolidation of Episodic Memories - pg 275 Ting Ting Wang - Gene Down-Regulations and Neuronal Implications of Adderall Induction of the Developing Brain - pg 278 Vonny Wong - Chronic Coffee and Caffeine Ingestion Effects on the Cognitive Function and Antioxidant System of Rat Brains - pg 281 Jiawei Zhang - Engraftment of Stem Cell Derived Dopamine Neurons offers a Possible Regenerative Treatment for Parkinson’s disease - pg 285 Yidong Zhan - BDNF overexpression rescues symptoms of Huntington’s disease by ameliorating neuronal loss in the striatum. - pg 288


The Potential Therapeutic Impact of an Enriched Environment on Animal Models of Post-Traumatic Stress Disorder Yasmine Abdelaal

Environmental enrichment has been previously known to improve the cognitive functions, including learning and memory, as well as the physiology of animals in an experimental setting. However, little has been known on the impact of an enriched environment on mitigating anxiety-like behaviors in mood disorders such as depression and post-traumatic stress disorder (PTSD). This review paper shows that environmental enrichment in animal models of PTSD, such as avoidance escape task and time-dependent sensitization model, could ameliorate the numbing/avoidance behaviors as well as anxiety-like symptoms. At the molecular level, western blot analysis also revealed an increase in hippocampal neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), as well as an increase in the expression levels of microtubule-associated protein light chain 3-II (LC3-II). These results suggest a possible critical role of autophagy signaling as well as neurotrophic factors in the process of neuronal plasticity and hence in the adoption of stress-resilient behaviour such as an improvement in numbing/avoidance behaviour during an EE procedure. However, the link between neurogenesis and autophagy signaling processes and the exact mechanism by which they could lead to amelioration of numbing/ avoidance behavior still remains unknown and needs to be further investigated. Since it has been shown that in previous experiments drugs such as paroxetine could ameliorate hypervigilant behaviour, this might indicate a therapeutic strategy that involves both pharmacological (paroxetine) as well as psychosocial approaches (enriched environment) to potentially treat patients with PTSD. Key words: environmental enrichment (EE); Post-traumatic stress disorder (PTSD); animal model; stress; autophagy; brain-derived neurotrophic factor (BDNF) Background There has been growing interest in the role of an enriched environment (EE) on the brain function, physiology and behavior. The use of an enriched environment as an experimental tool to study behavior has been documented since the 1970s and was defined as an environment that encompasses social interactions as well as inanimate objects such as a running wheel for physical activity, toys, tunnels and wooden blocks to stimulate an exploratory and motor behavior (Rosenzweig, Bennett, Hebert & Morimoto, 1978; Henriette, Gerd, & Fred, 2000). In general, the ‘enriched’ animals are kept in larger cages with larger groups to allow complex social interactions (Henriette, Gerd, & Fred, 2000; Takahashi, Shimizu, Shimazaki, Toda, & Nibuya, 2014). Previous studies have shown that animals kept in an enriched environment have better overall learning and memory compared to those in standard conditions. However, recently there has been a focus on the effect of an enriched environment on emotionality such as reducing fearfulness (Fernández-Teruel et al., 2002), reducing anxiety-like behaviors (Roy, Belzung, Delarue, & Chapillon, 2001) and adaptation to stress (Benaroya-Milshtein et al., 2004). Therefore the therapeutic effect of an enriched environment in treating mood disorders such as depression or post-traumatic stress-disorder (PTSD) can be further elucidated. Post-traumatic stress disorder (PTSD) is a longlasting maladaptive anxiety and stress response as a result of a severe traumatic event (DSM-IV). PTSD patients experience both avoidance as well as hypervigilant behaviors for long periods of time following the trauma. Although there have been several attempts to treat PTSD with antidepressant medications such

as escitalopram and paroxetine, however, many have been ineffective in treating patients and leading to replaces in some patients (Cohen, 2005; Davis, Frazier, Williford, & Newell, 2006; Baker, Nievergelt, & Risbrough, 2009; Stein, Ipser, & Sccdat, 2006). Additionally, paroxetine was shown experimentally to ameliorate hypervigilant behavior, but not avoidance behavior (Sawamura et al., 2004). Therefore antidepressant medications alone are not sufficient for effective treatment of PTSD. In a recent study researchers were able to use a rat model of PTSD to investigate the impact of an enriched environment on the exhibition of both numbing/avoidance and hypervigilant behaviors (Henriette, Gerd, & Fred, 2000; Takahashi, Shimizu, Shimazaki, Toda, & Nibuya, 2014). Results of an avoidance escape task (AET) revealed amelioration in numbing/avoidance behavior but not in hyper-vigilant behavior. It was also found that there was an increase in hippocampal neurotrophic factors such as brain-derived neurotrophic factor (BDNF) as well a concurrent increase in hippocampal autophagy signaling (Henriette, Gerd, & Fred, 2000; Takahashi, Shimizu, Shimazaki, Toda, & Nibuya, 2014). In another model of PTSD that used an inescapable foot-shock (IFS) paradigm, EE reduced anxiogenic behavior after IFS, which correlated with an increase in hippocampal cell proliferation (Hendriksen, Prins, Olivier, & Oosting, 2010). The above literature suggests that EE can reduce anxiety-like behavior via neurogenesis that involves the increase in BDNF levels. However, autophagy synaptic remodeling, which involves the degradation of unnecessary synaptic connections, was also shown to be involved in the process of neuronal plasticity and hence in 2


the adoption of stress-resilient behavior such as an improvement in numbing/avoidance behavior during an EE procedure (Henriette, Gerd, & Fred, 2000; Takahashi, Shimizu, Shimazaki, Toda, & Nibuya, 2014). In order to further understand the effect of an EE on neuronal plasticity as a mechanism to adapt to stress, the link between increased levels of neurotrophic factors such as BDNF and the concurrent increase in autophagy signaling needs to be addressed in future studies. Additionally, we can investigate the degradation of AMPA receptors in the hippocampus following EE treatment, which was previously found to be as a consequence of the activation of autophagy signaling (Shehata, Matsumura, Okubo-Suzuki, Ohkawa, & Inokuchi, 2012). Summary of Major Results

Environmental enrichment shows antianxiety effects in PTSD rat models

There have been consistent results in a number of studies showing reduced anxiety in rats housed under an enriched environment compared to a standard condition. In a recent study six-week-old male Wister rats were used as model organism for PTSD and the rats were divided up into the EE group (n=12) or the control group (n=16) for a period of two weeks (Takahashi, Shimizu, Shimazaki, Toda, & Nibuya, 2014). To study the antianxiety effects of an enriched environment the researchers used an elevated plus maze test and an open field test as behavioral parameters. The results revealed a significant increase in the time spent in the open arms, an increase in the number of entries to the open arms as well as a significant decrease in the distance traveled in the open field test (Figure 1) (Takahashi et al., 2014).

elevated plus maze. Additionally, the EE-treated mice were significantly more active by showing a higher rate of climbing in a staircase test. Another behavioral parameter that was taken into account in one of the studies is the enhanced and faster habituation to an unfamiliar environment using a free exploration paradigm following environmental enrichment (Elliott & Grunberg, 2005). The combined results suggest that an enriched animal would also adapt faster to an unfamiliar environment compared to those left in a standard condition.

Animal models of PTSD

There have been many attempts to develop an effective animal model that would provide analogues to the specific symptoms of PTSD. In one of the major studies an avoidance escape task (AET) paradigm was used to study the effect of an enriched environment on both numbing/avoidance and hypervigilant behaviors (Takahashi et al., 2014). In this task a group of rats were given a series of initial inescapable shocks (ISs) with inter-trial intervals (ITIs), then they were placed in a shuttle box and given 5 mins to habituate to the environment. The number of crossings and the locomotor activities during adaptation were both found to be decreased after IS. However this decrease was ameliorated in the EE-treated group. In the second part of the AET, a conditioned stimulus was presented along with a foot shock and the numbers of crossings during the ITIs, as well as the avoidance of the CS were measured. Results revealed amelioration in the numbing/avoidance behaviors following EE-treatment, but not in the hypervigilant behavior, indicated by the number of crossings during the ITIs (Figure 2) (Takahashi et al., 2014).

Figure 1. Antianxiety effects shown in Wister rats housed in an EE for 2 weeks. A) Result of an open field test showing a significant increase in the time spent in the open arms in the EE group compared to the control. B) Result of an open field test showing a significant increase in the number of entries to the open arms in EE group compared to control group. C) Result of open field test showing a significant decrease in the distance traveled in the EE group compared to the control.

The same results were observed in another study that used ten-week-old male C3H mice housed in an EE for a period of 6 weeks (Benaroya-Milshtein et al., 2004). The EE-treated rats also showed a significant increase in the time spent in the open arms and in the total number of entries to the open arms of an 3

Figure 2. Results showing numbing/avoidance and hypervigilant behaviors in an avoidance escape task (AET) paradigm. (A and B) The decrease in the number of crossings and in locomotor activity during a 5 min adaptation period after IS was ameliorated following 2 weeks of EE-treatment. (C and D) No significant difference between the EE and control groups in the avoidance and number of crossings during intertrial interval (ITI).


In other studies a time-dependent sensitization model was used (Benaroya-Milshtein et al., 2004; Pynoos, Ritzmann, Steinberg, Goenjian, & Prisecaru, 1996). This animal model of PTSD involved repeated exposure to situational reminders of an initial stressful stimulus. This stressful stimulus, such as 1 mA shock for 10 seconds, was capable of allowing the animal to exhibit PTSD-like symptoms after situational reminders. Results revealed an increase in freezing time over a period of 5 weeks of situational reminders to the electric shocks. However, EE-treated mice had a significantly lower freezing time during the same time period (Figure 3) (Benaroya-Milshtein et al., 2004).

Figure 4. Expression levels of BDNF and LC3-II in EE-treated group and control after initial ISs in an avoidance escape task paradigm. Showing a significant increase in the expression levels of BDNF (A and B) and LC3-II (C and D) in the EE-treated mice after administration of ISs compared to the controls.

Conclusions and Discussion Figure 3. Results of time-dependent sensitization model Showing a significant decrease in freezing time in EE-treated mice after 5 situational reminders of an electric shock.

The effect of environmental enrichment on neurotrophic factors and autophagy signaling

It has been previously reported that following treatment of mood disorders like depression, there was an enhancement in neuronal plasticity via the upregulation of various neurotrophic factors including brain-derived neurotrophic factor (BDNF) (Duman & Monteggia, 2006). However, a number of studies also showed an increase in the expression levels of BDNF specifically in the hippocampus of environmentally enriched rats (Ickes et al., 2000; Fernández-Teruel, Escorihuela, Castellano, González, Toben˜a, 1997). In one studies mentioned earlier that used the AET paradigm, the results of western blot analysis also revealed a significant increase of hippocampal BDNF expression as well as a concurrent increase in the expression levels of the active LC3-II, a biochemical marker of autophagy signaling, in inescapable stress (IS)-treated rats. This study was the first to show that an enriched environment could induce synaptic remodeling via autophagy signaling and in turn improve the numbing/avoidance behaviors in rat models of PTSD (Takahashi et al., 2014). In another study exposure to an enriched environment following an inescapable food shock procedure (IFS) lead to complete recovery by reducing the anxiety of male Sprague Dawley rats (Hendriksen et al., 2010). This behavioral recovery correlated with almost a 2 fold increase in cell proliferation in the dentate gyrus of the hippocampus (Hendriksen et al., 2010). The combined results suggest that an EE in animal models of PTSD might have an important role in neurogenesis via an increase in the levels of neurotrophic factors such as BDNF.

One of the key features of PTSD is the prolonged anxiety and stress response experienced by the patients and therefore researchers have been trying to develop an animal model that can exhibit those features and in turn use experimental techniques such as an enriched environment to decrease anxiety-like behaviors. From the experiments mentioned in the results section we can conclude that environmental enrichment can reduce anxiety by increasing the time spent in the open arms as well as increasing the number of entries in the open arms of an open field test (Benaroya-Milshtein et al., 2004; Takahashi et al., 2014; Elliott & Grunberg, 2005). Additionally, animals reared in an enriched environment were more active in the staircase test (Benaroya-Milshtein et al., 2004) and adapted quicker to novel environments by spending more time exploring freely the unfamiliar environment (Elliott & Grunberg, 2005). However, the different strains and gender of the rats/mice used in the above experiments should also be taken into consideration. Although using different strains including C3H mice, Wister rats and Sprague– Dawley rats in these experiments all revealed similar results in exhibiting antianxiety behavior following EE treatment, on the other hand other studies found that anxious BALB/c strains were affected by EE treatment to a larger extent than C57BL/6 strains (Pynoos, Ritzmann, Steinberg, Goenjian & Prisecaru, 1996). Additionally, mostly male rats or mice were used however; in one of the studies EE had an overall greater effect in female Sprague–Dawley rats than males (Elliott & Grunberg, 2005). Thus, we can conclude that both the strain and gender of animal models contribute to the overall effectiveness of environmental enrichment in mitigating anxiety-like behavior. 4


Animal models of PTSD

One of the animal models that were used to model PTSD in EE housing was the avoidance escape task (AET) paradigm (Takahashi et al., 2014). This model was effective since it allowed the researchers to investigate both numbing/avoidance and hyperarousal/hypervigilant behaviours at the same time by measuring the locomotor activity during the adaptation period and during inter-trial intervals following inescapable stress respectively (Takahashi et al., 2014; Sawamura et al., 2004; Wakizono et al., 2007; Kikuchi et al., 2008). Since it has been shown that in previous experiments drugs such as paroxetine could ameliorate hypervigilant behaviour, this might indicate a therapeutic strategy that involves a combination of pharmacological (paroxetine) as well as psychosocial approaches (enriched environment) to potentially treat patients with PTSD (Sawamura et al., 2004). The time-dependent sensitization model was another stress paradigm that allowed the researchers to use repeated situational reminders to remind the animal of the initial traumatic or stressful stimulus (Benaroya-Milshtein et al., 2004). The results of this model indicated that EE could be used to decrease the freezing time for the animal throughout the five repeated situational reminders over a period of 5 weeks and was sustained (Benaroya-Milshtein et al., 2004). This concludes that using EE as a potential therapeutic technique in PTSD has to be achieved over a long-period of time in order to be effective. Also, there is no single model that could feature all the symptoms of PTSD, therefore the time duration of the study as well as the type of traumatic stimulus has to be taken into consideration in future studies. The effect of environmental enrichment on neurotrophic factors and autophagy signaling There have been consistent results in the literature revealing a significant increase in the levels of BDNF in the hippocampus of animals following EE treatment (Takahashi et al., 2014; Ickes et al., 2000; Fernรกndez-Teruel et al.,1997). However, the most recent paper that revealed a concurrent increase in the levels of BDNF and LC3-II reveals a new mechanism by which EE could ameliorate the numbing/avoidance behavior in PTSD animal models (Takahashi et al., 2014). Since BDNF is known to be a key regulator of neurogenesis, which involves the formation of new synaptic connections, and LC3-II is a key component of the autophagy signaling process, this suggests that both processes are involved in neuronal plasticity in the rat hippocampus to ameliorate the numbing/ avoidance behavior of PTSD animal models. We also need to consider the results of another study that showed a correlation between the complete behavioral recovery of Sprague Dawley rats following IFS and the significant increase in the cell proliferation in their dentate gyrus (Hendriksen et al., 2010). This suggests that cell proliferation might play a role in the behavioral recovery following exposure to a traumatic or stressful stimulus, however from the experimental design we cannot conclude that cell proliferation is obligatory for complete behavioral recovery. 5

Criticisms and Future Directions Although the results revealed a significant therapeutic impact of EE on animal models of PTSD, there still remains some limitations and further experiments need to be conducted to investigate the role of neurogenesis and autophagy signaling in the EE procedure. One of the key strengths of one of the recent studies is that it involved both behavioural tests such as elevated plus maze and open field test to test for anxiety, as well as measuring the expression levels of molecular markers such as BDNF and LC3-II (Takahashi et al., 2014). However, a limitation of this study is that LC3-II was the only molecule used as biochemical marker for autophagy signaling. Another possibility is to use structural evidences of increased autophagosomes in hippocampal neurons following the EE procedure. In the majority of the experiments conducted, the levels of neurotrophic factors or autophagy signaling molecules were measured only in the hippocampal region, however PTSD has been also shown to affect other regions of the brain such as the amygdala and the prefrontal cortex and therefore they also need to be taken into consideration in future studies (Bremner, Elzinga, Schmahl, & Vermetten, 2008; Yehuda & LeDoux, 2007). Another limitation of the experiments discussed in this paper is that it was solely focused on environmental enrichments however, it was found in previous studies that physical activity alone using a running wheel, in the absence of an EE housing, could increase the hippocampal expression levels of neurotrophic factors such as BDNF as well as increasing cell proliferation and in turn could mitigate the anxiety symptoms experienced by rat models of PTSD (Bechara & Kelly, 2013). Therefore the effect of an enriched environment with and without physical activity needs to be further investigated.

Neurogenesis and autophagy signaling

As previously mentioned, one of the most recent studies revealed a concurrent increase in the levels of both hippocampal BDNF and autophagy signaling following EE treatment in the Wister rat model of PTSD (Takahashi et al., 2014). This was the first study to show a key involvement of autophagy signaling in the neuronal plasticity and behavioral recovery of PTSD rat models (Takahashi et al., 2014). However, the link between neurogenesis and autophagy signaling processes and the exact mechanism by which they could lead to amelioration of numbing/avoidance behavior still remains unknown. Autophagy signaling was shown in previous studies to be enhanced via inactivation of mammalian target of rapamycin (mTOR), a serine/threonine protein kinase, and in turn could exert anti-anxiolytic effects (Cleary et al., 2008). On the other hand, another proposed mechanism for autophagy signaling activation was via an mTOR-independent pathway after the administration of mood-stabilizers that decrease the concentrations of inositol triphosphate (IP-3) (Sarkar,


Ravikumar, Floto, & Rubinsztein, 2009). Therefore a future experiment can be designed to examine the link between enhanced BDNF and autophagy signaling activation via mTOR-dependent or mTOR-independent mechanisms in a similar EE procedure. In such an experiment the numbing/avoidance behavior can be measured using the avoidance escape task (AET) after an initial period of inescapable stress. In the experiment rats can be divided up into two groups: with or without BDNF/mTOR activation plus attenuated autophagy and with or without mTOR-independent autophagy activation. Biochemical markers such as mTOR and IP3 can be used to differentiate between those two mechanisms of autophagy signaling activation. Finally, the behavioural differences such as numbing/avoidance behavior, distance traveled in the open field test or time spent in the open arms of an elevated maze test can be measured as well. Finally, to further investigate the role of autophagy signaling in an EE procedure using rat model of PTSD, we can also look at the degradation of AMPA receptors in the hippocampus, which was previously found to be a consequence of activated autophagy processes (Shehata, Matsumura, Okubo-Suzuki, Ohkawa, & Inokuchi, 2012). Since the degradation of AMPA receptors requires protein phosphatase activity (PP1), PP1 can be used as a biochemical marker for this process. The effect of an enriched environment on the degradation of AMPA receptors and hence on autophagy signaling can then be determined. In conclusion, environmental enrichment has a potential therapeutic effect on animal models of PTSD and can be a promising psychosocial approach that can be used for treating patients with PTSD after more studies are conducted. Literature Cited

1. Benaroya-Milshtein, N., Hollander, N., Apter, A., Kukulansky, T., Raz, N., & Wilf, A. et al. (2004). Environmental enrichment in mice decreases anxiety, attenuates stress responses and enhances natural killer cell activity. Eur J Neurosci, 20(5), 1341-1347. doi:10.1111/j.14609568.2004.03587.x 2. Rosenzweig, M., Bennett, E., Hebert, M., & Morimoto, H. (1978). Social grouping cannot account for cerebral effects of enriched environments. Brain Research, 153(3), 563-576. doi:10.1016/0006-8993(78)90340-2 3. Henriette, P., Gerd, K., Fred, H. (2000) Neural consequences of environmental enrichment. Nat. Rev. Neurosci. 1, 191-198. 4. Pynoos, R., Ritzmann, R., Steinberg, A., Goenjian, A., & Prisecaru, I. (1996). A behavioral animal model of posttraumatic stress disorder featuring repeated exposure to situational reminders. Biological Psychiatry, 39(2), 129-134. doi:10.1016/0006-3223(95)00088-7 5. Roy, V., Belzung, C., Delarue, C., & Chapillon, P. (2001). Environmental enrichment in BALB/c mice: Effects in classical tests of anxiety and exposure to a predatory odor. Physiology & Behavior, 74(3), 313-320. doi:10.1016/s0031-9384(01)00561-3

6. Hendriksen, H., Prins, J., Olivier, B., & Oosting, R. (2010). Environmental Enrichment Induces Behavioral Recovery and Enhanced Hippocampal Cell Proliferation in an Antidepressant-Resistant Animal Model for PTSD. Plos ONE, 5(8), e11943. doi:10.1371/journal.pone.0011943 7. Cohen, J. (2005). Treating Traumatized Children: Current Status and Future Directions. Journal Of Trauma & Dissociation, 6(2), 109-121. doi:10.1300/j229v06n02_10 8. Davis, L., Frazier, E., Williford, R., & Newell, J. (2006). Long-Term Pharmacotherapy for Post-Traumatic Stress Disorder. CNS Drugs, 20(6), 465-476. doi:10.2165/00023210-200620060-00003 9. Baker, D., Nievergelt, C., & Risbrough, V. (2009). Post-traumatic stress disorder: emerging concepts of pharmacotherapy. Expert Opinion On Emerging Drugs, 14(2), 251-272. doi:10.1517/14728210902972494 10. Stein, D., Ipser, J., & Sccdat, S. (2006). Pharmacotherapy for PTSD. Cochrane Database Syst Rev, ppCD002795 11. Takahashi, T., Shimizu, K., Shimazaki, K., Toda, H., & Nibuya, M. (2014). Environmental enrichment enhances autophagy signaling in the rat hippocampus. Brain Research, 1592, 113-123. doi:10.1016/j.brainres.2014.10.026 12. Fernández-Teruel, A., Giménez-Llort, L., Escorihuela, R., Gil, L., Aguilar, R., Steimer, T., & Tobeña, A. (2002). Early-life handling stimulation and environmental enrichment. Pharmacology Biochemistry And Behavior, 73(1), 233-245. doi:10.1016/s0091-3057(02)00787-6 13. Sawamura, T., Shimizu, K., Nibuya, M., Wakizono, T., Suzuki, G., & Tsunoda, T. et al. (2004). Effect of paroxetine on a model of posttraumatic stress disorder in rats. Neuroscience Letters, 357(1), 37-40. doi:10.1016/j.neulet.2003.12.039 14. Wakizono, T., Sawamura, T., Shimizu, K., Nibuya, M., Suzuki, G., & Toda, H. et al. (2007). Stress vulnerabilities in an animal model of post-traumatic stress disorder. Physiology & Behavior, 90(4), 687-695. doi:10.1016/j. physbeh.2006.12.008 15. Kikuchi, A., Shimizu, K., Nibuya, M., Hiramoto, T., Kanda, Y., & Tanaka, T. et al. (2008). Relationship between post-traumatic stress disorder-like behavior and reduction of hippocampal 5-bromo-2′-deoxyuridine-positive cells after inescapable shock in rats. Psychiatry And Clinical Neurosciences, 62(6), 713-720. doi:10.1111/ j.1440-1819.2008.01875.x 16. Bechara, R., & Kelly, Á. (2013). Exercise improves object recognition memory and induces BDNF expression and cell proliferation in cognitively enriched rats. Behavioural Brain Research, 245, 96-100. doi:10.1016/j.bbr.2013.02.018 17. Cleary, C., Linde, J., Hiscock, K., Hadas, I., Belmaker, R., & Agam, G. et al. (2008). Antidepressive-like effects of rapamycin in animal models: Implications for mTOR inhibition as a new target for treatment of affective disorders. Brain Research Bulletin, 76(5), 469-473. doi:10.1016/j.brainresbull.2008.03.005

6


18. Sarkar, S., Ravikumar, B., Floto, R., & Rubinsztein, D. (2009). Rapamycin and mTOR-independent autophagy inducers ameliorate toxicity of polyglutamine-expanded huntingtin and related proteinopathies. Cell Death And Differentiation, 16(1), 46-56. doi:10.1038/cdd.2008.110 19. Shehata, M., Matsumura, H., Okubo-Suzuki, R., Ohkawa, N., & Inokuchi, K. (2012). Neuronal Stimulation Induces Autophagy in Hippocampal Neurons That Is Involved in AMPA Receptor Degradation after Chemical Long-Term Depression. Journal Of Neuroscience, 32(30), 10413-10422. doi:10.1523/jneurosci.4533-11.2012 20. Elliott, B., & Grunberg, N. (2005). Effects of social and physical enrichment on open field activity differ in male and female Sprague–Dawley rats. Behavioural Brain Research, 165(2), 187-196. doi:10.1016/j.bbr.2005.06.025 21. Duman, R., & Monteggia, L. (2006). A Neurotrophic Model for Stress-Related Mood Disorders. Biological Psychiatry, 59(12), 1116-1127. doi:10.1016/j.biopsych.2006.02.013 22. Ickes, B., Pham, T., Sanders, L., Albeck, D., Mohammed, A., & Granholm, A. (2000). Long-Term Environmental Enrichment Leads to Regional Increases in Neurotrophin Levels in Rat Brain. Experimental Neurology, 164(1), 45-52. doi:10.1006/exnr.2000.7415 23. Fernández-Teruel, A., Escorihuela, R., Castellano, B., González, B., Toben˜a, A. (1997). Neonatal handling and environmental enrichment effects on emotionality, novelty/ reward seeking, and age-related cognitive and hippocampal impairments: focus on the Roman rat lines. Behav. Genet., 27, 513–526. 24. Bremner, J., Elzinga, B., Schmahl, C., Vermetten, E. (2008). Structural and functional plasticity of the human brain in posttraumatic stress disorder. Prog Brain Res., 167, 171–186. 25. Yehuda, R., & LeDoux, J. (2007). Response Variation following Trauma: A Translational Neuroscience Approach to Understanding PTSD. Neuron, 56(1), 19-32. doi:10.1016/j. neuron.2007.09.006

7


Nanoparticle Drug Delivery and its many Benefits compared to Conventional Methods Adeoluwa Adesina

Overview: I discuss the history of nanoparticle use potentially important uses of nanoparticles as drug delivery aids and how the research on this topic has grown. I also mention the major results of a recent primary publication, the relevance of those results, and the implication they will have on future research in this field. Background The idea of nanoparticles seemed extremely futuristic in the 1900s, and the thought that people would actually be able to use them effectively to help improve the delivery of drugs seemed even more so. However, in the early-mid 1970s, some literature had already started to be published on nanoparticles and some of the things they can be used for. At this time, however, researchers weren’t exactly connecting the use of nanoparticles to drug delivery. Some were just injecting nanoparticles that they tagged with fluorescence to see where they would end up (1). One of the first few papers that used nanoparticles, or “liposomes”, as a drug delivery system encapsulated a form of insulin inside the liposomes. They then found that altering the liposomal surface properties could change the type of tissues the majority of the drug are eventually uptaken into (2). This was very promising, and led to more research being done on the use of nanoparticles for all sorts of things, including the controlled delivery of contraceptive steroids (3), the delivery of anesthetics (4), and the effective magnetic targeting of cancer treatment drugs in rats (5). Researchers were quickly starting to realize the potential implications these nanoparticles could have. Those earlier papers helped catapult the study of the use of nanoparticles for drug delivery to where it is today. By continuing down the drug delivery path of nanoparticles, we have learned more about what nanoparticles can do, such as their high permeability across the blood brain barrier (BBB)(6), and have expanded the range of diseases we attempt to come up with better treatments for through the use of nanoparticles and nanomedicine. For example, in the last few years, researchers have used nanoparticles to deliver drugs that help treat the symptoms of popular diseases, such as Alzheimer’s, with a lot of success (7, 8, 9). Even though it seems that we know plenty about nanoparticles and their uses, there are still some things we do not know. One thing being how we’re going to apply our nanoparticle experiments to humans, since they’ve only been done in mice or other model organisms. The reasons for this could be many, but I believe uncertainty about certain doses of the nanoparticle/drug combination as well as other potentially serious issues or side effects that could occur because of the more complex human brain are some of the things that may be hindering this from being used in an human participants.

Summary of Major Findings Ying-mei Lui et al. (2014) followed in the footsteps of some of the previous papers and decided to choose the drug of a disease that has had difficulty being successfully and efficiently administered; a disease like brain ischemia. They wanted to test the effectiveness of nanoparticles on the delivery of ischemic drugs, like NBP, to the brain, since many of these drugs have limited permeability across the BBB. Their results showed that their PEGylated lipid nanoparticles (PLNs) containing NBP increased its permeability across the BBB. In conjunction with a Fas ligand antibody, which allows their PLN/NBP nanoparticle to have more accurate targeting, they were able to get more of the NBP to the ischemic brain region than using the NBP alone. Also, the PLN/NBP/Fas combination was more effective using far smaller dosages (5 mg/ kg) compared to NBP alone (10 mg/kg). Lastly, the amount of ischemic damage in the brain was greatly reduced using the PLN/NBP/Fas combination versus using NBP alone (10).

Figure 1. Shows the neurological scores of the mice after the treatment of the induced ischemia by NBP alone versus treatment by PLN/NBP/Fas (10).

8


researchers were able to shed some light on other benefits of nanoparticle technology outside of simply allowing drugs easier access across the BBB. They showed that by adding specific antibodies on the surface of their nanoparticles, they can target specific tissues in the brain, which increases the effectiveness significantly as well as decreasing the usual required dose by at least half. Criticisms and Future Directions

Figure 2. Shows the effect of NBP alone on improving ischemic tissue in the brain versus NBP/ PLN/Fas (10).

Consistency with the results of other papers

The results of this article are not just due to chance. These results are accurate and precise, as there are many other researchers who used similar techniques and achieved the same result. This technique as well as the use of PLNs have been used years before this paper and have been shown to have similar results in drug delivery (11). The technique has also been replicated after this paper was published and, once again, similar results were documented (12) (though magnetic targeting was used instead of antibody targeting). It’s very clear that this technique, the use of drugs encapsulated by nanoparticles, and the results it produces are precise and consistent with the results of other papers which have used the same or a similar technique. Discussion and Conclusion

These results are very significant; not just for this paper, but for nanomedicine in general. This is because the paper does more than just reiterate the effectiveness of encapsulated drugs crossing the BBB more easily, which has already been shown by other papers (6, 13). It shows how this increase in BBB permeability for drugs, as well as the highly accurate targeting effect of antibodies like Fas, can equate to less of the drug being required to have a more significant neuroprotective effect in the ischemic brain region. This maximizes the effectiveness of the drug, which also implies that any of the issues or side effects that are present at higher doses will be highly reduced using this technique, and at the same time, the individual will be experiencing a significantly stronger neuroprotective effect. Lastly, it’s one of the first studies to show a different pharmaceutical strategy that has the potential to better treat cerebral ischemia than conventional uses, as it has been difficult trying to find other non-conventional strategies over the past few years (14).

Conclusion

In conclusion, this article makes a big contribution to the study of nanoparticles and nanomedicine. These 9

This paper was well done and there were a lot of good things one could take from it. However, there were a few things that this paper could have improved on. The main thing I felt was lacking was the discussion of any future directions that their results could lead to. They just showed how encapsulating drugs in nanoparticles can maximize the effect of the drug itself, particularly drugs for brain diseases, and they didn’t give any specific examples of how the application of this important revelation can potentially be beneficial in future research. Even though this technique has been used many times before and it may have been difficult for them to come up with a unique or original idea, they could have at least mentioned a different way of doing an experiment that has already been done while incorporating their results to show they have actually given some thought to future applications of their research.

Future Directions

As I mentioned in the conclusion, one of the things they didn’t really add to their paper were any future directions their results could take research in the future. One questions they could have addressed is if there are other beneficial effects of using nanoparticles instead of conventional methods. Perhaps one could start off by seeing if there are other benefits of nanoparticle encapsulated NBP or other drugs. As was stated in the discussion, there are implications that because less of a dose than usual of the drug is required through the use of nanoparticles, using nanoparticles with a drug that is known to have many side effects may be able to reduce the incidence of those side effects. This is because less of the drug is needed to have a substantial effect. This could mean drugs that are very potent and effective, but aren’t usually recommended because of the serious side effects they may cause or their toxicity, may become more viable via nanoparticle administration (15). Another future direction these results could lead to is nanoparticles being used as a gene delivery system rather than a drug delivery system, to combat the diseases that have a strong genetic component. One could create a genetic construct that will be able to cleave off the troublesome sequence in the genome permanently. Then, one could insert this construct into a nanoparticle to be transported into the body. A popular technique used for genome editing called CRISPR/Cas9, which is thought to be the next big thing, works in a very similar way, and papers have already been published showing its effectiveness in successful gene therapy (16). For this technique, researchers generally use a virus to transport their


genetic construct into the body, reaping generally favourable results. However, using nanoparticles for transporting the genetic construct instead of a virus may be more beneficial (17). References

1. Oppenheim, R.C., Marty, J.J. and Steward, N.F. The labelling of gelatin nanoparticles with g9m technetium and their in viva distribution after intravenous injection. Aust. J. Pharm. Sci., 7, 113-117 (1978). 2. Tanaka, T. et al. Application of Liposomes to the Pharmaceutical Modification of the Distribution characteristics of Drugs in the Rat. Chem. Pharm. Bull. 23 (12): 3069-3074 (1975). 3. Gao, Z. et al. Controlled Release of Contraceptive Steroids from Biodegradable and injectable gel formulations: In Vivo evaluation. Pharm. Research. 12(6): 864-868 (1995). 4. Wakiyama, N., Juni, K., and Nakano M. Preparation and Evaluation In Vitro of Polyactic acid Microspheres Containing Local Anesthetics. Chem. Pharm. Bull. 29(11): 3363-3368 (1981). 5. Witter, K. J. et al. Tumor Remission in Yoshida Sarcomabearing Rats by Selective Targeting of Magnetic Albumin Microspheres Containing Doxorubicin. Proc. Natl. Acad. Sci. 78(1): 579-581 (1981). 6. Ulbrich, K. et al. Transferrin- and transferrin-receptorantibody-modified nanoparticles enable drug delivery across the blood–brain barrier (BBB). Eur J. Pharm. Biopharm., 71, 251-256 (2009). 7. Song, Q. et al. Lipoprotein-Based Nanoparticles Rescue the Memory Loss of Mice with Alzheimer’s Disease by Accelerating the Clearance of Amyloid-Beta. Acs Nano. 8(3): 2345-2359 (2014). 8. Zhang, C. et al. Intranasal nanoparticles of basic fibroblast growth factor for brain delivery to treat Alzheimer’s disease. Int. J. Pharm., 461, 192-202 (2014). 9. Zhang, C. et al. Dual-functional nanoparticles targeting amyloid plaques in the brains of Alzheimer’s disease mice. Biomaterials, 35, 456-465, (2014). 10. Lu, Y. et al. Targeted therapy of brain ischaemia using Fas ligand antibody conjugated PEG-lipid nanoparticles. Biomaterials, 35, 530-537 (2014). 11. Calvo, P. et al. PEGylated polycyanoacrylate nanoparticles as vector for drug delivery in prion diseases. J. Neurosci. Methods, 111, 151-155 (2001). 12. Halupka-Bryl, M. et al. Doxorubicin loaded PEG-bpoly(4-vinylbenzylphosphonate) coated magnetic iron oxide nanoparticles for targeted drug delivery. J. Magn. Magn. Mater., 384, 320-327 (2015). 13. Kreuter J., et al. Covalent attachment of apolipoprotein A-I and apolipoprotein B-100 to albumin nanoparticles enables drug transport into the brain. J. Controlled Release, 118, 54-58 (2007). 14. Kilic, U. et al. Evidence that membrane-bound G proteincoupled melatonin receptors MT1 and MT2 are not involved in the neuroprotective effects of melatonin in focal cerebral ischemia. J. Pineal. Res., 52, 228-235 (2012).

15. Ren, J. et al. The targeted delivery of anticancer drugs to brain glioma by PEGylated oxidized multi-walled carbon nanotubes modified with angiopep-2. Biomaterials, 33, 33243333 (2012). 16. Ding, Q. et al. Permanent Alteration of PCSK9 With In Vivo CRISPR-Cas9 Genome Editing. Circ. Res., 115, 488-497 (2014). 17. Harris, T. J. et al. Tissue-specific gene delivery via nanoparticle coating. Biomaterials, 31, 998-1006, (2010).

10


Oxytocin enhances social bonding, an effect moderated by baseline individual differences in socio-emotional factors including empathy Ashima Agarwal

Melanie Feeser1,2,3, Yan Fan1,2,3, Anne Weigand1,2,3, Adam Hahn4, Matti Gärtner1,2,3, Heinz Böker5, Simone Grimm1,2,3,5, Malek Bajbouj1,2,3 1Cluster of Excellence “Languages of Emotion”, Freie Universität Berlin, Habelschwerdter Allee 45, 14195 Berlin, Germany; 2Department of Psychiatry, Campus Benjamin Franklin, Charité Berlin, Eschenallee 3, 14050 Berlin, Germany; 3Dahlem Institute for Neuroimaging of Emotion, Freie Universität Berlin, Habelschwerdter Allee 45, 14195 Berlin, Germany; 4 Social Cognition Center Cologne, University of Cologne, Richard-Strauss-Str. 2, 50931 Cologne, Germany; 5Department of Psychiatry, Psychotherapy and Psychosomatics, Hospital of Psychiatry, University of Zürich, 8032 Zürich, Switzerland

Social functioning and the development of social relationships rely on the ability to observe the behaviours and infer the mental states of others. Mentalizing abilities in particular have often been associated with social interaction, as they involve inferring the emotional states of others, and thereby contribute to the development and maintenance of relationships. Oxytocin (OXT), a neuropeptide, has long been implicated in enhancing social bonding (Liberwirth & Wang, 2014). In support of this notion, literature concerning OXT has established its ability to enhancing mentalizing capabilities (Luminet et al., 2011), a relationship that has become well established. However, previous research lacks in its ability to demonstrate the prevalence of a moderating influence between OXT and mentalizing. There are many variables that have been implicated to have an affect on socio-emotional interactions. For example, empathy has been correlated with social functions, and similar to mentalizing, there is current evidence for the fact that OXT administration is related to improved empathetic abilities (Uzefovsky et al., 2014). Concerning the ability of such socio-emotional traits to moderate the relationship between OXT and mentalizing abilities is important in our understanding of social relationships and interactions. Key words: oxytocin; neuropeptide; mentalizing; empathy; social interactions; social bonding Background Social relationships are essential in maintaining societal coherence. They affect behavioural, physiological and psychological outcomes (Baumeister and Leary, 1995). Specifically, persistent attachments have impacts cognitive, emotional, social and physical well being. Social belonging protects against depression and anxiety (Lee and Robbins, 2000), and relationships have been shown tin increase life expectancy (Drefahl, 2012). Positive associations have been determined with immune functionality and cardiovascular health (Kiecolt-Glaser et al., 2010). Past literature displays that the neuropeptide Oxytocin (OXT) is vital in the modulation of social-cognitive functions, promoting social memory, decreasing fear and anxiety, and stimulating social trust and approach (Feeser et al., 2015; Lieberwirth & Wang, 2014). If released in the hypothalamus, via the paraventricular and supraoptic nuclei, it acts as a neurotransmitter, which in turn has behavioural effects (Debiec, 2007). Alternatively, it is shown to act as a hormone released by the pituitary gland. In social interactions, it is important to perceive personal and others’ intentions. An operationalizing of this is mentalizing, which involves inferring mental and emotional states of other individuals, and is usually measured by the Reading the Mind in the Eye Test (RMET). Mentalizing and OXT seem to follow a similar trajec11

tory; this relationship has long been established in literature as well. Specifically, OXT administration has been able to enhance mentalizing abilities as shown by increased accuracy on the difficult items of RMET (Luminet et al., 2011) with a comparatively lesser effect on the easier items of the test (Domes et al., 2007). Simultaneously, Schultze et al. (2011) suggest that perhaps overly difficult items are too challenging, and that empathy operates best in moderation. Regardless, in order to put this relationship into perspective, Bartz et al. (2011) have proposed an interactionist model concerning the social effects of oxytocin in humans. They highlight the importance of both stable individual differences and contextual or situational factors that moderate the effect of OXT. The model proposes that situation moderators may include stimuli effects, familiarity, perceived reliability as well as task difficulty. The individual differences are attachment anxiety, or psychiatric disorders. A similar model has been identified by Olff et al. (2013) who focus on the importance of perceiving a safe situation as well as inter-individual factors such as gender, childhood trauma, attachment style and the presence of psychiatric disorders. However, little research has focused on the importance of individual traits within the soico-emotional domain, specifically. An example of this is empathy, or other baseline socio-cognitive and socio-emotional


Figure 1. Moderating factors of oxytocin. Situational cues and Interindividual factors predict the effect of oxytocin on social bonding and stress regulation. (Source: Olff et al., 2013).

traits that vary across individuals and that are still intrinsically biologically rooted, with nurturing elements. One such trait is baseline emotional regulation abilities which, demonstrated by Quirin et al. (2011), affect OXT application and its resulting effect. Another trait was also supplied by Leknes et al (2013)’s experiment that showed that individuals with less emotional sensitivity displayed improved empathic accuracy following OXT administration. Similarly, Grimm et al. (2014) identified that early stress influenced the effect of OXT on cortisol and neural activity and finally, Feeser et al. (2015) demonstrated that OXT administration was influenced by baseline empathetic ability. In short, these studies deduced that the degree of OXT susceptibility varies depending on baseline socio-emotional skills. Seemingly, these individual skills will help contribute to how OXT might affect an understanding of interpersonal interactions, social norms, different beliefs and different perspectives. However, literature on this topic should further capitalize on possible brain mechanisms associated with this relationship. Additionally, it has been shown that there are innate genetic differences in the level of socio-emotional traits (i.e. empathy) that are based on the oxytocin receptor; this is a point that needs to be further investigated in light of mentalizing abilities and its interaction with the moderating effect of individual differences. Finally, it would be useful to expand studies to consider other socio-cognitive functions that could potentially moderate the effect of OXT on mentalizing. Research Overview Summary of Major Results Feeser et al. (2015) recently conducted a study in which they investigated the effect of empathy on OXT administration. The researchers acknowledged the established relationship between empathy and mentalizing as well as the lack of consistency in OXT-administration effects that vary by baseline

socio-emotional traits. Given this, they hypothesized that OXT-induced results would enhance mentalizing, providing more distinct enhancements in the difficult items of the RMET as compared to easier items on the test. Furthermore, they suggested that OXT administration would enhance mentalizing abilities in individuals with low empathy as opposed to high empathy.

Demographics and individual characteristics

Overall, demographic and individual characteristics were controlled for in the study, in order to ensure the matching of groups without inter-individual differences. Results of the Mehrfach Wortschatz Intelligenztest (MWT), measuring verbal intelligence demonstrated that participant IQ was considered to be in the normal range or slightly above. Additionally, there were no significant personality differences assessed by the NEO Five-Factor Inventory (NEO-FFI), and no significant age differences were observed. Furthermore, the Multidimensional Mood State Questionnaire (MDBF) was administered prior to OXT administration and after the RMET task, to ensure there were no differences in mood, calmness and wakefulness.

Mentalizing Accuracy

Overall, the results of the study echoed previous research that established the link between mentalizing ability and OXT, and presented it in form of a group-by task difficulty relationship. In the 2 (oxytocin or placebo) x 2 (difficult condition or easy condition) study, when a dose of 24 International Units (I.U.) of OXT was given to participants they showed significant improvement in mentalizing accuracy as compared to the placebo participants. This effect was pronounced for the difficult items of the RMET, with a comparatively subdued effect on the easier items of the test. 12


Figure 2. Mean percentage of correct answers for item difficulty on the RMET (easy items vs difficult items) and experimental group (OXT vs placebo). Bars are characteristic of the mean percentage accuracy on the test ± the standard error of mean (**p < 0.01). (Source: Feeser et al., 2015)

Additionally, when observing a group-by-EQ interaction, Feeser et al. (2015) found an effect for empathy mediating this interaction. Notably, regression analysis suggested the presence of a significant interaction between OXT or placebo and empathy on mentalizing abilities. Figure 3 demonstrates that participants that were rated to have low empathy showed greater in improvement in mentalizing abilities after administration of OXT as compared to individuals taking a placebo. Conversely, there were no significant group differences in individuals’ RMET performance of participants with high empathy, operationalized to have EQ values of 1 standard deviation above the mean. Similarly, the results of both Hurlemann et al. (2010) and Uzefovsky et al. (2014) mirrored Feeser et al.’s (2015) results that empathy was shown to be privy to OXT stimulation. The neuropeptide enhanced empathic accuracy in those who were less socially proficient, by enhancing attentional selectivity towards relevant social stimuli (Hurlemann et al., 2010; Uzefovsky et al., 2014).

Figure 3. Mean percentage of correct answers determined by group (OXT vs placebo) and empathy scores assessed by Emotional Quotient. The data points are characteristic of mean percentage ± the standard error of mean (**p < 0.01). Low empathy was defined as participants with an EQ one standard deviation below the mean, while high empathy represents individuals with an EQ one standard deviation above the mean. (Source: Feeser et al., 2015) 13

Another interesting result emerges in observing the relationship between mentalizing and empathy between OXT and placebo groups. The OXT group displayed a lack of a relationship between empathy and mentalizing abilities. However, for the placebo group, there was evidence of a significant positive relationship. Higher empathy played a role in increasing mentalizing abilities in the placebo group, but failed to have an effect on individuals that were administered with OXT. This is in line with the results of a study conducted by Aoki et al. (2015). Aoki et al. (2015) determined that administration of 24 I.U. OXT increased the ability to infer the emotions of others, enhancing activity in the right anterior insula. Their results displayed OXT plays a role in understanding the emotions of others at both the behavioural and neurological level. As a result, similar results would have been seen to those of Feeser et al. (2015), as OXT improved empathy in the low empathy condition. Therefore, no difference would have been seen between the high empathy and the low empathy conditions in the OXT group. In accordance with the research conducted by Domes et al., (2007) a three-way interaction should emerge between group, accuracy and empathy for difficult items on the RMET, but fail to show significance with the easy items. Yet, analyses determined that this was not significant in the study. Conducting separate analyses did however show this effect, suggesting the presence of some evidence of this effect, but remained insignificant in the analyses conducted. This echoes an idea by Schultze et al. (2011) who suggest that OXT’s effects may be accentuated from tasks that are challenging, but not extensively difficult. Perhaps in accordance with this, significant moderating effects of OXT have been presented in other research in the field. More generally, Quirin et al. (2011) provided substantial proof of the fact that the effects of intranasal OXT is dependent on the difference between high and low emotional regulation abilities (ERA). Additionally, Leknes et al. (2013) determined that OXT improved empathetic abilities selectively in individuals with less emotional sensitivity. Similarly, early life stress had an effect on OXT’s ability to attenuate cortisol stress responses and reduced neural activity during psychosocial stress (Grimm et al., 2014). The findings of the studies demonstrate that OXT does have an effect in terms of improving mentalizing abilities, but that this relationship is significantly dependent on socio-emotional skills, one of which is empathy. In other words, such individual characteristics play a moderating role on the relationship between OXT and social function. Conclusions and Discussion Interpersonal communication relies on the ability to infer emotional mental states of others. OXT has been demonstrated to increase this ability, and therefore presumably enhances the ability to develop and maintain social relationships. Bartz et al. (2011)’s interactionist model concerning the social effects of OXT in humans, has previously defined the role of stable individual differences and


contextual factors in the moderation of OXT administration. This model has been determined to be appropriate as similar moderators have surfaced in the review conducted by Olff et al. (2013), who focused on similar situation and individual variables that presumably affected OXT. Despite research on individual differences such as gender and attachment levels present in these reviews, little research has focused on the importance of specific socio-emotional factors within this domain. The review draws attention to the idea that OXT application is not uniform in its effect, and is shown to improve mentalizing in individuals who are generally less proficient at social interactions. In the limited studies that have been conducted on the topic, the effects of OXT application have been shown to be a function of baseline emotional regulation abilities (Quirin et al., 2011), emotional sensitivity (Leknes et al., 2013), early emotional stress (Grimm et al., 2014) and empathy (Feeser et al., 2015). In short, the degree of OXT susceptibility varies depending on baseline socio-emotional skills. The significance of these findings points towards the notion that oxytocin is subtle in its effect on social cognitive and behavior, and strongly depends on baseline individual differences, specifically those that are within the socio-emotional. Therefore, investigating the effects of socio-emotional individual differences on OXT application can provide insights into how potential emotional abnormalities can benefit from OXT administration. This would grant many individuals such as those inflicted with autism spectrum disorder, schizophrenia, drug addiction and other psychiatric communities the ability to normally interact in cases where they would not have been able to do so otherwise (Leknes et al. 2013). As oxytocin receptors are found in the amygdala, striatum, hippocampus, nucleus accumbens and midbrain (Meyer-Lindenberg et al., 2011), the presence of this neuropeptide increases neural activity in these regions which have long been implicated with social bonding in neuroscience. The effects of OXT are clearly widespread with significant social, cognitive and behavioural effects. These studies provide a new pathway of investigation into the wide array of socio-emotional individual differences that permit social interaction and the development of relationships.

Criticisms and Future Directions

The adaptation of oxytocin in motivating prosocial behaviour is crucial in determining our social interactions and relationships. The results of the review provided justification that this neuropeptide has a positive effect on social function, and that socio-emotional traits in particular are important in moderating the effects of oxytocin on increased awareness of socially relevant information, as well as an enhanced ability to mentalize. This is an incremental advancement to literature on the topic, as it includes the possibility of a third variable that moderates a previously established relationship. Nevertheless, it provides a facet by which

to improve and understand social interactions. However, there exist some shortcomings in the methods employed. While the papers makes convincing arguments for the importance of oxytocin as well as its positive effect on mentalizing abilities (with regards to empathetic behavior), they fall short in being rather correlational, and are unable to determine exact causation. Firstly, empathetic ability in this study was defined by self-report measures, which are privy to bias. In remedy to this, one solution would involve assessing saliva samples of the participants, as polymorphisms in oxytocin receptor genes have been implicated to have a relationship with empathetic related traits such as emotional processing (Laursen et al., 2014). Alternatively, it would be helpful to implement performance-based computerized empathy tasks such as those proposed by Smith et al. (2014), or the Multifaceted Empathy Test (MET) that distinguishes between cognitive and emotional empathy (Hurlemann et al., 2010). Either of these proposed amendments would strengthen the evidence for the effect of empathy on the relationship between oxytocin and mentalizing abilities. Secondly, the studies’ strengths lie in their ability to account for the relationship of a third variable with oxytocin, yet they could be improved by observing the mechanism by which oxytocin facilitates prosocial behavior. By using functional magnetic resonance imaging (fMRI), brain activity could be monitored to determine where, how and to what extent oxytocin acts (Hu et al., 2015) especially considering the different socio-emotional differences that were defined above. These two main areas for improvement will perhaps provide cause for future directions by which the experiments’ causal factor can be better isolated. Additionally, it has been shown that there are innate genetic differences in the level of empathy that are based on the oxytocin receptor (Laursen et al., 2014); this is a point that needs to be further investigated in light of moderating effect of biological empathetic differences. Finally, the studies did not isolate for presumable gender differences and cultural differences related to oxytocin dependent effects. Taking into account the fact that these individual differences may play a role will provide a more holistic view of individual traits being able to mediate roles in oxytocin’s effect on social interactions across a wide array of the population. References 1. Aoki, Y., Yahata, N., Watanabe, T., Takano, Y., Kawakubo, Y., Kuwabara, H., ... & Yamasue, H. (2014). Oxytocin improves behavioural and neural deficits in inferring others’ social emotions in autism. Brain, awu231. 2. Bartz, J. A., Zaki, J., Bolger, N., & Ochsner, K. N. (2011). Social effects of oxytocin in humans: context and person matter. Trends in cognitive sciences, 15(7), 301-309. 3. Baumeister, R. F., & Leary, M. R. (1995). The need to belong: desire for interpersonal attachments as a fundamental human motivation. Psychological bulletin, 117(3), 497. 14


4. Dębiec, J. (2007). From affiliative behaviors to romantic feelings: a role of nanopeptides. FEBS letters, 581(14), 2580-2586. 5. Domes, G., Heinrichs, M., Michel, A., Berger, C., & Herpertz, S. C. (2007). Oxytocin improves “mind-reading” in humans. Biological psychiatry, 61(6), 731-733. 6. Drefahl S. (2012). Do the married really live longer? The role of cohabitation and socioeconomic status. J. Marriage Fam. 74, 462–475 10.1111/j.1741-3737.2012.00968.x 7. Feeser, M., Fan, Y., Weigand, A., Hahn, A., Gärtner, M., Böker, H., ... & Bajbouj, M. (2015). Oxytocin improves mentalizing–Pronounced effects for individuals with attenuated ability to empathize. Psychoneuroendocrinology. 53, 223- 232. 8. Hu, J., Qi, S., Becker, B., Luo, L., Gao, S., Gong, Q., ... & Kendrick, K. M. (2015). Oxytocin selectively facilitates learning with social feedback and increases activity and functional connectivity in emotional memory and reward processing regions. Human brain mapping. 9. Hurlemann, R., Patin, A., Onur, O. A., Cohen, M. X., Baumgartner, T., Metzler, S., ... & Kendrick, K. M. (2010). Oxytocin enhances amygdala-dependent, socially reinforced learning and emotional empathy in humans. The Journal of Neuroscience, 30(14), 4999-5007. 10. Hooker, C. I., Verosky, S. C., Germine, L. T., Knight, R. T., & D’Esposito, M. (2010). Neural activity during social signal perception correlates with self-reported empathy. Brain research, 1308, 100-113. 11. Kiecolt-Glaser, J. K., Gouin, J. P., & Hantsoo, L. (2010). Close relationships, inflammation, and health. Neuroscience & Biobehavioral Reviews, 35(1), 33-38. 12. Lee R. M., Robbins S. B. (2000). Understanding social connectedness in college women and men. J. Couns. Dev. 78, 484–491 10.1002/j.1556-6676.2000.tb01932.x 13. Leknes, S., Wessberg, J., Ellingsen, D. M., Chelnokova, O., Olausson, H., & Laeng, B. (2012). Oxytocin enhances pupil dilation and sensitivity to ‘hidden’emotional expressions. Social cognitive and affective neuroscience, nss062. 14. Lieberwirth, C., & Wang, Z. (2014). Social bonding: regulation by neuropeptides. Frontiers in neuroscience, 8. 15. Lischke, A., Gamer, M., Berger, C., Grossmann, A., Hauenstein, K., Heinrichs, M., ... & Domes, G. (2012). Oxytocin increases amygdala reactivity to threatening scenes in females. Psychoneuroendocrinology, 37(9), 1431-1438. 16. Luminet, O., Grynberg, D., Ruzette, N., & Mikolajczak, M. (2011). Personality-dependent effects of oxytocin: greater social benefits for high alexithymia scorers. Biological psychology, 87(3), 401-406. 17. Meyer-Lindenberg, A., Domes, G., Kirsch, P., & Heinrichs, M. (2011). Oxytocin and vasopressin in the human brain: social neuropeptides for translational medicine. Nature Reviews Neuroscience, 12(9), 524-538. 18. Olff, M., Frijling, J. L., Kubzansky, L. D., Bradley, B., Ellenbogen, M. A., Cardoso, C., ... & van Zuiden, M. (2013). The role of oxytocin in social bonding, stress regulation and mental health: an update on the moderating effects of context and interindividual differences. Psychoneuroendocrinology, 15

38(9), 1883-1894. 19. Quirin, M., Kuhl, J., & Düsing, R. (2011). Oxytocin buffers cortisol responses to stress in individuals with impaired emotion regulation abilities. Psychoneuroendocrinology, 36(6), 898-904. 20. Singer, T. (2006). The neuronal basis and ontogeny of empathy and mind reading: review of literature and implications for future research. Neuroscience & Biobehavioral Reviews, 30(6), 855-863. 21. Smith, M. J., Horan, W. P., Cobia, D. J., Karpouzian, T. M., Fox, J. M., Reilly, J. L., & Breiter, H. C. (2014). Performancebased empathy mediates the influence of working memory on social competence in schizophrenia. Schizophrenia bulletin, 40(4), 824-834. 22. Tabak, B. A., Meyer, M. L., Castle, E., Dutcher, J. M., Irwin, M. R., Han, J. H., ... & Eisenberger, N. I. (2015). Vasopressin, but not oxytocin, increases empathic concern among individuals who received higher levels of paternal warmth: A randomized controlled trial. Psychoneuroendocrinology, 51, 253-261. 23. Uzefovsky, F., Shalev, I., Israel, S., Edelman, S., Raz, Y., Mankuta, D., ... & Ebstein, R. P. (2015). Oxytocin receptor and vasopressin receptor 1a genes are respectively associated with emotional and cognitive empathy. Hormones and behavior, 67, 60-65 Received July, 7, 2014; revised December, 19, 2014; accepted December, 23, 2014. This work was supposed by the Cluster of Excellence, “Languages of Emotion” (project number 88120057). The authors thank Philipp Fuge, Karin Pestke and Emily Brandt for assistance with data collection. Address correspondence to: “Languages of Emotion”, Freie schwerdter Allee 45, 14195 +49 30 838 50599; fax:

Cluster of Excellence Universität Berlin, HabelBerlin, Germany. Tel.: +49 30 838 52887.

Copyright © 2015 Elsevier Ltd. All rights reserved


Increased Phosphorylation of CREB at Ser133 in the Dentate Gyrus Reverses Depressive Behavior in Rodents Ariba Alam

Depression is a mental disorder that impair an individual’s ability to concentrate resulting in individuals feeling hopeless for short or long periods of time. According to the World Health Organization, depression by 2030 is hypothesized to be the second leading cause of disability in the world. In 2012, there have been 350 million cases reported globally of people that suffer from depression. Fortunately, there is research going on in this field and this disorder has both psychosocial treatment as well as treatment by medicine. Depression is studied in labs through use of behavioral paradigms such as unpredicted chronic mild stress (UCMS), tail suspension test (TST), sucrose preference test, or forced swim test (FST). These studies induce stress on the animal by a foot shock or social isolation to induce depression like behaviors on the rodent. These depressive symptoms are reversed by the administration of antidepressants that target the CREB-BDNF pathway which essentially lead to the overexpression of CREB in the hippocampus. Many studies have reported the dentate gyrus to be the most involved in behavioral symptoms that rodents experience, and CREB upregulation in this part of the hippocampus has reversed depressive behavior the most compared to other areas of the hippocampus such as CA3 and CA1 pyramidal cells. CREB is a protein that is integrated in a pathway of other factors involved such as BDNF, Trk receptor, kinases that must be functional in order for CREB to be expressed in the hippocampus. Although the use of antidepressants that target upregulation of CREB-BDNF pathway, the causality of depression still has to be determined. These proteins are correlated with depression but the cause is still unknown. There has to be further studies that explore the core role of these proteins that will lead to a better understanding of depression. Key words: Depression; cAMP response element-binding protein (CREB); Brain Derived Neurotrophic Factor (BDNF); Dentate Gyrus; Hippocampus; Behavioral Test Paradigms; Antidepressent Drugs Background Studies have provided evidence that stress induces depression like behavior in mice. Depression is implicated to be due to an imbalance of CREB in the brain, particularly in the hippocampus. Depression was thought to be based on the monoamine hypothesis where deficiency in serotonin or noradrenaline caused depressive behavior (Mutlu et al., 2014; Chen, Shirayama, Shin, Neve & Duman, 2001; Gronli et al., 2006; Gass & Riva, 2007). However, this hypothesis does not explain all components of depression therefore is not the sufficient model that is followed (Mutlu et al., 2014). Alternatively, a recent hypothesis based on the CREB –BDNF pathway linked to depression specifically in the hippocampus is more commonly studied (Mutli et al., 2014; Chen, Shirayama, Shin, Neve & Duman, 2001; Gronli et al., 2006, Xiao et al., 2011; Gass & Riva, 2007). CREB is involved in neuronal plasticity and regulating transcription of genes that are associated with stress responses (Guan et al., 2013; Xiao et al., 2011; Gass & Riva, 2007). Stress prevents the phosphorylation of CREB (Ser133) in the dentate gyrus of the hippocampus. CREB therefore cannot act on the Brain Derived Neurotrophic Factor (BDNF) gene downstream in the pathway therefore preventing the expression of this gene. BDNF has the capability to phosphorylate CREB Ser133,that is further responsible for activating genes that code for cyclic AMP (Gronli et al., 2006; Xiao et al., 2011). Studies have also shown that knocking out one allele for BDNF does not cause depression, but

if that is linked with an inhibitor for mitogen-activated protein kinase (MAPK/MEK) that also acts on CREB by phosphorylating it would cause depression in the animal (Duman, Schlesinger, Kodama, Russell & Duman, 2007). Therefore BDNF which aids neuron survival, synaptic transmission, and synaptic plasticity complements the functions of CREB. Post-mortem brains of depressed patients have showed decrease of CREB protein in the hippocampus (Chen, Shirayama, Shin, Neve & Duman, 2001; Gass & Riva, 2007). This paper will focus on the expression of CREB protein in the hippocampus and it’s correlation with depression like behavior in rodents.

Primary Paper Introduction:

A study done by Guan L., Jia X., Zhao X., Zhang X., et al. (2013) analyzed the expression levels of CREB/ERK/Bcl-2 in rat brains and their immobility time through a swimming test after experiencing prenatal stress (PS). These levels were measured in the hippocampus, prefrontal cortex and striatum. The prenatal stress that was given was social isolation. The motive of the article is to understand the role of the ERK-CREB pathway and its changes that occur after PS exposure and how that reflects in a swimming test. These proteins were studied due to their important functions. CREB is involved in neuronal plasticity and regulating transcription of genes that are associated with stress response. ERK responds to extracellular stimuli by regulating gene expression, 16


cellular growth, synthesis of new proteins in order to protect cells. Bcl-2 is regulated by CREB and is an anti-apoptotic factor. It is involved in regulating cell death, cell plasticity and growth of new neurons. ERK is activated by NMDA receptor excitation. MK-801 is a drug used in the study as it is been demonstrated to be affiliated with antidepressant properties. It is a non-competitive antagonist of NMDA receptor therefore blocks glutamate from binding to this receptor. Saline was used alongside to MK-801.

Introduction to Additional Studies:

Many sorts of behavioral paradigms have been used in studies that test for depression. The more frequently used include a tail suspension test, forced swimming test, sucrose preference, and unpredicted chronic mild stress (UCMS) or chronic mild stress (CMS). The unpredictable chronic mild stress model stresses out the animal that mimics natural stress which would parallel with human stress. These include food starvation, light-dark cycle altered, empty water bottle in their cage, etc. After exposing these mice to such stresses, they are given an antidepressant: agomelatine or melatonin for treatment (Mutlu et al., 2014). Another study used foot shocks and then was given imipramine, fluoxetine, isofluran gas, amitriptyline (AMI) or saline to see the effects on the rodent (Chen, Shirayama, Shin, Neve & Duman, 2001; Gronli et al., 2006; Gourley et al., 2008). One study compared the results between antidepressants and a transgenic experiment where they injected Herpes Simplex Virus carrying CREB in the dentate gyrus. They wanted to see the effect of overexpressing CREB has on the animal (Chen, Shirayama, Shin, Neve & Duman, 2001). The animal can also be treated with MK-801, fluoxetine, desipramine, tranylcypromine, reboxetine that fixes CREB levels in the hippocampus after the animal experiences stress (Guan et al., 2013; Tardito et al., 2009). Acupuncture studies have also reversed depression behavior in rodents there is also used in many studies that study CREB-BDNF pathway related to stress (Yang et al., 2013; Sun et al., 2014). After the animals have been exposed to atleast one of these treatments, their CREB and BDNF and ERK levels are measured in the hippocampus and compared with the control group that was given no stress or the saline group. The saline group is given stress, but administering saline does not help them with their depressive behavior, therefore itâ&#x20AC;&#x2122;s represented as another reassurance of the experiment. Major results have indicated that these antidepressants indeed increase the levels of CREB, and BDNF, and ERK in the brain after these treatments and thus reversing depressive behavior. Research Overview Summary of Major Results

Method/Experiment of Primary Paper:

The method that was utilized by Guan L., Jia X., Zhao X., Zhang X., et al. (2013) consisted of mating sexually active male rats to females over night within 17

a room temperature of 22-26 degrees, humidity 60% and with a 12 hour day/night cycle (control group). Each pregnant rat was than separated into a control group, PS-Saline group, and PS-MK-801 group. The control group was not given any stress, but the other two groups were socially isolated 3 times a day for 45 minutes. The rats were given either saline or MK-801 on days 14-21 of pregnancy. The researchers than did a forced swimming test (FST) on the offspring to see the effects of PS on them. Also, RNA was extracted from the three brain areas (hippocampus, striatum and prefrontal cortex) and went through an RT-PCR to examine the intensity of ERK, CREB, and Bcl-2 mRNA expression in each.

Results from Primary Paper:

The results from Guan L., Jia X., Zhao X., Zhang X., et al. (2013) showed PS rats showed an increased immobility time. There was lower expression of ERK2 mRNA, CREB mRNA, Bcl-2 mRNA in the hippocampus, prefrontal cortex of PS rats with saline compared to control and MK-801 (modified the expression). The CREB levels were fixed by MK-801 as the levels of CREB were similar to that of the control even after experiencing stress prenatally. There was no significant difference seen in expression of mRNA expression among the three proteins in the striatum. These changes were all reflected in the increased immobility timing correlated to depressive behaviour.

Results from Additional Studies:

The model size ranged from 9 (Chen, Shirayama, Shin, Neve & Duman, 2001; Gronli et al., 2006; Duman, Schlesinger, Kodama, Russell & Duman, 2007; Tardito et al., 2009) to 15 (Mutlu et al., 2014, Guan et al., 2013; Xiao et al., 2011). The largest experimental size used was 159 (Gourley et al., 2008). The studies showed a decrease in antidepressant behavior after administering an antidepressant such as Agomelatine (Mutlu et al., 2014). This antidepressant allowed the upregulation of BDNF-CREB in the hippocampus to decrease immobility time and also to increase memory of the animal (Mutlu et al., 2014). Another study injected a Herpes Simplex Virus (HSV)-CREB in the dentate gyrus of the hippocampus, which also resulted in less immobility time, and decrease in escape failures (Chen, Shirayama, Shin, Neve & Duman, 2001). This study compared the effect of antidepressants compared to a transgenic experiment where CREB was overexpressed. The results demonstrated that antidepressents decreased escape failures by 65% and CREB overexpression by 45% (Chen, Shirayama, Shin, Neve & Duman, 2001). However, in a swim test they demonstrated 35% reduced immobility time after administering imipramine in the dentate gyrus in comparison with 45% decrease in immobility time through CREB overexpression (Chen, Shirayama, Shin, Neve & Duman, 2001). Therefore, depending on what stress the animal was given, different techniques to treat the depression would result in better outcomes. Phosphorylation of Ser-133 on CREB in one study also demonstrated a


higher preference for sucrose (Gronli et al., 2006). One study used the chronic unpredictable stress model which produced depressive behavior in mice. The results exhibited a 53% reduction of granule cell neurogenesis just after receiving seven days of stress, but this result was evident after a month of observation (Gronli et al., 2006). Although these studies used different methods, the end result was an increase in CREB expression that allowed the depressive behaviors to be reversed.

Figure 1. This figure from the paper by Gass & Riva (2007) show the pathway involved in depressant behavior. Protein CREB that binds to CRE on the DNA to activate BDNF is involved in depressive symptoms if down-regulated. CREB is phosphorylated by upstream factors that include Protein Kinase A, CaMKIV, and RSK proteins. The more these proteins are activated will allow this pathway to be expressed, and BDNF to get transcribed. Alterations in this pathway is correlated with depressive or antidepressive behavior.

Conclusions and Discussion After inducing different types of stresses in rodents, and then administering antidepressants or transgenically overexpression of CREB in the hippocampus resulted in expected results of increased sucrose preference, decreased immobility time during swimming tests and decreased escape failures (Mutlu et al., 2014; Chen, Shirayama, Shin, Neve & Duman, 2001; Gronli et al., 2006; Guan et al., 2013; Xiao et al., 2011; Tardito et al., 2009; Yang et al., 2013). One common factor in all of these studies is the CREB-BDNF pathway that is upregulated specifically in the dentate gyrus which results in antidepressant behavior in rodents (Gass & Riva, 2007). Despite, the drugs improving the performance of mice in these various experiments does not provide information on how long these drugs can be dependent upon. Would the mice ever become unresponsive to them or would a higher dose have to be given to sustain the antidepressant behavior? Therefore, are these drugs only for short term use? The protein CREB that is upregulated is influenced by many factors such as cAMP, BDNF, and kinases that allow CREB to be phosphorylated (Gass & Riva, 2007). Although, the involvement of CREB is evident in depression, but the role of this protein still has to be determined especially in all areas of the hippocampus (Gass & Riva, 2007). The upregulation of CREB only in the dentate gyrus is seen to have antidepressant like effects, and not in the CA3 or CA1 pyramidal cells of the hippocampus or even the prefrontal cortex (Chen, Shirayama, Shin, Neve & Duman, 2001; Gronli et al., 2006; Xiao et al., 2011). Therefore, is it essential to know why CREB only acts in the dentate gyrus and how that influences

Figure 2. This figure from the paper by Chen, Shirayama, Shin, Neve & Duman (2001) show escape failures in rodents. In the control there are low chances of the rats to encounter escape failures. The saline treated rats that were given inescapable foot shock (IES) show higher levels of escape failures. Whereas, fluoxetine and imipramine treated rats after giving them inescapable foot shocks demonstrated a significant decrease in number of escape failures compared to ones treated with only saline (which is not an antidepressant). Figure 3. Rats exposed to inescapable foot shock (IES), and then microinjected with herpes simplex virus control (IES-HSV-LacZ) or HSV-CREB that allowed CREB to be overexpressed in the hippocampus and prefrontal cortex. Overexpression levels of CREB helped determine its involvement in decreasing escape failures or reversing depression symptoms. Different parts of the hippocampus such as dentate gyrus, CA1 pyramidal layer and prefrontal cortex were examined to determine any differences between the areas. The area that was the most significant in decreasing escape failures after overexpressing CREB using Herpes Simplex virus as a transgenic experiment was the dentate gyrus region of the hippocampus. However, the escape failures did not reduce at such a significant level in either the CA1 pyramidal layer or the prefrontal cortex

18


the behavior of the rodent. Also, the role of this protein in the other regions of the hippocampus must also be determined to have a better understanding of depression. Knowing more about the projections that the dentate gyrus has would also help to determine where CREB gets transported to and if those areas have any involvement in altering behavior in mice. A future approach can be taken on determining the role of CREB in CA1 and CA3 pyramidal cells of the hippocampus, and also the mechanism involved in depression. Depressive behavior is examined when the CREBBDNF pathway is down regulated in the dentate gyrus. When the protein CREB is upregulated in the dentate gyrus reverses depressive behavior observed in many behavioral model paradigms. These behavioral paradigms include a sucrose preference test, tail suspension test (TST), or chronic mild stress model where the rodents are exposed to stressful scenarios that induces depressive behavior. After observing depression in rodents, an antidepressant such as MK-801 or imipramine is injected into the rodent in the hippocampus which reverses depression like behavior. These drugs are observed to act on upregulating CREB in the dentate gyrus.

Conclusions

Depression in people is becoming more frequent in all parts of the world according to the World Health Organization (Blendy, 2006). There is a 10-30% risk of women being affected by this, and 7-15% for men both of which are probable to occur (Blendy, 2006). The primary approach taken to treat depression was through monoamines, or Selective Serotonin Reuptake Inhibitors (SSRI), however this approach is now not the ideal way of treating depression. The monoamine hypothesis is now replaced with a CREB-BDNF upregulation pathway being involved in depression (Blendy, 2006; Gass & Riva, 2007; Chen, Shirayama, Shin, Neve & Duman, 2001; Gronli et al., 2006; Schmidt, 2011). Through various behavioral models used such as sucrose preference test, inescapable foot shock, tail suspension test, immobility test in swimming that demonstrate depressed behavior are used in studies to study depression. The mechanism in all the studies presented are similar where the rodents are presented with stress initially and then treated with saline, or antidepressents. The pathway in the brain that is targeted is the CREB-BDNF pathway that is dependent on many transcriptional factors and upstream proteins such as TrkB receptors, CRE binding region, cAMP, and PKA (Gass & Riva, 2007). The protein that is essential for reversing depressive behavior is CREB protein, and the area that is involved in antidepressive behavior significantly is the dentate gyrus.

Criticisms and Future Directions

The validity of these behavioral paradigms are questionable. Although they demonstrate behavioral symptoms in rodents, it does not necessarily parallel with human depression. Depression in humans can last for long periods or short periods depending on what 19

the individual goes through in their life. Some humans are more susceptible to depression and some are not (Dzirasa & Covington, 2012). For instance, how does a tail suspension test (TST) or a sucrose preference test demonstrate anhedonia. Humans experience stress either early in life or later, but they are not in the form of foot shocks. Therefore, inducing foot shocks in rodents may alter different pathways in the animal compared to pathways that are altered by other forms of stress such as food starvation. Maybe the mechanism by which these mice are expressing depression symptoms is through a completely different pathway than what occurs in the brain. Therefore, mimicking the right type of stresses is essential. Moreover, upregulation of CREB has been helpful in reversing depressive symptoms, but this is not the cause of depression. CREB is a protein that is affected by another entity that yet has to be determined. The true function of this protein was not explored in all parts of the hippocampus, which is essential to understand the underlying cause of depression. Next, the temporal resolution or the amount of stress that is needed to start the production of these proteins was also not indicated in the study (Duman, Schlesinger, Kodama, Russell & Duman, 2007). It was not clearly identified to how long the rodent express antidepressant behavior after being administered the drug or overexpression of CREB in the dentate gyrus. For instance, after how much exposure to stress does the animal require to start upregulating these proteins or does the increased expression patterns of these proteins start at the same time the rat is exposed to even a little bit of stress? By looking at different approaches to resolve these questions will help gain a better understanding of the roles that these proteins play in depression and also contribute to a holistic understanding of this disease. The models used must also be easily transferred in clinical trials to improve the validity of the tests (Schmidt, 2011). Validity is conquered through integrating most essential features of depression in the animal model. Therefore, the model has to reflect practical scenarios and introduction to new models with predictive ability will aid in unveiling neurobiological mechanisms associated with depression. Furthermore, measuring guilt, mood or suicidal feelings in rodents is not easily determined, but for humans is easily equitable through questionnaires. Therefore, equating animal models to humans is very difficult. Another limitation in these studies is the effect of drugs on depressed individuals. In mice, acute administration of antidepressents has an effect on reversing depressive behavior. However, in humans, acute administration of drugs does not reverse depression in all individuals (Dzirasa & Covington, 2012). If the drug has an effect on an individual it would not be apparent until a couple of weeks of administration. Every individual is different with different responses to treatment therefore one form of model in rodents may not be enough to overcome this complex brain disorder. References 1. Blendy, J. (2006). The Role of CREB in Depression and Antidepressant Treatment. Biological Psychiatry, 59(12), 1144-1150. doi:10.1016/j.biopsych.2005.11.003 2. Chen, A., Shirayama, Y., Shin, K., Neve, R., & Duman,


R. (2001). Expression of the cAMP response element binding protein (CREB) in hippocampus produces an antidepressant effect. Biological Psychiatry, 49(9), 753-762. doi:10.1016/ s0006-3223(00)01114-8 3. Duman, C., Schlesinger, L., Kodama, M., Russell, D., & Duman, R. (2007). A Role for MAP Kinase Signaling in Behavioral Models of Depression and Antidepressant Treatment. Biological Psychiatry, 61(5), 661-670. doi:10.1016/j. biopsych.2006.05.047 4. Dzirasa, K., & Covington, H. (2012). Increasing the validity of experimental models for depression. Annals Of The New York Academy Of Sciences, 1265(1), 36-45. doi:10.1111/j.1749-6632.2012.06669.x 5. Gass, P., & Riva, M. (2007). CREB, neurogenesis and depression. Bioessays, 29(10), 957-961. doi:10.1002/ bies.20658 6. Gourley, S., Wu, F., Kiraly, D., Ploski, J., Kedves, A., Duman, R., & Taylor, J. (2008). Regionally Specific Regulation of ERK MAP Kinase in a Model of AntidepressantSensitive Chronic Depression. Biological Psychiatry, 63(4), 353-359. doi:10.1016/j.biopsych.2007.07.016 7. Gronli, J., Bramham, C., Murison, R., Kanhema, T., Fiske, E., & Bjorvatn, B. et al. (2006). Chronic mild stress inhibits BDNF protein expression and CREB activation in the dentate gyrus but not in the hippocampus proper. Pharmacology Biochemistry And Behavior, 85(4), 842-849. doi:10.1016/j. pbb.2006.11.021 8. Guan, L., Jia, N., Zhao, X., Zhang, X., Tang, G., & Yang, L. et al. (2013). The involvement of ERK/CREB/Bcl-2 in depression-like behavior in prenatally stressed offspring rats. Brain Research Bulletin, 99, 1-8. doi:10.1016/j.brainresbull.2013.08.003 9. Koch, J., Kell, S., Hinze-Selch, D., & Aldenhoff, J. (2002). Changes in CREB-phosphorylation during recovery from major depression. Journal Of Psychiatric Research, 36(6), 369-375. doi:10.1016/s0022-3956(02)00056-0 10. Mutlu, Gumuslu, E., Sunnetci, D., Ulak, G., Komsuoglu Celikyurt, I., & Cine, N. et al. (2014). The Antidepressant Agomelatine Improves Memory Deterioration and Upregulates CREB and BDNF Gene Expression Levels in Unpredictable Chronic Mild Stress (UCMS)-Exposed Mice. Drug Target Insights, 11. doi:10.4137/dti.s13870 11. Schmidt, M. (2011). Animal models for depression and the mismatch hypothesis of disease. Psychoneuroendocrinology, 36(3), 330-338. doi:10.1016/j.psyneuen.2010.07.001 12. Sun, L., Liang, J., Guo, T., Guo, Z., Yang, X., & Wang, S. et al. (2014). Effect of Acupuncture on Expression of CREB and p-CREB in Hippocampus and Prefrontal Cortex of Depression Rats. The Journal Of Alternative And Complementary Medicine, 20(5), A84-A85. doi:10.1089/acm.2014.5222. abstract 13. Tardito, D., Musazzi, L., Tiraboschi, E., Mallei, A., Racagni, G., & Popoli, M. (2009). Early induction of CREB activation and CREB-regulating signalling by antidepressants. The International Journal Of Neuropsychopharmacology, 12(10), 1367. doi:10.1017/s1461145709000376 14. Xiao, L., Shu, C., Tang, J., Wang, H., Liu, Z., & Wang, G. (2011). Effects of different CMS on behaviors, BDNF/

CREB/Bcl-2 expression in rat hippocampus. Biomedicine & Aging Pathology, 1(3), 138-146. doi:10.1016/j. biomag.2010.10.006 15. Yang, L., Yue, N., Zhu, X., Han, Q., Liu, Q., Yu, J., & Wu, G. (2013). Electroacupuncture upregulates ERK signaling pathways and promotes adult hippocampal neural progenitors proliferation in a rat model of depression. BMC Complement Altern Med, 13(1), 288. doi:10.1186/14726882-13-288 April, 6, 2015 This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Ariba Alam, Human Biology Department, University of Toronto, Toronto, CA Email: rln@apc.edu Copyright Š 2015 Dr. Bill JU, Neurosciences, Human Biology Program

20


The rate of increase in adult hippocampal neurogenesis and spatial learning in C57BL/6J mice is greater in response to voluntary exercise than in response to sensory stimuli manipulations Samin Alikhanzadeh

Adult hippocampal neurogenesis refers to the continual formation of new neurons from progenitor cells. Previous studies on rodent models have shown that environmental enrichment possessing both sensory and motor stimuli increases neurotrophic levels which act to enhance neuritogenesis, cell survival, and neuronal differentiation. The aforementioned neurogenic benefits then are correlated with enhanced cognitive performance in test models. In later studies, the effect of the two components of enrichment were tested alone. The results indicated that enhanced adult hippocampal neurogenesis and spatial learning mice occurs solely following motor enrichment. This study conducted by Mustroph et al. (2012) tested the effect of voluntary wheel running and different sensory modalities including tactile, visual, dietary, auditory, and vestibular on neurogenesis and cognitive performance. Counting the number of co-labelled BrdU positive and NeuN positive cells per granule layer volume, it was shown that neurogenesis is greatest following motor enrichment. In the same study, testing for cognitive performance on a Morris water maze, it was shown that mice exposed to motor enrichment reduced path length to platform by 75% by the second day of the acquisition period while the learning period for mice in control and sensory enrichment group was 5 days. Consistent with previous findings, this study concludes that voluntary exercise confers neurogenic and cognitive benefit to rodents that are absent following sensory enrichment of different modalities. In many of the neurodegenerative and psychiatric disorders the rate of adult hippocampal neurogenesis is greatly reduced. Therefore, aerobic exercise can be used in conjunction with therapeutic interventions to enhance the proliferation of progenitor cells and survival of new neurons to reduce the burden of these conditions. Key words: Adult Hippocampal Neurogenesis (AHN)), Spatial learning, Neurotrophic factors, Environmental enrichment, Aerobic exercise, Sensory stimulation. Background Neurogenesis is the process of generating new neurons from the undifferentiated progenitor cells. This multi-step process involves regulatory factors which induce newborn cells to proliferate, mature, differentiate, and ensure their survival. In an adult brain there are two regions in which neurogenesis occurs throughout oneâ&#x20AC;&#x2122;s lifetime: the subventricular zone (SVZ) and the subgranular layer of the dentate gyrus (DG). Adult hippocampal neurogenesis (AHN) declines with age and is disrupted in neurodegenerative diseases such as Alzheimerâ&#x20AC;&#x2122;s disease. Therefore enhancing neurogenesis may have the potential to rescue learning and memory dysfunction in these conditions as adult born neurons have enhanced excitability and synaptic plasticity. Literature on AHN suggests that this process is influenced by external conditions which act to modulate the level of internal neurotrophic factors. For instance increasing VEGF and BDNF neurotrophic factors influence the proliferation of progenitor cells and survival of new born neurons respectively and thereby results in an enhanced rate of AHN. (Vithlani et al., 2013) Integration of these new neurons in existing neuronal circuitry has been suggested to improve spatial learning and memory. On the hand, research has shown that learning experiences can enhance AHN in rodent brains. In a study conducted by Ambrogini et al. (2000) it was shown that spatial learning enhances survival of the new born neurons of 21

the dentate gyrus. Therefore, while neurogenesis can enhance hippocampal dependent learning, in a feed forward mechanism spatial learning can also enhance AHN. One of the external factors that reduces AHN through the reduction of neurotrophic factors is stress. Stress can also have detrimental effects on the health of the existing neurons by inducing the formation of reactive oxygen species (ROS). ROS are accumulated in the body as a result of aging; this can partly account for the reduced survival of the neurons and ultimately the reduction of AHN in older mice. (van Praag, Shubert, Zhao, & Gage, 2005) In a study by Lemon, Rollo, & Boreham (2008) it was shown that intake of dietary anti-oxidants -a component of enriched environmentreduces the burden of ROS and conferred neurogenic benefits. Studying the effect of voluntary exercise â&#x20AC;&#x201C;a component of enriched environment- on aged mice, van Praag and colleagues showed that the decline in neurogenesis as a result of aging was ameliorated to half of the decline in an aged-match control group and behaviorally runner mice had improved learning and memory of the test maze. It was further suggested that the decline in synthesis of new neurons in major depressive disorders (MDD) and the associated depressive symptoms can be alleviated by exercise in a similar mechanism to the action of antidepressants by enhancing neurotrophic factors and increasing the number of new neurons. In one study Kempermann, Kuhn, & Gage (1998)


tested for the effect of sensory and motor enrichment on AHN. In this study the animals were housed in groups with the opportunity for sensory exploration, social interactions, and exercise. The results indicated an increase in survival of new neurons in aged mice of enrichment group as compared to mice of the control group. In a follow up study by Kobilo et al. (2011), sensory and motor components of environmental enrichment were tested separately. The results showed that presence of motor stimuli alone is responsible and sufficient for neurogenic and procognitive benefits in mice. By addressing the shortcoming of previous studies, Mustroph and colleagues aimed to analyze the impact of different novelty and modality of sensory stimulitactile, visual, dietary, auditory, and vestibular- and motor stimuli on AHN and cognitive abilities in singly housed male C57BL/6J mice. In this review we provide some details of their results and discus the implications of their findings in relation to other studies. Furthermore, we provide the future directions that this study may take. Research Overview Summary of Major Results

Average time spend interacting with sensory and motor stimuli

32 male C57BL/6J mice were singly housed in 4 different housing conditions as followed: Running wheel present in their cage (RUN), rotatable novel toys and diets presented in their cage (EE), RUN and EE, and standard housing conditions (Control). Video tracing of the animals were used to assess the time each animal spends doing physically activities and the time they spend interacting with toys. On average mice in RUN group spent 2.3 hours/day and mice in RUN+EE group1.8 hours/day on running wheels which exceeded the activity of mice in EE and Control group respectively. The difference between the activity of RUN and RUN+EE mice was not statistically significant. On the other hand, mice of the EE group spent 81% of their time in the enriched environment which exceeds the RUN+EE group by 13%. These data are used in assessment of the correlation of neurogenic and cognitive benefits to the sensory and motor stimuli in different housing conditions.

Motor stimuli enhances the rate of Adult Hippocampal Neurogenesis

The average granule layer volume in control animals was 0.46 μm3 ± 0.023. Running increased the volume of granule layer by 20% and environmental enrichment increased the volume of the granule layer by 12%. These effects were additive as the greatest increase was seen in EE+RUN group with granule layer volume of 0.65 μm3 ± 0.041. The numerical count using confocal microscopy indicated that the greatest BrdU+/NeuN+ cell density was in the Run group with 7.6 ± 0.77 (new neurons per cubic mm × 103). This was followed by mice

of RUN+EE condition with 6.0 ± 0.45, mice of EE condition with 5.2 ± 0.34, and mice of control condition with 4.3 ± 0.39 new neurons respectively. The immunohistochemical analysis indicated an approximate 80% overlap between BrdU+ cells and the NeuN+ neurons. (Fig. 1E) The co-expression of the two markers suggests that the dividing cells are differentiating into mature neurons in the hippocampus confirming enhancement of the AHN. Analysis of the co-variance showed significant correlation between the average distance traveled on the wheel and the BrdU+/NeuN+ cell density. (Fig.1G) However, posthoc pairwise analysis indicated no significant difference of co-labelled neurons between EE versus Control, and EE+RUN versus EE group. Consistent with these findings, in a study by Kohl et al. (2002) it was shown that while postweaning enrichment-enhanced physical activity- possesses significant neurogenic benefits, preweaning enrichment-sensory nourishments- has no lasting effect on AHN. Moreover in a more thorough study by van Praag and collaugues analyzing different components of motor and sensort stimuli, it was shown that the greatest enhancement in AHN occurs in mice following voluntary wheel running as compared to mice following social interactions or swimming.

Figure 1. Aerobic exercise is the critical component of environmental enrichment in inducing adult hippocampal neurogenesis. New neuron staining as an indication of neurogenesis in A) Control, B) EE, C)RUN, and D) EE+RUN mice. E) NeuN+ neuron stained in green and BrdU+ neuron stained in red. Double labeled BrdU+/ NeuN+ neuron is shown by overlap of green and red. F) Average number of new neurons as measured by the number of BrdU+/NeuN+ neurons in the dentate gyrus of mice in different groups. G) Correlation of the distance traveled and the number of BrdU+/NeuN+ neurons. (Mustroph et al., 2012)

Motor stimuli enhances spatial learning and memory Mice in all housing conditions spent more time on the quadrant with the hidden platform than other three quadrants of the Morris water maze.(Fig.2 B) Following the five days learning period all animals learned and retained memory of the location of the platform using outside environmental cues. Previous 22


work on exercise by van Praag and colleagues had shown that acquisition and retention of a Morris water maze in runner mice is better than the control nonrunner aged-match mice. Consistently in this study, there was a decrease in path length and latency to find the platform across the testing period; and mice in RUN group showed the fastest acquisition with a 75% decrease in length of the path by the second trial. (Fig.2 A) There are significant posthoc differences elicited on day two between mice of the RUN versus mice of all other groups (p<0.05). Enhanced spatial learning and memory following enhanced AHN is the cognitive benefit observed as a result of exercise in many studies. (Kempermann et al., 1998; Rhodes et al., 2003)

Figure 2. Performance on Morris Water Maze. A) The path length to find the hidden platform in mice of different housing condition over 5 days of the testing period. B) Duration of time spent in the quadrant containing the hidden platform. (Mustroph et al. 2012)

Conclusions and Discussion Confirming previous study by Kobilo and colleagues, the results obtained in the study by Mustroph et al. indicates that in an enriched environment physical exercise is the critical component in increasing AHN and spatial learning in adult male C57BL/6J mice. These results indicated that exercise can be used in conditions where the therapeutic aim is to enhance the proliferation and survival of neurons such as in MDD. Many research has been done to pinpoint the mechanism that accounts for enhanced AHN following environmental enrichment. It was previously thought that motor stimuli enhances the proliferation of progenitor cells and sensory stimuli enhances survival of the newly born neurons.(Olson, Eadie, Ernst, & Christie, 2006) Follow up studies by Fuss et al. (2010) showed that running enhances AHN by enhancing BDNF expression and increasing cell survival rather than proliferation. Therefore it can be concluded that 23

while environmental enrichment with sensory stimuli has no neurogenic benefits in C57BL/67 male mice, physical exercise enhances AHN by increasing the survival of new neurons. Even though mice in EE+RUN group had equal access and spent similar amount of time on the running wheels as mice in RUN group, they failed to display similar cognitive benefits. This result may seem contradictory as the overall number of BrdU+/NeuN+ cells were also similar between the two groups. However, the results can be explain in two different ways: neuronal density and neuronal plasticity. Due to the additive effect of motor and sensory stimuli on the granule layer volume, mice in EE+RUN group displayed the greatest volume which make the area less dense with new neurons than the granule layer of mice in RUN group. The density of neurons in that sense can then impact the size of neurons, the dendritic and axonal processes, and the neuronal communications. (Redila & Christie, 2006) Another possible explanation is that due to interaction with novel toys and for efficient processing of sensory stimuli, new neurons are recruited into existing neuronal circuitry. This integration of new neurons are absent in the RUN group which makes them more plastic and allows for enhanced spatial learning and memory. (Clark et al., 2012) The many modalities of environmental enrichment studied on singly housed mice in this experiment did not confer any of the neurogenic and cognitive benefits that were apparent following aerobic exercise. However, it cannot be concluded that sensory enrichment does not influence the brain. In a study by Schapiro (2002) it was argued that social interaction is an important component in an enriched environment. Although this experiment does not account for social enrichment, previous studies by Kobilo and colleagues tested for the effects of social interaction on AHN with no improvement in female C57BL/6J mice.

Conclusions

Previous research has shown that an enriched sensory and motor environment enhances neurogenesis and cognitive performance in mice. Provided these results, researchers later aimed to segregate the two components of environmental enrichment; female mice exposed to motor stimuli showed enhanced neurogenic and cognitive benefits when compared to mice exposed to sensory stimuli. However, the study could not thoroughly discount the importance of sensory stimuli on brain function as they were solely conducted in female mice in group housing and did not account for different modalities of sensory stimuli. By addressing these shortcomings this paper aimed to assess the impact of broad and novel sensory stimuli in single housed male mice. This study confirms the previous results of Kobilo and colleagues; showing that aerobic exercise is the essential component of environmental enrichment and that sensory stimuli of different modality and novelty do not confer any neurogenic and cognitive benefits in C57BL/67 male mice.


Criticisms and Future Directions

Previously Greenough, McDonald, Parnisari, & Camel, (1986) had shown differential brain changes including angiogenesis, dendritogenesis, and synaptogenesis within the visual cortex and the cerebellum following sensory stimuli. Therefore there are various brain changes that can occur in response to different experimental conditions. Structural changes such as angiogenesis, synaptogenesis, and astrogenesis confer cognitive benefits associated to the region in the brain in which they occur. Astrocytes in the tripartite synapses regulate development, maintenance, and plasticity of the cortex through the release of cytokines. While it is known that sensory deprivation can lead to astrocytic dysfunction, the effect of sensory enrichment on astrogenesis is not well understood. (Bengoetxea, Ortuzar, Rico-Barrio, Lafuente, & Argandoña, 2013) Density of cortical astrocytes between mice in RUN and EE group can be analyzed using immunohistochemical staining for S-100 β protein. Stress is a key modulator of AHN. Previous research on the hypothalamic-pituitary-adrenal (HPA) axis has shown that secretion of corticosterone is upregulated following stressful stimuli. Binding of this hormone to glucocorticoid and mineralocorticoid receptors can result in down regulation of AHN. Research has suggested that running and forced separation induces corticosterone release while complex environmental stimuli and social interactions reduce corticosterone levels. (Grégoire, Bonenfant, Le Nguyen, Aumont, & Fernandes, 2014) Using enzyme-linked immunoassay kits, the authors can measure the concentration of corticosterone in blood to assess the stress response of each animal to different sensory and motor stimuli. Diet encompasses frequency, total intake, and content of food. Although one component of sensory enrichment in this study was diet, the dietary supplement provided were cashews and other nuts high in polyunsaturated fatty acids in a single dietary regimen. Therefore, while the study fails to fully account for the effect of diet it concludes that dietary manipulations as a part of environmental enrichment did not contribute to the rate of neurogenesis and cognitive functions in the animal models. In order to understand the relative contribution of diet, the authors should measure the rate of neurogenesis and spatial memory in response to various mode of calorie restriction, intake of polyphenols which have neuro-protective effects, and intake of polyunsaturated fatty acids which are known to decrease BDNF and neurogenesis. (Murphy, Dias, & Thuret, 2014) References 1. Ambrogini, P., Cuppini, R., Cuppini, C., Ciaroni, S., Cecchini, T., Ferri, P., … Del Grande, P. (2000). Spatial learning affects immature granule cell survival in adult rat dentate gyrus. Neuroscience Letters, 286(1), 21–24. 2. Bengoetxea, H., Ortuzar, N., Rico-Barrio, I., Lafuente, J. V., & Argandoña, E. G. (2013). Increased physical activity is not enough to recover astrocytic population from dark-rearing. Synergy with multisensory enrichment is required. Frontiers in Cellular Neuroscience, 7(October), 170. http://doi.org/10.3389/fncel.2013.00170

Clark, P. J., Bhattacharya, T. K., Miller, D. S., Kohman, R. A., Deyoung, E. K., & Rhodes, J. S. (2012). New neurons generated from running are broadly recruited into neuronal activation associated with three different hippocampusinvolved tasks. Hippocampus, 22(9), 1860–1867. http:// doi.org/10.1002/hipo.22020 3. Fuss, J., Ben Abdallah, N. M. B., Vogt, M. A., Touma, C., Pacifici, P. G., Palme, R., … Gass, P. (2010). Voluntary exercise induces anxiety-like behavior in adult C57BL/6J mice correlating with hippocampal neurogenesis. Hippocampus, 20(3), 364–376. http://doi.org/10.1002/hipo.20634 4. Greenough, W. T., McDonald, J. W., Parnisari, R. M., & Camel, J. E. (1986). Environmental conditions modulate degeneration and new dendrite growth in cerebellum of senescent rats. Brain Research, 380(1), 136–143. http:// doi.org/10.1016/0006-8993(86)91437-X 5. Grégoire, C. A., Bonenfant, D., Le Nguyen, A., Aumont, A., & Fernandes, K. J. L. (2014). Untangling the influences of voluntary running, environmental complexity, social housing and stress on adult hippocampal neurogenesis. PLoS ONE, 9(1). http://doi.org/10.1371/journal.pone.0086237 6. Kempermann, G., Kuhn, H. G., & Gage, F. H. (1998). Experience-induced neurogenesis in the senescent dentate gyrus. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 18(9), 3206–3212. http:// doi.org/10.1016/S0149-7634(97)00008-0 7. Kobilo, T., Liu, Q.-R., Gandhi, K., Mughal, M., Shaham, Y., & van Praag, H. (2011). Running is the neurogenic and neurotrophic stimulus in environmental enrichment. Learning & Memory (Cold Spring Harbor, N.Y.), 18(9), 605–609. http://doi.org/10.1101/lm.2283011 8. Kohl, Z., Kuhn, H. G., Cooper-Kuhn, C. M., Winkler, J., Aigner, L., & Kempermann, G. (2002). Preweaning enrichment has no lasting effects on adult hippocampal neurogenesis in four-month-old mice. Genes, Brain and Behavior, 1(1), 46–54. http://doi.org/10.1046/j.16011848.2001.00009.x 9. Lemon, J. A., Rollo, C. D., & Boreham, D. R. (2008). Elevated DNA damage in a mouse model of oxidative stress: Impacts of ionizing radiation and a protective dietary supplement. Mutagenesis, 23(6), 473–482. http://doi. org/10.1093/mutage/gen036 10. Murphy, T., Dias, G. P., & Thuret, S. (2014). Effects of diet on brain plasticity in animal and human studies: Mind the gap. Neural Plasticity. http://doi.org/10.1155/2014/563160 11. Mustroph, M. L., Chen, S., Desai, S. C., Cay, E. B., DeYoung, E. K., & Rhodes, J. S. (2012). Aerobic exercise is the critical variable in an enriched environment that increases hippocampal neurogenesis and water maze learning in male C57BL/6J mice. Neuroscience, 219, 62–71. http://doi. org/10.1016/j.neuroscience.2012.06.007 12. Olson, A. K., Eadie, B. D., Ernst, C., & Christie, B. R. (2006). Environmental enrichment and voluntary exercise massively increase neurogenesis in the adult hippocampus via dissociable pathways. Hippocampus. http://doi. org/10.1002/hipo.20157 13. Redila, V. A., & Christie, B. R. (2006). Exercise-induced changes in dendritic structure and complexity in the adult hippo24


campal dentate gyrus. Neuroscience, 137(4), 1299–1307. http://doi.org/10.1016/j.neuroscience.2005.10.050 14. Rhodes, J. S., van Praag, H., Jeffrey, S., Girard, I., Mitchell, G. S., Garland, T., & Gage, F. H. (2003). Exercise increases hippocampal neurogenesis to high levels but does not improve spatial learning in mice bred for increased voluntary wheel running. Behavioral Neuroscience, 117(5), 1006–1016. http://doi.org/10.1037/0735-7044.117.5.1006 15. Schapiro, S. J. (2002). Effects of social manipulations and environmental enrichment on behavior and cell-mediated immune responses in rhesus macaques. Pharmacology Biochemistry and Behavior, 73(1), 271–278. http://doi. org/10.1016/S0091-3057(02)00779-7 16. Van Praag, H., Shubert, T., Zhao, C., & Gage, F. H. (2005). Exercise enhances learning and hippocampal neurogenesis in aged mice. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 25(38), 8680–8685. http://doi.org/10.1523/JNEUROSCI.1731-05.2005 17. Vithlani, M., Hines, R. M., Zhong, P., Terunuma, M., Hines, D. J., Revilla-Sanchez, R., … Moss, S. J. (2013). The ability of BDNF to modify neurogenesis and depressivelike behaviors is dependent upon phosphorylation of tyrosine residues 365/367 in the GABA(A)-receptor γ2 subunit. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 33(39), 15567–77. http://doi. org/10.1523/JNEUROSCI.1845-13.2013

25


subPCP induced alterations in gut microbiota associated with memory deficit in schizophrenia model Mie Andersen

Over the years, Schizophrenia has been intensely studied to find the underlying cause for the disorder. Many studies have focused on the genetic factors involved, but an ac-cumulation of data is now pointing toward a possible im-mune system mediated pathogenesis for the disorder. In line with this, there is an increasing interest in the gut-brain axis and the gut microbiota as possible players in the pathogenesis of schizophrenia. This was addressed by Jørgensen et al. Using the subchronic PCP induced schizophrenia rat model, they discovered a correlation between altered GM and cognitive deficits in the model. In this paper, their research will be reviewed with emphasis on the findings implying the GM in schizophrenia, and furthermore how they comply with other data. Furthermore arguments for and against the role of gut microbiota in the pathogenesis of schizophrenia will be discussed in this article. Key words: Acute phencyclidine (aPCP); Gut-brain axis; Gut microbiota (GM); Locomotor activity assay (MOTR); Novel object recognition (NOR); Schizophrenia; Subchronic phencyclidine (subPCP) Background Schizophrenia is a complex disorder characterized by a multitude of symptoms including positive and negative symptoms. The underlying mechanism for its pathology is not well understood, and both environmental and genetic factors seem to be responsible for the phenotype. In recent years, a bidirectional pathway between the gut and the brain â&#x20AC;&#x201C; termed the gut-brain axis â&#x20AC;&#x201C; has become more evident. Furthermore, the importance of the gut mi-crobiota (GM) with its regulatory role in the gut-brain axis is of increasing interest in disease and as possible therapeu-tic tool. Thus, variations in the GM have been implied in various CNS related disorders such as autism and multiple sclerosis2,3. For instance, the gut microbiota has been shown to trigger an autoimmune response leading to multi-ple sclerosis, thus presenting a possible target for treatment3. Hence, the research, reviewed in this article, focus on the possible involvement of the gut-brain axis in schizo-phrenia4. The gut microbiota plays an important role in regulation of the immune system, and thus alterations in the GM can lead to dysregulation of the immune system and cause inflammatory responses5. In search of genetic factors underlying schizophrenia numerous genome wide studies have been conducted, and interestingly genes commonly linked to schizophrenia are related to the immune system6,7, suggesting that alterations in the immune system is contributing to the pathogenesis of schizophrenia. In addition, autoimmune diseases has also been linked with schizophrenia8, further implicating the immune system in the disorder. Gastrointestinal dysregulation and inflammation has al-so been associated with schizophrenia. Namely, a there is considerable gastrointestinal comorbidity in schizophrenia, such as irritable bowel syndrome and inflammatory bowel disease observed in9.

In this fashion the GM and the gut brain axis is able to explain both genetic and environmental factors contributing to schizophrenia. However, despite this abundance of evidence linking the immune system and the GM with schizophrenia, it is not clear, whether the immune system constitutes a causative factor in the schizophrenic phenotype, or if the two are otherwise associated.

Figure 1 The gut brain axis. Abnormal CNS function leads to dysregulation of the gastrointestinal dynamics and alterations of gut microbiota, which in turn affect the brain. Source: Cryan and Dinan1

26


Figure 2 NOR performance by vehicle- and subPCP-treated rats, respectively, at 0 weeks (T0), 3 weeks, (T3) and 6 weeks (T6) after washout. DI: discrimination index (Source: Jørgensen et al13)

Research Overview Summary of Major Results

Duration of subPCP induced effects

The subPCP induced schizophrenia model is a widely used model for studying the effect of new therapeutic candidates in treating schizophrenia. The model mimics both positive and negative symptoms of schizophrenia. Thus, subPCP has been shown to increase locomotor sensitivity and to impair working memory. However, the duration of the subPCP-induced effect on memory had not previously been described, why Jørgensen et al wanted to examine this. After subjecting rats to subPCP-treatment followed by one week of washout, locomotor activity and memory were evaluated by acute PCP (aPCP) induced locomotor activity assay (MOTR) and novel object recognition (NOR), respectively. In agreement with previous findings10, the group found subPCP to increase locomotor activity in response to aPCP and to impair the memory performance. To study the duration of the memory deficit, the rats were tested NOR either immediately after, three weeks, or six weeks after washout, respectively. The group found that the decreased NOR performance resulting from subPCP was evident up until three weeks after washout (Figure 2), and that the increased locomotor activity was still evident at six weeks after washout – the latter serving as a control that subPCP were able to induce changes in all groups of rats tested. These results show that the subPCP-induced cognitive effects in this model last for 3 weeks after washout and are reversed after 6 weeks.

Roseburia and Dorea of the Lachnospiraceae family and the genus Odoriabacter tended to be elevated in subPCP treated rats immediately after washout. Likewise, an un-known genus belonging to the S24-7 family tended to be elevated at three weeks after washout. These results show a correlation between the GM and the behavioural changes observed in the subPCP-induced model.

A causative relation between GM and NOR

Jørgensen et al wanted to explore the nature of the dynam-ics between the GM changes and the impaired NOR in subPCP-treated rats to find a possibly causative relation between the two. In order to address this, the group repeated the experi-ments in rats that were administered ampicillin. It was found that NOR performance was similar between the subPCP treated group and the vehicle treated group (Figure 3) when the GM was reduced – thus, antibiotic reduction was able to rescue the cognitive deficits induced by subPCP. The ampicillin had no effect in MOTR. This suggest that the subPCP-induced changes in GM is upstream of the memory deficits seen in the model.

Changes in GM after subPCP

The authors hypothesize that variance within the subPCP induced model can be caused by variations in the GM. Thus, they investigated the effect of subPCP on GM and the association between GM and behaviour. In order to examine the influence of subPCP on the gut flora, samples of the GM were collected from the rats at 0 and three weeks after washout, and the samples were sequenced. Comparing the samples from subPCP treated and vehicle treated rats, the Jørgensen et al found a weak but significant difference between the groups. The genera 27

Figure 3 NOR performance by vehicle- and subPCPtreated rats that were either administered antibiotics or not. DI: dis-crimination index (Source: Jørgensen et al13)


Conclusions and Discussion The results suggest that the subPCP induced rat model can be used for studying pharmaceuticals against schizo-phrenia up to three weeks after washout, which is relevant as it permits testing for a longer period using the same animals, and this in turn means that fewer animals are needed in evaluations of new drugs. While the authors make a somewhat general statement that this is useful in utilizing the subPCP-induced animal model, it is important to keep in mind that they did only show this in the rat mod-el, and that other numbers may apply to the mouse model. The fact that the ampicillin treatment seemed to abolish the cognitive effects in the subPCP treated rats suggests that the GM is operational in causing the cognitive changes. Prior studies by the group showed similar changes in GM in two different stress models – elevated levels of Roseburia and Dorea in social disruption, and elevated Odoribacter in the trippletest11,12. The authors reason that this supports that changes in GM in the present is due to subPCP-induced stress. At three week after washout, an unknown genus be-longing to the S24-7 family tended to be elevated in com-parison to the vehicle treated rats. Another unknown genus of the S24-7 family has previously been associated with enhanced spatial memory13. As pointed out by the authors this could indicate that the rise in the unknown genus could be the initiation in restoring the memory, as the NOR per-formance is back to normal at 6 weeks. However, this would need further investigation before a conclusion can be made. Sequencing GM samples from rats at six weeks after washout might be useful in testing this theory. In addition, this may also show whether the GM has been completely normalized thus supporting the correlation between the GM and the memory deficit. In conclusion Jørgensen et al made two major findings: (1) that the effects of subPCP on NOR is evident in the rat model for three weeks following washout; and (2) that sub-PCP induced changes in GM correlated with decreased NOR performance, and that antibiotic reduction was able to rescue this memory deficit .

Criticisms and Future Directions

The authors argue that the findings are useful for future studies on schizophrenia using this model, as they de-scribed the period for which it can be used following wash-out and account for some variance within the model. How-ever, it is worth considering whether their findings in fact suggest that the model is not applicable in studying schiz-ophrenia. That is, if the cognitive deficits in actual schizo-phrenic individual is not caused by changes in the GM, then the pharmaceuticals that shows a positive impact on cognition in the model will not necessarily show the same effect in schizophrenic patients. Therefore, it is important to research the GM composition in other schizophrenia models that exhibit similar cognitive deficits. Even more relevant would be to examine the dynamics of GM in schizophrenic individuals. In fact, a recent study showed that minocycline, an anti-biotic compound, was able to reduce the cognitive

symp-toms in schizophrenic patients14, supporting the theory that these can actually be caused by dysregulation in the GM. Furthermore, studies have shown that thioridazine – a first generation antipsychotic drug used for treating schizophre-nia – has antibiotic abilities15. However, this drug was used to reduce the positive symptoms in schizophrenic patients and not the cognitive ones. On the contrary, a meta-analysis indicated a negative impact of thioridazine on working memory in schizophrenia16. These effects could in turn be due to other pathways than inflammation and thus not connected to the antibiotic effect of the drug. However, this would need further investigation. As mentioned by Jørgensen et al it is necessary to eliminate the possibility of a confounding factor between the ampicillin treatment and the rescue of memory impairment. This could be done by transplanting microbiota from the subPCP treated rats into a control group of germ-free rat, as done by others17,18, in order to see if the phenotypes change correspondingly. This could reveal whether ampicillin treatment has a direct impact on the brain. Additionally it would show if the GM alone could induce a memory deficit without any residual PCP. Furthermore, using specific antibiotics19 targeting each of the microbial species elevated by subPCP may lead to finding the microbe accountable for the phenotype. This could be the first step in elucidating the possible molecular pathway from GM to brain function observed in the subPCP induced schizophrenia model by Jørgensen et al. If in fact the genera Roseburia, Dorea and Odoribacter are contributing to the memory deficits in the rat model, it would be interesting to examine the NOR performance in the stress models that were previously shown to have ele-vated levels of those genera11,12. This might help under-stand the necessity or sufficiency of the microbiota in causing the phenotype. It is important to keep in mind that the study conducted by Jørgensen et al show that GM may be accountable for some but not all phenotypic traits of schizophrenia in the model. Nevertheless, these findings may lead to a better understanding of the disorder and maybe eventually a GM based treatment of said symptoms. References

1. Cryan, J. F. & Dinan, T. G. Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nature reviews. Neuroscience 13, 701-712, doi:10.1038/ nrn3346 (2012). 2. Adams, J. B., Johansen, L. J., Powell, L. D., Quig, D. & Rubin, R. A. Gastrointestinal flora and gastrointestinal status in children with autism--comparisons to typical children and correlation with autism severity. BMC gastroenterology 11, 22, doi:10.1186/1471-230X-11-22 (2011). 3. Berer, K. et al. Commensal microbiota and myelin autoantigen cooperate to trigger autoimmune demyelination. Nature 479, 538-541, doi:10.1038/nature10554 (2011). 4. Pyndt Jørgensen, B. et al. Investigating the long-term effect of subchronic phencyclidine-treatment on novel object recognition and the association between the gut microbiota and behavior in the animal model of schizophrenia. Physiology & behavior 141, 32-39, doi:10.1016/j.physbeh.2014.12.042 (2015).

28


5. Purchiaroni, F. et al. The role of intestinal microbiota and the immune system. European review for medical and pharmacological sciences 17, 323-333 (2013). 6. Stefansson, H. et al. Common variants conferring risk of schizophrenia. Nature 460, 744-747, doi:10.1038/ nature08186 (2009). 7. Shi, J. et al. Common variants on chromosome 6p22.1 are associated with schizophrenia. Nature 460, 753-757, doi:10.1038/nature08192 (2009). 8. Benros, M. E. et al. Autoimmune diseases and severe infections as risk factors for schizophrenia: a 30-year populationbased register study. The American journal of psychiatry 168, 1303-1310, doi:10.1176/appi.ajp.2011.11030516 (2011). 9. Severance, E. G., Prandovszky, E., Castiglione, J. & Yolken, R. H. Gastroenterology issues in schizophrenia: why the gut matters. Curr Psychiatry Rep 17, 574, doi:10.1007/ s11920-015-0574-0 (2015). 10. Damgaard, T. et al. Positive modulation of alpha-amino3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors reverses sub-chronic PCP-induced deficits in the novel object recognition task in rats. Behav Brain Res 207, 144-150, doi:10.1016/j.bbr.2009.09.048 (2010). 11. Bailey, M. T. et al. Exposure to a social stressor alters the structure of the intestinal microbiota: implications for stressorinduced immunomodulation. Brain, behavior, and immunity 25, 397-407, doi:10.1016/j.bbi.2010.10.023 (2011). 12. Bangsgaard Bendtsen, K. M. et al. Gut microbiota composition is correlated to grid floor induced stress and behavior in the BALB/c mouse. PloS one 7, e46231, doi:10.1371/ journal.pone.0046231 (2012). 13. Pyndt Jørgensen, B. et al. A possible link between food and mood: dietary impact on gut microbiota and behavior in BALB/c mice. PloS one 9, e103398, doi:10.1371/journal. pone.0103398 (2014). 14. Liu, F. et al. Minocycline supplementation for treatment of negative symptoms in early-phase schizophrenia: a double blind, randomized, controlled trial. Schizophrenia research 153, 169-176, doi:10.1016/j.schres.2014.01.011 (2014). 15. Thorsing, M. et al. Thioridazine induces major changes in global gene expression and cell wall composition in methicillin-resistant Staphylococcus aureus USA300. PloS one 8, e64518, doi:10.1371/journal.pone.0064518 (2013). 16. Fenton, M., Rathbone, J., Reilly, J. & Sultana, A. Thioridazine for schizophrenia. The Cochrane database of systematic reviews, CD001944, doi:10.1002/14651858.CD001944. pub2 (2007). 17. Alpert, C., Sczesny, S., Gruhl, B. & Blaut, M. Long-term stability of the human gut microbiota in two different rat strains. Current issues in molecular biology 10, 17-24 (2008). 18. Turnbaugh, P. J. et al. The effect of diet on the human gut microbiome: a metagenomic analysis in humanized gnotobiotic mice. Science translational medicine 1, 6ra14, doi:10.1126/ scitranslmed.3000322 (2009). 19. Citorik, R. J., Mimee, M. & Lu, T. K. Sequence-specific antimicrobials using efficiently delivered RNA-guided nucleases. Nature biotechnology 32, 1141-1145, doi:10.1038/ nbt.3011 (2014). 29


Environmental Enrichment: A Neurorehabiitation Method utilized to treat deficits conferred from Traumatic Brain Injury (TBI) Ami Baba

Traumatic brain injury (TBI) is a debilitating injury that is prevalent in the general population, and often results in various impairments in speech, memory, attention, mobility, and executive functions. In order to regain deficits that have been acquired after sustaining a TBI, environmental enrichment (EE) has been used as a neurorehabilitation model that exposes individuals with TBI to a social, interactive, and complex space. EE has found to be effective in improving deficits in cognitive and motor functioning in rodents that have sustained a TBI. One study investigated the efficacy of EE in rodents that have sustained a TBI, and compared if the benefits conferred from short-term and long-term EE exposure differed. The results of the study revealed that EE is an effective method for regaining back spatial memory and mobility; in addition, results revealed that short-term EE was equally as effective as long-term EE. As the study demonstrated that a long duration of EE is not necessary in order to recover cognitive and motor functioning, EE is a promising therapy model that has the potential to reach out to patients that cannot receive sufficient treatment due to various constraints. Further investigation into the effectiveness and optimum distribution of EE can change the landscape of TBI rehabilitation. Key words: traumatic brain injury (TBI), environmental enrichment (EE), neurorehabilitation, cognitive rehabilitation, motor recovery Background Traumatic brain injury (TBI) is an injury that results from both open-headed injuries and closed-headed injuries, resulting in mild TBI (concussions), or moderate-severe TBI1-3. TBI is pervasive and has a high incidence rate in the general population, and in the United States alone, around 1.7 million people are affected by TBI annually1. TBI affects a wide array of individuals, as the leading causes of TBI includes motor vehicle accidents, athletics, falls, and violent assaults, and those who sustain a TBI often experience a multitude of deficits that affect their quality of living and daily functioning, preventing individuals from pursuing an active lifestyle that would assist with their recovery1-4. Individuals with TBI experience deficits in cognitive, emotional, and motor functioning1-6. In addition, TBI has been observed to cause anatomical changes in the brain4. In order to regain functioning of impaired cognitive and motor abilities, a variety of therapy methods are used, including invasive methods such as pharmacotherapies: 5-HT1A receptor agonists 8-OH-DPAT, or dopamine receptor agonists bromocriptine and methylphenidate, and neurotrophic support3,7. However, non-invasive therapy methods are also utilized and are starting to be implemented as part of neurorehabilitation for TBI patients, such as voluntary exercise and environmental enrichment (EE)2,4-6,8,9. EE is a method that has been identified to be a promising therapy model that been successful in improving cognitive and motor functions that were impaired in those who have sustained a TBI2,4-11. EE is a therapy method that exposes a subject affected with TBI to a stimulating, social, complex space that allow for interaction and engagement with novel, interactive objects and activities2-5,7-13. Studies have found that animals

and humans that have cognitive, emotional, and motor impairments as a result of a TBI have conferred long-term benefits in their memory, mobility, executive functions, and attention after exposure to EE3-5,7-9,12. In addition to improvements in behaviour, anatomical changes in the brain has also been observed due to EE exposure â&#x20AC;&#x201C; the brain has exhibited enhanced synaptogenesis, spine remodeling, hippocampal neurogenesis, and maintenance of tissue integrity â&#x20AC;&#x201C; which has been correlated with improved behavioural functions conferred from EE2-7,9,10,13-15. While EE has shown to be a promising neurorehabilitation method, there are still some issues that are unclear. Studies have shown that the benefits conferred from EE are relatively the same regardless of the length of time that subjects were exposed to EE; therefore, it is unclear as to whether a longer EE duration is more beneficial7,8. In addition, most studies that have been conducted utilizing EE have investigated benefits conferred from EE in animal models. Since there are few studies that have examined the use and benefits of EE in human patients, the transferability of the benefits acquired from EE that have been observed in animal models has not been fully investigated. Research Overview Summary of Major Results Cheng et al. was interested in investigating the efficacy of EE in TBI rehabilitation, in addition to examining whether the cognitive and motor benefits conferred from EE exposure would be relatively equal in subjects that were exposed to the EE paradigm for varying durations9. In order to study this, the researchers utilized a rat model with experimental TBI, which was induced through controlled cortical impact (CCI). Two different housing environments were used for the duration of the experiment; rats were housed 30


Figure 1. Graphical representations of mean time (seconds) that rats remained on the balance beam9. (A) Phase 1 results. TBI+EE performed better on beam balance tasks than the TBI+STD group (*p<0.0117). The sham group (control) performed significantly better on the task compared to both TBI+STD and TBI+EE. (**p<0.0001)9. (B) Phase 2 results. TBI+EE, TBI+EE+STD group performed significantly better than TBI+STD group (*p<0.0021). No significant difference was found in performance between TBI+EE and TBI+EE+STD group (p>0.05)9.

in either a standard steel-wire mesh (STD) cage, or a multi-level environmental enrichment (EE) cage. Inside the EE cage, the rats had access to a variety of interactive, novel objects which created a complex, stimulating environment for the rats to live in. Both the TBI and control group rats were divided into groups randomly, and placed into either STD or EE housing. For phase 1 of the experiment, which lasted for 3 weeks, the rats stayed in their assigned housing; in phase 2, half of the rats in the EE cage stayed in their original cage, while the other half were moved to STD housing for the next 6 months. Therefore, researchers investigated three experimental groups: 31

Figure 2. Graphical representations of mean time (sec) spent finding the platform in the Morris Water Maze (MWM)9. (A) Phase 1 results. Control outperformed both TBI+EE and TBI+STD (**p<0.0001). The TBI+EE group was able to locate the platform faster than TBI+STD group (*p<0.0001)9. (B) Phase 2 results. Performance of TBI+EE and TBI+EE+STD group had no significant difference (p=0.53), but outperformed the TBI+STD group (*p<0.0001)9.

rats placed in the EE cage for 6 months and 3 weeks (TBI+EE), rats placed in EE housing for 3 weeks and STD housing for 6 months (TBI+EE+STD), and rats placed in STD housing for the entire duration of the experiment (TBI+STD). In order to study the cognitive and motor improvements after exposure to EE, the Morris Water Maze (MWM) and beam balance tasks were used9. In phase 1 of the experiment, the rats took part in the MWM and beam balance tasks on days 1-5 and 14-18, and in phase 2, tests were run once a month. Within the rats that have sustained a TBI, the results for both phase 1 and 2 indicated that the rats that


were exposed to EE for both short and long durations (TBI+EE, TBI+EE+STD) showed significantly better results on the Morris Water Maze than rats that were not exposed to EE at all (p<0.0001). In phase 2, all groups exposed to EE (TBI+EE, TBI+EE+STD) performed markedly better on the beam balance (p<0.0021) and MWM task (p<0.0001) than the TBI+STD group, but the performance between the TBI+EE and TBI+EE+STD group were equally comparable and did not show a significant difference (p>0.05). These results indicate that EE does result in better recovery in cognitive and motor function, as all groups that were exposed to EE showed significantly better performance on both tasks compared to the TBI group that was not exposed to EE at all9. Similar results have been reported in other studies – TBI rats that were exposed to early or continuous EE demonstrated better performance on beam-walking compared to rats with no EE exposure; in addition, better cognitive training was observed in rats with continuous EE exposure5,7. The results also show that there is no difference between the benefits conferred between TBI+EE and TBI+EE+STD. Conclusions and Discussion Cheng et al.’s study suggest that longer exposure to EE is not necessarily beneficial compared to a shorter exposure to EE, because the performance on both the MWM and beam balance tasks did not have a significant difference9. Research suggests that there is a minimum duration (1-4 weeks) of EE exposure that is necessary to observe behavioural benefits8, which supports Cheng et al.’s results by demonstrating that short exposure to EE is sufficient in acquiring improvements in cognitive and motor deficits6,7,9. Another study determined that the length of EE in terms of conferring behavioural benefits was not the most important factor for improvements in cognitive and motor function, as long as there was exposure to EE7. Rats that received exposure to EE for only 1-week directly after sustaining a TBI, then moved to STD (early EE) and rats that were exposed to the EE paradigm for three weeks continuously (continuous EE) both showed enhanced performance on beamwalking tasks7. In addition, rats that were exposed to EE for 21 days demonstrated similar learning rates to rats that received EE for 14 days, so long as there was a continuous exposure to EE for at least 2 weeks11 – strengthening the notion that there is a minimum necessary duration. Therefore, the results all indicate that a longer duration of EE exposure is not necessary to acquire benefits, as long as there is a short exposure to EE. The results suggest that there may be an upper-limit to the benefits that can be acquired from long-term EE, as these results indicate that longer durations of EE does not result in more cognitive and motor benefits9. While behavioural benefits may require a minimum of 1-4 weeks of exposure to an EE paradigm, plasticity changes in the brain were observed from as little as 1 hour of EE exposure per day6. Rats that sustained a TBI through fluid percussion (FP) were exposed to EE for 1 hour/day for 20 days, and researchers

observed that in their ipsilesional dentate gyrus, the survival of the neural progenitors that are endogenous to this region were protected, in addition to increased neurogenesis in the granule cell layer6. These results strengthen that EE benefits arise from short durations in the brain in terms of plasticity, even if it is not apparent behaviourally. Furthermore, plasticity changes in the brain seem to benefit from a continuous exposure to EE11. EE has demonstrated potential in improving behavioural functions, but also in maintaining and improving neuroplasticity and anatomy in the brain; EE had an effect on preventing atrophy in the hippocampus, slowing down of CA3 cell loss in the dentate gyrus, decreased size in site of lesion in the cerebral cortex, and an upward increase in spine density and dendritic growth4,7,9,10.

Criticisms and Future Directions

However, there is conflicting evidence regarding the effectiveness of longer durations of EE. Amaral et al. reported that rats exposed to the EE paradigm for a longer duration (8-weeks) gained behavioural improvements that were more persistent compared to rats that were exposed to EE for a shorter duration (4-weeks) of time, which suggests that longer durations of EE does have a benefit in making more permanent, fixated improvements. These results suggest that while the benefits that are conferred from a shorter duration of EE is equivalent to the benefits acquired from a longer duration of EE, the difference is in how long these benefits last for after EE treatment is over. Furthermore, longer periods of EE seem to allow more time for anatomical and neurochemical alterations in the brain to occur, which contributed to the persistence of the benefits8,10,11. Cheng et al.’s research did not investigate the post-EE long-term effects and persistence of the benefits acquired from the EE paradigm; therefore, it would be of value to conduct a study investigating the potential differences in persistence of cognitive and motor benefits acquired from short and long EE exposure. This could potentially be done by exposing groups of TBI rats to EE cages for a select duration that vary from 1-week to around 6-weeks, and then testing their performance on cognitive and behavioural tasks after 6-months from EE exposure. The benefits of long-term EE could then be elucidated in terms of the persistence of the benefits acquired, along with the anatomical changes through histological analysis. Further investigation will give insight into the optimum duration of EE that should be distributed during treatment. Furthermore, Cheng et al. mentions that the results obtained from the study would benefit TBI treatment. However, because the research that focuses on EE is predominantly conducted on animal models that have sustained an experimental TBI, the transferability of the benefits that have been observed to be associated with EE exposure was not studied. However, past research has shown that EE also does help humans recover from brain injuries. One study found that stroke patients that were in a facility that allowed for patients to partake in more interaction and activities experienced faster recovery of lost motor abilities, 32


while those who spent more time alone took longer to recover12. In addition, TBI patients that have identified to be involved in EE activities on the Lifestyle Activities Questionnaire (LAQ) also showed less deterioration in their hippocampus4. These results indicate that behaviour, brain anatomy, and plasticity recovery are also evident in humans as well; as such, EE is a promising neurorehabilitation method that could be incorporated in patientâ&#x20AC;&#x2122;s daily lifestyles for rehabilitation. To further investigate the benefits of EE in patients that have sustained TBI, a group of patients receiving a novel therapy model that exposes patients to an environment that facilitates cognitive, social, and physical aspects can be compared to another group of patients receiving standard care. In the EE paradigm, mind stimulating games such as crosswords and chess can be incorporated with physical activity and socialization opportunities.

Conclusion

The results from Cheng et al.â&#x20AC;&#x2122;s experiment demonstrated that rats that sustained a TBI conferred cognitive and motor improvements from EE exposure. Similar studies that were interested in looking into the effects of EE have also shown similar results, and express that EE is a beneficial recovery and therapy paradigm for regaining back impairments that resulted from TBI2-15. These findings validate that EE is a relevant rehabilitation model that indicate that exposure to a social, complex, and interactive environment facilitate recovery of important skills such as memory, attention, and mobility2-14.The results of these studies demonstrate that in treating TBI patients, rehabilitation and therapy should integrate activities and environments that focus on cognitive, physical, and social aspects2,4,12. With a better understanding of how EE should be distributed, along with how effective the model is for human patients, EE is a neurorehabilitation model that could potentially alter the current standard care used for TBI patients. References 1. Faul, M., Xu, L., Wald, M. M. & Coronado, V. Traumatic Brain Injury in the United States. Atlanta, GA: Centers for Disease Control and Prevention, National Center for Injury Prevention and Control (2010) 2. Frasca, D., Tomaszczyk, J., McFadyen, B. J. & Green, R. E. Traumatic brain injury and post-acute decline: what role does environmental enrichment play? A scoping review. Front. Hum. Neurosci. 7 (2013). 3. Sozda, C. N. et al. Empirical comparison of typical and atypical environmental enrichment paradigms on functional and histological outcome after experimental traumatic brain injury. J. Neurotrauma 27, 1047-1057 (2010). 4. Miller, L. S., Colella, B., Mikulis, D., Maller, J. & Green, R. E. Environmental enrichment may protect against hippocampal atrophy in the chronic stages of traumatic brain injury. Front. Hum. Neurosci. 7 (2013). 33

5. Passineau, M. J., Green, E. J. & Dietrich, W. D. Therapeutic effects of environmental enrichment on cognitive function and tissue integrity following severe traumatic brain injury in rats. Exp. Neurol. 168, 373-384 (2001). 6. Gaulke, L. J., Horner, P. J., Fink, A. J., McNamara, C. L. & Hicks, R. R. Environmental enrichment increases progenitor cell survival in the dentate gyrus following lateral fluid percussion injury. Mol. Brain Res. 141, 138-150 (2005). 7. Hoffman, A. N. et al. Environmental enrichment-mediated functional improvement after experimental traumatic brain injury is contingent on task-specific neurobehavioral experience. Neurosci. Lett. 431, 226-230 (2008). 8. Amaral, O. B., Vargas, R. S., Hansel, G., Izquierdo, I. & Souza, D. O. Duration of environmental enrichment influences the magnitude and persistence of its behavioral effects on mice. Physiol. Behav. 93, 388-394 (2008). 9. Cheng, J. P. et al. A relatively brief exposure to environmental enrichment after experimental traumatic brain injury confers long-term cognitive benefits. J. Neurotrauma. 29, 2684-2688 (2012). 10. Leggio, M. G. et al. Environmental enrichment promotes improved spatial abilities and enhanced dendritic growth in the rat.Behav. Brain Res. 163, 78-90 (2005). 11. Matter, A. M., Folweiler, K. A., Curatolo, L. M. & Kline, A. E. Temporal effects of environmental enrichment-mediated functional improvement after experimental traumatic brain injury in rats. Neurorehabil. Neural Repair. 25, 558-564 (2011). 12. De Wit, L. et al. Motor and functional recovery after stroke: a comparison of 4 European rehabilitation centers. Stroke. 38, 2101-2107 (2007). 13. Lambert, T. J., Fernandez, S. M. & Frick, K. M. Different types of environmental enrichment have discrepant effects on spatial memory and synaptophysin levels in female mice. Neurobiol. Learn. Mem. 83, 206-216 (2005). 14. Bennett, J. C., McRae, P. A., Levy, L. J. & Frick, K. M. Long-term continuous, but not daily, environmental enrichment reduces spatial memory decline in aged male mice. Neurobiol. Learn. Mem. 85, 139-152 (2006). 15. Bruel-Jungerman, E., Laroche, S. & Rampon, C. New neurons in the dentate gyrus are involved in the expression of enhanced long-term memory following environmental enrichment. Eur. J. Neurosci. 21, 513-521 (2005).


Creatine Supplementation on brain performance suggestive of potential therapeutic agent Vanessa C. Bracaglia

Background Creatine is a naturally synthesized molecule in vertebrates that plays an important role in energy metabolism. Catalyzed by creatine kinase, phosphorylated creatine (PCr) has the ability to transfer it’s high energy phosphate group to ADP in order to produce ATP. This process of ATP synthesis is quicker than production via oxidative phosphorylation or other de novo pathways (Rae et al., 2003). Creatine is used by cells both in skeletal muscle and in the brain where it has been advocated to provide a neuroprotective effect. One way it achieves this is through its buffer for energy homeostasis and ability to maintain the integrity of the membrane potential during stressful circumstances. Elevated levels of brain creatine have been observed as an outcome of mental training (Rae et al., 2003). Studies have indicated oral creatine supplementation is sufficient to increase total creatine levels in skeletal muscle and is associated with a greater rate of ATP regeneration most likely attributable to having a more readily available pool of PCr to begin due to the creatine supplementation and thus delaying muscular energy depletion (Greenhaff et al., 1994). In another study, increases in muscular phosphocreatine was observed after 16 weeks of creatine supplementation in patients with fibromyalgia. Although there was not any significant changes on the general symptoms of the disease, there were improvements with the upper and lower body muscle function demonstrating the potential of creatine as a therapeutic agent (Alves, 2013). Oral creatine supplementation does not only increase creatine stores within the muscles, but studies have also confirmed its ability to significantly increase neural creatine stores within the brain. Increases in total creatine levels were observed in brain regions such as the cerebellum, gray matter, and more amply within the thalamus and white matter (Dechent et al. 1999) Another study has associated neural creatine levels with brain and more specifically, memory performance. Using cognitive tests such as the Raven’s Advanced Progressive Matrices and Wechsler Auditory backward digit span (BDS) task, individuals undergoing a double-blind, placebo controlled, cross-over trial were able to demonstrate that creatine supplementation leads to increased brain creatine which was thus associated with improved working memory function and storage (Rae et al., 2003). Research Overview

Summary of Major Results

This was the first study performed in vivo examining the effects of Creatine monohydrate (CrM) supplementation on cognition and corticomotor excitability

during a state of hypoxia. Previous findings have suggested creatine to have neuroprotective aspects in vitro thus it is important that this study was able replicate consistent results in vivo (Shen and Goldberg, 2012). The current study used a double-blind placebo controlled design to assess the influence of creatine supplementation on neural creatine levels and how that impacts neuropsychological and neurophysiological features. Before the intervention trials, participants underwent baseline testing for neuropsychological data as well as were exposed to the hypoxia treatment. The state of hypoxia was created by inhaling a mixture of gas containing only 10% oxygen through a one-way face mask for 90 minutes. Using Magnetic Resonance Spectroscopy(MRS) imaging, it was observed that supplementing with CrM for 7 days was enough to increase neural creatine levels therefore individuals who were supplementing had greater amounts of creatine in the brain than those who given the placebo(Turner et al., 2015). Neuropsychological adequacy was tested using a standardized series of seven computerized tests assessing multiple factors such as complex attention, executive function, processing speed, visual memory, overall neurocognitive index score and more. Neurophysiological data was determined using peripheral nerve stimulation, transcranial magnetic stimulation and measuring motor evoked potential (MEP) amplitudes. Both neuropsychological and neurophysiological data was collected from participants at baseline as well as during the hypoxic state. CrM supplementation was able to prevent or at least reduce the cognitive deficits associated with being in an oxygen-deprived environment (Turner et al., 2015). Hypoxia causes a deterioration in mental functioning as observed by the 12% reduction in overall neurocognitive index score. Notably, complex attention appeared to be preserved the most when coupled with creatine supplementation as there was a 21% difference between treatment and placebo groups (Turner et al., 2015). Along with improved cognitive functions, creatine supplementation increased corticomotor excitability when in an oxygen-deprived environment. Interestingly, creatine supplementation alone did not increase excitability in normal conditions—it is not until an oxygen-deficient state is induced that creatine then demonstrates its ability to increase neuronal excitability by 70%(Turner et al., 2015). Due to it’s energy-buffering capacity, creatine supplementation prior to energy depletion has exhibited the ability to maintain the integrity of the cell’s membrane potential in vitro thus preventing axonal degradation (Shen and Goldberg, 2012). The creatine is suggested to have stimulated ATP-synthesis needed to drive the Na+/K+ ATP-ase which main34


tains the ion gradient that control neuron excitability (Shen and Goldberg, 2012). Previous studies have demonstrated in rat hippocampal samples that creatine is a potential modulator of Na+/K+ ATP-ase activity through the NMDA–calcineurin pathway (Rambo et al., 2012).

Figure 1. Creatine pretreatment reduced or prevented the cognitive deficits experienced during hypoxia. (Turner et al., 2015).

Figure 2: During an oxygen deprivation state, corticomotor excitability increased significantly in individuals who supplemented with creatine(black bar) compared to the placebo group. (Turner et al., 2015).

Discussion/Conclusions/Future Directives Supplementation or pre-treatment of creatine seems to be imperative in order to achieve its full neuroprotective benefits. Supplementation of creatine prior to energy depletion decreased axonal degradation by 50% and relieving damages related to ATP loss and depolarization (Shen and Goldberg, 2012). When creatine is added to neurons after inducing energy depletion, regular axonal deterioration was observed (Shen and Goldberg, 2012). Energy depletion compromises the structural and functional integrity of axons by a means of accumulation of calcium ions 35

producing adverse effects by activating downstream pathways and through excess Na+ ions(hence why tetrodotoxin—a Na+ channel blocker—reduced axonal damaged when applied and coupled with energy depletion) (Shen and Goldberg, 2012). Disruption of membrane potential and neuronal dysfunction is observed in in vitro stroke models and more commonly among many neurodegenerative disorders which is why the neuroprotective effects of creatine treatment is being explored for its potential as a therapeutic agent. It has been established that oral creatine supplementation is sufficient to increase creatine storage in multiple brain regions. This enriched creatine availability has been associated with increased brain performance and reduces cognitive defects related to conditions such as oxygen deprivation and energy depletion. A 16% reduction in fRMI Blood Oxygen Level Dependant was observed and associated with an increase in memory span after another study using creatine supplementation where these results were not seen in the placebo group (Hammett et al., 2010). These results suggest creatine as a potential therapeutic agent for treating Alzheimer ’s disease as individuals carrying the ApoE E4 allele (and therefore predisposed to a higher risk of developing AD) exhibit increases in BOLD response and decreases in memory function (Hammett et al., 2010). The authors of this study hypothesize the reduction in BOLD due to an increase in oxidative glycolysis; However, in the present study, oxidative glycolysis becomes compromised as a result of the hypoxia and yet increased creatine stores were still able to contribute to phosphocreatine-mediated ATP-synthesis leading to enhanced cognitive performance. Further investigations are warranted to see if reductions in BOLD response are observed during hypoxia treatment and if that response is associated with preventing cognitive function. Mutations within the mitochondria leading to disrupted energy homeostasis in the brain appear to be a commonality among neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s Disease, Huntington’s Disease and ALS. An oxidative form of cytosolic-brain creatine kinase (frequently seen in AD patients among other oxidative protein modifications) results in drastically less activity levels than its wildtype counterpart leading to altered energy metabolism within the brain (Burklen et al., 2006). Another study observed less brain phosphocreatine levels within AD patients compared to healthy individuals which further sanctions the importance of the creatine kinase/phosphocreatine shuttle in maintaining energy homeostasis (Burklen et al., 2006). Since neurodegeneration and aging appear to utilize similar pathways, one study investigated the role of creatine supplementation in regular aging mice compared to mice who were not given creatine pre-treatment. An average life span increase of 9% was seen accompanied with improved neurobehavioral test scores as well as less reactive oxygen species within the brain revealing its potential antioxidant properties (Klopstock et al., 2011). Immunohistochemical methods have also revealed the expression level of the creatine transporter to be widespread within the brain, considerably in large projection neurons, whereas less expression is seen in cells that are known to be involved in neurodegeneration—


medium the spiny neurons of the striatum (implicated in Huntington`s Disease), and the dopaminergic neurons in the substantia nigra region (Parkinson`s) (Lowe et al., 2015). It is evident that creatine-related mechanisms plays a role in neurodegeneration, and since creatine has exhibited neuroprotective features, it is not surprising that it is being considered as a possible therapeutic agent. However, further studies are needed to elucidate these neuroprotective characteristics and how creatine supplementation influences the phosphocreatine-creatine kinase shuttle and creatine transporter expression—both of which impact energy metabolism and brain plasticity. References

Received Month, ##, ##, 200#; accepted

200#; Month,

revised ##,

Month, 2013.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program

1. Alves C.R.R. (2013) Creatine Supplementation in Fibromyalgia: A Randomized, Double-Blind, Placebo-Controlled Trial. Arthritis Care and Research. 65:1449-1459. 2. Burklen TS, et al. (2006) The Creatine Kinase/Creatine Connection to Alzheimer’s Disease: CK Inactivation, APP-CK Complexes, and Focal Creatine Deposits. Journal of Biomedicine and Biotechnology. 2006:1-11. 3. Dechent P, Pouwels PJ, Wilken B, Hanefeld F, Frahm J (1999) Increase of total creatine in human brain after oral supplementation of creatine monohydrate. Am J Physiol 277:R698 –R704 4. Greenhaff P.L., Bodin K, Soderlund K, Hultman E (1994) Effect of oral creatine supplementation on skeletal muscle phosphocreatine resynthesis. American Physiological Society. Am J Physiol. 266: E725–E730. 5. Hammett ST., Wall MB., Edwards TC., Smith A.T. (2010) Dietary supplementation of creatine monohydrate reduces the human fMRI BOLD signal. Neuroscience Letters. 479:201205. 6. Klopstock T, Elstner M, Bender A (2011) Creatine in mouse models of neurodegeneration and aging. Springe. 40:1297–1303 7. Lowe M, Faull R, Christie D, Waldvogel H . (2015) Distribution of the Creatine Transporter Throughout the Human Brain Reveals a Spectrum of Creatine Transporter Immunoreactivity. The Journal of Comparative Neurology. 523:699–725 8. Rae C, Digney A, McEwan S, Bates T.C. (2003) Oral creatine monohydrate supplementation improves brain performance: a double-blind, placebo-controlled, cross-over trial. Proc. R. Soc. Lond. 270: 2147–2150. 9. Rambo LM, et al. (2012) Creatine increases hippocampal Na+,K+-ATPase activity via NMDA–calcineurin pathway. Elsevier 88: 553–559 10. Shen H, and Goldberg MP (2012) Creatine pretreatment protects cortical axons from energy depletion in vitro Neurobiol Dis. 47:184-193 11. Turner CE., Byblow WD, Gant N (2015) Creatine Supplementation Enhances Corticomotor Excitability and Cognitive Performance during Oxygen Deprivation. The Journal of Neuroscience. 35:1773-1780. 36


The Neural Mechanisms of Socio-Sexual Partner Preference Alana Brown

This review focuses mainly upon a study involving the induction of same-sex socio-sexual partner preference conditioning in male rats that experience cohabitation with other male rats under the enhanced influence of D2-type receptor and/or oxytocin activity (Triana-Del Rio et al., 2015). This review examines the history behind sexual preference research, the results of this particular experiment, a critical evaluation of its conclusions and suggestions for further research. Using this experiment, the significance of the D2 receptor in partner preference formation is explored, and the novel implication of oxytocin in this complex system in the nucleus accumbens (as it pertains to mate selection) is considered in more detail. The sizes of the sexually dimorphic nucleus of the medial preoptic area (SDN-POA) and supraoptic nucleus of the hypothalamus (SON) are not seen to be correlated with same-sex partner preference conditioning; this relevance is questioned and the nucleus accumbens is discussed as a brain region more likely to be involved with partner preference alteration. Study shortcomings and propositions are described and an experiment involving a MC4 receptor agonist in the nucleus accumbens is suggested to hone understanding of the interrelationship between oxytocin and dopamine as it relates to partner preference and social cognition. Key words: conditioning, social cognition, partner preference, homosexual, sex, oxytocin, dopamine, nucleus accumbens, sexually dimorphic nuclei Background The mechanism underlying what causes a male animal to seek a female mating partner remains a complex issue of considerable dispute, for partner preference is the result of a multifarious relationship between genetics, hormones and learning (Kamiya et al., 2014). It is known that in nature there are varying types of social attachments. These attachments are acquired as a result of cohabitation and are often measured in terms of increases in social recognition, motivation and reward. The interaction between oxytocin and D2 receptors in the nucleus accumbens seems to facilitate partner preference and attachment, while D1 receptors have been seen to facilitate parental attachment (Coria-Avila et al., 2014). Dopamine in the nucleus accumbens is considered critical for pair-bond formation in male prairie voles (Aragona, Liu, Curtis, Stephan, & Wang, 2003). Dopamine, particularly in the rostral shell of the nucleus accumbens, seems to be important to pair-bond formation in male prairie voles, with enhanced D2-type receptors facilitating pair-bond formation and enhanced D1-type receptors preventing it (Aragona et al., 2005). Furthermore, it has been made clear that an individual’s experience with reward (e.g. dopamine) can overturn presumably “innate” mate choices (e.g. male rats experiencing female partner preference) by means of Pavlovian conditioning. Prior studies have shown that pleasure seems to be a more powerful predictor of social behavior than genetics or reproductive fitness (CoriaAvila, 2012). The Triana-Del Rio et al. (2015) study of focus reiterates previous conclusions suggesting that cohabitation can affect partner preference via conditioning while also recapitulating the finding that sexually naïve male rats injected with the D2 agonist 37

quinpirole show same-sex partner preference for scented sexually receptive male rats that they have cohabitated with over sexually receptive female rats (Cibrian-Llanderal et al., 2012). The current study is noteworthy for implicating both D2-type receptors and oxytocin in same-sex partner preference development. It demonstrates that enhanced oxytocin alone (without quinpirole) can induce same-sex partner preference in male rats who cohabitate with other male rats. Implicating oxytocin directly with this sexual preference behavior is important for furthering research that looks at oxytocin as a mediator for prosocial behavior, particularly in terms of how it interacts with dopamine to promote partner preference formation (Modi et al., 2015). Oxytocin has been seen to lessen aggression levels and enhance social exploration; therefore it may be important to look more precisely at the behavior patterns in rats to experimentally tease apart those more influenced specifically by oxytocin or dopamine (Calcagnoli, Kreutzmann, de Boer, Althaus & Koolhaas, 2015). The Triana-Del Rio et al. (2015) study also investigates associations between reductions in size of the sexually dimorphic medial preoptic area (SDMPOA) and supraoptic nucleus of the hypothalamus (SON), as past research has suggested that lesions of SDM-POA induce same-sex partnership in male ferrets (Alekseyenko, Waters, Zhou, & Baum, 2006). No such associations were found in the study being evaluated here. Researchers might consider exploring further by prolonging the experiment (to see if there are any changes in size that take longer to develop) or looking more closely at the interaction between dopamine and oxytocin in the nucleus accumbens, an area that may be more relevant to partner preference and copulatory behavior (Liu & Wang, 2003).


Research Overview

Summary of Major Results

Male rats received an injection of saline, quinpirole, oxytocin, both quinpirole and oxytocin or no injection at all during either cohabitation with a male rat or alone. Rats in the cohabitation groups experienced three 24-hour trials of cohabitation with an almondscented male (the conditioned stimulus). Social and sexual preference was measured after the last trial, drug-free (to ensure results were due to learning). Subjects later chose between their familiar scented male and an unscented, sexually receptive female (see Figure 1). Preference was measured in terms of mounts, contacts, genital investigations, intromissions, ejaculations, non-contact erections and female-like solicitations. After the first experiment, subject brains were processed for Nissl dye (stained with cresyl violet) to aid in measuring the sexually dimorphic nucleus of the medial preoptic area (SDN-POA) and supraoptic nucleus of the hypothalamus (SON). Digital photographs enabled software to calculate nuclei areas (Triana-Del Rio et al., 2015). Same-Sex Partner Preference Induction Male rats who received saline, quinpirole, oxytocin or no injection without cohabitation showed preference for females in terms of higher visit incidence, more body contact, mounting, non-contact erections and olfactory investigations. Rats who received quinpirole, oxytocin and quinpirole and oxytocin together, all with cohabitation, displayed same-sex preference for their male partner in terms of increased visit frequency and duration, shorter contact latency, more body contact, olfactory investigation, female-like solicitation, and noncontact erection with the male partner (see Figure 1). This research validates previous findings that same-sex socio-sexual preference can be induced in male rats injected with quinpirole that cohabitate with other male rats, while also providing support for the novel conclusion that oxytocin injections with cohabitation can also induce same-sex socio-sexual preference (Triana-Del Rio et al., 2015). The most significant findings suggest that with increased dopamine receptor and oxytocin activity, conditioned same-sex social and sexual partner preference can develop when accompanied by cohabitation. Dopamine and oxytocin injections without cohabitation were not seen to result in same-partner social and sexual preference. Brain dimorphism Areas of the SDN-POA and SON were not seen to correspond to same-sex socio-sexual preference development (see Table 1). Males who received oxytocin had smaller SDN-POA sizes, no matter if they showed female or male socio-sexual preference. Males that cohabitated with other males and received quinpirole and both quinpirole and oxytocin injections had the largest SON nuclei. Same-sex partner preference does not seem to be correlated with changes in the sizes of the SDN-POA or SON. These findings do not validate other research that shows lesions of the SDN-POA can induce same-sex partner preference in male ferrets (Alekseyenko, Waters, Zhou, & Baum, 2006).

Figure 1. Mean total time of visit demonstrated by experimental male rats toward stimuli (male vs. sexual receptive female) (Triana-Del Rio et al., 2015).

Conclusions and Discussion Triana-Del Rio et al. (2015) conclude that Pavlovian associations under the influence of cohabitation and enhanced D2 and oxytocin can facilitate the development of same-sex socio-sexual partner preference in male rats. Consistent with past research, D2 receptors are implicated in the induction of same-sex partner preference, although a D1-type receptor agonist was not experimented with in this particular study. This was an appropriate decision. The conclusion that oxytocin injections with cohabitation can induce same-sex partner preference is novel. There is also immense strength in the observation that the males influenced by enhanced quinpirole and oxytocin (separately) exhibit similar preference behaviors after cohabitation conditions. Researchers acknowledge that there is a significant relationship between oxytocin and D2 activity in the nucleus accumbens as it pertains to partner preference development, and they confirm that this has little correlation with hypothalamic areas like SON (Triana-Del Rio et al., 2015). The results of this study fail to support the notion that same-sex partner preference in males is associated to a smaller, more female-like SDN-POA. Researchers suggest that this may be due to the dimorphic structures in question being organized during a perinatal period, making them less modifiable during the conditioning of same-sex preference. It is possible that after same-sex preference conditioning the nucleus accumbens takes over control of preference motivation (Triana-Del Rio et al., 2015). It is important that this research is able to take the SDN-POA and SON out of the equation, in a sense, in order to apply a more solid foundation for future studies of the nucleus accumbens. This validation that there is an interrelationship between dopamine and oxytocin is perhaps the most significant component of this study. Authors note that dopamine release in the nucleus accumbens increases quickly in male rats just before ejaculation. After ejaculation, dopamine in the nucleus accumbens seems to decrease rapidly and substantially. Researchers posit 38


that during this decrease, oxytocin plays a significant role in crystalizing new social attachments, as it may be involved with enhancing trustfulness and calmness (Fiorino, Coury, & Phillips, 1997). It is likely that dopamine works to enhance attention and arousal during a sexual encounter, while oxytocin may be involved with contact, consummatory behavior and bonding (Pfaus, 2009). This does not necessarily explain why separate oxytocin and quinpirole injection cohabitation conditions result in similar patterns of behavior for the male rats; however, it is relevant to future discussion involving the precise pathways of oxytocin and D2 receptors as they affect partner preference, for it is clear that they are interrelated.

Table 1. Main results: partner preference and brain dimorphism after conditioning (groups are intact- (involving no injection and no cohabitation), saline (SAL) with (+) and without (-) cohabitation, quinpirole (QNP) with and without cohabitation and oxytocin with and without cohabitation) (Triana-Del Rio et al., 2015).

Criticisms and Future Directions

Critical Analysis

The impact of this study is moderate, as it connects oxytocin distinctively to the process of partner preference induction involving dopamine, but it does not necessarily elucidate the connection. Researchers note that blocking either oxytocin or D2-type receptors prevents heterosexual partner preference induced by injections of oxytocin or D2 agonists in prairie voles and therefore opt to utilize only quinpirole and no D1-type receptor agonist (Liu & Wang, 2003). This enhances the experimentâ&#x20AC;&#x2122;s specificity and acknowledgment of inducing partner preference as opposed to the parental attachment associated with D1-type receptors. Triana-Del Rio et al. (2015) also recognize the importance of delving more deeply into the interrelationship between D2-type receptors and oxytocin, although they make few suggestions regarding how to do so. They investigate many different socio-sexual behaviors, but do not attempt to experimentally separate the ones associated specifically with oxytocin or D2-type receptors. Increased attempt to investigate the roles of oxytocin and dopamine in the nucleus accumbens would have likely been more insightful. Future Directions In terms of furthering this research, it may be worth considering the addition of a vasopressin injection condition (with and without cohabitation), as vasopressin has previously been shown to facilitate social attachment and may also contribute to the develop39

ment of same-sex preference (Bielsky & Young, 2004). This additional condition might be important for dissociating the effects of vasopressin on attachment from those of dopamine and oxytocin. It might also be interesting to prolong this experiment (e.g. for months, as opposed to weeks). Drug-free preference tests could take place intermittently to measure how long-lasting the conditioned preference is. Authors show that this conditioned partner preference may last only a few weeks, but posit that experiments involving extending the time to longer periods may be beneficial. It might also be advantageous to conduct an experiment during which oxytocin receptor activity is blocked by injecting oxytocin antagonist bilaterally into the nucleus accumbens of male rats to see if cohabitation will still have an effect when increased levels of oxytocin or quinpirole are injected as well (Liu & Wang, 2003). This might help to differentiate the socio-sexual behaviors induced by oxytocin and quinpirole (e.g. dopamine may be more relevant to formation of the preference behavior and oxytocin more relevant to expression of partner preference), and perhaps show whether one is dependent on the other to facilitate same-sex preference (Young et al., 2001). Triana-Del Rio et al. (2015) also suggest that future research might involve attempting to induce samesex socio-sexual preference in male rats that are not sexually naĂŻve (that have had sexual experiences with a receptive female prior to any conditioning). This experimentation would be important for demonstrating the effects of conditioning strength on previous learning and reward, particularly because this sort of situation


is more pertinent to humans, who are consistently exposed to sexual preference conditioning. It would also be immensely beneficial to further this research at a more specific molecular level. The MC4 receptor (MC4R) has been shown to interact with neurochemical systems involving social and emotional behaviors in the nucleus accumbens, particularly those associated with oxytocin and dopamine (Modi et al., 2015). Agonists of MC4R have been seen to enhance partner preference formation in the prairie vole, while co-administration of an oxytocin receptor antagonist has the capacity to prevent this partner preference, demonstrating that MC4R and oxytocin interact and impact partner preference (Modi et al., 2015). An experiment similar to that of Triana-Del Rio et al. (2015) involving a MC4R agonist would be valuable. One might consider injecting the MC4R agonist in a male mouse during cohabitation to see if same-sex socio-sexual preference could be induced through mere engagement of the oxytocin system in the nucleus accumbens (rather than through increased levels of oxytocin itself). This may also aid in implicating dopamine in the nucleus accumbens. Infusing the agonist in other brain areas (such as the ventral tegmental area or the amygdala) could also be informative. On a larger scale, partner preference induction in rats may be illustrative of a strategy to enhance social cognition in humans who have deficiencies in social functioning (e.g. in people with autism or schizophrenia) (Modi et al., 2015). MC4R agonists may be the key to implicating the involvement of both oxytocin and dopamine in partner preference formation and perhaps other significant clinical facets of social functioning. References 1. Alekseyenko, O. V., Waters, P., Zhou, H., & Baum, M. J. (2007). Bilateral damage to the sexually dimorphic medial preoptic area/anterior hypothalamus of male ferrets causes a female-typical preference for and a hypothalamic fos response to male body odors. Physiology & Behavior, 90(2-3), 438-449. 2. Aragona, B. J., Liu, Y., Curtis, J. T., Stephan, F. K., & Wang, Z. (2003). A critical role for nucleus accumbens dopamine in partner-preference formation in male prairie voles. The Journal of Neuroscience, 23(8), 3483-3490. 3. Aragona, B. J., Liu, Y., Yu, Y. J., Curtis, J. T., Detwiler, J. M., Insel, T. R., & Wang, Z. (2005). Nucleus accumbens dopamine differentially mediates the formation and maintenance of monogamous pair bonds. Nature Neuroscience, 9(1), 133-139. 4. Bielsky, I. F., & Young, L. J. (2004). Oxytocin, vasopressin, and social recognition in mammals. Peptides, 25(9), 1565-1574. 5. Calcagnoli, F., Kreutzmann, J. C., de Boer, S. F., Althaus, M., & Koolhaas, J. M. (2015). Acute and repeated intranasal oxytocin administration exerts anti-aggressive and pro affiliative effects in male rats. Psychoneuroendocrinology, 51, 112-121.

6. Cibrian-Llanderal, T., Rosas-Aguilar, V., Triana-Del Rio, R., Perez, C. A., Manzo, J., Garcia, L. I., & Coria-Avila, G. (2012). Enhaced D2-type receptor activity facilitates the development of conditioned same-sex partner preference in male rats. Pharmacology, Biochemistry and Behavior, 102(2), 177-183. 7. Coria-Avila, G. A., Manzo, J., Garcia, L. I., Carillo, P., Miquel, M., Pfaus, J. G. (2014). Neurobiology of social attachments. Neuroscience & Behavioral Reviews, 43, 173-182. 8. Coria-Avila, G. A. (2012). The role of conditioning on heterosexual and homosexual partner preference in rats. Socioaffective Neuroscience & Psychology, 2, 1-12. 9. Fiorino, D. F., Coury, A., & Phillips, A. G. (1997). Dynamic changes in nucleus accumbens dopamine efflux during the Coolidge effect in male rats. The Journal of Neuroscience, 17, 4849-4855. 10. Kamiya, T., Oâ&#x20AC;&#x2122;Dwyer, K., Westerdahl, H., Senior, A., & Nakagawa, S. (2014). A quantitative review of MHC-based mating preference: the role of diversity and dissimilarity. Molecular Ecology, 23, 5151-5163. 11. Liu, Y. & Wang, Z. X. (2003). Nucleus accumbens oxytocin and dopamine interact to regulate pair bond formation in female prairie voles. Neuroscience, 121(3), 537-544. 12. Modi, M. E., Inoue, K., Barrett, C. E., Kittelberger, K. A., Smith, D. G., Landgraf, R., & Young, L. J. (2015). Melanocortin receptor agonists facilitate oxytocin-dependent partner preference formation in the prairie vole. Neuropsychopharmacology,1-10. 13. Pfaus, J. G. (2009). Pathways of sexual desire. Journal of Sexual Medicine, 6(6), 1506-1533. 14. Triana-Del Rio, R., Tecamachaltzi-Silvaran, M. B., DiazEstrada, V. X., Herrera-Covarrubias, D., Corona Morales, A. A., Pfaus, J. G., & Coria-Avila, G. A. (2015). Conditioned same-sex partner preference in male rats is facilitated by oxytocin and dopamine: Effect on sexually dimorphic brain nuclei, Behavioural Brain Research, 283, 1-9. 15. Young, L. J., Lim, M. M., Gingrich, B., & Insel, T. R. (2001). Cellular mechanisms of social attachment. Hormones and Behavior, 40(2), 133-138. Received Month, ##, ##, 200#; accepted

200#; Month,

revised ##,

Month, 2013.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright Š 2015 Dr. Bill JU, Neurosciences, Human Biology Program

40


Impact of KIBRA Polymorphism On The Hippocampus Megan E. Cabral

The KIBRA gene is found throughout both the brain and kidney in humans and has recently been linked to memory and cognition by a number of studies. As interest in the gene grows more researchers are seeking answers to how a single nucleotide polymorphism in the gene (Cď&#x192; T) affects both the brain and behaviour. CC- homozygotes were found to preform worse on average on memory and cognition tasks than their T-allele carrying counterparts (Wersching et al, 2011). The KIBRA protein is found in the highest concentrations in the hippocampus making this structure an area of high interest in relation to the genes function and effects. In a study conducted by Palombo et al. (2013) it was found that T-allele carriers of the gene have significant increases in volume in both the Cornu Ammonis and Dentate Gyrus of the hippocampus providing preliminary evidence that the KIBRA genotype does affect the volume of hippocampal sub-regions. Key words: KIBRA; Cognition; memory; Hippocampus; Cornu Ammonis (CA); Dentate gyrus (DG); Structural MRI Background KIBRA was first identified in a study by Kremerskothen et al in 2003 as a protein of the WWC family, found in both the brain and kidney that interacts with the postsynaptic protein dendrin. A study by Papassotiropoulos et al in 2006 later expanded on this finding making it a gene of interest to all researchers in the scientific community studying memory, cognition and related diseases. The KIBRA protein was found to exist in higher concentrations in the Cornu Ammonis (CA) and the Dentate gyrus (DG) of the hippocampus. KIBRA was found to be encoded for by the WWC1 gene and has been identified as a regulator of the hippocampal signaling pathway as well as being involved in cell polarity, membrane and vesicular trafficking, mitosis and cell migration (Zhang et al, 2014). In 2006, evidence was found suggesting a polymorphism in the KIBRA gene was involved in memory and cognition performance (Papassotiropoulos et al, 2006). A single nucleotide polymorphism (SNP) in this gene from cytosine to thymine on the ninth intron of the gene has been linked to significant increases in performance on episodic memory tasks, especially those involving consolidation or delayed retention, than c-homozygotes. The same study found that brain activity recorded via fMRI, in areas related to memory retrieval were higher in people who did not carry the t-allele (Papassotiropoulos et al, 2006). Since these original findings the KIBRA gene has been an area of interest in many labs studying memory and cognition, and the KIBRA gene has also been implicated as a possible risk factor for developing late onset Alzheimerâ&#x20AC;&#x2122;s disease as well as dementia (Schneider, 2010). Being a CC homozygote has been associated with decreased memory performance and less efficient MTL activation (Schwab et al, 2014). Carriers of the T allele were recently found have increased hippocampal volume, especially in two sub regions of the hippocampus: the DG and CA (Palombo et al, 2013). This finding is contrary to a prior study, which had 41

found no volumetric difference between carriers and non-carriers using automated segmentation (Papassotiropoulos et al, 2006) Conclusions and Discussion

Summary Of Major Results

The purpose of the study conducted by Palombo et al in 2013, is to look for any volumetric differences associated with the SNP of the KIBRA gene in the hippocampus and associated MTL structures. The study hypothesizes that carriers of the T-allele will have volumetric differences significantly different than those of non-carriers in these areas. Carriers and noncarriers of the t-allele were separated into groups and matched on performance on behavioral tasks as well as other genes which have been implicated in episodic memory, including APOE, BDNF and COMT. Highresolution T2 weighted images, taken perpendicular to the long axis of the hippocampus were obtained and analyzed using Region of Interest (ROI) segmentation (see figure 1 for an example). Areas analyzed were separated into the CA1, DG/CA, subiculum, medial temporal lobe (further subdivide into perirhinal cortex, entorhinal cortex, and parahippocampal cortex) and the head and tail of hippocampus. The study used three-mixed design ANCOVAs in order to to test for significant differences in the hippocampus, segmented hippocampus and MTL cortices between t-allele carriers and cc homozygotes. These two areas were further subdivided into the CA1, DG/ CA, subiculum, entorhinal cortec (ERC), perirhinal cortex (PRC) and parahippocampal cortex (PHC). Their hypothesis was validated when they found that T-carriers had larger overall hippocampal volume than CC-homozygotes as well as significantly larger segmented hippocampi than non- carriers. Using post-hoc analysis the CA1 and DG/CA were found to be significantly larger in T-carriers. The subiculum


volume. Prior research studies on both animals and older populations have found a functional differentiation between these two hippocampal subregions. The CA has been shown to be involved in late retrieval and memory consolidation while the DG has been associated with encoding and early retrieval (Milnik et al, 2012). These differences were observed in the absence of any behavioral differences due to the matched subject groups which allows us to separate and describe the independent effects of KIBRA.

Table 1. In parentheses the standard error is shown. Segmentation of hippocampus is as follows: CA, DG/CA, and Sub (subiculum). Segmentation of MTL cortices is as follows: ERC, PRC, and PHC. Columns with * contain significant differences between groups (p<0.05) and ** contain significant differences of (p<0.10). (Palombo et al, 2013).

Conclusions

In conclusion, the KIBRA polymorphism of a CT was found to be associated with increased Figure 1. Depicted on the left is a 3D representation of the hippocampus. hippocampal volume. This finding was found to The yellow lines mark coronal slices which are shown to the right in be strongest in two sub regions of the hippoT2 weighted slices. The middle column depicts and un-segmented view of MTL scans while the furthest right is an example of a segmentedcampus: the DG and CA. This finding is one step scan. The colors denote different structures green=CA1, dark blue=DG/towards identifying one of KIBRA’s many differential CA, red=Sub, orange= head of the caudate, brown=tail of the caudate,effects on the brain and memory. By identifying the yellow= PHC, pink=PRC, light blue= ERC.(Palombo et al, 2013). effects of the KIBRA polymorphism we may be able to develop ways of applying this knowledge towards clinical treatments to aid patients with damage to the was found to be relatively larger in non-carriers than memory and cognition centers affected by KIBRA, carriers of the T-allele. There were no significant like patients suffering from Alzheimer’s disease and group interactions and KIBRA was found to have dementia. no significant effect on most of the MTL structures. Using post-hoc analysis, T-carriers were found to Criticisms and Future Directions have a small but significant increase in volume of the parahippocampal cortex indicating some small effect The hippocampus and surrounding MTL structures of KIBRA here. The mean volumes observed in both carriers and non-carriers in these sub-regions of the have been researched previously in their entirety to hippocampus and MTL cortices can be found in Table look for any volumetric differences associated with the 1: A & B below and are further divided by hemisphere. SNP of the KIBRA gene and results have been null (Papassotiropoulos et al., 2006). Within the same study it was also found that expression of KIBRA in Conclusions and Discussion the brain varies and is higher in the hippocampus and more specifically two of its sub-regions: the Cornu The study used structural imaging to investigate Ammonis (CA) and the Dentate Gyrus (DG). These the effects of KIBRA on both hippocampal and MTL variances in concentration may suggest affects of the volume. They were ultimately able to show evidence KIBRA gene also vary regionally. supporting the association between the t-allele SNP The study conducted by Palombo et al. (2013) is of the KIBRA gene and increased CA and DG/CA unique in its approach by regionally segmenting 42


and analyzing the hippocampus as well as looking at overall hippocampus and MTL structure volumes. Using this method they found significant changes in regional substructures associated with higher KIBRA expression: CA1 and the DG. These differences may not have been found in the earlier study discussed due to differences in segmentation and demarcation strategies between researchers which is a common challenge in the field. Past studies also did not match participants between groups on behavioral performance to allow KIBRA related differences to be shown independently, which may also account for some of the differences in findings (see Papassotiropoulos et a., 2006). The finding of regional hippocampal volumetric differences between carriers and non-carriers provides a possible mechanism for differences observed in episodic memory performance found in multiple other studies (Milnik et al, 2012; Corneveaux et al, 2010; Papenberg et al, 2015). By working to identify the mechanism of the KIBRA SNP the current study contributes to the creation of new targets for possible development of clinical in associated diseases like dementia and AD. Wersching et al (2011) found a complex interaction of KIBRA on cognitive function that is modified by both gender and arterial hypertension. The current study did not take effects of gender into account and the majority of its participants were female. This inequality in gender ratio may have skewed the findings because of possible effects of gender, leading to different effects on volume gene interactions. One simple possible future study that could be preformed would look to see if sex alters the effects of KIBRA on regional hippocampal volumes by separating the two genders and looking for any significant differences between the two, using the same methodology as the current study. A case has also been made for the differing effect of KIBRA with age, suggesting that the effects of the gene may accumulate, as differences in cognitive abilities between the T and C allele carriers tend to both appear and/or become larger with age (Papenberg et al, 2015). A longitudinal study is needed in which individuals are first given a genotypic screening to determine allele type and a preliminary cognitive performance assessment. After being matched for performance and placed into T and C carrier groups they would then be given episodic memory tasks as well as a structural MRI’s on intervals (~ every 1-2 years) over a period of 10-15 years. The data would then be analyzed for any significant accumulation effects of allele type in episodic memory, regional hippocampal volumes, as well as interactions and correlations between the two. Findings from this study or a similar longitudinal study would shed light on mechanisms behind the increasing gap in cognitive performance tasks we see between the two variant KIBRA allele groups. With data from both gender and longitudinal studies we would e able to make more concrete conclusions about the total effect of the KIBRA polymorphism on hippocampal structures volumes. 43

References 1. Corneveaux, J. J., Liang, W. S., Reiman, E. M., Webster, J. A., Myers, A. J., Zismann, V. L., … Huentelman, M. J. (2010). Evidence for an association between KIBRA and late-onset Alzheimer’s disease. Neurobiology of aging, 31(6), 901–9. doi:10.1016/j.neurobiolaging.2008.07.014 2. Kremerskothen, J., Plaas, C., Büther, K., Finger, I., Veltel, S., Matanis, T., … Barnekow, A. (2003). Characterization of KIBRA, a novel WW domain-containing protein. Biochemical and biophysical research communications, 300(4), 862–7. 3. Milnik, A., Heck, A., Vogler, C., Heinze, H.-J. J., de Quervain, D. J., & Papassotiropoulos, A. (2012). Association of KIBRA with episodic and working memory: a meta-analysis. American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics, 159B(8), 958–69. doi:10.1002/ ajmg.b.32101 4. Palombo, D. J., Amaral, R. S., Olsen, R. K., Müller, D. J., Todd, R. M., Anderson, A. K., & Levine, B. (2013). KIBRA polymorphism is associated with individual differences in hippocampal subregions: evidence from anatomical segmentation using high-resolution MRI. The Journal of neuroscience : the official journal of the Society for Neuroscience, 33(32), 13088–93. doi:10.1523/JNEUROSCI.1406-13.2013 5. Papassotiropoulos, A., Stephan, D. A., Huentelman, M. J., Hoerndli, F. J., Craig, D. W., Pearson, J. V., … de Quervain, D. J. (2006). Common Kibra alleles are associated with human memory performance. Science (New York, N.Y.), 314(5798), 475–8. doi:10.1126/science.1129837 6. Papenberg, G., Salami, A., Persson, J., Lindenberger, U., & Bäckman, L. (2015). Genetics and Functional Imaging: Effects of APOE, BDNF, COMT, and KIBRA in Aging. Neuropsychology review. doi:10.1007/s11065-015-9279-8 7. Schneider, A., Huentelman, M. J., Kremerskothen, J., Duning, K., Spoelgen, R., & Nikolich, K. (2010). KIBRA: a new gateway to learning and memory? Frontiers in aging neuroscience, 2. doi:10.3389/neuro.24.004.2010 8. Schwab, L. C., Luo, V., Clarke, C. L., & Nathan, P. J. (2014). Effects of the KIBRA Single Nucleotide Polymorphism on Synaptic Plasticity and Memory: A Review of the Literature. Current neuropharmacology, 12(3), 281–8. doi:10.2174/157 0159X11666140104001553 9. Wersching, H., Guske, K., Hasenkamp, S., Hagedorn, C., Schiwek, S., Jansen, S., … Floel, A. (2011). Impact of common KIBRA allele on human cognitive functions. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 36(6), 1296–304. doi:10.1038/npp.2011.16 10. Zhang, L., Yang, S., Wennmann, D. O., Chen, Y., Kremerskothen, J., & Dong, J. (2014). KIBRA: In the brain and beyond. Cellular signalling, 26(7), 1392–9. doi:10.1016/j.cellsig.2014.02.023

Received Month, 04, 2015; revised Month, 04, 2015; accepted Month, 04, 2015.


α5GABAA Receptors Mediate Inflammation-Induced Memory Deficits in the Hippocampus Sammy Cai

The mechanism by which systemic inflammation induces learning and memory deficits still remains poorly understood. This study investigates the pathogenesis of inflammation-induced memory deficits using a combination of behavioral, electrophysiological, and biochemical methods combined with genetic and pharmacological approaches. The results suggest that acute systemic inflammation leads to contextual fear memory deficits in wild-type mice primarily due to the reduction in amplitude of long-term potentiation in CA1 hippocampal slices. It was determined that inflammation-induced memory deficits were reversible upon pharmacological inhibition or gene deletion of α5-subunit-containing γ-aminobutyric acid type A (α5GABAA) receptors. Inflammatory cytokines, primarily interleukin-1β (IL-1β), increase the inhibitory tonic current generated by α5GABAA receptors via the p38 mitogen-activated protein kinase signaling (MAPK) cascade. Activation of this pathway resulted in an increase in surface expression of α5GABAA receptors. IL-1β-mediated upregulation of α5GABAA receptors was attenuated via pharmacological inhibition of p38 MAPK. Collectively, these results show that α5GABAA receptors are upregulated by IL-1β and can mediate memory deficits during acute systemic inflammation. Key words: inflammation; hippocampus; α5GABAA receptors; electrophysiology Background Learning and memory deficits can be caused by acute systemic inflammation, which can be induced by autoimmune disease, infection, and stroke. In humans, acute systemic inflammation results in impaired explicit recall whereas it impairs acquisition of fear-associated memories in mice1. Chronic inflammation can contribute to neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis1. Systemic inflammation results in increased production of cytokines in the brain, including interleukin-1β (IL-1β), IL-6, and tumour necrosis factor-α (TNFα). It is known that there is a correlation between increased IL-1β plasma levels with memory deficits in patients. In the laboratory, mice that underwent orthopedic surgery had elevated levels of IL-1β in the hippocampus, which was accompanied with memory deficits2. In addition, the effects of IL-1β on memory consolidation only affected hippocampal dependent memories, whereas hippocampal independent memories were unchanged3. The binding of the neurotransmitter γ-aminobutyric acid (GABA) to GABA Type A (GABAA) receptors modulates the inhibitory tone found throughout the CNS3. GABAA receptors are known to generate two forms of inhibitory currents: a phasic, fast inhibitory postsynaptic current and tonic, which is mediated by extrasynaptic GABAA receptors. The inhibitory tone found in the CA1 region of the hippocampus is primarily generated by tonic currents mediated by the α5-subunit-containing GABAA (α5GABAA) receptors4. Studies have shown that drugs that increase α5GABAA receptor activity can result in memory deficits5. Alternate studies have shown that reducing α5GABAA receptor function or expression in mice can result in improved performance in trace fear-conditioning as opposed to contextual fear-conditioning6.

The binding of IL-1β to IL-1 receptors during inflammation activates a variety of signalling pathways in neurons, such as p38 mitogen-activating protein kinase (MAPK), c-Jun N-terminal kinases (JNKs), and phosphatidylinositol 3-kinases (PI3Ks)7. The mechanism of GABAA receptor trafficking is currently under debate as findings from various studies have been contradictory. For example, one study demonstrates that activation of p38 MAPK and PI3K via TNF-α downregulates cell-surface expression of GABAA receptors within the hippocampus8. Conversely, another study showed that TNF-α had no effect on the tonic inhibitory current9. It is hypothesized that α5GABAA receptors are upregulated in inflammationinduced memory deficits. Despite the efforts made to elucidate the link between inflammation and memory deficits, no treatments are available to effectively prevent or reverse the memory deficits associated with neuroinflammation. General inhibition of IL-1β binding to IL-1 receptors are impractical treatments as that would delay wound healing and increase the risk of infection10. More studies are required to identify additional downstream mediators of neuroinflammation in order to develop more effective treatments. Research Overview

α5GABAA Receptors Regulate InflammationInduced Contextual Fear Memory Deficits

Both wild-type (WT) and α5-subunit null mutant (Gabra5-/-) mice were treated with IL-1β to mimic acute systemic inflammation. Three hours after the treatment, the mice were trained to pair an electric foot shock (unconditioned stimulus) with an auditory tone (conditioned stimulus) for contextual fear learning, which is hippocampal dependent. To test for cued fear 44


mice were reversed after treatment with L-655,708 or MRK-016. Both WT and Gabra5-/- mice treated with either IL-1β or LPS exhibited no deficits in cued fear memory (Figure 1D; n = 14-16). Collectively, these results show that inflammation only impairs hippocampal-dependent memories3.

α5GABAA Receptors Reduce the Amplitude of Long-Term Potentiation During Inflammation

Figure 1. Inflammation-Induced Contextual Fear MemoryDeficits Is Absent in Gabra5-/- Mice and Can Be Prevented in WT Mice With Pharmacological Inhibition of α5GABAA Receptor3 A. IL-1β lowered freezing scores for contextual fear in WT mice. B. L-655,708 or MRK-016 restored freezing scores of IL-1βtreated WT mice to control values. C. LPS reduced freezing scores in WT mice only. Treatment with LPS then L-655,708 restored freezing scores to control values. D. IL-1β did not affect freezing scores in cued memory response to tone in WT and Gabra5-/- mice.

memory, which is hippocampal independent, the mice were reintroduced to the tone after training11. It was found that mice treated with IL-1β had impaired contextual fear memory, as seen in the lower freezing scores compared to controls (Figure 1A; n = 14-16, p < 0.05). This is consistent with previous studies1. Gabra5-/- mice treated with IL-1β exhibited no memory deficits (Figure 1A; n = 14-16; p > 0.05). Inhibition of the α5GABAA receptor with L-655,708 or MRK-016 did not modify contextual memory in either WT or Gabra5-/- mice under control conditions (Figure 1B; n = 16). Treatment with L-655,708 or MRK-016 in IL-1β-treated WT mice exhibited attenuation of impaired contextual fear memory3. Systemic inflammation was induced in WT and Gabra5-/- via injection of lipopolysaccharide (LPS). After three hours, WT, but not Gabra5-/- mice exhibited impairment of contextual fear memory (Figure 1C; n = 10-15). The deficits found in WT 45

Brain slices were prepared three hours after mice were injected with LPS. Long term potentiation (LTP) was induced via theta burst stimulation of the Schaffer collateral pathway in the CA1 region of the hippocampus (Figure 2A, inset). The field postsynaptic potentials (fPSPs) were measured after stimulation. In vehicle-treated WT mice, stimulation increased the slope of fPSPs to 136.1% ± 5.6% of baseline (n = 9). In contrast, LPS-treated mice had only a 113.1% ± 2.5% increase of fPSP from baseline (Figures 2A and 2B; n = 10; p < 0.05). Pharmacological inhibition of α5GABAA receptors of the LPS-treated brain slice using L-655,708 eliminated the reduction of LTP induced by LPS (Figure 2B). LPS failed to reduce LTP in brain slices from Gabra5-/- mice, having an fPSP slope of 133.1% ± 4.3% (n = 15; p > 0.05 compared with control) for the LPS treatment compared to 135.4% ± 5.9% (n = 13) for the vehicle treatment (Figure 2B)3. This suggests that α5GABAA receptors are required for impairing LTP via inflammation. IL-1 receptor antagonists (IL-1ra) were applied to LPS-treated mice brain slices. IL-1ra) restored LTP to 126.2% ± 3.9% of baseline (Figure 2C; n = 10; p < 0.05 compared with LPS). These results confirm the findings from previous studies, suggesting that reduction in LTP is largely mediated by increased IL-1β activity12.

IL-1β Increases α5GABAA Receptor Activity in Neuronal Cultures

Whole-cell currents were recorded from hippocampal neurons to determine whether IL-1β directly enhances tonic inhibitory conductance. Neurons treated with IL-1β had an increase in tonic current by 45% (IL-1β 1.6 ± 0.1 pA pF-1, n = 22, versus control 1.1 ± 0.1 pA pF-1, n = 21; p < 0.001 compared with control; Figure 3A). Increasing concentrations of IL-1β resulted in an increase in current amplitude. After 12-15 hours, no further increase in current amplitude was observed3. The effects of TNF- α and IL-6 were also examined, as they are known to increase along with IL-1β during acute inflammation1. When neurons were treated with TNF- α or IL-6, no changes were observed (1.0 ± 0.1 pA pF-1; n = 10-14, and 0.9 ± 0.05 pA pF-1 respectively; n = 5, vs control 1.0 ± 0.06 pA, n = 5). To examine whether IL-1β enhanced tonic currents were mediated by α5GABAA receptors, α5GABAA receptor antagonists and genetic approaches were used. Using L-655,708, it was found that it decreased tonic current in WT neurons by 56.6% ± 9.2%3. No observable changes for tonic current was recorded in Gabra5-/- mice injected with


IL-1β (Figure 3B). This suggests that IL-1β enhances the tonic current generated by α5GABAA receptor. To see the effects of endogenous IL-1β, neurons cocultured with microglia were treated with LPS. Treatment with LPS resulted in an increase in tonic current, which was reversible when treated with IL-1ra. When testing neurons alone, LPS did not elicit any changes (Figure 3C). This suggests that IL-1β was released from microglia.

IL-1β Increases α5GABAA Receptor Activity via the p38 Mitogen-Activated Protein KinaseDependent Pathway

Hippocampal neurons were treated with selective kinase inhibitors to identify the predominant signalling pathway of IL-1β. Using a p38 MAPK inhibitor, SB203,580, blocked the increase in tonic current induced by IL-1β, whereas, SB202,580, the inactive analog, had no effect (Figure 4A; n = 10-14; p < 0.05 compared with control). This suggests that p38 MAPK mediates IL-1β-induced increase in tonic current. No change in IL-1β-induced tonic current was reported when using selective inhibitors for JNKs and PI3Ks (Figures 4B and 4C)3. To determine whether IL-1β increased mobilization of α5GABAA receptors, hippocampal slices were treated with IL-1β and then analyzed using a quantitative western blot analysis. It was found that surface expression of the α5-subunit protein increased to 157.4% ± 17.6% of baseline in vehicle-treated control slices (Figure 4D; n = 6)3. This suggests that IL-1β increases surface expression of α5GABAA receptors. Discussion These findings suggest that neuroinflammation can cause memory loss by increasing tonic inhibitory conductance via α5GABAA receptors. Pharmacological or genetic inhibition of α5GABAA receptors was capable of preventing contextual fear memory deficits

induced by IL-1β or LPS. Increased tonic inhibitory conductance and reduction in LTP was due to an increase in surface expression of α5GABAA receptors, which was mediated by the p38 MAPK pathway. These results are consistent with findings from other studies13. Although other signalling pathways are activated, such as JNKs and PI3Ks, they do not affect expression of α5GABAA receptors. There are two proposed mechanisms of the p38 MAPK pathway. Phosphorylation of radixin, an actin-binding protein that anchors α5 subunits to cytoskeletal elements, increases the stability of α5GABAA receptors14. Alternatively, activation of p38 MAPK can increase the activity of cAMP response element-binding proteins, which can also enhance surface expression of α5GABAA receptors9.

Figure 3. IL-1β Increases Tonic Currents Generated by α5GABAA Receptors3 A. IL-1β increases tonic currents generated by α5GABAA receptors in a dose-dependent manner. B. α5GABAA receptors are required for generation of the tonic current. C. Tonic currents were increased in neuron and microglia cocultures, but not neurons alone. Changes were reversible upon treatment with IL-1ra.

Figure 2. Inflammation Reduces LTP in CA1 Region in WT Mice and This Can Be Prevented by Pharmacological Inhibition of α5GABAA Receptors3 A. LPS impaired LTP induced by theta burst stimulation only in brain slices of WT mice. B. LPS-mediated reduction of LTP was mediated by IL-1β.

46


Figure 4. p38 MAPK Pathway Mediates Inflammation-Induced Enhancement of α5GABAA Receptor Tonic Current3 A. SB203,580, a p38 MAPK inhibitor, abolished the effects of IL-1β whereas SB202,580, its inactive analog, did not block the tonic current (right). B. Treatment with a JNK antagonist did not block the IL-1βinduced tonic current. C. Treatment with a PI3K antagonist did not block the IL-1βinduced tonic current. D. IL-1β increased surface expression of the α5 subunit in hippocampal slices compared to vehicle-treated control slices.

There are currently no treatments that are available to reduce memory deficits induced by neuroinflammation. Potential treatment strategies for inflammation-induced memory loss can include administration of inverse agonists for α5GABAA receptors. Compared to nonselective GABAA receptor antagonists, the CNS has a higher tolerance for inverse agonists because they lack anxiogenic effects15. GABAA receptor expression is not restricted only to the CNS16. Because of this, acute systemic inflammation may also upregulate GABAA receptors in the periphery. It may be of interest for future studies to investigate the effects of GABAA receptors on organ dysfunction after acute or chronic systemic inflammation. Criticisms and Future Directions Despite finding the pathway by which IL-1β mediates α5GABAA receptor activity to impair hippocampaldependent memories, there are several limitations associated with this study. While this study looked at the effects of IL-1β on α5GABAA receptor activity, it is possible that there is an increase in GABA concentration in the extracellular space of the CNS during acute systemic inflammation. It is known that events such as stress, stroke, or surgery can increase extracellular concentrations of GABA2. Rather than increased vesicular release 47

of GABA, it is believed that there is a reduction in GABA transporter activity, thus reducing GABA reuptake17. Future studies can look at the effects of IL-1β on GABA transporters to determine whether acute systemic inflammation affects GABA reuptake. Electrophysiological recordings can be performed to analyze the activity of GABA transporters, specifically GABA transporter-1, after application of IL-1β to cultured neurons. Although the findings suggests that inflammation induces increased α5GABAA receptor activity within the hippocampus, the use of Gabra5-/- results in global deletion of α5GABAA receptors within the CNS. Global deletion of α5GABAA receptors may result in effects that are mediated by other structures within the CNS since α5GABAA receptors are also expressed outside the hippocampus3. To restrict loss of α5GABAA receptors to the CA1 region of the hippocampus, future studies can explore the use of Cre-Lox recombination. Previous studies have shown that the use of a CaMKII promoter can restrict gene modifications specifically in the CA1 region of the hippocampus18. After deletion of the α5-subunit containing gene, behavioural studies, such as Pavlovian fear conditioning, can be performed to determine whether memory deficits induced by inflammation are specific to α5GABAA receptors within the hippocampus. Another area of interest would be to restrict inflammation to the hippocampus. In the original study, intraperitoneal injections of IL-1β or LPS was used to induce acute systemic inflammation. While this provides a model that is similar to acute systemic inflammation in humans, it is not restricted within the hippocampus3. Potential studies can explore the use of mice expressing IL-1β excisional activation transgene (IL-1βXAT) within the hippocampus. Hippocampal-restricted overexpression of IL-1β can be achieved via intrahippocampal injections of retroviral Cre into IL-1βXAT mice19. Memory deficits caused by hippocampal inflammation can then be tested for by using Pavlovian fear conditioning. No treatments were available for inflammationinduced memory deficits prior to 20123. A recent study has determined that a salt extracted from the Glycyrrhiza glabra root, glycyrrhizin (GRZ), was able to attenuate inflammation-induced memory deficits in a dose dependent manner. GRZ has been found to reduce IL-1β mRNA levels within brain tissue, thus potentially reducing the effects of the p38 signaling cascade20. Future studies could examine the effects of GRZ on α5GABAA receptor surface expression by inducing inflammation via intraperitoneal injection of LPS, followed by oral administration of GRZ. This can be used to determine whether reduction of IL-1β is an effective treatment strategy for inflammation-induced memory deficits. References 1. Yirmiya, R. & Goshen, I. Immune modulation of learning, memory, neural plasticity and neurogenesis. Brain Behav. Immun. 25, 181–213 (2011). 2. Cibelli, M. et al. Role of interleukin-1beta in postoperative


cognitive dysfunction. Ann. Neurol. 68, 360–8 (2010). 3. Wang, D.-S. S. et al. Memory deficits induced by inflammation are regulated by α5-subunit-containing GABAA receptors.Cell Rep 2, 488–96 (2012). 4. Caraiscos, V. B. et al. Tonic inhibition in mouse hippocampal CA1 pyramidal neurons is mediated by alpha5 subunit-containing gamma-aminobutyric acid type A receptors. Proc. Natl. Acad. Sci. U.S.A.101, 3662–7 (2004). 5. Cheng, V.Y. et al. a5GABAA receptors mediate the amnestic but not sedative-hypnotic effects of the general anesthetic etomidate. J. Neurosci. 26, 3713–3720 (2006) 6. Collinson, N. et al. Enhanced learning and memory and altered GABAergic synaptic transmission in mice lacking the alpha 5 subunit of the GABAA receptor. J. Neurosci. 22, 5572–80 (2002). 7. O’Neill, L.A. Signal transduction pathways activated by the IL-1 receptor/toll-like receptor superfamily. Curr. Top. Microbiol. Immunol. 270, 47–61 (2002). 8. Pribiag, H. & Stellwagen, D. TNF-α Downregulates Inhibitory Neurotransmission through Protein Phosphatase 1-Dependent Trafficking of GABAA Receptors. Journal of Neuroscience 33, 15879–15893 (2013). 9. Srinivasan, D., Yen, J.-H. H., Joseph, D. J. & Friedman, W. Cell type-specific interleukin-1beta signaling in the CNS. J. Neurosci. 24, 6482–8 (2004). 10. Fleischmann, R. M. et al. Safety of extended treatment with anakinra in patients with rheumatoid arthritis. Ann. Rheum. Dis. 65, 1006–12 (2006). 11. Fanselow, M. S. & Poulos, A. M. The neuroscience of mammalian associative learning. Annu. Rev. Psychol. 56, 207–34 (2005). 12. Lynch, M.A. Long-term potentiation and memory. Physiol. Rev. 84, 87–136 (2004). 13. Coogan, A. N., O’Neill, L. A. & O’Connor, J. J. The P38 mitogen-activated protein kinase inhibitor SB203580 antagonizes the inhibitory effects of interleukin-1beta on long-term potentiation in the rat dentate gyrus in vitro. Neuroscience 93, 57–69 (1999). 14. Koss, M. et al. Ezrin/radixin/moesin proteins are phosphorylated by TNF-alpha and modulate permeability increases in human pulmonary microvascular endothelial cells. J. Immunol. 176, 1218–27 (2006). 15. Atack, J. R. Preclinical and clinical pharmacology of the GABAA receptor alpha5 subtype-selective inverse agonist alpha5IA. Pharmacol. Ther. 125, 11–26 (2010). 16. Watanabe, M., Maemura, K., Kanbara, K., Tamayama, T., and Hayasaki, H. GABA and GABA receptors in the central nervous system and other organs. Int. Rev. Cytol. 213, 1–47 (2002). 17. Wu, Y., Wang, W., Díez-Sampedro, A. & Richerson, G. B. Nonvesicular inhibitory neurotransmission via reversal of the GABA transporter GAT-1. Neuron 56,851–65 (2007). 18. Tsien, J., Huerta, P. & Tonegawa, S. The Essential Role of Hippocampal CA1 NMDA Receptor–Dependent Synaptic Plasticity in Spatial Memory. Cell 87, 1327-1338 (2000). 19. Hein, A. et al. Behavioral, structural and molecular changes following long-term hippocampal IL-1β overexpression in transgenic mice. J. Neuroimmune Pharmacol. 7, 145–55 (2012).

20. Song, J.H. et al. Glycyrrhizin Alleviates Neuroinflammation and Memory Deficit Induced by Systemic Lipopolysaccharide Treatment in Mice. Molecules 18, 15788-15803 (2013). Received Month, ##, ##, 200#; accepted

200#; Month,

revised ##,

Month, 2013.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program

48


Evaluating syanpto-protection in a three compartmented microfluidic chip model following a chemically induced axotomy. Qasid Chaudhry

Microfluidic chips allow for the manipulation, at small quantities of neuronal cells. Further, these chips allow for precise temporal and spatial control, allowing for a model that can be useful in the framework of neurodegeneration. Deleglise et al (2013) fabricated a 3 chamber microfluidic chip. The chambers held one of: coritical neuron soma and dendrites, cortical axons, or striatal neurons. The chip was designed to replicate an oriented neuronal network, with connections going from the coritcal to the striatal neurons. Through the use of a chemically induced axotomy, by adding fluid to the central chamber (housing the cortical axon), Deleglise et al (2013) showed that their chip could be used to simulate a lesion in the neuronal network. An emphasis was placed on the protection of synapses, an event that in axotomy studies, traumatic injury and in many neurodegenerative disorders precedes the loss of neuronal cell soma and axons. They then showed that zVAD-fmk, a caspase inhibitor and resveratrol did not show synaptic protection, while NAD+ and Y27632, a Rho Kinase inhibitor showed significant synaptic protection, despite the mechanism not being clear. NAD+ and rho kinase inhibition point at potential therapeutic targets for neurodegeneration. This can also be further looked at from the functionality of the chip - it is a useful tool in the evaluation of drugs in the axotomy model was presented in the study. Key words: Microfluidic Chip; synpato-protectoin; axotomy; neural network Background When studying neurodegenerative diseases or other brain injuries that result in neurodegeneration, we are lacking in a good in vitro model. Currently, commonly used models consist of either the use of whole brains or dissociated cell culture systems. While both do have their benefits, the use of entire brains limits the ability to interact with and manipulate individual cells, while cell cultures do not have the intricate networks found within the brain. A solution would be the use of a microfluidic chip, which would allow for the manipulation of single cells, while also allowing for the growth of an in vitro neural network. Microfluidic chips have been used as early as the early 1990s (Chin et al, 2006). Microfluid chips have been used to study a variety of different processes and systems such as genetic analysis (Liu et al, 2009), drug screening (Caplin et al, 2015) and cancer diagnosis (Ying et al, 2013). In neurons, microfluidic chips have been used to study developmental processes such as axonal guidance (Huang et al, 2014) and neurodegeneration (Deleglise et al, 2013; Kilinc et al, 2010) among others. The diversity of microfluidic chips shows how potentially powerful this technique is. The strength of microfluidic chips, especially when looking at neuronal systems is in the simplification of vast, complex networks into easily manipulable, both temporally and spatially, chips. When investigating neurodegeneration, the death of the soma occurs after synapses are lost (Deleglise et al, 2013). This is evident in axotomy and in early stages of neurodegenerative diseases and results in a further dying of downstream neurons. Yet little has been done in terms of investigating potential therapies in regards to synapto-protection. Both the need of synaptic protection and a model simulating neural networks are important when considering the effect of neurodegeneration and testing the

49

efficacy of drugs to prevent it from occurring. Deleglise et al (2013) look at the effect of several drugs in respect to dealing with chemically induced damaged resulting in axotomy. More interestingly, the model that they used to evaluate the drugs of interest was a threechambered microfluidic chip. This study spans two important fields within neuroscience â&#x20AC;&#x201C; neurodegeneration and the need for good in vitro models. This study, further used a microfluidic chip, but rather than simply use it to separate the axon from the somatodendritic portion, it also added a third chamber which held a full neuron (soma, dendrite and axon) and had one way synaptic connections. This microfluidic chip method is a step forward in creating complex in vitro models, which at the same time provide good spatial and temporal control (Siddique et al, 2014) â&#x20AC;&#x201C; something that could be used to study a variety of neuronal phenomena, including neruonal development, neurodegenerative disease, and in the case of the study, traumatic injuries. Research Overview

Summary of Major Results and Discussion

Deleglise et al (2013) created a three chambered microfluidic chip in order to study the effects of synaptoprotective drugs following axotomy. The chip used was composed of 3 separate compartments; one for the cortical cells, one for striatal cells and one for the axons of the cortical cells. The compartments allowed, through micro channels, the axons from the cortical cells to send axons to the striatal cells. Each compartment could be manipulated separately through fluids, due to 2 reservoirs on each compartment (Fig. 1a). The ability of this chip to manipulate specific parts of the neuron and study the effects on connected neurons is one that could lead to many different uses. For one, due to the simplicity of the model, mecha-


nistic pathways of neurodegeneration and of therapies could more readily be assessed. The efficacy of drug therapies involved in treating neuronal conditions could also be screened in a spatially and temporally controlled environment. The inherent nature of the chip allows for the use of fewer neuronal cells and allows for results to be obtained quicker. The applications of the chip, because of the capacity for different designs is almost limitless and extends to beyond the brain (Liu et al, 2009; Caplin et al, 2015; Ying et al, 2013). The cells were seeded onto the chip and the network was allowed to mature for 14 days prior to axotomy

Figure 1. a: A schematic for the 3 compartment microfluidic chip is shown, the reservoirs are labelled R. b: A phase contrast image of the microfluidic chip. The left side shows the cortical neuron somas, while the left portion shows the striatal neurons. The two are connected by microchannels. The decreasing diameter of the microchannels when going from the cortical to striatal cells can be seen. Source: Deleglise B, Lassus B, Soubeyre V, Alleaume-Butaux A, Hjorth J, Vignes M, ... Peyrin J (2013) Synapto-protective drugs evaluation in reconstructed neuronal network. PLoS ONE 8(8), e71103

Neural Network

Once 15 days had passed from the seeding, Deleglise et al (2013) showed that the neural network had grown as predicted. They found that 80% of the cortical axons that made it to the central compartment made connections and synapsed on the dendrites of the striatal neurons. This was evidenced by the association of VGLUT1 positive presynaptic terminals from the cortical axons and MAP-2 positive dendrites of the striatal cells in the receiving compartment. The decreasing diameter of the microchannel proved effective in the prevention of allowing striatal axons from projecting into the microchannel (Fig. 1b). This all points to the formation of a neural network, with unidirectional projections as found by Peyrin et al (2011) as well under a similar design. The study by Deleglise et al (2013) showed that the addition of reservoirs and a compartment to the microchannels didn’t alter the functional or morphological aspects of

the neurons in the network. Further, these results can be further extended - due to the polarizing of the axons, a further receiving chamber, downstream of the striatal neurons could be added to allow for a more complex network.

Axotomy

Prior to assessing the efficacy of the synaptoprotective drugs, the axons needed to be lesioned. This was carried out through chemical axotomy, through the use of a 0.1% Triton in DMEM solution, along with a control DMEM only solution treatment. The solution was added to the reservoirs of the middle compartment, housing the cortical axons. The Triton solution was shown to result in a small lesion, while not affecting other portions of the axons (Fig 2).

Figure 2. Following axotomy, the lesion seemed to be contained to the central channel, while the surrounding axonal segments seemed unharmed. The axons were stained for α-tubulin. Source: Deleglise B, Lassus B, Soubeyre V, Alleaume-Butaux A, Hjorth J, Vignes M, ... Peyrin J (2013) Synapto-protective drugs evaluation in reconstructed neuronal network. PLoS ONE 8(8), e71103

Following the axotomy, the cortical neurons showed no differences in either their dendrites or soma, as shown through staining using MAP-2 and α-tubulin, and the portion of the axon still attached to the cortical soma could be regrown. The portion of the cortical axon that was no longer attached to the cortical soma began to show some degeneration after four hours, and was fully fragmented after six. Interesting to note is that there was no difference in the structure of the axons of the control (DMEM) and the 0.1% Triton treated axons. The striatal post synaptic neurons did not show any architectural changes over the six hours, however, even just two hours, there was a significant decrease in the presynaptic clusters (60% decrease), and within six hours, the synapses seemed to have disappeared 50


(v-GLUT1 staining, indicative of presynaptic clusters disappeared) (Fig 3). In addition, the postsynaptic striatal neurons did not show any degeneration over the six hour time period of the, which the authors took to suggest that the structure of the striatal cells could be preserved and rescued for at least that time period. The six hour period points to a critical window in which the striatal neurons could potentially be rescued with some of the synapses still being maintained that long. The 60% decrease in synaptic clustering within the first two hours is alarming and points further to the importance of immediate treatment following any sort of axonal lesion. The time period over which the post synaptic striatal cells are shown to still be viable could be used in future assays of neuroprotection.

resveratrol pre-treatment did not show any significant synapto-protection. Y27632 pre-treatment of 1 hour prior to axotomy showed a retention of 75% of the synapses (Fig 4). Y27632 and NAD+ provide interesting potential future therapeutic targets for dealing with trauma in the brain.

Figure 4. The relative efficacy of all of the drugs evaluated in the study in protecting from synaptic degeneration 3 hours following the initial axotomy is shown. Resveratrol and z-VAD-fmk show no significant difference from the untreated axotomized neurons, while NAD+ and Y27632 treated neurons do. Source: Deleglise B, Lassus B, Soubeyre V, Alleaume-Butaux A, Hjorth J, Vignes M, ... Peyrin J (2013) Synapto-protective drugs evaluation in reconstructed neuronal network. PLoS ONE 8(8), e71103 Figure 3. Through staining with MAP-2 (blue) and v-GLUT1 (red) staining, loss of synaptic association of the axons can be seen, as decreased v-GLUT1 around the MAP-2 stained dendrites points to a loss of axonal projections in c: control condition, and after the axotomy at d: 2 hours e: 4 hours f: 6 hours. Source: Deleglise B, Lassus B, Soubeyre V, Alleaume-Butaux A, Hjorth J, Vignes M, ... Peyrin J (2013) Synapto-protective drugs evaluation in reconstructed neuronal network. PLoS ONE 8(8), e71103

Synaptoprotective Effects

The cell cultures were also exposed to NAD+, z-VADfmk (caspase inhibitor), resveratrol (NAD+ dependant histone deacetylase activator), and Y27632 (Rho kinase inhibitor) prior to axotomy. Only Y27632 and NAD+ showed any significant protective effects on synapses. 3 hours after axotomy, cells not treated with any of the drugs showed a decrease to 25% of the initial number of synapses. Treating with NAD+ for 24 hours prior to axotomy showed a retention of 65% of their synapses. Pre-treatment with z-VAD-fmk for 1 hour did not show any significant synapto-protection compared to the non-treatment group. Similarly,

51

Conclusions The study by Deleglise et al (2013) provides a look at a modification to the use of microfluidic chips in studying neuronal cultures to the chip used by Peyrin et al (2011). The addition of the reservoir to the microchannels allows for the manipulation of the axons and provides more control when manipulating neurons. The use of microfluidic chips themselves allows for the study of small populations of neuronal cells and allows for the control of multiple sections of neurons, such as the soma or axons of individual populations. Further, due to the flexibility of the design of the chip, microfluidic chips can be used to model multiple degenerative and developmental pathways. Peyrin et al (2011) also put forward that modifying the size of the microchannels, the size and amount of axons that could pass through could be controlled and a neural network that would mimic in vitro growth conditions could be obtained. The orientation of the network could easily be manipulated by modifying the size of microchannels, and through the use of different fluids in the chambers multiple conditions could be mimicked (Deleglise et al, 2013). Deleglise et al (2013) further showed that Rho


kinase inhibitor Y27632 and NAD+ are both effective in protecting synapses from degeneration, while caspase inhibitors do not. Treating cells with Y27632 or NAD+ prior to the axotomy resulted in a lower loss of synapses three hours after the axotomy. Despite the pathway being unclear, the effects seem to be significant when compared to zVAD-fmk, a caspase inhibitor, and resveratrol. One of the earliest changes observed in neuronal degeneration is the loss of synaptic and axonal integrity (Shahidullah et al, 2013). Protecting against these effects could provide direction for further targets that could be used to prevent the degeneration of neurons in neurodegenerative diseases. Criticisms and Future Directions As previously mentioned, one of the greatest strengths of using a microfluidic chip when looking at neurons is the amount of control that it provides, both temporally and spatially. Due to it being an in vitro method, visualizing the cells become easier. The different compartments allow for very specific targeting of chemicals to axons or the cell soma – something that would be difficult in in vivo models. The chip also provides a good temporal resolution. The chip, being clear allows for fluorescence to be observed outside it with no issues, and can thus easily be recorded. Another strength is that microfluidic chips increase the viability of neurons (Huang et al, 2012). The level of control however could also be seen as a flaw when considering translating the knowledge obtained in these systems to in vivo systems. As mentioned before, chemicals, through the 3 compartments could be specifically targeted to a specific area of the neuron, this would not be the case in in vivo environment. While the control helps to create the initial in vivo environment, the fact that the compartments are distinct is a reason for caution, and would have to be addressed. Another potential flaw in the use of microfluidic chips was the use of polydimethylsiloxane. Despite its benefits of being clear, flexible and biocompatible, polydimethylsiloxane also has problematic properties, such as its ability to take up small proteins (Huang et al, 2012). The intake and release of proteins can be random, and as such could be a source of error. This points to the need to be able to make disposable chips. The effects of the drugs (NAD+ and Y27632) in the study were only evaluated for three hours after the axotomy – a very limited time scope. Further studies should look at extended time periods to determine the length of time that they are effective for. In addition, Deleglise et al (2013) pretreated the chips with the drugs of interest up to 24 hours before. Though there was an increase in synaptic viability using NAD+ and Y27632, the results should be taken with some doubt. NAD+ as Deleglise et al (2013) state, is involved in a wide manner of cellular including nuclear signalling and metabolism. Due to the addition of these potential therapeutic agents significantly before the axotomy, there will be multiple downstream pathways that would need to be further investigated. Further, resveratrol indirectly stimulates NAD+ produc-

tion, yet does not induce the same synaptic protection as NAD+ does in the axon. Again, as Deleglise et al (2013) mention, the effects of resveratrol may be due to long distance signalling, as resveratrol has been shown to have effect in delaying Wallerian degeneration (Calliari et al, 2014). Another caveat to introducing these chemicals before the axotomy is that it is not something that would be observed in the real world – pre-exposing neurons with these chemicals to prevent synaptic degeneration is not a realistic treatment. But, this does warrant further investigation in a in vivo model and in respect to their effectiveness after axotomy. These pathways could also be useful in determining other agents to protect against synaptic degeneration. The use of microfluidic chips is an interesting approach in neuroscience. Despite the use in observing single and even two neuronal populations, there is still significant amounts of further use that could potentially be gained. Microfluidic chips are very versatile in that they can be used to study almost any neurodegenerative process in the brain. For example, this study looked at trauma, however, it used a very simple model of two neural populations. We know that in vivo, neural networks extend over significantly more neurons, which is one of the possible ways in which microfluidic chips can be further used. This study used a single synaptic connection, but in future studies, this could be extended to larger pathways. This combined with a 3-dimensional brain-on-a-chip (Park et al, 2015) could lead to the recreation of very complex networks, which, could even more closely resemble the in vivo environment in the cell. As in the study by Park et al., this could be applied to Alzheimer’s disease. Using the microchannels and separated chambers from the Deleglise et al. study in conjunction with the neurospheroids of the Park et al. study, a very convincing model for Alzheimer’s disease in the brain could be produced. This could be used to further test therapies for Alzheimer’s and to further understand the mechanism in a much simpler, but still complex and manipulable model. Due to the diversity of the microfluidic chip, this could be further used for other forms of neurodegenerative diseases such as Parkinson’s. Another level of complexity could be added by introducing glial cells into the chip as well, to further emulate the in vivo environment (Soe et al, 2012). In essence, microfluidic models could become very similar to mimicking in vivo models, despite being in vitro. As it is with most in vitro studies, there needs to be some translatability to in vivo models when evaluating the drug therapies. Synaptoprotective therapies have been shown to be beneficial in the treatment of Alzheimer’s disease. The use of magnesium-L-threonate in late stages of Alzheimer’s was also shown to beneficial (Li et al, 2014). Considering Y27632 and the possible therapeutic synaptoprotective properties, the next step would be to either use an in vivo mouse model, to see the global and long term effects of the two in the brain (NAD+ has already been shown to be effective in vivo (Deleglise et al, 2013)). The second option would be to test the two using an in vitro model 52


of human cells. Both of these would be necessary before testing in in vivo human models, as again, with using in vitro studies, there are numerous other complicating factors in vivo. Furthermore, despite being a good model, the mouse and human brains are inherently different, and this would also be needed to be taken into consideration when looking at the applicability to therapies in humans. In essence, it would be of interest to almost repeat the experiment, but using human neurons and to also using the same controls and treatments, observe longer term effects on mice (the study used a three hour period after the axotomy). References 1. Calliari A, Bobba N, Escande C, Chini EN (2014) Resveratrol delays Wallerian degeneration in a NAD(+) and DBC1 dependent manner. Exp Neurol 251:91-100 2. Caplin JD, Granados NG, James MR, Montazami R, Hashemi N (2015) Microfluidic organ-on-a-chip technology for advancement of drug development and toxicology. Adv Healthc Mater doi:10.1002/adhm.201500040 3. Chin CD, Linder V, Sia SK (2007) Lab-on-a-chip devices for global health: past studies and future opportunities. Lab Chip 7:41–57 4. Deleglise B, Lassus B, Soubeyre V, Alleaume-Butaux A, Hjorth J, Vignes M, ... Peyrin J (2013) Synapto-protective drugs evaluation in reconstructed neuronal network. PLoS ONE 8(8), e71103 5. Huang H, Jiang L, Li S, Deng J, Li Y, Yao J, Li B, Zheng J (2014) Using microfluidic chip to form brain derived neurotrophic factor concentration gradient for studying neuron axon guidance. Biomicrofluidics 8(1) doi: 10.1063/1.4864235 6. Huang Y, Williams J, Johnson S (2012) Brain slice on a chip: Opportunities and challenges of applying microfluidic technology to intact tissues. Lab Chip 12:2103-2117. 7. Kilinc D, Peyrin JM, Soubeyre V, Magnifico S, Saias L, Viovy JL, Brugg B (2011) Wallerian-like degeneration of central neurons after synchronized and geometrically registered mass axotomy in a three-compartmental microfluidic chip. Neurotox Res 19(1):149-61 8. Li W, Yu J, Liu Y, Huang X, Abumaria N, Zhu Y, ... Liu G (2013) Elevation of brain magnesium prevents synaptic loss and reverses cognitive deficits in Alzheimer’s disease mouse model. J Neurosci 33(19):8423-41 9. Liu P, Mathies RA (2009) Integrated microfluidic systems for high-performance genetic analysis. Trends Biotechnol 27(10):572-81 10. Park J, Lee BK, Hyun J, Jeong GS, Lee CJ, Lee SH (2015) Three-dimensional brain-on-a-chip with an interstitial level of flow and its application as an in vitro model of Alzheimer’s disease. Lab Chip 15(1):141-150. 11. Peyrin JM, Deleglise B, Saias L, Vignes M, Gougis P, Magnifico S, … Brugg B (2011) Axon diodes for the reconstruction of oriented neuronal networks in microfluidic chambers. Lab Chip 11:3663-73 12. Shahidullah M, Le Marchand SJ, Fei H, Zhang J, Pandey UB, Dalva MB, Pasinelli P, Levitan IB (2013) Defects in synapse structure and function precede motor neuron degeneration in Drosophila models of FUS-related ALS. J Neurosci 33(50): 19590-98 53

13. Siddique R, Thakor N (2014) Investigation of nerve injury through microfluidic devices. J R Soc Interface 11(90) doi: 0.1098/rsif.2013.0676 14. Soe A, Nahavandi S, & Khoshmanesh K (2012) Neuroscience goes on a chip. Biosens Bioelectron 35:1-13. 15. Ying L, Wang Q (2013) Microfluidic chip-based technologies: emerging platforms for cancer diagnosis. BMC Biotechnol 13:76

Received Month, ##, 200#; revised ##, 200#; accepted Month, ##,

Month, 2013.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program


Potential link between intestinal microbiota and anxiety Chun-Chi Chu

The importance of the intestinal microbiota that is developed in our first few days of life has been established. However, the relationship between the intestinal microbiota and the central nervous system is still poorly understood. This literature review examines an experiment conducted by Neufeld et al. and derives potential future researches to further explore this area. Neufeld et al. collected both behavioural testing and measured anxiety-related brain mRNA expression level from adult germ free (GF) and specific pathogen free (SPF) Swiss Webser female mice. They found that GF mice presented less anxiety-related behaviours and more exploratory behaviours compared to SPF mice. GF mice also increased in the mRNA expression of brainderived neurotrophic factor (BDNF) and decreased in the mRNA expression of both 5HT1A serotonin receptor and N-methyl-D-aspartate (NMDA) NR2B subunit. Key words: anxiety; intestinal microbiota; elevated plus maze; central nervous system; BDNF; NMDA; 5HT1A Background Previous studies have shown and established the importance of intestinal microbiota, which is formed in the first few days after birth, on the development and function of gut, immune, and endocrine systems. It helps the body to maintain homeostasis and regulate inflammation.1 Although it has not been fully investigated, several studies have suggest the connection between gut microbacteria and the central nervous system. In a cohort study, researchers found that the prevalence for anxiety, mood, and other psychological disorders tend to be higher in those who have disturbed intestinal microbiota, or bowel diseases.2 Diet, which changes intestinal microbiota, also alters learning and memory.3 The direct interaction between microbiota and the brain/behaviour is, however, poorly understood. A study conducted by Neufeld et al.4 attempts to close this gap. They elucidated and demonstrated the effect of intestinal microbiota on behaviour and on the central nervous. Neufeld et al. measured mice’s anxiety behaviours using the elevated plus maze and mRNA expression of brain-derived neurotrophic factor (BDNF), 5HT1A serotonin receptor, and N-methylD-aspartate (NMDA) subunit. These proteins have been found to be associated with anxiety behaviors. They found that germ free (GF) mice with no intestinal microbiota have lower anxiety and higher exploratory behaviours compared to mice raised in standard conditions, or specific pathogen free (SPF) mice. Research Overview

Summary of Major Results

Eight-week-old GF and SPF female Swiss Webster mice were used. Fifty-one hours after the mice arrived, their anxiety-related behaviours were tested using elevated plus maze. Blood and brain samples were also collected from a separate group of mice to test for corticosterone, BDNF, 5HT1A serotonin receptor, and NMDA subunit levels.4

Elevated Plus Maze

Using elevated plus maze, the mice’s number of arm entries and duration in each arms were recorded. Figure (A) and (B) traces SPF’s and GF’s movements in the maze. GF mice spent more time in the open arms, less time in the closed arms, and entered open arms more frequently compared to SPF mice.4

Corticosterone Levels

A standard radioimmunoassay kit was used to measure the corticosterone levels. GF mice’s plasma corticosterone level was higher than SPF mice’s.4

In situ Hybridization

And, in situ hybridization was used to identify and measure the mRNA expression levels of BDNF, 5HT1A receptor and NMDA subunit. Then, statistical programs were used to compare and determine the statistical significance of the data. GF mice increased in BDNF mRNA gene expression, specifically in the dentate gyrus of the hippocampus, while the expressions in other regions, CA1 and CA3, did not differ compared to SPF mice (Figure (C)). On the other hand, compared to SPF mice, GF mice’s 5HT1A receptor (Figure (D)) and NMDA mRNA expression decreased in the dentate gyrus and central amygdala, respectively. The expression of 5HT1A mRNA expression did not differ between GF mice and SPF mice in the CA1 region. The NMDA subunit that showed significant decrease was the NR2B subunit (Figure (E)).4

Conclusions and Discussion

The presence or the absence of intestinal microbiota influences the development of behaviour and central nervous system in mice. GF mice with no microbiota decreased in anxiety-like behaviours and increased in exploratory behaviours. They also expressed more BDNF and expressed less 5HT1A and NMDA subunit NR2B in the brain.4 Altered gene expression in these 54


proteins is consistent with the behavioural findings and contributes to the exploratory behaviour observed. Previous studies have shown that low BDNF levels in the dentate gyrus increase anxiety-like behaviours5; the decrease in serotonin level from 5HT1A receptor

increases exploratory behaviour6; and NR2B antagonist blocks amygdala synaptic plasticity and fear learning7. Thus, higher BDNF levels and lower 5HT1A and NR2B levels in GF mice are related to reduced anxiety-like behaviour observed.

Figure (A) presents the movement of specific pathogen free (SPF) mice in the elevated plus maze (EPM). (B) presents the movement of germ free (GF) mice in the EPM. (C), (D), and (E) show the mRNA expression of BDNF, 5HT1A, and NR2B, respectively.

55


Criticisms and Future Directions The first few days of life after birth define the lifelong mutual relation we have with the microbacteria in our gut. This relation is not only essential for the development and function of gut, immune, and endocrine system but also for the development and function of the brain/behavior. Neufeld et al.4 found that GF mice with no intestinal microbiota have lower anxiety and higher exploratory behaviours compared to mice reared in SPF environments.4 This study ties the gap between intestinal microbiota and the brain/behavior interaction. It also provides new insights to therapeutic approaches in mental health. Innovating methods to treat and prevent psychiatric illnesses, specifically, anxiety-related disorders, can be derived. Using the elevated plus maze model and measuring anxiety and fear related protein mRNA levels, Neufeld et al. showed that GF mice spent less time in the open arms and expressed higher BDNF levels and lower 5HT1A and NR2B levels. A group of mice were used for behavioral testing, and a separate group of mice were used for sample testing.4 This study, however, failed to account for the effect of menstrual cycles, the unexpected increase in corticosterone levels, and the effect of restoring microbiota. Researchers did not take mice’s reproductive cycles into consideration and used eight-week-old adult female Swiss Webster mice for the experiment. These mice underwent hormone level changes that could have resulted in behavioural alterations. A study has shown that rats in the proestrus phase with high levels of progesterone and estrogen of the cycle reduced in anxiety-like behaviours.8 This means GF mice’s exploratory behaviours may be due to their proestrus phase rather than their lack of gut microbiota. To rule out this confounding factor, one should replicate the experiment using male mice. If the same results are found, the correlation between gut microbiota and behavior can be established and confirmed. Neufeld et al. also failed to explain the unexpected high levels of corticosterone in GF mice that showed reduced anxiety-like behavior. High corticosterone levels tend to be accompanied by increased anxiety behaviours and low corticosterone levels by decreased anxiety behaviours.9 In this study, however, an inverse relation was observed. Mice with elevated corticosterone levels surprisingly showed less anxiety behaviours.4 To follow up on this finding, one measure the corticosterone samples from the group of mice that underwent behavioural testing instead of measuring from a separate group of mice. The blood samples should be collected immediately after testing. The possibility of replenishing the gut microbiota and its effect on behaviour was not explored. When GF mice’s microbiota is re-established by introducing Bifidobacterium infantis, GF mice’s anxiety-like behaviours increase.10 For future experiments, one could administer pro-biotic supplements to facilitate the growth of microbiota in GF mice and antibiotics to suppress the growth in SPG mice and observe the behaviour/brain changes. These manipulations should be done at different periods after birth to discover the time frame in which the interaction between the brain and the microbiota is still plastic.

Further experiments on male mice, on corticosterone levels, and on pro-biotic and antibiotic should be conducted to fill in the gaps in this study and understand more on anxiety disorders. References 1. Backhed, F., Ley, R.E., Sonnenburg, J.L., Peterson, D.A., & Gordon, J.I. (2005). Host-bacterial mutualism in the human intestine. Science, 307, 1915–1920. 2. Walker, J.R., Ediger, J.P., Graff, L.A., Greenfeld, J.M., Clara, I., Lix, L. et al. (2008). The Manitoba IBD cohort study: a population-based study of the prevalence of lifetime and 12-month anxiety and mood disorders. Am J Gastroenterol, 103, 1989–1997. 3. Li, W., Dowd, S.E., Scurlock, B., Acosta-Martinez, V., Lyte, M. (2009). Memory and learning behavior in mice is temporally associated with diet-induced alterations in gut bacteria. Physiol Behav, 96, 557–567. 4. Neufeld, K.M., Kang, N., Bienenstock, J., & Foster, J.A. (2011). Reduced anxiety-like behaviour and central neurochemical change in germ-free mice. Neurogastroent Motil 23, 255-e119. 5. Chen ZY, Jing D, Bath KG et al. (2006). Genetic variant BDNF (Val66Met) polymorphism alters anxiety-related behavior. Science, 314(5796), 140–143. 6. Holmes A, Yang RJ, Lesch KP, Crawley JN, Murphy DL.(2003). Mice lacking the serotonin transporter exhibit 5-HT1A receptor-mediated abnormalities in tests for anxiety-like behavior. Neuropsychopharmacology, 28(12), 2077–2088. 7. Rodrigues SM, Schafe GE, LeDoux JE. (2001). Intraamygdala blockade of the NR2B subunit of the NMDA receptor disrupts the acquisition but not the expression of fear conditioning. J Neurosci, 21(17), 6889–68896. 8. Sayin, A., Derinoz, O., Yuksel, N., Sahin, S., & Bolay. H. (2014). The effects of the estrus cycle and citalopram on anxiety-like behaviors and co-fos expression in rats. Pharmacol Biochem Behav 124, 180-187. 9. Conboy, L., & Sandi, Carmen. (2010). Stress at learning facilitates memory formation by regulating AMPA receptor trafficking through a glucocorticoid action. Neuropsychopharmachology 35, 674-685. 10. Sudo, N. et al. (2004). Postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice. J Physiol 558.1, 263-275. Received Month, 03, 04, 2015; Accepted

2015; Revised Month, 04,

Month, 2015.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Chun-Chi Chu, Human Biology Department, 300 Huron Street, Wetmore Hall Rm105, Toronto, ON M5S 3J6 Email: Catherine.chu@mail.utoronto.ca Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program 56


Elevations in the Serum Levels of the Brain Derived Neurotrophic Factor during Aerobic Physical Activity - A Simple, yet Often Disregarded Remedy for Frontotemporal Dementia Melissa Colaluca

Abstract: Within the last few decades, researchers in the field of neuroscience have taken an interest in exercise-meditated cognitive enhancement, with the intent of identifying plausible techniques and therapies to successfully reduce or delay cognitive decline in the elderly. A multitude of observational studies have found improved cognitive performance on a series of executive function assessments subsequent to aerobic activity, whereas stretching and toning training has been shown to have little to no effect on a subjects reasoning and rationalizing skills. More recently, researchers have identified surges in serum brain derived neurotrophic factor (BDNF) levels subsequent to aerobic activity and thus, have come to deduce that this protein mediates improved executive control subsequent to exercise. Leckie et al. (2014) sought to demonstrate the effect of BDNF on executive function in an elderly subject pool by having them complete a 1-year aerobic activity or stretching and toning intervention. Findings revealed that only subjects completing daily aerobic activity showed elevations in serum BDNF levels and improved performance on a test of executive function, the task-switch paradigm. Such is the case due to increased blood flow to cortical sites during aerobic activity, which increased the expression of BDNF, up-regulated neuronal outgrowth and inhibited apoptotic factors. Such enabled neural structures involved in executive function - the prefrontal cortex (PFC) and the anterior cingulate cortex (ACC) to perform cognitive processing at an optimal level. Key words: brain derived growth factor (BDNF); insulin-like growth factor (IGF-1); Vascular endothelial growth (VEGF), prefrontal cortex (PFC); anterior cingulate cortex (ACC); task-switch paradigm, frontotemporal dementia; long term potentiation (LTP); grey matter volume (GMV); white matter volume (WMV); Event related potential (ERP) Background For centuries, several experts in the field of science have urged the elderly to participate in daily physical exercise to hinder the onset of debilitating physical diseases. Though several scientists agree that exercise regulates vascular disease symptoms - there is currently heated debate on its ability to initiate the cellular and molecular mechanisms that delay the onset of various neurodegenerative diseases. Exercise in popular media has been portrayed as the under the radar simple remedy to many of modern societies psychical ailments. Unfortunately, exercise is but an arduous and unpreferred way the elderly wish to spend their leisure time. Though several individuals are fit enough to walk around the block or jog on the spot in the comfort of their own household, few take the initiative to practice this behavior. Some use the excuse that their jam-packed busy schedules impede them from exercising or on the contrary, that their lazy disposition in a technologically dependent culture decreases their drive to stay fit. Often sedentary, older adults in Western States appear to have a high incidence of cardiovascular disease, but a more intriguing trend is that many have been diagnosed with one or more cognitive deficits. Though humans anticipate a loss of memory in old age, they fail to realize that this outcome can indeed be reversed given that neurogenesis and synaptogenesis bare no age limits. Many recent studies have linked lower BDNF levels - the brain derived neurotrophic factor - with inactivity in old age. Increased expression 57

of this protein at cortical sites functions to enhance neuronal survival and outgrowth and so, if up regulated during exercise, neurons that would otherwise undergo apoptosis, thrive. After decades of observational and behavioral research on physical activities ability to prevent executive decline, scientistâ&#x20AC;&#x2122;s prime interest is to now pinpoint the neuronal proteins, diffusion patterns of pleasure inducing neurotransmitters and/or classes of endorphins involved in preventing cognitive decline. Of the studies conducted, it is evident that neurotrophic factors during and subsequent to physical activity show increased expression and transmittance to optimize and improve brain functioning in elderly subjects. Due to innovations in neuroimaging techniques and the rapid advancements in immunofluroescent technologies, neuroscientists have been able to demonstrate that a strict exercise plan leads to increased performance on tests of executive function as BDNF expression and the many downstream molecules it stimulates, increase. Unfortunately, the visualization of proteins in the human cortex has not been perfected and so many preliminary studies on executive function augmentation as mediated by BDNF during exercise were conducted on rodents. One such immunofluroescent study found that as BDNF levels increased subsequent to a 20-minute exercise condition, CAMKII levels elevated, a protein known to initiate and increase long-term potentiation (LTP) via trafficking of AMPA receptors to the post-synaptic membrane of neurons. An increase of this protein at the frontal cortex correlated with improvements on tasks of executive function. Larson


et al. (2006) investigated the molecular mechanisms that mediate the effect of exercise on executive function by at protein expression at the frontal cortex of rodents, a model organism that holds several parallels in terms of neuronal structure and function to humans. Rats completed a 5-day treadmill exercise intervention for 15 or 30 minutes. Western blotting revealed elevations in BDNF expression in subjects completing 15 minutes of exercise. However, rats in the 30-minute condition showed diminutions in BDNF. Thus, it seemed as though this duration of exercise induced a stress response rather than having neuroprotective value and so moderate rather than vigorous exercise increases BDNF levels and improves cognitive functioning. The same study identified elevations in PI3K, CREB and MAPK proteins involved in the downstream signaling pathway of BDNF that work to inhibit apoptosis. Psychologists have also studied the influence of aerobics on cognition via longitudinal observational studies such as the CAIDE investigation, which found that exercise for a duration of one year enhanced cognitive performance by 52% in subjects over the age of 65 (Cotman, Berchtold & Christie, 2007). These subjects demonstrated near perfect scores on a series of executive function tasks. Kluding, Tseng and Billinger (2011) conducted a similar study whereby they had older adults complete a 6-month aerobic exercise program. Subsequently, subjects completed a flanker task - where they were to respond to target stimuli and disregard distractors - prior and subsequent to the intervention. Subjects demonstrated an enhanced ability to discriminate between distractors and target stimuli as a function of increased activity at the frontal sites. Erickson et al. (2012) - one of the leading neuroscientists in a novel field of research investigating the effects of neurotrophic factors such as IGF-1 and BDNF on cognition - carried out an MRI study on elderly subjects looking at their grey matter volume (GMV) in the PFC and ACC during a 6-month aerobic exercise intervention. Subjects demonstrated increased volume at the PFC and ACC demonstrating there to be an association between physical activity and the integrity of grey matter microstructure. This was correlated with the improved performance on a Stroop task where individuals were to report the colour and not the semantics pertaining to a word, a difficult assignment considering that humans are more inclined to verbalize words rather than font colour. Thus, the following task requires that the elderly subject inhibit a reflexive response, a task that requires executive function. Furthermore, Vaynman, Ying and Gomez-Pinilla (2007) reported elevations in cerebral blood volume as visualized using MRI in the hippocampus of 11 elderly subjects after a three-month aerobic exercise program. This was correlated with elevations in oxygenation levels at the cortex and improvements on tasks of executive function and memory. Thus, CBI may be a biomarker for neurogenesis in humans. Colcombe et al. (2006) took to using MRI on a subject pool of older adults subsequent to an aerobic or toning intervention. Those in the aerobic inter-

vention - required to walk for 1 hour 2 days a week - showed elevations in white matter volume (WMV) at the frontal and temporal cortex. Volumetric increases in the nonaerobic control group as well as in a condition of middle-aged participants showed no changes in WMV. Similarly, Benedict et al. (2012) demonstrated increased synaptic connectivity via DTI in elderly subjects subsequent to a 12-week aerobic exercise intervention. The long fiber white matter tracts at the frontal cortex of these subjects displayed decreased functional anisotropy (sheering) and increased diffusion (Figure 1). Thus, neuronal coherence decreases in older subjects permitted that they remain active.

Figure 1: The following image illustrates a negative correlation between elderly subjects reaction time during a task of executive function and fractional anisotropy at the frontal cortex, subsequent to aerobic activity. Contrary to findings in the following study, the following demonstrates younger adults as showing greater improvements in cognitive functioning than the elderly (Benedict et al., 2012).

Event related potential (ERP) studies have also revealed that chronic, prolonged, rather than acute aerobic exercise in elderly subjects is correlated with increased amplitude in the P300 component at 300-800ms. This brain wave activity is associated with motivational attention, an updating of memory and decision-making. Thus, as performance on a task-switch paradigm increased so too did the P300 amplitude in elderly neurotypical subjects that exercised more than 4 times a week (Savikko, Timo, & Kaisu, 2009). A less supported hypothesis has proposed that during exercise IGF-1 along with BDNF transmission is up regulated. Blocking BDNF signaling using antibodies to TrkB - that is the receptor for this neurotrophic factor - thwarted improvements in cognitive function, specifically improvements in executive function (Figure 2) (Trejo et al., 2007). In the study, elevations in neurospheres â&#x20AC;&#x201C; that is neural stem cells - at the prefrontal cortex, evidence of neuronal outgrowth (Figure 3). Blocking IGF-1 using antibodies that act on its receptor also produced deficits in cognitive performance of subjects. Subsequent studies have shown that low levels of IGF-1 leads to an attenuation of Synapsin I and CAMKII, proteins involved in synaptic plasticity. When IGF-1 was infused into rodents or its receptors 58


were overexpressed, an antidepressant effect, that is improvements in executive function, preceded. These, subjects showed diminished hypofrontality due to increased neurogenesis at prefrontal site.

Figure 2: When Trk-B receptors are blocked via antibodies (TrkB-Fe), the magnitude of LTP measured using theta burst stimulation is reduced, evidence that BDNF is involved in synaptic plasticity and strengthening (Trejo et al., 2007).

ventions: a daily aerobic activity condition or a daily stretching and toning activity condition. Prior to intervention, subjects had blood drawn so as to quantify their preliminary serum BDNF levels and to rule out any health conditions that may limit their participation in the study. The aerobic exercise condition had subjects complete 5 minutes of cardiovascular activity daily, that being a light jog or power walking. Subjects were to increase the duration of this activity by 5 minutes until they reached a maximum of 40 minutes of daily aerobic activity. Individuals in the stretching and toning exercise condition completed 10 minutes of daily weight training, yoga and one exercise of their choosing. Intermittently, a participant was required to complete a task-switch paradigm, a test used by psychologists to assess an individual’s executive function. Completed in isolation, these elderly subjects were to make very rudimentary judgments, that being, whether a number was even or odd, or higher or lower than the number five. However, the paradigm was divided into two conditions, a single task condition wherein the participants were to make only higher/ lower or even/odd judgments. Whereas, in a mixed condition, subjects were to make higher/lower judgments intermixed with even/odd judgments. When the computer screen background was blue, participants were to press the X key when the number presented was higher than five or the Z key when the number was lower then 5. Conversely, when the background was pink, if the number was odd they were to press the N key and when even, the M key. Thus, this task demanded appropriate discriminatory behavior, the ability to keep track of stimuli and inhibit inappropriate responses. Accuracy, as measured via percent correct responses, was extrapolated to quantify the subject’s executive skills. The subject’s serum BDNF levels were measured at the end of the intervention.

Results and Discussion Figure 3: The following demonstartes and increase in neural stem cell outgrwoth subsueqnt to the increased expression of BDNF as mediatted by aerobic activit (Trejo et al., 2007).

Thus, by old age, due to frequent mild blows to the skull, stress or other pre-existing psychiatric illnesses leads to ventricle enlargement, hemorrhaging of the underlying white matter structures beneath sites of focal contact, as well as hypoxia and cerebral perfusion often at the frontal cortex. These symptoms can be reversed via aerobic exercise, which increases the delivery of oxygenated blood to the brain by inducing vasodilation of capillaries. Increased oxygen delivery leads to increased metabolic activity and thus, greater BDNF transmission. Research Overview Methods In the following investigation, Leckie et al. (2014) sought to deduce whether elevations in serum BDNF in elderly subjects arbitrates the effect exercise has on improving executive function. 92 elderly participants were randomly assigned to one of two exercise inter59

Participants assigned to the 1-year aerobic exercise condition showed striking elevations in post-serum BDNF levels as performance on the task-switch paradigm improved drastically. Even more remarkable and unexpected to Leckie et al. (2014) was that levels of BDNF increased as a function of age. Thus, subjects that were older showed marked improvements on the task-switch paradigm raising a not yet proposed question, “does age moderate the effect of aerobic exercise on serum BDNF levels?” Global accuracy, that is the measurement used to quantify whether a subject showed improvements in executive functioning during the cognitive task, looked at the difference in accuracy scores form the mixed trial and single trial conditions. It was evident that subjects older than 71 years of age in comparison to younger subjects showed increased global accuracy as a function of increased serum BDNF levels. Thus, BDNF seemed to improve some aspect of cognitive functioning during exercise by increasing neuronal outgrowth and cell survival. Participants in the stretching and toning condition did not show elevations in BDNF levels but rather marked decreases in post-serum levels as performance on the task-switch paradigm declined. Subjects were unable to shift between making one judgment and switching


to another. Evidently, the stretching and toning condition exerted excessive stress not only on the subjectâ&#x20AC;&#x2122;s muscles, but on their mental health and thus, likely increased cortisol levels. Therefore, Leckie et al. suggests that elderly subjects should be encouraged by general practitioners to participate in daily aerobic exercises, rather than flexibility training, which has more consequences than benefits.

Conclusions

The following study by Leckie et al. (2014) clearly demonstrated that the age of elderly subjects moderates changes in BDNF serum levels as demonstrated by significantly higher amounts of neurotrophic factor in subjects over the age of 65. Subjects in aerobic exercise condition, over the age of 71 displayed better task-switch performance, with higher accuracy in mixed trials that demanded executive control. Thus, elevated serum BDNF levels due to aerobic exercise mediate the effect of physical activity on task-switch performance. However, stretching and toning did not elevate BDNF levels and thus performance on the task-switch paradigm declined. Thus, elderly individuals should be encouraged to partake in daily aerobic exercise, rather than flexibility exercise to prevent the waning of executive function. Leckie et al. (2014) demonstrated that an increase in serum BDNF levels mitigates neurodegeneration, most likely - though not demonstrated - in regions involved in executive control.

Future Directions

Clearly, however, the benefits of aerobic exercise are far greater than that of flexibility training in terms of hindering executive dysfunction. However, though exercise does improve mental health, the exact mechanism in which it does so was not effectively demonstrated in the following study. Further studies should be conducted so as to identify a means of preventing frontotemporal dementia onset or diminishing executive disruption in individuals with pre-existing cognitive impairments. This is necessary as the proportion of elderly individuals with dementia on a global scale continues to surge. One major fallout and criticism of the following study, rests in the fact that no neuroimaging techniques were correlated with serum BDNF levels and the behavioral measures acquired from the task-switch trial, so as to elucidate whether elevations in BDNF occur at the frontal cortex during exercise to improve cognitive processing. The particular mechanism or neural substrates targeted by BDNF are not explicated in this study. It is not known whether elevations in BDNF improved cognition, for there is no way to illustrate that the PFC and ACC involved in executive functioning show increased GMV, elevated activity or more importantly, increased BDNF transmission. Furthermore, findings from many studies on exercisemeditated cognitive enhancement have demonstrated that aerobic interventions are far more effective in middle aged subjects rather than the elderly. Thus, Leckie et al. (2014) should take to deducing whether

BDNF will better mediate the effect of exercise on middle-aged subjects in comparison to elderly individuals. This may be due to the fact that middle-aged adults for one are typically more active and so the oxygenated blood flow to the cortex is far greater during exercise and so BDNF expression is increased. Furthermore, they are less likely to have had several mild traumatic brain injuries and so the amount of atrophy, sheering of white matter tracks and inflammation of cortical structures is diminutive and so apoptotic factors are scarcely activated. They are also less likely to have a preexisting medical condition that impedes production of BDNF such as hypertension, cardiovascular disease and bouts of major depression or anxiety. Thus, Leckie et al. (2014) should look at whether physical activity provides greater neuroprotective benefits in middle age, contrary to the finding in the following study. Furthermore, the findings in several studies suggest that women respond more to exercise interventions than males, quite possibly due to elevations in estrogen levels. Higher bouts of estrogen secretion during menstrual cycles are believed to increase the secretion of BDNF at cortical sites as well as the hippocampus. One observational study found that the risk of Alzheimerâ&#x20AC;&#x2122;s Disease and cognitive decline in woman participants over 65 years of age was annulled by 50% for those who exercised more than 4 times a week compared to those less active. However, there was no such difference in cognitive function for men that were more active (Fratiglioni, Viitanen, & Von Strauss, 1997). A smaller study demonstrated a reduction in cognitive impairment by a whopping 88% in females who partook in a 5-year exercise intervention compared to controls that did not participate in daily exercise activity (Lautenschlager, Cox, & Cyarto, 2012). These less active woman had a five times greater risk of developing a cognitive impairment however, in an identical study with male subjects, there was little difference between active and inactive participants. Thus, Leckie et al. (2014) should take to comparing the enhancement in cognitive performance between male and female subjects. Other such studies have demonstrated that cognitive impairments are more greatly ameliorated when subjects partake in meditative exercise and stretching activities where as those that partake in cardiovascular activity show higher levels of stress and discomfort and so exhibit little improvements in cognitive function, as quantified by longer reaction times and reduced performance on the IOWA gambling task, task-switch paradigm and the N-back test. It would be interesting to tag BDNF and IGF-1 and then deduce whether stretching and toning or aerobic activity more greatly increases their expression at the frontal cortex. The following study did not clearly elucidate whether physical exercise need be moderate or vigorous, chronic or acute, in order for physical activity to take its effect on cognitive centers in the brain to improve metabolic activity. A recent study, however, found that Tai Chi - a multimodal physical activity incorporating aerobic and flexibility exercises - successfully improved cognitive performance on a shift card test, digit span and Stroop test in a large sample of 2553 elderly adults (Wayne et al., 2014). 60


Additionally, Leckie et al. (2014) did not look at the effect of aerobic activity on elderly individuals with pre-existing executive function impairments such as psychiatric disorders, including bipolar disorder and schizophrenia with characteristic hypofrontality. Subjects with bipolar disorder showed improvements in performance on tasks of executive function subsequent to aerobic activity (Figure 4) (Sylvia, Ametrano, & Nierenberg, 2008). What was not demonstrated in this study was an elevation in BDNF serum levels, thus it is possible that a dissimilar protein acts to increase activity at the frontal cortex to improve the subjects ability to make accurate and appropriate discriminatory judgments and to inhibit inappropriate responses. Another such study found that in comparison to neurotypical controls, patients clinically diagnosed with panic disorder, characteristic of poor executive function due to frequent displays of impulsive behavior and uncontrolled aggression. Subsequent to a 30-minute aerobic exercise intervention, exercise was shown to increase BDNF levels in panic disorder patients.

Figure 4: BDNF levels in panic disorder patients showed significant elevations subsequent to exercise (Sylvia, Ametrano, & Nierenberg, 2008).

Leckie et al. (2014) should also take to looking at the increased expression of the neurotransmitter dopamine subsequent to aerobic activity, which has also been proposed as contributing to the up-regulation of BDNF. For quite some time, dopamine has been known to act on receptors in the prefrontal cortex wherein it improves executive function. Thus, subsequent to physical activity, many individuals report feelings of ease, content and elation. Once such study demonstrated that exercise increases serum calcium levels and dopamine levels after a daily 15-minute aerobic activity (Hogan, Mata, & Carstensen, 2013). Controls that did not partake in this intervention showed no differences in serum calcium and dopamine levels. Thus, it can be inferred that aerobic activity works to increase calcium influx into various neurons, which in turn increases dopamine and BDNF levels. Thus, Leckie et al. (2014) should employ PET imaging to correlate a subjectâ&#x20AC;&#x2122;s dopamine transmittance at the prefrontal cortex with increased serum BDNF levels to demonstrate that neurotransmitters play a role in cognitive improvement. Given the large body of evidence in support of the role of insulin growth factor-1 (IGF-1) in executive function, Leckie et al. (2014) should also take to 61

measuring serum levels of this protein. Though this growth factor acts peripherally, it has been shown to enhance cognitive performance. Subjects in an aerobic activity condition demonstrated significantly higher levels of serum IGF-1 as well as increased LTP at various cortical neurons as measured via thetaburst stimulation, evidence of synaptic strengthening. (Wieczorek-Baranowska et al., 2011). The researchers should also genotype the subjects to deduce whether they have the Val66Met isoform of the BDNF gene or the Val66Val polymorphism. Those with the heterogeneous isoform are likely to show less responsiveness to the exercise intervention due to a decrease expression and transmission of BDNF and thus reduced neuronal outgrowth at frontal sites. Elderly with the Val66Met polymorphism are likely to show declinations in cognitive function despite the duration, length and type of intervention they are assigned to (Figure 5) (Swathi et al., 2014).

Figure 5: Individuals with the Val66Met polymorphism show lower cortical thickness at frontal sites and thus deficits in executive function (Swathi et al., 2014).

Cortisol levels in subjects should also be measured to rule out whether increased stress impedes the effect of exercise on neurogenesis and synaptogenesis. Chronic activation of the HPA axis due to increased anxiety in old age (as a result of decreased mobility and ailments) may impede the effects of BDNF on executive function (Figure 6) (Strohle et al., 2010).

Figure 6: As serum BDNF levels in the elderly decreased, arousal increased. Subjects lower than normal BDNF levels displayed severe executive function deficits (Strohle et al., 2010).


References 1. Baker, L. D., Frank, L. L., Foster-Schubert, K., Green, P. S., Wilkinson, C. W., McTiernan, A., … Craft, S. (2010). Effects of Aerobic Exercise on Mild Cognitive Impairment: A Controlled Trial. Archives of Neurology, 67(1), 71-79. 2. Benedict, C., Brooks, S.J., Jullberg, J., Nordenskjold, R., Burgos, J., Le Greves, M., Kilander, L., Karsson, L., Ahlstrom, H., Lind, L., & Schioth, H.B. (2012). Association between physical activity and brain health in older adults. Neurobiol of Aging. 34(1), 83-90. 3. Colcombe, J.C., Erickson, K.I., Scalf, P.E., Kim, J.S., Prakash, R., McAuley E., Elavsky, S., Marquez, D.X., Hu, L., & Kramer, A.F. (2006). Aerobic Exercise Training Increases Brain Volume in Aging Humans. Journal of Gerontology, 58(2),176-180. 4. Cotman, C.W., Berchtold, N.C, & Christie, L.A. (2007). Exercise builds brain health: key roles of growth factor cascades and inflammation. Trends Neurosci, 30(9), 464-472. 5. Dahl, A., Hassing, L.B., & Fransson, E. (2009). Being overweight in midlife is associated with lower cognitive ability and steeper cognitive decline in late life. J. Gerontol. A Biol. Sci. Med. Sci, 65(1), 57-62. 6. Erickson, K. I., Weinstein, A. M., Sutton, B. P., Prakash, R.S., Voss, M. W., Chaddock, L., … Kramer, A. F. (2012). Beyond vascularization: aerobic fitness is associated with N-acetylaspartate and working memory. Brain and Behavior, 2(1), 32–41. 7. Fratiglioni, L., Viitanen, M., & Von Strauss, M. (1997). Very old women at highest risk of dementia and Alzheimer’’s disease: incidence data from the Kungsholmen project, Stockholm. Neurology, 48(1), 132-138. 8. Gold, B. T., Powell, D. K., Xuan, L., Jicha, G. A., & Smith, C. D. (2010). Age-related slowing of task switching is associated with decreased integrity of frontoparietal white matter. Neurobiology of Aging, 31(3), 512. 9. Gomez-Pinilla, F. (2008). Brain derived neurotrophic factor functions as a metabotrophin to mediate the effects of exercise on cognition. Eur J Neurosci, 28(22), 2278-2287. 10. Hogan, C. L., Mata, J., & Carstensen, L. L. (2013). Exercise Holds Immediate Benefits for Affect and Cognition in Younger and Older Adults. Psychology and Aging, 28(2), 587-594. 11. Kluding, P. M., Tseng, B. Y., & Billinger, S. A. (2011). Exercise and Executive Function in Individuals with Chronic Stroke: A Pilot Study. Journal of Neurologic Physical Therapy : JNPT, 35(1), 11-17. 12. Larson, E.B., Wang, L., Bowen, J.D., McCormick, W.C., Teri, L., Crane, P., & Kukull, W. (2006).Exercise is associated with reduced risk for incident dementia among persons 65 years of age or older. Ann Intern Med, 144(30), 73-81. 13. Lautenschlager, N.T., Cox, K., & Cyarto, E.V.(2012).The influence of exercise on brain aging and dementia.Imaging Brain Aging and Neurodegenerative Disease,1822(3), 474-481. 14. Leckie, R. L., Oberlin, L. E., Voss, M. W., Parkas, R. S., Szabo-Reed, A., Chaddock-Heyman, L., …Erickson, K. I. (2014). BDNF mediates improvements in executive function

following a 1-year exercise intervention. Front. Hum. Neurosci, (8) 985, 1-10. 15. Lopez-Lopez, C., LeRoith, T., & Torres-Aleman, I. (2004). Insulin-like growth factor I is required for vessel remodeling in the adult brain. Proceedings of the National Academy of Sciences of the United States of America, 101, 9833-9838. 16. Raji, C. A., Ho, A. J., Parikshak, N., Becker, J. T., Lopez, O. L., Kuller, L. H., … Thompson, P. M. (2010). Brain Structure and Obesity. Human Brain Mapping, 31(3), 353-364. 17. Savikko, N., Timo, E.S., & Kaisu, H.P. (2009). Effect of physical exercise on cognitive performance in older adults with mild cognitive impairment or dementia. Dementia and Geriatric Cognitive Disorders, 38 (5). 347-365. 18. Strohle, A., Stoy, M., Graetz, B., Michael, S., Wittmann, A., Gallinat, J., Lang, U.E., Dimeo, F., & Hellweg, R. Acute exercise ameliorates reduced brain-derived neurotrophic factor in patients with panic disorder. (2010). Psychoneuroendocrinology, 35(3), 364-368. 19. Swathi, G., Manuck, S.B., Ferrell, R.E., Flory,J.D., & Erickson, K.I.(2014).The BDNF Val66Met polymorphism does not moderate the effect of self-reported physical activity on depressive symptoms in midlife. Psychiatry Research 218(2),93–97. 20. Sylvia, L.G., Ametrano, R.M., & Nierenberg, A.A. (2008). Exercise treatment for bipolar disorder: potential mechanisms of action mediated through increased neurogenesis and decreased allostatic load. Eur J Neurosci, 20(10), 2580-2590. 21. Trejo, J.L., Piriz, J., Llorens-Martin, M. V., Fernandez, A.M., & Bolós, M. (2007). Central actions of liver-derived insulin-like growth factor I underlying its pro-cognitive effects, Molecular psychiatry, 12(12), 1118-1128. 22. Vaynman, S., Ying, Z., Gomez-Pinilla, F. (2007). Hippocampal BDNF mediates the efficacy of exercise on synaptic plasticity and cognition. Neurochem Research, 33(1), 51-58. 23. Wayne, P. M., Walsh, J. N., Taylor-Piliae, R. E., Wells, R. E., Papp, K. V., Donovan, N. J., & Yeh, G. Y. (2014). The Impact of Tai Chi on Cognitive Performance in Older Adults, Journal of the American Geriatrics Society, 62(1), 25-39. 24. Wieczorek-Baranowska, A., Nowak, A., Michalak, E., Karolkiewicz, J., Pospieszna, B., Rutkowski, R., Laurentowska, M., & Pilaczyńska-Szcześniak, L. (2011). Effect of aerobic exercise on insulin, insulin-like growth factor-1 and insulin-like growth factor binding protein-3 in overweight and obese postmenopausal women. J Sports Med Phys Fitness, 51(3), 525-32.

62


High fat diet intake is related to impaired hippocampal dependent memory in juvenile rats Erica Confreda

Recent studies in the literature have indicated that there is a link between obesity and cognitive dysfunction. This is a prevalent issue in today’s society and raises a lot of concern due to the dramatic increase of obesity among children and adolescents. This study conducted by Boitard et al. investigated whether adolescence is a life stage that is particularly vulnerable to the negative effects of a high fat diet. The authors hypothesized that when juvenile rats are exposed to a high fat diet, the levels of pro-inflammatory cytokines in the hippocampus increase and as a result hippocampal dependent memory is impaired. Results showed that juvenile high fat diet exposure significantly impaired long-term memory and spatial flexibility but not short-term memory. Furthermore, the levels of interleukin-1β and tumor necrosis α were significantly increased within the hippocampus of these juvenile rats after administration of LPS. Interestingly, the same composition and duration of the high fat diet did not affect long-term memory, spatial flexibility and short-term memory nor cytokine expression in adult rats. These results indicate that adolescents are specifically vulnerable to the negative effects a high fat diet has on the hippocampus and that elevated levels of pro-inflammatory cytokines impair spatial memory. Key words: Spatial memory; obesity; cytokines; hippocampus; interleukin-1β; tumor necrosis α

Background Obesity is a prevalent issue in today’s society since it has risen dramatically among children and adolescents. For instance, In the United States the occurrence of obesity is 31%8. Obesity is an important health issue that needs to be addressed since it is associated with other health concerns such as cardiovascular disease, type II diabetes and certain cancers. Moreover, recent studies show that there is a relationship between obesity and adverse neurocognitive functioning8. However, although research shows there is a relationship between obesity and neurocognitive functioning, little is known on exactly how they are connected. In the literature, inflammation is one proposed mechanism to explain this relationship9. The hormone leptin, through its signalling pathway, produces pro-inflammatory cytokines, reactive oxygen species and increase macrophage phagocytosis6. As a result, these cytokines promote insulin resistance by preventing phosphorylation of the insulin receptor6. In particular, elevated levels of the cytokine interleukin- 1 beta (IL-1β) for a long period of time impairs hippocampal dependent memories13. This may be because of the higher concentration of microglia within the hippocampus and therefore this part of the brain might be more vulnerable to inflammation13. In some studies, the authors administered lipopolysaccharide (LPS) to exaggerate the immune response of animals. Some examples of cytokines that are increased after administration are: interleukin 6, Interleukin-1β and tumor necrosis factor α (TNFα)5. Some research also indicates that obesity may play a role in neurodegenerative diseases such as Parkinson’s and Alzheimers4. The authors Boitard et al. conducted this study on juvenile rats in order to see whether a high fat diet influences hippocampal 63

dependent spatial memory and if increased levels of cytokines play a role3. They also wanted to address the age that is more vulnerable to high fat diets. The authors hypothesized that the levels of inflammatory cytokines in the hippocampus increase when juvenile rats are exposed to a high fat diet, and as a result spatial memory is altered. Research Overview

Summary of Major Results

The authors used male rats that were either 3 weeks old (juvenile group) or 12 weeks old (adult group) and had no weight differences. Animals of both age groups were subdivided into two treatment conditions. One received a control diet containing 2.5% lipids and the other received a high fat diet containing 24% lipids. The rats were exposed to these diets for two months and then behavioural tests were performed. One behavioural test used was the Morris water maze in order to assess spatial memory and the other was a reversal-learning test to assess spatial flexibility. After these behavioural tests were performed, the rats were either injected with saline, with lipopolysaccharide (LPS) or were not injected at all. The rats were then killed and the levels of insulin, leptin and cytokines were measured. The authors assessed short-term memory two hours after the acquisition phase and assessed long-term memory four days after the acquisition phase. Results showed that long-term memory and spatial flexibility were significantly impaired in the juvenile high fat diet group whereas there was no significant difference in short- term memory (figure 1). In addition, there were increased levels of interleukin- 1β and tumor necrosis


factor α (TNF- α) within the hippocampus after LPS was administered (figure 2). In contrast, long-term memory, short-term memory and spatial flexibility were not impaired in the adult high fat diet group and there were no significant changes in the levels of cytokines (figure 1, figure 2).

Figure 1. The left diagram demonstrates there is no significant difference in short-term memory for both control and high fat juvenile diet groups. However long-term memory is significantly reduced for the juvenile high fat diet group. The right diagram demonstrates there is no significant change in short-term and long-term memory for both adult diet groups. Picture from: Boitard C. et al (2014) Impairment of hippocampal-dependent memory induced by juvenile high-fat diet intake is associated with enhanced hippocampal inflammation in rats. Brain, Behavior, and Immunity 40:9-17

Conclusions and Discussion The results illustrate that juvenile rats are more vulnerable to the effects a high fat diet has on the hippocampus. Long-term memory and spatial flexibility were altered and there was a higher inflammatory immune response when LPS was administered. In contrast, the same duration and percentage of high fat diet did not have the same significant affect in the adult diet groups. The result of the current study is in agreement with the findings of Acebes et al. such that a high fat diet has a more serious consequence on memory performance in adolescent mice rather than young adults mice1. In addition, their results indicated that it is not caloric intake but rather food composition that affects memory1. These two studies illustrate that adolescence is a life stage that is critical for the maturation of the hippocampus to control memory. In contrast, other studies showed that adult rats do in fact experience hippocampal dependent memory impairments when exposed to a high fat diet. Heyward et al. revealed that when adult rats are exposed to a higher percentage of fat for a longer duration they experience memory impairment7. Therefore, duration and fat composition act as potential confounders. Additionally, Pistell et al. noted that when 12-month-old male mice were exposed to a diet consisting of 60% lipids for 16 weeks, they experienced significant behavioural changes and had increased levels of TNF- α10. The discrepancy in data between these two studies may be due to the different composition of fat administered, the duration of the diet and the different behavioural

tests that were used. The results from the current paper show that interleukin-1β is a significant cytokine that when elevated at high levels for long durations impair spatial memory. In another study conducted by Sobesky et al. inflammation is reduced when an antagonist blocks the interleukin-1β receptor and as a result eliminated the effect of the high fat diet by increasing the freezing times of rats13. This result indicates that inflammation plays a key role in memory decline. Sobesky et al. noted that obesity may prime the cells in the brain such that when a secondary challenge is administered there is an exaggerated inflammatory response13. This is in agreement with the current study since at basal levels there was no difference in cytokine production, but after administration of LPS there were elevated levels of interleukin- 1β and tumor necrosis factor α. However it is important to note the stressfulness of the diet being administered. The current study has several strengths and limitations that should be considered when interpreting the data. This is one of the first studies to investigate how a high fat diet affects hippocampal dependent memory in juvenile rats. In addition, the study eliminated weight gain as a potential confounder and the diet was not stressful enough to cause insulin resistance thus also eliminating that as a potential confounder. A limitation of the study is that the rats were only exposed to the high fat diet for a short length of time. Another limitation is that the authors only used the Morris water maze and reversal learning as behavioural tests. Other tests should be used to see if similar results are obtained.

Figure 2. Demonstrates the effect of diet on cytokine expression in juvenile and adult treatment groups. Interleukin- 1β and Tumor Necrosis Factor α are significantly increased within the hippocampus of the juvenile high fat diet group receiving LPS. In contrast, these cytokines did not change in any of the adult diet groups. Picture from: Boitard C. et al (2014) Impairment of hippocampal-dependent memory induced by juvenile high-fat diet intake is associated with enhanced hippocampal inflammation in rats. Brain, Behavior, and Immunity 40:9-17. 64


Conclusions In conclusion, the data from Boitard et al. suggest that exposure to a high fat diet containing 24% lipids impairs spatial flexibility and long-term memory in juvenile rats but not adult rats. Additionally, a high fat diet leads to increases in pro-inflammatory cytokines, specifically interleukin-1β, within the hippocampus of juvenile rats. Although the exact mechanism on how elevated cytokines impair hippocampal dependent memories is poorly understood, adolescents are specifically vulnerable to the deleterious effects of a high fat diet. This study addresses an important issue since obesity is increasing dramatically among children and adolescents.

Criticisms and Future Directions

The results from this study indicate that the levels of interleukin-1β increases within the hippocampus of juvenile rats after they were exposed to a high fat diet. In order to see if this cytokine is critical for impairing hippocampal dependent memories, this study should be repeated with injecting interleukin-1β antagonists into the group of rats consuming a high fat diet. The rats would then undergo a behavioural test such as the Morris water maze, and if preference for target annulus increases then interleukin-1β is impairing spatial memory. An additional experiment would be to expose both age groups to a diet containing higher percentage of lipids for a longer period of time. This would allow the authors to see if spatial memory of adult rats is altered depending on the severity of the diet. Moreover, less stressful behavioural tests can be used in order to eliminate the amygdala as a possible confounder. One example would be to use novel location recognition behavioural task since it is less stressful than the Morris water maze but still hippocampal dependent1. Future studies should conduct a similar experiment on female rats to see if a high fat diet has similar negative consequences. Also, future studies should test to see if it is possible to reverse the effects of high fat diet, either through diet or exercise, and see if spatial performance is improved. Future experiments that illustrate why obesity increases the levels of pro-inflammatory cytokines within the hippocampus and how they influence spatial memory, are needed to describe the link between obesity and cognitive dysfunction. References 1. Acebes I. et al (2013) Spatial memory impairment and changes in hippocampal morphology are triggered by high-fat diets in adolescent mice. Is there a role of leptin? Neurobiology of Learning and Memory 106:18-25. 2. Arnold SE. et al (2014) High fat diet produces brain insulin resistance, synaptodendritic abnormalities and altered behavior in mice. Neurobiology of Disease 67:79-87. 3. Boitard C. et al (2014) Impairment of hippocampaldependent memory induced by juvenile high-fat diet intake is associated with enhanced hippocampal inflammation in rats. Brain, Behavior, and Immunity 40:9-17. 65

4. Cai D (2013) Neuroinflammation and neurodegeneration in overnutrition-induced diseases. Trends in Endocrinology and Metabolism 24:40- 47. 5. Chen J. et al (2008) Neuroinflammation and disruption in working memory in aged mice after acute stimulation of the peripheral innate immune system. Brain Behavior and Immunity 22:301-311. 6. Gil A. et al (2007) Altered signalling and gene expression associated with the immune system and the inflammatory response in obesity. British Journal of Nutrition 98: 121-126. 7. Heyward FD. et al (2012) Adult Mice Maintained on a High-Fat Diet Exhibit Object Location Memory Deficits and Reduced Hippocampal SIRT1 Gene Expression. Neurobiology Learning Memory 98: 25-32. 8. Liang J (2014) Neurocognitive correlates of obesity and obesity-related behaviors in children and adolescents. Nature 38:494-506. 9. Miller AA, Spencer SJ (2014) Obesity and neuroinflammation: A pathway to cognitive impairment. Brain, Behavioural, and Immunity 42:10-21. 10. Pistell P. et al (2010) Cognitive Impairment Following High Fat Diet Consumption is Associated with Brain Inflammation. J Neuroimmunol 219:25-32. 11. Prada PO, Areias M (2015) Mechanisms of insulin resistance in the amygdala: Influences on food intake. Behavioural Brain Research 282: 209-217. 12. Sainz N. et al (2015) Leptin resistance and diet-induced obesity: central and peripheral actions of leptin. Metabolism Clinical And Experimental 64:35-46. 13. Sobesky JL. et al (2014) High-fat diet consumption disrupts memory and primes elevations in hippocampal IL-1b, an effect that can be prevented with dietary reversal or IL-1 receptor antagonism. Diet, Inflammation and the Brain 42:2232. 14. Wang D. et al (2015) Cardiotrophin-1 (CT-1) Improves High Fat Diet-Induced Cognitive Deficits in Mice. Neurochem Res 40:843-853. 15. Winer AD. et al (2014) B Lymphocytes in obesity-related adipose tissue inflammation and insulin resistance. Cell. Mol. Life. Sci 71:1033-1043.


Caffeine prevents memory consolidation impairments associated with sleep deprivation Akua Obeng-Dei

Numerous of studies have been able to report strong correlations between sleep and the positive contribution it makes to memory consolidation. Studies have demonstrated that sleep deprivation negatively contributes to memory consolidation that impairs learning and memory. The induction of late phase long-term potentiation (L-LTP) is required for the consolidation of short-term memory to long-term memory through the strengthening of synapses. Caffeine has been shown to have cognitive protective properties in rat models of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease preventing some of the cognitive decline that is associated with these aliments. Chronic caffeine treatments were given to the rats over the course of 4 weeks before the sleep deprivation period, rats in this treatment group committed fewer errors when compared to the control during in the RAWM task. Furthermore, Sleep deprived rats treated with caffeine showed L-LTP induction that had an amplitude and slope similar to that of the control. Additional, P-CREB levels increase within the control rats and those treated with caffeine, but the rats that were sleep deprived showed no increase in P-CREB levels. When sleep deprived rats were treated with caffeine, the P-CREB levels were similar to levels exhibited in the control group. The significance of these present results illustrate a possible mechanism in how sleep deprivation may impair the process of consolidation and but provides evidence that caffeine is able to act as a protective against cognitive impairments associated with hippocampal-dependent spatial long-term memory. Key words: sleep deprivation; caffeine; radial arm water maze (RAWM); late long-term potentiation (L-LTP); cAMP response element binding protein (CREB); brain-derived neurotrophic factor (BDNF) Background Previous studies have drawn strong correlations between sleep and the positive contribution it makes to memory consolidation. Two pivotal hypotheses that elaborate on the phenomenon of sleep and memory consolidation are synaptic homeostasis and the active system consolidation1. Synaptic homeostasis hypothesis proclaims that during REM sleep there is a synaptic downscaling, on the global scale, permitting consolidation to occur in the brain1. Active system consolidation hypothesis states that during REM sleep there is selectively re-activating of the memories allowing for memory consolidation to occur1. Numerous of studies have demonstrated that sleep deprivation negatively contributes to memory consolidation that impairs learning and memory. Spatial learning tasks performed by human participants have shown that sleep after learning enhances performance while the opposite is associated with sleep deprivation, where consolidation of memories is hindered, thereby participants perform poorly2. Sleep deprivation leads to reduction AMPA receptor phosphorylation occurring at GluR1-S845 site and twelve hours after rats performed novel arm recognition task3. Sleep deprivation before learning impairs the ability for learning to occur and decreases the magnitude of L-LTP in the CA1 region of the hippocampus4, 5. The induction of late phase long-term potentiation (L-LTP) is required for the consolidation of short –term memory to long-term memory through the strengthening of synapses. The mechanism by which L-LTP allows for the strengthen of synapses involves an electrical stimulation to the Schaffer collaterals in the CA1 region of the hippocampus, glutamate will be release from the presynaptic membrane and will bind to NMDA receptors on the

post-synaptic membrane. Subsequently, this lead to the influx of calcium into the post synaptic cell allowing for the activation of CaMKIV, which will go on to phosphorylate CREB leading to the activation of genes that is required for the induction of L-LTP6, 7. Normally, after the induction of L-LTP once learning has occurred there is an increase in the expression of CREB and BDNF in the hippocampus, in sleep deprived rats there is a decrease in the expression P-CREB and BDNF levels exhibited in hippocampus8. Caffeine has been shown to have cognitive protective properties in rat models of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease permitting the prevention of the cognitive decline that is associated with these aliments9, 10. The implications associated with the cognitive protective effect of caffeine on impairments of hippocampal-dependent spatial long-term memory due to sleep deprivations have not been fully studied. This review will highlight the findings of Alhaider et al paper and elaborate on concepts that could be further elucidated in future research. Research Overview

Summary of Major Results

Chronic caffeine treatments prevents impairments to spatial long-term memory exhibited due to sleep deprivation

The impact of caffeine was investigated in sleep-deprived rats to see whether or not caffeine has a positive effect in the spatial long-term memory defects associated with sleep deprivation. The experimental behavioral approach that was implication was the radial arm water maze (RAWM), longterm memory is measured by comparing the number of errors done by the various treatment groups to the control. 66


The rats that were sleep deprived committed more mistakes after the learning phase than the control groups. Chronic caffeine treatments were given to the rats over the course of 4 weeks before the sleep deprivation period, the rats in this treatment group committed fewer mistakes when compared to the control group. (Refer to figure 1)

Chronic caffeine treatments prevents the decrease of L-LTP magnitude in sleep deprived rat

Multiple high frequency stimulation (MHFS) was applied to the Schaffer collaterals in the CA3 region of the hippocampus to induce L-LTP, the slope of fEPSP and the amplitude of pSpike were measured. Sleep deprivation in the rats was still able to evoke L-LTP, but even though there was a significant increase in the amplitude of pSpike and the slope of fEPSP, the increase was smaller when compared to the control rats. Sleep deprived rats treated with caffeine showed a stronger overall induction of L-LTP that was similar to that of the control.

Levels of P-CREB, total CREB, and BDNF proteins after the induction of L-LTP

Five hours after the induction of L-LTP, the hippocampus was removed and the protein levels of P-CREB, total-CREB, and BDNF were measured using immunoblotting techniques. The P-CREB levels increase within the control rats and those treated with caffeine, but the rats that were sleep deprived showed no increase in P-CREB levels. When the sleep deprived rats were treated with caffeine the P-CREB levels were similar to levels exhibited in the control group. However, the total levels of CREB were increased in all of the experimental groups. BDNF levels in sleep-deprived rats exhibit no increase after the induction of L-LTP unlike the control or rats that were only treated with caffeine. (Refer to figure 2)

Conclusions and Discussion

Alhaider et al.11 were able to show that chronic treat-

ment of caffeine was able to prevent the impairments of hippocampal-dependent learning and memory associated with sleep deprivation in rats. The findings from the hippocampal-dependent spatial memory task, RAWM, suggest that sleep deprivation is the cause of long-term memory impairments this is marked by the increase number of errors compared to the control. Caffeine treatments have been shown to alleviate the impairments induced by sleep deprivation associated with memory consolidation. When normal rats that were not sleep deprived but were treated with caffeine, there was not further reduction in the errors made, suggesting that caffeine acts as a neuroprotective rather than an enhancer consolidation. These results correlate with numerous of studies that have shown a positive correlation between impairments during hippocampal-dependent spatial memory tasks and sleep deprivation, in rats and well as humans2, 3, 4. Additional, there are studies that have shown that sleep deprivation has no correlation at all with impairment memory12; this could be due to the different experimental conditions such as the behavioral model or the method by which sleep deprivation was induced in the rats. The findings from the electrophysiological induction of L-LTP suggest that the reduction in L-LTP coincide with the memory impairments seen during the RAWM task. Caffeine will prevent the sleep deprivation association of L-LTP impairment in the CA1. Previous studies have demonstrated LTP impairments associated with sleep deprivation that was reported in both vivo and vitro models5. The protein levels of P-CREB in sleep-deprived rats suggest that the reduction in the phosphorylation of CREB could be a possible mechanism to explain the impairments associated with sleep deprivation. Furthermore, the decrease in BDNF in sleep-deprived rats also seems to contribute to the impairments associated with memory consolidation. Caffeine treatments seem to prevent the decline that is seen in the sleep deprived rats pertaining to the levels of P-CREB and BDNF protein expression, suggesting that caffeine acts prevents the negative impairments of sleep deprivation.

Figure 1. The impact of caffeine on sleep deprivation mediated spatial long-term memory impairments was investigated using the radical arm water maze (RAWM). All of the groups underwent a learning phase and then there was a 24-hour break where some of the groups were sleep deprived. Then the researcher measured the number of errors made by all of the rat groups when trying to find the hidden platform and compared it to the control. Rats that were sleep deprived made more mistakes after the learning phase compared to the control rats and S-caffeine/sleep deprivation created similar number of error to the control rats. Source: Alhaider et al (2011) 11 67


Figure 2. They investigated the amounts of the signaling molecules P-CREB within hippocampal extracts using immunoblot assay. Five hours after the induction of L-LTP, there was a significant increase in phosphorylated CREB in S-control, S-caffeine, and S-caffeine/sleep deprivation. Source: Alhaider et al (2011) 11

Conclusions Through the use of three different experimental approaches, the researcher were able to conclude that without the increase in the phosphorylation of CREB and BDNF is important for L-LTP to occur therefore impaired learning and memory. The reduction in the proteins essential for L-LTP illustrates a possible mechanism to the spatial long-term memory impairments associated with sleep deprivation in the rats. Additional, caffeine was shown to prevent the cognitive impairment permitting a stronger induction of L-LTP in sleep-deprived rats thereby allowing the levels of P-CREB and BDNF to match levels in the control mice. The significance of the results presented is that not only does it provide for a mechanism into how sleep deprivation may impair the process consolidation but also illustrates that caffeine has protective properties against these cognitive process associated with hippocampal-dependent spatial memory. Criticisms and Future Directions Alhaider et al. failed to provide a reasonable explanation for the results that showed that caffeine treatments only partially improved the impairments to long-term memory induced by sleep deprivation while L-LTP impairments fully recovered in the sleepdeprived rats. Microdialysis-HPLC assay can be conducted to measure the levels of Glutamate, GABA and Histidine, which are associated with wakefulness in the hippocampus of sleep-deprived rats before and after caffeine treatments13. In previous studies it has been shown that caffeine is able to induce the release of glutamate in the nucleus accumbens14, providing rational that this can be also occurring in the hippocampus. It has been proposed that caffeine act through the adenosine receptor A2 to increase glutamate release in the glutamatergic neurons, which will then allow NMDA receptor activation for LTP to occur13, explaining the inconsistent results. Furthermore, why the caffeine treatments in the control rats

that were not sleep deprived did not exhibit further improvements to learning and memory was also not accurately discussed. To address the results that showed no further increase in learning and memory in the control group of rats, conduct EEG while the control rats are either injected with caffeine or saline as they conduce various neurocognitive tasks allowing for real-time information that can be record as learning and memory occurs15. Previously is has been shown that caffeine is able to improve cognitive function15, suggesting that in order for the control rats to show an improvement in cognitive function the researchers will need to administrate a higher dose of caffeine. In order to test for whether the behavioral task, RAWM, is creating stress within the rats leading to misleading results need to physically measure for corticosterone levels before and after the RAWM task to rule out stress has a factor3. The two different experiments outlined will be able to give a broader picture and new understanding on the mechanism by which caffeine is able to act as a neuroprotective to improve hippocampal-dependent spatial learning and memory in sleep deprived rats. References 1. Diekelmann, S., & Born, J. The memory function of sleep. Nature Reviews Neuroscience. 11, 114-126 (2010). 2. Ferrara, M. et al. Sleep to find your way: the role of sleep in the consolidation of memory for navigation in humans. Hippocampus. 18, 844-851 (2008). 3. Hagewoud, R., Havekes, R., Novati, A., Keijser, J.N., Van Der Zee E.D., & Meerlo, P. Sleep deprivation impairs spatial working memory and reduces hippocampal AMPA receptor phosphorylation. J. Sleep Res. 19, 280-288 (2010). 4. Li, S., Tian, Y., Ding, Y., Jin, X., Yan, C., & Shen, X. The effects of rapid eye movement sleep deprivation and recovery on spatial reference memory of young rats. Learning & Behaviour. 37, 246-253. (2009). 5. Kim, EY., Mahmoud, GS., & Grover, LM. REM sleep deprivation inhibits LTP in vivo in area CA1 of rat hippocampus. Neuroscience Letters. 388, 163-167 (2005). 6. Bito, H., Deisseroth, K., & Tsien, RW. CREB phosphorylation and dephosphorylation: a Ca2+ - and stimulus duration-dependent switch for hippocampal gene expression. Cell. 87, 1203-1214 (1996). 7. Tokuda et al. Involvement of calmodulin-dependent protein kinase-I and –IV in long-term potentiation. Brain Research. 755, 162-166 (1997). 8. Guzman-Marin, R et al. Suppression of hippocampal plasticity-related gene expression by sleep deprivation in rats. J. Physiol. 573, 807-819 (2006). 9. Gevaerd, M.S., Takahashi, R.N., Silveira, R., & Da Cunha, C. Caffeine reverses the memory disruption induced by intra-nigral MPTP-injection in rats. Brain Research Bulletin. 55, 101-106 (2001). 10. Arendash, GW et al. Caffeine protects alzheimer’s mice against cognitive impairment and reduces brain β-amyloid production. Neuroscience. 142, 941-952 (2006). 68


11. Alhaider, I. A., Aleisa A.M., Tran T.T., & Alkadhi K. A. Molecular and Cellular Neuroscience. 46, 742-751 (2011). 12. Samkoff, J.S., Jacques, C.H., A review of studies concerning effects of sleep deprivation and fatigue on residents’ performance. Acad. Med. 66, 687-693 (1991). 13. ohn, W., Kodama, T,. & Siegel, JM,. Caffeine promotes glutamate and histamine release in the posterior hypothalamus. Am J Physiol Regul Integr Comp Physiol. 307, 704-710 (2014). 14. Solinas, M., Ferré, S,. You, ZB,. Karcz-Kubicha, M,. Popoli, P,. & Goldberg, SR. Caffeine induces dopamine and glutamate release in the shell of the nucleus accumbens. J Neurosci. 22, 6321-6324 (2002). 15. Bruce, SE., Werner, KB., Preston, FP., & Baker, LM. Improvements in concentration, working memory and sustained attention following consumption of a natural citicoline-caffeine beverage. Int J Food Sci Nutr. 8, 1003-1007 (2014). Received Month, ##, ##, 200#; accepted

200#; Month,

revised ##,

Month, 2013.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program

69


Conflicting or Corroborating Evidence? Interleukin-6 and the JAK-STAT Signaling Pathway in Neural Precursor Self-Renewal Daniel Derkach

Maternal cytokine surges have been implicated in long-lasting neurological consequences in progeny, such as autism spectrum disorder and schizophrenia-like behavior. However, the precise mechanism(s) underlying these effects are yet to be fully understood. This review analyzes and evaluates the findings of Gallagher et al., which support the notion that a maternal IL-6 surge, which can be caused by maternal infections or distresses, deregulates the proliferation and self-renewal of neural precursor pools in the mammalian embryonic forebrain. The authors report that a single maternal IL-6 injection may result in increased adult forebrain precursor proliferation, increased precursor self-renewal, and sustained precursor pluripotency long into adulthood. These findings contribute to the current archetype of neural precursor regulation by suggesting and investigating a novel signaling pathway, which has yet to be thoroughly clarified. However, these findings are only an incremental advance in this field of research, where several questions remain to be answered. In addition, similar studies exhibit findings that may appear to be conflicting with the article of focus, but further research is necessary to resolve any apparent discrepancies. Key words: neural precursor cells (NPCs); neural stem cells (NSCs); cytokines; interleukin-6 (IL-6); JAK-STAT; neurogenesis; cognitive disorders; schizophrenia Background Abnormalities associated with stem cells can result in long-lasting impairment of tissue maintenance and repair, as well as functionality (Simons & Clevers, 2011). However, the mechanisms underlying the regulation of adult stem cell pool growth and composition are still not understood. Investigations seeking to uncover these mechanisms are significant because it has been shown that human cognitive function and adult neurogenesis are directly affected by variations in adult neural precursor cells (NPCs) (Ming & Song, 2011). In order to link NPC variation with cognitive function, Gallagher et al. (2013) investigate a maternal cytokine surge, which may occur during prenatal perturbations such as maternal infection or stress exposure. In humans, this cytokine surge is implemented in long-term cognitive outcomes such as schizophrenia and autism spectrum disorder (ASD) (Patterson, 2007, 2011). Cytokines such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α chemically mediate inflammation, and may cross the blood-brain barrier, thereby facilitating maternal to fetal transmission, but the mechanisms underlying their effects on fetal brain development are unclear (Boksa, 2008). Gallagher et al. focus on a specific cytokine, IL-6, which is thoroughly studied in relation to NPC pool size, composition, and self-renewal. Some regulatory factors of embryonic NPCs have previously been identified, such as epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF2), but IL-6 is a relatively new candidate. It is currently understood that IL-6 is associated with stem cell proliferation in muscles (Muñoz-Cánoves, 2013) and the spinal cord (Kang, 2008), but research involving its role in the mammalian brain is limited. The current investigation by Gallagher et al. provides an incremental advance for cytokine and NPC research because it expands upon the pre-established functions of IL-6, specifically examining its association with NPC regulation in the mammalian forebrain, whereas it has

conventionally been assumed to be an immune regulator. It is currently understood that IL-6 activates the Janus kinase-signal transducer and activator of transcription (JAKSTAT) pathway, but requires the formation and activation of a glycoprotein 130 (gp130) and IL-6 receptor (IL6R) complex. IL-6 binds its receptor (IL6R), which forms a complex with gp130, thereby activating JAK. In turn, JAK phosphorylates tyrosine residues on the cytoplasmic aspect gp130, which act as docking sites for STAT. JAK subsequently phosphorylates STAT, which forms homodimers before localizing to the nucleus where STAT acts as a transcriptional activator (Dittrich et al., 2012). As previously identified by Barnabé-Heider et al. (2005), gp130 expression is exhibited by NPCs in the embryonic forebrain. These factors have the potential to contribute to more expansive research involving the downstream events resulting from JAK-STAT signal activation and deregulation. Research Overview

Summary of Major Results

To investigate the potential effects of IL-6 on NPC proliferation, Gallagher et al. initially administered a single intraperitoneal injection of IL-6 into pregnant mice on gestational day 13.5 (G13.5) and subsequently immunostained and analyzed the subventricular zone (SVZ) of 2-month-old adult mice. Compared to wild type, maternally exposed IL-6 embryos showed 2-fold more proliferating BrdU-positive SVZ cells and significantly increased levels of Sox2-positive precursor cells. Additionally, an almost 1.5-fold increase was seen in neurosphere-initiation SVZ cells compared to wild type. As elucidated by previous research, NPCs in the adult SVZ originate from the dorsal cortex and ventral ganglionic eminence (GE) (Ventura & Goldman, 2007; Young et al., 2007). To determine if cortical contribution of NPCs to the SVZ is modified by maternal IL-6 upregulation, Gallagher 70


et al. used an electroporation experiment to induce green fluorescence protein (GFP) expression for lineage tracing. Compared to wild type, a maternal IL-6 surge resulted in a greater contribution from the dorsal cortex, which led to a 2-fold increase in GFP-expressing NPCs in the adult SVZ. Concurrently, additional in vivo analysis showed that maternal IL-6 injection resulted in a 2-fold increase in neurosphere generation at clonal density in the embryonic cortex and ventral GE. Since it was previously demonstrated that gp130 receptors are expressed by NPCs in the embryonic cortex, the authors continued their investigation by examining if IL6Rs are also expressed by these NPCs. By isolating Sox2-positive cortical NPCs in embryos, RT-PCR and immunostaining revealed the presence of IL6R mRNA at embryonic day 13 (E13) in the cortex and SVZ. Since both IL6R and gp130 were found to be expressed by cortical NPCs, the authors investigated if IL-6 injection led to activation of the IL6R/gp130-mediated JAK-STAT pathway. Western blot analyses revealed almost 2-fold increases in phosphorylated STAT3 levels in embryonic cortices at E12.5, both in vivo and in vitro. The authors then went on to see if this downstream signaling promoted proliferation of cortical precursors. In vitro cultural analyses following immunostaining for BrdU, Ki67, phospho-histone H3, and Pax6 each demonstrated increased percentages of proliferation in radial precursors treated with IL-6 compared to wild type. After showing that IL-6 mediates proliferation of NPCs, the authors explored the possibility of IL-6-mediated enhancement of forebrain NPC self-renewal. Via clonal analysis, it was demonstrated that IL-6-treated cortical precursors formed clones with significantly greater multicellularity, as well as more diverse clonal bodies. Compared to wild type, IL-6 treatment resulted in a slight decrease in clones containing neurons only, and nearly doubled the amount of mixed clones containing a mixture of BIII-tubulin-positive neurons, glial fibrillary acidic protein (GFAP)-expressing glia, and undifferentiated neural precursors. Cytokine antibody dot blot experiments revealed that IL-6 was also synthesized and secreted by cortical precursors in a precursor-conditioned medium, whereas other cytokines, such as IL-4/5/9/10 were not. Moreover, immunostaining and cultural analysis of IL-6-/- and IL-6+/+ cortical precursors revealed similar rates of cell death, but significantly decreased proliferation of IL-6-/- precursors. Finally, immunostaining and siRNA-mediated knock-

down of IL6R resulted in significantly decreased levels of Sox2-positive precursors and increased levels of Satb2-positive neurons. Likewise, immunostaining revealed parallel results in IL-6-/- embryos relative to wild type embryos (Fig. 1).

Discussions and Conclusions

Although the evidence provided by Gallagher et al. strongly support their hypothesis, claiming that a maternal IL-6 surge upregulates NPC proliferation and self-renewal, several questions remain unanswered and controversy is still present among research in this area. Multiple studies report that gestational perturbations have long-lasting effects on adult hippocampal neurogenesis and cell proliferation, but such effects are also shown to be independent of maternal IL-6 (Coe et al., 2003; Uban et al., 2010). These reports suggest that hippocampal and SVZ precursor populations are inherently distinct. Similarly, Li et al. (2013) report that hippocampal and SVZ precursor populations derive from discrete populations of embryonic progenitors. A study by Bowen et al. (2010) supports the findings of Gallagher et al., showing that a dearth of IL-6 results in decreased proliferation of adult SVZ precursors. However, the findings of Bowen et al. contradict those of Coe et al., Uban et al., and Li et al., who all report differences between hippocampal and SVZ precursor cell populations. On the other hand, Bowen et al. report that IL-6-/- mice exhibited significantly decreased NPC survival in both the dentate gyrus and the SVZ, relative to wild type mice. This suggests similarities between hippocampal and SVZ progenitor populations, which conflicts with several other studies. The findings of Gallagher et al. also raise the question of how JAK-STAT signaling maintains NPC pluripotency. Although the authors show an increase in phosphorylated STAT3 in the E12.5 progeny of maternally exposed IL-6 mice in vivo and in NPCs directly exposed to IL-6 in vitro, no direct association is illustrated between STAT3 and sustainment of NPC pluripotency. Additionally, Gallagher et al. face an array of opposition concerning their results that show IL-6-mediated downstream signaling to preserve pluripotency and defer differentiation. Several studies support the claim that IL-6-mediated downstream JAK-STAT signaling promotes astrocytic differentiation. Using Western blot and immunocytochemical analysis, Gu et al. (2005) show that STAT3 suppression directly

Figure 1 (Gallagher et al., 2013). BrdU (red) proliferation marker and Sox2 (green; left) precursor marker or Satb2 (green; right) neuron marker. Left: Analysis of proportion of precursors in IL-6 knockout mice relative to wild type (control). Right: Analysis of proportion of differentiated neurons in IL-6 knockout mice relative to wild type (control).

71


inhibited astrogliogenesis and induced neurogenesis. Further-more, Nakanishi et al. (2007) report that microglia-derived IL-6 did not increase NPC proliferation. Instead, it was shown that microglia-derived IL-6 activated the JAK-STAT pathway, leading to astrocytic differentiation of E16 NPCs. This was affirmed by inhibiting the JAK-STAT pathway, leading to reduced astrocytic differentiation. However, a more thorough analysis creates the possibility that both views may be valid, but at different stages of embryogenesis. Fan et al. (2005) perform an experiment involving a DNA methyl-transferase 1 deletion (Dnmt1-/-), resulting in accelerated demethylation of the GFAP promoter and subsequent JAK-STATmediated astrogliogenesis. Interestingly, this concept is expanded upon by Takizawa et al. (2001), reporting that the STAT3 binding element in the wild type GFAP promoter is methylated at E11.5, but demethylated at E14.5 (see Fig. 2). Since Nakanishi et al. examined the JAK-STAT pathway and astrogliogenesis at E16, it is likely that the STAT3 binding element in the GFAP promoter was demethylated, thereby allowing GFAP transcription and astrocytic differentiation. On the other hand, Gallagher et al. examined the JAK-STAT signaling pathway at E12.5, when the STAT3 binding element in the GFAP promoter was likely still methylated. Even if these are valid conditions and JAK-STAT signaling results in astrocytic differentiation only after E14.5, but not before, the question remains: How does JAK-STAT signaling maintain NPC pluripotency prior to E14.5? If JAK-STAT signaling prior to E14.5 causes sustainment of NPC pluripotency, it then also raises the question of whether or not STAT3 binds targets other than the GFAP promoter. Boksa (2008), in conjunction with Khan & Brown (2002), give reason to hypothesize that it may not necessarily be the IL-6-mediated JAK-STAT signaling pathway that is responsible for behavioral disorders in the progeny of infected mothers, but may potentially be caused by fever-induced apoptosis of neocortical cells, instigated by a maternal IL-6 surge. Khan & Brown affirm this by demonstrating elevated activation of caspase 3 in E17 cortical cells 10 hours after a heat shock.

Figure 2 (Taga & Fukuda, 2005). Mechanism of IL-6-mediated JAK-STAT signaling and GFAP promoter activation in neural precursors at E11.5 (methylated) versus E14.5 (demethylated).

Conclusions The experimental findings of Gallagher et al. provide strong evidence in support of their hypothesis, claiming that a maternal IL-6 surge, which may be caused by maternal infection in mammals, has long-lasting implications on NPC pools in progeny. Based on the authorsâ&#x20AC;&#x2122; findings of cytokine antibody dot blot experiments, it can be concluded that IL-6 is endogenously synthesized and secreted by embryonic forebrain NPCs in wild type mice. Moreover, RT-PCR and immunostaining support the hypothesis that embryonic forebrain NPCs also express IL6Rs, suggesting that IL-6 signaling functions in an autocrine/paracrine manner. Mechanistically, as shown in Western blots depicting upregulated STAT3 levels by Gallagher et al. and demonstrated in several other reports, it can be concluded that IL-6 has downstream effects in the mammalian forebrain via JAK-STAT-mediated signaling. However it cannot be firmly concluded that JAK-STAT signaling directly and specifically promotes either sustained pluripotency of NPCs or astrocytic differentiation in the embryonic forebrain of mice. It may, however, be a possibility that astrocytic/glial differentiation is observed due to the specific inhibition of neuronal differentiation, or may be due to a different mechanism altogether. Although not explicitly investigated by Gallagher et al., but relevant to the topic of embryonic NPC variation nonetheless, discrepancies between studies comparing the nature of hippocampal and SVZ precursor populations give reason to take caution when deducing a conclusion, and supplementary experimentation is necessary. Finally, although one may naturally assume that a deficiency in NPCs would result in cognitive deficits, Gallagher et al. demonstrate that IL-6 may, in fact, play a role in prompting harmful functional consequences by promoting the over-accumulation of neural precursors.

Criticisms and Future Directions

As research in neural stem cells has widespread potential in modern biomedical applications, there is a plethora of additional research to be carried out, especially concerning proliferation and self-renewal of NPCs. Although Gallagher et al. perform a broad range of experiments to identify the IL-6-medited effects on embryonic NPCs, there are several questions left unanswered. The authors determine that IL6R is expressed by NPCs, allowing autocrine/paracrine IL-6 signaling. However, it is not elucidated as to which type of IL6R is predominantly incorporated in the activation of the JAK-STAT signaling pathway. Since classic membrane-bound IL6R signaling and soluble IL6R (sIL6R) trans-signaling have antagonistic inflammatory effects, it would be beneficial to further investigate the specificity of IL-6 signal transduction in the mammalian embryonic forebrain. It is understood that classic signaling has anti-inflammatory effects, transsignaling has pro-inflammatory effects, and that sIL6R in the trans-signaling pathway can activate the membranebound gp130 on any cell, unlike membrane-bound IL6R, which can only activate gp130 in an autocrine manner (Rabe et al., 2008). In order to further investigate this concept, experiments incorporating inhibition of sIL6R can be performed by transgenically overexpressing soluble 72


gp130 (sgp130), which exclusively inhibits sIL6R, allowing predominant anti-inflammatory membranebound gp130 signaling. Coupling such an experiment with immuno-cytochemical analysis of NPC proliferation and pluripotency would contribute to the clarification of the mechanism responsible for IL-6 mediated regulation of NPCs. This research could also help to elucidate the anti-inflammatory effects of NPC deregulation in respect to previously reported IL-6-associated behavioral disorders (Smith et al., 2007). Additional clarification of STAT3 targeting is also needed to resolve the controversial observations reported by various authors (Gu et al., 2005; Nakanishi et al., 2007). By evaluating STAT3-mediated GFAP expression in embryonic neural precursor pools, future experiments should be performed to investigate differences in two related aspects. Firstly, phosphorylated STAT3 levels following IL-6 administration should be quantified at varying times or stages in embryonic development, both before E11.5, after E14.5, and in between. Secondly, such quantifications should be made in a spatially comparative manner, for example, the hippocampus versus the SVZ precursor pools. In addition to these analyses, ChIP experiments could potentially be utilized to determine if promoters or regulator regions in genes other than the GFAP gene are implemented in IL-6mediated JAK-STAT signaling in the embryonic forebrain. Finally, Western blot analyses should be implemented in order to discern whether other (non-STAT3) mammalian STAT family members are activated by JAK during a maternal IL-6 surge. Coupling these aforementioned experiments with immunocytochemical analyses of NPC proliferation and pluripotency may result in valuable findings in the growing field of neural stem cell research. References 1. Barnabé-Heider, F., Wasylnka, J.A., Fernandes, K.J.L., Porsche, C., Sendtner, M., Kaplan, D.R., & Miller, F.D. (2005). Evidence that embryonic neurons regulate the onset of cortical gliogenesis via cardiotrophin-1. Neuron. 48, 253-265. 2. Boksa, P. (2008). Maternal infection during pregnancy and schizophrenia. Journal of Psychiatry & Neuroscience. 33, 183-185. 3. Bowen, K.K., Dempsey, R.J., & Vemuganti, R. (2010). Adult interleukin-6 knockout mice show compromised neurogenesis. NeuroReport. 22, 126-130. 4. Coe, C.L., Kramer, M., Czéh, B., Gould, E., Reeves, A.J., Kirschbaum, C., & Fuchs, E. (2003). Prenatal stress diminishes neurogenesis in the dentate gyrus of juvenile Rhesus monkeys. Biological Psychiatry. 54, 1025-1034. 5. Dittrich, A., Quaiser, T., Khouri, C., Görtz, D., Mönnigmann, M., & Schaper, F. (2012). Model-driven experimental analysis of the function of SHP-2 in IL-6-induced Jak/STAT signaling. Molecular BioSystems. 8, 2119-2134. 6. Fan, G., Martinowich, K., Chin, M.H., He, F., Fouse, S.D., Hutnick, L., Hattori, D., Ge, W., Shen, Y., Wu, H., Hoeve, J.T. Shuai, K., & Sun, Y.E. (2005). DNA methylation controls the timing of astrogliogenesis through regulation of JAK-STAT signaling. Development. 132, 3345-3356. 7. Gallagher, D., Norman, A.A., Woodard, C.L., Yang, G., Gauthier-Fisher, A., Fujitani, M., Vessey, J.P., Cancino, G.I., Sachewsky, N., Woltjen, K., Fatt, M.P., Morshead, C.M., Kaplan, 73

D.R. & Miller, F.D. (2013). Transient maternal IL-6 mediates long-lasting changes in neural stem cell pools by deregulating an endogenous self-renewal pathway. Cell Stem Cell. 13, 564-576. 8. Gu, F., Hata, R., Ma, Y.J., Tanaka, J., Mitsuda, N., Kumon, Y., Hanakawa, Y., Hashimoto, K., Nakajima, K., & Sakanaka, M. (2005). Suppression of Stat3 promotes neurogenesis in cultured neural stem cells. Journal of Neuroscience Research. 81, 163-171. 9. Kang, M.K., & S.K. (2008). Interleukin-6 induces proliferation in adult spinal cord-derived neural progenitors via the JAK2/STAT3 pathway with EGF-induced MAPK phosphorylation. Cell Proliferation. 41, 377-392. 10. Khan, V.R., & Brown, I.R. (2002). The effect of hyperthermia on the induction of cell death in brain, testis, and thymus of the adult and developing rat. Cell Stress & Chaperones. 7, 73-90. 11. Li, G., Fang, L., Fernández, G., & Pleasure, S.J. (2013). Neuron. 78, 658-672. 12. Ming, G.L., & Song, H. (2011). Adult neurogenesis in the mammalian brain: significant answers and significant questions. Neuron. 70, 687-702. 13. Muñoz-Cánoves, P., Scheele, C., Pederson, B.K., & Serrano, A.L. (2013). Interleukin-6 myokine signaling in skeletal muscle: a double-edged sword? FEBS Journal. 280, 4131-4148. 14. Nakanishi, M., Niidome, T., Matsuda, S., Akaike, A., Kihara, T., & Sugimoto, H. (2007). Microglia-derived interleukin-6 and leukaemia inhibitory factor promote astrocytic differentiation of neural stem/progenitor cells. European Journal of Neuroscience. 25, 649-658. 15. Patterson, P.H. (2007). Maternal effects on schizophrenia risk. Science. 318, 576-577. 16. Patterson, P.H. (2011). Maternal infection and immune involvement in autism. Trends in Molecular Medicine. 17, 389-394. 17. Rabe, B., Chalaris, A., May, U., Waetzig, G.H., Seegert, D., Williams, A.S., Jones, S.A., Rose-John, S., & Scheller, J. (2008). Transgenic blocking of interleukin 6 transsignaling abrogates inflammation. Blood. 111, 1021-1028. 18. Simons, B.D., & Clevers, H. (2011). Strategies for homeostatic stem cell self-renewal in adult tissues. Cell. 145, 851-862. 19. Smith, S.E.P., Li, J., Garbett, K., Mirnics, K., & Patterson. P.H. (2007). Maternal immune activation alters fetal brain development through interleukin-6. The Journal of Neuroscience. 27, 10695-10702. 20. Taga, T., & Fukuda, S. (2005). Role of IL-6 in the neural stem cell differentiation. Clinical Reviews in Allergy & Immunology. 28, 249-256. 21. Takizawa, T., Nakashima, K., Namihira, M., Ochiai, W., Uemura, A., Yanagisawa, M., Fujita, N., Nakao, M., & Taga, T. (2001). DNA methylation is a critical cell-intrinsic determinant of astrocyte differentiation in the fetal brain. Developmental Cell. 1, 749-758. 22. Uban, K.A., Sliwowska, J.H., Lieblich, S., Ellis, L.A., Yu, W.K., Weinberg, J., & Galea, L.A.M. (2010). Prenatal alcohol exposure reduces the proportion of newly produced neurons and glia in the dentate gyrus of the hippocampus in female rats. Hormones and Behavior. 58, 835-843. 23. Ventura, R.E., & Goldman, J.E. (2007). Dorsal radial glia generate olfactory bulb interneurons in the postnatal murine brain. The Journal of Neuroscience. 27, 4297-4302. 24. Young, K.M., Fogarty, M., Kessaris, N., & Richardson, W.D. (2007). Subventricular zone stem cells are heterogeneous with respect to their embryonic origins and neurogenic fates in the adult olfactory bulb. The Journal of Neuroscience. 27, 8286-8296.


Rachel Duncan

Trans-Cranial Direct Stimulation: A device for out of the box thinking

Newell and Simon proposed that to solve a problem, steps need to be taken from the current state to the goal state within relevant constrains such as time (Newell and Simon, 1972). However, what makes insight problems particularly challenging is that unlike well defined problems which rely on past experience and relevant knowledge, insight problems are often ill-defined (DyYoung, Flanders, Peterson, 2008). Previous knowledge, expectation and goals may bias how entering information is processed through “top down” cognitive processing which may lead to impasses and cognitive rigidity when solving insight problems (Corbetta and Shulman, 2002). In noninsight problems, the operations required to get to the goal state as well as how the current/goal states themselves are perceived is unpredictable (DyYoung, Flanders and Peterson, 2008). They often require the subject to reconstruct their perspective on the situation including inappropriate constrains in order to overcome the impasse. Reliance on a routine frame to solve a problem has also been called the “mental-set effect”, a phenomena associated with left hemisphere dominance (Chi and Snyder, 2011). While top down cognitive processes involve a flow of information from higher to lower cortical areas, bottom up cognitive processes have minimal influence from higher order cognition on how sensory stimuli are salient, allowing novel and unexpected sensory information to direct the content of attention (Corbetta and Shulman, 2002). Learned or habitual thought patterns fuel top down processes can cause blindness to obvious solutions. One area of research that has been getting attention because of it’s effects on the quality of attention is mindfulness meditation. Mindfulness practices cultivate an orientation to experience through “fresh eyes” as though an individual is experiencing the stimuli for the first time (Bishop et al, 2004). It practices an objective, empirically based orientation rather than one clouded by expectation, emotion and subjective filter (Bishop et al, 2004). Researchers have been studying the relationship between mindfulness practice and mental set effects- a reliance on previous knowledge or experience. Greenberg, Reiner and Meiran (2012) found that compared to unexperienced meditators, experienced meditators were better able to identify simple or novel solutions to the Einstellung water task and were less blinded by rigid, experienced based problem solving strategies. Other researchers have found support for trait mindfulness and state induced mindfulness on increased insightful problem solving ability and creating thinking even when controlling for positive affect on the prisoner’s rope, antique coin and steel pyramid insight tasks (Ostafinand Kassman, 2012). Moore and Malinowski (2009) found that measures of attention and cognitive flexibility were higher for experienced meditators who showed less Stroop interference on the Stroop

task; a measure of the participant’s ability to detect novelty among visual stimuli. In these studies, heuristically or top down driven processes of thinking had less influence, as the mindfulness groups were better at overcoming habitual problem solving strategies in order to solve the novel insight tasks. Chi and Snyder (2011) investigated the effects of temporarily reducing cognitive rigidity using noninvasive trans-cranial direct current stimulation (tDCS). Their hypothesized was drawn from research of “paradoxical facilitation”; a cognitive style that is less influenced by prior knowledge and experience in individuals with left temporal lobe impairments. Interestingly, these individuals can have an enhanced ability for solving insight problems and creating thinking. Cognitive processes facilitated by creativity and novel meaning making draw from a similar vein as the mindfulness research. Experienced meditators may be less prone to mental-set effects having practiced a fresh eyed awareness that relies less on habitual patterns of thinking than their unexperienced counterparts. However, unlike the mindfulness manipulation, Chi and Snyder used tDCS on to influence an insight prone cognitive style by stimulating the right and left anterior temporal lobe areas of healthy right handed, left hemisphere dominant individuals. The researchers amplified and muted the left and right anterior temporal lobes (ATL) to reduce heuristically driven mental set effects on a novel insight problem: matchstick arithmetic. Likewise, other studies have tried to reversed mental set effects by stimulating the dorsolateral prefrontal gyrus and left angular gyrus using tDCS and included neurophysiological imaging (Dandan et al. 2013).

Image 1: Example of three types of problems and their accompanied solutions atypical of matchstick arithmetic. To overcome the mental impasse in the first two problems, participant must turn a 3D display into a 2D display. (Figure source: Chi and Snyder, 2011)

Methods Sixty undergraduate participants without prior experience with the matchstick arithmetic paradigm were recruited ands randomly assigned to one of three groups: L- R+, L+ R-, or control. All three groups were asked to solve 27 type 1 problems (see figure 1) to induce a mental 74


set effect whereby each of the 27 questions required the same ‘X’ to ‘V’ maneuver to reach the solution, during the mental set phase participants who did not reach a solution after two minutes per problem were given the solution. Following the mental set phase, participants were hooked up to one of three tDCS manipulations. Participants in the left cathodal/right anodal ATL (L-R+) group and L+ R- group experienced two minutes of active 1.6mA stimulation for the duration of the test. Meanwhile, participants in the sham group were hooked up to a device with an ‘on’ display setting at minimal stimulation, to imply active simulation at minimum sensation of 1.6 mA for 30s followed by 5 minutes of waiting for the minimal effect to wear off. Following the mental set phase, groups were asked to solve one of each type 2 and type 3 problem with 6 minutes per puzzle. The researchers predicted that reliance on the first strategy ‘X’ to’ V’ to would hinder their performance when solving type 2 and 3 problems which require a ‘+’ to ‘=’ sign change. Participants from the three groups were measured based on time to ‘event’; number of seconds until they reached the solution. Statistical analysis was performed using a two tailed Fisher’s exact test for performance between stimulation groups and a logrank test to compare time to event. Results Neither age, gender, nor time required to complete the mental set phase was a predictor for solving the type two problem. The majority of participants (95%) were able to solve the 27 type 1 problems in the mental set phase. However, at the end of the 6 minutes given for the type 2 problem, 60% of participants in the L- R+ stimulation group reached the correct solution compared to only 20% of participants in the L+ Rand sham groups. This result supported the author’s hypothesis. These findings were not observed in the type 3 problem, as both L+ R- and L- R+ stimulation groups showed smaller differences between group but both outperform participants in the sham group by 40%. However, this doesn’t disprove the author’s hypothesis because they were expecting to see improvement for the L- R+ for type 2 problems only, a finding in line with previous research on individuals with brain lesions ability to solve type 2 but not type 3 problems. Discussion Although the results of this investigation were in line with the author’s hypothesis, the mechanism by which tDCS influenced participants cognition and behavior is unclear. They suggested but were not able to prove that the enhanced performance of L- R+ group may have been facilitated by increased excitability to the right ATL rather than decreased excitability in the left ATL. Chi and Snyder (2011) suggested that a single or combination of the following mechanisms could have been at work behind their results: reduced topdown processing (paradoxical facilitation), facilitated insight (increased right hemispheric firing), diminished mental set effect (decreased left hemispheric firing), and switching hypotheses. They also considered the 75

Figure 2 (above left) shows group comparisons for solving the Type 2 insight problem while Figure 3 (above right) indicated groups comparisons for solving the Type 3 insight problem. Figure source: (Chi and Snyder, 2011).

possibility of a ceiling effect whereby tDCS wouldn’t be able to induce further mental set effects. This paper particularity has been met with controversy in the media; some suggest that the limitations of replicability and the possibility of confounding factors may outweigh it’s significance. Considering target area of electrodes ranged 35cm^2, the researchers could included neurophysiological imaging techniques like an FMRI to determine if the tDCS stimulation was influencing the right/left ATL independently of other cortical areas or if it’s activation/inhibition influence had spread (Dandan et al, 2013). It is worthwhile to be aware that other studies have shown that as little as 5% of drift in electrode position may have significant influence on current intensity for particular cortical regions (Wood, et al. 2014). Also, they could have also tested for state-dependent contextual information (including arousal levels, affect valence, amount of sleep) anything that could have account for behavioral or cognitive priming that may inflate the effects of tDCS (Smith, Vartanian and Goel, 2014; Horvath, Forte and Carter, 2015) Limitations of this study include the demographics of the sample. Only twenty participants were included in each strimulation group and the average age was 22. However, taken


with a grain of salt, the article presents a small cue of the use of tDCS which in itself is a safe, non-invasive, non-pharmacological procedure. Future Directions It would be interesting for future studies to explore an older age group. Considering the brains of young people may be working at optimal plasticity levels, perhaps even greater effects would be seen in older adults (65+) who may have life long experience with habitual heuristic processing and declines in working memory and problem solving abilities. Additionally, they could recruit left-hand dominant participants to see if (L-R+) stimulation helped them reach the solution more efficiently than in the sham control group, or if any mental set effects would occur in (L+R-) stimulation. Left hand dominant participants may be less susceptible to mental set effects. Although most studies shy away from left hand dominant participants it would be interesting to include their results to the data set. As well, they could have included other insight problems like the nine dot problem to further investigate inter hemispheric rivalry in tDCS (Chi and Snyder, 2012). However, the nine dot problem and matchstick arithmetic are not a typical problems of everyday life. To make their experiment more relevant to everyday life, they could present participants with cognitive tasks that are more realistic and require breakdown of existing heuristics such as the prisoner’s rope, the antique coin, steel pyramid or stroop tast in conjunction with tDCS and FMRI imaging (Dandan et al, 2013; Ostafin and Kassman, 2012; Moore and Malinowski 2009).

tions from single-session transcranial direct current stimulation (tDCS). Brain Stimulation, doi:10.1016/j.brs.2015.01.400 8. Moore, A., & Malinowski, P. (2009). Meditation, mindfulness and cognitive flexibility. Consciousness and Cognition, 18(1), 176-186. doi:10.1016/j.concog.2008.12.008 9. Nelson, T. O., Kershaw, T. C., & Ohlsson, S. (2004). Multiple causes of difficulty in insight: The case of the nine-dot problem. Journal of Experimental Psychology: Learning, Memory, and Cognition, 30(1), 3-13. doi:10.1037/0278-7393.30.1.3 10. Newell, A., & Simon, H. A. (1972). Human problem solving. Englewood Cliffs, NJ: Prentice-Hall. 11. Ostafin, B. D., & Kassman, K. T. (2012). Stepping out of history: Mindfulness improves insight problem solving. Consciousness and Cognition, 21(2), 1031-1036. doi:10.1016/j. concog.2012.02.014 12. Smith, K. W., Vartanian, O., & Goel, V. (2014). Dissociable Neural Systems Underwrite Logical Reasoning in the Context of Induced Emotions with Positive and Negative Valence. Frontiers in Human Neuroscience, 8, 736. doi:10.3389/ fnhum.2014.00736 13. Woods, A., Bryant, V., Sacchetti, D., Gervits, F., & Hamilton, R. (2014). Effects of electrode drift in transcranial direct current stimulation. Brain Stimulation, 8(2), 320-321.

References 1. Bishop, S. R. (2004). Mindfulness: A proposed operational definition. Clinical Psychology: Science and Practice, 11(3), 230-241. doi:10.1093/clipsy/bph077 2. Corbetta, M., & Shulman, G. L. (2002). Control of goaldirected and stimulus-driven attention in the brain. Nature Reviews Neuroscience,3, 201-215. 3. Chi RP, Snyder AW (2011) Facilitate Insight by Non-Invasive Brain Stimulation. PLoS ONE 6(2):e16655 doi:10.1371/ journal.pone.0016655 4. Dandan, T., Haixue, Z., Wenfu, L., Wenjing, Y., Jiang, Q., and Qinglin, Z. (2013). Brain activity in using heuristic prototype to solve insightful problems. Behav. Brain Res. 253, 139–144. doi:10.1016/j.bbr.2013.07.017 5. DeYoung, C. G., Flanders, J. L., & Peterson, J. B. (2008). Cognitive abilities involved in insight problem solving: An individual differences model. Creativity Research Journal, 20(3), 278-290. doi:10.1080/10400410802278719 6. Greenberg, J., Reiner, K., & Meiran, N. (2012). “Mind the trap”: Mindfulness practice reduces cognitive rigidity. PLoS One, 7(5) doi:http://dx.doi.org/10.1371/journal.pone.0036206 7. Horvath, J. C., Forte, J. D., & Carter, O. (2015). Quantitative review finds no evidence of cognitive effects in healthy popula-

76


Hippocampal Neurogenesis, Forgetting and the Effects of Exercise, Aging, and Stress on Memory Saadia Esat

The following review discusses the role of neurogenesis in forgetting, and the substantial correlation that appears to exist. Additionally, exercise has been shown to increase the survival of newborn neurons and therefore improve neurogenesis, speeding up the forgetting process. Aging, however, has the opposite effect as it slows neurogenesis and allows the existing memories to be recalled. Looking at stress, it can have positive and negative effects in relation to memory depending on the extent and for what treatment it is being used. Studying the correlation between neurogenesis and forgetting is helpful in understanding how to maximize learning and memory in terms of hippocampal-dependent memories, as well as improving the mental health of those who are suffering from chronic stress. Key words: hippocampus; neurogenesis; forgetting; fear conditioning; exercise; memory Background The hippocampus has been vastly studied as it is essential to the formation and retrieval of contextual memories, a process important for many cognitive activities including learning, prediction-making, problem solving, and decision making. Studies have been done in various scenarios to see the effects of different variables on memory retrieval, specific to those memories stored in the hippocampus. Variables such as exercise, stress, post-traumatic stress disorder (PTSD), and contextual and non-contextual dependent memories demonstrate an effect on one key process in the hippocampus â&#x20AC;&#x201C; that is neurogenesis. As these studies are discussed, this review will cover the process of neurogenesis, how it is affected, and what that means for neurogenesis and learning. Learning, overall, is greatly affected by how much an individual can remember. Specific to the hippocampus, learning in the use of spatial memory and context dependency will be used. In the study by Winocur et al. (2012), neurogenesis was disrupted in adult rats. It was then demonstrated through a learned discrimination that rats placed in a high-interference environment had an impaired performance on the task, where as those in a low-interference environment did not. This is because the rats in the high-interference environment relied heavily on the contextual cues for performance, which were now unavailable to them due to the disruption in the hippocampus. From this, it is concluded that the hippocampus is context-dependent and that the following discussion of memory will be based on this (Winocur, 2012). Neurogenesis has been shown to be affected by other internal factors including exercise and stress. These factors, as they affect how much is information is remembered, in turn affect learning. However, the interesting aspect of the process of remembering is that it appears to come hand in hand with forgetting. Akers et al. (2014) experiment on the effects of hippocampal neurogenesis and forgetting to determine the extent of the correlation between neurogenesis and forgetting, and how that is further interfered with by 77

exercise. From studying this, it may lead to developments in maximizing learning and memory by being able to balance the tradeoffs. In addition, it is important in order to study the effects of stress on both the processes of remembering and forgetting, and where it can help with those with PTSD. Research Overview SUMMARY OF MAJOR RESULTS & DISCUSSION Akers et al. (2014) experimented with infant and adult mice, to look at the difference between the various amount of neurogenesis occurring and how it affected memory of a fear-conditioned contextdependent stimulus. In infants, neurogenesis is rapid and occurs to a larger extent than it does in adult mice. Additionally, the effects of having access to an enriched environment (a running wheel) were also used as a variable. Finally, this was tested on TK+ mice vs. wildtype mice, in which the modified mice were impaired for the process of neurogenesis. The major results here indicated that with increased neurogenesis, there was also increased amount of forgetting. This was true with the adult vs. infant condition, in which after the fear condition, both groups tested a day later showed the same amount of freezing time, whereas when both were tested 28 days later, the adults showed more freezing than the infants. In addition, the above was true in the case of enriched vs. non-enriched rats, in which those who voluntarily accessed a running wheel showed more neurogenesis with GFP tracking in the dentate gyrus, as well as a reduced response the conditioned stimulus context. Interestingly, the transgenic TK+ mice that were impaired in the neurogenesis process were unable to forget the conditioned stimulus and did not reduce their reaction time during the tested context 28 days later (Akers, 2014). The finding that enriched environment does promote forgetting, is in parallel with other evidence suggesting that in fact volunteer running promotes neurogenesis by increasing the survival chances of 1-3 week old


neurons (Zhao, 2008). By promoting the growth of these neurons, memory on spatial tasks and trace conditioning may be improved, though other memories are forgotten in the process (Frankland, 2013). The evidence for this lies in both the experiment by Akers et al. and how over a delayed time period, the memory of the fear conditioning was forgotten. Additionally, Winocur et al. (2006) performed experiments with spatial tasks and trace conditioning to show that in fact impairing the adult neurogenesis will cause disruption for the rat to recalls memories over a long time delay, as well as in contextual circumstances. Hence, hippocampus is important in these areas, and that the survival of these new neurons is important for an extended recall of memories, though it affects the memory of other retrieval patterns. Memories formed in the hippocampus are proven to be formed on the idea of pattern separation (Mongiat 2014). Pattern separation is the idea that in circumstances where conditions are similar, little contextual cues, indicated by the hippocampus, allow for the appropriate response. In this case, a memory would be considered a specific retrieval pattern, and forgetting would occur when one is unable to recall that exact retrieval pattern. Putting together the two above ideas, this indicates that when neurogenesis occurs, the new neurons disrupt the old pathways and cause forgetting of the old retrieval pathways. Interestingly, however, neurogenesis is very helpful in cases where new information learned conflicts with old information (Winocur 2006). This leads to another point, in that there may be tradeoffs for how much one can learn and how much they will remember, based on the process of neurogenesis. If there is too much neurogenesis, then it appears one will forget a lot more; if there is too little then one will not be able to learn anything new (make new retrieval patterns). This is illustrated in the following diagram:

Conclusions and Discussion As mentioned, it appears there is a tradeoff level between how much can be learned and remembered. As Akers et al. proved, there is a correlation between neurogenesis and forgetting. This brings to light an interesting discussion on where the tradeoff is and how can one maximize this learning and retention when in life. One aspect of this tradeoff is affecting by the aging process. Many studies have shown that with age comes impaired performance in spatial memory, or tasks that involve the hippocampus. Not surprisingly, neurogenesis also reduces with age, as well as synaptic plasticity (Barak, 2014). However, Barak et al. (2014) showed that with fitness and aerobic exercise, one can reduce the effects of age-related impairment in memory. This is very much in line with Akers et al. experiment in that there conditions with adult vs. infant rats showed the difference between neurogenesis with the age gap and that in the adult condition, some rats had access to a running wheel and some did not.

Conclusions

In exploring the relationship of the tradeoff between learning and forgetting, as well as factoring age and exercise, it can begins the process of studying how to maximize memory and learn efficiently. Akers et al. provided a novel insight to just how much correlation there is between learning and forgetting, as much of the literature on forgetting, in this aspect, is just theory. Being able to know when and how much certain aspects of learning, in relation to the hippocampus, should occur is essential to maximizing human interaction with the world. Additionally this novel experiment has shown how much forgetting is related to learning, and can be evidence for the processes of both LTP and LTD. The study provided confirmation to certain aspects of hippocampal memory, as discussed above, but also allowed for new insight of forgetting. Additionally, Akers et al. checked to see if their hypothesis was transfer appropriate, by also testing on guinea pigs. The correlation carried through, hence there is a substantial correlation between forgetting and hippocampal neurogenesis.

Criticisms and Future Directions

http://www.sciencemag.org.myaccess.library.utoronto.ca/ content/344/6184/594/F1.expansion.html Figure 1. The rats respond to learning what is announced by the radio. When too little neurogenesis occurs, there is a limitation on how much can be learned, as well as remembered. When too much neurogenesis occurs, then a lot can be learned, but very little can be remembered. It is then suggested, a tradeoff level where neurogenesis balances with forgetting and so learning and retention is maximised (Mongiat 2014).

In future, in addition to studying the tradeoff relationship, it would worthwhile to study the effects of stress and neurogenesis. Stress is a part of everyday lives, and in small doses, is said to be helpful for learning, memory, and performance, but chronically it can impair all three. Chronic stress is shown to alter the hippocampus by affecting the NMDA-dependent excitatory pathway, and thereby inhibiting neurogenesis in the dentate gyrus (Gould 1999). This is demonstrated by individuals with PTSD, who have proven to have a smaller hippocampus than those without (McNamara 2006). Studying these effects can help alleviate consequences from stress by being able to counteract the effects of stress on the hippocampus. For example, with the administration of Ziprasidone, anxietylike behaviours in rats decreased and neurogenesis was then up-regulated (Zhengqu 2013). 78


However, in another experiment where a categorized list was learned, and then the individual was exposed to a stressor or control environment, those under stress showed an improvement in memory in that they did not suffer from retrieval-induced forgetting (Koessler 2009). Additionally, veterans with PTSD showed that selective retrieval of trauma related stimuli leads to enhancement of induced forgetting, meaning that it helped to alleviate the effects of PTSD (Brown 2012). Looking at both sides of the spectrum, it appears that the balance of memory and forgetting can be regulated by stress and anti-depressants/stress treatments (Dranovsky 2006). Being able to do this, is key to the mental health of individuals and finding alternate methods of dealing with chronic stress and further maximising learning and memory in the hippocampus. Another part of the brain that also influences memories in the hippocampus is the amygdala. Young rats exposed to chronic childhood stress, were more succumbed to stress in adulthood and showed a more activated amygdala during times of stress (Tsoory 2007). To put these three aspects: stress, the amygdala, and hippocampal neurogenesis together would be a crucial aspect of studying mental health and being able to create environments that are appeasing to all three. Additionally, helping those with chronic stress and the long term effects of it (like the amygdala response) would greatly be effected by studies on neurogenesis and forgetting. Potentially, the same experiment from the Akers et al. study could be replicated but over an extended period of time. Stressors and learning can be alternated throughout growth to see what the effects of neurogenesis end up being, and an MRI scan can be used to look at the size of both the hippocampus and the amygdala. Akers et al. experiment has provided the first stepping stone to looking further into the correlation between forgetting and memory and moving toward the most efficient treatments for stress, as well as the most effective methods for learning and memory. References 1. Akers K, et al. (2014). Hippocampal Neurogenesis Regulates Forgetting in Adulthood and Infancy. Science 344(6184), 598-602. 2. Barak B, et al. (2014). Cardiovascular Fitness and Cognitive Spatial Learning in Rodents and in Humans. J Gerontol A Biol Sci Med Sci. 3. Brown A, et al. (2011). Forgetting Trauma: Socially Shared Retrieval-induced Forgetting and Post-traumatic Stress Disorder. Appl. Cognit. Psychol. 26:24-34. 4. Dranovsky A, Hen R (2006). Hippocampal Neurogenesis: Regulation by Stress and Antidepressants. Biol Psychiatry 59: 1136-1143. 5. Frankland P, et al. (2013). Hippocampal neurogenesis and forgetting. Trends in Neurosciences, 36(9): 497-503. 6. Gould E, Tanapat P (1999). Stress and Hippocampal Neurogenesis. Biol Psychiatry, 46: 1472-1479. 7. Koessler S, et al. (2009). No Retrieval-Induced Forgetting Under Stress. Psychological Science, 20(11): 1356 79

â&#x20AC;&#x201C; 1363. 8. McNamara D (2006). Chronic PTSD linked to smaller hippocampus. Clinical Psychiatry News, 34(5), 19. 9. Mongiat L, Schnider F (2014) A Price to Pay for Adult Neurogenesis, Science 344(6184): 594-595. 10. Tsoory M, et al. (2007). Amygdala modulation of memory-related processes in the hippocampus: potential relevance to PTSD. Progress in Brain Research, 167: 35-51. 11. Winocur G, et al. (2012). Adult hippocampal neurogenesis and memory interference. Behavioural Brain Research, 227: 464-469. 12. Winocur G, et al. (2006). Inhibition of Neurogenesis Interferes with Hippocampus-Dependent Memory Function. Hippocampus, 16: 296-304 13. Zhao C, et al. (2008). Mechanisms and Functional Implication of Adult Neurogenesis. Cell, 132(4): 645-660. 14. Zhengqu P, et al. (2013). Ziprasidone ameliorates anxiety-like behaviours in rat model of PTSD and up-regulates neurogenesis in the hippocampus and hippocampus-derived neural stem cells. Behavioural Brain Research, 244: 1-8. Received Month, ##, 200#; revised ##, 200#; accepted Month, ##,

Month, 2013.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright Š 2015 Dr. Bill JU, Neurosciences, Human Biology Program


Deep brain stimulation and Alzheimer’s disease: Benefits, cost-effectiveness and feasibility of deep brain stimulation on Alzheimer’s disease and cognitive dysfunction. Vanessa Ferlaino

Many neurodegenerative diseases are associated with common neurological and psychiatric conditions and are often the result of disruptions to neurological circuits. Due to the complexity of neurological circuits involved in neurodegenerative diseases that result in a vast array of symptoms, as identified in Alzheimer’s disease (AD), there are very limited effective treatments available for AD patients. Deep brain stimulation (DBS) is a new technique that has shown great efficacy and benefits in other neurodegenerative diseases, including Parkinson’s diseases (PD), Obsessive Compulsive Disorder (OCD), and depression. It has been recently used to stimulate various targets of the brain , including the fornix, anterior thalamic neucli and the nucleus basilis of meynert to improve cognitive function and memory in AD patients. Additionally, DBS has been coupled with imaging techniques to enhance understanding of the neural circuitry underlying AD, suggesting glucose cerebral metabolism plays a role in AD symptoms. However, there are many drawbacks of DBS to AD, including its use being limited to patients with mild AD, its cost-effectiveness and its feasibility as very few patients qualify for DBS treatment. As a result, this review assesses the use of DBS as a treatment for AD and includes an analysis of its cost-effectiveness and feasibility in the healthcare field. We conclude that DBS in conjunction with imaging techniques is very valuable to understanding neurological circuits of AD, and will be truly effective as a treatment if its feasibility can be increased to include treating patients at higher stages of AD or if combined with imaging techniques that can screen patients earlier in the AD development process. Key words: Deep brain stimulation (DBS); Alzheimer’s disease (AD); fornix; anterior thalamic nuclei (ATN); nucleus basilis of Meynert (NBM);midline thalamic nuclei (MTN); feasibility; cost-effectiveness; PET; FDG-PET. Background Lozano and Lipsman stated that many neurodegenerative diseases are associated with common neurological and psychiatric conditions that are often the result of changes, damage, and death of neurons in neurological systems. As a result, because numerous multiple neurological systems tend to be involved a variety of symptoms emerge, including cognitive and motor function deficits, leading to a large gap in terms of treatments for these patients as these neurological systems are multi-factorial and difficult to study. Lyketsos et al. describe Alzheimer’s disease (AD) as a neurodegenerative disease characterized by progressive cognitive dysfunction. Hirao, Pontine and Smith state the most common symptoms include depression, apathy and irritability. Pathologically, the disease appears to be due to accumulation and deposition of Beta-amyloid protein (Aβ) resulting in loss of neuronal function and neuronal death. Again, the neural circuits involved in AD are not completely understood making the development of a drug or other treatment quite difficult. However, a recent method known as Deep Brain Stimulation (DBS) has proved to be a beneficial treatment for AD patients as shown by Smith et al. DBS is best described by Lozano and Lipsman as a technique that involves the neurosurgical implantation of an electrode into a target brain region, ex. fornix. It is connected to a pulse generator, implanted under the skin below the collarbone, and settings such as stimulation type, frequency, amplitude, and pulse width can be controlled externally allowing it to be used to the effects of DBS as a potential treatment for

numerous neurodegenerative diseases. It has been successful for treating Parkinson’s disease, obsessive compulsive disorder (OCD), and depression (Pereira et al.), and has been incredibly useful as a technique to study the neural circuits of these diseases. However, DBS has many drawbacks, such as its beneficial effects being more prevalent in those with early AD thus limiting its feasibility as a treatment. Additionally, as the health care field prepares to shift to patientcentered care of chronic diseases, the feasibility of innovative techniques is important to assess. This review assesses the use of DBS as a treatment for AD and includes an analysis of its cost-effectiveness and feasibility in the healthcare field. We conclude that DBS in conjunction with imaging techniques is very valuable to understanding neurological circuits of AD, and will be truly effective as a treatment if its feasibility can be increased to include treating patients at higher stages of AD or if combined with imaging techniques that can screen patients earlier in the AD. Research Overview

DBS of the fornix is critical for controlling spatial memory in mild AD patients as it may be related to cerebral glucose metabolism

DBS of the fornix has been especially popular for treatment of AD. Initially, Hamani et al. had used DBS of the fornix to treat an obese patient, though it unexpectedly resulted in the upbringing of autobiographical

80


memory events in this patient. As a result, the authors began assessing the hypothalamic mechanism behind this memory. The authors concluded that the patient had enhanced cognition after hypothalamic stimulation as well as increased activity in the hippocampus, showing that electrical stimulation of the hypothalamus modulates limbic activity and improves hippocampusdependent memory. They hypothesized the effects of this hypothalamic stimulation on memory were due to activation of the fornix. Recognizing the role of the fornix in memory enhancement, Smith et al. investigated stimulation of the fornix and its role in memory enhancement in AD in a breakthrough study that involved DBS of the fornix for one year in 5 patients. Figure 1 shows PET scans that identified a frontal-temporal-parietal-striatal-thalamic network, important for memory and other cognitive functions, and a frontal-temporal-parietal-occipital-hippocampal network, important for the default mode network, after 1 year of DBS at constant electrode settings. High baseline metabolism in brain regions commonly affected by AD indicated less global cognitive decline and increased quality of life, denoted by a decline in ADAS-cog and QOL-AD scores, and correlated with increased cerebral metabolism after 1 year of DBS. Low baseline metabolism in brain regions less commonly affected by AD indicated less global cognitive decline and correlated with decreased metabolism after 1 year of DBS. However, they concluded that patients with mild AD benefitted more from DBS of the fornix as they showed more memory improvement. Their results also suggested that glucose metabolism plays a role in memory enhancement in AD, as indicated by PET imaging. Gao et al. investigated this relationship by using FDG-MicroPET to quantify baseline and postDBS treatment cerebral glucose levels in the brain of mice to show that bilateral anterior thalamic nucleus (ATN) stimulation increased glucose uptake in the thalamus and hippocampus. DBS in mice with lesions in the ATN did not show any increased glucose uptake post-treatment, thus glucose metabolism is regulated by the ATN. This is consistent with Smith et al. as the ATN is present in the frontal-temporal-parietalstriatal-thalamic network, important for memory and other cognitive functions, therefore cerebral glucose plays an important role in memory and further studies may reveal its importance in AD as well as its potential use as a screening technique. Additionally, it is clear that DBS is an exceptional tool for studying neurological systems especially when compared with imaging techniques. Hescham et al. also used DBS to stimulate the fornix at 200 µA, 100 µA, and 50 µA in mice treated with scopolamine, a muscarinic acetylcholine receptor antagonist that induces memory dysfunction. Their main goal was to identify the stimulation parameters that allowed optimal improved memory in experimental dementia. Although this paper did not exclusively look at AD, Pereira et al. state dementia is the result of progressive AD. Object location task and open field (OF) tests were used to assess memory recognition and anxiety. They concluded that 200 µA at 10 Hz as well as 100 µA at 10 Hz and 100 HZ enabled the best enhanced memory performance in the object location task. The OF results showed no significant 81

difference between sham rats and experimental rats, indicating no side-effects on locomotor and anxietyrelated behaviours. In conclusion, DBS of the fornix in humans and mice models has shown that the fornix appears to be critical for controlling spatial memory function and can be shown to improve this memory function in patients with mild AD and has clear benefits as a therapeutic treatment.

Figure 1. Frontal-temporal-parietal-striatal-thalamic network and (red) frontal-temporal-parietal-occipital-hippocampal network (blue) associated with increased cerebral metabolism (Smith et al.).

DBS of the midline thalamic nuclei and nucleus basilis of meynert may help improve cognitive dysfunction and memory

Despite the clear benefits of DBS of the fornix, other targets have been found to be beneficial for AD, including the midline thalamic nuclei (MTN) and the nucleus basalis of Meynert (NBM). Arrieta-Cruz, Pavlides and Pasinetti initiated DBS first in the Schaffer Collateral (SC) of TgCRND8 hippocampal slices to activate CA1 neurons and found that TgCRND8 mice did not undergo short-term potentiation until after high frequency stimulation (HFS) at 200 Hz in contrast to wild type slices. They also used c-Fos to show increased activity of α-secretase in TgCRND8 mice after HFS at 50, 100 and 200 Hz but there was no effect on β-secretase activity. They then performed HFS of midline thalamic nuclei in TgCRND8 mice followed by an object recognition task immediately after stimulation. TgCRND8 mice showed enhanced short-term memory acquisition after DBS in this task, which is again only associated with early AD as this is the first type of memory affected in AD (Tramatula et al.). However, Chen et al. replicated these results in long term memory by injecting mice with Aβ1-40 and


then performing ANT-DBS. These mice had increased platform-traversing time and time spent in the target quadrant in the Morris Water Maze compared to AD mice injected with Aβ1-40 but did not undergo ANT-DBS. Therefore, cognitive dysfunction and memory of AD can be treated by ANT-DBS in mice. Kuhn et al. performed bilateral stimulation for one year of the Ch4 region in the NBM, as it is known to be most affected by AD, resulting in increased acetylcholine release in this area, correlating with increased cognitive performance. Figure 2 shows ADAS-cog scores showing improved memory, though authors could not make any conclusions as to whether or not the hippocampus or other memory-dependent circuits were affected. Consistent with Smith et al., these authors also found an increase in glucose metabolism in the entire cerebrum in three out of four patients that underwent PET post-DBS after 1 year of treatment. Therefore DBS of both the fornix and the NBM result in increased cerebral glucose metabolism, again suggesting the importance of glucose metabolism in AD and proving that DBS is an excellent tool for understanding neural circuitry when used in conjunction with imaging techniques.

DBS is a safe and feasible treatment, but targets very few patients with mild AD

Kuhn et al. also assessed the safety of DBS technique and concluded there were no dangerous side effects. They also noted that out of six patients, quality of life appeared to only improve in two. Two others indicated a decrease and another two patients indicated

no change at all, while the quality of life of relatives did not show a significant increase. In regards to the popularity of the use of DBS, one patient and one relative of another patient indicated they would not choose to use the treatment again, suggesting that although DBS has promising results its feasibility may not be realistic for treatment if its interest is not perceived well by the public. As a result, feasibility of DBS was investigated by Fontaine et al. After a one year period of inclusion, 9/110 patients fit the inclusion criteria, including having episodic memory impairments. 4/9 originally accepted the idea, though only 2/4 gave consent. In the end, only 1 patient received bilateral DBS of the fornix for one year as the other patient withdrew consent. Fontaine et al. reported the surgery was well-received but many global cognitive functions did not improve until after 6 months of treatment and were then stabilized. Nonetheless, they were able to conclude that DBS is a safe procedure that should not result in any adverse complications and does not appear to impair daily living activities. However, they were only able to operate on one patient suggesting their restriction criteria, which required AD patients with impairments in episodic memory often associated with later stages of AD, was too specific. As this coincides with Smith et al. in terms of AD being most effective for patients with mild AD, this also indicates that a small percentage of patients are capable of receiving DBS. They also list factors such as lack of awareness of DBS, its invasiveness, as well as patient denial in regards to their cognitive decline leading to an underestimation of the benefit/risk ratio as leading

Figure 2. Mean scores reflecting long term effects of DBS on memory, cognition and global functioning in 6 AD patients (Kuhn et al.). 82


to this low acceptance level. That being said, the authors contrast the high acceptance rate of DBS with its low feasibility rate and question whether DBS is a treatment to invest in when so little can be treated or accept to be treated with it. Mirsaeedi-Farahani et al. also conducted a costeffectiveness analysis of DBS for AD treatment, looking at the clinical and economic thresholds especially as the cost of healthcare increases. They performed a literature review and determined that in order for DBS to be successful, its success rate must be at 3% to overcome effects of possible surgical complications on quality of life. Cost-effectiveness of DBS depends on society’s willingness to pay DBS. The authors concluded that DBS is cost-effective if its success rate is 20% or 74% for mild AD. With a success rate of 80%, DBS is more clinically effective and more cost-effective. In conclusion, DBS is highly effective in comparison to standard treatment of AD and that it is cost-effective if society is willing to pay. That being said, DBS is an expensive treatment; at a 20% success rate Mirsaeedi-Farahani et al. reported a cost of $200K and $50K for a 74% success rate. Kuhn et al., Fontaine et al. and Smith et al. showed recruitment of patients with mild AD was difficult as most patients suffer from progressive AD and also confirmed that DBS was mostly beneficial for mild-AD patients. Thus as so little will benefit from AD, it may not be entirely cost-effective at the healthcare level which seeks to provide treatments that will serve a greater proportion of the general public. Additionally, the success rate needs to be determined experimentally which may deviate greatly from this mathematical model as only so little patients benefit from AD. Thus, perhaps another way to tackle this issue is to investigate the use of better scanning techniques that will recognize neurodegenerative diseases like AD at earlier stages, such as imaging techniques described by Shivamurthy et al., Nasrallah and Wolk, and Laske et al. Conclusions As reported in this review, there are many benefits from the use of DBS of the fornix, ATN and NBM as a sole treatment for treating memory and cognitive function associated with AD. DBS of the ATN and NBM showed enhanced memory and cognitive function in mice as shown by Kuhn et al., Chen et al., as well as Arrieta-Cruz, Pavlides and Pasinetti. Additionally, Smith et al., Gao et al and Kuhn et al. have shown that pairing DBS with imaging techniques can help in establishing and understanding neural circuits underlying AD, including the role of glucose cerebral metabolism. DBS of the fornix is proven to be critical for controlling spatial memory in both AD patients and mice models, as indicated by Hescham et al. However, Smith et al. showed memory in humans is better enhanced in mild AD patients. As a result, despite DBS being effective in improving cognition, Fontaine et al. and Mirsaeedi-Farahani et al. proved DBS to be feasible and cost-effective but unrealistic as it has been best proven for mild AD patients in many cases and thus there may not be a 83

market for DBS as a treatment among AD patients. Thus, perhaps the real potential of using DBS lies within its ability to aid in the understanding of neural circuitry in AD and the effects of glucose metabolism effects in conjunction with imaging techniques to help understand the disease and aid in the development of treatments and medications that are more feasible and acceptable by society. That being said, with the advance of neuroimaging techniques as screening tools for diagnosis at earlier stages of disease we may see the efficacy of DBS increase as DBS will be able to target more patients. Nonetheless, whether DBS is used as a treatment alone or in conjunction with imaging techniques to enhance understanding of the disease, it certainly is beneficial for AD.

Future Directions

As indicated in this review, plenty of evidence exists in supporting DBS as a therapeutic treatment for mild AD symptoms. Thus, in the future, the study of the effects of cerebral glucose metabolism as well as the effects of DBS on neurogenesis, BDNF transport and Aβ pathology will be useful to further assess the benefits of DBS as a sole treatment and maybe even a potential cure for AD. Cell and molecular biology techniques can be used to study the effects of increased cerebral glucose metabolism and neurogenesis on the brain, as previously shown by Gao et al as well as Arrieta-Cruz, Pavlides and Pasinetti . Additionally, Stone et al. showed DBS of the entorhinal cortex (EC) in mice participating in a water maze task resulted in activated neurons in the Dentante Gyrus (DG) with increased cFos and IdU expression, indicating new DG neurons integrated into hippocampal memory circuits. To assess the effect of DBS on Aβ metabolism, Aliaga et al. determined a correlation between BDNF levels and Aβ levels to use BDNF levels as a marker for Aβ presence. They used real-time PCR to show that sublethal concentrations of Aβ led to decreased BDNF mRNA levels and trkB mRNA levels in neurons. p75 mRNA levels did not change, but protein expression decreased as a result of internalization. Protein expression of trkB did not significantly change. Finally, Mark et al. showed that Phloretin, increased Aβ concentrations and FeSO4 presence resulted in decreased glucose uptake. Glucose transport impairment occurs quicker when exposed to HNE, a cytotoxic product of lipid peroxidation due to Aβ production and also occurred before decreased cell ATP; in conjunction with the observation that phloretin resulted in neurotoxicity led to the conclusion that Aβ-induced impairment of glucose transport is a result of Aβ-induced neurotoxicity. In conclusion, combining DBS, PET, FDG-MicroPET and cell and molecular biology techniques to study cerebral glucose metabolism and its effects on neurogenesis, BDNF transport and Aβ pathology in mouse models may be useful to enhance understanding of AD circuitry in the brain to aid in development of medications and other treatments for AD. Additionally, these studies may also increase the feasibility of DBS as a treatment to assist hospitals in their transition to treating chronic diseases, including debilitating neurodegenerative diseases.


References 1. Aliega E, Silhol M, Bonneau , Maurice T, Arancibia S, Tapia-Arancibia L (2010). Dual response of BDNF to sublethal concentrations of beta-amyloid peptides in cultured cortical neurons. Neurobiol Dis 37:208-217. 2. Arrieta-Cruz I, Pavlides C, Pasinetti GM (2010). Deep brain stimulation in midline thalamic region facilitates synaptic transmission and short-term memory in a mouse model of Alzheimer’s disease. Translational Neuroscience 3:188-194. 3. Chen N, Dong S, Yan T, Ma Y, Yu C (2014). Highfrequency stimulation of anterior nucleus thalamus improves impaired cognitive function induced by intra-hippocampal injection of Aβ1-40 in rats. Chin Med J 1:129-139. 4. Fontaine D, Deudon A, Lemaire JJ, Razzouk M, Viau P, Darcourt J, Robert P (2013). Symptomatic treatment of memory decline in Alzheimer’s disease by deep brain stimulation: A feastibility study. Journal of Alzheimer’s disease 34:315-323. 5. Gao F, Guo Y, Zhang H, Wang S, Wang J, Wu JM (2009). Anterior thalamic nucleus stimulation modulates regional cerebral metabolism: An FDG-MicroPET study in rats. Neuorbiology of Disease 34:477-483. 6. Hamani C, McAndrews MP, Cohn M, Oh M, Zumsteg D, Shapiro CM, Wennberg RA, Lozano AM (2008). Memory enhancement induced by hypothalamic/fornix deep brain stimulation. Ann Neurol 63:119-123. 7. Hescham S, Lim LW, Jahanshahi A, Steinbusch HWM, Prickaerts J, Blokland A, Temel Y (2013). Deep brain stimulation of the forniceal area enhances memory functions in experimental dementia: The role of stimulation parameters. Brain stimulation 6:72-77. 8. Hirao K, Pontone GM, Smith GW (2014). Molecular imaging of neuropsychiatric symptoms in Alzheimer’s and Parkinson’s disease. Neuroscience and Biobehavioural Reviews 49:157-170. 9. Kuhn J, Hardenacke K, Lenartz D, Gruendler T, Ullsperger M, Bartsch C, Mai JK, Zilles K, Bauer A, Matusch A, Schulz RJ, Noreik M, Buhrle P, Maintz D, Woopen C, Haussermann P, Hellmich M, Klosterkotter J, Wiltfang J, Maarouf M, Freund HJ, Sturm V (2015). Deep brain stimulation of the nucleus basalis of Meynert in Alzheimer’s dementia. Molecular Psychiatry 20:353-360. 10. Laske C, Sohrabi HR, Frost SM, López-de-Ipiña K, Garrard P, Buscema M, Dauwels J, Soekadar SR, Mueller S, Linnemann C, Bridenbaugh SA, Kanagasingam Y, Martins RN, O’Bryant SE (2014). Innovative diagnostic tools for early detection of Alzheimer’s disease. Alzheimers Dement 14:2463-24637. 11. Lyketsos CG, TargumSD, Pendergrass JC, Lozano AM (2012). Deep brain stimulation: A novel strategy for treating Alzheimer’s disease. Innovations in clinical neuroscience 9:10-17. 12. Lozano AM, Lipsman N (2013). Probing and regulating dysfunctional circuits using Deep Brain Stimulation. Neuron Review 77:406-424. 13. Mark RJ, Pang Z, Geddes JW, Uchida K, Mattson MP (1997). Amyloid beta-peptide impairs glucose transport in

hippocampal and cortical neurons: involvement of membrane lipid peroxidation. J Neurosci 17:1046-1054. 14. Mirsaeedi-Farahani K, Halpern CH, Baltuch GH, Wolk DA, Stein SC (2015). Deep brain stimulation for Alzheimer disease: a decision and cost-effectiveness analysis. Advanced online publication. DOI 10.1007/s00415-015-7688-5 15. Nasralla I, Wolk DA (2014). Multimodality imaging of Alzheimer disease and other neurodegenerative dementias. J Nucl Med. 12:2003-2011. 16. Pereira JL, Downes A, Gorgulho A, Patel V, Malkasian D, De Salles A (2014). Alzheimer’s disease: The role for neurosurgery. Surg Neurol Int. 5:385-390. 17. Sankar T, Chakravarty MM, Bescos A, Lara M, Obuchi T, Laxton AW, McAndrews MP, Tang-Wai DF, Workman CI, Smith GS, Lozano AM. Deep Brain Stimulation Influences Brain Structure in Alzheimer’s Disease. Brain Stimulation (2015), doi:10.1016/j.brs.2014.11.020. 18. Shivamurthy VK, Tahari AK, Marcus S, Subramaniam RM (2015). Brain FDG PET and the diagnosis of dementia. AJR Am J Roentgenol 204:76-85. 19. Smith GS, Laxton AW, Tang-Wai DF, McAndrews MP, Diaconescu AO, Workman CI, Lozano AM (2012). Increased cerebral metabolism after 1 year of deep brain stimulation in Alzheimer’s disease. Archives of Neurology 69:1141-1148. 20. Stone SS, Teixeira CM, Devito LM, Zaslavsky K, Josselyn SA, Lozano AM, Frankland PW (2011). Stimulation of entorhinal cortex promotes adult neurogenesis and facilitates spatial memory. J Neurosci 38: 13469-13484. 21. Tramutola A, Triplett C, Di Domenico F, Niedowicz DM, Purphy MP, Coccia R, Perluigi M, Butterfield DA (2015). Alteration of mTOR signalling occurs early in the progression of Alzheimer disease (AD): analysis of brain from subjects with pre-clinical AD, amnestic mild cognitive impairment and late-stage AD. Journal of Neurochemistry 10:1-11. Received April, 01, 01, 2015; accepted

2015; April,

revised 06,

April, 2015.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program

84


The Efficacy of Neurofeedback Training as a Treatment for Attention-Deficit Hyperactivity Disorder Floriana Ferri

The present study examined the efficacy of neurofeedback training in treating attention deficit hyperactivity disorder (ADHD) in children and adolescents by comparing it to the standard pharmacological intervention. Of the 63 recruited participants, 23 participants, 11 boys and 12 girls, were selected and completed the study. Through random selection, half of the participants (N=11) began taking daily doses of methylphenidate (standard medication), while the other half (N=12) completed 40 sessions of neurofeedback (NF) training. According to results in the behavioral rating scales, which were completed by parents and teachers, the participants that received NF training showed significant improvements in inattention, functional impairment, academic performance and overall ADHD symptoms. The improvements were parallel to those receiving methylphenidate, however, only the NF group showed significant improvement in academic performance. These results indicate that NF has the potential to be used as an alternative treatment for ADHD as it leads no side effects and it has an additional advantage of increasing academic performance. Key words: neurofeedback; attention deficit/hyperactivity disorder; children; randomized-control trial; two and six-month follow-up. Background Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that affects close to 5% of children worldwide (Polanczyk, de Lima, Horta, Biederman & Rohde, 2007) making it one of the most common childhood psychiatric disorders (Campbell, 2000). ADHD is also common among adults but remains highly undiagnosed in this segment of the population (Schweitzer, Cummins & Kant, 2001). Some of the core symptoms of ADHD are hyperactivity, impulsivity, inattention and often, but not always, increased executive functioning impairments (Biederman et al., 2004). As a result of these symptoms, children with ADHD often have reduced academic outcomes (Mautone, DuPaul & Jitendra, 2005) and express higher rates of physical and verbal aggression, attention-seeking behavior and non-compliance in comparison with their peers (Junod, DuPaul, Jitendra, Volpe & Cleary, 2006). In addition, children with ADHD are also more likely to be part of the special education program at their school, have to repeat a grade or be expelled or suspended (Klein & Abikoff, 1997). Of the cases that persist into adolescence and adulthood, which is 40-60%, problems such as poor socialization, unsatisfactory academic performance and increased chance of traffic accidents are common (Faraone, Biederman & Mick, 2006). The present-day method for treating ADHD is primarily through pharmaceutical treatments; more specifically, through psychostimulant medications. Psychostimulants are drugs that increase psychomotor activity in the central nervous system and they have shown to be efficacious in reducing symptom severity of ADHD (Schachter, Pham, King, Langford, & Moher, 2001), however, they have also shown to cause adverse side effects (Steiner, Frenette, Rene, Brennan, & Perrin, 2014). According to recent studies, psychostimulant medications are associated with growth suppression (Germinario et al., 2013), decrease of appetite 85

and development of insomnia (Wigal et al, 1997); these effects have been reported to reverse only after discontinuation of treatment (Germinario et al., 2013; Wigal et al., 1997). Additional issues regarding ADHD pharmaceutical treatments include low adherence rates to the medication, as only 13%-64% of the children continue long-term use of the medication (Van de Loo-Neus, Rommelse & Buitelaar, 2011), and incompetency to cure symptoms after long-term use, as symptoms return after treatment discontinuation (Steiner et al., 2014). Additionally, 20-30% of children suffering with ADHD are irresponsive to the available medications, reporting lack of progress during use of treatment (Wigal et al, 1997). These finding raise the importance of finding new efficacious methods of treating ADHD. One such new treatment that is gaining more attention in the research field is neurofeedback. Neurofeedback is an operant conditioning technique that trains people to self-regulate their brain activity through real-time feedback of their neurophysiological signals (Arns, de Ridder, Strehl, Breteler, & Coenen, 2009). The neurophysiological signals are measured using EEG and are presented to the participant in a form of visual or auditory match (game), such as a race or a puzzle. Since previous studies have shown that ADHD is associated with abnormalities in electrophysiology, specifically increased frontal theta wave activity in the brain and decreased beta activity, neurofeedback games are designed to make the participant suppress theta activity and increase beta activity, resulting in reduced inattention and hyperactivity and improved cognitive functioning (Arns et al., 2009). The literature on the efficacy of neurofeedback training to treat ADHD has yet to expand seeing as neurofeedback is a moderately new approach. Some of the primary studies that have examined the efficacy of neurofeedback were weak in that they lacked randomization, adequate blinding of participants,


control treatments, and reliable outcome measures consequently resulting in inconsistent and divisive study outcomes (Lofthouse, Arnold, Hersch, Hurt, & DeBeus, 2011). Taking that into consideration, the studies from the past five years have attempted to control for previous limitations and have found much more statistically significant results. Duric, Assmus, Gundersen and Elgen (2012), performed a randomized and controlled study to evaluate neurofeedback as a treatment for ADHD in children, where 91 children, randomized into three groups, 1/3 receiving methylphenidate (MF) treatment, 1/3 sessions of neurofeedback training and 1/3 receiving both. After completion of the study, as reported by parents, no significant differences between treatment groups were observed, meaning that NF was shown to be as effective as methylphenidate in treating ADHD. In 2014, Duric, Abmus and Elgen, used self-reports to examine the efficacy of NF in children and similarly found that NF was as effective as methylphenidate in improving attention and hyperactivity, however, only NF lead to significant improvement in school performance, which is important to examine further in future studies. Overall, recent studies are strong indicators that NF is a efficacious method of treating ADHD as they have moderate sample sizes, include treatment control conditions and randomization, use self and observation reports to measure outcomes, and control for co-morbidity and concomitant treatments. In spite of these positive effects, these studies lack a long-term post-treatment follow-up assessment, which is why this study aims to evaluate the efficacy of NF in comparison to standard medication, using a randomized and controlled trial with two and sixmonth follow-up. Research Overview

Summary of Major Results

Pre-assessment of participants was conducted one week prior to the study. The participants were selected based on age, sex, IQ and ADHD symptoms and did not differ significantly based on these criteria. Behavioral changes were assessed at pre-treatment (PRE), post-treatment (POST), two-month followup (FU1) and six month follow-up (FU2) using the following standardized measures: ADHD rating scale, Weiss Functional Impairment Rating and Oppositional defiant disorder rating scale. Based on parent reports, the NF group showed significant improvement in ADHD symptoms, functional impairment, inattention and academic performance; the teachers reported moderate and insignificant improvements in those categories. Regarding hyperactivity and oppositional defiant behavior, mother and teachers reported less than moderate improvements. The MPH group, on the other hand, showed significant improvements in ADHD symptoms, including hyperactivity, and inattention and the teachers also reported a significant reduction in oppositional defiant behavior. The MPH group, however, did not show

significant improvement in academic performance by neither parent nor teacher reports. As measured by statistical tests, the most significant difference between the two groups was the change in academic performance. Although assessments showed that the NF group maintained the achieved improvements at FU1 and FU2, after the completion of the study, the parents were free to start medicating their children, and at FU1, 6 of the participants were medicated and at FU2, 8 were medicated.

Fig 1. Changes in Academic Performance scores at pre-treatment (PRE), post-treatment (POST), two-month follow-up (FU1) and six-month follow-up (FU2) for the neurofeedback (NF) versus methylphenidate (MPH) participants

Discussion and Critical Analysis

From the results of this study, neurofeedback training shows to be equally capable of treating primary symptoms and associated functional impairments of ADHD as the standard pharmacological medication. The strength of this study relies on its randomizedcontrolled trial design, in which the efficacy of NF is evaluated through comparison with the current standard treatment for ADHD. As previous studies have simply used placebo-control interventions, this study overcame that limitation by comparing NF to a standard/highly effective treatment, which offers more compelling support for the efficacy of NF as a treatment for ADHD. Importance of this study also includes two naturalistic follow-up assessments, at two and six months following the intervention, use of two groups of evaluators (parents and teachers) and the use of a varying and standardized\behavioral rating scales. These assessments were useful to demonstrate that the progression resulting from NF can be maintained over a period of time as the majority of the NF participants maintained their cognitive improvement and even continued to progress after discontinuation of NF training. Above all, three of the children maintained their progression even six months after the treatment, being able to cope without the use of pharmacological interventions; this suggests that training the brain through an operant-conditioning method can have 86


lasting benefits, in contrast to pharmaceutical interventions, where discontinuation causes full return of symptoms (Steiner et al., 2014). Although this study overcame previous limitations, it also presented a few limitations of its own. The primary limitation of the current study is the small sample size of 27 participants, which decreases the feasibility of the conclusions drawn from this study. As only 12 participants completed the NF training and only 4 remained medication-free at six-month follow-up, it cannot be concluded that the effects of NF training are long-lasting until these effects are shown in larger number of participants. Secondly, this study lacked blinding of participants and assessors in its design, which could indicate that findings of this study are partially a result of performance bias and outcome assessment bias. A 2013 study, for example, found that placebo-neurofeedback was equally effective in treating ADHD symptoms as EEG-neurofeedback (van Dongen-Boomsma, Vollebregt, Slaats-Willemse, & Buitelaar, 2013), showing that motivation and performance bias are capable of affecting the progression acquired from NF training. Thus, it is important for future studies to control for such biases. More importantly, a feasibility study, using a double-blind placebo-controlled design showed that, regarding NF, double-blind studies are not feasible as the reward thresholds have to be manually adjusted, however, blinding of the parents and the children is valuable and should be incorporated into future study designs (Lansbergen, van Dongen-Boomsma, Buitelaar, & Slaats-Willemse, 2011). Thirdly, parent and teacher reports were used as outcome measure, which can be biased and inconclusive; another study justified using parent reports, as they were able to correctly determine the clinical range of the children’s ADHD symptoms (Steiner et al, 2014). In this study, however, the fathers’ reports differed from those of mothers’ and teachers’ in that they detected less behavioral improvements, which shows inadequacy in either observation reports or in the behavioral rating scales. Generally, using parents as proxy respondents has shown to not be very efficacious as parent reports correlate poorly with those of their children (Duric et al. 2014). As other studies such as that of Duric, Aßmus, and Elgen (2014) have used only self-reports to evaluate changes in ADHD symptoms, to increase the validity of the results, it would wise to use of both parent/teacher and selfreports in future studies. Lastly, a critical weakness in this study is the onset of medication use by the participants in the NF group at two and six-month follow-up. Although the gained benefits of NF were maintained in the NF participants according to the behavioral reports, regardless of medication use, it is not clear whether medication helped maintain the progress and whether NF benefits can be maintained after discontinuation of treatment. This does not, however, indicate that NF is less proficient than medication in treating ADHD long-term, as during the follow-up period, the children in the medication group continued their regular pharmaceutical treatment, while those in the NF terminated their treatment. In future studies, the children in the medication 87

group should also cease to continue their treatment during the follow-up period in order to determine whether progression is preserved equally after both interventions.

Conclusions and Future Directions

In conclusion, this study suggests that NF is an effective long-term alternative treatment and also a complementary treatment to medication for treating ADHD, as it enhances cognitive functioning and improves academic performance. Due to the small sample size and medication use during follow-up period, the results from this study should be interpreted carefully until the results are replicated in future studies. A study design necessary to overcome some of the limitation in this study would have to be a randomized single-blind study with a large sample size, and three groups: neurofeedback-placebo group, a pharmacological intervention group and a neurofeedback intervention group. The length of the study would be at least one year, as regulation of brain waves can be time-dependent and attrition rates would be used to indicate lack of efficacy of the interventions. The outcomes would be measured through tests that evaluate attention and impulsivity specifically in the children and not general reports of behavior, while proxy reports by teacher and parents would only be used to support the findings. Factors such as feedback animations and reward thresholds would be maintained in the design as they have shown to be important in encouraging the participants to strive towards achievement of cognitive regulation (Gevensleben et al., 2012) and implementation of active learning strategies to supplement the NF training would be added as recent studies have indicated that learning strategies are important for enhancing the efficacy of NF (Sherlin et al., 2011). Follow-up assessments would be non-naturalistic, where both groups would have the choice of continuing NF training and/or using medication. References 1. Arns, M., de Ridder, S., Strehl, U., Breteler, M., & Coenen, A. (2009). Efficacy of neurofeedback treatment in ADHD: the effects on inattention, impulsivity and hyperactivity: a metaanalysis. Clinical EEG and neuroscience, 40(3), 180-189. 2. Biederman, J., Monuteaux, M. C., Doyle, A. E., Seidman, L. J., Wilens, T. E., Ferrero, F., ... & Faraone, S. V. (2004). Impact of executive function deficits and attention-deficit/ hyperactivity disorder (ADHD) on academic outcomes in children. Journal of consulting and clinical psychology, 72(5), 757. 3. Campbell, Susan B. “Attention-deficit/hyperactivity disorder.” In Handbook of developmental psychopathology, pp. 383-401. Springer US, 2000. 4. Duric, N. S., Aßmus, J., & Elgen, I. B. (2014) Selfreported efficacy of neurofeedback treatment in a clinical randomized controlled study of ADHD children and adolescents. Neuropsychiatric disease and treatment, 10, 1645. 5. Duric, N. S., Assmus, J., Gundersen, D., & Elgen, I.


B. (2012) Neurofeedback for the treatment of children and adolescents with ADHD: a randomized and controlled clinical trial using parental reports. BMC psychiatry, 12(1), 107. 6. Faraone, S. V., Biederman, J., & Mick, E. (2006). The age-dependent decline of attention deficit hyperactivity disorder: a meta-analysis of follow-up studies.Psychological medicine, 36(02), 159-165. 7. Gevensleben, H., Rothenberger, A., Moll, G. H., & Heinrich, H. (2012). Neurofeedback in children with ADHD: Validation and challenges. Expert Review of Neurotherapeutics, 12, 447–460. 8. Germinario, E. A., Arcieri, R., Bonati, M., Zuddas, A., Masi, G., Vella, S., ... & Panei, and the Italian ADHD Regional Reference Centers, P. (2013). Attention-Deficit/ Hyperactivity Disorder Drugs and Growth: An Italian Prospective Observational Study. Journal of child and adolescent psychopharmacology,23(7), 440-447. 9. Junod, R. E. V., DuPaul, G. J., Jitendra, A. K., Volpe, R. J., & Cleary, K. S. (2006). Classroom observations of students with and without ADHD: Differences across types of engagement. Journal of School Psychology, 44(2), 87-104. 10. Klein, R. G., & Abikoff, H. (1997). Behavior therapy and methylphenidate in the treatment of children with ADHD. Journal of Attention Disorders, 2(2), 89-114. 11. Lansbergen, M. M., van Dongen-Boomsma, M., Buitelaar, J. K., & Slaats-Willemse, D. (2011) ADHD and EEGneurofeedback: a double-blind randomized placebo-controlled feasibility study. Journal of Neural Transmission, 118(2), 275-284. 12. Lofthouse, N., Arnold, L. E., Hersch, S., Hurt, E., & DeBeus, R. (2011). A review of neurofeedback treatment for pediatric ADHD. Journal of attention disorders, 1087054711427530. 13. Mautone, J. A., DuPaul, G. J., & Jitendra, A. K. (2005). The effects of computer-assisted instruction on the mathematics performance and classroom behavior of children with ADHD. Journal of Attention Disorders, 9(1), 301-312. 14. Polanczyk, G., de Lima, M. S., Horta, B. L., Biederman, J.,& Rohde, L. A. (2007). The worldwide prevalence of ADHD: a systematic review and metaregression analysis. The American journal of psychiatry, 164(6), 942-948. 15. Schachter, H. M., Pham, B., King, J., Langford, S., & Moher, D. (2001). How efficacious and safe is short-acting methylphenidate for the treatment of attention-deficit disorder in children and adolescents? A meta-analysis. CMAJ: Canadian Medical Association Journal, 165(11), 1475–1488. 16. Schweitzer, J. B., Cummins, T. K., & Kant, C. A. (2001). Attention-deficit/hyperactivity disorder. Medical Clinics of North America, 85(3), 757-777. 17. Sherlin, L. H., Arns, M., Lubar, J., Heinrich, H., Kerson, C., Strehl, U.,et al. (2011). Neurofeedback and basic learning theory: Implications for research and practice. Journal of Neurotherapy, 15, 292–304. 18. Steiner, N. J., Frenette, E. C., Rene, K. M., Brennan, R. T.,& Perrin, E. C. (2014). Neurofeedback and cognitive attention training for children with attention-deficit hyperactivity disorder in schools. Journal of Developmental & Behavioral Pediatrics, 35(1), 18-27.v

19. an de Loo-Neus, G. H., Rommelse, N., & Buitelaar, J. K. (2011). To stop or not to stop? How long should medication treatment of attention-deficit hyperactivity disorder be extended?. European Neuropsychopharmacology, 21(8), 584-599. 20. van Dongen-Boomsma, M., Vollebregt, M. A., SlaatsWillemse, D., & Buitelaar, J. K. (2013). A randomized placebo-controlled trial of electroencephalographic (EEG) neurofeedback in children with attention-deficit/hyperactivity disorder. J. Clin. Psychiatry, 74, 821-827. 21. Wigal, T., Swanson, J. M., Regino, R., Lerner, M. A., Soliman, I., Steinhoff, K., ... & Wigal, S. B. (1999). Stimulant medications for the treatment of ADHD: Efficacy and limitations. Mental Retardation and Developmental Disabilities Research Reviews, 5(3), 215-224.

Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program

88


Review of Intentional and Incidental forgetting Chantel George

Rizio & Dennis (2013) studies cognitive processes involved in encoding and maintaining information. Specifically, the neural correlates and cognitive processes existing for incidental and intentional forgetting are under question. It is hypothesized that incidental forgetting is involved in encoding attempts whereas intentional forgetting is involved in inhibitory processes and as a result, have different brain activity. A directed forgetting paradigm is used to acquire intentional and incidental forgetting in participants. .An MRI is also used to visualize the brain regions that show activity during incidental and intentional forgetting. Results indicate that intentional forgetting in participants is involved with right parietal cortex activity, prefrontal cortex activity and less medial temporal lobe activity. Furthermore, incidental forgetting is involved with more activity in the left inferior frontal gyrus, left superior frontal gyrus, early visual cortex, and left superior parietal lobe.Therefore, intentional and incidental forgetting are two separate processes with different neural correlates. Further research is discussed in order to advance knowledge of forgetting and ultimately the control of cognitive processes and memory. Background Rizio & Dennis (2013) studies neural activity and processes occurring during remembering and forgetting. The neural activity expressed during forgetting is essential to understanding cognitive processes involved in the encoding and maintenance of information in the brain. The two types of forgetting are incidental and intentional forgetting. The difference between intentional and incidental regarding neural activity. Concrete evidence of activity in certain parts of the brain for intentional forgetting and different activity for incidental forgetting is needed. It is questionable whether incidental forgetting is related to intentional forgetting in the sense that both follow the same neural processes or if both adopt different neural activity. Rizio & Dennis (2013) proposes that if they have different neural activity, incidental forgetting should adopt neural activity involved in the inadequacy of encoding information and intentional forgetting should adopt neural activity involved in control and suppression. Many studies have shown that the prefrontal cortex (PFC) is associated with inhibitory cognitive processes and control. Depue et al., (2007) shows that there is increased PFC activity and decreased hippocampus activity when analyzing participants trying to subdue emotional memories. Anderson et al., (2004) also found that when analyzing neural correlates of participants trying to suppress undesired memories, there was more prefrontal cortex activity and less hippocampus activity. In addition, Benoit & Anderson (2012) used FMRI imaging to investigate neural correlates underlying intentional forgetting and found that there was an increase in PFC as well. Berkman et al., (2009) study investigates the intentional forgetting of emotional stimuli and found more prefrontal cortex activity and less amygdala activity. Regarding the encoding of information, Dougal et al., (2007) illustrates that the medial temporal lobe (MTL) plays an important role. When using an FMRI to measure brain activity in participants encoding information, the MTL activity was shown significantly.. Although neural correlates underlying cognitive encoding and inhibition is observed, the connection to 89

incidental and intentional forgetting is uncertain. Rizio & Dennis (2013) seeks more concrete evidence of the PFC activity and MTL suppression through imaging. Therefore if incidental and intentional forgetting stimulate different cognitive processes, incidental forgetting should have more prefrontal cortex and MTL activity. Alternatively, intentional forgetting should have more prefrontal cortex and parietal lobe activity. Dennis et al explores the neural correlates underlying intentional forgetting and incidental forgetting. As a result, the role of MTL, parietal lobe and prefrontal cortex in the context of memory is investigated. Research Overview SUMMARY OF MAJOR RESULTS Neural activity in intentional and incidental forgetting To prompt intentional and incidental forgetting, Rizio & Dennis (2013) use a directed forgetting paradigm was executed with participants from18-26 years of age. In the first stage, participants were instructed to either forget or remember words that were presented to them. Then, there was a distraction task. Lastly, there was a retrieval stage in which participants informed whether they recalled words that were presented to them. The words included old words from the first stage and new words that they were not shown before. The retrieval stage indicated whether words were intentionally forgotten or incidentally forgotten. A word was deemed intentionally forgotten if it was directed to be forgotten in the first stage and was not recalled in the third stage. A word was deemed incidentally forgotten if participant was told to remember it in the first stage but they ended up forgetting it in the third stage. An MRI scanner was utilised in order to show what brain regions were active during incidental and intentional forgetting. The right parietal cortex and prefrontal cortex is active during intentional forgetting. During incidental forgetting, the left inferior frontal gyrus, left superior frontal gyrus, early visual cortex, and left superior parietal lobe are shown to have more activity. In addition, there is an increase


in prefrontal cortex activity and a decrease in medial temporal lobe activity during intentional forgetting suggesting inhibition by the prefrontal cortex. On the contrary, there is no such inhibition by the prefrontal cortex activity suppressing medial temporal lobe activity during incidental forgetting.

Image from: Dennis, N. A., Rizio, A. A. (2013). The Neural Correlates of Cognitive Control: Successful Remembering and Intentional Forgetting. Journal of Cognitive Neuroscience, 25(2), pp. 297-312. Figure 1. shows neural correlates in incidental and intentional forgetting

Conclusions and Discussion Rizio & Dennis (2013) et al reveals that memory inhibition and memory loss entail different neural pathways depending on whether memories are incidentally or intentionally forgotten. The hypothesis that incidental and intentional forgetting are separate and have different underlying neural activity is evident. The right parietal cortex and prefrontal cortex activity are shown to be involved in cognitive control and therefore are seen to be active during processes that allow one to control memory such as intentional forgetting. Since there a decrease in MTL activity and an increase in PFC activity during intentional forgetting, it suggests that an inhibitory processes may be in place in which PFC has an inhibitory role of suppressing MTL activity. In contrast, results indicate that incidental forgetting is the consequence of the aim but lack of success in encoding information.

Criticisms and Future Directions

Although Rizio & Dennis (2013)) provides substantial evidence of incidental and intentional forgetting being two different processes, further considerations can be made to improve research on the cognitive manipulation of memory. Rizio & Dennis (2013) studied participants between the ages of 18 and 26. Studying other age groups aids in the understanding of the control of memory regarding intentional and incidental forgetting. Rizio & Dennis (2013) observes intentional forgetting for young and middle age adults as well as the elderly. Results show that younger adults have more prefrontal cortex activity during intentional forgetting. Hence, age makes a difference

when observing neural correlates in forgetting and should be considered in future research. Another important variable that may affect results is the amount of attention allocated to the memory task. Chiu (2014) uses probes to serve as stimuli during a memory test in order to observe its affect on oneâ&#x20AC;&#x2122;s ability to control memory. It is done in order to assess any trade offs for cognitive resources. In another study, Fawcett(2011) uses a directed forgetting and remembering task and then a task involving the recognition of colours to observe how fast participants were able to respond. Results show that after participants were directed to voluntarily forget a word, they were slower at recognising colours during the second task. This suggests that there intentional forgetting may use cognitive resources in attempt to control working memory. Regarding the directed forgetting paradigm initiated in Rizio & Dennis (2013), it gives rise to the question of cognitive resources and if there are trade offs between attention to oneâ&#x20AC;&#x2122;s surroundings and forgetting. Rizio & Dennis (2013) did not test for differences in gender for intentional and incidental forgetting. Yang (2013) observes the affect of female and male voice on directed forgetting and memory. Thus, listening to words being verbally spoken instead of just being shown may have an affect on incidental and intentional forgetting and should be included in further studies. In addition, a test for gender differences in forgetting is beneficial. Rizio & Dennis (2013) did not explain the affect of timing on intentional and incidental forgetting. Mcgregor (2014) studies the recollection of memories over a 24 hour period. This brings into question the role of timing of recognition in the current study. By testing different time periods participants are given to make a decision as to whether they recall or do not recall a word will aid with observing the role of timing in recollection. For the directed forgetting paradigm, Rizio & Dennis (2013) chose words randomly from a medical database. Things brings into question the types of words chosen for the directed forgetting paradigm. Sahakyan (2008) tests the strength of words in intentional forgetting. Specifically, word strength was primed by associating words with a positive emotion in comparison to other words, allotting more time to process some words but not others, and allowing some words to be repeated over some time in comparison to some words being repeated consecutively. The current study can be improved by incorporating the strength of words and the affect strong and weak words it has on the ability to intentionally and incidentally forget. Festini(2013) tests for the familiarity of words and the ability to intentionally forget. Festini(2013) notes that information learned in the past(familiar information) can interfere with the learning of new material. Therefore, further studies should be initiated in order to test the affect of familiarity on intentional and incidental forgetting by using a memory test inducing familiar words and a test to recall them. The affect of emotion on intentional and incidental forgetting is not addressed in the Rizio(2013) study. Maddock (2009) reveals the importance of emotion 90


in memory as results show that words associated with positivity are increased in spatial and temporal memory and are recalled more in comparison to words associated with negativity. In addition, Padovani (2011) studies memory by presenting words that encourage emotional responses and feelings. Therefore, along with studying neutral words, an experiment using emotional words can aid in elucidating the affect of emotion on incidental and intentional forgetting. Learning about memory control helps with one’s understanding of memory control. However, the next step can to be to learn more and apply the knowledge in issues today. One way would be to apply knowledge about forgetting to post traumatic disorders so that memory control involved in traumatic experiences can be understood. Trauma involves occurrences that result in negative and shocking emotions. Bailey (2012) study reveals that participants have more difficulty with forgetting emotionally driven words because emotions hinder ones cognitive ability to control memories. Zwissler (2012) investigates intentional forgetting in Post traumatic stress disorder patients. Findings show that patients exhibit less intentional forgetting. Therefore, more research on intentional and incidental forgetting may facilitate a better understanding of memory and existing issues such as post traumatic stress disorder. References 1. Bailey (2012). When can we choose to forget? An ERP study into item-method directed forgetting of emotional words 2. Chiu, C., Egner, T. (2014). Inhibition-Induced Forgetting: When More Control Leads to Less Memory. Psychological science, 26(1), pp.27-38. 3. Padovani, T., Koenig, T., Brandeis, D., Perrig, W. T. (2011). Different Brain Activities Predict Retrieval Success during Emotional and Semantic Encoding. Journal of Cognitive Neuroscience, 23(12), pp. 4008–4021. 4. Rizio, A. A., Dennis, N. (2013). The Neural Correlates of Cognitive Control: Successful Remembering and Intentional Forgetting. Journal of Cognitive Neuroscience, 25(2), pp. 297-312. 5. Dennis, N. A., Rizio, A. A. (2013). The Neural Correlates of Cognitive Control: Successful Remembering and Intentional Forgetting. Journal of Cognitive Neuroscience, 25(2), pp. 297-312. 6. Depue, B. E., Curran, T., & Banich, M.T. (2007). Prefrontal regions orchestrate suppression of emotional memories via a two-phase process. Science, 317, 215-219. 7. Fawcett & Taylor(2012). The control of working memory resources in intentional forgetting: Evidence from incidental probe word recognition 8. Festini (2013)Cognitive control of familiarity: Directed forgetting reduces proactive interference in working memory. 9. Maddock (2009). Reduced memory for the spatial and temporal context of unpleasant words 10. Mcgregor (2014). What a Difference a Day Makes: Change in Memory for Newly Learned Word Forms Over 24 Hours 91

11. Anderson, M. C., Ochsner, K. N., Kuhl, B., Cooper, J., Robertson, E., Gabrieli, S.W., et al (2004). Neural systems underlying the suppression of unwanted memories. Science, 303, 232-235. 12. Benoit, R. G., & Anderson, M. C., (2012). Opposing Mechanisms support the voluntary forgetting of unwanted memories. Neuron 76, 450–460. 13. Berkman, E. T., Burkland L., Lieberman M. D. (2009). Inhibitory spillover: Intentional motor inhibition produces incidental limbic inhibition via right inferior frontal cortex. NeuroImage 47, 705–712. 14. Dougal S., Phelps E. A., & Davachi, L. (2007)/ The role of medial temporal lobe in item recognition and source recollection of emotional stimuli . Cognitive, Affective, & Behavioral Neuroscience 7 (3), 233-242. 15. Sahayakan (2008). Intentional Forgetting Is Easier After Two “Shots” Than One. 16. Rizio, A., & Dennis, N. (2014). The Cognitive Control of Memory: Age Differences in the Neural Correlates of Successful Remembering and Intentional Forgetting. PLoS ONE, 9(1), pp. 1-12. 17. Yang, Sujin & Gih0 (2013). Her Voice Lingers on and Her Memory Is Strategic: Effects of Gender on Directed Forgetting 18. Zwissler (2012). Memory control in post-traumatic stress disorder: evidence from item method directed forgetting in civil war victims in Northern Uganda

Received Month, ##, 200#; revised ##, 200#; accepted Month, ##,

Month, 2013.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program


Narrowing It Down to One Locus, to One Chromatin Remodeling by G9a David Giang

Chronic stress and drug addiction have been known to modify the transcription factors of both rodents and humans. The process of histone post-translational modification achieves this, which will either allow for up-regulation or down-regulation of a gene expression of specific transcription factors. However, specificity of locus causality to the observed behaviour plasticity was poorly understood, due to the nature of genome-wide epigenetic modifications and chromatin remodeling. With the uses of engineered transcription factor and the novelty of using them in vivo, the ΔFosB transcription factor was one of the many candidates that can be investigated in detail of their direct contribution and their possible molecular mechanism. It is suggested that the ΔFosB may play a role in a feed-forward loop that stabilizes the ΔFosB levels by phosphorylation by CaMKII. Other proposed mechanism involves the levels of CREB being phosphorylated by the downstream action of the ΔFosB. In hopes to be applied in a clinical setting, the use of engineered transcription factors shows promising future in neuropsychiatric treatment, as well as generalizing to possible gene therapy of other neurological disorders by epigenetic approach. Background Drug addiction and stress have been recognized to cause changes within the human genomes, which have been correlated with the change in baseline levels of transcription factors. The regulations of these transcription factors consist of either an increase levels from activation or decrease levels from repressive mechanisms. One fundamental way to regulate the transcription factors responsible for the behaviour plasticity we observed is due to epigenetic changes at the sites of crucial gene loci.1 Drug abuse, such as repeated cocaine administration, and stress are environmental factors that can result the respective behaviours of addiction and stress-evoked depression.1,2 The main determinant of the penetrance of causing these behaviours is the amount of histone modifications associated on the gene of interest from drug or stress induction.1,2 As a result, one main focus for epigenetic for addiction and depression is the role of chromatin remodeling in their corresponding pathways and which genes and enzymes are involved.2,4 The focus of this study is the action of the main enzyme is the histone methyltransferase is the G9a enzyme, which dimethylize on histone 3, lysine 9 (H2K9me2) and the FosB gene.3,4 In particular, the FosB and its splice variants ΔFosB transcription factor have been found to play an important in the behaviour plasticity in cocaine addiction. When cocaine is administrated, the ΔFosB transcription factor is induced and overaccumulation of ΔFosB in the nucleus accumbens (NAc) leads to increase locomotor sensitivity, consistent with cocaine addiction.1,4,5 The molecular mechanism proposed was that CaMKIIalpha was stabilizing the ΔFosB after the induction of CaMKIIalpha gene expression by ΔFosB.2 This feed-forward loop allows for the stabilization of ΔFosB and the addictive behaviour observed. Additionally, stress-evoked depression and chronic stress were both shown to exhibit reduced Fosb/ ΔFosB levels in humans and rodents1,2 Ultimately, ΔFosB plays a key role in both of these reward behaviours.

However, these inferences were made under the limitation that the epigenetic modifications were done on a global genome level.5 Many loci are affected simultaneously by epigenetic changes, so a causal relationship of a certain histone modification on a specific gene cannot be translated into the observed behaviours of humans and rodents. In order to bypass this problem, the authors of this article plan to utilize zinc-finger proteins (ZFP) to act on specific site on the genome when fused with the G9a catalytic subunits.3,6 ZFP are transcription factors that can provide a means to regulate certain loci in the genome. When fused with a catalytic subunit, the preferential histone modification may occur at the locus of interest. In addition, transcription activator-like effectors (TALEs) were also used in order to allow for increased level of gene expression by histone acetylation. ZFPs and TALEs, even though are engineered transcription factors to enhance specificity and proof on epigenetic changes, were not used,in an intact biological context in retrospect.1 Therefore, the goal of this study is to obtain this specificity in an in vivo setting for locusspecific epigenetic causality, using these bidirectional transcription factors. Research Overview

Summary of Major Results

The experiment conducted for this article consisted of the rodent model of mice, injecting the viral vectors at the site of the NAc. A control virus was used, as well as saline to control for the cocaine injections. Two series of models were used for each behaviour plasticity. For addiction, repeated cocaine treatment was given with the intention of a sensitizing treatment or a subthreshold treatment. The difference between the two is that the mice with the subthreshold treatment will not have the locomotor sensitivity that the sensitizing treatment will have, but are more susceptible 92


than the control mice without either dosing. The mice were then transfected with a herpes simplex virus (HSV) that have either a ZFP or TALE transcription factors that binds to the Fosb gene, as well the G9a methyltransferase catalytic subunit or the p65 catalytic subunit, which is responsible of activating transcription by histone acetylation. A non-functional domain (NFD) was also incorporated in order to control for the catalytic domain’s presence being sufficient to cause ΔFosB-dependant behaviours.

TALEs and underwent a chronic social defeat stress, leaving the mice in a subthreshold social stress. It was observed that the mice infected with HSV-FosbZFP35-G9a have a reduction in social interaction, as well as less time in the open arms of the elevated plus maze. These indicate increased anxiety and depression-like behaviour responses in comparison to the control virus. These results observed from this study were consistent on other publications’ result on the association that ΔFosB has in the roles of these reward behaviours. The authors were able to obtain the expected result from H3K9me2 on the Fosb gene, where overexpression of this histone modification leads to blocking locomotor sensitivity or stress-evoked depression. On the other hand, transcriptional activation of VP64 and p65 subunits overexpressed ΔFosB and Fosb when the analyzing mRNA levels by quantitative reverse transcription PCR. Conclusions and Discussion

(Heller E.A. et al, 2014) Figure A & B– Schematic setup for the experiment of mice that were infected with the ZFP-p64 (“On”), as well as ZFP-TALE1v64 (“On”) or ZFP-G9a (“Off”). NFD strain is representing a ZFP with no functional domain. Figure C – The locomotion shown in the rats, where elevated locomotion were found a trend between days and the high cocaine dose for figure C. Figure D - The low dose of cocaine that is subthreshold (cause no locomotion for normal mice with this cocaine dose) It was observed that enhanced locomotion from day 4 to day 16, and indication of a trend of dose and days. Both high dose and low dose cocaine treatment can be blocked by ZFP-G9a injection. Figure E – Control ZFP with NFD strain Figure G to J – Shows the depression behaviour of the mice that were injected with H3K9me2 enrichment. Decrease in social interaction and exploration of open arm maze.

When the mice were injected with an HSV-FosbZFP35-G9a, it was found that its expression was proficient to block cocaine locomotor sensitivity. On the other hand, HSV-fosb-ZFP35-p65 and HSVTALE1-VP64, another activator catalytic subunit were able to increase the sensitivity of the locomotion, indicating a more heightened response and susceptibility to cocaine addiction. The findings in this study indicate that an increase in G9a activity can prevent locomotion sensitivity, while activating the ΔFosB gene will augment the sensitization of cocaine. Heat maps and the amount of beam break counts measured the results observed above. For measuring stress-evoked depression in the mice that were transfected with the same sets of ZFP and 93

The authors were able to confidently display how a locus-specific interaction was able to regulate the behaviour plasticity of the mice that would normally show either resilience to depression or increased locomotor activity that is consistent with repeated cocaine administration.1,7,8 In order to establish the efficacy of engineered transcription factors, ZFP and TALE were used to target the ΔFosB gene. Since the function of ΔFosB in addiction and depression is well understood, it is clear that the epigenetic changes on a single locus is causing the behaviour changes observed and not any other factors, such as a confound phenomenon controlled from using the FosB gene or any technical confounds. These confounds, such as the administration of an injection, a catalytic subunit, or the use of HSV lead to the results that are observed. In addition, 28 off-target genes were also observed to control for ΔFosB expression in the NAc having adverse effects. Other related histone modifications were investigated, such as other methylations within the same histone, in order to establish the mechanism of action by the G9a subunit. The authors believe that the results they have received can only be explained from the G9a subunit activities acting on the H3K9 site of the Fosb gene promoter, where it is only this one kind of histone modification and one locus of the genome. It was a fairly clean experiment, where all confounds that can arise in an in vivo setting can skew the results were controlled for, from the mechanism of action by the enzyme to the techniques of transfection. Overall, this ruled out any data obtained stochastically. A possible molecular mechanism that may result from the H3K9me2 that the authors presented is that it involves the molecule CREB.1,9 H3K9me2 is believed to prevent the phosphorylation of the CREB at the Fosb gene, preventing further expression of ΔFosB and Fosb proteins alike. This was observed in the qChIP analysis, where cocainetreated mice had a 3.9-fold increase in phosphor-CREB levels when compare to the saline injection and did not affect total number of CREB or increased CREB binding. This suggest that the M3K9me2 is only specific to halting phosphorylation of CREB, in turn leading to ΔFosB levels to be blocked and causing the observed reward behav-


iours that are expected with this gene. The significance of this paper was one of the first innovators in the field to use engineered transcription factors as a way to alter the behavioural plasticity in depression and addiction. Epigenetic have been a field for how gene regulation can impact human health from a neuropsychiatric stand point, but were not able to obtain any possible causality due to the limits of global chromatin remodelling that can occur. By utilizing ZFP and TALE, the ΔFosB gene was well regulated by H3K9me2 or activation.1,5,7 This suggests that the novel use of single locus regulation can not only help study the epigenetic basis of addiction and depression better, but also be able to impact the treatment for these neuropsychiatric disorders. The impact this paper has shown is the possibility that the future of gene therapy is possible and that may have hopes of generalizing this approach to other diseases with a epigenetic basis.

Criticisms and Future Directions

As mentioned earlier, the paper was able to successfully present that a single locus that is regulated by epigenetic mechanisms play a role in addiction and depression behaviour. However, being a novel field in using engineered transcription factor in an intact biological context, more insight will be required to determine whether or not they will be sufficient enough to be used in a clinical setting. Also, the data were based off of repeated cocaine administration in the mice but any indications for acute drug administration were not investigated. ΔFosB have been recognized by other literatures as the molecule switch for addiction. To appropriate evaluate the role of ΔFosB requires fine regulation of the gene promotion, which have became possible from the revolution of this method. The use of injecting HSV vector virus may not be the only virus that should be used, as it has its own limitations. Therefore AAV and other virus to use as a vector should be considered. In addition to the experiment, mice were put under the chronic stress model that involved an aggressor. That is a fear-based response and is too simple compare to the kind of depression a human may face from losing a loved one or undergoing meaninglessness in their everyday life. This may involve different mechanisms since the response to anger and tragedies do have variable differences. In addition, elevated plus maze was the only model to measure the mice for depression based off of their will to explore, but did not cover any other aspects of depression such as their lost of appetite or possible cortisol measurement to determine if it was truly stress-dependent. Overall, stress-evoked depression was not covered as explicitly as cocaine-addiction and further works to conduct in chronic stress could lead to a better understanding. Other future directions this paper should consider would be to investigate other gene targets in the genome in this locus-specific manner in order to see its relevance in other fields of neuropsychiatric treatment. For example, HDAC2 has been found to be affecting the responses in antipsychotic treatment. By being able to regulate the expression of the mGluR2 promoter activity, this may lead to increase efficacy of antipsychotic drug treatment,

yielding better response and aspiring for a bright future in clinical treatment for schizophrenia.10,11 In addition to HDAC2 as an epigenetic approach to target gene, stress and depression can also be regulated from another pathway involving the epigenetic changes in RAC1.11,12, Though the evidence for this is recent, this publication was carried out under the limitation of multiple genome-wide epigenetic.13 By applying the same use of engineered transcription factors, it may bring more insight into the synaptic remodelling that occurs in this other gene involved in stress evoked depression.14,15 References 1. Heller, E.A. et al. Locus-specific epigenetic remodeling controls addiction- and depression-related behaviours. Nat. Neurosci. 17, 1720-1727 (2014). 2. Robison, A.J. et al. Behavioural and structural responses to chronic cocaine requires a feedforward loop involving ΔFosB and calcium calmodulin-dependent protein kinase II in nucleus accumbens shell. J. Neurosci. 33, 4295-4307 (2013). 3. McNamara, A.R. et al. Zinc finger protein targeted epigenetic gene regulation toward direct long-term gene control. Mol. Ther. 9, S123-s124 4. Maze, I. et al. Essential role of the histone methyltransferase in cocaine-induced plasticity. Science. 327,213-216 (2010). 5. Shinkai, Y. & Tachibana, M. H3K9 methyltransferase G9a and the related molecule GLP. Genes Dev. 25, 781-788. (2011) 6. Kelly, M.A. et al. Locomotor activity in D2 dopamine receptor-deficient mice is determine by gene dosage, genetic background and developmental adaptation. J. Neurosci. 18, 3470-3479. (1998) 7. Oh S-T. et al. H3K9 histone methyltransferase G9a-mediated transcriptional activation of p21. FEBS Letters. 588, 685-691. (2014) 8. Rice, C.J. et al. Histone methyltransferase direct different degrees of methylation to define distinct chromatin domains. Mol. Cell 12, 1591-1598. (2003) 9. An essential role for ΔFosb in the nucleus accumbens in morphine action. Zachariou, V. et al. Nat. Neurosci. 9, 205-211. (2006). 10. HDAC2 regulates atypical antipsychotic responses through the modulation of mGlu2 promotor activity. Kurita, M. et al. Nat. Neurosci. 17, 1245-1254. (2012). 11. Epigenetic regulation of RAC1 induces synaptic remodeling in stress disorders and depression. Golden, S.A. et al. Nat. Med. 19, 337-344. (2013). 12. Hyman, S.E. Target practice: HDAC inhibitors for schizophrenia. Nat Neurosci. 15, 1180-1181. (2012). 13. Damez-Werno, D. et al. Drug experience epigenetically primes Fosb gene inducibility in rat nucleus. J. Neurosci. 32, 10267-10272. (2012). 14. Nestler, E.J. et al. FosB: a sustained molecular switch for addiction. PNAS. 98, 11042-11052. (2001) 15. Garcia-Perez et al. Glucocorticoids regulation of Fosb/ ΔFosb expression induced by chronic opiate exposure in the brain stress system. PLoS ONE. 9, 1-13. (2012) 94


The Novel Role of mTOR-Dependent Macroautophagy in Autism Spectrum Disorder Jessica Gosio

Autism spectrum disorders (ASD) is characterized by deficits in cognitive abilities including communication skills, social interactions, and emotional control, and yet is poorly understood at a biological level. One common characteristic of the disorder is aberrant excessive cortical dendritic spine growth and reduced pruning of postsynaptic glutamatergic synapses. Tang et al. hypothesize mutations in genes that inhibit the mammalian target of rapamycin (mTOR) kinase to be linked to ASD, as overactive mTOR is thought to lead to excessive synaptic protein synthesis. mTOR also acts downstream to inhibit macroautophagy (autophagy) – a process involved in neuronal pruning. They found that the hyperactivity of mTOR lead to reduced autophagy and loss of autophagy caused increased spine densities in late postnatal development in ASD-model mice. The findings by Tang et al. enhance the understanding of ASD at a cellular level thereby providing molecular targets for novel therapeutics, as well as establish a foundation upon which future ASD research may be conducted. Key words: Autism Spectrum Disorder (ASD); mammalian target of rapamycin kinase (mTOR); rapamycin; autophagy; TSC2; synaptic pruning; dendritic spines Background Autism spectrum disorders (ASDs) are characterized by cognitive and social deficits, as well as aberrant changes in cortical size. Structural differences in the cortices of ASD patients have been hypothesized to play a role in the behavioral phenotypes observed. In non-ASD subjects, synapse formation and high dendritic spine densities are found early in human development and are balanced with protein degradation creating a reduction in spine density and increased synaptic pruning during childhood and adulthood (Penzes, Cahill, Jones, VanLeeuwen, & Woolfrey, 2011) in order to maintain homeostasis (Purves & Lichtman, 1980). In ASD patients, these processes are disrupted, resulting in increased spine density in excitatory pyramidal cells of the frontal, parietal, and particularly strong increase found in cells of the temporal lobe (Hutsler & Zhang, 2010), thought to be due to decreased synaptic pruning (Zhan et al., 2014). These changes create the differences in cortical size reported in ASD subjects, as well as provide structural evidence that may explain earlier reported anomalous changes in brain circuitry connections(Belmonte et al., 2004), as synaptic pruning and spine density reductions are critical for correct formation of synaptic circuits in a developing brain. Further investigation is required to understand the importance of spines and pruning in the onset and progression of ASD. Although only a small proportion of ASDs are due to known genetic mutations, some cases with genetic origin are caused by mutations in Tsc1/Tsc2 - genes that normally act to inhibit the mammalian target of rapamycin (mTOR) kinase (Bourgeron, 2009). mTOR is a regulator of cell growth and activates protein synthesis at the synapse (S. J. Tang et al., 2002). It has been found to be associated with proteins found in neuronal synapses and dendritic spines, such as Shank (Peça & Feng, 2012), a protein that has recently been reported to share a protein binding partner with Tsc1/Tsc2 at neuronal 95

synapses (Sakai et al., 2011), connecting two molecular pathways related to ASD (Peça & Feng, 2012). It is predicted that overactive mTOR signaling due to described mutations in mTOR-inhibitory genes results in excessive synaptic protein synthesis observed in ASD. ASD, though, is also associated with decreased synaptic pruning – a process involving synaptic protein degradation and therefore macroautophagy (also referred to as autophagy) – the removal of damaged or degraded proteins in a cell. mTOR lies upstream of autophagy and acts to inhibit its processes (Kim, Kundu, Viollet, & Guan, 2011). It can be inferred then that loss of mTOR inhibition also leads to strong inhibition of autophagy. Tang et al. therefore predicted that mTOR-dependent autophagy coupled with mTOR over-activity is responsible for the reduction in synaptic pruning and increase in dendritic spine production observed in ASD subjects (G. Tang et al., 2014). Evidence supporting this new theory of ASD stems from previous studies of tuberous sclerosis model mice where heterogeneous inactivation of their Tsc2 gene (Tsc2+/-) showed deficits of learning and memory related to mTOR hyperactivity, and rapamycin administration (an inhibitor of mTOR kinase) reversed learning and behavioral deficits observed in the mice (Ehninger et al., 2008). ASD behavioralphenotypes have not been assessed in this paradigm, though autism and tuberous sclerosis are both functionally related to mutations in the mTOR pathway (García-Peñas & Carreras-Sááez, 2013). Few studies have assessed autophagy in relation to ASD, but a recent study identified ASD-related mutations in genes encoding proteins for autophagy processes (Poultney et al., 2013). Autophagy, however, has been assessed in synaptic remodeling paradigms involving C. elegans (Rowland, Richmond, Olsen, Hall, & Bamber, 2006) and Drosophila (Shen & Ganetzky, 2009), but never in a developing mammalian model system. Tang et al. therefore tested their hypothesis, and found mTOR-dependent autophagy to be required for correct synaptic pruning and spine


growth in the brains of developing mice, and mTOR over-expression to underlie ASD behavioral and physical pathologies. Research Overview

Summary of Major Results

Dendritic spine pruning deficits in temporal lobe of human ASD patients compared to controls

Tang et al. began by confirming previously reported increased dendritic spine density in layer V pyramidal neurons of the superior middle temporal lobe from the brains of post-mortem ASD patients, an area known for its participation in social and communication networks in the brain. They also found ASD patients displayed greater dendritic spine density throughout later stages of life, in-line with predicted reduced spine reduction throughout development (Fig 1a, b).

Figure 1. a) Representative Golgi images of human temporal lobe for two control subjects (C = aged 8 years and 18 years) and 2 ASD subjects (A = aged 7 years and 15 years). Images depict a greater density of basal dendritic spines found in layer V of the human temporal lobe. b) Linear regression displaying increasing spine density between child and adolescent autistic patients (n=10) compared to controls (n=10). (G. Tang et al., 2014).

Tsc-deficient mouse models of ASD displayed spinepruning defects

Using Tsc2+/- mutated mice, since Tsc1 and Tsc2 mutations lead to mTOR-hyperactivation and ASD-like behaviors in mice (cite pg 1133 of paper), behavioral assays were performed to determine if mice displayed ASD-phenotypes. Tsc2+/- mice were found to display reduced social preference in a novel object recognition test compared to wild-type mice, later confirmed with a three-chamber social test, but ASD repetitive behaviors were not observed. Researchers then assessed

the cellular phenotypes of the mutated mice, finding a substantial amount of spine pruning between post-natal days (P)19-(P)20 and P29-P30 in wild-type mice, and a lack of this normal developmental pruning in Tsc2+/- mice. These increased dendritic spine density in later stages of life of Tsc2+/- mice are similar to patterns observed in human ASD subjects (Fig 2a,b). Tsc2+/- mice were further administered rapamycin as an mTOR antagonist, with similar inhibitory activity as the functional Tsc2 gene, and found similar dendritic spine morphologies as Tsc2+/+ wild-type mice and no effects on these control mice as predicted (Fig 2b). This result, in combination with earlier behavioral data suggests Tsc2+/- mice can be used as an ASD model organism as its behavioral and cellular phenotypes recapitulate those observed in human ASD subjects. Rapamycin only decreased spine density in later stages of development; therefore its effects on spine pruning represented both early and late non-ASD mouse development (Fig 1b, 2b), suggesting the importance of mTOR inhibition in mammalian cortical development.

Figure 2. a) Confocal images of increased dendritic spine density in Tsc2+/- mice and reduce pruning between postnatal day 20-21 and 29-30. Reduced spine pruning was corrected to control levels with administration of rapamycin (Rapa). Scale bar, 2 um. b) Linear regression representing (a), n=7-10 mice per group, **compared with wildtype at P29-P30, p < 0.01 (two-way ANOVA). (G. Tang et al., 2014).

Impaired autophagy due to mTOR disinhibition underlies neuronal spine pruning defects in ASD-model mice with mutated Tsc2+/ Tang et al. could now begin to assess their prediction of a Tsc2/mTOR pathway controlling autophagy required for the pruning at synapses in their ASD-model mice. A western blot revealed highest mTOR activity in Tsc2+/- compared to 96


wild-type mice, and also found a strong reduction in synthesis of proteins involved in autophagy (Fig 3a), as predicted by the researchers. To further determine if autophagy is required for correct spine pruning in temporal lobe pyramidal neurons and if autophagy deficiency underlies ASD spine pruning pathology, autophagy knockout mice (Atg7CKO) coupled with mice over-expressing mTOR (Tsc2+/-) were compared to control mice (Tsc2+/+; Atg7flox/flox) (Fig 3b, c). Controls depicted typical early high spine density followed by a reduction in spine density later in development, and no differences were observed upon rapamycin administration for controls, and no ASDlike behaviors observed upon testing of sociability and social novelty in a three-chamber test (behavioral data figures not included). Tsc2+/-; Atg7flox/flox mice with functioning autophagy, were found to produce ASD-like spine densities that were corrected with rapamycin administration, similar to results in Fig 2b, and displayed ASD-behavioral phenotypes corrected to those of controls after rapamycin. Both Tsc2+/+ and Tsc2+/- mice with Atg7CKO experienced high spine density throughout early and late stages of development that were not reduced to control levels with rapamycin, and ASD-behavioral phenotypes were not corrected. This provides strong evidence supporting the predictions made by Tang et al., that mTOR hyperactivity caused by mutations in mTORinhibitory genes that effects downstream expression of autophagy proteins, inhibiting autophagy functioning, and that autophagy is the underlying mechanism behind neuronal synaptic pruning defects observed in ASD model mice. Discussion and Conclusion Tang et al. analyzed spine density during development and found a greater dendritic spine density in ASD subjects at later developmental time points than non-ASD subjects. These atypical neurons were excitatory pyramidal cells found in layer V of the temporal lobe, suggesting that their increased dendritic spine density actually indicates strengthened local excitatory connectivity – a feature of ASD (Belmonte et al., 2004). The approximately linear decrease in spine density continuing all the way into the 19th year of human development showed a greater reduction in synapses in normal controls than in ASD patients. This may explain why ASD patients often suffer from deficits in higher cognitive functions such as reasoning and judgment that develop during a person’s late teens (Sternberg & Berg, 1992), as well as provide clinicians with an idea for most efficacious times for therapeutic intervention. Although it is likely that not all ASD subjects studied possessed TSC mutations, the researcher’s findings of pruning deficits along with mTOR signaling dysregulation suggests that mTOR is a common harmonizing pathway in ASD. The replication of these described dysfunctioning mTOR pathways along with increased spine numbers, decreased synaptic pruning, and ASD-behavioral phenotype in development designates Tsc2+/- mice as a strong mammalian model for ASD. This study also explored the amending role of rapamycin in ASD and its relation to autophagy, 97

Figure 3. a) Western blot revealing p-mTOR (mTOR activity) highest in Tsc2+/- mice and lead to decreased autophagy activity (LC3-II), which were corrected with rapomycin. b) Representative images of dendritic spines administered either DMSO vehicle or rapamycin. Scale bar, 2 um. c) Graphic depiction of (b) Mean +/- SD. (b-c) showed Tsc2+/- mice that also had no autophagy (Atg7CKO ) were treated with rapamycin and found no correction of pruning and dendrite density of the Tsc2+/-:Atg7CKO mice or just Ast7CKO mice, like the corrections observed with Tsc2+/- mice. (G. Tang et al., 2014).

and has already been implicated in clinical trials for treatment of ASD (Sahin, 2012). Tang et al. also confirmed that by blocking neuronal autophagy, ASDpathological declines in spine density and stereotypical ASD behaviors were observed and could be corrected by pharmacologically activating autophagy via mTOR kinase inhibition, indicating a link between mTOR and autophagy that is required for proper synaptic spine pruning. Therefore, Tang et al. demonstrated a novel foundational mechanism underlying ASD cellular and


behavioral phenotypes that entails mTOR hyperactivation inhibiting downstream neuronal autophagy that leads to structural and functional deficits in postnatal development of mice. This is not only the first mammalian evidence of synaptic remodeling through autophagy, but also emphasizes the importance of the role of autophagy in ASD that was previously overlooked. Greater understanding of this mTORdependent autophagy pathway may provide potential novel ASD therapeutic targets in previously unexplored autophagy pathways downstream mTOR signaling and acts to advance knowledge on the mechanisms underlying the debilitating ASD. Criticisms and Future Directions Although Tang et al. found their gene mutation studies to lead to mice with reduced social preference (characteristic of ASD) using a dyadic social interaction and reduced exploration in a novel-object recognition paradigm, researchers failed to demonstrate that their mice displayed self-grooming repetitive behaviors (also characteristic of ASD), decreasing the confidence in their ASD mammalian model. I purpose the researcher’s perform a marble-burying test to examine repetitive behavior further (Silverman, 2010). Studies assessing similar developmental disorders such as idiopathic autism have found decreases in mTOR activity responsible for pathologies (Nicolini et al., 2015), where as Tang et al. are reporting hyperactive mTOR activity as a contributing mechanism responsible for decreased spine pruning in the temporal lobe. This discrepancy in ASD-related cellular functioning may be due to a confound created from the Tsc2 gene knockout in the mice used by Tang et al. Tsc2 inhibits mTOR activity, which is also a member of the Akt cell survival pathway – therefore Tsc2 knockout mice will result in widespread functional impairment of this critical cell survival pathway molecule in other brain and body areas, skewing the validity of experimental results. An improved means of gene mutational analysis lies in the use of a CRISPRCas9 knock-in mouse model recently described by the Zhang lab at MIT, a direct genomic editing method (Platt et al., 2014). With this model, researchers will be able to inject a virus targeting excitatory neuronal cells which will deliver single guide RNA’s that act to block multiple genes acting upstream to inhibit mTOR such as Tsc1/Tsc2, NF1, and Pten, instead of solely mTOR. This will allow for direct genome editing creating a loss of function for genes of interest and only in the areas that receive viral injection, such as the superior temporal gyrus and fusiform gyrus. Researchers can also examine downstream effects of mTOR if multiple inhibitory genes were removed. Further analysis can be done using the CRISPRCas9 mouse model to directly overexpress mTOR by creating a knock-in of a highly active promoter in front of the mTOR locus, instead of creating mTOR hyperactivity indirectly through mutating its regulatory genes. This will attenuate the effects of mTOR hyperactivity in specific brain regions to determine clearly how ASD biological and behavioral phenotypes can be seen.

Assessment of the mTOR pathway in association with valproic acid, a substance observed to activate dendritic spines, would be interesting as valproic acid induces autism in fetal mice (Nicolini et al., 2015), and increase the neuronal progenitor cell pool (Go et al., 2012). In summary, there is much confusion and unknowns when it comes to the biological pathology of autism, but with advances in research like Tang’s group, more doors will open leading to greater findings in the future of autistic research.

ACKNOWLEDGEMENTS

Special thank you to Tang et al. 2014 for their work on ASD, as well as Dr. Bill Ju, Human Biology, at the University of Toronto Canada for the opportunity for this literature review, and the Neuroscience Specialist degree program in Human Biology, at the University of Toronto Canada for the opportunity to take HMB300H1S in 2015. References 1. Belmonte, M. K., Allen, G., Beckel-Mitchener, A., Boulanger, L. M., Carper, R. A., & Webb, S. J. (2004). Autism and abnormal development of brain connectivity. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 24(42), 9228–31. doi:10.1523/JNEUROSCI.3340-04.2004 2. Bourgeron, T. (2009). A synaptic trek to autism. Current Opinion in Neurobiology, 19(2), 231–4. doi:10.1016/j. conb.2009.06.003 3. Ehninger, D., Han, S., Shilyansky, C., Zhou, Y., Li, W., Kwiatkowski, D. J., … Silva, A. J. (2008). Reversal of learning deficits in a Tsc2+/− mouse model of tuberous sclerosis. Nature Medicine, 14(8), 843–848. doi:10.1038/nm1788 4. García-Peñas, J. J., & Carreras-Sááez, I. (2013). [Autism, epilepsy and tuberous sclerosis complex: a functional model linked to mTOR pathway]. Revista de Neurologia, 56 Suppl 1, S153–61. Retrieved from http://www.ncbi.nlm.nih. gov/pubmed/23446718 5. Go, H. S., Kim, K. C., Choi, C. S., Jeon, S. J., Kwon, K. J., Han, S.-H., … Shin, C. Y. (2012). Prenatal exposure to valproic acid increases the neural progenitor cell pool and induces macrocephaly in rat brain via a mechanism involving the GSK-3β/β-catenin pathway. Neuropharmacology, 63(6), 1028–41. doi:10.1016/j.neuropharm.2012.07.028 6. Hutsler, J. J., & Zhang, H. (2010). Increased dendritic spine densities on cortical projection neurons in autism spectrum disorders. Brain Research, 1309, 83–94. doi:10.1016/j. brainres.2009.09.120 7. Kim, J., Kundu, M., Viollet, B., & Guan, K.-L. (2011). AMPK and mTOR regulate autophagy through direct phosphorylation of Ulk1. Nature Cell Biology, 13(2), 132–41. doi:10.1038/ncb2152 8. Nicolini, C., Ahn, Y., Michalski, B., Rho, J. M., & Fahnestock, M. (2015). Decreased mTOR signaling pathway in human idiopathic autism and in rats exposed to valproic acid. 98


Acta Neuropathologica Communications, 3(1). doi:10.1186/ s40478-015-0184-4 9. Peça, J., & Feng, G. (2012). Cellular and synaptic network defects in autism. Current Opinion in Neurobiology, 22(5), 866–72. doi:10.1016/j.conb.2012.02.015 10. Penzes, P., Cahill, M. E., Jones, K. A., VanLeeuwen, J.-E., & Woolfrey, K. M. (2011). Dendritic spine pathology in neuropsychiatric disorders. Nature Neuroscience, 14(3), 285–93. doi:10.1038/nn.2741 11. Platt, R. J., Chen, S., Zhou, Y., Yim, M. J., Swiech, L., Kempton, H. R., … Zhang, F. (2014). CRISPR-Cas9 Knockin Mice for Genome Editing and Cancer Modeling. Cell, 159(2), 440–455. doi:10.1016/j.cell.2014.09.014 12. Poultney, C. S., Goldberg, A. P., Drapeau, E., Kou, Y., Harony-Nicolas, H., Kajiwara, Y., … Buxbaum, J. D. (2013). Identification of small exonic CNV from whole-exome sequence data and application to autism spectrum disorder. American Journal of Human Genetics, 93(4), 607–19. doi:10.1016/j. ajhg.2013.09.001 13. Purves, D., & Lichtman, J. (1980). Elimination of synapses in the developing nervous system. Science, 210(4466), 153–157. doi:10.1126/science.7414326 14. Rowland, A. M., Richmond, J. E., Olsen, J. G., Hall, D. H., & Bamber, B. A. (2006). Presynaptic terminals independently regulate synaptic clustering and autophagy of GABAA receptors in Caenorhabditis elegans. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 26(6), 1711–20. doi:10.1523/JNEUROSCI.2279-05.2006 15. Sahin, M. (2012). Targeted treatment trials for tuberous sclerosis and autism: no longer a dream. Current Opinion in Neurobiology, 22(5), 895–901. doi:10.1016/j. conb.2012.04.008 16. Sakai, Y., Shaw, C. A., Dawson, B. C., Dugas, D. V., Al-Mohtaseb, Z., Hill, D. E., & Zoghbi, H. Y. (2011). Protein Interactome Reveals Converging Molecular Pathways Among Autism Disorders. Science Translational Medicine, 3(86), 86ra49–86ra49. doi:10.1126/scitranslmed.3002166 17. Shen, W., & Ganetzky, B. (2009). Autophagy promotes synapse development in Drosophila. The Journal of Cell Biology, 187(1), 71–9. doi:10.1083/jcb.200907109 18. Silverman, J. L., Yang, M., Lord, C., & Crawley, J. N. (2010). Behavioural phenotyping assays for mouse models of autism. Nature Reviews. Neuroscience, 11(7), 490–502. doi:10.1038/nrn2851 19. Sternberg, R. J., & Berg, C. A. (1992). Intellectual Development (Vol. 9). Cambridge University Press. Retrieved from https://books.google.com/books?hl=en&lr=&id=lEdlv 99Ql2gC&pgis=1 20. Tang, G., Gudsnuk, K., Kuo, S. H., Cotrina, M. L., Rosoklija, G., Sosunov, A., … Sulzer, D. (2014). Loss of mTOR-Dependent Macroautophagy Causes Autistic-like Synaptic Pruning Deficits. Neuron, 83(5), 1131–1143. doi:10.1016/j.neuron.2014.07.040 21. Tang, S. J., Reis, G., Kang, H., Gingras, A.-C., Sonenberg, N., & Schuman, E. M. (2002). A rapamycin-sensitive signaling pathway contributes to long-term synaptic plasticity in the hippocampus. Proceedings of the National Academy of 99

Sciences of the United States of America, 99(1), 467–72. doi:10.1073/pnas.012605299 22. Zhan, Y., Paolicelli, R. C., Sforazzini, F., Weinhard, L., Bolasco, G., Pagani, F., … Gross, C. T. (2014). Deficient neuron-microglia signaling results in impaired functional brain connectivity and social behavior. Nature Neuroscience, 17(3), 400–6. doi:10.1038/nn.3641 Received Month, ##, 200#; revised ##, 200#; accepted Month, ##,

Month, 2013.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu


The pivotal role of TNF-α in inducing cognitive dysfunction

Man Lai Ho

Inflammation, if prolonged, is known to cause adverse effects on the CNS and consequent cognitive dysfunction, via pro-inflammatory cytokines produced during the inflammatory process. The cytokine TNF-α is one of major mediators of the innate immune response, and is implicated in neurodegenerative diseases. Therefore, it is of interest to study the effects of TNF-α on the central nervous system and cognition. This review examines, in detail, Jing et al.’s investigation on the effects of intra-amygdala injection of TNF-α on fear conditioning in rats, provides insight on the study, and proposes future directions for further research. Key words: tumor necrosis factor (TNF-α); glutamate toxicity; amygdala; NMDAR; fear learning Background Inflammation is an integral part of the innate immune system that aids the human body in its defense against harmful stimuli such as pathogens during infection, by attracting various immune cells to the site of infection to eradicate the invasive stimuli, removing damaged tissues and cells, and initiating tissue repair and recovery (Allan & Rothwell, 2003) However, if inflammation is left unchecked and prolonged, it may have detrimental instead of beneficial effects. Neurodegenerative diseases are usually accompanied by chronic neuroinflammation; as such, past studies have shown that pro-inflammatory cytokines produced during the inflammatory process, are consistently associated with several of these neurological disorders including Parkinson’s disease, Amyotrophic lateral sclerosis (ALS), and Alzheimer’s disease, and can cause intellectual deficiencies (Cunningham et al., 2009; Mogi et al., 1994; Paganelli et al., 2002; Poloni et.al, 2000; Reichenberg et al., 2001). The study by Jing, Hao, Bi, Zhang, & Yang (2015) examines, in particular, the pro-inflammatory cytokine tumor necrosis factor α (TNF-α) and its effects on cognition by injecting it directly into the brain of rats. TNF-α is one of the major immune mediators generated during systemic infection, and it is known that TNF-α plays both pathophysiological and homeostatic roles in the central nervous system (CNS) (Montgomery & Bowers 2011). TNF-α has been shown to reduce long-term potentiation (LTP), an essential mechanism underlying learning and memory, in hippocampal slices (Tancredi et al., 1992). Furthermore, TNF-α overexpression appears to interfere with proper spatial learning and tasks in rats (Aloe et al, 1999). Jing et al. (2015) focuses specifically on the effects of TNF-α on fear learning, which is known to be facilitated by the amygdala (Maren, 2003) Past research has demonstrated that TNF-α induces excitotoxicity and that the glutamate cytotoxicity can be inhibited by the addition of NMDAR (ionotropic glutamate receptor) antagonists (Olmos & Lladó, 2014). Excitotoxicity refers to the neuronal damage or death that occurs due to excessive stimulation by excitatory neurotransmitters, with glutamate being the primary as it is the main excitatory neurotransmitter of the CNS. Thus, Jing et al. (2015) further postulate that glutamatergic transmission mediates the cognitive effects induced by TNF-α injection.

Research Overview

Summary of Major Results

Indeed, Jing et al. (2015) have found that the intraamygdala injection of TNF-α, in which delivery was facilitated by the surgically implanted cannulae , can induce learning and memory deficits in rats. Through the use of the classical auditory fear conditioning paradigm, learning and memory function of the rodents was assessed by scoring the freezing responses exhibited by the rats. The paradigm consists of a tone (CS) habituation session, a conditioning session where the tone was paired with a foot shock (US), and an extinction session. Rats that were administered arterial cerebrospinal fluid (ACSF), the control group, displayed a rapid increase and a gradual decrease in freezing behaviour, during the conditioning and extinction phases respectively. In contrast, the TNF-α-treated rats, the experimental group, demonstrated deficient acquisition and extinction of the fear response, as indicated by a much slower increase in freezing behaviour during the conditioning session and a delayed extinction of the freezing response. There were no differences in the foot shock sensitivities of both groups, therefore, increased foot shock sensitivity due to TNF-α as a possible confound, is eliminated. In order to confirm determine the involvement of the glutamatergic pathway in TNF-α-induced cognitive impairment, Jing and his team subsequently 1) used high performance liquid chromatography (HPLC) to measure glutamate and GABA (control) levels in TNF-α-treated and vehicle-treated rats, and 2) performed a second auditory fear conditioning experiment in which the rodents were administered PBS+TNF-α (control), MK-801 (an NMDAR antagonist), or MK-801+TNF-α before undergoing the trials. TNF-α-treated rodents were found to have higher levels of glutamate in the amygdala compared to those treated with the ACSF; however, there were no significant differences in GABA levels. In the latter experiment, rats injected with MK-801 showed appropriate acquisition and extinction of fear conditioning, while fear learning is impaired in PBS+TNF-α-treated rats, similar to the rodents infused with TNF-α solely. Furthermore, the administration of TNF-α with MK-801 to rats appears to be able to rescue proper fear learning. 100


Conclusions and Discussion

Jing et al. (2015) have demonstrated that infusion of TNF-α into the amygdala impairs acquisition and extinction of fear conditioning, possibly through the overstimulation of the glutamatergic pathway since high glutamate levels were found in the amygdala and the application of an NMDAR antagonist is seen to be able to neutralize the detrimental effects of TNF-α on fear learning. This mechanism is supported by previous research showing that TNF-α elevates synaptic glutamate via 1) increasing glutamate release from astrocytes and 2) inhibiting glutamate reuptake by astrocytes. (Danbolt, 2001; Olmos & Lladó, 2014). Glutamate cytotoxicity is achieved via the activation of the NMDAR, initiating a cascade of downstream events that eventually leads to cellular death, either necrosis or apoptosis, and subsequent deterioration of cognitive function (Floden 2005). As previously mentioned, there is an overabundance of circulating TNF-α in patients diagnosed with AD, a debilitating neurological disorder with symptoms of shortmemory loss, behavioral abnormalities, and learning deficits (Fillet et al., 1991). It is well-established that AD is characterized by amyloid-β plaques; in in vitro studies, TNF-α has been shown to increase the expression of amyloid-β precursor protein and Aβ, components of the extracellular aggregates, in glial and immune cells (Cunningham et al., 2009). Together with the fact that TNF-α induces glutamate-mediated neurotoxicity, it’s apparent that TNF-α plays a pivotal role in the development of AD pathology. Therefore, in regards to the treatment of AD, Jing et al. (2015)’s study is of significant importance as it provides further in vivo evidence that implicates TNF-α and the glutamatergic pathway as potential targets for therapeutical intervention.

Criticisms and Future Directions

Contrary to the results from Jing et al. (2015)’s study, there has been past evidence demonstrating TNF-α infusion into the CNS had beneficial rather than detrimental effects on cognition – administration of TNF-α centrally in the brain of rats resulted in improved performance on avoidance tasks, indicating that cognitive effects of TNF-α may vary depending on the site of infusion (Brennan & Tieder, 2006). Hence, for further research, an experiment testing hippocampaldependent spatial learning after intra-hippocampal TNF-α injection is proposed, and learning and memory function would be assessed using models such as the Barnes Maze or Morris Water Maze (MWM). It is also known that, aside from NMDAR, AMPAR (glu is also capable of inducing glutamate cytotoxicity (Olmos & Lladó, 2014). It is of interest to see whether the pharmalogical blockade of AMPAR via antagonists yields the same recovery of fear learning like the application of MK-801 after intra-amygdala TNF-α injection. References 1. Allan, S., & Rothwell, N. (2003). Inflammation in central nervous system injury. Philosophical Transactions Of The Royal Society B: Biological Sciences, 358(1438), 16691677. doi:10.1098/rstb.2003.1358 101

2. Aloe, L., Properzi, F., Probert, L., Akassoglou, K., Kassiotis, G., Micera, A., & Fiore, M. (1999). Learning abilities, NGF and BDNF brain levels in two lines of TNF-α transgenic mice, one characterized by neurological disorders, the other phenotypically normal. Brain Research, 840(1-2), 125-137. doi:10.1016/s0006-8993(99)01748-5 3. Brennan, F., & Tieder, J. (2006). Centrally administered tumor necrosis factor-α facilitates the avoidance performance of Sprague–Dawley rats. Brain Research, 1109(1), 142-145. doi:10.1016/j.brainres.2006.06.040 4. Cunningham, C., Campion, S., Lunnon, K., Murray, C., Woods, J., & Deacon, R. et al. (2009). Systemic Inflammation Induces Acute Behavioral and Cognitive Changes and Accelerates Neurodegenerative Disease. Biological Psychiatry, 65(4), 304-312. doi:10.1016/j.biopsych.2008.07.024 5. Cunningham, C., Campion, S., Lunnon, K., Murray, C., Woods, J., & Deacon, R. et al. (2009). Systemic Inflammation Induces Acute Behavioral and Cognitive Changes and Accelerates Neurodegenerative Disease. Biological Psychiatry, 65(4), 304-312. doi:10.1016/j.biopsych.2008.07.024 6. Danbolt, N. (2001). Glutamate uptake. Progress In Neurobiology, 65(1), 1-105. doi:10.1016/ s0301-0082(00)00067-8 7. Fillit, H., Ding, W., Buee, L., Kalman, J., Altstiel, L., Lawlor, B., & Wolf-Klein, G. (1991). Elevated circulating tumor necrosis factor levels in Alzheimer’s disease. Neuroscience Letters, 129(2), 318-320. doi:10.1016/0304-3940(91)90490-k 8. Floden, A. (2005). -Amyloid-Stimulated Microglia Induce Neuron Death via Synergistic Stimulation of Tumor Necrosis Factor and NMDA Receptors. Journal Of Neuroscience, 25(10), 2566-2575. doi:10.1523/jneurosci.4998-04.2005 9. Jing, H., Hao, Y., Bi, Q., Zhang, J., & Yang, P. (2015). Intra-amygdala microinjection of TNF-α impairs the auditory fear conditioning of rats via glutamate toxicity. Neuroscience Research, 91, 34-40. doi:10.1016/j.neures.2014.10.015. 10. Maren, S. (2003). The Amygdala, Synaptic Plasticity, and Fear Memory. Annals Of The New York Academy Of Sciences, 985(1), 106-113. doi:10.1111/j.1749-6632.2003. tb07075.x 11. Mogi, M., Harada, M., Riederer, P., Narabayashi, H., Fujita, K., & Nagatsu, T. (1994). Tumor necrosis factor-α (TNF-α) increases both in the brain and in the cerebrospinal fluid from parkinsonian patients. Neuroscience Letters, 165(12), 208-210. doi:10.1016/0304-3940(94)90746-3 12. Montgomery, S., & Bowers, W. (2011). Tumor Necrosis Factor-alpha and the Roles it Plays in Homeostatic and Degenerative Processes Within the Central Nervous System. Journal Of Neuroimmune Pharmacology, 7(1), 42-59. doi:10.1007/ s11481-011-9287-2 13. Olmos, G., & Lladó, J. (2014). Tumor Necrosis Factor Alpha: A Link between Neuroinflammation and Excitotoxicity. Mediators Of Inflammation, 2014, 1-12. doi:10.1155/2014/861231 14. Paganelli, R., Di Iorio, A., Patricelli, L., Ripani, F., Sparvieri, E., & Faricelli, R. et al. (2002). Proinflammatory cytokines in sera of elderly patients with dementia: levels in vascular injury are higher than those of mild–moderate Alzheimer’s disease


patients. Experimental Gerontology, 37(2-3), 257-263. doi:10.1016/s0531-5565(01)00191-7 15. Poloni, M., Facchetti, D., Mai, R., Micheli, A., Agnoletti, L., & Francolini, G. et al. (2000). Circulating levels of tumour necrosis factor-α and its soluble receptors are increased in the blood of patients with amyotrophic lateral sclerosis. Neuroscience Letters, 287(3), 211-214. doi:10.1016/ s0304-3940(00)01177-0 16. Reichenberg, A., Yirmiya, R., Schuld, A., Kraus, T., Haack, M., Morag, A., & Pollmächer, T. (2001). Cytokine-Associated Emotional and Cognitive Disturbances in Humans. Arch Gen Psychiatry, 58(5), 445. doi:10.1001/archpsyc.58.5.445 17. Tancredi, V., D’Arcangelo, G., Grassi, F., Tarroni, P., Palmieri, G., Santoni, A., & Eusebi, F. (1992). Tumor necrosis factor alters synaptic transmission in rat hippocampal slices. Neuroscience Letters, 146(2), 176-178. doi:10.1016/03043940(92)90071-e 18. Yirmiya, R., & Goshen, I. (2011). Immune modulation of learning, memory, neural plasticity and neurogenesis. Brain, Behavior, And Immunity, 25(2), 181-213. doi:10.1016/j. bbi.2010.10.015

102


AKAP150 Underlies Deficits Seen in Spatial Memory Following Short-Term Sleep Deprivation Patrick Hopper

Sleep is a process, which has been found to be vital for the consolidation of memories and synaptic plasticity, with even short-term sleep deprivation being sufficient to disrupt these processes. Hagewoud et al investigated whether or not short-term sleep deprivation would impact working spatial memory, when tested in a novel arm recognition task. They found that sleep deprived mice of 12 hours had significant declines in their working spatial memory, when compared to controls. Western Blot Analysis was conducted, to determine if there were any changes in cellular proteins and mechanisms, following the sleep deprivation. The researchers found that both the degree of phosphorylation on the serine 845 residue of the AMPA receptors and the level of AKAP150 protein both decreased significantly in the 12 hour sleep deprived mice. The authors concluded the decreased levels of phosphorylation were a result of decreased AKAP150, a scaffold protein which is responsible for tethering and moving PKA to the AMPA receptor for phosphorylation for serine 845. Furthermore, due to the importance of the AMPA receptor in LTP, the researchers believed these results were responsible for the memory deficits observed, Thus, the researchers provided evidence on how decreases in AKAP150 underlie deficits in hippocampal working spatial memory, produced by even short-term sleep loss. Key words: A-Kinase Anchoring Proteins (AKAP150); Hippocampus; Short-term Sleep Deprivation; AMPA Receptor Background One of the most vital aspects for the health and proper function of neurons is detailed and precise control of signaling, both within time and across different locations1. These signaling events are able to trigger cascades that have dramatic effects within the cell, which if not controlled properly can lead to disruption of many critical pathways2. This crucial form of regulation is accomplished by using scaffold proteins, a subset of proteins which bind and transport signaling molecules to specific locations in the cell, in order to localize the signaling event and its actions1. One such family of proteins are called A-Kinase Anchoring Proteins (AKAPs) and are found in the post-synapses of many neurons in the brain. Three varieties of AKAPs exist: AKAP150 in rodents, AKAP79 in humans, and AKAP75 in bovine, with the majority of studies focusing on AKAP150 due to use of rats and mice as research subjects3. AKAP150 has been found to bind many intracellular signaling molecules, kinases, and receptor proteins, including PKA, PKC, calcium channels, and Calcineurin (CaN)4. Within the brain, AKAPs are expressed in almost every brain region, with highest expression occurring in the striatum, cerebral cortex, and the hippocampus, all of which are implicated in learning and memory3. Due to this finding and its ability to bind multiple signaling molecules, researchers focused on its possible involvement with synaptic plasticity and learning in the brain3. Past research has found that AKAP150 is critical for delivering PKA to the GluR1 subunit of AMPA receptors for the phosphorylation of serine 845. This process is believed to cause incorporation of the AMPA receptor into the postsynaptic membrane, enhancing LTP and increasing synaptic plasticity5. Furthermore, another study found that AKAP150 can also function to deliver CaN to AMPA receptor for actions opposing those of PKA: dephosphorylation at the serine 845 residue, 103

resulting in channel closure and internalization6. Further studies agree with these findings, such as Lu et al who injected a stop codon into the gene coding for AKAP150, eliminating the ability of the protein to bind and transport PKA, resulting in observable deficits in LTP and AMPA receptor phosphorylation5. Furthermore, Sanderson et al found the opposite when they knocked-out the CaN binding domain on AKAP150, decreasing the amount of LTD and increasing AMPA receptor phosphorylation6. Sleep has been found to be a process critical for not only the elimination of waste products and neurotoxins, but also required for the formation and strengthening of neurons, during learning experiences7. Sleep deprivation (both long and short term), has been found to produce deficits in many types of hippocampal based memory and learning, including working spatial memory8. However, no studies have addressed whether AKAP150 could mediate these observed deficits, despite evidence of it mediating changes in LTP and LTD. Therefore, Hagewoud et al sought to determine the role (if any) AKAP150 played. Research Overview

Summary of Major Results & Discussion

In their study, Hagewoud et al studied the impact of short-term sleep deprivation on working spatial memory. 10 week old mice were subjected to sleep deprivation, of either 6 or 12 hours, which was induced by mild stimulation of their cage. The mice were tested in a novel arm recognition task, using a Y shaped maze, in order to assess their level of working spatial memory following their period of sleep deprivation. The researchers found that even those short amounts of sleep deprivation were enough to induce deficits in the spatial memory of the mice8. While the


amount of exploration time and number of arm entries remained the same during both trials (removing motor deficits and lack of activity as a possible explanation), the amount of time spent exploring the novel arm was significantly higher for the control group when compared to the 12 hour sleep deprived mice (with the 6 hour sleep deprived mice showing deficits, which were at almost significant levels of impairment)8. This result agrees with the previous findings of Xie et al, who found that even small amounts of sleep loss were enough to produce significant deficits in hippocampal working memory7. Furthermore, Yoo et al found that sleep loss in general (whether short or long term) reduced hippocampal neuronal function, causing LTP impairment and consolidation deficits9. Therefore, the results of this study agree with past work done in the field and provide evidence that even short amount of sleep loss are able to produce problems with synaptic plasticity and strength, leading to deficits in various forms of hippocampal memory. This finding is of particular relevance for students, as it provides evidence of how sleep loss for even short amounts of time can be detrimental to learning and thus how the practice of all-nighters (common among students during exams) can cause more harm than benefits. However, as detailed previously, many past studies have already investigated not only sleep loss (both short and long term) and its impact on hippocampal forms of memory. Therefore, this finding from Hagewoud et al, while interesting, offers no novel information on the effects of short-term sleep loss and thus is offers little impact in the field.

significantly less than controls, produced immediate and observable deficits in spatial memory10. As a result of their study, Hagewoud et al determined that changes in AMPA receptor level could not be responsible for the deficits in spatial working memory. However, the two previous studies provide evidence for the decline level of AMPA receptor during sleep loss and declining AMPA receptors being responsible for spatial working memory deficits, standing against the results and hypothesis of the Hagewoud et al study, who concluded that since there was no decrease in AMPA receptor level, it cannot explain the decline working spatial memory. While this seems to be a logical conclusion, it disagrees with previous studies done in the field and thus further studies are need to explain this observed result. If the results are found to be in fact true, then this could be considered a novel and significant impact in the both memory and sleep research, overturning previously determined results and producing newer and more accurate lines of research, to better understand memory. Additionally, the researchers found that the amount of phosphorylation of serine 845 on the GluR1 subunit of the AMPA receptor decreased significantly in the 12 hour sleep deprived mice, when compared to the controls (with 6 hour sleep deprived mice once again showing near significant levels of decline). The authors hypothesized this to underlie the deficits in spatial working memory during the novel arm recognition task. This hypothesis of their observed results agrees with previous findings, in which decreased levels of serine 845 phosphorylation has been noted in decreased learning and memory. Specifically, Lee et al created a mutant strain of mice, in which the phosphorylation sites on the GluR1 subunit where knocked out and found not only decreases in synaptic plasticity but also decreased levels of spatial memory, when tested in a morris water maze task13.

Figure 1) The exploration ratio (time spent in novel arm relative to the time spent in familiar arms) in control mice and 6 & 12 hour sleep deprived mice (Hagewoud et al. Exploration Ratio. (2010).)8

Using a Western Blot analysis, the researchers next measured the levels of AMPA receptors and AMPA receptor phosphorylation expressed in the hippocampus. Hagewoud et al found that the level of AMPA receptors did not change between the control and sleep deprived groups of mice. This result contradicts and stands against previous work done in sleep research. One study by Xie et al, found that sleep deprivation of only 4 hours was enough to cause a decrease in hippocampal AMPA receptor expression7. Furthermore, an additional study by Sanderson et al found that knocking out the expression of the AMPA receptor gene, so the receptor was expressed

Figure 2) The degree of phosphorylation of Serine AMPA receptors, in the hippocampus of control mice and 6 & 12 hour sleep deprived mice (Hagewoud et al. Exploration Ratio. (2010).)8

Finally, the researchers used the Western Blot analysis to determine the levels of CaN, PKA, and AKAP150 present in the hippocampus, following the sleep deprivation of the mice. The results indicated that while the levels of CaN and PKA remained similar to levels present in control mice, there was a significant decline in the level of AKAP150 in the 104


12 hour sleep deprived mice (with a decline in the 6 hour sleep deprived mice, which was almost deemed to be significant). PKA is a protein kinase, responsible for phosphorylating the serine 845 residue on the AMPA receptor, while CaN is responsible for the dephosphorylation the same residue5,6. It is believed that the state of phosphorylation on serine 845, regulated by the opposing action of those two proteins, determines whether or not AMPA receptors are incorporated into the cell membrane, in addition to whether or not the receptor is opened. These changes have been observed to underlie whether LTP or LTD is induced and whether there are in impairments in memory11. However, the results of Hagewoud et al’s study show that levels of PKA and CaN expression remained the same, thus they could not be responsible for the working spatial memory deficits8. As previously described, AKAP150 is a scaffold protein, which is responsible for tethering and delivering both PKA and CaN to their proper location in the cell, thus acting as a regulator of their actions3. While no previous studies have investigated AKAP150 in relation to sleep induced memory impairments, there are numerous studies, which provide evidence for its role in various forms of memory impairment, due to its role as a scaffold protein. One study by Tunquist et al has found that mice who had the AKAP150 knocked out, experienced deficits in spatial memory, when tested in a Morris water maze. Using a combination of immunofluorescent and electrophysiological readings, it was that altered neuronal processes were underlying these changes in memory12. Therefore, when compared to previous research, AKAP150 mediating the changes in working spatial memory is a reasonable and logical conclusion. This result has little impact and significance, as AKP150 was previously known to be a regulator of LTP, LTD, and other types of memory5,6. However, previous studies have not established for sleep deprivation is able to produce deficits in learning and memory, thus the results of this study are novel to sleep research and provide groundwork, in which future studies can take place.

Figure 3) The amount of AKAP150 scaffold protein in control mice and 6 & 12 hour sleep deprived mice (Hagewoud et al. Exploration Ratio. (2010).)8

105

Conclusions The authors concluded that like long amounts of sleep deprivation, even short amounts can be detrimental to learning and memory, with mice showing both behavioral and cellular deficits, as a result8. Furthermore, due to the importance of the AMPA receptor and GluR1 subunit in hippocampal forms of memory, Hagewoud et al. concluded that this decrease in spatial working memory was due a decreased degree of phosphorylation of the GluR1 subunit, on S8458. Finally, since the levels of the APAK150 protein (responsible for targeting the S845 kinase to the membrane) were lower, the authors concluded that this was responsible for the decreased phosphorylation levels8. These conclusions made by the authors agree with past work done in how sleep deprivation can affect learning and memory and the cellular machinery mediating those processes. However, the researchers found that the level of AMPA receptors did not decrease, contradicting past research. Therefore, further research is needed to solve this discrepancy. The conclusions determined by this study are significant for the field of neuroscience as a whole, because it offers greater insight into how learning and memory occur in the brain. Furthermore, it also illustrates how simple cellular processes in a specific region in the brain, can translate into larger behavioral and cognitive changes.

Criticisms and Future Directions

One criticism of Hagewoud et al’s study is that they did not measure the levels of AKAP150 in other brain areas, only measuring the amount in the hippocampus. In their research on AKAP150, Ostroveanu et al found widespread amounts of the scaffold protein present in the entire brain, with the highest levels occurring in the striatum and cerebral cortex. These brains areas are not only involved with the storage and processing of memory, but also express higher amounts of AKAP150 than the hippocampus. In addition, AKAP150 is capable of binding many different proteins, including PKA, PSD-95, PKC, and CaN. Therefore, the short-term sleep deprivation could have possibly elicited changes in AKAP protein in other areas of the brain, which could be responsible for the decline in memory observed. Further experiments, using immunochemistry and western blot analysis could be conducted to view the levels of AKAP150 following sleep deprivation in those brain areas, in order to determine if the observed results in Hagewoud et al’s study were unique only to the hippocampus. This would allow for clarification on whether the observed results were truly due to changes in the hippocampus or widespread changes in the entire brain. Another criticism of this paper, was that no in vivo experiments were conducted. This study and many similar ones, simply measured the levels of AKAP150 using Western Blot techniques, while neglecting in vivo techniques. Many other researchers have attempted to use in vivo models, such as Lu et al, who injected a stop codon sequence, causing AKAP150 to no longer bind and transport PKA to the membrane surface. They observed decreases in LTP and phosphorylation, as a result5. Additionally, Sanderson et al created a strain of mutant mice, in which the CaN binding domain was


knocked out and they found LTD decreased, while LTP and AMPAR phosphorylation levels were increased6. However, further studies are need, in order to better understand how AKAP150 can produce the behavioral deficits in memory, observed in Hagewoud et al’s study. Therefore, a beneficial follow-up experiment would use a viral injection method, in order to create two new lines of mutated mice. One would lack both PKA and CaN domains, thus AKAP150 would be unable to bind both. One confusing aspect of Hagewoud et al’s experiment is that decreases in PKA and CaN delivery lead to a net decrease in phosphorylation, when one would expect them to have opposing actions and thus balance each other out. Thus, this in vivo model would help to clarify that abnormality. The second line would cause the total levels of AKAP150 to be overexpressed compared to controls. Havekes et al, recently found that after a period of sleep deprivation, by increasing the levels of cAMP, via injection, certain impairments in memory could be restored to levels similar to controls14. Furthermore, if decreases in AKAP150 was truly responsible for deficits in working spatial memory, then we would expect to see increases in working spatial working memory, when levels of AKAP150 are increased beyond endogenous levels. Therefore, in vivo studies as a whole would offer a better understanding of the relationship between AKAP150, sleep deprivation, and memory. A final gap in the research presented by this paper is that it does describe or even attempt to find how sleep affects the expression levels of AKAP150 in the hippocampus. Vecsey et al used mice deprived of sleep for 5-6 hours and performed microarray, Western Blot, and PCR analyses, in order to examine the expression of various hippocampal genes following sleep deprivation and whether or not they were up or down regulated15. Vecsey et al found that 12 genes were upregulated and 9 genes down regulated, implicating the mTOR gene as a significant cause of cognitive impairment due to sleep deprivation15. An addition study would be to conduct a similar study, using solely microarray and PCR studies, to focus on the gene encoding for AKAP150 (akap5), as this was not reported or included in their study. Additionally, a functional analysis would be added, in order to see if it was related to and experienced changes similar to the genes reported in Vecsey et al’s study. These further experiments would provide in sight into whether lack of sleep caused changes in the translation of AKAP150 is responsible for the observed spatial memory decline.

4. Lu, Y. et al. A Kinase Anchor Protein 150 (AKAP150)associated Protein Kinase A Limits Dendritic Spine Density. Journal of Biological Chemistry 286, 26496–26506 (2011). 5. Lu, Y. et al. Age-dependent requirement of AKAP150anchored PKA and GluR2-lacking AMPA receptors in LTP. The EMBO Journal 26,4879–4890 (2007). 6. Sanderson, J. et al. AKAP150-Anchored Calcineurin Regulates Synaptic Plasticity by Limiting Synaptic Incorporation of Ca2+-Permeable AMPA Receptors. Journal of Neuroscience 32, 15036–15052 (2012). 7. Xie, M. et al. Short-term sleep deprivation impairs spatial working memory and modulates expression levels of ionotropic glutamate receptor subunits in hippocampus. Behavioural Brain Research 286,64–70 (2015). 8. Hagewoud et al. Sleep deprivation impairs spatial working memory and reduces hippocampal AMPA receptor phosphorylation. Journal of Sleep Research 19, 280–288 (2009). 9. Sanderson, D. et al. Deletion of glutamate receptor-A (GluR-A) AMPA receptor subunits impairs one-trial spatial memory. Behavioral Neuroscience 121, 559–569 (2007). 10. Yoo, S., Hu, P., Gujar, N., Jolesz, F. & Walker, M. A deficit in the ability to form new human memories without sleep. Nature Neuroscience 10,385–392 (2007). 11. Snyder, E. et al. Role for A Kinase-anchoring Proteins (AKAPS) in Glutamate Receptor Trafficking and Long Term Synaptic Depression.Journal of Biological Chemistry 280, 16962–16968 (2005). 12. Tunquist, B. et al. Loss of AKAP150 perturbs distinct neuronal processes in mice. Proceedings of the National Academy of Sciences105, 12557–12562 (2008). 13. Lee, H et al. Phosphorylation of the AMPA Receptor GluR1 Subunit Is Required for Synaptic Plasticity and Retention of Spatial Memory. Cell 112, 631–643 (2003). 14. Havekes, R. et al. Transiently Increasing cAMP Levels Selectively in Hippocampal Excitatory Neurons during Sleep Deprivation Prevents Memory Deficits Caused by Sleep Loss. Journal of Neuroscience 34,15715–15721 (2014). 15. Vecsey, C. et al. Genomic analysis of sleep deprivation reveals translational regulation in the hippocampus. Physiological Genomics 44,981–991 (2012).

References 1. Weisenhaus, M et al. Mutations in AKAP5 Disrupt Dendritic Signaling Complexes and Lead to Electrophysiological and Behavioral Phenotypes in Mice. PLoS ONE 5, (2010). 2. Jurado, S., Biou, V. & Malenka, R. A calcineurin/AKAP complex is required for NMDA receptor–dependent long-term depression.Nature Neuroscience 13, 1053–1055 (2010). 3. Ostroveanu, A., Dolga, A., Luiten, P., Eisel, U. & Nijholt, I. A-kinase anchoring protein 150 in the mouse brain is concentrated in areas involved in learning and memory. Brain Research 1145, 97–107 (2007).

106


Maternal Behavior Hormone Receptor might be a crucial player in the development of social and mood disorders Patrick Hornlimann

The commonly with maternal behaviours associated hormone Oxytocin has more recently been associated with a variety of social and mood disorders. The cur-rent study intended to find effects of early life stress (ELS) on the susceptibility of certain genotypes to depression, anxiety and stress. The study involved 653 subjects that were genotyped, had to fill out an ELS questionnaire and were assessed on a depression, anxiety and stress scale (DASS). 4 tests were performed and one single nucleotide polymorphism (rs139832701) was found to be associated with higher DASS scores in the face of ELS. Also, brain tissue was gained to monitor downstream effects of specific SNPs, which revealed that rs3831817 alters OXTR levels. The current study supports the role of oxytocin in the development of mood and anxiety disorders. Key words: Stress; Anxiety; Depression; DASS scale; Oxytocin; RNA expression; SNP Background Oxytocin is a mammalian hormone that is commonly associated with maternal behaviour, parturition and lactation. It is produced in the hypothalamus but also in other parts of the brain and is transported to the posterior pituitary before being releasing into blood circulation. Oxytocin targets Oxytocin receptors (OXTR) that are located in regions of the brain that are similar to the hormoneâ&#x20AC;&#x2122;s production sites. Various reports have suggested that Oxytocin is involved in social and brain disorders. Uvnas-Moberg1 found that social interactions are affected by Oxytocin, while Heinrichs et al.2 and Scantamburlo et al.3 suggested its involvement in anxiety and depression, respectively. More recently, studies have revealed that Oxytocin concentrations differ as a result of adverse childhood experience4. Furthermore, its concentration seems to affect the severity of symptoms in patients with anxiety disorders5. On the basis of those findings, several studies intended to spot genetic variations that can be associated with mood and anxiety disorders in the face of adverse early life experiences. Besides the present study that examined the association between Oxytocin receptor (OXTR) variations and depression, anxiety and stress scale (DASS) score in the context of early life stress (ELS)6, there are a number of other studies that were conducted for similar purposes. rs2254298 and rs53576 were two of the identified SNPs that were reported. As a result of those being found, further research was conducted to identify the specific base changes that lead to higher susceptibility for certain disorders. Costa7 reported that OXTR rs2254298 GG carriers had higher levels of depression and anxiety compared to GA and AA groups. Likewise, Thompson et al.8 found that the same SNP in individuals who experienced early life adversity resulted in anxiety and depression occurring more often, however, this study reported the AG allele to be responsible for those effects. Similarly, for the rs53576 SNP, a correlation between GG allele carrier and reactivity to stress was found9. Those findings were confirmed and extended by McQuaid et al.10, who found that not only GG but also GA carriers displayed higher incidence of depres-sion in individuals that experienced early107

life adversity. In contrast, a higher susceptibility for depressive disorders was associated with AA and GA allele carriers by Saphire-Bernstein et al.11. Now, the present study does not attempt to clarify those issues but rather it intends to find new OXTR SNPs that might be causative for social and mood disorders in the context of ELS. Previous research of other SNPs could be used as a guideline for the conduction of future studies on newly detected gene variations. Research Overview

Summary of Major Results

The current article suggests that OXTR variants indeed interact with ELS to determine an individualâ&#x20AC;&#x2122;s likelihood to develop anxiety, stress and depression symptoms6. It is thus not only the genetics that deter-mine whether or not social and mood disorders mani-fest but much rather a combination of genetics and environmental influences. Furthermore, the present study revealed a new OXTR SNP that might be an important predictor for depression, which is the rs139832701 SNP. The findings suggest that rs139832701 is involved in all of the three measures of DASS score as displayed in table 16. They not only show the effects of the SNP on the symptoms but also the influence of ELS on the relationship between the genotype and the symptoms, which all depicted significant results. However, the findings suggest that this study has been conducted independently as this SNP appears not to be linked to previously found genetic variants6 (Figure 16). This either implies that there was a problem in the current study that led to those differing results or it is indeed the discovery of OXTR variants that is of importance in this context that previous studies have not been able to detect. To clarify this issue and thus the true relevance of these findings, further studies that examine rs139832701 must be conducted. The authors came to their conclusion after having


Table 1: This table shows the correlations between genotypes and each of the DASS components without ELS interaction at the left side and with interaction at the right side. The RAW values display unadjusted p-values. SNP adjusted and Corrected values are adjusted. Bold values indicate p-values < 0.05.

Another SNP that did not display any distinct patterns in DASS outcomes, however, showed changing in OXTR expression levels in the brain cohorts was the rs3831817 SNP. The linkage disequilibrium displays a moderate value of 0.74 with the rs139832701 variant, suggesting that they are inherited more often together than not. Also, rs139832701 showed high linkage dis-equilibrium (r2â&#x2030;Ľ0.8) with previously found OXTR vari-ants (rs53576, rs237897)6. This indicates that rs53576 and rs237897 variants might be the cause for the changes in transcript levels.

Figure 1: This figure shows a linkage disequilibrium plot of the SNP found in the present study at the very right and other SNPs that were found in previous studies.

con-ducted four tests that were intended to detect new SNPs that resulted in higher DASS scores depending on ELS. The required data of the participants were attained by genotyping, ELS questionnaire and DASS score self-report. Moreover, brain tissue was required to determine downstream functional effects of certain SNPs. The tests were conducted according to Figure 2. The SNP that was found as a result of those tests was then set up in a linkage disequilibrium plot to ex-amine its correlations with previously found SNPs in a similar context (Figure 16). The sample size was with 653 participants quite large, which increases the relevance of this study.

Figure 2: The four tests that were performed; Test 1: Relationship between ELS and DASS score; Test 2: Influence of covariates; Test 3: Models to determine the main effects of the SNP genotype on symptoms as well as the effect of ELS on that relationship; Test 4: Testing for downstream effects of SNPs

108


Conclusions and Discussions The only OXTR variant that showed significant interaction with early life stress experience in order to trigger a higher severity in depressive and stress symptoms was rs139832701 (Figure 3). This led the authors draw their main conclusion that this specific genotype re-sults in increased incidence of anxiety and mood dis-orders in the face of ELS. As the current study repre-sents the first report of this SNP in the given context, it can be considered a novelty finding. This is further supported regarding the fact that rs139832701 is in linkage equilibrium with previously found SNPs, as it confirms the independence of the present study6. The large sample size is one of the major strengths of this study because it makes it more representative for the population as a whole. However, considering that the brain tissues were not gained from the same popu-lation as the actual participants, the generalizability of the study can be questioned due to the altering genetic variation between peoples. This can influence the outcome of the study and thus decreases its relevance. Despite the fact that the authors do a rather good in comparing their results to the ones from other studies, they poorly address how the current findings could be meaningfully integrated and used in the context. It does neither come out clearly what next step of research or follow-up study they suggest, nor in what respect this study might contribute to the progress of this field of research. As this study is the first one to find rs139832701 being involved in increasing the people’s likelihood to fall into depression when in combination with ELS, it is difficult to directly compare it to other literature, however, the authors do acknowledge similar findings and also try to relate them to the present study.

Figure 3: This figure shows the proposed model of this study

Criticism and Future Directions

Issues with the current study

The result section is very well structured. The different paragraphs that are arranged according to the tests make them easily understandable and interpretable. However, the analysis seems to simplify some of the data slightly too much. The authors state in one of the paragraphs: “we found that none of our demographic variables (gender, age or years of education) were significant covariates”6 yet when having a close look at test 2 in Table 26, one can see that there are significant results displayed for age and education for 109

anxiety measures. Nevertheless, the other tests are analysed thoroughly and exactly. Test 1 and 3 showed that ELS correlates with DASS score and OXTR variants correlate with DASS score, respectively. For the latter association, it is clearly distinguished that only stress and depression scores are correlating but not anxiety parameters. As anxiety here again did not behave similar to depression and stress parameters, it might have been important to study the results of test 2 more exactly. Maybe anxiety cannot be put in context with OXTR variants in the way depression and stress can and should therefore be separately analysed. However, the rs139832701 SNP according to the re-sults seems to clearly have an association with DASS outcome when ELS was considered.

Table 2: This table displays the correlation between covariants and each of the DASS measures in p-values. The bold values are p<0.05.

Comparison to other studies

When compared to other studies that investigated similar models, several differences can be spotted. First of all, as previously said, the sample size is with 5636 quite large when put in context with sample sizes of comparable studies that had 23612, 28810, 939 and 129 subjects8, respectively. All the subjects are Cau-casian decent and belong to the same ethnicity, which in other studies is often not the case and is of particu-lar relevance when it comes to genetic variations. The same applies to the brain tissues that were in this par-ticular study6 sampled from different population than the subjects themselves and can have implications for the results. Further, there are a lot of different measures for both ELS and depression, anxiety and stress parameters that will have an influence on the results of a study too. To give an example, McQuaid et al.10 used Beck Depression Inventory13 and Thompson et al.8 made use of Children’s Depression Inventory14, while in the present study DASS score was used as a measure. Moreover, the age of the subjects should be considered and in the present study displays a big spreading between 6 and 87 years. Norman et al.9 in comparison chose all subjects to be between 50 and 68.

Outlook

Further studies should try to achieve samples sizes similar to the present study and also to maintain the ethnic homology among the subjects. According to the already known SNPs such as rs53576, that is currently heavily investigated15,16,17, the way to go for this newly found SNP is already prepared. Not only is it important to now examine the downstream effects of rs139832701 but also should the findings be confirmed by further studies that might use brain


tissues from the same population as the subjects. Moreover, the OXTR rs139832701 polymorphism should be further investigated in order to determine the base changes that are involved and thus which specific allele is responsible for the association. As this study has also shown that rs3831817 has an influence on OXTR levels6 and silencing of OXTR were associated with autism18, it might also be interesting to further examine rs3831817 in that context. References 1. Uvnas-Moberg, K.. Oxytocin may mediate the benefits of positive social interaction and emo-tions. Psychoneuroendocr inol;23:819e35. (1998) 2. Scantamburlo, G., Hansenne, M., Fuchs, S., Pit-chot, W., Marechal, P., Pequeux, C., et al. Plasma oxytocin levels and anxiety in patients with major depression. Psychoneuroendocrinol 2007;32:407e10. (2007) 3. Heinrichs, M., Baumgartner, T., Kirschbaum, C., Ehlert, U.. Social support and oxytocin interact to suppress cortisol and subjective responses to psychosocial stress. Biol Psychiatry;54:1389e98. (2003) 4. Heim, C., Young, L. J., Newport, D. J., Mletzko, T., Miller, A. H., Nemeroff, C. B.. Lower CSF oxy-tocin concentrations in women with a history of childhood abuse. Mol Psychiatry;14:954e8 (2009) 5. Hoge, E. A., Pollack, M. H., Kaufman, R. E., Zak, P. J., Simon, N. M.. Oxytocin levels in social anxiety disorder. CNS Neurosci Ther; 14:165e70.(2008) 6. Myers, A. J., Williams, L., Gatt, J. M., McAuley-Clark, E. Z., Dobson-Stone, C., Schofield, P. R., Nemeroff, C. B.. Variation in the oxytocin receptor gene is associated with increased risk for anxiety, stress and depression in individuals with a history of exposure to early life stress. J Psychiatr Res. 2014 Dec;59:93-100. 7. Costa, B., Pini, S., Gabelloni, P., Abelli, M., Lari, L., Cardini, A., Muti, M., Gesi, C., Landi, S., Galderisi, S., Mucci, A., Lucacchini, A., Cassano, G. B., Martini, C.. Oxytocin receptor polymor-phisms and adult attachment style in patients with depression. Psychoneuroendocrinology;34(10):1506-14. (2009) 8. Thompson, R. J., Parker, K. J., Hallmayer, J. F., Waugh, C. E., Gotlib, I. H.. Oxytocin Receptor Gene Polymorphism (rs2254298) Interacts with Familial Risk for Psychopathology to Predict Symptoms of Depression and Anxiety in Adoles-cent Girls. Psychoneuroendocrinology; 36(1): 144–147. (2011) 9. Norman, G. J., Hawkley, L., Luhmann, M., Ball, A. B., Cole, S. W., Berntson, G. G., Cacioppo, J. T.. Variation in the oxytocin receptor gene influ-ences neurocardiac reactivity to social stress and HPA function: a population based study. Horm Behav.;61(1):134-9. (2012) 10. McQuaid, R. J., McInnis, O. A., Stead, J. D., Matheson, K., Anisman, H.. A paradoxical associ-ation of an oxytocin receptor gene polymorphism: early-life adversity and vulnerability to depression. Front Neurosci;7:128. (2013) 11. Saphire-Bernstein, S., Way, B. M., Kim, H. S., Sherman, D. K., Taylor, S. E.. Oxytocin receptor gene (OXTR) is

related to psychological re-sources. Proc Natl Acad Sci U S A; 108:15,118e15,122. (2011) 12. Malik, A. I., Zai, C. C., Abu, Z., Nowrouzi, B., Beitchman J. H.. The role of oxytocin and oxytocin receptor gene variants in childhood-onset aggression. Genes Brain Behav;11:545e51. (2012) 13. Beck A. T., Ward C. H., Mendelson M., Mock J., Erbaugh J.. An inventory for measuring depres-sion. Arch. Gen. Psychiatry 4, 561–571. (1961) 14. Kovacs, M.. The Children’s Depression Inventory (CDI). Psychopharmacol. Bull. 21, 995-1124. 1985) 15. Thompson S. M., Hammen C., Starr L. R., Najman J. M.. Oxytocin receptor gene polymorphism (rs53576) moderates the intergenerational transmission of depression. Psychoneuroendocri-nology;43:11-9. (2014) 16. Kim Y. R., Kim J. H., Kim C. H., Shin J. G., Treasure J. Association between the Oxytocin Receptor Gene Polymorphism (rs53576) and Bu-limia Nervosa. Eur Eat Disord Rev.. (2015) 17. Chang W. H., Lee I. H., Chen K. C., Chi M. H., Chiu N. T., Yao W. J., Lu R. B., Yang Y. K., Chen P. S.. Oxytocin receptor gene rs53576 polymor-phism modulates oxytocindopamine interaction and neuroticism traits--a SPECT study. Psycho-neuroendocrinology;47:212-20. (2014) 18. Gregory S. G. , Connelly J. J., Towers A. J., Johnson J., Biscocho D., Markunas C. A., Lintas C., Abramson R. K., Wright H. H., Ellis P., Lang-ford C. F., Worley G., Delong G. R., Murphy S. K., Cuccaro M. L., Persico A., Pericak-Vance M. A.. Genomic and epigenetic evidence for oxytocin receptor deficiency in autism. BMC Med.;7:62. (2009)

110


Consolidation of Memories Following Sleep is the Result of Synaptic Potentiation Justin Huang

Many studies have shown that sleep leads to consolidation of long-term memories. Yet what is unknown is how the mechanism by which sleep states affect memory. A popular theory over the past decade is the Synaptic Homeostasis Hypothesis coined by Tononi and Cirelli (2003, 2014). This theory postulates a role of sleep in the synaptic depression of unused synapses to rebalance the metabolic demands of neuronal activity. Although many studies do provide evidence for this theory, an equally impactful number of studies have suggested sleep is tightly linked to synaptic potentiation of various forms of memory. One of them, a study performed by Aton et al. (2014), has attempted to undeniably show this effect. By acutely affecting the sleeping behaviour of mice, Aton et al. (2014) were able to show a form of sleep-dependent synaptic plasticity. Subsequent experiments were performed to control for experimental conditions and test for undesired effects due to unexpected stresses. However, the study has consistently shown a sleep-dependent synaptic potentiation in principal neurons and fast-spiking interneurons of the visual cortex. Given the novelty of this study, it is crucial to scrutinize the data in an attempt to understand what impact these findings will have on our current understanding of sleep, and how we should approach future studies linking sleep and memory consolidation. Key words: in vivo recording, sleep, synaptic plasticity, thalamocortical oscillations, visual system, visual cortex, synaptic homeostasis hypothesis. Background Sleep, although ubiquitous in nature, is puzzling in terms of its purpose and its mechanism of action. In learning, the sleep state is viewed important in the consolidation of memories, the transformation of newly acquired memories during one’s wake into more long-term, robust forms of memory. Declarative and procedural memories are positively reinforced through sleep (Seehagen et al., 2015; Plihal and Born, 1997). Sleep also has a reinforcing effect on the formation of emotional memories (Wagner et al., 2001; Payne et al., 2008; Nishida et al. 2009). These studies provide evidence for the importance of sleep in memory learning and consolidation. However, information regarding the possible mechanism by which sleep carries out its augmenting role in memory consolidation is less prevalent. There has been an emerging theory known as the “Sleep Homeostasis Hypothesis” (SHY) (Tononi and Cirelli, 2003; 2014) which posits sleep as a mechanism for homeostatic renormalization, offsetting the net synaptic potentiation acquired during one’s wake. In this way, sleep would be consolidating memories and enhancing the ability to learn. The foundation of this hypothesis consists of three points. Firstly, increased synaptic strength is energetically unfavourable, and the visual awake in an awake rodent is dominated by synaptic inhibition (Haider et al., 2012). Second, the strengthening of synapses should occurring during an individual’s wake, given that this period is when he or she is interacting with the environment. Finally, given the first two components, the SHY suggests synaptic renormalization occurs during sleep through synaptic depression of underused synapses. However, a series of studies have also emerged suggesting the opposite. One of them, by Aton et 111

al. (2014), challenges the SHY by suggesting sleep facilitates memory consolidation through potentiating synapses (as opposed to synaptic depression according to the SHY). Their previous study investigating ocular dominance plasticity through monocular deprivation demonstrated a sleep-dependent increase in neuron remodelling and synaptic potentiation (Aton et al., 2009), following a mechanism similar to longterm potentiation involving NMDAR and PKA activity (Frenkel et al., 2006). To further elucidate the role of sleep, Aton et al. (2014) examined orientation-specific response potentiation (OSRP) in mice – a naturally occurring form of synaptic plasticity whereby exposure to a visual stimulus of a specific manner results in a promoted response to stimuli of the same orientation. The current study (Aton et al., 2014) is one of the first to explicitly show in vivo that cortical activity as a result of a specific visual stimulus can be reinforced through sleep. In this review, we will be examining the major findings and interpretations of this paper in an attempt to elucidate what future steps we should take towards understanding sleep. By refining our understanding of the sleep mechanisms, we may be able to better our treatments for common disorders involving sleep deficits, such as Alzheimer’s disease. Research Overview

Sleep facilitates memory consolidation in mice by promoting OSRP

To evaluate how OSRP is affected by sleep behaviour, mice were either sleep-deprived (n=3) or allowed ad libitum sleep (n=4) for six hours following the stimulus (Figure 2A). OSRP was identified by measuring the % change in average orientation preference (Figure


2C) as well as the distribution of neurons experiencing increase and decreases during the experiment. OSRP was apparent in V1 principal neurons and fast-spiking interneurons, but only in mice in the ad libitum sleep group (Figure 2B, P<0.05). Mice who were sleepdeprived did not experience OSRP. These results also suggested a correlation between slow wave sleep (SWS) and REM sleep with OSRP in the visual cortex (Figure 2D, R = 0.78). These findings provide in vivo evidence for the theory that sleep promotes synaptic potentiation, contrary to the SHY proposed by Tononi and Cirelli (2003; 2014). Originally, a prior study by Aton et al. (2009) had shown OSRP being driven by a mechanism similar to LTP. Despite the consistent findings of the 2009 study, Tononi and Cirelli (2014) had denied the implications for their hypothesis, citing an “unnatural experimental design” using monocular deprivation for ocular dominance plasticity studies in mice. In response, Aton et al. (2014) circumvented this issue by experimenting in a room devoid of light while still showing the naturally occurring OSRP, the expected response if sleep promoted synaptic potentiation and not synaptic depression.

Figure 1. The Synaptic Homeostasis Hypothesis as outlined by Tononi and Cirelli (2014).

The results were not impacted by any flaws in the experimental design

involved mice being equally sleep-deprived across either halves of the sleep phase (Figure 3A). Both interventions resulted in similar blocking of OSRP in principal neurons and fast-spiking interneurons (Figure 3C). In both experiments, the amount of SWS (R=0.58) and REM sleep (R=0.59) positively correlated with OSRP (Figure 2D). These experiments were crucial to addressing issues brought by advocates of the SHY, namely the unnatural settings of the study. According to Tononi and Cirelli (2014), previous endeavours by Aton’s involving monocular deprivation were unrepresentative of the natural learning conditions of mice. Therefore they did not necessarily reflect the effects of sleep on memory learning and consolidation. These current findings serve to meet their criticisms by demonstrating the earlier results were in line with the original hypothesis, and that the resulting synaptic potentiation could not have been a result of the experiment.

Evoked visual responsiveness was increased during OSRP, proportional to slow wave sleep spindle oscillations

Recall orientation-specific response potentiation is a measurement of the responsiveness to specific visual elements for neurons in the visual cortex. As OSRP is mechanistically similar to LTP (Aton et al., 2009), Aton et al. (2014) were led to investigate the changes in neuronal activity in addition to their heightened orientation sensitivity. The evoked responsiveness index (ERI, maximum vs. spontaneous activity) was enhanced in accordance with the sleep-dependent OSRP (P<0.05, Figure 4A, 4B). Although no changes were observed in firing coherence to REM gamma or slow-wave sleep delta oscillations, there was a high spike-field coherence between slow wave sleep spindle oscillations compared to both OSRP and ERI (Figure 4C). These results suggest generation of slow wave sleep spindles by the V1 is important to OSRP, as other frequencies showed no correlation. The influence of spindle oscillations was also implicated in Aton’s previous findings where sleepdependent plasticity following monocular deprivation was proportional to the synchronization of principal neuron firing to spindle oscillations (Aton et al., 2009). Recall of episodic-like memory was also associated with the amplitude of the spindle oscillations, while object recognition memory depending on the percentage of slow wave sleep during memory consolidation (Oyanera et al., 2014).

In order to evaluate the acute stress-related effects of the experimental design, as well as the time-ofday effects on OSRP, mice were provided the visual stimulus during the morning (AM, n=4) or evening (PM, n=4) with ad libitum sleep according to their natural behaviours. As seen in the prior experiment, both principal neurons and fast-spiking interneurons showed significant OSRP across a sleep phase (morning stimulus P<0.05, Figure 3C). An additional control for the acute effects of sleep deprivation 112


Figure 2. Orientation-specific response potentiation is observed when post-stimulus sleep is permitted. A: Timeline of the experiment. A 1-hour visual stimulus (visual gratings of a specific orientation) was presented to each mice, followed by a period of either ad libitum sleep or no sleep for a six hour period. Visual response measurements were recorded at the timepoints A (after baseline), B (following stimulus), C (following the intervention). B: Visual response data for sleeping (left) and sleep-deprived (right) mice. Changes in the firing responses at each were quantified as a measurement of OSRP. C: The percent change in orientation-specific response in V1 neurons (principal neurons and fast-spiking interneurons). OSRP was observed in both groups in sleeping mice. P<0.05, Holm-Sidak post hoc test. D: Correlation between sleep states (NREM, REM, Awake) versus the change in the orientationspecific response. OSRP was positively correlated to cumulative time spent in NREM and REM sleep, while negatively correlated to mice who stayed awake. From Aton et al. (2014). Figure 3. Orientation-specific response potentiation is present only following the natural sleep cycle in mice. A: Timeline of the experimental study. The visual response test was either performed in the morning (AM) or evening (PM) to experimentally test the effects of sleep according to the miceâ&#x20AC;&#x2122;s circadian time. An additional control experiment was conducted where mice were sleep-deprived for an equal amount early and late during their natural sleep. B: Visual response data for AM and PM conditions. Changes in the firing responses at each were quantified as a measurement of OSRP. C: Percent change in orientation-specific response versus the treatment, which shows a detectable OSRP only following sleep. D: Sleep is positively correlated to OSRP, while sleep-deprivation is negatively correlated to OSRP. From Aton et al. (2014).

Figure 4. OSRP was proportional to spike-field coherence. A: % changes in evoked responsiveness index was evident following a sleep period. B: For all sleeping mice, the % change in ERI was positively correlated with the % change in orientation preference. C: SWS spike-field coherences at baseline (solid) and 2h following the visual stimulus (dashed lines). Synchrony is observed poststimulus for spindle oscillations. D: Correlation between spindle spike-field coherence and the first two parameters (ERI, orientation preference). From Aton et al. (2014). 113


Conclusions and Discussion

Discussion

Altogether, the findings in these experiments ultimately support the role of sleep in memory consolidation. According to Aton et al. (2014), the data suggests sleep is necessary for OSRP to occur, as sleep deprivation impaired the response regardless of time and experimental effects (Figure 2). This is further supported by the positive correlation between OSRP and sleep (both SWS and REM sleep), and the negative correlation with an awake status. Two possible explanations arise from these results: either the state of sleep provides an appropriate, facilitative context for OSRP and therefore memory consolidation, or the awake phase serves detrimental to this process and the forms are permissive to its taking place. Therefore, although it can be concluded that sleep is necessary for OSRP, we are now prompted to elucidate how sleep promotes synaptic potentiation. The experiments analyzing the state-specific activity patterns provide a small glint into the possibilities surrounding this newly defined focus. In addition to the increased neuronal firing of V1 principal neurons (Figure 4A, 4B), there was an observed synchronizing of their firing patterns to SWS spindle oscillations (Figure 4C). Given the similarities between OSRP and other forms of synaptic plasticity (long-term potentiation, ocular dominance plasticity), Aton et al. (2014) hypothesizes a link between synaptic potentiation and the increased neuronal firing in accordance to thalamocortical oscillations. The novelty within these studies lie in their contrast to the SHY which prescribes a synaptic depression event with sleep (Tononi and Cirelli, 2003). As a link in a chain of emerging studies, we are prompted to re-examine our current knowledge regarding the role of sleep in memory formation. Advances will provide new avenues to understanding and treating disorders comprised of cognitive and sleep deficits, such as Alzheimer’s disease.

Conclusion

In conclusion, the collection of these in vivo results by Aton et al. (2014) suggests, contrary to the synaptic homeostasis hypothesis, sleep promotes synaptic potentiation in the adult cortex. This response may be promoted by SWS oscillations. Further research is required to elucidate the mechanism by how sleep leads to synaptic potentiation.

Criticisms and Future Directions

The study by Aton et al. (2014) has demonstrated an experience-dependent synaptic potentiation in the primary visual cortex (V1) of rats that was promoted by sleep behaviour. Specifically, the tested perceptual learning was sleep-dependent, proportional to the time asleep. This OSRP from repeated sensory experience also requires an increased neuronal firing synchronized to SWS spindle oscillations. According to Cooke and Bear (2014), OSRP results in an increased V1 responsiveness in awake mice in the absence of reward or punishment (Cooke et al., 2015), perhaps from a mechanism similar to N-methyl-D aspartate receptor activity in long-term potentiation. The signifi-

cance in this study is in its implications: alongside other similar recent findings (Chauvette et al., 2012; Grosmark et al., 2012; Aton et al., 2009) this study effectively brings into question the reigning “synaptic homeostasis hypothesis” (SHY) which suggests sleep functions to reduce net synaptic potentiation during the waking period to baseline levels through a reduced noradrenergic system (Tononi and Cirelli, 2014). According to the SHY, synaptic potentiation is predominantly occurring during one’s wake, yet the previously described findings by Aton et al. (2014) clearly issue against this notion. Regarding the methodology behind the study by Aton et al. (2014), drivable headstages (EIB-36, Neuralynx) were implanted into C57Bl/6j mice. Within the headstages, stereotrodes were implanted into various brain regions including the primary visual cortex to assess OSRP following different experimental sleep models. Conceptually, Aton et al. (2014) provided sound experimental groupings by testing for the effects of sleep deprivation, its time of induction (early vs. late following stimulus), whilst controlling for acute stress and OSRP recovery by repeating the experiments while abiding to their natural sleep behaviour and allowing post-deprivation sleep respectively. As aforementioned, the weakness in the previous study by Aton et al. was their choice in observing monocular deprivation, which was considered “unnatural” (Tononi and Cirelli, 2014). However, it should not be assumed that the synaptic homeostasis hypothesis has been overturned. Although synaptic potentiation would no doubt be important in the consolidation of long-term memories, a downscaling of unused synapses and short-term memories is also logically a plausible function of sleep. As more information emerges supporting either hypothesis, some have suggested we should instead be focusing on a combined hypothesis, where both are important to the role of sleep (Heller, 2014). Nonetheless, given the meticulous experimental design by Aton et al. (2014), it would be ridiculous to discount synaptic potentiation to occur during sleep. However, remaining is the question of how exactly sleep promotes synaptic potentiation. As the current study suggests a role of synaptic reinforcement during sleep, what is the mechanism behind the increase in OSRP under both SWS and REM sleep? Previous studies have shown a lack of selectiveresponse potentiation correlating to decreases in expression of the Arc gene (McCurry et al., 2010), and that Arc null mutant mice retained no memories nor synaptic potentiation after 2 hours (Plath et al., 2006). In addition, Shepherd et al. (Shepherd et al., 2006) demonstrated an induction of Arc transcription in CA1 hippocampal neurons following 5 minutes of spatial exploration. These studies, in conjunction to the sleep-dependent nature of OSRP, implicate Arc expression in the promotion of synaptic potentiation and memory consolidation in sleep. In order to elucidate the potential role of Arc in the sleep-dependent OSRP, Arc(-/-) mice can be generated and subjected to the same experimental trials performed by Aton et al. (2014). The knockouts can be experimentally induced, such as through a Tet-Off system, to rule out the possibility of developmental compensatory effects. In addition to the prospective results of the Arc(-/-) 114


mice, a western blot or qPCR experiment should be run to confirm the knock-out procedure. Lastly, since the competing SHY suggests sleep instead carries out long-term depression (LTD) (Tononi and Cirelli, 2014), an important control experiment is to test whether or not LTD occurs following sleep (with and without the induction of OSRP). This can be performed by monitoring the synaptic response under pharmacological intervention (Ca2+ chelators for example have been shown to block LTD [Brocher et al., 1992]). In summary, modifications of the experiment by Aton et al. (2014) may provide a clearer investigation into the role of sleep in synaptic potentiation and memory consolidation. References 1. Aton SJ, Suresh A, Broussard C, Frank MG. (2014). Sleep promotes cortical response potentiation following visual experience. Sleep. 37(7):1163-70. 2. Aton SJ, Seibt J, Dumoulin M, Jha SK, Steinmetz N, Coleman T, Naidoo N, Frank MG. (2009). Mechanisms of sleep-dependent consolidation of cortical plasticity. Neuron. 61(3):454-66. 3. Brocher S, Artola A, Singer W. (1992). Intracellular injection of Ca2+ chelators block induction of long-term depression in rat visual cortex. Proc Natl Acad Sci USA. 89:123-127. 4. Chauvette S, Seigneur J, Timofeev I. (2012). Sleep oscillations in the thalamocortical system induce long-term neuronal plasticity. Neuron. 75(6):1105-13. 5. Cooke SF, Cooke SF, Bear MF. (2014). How the mechanisms of long-term synaptic potentiation and depression serve experience-dependent plasticity in primary visual cortex. Philos Trans R Soc Lond B Biol Sci. 369(1633). [Pubmed: 20140021] 6. Cooke SF, Komorowski RW, Kaplan ES, Gavornik JP, Bear MF. (2015). Visual recognition memory, manifested as long-term habituation, requires synaptic plasticity in V1. Nat Neurosci. 18(2):262-71. 7. Frenkel MY, Sawtell NB, Diogo AC, Yoon B, Neve RL, Bear MF. (2006). Instructive effects of visual experience in mouse visual cortex. Neuron. 51(3):339-349. 8. Grosmark AD, Mizuseki K, Pastalkova E, Diba K, Buzsáki G. (2012). REM sleep reorganizes hippocampal excitability. Neuron. 75(6):1001-7. 9. Haider B, Hausser M, Carandini M. (2013). Inhibition dominates sensory responses in the awake cortex. Nature. 493:97-100. 10. Heller C. (2014). Ups and Downs of Synapses During Sleep and Learning. Sleep. 37(7):1157-1158. 11. McCurry CL, Shepherd JD, Tropea D, Wang KH, Bear MF, Sur M. (2010). Loss of Arc renders the visual cortex impervious to the effects of sensory experience of deprivation. Nat Neurosci. 13(4):450-7. 12. Nishida M, Pearsall J, Buckner RL, Walker MP. (2009). REM sleep, prefrontal theta, and the consolidation of human emotional memory. Cereb Cortex. 19:1158–1166. 13. Oyanedel CN, Binder S, Kelemen E, Petersen K, Born J, 115

Inostroza M. (2014). Role of slow oscillatory activity and slow wave sleep in consolidation of episodic-like memory in rats. Behav Brain Res. 275:126-130. 14. Payne JD, Stickgold R, Swanberg K, Kensinger EA. (2008). Sleep preferentially enhances memory for emotional components of scenes. Psychol Sci. 19:781–788. 15. Plath N, Ohana O, Dammermann B, Errington ML, Schmitz D, Gross C, Mao X, Engelsberg A, Mahlke C, Welzl H. (2006). Arc/Arg3.1 is essential for the consolidation of synaptic plasticity and memories. Neuron. 52(3):437-44. 16. Plihal W, Born J. (1997). Effects of early and late nocturnal sleep on declarative and procedural memory. J Cogn Neurosci. 9:534–547. 17. Seehagen S, Konrad C, Herbert JS, Schneider S. (2015). Timely sleep facilitates declarative memory consolidation in infants. Proc Natl Acad Sci. 112(5):1625-1629. 18. Shepherd JD, et al. (2006). Arc/Arg3.1 mediates homeostatic synaptic scaling of AMPA receptors. Neuron. 52(3):475-84. 19. Tononi G, Cirelli C. (2014). Sleep and the price of plasticity: from synaptic to cellular homeostasis to memory consolidation and integration. Neuron. 81(1):12-34. 20. Tononi G, Cirelli C. (2003). Sleep and synaptic homeostasis: a hypothesis. Brain Res Bull. 62(2):143-50. 21. Wagner U, Gais S, Born J. (2001). Emotional memory formation is enhanced across sleep intervals with high amounts of rapid eye movement sleep. Learn Mem. 8:112–119. Received April 06, 2015; revised ##, 200#; accepted Month, ##,

Month, 2013.

This work was supported by University of Toronto’s Human Biology Program. The authors thank Dr. Ju for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Justin Huang, Human Biology Department, 300 Huron Street, Wetmore Hall, University of Toronto. Toronto, ON M5S 1C6. Email: justin.huang@mail. utoronto.ca


A novel pharmacogenetic approach: Transient neuronal activation through TRPV1 and capsaicin

Sonja Ing

The ability to precisely induce activity in neurons is essential in deciphering how a neuronal population might interact within complex circuits and in elucidating behavioural correlates. Various techniques have been developed to this effect, such as optogenetics and genetically engineered receptors. However, while these techniques have been incredibly successful in controlling neural activity in vivo, they are not without their limitations – the former is both labour-intensive and invasive, and the latter often has either low temporal resolution or lack of cellular specificity. In this paper, a novel noninvasive pharmacogenetic model developed by Güler et al is presented, where neural activity in genetically defined populations can be induced directly, rapidly and reversibly by selective expression of capsaicin receptor TRPV1. Demonstrating that capsaicin can successfully induce transient activity in two distinct neural populations indicates the translatability of Selective TRPV1 ExpressionMediated Activation (STEMA) across neural systems. Addition of STEMA to the repertoire of neural effectors may prove instrumental in elucidating complex neural circuits. Key words: pharmacogenetics, neurogenetics, TRPV1, capsaicin, STEMA Background The ability to precisely and acutely control electrical activity in specific neuronal populations is essential in elucidating their function within complex circuits. Precisely manipulating neural activity in vivo allows one to directly correlate behavioural responses. The earliest neuron perturbation techniques, conventional pharmacology and electrical stimulation, were unable to achieve both molecular specificity and spatial acuity, and so were inadequate to definitively assign functional circuit roles to neuronal populations1. In recent years, novel techniques have been developed that encompass both spatial and molecular specificity, primarily though taking advantage of advances in transgenic techniques and neuron-specific gene expression2. The current leading techniques include optogenetics and genetically engineered designer receptors. While each of these technologies has proven invaluable in studying causal relationships between neural activity and behavioural output, they are not without their limitations. For example, while optogenetics possesses high spatial resolution and extraordinarily precise control of neuron spike timing and firing patterns, it is highly invasive, labour-intensive, and not well-suited to controlling diffuse signalling networks1,2,3. On the other hand, while designer receptors have high spatial acuity and are non-invasive, they exhibit low to medium temporal resolution, depending on the phamacokinetic properties of the specific ligand2,3. In their paper “Transient activation of specific neurons in mice by selective expression of the capsaicin receptor”, Güler et al present a novel pharmacogenetic technique that addresses some of the limitations posed by optogenetics and designer receptors. The authors demonstrate that Selective TRPV1 ExpressionMediated Activation (STEMA) is capable of transiently, rapidly and dose-dependently inducing neural activity in genetically defined neuronal populations through selective activation of the capsaicin receptor TRPV13. TRPV1 is a non-selective cation channel, normally expressed in the peripheral nervous system, that

may be stimulated by capsaicin, noxious heat and pH4. When activated, TRPV1 depolarizes neurons and generates action potentials4. To avoid peripheral and painful TRPV1 activation, the authors engineered mice that expressed the receptor solely in genetically defined populations and not at the endogenous locus. With STEMA, activation of TRPV1 by capsaicin, either by systemic injection or voluntary consumption, was sufficient to induce both neural activity and behaviour characteristics of the neurotransmitter system being activated3. In their paper, Güler et al successfully applied STEMA to the two distinct neuronal populations of dopamine (DA) and serotonin (5HT), respectively3. STEMA is a valuable addition to the neuroscience toolbox of neuron perturbation techniques since it addresses some of the limitations presented by other methods. Similar to other orthogonal pharmacogenetic approaches, STEMA has high spatial acuity and is also non-invasive, as surgical procedures are required to neither express the TRPV1 receptor nor deliver its ligand capsaicin2,3. Further, while it does not act on the same kinetic timescale as optogenetics, STEMA’s temporal resolution is greatly improved compared to other designer receptor2,3. Research Overview

Summary of Major Results

TRPV1 is exclusively expressed in DA neurons Güler et al genetically targeted TRPV1 to DA neurons through a triple transgenic approach. The first transgenic line consisted of Trpv1-knockout mice (B6.129X1-Trpv1tm1Jul/J), to eliminate peripheral expression of TRPV1. These mice were crossed to both Gt(ROSA)26Sor-stopflox-Trpv1-ires-ECFP and Slc6a3Cre mice. The resulting DAT-TRPV1 mice selectively expressed the Trpv1 gene in neurons expressing Cre-recombinase under the control of the dopamine transporter promoter Slc6a3 (or DAT) (Fig 1a)3. 116


Selective expression of TRPV1 was confirmed in vitro in VTA slices through double immunohistochemistry of neural activity marker cFos and DA neuron marker tyrosine hydroxylase (TH) following capsaicin administration (Fig 1b)3. 96.2±0.7% of cells tested positive for both cFos and TH, compared to only 4.8±2.1% of vehicle-injected mice3. Furthermore, cFos levels were increased in most DA targets, such as the lateral habenula and piriform cortex, of DAT-TRPV1 mice3. These results demonstrate that capsaicin is capable of eliciting activity-dependent gene expression specifically in DA neurons.

Capsaicin administration leads to specific activation of DA neurons and DA release

To confirm capsaicin-dependent activity of DA cells in DAT-TRPV1 mice, whole cell, voltage-clamp recordings were performed on midbrain slices in vitro. Putative DA neurons were first identified by characteristic waveform dynamics and firing pattern criteria, and large inward currents were rapidly induced in these DA neurons following a large application of capsaicin, similar to endogenous capsaicin-induced currents in the periphery3,5. In addition, comparable electrophysiological results were achieved in awake and freely moving mice. After using stereotactic coordinates to implant four-tetrode microdrives in the VTA, putative DA neurons were identified through characteristic baseline recordings3. The kinetics of the waveforms were not significantly different between DAT-TRPV1 and control mice, both before and after capsaicin administration, which indicates that STEMA does not interfere with normal physiological function3. Both the peak firing rate and burst activity increased in DAT-TRPV1 mice following capsaicin administration in a dose-dependent manner, while no changes were observed in controls3. These results indicate that capsaicin is capable of inducing DA activity in vivo. Moreover, in vivo fast-scan cyclic voltammetry confirmed that capsaicin is capable of enhancing DA release in DAT-TRPV1 mice3.

Behavioural responses characteristic of DA activity were induced by capsaicin

First, DA facilitates movement by modulating basal ganglia circuits, leading to a general increase in locomotion6. To monitor locomotor behaviour following capsaicin administration, mice were placed in an arena and consecutive beam breaks were measured3. Compared to controls, DAT-TRPV1 mice demonstrated increased activity following capsaicin application, and activity levels subsequently returned to control levels within 15 minutes (Fig 1c)3. These results indicate that capsaicin can induce locomotion in a reversible manner, which is representative of DA’s normal role in motor behaviour6. Second, DA facilitates goal-directed behaviour through the nigrostriatal pathway7. To investigate whether capsaicin-induced activity would modulate behavioural feeding responses, mice were trained to press a lever for food. Following high doses of capsaicin, lever-pressing was inhibited3; these results are in concordance with

117

studies on DA agonists where the drugs were capable of inhibiting food motivation8. However, following low doses of capsaicin, lever-pressing increased3; augmented food incentive behaviours can similarly be seen in some hypodopaminergic mouse models9. These results suggest that capsaicin-induced activity can either suppress or enhance incentive for food in a dose-dependent manner. Third, DA plays a significant role in reward, also through the nigrostriatal pathway7. To examine whether capsaicin-induced activity influenced the reward associated with capsaicin in a two-bottle capsaicin preference test, mice were presented with two solutions with either almond or vanilla flavouring, where one flavour was paired with capsaicin and the other with vehicle3. Mice were first allowed access to only one of the solutions during an 8 day association phase, and then were given free access to both solutions3. As capsaicin is the active ingredient that makes chili peppers spicy, wild type mice will not normally consume capsaicin, whereas TRPV1-knockout mice are indifferent3,4. While control mice exhibited no preference for either flavour, DATTRPV1 mice greatly preferred the solution containing capsaicin, which indicates that capsaicin consumption was sufficient to induce DA activity that resulted in increased reward value3.

Capsaicin-dependent activation of 5HT neurons

To demonstrate the adaptability of STEMA across neural systems, triple transgenic ePet-TRPV1 mice were created by crossing R26-TRPV1 mice with ePetCre mice, where Trpv1 was selectively expressed in neurons expressing Cre-recombinase under the control of 5HT transporter ePet3,10. The selective expression in 5HT neurons was confirmed by capsaicin administration followed by double immunohistochemistry for cFos and tryptophan hydroxylase, where 71.2±3.4% of neurons were positive for both markers3. Further, capsaicin-induced activity elicited behaviours characteristic of 5HT activation. For example, in an open-field anxiety test, ePet-TRPV1 mice spent less time in the center of the field as compared to controls, but returned to control levels within 10 minutes3. This result is comparable to the anxiogenic effects of 5HT agonists11, which indicates that capsaicin is capable of inducing 5HT-like effects in ePet-TRPV1 mice. Discussion and Conclusions In both DAT-TRPV1 and ePet-TRPV1 lines, TRPV1 was selectively expressed in the appropriate neuronal population, where capsaicin-induced activity was representative of the appropriate neurotransmitter. The capsaicin-induced activity was both rapid and reversible, which indicates that STEMA possesses improved temporal resolution over other designer receptor systems1. Moreover, the transience of the activity highlights an advantage of this technique, as many of the agonists and drugs that can currently activate DA or 5HT systems exert effects on the timescale of hours2,3. Further, STEMA is noninvasive, as surgical procedures are required for neither insertion of TRPV1 nor administration of capsaicin.


Figure 1. (a) DAT-TRPV1 triple transgenic mice, created upon a TRPV1-knockout background, selectively express capsaicin receptor TRPV1 in neurons expressing Cre-recombinase under the control of DA transporter Slca3+/Cre. (b) Following capsaicin administration, double immunohistochemistry for cFos and tyrosine hydroxylase in VTA slices demonstrates selective expression of TRPV1 in DA neurons. (c) Capsaicin administration in DAT-TRPV1 mice is sufficient to induce DA-like locomotor activity, as indicated by beam breaks/15 s made by DAT-TRPV1 (red) or control (black, blue) mice following capsaicin (darker) or vehicle (lighter) injection. Adapted from “Transient activation of specific neurons in mice by selective expression of the capsaicin receptor” by Güler et al, Nature commun, 3, 746 (2012).

These advantages, among others, help to distinguish STEMA from other techniques and allow it to be a valuable addition to the neuroscience toolkit. In recent years, various studies have chosen STEMA as the most suitable neuron perturbation technique for their specific investigations. For example, Han et al created MrgprA3+-TRPV1 neurons to demonstrate that the MrgprA3+ nociceptors were specific to itch12, while Wang et al used STEMA to enhance the activity of medial prefrontal cortex neurons while examining their role in vulnerability and resistance to stress within a depression context13.

Critical Analysis

The usefulness of a pharmacogenetic technique to a neuroscience study relies on whether the technique’s specific performance characteristics are appropriately tailored to the unique and specific objectives of the experiment. Such characteristics can be evaluated at the receptor level, the ligand level or the receptor-ligand interaction level2. In many respects, STEMA possesses advantages, though it is not without its limitations. Receptor: TRPV1 At the receptor level, TRPV1 can be expressed with high spatial resolution, since it can be specifically targeted to genetically defined neuronal populations via transgenic techniques1,2. While TRPV1 is normally endogenously present in the peripheral nervous system and is typically activated by noxious stimuli, the transgenic mice of STEMA were created on a Trpv1 knockout background4. Thus, exogenous administration of capsaicin only exerts effects on TRPV1 receptors that have been engineered into the CNS, contributing to the high spatial acuity. In addition, delivery of TRPV1 to specific cell types

is readily achieved, since the coding sequence for Trpv1 is approximately 2.5kb and this small size can be easily accommodated by either lentivirus or adenoassociated virus constructs2. Transgenic, rather than surgical, insertion of TRPV1 also indicates that STEMA is a noninvasive process3. Furthermore, as a ligand-gated ionotropic channel (LGIC), TRPV1 activation directly affects membrane excitability, thereby bypassing some of the challenges inherent to designer GPCRs, which function through second messenger cascades. Such activation of designer GPCRs may result in sequestration of second messengers, which would indirectly affect the function of endogenous receptors14. G-proteinmediated cascades could also exert other unwanted side effects such as altering gene expression regulation, particularly if GPCR activation is sustained14. Therefore, designer GPCRs, but not STEMA, may impose a constraint of compatibility with the endogenous system, since there is potential to interfere with normal physiological function2. However, as a LGIC, the ionic selectivity of TRPV1 must be considered. While TRPV1 is a nonselective cation channel, it has a high permeability to Ca2+ ions1. The resulting Ca2+ influx upon receptor activation may lead to confounding effects via Ca2+-mediated signaling pathways or even cell death2,3. While the former does require consideration, Ca2+-mediated cell death, however, is not a significant concern. Güler et al demonstrated that microglial activation, an early marker of cell damage, was not present 24 hours following capsaicin administration. Further, when capsaicin was repeatedly applied over a 30 day period, there was no significant reduction in DA neurons3. Nonetheless, it is possible that administration of higher capsaicin doses would result in TRPV1-dependent excitotoxicity. 118


Ligand: capsaicin At the ligand level, capsaicin provides many advantages as an effector. First, capsaicin can be conveniently and noninvasively administered in a variety of ways, each of which results in high CNS penetration: orally, intraperitoneally and intravenously1,2. If delivered orally, capsaicin may be self-administered, which provides an opportunity to study reward and addiction models, particularly if TRPV1 is selectively expressed in dopamine neurons2,3. In addition, capsaicin has high specificity and affinity for TRPV1, which contributes to the high spatial acuity of STEMA3. However, capsaicin is not the only ligand capable of acting on TRPV1, which limits some of the specificity of STEMA. For example, CNS endogenous ligands, such as endocannabinoid anandamide and N-arachidonoyl dopamine (NADA), have the potential to enhance neural activity independently of capsaicin, though they are not comparable to capsaicin in terms of potency at TRPV115,16. Although Güler et al did not observe changes in baseline firing rates of DA neurons in DAT-TRPV1 mice, the possibility of TRPV1 activation by endogenous ligands cannot be ruled out3. Another advantage to using capsaicin is its rapid metabolism, which contributes to the improved temporal resolution of STEMA17. Following capsaicin administration, neural activity onset can be seen within 2-5 minutes and capsaicin can be cleared in less than 15 minutes2, which makes it an ideal effector if one is investigating transient effects. Receptor-ligand: TRPV1-capsaicin The improved temporal resolution can be further explained at the interaction level, as the on and off kinetics of a system depends on both ligand and receptor properties. As described above, capsaicin has excellent pharmacokinetic properties due to its rapid metabolism and it also possesses high affinity for TRPV1,2,3. Further, as an inducible effector system, STEMA provides advantages over traditional transgenic models of knockout/knockdown mice or over-expression mice18. These mice inevitably display abnormal behaviours, substantial neurotransmitter regulatory changes, and other side effects, which introduces significant confounds if one is trying to correlate neural signaling with behaviour18. Although TRPV1 transgenic mice extensively eliminate these problems and thus are hugely advantageous, the TRPV1-knockout mice are not completely identical to wild-type mice3. The most significant discrepancies include impaired sensitivity to noxious temperatures as well as decreased inflammation-induced thermal hyperalgesia4. Future Directions While the kinetics of STEMA are superior to other designer receptor models, STEMA lacks the strong temporal resolution of optogenetics, where neural activity onset and termination occur on the order of milliseconds19. In the future, advancing this technique could involve improving the kinetic acuity by incorporating some elements of optogenetics. One possibility 119

involves activating TRPV1 with photo-releasable ligands such as caged vanilloids, which are biologically inert precursors that yield active ligands when photolyzed20. A second prospective activation strategy uses the intrinsic thermosensitivity of TRPV1, whereby a short pulse of infrared light may be sufficient to stimulate the receptor21. Future experiments would investigate if either of these activation strategies in DAT-TRPV1 mice is capable of sufficiently improving temporal resolution, through stimulating the receptor while making electrophysiological recordings. Further, these experiments would explore whether the activation strategies could elicit characteristic dopamine activity and behaviour, through tests such as electrophysiology in freely moving mice, locomotor or food consumption assays. Additional future experiments could involve addressing some of the limitations of STEMA and trying to clarify any possible confounds, such as potential effects of endogenous ligands on TRPV1, excessive activation of Ca2+-mediated signaling pathways, or behavioural side effects resulting from TRPV1-knockout mice15,16,18. In the case of the former, future experiments could be conducted on endocannabinoid anandamide-knockout or NADA-knockout lines to see if there are any significant differences in baseline firing rates compared to control wild type lines. Such an experiment could eliminate the potential confound of endogenous ligands, which is essential when trying to establish causal relationships. References 1. Sternson, S.M. & Roth, B.L. Chemogenetic tools to interrogate brain functions. Annu Rev Neurosci, 37, 387-407 (2014). 2. Shapiro, M.G. et al. Unparalleled control of neural activity using orthogonal pharmacogenetics. ACS Chem Neurosci. 3(8), 619-629 (2012). 3. Güler, A.D. et al. Transient activation of specific neurons in mice by selective expression of the capsaicin receptor. Nat commun. 3, 746 (2012). 4. Caterina M.J. et al. Impaired nociception and pain sensation in mice lacking the capsaicin receptor. Science. 288, 306–313 (2000). 5. Vellani V., Mapplebeck S., Moriondo A., Davis J.B. & McNaughton P.A. Protein kinase C activation potentiates gating of the vanilloid receptor VR1 by capsaicin, protons, heat and anandamide. J Physiol. 534, 813–825 (2001). 6. Kravitz A.V. et al. Regulation of parkinsonian motor behaviours by optogenetic control of basalganglia circuitry. Nature. 466, 622–626 (2010). 7. Wise R.A. Dopamine, learning and motivation. Nat Rev Neurosci. 5, 483–494 (2004). 8. van der Hoek G.A. & Cooper S.J. The selective dopamine uptake inhibitor GBR 12909: its effects on the microstructure of feeding in rats. Pharmacol Biochem Behav. 48, 135–140 (1994). 9. Beeler J.A., Frazier C.R. & Zhuang X. Dopaminergic enhancement of local food-seeking is under global homeostatic control. Eur J Neurosci 35(1), 146-59 (2012).


10. Scott M.M. et al. A genetic approach to access serotonin neurons for in vivo and in vitro studies. Proc Natl Acad Sci USA. 102(45), 16472â&#x20AC;&#x201C;16477 (2005). 11. Stiedl O, et al. Activation of the brain 5-HT2C receptors causes hypolocomotion without anxiogenic-like cardiovascular adjustments in mice. Neuropharmacol. 52, 949â&#x20AC;&#x201C;957 (2007). 12. Han, L. et al. A subpopulation of nociceptors specifically linked to itch. Nat Neurosci, 16(2), 174-182 (2013). 13. Wang, M., Perova, Z., Arenkiel, B.R. & Li, B. Synaptic modifications in the medial prefrontal cortex in susceptibility and resilience to stress. J Neurosci. 34(22), 7485-7492 (2014). 14. Nichols, C.D. & Roth, B.L. Engineered G-protein coupled receptors are powerful tools to investigate biological processes and behaviors. Front Mol Neurosci. 2 (2009). 15. Smart, D. et al. The endogenous lipid anandamide is a full agonist at the human vanilloid receptor (hVR1). Br J Pharmacol. 129(2), 227-30 (2000). 16. Huang, S.M. et al. An endogenous capsaicin-like substance with high potency at recombinant and native vanilloid VR1 receptors. Proc Natl Acad Sci USA. 99(12), 8400-5 (2002). 17. Chanda, S., Bashir, M., Babbar, S., Koganti, A. & Bley, K. In vitro hepatic and skin metabolism of capsaicin. Drug Metab Dispos. 36, 670-675 (2008). 18. Haenisch, B. & Bonisch, H. Depression and antidepressants: insights from knockout of dopamine, serotonin or noradrenaline re-uptake transporters. Pharmacol Ther. 129, 352-368 (2011). 19. Yizhar, O. et al. Optogenetics in neural systems. Neuron. 71, 9-34 (2011). 20. Zhao, J. et al. Caged vanilloid ligands for activation of TRPV1 receptors by 1-and 2-photon excitation. Biochem. 45(15), 4915-4926 (2006). 21. Tzabazis, A.Z. et al. Selective nociceptor activation in volunteers by infrared diode laser. Mol Pain. 7, 18 (2011).

120


Differential Brain Activation in Sommeliers: Effects of expertise on flavour integration Sylvia Jennings

The purpose of this study was to study the effects of expertise on perception of flavour. The study uses wine experts to understand the integration of a complex stimulus across modalities. Using fMRI and subtracting from control wine novices, the authors were able to isolate key differences in brain activation when experts and novices tasted wine. Experts had more immediate, stronger, and widespread activation, and activated more areas involved in memory. Experts also activated perceptual areas not involved in this study, which suggests that the brains of wine experts are wired to detect stimuli with many modalities. Further studies should investigate this integration using more modalities to truly demonstrate wine experts’ adaptations. This study was an important step in our knowledge pertaining to the structural and functional changes that occur in the brain as a result of expertise. It highlights that expertise is affecting both perception and cognition, making an expert more adept, and also more efficient. Key words: fMRI, flavour, expertise, olfaction pathways, wine, taste Background The purpose of this study is to examine the effects of expertise on taste perception. The authors investigated this using neuroimaging during wine consumption. The investigating these effects involves three major areas of research: taste perception, integration of modalities, and the neurological and psychological effects of expertise. There are many ways in which taste perception can be modified, and each of these has an effect on eating behaviour. Eating behaviour is a complicated but urgent issue, as it impacts obesity, nutrition, and the environment (Pazart et al., 2014). Flavour integration has a direct impact on eating behaviour (Okamato and Dan, 2013). Understanding the mechanisms behind flavour integration will further our insight into eating behaviour. Studying expertise’s effects is a convenient way to explore this integration and how it can differ depending on prior experience. Taste alone has been found to activate areas of the brain involved in both perception and affect (O’Doherty et al., 2001). Tasting activates areas of the thalamus, orbitofrontal cortex, amygdala, and insular taste cortex. Location and intensity of activation in the amygdala and orbitofrontal cortex will vary depending if the stimulus is negative or positive (O’Doherty et al., 2001). Some fMRI studies have shown that there is a significant top-down effect on taste perception (Kobayashi et al., 2004). In particular, taste imagery will affect perception. The other most important influence on flavour perception is smell. Although many factors such as sight, hearing and semantic cues can influence perception, the integration of taste and olfaction is the main mode of taste perception (Auvray and Spence, 2008). PET studies have shown that when olfaction and gustatory senses are stimulated simultaneously, their primary cortices are less active than when stimulated alone (Small et al., 1997). These studies also showed that novel taste and smell experiences activate the basal forebrain and amygdala. FMRI studies show that the insula, caudal orbitofrontal cortex, anterior cingulate cortex, and frontal operculum are involved in the 121

integration, especially when confronted with a novel stimulus (Small et al., 2004). The fact that novel stimuli affect activation implies that familiarity is an important factor in taste perception. The differences between experts and novices has long been studied in psychology, and more recently in neuroimaging. Most heavily studied area of expertise is visual recognition. Neuroimaging studies have shown that experts have much more activation in response to their domain-specific stimulus than novices, but some studies have shown that this effect is modified by level of engagement (Harel et al., 2010). In odor experts, it’s been shown that activation is modified compared to novices such that their brains are structurally and functionally different (Thomas-Danguin et al., 2014). Odor training results in increased sensitivity and identification ability. Experts have also shown to develop odor mental imagery, not found in novices. This implies that the structural changes are creating a very different experience towards odorants, which would heavily impact flavour perception/eating experience. In this study the authors examined the differential brain activation between wine experts and novices while consuming wine. The consumption was tightly controlled, such that the participants could only taste and retronasally smell the wine. FMRI monitored activation during a taste phase and after-taste phase. Research Overview

Summary of Major Results

The results of this study highlight key differences between experts and novices. All participants had activation in the insula, frontal lobe, pallidum, parahippocampal gyrus and the thalamus. Activation persisted in the insula and frontal lobe during the after-taste phase. To analyze the differences between experts and the control novices, the authors subtracted one group’s activation from the other. This showed that during the taste phase, experts had twice as many


brain regions activated. During the after-taste phase, the opposite effect was shown: novices had many more brain regions activated compared to controls. See figure 3 in appendix for full results of activation. There was also a difference in type of brain activation. Novices showed widespread parietal activation during the taste phase, whereas experts activated many areas of the temporal lobe, brain stem, and the occipital associative cortex. Not until the after-taste phase do the novices show greater activation in the temporal lobe. They also show greater activation in the frontal and parietal lobe. Experts show greater activation in the hippocampus during this phase. This difference in activation is significant because it shows that experts are processing stimuli faster, and with a more complex perception. Because of the differential brainstem activation, it’s clear that experts are processing stimuli differently at the most basic levels. During the after-taste phase, experts had completed the processes related to flavour integration and only memory processes remain. A clear difference between experts and controls is that only experts activated the hippocampus or parahippocampal region. Controls were still activating integration processes during this phase.

Conclusions and Discussion

Wine is a particularly good test of expertise. It’s been shown in previous studies that wine experts have a superior sense of smell, and have developed scent imagery – a skill not ordinarily possessed (Royet et al., 2013). Experts in this area have developed a semantic component to the integration of scent and taste that others have not. This ability shows that experts are different from novices in a perceptual and intellectual way. Wine experts are intensely practiced such that they can integrate information from sight, taste, smell and semantic cues to quickly assess many qualities. Wine experts had an immediately different reaction to wines from the instant of perception. Their brainstem was more activated, implying they had a stronger perception of flavour. Their temporal lobe was very strongly activated in many areas, implying that processing of the stimuli was happening immediately. The orbitofrontal, operculum, and insula, all essential for the integration process (Small and Prescott, 2005), were activated during the earlier phase in experts, but not as clearly activated in controls until the after-taste phase. Experts had a much earlier reaction and ability to integrate flavours. Their activation was also much more concise. Though they had much more activation in the first phase, it was located mostly in the temporal lobe, with specific projections into the frontal lobe, presumably to enable complex processing. The controls showed little temporal lobe activation, but widespread parietal lobe activation, which the experts demonstrated almost none of. This suggests that this entire portion of the cortex is unnecessary for extensive wine analysis. By the after-taste phase there are very clear differences between the experts and controls. Novices were still integrating senses via the operculum, orbitofrontal cortex and insula. Novices had begun to activate the temporal lobe in a more widespread manor, but the experts appear to have only memory-related processes left over. Activation in the occipital association cortex,

prefrontal lobe, and hippocampus demonstrate the experts’ extensive memory for wine, as they’re all associated with memory processing , and not directly with perception (Parr et al., 2004). Thus, experts are automatically recalling and comparing the wines.

Figure 1. Graph shows experts (red) vs. controls (blue). Highlights the conciseness of the expert’s activation in the key areas for integrating taste and scent (Pazart et al., 2014).

Figure 2. Graph shows experts (green) vs. controls (blue). Highlights the extensive activation in key areas for memory found in experts compared to controls (Pazart et al., 2014).

Conclusions The main conclusions to be drawn from the study are that expertise promotes faster and more efficient flavour processing. Further, the brain areas involved appear to be memory-related, implying a deeper understanding of the flavour (associated origins, familiar characteristics). Expertise implies faster processing at the appropriate levels of the brain to integrate flavour from various modalities. 122


Criticisms and Future Directions

A large problem with this study was the absence of stimuli. Wine tasting traditionally has three phases: swirling and visually examining, sniffing, and then tasting. The difference between wine experts and novices would be most apparent when other sources of information about the wine (such as orthonasal scent and sight) are present. Wine experts have developed a particular skill of integrating these senses, and the more senses that are integrated, the faster and more refined the experts’ activation would be compared to novices. Assessing wine experts activation in an unnatural way could severely impact their ability to succinctly perceive and retrieve information. Sight is a major component to wine tasting particularly pertaining to colour. Previous studies have investigated the general effects of colour on flavour (Spence et al., 2010), and these effects would certainly be present in wine tasting. As the results of this study showed, the visual association cortex was activated even without any visual stimulus, demonstrating that the automatic reaction of experts includes visualization as a key component. Very importantly, wine experts will sniff the wine before tasting. Omitting this component is a large flaw in understanding the effects of expertise. Studies have shown that taste and smell are not simply additive (Seubert et al., 2014). The combined effects activate a different pathway. Including an orthonasal component in this study could make an even faster, more efficient, and profound effect between experts and novices. Another issue with this study could be the perceived pleasantness between wine experts and novices. It’s been shown that wine experts have a greater preference for dry wines, such as used in this study (Blackman et al., 2010). The novice participants might have had an aversive reaction to the wines, and the experts a positive reaction. This difference in preference would have a large effect on the contrasting activation. In particular, the temporal lobe is highly associated with responding to positive or negative stimuli, and this might be responsible for some of the widespread temporal activation in experts. To control for this, a future study could pre-screen the wines to be sure there is no difference in preference between a typical novice compared to experts. Future studies need to integrate as many aspects of the traditional wine tasting process as possible. Studies should also consider differences in wine preference, as inappropriate stimuli for novices could be a confounding variable. References 1. Auvray M, Spence C (2008) The multisensory perception of flavor. Conscious Cogn 17:1016–1031. 2. Blackman J, Saliba A, Schmidtke L (2010) Sweetness acceptance of novices, experienced consumers and winemakers in Hunter Valley Semillon wines. Food Qual Prefer 21: 679–683. 123

3. Harel A, Gilaie-Dotan S, Malach R, Bentin S (2010) Topdown engagement modulates the neural expressions of visual expertise. Cereb Cortex 20:2304–2318. 4. Kobayashi M, Takeda M, Hattori N, Fukunaga M, Sasabe T, Inoue N, et al (2004) Functional imaging of gustatory perception and imagery: “top-down” processing of gustatory signals. Neuroimage 23:1271–1282. 5. O’Doherty J, Rolls E T, Francis S, Bowtell R, McGlone F (2001) Representation of pleasant and aversive taste in the human brain. J Neurophysiol 85:1315–1321. 6. Okamoto M, Dan I (2013) Extrinsic information influences taste and flavor perception: a review from psychological and neuroimaging perspectives. Semin Cell Dev Biol 24:247–255. 7. Parr WV, White KG, Heatherbell DA (2004) Exploring the nature of wine expertise: what underlies wine experts’ olfactory recognition memory advantage? Food Qual Prefer 15: 411–420. 8. Pazart L, Comte A, Magnin E, Millot J-L and Moulin T (2014) An fMRI study on the influence of sommeliers’ expertise on the integration of flavor. Front Behav Neurosci 8:358. 9. Royet JP, Plailly J, Saive AL, Veyrac A, Delon-Martin C (2013) The impact of expertise in olfaction. Front Psychol 4:928. 10. Seubert J, Ohla K, Yokomukai Y, Kellermann T, Lundström JN (2014) Superadditive opercular activation to food flavor is mediated by enhanced temporal and limbic coupling. Hum. Brain Mapp. doi: 10.1002/hbm.22728 11. Small DM, Jones-Gotman M, Zatorre RJ, Petrides M, Evans AC (1997) Flavor processing: more than the sum of its parts. Neuroreport 8:3913–3917. 12. Small DM, Voss J, Mak YE, Simmons KB, Parrish T, Gitelman D (2004) Experience-dependent neural integration of taste and smell in the human brain. J Neurophysiol 92: 1892–1903. 13. Small DM, Prescott J (2005) Odor/taste integration and the perception of flavor. Exp Brain Res 166: 345–357. 14. Spence C, Levitan CA, Shankar MU, Zampini M (2010) Does Food Color Influence Taste and Flavor Perception in Humans? Chemosensory Perception 3(1): 68-84. 15. Thomas-Danguin T, et al. (2014) The perception of odor objects in everyday life: a review on the processing of odor mixtures. Cogn Sci 5: 504.


Modeling and Treatment of Familial Parkinson’s Disease Using iPSCs

Nimara Dias

This review will discuss the way in which induced pluripotent stem cell (iPSC)-derived neurons, generated using skin fibroblasts from individuals with Parkinson’s disease (PD), are used as a means of observing the neurodegenerative phenotype associated with familial PD. How these derived neurons interact with specific cellular stressors, particularly with mutations for example, found in the PTEN-induced putative kinase 1 (PINK1) gene as well as the leucine-rich repeat kinase 2 (LRRK2) gene that are commonly involved in the familial, or inherited, form of Parkinson’s disease will also be analysed. By using iPSC-derived neurons from PD patients, it becomes possible to create a closely representative model of PD and from there, see what factors cause or drive the progression of the disease as well as attempt to rescue the ensuing phenotype. Pharmacological treatment for individual patients who may respond differently depending on their specific genotype is just one method of treatment among other possible future directions. Key words: Parkinson’s Disease (PD); induced pluripotent stem cells (iPSCs); fibroblasts; dopamine (DA); PTEN-induced putative kinase 1 (PINK1); leucine-rich repeat kinase 2 (LRRK2); sporadic PD; familial PD; mitochondrial reactive oxygen species (mROS); cellular stressors Background Parkinson’s disease (PD) is characterized by an ongoing degeneration of dopamine-generating neurons and synapses of the nigrostriatal pathway1. This neurodegeneration leads to a slow onset of clinical symptoms such as resting tremor, bradykinesia and a shuffling gait2, as well as nonmotor, cognitive symptoms as the disease progresses like depression, hallucination, and dementia among others3. The majority of PD cases are sporadic (idiopathic or lateonset PD), meaning that they may be brought forth by both genetic and environmental factors4. However, there are rare cases of familial, or inherited/earlyonset PD, and through studies of this form, causative mutations have been identified and knowledge of Parkinson’s disease has significantly expanded1. The most prominent mutations that have been identified are found in the leucine-rich repeat kinase 2 (LRRK2) gene, the PTEN-induced putative kinase 1 (PINK1) gene, the parkin gene (PARK2) and the α-synuclein gene (SNCA)4. The dominant mutation of LRRK2, that is involved in both familial (predominantly) and sporadic PD, causes the impairment of the function of mitochondria and is involved with loss of dopamine neurons5. Like LRRK2, PINK1 also encodes a kinase, this one particularly found in the membrane of the mitochondria4. It is thought to play a part in neuroprotection, and recessive mutations in this gene causes disruption in its kinase-signalling pathway6 leading to early-onset, familial PD1. Parkin and α-synuclein are highly associated in that they are commonly found localized together in Lewy bodies (LB), a hallmark of PD pathology7. Parkin may actually be involved in LB formation and aggregates of α-synuclein are characteristic of Lewy bodies7. The most problematic factor of understanding the true pathology of PD was that an appropriate model that closely resembled Parkinson’s disease in humans was not possible to find. Cultures of neurons from

animal models were difficult to sustain and differences in genes provided an unreliable model. With the use of iPSCs derived from the fibroblasts of the patients themselves which were reprogrammed back into a pluripotent state, and with the correct factors, differentiated into dopaminergic neurons, the mutations identified in the familial form of PD could be understood much more clearly8. Mechanisms by which the phenotype of PD arose, caused by the aforementioned mutations, could now be defined4. Typical experiments involving these iPSCs include the addition of cellular stressors to the iPSCs of patients that contain mutations in PD-associated genes, to observe what generates the pathology of PD4. Mitochondrial reactive oxygen species (mROS) levels are then analysed as a measure of vulnerability of the derived cells, mROS being a chemically inducible source of cellular stress1. From here, ways of rescuing the phenotype are then studied, for example, through gene correction5 or pharmacological treatment1. Research Overview

Summary of Major Results

Cooper et al. conducted experiments looking at specific mutations in genes that impact the activity of kinases involved with mitochondrial function: LRRK2 and PINK1, that seem to increase the risk of developing familial Parkinson’s disease. By using iPSCs derived from fibroblasts of familial PD patients as well as healthy patients without the disease and patients with the mutations who have not yet shown signs of PD, to form dopaminergic (DA) neural cells, researchers from several labs were able to combine assay results to compare the cell phenotypes from each1. 124


Chemical Stressors and Vulnerability

The mitochondria and proteins of the derived DA neurons from all subjects were first tested for vulnerabilities (dysfunction and degradation respectively) using ten different chemical stressors, where the vulnerability was measured in terms of the amount of lactate dehydrogenase (LDH) released from the cells1. The neural cells containing the recessive homozygous Q456X mutation in PINK1 showed higher vulnerability to valinomycin, MPP+, and concanamycin A among others compared to healthy individuals1. This was shared with both heterozygous and homozygous LRRK2 mutations, demonstrating that both asymptomatic individuals carrying the mutation and PD patients show vulnerabilities to similar chemical stressors1. In addition, after immunocytochemistry and cell count assays, it was observed that these same neural cells also contained less DA neurons after application of chemical stressors1. In keeping with a separate study observing the association of MPP+ with DA neuronal cell death, a significant loss of DA neurons after exposure to a low dosage of MPP+ was also shown2.

mROS

Neural cells from patients with PD carrying the PINK1 Q456X mutation showed increased levels of mROS when a low concentration of valinomycin was applied, however this increase did not occur with the addition of any other chemical stressors1. Typically the antioxidant GSH acts as a protective measure against harm that arises from increased levels of mROS1. These neural cells were observed to have GSH present, and at lower levels in comparison to healthy individuals, after addition of valinomycin, MPP+ and concanamycin A, meaning that cellular oxidative stress also causes high vulnerability for those carrying the PINK1 mutation1 (Figure 1). A study that looked at GSH distribution in the substantia nigra (SN) confirmed that there is a depletion of GSH within the SN of PD patients through mercury orange histofluorescence on samples of brain tissue9 (Figure 2).

Graziotto, J. et al. Pharmacological Rescue of Mitochondrial Deficits in iPSC-Derived Neural Cells from Patients with Familial Parkinsonâ&#x20AC;&#x2122;s Disease. Sci Transl Med. 4, 141ra90-141ra90 (2012).

Figure 1 - Measuring levels of GSH in response to increasing concentrations of cellular stressors added. D,E,F, and G show a reduction in GSH levels in PINK1 Q456X mutant neural cells at varying concentrations of particular cellular stressors in comparison to healthy subjects, whereas H, and I show no change between healthy and PD patients.

Mitochondrial Respiration

The oxygen consumption rates of derived neural cells were determined by the use of compounds targeting ATP synthase and components of the electron transport chain (ETC) in mitochondria1. The basal rate of oxygen consumption in those carrying the PINK1 mutation was increased in comparison to healthy individuals and was not changed with the addition of oligomycin (targets ATP synthase). However those carrying either the heterozygous or homozygous mutation of LRRK2 showed decreased basal oxygen consumption rates and similar reactions to oligomycin, FCCP and rotenone (the latter two targeting components of the ETC)1.

Mobility of Mitochondria

Using live cell imaging, it was found that PD patients only carrying the LRRK2 mutations showed an increase in mobility of mitochondria in a more bidirectional manner as well as a decrease in length, where the mitochondria in axons of neural cells containing this mutation were 125

Pearce, R.K.B., Owen, A., Daniel, S., Jenner, P., Marsden, C.D. Alterations in the distribution of glutathione in the substantia nigra in Parkinsonâ&#x20AC;&#x2122;s disease. J Neural Transm. 104, 661-677 (1997).

Figure 2 - (A,C) transmitted light, (B,D) fluorescence. A and B show PD substantia nigras stained for GSH with less expression of GSH in comparison to the control (C and D) substantia nigras.


20% shorter, in comparison to both healthy individuals and those carrying the PINK1 mutation1. Interestingly, the axons themselves of the iPSC-derived PD neural cells, or those carrying the mutations, were not of a different length in comparison to healthy subjects, however this does not seem to match the literature in which a decrease in length of neurites is often seen in LRRK2 mutant cell forms of PD patients10.

Pharmacological Rescue

To see if vulnerability of neural cells that carried the PINK1 and LRRK2 mutations could be rescued pharmacologically, coenzyme Q10 or rapamycin (antioxidants), or an LRRK2 inhibitor was used1. The results showed that coenzyme Q10 reduced the release of LDH in neural cells carrying any mutation (if exposed to low concentrations of valinomycin but not high concentrations), rapamycin reduced the vulnerability of neural cells with the LRRK2 mutation only to valinomycin, but no other mutant neural cell, and the LRRK2 inhibitor reduced LDH release of any neural cell mutant from exposure to valinomycin1. In addition rapamycin and the LRRK2 inhibitor reduced mROS levels from neural cell PINK1 mutants exposed to valinomycin1. Several studies have also discussed possible herbal remedies that can be used to reduce oxidative damage, such as green tea component epigallocatechin 3-gallate (EGCG) that was shown to prevent loss of DA neurons from exposure to MPTP11, however these experiments use mice models and so this may not be representative of human PD. Discussion From the initial experiments that assessed vulnerability levels in iPSC-derived neural cells from patients with familial PD and pre-symptomatic patients who carry the mutations as well, it was shown that these cells displayed higher vulnerability when exposed to low concentrations of chemical stressors such as valinomycin1. Valinomycin is a chemical stressor which causes the depolarization of mitochondria with an influx of K+ ions1. However they do not show vulnerability to FCCP, a chemical stressor that does the same function except using protons. This may show that the mutations in the derived neural cells cause the inability to respond to mitochondria that has been damaged by K+ ions1. Oxidative stress is one of the major contributors to the characteristic loss of DA neurons causing Parkinson’s Disease.12 Nitric oxide (NO) and H2O2 are substances known as reactive oxygen species, and these are formed as metabolism by-products12. An increase in these substances will cause DNA, lipid and protein damage (oxidative damage)12. Antioxidants such as reduced GSH counteract the effects of oxidative damage12, however experiments show that PD patients, or those carrying the familial PD mutations, have depleted levels of GSH in response to chemical stressors1. This is to be expected and confirms that a proper PD model is being used as autoxidation of dopamine is what both generates H2O2 and reduces GSH allowing free radicals to accumulate, oxidative damage to continue and loss of DA neurons to progress12.

It was shown that the basal rate of oxygen consumption in those carrying the PINK1 mutation was increased in comparison to healthy individuals but remained unchanged with the addition of oligomycin that inhibits ATP synthase1. This is showing that ATP-independent respiration was taking place and that protons were increasingly moving passively from the membrane of the mitochondria1. However in LRRK2 mutant neural cells there was a decreased basal oxygen consumption rate and similar reactions to oligomycin, FCCP and rotenone1. So therefore in opposition to those carrying the PINK1 mutation, proton leakage was not enhanced1. In terms of the mobility of mitochondria, only the neural cell lines that carried the LRRK2 mutations showed any differences from the normal axonal transport process1. Studies using Drosophila as a model of PD clearly showed that PINK1 had strong implications as a regulator of mitochondrial transport and that knockdowns of it would cause dysfunctional mitochondria and impaired mitochondrial distribution13. This could possibly be considered an example of discrepancies that occur between models, where the iPSC line derived specifically from the fibroblasts of the patient themselves is more accurate in describing the mechanisms behind human PD, as opposed to animal or insect models. Using iPSCs offers a major benefit in understanding what products could be used to rescue a diseased phenotype. Pharmacological rescue of vulnerability was displayed by antioxidants like coenzyme Q10 and rapamycin, as well as an LRRK2 inhibitor1, but there are so many more compounds that can be used to target different aspects of cellular stress that may be influencing the neurodegenerative phenotype of PD. For example, glial-derived neurotrophic factor (GDNF) was shown in a separate study to reverse the effects of MPP+ (an inhibitor of mitochondrial complex I also involved in loss of DA neurons1) where the presence of GDNF allowed for 90% cell survival (as opposed to the 50% cell survival in the presence of MPP+ alone)2. Conclusion It is through the use of iPSCs that the most accurate information can be gathered about human Parkinson’s disease. Throughout the literature discrepancies between this model representing the patients themselves, and animal models could be identified. The continuous degeneration of dopamine-generating neurons in the nigrostriatal pathway is the key feature of Parkinson’s disease and understanding how this disease arises is necessary for understanding how to rescue the phenotype. The iPSCs generated in this study were efficient in responding to low concentrations of cellular stressors that can be thought to mimic the gradual amassing of dysfunctional mitochondria (as you would see in aging PD patients) and so they provide an opportunity to delve into how these significant mutations affect the degenerative aspects of this disease1. Individual treatment is possible by using iPSCs, and can be done by using cellular reprogramming technology as seen from the data collected of 126


which mutations respond to which antioxidants for pharmacological rescuing. In short, these neural cells derived from iPSCs allow for major advances in understanding the foundation of PD and possible treatments.

Criticisms and Future Directions

The literature surrounding PD iPSC-derived neural cells as a proper model of neurodegenerative diseases and as a therapeutic model is slowly becoming more significant. This is just the beginning of recognizing the true potential of understanding the mechanisms by which Parkinson’s disease arises and can be stopped. There are limits to what animal models, cellular models and in vitro models can offer4 and in an era of individualized medicine, the use of iPSCs has no end. From Cooper et al.’s paper what can be seen already is a more defined mechanism by which loss of DA neurons occurs, a difference in what phenotypes arise from each familial PD mutation and differences in the pharmacological substances that will rescue each phenotype the best. Critically speaking though, even though this paper was about pharmacological rescue of mitochondrial deficits, a lot of the focus was put on rescuing vulnerability to two particular chemical stressors1. Focusing on specific aspects of the overall degeneration that comes with PD was repeated often in the literature and represents the huge gap in knowledge of all the known aspects put together. Little research has contemplated how many unknown factors actually come in to play. The most important future direction that the majority of the literature surrounding the rare familial cases of PD point to, is how to use this information to understand and potentially diminish the much more common cases of sporadic PD. Since both familial and sporadic PD forms have similar implications in impaired mitochondrial function, axonal transport, improper protein aggregation, etc. all eventually leading to loss of neurons, and both are related to age14, the use of iPSCs has also given an incredible advantage in the ability to extrapolate what can be learned from genetic cases, and apply it to idiopathic ones. Also, although pharmacological treatment for individual cases is often researched, another plausible method of treatment is gene correction. Sanders et al. found that the damage done to mtDNA by the LRRK2 G2019S mutation was rescued by ZFN-mediated correction of the mutation in the derived iPSC lines15. This opens up a brand new pathway for treatment and one in which a mixture of pharmacological products would not be required to rescue the disease phenotype. With the transition from animal models to iPSCs, research has surged forward in an unprecedented manner. An accurate model has provided much more potential to identify the cause of PD and finally establish safe and effective treatment methods. References 1. Graziotto, J. et al. Pharmacological Rescue of Mitochondrial Deficits in iPSC-Derived Neural Cells from Patients with Familial Parkinson’s Disease. Sci Transl Med. 4, 141ra90-141ra90 (2012). 127

2. Peng, J., Liu, Q., Rao, M.S., Zeng, X. Using Human Pluripotent Stem Cell– Derived Dopaminergic Neurons to Evaluate Candidate Parkinson’s Disease Therapeutic Agents in MPP+ and Rotenone Models. J Biomol Screen. 18, 522-523 (2013). 3. Chaudhuri, K.R., Healy, D.G., Schapira, A.H.V. Nonmotor symptoms of Parkinson’s disease: diagnosis and management. Lancet Neurol. 5, 235–245 (2006). 4. Beevers, J.E., Caffrey, T.M., Wade-Martins, R. Induced pluripotent stem cell (iPSC)-derived dopamingergic models of Parkinson’s disease. Biochem.Soc Trans. 41, 1503-1508 (2013). 5. Xu, Q., Shenoy, S., Li, C. Mouse models for LRRK2 Parkinson’s disease. Parkinsonism Relat D. 18S1, S186-S189 (2012). 6. Gandhi, S, et al. PINK1 protein in normal human brain and Parkinson’s disease. Brain. 129, 1720-1731 (2006). 7. Schlossmacher, G.M. et al. Parkin Localizes to the Lewy Bodies of Parkinson Disease and Dementia with Lewy Bodies. Am J Pathol. 160, 1655-1667 (2002). 8. Soldner, F. et al. Generation of Isogenic Pluripotent Stem Cells Differing Exclusively at Two Early Onset Parkinson Point Mutations. Cell. 146, 318-331 (2011). 9. Pearce, R.K.B., Owen, A., Daniel, S., Jenner, P., Marsden, C.D. Alterations in the distribution of glutathione in the substantia nigra in Parkinson’s disease. J Neural Transm. 104, 661-677 (1997). 10. Burke, R.E., O’Malley, Karen. Axon degeneration in Parkinson’s disease. Exp Neurol. 246, 72-83 (2013). 11. Choi, J. et al. Prevention of Nitric Oxide-Mediated 1-Methyl-4-Phenyl-1,2,3,4-Tetrahydropyridine-Induced Parkinson’s Disease in Mice by Tea Phenolic Epigallocatechin 3-Gallate. NeuroToxicology. 23, 367-374 (2002). 12. Surendran S., Rajasankar S. Parkinson’s disease: oxidative stress and therapeutic approaches. Neurol Sci. 31, 531-540 (2010). 13. Liu, S. et al. Parkinson’s Disease-Associated Kinase PINK1 Regulates Miro Protein Level and Axonal Transport of Mitochondria. PLoS Genet. 8, e1002537 (2012). 14. Sanchez, G. et al. Unaltered Striatal Dopamine Release Levels in Young Parkin Knockout, Pink1 Knockout, DJ-1 Knockout and LRRK2 R1441G Transgenic Mice. PLoS ONE. 9, e94826 (2014). 15. Sanders, L.H. et al. LRRK2 mutations cause mitochondrial DNA damage in iPSC-derived neural cells from Parkinson’s disease patients: Reversal by gene correction. Neurobiol Dis. 62, 381-386 (2014). Received April 6, 2015; revised April 6, 2015; accepted April 6, 2015. This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The author thanks Dr. Ju, and the students in HMB300 for technical assistance, execution, and feedback on this assignment. Address correspondence to: Department, 40 Willcocks Toronto, ON M5S 1C5

Nimara Dias, Human Biology St, University of Toronto, Email: dias.nimara@gmail.com

Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program


To accomplish more or loss less: the story of sleep deprivation and Alzheimer’s disease

Xin Yue Kou

It is a difficult question to define what is sleep, and would take a whole field of research to try to explain that question, which we still don’t quite have the answer to yet. What we do know is that sleep is vital, many processes occurs during sleep, restoring our body to optimal condition. Based on experiences, we know that when we temporarily loose a large amount of sleep we lack the ability to physically and cognitively function properly, however when we spread the amount of sleep lost over a longer period of time, it might be harder to feel the same effects, but chronic sleep deprivation is in fact more detrimental than how we physically feel about it. Previous studies have looked at the link between sleep deprivation and neurodegenerative diseases such as Alzheimer’s disease (AD), where sleep abnormalities can increase the risk of an individual to develop AD, although there is also evidence vice versa suggesting changes in sleep-wake cycles can cause significant increase in AD progression through increased amyloid-beta plaques. However it is uncertain whether SD is a causal risk factor or simply a disease biomarker, due to that lack of intensive knowledge for effects on other important AD phenotypes. Hence this review will set to determine the role of sleep deprivation in AD. Key words: Sleep deprivation, chronic stress, Alzheimer’s disease, amyloid precursor protein, tau metabolism, astrocytes. Background Neurological dementias such as Parkinson’s disease, dementia with Lewy bodies, Alzheimer’s disease and many more are becoming increasingly common in our society. As more and more death are caused by these diseases, it has became the pressing concern to find an effective cure. Alzheimer’s disease being the most common of the neurodegenerative diseases have definitely been intensively studied, and we have learned much more about the disease since it was first diagnosed, however we have still yet to find the defining evidence that will lead us to the cure. Defining features of AD include the amyloid-beta plaques caused by the cleaved form of the amyloid precursor protein (APP), amyloid-beta 40 and 42, and the neurofibrillary tangles caused by aggregating hyper-phosphorylated tau proteins [1,2]. However recent studied show that neuropathological events such as the loss of neurons occur far before the disease is clinically recognized [3,4]. Hence it is critical to find the appropriate biomarker that can detect the earliest onset of AD. One way to look for early associative biomarkers is to find potential risk factors that may lead to AD, which would be useful in terms of narrowing down subjects who may be more likely to develop AD, and therefore track the development of AD. Finding a risk factor is also important in terms of prevention, and developing treatment as well. Studies have shown evidence of chronic stress associated with cognitive decline similar or related to AD [5,6], especially the link between sleep deprivation and AD have caught the attentions of many scientists. Many evidences show that chronic sleep deprivation or changes in sleep patterns such as sleep fragmentation is associated with phenotypes of AD [7], for example amyloid-beta plaques were shown

to correlate positively with sleep deficits [8]. Even though many evidence have illustrated that there is a relationship between sleep deficits and AD, there still lacks very clear evidence showing that chronic sleep deficits do in fact cause an increased risk of AD rather than just an associative biomarker as the disease progresses. One of the first study conducted to look at the various AD phenotypes in relation to sleep deprivation is by Di Meco et al, where they used the 3xTg mouse model and introduced the mice to chronic sleep deprivation over 2 month trial. The mice were then later sacrificed for brain examination by biochemistry assays as well as immunohistochemistry studies, and results demonstrated that chronic sleep deprivation do in fact likely contribute to the development of AD [9]. This review will critically analyze the results of the aforementioned article as well as expanding on related evidences provided by other studies. Research Overview

Major Results and Discussion

Sleep deprivation decrease cognitive functions The 2 different groups of 3xTg mice were tested using the Y-maze, fear conditioning which showed insignificant result, and only in the Morris water maze where sleep deprived mice showed significantly decreased spatial memory [9]. Most studies confirms that cognitive function such as learning and memory is greatly affected by sleep deprivation [10], where not only spatial memory is affected, but episodic memory as well, as sleep plays an important role in memory consolidation and improves synaptic plasticity [11]. 128


Sleep deprivation and Amyloid-beta Surprisingly the assay results did not show significant difference of the plaque forming amyloid-beta 1-40 and 1-42, although the results suggested to be not very reliable due to the young age of the mice [9]. This definitely did not support other studies, previous evidence shown in APP-PS1 mice suggested that amyloid-beta plaque deposition is significantly associated with sleep deprivation [8]. This association has been tested in human subjects as well based on recording of decreased REM sleep and increased SWS fragmentation. The study by Sanchez-Espinosa et al looked at the relationship between sleep deficits and plasma amyloid-beta level in amnestic mild cognitive impairment (aMCI) subjects, often considered the prestage of developing AD, as well as normal healthy old (HO) adults. Results show that higher level of amyloidbeta deposition is significantly positively correlated with increased SWS arousals only in aMCI subjects, not HO (figure1) [12]. Therefore it is likely that sleep deficits facilitate plaque deposits in AD individuals, however is it still unsure whether sleep deficits can cause plaque deposition under non-AD condition.

conformational change, which correlates to the results of increased MC-1 antibody immunoreactivity, which is used to recognize forms of pathogenic tau, in sleep deprivation mice[9]. However other studies do suggest that tau metabolism is not significantly affected by sleep deficits [13].

Sleep deprivation and neuroinflammation

Glial fibrillary acidic protein (GFAP) as an astrocytosis marker were found at higher expressions in the brains of the sleep deprived animals. Astrocytes may also be a progressive marker for AD, some study actually consider that astrocytes deteriorate prior to the actual neurons [14]. Conclusion Everyone knows that sleep is important, we need a good night sleep to function properly and to be physically awake during the day. However as our society evolved, we tend to prioritize other things before adequate sleep, for example, workers have overtime, students cram for exams, and sometimes enjoying the night life with friends is just more exciting to us than going to bed before midnight. But not many people is aware of the long term consequences that comes with chronic sleep deprivation Based on current evidences, it is still difficult to clarify that whether sleep deprivation leads to the various AD phenotypes or vice versa, especially the underling mechanisms are yet to be unveiled. Even though there is no definite proof that chronic sleep deprivation leads to AD, but it is still a risk factor that do in fact facilitate progression of AD. So whether to accomplish “more” or lose “less”, the choice is yours.

Criticisms and Future Directions

Figure 1. a)HO have significantly more REM sleep and less SWS fragmentation. b)HO have significantly less amyloid-beta 40 and 42 plaque forming peptides. c) Positive correlation between SWS arousal and amyloid-beta 42 in aMCI subjects.

Sleep deprivation and tau metabolism

Brain assay of the sleep deprivation group showed decreased tau phosphorylation at several AD-relevant epitopes. After investigation, a significant decrease of cdk-5 kinase activity in sleep deprived mice seems to be responsible[9]. Overall sleep deprived animals had significantly higher amount of total insoluble tau, possibly due to 129

The main article was interesting that it covered almost complete aspects of the AD phenotype and how it is affected by chronic sleep deprivation, however potentially due to that the study covered such a wide spectrum, each separate individual experiments was not performed very detailed or thoroughly explained, and did not clearly test for confounding factors. Another factor to note is that this article is using an AD mouse model, meaning that the subject itself is predetermined to develop or have developed AD. Hence even if the results can be supported, it would only mean that sleep deprivation can increase the progression of AD, and we still would not be able to say that chronic sleep deprivation can cause onset of AD in a previously healthy individual. In other words, it has not been confirmed that sleep deprivation can causes development of AD, but it does in fact increase the risk and progression of developing AD. Other studies also suggest that not only sleep deprivation contribute to AD, in fact chronic stress in general such as depression and anxiety also pose as risk factors of AD [10]. Therefore a more direct way of looking at chronic stress factors is to directly monitor changes in cortisol level [15].


Even though genetic causes of AD is only about 5%, prevention for all forms of AD may have a genetic solution, with the increasing advancements in genetic technologies, developing a genetic solution for the prevention as well as treatment of the disease seems to be an appropriate next step [16]. References 1. Wurtman, R. Biomarkers in the diagnosis and management of Alzheimer’s disease. Metabolism Clinical And Experimental. 64, 547-550 (2015). 2. Agostiho, P., Pliassova, A., Oliveira, C.R., Cunha, R.A. Localization and trafficking of amyloid-β protein precursor and secretases: Impact on Alzheimer’s disease. Journal of Alzheimer’s Disease. 45, 329-347 (2015). a7 3. Bernard, C. et al. Time course of brain volume changes in the preclinical phase of Alzheimer’s disease. Alzheimers Dement. 10,143–51 (2014). 4. Sperling, R.A. et al. Toward defining the preclinical stages of Alzheimer’s disease: recommendations from the National Institute on Aging-Alzheimer’s Association workgroups on diagnostic guidelines for Alzheimer’s disease. Alzheimers Dement. 7, 280–292 (2011). 5. Wilson, R.S., Begeny, C.T., Boyle, P.A., Schneider, J.A., Bennett D.A. Vulnerability to stress, anxiety, and development of dementia in old age. Am J Geriatr Psychiatry. 19, 327-334 (2011). 6. Ravona-Springer, R., Beeri, M.S., Goldbourt, U. Younger age at crisis following parental death in male children and adolescents is associated with higher risk for dementia at old age. Alzheimer Dis Assoc Disord. 26, 68-73 (2012). 7. Pan, W., Kastin A.J. Can sleep apnea cause Alzheimer’s disease? Neuroscience and Biobehavioral Reviews. 47, 656-669 (2014). 8. Roh, J.H. et al. Sleep-wake cycle and diurnal fluctuation of amyloid-β as biomarkers of brain amyloid pathology. Sci Transl Med. 4(150), 150ra122 (2012). 9. Di Meco, A., & Joshi, Y. B., & Pratico, Domenico. Sleep deprivation impairs memory, tau metabolism, and synaptic integrity of a mouse model of Alzheimer’s disease with plaques and tangles. Neurobiologi of Aging. 35, 1813-1820 (2014). 10. Kumar, A., Chanana, P. Sleep reduction: A link to other neurobiological diseases. Sleep and Biological Rhythms. 12. 150-161 (2014). 11. Tononi, G., Cirelli, C. Sleeo and the price of plasticity: from synaptic and cellular homeostasis to memory consolidation and integration. Neuron. 81, 12-34 (2014). 12. Sanchez-Espinosa, M.P., Atienza, M., Cantero, J.L. Sleep deficits in mild cognitive impairment are related to increased levels of plasma amyloid-β and cortical thinning. NeuroImage. 98, 395-404 (2014). 13. Rothman, S.M., Herdener, N., Frankola, K.A., Mughal, M.R., Mattson, M.P. Chronic mild sleep restriction accentuates contextual memory impairments, and accumulations of cortical Aβ and pTau in a mouse model of Alzheimer’s disease. Brain Res. 1529, 200–8 (2013).

14. Sica, R.E. Could astrocytes be the primary target of an offending agent causing the primary degenerative diseases of the human central nervous system? A hypothesis. Medical Hypotheses. 84. 481-489 (2015). 15. Duncan, M. J. et al. Effects of aging and genotype on circadian rhythms, sleep, and clock gene expression in APPxPS1 knock-in mice, a model for Alzheimer’s disease. Experimental Neurology. 236, 249-258 (2012). 16. Alonso Vilatela, M.E., Lopez-Lopez, M., Yescas-Gomez, P. Genetics of Alzheimer’s disease. Arch Med Res. 43(8), 622–31 (2012).

Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program

130


Reconsolidation and Extinction Are Dissociable and Mutually Exclusive Processes: Behavioral and Molecular Evidence The Importance of Specificity in Neuroscience

Alexandra Kubica

Understanding how much the processes of extinction and reconsolidation differ is important for the increase in knowledge of the memory system as well as improvement of anxiety therapies. Merlo, Milton, Goozée, Theobald, & Everitt, (2014) were able to show that extinction and reconsolidation are mutually exclusive processes by observing how calcineurin levels change based on amount of exposure to conditioned stimulus. However, more research needs to be completed as lack of specificity of calcineurin and confounding factors such as increased anxiety were not taken into account in the execution of this experiment. Key words: reconsolidation; extinction; calcineurin; NMDA receptors; fear conditioned learning; Lister Hooded rat; memory; neuroscience; Background Originally it was thought that memory once encoded would remain stable even if retrieved. However, with extensive research, memories have been found to change and can be reconsolidated once retrieved. Reconsolidation is the process of a memory being reactivated and thus being liable and susceptible to change (Nader & Hardt, 2009). This updated version of the memory is then stored again, affecting the original memory. Extinction, however also uses the same mechanism of retrieving memories in order to change them. In the process of extinction the organism is exposed to the stimulus it was trained to react to in a certain way, over and over again until it is habituated and does not respond in the same way it did when it was originally trained (Lin et al., 2003). This new memory of not reacting to the stimulus then inhibits the old memory of reacting to it and the behaviour is extinct. In order for a memory to be consolidated a kinase must be activated so that protein transcription can start (Glanzman, et al., 1989). Only once this occurs can a memory be stable and eventually be stored in the cortex, and if a protein is not formed the memory cannot be consolidated, as in the case of short term memory (Nader, Schafe, & LeDoux, 2000). Calcineurin is a protein that has been found to help with the extinction of fear based memories by inhibiting phosphorylation and not allowing protein synthesis to occur (Lin et al., 2003). NMDA receptors in the amygdala release calcineurin and were found to be responsible for facilitating fear memory consolidation (Falls, Miserendino, & Davis, 1992). Researchers then became interested in discovering if these two processes could occur at the same time. Merlo, Milton, Goozée, Theobald, & Everitt, (2014), were interested in observing if these two processes, reconsolidation and extinction, were mutually exclusive or if they could occur at the same time. Research Overview

Summary of Major Results

Merlo et al., (2014) trained rats to anticipate a shock

131

through the floor of the box they were placed in, when a certain auditory stimulus was presented. 24hours later the rats were injected with either saline solution, a NMDA receptor agonist DCS (D-cycloserine) or a NMDA receptor antagonist MK-801. The researchers believed that when the NMDA receptors were inhibited using MK-801 it would release less calcineurin and extinction should not occur. However, when NMDAR activity was increased with DCS it meant that there was more calcineurin and thus extinction should occur. After being injected, the rats either received the shock stimulus 1, 4 ,7 or 10 times. Rats were then either tested 24 hours after reactivation of the memory or were biopsied an hour after to observe calcineurin levels. Results found that in the 1CS (control stimulus) paired with DCS condition, the rats showed the same amount of freezing as with saline (Figure 2). 1CS paired with MK-801 showed significantly less freezing responses. In the 10CS with MK-801 a significant amount freezing is observed compared to saline and DCS. In 10CS and DCS condition there is a decrease in freezing compared to control, but a very large decrease compared to MK-801. In 4CS time spent freezing appeared to be about the same over all injection conditions. In 7CS condition similar to 10CS MK-801 had significantly more freezing with a decrease in saline condition and even more of a decrease in DCS condition. In western blots performed after the second day more calcineurin was found in the 10CS condition rats compared to 1CS (Figure 1). About the same amount of calcineurin was found across all CS conditions with MK-801. Brain activation was observed to be the same for both processes in the basolateral amygdala. Theses results are in line with a previous study done by Pérez-Cuesta and Héctor Maldonado in 2009, where they tested reconsolidation and extinction in crabs and found extinction cannot happen with only one exposure to the stimulus, only reconsolidation will occur. However, they also found reconsolidation and extinction can occur simultaneously when there is more than one exposure to the conditioned stimulus, going against what Merlo et al., found in their 10 and 7 condition stimulus conditions.


Figure 1. Interpretation of western blots done one hour after re-exposure to conditioned stimulus on the second day for varying amount of exposure to the stimulus .

Conclusions and Discussion With these results the researchers concluded that extinction and reconsolidation cannot happen at the same time, they are mutually exclusive due to the effects of calcineurin on fear memory. Calcineurin does not affect reconsolidation as increasing calcineurin with DCS in the one conditioned stimulus exposure condition, did not affect the freezing behaviour compared to control. In the 10CS with MK-801 there was and large increase in freezing because the lack of calcineurin does not allow extinction to occur and thus the fear-based memory from previous trails is remembered and so fear responses are not extinguished. With 10CS and DCS there is less freezing than even the control as increasing calcineurin production allows for extinction to take place and the rats no longer associate the stimulus with fear and show less fear responses when presented. In the 4CS freezing responses are very similar when injected with MK-801 because calcineurin is not needed for reconsolidation, but is for extinction, no matter how many exposures to the stimulus happens the calcineurin levels will be similar to reconsolidation levels as activation of any more calcineurin is being inhibited. In western blots more calcineurin was found in extinction or 10 conditioned stimulus rats as calcineurin is needed for extinction and not reconsolidation so the levels in the 1CS were lower. Calcineurin levels may be specific, but the brain activation seems to be the same for both processes. Though this does help to explain some things on how memories transition from a state of reconsolidation to extinction based on amount of exposures to stimulus. It is still not understood how the distinction is made in the body in situations where there is not enough exposures for extinction, but too many for reconsolidation and which process should take place. How exactly reconsolidation or extinction happen molecularly is not entirely known. The processes neurologically appear to be similar, however, which has made researchers try to understand if they these processes can happen in conjunction or cannot happen while the other is occurring. Being able to make this distinction will allow for improvements in therapy when considering therapies associated with both processes. Systematic desensitization is used for anxiety disorders where people who have learned adverse reactions to harmless stimuli and learn to not be scared of it anymore by being exposed to it over and over again in

stages and realize they are not in danger and they no longer feel anxiety in those situations (Wolpe, 1958). Reconsolidation therapies have used by researcherâ&#x20AC;&#x2122;s interested in those suffering from post traumatic stress disorder (Brunet, 2008). These individuals are unable to continue living normal lives with intrusive thoughts constantly bombarding them throughout the day. Interrupting this reconsolidation in humans by administering propranolol, a beta-blocker that inhibits fear responses and thus interferes with fear-based consolidation; after reactivation that were trained with aversive stimulus has been found to inhibit the response behaviour to the stimulus (Kindt et al., 2009) Interrupting reconsolidating and allowing these traumatizing memories of past events to become less distressing would permit these individuals to live normal lives. Criticisms and Future Directions Though mutual exclusion was proven, the experiment failed to show if calcineurin was specifically affecting extinction or if it was just responsible for LTP (long term potentiation) in general. Is it actually creating this new memory that inhibits the old one and allows for this new knowledge to be stored and thus the freezing responses are less or is it that calcineurin allows for LTP to take place and when it is blocked then the memory is not stored as well. This may also be the case with reconsolidation as with just one exposure may not allow for more strengthening of the synapses. If calcineurin helps with LTP and strengthening of the synapse then blocking it will lead to more freezing, learning is not occuring in general. An example of this was seen with PKMzeta which was thought to be the protein made in LTP and this protein needed to be reactivated in order to use the memory again. Researchers thought that ZIP inhibited PKMzetaâ&#x20AC;&#x2122;s activation thus inhibiting the memory (Pastalkova et al., 2006) It was found much later that ZIP actually had a lack of specify for PKMzeta and decreased LTP in other proteins as well even if the mice did not possess the PKMzeta protein (Volk et al., 2013). To test this further an experiment needs be done to see if doing the reconsolidation test or 1CS condition over multiple days leads to more calcineurin as well showing that it may just be responsible for LTP. Three days may not be enough time for the memory to be consolidated as well as reconsolidated in the cortex. Most of the experiments done for the last session were only 24 hours later with one being done 96hours later, but there have been experiments where rats are tested 25 days later with associated memories still intact (Shelma, Sacktor & Dudai, 2007). Seeing if these high calcineurin levels are found many days later or if it is just seen as the learning occurs would be another future experiment. Researchers have recently discovered that people with anxiety disorders do not inhibit or reconsolidate fear memories as well as people without these disorders (Soeter, Kindt, & Perales, 2013). These researchers showed participants an aversive image and then had an eye-blink stimulus presented after it and these memories were reactivated on the second day in conjunction with being given propranolol. On 132


Figure 2. Rats were trained with fear-conditioning to perform freezing behaviour in response to a conditioned stimulus. Rats were trained on the first day and were re-exposed to the stimulus on the second day as well as injected with either saline, MK-801 or DCS. Rats were exposed to the conditioned stimulus on the second day either, once (B), four (C), seven (D), or ten times (E). Merlo et al., (2014)

the third day of testing those given propranolol that had high trait anxiety had very little reduction in blink response, previous experiments done like this showed a lot more reduction in those without anxiety. An experiment needs to be done on rats that are genetically modified to be more anxious and observe if the same affects of calcineurin are seen. The discovery of proteins in correlation with memory has a very complex history. Though proteins may have been discovered in conjunction with memory the extent to which they affect it is still up for debate. References 1. Brunet, A., Orr, S., Tremblay, J., Robertson, K., Nader, K., & Pitman, R. (2008). Effect Of Post-retrieval Propranolol On Psychophysiologic Responding During Subsequent Scriptdriven Traumatic Imagery In Post-traumatic Stress Disorder. Journal of Psychiatric Research, 42, 503-506. 2. Falls, W. A., Miserendino, J. D., Davis, M. (1992) Extinction of fear-potentiatedstartle: blockade by infusion of an NMDA antagonist into the amygdala. J Neurosci, 12, 854–863. 3. Glanzman, D., Mackey, S., Hawkins, R., Dyke, A., Lloyd, P., & Kandel, E. (1989). Depletion of serotonin in the nervous system of Aplysia reduces the behavioral enhancement of gill withdrawal as well as the heterosynaptic facilitation produced by tail shock. The Journal of Neuroscience, 9(12), 4200-4213. 4. Kindt, M., Soeter, M., & Vervliet, B. (2009). Beyond Extinction: Erasing Human Fear Responses And Preventing The Return Of Fear. Nature Neuroscience, 12(3), 256-258. 5. Lin, C., Yeh, S., Leu, T., Chang, W., Wang, S., & Gean, P. (2003). Identification of Calcineurin as a Key Signal in 133

the Extinction of Fear Memory. The Journal of Neuroscience, 23(5), 1574 –1579-1574 –1579. 6. Merlo, E., Milton, A., Goozée, Z., Theobald, D., & Everitt, B. (2014). Reconsolidation and Extinction Are Dissociable and Mutually Exclusive Processes: Behavioral and Molecular Evidence. The Journal of Neuroscience, 34(7), 2422–2431. 7. Nader, K., & Hardt, O. (2009). A single standard for memory; the case for reconsolidation.Nature Reviews, 10, 224-234. 8. Nader, K., Schafe, G. E., LeDoux, J. E. (2000) Fear memories require protein synthesis in the amygdala for reconsolidation after retrieval. Nature, 406, 722–726. 9. Pastalkova, E., Serrano, P., Pinkhasova, D., Wallace, E., Fenton, A., & Sacktor, T. (2006). Storage of Spatial Information by the Maintenance Mechanism of LTP. Science, 313(5790), 1141-1144. 10. Perez-Cuesta, L., & Maldonado, H. (2009). Memory reconsolidation and extinction in the crab: Mutual exclusion or coexistence? Learning & Memory, 16, 714-721. 11. Shema, R., Sacktor, T., & Dudai, Y. (2007). Rapid erasure of long-term memory associations in the cortex by an inhibitor of PKM zeta. Science, 317(5840), 951-953. 12. Soeter, M., Kindt, M., & Perales, J. (2013). High Trait Anxiety: A Challenge for Disrupting Fear Memory Reconsolidation. PLoS ONE, 8(11), E75239-E75239. Retrieved from http://journals. plos.org/plosone/article?id=10.1371/journal.pone.0075239 13. Wolpe, J. (1958). Psychotherapy by Reciprocal Inhibition. Stanford, CA.: Stanford University Press. 14. Volk, L., Bachman, J., Johnson, R., Yu, Y., & Huganir, R. (2013). PKM-ζ is not required for hippocampal synaptic plasticity, learning and memory. Nature, 493(7432), 420-423. Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program


The Effects Of Kynurenic Acid On The Brain And Its Implications In Schizophrenia

Shikha Kuthiala

Schizophrenia is a neurological disorder that has been shown to appear in late adolescence and is characterized by positive, negative and cognitive symptoms. Recently, kynurenic acid, a metabolite made from the breakdown of tryptophan, has been implicated in the development of schizophrenia. Kynurenic acid is an antagonist of both NMDA receptors and alpha-7 nicotinic acetylcholine receptors and as such may interfere with signaling in the brain. It is also thought to play a role in the development of cognitive symptoms in schizophrenia by acting upon the hippocampus. The article by DeAngeli et al. looked at the changes in the hippocampus upon administration of elevated levels of L-KYN, a kynurenic acid precursor and its implications in schizophrenia. They demonstrated that there are deficiencies in learning and memory as well as changes in reward-seeking behaviors in rats treated with L-KYN during early adolescence. They also highlighted that the effects of kynurenic acid on the brain were seen only when the elevated levels were applied in adolescence and not when applied in adulthood. Overall their results showed that kynurenic acid exposure caused neural changes, which may play a causal role in schizophrenia. It is postulated that treatment centered on reducing KYNA can be beneficial to the afflicted individuals. Key words: kynurenic acid (KYNA); hippocampus; schizophrenia; reward-seeking; long term potentiation (LTP); neuroscience; physiology Background Schizophrenia is a syndrome that affects the brain leading to positive symptoms such as hallucinations and delusions. Additionally, there are negative symptoms such as social withdrawal and cognitive symptoms like increased addictive behavior (Jones et al., 2011). Medications have been developed to help deal with positive symptoms but there is a lack of treatment for cognitive symptoms, which are often debilitating to the individual (Holder & Wayhs, 2014). Kynurenic acid (KYNA) has been shown to play a role in the development of cognitive symptoms. It is made by astrocytes during the breakdown of tryptophan and in normal human brains it is found in concentrations of 10-150nM (Rozsa, 2008). It acts on both NMDA and alpha7 nicotinic receptors in the brain. When exposed to high levels of KYNA as an adolescent, rats will display schizophrenic like symptoms after they mature. As adults, these rats presented with cognitive deficits. They also exhibited addictive behavior, which is thought to be due to alterations in the neural reward pathway, and they showed diminished ability to learn and to undergo long-term potentiation (LTP) (DeAngeli et al., 2015). Therefore, understanding the mechanism and downstream effects of KYNA in neural functions is important to elucidate its role in schizophrenia and to create effective treatments. DeAngeli et al. showed that cognition was altered by administering L-KYN, a KYNA precursor to young rats and observing changes in their abilities as adults. They first tested for addictive behavior by testing sign-tracking behaviors in the rats, and found that those exposed to L-KYN displayed greater reward-seeking actions. They then tested the ability to undergo LTP by stimulating the Schaffer Collateral neurons in vitro and measuring the change in the CA1 neurons. It was found that treated rats had a decreased ability to potentate, and therefore

had diminished learning and memory capabilities. It was also shown that KYNA has temporal specificity, if exposure to the metabolite happened in adolescence the rat became schizophrenic. Conversely, if the exposure happened in adulthood there were no observable detrimental effects. Therefore, DeAngeli et al. provided strong evidence that KYNA plays a role in schizophrenia development. These findings are impactful because this study was the first to show how KYNA had a negative effect during development and it provided the initial research towards helping cognitive symptoms. Other experimenters have also investigated the role of KYNA in the development of schizophrenia. Additional studies have provided insight into the mechanism of action used by KYNA during development (Rosza et al., 2008). The study by Rosza et al. showed how KYNA affects the brain and how its modulation can be used as a potential treatment for schizophrenia. Pocivavsek et al. used behavioral testing to see how learning and memory are changed in response to KYNA, which expands the conclusion put forward by the original study. Kozak et al. and Potter et al. used different methods to show that inhibiting enzymes in the KYNA formation pathway can have positive effects, therefore further implicating the role of KYNA in schizophrenia. It has also been shown in some individuals that stress increases KYNA in-vivo (Chiappelli et al., 2014). This result shows a potential endogenous way in which KYNA levels can become deleterious and provides insight on how KYNA can be modulated in the body. The spatial effects of the metabolite through the brain have been highlighted by Sathyasaikumar et al., who studied the prefrontal cortex, to show that it was affected differently than the hippocampus. The primary article has shown that KYNA can cause cognition to change and supplementary studies have helped to further understand the implications of KYNA in both development and 134


schizophrenia. There is still a great deal of work to do, but the understanding of this metabolite in relation to the diseased state has come a great way. Research Overview

Summary of Majore Results

Kynurenic Acid and Cognition The primary article by DeAngeli et al. showed that increased levels of KYNA during adolescence lead to cognitive impairments in rats. The experimental rats showed a lack of ability to undergo LTP when using electrical stimulation on hippocampal slices. These changes showed that excess KYNA, which antagonizes NMRA and alpha-7-nAChR, can cause behavioral and cognitive deficits. The decline in cognition was demonstrated by the inability of experimental rats to learn and perform other hippocampal behaviors, such as social behaviors, when compared to controls. This study also showed the temporal specificity of KYNA; if the increased exposure occurred during adolescence cognitive changes were seen, whereas exposure as an adult did not cause these problems (DeAngeli et al., 2015). This result was supported by another study by Trecartin and Bucci. This experiment was conducted on 16 adolescent male rats, which were treated with L-KYN. These rats showed that social behavior decreased after KYNA exposure. When the same experiment was repeated on 16 adult rats there were no apparent deficits. Social behavior was measured by noting the number of times the treated rat approached the area near an unfamiliar rat when both were placed in a tub (Trecartin & Bucci, 2011). This result is important because it provides a potential cause of cognitive symptoms, which are currently neglected in treatment. Kyneuric Acid and Changes To the Brain The original paper states that the changes in the treated rats are due to the effects of KYNA on the hippocampus. It is postulated that KYNA binds to and antagonizes the NMDA and alpha-7-NAChR, thus changing the functionality of the hippocampus (DeAngeli et al., 2015). This conclusion is furthered by Pocivavek et al., who showed that when KYNA synthesis was inhibited, more glutamate was released in the hippocampus. This was shown by administering ESBA, which inhibits the formation of KYNA, and then measuring the amount of glutamate in the extracellular environment. The levels of glutamate were compared in treated and control animals. This result indicated that KYNA does impair the ability of the hippocampus and altered behavior by blocking normal glutamate functioning (Pocivavek, 2011). Changes to the hippocampus were also shown more directly by Pershing et al., who conducted a morphological study of the hippocampus. Rats were treated with KYNA and the structure was analyzed by Golgi staining hippocampal slices and comparing the slices from control and treated animals. The study found decreased dendritic density in rats treated with KYNA (Pershing et al., 2015). This result showed how the hippocampus changed, furthering the conclusion presented by DeAngeli et al. 135

Overall, it was shown that KYNA affects the structure, function and output of the hippocampus and early treatment can help preserve hippocampus-mediated behaviors. Kynurenic Acid and Dopamine Sensitivity In the study, DeAngeli et al. state that addiction and schizophrenia are co-morbid due to changes in the reward system of the brain. The article posited that the dopamine receptors increase in sensitivity in response to adolescent exposure to KYNA. This hypothesis was tested by training the rats to press a lever to receive a food reward. The experiment revealed that the treated rats display more sign-tracking and more addictive behaviors. This finding is impactful because it shows a particular region of the brain that is altered by the metabolite and could therefore be targeted for therapeutics. Erhardt et al. also showed a similar conclusion by increasing the KYNA concentration three to nine times the normal amount in the brain. They found that dopamine neurons in the ventral tegmental nucleus (VTA), part of the reward pathway, increased their firing rate, and remained depolarized for greater periods of time in response to the KYNA stimulus. However, they also showed that dopamine neurons fired less in the prefrontal cortex (Erhardt et al., 2007). Therefore, this study showed how hyperactivity of dopamine can cause the positive symptoms of schizophrenia in one region and hypoactivity of dopamine can cause negative symptoms in another. These results show that treatment for KYNA may benefit the full spectrum of symptoms seen in schizophrenia.

Figure 1. This figure shows the diminished ability to undergo LTP in rats exposed in adolescences to L-KYN, in comparison to control rats treated only with vehicle (DeAngeli et al, 2015).

Discussion and Conclusion DeAngeli et al. studied the changes in adolescent rats exposed to high levels of kynurenic acid using both electrophysiology and behavioral tasks. They concluded in their experiments that KYNA played a causal role in the development of schizophrenia and its associated cognitive symptoms. Their results are significant because the study showed a metabolite that could be the target of new therapeutics. These treatments have the potential to surpass current medications like antipsychotic drugs, which only help positive symptoms of schizophrenia like hallucinations


Table 1. KYNA treated rats showed more sign tracking behaviors than the control rats when the conditioned stimulus was present (DeAngeli et al, 2015).

and delusions (Holder &Wayhs, 2014). Treatments to antagonize KYNA have the potential to help cognitive symptoms and also negative symptoms, another currently untreated aspect of schizophrenia (Erhardt et al., 2007). This study was also the first to analyze how changes in metabolite concentration during development can be implicated in schizophrenia. This finding provided insight into a potential early marker for schizophrenia. In addition, measuring higher levels of KYNA in adolescence may be indicative of the individualâ&#x20AC;&#x2122;s susceptibility to developing a schizophrenic phenotype as an adult. By targeting KYNA, treatments for schizophrenia can be preventative instead of symptomatic treatments after the syndrome has already developed (DeAngeli et al., 2015). The authors presented 3 major conclusions in the study. First, was that KYNA exposure will decrease learning and memory abilities by down-regulating LTP in the hippocampus. This conclusion showed the potential basis for cognitive symptoms and has been expanded on by Pershing et al., who showed that dendritic density changes when exposed to KYNA. This conclusion is important because it presents a location and a mechanism that treatments can target to up-regulate LTP and help cognitive symptoms. The result also showed the specific changes in the hippocampus, which affect behavior. Therefore, this conclusion can be extrapolated to other neurological disorders that stem from hippocampal changes (Sublette et al., 2011). Overall, the evidence from these studies can help develop protective therapies that can benefit individuals with schizophrenia as well as individuals suffering from other syndromes. The second conclusion of the study was that the KYNA exposure would lead to a change in the reward circuitry of the brain, including the VTA and nucleus accumbens, increasing reward-seeking behaviors. This finding was shown using behavioral tests and indicated that KYNA can alter the firing of dopamine neurons in the VTA. A study by Erhardt et al. proved this by measuring the changes in dopamine neuron firing in the VTA with and without KYNA exposure. They demonstrated that the application of KYNA lead to hypoactivity of the dopamine neurons and that administration of a stimulating substance, which increased dopamine, can reverse the effect. This finding may indicate why rats in the original study had more reward seeking behavior; since the rats are continually in a state of low dopamine they are more likely to become addicted to any behavior that will increase their dopamine levels (Erhardt et al., 2007). This finding allows for the development of a dopa-

mine agonist treatment that will treat the root cause of addiction in schizophrenic individuals. The final conclusion presented in the paper was that KYNA has temporally specific effects. The study showed that treatment in adolescence lead to cognitive and behavioral changes, but exposure did not have the same effect in adults. This conclusion highlights the importance of detecting potential risk factors early so that treatments can be put into place before the disorder develops in late adolescence (Uhlhaas and Singer, 2011). This suggests that there is vulnerability at a younger age that is no longer applicable in adults. This conclusion was supported by Pocivavsek et al., who showed that pre and postnatal exposures to high levels of KYNA lead to cognitive deficits when older. The conclusion was also corroborated by showing that adult injections of KYNA would not change social behaviors but adolescent exposure lead to increased avoidance and decreased interactions (Trecartin & Bucci, 2011). These findings show that inhibitory treatments towards KYNA must be done early. This provides not only a target, but also a critical window in which treatment must be administered so that symptoms of schizophrenia can be minimized and potentially eliminated. The significance of this study is that it progresses the current treatment plan for schizophrenia into a more holistic treatment. By targeting KYNA we can treat cognitive symptoms, which have thus far been a debilitating but untreatable component of schizophrenia. KYNA treatments have also been postulated to work on negative symptoms, but further research is required confirm this conclusion (Erhardt et al., 2007). Additionally, treatment that antagonizes KYNA can help addictive behaviors, which allows this treatment to not only help in schizophrenia, but possibly also other disorders with addictive components. These studies provide evidence to advance current schizophrenia treatments as well as information to help in the development of preventative therapies. Criticisms and Future Directions While the work done by DeAngeli et al. has shown a great deal about KYNA and its functions there are points at which the study can be furthered. These additional experiments would allow for a greater understanding of the changes caused by KYNA and the eventual treatments that could be developed. The first experiment, which could lead to a more complete understanding, is to conduct behavioral testing for learning and memory. While the researchers used electrophysiological experiments to show that LTP 136


ability had decreased, by adding a behavioral test such as a Morris Water Maze it could show the behavioral implications of KYNA (Ma et al, 2014). In the second experiment, conducting an in-vitro experiment could have furthered the conclusion. While it was shown that addictive behaviors become more prominent, measuring the change in the firing rate of VTA neurons would elucidate if the VTA was directly being effected and how so. This could be done by exposing the VTA neurons to a typical stimulant and measuring the changes in firing patterns of the dopamine neurons in treated and control rats (Erhardt et al., 2007). Outside of the experimental design, some of the conclusions presented in the paper could also be further investigated. The authors concluded that the hippocampus and its associated behaviors were affected by KYNA as shown by the change in learning and memory. Expanding on this conclusion by testing other areas often associated with schizophrenia, like the pre-frontal cortex (Jones et al., 2011), would show how other brain regions are affected by KYNA exposure. Additionally, analyzing hippocampal changes at the cellular level in response to KYNA would elucidate the basic unit of change that could be targeted with preventative therapeutics. The researchers also concluded that reward-seeking behaviors had changed. This conclusion could be expanded to see if it is simply dopamine neurons in the VTA that are being effected or dopamine neurons throughout the brain. This study would eliminate other possibilities for observed behaviors and would strengthen the presented conclusion. The study could be conducted by comparing the dopamine released from regions like the substantia nigra in KYNA treated animals and controls. This would show if the changes in dopamine neurons were limited to the reward pathway or if it was a diffuse effect. The final conclusion presented is that KYNA has an age specific effect; while this conclusion has been supported it could be advanced by administering KYNA at different time points throughout adolescence instead of during the whole time frame (Trecardin & Bucci, 2011). This would develop a more precise time scale as to when KYNA has an effect and when it does not. The collected data would allow for a better understanding of the critical time period in which changes occur, and could provide a treatment window. In addition, by administering different doses, the deleterious level of KYNA could be uncovered. Ultimately, these studies could be expanded in the future to develop preventative measures that are both temporally specific and given at the optimal dosage. KYNA levels can be targeted multiple ways; its effect can be blocked with an antagonist or its formation can be prevented by inhibiting enzymes in the tryptophan metabolism pathway. Once the best method to inhibit KYNA is found, it could be combined with the current anti-psychotic treatments for positive symptoms leading to a treatment that is able to act on positive, negative and cognitive symptoms (Jones et al., 2011). This can increase the quality of life for those with schizophrenia, as they are able to regain lost functions and eliminate unwanted positive symptoms. Another future goal for KYNA and schizophrenia is to develop a test, analogous to an amniocentesis, which would be able to see if KYNA levels are increased in fetuses (Nicolaides et al., 2012). This information can 137

be used to develop a treatment to administer while in utero or a treatment to administer once the child is born to decrease KYNA levels. If there is no increase in KYNA in fetuses, another future direction would be to develop methods to continually check the levels of KYNA in children. This could potentially done by sampling CSF using a lumbar puncture (Sharief, 2006). This would allow for early detection of elevated levels, which can then be treated. These future plans would not only treat schizophrenic symptoms but also prevent the cortical changes seen in the disorder. Overall, there is a great deal of work to be done on schizophrenia, and expanding the work done in the original article can lead to very positive, life long effects. References 1. DeAngeli, NE et al. Exposure to kynurenic acid during adolescence increases sign-tracking and impairs long-term potentiation in adulthood. Front Behav Neurosci 8:451-60 (2015). 2. Jones, C.A., Watson, D.J.C., Fone, K.C.F. Animal Models of Schizophrenia. Br J Pharmocol 164:1162-94 (2011). 3. Potter, M.C. et al. Reduction of endogenous kynurenic acid formation enhances extracellular glutamate hippocampal plasticity and cognitive behavior. Neuropsychopharacology 35:1734-42 (2010). 4. Holder, S.D., Wayhs, A. Schizophrenia. American Family Physician 90: 775-82 (2014). 5. Rozsa, E., Robotka, H., Vecsei, L., Toldi, J. The Janusface kynurenic acid. J Neural Transm 115:1087-91 (2008). 6. Pocivavsek, A. et al. Fluctuations in Endogenous Kynurenic Acid Control Hippocampal Glutamate and Memory. Neuropsychopharamology 36:2357-67 (2011). 7. Kozak, R. et al. Reduction of Brain Kynurenic Acid Improves Cognitive Function. J Neurosci 34:10592-602 (2014). 8. Chiappelli, J. et al. Stress-Induced Increase in Kyneuric Acid as a Potential Biomarker for Patients With Schizophrenia and Distress Intolerance. JAMA Psychiatry 71:761-8 (2014). 9. Sathyasaikumar, A. et al. Impaired Kynurenine Pathway Metabolism in the Prefrontal Cortex of Individual With Schizophrenia. Schizophrenia Bull 37:1147-56 (2011). 10. Trecartin, K., Bucci, D. Administration of Kynurenine during Adolescence, but not during Adulthood, Impairs Social Behavior in Rats. Schizophr Res 133:156-58 (2011). 11. Pershing, M.L. et al. Elevated levels of kynurenic acid during gestation produce neurochemical, morphological, and cognitive deficits in adulthood: implications for schizophrenia. Neuropharmacology 90:33-41 (2015). 12. Erhardt, S., Schwieler, L., Nilsson, L., Linderholm, K., Engberd, G. The kynurenic acid hypothesis of schizophrenia. Stockholm, Sweden: Elsevier (2007). 13. Sublette, M. et al. Plasma Kynurenine Levels are Elevated in Suicide Attempters with Major Depressive Disorder. Brain Behav Immun 25:1272-78 (2011). 14. Pocivavsek, A., Wi, H.Q., Elmer, G.I., Bruno, J.P., Schwarcz, R. Pre- and Postnatal Exposure to Kynurenine causes Cognitive Deficits in Adulthood. Eur J Neurosci 35:1605-12 (2012).


15. Uhlhaas, P.J., Singer, W. The development of neural synchrony and Large Scale Cortical Networks During Adolescence: Relevance for the Pathophysiology of Schizophrenia and Neurodevelopmental Hypothesis. Schizophrenia Bull 37: 514-23 (2011). 16. Ma, Q.L. et al. Loss of MAP Function leads to Hippocampal Synapses Loss and Deficits in the Morris Water Maze with Aging. J Neurosci 34:7124-36 (2014). 17. Nicolaides, K.H. et al. Noninvasive prenatal testing for fetal trisomies in a routinely screened first-trimester population. Am J Obstet Gynecol 207:374e1-e6 (2012). 18. Sharief, M. Lumbar puncture and CSF examination. Medicine 32: 44-46 (2006).

Received March, 05 20 2015 accepted

2015; April,

revised 02,

March, 2015.

This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright Š 2015 Dr. Bill JU, Neurosciences, Human Biology Program

138


Selectively Activating Endogenous A3 Receptors is The New Therapeutic Solution to Chronic Pain Soonji Kwon

Most effective treatments of chronic pain typically involve endogenous opioids, adrenergic and calcium channels. These clinical treatment methods however, have detrimental side effects and addictive qualities over time. The study conducted by Little et al. highlights the potentials of using a highly specific agonist of a G protein-coupled adenosine receptor (AR) subtype A3 MRS5698 in reversing chronic neuropathic pain in a state- and dose-dependent manner. Although there have been developments in the analgesic uses of other AR subtype agonists, specifically A1AR and A2AAR agonists, there were unwanted cardiovascular side effects. Conversely, agonists of A3AR produce only positive results. They are highly expressed in cells important for carrying out neuroprotective effects, such as inflammatory cells and peripheral sensory nerves and have anti-tumor capacity. Additionally, there are already clinical trials using A3AR agonist IB-MECA [N6-(3-iodobenzyl)-adenosine-50-N-methyluronamide] as a means to decrease pain caused by chemotherapeutic agents and constriction of sciatic nerve without serious side effects. Furthermore, activation of A3AR following administration of MRS5698 at spinal and supraspinal (rostral ventromedial medulla (RVM)) sites show promising signs of becoming the most effective treatment of chronic pain without side effects. Key words: chronic pain; neuropathic; adenosine; A3AR agonist; IB-MECA; MRS5698; anti-tumor; neuroprotective Background Early theories of pain and pain perception date back to the 1800’s1. With the advancement in technology including many imaging techniques, descending pathways involved in pain are now generally understood as the anti-nociceptive or analgesic system1. Chronic pain is distinct from normal pain since it can alter activity in the CNS, lead to sensitization and even rearrangements within networks of neurons1. This modulation of pain stimuli typically begins in the dorsal horn of the spinal cord where nociceptive-specific neurons and wide dynamic range (WDR) neurons are found2. In chronic pain states, WDR neurons receive persistent C-fiber (unmyelinated) stimulation and they remain turned “on”, continually relaying pain information to the brain2. Within the brain, the major regions involved in noxious stimuli processing include the primary and secondary somatosensory cortices, anterior cingulate cortex (ACC), insula, prefrontal cortex (PFC), thalamus and cerebellum3. Additionally, projections from the frontal lobe and the amygdala are received by the periaqueductal gray (PAG), which govern nociceptive neurons of the spinal cord through the rostral ventromedial medulla (RVM) and the dorsolateral pontine tegmentum (DLPT)2. Chronic neuropathic pain is a prevalent health concern but the plastic nature of the pain pathway adds complexity to the development of successful treatment strategies. Pain management studies show that injection of cholesystokinin (CKK) antagonists into supraspinal RVM reverses allodynia resulting from spinal nerve ligation2. Injection into the spinal cord itself is also another important site of injection and it contains important modulatory systems and contains many opioid receptors2. Historically, opioid, adrenergic and calcium channel pathways were common targets for treatment of chronic pain4. However, these drugs are often highly costly with incomplete pain relief and accompanied by adverse side effects that lead to its discontinued use4. In contrast, mechanisms involving adenosine may be the best therapeutic solution to chronic pain. 139

There are four subtypes of the G-protein-coupled adenosine receptors (AR), A1, A2A, A2B, and A35. Under normal conditions, it has been shown that there are tonic low activation levels of A3 receptors6. When the extracellular concentrations of adenosine increase, it acts as a signal to neighbouring cells to induce protective responses5. Previous studies of A3AR agonists IB-MECA [N6-(3-iodobenzyl)adenosine-5’-N-methyluronamide] and its chlorinated counterpart Cl-IB-MECA [2-chloro-N6-(3-iodobenzyl)-adenosine-5’-N-methyluronamide] shows it blocks the development of neuropathic pain induced by chronic constriction injury (CCI)7. An extension of this study has been conducted by Little et al. using multiple models of pain and has shown that these results are reproducible. Additionally, the translational capacity of activating A3 receptors as a means to prevent chronic pain is very high since A3R agonists have also been shown to have anti-cancer effects4. Research Overview

Summary of Major Results

The first major finding of the study conducted by Little et al. shows an increase in extracellular concentration of adenosine following administration of ABT-702, a selective adenosine kinase inhibitor4. This increase in adenosine, which was previously shown to act as a protective signal5, reversed mechano-allodynia in a rodent model of CCI and chemotherapy-induced peripheral neurpathy (CIPN)4. Behaviourally, the ABT-702 treatment group had a higher paw withdrawal threshold compared to vehicle and A3AR antagonist MRS1523 treated groups4. Most notably, the administration of MRS5698, a highly specific A3AR agonist, was shown to be effective across many well-characterized models of pain4. It is bioavailable orally, its effects have a fast onset of less than 30 minutes and Rotarod tests do not show any debilitating motor effects4. There were three models of pain used to


A Figure 1 (A) Dose-dependent decrease in behavioural indication of spontaneous pain Day 10 post-cancer-induced-bone pain. (B) A comparison of A3AR agonist MRS5698 with morphine in daily injections from Days 8-15. Adapted from “Endogenous adenosine A3 receptor activation selectively alleviates persistent pain states,” by Little JW, et al. 2014. Brain. doi:10.1093/brain/awu330.

B

Figure 2 Western blot showing lower lumbar (L5-6) spinal cord and RVM expression levels of mRNA. Hprt1 and β-actin used as endogenous control gene. Adapted from “Endogenous adenosine A3 receptor activation selectively alleviates persistent pain states,” by Little JW, et al. 2014. Brain. doi:10.1093/brain/awu330.

support its efficacy: spared nerve injury, spinal nerve ligation and cancer-induced bone pain. MRS5698 reversed mechano-allodynia and decreased behavioural indication of pain (such as guarding and flinching as shown in Figure 1A) in a dose-dependent manner4. While repeated injections of morphine on Days 8-15 post-CCI resulted in drug tolerance, MRS5698 retained its anti-nociceptive effects (Figure 1B)4. Additionally, the therapeutic effects of MRS5698 treatment did not compromise the ability to respond to normal physiological pain. Thus, there was no effect on flick tail latency and hot-plate test. One of the most important findings in this paper is that Little et al. determined two main optimal injection sites of injection to induce anti-nociceptive effects: the spinal cord and the supraspinal RVM4. A3AR mRNA transcript and protein levels were measured and compared by Western blot and determined that both sites were important for A3AR activation, as seen in figure 2. Then, they showed that subcutaneous injection of MRS5698 was also able to reduce the activity of WDR neurons involved in chronic pain, as described in the introduction. There was a significant reduction in neuronal excitability compared to the baseline levels of activity following spinal nerve ligation4. Lastly, to test whether this adenosine pathway involves endogenous opioid and cannabinoid pathways, antagonists of opioid and cannabinoid receptor antagonists, Naloxone, rimonabant and SR144528, were used4. Pretreatment of the antagonists did not affect the MRS5698 A3AR activation4. In figure 3, a flow chart summarizes and depicts the interaction between adenosine & spinal and RVM A3AR activation. Systemic injection of MRS1523 if given with ABT-702 will diminish the anti-nociceptive effects of ABT-702. Conversely, systemic injection of MRS5698, which are A3AR agonists, will increase the anti-nociceptic effects by decreasing the neuronal excitability to normal levels.

Figure 3 Summary flow chart depicting the effects of extracellular adenosine concentration at spinal and supraspinal RVM sites. MRS1523 is the selective inhibitor of A3AR and MRS5698 is the selective agonist of A3AR. Decreased neuronal excitability results in anti-nociceptive effects. Adapted from “Endogenous adenosine A3 receptor activation selectively alleviates persistent pain states,” by Little JW, et al. 2014. Brain. doi:10.1093/brain/awu330.

Discussion and Conclusion The anti-nociceptive function of adenosine was initially discovered and examined in receptor agonists of subtypes A18,9 and A2A10. However, further in vivo studies using animal models of pain demonstrated adverse cardiovascular side effects. Therefore, combining the results stated above, the most important implication of the highly specific A3AR agonist, MRS5698, is the translational capacity of the therapeutic drug for the management of cancer-induced pain as well as having anti-tumour effects. Although chemotherapy may be effectively removing the tumour, in some instances, unbearable pain will result in termination of the treatment. Paclitaxel, or its trade name Taxol, is currently a chemotherapeutic drug used to treat breast, ovarian, non-small cell lung carcinomas, and Kaposi sarcoma11. However, paclitaxel causes neuropathic pain when given in optimal dosages11. A recent study has demonstrated that administration of IB-MECA, an A3AR agonist, prevents paclitaxel-induced neuropathic pain by inhibiting the activity of spinal NADPH oxidase and downstream redox systems11. Notably, the anti-tumor function of paclitaxel was not compromised. Similar effects of IB-MECA administration was found in other chemotherapeutic drugs such as oxaliplatin, used for metastatic colon cancer, and bortezoimib, used for multiple myelomas11. The use of A3AR agonists to reverse chemotherapy140


induced peripheral neuropathy (CIPN) is a new and upcoming field of research interest. Another study conducted by Yao et al. examined the anti-cancerous effects of IB-MECA and Cl-IB-MECA against HL-60 leukemia and U-937 lymphoma cells6. Flow cytometry and immunofluorescent staining showed that these incubating A3AR agonists with HL-60 and U-937 cells resulted in an increase in apoptotic cells6. Thus, the antitumor effects of administrating A3AR agonists in patients experiencing CIPN would benefit from its dual actions. Pain management studies have finally paved way for a new potential drug to combat chronic/persistent pain without detrimental side effects. This study by Little et al. demonstrated the effectiveness of a non-narcotic agonist of A3AR, MRS5698, in many different pain models4. Although previous research that focused on targeting A1AR and A2AR activation has resulted in cardiovascular side effects in preclinical and clinical trials, no serious side effects have been reported in clinical trials of A3AR agonists, IB-MECA and Cl-IBMECA. Thus, clinical implications of MRS5698 is significant since patients will not become dependent or sensitized to the chronic pain treatment as they would using opioid and cannabinoid agents, such as morphine. With A3AR activation, normal pain thresholds were not compromised and inherent reward is not activated in healthy rats, which suggests highly selective alleviation of persistent neuropathic pain4. It is state- and dose-dependent and is able to reverse mechano-allodynia in CCI-induced neuropathic pain and even against CIPN4. Clinical trials of using A3AR agonists for cancer treatments are already underway, meaning this drug has potential duality of eliminating both pain and cancerous cells. Criticisms and Future Directions The paper mentions that injection of MRS5698 reversed mechano-allodynia in spared nerve injury and spinal nerve ligation, similar to the CCI pain model4. However, almost all of the figures only show results of post-CCI. In order to effectively convince the readers of the widespread effects of this new potential therapeutic drug, figures showing efficacy in multiple pain models should be included. The next steps that should be taken are to examine whether the results are reproducible across all (available) models of chronic pain and chemotherapeutic agents. Additional CIPN animal models that are available for further tests include vincristine-, toxol-, and cisplatin-induced peripheral neuropathy models (VIPN, TIPN, CIPN respectively)12,13. Given that A3AR should always be activated in chronic pain states, the prospect of using A3AR agonists as a universal treatment for all chemotherapeutic-induced nociception is remarkable. Currently, further advancements are being made in the molecular design of better, more specific A3AR agonists. Tosh et al. have made modifications to MRS5698 and have synthesized multiple new drugs that surpass all the benefits of the existing A3AR agonists14. Some of the modifications include decreasing the molecular weight of the compound in order to overcome the blood brain barrier and maximize delivery throughout the body. Thus, further molecular advancements will result in the creation of a therapeutic drug that has translational capacity of treating chronic neuropathic pain and ultimately increase the quality of life in affected individuals. 141

References 1. Perl E. Ideas about pain, a historical view. Nature Reviews Neuroscience 8, 71-80 (2007). 2. Jay GW. Chronic Pain. London, GBR: CRC Press. (2007). Retrieved from: http://www.ebrary.com 3. Bushnell M, Čeko M, & Low L. Cognitive and emotional control of pain and its disruption in chronic pain. Nature Reviews Neuroscience 14, 502-511 (2013). 4. Little JW, Ford A, Symons-Liguori AM, Chen Z, Janes K, Doyle T, Xie J, Luongo L, Tosh DK, Maione S, Bannister K, Dickenson AH, Vanderah TW, Porreca F, Jacobson KA, & Salvemini D. Endogenous adenosine A3 receptor activation selectively alleviates persistent pain states. Brain (2014) doi: 10.1093/brain/awu330. 5. Fredholm BB, IJzerman AP, Jacobson KA, Linden J, & Muller CE. International Union of Basic and Clinical Pharmacology. LXXXI. Nomenclature and classification of adenosine receptors–an update. Pharmacol Rev 63, 1–34 (2011). 6. Yao Y, Sei Y, Abbracchio MP, Jiang J-L, Kim Y-C, & Jacobson KA. Adenosine A3 Receptor Agonists Protect HL-60 and U-937 Cells from Apoptosis Induced by A3 Antagonists. Biochemical and Biophysical Research Communications 232(2), 317-322 (1997). 7. Chen Z, Janes K, Chen C, Doyle T, Bryant L, Tosh D, Jacobson KA, Salvemini D. Controlling murine and rat chronic pain through A3 adenosine receptor activation. The FASEB Journal 26, 1855-1865 (2012). 8. Kiesman WF, Elzein E, and Zablocki J. A1 adenosine receptor antagonists, agonists, and allosteric enhancers. Handb. Exp. Pharmacol. 193, 25–58 (2009). 9. Zylka MJ. (2011) Pain-relieving prospects for adenosine recep- tors and ectonucleotidases. Trends Mol. Med. 17, 188–196
 10. Loram LC, Harrison JA, Sloane EM, Hutchinson MR, Sholar P, Taylor FR, Berkelhammer D, Coats BD, Poole S, Milligan ED, Maier SF, Rieger J, & Watkins LR. Enduring reversal of neuropathic pain by a single intrathecal injection of adenosine 2A receptor agonists: a novel therapy for neuropathic pain. J. Neurosci. 29, 14015–14025 (2009). 11. Janes K, Esposito E, Doyle T, Cuzzocrea S, Tosh DK, Jacobson KA, Salvemini D. A3 adenosine receptor agonist prevents the development of paclitaxel-induced neuropathic pain by modulating spinal glial-restricted redox-dependent signaling pathways. PAIN 155(12), 2560-2567 (2014). 12. Wang L & Wang Z. Animal and cellular models of chronic pain. Advanced Drug Delivery Reviews 55(8), 949-965 (2003). 13. Mogil J. Animal models of pain: Progress and challenges. Nature Reviews Neuroscience 10, 283-294 (2009). 14. Tosh DK, Finley A, Paoletta S, Moss SM, Gao Z-G, Gizewski ET, Auchampach JA, Salvemini D, & Jacobson KA. In Vivo Phenotypic Screening for Treating Chronic Neuropathic Pain: Modification of C2-Arylethynyl Group of Conformationally Constrained A3 Adenosine Receptor Agonists. Journal of Medicinal Chemistry 57(23), 9901-9914 (2014). This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address Biology Potential

correspondence to: Dr. Rita L. Neurotrophin, Department, 123 Growth Cone Avenue, Action College, Hillock, IL 60101 Email: rln@apc.edu

Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program


Working memory training is most effective in healthy young adults to improve cognitive skills

Shonali Lakhani

Previous studies suggest that training working memory activates the medial temporal lobe, which can contribute to better episodic memory by stimulating interacting brain areas. Most studies do not examine the small effects of training on episodic memory processes, such as familiarity in the perirhinal cortex and recollection in the hippocampus. A recent finding indicated that a high demand on executive function to process complex spatial information, increased prefrontal cortex activity. Cognitive training of working memory typically involves a variety of tasks that may be too complicated or take up too much time. A new spatial memory task was developed to improve the episodic memory abilities for familiarity and recollection as well as fluid intelligence. Development of a new spatial task targeting both episodic memory processes necessitates participants to adjust their viewpoint accordingly. Thus, multiple training tasks are not required to improve cognition, as their spatial working memory task led to stronger long-term memory and fluid intelligence for abstract reasoning. Key words: cognitive neuroscience; working memory; fluid intelligence; performance training Background The use of cognitive training was investigated to improve the speed and accuracy of cognitive functions (Thorndike and Woodworth, 1901). Several functions were part of the focus, namely training working memory influenced attention, observation and discrimination. This led to many more studies by other researchers into the interaction between working memory and how it is the foundation for many other cognitive functions, such as spatial representation. More recently, Lee and Rudebeck (2010) used functional neuroimaging to show the effects of increasing the demand on working memory during complex spatial processing. The effects included activation of posterior medial temporal lobe structures, which was greater when there was a high demand on spatial processing, irrespective of the demand on working memory. Thus, this finding is significant because it implies that making the most of working memory training requires the incorporation of spatial tasks. In addition, Huntley and colleagues (2010) continued this investigation by administering a range of spatial and verbal tasks to Alzheimer’s patients in sequences that were not structured randomly. In this way, strategic methods of encoding data, such as chunking information, reduced the demand on working memory and improved recollection. They also found that it is most beneficial to target patients in the earliest stages of the disease for cognitive training gains. Another factor may affect cognition in those carrying certain versions of the LMX1A gene may have an advantage during training, as their working memory is enhanced more than the individuals carrying a different version of the gene. This research is yet to be confirmed by comparing the results obtained from a future study study repeated on a larger population in order to generalize the results. Nonetheless, this is promising for those who carry the advantageous allele into old age (Bellandera et al., 2011). On the one hand, cognitive training that focused on improving major deficits in recollection, for those with

mild to moderate forms of Alzheimer’s disease, has shown general benefits to working memory. The use of verbal and visual modalities, along with spatial and temporal memory, allowed Boller and colleagues (2012) to take a multi-domain approach. On the other hand, a domain-general paradigm was used to conduct working memory training on healthy groups of young and old adults (Brehmer, Westerberg & Bäckman, 2012). They found that both groups had better performance, but the younger adults gained more than the older adults overall because they initially made greater improvement. However, when Lee et al. (2012) trained young adults on a video game that required working memory processes, they did not see much benefit to other cognitive processes when those processes did not bear any similarity to the trained tasks. By comparison, Cheng et al. (2012) found that healthy elders benefit more from multi-domain training that targets diverse capacities than from a single-domain approach. This research supports Rudebeck et al.’s (2012) development of a single spatial working memory task that targeted overlapping pathways, but they only trained healthy young adults. In contrast to these findings, a study published a year earlier by Bergman Nutley and colleagues (2011) revealed that working memory in young children improved with training, but did not affect problem-solving skills. Therefore, the use of visual and spatial tasks in this study has demonstrated that such training is not as effective in all age groups, as the study being reviewed only included adults. Research Overview

Summary of Major Results

Both the high gain and low gain training groups achieved greater scores for episodic memory processes with time, but there are significant differences between them, as well as the high gain compared to the control, and the low gain versus the control. The training group 142


performed significantly better on a reasoning task, in comparison with the control group. However, low pre-training scores lead to higher reasoning scores, irrespective of training task gain. In addition, the gain scores correlate positively with the recognition tasks for both episodic memory processes, so there is a significant difference between the high gain group compared with the control, or compared with the low gain group. Even if the object and scene tasks are considered separately, there is still no significant difference between the scores for the low gain and control groups. Therefore, training score improvement is linked to increased recognition, which is demonstrated by the scores for the episodic memory process of familiarity, whereas poor recollection pre-training predicted a marked improvement only in recollection scores, regardless of training scores (Rudebeck et al., 2012).

Conclusions and Discussion

For optimal encoding and retrieval of episodic memory, the ability to maintain information in working memory is crucial. Also, neural mechanisms overlap as medial temporal lobe lesions affect working memory when the stimuli are difficult to verbalize or relational processing is complicated. Moreover, improved reasoning is due to the task-induced activation of a common network from the lateral prefrontal cortex to the parietal cortex, leading to better episodic memory (Rudebeck et al., 2012). Likewise, Cheng et al. (2012) showed improved reasoning in healthy older adults with multi-domain training, which may be due to connections between different brain areas. Hence, the more working memory is improved, the larger transfer effect on episodic memory, which is why the prefrontal cortex and medial temporal lobe structures are involved in non-specific gains. As a result, depending on the cognitive skills required, appropriate training tasks must be created based on existing ability and training task gains pursued (Rudebeck et al., 2012). This may be why Boller et al. (2012) carefully designed their training task to address Alzheimer’s patients’ specific cognitive impairments and measure the extent of transfer to episodic memory processes, such as recall and recognition. This is important, as it allowed participants to improve recollection at mild to moderate stages of the disease. Yet, Lee et al.’s (2012) results suggest that older adults may benefit from video game training, only if improved working memory is desired. Furthermore, the hippocampus is important for both recollection and familiarity as well as object and scene recognition (Rudebeck et al., 2012), implying that further research would allow generalization to all forms of episodic memory in various populations by using different kinds of stimuli and targeting certain neural processes. When Brehmer, Westerberg & Bäckman (2012) studied the difference between younger and older adults, adaptive training groups had higher gains in near transfer tasks for both groups. Whereas younger adults had more gains in comparison with the active control group, who were not challenged progressively by an adaptive training procedure. Also, young adults in adaptive training performed the best in 143

Figure 1. Lee et al. (2012)’s results show that the hybrid-variablepriority training group that focused on learning each rule of the game one by one outperformed the group that was instructed to give full emphasis to all aspects of the training task. This suggests that the specific skills to do well on the game are retained when participants focus on grasping one skill at a time.

the far transfer tasks, such as reasoning. Bergman Nutley et al.’s (2011) results in children may be explained by the gender imbalance, as more boys were a part of the study and tended to be less motivated to engage with the task. Still, their results do indicate that training on non-verbal reasoning tasks improved fluid intelligence in young children, so it seems that the domains involved in training must be specific.

Figure 2. Brehmer, Westerberg & Bäckman (2012) measured working memory performance over a period of four weeks, in which they found that younger adults made more improvement than the older adults between the first and second week.

Conclusions The research conducted by Rudebeck et al. is significant because it can be applied to help the aging population maintain good cognitive function for independence. This has a great impact for patients who suffer from memory impairments or dementia. Thus, this research may have led Kanaan S et al. (2014) to portray that it is feasible to transfer improved performance on practiced training tasks. This achieves better cognition in Alzheimer’s patients, which carries over to general tasks, even after two to four months of training. Knowledge of different neural pathways was integrated to find an overlap between the ones for working memory and episodic memory (Rudebeck et


al.). This led to the development of a new task that targets the neural correlates for both types of memory. Thus, the type of advance made in the field of cognitive science is incremental.

Criticisms and Future Directions

Rudebeck et al. could take their study further by carrying out experiments to measure the amount of oxygen and energy delivered to highly active brain areas. For instance, Buschkuehl, Garcia, Jaeggi, Bernard, & Jonides J (2014) report increased blood flow in areas of the brain during training, which is maintained to an extent afterwards. However, Rudebeck et al did not test for a transfer from the n-back training task to other sensory modalities, such as audition to fully predict the participant’s real potential. Thompson et al. (2013) disagree that training working memory transfers to a higher speed of processing, but their participants had a gender imbalance, a high IQ and were from top universities. Unlike Rudebeck et al’s study, training was not done daily to be consistent over three weeks, which is the optimal period to improve cognition. Also, testing was carried out in a stressful university environment. Rudebeck et al’s study recruited participants from the community and allowed them to train from home at their own convenience, which makes it more representative of the general population in terms of age and mental health. Stamenova et al. (2014) found that older adults with better cognitive function were more likely to benefit from recollection training when verbal memory was used to encode information. On the contrary, there is no substantial evidence that the gains in recognition memory transfer to any other types of stimuli that may be used for the rest of the cognitive domains. Thus, the task must be very precise in order to improve cognitive abilities in lower functioning older adults, which also requires that the task is manageable enough for them to make any progress. In contrast, Rudebeck et al.’s study used spatial working memory training on purpose, in order to avoid verbal encoding of data because it would not transfer well to other untrained tasks. Thus, Rudebeck et al. could consider why Bergman Nutley et al.’s study found that young children did not improve their cognitive abilities across different tasks the case and if it is possible to design a task that elicits the same results across all age groups. This is important because older adults tend to improve more with training when their existing cognitive capacities are good. To take future directions, Rudebeck et al. can add more dimensions to their procedure by measuring the effects of lifestyle factors that may contribute to the biological correlates for improved cognition. For example, a study by Scullin et al. (2012) found that when Parkinson’s disease patients took dopaminergic medication and got enough sleep at night, the effects of training working memory were enhanced. This is a confounding variable that can affect the results of the study, so it should be taken into account. In addition, Hyer, Scott, Lyles, Dhabliwala, & McKenzie (2014) used a comprehensive approach to help older adults with mild to moderate memory impairments retain and improve working memory. The participants applied

mnemonic strategies to their daily life, while engaging in various activities that affect memory processes. This involved leading a healthier lifestyle by exercising four times a week, eating a Mediterranean diet, reducing stress to affect beta amyloid plaques, socializing more, meditating, and identifying their purpose in life. Therefore, it is evident that targeted cognitive training is most effective for adults with unimpaired cognition from the findings, which show that those who have strong cognition in old age and are at the lowest risk of dementia are the ones who benefit the most from training. This finding can inform the measures taken in the present to provide training for the population, so that when they have aged, they will not be at a disadvantage. A recent study by Jiang et al. (2015) illustrated how spatial training induced memory improvement in a rat model of Alzheimer’s disease has an underlying process that is dependent on CaMKII, leading to dendrite growth and spine generation. Hence, future studies could investigate the effects on the levels of this molecule during different types of memory training in different populations to objectively measure the effects on cognitive processes. References 1. Bellandera M, Brehmera Y, Westerberga H, Karlssona S, Fürtha D, Bergmanb O, Erikssonb E, Bäckman L (2011) Preliminary evidence that allelic variation in the LMX1A gene influences training-related working memory improvement. Neuropsychologia 49:1938–42. 2. Bergman Nutley S, Söderqvist S, Bryde S, Thorell LB, Humphreys K, Klingberg T (2011) Gains in fluid intelligence after training non-verbal reasoning in 4-year-old children: a controlled, randomized study. Developmental Sci 14:591–601. 3. Boller B, Jennings JM, Dieudonné B, Verny M, Ergis A-M (2012) Recollection training and transfer effects in Alzheimer’s disease: Effectiveness of the repetition-lag procedure. Brain Cognition 78:169-177. 4. Brehmer Y, Westerberg H, Bäckman L (2012) Workingmemory training in younger and older adults: training gains, transfer, and maintenance. Front Hum Neurosci 6:63. doi: 10.3389/ fnhum.2012.00063. 5. Buschkuehl M, Garcia L, Jaeggi S, Bernard J, Jonides J (2014) Neural Effects of Short-Term Training on Working Memory. Cogn Affect Behav Neurosci 14:147-60 6. Cheng Y, Wu W, Feng W, Wang J, Chen Y, Shen Y, Li Q, Zhang X, Li C (2012) The effects of multi-domain versus single-domain cognitive training in non-demented older people: a randomized controlled trial. BMC Med 10:30. doi:10.1186/1741-7015-10-30. 7. Huntley J, Bor D, Hampshire A, Owen A, Howard R (2011) Working memory task performance and chunking in early Alzheimer’s disease. Br J Psychiatry 198:398–403. 8. Hyer L, Scott C, Lyles J, Dhabliwala J, McKenzie L (2014) Memory intervention: the value of a clinical holistic program for older adults with memory impairments. Aging Ment Health 18:169-78 9. Jiang X, Chai G-S, Wang Z-H, Hu Y, Li X-G, Ma Z-W, Wang Q, Wang J-Z, Liu G-P (2015) CaMKII-dependent dendrite ramification and spine generation promote spatial training-induced memory improvement in a rat model of sporadic Alzheimer’s disease. Neurobiol Aging 36:867-76 10. Kanaan S, McDowd JM, Colgrove Y, Burns JM, Gajewski B, Pohl PS (2014) Feasibility and Efficacy of Intensive Cognitive Training in Early-Stage Alzheimer’s Disease. Am J Alzheimers Dis Other Demen 29:150-8. 11. Lee AC, Rudebeck SR (2010) Investigating the interaction between spatial perception and working memory in the human medial temporal lobe. J Cogn Neurosci 22:2823-35. 144


12. Lee HK, Boot WR, Basak C, Voss MW, Prakash RS, Neider M, Erickson KI, Simons DJ, Fabiani M, Gratton G, Low KA, Kramer AF (2012) Performance gains from directed training do not transfer to untrained tasks. Acta Psychol 139:146-58. 13. Rudebeck S, Bor D, Ormond A, Oâ&#x20AC;&#x2122;Reilly J, Lee A, Chao L (2012) A Potential Spatial Working Memory Training Task to Improve Both Episodic Memory and Fluid Intelligence. PLoS ONE 7:e50431. 14. Scullin MK, Trotti LM, Wilson AG, Greer SA, Bliwise DL (2012) Nocturnal sleep enhances working memory training in Parkinsonâ&#x20AC;&#x2122;s disease but not Lewy body dementia. Brain 135:2789-97 15. Stamenova V, Jennings JM, Cook SP, Walker LAS, Smith AM, Davidson PSR (2014) Training recollection in healthy older adults: clear improvements on the training task, but little evidence of transfer. Front Hum Neurosci 8:898. doi: 10.3389/fnhum.2014.00898 16. Thompson TW, Waskom ML, Garel K-LA, Cardenas-Iniguez C, Reynolds GO, Winter R, Chang P, Pollard K, Lala N, Alvarez GA, Gabrieli JDE (2013) Failure of Working Memory Training to Enhance Cognition or Intelligence. PLoS ONE 8:e63614. 17. Thorndike EL, Woodworth RS (1901) The influence of improvement in one mental function upon the efficiency of other functions: III. Functions involving attention, observation and discrimination. Psychol Rev 8:553-564.

Address correspondence to: Shonali Lakhani, Human Biology Department, University of Toronto, Toronto, ON 60101 Email: Shonali.lakhani@mail.utoronto.ca

145


Neural Correlates of Artistic Imagination through the Visual Modality

Dong-Eun Lee

Honing imaginative skills allows us to adapt/form novel paradigms for perceiving incoming stimuli. But investigating potential co-occurring alterations in extant neural mechanisms to effect such perceptual changes has been a difficult feat, due to multiple confounds that render imagination an individually unique experience. To simplify matters, then, Schlegel and colleagues approached this investigation by focusing on a simplified art form: visual representational art, where an artist must create an expressive image faithful to the actual object or scene.1 As such, three types of cognition associated with the visual art process were considered: intrinsic imagination, perception of visual stimuli, and skilled action, for outward expression of such perception. To investigate, undergraduates enrolled in a drawing/painting class were compared to undergraduates studying other subjects similar in intensity, with fMRI and DTI recordings throughout the four-month class. As courses progressed, changes in the frontal lobe activation were observed with co-occurring changes in cerebellar activity in art learners, establishing that neural circuits rewire as representational art skills are learned. However, for these findings to imply a potential mechanism in which imaginative abilities are cultivated, visual representational art must have construct validity as a model for artistic creativity. In addition, the control group’s organic chemistry course, considered as acquiring problemsolving skills in closed systems, must control for only the confounding effects, and must itself discernibly be a closed system in comparison. This review evaluates Schlegel and colleagues’ experimental design and robustness in their consequent results for offering transferable insights about central mechanisms effecting artistic creativity. Key words: representational art; functional magnetic resonance imaging (fMRI); diffusion tensor imaging (DTI); frontal lobes; cerebellum Background Creativity is ubiquitous and necessary in a human life. It allows humanity to adapt new ideas that enrich quality of life and/or provide new tools for a particular niche, like Marie-Guillemine Benoist’s Portrait d’une négresse2 (Figure 1a), and Hama and colleagues’ optical method, ScaleA23 (Figure 1b). Although both are creative products of the imaginers’ novel perceptions about the world, as sclerotic vessel4 is to fibrotic interstitium-endothelium5, both are also born from different mechanisms (Figure 1). Then, are there universal neural activation motifs in a creative process or is the mechanism giving rise to Benoist’s work discernibly different from that producing Hama’s group’s ScaleA2? Schlegel and colleagues decide to examine brain activations in individuals learning visual representational art to instigate a response. Choosing one art form, and this one in particular, affords advantages for the experimenters. Firstly, studying a single style in a single modality eliminates obscurity in definitions and consequent subjective gradations between different styles of artistic expressions.6 Furthermore, also known as figurative art, a representational artist expresses concepts or processes in depictions of his/ her observations of the world.7 Thus, confounding contextual factors, such as culture, environment of upbringing, and affect, which otherwise would be focal points for other styles, such as pop art,6,8 are remote and peripheral as a representational artist must be faithful to the observed scene/subject (Figure 1a). Extant studies examine corresponding neural circuits to representational art appreciation. In a TMS & EEG study, disrupting the left dorsolateral prefrontal cortex and right posterior parietal cortex significantly reduced intrinsic windbags are great esthetic appreciation of

representational art.10 In another study, frontotemporal dementia patients, with disrupted semantic knowledge and sense of self, exhibited preserved preferences in esthetic appreciation of art.11 However, neural circuits associated with learning and producing representational art is a novel investigation. Schlegel and colleague focus on three aspects of cognition considered in visual art production: creative cognition, perception via visual modality, and translation into precise motor ability. The first aspect, as implied, is the imaginative process in which original ideas and patterns are derived. This is the mechanism least understood and principally significant. Debates about mechanistic categorizations range from cogent to divergent,12,13 but meta-analysis of studies about creativity indicated diffuse findings of lower frontal lobe white matter fractional anisotropy (FA).14 Moving on, visual perceptual abilities, with respect to representational art, requires the artist to create precise, unassumed two-dimensional images of the world. To achieve this, Bayesian inferences acting to infer from subjective experiences must be tightly regulated. There is no agreement on whether artists have rewired mechanisms to regulate inferential processes,15,16 leaving Schlegel’s group to approach with an open mind. Lastly, the perceptuomotor abilities of an artist to translate her/his perception to an artwork is important. Visual system, as with other modalities, contains the dorsal or “where” stream, about spatial arrangement and movement, and the ventral or “what” stream, about object identity. For the purpose of artwork creation, the dorsal, translation to action stream was thought to be more relevant. Therefore, these factors and previous findings were considered for constructing the authors’ experimental design. 146


Figure 1. (a) Marie-Guillemine Benoist’s Portrait d’une négresse, 1800, housed in Musée du Louvre.9 (b) Hama and colleagues’ ScaleA2 technique: c. mouse brain incubated in ScaleA2 reagent for >2 weeks; d. preserved fluorescent labeling of >2 week ScaleA2 reagent-incubated mouse brain; e. mouse embryos incubated in phosphate buffered saline (PBS, left) and ScaleA2 reagent (right) for >2 weeks.3

Research Overview

Summary of Major Results

35 undergraduate students within 19-22 years of age, 17 enrolled in one of two introductory observational drawing or painting class – the treatment group – and 18 enrolled in introductory organic chemistry class – the control group – participated as subjects. To behaviorally evaluate creative cognition, an artistic creative thinking analysis measure, called the Torrence Tests of Creative Thinking Figural Form A (TTCT), were administered to subjects twice, before the course began and after the course ended to show significant change in the treatment group (Figure 2a). By dividing the TTCT scale into 5 factors, and of them, the treatment group increased in factors 1, 2, and 3, which translate to: divergent thinking, or the ability to produce multiple original constructs; effective systematic illustrative modeling; and forming rich, complex imagery, respectively (Figure 2b). To track progressive neurological changes from before the course to the last month of the course, diffuser tensor imaging data were obtained for both treatment and control groups. The results indicated that, white matter FA in the voxel areas of the prefrontal cortex significantly declined in the treatment group students while control group students showed no change throughout in those voxels (Figure 3). To track progress in visual perception skills, optical illusion tasks were administered to subjects longitudinally throughout course progression: the Craik-O’Brien-Cornsweet illusion with differences in luminance, and the Mueller-Lyer illusion. In conjunction, functional magnetic resonance images (fMRI) were also acquired. No significant changes were observed, in behavioral and fMRI data. Lastly, to longitudinally determine trends in perceptuomotor skills throughout course progression, gesture drawing tasks were administered to subjects while DTI were also acquired in tandem. From the gesture drawing tsk results, treatment group subjects exhibited a steady 147

Figure 2. Results of artistic creative thinking from figure synthesis to colorfulness of imagery. (a) TTCT results at the end of course compared to results of TTCT taken at before start of course. (b) Factor analyses of TTCT submeasures. The asterisks indicate significant differences between exp (treatment group) and con (control). F1 = divergent thinking; F2 = effective systematic modeling; F3 = complex imagery; F4 = verbal creativity; F5 = originality and synthesis of lines

increase, while control did not exhibit significant changes (Figure 4a). And by statistically comparing trends, the treatment group exhibited significant improvement in the gesture drawing scores at the second month of classes onwards (Figure 4b). In the subsequent DTI data that followed, the treatment group subjects exhibited significant increase in white matter activation in the right anterior cerebellum throughout course progression (Figure 4c). Discussion & Conclusions In keeping with previous findings, Schlegel and colleagues found lower white matter FA in the frontal lobes, while behaviorally observing improved creative cognition within the visual art paradigm (Figure 2). However, decreased white matter activation in a particular cluster of voxels may indicate multiple reasons. Secondly, authors report no significant change in neural activations or in behavior relevant to visual perception, indicating that changes with regards to visual perception are not required for cultivating visual representational art skills (Figure 3). Lastly, authors observed significant increase in gesture drawing skills and rewiring changes for the art learners (figure 4), making perceptuomotor skills within the dorsal visual stream an important cognition in honing visual representational art. The implicated brain area of which rewiring was observed was the right anterior cerebellum, as higher white matter FA was observed (Figure 4). This area, from previous works, is correlated to proprioceptive feedback and is found to project to hand and arm areas of the left


Figure 3. DTI results, longitudinally tracked throughout course progression. (a) Significant voxel areas that exhibited progressively decreased activation in the treatment group (exp). (b) Time course of FA normalized to DTI results obtained before the beginning of courses in voxels exhibiting significant changes within the treatment group data. Exp = treatment group; con = control group.

primary motor cortex, and enhance hand and eye movements.17,18 This work expresses that rewiring changes in the prefrontal cortex causes artistic creativity in cultivation of artistic skills, and an artist need not adapt novel ways to perceive exteroceptive cues but perfect fine tune motor abilities to externally display her/his point of view more accurately. Criticisms and Future Directions From here on, Schlegel and colleagues’ work is evaluated in their experimental design and analyses of results. Also, suggestions for potential post hoc studies are discussed.

Experimental Design

Schlegel and colleagues effectively approach a novel question by longitudinally mapping different cognitive changes with neural activation changes. In comparison to previous works, this experimental design offers more robust evidence, from functional (fMRI), connectivity (DTI), and behavioral/cognitive data. The findings are made more salient by the authors’ choice to study subjects who are acquiring or improving on pre-existing artistic creativity, since baseline recordings would also exist in the treatment group subjects as well for comparison. However, issues lie in the authors’ definition of visual representational art with respect to the choice of control. Authors contend that this art form is problem-solving in an open system more so than organic chemistry, which is claimed to foster problemsolving in a closed system. Representational artists must produce two-dimensional images recognizable as objects or scenes in reality; they must evoke their point of view within the constraints of the realized world. Similarly, organic chemists must formulate a string of reactions to target a product molecule within constraints of electron sinks and sources. The visual representational artist, unlike surrealist or abstract art,6,8 is limited in her/his expressive freedom by

extant objects and scenes in the world, not unlike the limitations placed by electrostatic and other chemical interactive properties of compounds and atoms for synthetic chemists. Two groups of undergraduates taking either groups of classes would undoubtedly require creativity to produce new ideas and solutions within these disciplines. They would only differ about the context with which creativity is accessed, artistic vs. scientific. Instead, choosing undergraduate students in an intense program not involved in artistic endeavours may have been better. In doing so, by including variable disciplines, no biased results would arise from control conditions. In addition to the issues with defining control conditions’ program/class of enrollment, including a third condition not undertaking intensive programs or not actively learning in class, perhaps young professionals, could also solidify appropriateness in their choice of control group conditions to be undergraduate students in an intensive program. Also adding a cohort of professional representative artists to compare potential differences in maturity level of skills and creativity may have afforded more insight about their question. Furthermore, including follow-up behavioral, fMRI, and DTI data a month or more after courses ended may have also outlined longevity of the learned artistic creativity.

Analyses of Results

Since huge degree of cognitive problem-solving would require the prefrontal cortex, one could argue that, in learning the specific skills for transforming a 3-D image into a 2-D one, a more skilled person may not need to calculate or guess as much, hence having less activation in the prefrontal cortex, and perhaps more activation in the cerebellum and neurons imprinted with automatic procedural memory (perhaps parietal lobes). In this regard, the rewiring observed may predominately be due to maturation of certain skills, and less to do with increased artistic creativity, as authors have defined. 148


Figure 4. (a) Time course results of the gesture drawing tasks administered to both treatment and control subjects throughout class progression. (b) Statistical analysis based on data patterns compared between gesture drawing task results of treatment and control groups, where the neon green color indicates significant increase of treatment group results compared to control. (c) Significant voxel areas selected per monthly DTI acquisition, green showing significantly higher FA in treatment group subjects and orange showing significantly lower FA, compared to control. Exp = treatment group; con = control group.

Potential Post hoc Studies

Since connectivity and structural studies were done, a stimulation study should be implemented on both cohorts using repetitive transcranial magnetic stimulation (rTMS). As 1Hz frequency stimulation (low freq) inhibits targeted areas and 10Hz-20Hz stimulation (high freq) activates targeted areas,19 the cohorts should be given stimulations reciprocal to findings before performing the behavioral tasks to discern whether the implicated areas are causally responsible. Therefore, the art learners should be subjected with low freq stimulation of the right anterior cerebellum (as accurately as possible) and high freq stimulation of the frontal lobes, while the control group should be given the opposite. If the art learners perform poorly or exhibit reduced performance, then the rewiring changes are indeed responsible. 149

To further investigate implications of the lower white matter FA in prefrontal cortex, lesion studies should be conducted. By examining patients experiencing schizophrenia, known to have cortical thinning and overall volume decrease,20,21 or those with dementia,22 the ambiguities associated with the aforesaid result can be explored. In addition, post-mortem cellular studies should also be performed to discern whether extra-axonal network is responsible for the lower white matter FA in the frontal lobes. By immunostaining a cryosection of the implicated voxel area for glial fibrillary acidic protein (GFAP) of a professional visual representational artist and of a layman would also offer insight about the observed result.23 If the artist cryosection indicates significantly higher glial cell support system compared to a laymanâ&#x20AC;&#x2122;s, then the decreased prefrontal white


matter activation is due to a more developed glial cell population. Lastly, different affective and cognitive skills have also been implicated with creativity, such as mood disorders, personality disorders,21,24 and meditation.25,26 Since there is a wealth of studies dedicated to these, a meta-analysis study scanning for works investigating creativity and these conditions or topics might also offer insight about potential rewiring changes or neural circuits responsible for creativity. References 1. Schlegel, A. et al. The artist emerges: Visual art learning alters neural structure and function. Neuroimage 105, 440–451 (2015). 2. Farrington, L. E. Reinventing Herself: The Black Female Nude. Woman’s Art J. 24, 15–23 (2004). 3. Hama, H. et al. Scale: a chemical approach for fluorescence imaging and reconstruction of transparent mouse brain. Nat. Neurosci. 14, 1481–1488 (2011). 4. Lahoute, C., Herbin, O., Mallat, Z. & Tedgui, A. Adaptive immunity in atherosclerosis: mechanisms and future therapeutic targets. Nat. Rev. Cardiol. 8, 348–358 (2011). 5. Zeisberg, E. M. et al. Endothelial-to-mesenchymal transition contributes to cardiac fibrosis. Nat. Med. 13, 952–961 (2007). 6. Gartus, A., Klemer, N. & Leder, H. The effects of visual context and individual differences on perception and evaluation of modern art and graffiti art. Acta Psychol. (Amst). 156, 64–76 (2015). 7. Figurative art. A Dictionary of Media and Communication (2011). 8. Costello, D. Kant and the problem of strong non-perceptual art. Br. J. Aesthet. 53, 277–298 (2013). 9. Benoist, M.-G. Portrait d’une negresse. (1800). at <http:// en.wikipedia.org/wiki/Marie-Guillemine_Benoist#/media/ File:Marie-Guillemine_Benoist_-_portrait_d%27une_negresse.jpg> 10. Cattaneo, Z. et al. The role of prefrontal and parietal cortices in esthetic appreciation of representational and abstract art: A TMS study. Neuroimage 99, 443–450 (2014). 11. Halpern, a R. & O’Connor, M. G. Stability of Art Preference in Frontotemporal Dementia. Psychol. Aesthetics, Creat. Arts 7, 95–99 (2013). 12. Sternberg, R. J. Creativity or creativities? Int. J. Hum. Comput. Stud. 63, 370–382 (2005). 13. Dietrich, A. & Kanso, R. A review of EEG, ERP, and neuroimaging studies of creativity and insight. Psychol. Bull. 136, 822–848 (2010). 14. Jung, R. E., Grazioplene, R., Caprihan, A., Chavez, R. S. & Haier, R. J. White matter integrity, creativity, and psychopathology: Disentangling constructs with diffusion tensor imaging. PLoS One 5, (2010). 15. Perdreau, F. & Cavanagh, P. Is artists’ perception more veridical? Front. Neurosci. 7, 1–11 (2013). 16. Graham, D. & Meng, M. Lightness constancy in visual artists. J. Vis. 11, 371 (2011). 17. Miall, R. C. & Reckess, G. Z. The cerebellum and the timing of coordinated eye and hand tracking. Brain Cogn. 48, 212–226 (2002). 18. Chamberlain, R. et al. Drawing on the right side of the brain: A voxel-based morphometry analysis of observational drawing. Neuroimage 96, 167–173 (2014). 19. Cudeiro, J. et al. Effects on EEG of Low (1Hz) and High (15Hz) Frequency Repetitive Transcranial Magnetic Stimulation of the Visual Cortex: A Study in the Anesthetized Cat. Open Neurosci. J. 1, 25–30 (2007). 20. Buchsbaum, M. S. The frontal lobes, basal ganglia, and temporal lobes as sites for schizophrenia. Schizophr. Bull. 16, 379–389 (1990).

21. Carson, S. H. Creativity and psychopathology: A shared vulnerability model. Can. J. Psychiatry 56, 144–153 (2011). 22. Crutch, S. J. & Rossor, M. N. Artistic Changes in Alzheimer’s Disease. Int. Rev. Neurobiol. 74, 147–161 (2006). 23. Andreiuolo, F. et al. GFAPδ immunostaining improves visualization of normal and pathologic astrocytic heterogeneity. Neuropathology 29, 31–39 (2009). 24. Motzkin, J. C., Newman, J. P., Kiehl, K. a. & Koenigs, M. Reduced Prefrontal Connectivity in Psychopathy. J. Neurosci. 31, 17348–17357 (2011). 25. Horan, R. The Neuropsychological Connection Between Creativity and Meditation. Creat. Res. J. 21, 199–222 (2009). 26. Deshmukh, V. D. Cognitive pause-and-unload hypothesis of meditation and creativity. 5, 217–231 (2013).

Received March, 12,

February, 2015;

10, accepted

2015; April, 06,

revised 2015.

This work was supported by The Neuroscience Association of Undergraduate Students (NAUS), The University of Toronto Human Biology Faculty (HMB), and The Neurobiology of Behavior 1 Series (HMB300H1). The author thanks Dr. Bill Ju, Dr. Alexander Schlegel, Dr. Prescott Alexander, and colleagues of Dartmouth College for execution, experiments, and results explored in this review. Address correspondence to: Miss Dong-Eun Lee, Neuroscience and Human Physiology Undergraduate Program, University of Toronto, Toronto, ON M5S 3J6 Email: donge.lee@utoronto.ca. Copyright © 2015 Dr. Bill JU, Miss Dong-Eun LEE, Neurosciences, Human Biology Program

150


Overcoming social difficulties with the help of medications

Victor Lee

Social deficits have been shown to occur in a variety of psychiatric disorders such as schizophrenia and autism spectrum disorder. IRSp53 is an excitatory synaptic signaling protein and mice that lack the protein demonstrated impaired social interaction and communication as well as hyperactive NMDA receptors. Treatment of the IRSp53 knockout mice with memantine, which is a NMDA receptor antagonist, or MPEP, which is a metabotropic glutamate receptor 5 antagonist, rescued social interaction. NMDA receptor function, hippocampal plasticity, and neuronal firing in the medial prefrontal cortex was also normalized along with social interaction. Reduced NMDA receptor function has been implicated in social impairments as well, which suggeset that deviation of NMDA receptor activity from a regular level can lead to social deficits and that correction of the receptor activity can rescue social interaction. Key words: Social deficit, IRSp53, NMDA receptor, mGluR5 Background Social deficits are characteristic of many neuropsychiatric disorders such as attention deficit hyperactive disorder, autism spectrum disorder, and schizophrenia.1,2,3 IRSp53 is an excitatory synaptic signaling protein that plays a role in the control of the cytoskeletal actin filaments.4,5 IRSp53 knockout mice have been shown to have lower AMPA/NMDA ratio.6 The knockout mice also demonstrate increased NMDA receptor function, increased long term potentiation dependent on NMDA receptors, and decreased hippocampus-dependent learning and memory. The drugs used in this paper are the NMDA receptor antagonist memantine7 and the metabotropic glutamate receptor 5 antagonist MPEP.8 Memantine has been shown to be effective in treating Alzheimerâ&#x20AC;&#x2122;s Disease in humans, which is a neurodegenerative disorder,9 and MPEP has been shown to have antidepressant like effects on mice.10 In this paper, wild type mice and IRSp53 knockout mice were used and drugs were delivered to the mice by injection. Various behavioural experiments were used to assess the social aptitude of both mice. The three-chambered test is a prominent social interaction assay which measures the amount of time a subject mouse spends in either the chamber with a novel stranger mouse or the chamber with a novel object.11 Long term depression (LTD) was measured to test for plasticity. Brain slices have long been used to study long term potentiation and LTD as indicators of synaptic plasticity.12 Experiments in this paper that tested for LTD utilized sagital and coronal brain slices. Drugs were delivered to the slices by infusion into the artificial cerebrospinal fluid bathing the slices. Whole cell patch clamp recordings and field potential recordings were used to measure excitatory post synaptic currents. Neurons were stained with antibodies and phalloidin, which is commonly used to stain for actin,13 to measure F-actin stability. The F-actin stability may contribute to the hyperactivation of NMDA receptors by reducing LTD of NMDA receptors. Currently, it is known that F-actin is severed by cofilin, which is activated through phosphorylation.14 The stabilized F-actin becomes resistant to

151

activated cofilin but the mechanism of how this occurs is unclear. There are many proteins that are upstream of cofilin such as p21- activated kinase, LIM kinase, Rho-associated kinase, Rac/cdc42, and Rho.15 Though this paper has observed the effects of drug treatment on social behaviour in knockout mice, drug treatment on cofilin resistant actin in knockout mice remains unexamined. Unraveling the mechanism of the cofilin resistance is a potential next step in determining new treatments for synaptic dysfunction (by revealing novel drug targets) and ultimately treatment of social deficits. Research Overview

Summary of Major Results

Social deficits and rescue of social interaction Measurements of social interaction demonstrated that IRSp53 knockout mice had social deficits compared to wild type mice. The three chambered test revealed that knockout mice spent less time with the stranger mouse than the wild type mice. Knockout mice spent less time sniffing cages and other mice despite demonstrating normal olfactory function. Knockout mice moved greater distances than wild type mice within a 48 hour period. Knockout mice also emitted less ultrasonic vocalizations. All of these results confirm deficits in many different aspects of social interaction in the knockout mice. Heterozygotic mice were also tested for social function and were confirmed to have social behaviour similar to that of wild type mice. All mice were given intraperitoneal injections of memantine (10 mg/kg) or MPEP (30 mg/kg) and it was found that memantine and MPEP rescued certain aspects of social deficits in the knockout mice, such as performance in the three chambered test (Figure 1). However, some forms of social function such as hyperactivity and ultrasonic vocalizations were not normalized. Furthermore, a dose of MPEP at 10 mg/ kg was not sufficient to rescue social deficit.


Figure 1. Quantification of time the wild type mice (WT) and IRSp53 knockout mice (KO) spent in a chamber with a novel object (O) and a chamber with a stranger mouse (S).

LTD of NMDA receptors in hippocampus Excitatory postsynaptic potentials were measured in the SC-CA1 synapses of the hippocampus and it was found that LTD was impaired for NMDA receptors in the synapses for IRSp53 knockout mice but there was normal LTD of AMPA receptors. It has been shown that retention of NMDA receptors in the synapse requires stable F-actin16 and that depolymerization of actin is needed for long LTD of NMDA receptors.17 In this study, it was found that reduced LTD was also associated with stable F-actin. It was found that F-actin depolymerization in synapses was less in knockout mice as compared to wild type mice, and even less in Shank positive (excitatory) synapses (Figure 2a-d). It was also found that cofilin, a negative regulator of F-actin, was found to be expressed at similar levels in both wild type and knockout mice (Figure 2e). Furthermore, it was found that the IRSp53 knockout mice had higher levels of cofilin phosphorylation (Figure 2f), a measure of cofilin inactivation, but higher levels of NMDA-induced cofilin dephosphorylation (Figure 2g,h). Treatment of brain slices with memantine was found to have restored LTD of NMDA receptors and normalized NMDA receptor activity levels in IRSp53 knockout mice. These drugs did not show such an effect in wild type mice. MPEP was found to normalize AMPA/ NMDA ratios in knockout mice as well. Memantine was not used to test for normalization of AMPA/ NMDA ratio due to its voltage dependent blockade of NMDA receptors. Reduced dendritic complexity and firing rate of mPFC The medial prefrontal cortex (mPFC) is an area that is known to be involved in social function.18 The layer II and III neurons was found to have reduced dendritic complexity in the apical dendrites (but not the basal dendrites). The firing rate and amplitude of the miniature excitatory postsynaptic currents was also found to

be lower in the IRSp53 knockout mice layer II and III neurons when compared to the wild type mice layer II and III neurons. When single unit recordings were used on live anesthesized mice, it was found that IRSp53 deficient mice had reduced firing only in excitatory synapses and inhibitory synapse firing rates were left unchanged. Memantine was found to increase the firing rate of neuronal firing in both wild type and IRSp53 knockout mice but the effect was found to be larger in the knockout mice. These results suggest that the removal of IRSp53 reduces firing rate in the mPFC but can be rescued with memantine. Furthermore, it was found that memantine does not incraese the firing rate of hippocampal CA1 neurons in both wild type and IRSp53 knockout mice. However, firing rate of memantine treated IRSp53 knockout mice was significantly higher than the firing rate of memantine treated wild type mice. This suggests that memantine induces a difference in firing rate between the wild type mice and IRSp53 knockout mice. Conclusions and Discussion All the data provided seems to suggest that social deficits in IRSp53 knockout mice are caused by hyperactivity of NMDA receptors in the hippocampus. Memantine rescued social interaction and LTD of NMDA receptors in the hippocampus. MPEP also rescued social interaction but was shown to increase AMPA/NMDA ratios as well. However, LTD of metabotropic glutamate receptor 5 in the hippocampal synapses appear to be normal so this suggests that the mechanism of how MPEP rescues social deficits does not involve modulating LTD of metabotropic glutamate receptor 5 but rather, works indirectly to modulate NMDA receptor activity. The drugs used in this study, memantine and MPEP, could rescue some aspects of social function, such as time spent with stranger mouse in a three chambered test, but could not rescue some other aspects of social function, such as ultrasonic vocalizations or hyperactivity. Drug induced social rescue in other mouse lines have rescued symptoms such as hyperactivity. For example, Cntnap2 knockout mice have had their hyperactivity reduced with the antipsychotic drug risperidone.19 The selectivity of the rescues by these drugs may ease further study of the mechanisms. The hippocampus of the IRSp53 knockout mice showed less LTD of the NMDA receptors and this may be due to stabilized F-actin in those mice which prevent NMDA from leaving the membrane. However, F-actin may also be stimulating the activity of the NMDA receptors on the membrane through interaction mediated by alpha actinin.20 The results that show that there is significant decrease in dendritic complexity of mPFC neurons are the first to show in vivo that IRSp53 upregulates dendritic spines. Interestingly enough, the hippocampal neurons display normal dendritic complexity in the knockout mice despite the fact that there is hyperactivity of NMDA receptors in the synapses of the hippocampus. Furthermore, memantine restoring 152


Figure 2. Data reflecting the stabilized F-actin and lower basal cofilin activity in IRSp53 knockout mice hippocampal synapses. (a,b) Select images of hippocampal synapses of both wild type and knockout mice. MAP2 and Shank were used to stain for dendrites and excitatory synapses respectively and phalloidin was used to stain for F-actin. (c,d) Quantified results of a and b. (e,f) Cofilin levels were found to be similar in wild type and knockout mice but basal levels of phosphorylated cofilin appeared to be higher in knockout mice. (g,h) Greater levels of dephosphorylation were found in knockout mice than wild type mice when stimulated with NMDA.

the low firing rates of the mPFC neurons implies that the restoring neuronal firing may play a role in restoring social interaction in the knockout mice. These results suggest that NMDA receptor hyperfunction is implicated in social deficit. However, other results have shown that NMDA receptor hypofunction is also implicated in social deficit.21 As is the case with many biological models, balance is key in maintaining proper function for the organism. IRSp53 has been implicated with Autism spectrum disorder (ASD).22 However, it has not yet been established as to whether NMDA receptor hyperactivity is associated with ASD. Memantine has been shown to help with social deficits in ASD,23 which suggests that NMDA receptor hyperactivity may indeed contribute to social deficits in ASD.

Conclusions

In conclusion, the data shows that NMDA receptor hyperactivity in IRSp53 knockout mice causes social deficits. However, there is potential for therapeutic treatment through NMDA receptor inhibition. This study has unraveled part of the mechanism that causes social dysfunction but there is still more work to be done in the field. Further understanding of molecular 153

mechanisms involved in social deficits can help reveal more drug targets that can potential treat conditions such as ASD. Criticisms and Future Directions While this paper has examined many perspectives of the problem, many aspects of it remain unexamined. The study acknowledged that memantine and MPEP could not rescue some social dysfunction symptoms such as hyperactivity but did not attempt to rescue them with drugs that are known to rescue such symptoms such as risperidone. Regardless of outcome, conducting such experiments would provide insight of mechanisms of social deficit and reveal potential drug targets. The data revealed that IRSp53 knockout mice had reduced long term depression of NMDA receptors in the hippocampus. This may have been caused by the stabilization of F-actin in the dendrites. The experiments demonstrated that the stabilization of F-actin is in part due to the F-actin becoming resistant to cofilin. However, the mechanism was unexplored. The paper neglected to check expression of genes upstream of cofilin such as LIM kinase, p21- activated kinase, Rho-associated kinase, Rac/cdc42, and Rho.


Overall,. it would be a good next step to uncover what may be causing the F-actin stability and resistance to cofilin. Upregulating and downregulating these genes is another approach that may be done. Discovering other proteins that are involved in this pathway would offer insight onto what proteins to create drug targets for to treat social deficits and can potentially be used as treatments for conditions such as ASD. References 1. Rich, E. C., Loo, S. K., Yang, M., Dang, J. & Smalley, S. L. Social functioning difficulties in ADHD: Association with PDD risk. Clin. Child Psychol. Psychiatry 14, 329–344 (2009). 2. Schultz, R. T. Developmental deficits in social perception in autism: the role of the amygdala and fusiform face area. Int. J. Dev. Neurosci. Off. J. Int. Soc. Dev. Neurosci. 23, 125–141 (2005). 3. Häfner, H., Nowotny, B., Löffler, W., an der Heiden, W. & Maurer, K. When and how does schizophrenia produce social deficits? Eur. Arch. Psychiatry Clin. Neurosci. 246, 17–28 (1995). 4. Soltau, M. et al. Insulin receptor substrate of 53 kDa links postsynaptic shank to PSD-95. J. Neurochem. 90, 659–665 (2004). 5. Scita, G., Confalonieri, S., Lappalainen, P. & Suetsugu, S. IRSp53: crossing the road of membrane and actin dynamics in the formation of membrane protrusions. Trends Cell Biol. 18, 52–60 (2008). 6. Kim, M.-H. et al. Enhanced NMDA receptor-mediated synaptic transmission, enhanced long-term potentiation, and impaired learning and memory in mice lacking IRSp53. J. Neurosci. Off. J. Soc. Neurosci. 29, 1586–1595 (2009). 7. Lipton, S. A. The molecular basis of memantine action in Alzheimer’s disease and other neurologic disorders: low-affinity, uncompetitive antagonism. Curr. Alzheimer Res. 2, 155–165 (2005). 8. Rutten, K., Van Der Kam, E. L., De Vry, J., Bruckmann, W. & Tzschentke, T. M. The mGluR5 antagonist 2-methyl-6(phenylethynyl)-pyridine (MPEP) potentiates conditioned place preference induced by various addictive and non-addictive drugs in rats. Addict. Biol. 16, 108–115 (2011). 9. Reisberg, B. et al. Memantine in moderate-to-severe Alzheimer’s disease. N. Engl. J. Med. 348, 1333–1341 (2003). 10. Li, X., Need, A. B., Baez, M. & Witkin, J. M. Metabotropic glutamate 5 receptor antagonism is associated with antidepressant-like effects in mice. J. Pharmacol. Exp. Ther. 319, 254–259 (2006). 11. Yang, M., Silverman, J. L. & Crawley, J. N. Automated threechambered social approach task for mice. Curr. Protoc. Neurosci. Editor. Board Jacqueline N Crawley Al Chapter 8, Unit 8.26 (2011). 12. Teyler, T. J. Use of brain slices to study long-term potentiation and depression as examples of synaptic plasticity. Methods San Diego Calif 18, 109–116 (1999). 13. Wulf, E., Deboben, A., Bautz, F. A., Faulstich, H. & Wieland, T. Fluorescent phallotoxin, a tool for the visualization of cellular actin. Proc. Natl. Acad. Sci. U. S. A. 76, 4498–4502 (1979). 14. Gu, J. et al. ADF/cofilin-mediated actin dynamics regulate AMPA receptor trafficking during synaptic plasticity. Nat. Neurosci. 13, 1208–1215 (2010). 15. Ng, J. & Luo, L. Rho GTPases regulate axon growth through convergent and divergent signaling pathways. Neuron 44, 779–793 (2004). 16. Allison, D. W., Gelfand, V. I., Spector, I. & Craig, A. M. Role of actin in anchoring postsynaptic receptors in cultured hippocampal neurons: differential attachment of NMDA versus AMPA receptors. J. Neurosci. Off. J. Soc. Neurosci. 18, 2423–2436 (1998). 17. Morishita, W., Marie, H. & Malenka, R. C. Distinct triggering and expression mechanisms underlie LTD of AMPA and NMDA synaptic responses. Nat. Neurosci. 8, 1043–1050 (2005).

18. Yizhar, O. et al. Neocortical excitation/inhibition balance in information processing and social dysfunction. Nature 477, 171–178 (2011). 19. Peñagarikano, O. et al. Absence of CNTNAP2 leads to epilepsy, neuronal migration abnormalities, and core autism-related deficits. Cell 147, 235–246 (2011). 20. Cingolani, L. A. & Goda, Y. Actin in action: the interplay between the actin cytoskeleton and synaptic efficacy. Nat. Rev. Neurosci. 9, 344–356 (2008). 21. Won, H. et al. Autistic-like social behaviour in Shank2-mutant mice improved by restoring NMDA receptor function. Nature 486, 261–265 (2012). 22. Toma, C. et al. Association study of six candidate genes asymmetrically expressed in the two cerebral hemispheres suggests the involvement of BAIAP2 in autism. J. Psychiatr. Res. 45, 280–282 (2011). 23. Hosenbocus, S. & Chahal, R. Memantine: a review of possible uses in child and adolescent psychiatry. J. Can. Acad. Child Adolesc. Psychiatry J. Académie Can. Psychiatr. Enfant Adolesc. 22, 166–171 (2013).

Received November, 12, 2014; accepted December, 16, 2014. This study was supported by the National Research Foundation of Korea (to D.K., 2012-0008795; to Y.C.B., 2012-0009328) and the Institute for Basic Science (IBS-R002-D1 to E.K. and IBS-R002-G1 to M.W.J.). Address correspondence to: Dr. Eunjoon Kim, Department of Biological Sciences, KAIST, Daejeon, Korea. Email: kime@kaist.ac.kr Copyright © 2015 Nature America, Inc. All rights reserved.

154


Role of mu-opioid receptors in stress affecting vulnerability to substance abuse

Ella Lew

The mu-opioid receptor (MOR) plays a significant role in executive functioning in the orbitofrontal lobe as well as the reward system in the mesolimbic area. Stress increases production of endogenous opiates that bind to MOR implicating both regions of executive functioning and rewards. This notion was shown recently in a study on male mice where social defeat stress inhibited behavioral flexibility from a decrease in MOR binding. This review aims to evaluate the literature on MOR binding and the association with mental illness and drug addictions. This review will focus on the role of MOR, the SNP MOR variant A118G, effects of social defeat, and the implications MOR has on an individual’s vulnerability to substance abuse. This review will also look at the efficacy of treating alcoholism with the popular MOR antagonist, Naltrexone. An often overlooked area of sex differences in stress-induced MOR binding will be evaluated which calls for a paradigm shift in future research and treatment to accommodate for sex-dependent MOR binding and stress effects. Key words: drug abuse, stress, sex differences, social defeat, mu-opioid receptors (MOR), Barnes maze Background Behaviors can normally be driven autonomously but is difficult in reward-seeking addictions. The mu-opioid receptor (MOR), part of the G-protein coupled opioid receptor family, has a role in both reward (Thorsell, 2013; Wang et al., 2012) and behavioral flexibility in changing environments (Legardo et al., 2015). MOR is expressed widely in the brain from the locus coeruleus, orbitofrontal cortex, hippocampus, and VTA making it a challenge to completely elucidate MOR’s role. MOR bind to endogenous ß-endorphins and act on neurons through G-proteins to open presynaptic inward rectifying K+ channels and inhibit pre-synaptic Ca2+ channels reducing membrane potential and neurotransmitter release (Thorsell, 2013). In GABAergic neurons, reduced GABA transmission resulting in disinhibition and increased dopamine release in the ventral striatum (Thorsell, 2013). MOR is also the binding site for common opiates in drug abuse such as morphine and heroin (Bond et al., 1998; Thorsell, 2013). This makes MOR a probable mediator in opiate addictions and alcoholism with research showing MOR inactivation can help to ameliorate reward reinforcements from drugs and alcohol (Bond et al., 1998; Johnston, Herschel, Lasek, Hammer, & Nikulina, 2015; Komatsu et al., 2011; Wand et al., 2002). Many groups have looked at possible MOR-antagonists and knock-downs to elucidate the stress and addictions pathway and help explain the variability in treatment efficacy among people. Normally, stress is a signal for aversive events and it is adaptive to remember for future encounters. However, MOR binding and learning is implicated by stress, in particular social defeat stress. Studies evaluating MOR knockout mice under chronic defeat stress find male mice have decreased BDNF levels in the hippocampus and are unable to learn to avoid aversive situations (Komatsu et al., 2011; Wang et al., 2012). Interestingly, while distressed male mice exhibited decreased MOR binding and were unable to adapt to a reversal phase of the Barnes Maze, this impairment was not seen in females (Legardo et al., 2015). The inability to properly adapt in MOR modulated stress mirrors the struggle of drug addictions. MOR SNPs have been identified in humans and 155

animals which prompted investigation in the functional differences among the MOR SNPs (Xu et al., 2014). Most extensively studied is the A118G SNP in the first exon of the OPRM1 MOR gene where Asn from A118 is replaced by Asp in the G118 allele affecting the N-glycosylation site (Bond et al., 1998; Thorsell, 2013). While the types of ligand bound to the receptor were unaffected, some studies find that G118 increases binding affinity to ß-endorphin and potency on G-protein signaling by 3 times (Bond et al., 1998; Komatsu et al., 2011). Difference in opioid sensitivity may explain the variation in stress response and severity of substance abuse among individuals. This is supported by substance dependent individuals with the 118G allele being more responsive to MOR-antagonist treatments, is more prevalent in normal no-drug abuse populations, and has greater HPA axis suppression than individuals with the A118 allele (Wand et al., 2002). However, Befort et al. (2001), Beyer et al. (2004), Ramchandani et al. (2011) were unable to replicate findings of increased binding affinities from the A118G SNP (as reviewed in Thorsell, 2013). This suggests that the G allele itself may not be enough to cause functional change but that there are other variables to consider for future research such as stressor type, other opioid receptors, serotonin levels to consider in stress and addiction management. Research Overview

Results & Discussion

MOR on GABAergic neurons regulates dopamine release and is important in reinforcing behaviors through the mesocorticolimbic reward pathway. When MOR activation is limited, there is less positive reinforcement and dopamine release. Tanda and Di Chiara found that inactivating MOR with a MORantagonist, naloxonazine injections in the VTA, can reduce and abolish the rewarding dopamine release from morphine and nicotine in the NAcc of male rats (1998). MOR’s role in the reward system is also seen in mice models with alcohol dependence


where lacking MOR prevents experiencing the positive effects of alcohol seen in wild-type mice and the KO mice discontinue self-administered alcohol (Ghozland, Chu, Kieffer, & Roberts, 2005). Furthermore, through chronic morphine treatment, a MOR agonist, an enhanced basal MOR signaling was developed that may lead to forming an addiction (Wang et al., 2004). These findings suggest that MOR is involved in positive reinforcements for substances in the reward pathway where drug addictions can develop. MOR’s involvement in the reward system strongly supports the MOR-antagonist therapeutic drugs to interfere with the reward system that has shown to have powerful effects in reducing drug/alcohol-seeking behavior. Naltrexone is an opioid receptor antagonist drug approved by the US FDA since 1994 that has effectively reduced chances of alcohol relapse (O’Malley, Jaffe, & Chang, 1992), alcohol craving, the number of heavy drinking days, and pleasure from alcohol in dependent animal models (Swift, Whelihan, & Kuznetsov, 1994). Dopamine released from alcohol consumption was suppressed in a dose-dependent manner by naltrexone (Thorsell, 2013). However, naltrexone is not a perfect drug with unwanted symptoms and low compliance (Thorsell, 2013). Differences in drug efficacy are likely due to the variation in MOR SNPs. MOR SNPs were first investigated by Bond et al. in 1998 by DNA sequencing 113 former heroin addicts and 39 controls with no prior drug abuse. The MOR A118G SNP was the most prevalent in the total study population. The same group reported that the G118 variant did not change the type of ligands the receptor can bound to but had a 3 times higher affinity and potency in G-protein signaling to B-endorphins. Notably, the G allele was found significantly higher in the control group than the heroin group. The authors believe that through increased B-endorphin affinity the G allele confers a form of protection from addiction. Some other groups after have been unable to replicate these findings and suggest that the G-allele alone may not be definitive in whether an addiction will or will not be established. However, the G-allele has shown to have functional differences in stress and addiction. Wand et al. investigated the difference in individuals with A versus G allele with a MOR-antagonist Naloxone (2002). In the absence of MOR activity, G118 individuals had an increase in cortisol response compared to A118. This indicates that G118 acts as a greater HPA axis inhibitor and lowers stress response. This study was conducted without a stressor and measured basal levels however, it would be significant to perform the same study with different forms of stressors and evaluate the impact stress has on the G variant compared to A. This study was only conducted on male mice. However, females are known to have different hormone levels that influence stress, increased stress sensitivity, and cope with different stress responses, it would be worthwhile to investigate the different effects G-allele has between the sexes. Similar findings were found in rhesus monkeys with a C77G SNP in the MOR similar to the human A118G SNP exhibited increased B-endorphin affinity by 3.5 times and lowered cortisol levels (Miller, Bendor, Tiefenbacher, Yang, Novak, & Madras, 2004)/ Chronic HPA activation can lead to disease states and also heightened catecholamine effects and can make drug abuse more susceptible

(Wand et al., 2002). Furthermore, naltrexone treatment is more effective in the G allele compared to negligible effects in the A allele. This explains the drug’s report in low compliance since the G-allele is less frequent in the addict populations and only the few who carry the G-allele will see significant treatment effects. In a meta-analysis, individuals with the 118G variant reported less relapse in heavy drinking (Chamorro, Marcos, & Miron-Canelo, 2012). These findings support Bond et al.’s proposal that the G variant can better protect from drug addictions than the A variant. Studies have shown that stress can negatively impact learning leading to maintenance of a drug addiction. Komatsu et al. investigated male C57BL/6J control mice and MOR knock-outs (KO) under social defeat stress (2011). After defeat stress control mice exhibited social aversion and spent less time in the social interaction zone with an unfamiliar peer in the open field test. This may also explain the hesitancy for depressed or stressed individuals seeking help from a therapist in times of stress. In the MOR KO, mice showed reduced social aversion and also a reduction in BDNF mRNA in the hippocampi compared to controls. It can be speculated that MOR KO mice were unable to accommodate learning from the initial social defeat condition. This supports the finding that MOR agonists in VTA increase Fos expression in dopaminergic projections necessary for learning (Nikulina et al., 2008). Likewise, socially defeated male mice showed decreased MOR binding in an autoradiography and impaired behavioral flexibility in a reversed Barnes Maze trial (Legardo et al., 2015). These findings suggest that MOR activation is necessary to facilitate learning from stressful events. These findings are highly relevant in stress-induced mental illnesses like PTSD, GAD, and depression where MOR binding is reduced from chronic stress and learning and seeking help from others can be challenged in these conditions. These findings suggest that the popular cognitive-behavior therapy that utilizes behavioral changes may be less effective in socially defeated individuals with downregulated MOR binding.

Conclusions

Understanding the role MOR plays in addictions and stress can reduce vulnerability in developing drug addictions and mental illness as well as creating more targeted and efficacious therapeutics. Research in MOR has been very progressive in understanding its function, the A118G SNP, and translating findings into efficacious treatments. MOR influences the reward system and dopamine release relevant in drug addictions. MOR activation also has a role in learning by increased Fos expression in dopaminergic projections and BDNF mRNA in the hippocampi. Thus, abnormal MOR functioning can decrease the ability to learn and can make one more susceptible to drug addictions. Social defeat stress that reduces MOR binding and its downstream effects exhibits decreased learning and behavioral flexibility. MOR proves to be responsive to pharmacological agents and this understanding is significant in finding therapeutic treatments for drug addiction and mental illness. Research in MOR-antagonists has proven to be powerful treatments but is limited to select G118 individuals. However, further investigations of the differ156


ences between the A and G118 SNP can help devise more targeted treatments between the phenotypes. Criticisms and Future Directions There is a large paucity in the sex differences that exist in MOR modulated stress and drug addiction research. The majority of studies are done on male mice subjects and individuals and thus the results cannot be confidently translated to female subjects. Especially, with the general understanding that women respond to stress differently from men and that levels of estrogen hormones can influence stress. Milner et al. performed a labelled immunoelectron microscopy with silver-intensified gold particles to evaluate the MOR density and trafficking in the hippocampus of male and female rats (2013). They found that the sexes responded differently in both acute and chronic stress. While females showed increased density and trafficking of MOR in PARV-labeled dendrites after chronic stress, males saw no change in MOR density. This implicates that learning occurs in females but not males under chronic stress. In another study, MOR binding was downregulated and behavioral flexibility was impaired in socially defeated male mice but not female mice (Legardo et al., 2015). Future research should look at how stress and MOR binding affects the sexes differently and devise more appropriately sex-targeted treatments to accommodate for the different stress mechanisms. While many studies employ different stress conditions, future studies should clearly identify the types of stressors (social, physical, emotional) to determine whether different stressor types have a significant impact on MOR binding and learning. Additionally, while the MOR-antagonist Naltrexone has limited responses to the extracellular modification in A118G SNPs, future therapeutics can look at terminating receptor signaling intracellularly through phosphorylation by a cytoplasmic kinase or through endocytosis or desensitization of MOR. Furthermore, knowing that the G allele is suggested to confer protective properties against addiction, CRISPR can be utilized to modify the 118 SNP in individuals with the A allele to express the G allele. Individuals with the G variant are more responsive to treatment and fare better at stress management. Other variables that would influence reward systems or interact with MOR binding should also be studied such as serotonin receptors and other types of opioid receptors. References 1. Bond, C., LaForge, K.S., Tian, M., Melia, D., Zhang, S., Borg, L., … Yu, L. (1998). Single-nucleotide polymorphism in the human mu opioid receptor gene alters B-endorphin binding and activity: Possible implications for opiate addiction. Proc Natl Acad Sci USA, 95, 9608-9613. 2. Chamorro, A.J., Marcos, M., & Miron-Canelo, J.A. (2012). Association of micro-opioid receptor (OPRM1) gene polymorphism with response to naltrexone in alcohol dependence: a systematic review and meta-analysis. Addict Biol, 17, 505-512. 3. Ghozland, S., Chu, K., Kieffer, B.L., & Roberts, A.J. (2005). Lack of stimulant and anxiolytic-life effects of ethanol and accelerated development of ethanol dependence in mu-opioid receptor knockout mice. Neuropharmacology, 49(4), 493-501. 157

4. Greenfield, S.F., Pettinati, H.M., O’Malley, S., Randall P.K., & Randall, C.L. (2010). Gender differences in alcohol treatment: an analysis of outcome from the COMBINE study. Alcohol Clin Exp Res, 34(10), 1803-12. 5. Iniquez, S.D., Riggs, L.M., Nieto S.J., Dayrit, G., Zamora, N.N., Shawhan, K.L., Cruz, B., & Warren, B.L. (2014). Social defeat stress induces a depressionlike phenotype in adolescent male c57BL/6 mice. Stress, 17(3), 247-55. 6. Johnston, C.E., Herschel, D.J., Lasek, A.W., Hammer, R.P., & Nikulina, E.M. (2015). Knockdown of ventral tegmental area mu-opioid receptors in rats prevents effects of social defeat stress: implications for amphetamine cross-sensitization, social avoidance, weight regulation and expression of brain-derived neurotrophic factor. Neuropharmacology, 89, 325-34. 7. Komatsu, H., Ohara, A., Sasaki, K., Abe, H., Hattori, H., Hall, F.S., Uhl, G.R., & Sora, I. (2011). Decreased response to social defeat stress in µ-opioid-receptor knockout mice. Pharmacol Biochem Behav, 99(4), 676-82. 8. Laredo, S.A., Steinman, M.Q., Robles, C.F., Ferrer, E., Ragen, B.J., & Trainor, B.C. (2015). Effects of defeat stress on behavioural flexibility in males and females: modulation by the mu-opioid receptor. European Journal of Neuroscience, 1-8. 9. Miller, G.M., Bendor, J., Tiefenbacher, S., Yang, H., Novak, M.A., & Madras, B.K. (2004). A mu-opioid receptor single nucleotide polymorphism in rhesus monkey: association with stress response and aggression. Molecular Psychiatry, 9, 99-108. 10. Milner, T.A., Burstein, S.R., Marrone, G.F., Khalid, S., Gonzalez, A.D., Williams, T.J., … Waters, E.M. (2013). Stress Differentially Alter Mu Opioid Receptor Density and Trafficking in Paravalbumin-Containing Interneurons in the Female and Male Rat Hippocampus. Synapse, 67, 757-772. 11. Nikulina, E.M., Arrillaga-Romany, I., Miczek, K.A., & Hammer R.P. (2008). Long-lasting alteration in mesocorticolimbic structures after repeated social defeat stress in rats: time course of mu-opioid receptor mRNA and FosB/DeltaFosB immunoreactivity. Eur J Neurosci, 27(9), 2272-84. 12. Nikulina, E.M., Hammer, R.P., Miczek, K.A., & Kream, R.M. (1999). Social defeat stress increases expression of mu-opioid receptor mRNA in rat ventral tegmental area. Neuroreport, 10(14), 3015-9. 13. O’Malley, S.S., Jaffe, A.J., & Chang, G. (1992). Naltrexone and coping skills therapy for alcohol dependence. A controlled study. Arch Gen Psychiatry, 49, 881-7. 14. Swift, R.M., Whelihan W., & Kuznetsov, O. (1994). Naltrexone-induced alterations in human ethanol intoxication. Am J Psychiatry, 151, 1463-1467. 15. Tanda, G., & Di Chiara, G. (1998). A dopamine-mu1 opioid link in the rat ventral tegmentum shared by palatable food (Fonzies) and non-psychostimulant drugs of abuse. Eur J Neurosci, 10(3), 1179-87. 16. Thorsell, A. (2013). The µ-Opioid Receptor and Treatment Response to Naltrexone. Alcohol and Alcoholism, 48(4), 402-408. 17. Verzillo, V., Madia, P.A., Liu, N.J., Chakrabarti, S., & Gintzler, A.R. (2014). Mu-opioid receptor splice variants: sex-dependent regulation by chronic morphine. J Neurochem, 130(6), 790-6. 18. Wand, G.S., McCaul, M., Yang, X., Reynolds, J., Gotjen, D., Lee, S., & Ali, A. (2002). The Mu-Opioid Receptor Gene Polymorphism (A118G) Alters HPA Axis Activation Induced by Opioid Receptor Blockade. Neuropsychopharmacology, 26, 106-114. 19. Wang, D., Raehal, K.M., Lin, E.T., Lowery, J.J., Kieffer, B.L., Bilsky, E.J., & Sadee, W. (2004). Basal signaling activity of mu opioid receptor in mouse brain: role in narcotic dependence. J Pharmacol Exp Ther, 305, 512-520. 20. Xu, J., Lu, Z., Xu, M., Pan, L., Deng, Y., Xie, X., … Pan, Y.X. (2014). A heroin addiction severity-associated intronic single nucleotide polymorphism modulates alternative pre-mRNA splicing of the µ opioid receptor gene OPRM1 via hnRNPH interactions. J Neurosci, 34(33), 11048-66. Received April 2015. Address correspondence to: Ella Lew, Human Biology Department, 30 Wilcox Street, University of Toronto, ON, Canada Email: ella.lew@mail.utoronto.ca Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program


Seeking Autism-Linked Performance Within the Synaptic World: Effect of Neurexins and Related Proteins

Vivian Liu

Autism spectrum disorder (ASD), a neurodevelopmental disorder tagged with high genetic concordance, is a concern among many parents. Given the genetic correspondence, researchers have been exploring many candidate genes and testing for behavioral changes upon mutations. That being said, autism has a wide range of disorders which vary form patient to patient, and is most likely the result of a multifactorial cause. It is important to note that many co-occuring conditions are also associated with autism. Therefore, there is currently no â&#x20AC;&#x153;trueâ&#x20AC;? animal model of autism, but rather multiple mouse models of autism. Previous studies have implicated autism as a result of synaptic transmission defects, especially mutations (in most cases, knockouts) involving synaptic proteins. Many mouse models involving the knockout of certain synaptic proteins serve to recapitulate some, but not all of the autistic-associated phenotypes. These potential synaptic proteins at hand include as neuroligins, synapsins, SHANK and neurexins, all which contribute to proper facilitation and organization of neuronal synapses. Behavioral measurements such as the open field test, novel object recognition task, ultrasonic vocalizations and three-The discovery of causal genes can then allow researchers and clinicians to apply the innovative diagnostic methods to young patients or pregnant women, encouraging early detection and therapeutic approaches. The focus of the present literature review aims to analyze past research on synapticrelated proteins and their relations to autism, with a strong emphasis on neurexins, a recently explored gene. This review will also suggest next steps to enhance the current knowledge of autism, and the issues at hand with gene elucidation using mouse models. Key words: autism; neuroligins; synapsins, SHANK; neurexins; ultrasonic vocalizations; synaptic; multifactorial Background The Autism Spectrum Disorder (ASD) has one of the highest genetic rates within neurodevelopmental disorders, constituting about 0.85-0.92 concordance among monozygotic twins1. ASD is well established prior to when the child turns three years of age, producing an early onset of core symptoms. The crucial three symptoms include insufficiency in social interactions including gestures and communication, repetitive actions or behaviors and limited or self-deprivation of interests. Comorbid conditions that are seen occurring with autism, but are not the main diagnostic markers include anxiety disorders, depression and fragile X syndrome. Recent genomic analysis have narrowed down hundreds of genetic variants, some common and some rare, which are all to some extent, associated with ASD. That being said, previous research has explored a variety of candidate genes related to synaptic functioning that may be in association with autism. Four of the major ones include: Neuroligins, synapsins, SHANK3 and neurexins. Each of these proteins have demonstrated relevance to autistic behavior in one aspect or another. To begin, neuroligins function as cell-attachment proteins that reside on the post-synaptic membrane, interacting with their pre-synaptic partner, the neurexins. Prior research done on neuroligin-3 (NL3) mutations within mice displayed an increase in repeated motor actions of adult mice, a prominent autistic-like behavioural phenotype2. It was depicted that elimination of NL3 in the dorsal stratium has little effect on rotarod execution, but the same deletion in the NAc resulted in increased performance on the rotarod, suggesting that the NAc-NL3 interactions could facilitate repetitive behaviors2.

In addition, mutated synapsins also serve to cause autistic-like phenotypes in mice with the co-presence of epilepsy, which has a quarter chance of occurring. Synapsins are neuronal phosphoproteins, which contact lipid counterparts of presynaptic vesicles and actin3. Researchers compared Syn1 and Syn3 KO mice prior and subsequently to epilepsy occurrence, and concluded that the deficits in social preferences and temporary social recognition existed independent of epilepsy4. Excessive self-grooming activity and repetitive locomotion behaviours were also apparent in Syn2 KO mice4. Earlier research claimed synpasins to be one of the synaptic proteins enhanced by neurexins3. To extend, prior research have also investigated the Shank proteins (1-3), a group of scaffold that consist of sites for protein-protein contact, especially membrane proteins. These Shank proteins reside on the postsynaptic area of excitatory synapses and is said to be involved in transduction processes, especially in metabotropic contexts5. Anxiety characteristics and exploratory activity were noted in Shank1 KO mice in comparison to Shank 1 heterozygote and Shank 1 WT mice6. This synaptic dysfunction resulted in the absence of social affiliation and repetition in peeking behavior7. It was also previously found that ProSAP2/ Shank 3 could affect synaptic proteins through neurexinneurolgin co-operation. Given that neurexins seem to have a connection with many other synaptic proteins such as the three aforementioned, it was thought to have a crucial role in contributing to autistic behaviours. It is well known that neurexins are a category of synaptic linkage proteins that reside at the pre-synaptic terminal. The family of neurexins consist of NRXN1-3 genes, yielding ether promoters a or b. Graytonâ&#x20AC;&#x2122;s team 158


focused their research with the knockout of Nrxn1a in mice, depicting that male Nrxn1a KO mice present a more violent phenotype towards other rodents, female Nrxn1a KO mice partake in reduced social care (nest-building) and both genders had decrease in locomotion8. Measurement tests included openfield test, elevated plus maze, three-chamber social approach task and the social investigation task. Further research in regards to neurexins were then pursued, one of them being a major article reviewed here. In the primary article of interest, researcher J Dachtler and his team tested eight weeks old Nrxn 2a KO mice for autistic performance. The assumed hypothesis was that elimination of the fist exon of the Nrxn2 gene would display some autistic consistent behavior. It is important to explore not only one specific gene of the Nrxn family of proteins, but the other available genes as well. Nrxn1a KO may provide some of the spectrum of autistic-like traits, while Nrxn2a KO may provide the other missing characteristics that were not observed. Assaying as much candidate genes as possible allows scientists to have a scale of the most dangerous mutations to the least, some causing more severe symptoms than others. Research Overview

Summary of Major Results

Limited Social Interests The current study being reviewed had a dual approach in confirming their hypothesis: Behavioural measurements and quantification assays. The experimental mice at hand all exceeded eight weeks of age. To begin, the common three-chambered assay test was employed to measure the range of social interactions among mice. The target mice were placed in the middle sector, where the chambers to the side contained a novel conspecific and a vacant wire cage. Openings in between the chambers allow for social exploration, but results evidently displayed that Nxn2a KO mice failed to show interest in their new neighbor9. Moreover Nrxn2a KO mice were depleted in terms of curiosity for novel object awareness in comparison to WT mice9. Past studies of Syn1 KO mice showed that they roamed less in novel bedding and covered buried lower numbers of marbles4. Both studies seem to converge on one point: Synaptic defects seem to contribute to environmental ignorance of mutated mice, which essentially can include social contexts, in which contact and interests are limited. Elevated Anxiety Levels To extend, researchers also tested for state anxiety levels. State anxiety is a temporary response to a danger stimulus or fear. The open-field and EPM test were employed to measure state anxiety levels. The open field test depicted thatNrxn2a KO mice would much rather commit to thigmotaxis (wall-hugging tendency) than enter the centre zone, where it is both exposed and bright9. The same results were recapitulated in NL2 KO mice, where they approached the centre zone much less than the WT mice even 159

Figure 1.Nrxn2aKO and WT mice behaviour during the ThreeChambered Assay. Nrxn2a KO mice showed a lack of interest for the stranger conspecific, in comparison to the WT mice. For the vacant cage, both types of mice had insignificant differences in exploration time, suggesting the Nrxn2a KO most likely stayed put in their initial cage for the rest of the elapsed time.

though the distance roamed were almost equivalent10. The Nrxn2a seems to be more bothered presence of a stressful stimulus, making them more vulnerable to rises in anxiety levels.

Figure 2. Nrxn2a KO spent drastically less time in the centre zone, where they are exposed to unrestricted, luminous space

In terms of the Elevated Plus Maze (EPM), this task consisted of enclosures and open arms, allowing mice to peek and explore the area above them (open, luminous space). As predicted, Nrxn2a KO mice preferably spent a large amount of time within enclosed arms, whereas WT mice showed much more exploration towards the novel area9. The latency to emerge to a new surrounding was undoubtedly much longer in Nrxn2a KO mice than in WT mice. Hippocampal Protein Munc18-1 Loss Real-time PCR was used to assay the mRNA levels of various synaptic genes that either interact with


Figure 3. NL2KO mice clearly display elevated latency times to cross in the centre zone in comparison to WT littermates. The NL2KO mice also lingered longer in the dark zones of the open field test

neurexins at the presynaptic terminal or neuroligins at the postsynaptic level. An evident decrease was seen with the Stxbp1 gene within the hippocampus9. Western blotting was then applied to quanitify the Munc18-1 protein presence, which is encoded by the Stxbp1 gene, and low levels were found9. However, special deficits were not discovered when the fearmotivated task was applied. Both Nrxn2a KO and WT mice could still subsequently recall that the dark chamber was associated with a shock one day later9. This was an alarming result, as this major loss of Munc18-1 in the hippocampus did not seem to affect hippocampal-dependent activities.

Figure 4. Homogenates of the frontal cortex and the hippocampus were isolated and compared against for Munc18-1 levels. Western blotting was used for quantification. Blotting showed that the difference in Munc18-1 proteins had almost undetectable changes in the frontal cortex, but apparent changes in the hippocampus.

Discussions and Conclusions To this day, the etiological means of autism are still not transparent. However accumulation of research results have shed some insight on aligning and contradictory results. One major finding that Dachtler and his team seem to duplicate in their Nrxn2a KO research is the lack of

social interaction and contact. NL2 KO mice2, Syn1 KO mice3 and Shank3B7 KO mice were all shown to pay less attention towards social novelty than their WT littermates. Nrxn2a KO mice did not offer curiosity towards their fellow conspecific either, emphasizing the alignment of results9. In the case that the Nrxn2a KO mice may have had olfactory deficits, the researchers employed the food burial task. Both groups of mice had the ability to search out the food in a reasonable amount of time, proving that an inability to sense social odors did not contribute to the Nrxn2a KO miceâ&#x20AC;&#x2122;s reluctance to interact with a novel conspecific9. For future references, it is likely that the causal gene(s) of autism would have to accomplish deficits in social behavior and engagement in order to be of significance. Anxiety-associated phenotypes were observed in the open field test and elevated plus maze. Within the open field test, Nrxn2a KO showed increased thigmotaxis to the periphery of the arena in comparison to WT mice9. On the contrary, WT mice wandered into the centre zone much more frequently. In other words, Nrxn2a KO mice elicited more anxiety in response to uncomfortable situations. ASD can be characterized by sensitivity to selective contexts, which in return produce rising anxiety levels. Similar results were observed in the elevated plus maze, where the Nrxn2a KO mice took substantially longer to emerge out of the closed arms than the WT mice9. This suggests that Nrxn2a may have more fear to new contexts, therefore having higher state anxiety levels, resulting in a delay in emergence. One way of interpreting this may be that WT are less prone stir up anxiety due to changes in surroundings, and are more adaptive than Nrxn2a KO mice. These results are in alliance with Shank1-/- mice6 and Syn2 -/mice3, where exploratory activity was reduced in open field testing, proposing that the measure of anxiety could be a reliable indicator of autism if more mouse models continue to show this trend. Although Western Blot revealed that Munc18-1 had a dramatic decrease in the hippocampus, researchers found no interference with spatial recall a day after training for passive evasion9. On the contrary, previous research has shown that NL1 KO mice resulted in an 160


approximate 20% decrease in Munc18-1 protein within the hippocampus, and presented special deficits in the Morris Water Maze10. A day after training, WT mice spent elongated periods in the target area while Nlgn1 KO mice did not, showing reduced spatial memory. So far, the knowledge about Munc18-1 is limited- it guides and solidifies SNARE complex fusion, meaning that is an important protein for both presynaptic and postsynaptic processes. This suggests that possibility that Munc18-1’s effects could be context-dependent, and that its’ synaptic role differs when interacting with ether neuroligins or neurexins. Consequently, this could inconclusively explain why special processing interference was seen in one study but not the other, but further research is this area would be necessary. Aforementioned in the introduction, three of the four candidate genes of autism had consistent self-grooming actions upon targeted mutations. Ironically, the Nrxn2a KO study did not reproduce such results; both types of mice were indifferent in terms of the amount of self-grooming performed. Prior research has strong linkage to genetic defects and repetition: NL3-KO and NLR451R1C mutant mice achieved higher performance on the rotarod, a repetitive task of staying on a spinning rod, than WT companions2. Syn2 KO mice self-combed much more than WT mice when left in a cage and Shank3 KO mice engaged in more head pokes to exposed space. The light-dark emergence and zero-maze testing also showed greater number of head peeks for Shank3 KO mice7. It is important to note that the mice did not actually enter the “light” or “exposed” zones, suggesting that they were NOT drawn to novelty but rather performing habitual movements. If the Shank3 KO were truly curious about their surroundings, a high number of entries into the light zones or open arms would have occurred. The discussion of why the Nrxn2a got the null result for self-grooming will be discussed in the critical analysis section. Although no clear establishment exists, the Nrxn2a KO study has succeeded in showing that neurexin dysfunction does serve some relevance to recapitulate anxiety-like behaviors, such as interference with social interactions and prominent anxiety levels. Just like all the other previous studies, however, the correspondence is still premature and requires much more credible evidence to build upon these surface level findings. It would make sense to extend the research to Nrxn3 and its relevance to autism, because only then can scientists classify which autistic-like traits are shared within defects of the neurexin family and which are not.

Critical Analysis

Like all scientific studies, there are notable aspects, as well as room for improvement. To begin, Dachtler and his team did a thorough job in testing and analyzing autistic-associated factors and symptoms for Nrxn2a KO mice. Similar to many other behavioral studies, a variety of tests were utilized to test the different aspects of autism. This included the major behavioral measures such as the open field test and elevated plus maze to analyze state anxiety, the novel object recognition task for trait anxiety, the three –chambered assay to rate social interactions, and even the quantification of 161

Munc18-1 levels in the hippocampus. That being said, it seemed as if the experiment had concentrated more on the comorbid associations rather than the fundamental symptoms of autism. These disorders may be present along with autism, but are not early determinants of autism itself. The hallmark characteristics of autism such as repetition (in this grooming) failed to be measured properly and social callings (communication deficits) were not considered. Within this study, selfgrooming was measured alongside with the open field test when the mice were allowed to roam. However, it is logical that self-grooming usually occurs under optimal conditions when the mice feels comfortable with the surrounding. Measuring self-grooming during the open field test makes the data flawed because external factors are being introduced, such as the lighting being adjusted to a high level 200 lux and the mice being exposed to an open area. Hence, there may be a possibility that the mice is much more concentrated with natural avoidance rather than performing self-grooming. A preceding Nrxn1a removal study showed that under optimal conditions, twice the grooming can be observed in comparison to control mice – in that case, it was red light set at 40 lux in a vacant cage with clean bedding11. In addition, a direct testing on mice social callings would have given researchers some insight into genetics mutations that can cause verbal deficits in humans, a hallmark for autism. In prior research done with SHANK -/- isolated mice pups, the amount of “calling” for the mother was certainly less in comparison to the WT conspecifics. For future experiments, if the Nrxn3 gene were to be explored, ultrasound vocalizations should be recorded and examined. What was also unclear within this experiment was what kind of role did Munc 18-1 play in contributing to the autism-like happenings, if any. Deletion of Nrxn2a KO mice did manifest into autistic-like performance, but it is uncertain whether this effect is direct or indirect. Such abnormal behaviors could have risen from the depletion of the Nrxn2 gene itself, or from the indirect reduction of Munc18-1.

Future Directions

To properly measure repetition in behavior, any sort of separate testing will be fine, as long as it is not combined with another behavioral measure. An example would be placing mice would in a vacant cage with clean bedding and soft lighting for half an hour. Inside the cage will be a large cotton fibre ball. The amount of cotton remaining intact depicts the level of repetitive, compulsive behavior in the mice. For future experiments, if the Nrxn3 gene were to be explored, ultrasound vocalizations should be recorded and examined. A proposed approach would be to remove target mice from mother at day eight, as researchers should aim to recapitulate the early onset of social impairments seen with toddlers or young children. Detached young mice will be placed in a vacant cage with clean bedding for about a half hour, with a recording microphone placed above the cage to track noises made. It is expected that the mutated mice will have reduced calling due to insensitivity of social expression.


To solve this hippocampal Munc18-1 dilemma, researchers can do a similar study as Dachtler and his team, but instead truncate the Stbxp1 gene without deleting the Nrxn2a gene. Deletion of the Stbxp1 gene should not occur because that will result in a “silent” mouse with zero neurotransmitter release and termination to exocytosis14. If the same autisticassociated behaviors can be observed, then that signifies that Munc18-1 is the crucial protein at hand and not Nrxn2a. Nrxn2a would just then serve as one of the ways to affect Munc18-1 levels, but it is really Munc18-1 that encourages the abnormal behavior. One recent review discussed the efficacy for mice models to improve autism research. 90 million years have passed since rodents and humans have had a mutual ancestor, and so the idea that of having a true mouse model of autism seems impossible15. Steven Hyman, the author, brought two key issues to light. The translation from genotypes to phenotypes due to crucial mutations may not be accurate using mouse lines because behavioral testing between the animal and humans differ greatly15. This raises the second concern: How do researchers know for a fact that the mouse molecular targets serve the same purposes as they do in humans; are there cases of evolutionary maintenance? It is important to consider the relevancy, because drugs that target molecular pathways of the mice may not be as effective in humans due to evolutionary changes. Ongoing research on autism have proposed many possible genes related to autism and with the new technical advancements, our future does look promising as long as every step is a careful and evaluative one.

9. Dachtler J, Glasper J, Cohen RN, Iovrra J L, Swiffen D J, Jackson A J et al. Deletion of a-neurexin 2 results in autism-related behaviours in mice. Translational Psychiatry. 2014; 4: 484; doi:10.1038/tp.2014.123 10. Blundell, J., Tabuchi, K., Bollinger, M., Brose, N., Liu, X., Sudhof C. and Powell C. Increased Anxiety-like Behaviour in Mice Lacking the Inhibitory Synapse Cell Adhesion Molcule Neuroligin 2. Genes Brains Behaviour. 2009; 8(1): 114-126; doi: 10.1111/j.1601183X.2008.00455.x 11. Etherton, M., Blaiss, C., Powell, C. and Sudof, T. Mouse Neurexin1a Deletion Causes Correlated Electrophsyiological and Behavioural Changes Consisten with Cognitive Impairment. 2009 Proc. Natl. Acad. Sci. USA 106, 17998–18003; doi: 10.1073/pnas .0910297106. 12. Wohr M, Roullet F, Hung A, Sheng M and Crawley J. Communication Impairments in Mice Lacking Shank1: Reduced Levels of Ultrasonic Vocalizations and Scent Marking Behaviour. PLoS One. 2011;6(6): doi: 10.1371/journal.pone.0020631 13. Hamdan F, Gautheir J, Dobrzeniecka S, Lortie A, Mottron L, Vanasse M et al. Intellectual disability without epilepsy associated with STXBP1 disruption. European Journal of Human Genetics. 2011; 19: 607-609: doi:10.1038/ejhg.2010.183; 14. Toonen, R. Role of Munc18-1 in Synaptic Vesicle and Large DenseCore Vesicle Secretion. Biochem. Soc. Trans. 2003; 31: 848-850 15. Hyman, S. How Far Can Mice Carry Autism Research? Journal Cell Science. 2014; 158: 13-14 doi:10.1016/j.cell.2014.06.032

References 1. Miles, J.H. Autism spectrum disorder-A genetics review. Genetics in Medicine. 2011; 13: 278-294 2. Rothwell, P., Fuccillo, M., Mexeiner, S., Hayton, S., Gockce, O., Lim, B.K., Fowler, S., Malenka, R. and Sudhof, T. Autism-Associated Neuroligin 3 Mutations Commonly Impair Striatal Circuits to Boost Repetitive Behaviours. Journal of Cell Science. 2014; 158: 198-212; doi:10.1016/j.cell.2014.04.045 3. Chen, J., Yu, S. Fu, Y., and Li X. Synaptic Proteins and Receptor Defects in Autism Spectrum Disorders. Front Cell Neurosci. 2014; 8:276; doi: 10.3389/fncel.2014.00276 4. Greco B., Manago, F., Tucci, V., Kao, H.T., Valtorta, F. and Benfenati. Behaviour Brain Resources. Autism Related Behaviour Abnormalities in Synapsin Knockout Mice. 2013; 251(100): 65-74; doi: 10.1016/j. bbr.2012.12.015 5. Sheng, M. and Kim, E. The Shank Family of Scaffold Proteins. Journal of Cell Science. 2000; 113: 1851-1856 6. Silverman, J., Turner, S.M., Barkan, C.L., Tolu, S.S., Saxena, R., Hung, A., Sheng, M. and Crawley, J. Sociability and Motor Functions in Shank1 Mutant Mice. Behaviour Brain Resources. 2011. 1380; 120-137. doi: 10.1016/j.brainres.2010.09.026 7. Wang, X., McCoy, P., Rodriguez M., Shawn J., Roberts, A., Colvin, J., Rousquet-Moore, D., Weinberg, R., Philpot, B.D., Beaudet, A.L. Wetsel, W.C. and Jiang, Y.H. Synaptic Dysfunction and Abnormal Behaviours in Mice Lacking Major Isoforms of Shank 3. Human Molecular Genetics. 2011; 20(15): 3093-3108; doi: 10.1093/hmg/ddr212 8. Grayton, H.M., Missler, M., Collier, D.A. and Fernandes, C. Altered Social Behaviours in Neurexin1a Knockout Mice Resemble core Symptoms in Neurodevelopmental Disorders. PloSOne. 2013; 28(8): 86-92; doi: 10.1371/journal.pone.0067114. 162


Effects of systems consolidation, optogenetic inhibition, and adult neurogenesis in hippocampal memory traces

Yi Xuan Li

Distinct memories are thought to be encoded in sparse neural networks called memory traces. A transgenic mouse line is created to distinctively label neural activity during encoding and retrieval of contextual fear conditioning (CFC) memories in the dentate gyrus (DG) and CA3. Greater freezing and signal overlap was observed in mice re-exposed to the fear inducing context as opposed to a novel context. Signal overlap decreased over time while extent of freezing remained the same in re-exposure mice. This provided physical evidence for systems consolidation. Optogenetic inhibition of neurons recruited during CFC reduced extent of freezing during re-exposure. Based on this result the authors believe these neurons form the memory trace of the fear memory. An unaddressed alternative explanation is that the neurons do not encode the memory, but merely serve as a pointer to the true memory trace downstream. Optogenetic activation of downstream neocortical neurons in an unrelated context is recommended for future experiments. Ablation of adult neurogenesis in DG reduced extent of freezing and signal overlap in CA3 but surprisingly not DG. The result may relate to the hypothesis that adult born neurons (ABN) are modulators of CA3 activity. The role of ABN in CFC is still poorly understood and a gain of function test on neurogenesis is recommended for future studies. Key words: memory trace; dentate gyrus; transgenic mice; CA3; contextual fear conditioning; optogenetic inhibition; adult neurogenesis; social defeat; neuroscience Background Memories are believed to be physically stored in defined, sparse networks of brain neurons called memory traces(1). Due to the sparse distribution these neurons have been difficult to locate and study(2). Recently studies on lateral amygdala (LA) neurons have observed defined neuron ensembles that activate during both encoding and retrieval of distinct fear conditioning memories(3). Furthermore, memory expression is eliminated when the neurons are selectively ablated or inhibited, suggesting that these neurons form an essential part of the memory trace. The hippocampus (HPC) has since been identified as another structure ideal for identifying and studying memory traces(4). HPC is crucially involved in the formation and consolidation of declarative memories(5). Aside from LA, HPC also plays a critical role in fear conditioning by facilitating the association of the fear to the related context(6). The two HPC subfields analyzed for this study, DG and CA3, are involved in pattern separation, which is the disambiguation of sensory inputs about similar contexts into different representations downstream(7)(8). Immediate early genes (IEG) Arc and c-fos were used as markers for neuron activation due to their rapid and transient expression following input-specific activation(9). A transgenic mouse line was designed to induce a permanent labeling with enhanced yellow fluorescent protein (EYFP) in neurons that expressed IEG in the presence of tamoxifen (TAM). Mice were subjected to CFC training shortly after TAM injection to tag neurons activated during encoding with EYFP. This allows the encoding signal to be distinguished from and merged with immunohistochemical signals of Arc or c-fos that represent the retrieval signal(10). Retrieval of declarative memories gradually becomes HPC independent over time, so in order to observe changes in hippocampal memory trace over the long term, retrieval test is delayed for a subset of mice(11). To to selectively inhibit neurons activated during

163

encoding, the same transgenic model was used but the position of EYFP was replaced by the optogenetic inhibitor Archaerhodopsin-3 (Arch). This allowed convenient alternation between inhibited/uninhibited states by switching on/off a photostimulator and enabling real-time observations of changes in memory expression(10). The subgranular zone (SGZ) of DG is among the few brain regions where neurogenesis continues into adulthood. ABN are incorporated both anatomically and functionally into the the hippocampal circuit (2a). Previous studies assessing the role of ABN in CFC have demonstrated that mice with arrested adult neurogenesis have decreased response and colabeled DG signals in one-shock CFC, but not three-shock CFC(12). Although not the site of neurogenesis, signals in CA3 appear to be affected in the same way as DG(13). This study examines both DG and CA3 in the same experiment to compare the role of ABN in both regions. Research Overview

Effect of Context and Time on Activation Patterns and Memory Expression

The transgenic mouse line ArcCreERT2 x R26RSTOP-floxed-enhanced yellow fluorescent protein (EYFP) was created to enable separate signaling of activation during CFC encoding and retrieval. Arc was co-expressed with a Cre recombinase â&#x20AC;&#x201C; estrogen receptor fusion protein (Cre-ER). Upon binding to TAM, an ER agonist, Cre-ER would localize to the nucleus and interact with loxP to delete the STOP codon upstream of EYFP (Figure 1A). In CA3, c-fos was used instead of Arc as the neuron activation marker, due to Arc labeling in CA3 being mostly dendritic(10). Mice were injected with TAM and subjected to CFC in Context A 5 hours later. After 5 (recent) or 30 days (remote), mice were either re-exposed to Context A or introduced to a novel Context B. Extent of freezing was


Figure 1. (A), Schematic representation of the two transgenes. The upward kink flanked by loxP is a STOP codon. (B), Schematic view of a dorsal HPC coronal slice under a confocal microscope, showing encoding signals (EYFP+) in green, retrieval signals (Arc+/c-fos+) in red, and co-labeled signals in yellow

recorded, and coronal slices of dorsal HPC were obtained from mice shortly after and put under a confocal microscope (Figure 1B). The amount of EYFP+ and Arc+/c-fox+ signals was counted and signal overlap calculated.

Therefore, ArcCreERT2 x R26R-CAG-STOP-floxedAch-3–GFP line was created. The same transgenic system as outlined in Figure 1A was used but the position of EYFP was replaced by Arch. Mice were surgically implanted with fibre optics above either DG or CA3 at 8-12 weeks of age. Mice underwent CFC in Context A 5 hours after TAM injection to induce Arch-GFP expression in activated cells. Mice were then re-exposed to Context A two weeks later, where photostimulation at 593.5 nm was turned on for the first 3 minutes to elicit strong hyperpolarization in Arch-GFP+ neurons, and turned off during the remaining 3 minutes. Two days later mice were introduced to Context B with the same light epochs. Control mice that lacked the ArchCreER transgene underwent the same paradigm. To address the alternative explanation that inhibition of any group of neurons may disrupt function of the region as a whole and impair memory expression, the experiment was repeated on another group of mice with the exception of undergoing CFC training in a distinct Context C as opposed to Context A. In mice that underwent conditioning in Context A, optogenetic inhibition of DG and CA3 both reduced the extent of freezing as compared to control when re-exposed to context A (p = 0.02). When lights

Figure 2. Number of EYFP+ signals is shown in (C), (F), (I), (L), Arc+/c-fos+ in (D), (G), (J), (M), and signal overlap as % co-labeled neurons in (E), (H), (K), (N). White bar represents re-exposure to Context A, black represents novel Context B.

Among the recent retrieval cohort, significantly more freezing were observed in those placed in Context A (P < 0.001). In the DG and CA3, while EYFP+ and Arc+/c-fos+ signal was similar, the signal overlap was much higher in Context A (Figure 2E, H). These results demonstrated high input specificity of DG and CA3 neurons, supporting their role in pattern separation(7). In contrast to the recent cohort, similar levels of freezing and signal overlap were observed in the remote cohort (Figure 2K, N). This indicates a generalization of similar inputs over time(11). Among mice re-exposed to Context A, signal overlap was significantly lower in the remote cohort for both CA3 and DG in mice from Context A (p<1), while freezing level and by implication, memory retrieval remained strong. This provides the physical evidence for systems consolidation, the process which memories become HPC-independent and encoded in more permanent areas in the cortex(11).

Effect of Optogenetic Inhibition on Memory Expression

To truly determine if the tagged neurons are part of the memory trace, selective inhibition is needed to see if these neurons are necessary for memory retrieval.

Figure 3. Extent of freezing is shown with control mice in Context A set as 100%. Mice that underwent CFC training in Context A is shown in (F – H) and Context C in (K – N). The lighter green bar represents control mice.

were turned off at minute four, freezing immediately resumed in ArcCreER+ mice to the same level as control (Figure 3F, H). In contrast, in mice that underwent conditioning in Context C, optogenetic inhibition failed to reduce extent of freezing (Figure 3K, M). The results from Context B were not significant (10. Since memory expression remained intact when neurons recruited for unrelated memories were blocked, the alternative explanation could be rejected. Based on these results, the the authors believe these neurons form the memory trace of the fear memory(10).

Effect of Adult Neurogenesis Ablation on Activation Patterns

ArcCreERT2 x R26R-STOP-floxed-EYFP mice were irradiated with x-ray to ablate ABN six weeks prior to CFC. X-ray irradiated mice and sham mice then underwent the same CFC paradigm as the recent cohort 164


described earlier, with the exception of three shocks administered during encoding phase of 3-Shock CFC.

Figure 4. Number of EYFP+ signals is shown in (E), (H), (K), (N), Arc+/c-fos+ in (F), (I), (L), (O), and signal overlap in (G), (J), (M), (P). The lighter red bar represents sham mice.

Significant reduction in freezing (p < 0.05) was observed in x-ray irradiated mice from 1-Shock CFC and was in accordance with previous studies. The unexpected result was the significantly lower signal overlap compared to sham x-irradiated mice in CA3 (p < 0.01) but not DG (Figure 4G, J). While the result was surprising, it might relate to the recent hypothesis that ABN function as a modulator of CA3 neurons(14). If ABN did not modulate DG, then the lack of signal overlap difference was unsurprising since ABN only made up 5 – 10% of total granule cell populations(10) No significant difference in freezing and CA3 signal overlap was observed in 3-Shock CFC. This indicates that stronger encoding can rescue fear conditioning, in accordance with previous studies (12). Future Directions The role of ABN in CFC remains poorly understood after this study mice. Instead of ablation, a gain of function experiment can be conducted to see if enhanced ability to distinguish similar contexts results. The same transgenic system is used but with loxP flanking the pro-apoptotic gene Bax(15). Increase in adult neurogenesis can be monitored with immunostaining for Dcx, a marker for ABN. While memory expression deficits from optogenetic inhibition have demonstrated the essentiality of recruited neurons in memory retrieval, a further step can be taken to test if activation of these neurons is sufficient to elicit the memory in the absence of environmental cues. Optogenetic activators such as ChEF can be expressed in place of Arch using the same transgenic machinery. Subject mice to CFC in a particular context, then directly activate the tagged neuron populations when mice are in an unrelated context to test if memory response can be elicited(4). An alternative explanation for the optogenetic results is that the neurons do not encode the memory itself. Instead the neurons merely serve as a gateway for the true memory trace downstream. This can be tested via optogenetic activation of neocortical areas directly downstream of HPC. If direct activation elicits the full memory response, it indicates that the hippocampal neurons are not part of the memory trace(16). 165

Critical Analysis The experimenters designed a very flexible transgenic system consisting of just two transgenes. Expression of different genes could occupy the same position in the system and be expressed in the same manner. TAM as a regulator was flexible temporally. The experiment cleverly addressed in an alternative explanation for optogenetic inhibition results that silencing any group of hippocampal neurons would inhibit the specific memory. However, it did not address another alternative explanation that hippocampal neurons might be pointers to memory trace instead of being part of the trace. References 1. Josselyn SA (2010). Continuing the search for the engram: examining the mechanism of fear memories. J Psychiatry Neurosci 35(4): 221–228. 2. Han JH, Kushner SA, Yiu AP, Hsiang HL, Buch T, Waisman A, Bontempi B, Neve RL, Frankland PW, Josselyn SA (2009). Selective Erasure of a Fear Memory. Science 323 (5920): 1492-1496. 3. Reijmers LG, Perkins BL, Matsuo N, Mayford M (2007). Localization of a Stable Neural Correlate of Associative Memory. Science 317 (5842): 1230-1233. 4. Liu X, Ramirez S, Pang PT, Puryear CB, Govindarajan A, Deisseroth K, Tonegawa S. (2012). Optogenetic stimulation of a hippocampal engram activates fear memory recall. Nature 484(7394):381-5. doi: 10.1038 5. Eichenbaum H. (2000). A cortical–hippocampal system for declarative memory. Nat Rev Neurosci 1(1):41-50. 6. Phillips RG, LeDoux JE. (1992). Differential Contribution of Amygdala and Hippocampus to Cued and Contextual Fear Conditioning. Behav Neurosci 106(2):274-85. 7. Bakker A, Kirwan CB, Miller M, Stark CE (2008). Pattern separation in the human hippocampal CA3 and dentate gyrus. Science. 319(5870):1640-2. doi: 10.1126 8. McHugh TJ, Jones MW, Quinn JJ, Balthasar N, Coppari R, Elmquist JK, Lowell BB, Fanselow MS, Wilson MA, Tonegawa S. (2007). Dentate Gyrus NMDA Receptors Mediate Rapid Pattern Separation in the Hippocampal Network. Science 317 (5834): 94-99. 9. Kubik S, Miyashita T, Guzowski JF. (2007). Using immediate-early genes to map hippocampal subregional functions. Learn Mem 14(11): 758-70 10. Denny CA, Kheirbek MA, Alba EL, Tanaka KF, Brachman RA, Laughman KB, Tomm NK, Turi GF, Losonczy A, Hen R. (2014). Hippocampal memory traces are differentially modulated by experience, time, and adult neurogenesis. Neuron 83(1): 189-201. 11. Goshen I, Brodsky M, Prakash R, Wallace J, Gradinaru V, Ramakrishnan C, Deisseroth K. (2011). Dynamics of retrieval strategies for remote memories. Cell 147(3): 678-89. 12. Drew MR, Denny CA, Hen R. (2010). Arrest of adult hippocampal neurogenesis in mice impairs single- but not multiple-trial contextual fear conditioning. Behav Neurosci. 124(4): 446-54. 13. Niibori Y, Yu TS, Epp JR, Akers KG, Josselyn SA, Frankland PW. (2012). Suppression of adult neurogenesis impairs population coding of similar contexts in hippocampal CA3 region. Nat Commun 3:1253 14. Sahay A, Wilson DA, Hen R. (2011). Pattern separation: a common function for new neurons in hippocampus and olfactory bulb. Neuron 26;70(4):582-8. doi: 10.1016 15. Hill AS, Sahay A, Hen R. (2015). Increasing Adult Hippocampal Neurogenesis is Sufficient to Reduce Anxiety and Depression-Like Behaviors. Neuropsychopharmacology. doi: 10.1038 16. Cowansage KK, Shuman T, Dillingham BC, Chang A, Golshani P, Mayford M. (2014). Direct reactivation of a coherent neocortical memory of context. Neuron 84(2):432-41.


Adult hippocampal neurogenesis and its role in Alzheimer’s disease in transgenic mice models

Ziteng Li

The hippocampus is a critical brain structure involved in learning and memory and is particularly susceptible to damage during the early stages of Alzheimer’s disease (AD). There is a growing body of evidence that suggests impaired adult hippocampal neurogenesis in diseased AD patients is a major underlying factor contributing to the cognitive decline and memory impairments in affected individuals. Conversely, studies have also shown that enhanced neurogenesis contributes to memory rescue. Several key AD associated molecules such as APP, AopE, and PS1 and variants have been identified in the positive and negative regulation of these new neuronal cells while many social and lifestyle factors have been implied in increased endogenous neurogenesis. Here, in this review, we will summarize the current research on the neurogenic roles of molecules that cause adult hippocampal neurogenesis decline in AD, conditions that stimulate endogenous neurogenesis as well as the potential application of these new neurons in the treatment and diagnosis of AD. Key words: Adult neurogenesis, Alzheimer’s Disease, mouse models, memory decline, hippocampus, APP, AopE, PS1 Introduction First described by German physician Dr Alois Alzhimer in 1906, Alzhimer’s disease (AD) is an age related debilitating neurodegenerative disease that is characterized by progressive dementia throughout the affected persons life (Goedert M, Spillantini MG, 2006). At present, the mechanisms and the neuro-circuits underlying the disease is largely unknown and there is no one definitive reason for its onset. However, it has is become increasingly clear that it develops due to a complex series of events and is likely due to a combination of environmental, genetic and lifestyle factors life (Goedert M, Spillantini MG, 2006). Therefore reason of onset and the risk of developing AD will vary from person to person. Despite this, the majority of patients who do develop Alzheimer’s will do so later in life in which the apolipoprotein E (apoE) genotype is the greatest risk factor (Nichol K et al., 2009). The rare early-onset familial form of AD (FAD) represents less then 5% of AD patients and is cause by mutations in genes encoding presenilin-1 (PS1), presenilin-2 (PS2), and amyloid precursor protein (APP) (Wen PH et al.,2004) Individuals with the disorder usually suffer from severe cognitive decline, memory loss, attention deficits and changes in mood and personality (Snyder JS et al., 2001). The gradual accumulation of extracelluar β-amyloid (Aβ) plaques and intracellular neurofibrillary tangles (NFTs) along with massive neuronal death are the neuropathological hallmarks of AD (Gadadhar A et al., 2011). As the disease progresses, neurofibrillary tangles and amyloid plaques spread throughout the brain and in the late stages of AD, all patients have significantly shrunken brains due to the gross atrophy of neurons. These pathologies are evident in specific areas of the brain including the cerebral cortex, ventricles and the hippocampus (Caille I et al. 2004). In particular, the hippocampus is one of the first brain structures to be affected by AD pathology (Goedert M, Spillantini MG, 2006). The hippocampus is located in the medial temporal lobe of the brain and is known to have trisynaptic circuitry (Fig 1) (Stone SS et al.,

2011). Briefly, the information from the entorhinal cortex (EC) is received by the dente gyrus (DG) a structure found within the hippocampus. The information flow then proceeds from DG to CA3 to CA1 and finally to the subicululm, which sends the information, back into the deep layers of the EC (Stone SS et al., 2011). It has been suggested that the hippocampus is involved in learning and memory as well as long term potentiation (LTP) (Wen PH et al.,2004). The discovery of neurons being produce de novo in the DG of the adult hippocampus has suggested a new from of neural plasticity that can be involved in memory processes (Van Praag H et al., 2002). Currently there is a growing body of evidence that suggests that adult hippocampal neurogenesis promotes improved spatial and episodic memory while a decline in adult hippocampal neurogenesis maybe underlying the cognitive impairments associated with neurodegenerative diseases such as AD (Van Praag H et al., 2002) In this review we will summarize the current research on the neurogenic roles of molecules that cause adult hippocampal neurogenesis decline in AD, conditions that stimulate endogenous neurogenesis as well as the potential application of these new neurons in the treatment and diagnosis of AD. Results Molecules affecting Neurogenesis in the Hippocampus Adult neurogenesis has been established to occur consistently in two regions of the adult brain; the subventricular zone (SVZ) of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus (DG) in the hippocampus (Hsiao et al. 2014). In the SGZ, new cells are differentiated into glial cells and neurons (Hsiao et al. 2014). The de novo neurons are is what is incorporated in to the granule cell layer of the dentate gyrus (Hsiao et al. 2014) Fig 2. Various studies have shown that these newborn neurons contribute to hippocampal dependent memories and learning demonstrated in tasks such as trace eyeblink conditioning and spatial tests (Shors et al., 166


Fig 1. Neural circuitry and network in a mouse hippocampus (Deng W et al 2010). a. Illustration of the trisynaptic circuitry in the hippocampus b. network and information of the trisynaptic pathway from the entorhinal cortex (EC) to the dente gyrus to CA3 then to CA1 Schaffer collaterals which ultimately project information back into the EC

2001). Ablation of neurogenesis have shown to impair contextual fear conditioning, but conflicting reports have also been made citing that ablation has no effect on the Morris water maze nor contextual fear conditioning (Shors et al., 2002; Snyder et al., 2005). In more recent years, many molecules that are central to AD have been found to have regulatory roles in adult neurogenesis. In P117L familial AD (FAD) mice model, PS1 mutants impaired de novo neuron production in the adult hippocampus by decreasing neural progenitor survival (Wen PH et al.,2004). In the PS1M146V knockin mice, PS1 mutations exhibited impaired hippocampus dependent learning measured by contextual fear conditioning—which correlated with decreased adult neurogenesis in the hippocampus (Ghosal K et al., 2010). PDAPP mutants with APP mutations also demonstrated decrease in neurogenesis in the SGZ and the soluble form of APP (sAPP) has a positive regulatory role in the proliferation of progenitor cells in the adult SGZ (Donovan M et al., 2006; Caille I et al. 2004). Lastly, a knockout mutant of ApoE and a knockin mutant of ApoE4 also demonstrated reduced levels of neurogenesis (Li G et al., 2009). These studies using various transgenic mice models of AD have generated a surmounting body of evidence that supports the idea that adult hippocampal neurogenesis plays a role in the cognitive dysfunction of AD. We have also identified key AD-associated molecules that play a regulatory role in the synthesis of these new neurons including APP, AopE, and PS1 and their variants. Social Interaction, Exercise and Environmental Enrichment Although at present, there is no definitive evidence to support any one treatment in delaying the progres167

sion of AD. Maintaining strong social contacts, healthy lifestyle and being mentally active as one ages has been strongly implicated to decrease risk of cognitive decline and onset of the disease. Recent studies have found that social interaction, environment enrichment (eg. improved standard of living), as well as exercise can rescue deficits of AD by promoting neurogenesis. Hsiao et al. (2014) found in the APP/PS1 animal mouse model, social interactions between mutant mice and wild type mice rescued memory deficits and decreased the progression of AD in mutant mice. The researchers found increased BDNF-mRNA and protein production after cohousing, which lead to neurogenesis and ultimately rescue of memory in mutant mice. They also found that overexpression of BDNF mimicked memory-improving effect while genetic knockdown and chemically blocking cell proliferation blocked this memory improvement. These findings provide evidence that social interactions improve memory and cognition in the mouse model of AD via BNDF expression and associated neurogenesis in the hippocampus. Alternatively, Hsiao et al. (2011) also looked into what would happen in the absence of social interaction or rather what would occur if the APP/PS1 mice were placed in social isolation. They found elevated levels of hippocampal Aβ detected by increasing β-and γ-secretase activities which contributes directly to the pathogenesis of AD including neurodegeneration. The researchers also found that isolated mice had lower levels of LTP in hippocampal CA1 neurons, which exacerbated the already present memory deficits. Barrientos et al. (2003) also found that social isolation following memory and cognitive impairment significantly decreased BDNF-mRNA in the dentate gyrus and the CA3 region of the hippocampus. These findings suggest that social isolation may accelerate the progression of AD in diseased individuals while social interactions may rescue the impairments via neurogenesis. Physical exercise such as wheel running in mice models have been found to improve cognition and hippocampal plasticity (Nichol K et al., 2007). In one study, ApoE mutant mice that previously exhibited deficits in cognition on the radial arm water maze test (RAWM) (a hippocampal dependent spatial memory task) showed significant improvement in the tasks as well has increased BDNF levels after 6 weeks of wheel running (Nichol K et al., 2009). Similarity, the aged Tg2576 AD mice model also demonstrated that exercise can improve cognitive performance and promote neurogenesis even after the development of AD pathology (Nichol K et al., 2007). Enriched environments (EE) have also been found to be positive regulators for adult neuronal hippocampal neurogenesis and have been shown to increase improve cognitive performance, decrease Aβ levels an also increase hippocampal LTP in APPswe/PS1DE9 mice (Hu Y et al., 2010). Exercise along with EE has also been shown to improve water maze performance and also increase newborn granule cells in the DG of APP23 mice (Mirochnic S et al. 2009). However there are contradicting studies that have shown that EE does not enhance neurogenesis in PS1 knock out mice or FAD-linked PS1 variants (Feng R et al.


2001). In a more recent study, EE has been even shown to suppress neurogenesis in ApoE4 mice (Levi O, Michaelson DM, 2007). These results imply that EE has various effects on different mice models of AD.

Fig 2. Adult hippocampal neurogenesis in the SGZ (Mu Y, Gage F 2011). Type 1 and Type 2 neural stem cells generate astrocytes and neuroblasts. The neuroblasts will migrate to the granule cell layer of the dentate gyrus where it will become dentate granuale cells. These new cells will then form extensive dendritic trees that receive information of the entorhinal cortex and project to CA3 neurons.

Conclusion and Discussion In summary, we have concluded by using various mutant mouse model of AD, that known AD-associated molecules such APP, AopE, and PS1 also play a important role in the regulation of hippocampal neurogenesis in the adult mice brain. These finding further support the ongoing hypothesis that a decline in neurogenesis in SZG of adults play a crucial role in the onset and progression of early and late-onset Alzheimer’s disease. Notably, alteration of these new neurons occurs in the very early stages of AD even prior to neuronal atrophy, amyloid deposition, and tau tangles (Goedert M, Spillantini MG, 2006). This suggests that neurogenesis is one of the key elements in the disease pathology of AD. Currently, although there is no conclusive drug or therapeutic treatment of AD, there have been strides in research to prevent its early onset. In particular, it has been found that there are extrinsic conditions that can facilitate endogenous neurogenesis in the hippocampus including; maintaining strong social interactions, physical exercise as well as being in an enriched environment as we age. Although the number newly synthesized neurons in the SZG are pale in comparison to the number degenerating neurons, we have found promising results in the rescuing of memory impairments from these de novo cells (Hsiao et al. 2014; Shors et al., 2001). While it is very unlikely that neurogenesis will provide global repair to the deficits caused by AD, it is very plausible that it can aid in slowing down the progression of the disease. Lastly due to its very early onset, declining neurogenesis may in the future act as a neuro-biologal marker for the diagnosis as well as facilitate understanding the underlying neuromechanisms of the disease.

Critical Analysis and Future Directions Although there have been many comprehensive studies in this field of research that support hypothesis that neurogenesis is occurring and is an underlying factor in AD. There are also many gaps and inconsistencies in the literature that needs to be addressed. Firstly, although the majority of studies have found an increased number of new neuronal cells synthesized, there are many opposing articles that have reported the opposite. This disjuncture maybe explained by the different AD mutant mice models used in the respective studies. Since different mutations and promoters of various transgenic mice lines express different neuronal cell populations of the transgenes, they are likely to express distinct levels AD-related proteins. Therefore, it is very hard to compare the results from two different transgenic lines. As a result, a standard or systematic comparison of transgenic mice with consistent gender, age, genetic background, progression in AD and neurogenic analysis should be conducted so conclusive results can be drawn. Secondly, in the current mice models of AD, most transgenic lines only exhibit one or partial pathology of AD. This is unrealistic portrayal of the disease, since combined pathologies may interact and yield widely different results from a single or partial diseased state. Therefore the discovery of a new strain of transgenic mice that accurately reflect all AD pathologies can be a future initiative in this field of research. Lastly it is hard to generalize mice models to humans due to the intrinsic physiological and genetic differences and much of the research reviewed in this paper have never been tested in human trials. Therefore, to accurately assess the applications of this research to the human AD, human trials and post-mortem examinations should be conducted on willing diseased individuals. Some possible future directions in this field of research include a drug therapy that specifically targets and promote adult neurogenesis. Recently, allopreganolone has been cited as a neurosteroid that can aid neurogenesis in the brain (Brinton RD et al., 2006). However promising, this compound has not been pursued for clinical use due to its short half-life (Brinton RD et al., 2006). Current active drug therapies mask the symptoms of AD rather then treat the underlying disease by stopping its progression. Therefore an effective therapy for AD is still unavailable for diseased patients. However the current research and existing animal models that were reviewed in this paper may provide a basis and better insight into the prevention, treatment and management of cognitive decline such as Alzheimer’s disease associated dementia. References 1. BarrientosR. et al. Brain-derived neurotrophic factor mRNA downregulation produced by social isolation is blocked by intrahippocampal interleukin-1 receptor antagonist. Neuroscience 121:847-853 (2003) 2. Brinton RD, Wang JM (2006) Therapeutic potential of neurogenesis for prevention and recovery from Alzheimer’s disease: allopregnanolone as a proof of concept neurogenic agent. Curr Alzheimer Res. Jul;3(3):185-90 3. Caille I, Allinquant B, Dupont E, Bouillot C, Langer A, Muller 168


U, Prochiantz A (2004) Soluble form of amyloid precursor protein regulates proliferation of progenitors in the adult subventricular zone. Development 131:2173-2181. 4. Deng W, Aimone J, Gage F (2010) New neurons and new memories: how does adult hippocampal neurogenesis affect learning and memory. Nat Rev Neurosci 11(5): 339–350. 5. Donovan MH, Yazdani U, Norris RD, Games D, German DC, Eisch AJ (2006) Decreased adult hippocampal neurogenesis in the PDAPP mouse model of Alzheimer’s disease. J Comp Neuron 495:70-83. 6. Feng R, Rampon C, Tang YP, Shrom D, Jin J, Kyin M, Sopher B, Miller MW, Ware CB, Martin GM, et al (2001) Deficient neurogenesis in forebrain-specific presenilin-1 knockout mice is associated with reduced clearance of hippocampal memory traces. 7. Gadadhar A, Marr R, Lazarov O (2011) Presenilin-1 regulates neural progenitor cell differentiation in the adult brain. J Neurosci 31:2615-2623. 8. Ghosal K, Stathopoulos A, Pimplikar SW (2010) APP intracellular domain impairs adult neurogenesis in transgenic mice by inducing neuroinflammation. PLoS One 5:e11866 9. Goedert M, Spillantini MG (2006). A century of Alzheimer’s disease. Science 314:777-781. 10. Hsiao YH, Chen PS, Chen SH, Gean PW (2011) The involvement of Cdk5 activator p35 in social isolation-triggered onset of early Alzheimer’s disease-related cognitive deficit in the transgenic mice. Neuropsychop- harmacology 36:1848 –1858. 11. Hsiao YH, Hung HC, Chen SH, Gean PW. (2014) Social Interaction Rescues Memory Deficit in an Animal Model of Alzheimer’s Disease by Increasing BDNF- Dependent Hippocampal Neurogenesis. The Journal of Neuroscience, 34(49), 16207-16219 12. Hu YS, Xu P, Pigino G, Brady ST, Larson J, Lazarov O (2010) Complex environment experience rescues impaired neurogenesis, enhances synaptic plasticity, and attenuates neuropathology in familial Alzheimer’s disease-linked APPswe/PS1DeltaE9 mice. Faseb J 24:1667-1681. 13. Levi O, Michaelson DM (2007) Environmental enrichment stimulates neurogenesis in apolipoprotein E3 and neuronal apoptosis in apolipoprotein E4 transgenic mice. J Neurochem 100:202-210. 14. Li G, Bien-Ly N, Andrews-Zwilling Y, Xu Q, Bernardo A, Ring K, Halabisky B, Deng C, Mahley RW, Huang Y (2009) GABAergic interneuron dysfunction impairs hippocampal neurogenesis in adult apolipoprotein E4 knockin mice. Cell Stem Cell 5:634-645. 15. Li Y, Mu Y, Gage FH (2009). Development of neural circuits in the adult hippocampus. Curr Top Dev Biol 87:149-174. 16. Mirochnic S, Wolf S, Staufenbiel M, Kempermann G (2009) Age effects on the regulation of adult hippocampal neurogenesis by physical activity and environmental enrichment in the APP23 mouse model of Alzheimer disease. Neuron 32:911-926 17. Mu Y, Gage F (2011) Adult hippocampal neurogenesis and its role in Alzheimer’s disease. Molecular Neurodegeneration 6:85 18. Nichol K, Deeny SP, Seif J, Camaclang K, Cotman CW (2009) Exercise improves cognition and hippocampal plasticity in APOE epsilon4 mice. Alzheimers Dement 5:287-294. 19. Nichol KE, Parachikova AI, Cotman CW (2007) Three weeks of running wheel exposure improves cognitive performance in the aged Tg2576 mouse. Behav Brain Res 184:124-132. 20. Shors TJ, Miesegaes G, Beylin A, Zhao M, Rydel T, Gould E (2001) Neuro- genesis in the adult is involved in the formation of trace memories. Nature 410:372–376. 21. ShorsTJ,TownsendDA,ZhaoM,KozorovitskiyY,GouldE (2002) Neuro- genesis may relate to some but not all types of hippocampaldependent learning. Hippocampus 12:578 –584. 22. Snyder JS, Hong NS, McDonald RJ, Wojtowicz JM (2005) A role for adult neurogenesis in spatial long-term memory. Neuroscience 130:843– 852. 23. Snyder JS, Kee N, Wojtowicz JM (2001) Effects of adult neurogenesis on synaptic plasticity in the rat dentate gyrus. J Neurophysiol 85:2423-2431. 169

24. Stone SS, Teixeira CM, Devito LM, Zaslavsky K, Josselyn SA, Lozano AM, Frankland PW (2011) Stimulation of entorhinal cortex promotes adult neurogenesis and facilitates spatial memory. J Neurosci 31:13469-13484. 25. Van Praag H, Schinder AF, Christie BR, Toni N, Palmer TD, Gage FH (2002) Functional neurogenesis in the adult hippocampus. Nature 415:1030-1034 26. Wen PH, Hof PR, Chen X, Gluck K, Austin G, Younkin SG, Younkin LH, DeGasperi R, Gama Sosa MA, Robakis NK, et al. (2004) The presenilin-1 familial Alzheimer disease mutant P117L impairs neurogenesis in the hippocampus of adult mice. Exp Neurol 188:224-237


Improved cognitive function through the elucidation of alcoholically induced changes in the brain

Bernie Longange

Alcohol has the ability to affect both the body and the brain in a variety of ways. In recent years studies have found that moderate levels of alcohol may have positive effects on cognition. Susceptibility to these effects may be related to the period of mental development, gender, drinking history, as well as many other unforeseen factors. At the moment the proper levels of alcohol consumption for cognitive improvement are being determined, and eventually the pathways that cause changes in mental functioning may be elucidated. Key words: alcohol, consumption, moderate, pathways, nondrinkers and cognitive function Background Cognitive function serves not only as a reflection into the way the mind works and how intelligence is measured or attained, but also a glimpse into the future of how the brain will develop1. Studies have been conducted in attempts to improve cognitive functionality, but few definitive answers have been obtained2. Even previously rigid observations are being called into question with new discoveries in the field. For years, alcohol consumption was believed to be the cause of reduced mental ability due to both short term cognitive impairments and damage caused to the brain in the long run3.Studies had shown that increased alcohol consumption had an inverse relationship with increases in cognitive function. The more alcohol you would drink the less intelligent you would become4. Drinking alcohol increased the risk of cognitive impairment5 and dementia6. Further evidence shows that drinking increases the risk of cardiovascular diseases, and cardiovascular diseases are in turn related with “cognitive aging” or decreases in mental ability7. Although being considered fact for many years, this observation has been under scrutiny as of late, as more recent studies have been showing contrary results. People who drink moderately appear to exhibit increased cognition8. This does not extend to those who are considered problem drinkers, as too much alcohol destroys the brain9. This shift has changed the focus of studies relating alcohol consumption to cognition. Research has been considering what levels of alcohol consumption resulted in the highest increases in mental ability10. Studies have continued to attempt to explain why and how alcohol improves cognitive function at certain levels. This relates to the many experiments being conducted in understanding brain function in relation to moderate doses of different drugs, as similar research is also at the forefront of studies in methamphetamine usage and dosage11. The changes the brain undergoes after consumption are the main targets in studies of this nature today. The paper by Pia Horvat et al. “Alcohol consumption, drinking patterns, and cognitive function in older Eastern European adults” looked at the association between quantity, frequency and changes in alcohol consumption and changes in mental ability. This is an in depth look at the correlation between cognitive function and alcohol intake than has been taken in the past and is the one of the first steps in discovering the pathways in which cognitive improvements can be made.

Research Overview

Summary of Major Results

Moderate consumption of alcohol accompanied increased cognitive function in the studied individuals. Approximately 28,947 men and women between the ages of 45 – 69 were randomly selected from regions of Eastern Europeans where alcohol is one of the leading causes of illnesses and premature death. Individuals were first categorized by levels of selfreported alcohol consumption. There were 4 levels of intake that ranged from nondrinkers (0 g/d) to heavy drinkers (≥20/40 g/d), and a separate category for binge drinking, which was defined as consumption of ≥60/100 g of alcohol in one session, at least once a month. Four cognitive tests were conducted by trained nurses. These tests included word recall tests (immediate and delayed recall), a verbal fluency test, and a letter cancellation test. These examinations looked at verbal memory, learning, verbal fluency, attention, mental speed and concentration. After 1-6 years had passed participants were reexamined for cognitive function, and had to report any changes in their alcohol intake. Here individuals were placed into 6 categories; stable nondrinkers, ex-drinkers, reduced drinkers, increased drinkers, and people who abstained during the first test but had started drinking. Cognitive function in men Nondrinkers were found to have lower cognitive scores that moderate drinkers, but after adjusting for socioeconomic and lifestyle confounds, these results were not significant. An exception was found when the cognitive scores of nondrinkers were cross-sectionally compared to the reference group (the lowest level of drinking) which showed significant results. In the follow-up, participants who had stopped drinking had “significantly lower cognitive scores than stable drinkers. This effect was observed especially in men. Verbal performance was shown to be significantly lower for those who had stably abstained from drinking. Cognitive function in women Light drinkers scored consistently higher than nondrinkers. Moderate drinking correlated with better performance in comparison to lower levels of alcohol consumption. Drinking a few times a month seemed 170


1

2

3

4

Figure 1. Male cognitive test scores for immediate word recall. This tested for verbal memory and learning. Figure 2. Male cognitive test scores for delayed word recall. This tested for verbal memory and learning. Figure 3. Male cognitive test scores for verbal fluency recall. This tested for verbal fluency. Figure 4. Male cognitive test scores for letter fluency. This tested for attention, metal speed nd concentration.

to have a positive effect on the cognitive test scores. In the follow-up, participants who had stopped drinking had “significantly lower cognitive scores than stable drinkers. Women who had started drinking as well as consistent nondrinkers had lower cognitive scores than they had during the first examination.

Discussion

The effects of drugs on humans are never as straight forward as they appear. There always seems to be a negative side effect to drugs that are deemed to be “good”, but as of late there is increasing evidence of “bad” drugs having positive side effects. Alcohol research in particular has taken a large turn in the last decade. The focus has shifted from all the negative effects alcohol has on the body, to the potential positive effects it has. The Pia Horvat et al. study continues along the lines of the paper “Alcohol Consumption and Cognitive Function in the Whitehall II Study” by Annie Britton and colleagues. The paper looks to the change in cognition caused by different levels in alcohol consumption. The more recent study is one of the first to look at quantity and frequency in the association between alcohol and the functioning of the brain. Overall the authors are showing that moderate levels of 171

alcohol serve for better mental functioning. Although in males some of the results were not significant, the same patterns are still present. Increases in cognitive ability are still observed in those who drink alcohol in moderation, in comparison to those who drink obscene amounts of alcohol, as well as those who do not drink at all. With these results, the authors are eluding to the idea that moderate levels of alcohol are involved in a pathway that increases cognitive function, lesser amounts of alcohol does not have a strong enough effect, and too much alcohol is detrimental to the brain’s function. An exact amount that produces the best results was not discovered, but an approximate range was. With the data from the follow-up it was observed that continued moderate drinkers had the best results. Those who didn’t drink at all, or that had only started drinking had worse scores in comparison to their original scores. Looking at those who started drinking after the original assessment it is possible that after a certain amount of time improvements are no longer possible with alcohol and it actually decreases mental functioning. This could mean that at certain levels of mental development, such as adolescence, the consumption of alcohol actually aids brain development. The beneficial effects of alcohol on cognitive function are also stronger in women than in men. It is possible that the male and female brains have minute differ-


ences in development that are facilitated differently through alcohol. On the contrary, this may also mean that the differences in the male and female anatomy affect how the development of their brains is altered (ie. Levels of fat in the body change the overall effect of alcohol in the body). Conclusions A study in the frequency and quantity of alcohol consumed in relation to changes in cognitive function is the avenue this area of study was expected to take. Knowing that alcohol increases mental functioning, is strong but dangerous information, as it may promote alcoholism. This topic needs to be properly researched so that facts can be elucidated from it. Once optimal levels of alcohol consumption have been discovered the next step in the study will be at the forefront of research, and an answer that has evaded civilization for centuries will finally be answered. What substance can undoubtedly make humans smarter?

Criticisms and Future Directions

A problem with this study is that people were asked to self-report their levels of alcohol consumption. This could greatly affect the results, as some people may be ashamed of how much they drink, and would report lower levels of intake, or would boast about how much they consumed and inflate their numbers. Although confounds for lifestyle and socioeconomic status were taken into consideration, this study remains open to a lot of potential errors. This study should be replicated, with a different animal, with more controls to reduce confounds. Mice have been commonly used to observe the effects of alcohol and other drugs on the brain. Using mice, the effects of moderate levels of alcohol consumption on the brain could be observed. These results would then be compared to the brains from past studies of alcoholic mouse brains. Considering the differences in the two brain types (such as changes in receptors, production of proteins etc.), the cause of cognitive improvement could be assumed. Once confounds in the results are eliminated the actual pathways that cause increases and decreases in mental function can be considered. Certain properties of ingesting ethanol can be tested in different areas of the brain, to see what actually causes the differences in mental functioning. Learning what changes in the brain would open a field of research, focused on breaking down boundaries on the human brain. This could be the first step in making the cognitive abilities of humans limitless.

on Adolescents and College Students. Prev Med 40: 23-32. 4. Sabia S (2014) Alcohol Consumption and Cognitive Decline in Early Old Age. Neurology 82: 332-39. 5. Virtaa JJ et al. (2010) Midlife alcohol consumption and later risk of cognitive impairment: a twin follow-up study. J Alzheimers Dis. 22:939–948. 6. Järvenpää T, Rinne JO, Koskenvuo M, Räihä I, Kaprio J (2005) Binge Drinking in Midlife and Dementia Risk. Epidemiology 16: 766-71. 7. Rehm J, Sempos CT, Trevisan M (2003) Alcohol and cardiovascular disease--more than one paradox to consider. Average volume of alcohol consumption, patterns of drinking and risk of coronary heart disease--a review. J Cardiovasc Risk 10:15-20 8. Bond GE et al. (1999) Alcohol, Aging, and Cognitive Performance in a Cohort of Japanese Americans Aged 65 and Older: The Kame Project Int Psychogeriatr 13: 207-23. 9. Harper C (2009) The Neuropathology of Alcohol-Related Brain Damage. Alcohol Alcoholism 44: 136-40. 10. Britton A et al. (2004) Alcohol Consumption and Cognitive Function in the Whitehall II Study.” Am J Epidemiol 160: 240-47. 11. Ricaurte GA, Schuster CR, Seiden LS (1980) Long-term Effects of Repeated Methylamphetamine Administration on Dopamine and Serotonin Neurons in the Rat Brain: A Regional Study. Brain Res 193: 153-63. 12. Horvat P et al.(2014) Alcohol consumption, drinking patterns, and cognitive function in older Eastern European adults. Neurology 84: 287-295

References 1. Amieva H (2005) The 9 Year Cognitive Decline before Dementia of the Alzheimer Type: A Prospective Population-based Study. Brain 128:1093-101. 2. Hillman CH, Erickson KI, and Kramer AF (2008) Be Smart, Exercise Your Heart: Exercise Effects on Brain and Cognition.” Nat Rev Neurosci 9: 58-65 3. Zeigler DW, et al (2005) The Neurocognitive Effects of Alcohol 172


Down-Regulation of Amyloid-Beta Peptide Binding P75 in Basal Forebrain Cholinergic Neurons Rescued Neurodegeneration and Behavioral Deficits in AD Mouse Models Tong Mai

The neurotrophin receptor p75 binds to different ligands to induce various functions including cell survival, cell death, and differentiation. It’s interaction with the amyloid-beta peptide is believed to contribute to the neurodegeneration of cholinergic neurons of basal forebrain in Alzheimer’s disease. Studies on mouse models showed that down-regulation of p75 level can rescue the neuronal functions and cognitive deficits. Its limited expression in the brain served as a good therapeutic target for AD. Key words: Alzheimer’s Disease, p75 neurotrophin receptor, amyloid-beta, mouse models, neurodegeneration, LM11A-331, Tg2576, cognitive deficits, Cholinergic neurons Background Alzheimer’s disease is an age-related neurodegenerative disorder that is affecting many of the elders worldwide. It is characterized by the accumulation of extracellular amyloid plaques and formation of intracellular tangles. The neuronal degeneration often leads to cognitive impairment and functional deficit (Xia et al, 2014). The major regions of the brain damaged in AD include the entorhinal cortex and the basal forebrain (Fombonne et al, 2009). The cholinergic neurons of basal forebrain are enriched with the low-affinity neurotrophin receptor p75, which is sparsely distributed in other areas of the brain. Previous researches have showed that p75 have multifaceted roles to induce either cell survival or cell death depending on the expression of co-receptors and the ligands (Ovsepian et al, 2013). It is a transmembrane receptor with a death domain that could activate cell apoptosis upon binding of ligand (Xia et al, 2014). The amyloid cascade hypothesis of Alzheimer’s disease suggests that the amyloid plaque formation resulting from the overproduction or the failure to break down Aβ is the major cause for the dementia (Ovsepian et al, 2013). The binding of soluble oligomeric form of amyloid-beta to p75 induces toxicity results in neuronal dysfunction and cell apoptosis in AD (Xia et al, 2014; Fombonne et al, 2009). Elevated level of amyloid-beta is associated with aggravated memory impairment, LTP inhibition, and cell death in AD patients (Xia et al, 2014). The enhanced expression of amyloid-beta in AD also showed an upregulate effect on the number of p75 in basal forebrain (Chakravarthy et al, 2010). Previous studies on the relationship of p75 and AD using mouse models have shown many conflicting results. Careful manipulation on the genetic background of the mice is important (Greferath et al, 2000). Various transgenic and knock out mouse models researchers used to study for p75. Upregulation of p75 enhanced cell death and increase vulnerability to AD and amyloid-beta toxicity whereas p75 knockout mice have increased neuronal size, slowed neurodegeneration, and increased cholinergic innervation (Yeo et al, 1997; Barrett et al, 2010). Yet most of the studies have focused on the brain pathologies upon p75 manipulation, few have demonstrated the effect of changing p75 level on behavioral and cognitive functions. 173

Research Overview

Summary of Major Results

Murphy et al. (2014) conducted a study on the Tg2576 transgenic mice containing human APP gene with different levels of p75 expressions. Several memory experiments were performed: fear conditioning testing for fear memory; Y maze testing for short term memory; and Barnes maze testing for spatial memory. The mice were between 4 to 8 months old (early phase of AD) in the tests except for the Barnes maze test which used 2 age groups (4-8 months and 12-14 months). They were able to show that reducing the level of p75 receptors in the Tg2576 mice showed significant improvement in performance in all of the cognitive tests. The Tg2576 mice exhibited less shock response in the contextual fear conditioning test compare to the other three groups with p75 reduction. The Tg2576/ p75+/- mice preferred to use more spatial search strategy in the Barnes Maze and have longer memory retention about the familiar arms in the Y maze. The synaptic transmission of the hippocampal CA1 neurons was enhanced after the reduction of p75. The LTP of the Tg2576/p75+/- and wild type exhibited similar magnitudes whereas the Tg2576 had a reduction in LTP. There was an increase in human Ab expression in the Tg2576 mice with reduction of p75. Conclusions and Discussion Reduction of p75 on AD mouse models rescued the neurodegeneration as well as the behavioral/cognitive deficits. The level of p75 negatively regulates the cholinergic system, which inhibit hippocampal function and impair spatial memory (Barrett et al, 2010). The p75 knockout mice consistently performed greater in Barnes maze task compare to the control. The p75 enables amyloid-beta peptide to induce cell apoptosis. Downregulation of p75 was showed to enhance the neuronal size and function but have very little effect on the neuronal numbers (Greferath et al, 2010; Boskovic et al, 2014). The change in p75 expression only affected the basal forebrain cholinergic neurons but have no effect on neurons of other regions of the brain (Yeo et al, 1997).


Because of its limited and specific expression, it is a very good therapeutic target for treating early- and mid- stage of AD. Mouse models expressing various levels of p75 exhibit gene dosage dependent effect on their functional impairments. The heterozygous mice with only one functional p75 had intermediate performance on cognitive tasks, whereas the p75-deficient mice performed the best and the worst for the control (Barrett et al, 2010; Murphy et al, 2014). The direct effect of p75 on the cholinergic neuronal function is undoubtable, whereas the effect is dependent on the co-receptor and ligand. The NGF binds to p75 to promote cell survival or cell death depending on the presence of the co-receptor TrkA (Simmons et al, 2014). While reduction on p75 has no effect on levels of amyloid-beta peptide, number of amyloid-beta is positively correlated with p75 (Chakravarthy et al, 2010). A small non-peptide ligand LM11A-31 was found to bind p75 and reversed the neurodegeneration in mouse models at the mid- and late AD stage (Simmons et al, 2014). After oral administration, mice had increased performance in Y maze tasks and decreased in synaptic loss (Knowles et al, 2013). The binding of LM11A-31 to p75 activates the survival signalling pathway and inactivates the cell death cascade.

Conclusions

Amyloid-beta peptides bind to p75 at the cholinergic neurons of the basal forebrain causing synaptic dysfunction and impair cognitive performance. Downregulation of p75 in various AD mouse models with different genetic backgrounds has shown that p75 exhibits a gene-dose dependent effect. Lower expression of p75 in previous studies has shown the reversed brain pathologies. Murphy et al. (2014) further showed that reduction of p75 in Tg2576 not only attenuated the neurodegeneration; the behavioral deficits were also rescued and the performances of the Tg2576/ p75+/- mice were comparable to the wild type.

Criticisms and Future Directions

Previous studies provide good evidence that reduction of p75 expression can rescue neurodegeneration and cognitive deficits in AD mice models. However, most of mice in the studies were at the early or midprogression of AD, more research is needed to be done on the late AD phase. Furthermore, the cognitive tests conducted in the studies were mostly tasks associated with spatial memory. It is known that p75 caused degeneration of cholinergic neurons which interfere with hippocampal function leading to deficit on spatial memory (Barrett et al, 2010). Yet in human patients with Alzheimer’s disease, the cognitive declines are more serious and multi-dimensions. While previous studies could only showed that reduction of p75 could enhanced performance of mice on tasks related to spatial memory, it is hard to conclude that downregulation of p75 will be able to rescue other cognitive deficits (i.e. episodic memory, language). Although the small ligand LM11A-31 has shown to prevent the cell loss in AD mouse models, researchers need to further test on the specificity and side-effect of the ligand and whether the change in neuropathology have any impact on the functional impairment.

References 1. Barrett, G. L., Reid, C. A., Tsafoulis, C., Zhu, W., Williams, D. A., Paolini, A. G., Trieu, J., Murphy, M. (2010). Enhanced Spatial Memory and Hippocampal Long-Term Potentiation in p75 Neurotrophin Receptor Knockout Mice. Hippocampus, 20, 145-152. 2. Boskovic, Z., Alfonsi, F., Rumballe, B. A., Fonseka, S., Windels, F., Coulson, E. J. (2014). The Role of p75NTR in Cholinergic basal forebrain structure and function. J Neurosci., 34(39), 1303313038. 3. Chakravarthy, B., Gaudet, C., Menard, M., Atkinson, T., Brown, L., LaFerla, F. M., Armato, U., Whitfield, J. (2010). Amyloid-β peptides stimulate the expression of the p75NTR neurotrophin receptor in SH-SY5Y human neuroblastoma cells and AD transgenic mice. J Alzheimers Dis, 19, 915-925. 4. Fombonne, J., Rabizadeh, S., Banwait, S., Mehlen, P., Bredesen, D. E. (2009), Selective vulnerability in Alzheimer’s Disease: Amyloid Precursor Protein and p75NTR interaction. Ann. Neurol. 65, 295-303. 5. Greferath, U., Bennie, A., Kourakis, A., Bartlett, P. L., Murphy, M., Barrett, G. L. (2000). Enlarged cholinergic forebrain neurons and improved spatial learning in p75 knockout mice. Eur. J. Neurosci., 12, 885-893. 6. Knowles, J. K., Simmons, D. A., Nguyen, T. V., Griend, L. V., Xie, Y., Zhang, H., Yang, T., Pollak, J., Chang, T., Arancio, O., Buckwalter, M. S., Wyss-Coray, T., Massa, S. M., Longo, F. M. (2013). A small molecule p75NTR ligand prevents cognitive deficits and neurite degeneration in an Alzheimer’s mouse model. Neurobiol Aging, 34, 2052-2063. 7. Murphy, M., Wilson, Y. M., Vargas, E., Munro, K. M., Smith, B., Huang, A., Li, Q., Xiao, J., Master, C. L., Reid, C. A., Barrett, G. L. (2014). Reduction of p75 neurotrophin receptor ameliorates the cognitive deficits in a model of Alzheimer’s disease. Neurobiol Aging, 1-13. 8. Ovsepian, S. V., Antyborzec, I., O’Leary, V. B., Zaborszky, L., Herms, J., Dolly, J. O. (2013). Neurophin receptor p75 mediates the uptake of the amyloid beta (Aβ) peptide, guiding it to lysosomes for degradation in basal forebrain cholinergic neurons. Brain Struct Funct, 219, 1527-1541. 9. Simmons, D. A., Knowles, J. K., Belichenko, N. P., Banerjee, G., Finkle, C., Massa, S. M., Longo, F. M. (2014). A small molecule p75NTR ligand, LM11A-31, Reverses cholinergic neurite dystrophy in Alzheimer’s Disease mouse models with mid- to late-stage disease progression. Plus one, 9(8). 10. Xia, M., Cheng, X., Yi, R., Gao, D., Xiong, J. (2014). The Binding Receptors of Aβ: an Alternative Therapeutic Target for Alzheimer’s Disease. Mol. Neurobiol. Doi: 10.1007/s12035-0148994-0. 11. Yeo, T. T., Chua-Couzens, J., Butcher, L. L., Bredesen, D. E., Cooper, J. D., Valletta, J. S., Mobley, W. C., Longo, F. M. (1997). Absence of p75NTR Causes Increased Basal Forebrain Cholinergic Neuron Size, Choline Acetyltransferase Activity, and Target Innervation. J. Neurosci., 17(20), 7594-7605. Received Month, ##, 200#;

##, accepted

This work was supported by Undergraduate Neuroscience ment for Science Education Research Foundation (EA). Dr. Amy G. Dala, and the nical assistance, execution,

200#; Month,

revised ##,

Month, 2013.

The Association for the Development of Education (SRA & RLN), The Endow(EA), and The Synaptic State Faculty The authors thank Mr. Spine L. Cord, students in Neuroscience 101 for techand feedback on this lab exercise.

Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu

174


Discovering Biomarkers to Detect Early Onset of Stroke

Fazila Malek

One of the highest death rate is associated with stroke world wide and especially in third world countries where certain diets consist of unhealthy saturated fats and oils, and lack of MRI machines or CT scans. Detecting biomarkers for stroke in the blood serum can be an easy tool to determine whether or not a person has suffered from stroke, upon which rapid treatment would be available preceding quick diagnosis. Biomarkers like NSE have been found to correlate strongly with stroke onset, and can be a determinant of stroke occurrence. NSE is an enzyme released in the CSF upon cell death and crosses the blood brain barrier (BBB) into the blood stream. A control group with people of no stroke symptoms and a study group of people with some signs and symptoms of acute stroke were chosen. Taking blood samples from these groups and measuring serum levels of NSE, showed that all controls had NSE levels below 25 ng/ml and stroke patients had most levels arising in the greater than 25 ng/ml range. NSE is a promising biomarker in serum allowing to detect stroke occurrence in countries where medical imaging procedures or not available or are too costly for people to afford. Key words: neuron specific enolase (NSE); acute and ischemic stroke; degree of disability; biomarker Background As stroke is one the leading causes of death and long term rehab hospitalization of patients, it would be affective to diagnose and treat stroke early to increase survival rates and prevent severity in stroke patients to rise. Many countries in the world do not have access to expensive technology such as CT scans or MRI machines. Some areas of the world may not be able to afford expensive machinery, and the first world countries which are able to provide these services could greatly cut down the costs and make use of the finances elsewhere in the healthcare field. A study done in the United Kingdom found that £8.9 billion were used just in stroke treatment and diagnosis alone1. Thus, being able to use biomarkers within the blood would be an ideal and easy solution to diagnosing and treating stroke. The paper by Bharosay et al. looks at biomarkers in the blood to discover early onset of stroke in patients within 72 hours. Taking blood samples from a control group with no clinical signs and symptoms of stroke, and then repeating the same with patients with stroke occurrence within 72 hours. Using an antibody against the γ, γ-Neuron specific enolase, they were able perform an enzyme immunoassay. They also used National Institute of Health Stroke Scale (NIHSS), which is a set of questions, and the score obtained would determine severity of stroke.1 Many studies have been done to look at specific biomarkers to use to diagnose stroke, which will be discussed in this review for future directions. Some biomarkers discovered and studied were microRNAs3, ubiquitin fusion degradation protein 1 (UFD1)4, and glutathione S-transferase-π (GST- π)5.This paper will review some of the advantages and disadvantages to each type of biomarker for early detection of stroke.

had signs and symptoms of stroke within 72 hours, the following results were found. The control group consisted of 101 people, and 82% of them were in the 46-65 years age range. In the study group of 156 stroke patients, consisted of 59% of people in the 46-65 age range. Also, the study group consisted of 63% males. Other risk factors like hypertension, atrial fibrillation, and diabetes mellitus were generally found more with in the study group compared to the control.

Neuron Specific Enolase (NSE) levels in Control Group vs. Study Group In the study group, 47% of the population had NSE levels greater than 25 ng/ml and ~9% of the people had NSE levels greater than 35 ng/ml. In contrast, everyone in the control group had lower than 25 ng/ ml of NSE in serum. See Figure 1. NSE levels and Severity of Stroke Elevated levels of NSE were 92% positively correlated with the severity of stroke, suggesting NSE level being important for cerebrovascular stroke. NSE and Degree of Disability Degree of disability was determined using the

Research Overview

Summary of Major Results

Control vs. Cerebrovascular Stroke Patients By having a control group of people who had no signs and symptoms of stroke and a group of people who 175

Figure 1. Control group consisted of less than 25 ng/ml NSE level (red). Study group had highest NSE level in 25.1 – 35 ng/ ml range, and some in greater than 35 ng/ml. Source: 1) Bharosay et al.


National Institute of Health Stroke Scale (NIHSS), and categorized into mild, moderate, and severe degree of disability. There was a high correlation between NSE levels and the degree of disability.

NSE levels and Neurological Worsening Neurological worsening was determined by comparing the NIHSS score at the time of admission and after 7 days of admission. If the score at 7 days was more than 2 points greater, the patient was categorized as having neurological worsening. There was a high correlation found between NSE levels and neurological worsening also. Conclusions and Discussion In this study, NSE levels were found to be increased greater levels in stroke patients than in normal individuals who had no sings or symptoms of stroke. Firstly, there are a number of studies, which use NSE as a biomarker, such as concussion studies, seizures, and last but not least stroke studies. NSE indicates to be a useful biomarker because it has a half-life of about 48 hours, and is released upon cell death â&#x20AC;&#x201C;apoptosis. Its ability to cross the blood brain barrier is important as it can now be detected in the blood and measured for diagnosis of acute stroke1. In the study done by Gelderblom et al., in vivo stroke animal models were used to measure NSE levels, and found that there were significant amounts of increased NSE in the stroke patients both in acute and ischemic6. Another study done by Hatfield and McKernan focused on NSE being a biomarker for ischemic stroke, and also found that post 3 days of stroke occurance, there were significantly elevated levels of NSE in the serum7. See figure 2. Therefore, there is significance to NSE levels after stroke and seems like the same hypothesis has been proven with multiple studies.

Figure 2. Source: Hatfield and McKernan. Increase levels of CSF NSE in ischemic stroke rats post 3 days of stroke.

NSE levels were also an indicator for the degree of disability, where a strong positive correlation was found between the NSE levels and degree of disability in Bharosay et al. Another study, by Pandey et al. looked at levels of NSE and also at the degree of disability. Pandey et al. using NSE and C-recactive protein (CRP) as biomarkers. CRP was used since it is normally not present in the blood, but is a targeted

production by the liver after stroke onset and released in the bloodstream, therefore this could potentially be a good marker for stroke in addition to NSE. This study is similar to Bharosay et al., since Pandey et al. also used the NIHSS scoring at the admission time and 7 days after stroke. It was found that both NSE and CRP levels were elevated in the bloodstream after stroke, but CRP levels were particularly elevated with the degree of disability. The more severe disability from stroke onset, the greater amounts of CRP in the blood8.

Conclusions

Neuron specific enolase (NSE) shows to be a very effective and important biomarker of stroke and other brain injury conditions. Numerous studies such as Bharosay et al., and Gelderblom et al. The importance of finding a good biomarker in serum is due to the fact that many countries do not have access to CT scan machines or MRI machines. Using a biomarker to detect stroke can be as simple as drawing blood from the patient and testing for NSE levels. Conclusions and Discussion This study by Bharosay et al., used a biomarker, specifically, neuron specific enolase (NSE) available in the cerebrovascular system, as it is found in the cerebrospinal fluid. Being easily accessible in the blood serum, an immunoassay was done. This is quicker than the typical CT or MRI scans that may take more time or simply the wait time to have these tests done is lengthy2,3. One of the strengths of this study is that the method of diagnosing stroke is very rapid. It saves time and costly machines are not needed. This would increase rates of quick treatment for patients, and decrease death rates from stroke due to not treating patient on time. A limitation of this study was that diagnosis of stroke using biomarkers occurs after the onset. A gap to fill for future directions would be to try and detect stroke early on before it actually occurs.5 NSE equally present in low amounts and moderatehigh amounts in stroke patients The results from Bharosay et al. are quite convincing that NSE is a good biomarker for detecting stroke, however a drawback for the paper was Figure 1, which is presented above. 67 cases of the study group have NSE levels below 25 ng/ml and 70 cases of the study group have NSE levels between 25-35 ng/ ml, and only 13 cases in the greater than 35 ng/ ml range. This can weaken the conclusion that NSE is indeed a good biomarker for stroke occurrence, since there were similar number of cases for NSE below 25 ng/ml and for 35-45 ng/ml. There is not a large statistical difference between the case numbers, suggesting that NSE can be both in low amounts and in moderate-high amounts in stroke patients2. miRNA as biomarker In addition, for future studies, the authors could target miRNAs in stroke patients that could differ from normal people, who have not had stroke. This can be done by collecting plasma from stroke patients and controls,

176


and isolating RNA using TRIzol reagent, as done in the study by Wang et al. Next, a microarray and qRT-PCR can be used to determine significant differences between the stroke patients and controls. The miRNAs that had 2-fold difference were chosen to be tested for biomarkers. By using SYBRGreen dye, out of all the miRNAs, it was found by Wang et al. that has-miR-1065b-5P and has-miR-4306 had significant increase in acute stroke patients as compared to controls. Looking at miRNA as biomarkers would be very good because certain miRNA can be specific to certain injuries and tissues/cells, or brain damage. In addition, miRNAs are also quite stable structures, making it easy to work with without having to worry about degradation or making cohort with other molecules. 3 NSE, on the other hand is an enzyme and authors can run the risk of NSE being degraded easily. Ubiquitin Fusion Degradation Protein 1 (UFD1) Another biomarker that could be used to detect stroke is ubiquitin fusion degradation protein 1 (UFD1) in blood samples and compare to it to cohort studies. A study by Allard et al. looked at a Swiss cohot, Spanish cohort, and North American cohort to compare. UFD1 was found to be elevated in all three cohorts and is also associated with brain injury, by being present in cerebrospinal fluid.4 UFD1 can be found in the blood stream, once there is damage to the blood brain barrier, allowing UFD1 to spill into the blood stream. Note, this could be a drawback to use as a potential biomarker, as brain injury does not necessarily guarantee damage of blood brain barrier.9 Glutathione S-Transferase-π (GST-π) Further, the researchers could look at trying to detect stroke by looking at a pattern or window of stroke occurrence. A study done by Turck et al. suggested looking at glutathione s-transferase-π, which was an elevated enzyme within 3 hours of occurrence of stroke in patients. It was an immediate increase in stroke patients as compared to controls. This could allow early treatment of thrombolysis, which would cause breakdown of clots.5 References 1. Saka, O et al. Cost of Stroke in the United Kingdom. Age and Ageing. (2009). 38: 27-32. 2. Bharosay, A et al. Correlation of Brain Biomarker Neuron Specific Neolase (NSE) with Degree of Disability and Neurological Worsening in Cerebrovascular Stroke. Ind J Clin Biochem (Apr-June 2012) 27(2): 186-190. 3. Wang, W et al. Circulating MicroRNAs as Novel Potential Biomarkers for Early Diagnosis of Acute Stroke in Humans. Journal of Stroke and Cerebrovascular Diseases. 23(10). (Nov-Dec 2014). 2607-2613. 4. Allard, L et al. Ubiquitin Fusion Degradation Protein 1 as a Blood Marker for The Early Diagnosis of Ischemic Stroke. Biomarker Insights (2007). 2: 155-164. 5. Turck, N et al. Blood Glutathione S-Transferase- π as a Time Indicator of Stroke Onset. Plos One. (Sept 2012). 7(9):1-9. 177

6. Gelderblom et al. Plasma levels of neuron specific enolase quantify the extent of neuronal injury in murine models of ischemic stroke and multiple sclerosis. Neurobiology of Diease. (2013) 59: 177-182. 7. Hatfield, R and McKernan, R. CSF neuron-specific enolase as a quantitative marker of neuronal damage in a rat stroke model. Brain Research. (1992) 577: 249-252. 8. Pandey, A et al. Neuron Specific Enolase and C-Reactive protein Levels in Stroke and its subtypes: Correlation with Degree of Disability. Neurochemical Research. (2014) 39: 1426-1432. 9. Laborde, C et al. Potential Biomarkers for Stroke. (2012) Expert Review of Proteomics. 9.4: 437-439.

Received April, 6, 2015; revised Month, ##, 200#; accepted Month, ##, 2013. This work was supported by Undergraduate Neuroscience ment for Science Education Research Foundation (EA). Dr. Amy G. Dala, and the nical assistance, execution,

The Association for the Development of Education (SRA & RLN), The Endow(EA), and The Synaptic State Faculty The authors thank Mr. Spine L. Cord, students in Neuroscience 101 for techand feedback on this lab exercise.

Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu


Divya Mamootil

Erasing Fear Memories– Is it possible?

Using Pavlonian conditioning, rats can readily learn to fear a neutral stimulus such as a tone when paired with an aversive stimulus like foot shock. This learned fear of the tone (CS) can be reduced by extinction, a process where fear responses decline due to the repeated presentations of the CS alone11. Sometimes, extinguished fear responses can be renewed with a change of context, and the hippocampus regulates this fear renewal following extinction3. The paper we will review by Stephen Maren (2014)8 explores the intermediary role of the hippocampus in novelty-induced fear. Rats were injected with the GABAA inhibitor, muscimol, or saline to see if they would remember extinguished fear with a novel stimulus or context. This study provides potential for eliminating fear memories in clinical applications, such as PTSD. Although it may not be possible to completely erase a painful memory, reducing its aversive effects on an individual can be of critical significance in psychological and medical fields. Here we review the main results of Maren’s research and examine related studies that have explored neural substrates involved in the renewal of extinguished fear memories. Key words: hippocampus; fear conditioning; PTSD; extinction; amygdala; muscimol; renewal; GABA; prefrontal cortex Background Fears that are maladaptive or inappropriate can be reduced through extinction training. Extinction is at the heart of exposure-based therapies, which are a main treatment choice for anxiety disorders2. However, studies have found that extinction cannot completely erase memories of the original tone-shock pair; instead, it temporarily masks the expression of the original fear memory and reduces fear responses2. Extinction is highly context-sensitive; for example, exposure to a CS outside of the extinction context often causes the renewal of fear. Lesion and inactivation studies have shown that the contextualization of extinction depends on the hippocampus15. Therefore, understanding the neural mechanisms of fear renewal may provide insight into the long term efficacy of exposure therapy. Along with the hippocampus, the amygdala and medial prefrontal cortex are also important brain regions that mediate fear learning, extinction, and renewal10. The amygdala is an important part of the brain for regulating one’s emotions and motivational behaviour. In relation to fear, Walker & Davis (2002)13 described the importance of NMDA and AMPA glutamatergic receptors in mediating fear learning. Their studies found that injecting the AMPA receptor antagonist, NBQX, into the basolateral amygdala led to less freezing behaviour in rats, whereas the NMDA receptor antagonist did not have this effect of inhibiting fear renewal. Therefore, AMPA receptors seem to be the most critical for expressing fear13. The medial prefrontal cortex interacts closely with the amygdala and is also involved in fear regulation. Lebron et al (2004)7 experimented with lesions in this brain region and found that lesions of the ventromedial prefrontal cortex resulted in poor extinction memory in rats. This led them to believe that the vmPFC has an important role in housing extinction neurons, which inhibit the expression of fear responses, such as freezing. Thus, many brain regions are involved in fear learning and the loss of fear; however, specific receptors and pathways are still being studied. Previous research by Cole et al (2013)2 studied the

kappa opioid receptors (KOR) in the hippocampus, which are associated with fear learning and anxiety. They found that the KOR antagonist norbinaltorphamine hydrochloride (norBNI) reduces fear renewal in rats when injected into the ventral hippocampus (but not the dorsal), compared to saline controls. Another study by Baker-Andresen et al (2013)1 looked at DNA methylation of BDNF exon IV in the medial prefrontal cortex of female mice (whom are resistant to fear extinction). This methylation reduced BDNF signalling that is essential to fear learning and memory. However, they found that the trkB agonist 7,8-dihydroxyflavone increases BDNF signalling and thus, blocks the return of fear in female mice after extinction training. These studies represent a novel approach to treating fearrelated anxiety disorders such as PTSD1, however, they are very invasive methods that are difficult to use in human clinical treatments. Other research has explored more non-invasive strategies such as the use of pharmacological drugs. Zelikowsky et al (2013)15 studied the effects of the drug Scopolamine, a cholinergic antagonist, in inhibiting the contextualization of fear extinction. They administered the drug systemically into the hippocampus in low doses, and it proved to significantly reduce fear renewal in both the original training context as well as a novel context. This drug also slowed the rate of long-term extinction memory formation. Therefore, low doses of Scopolamine may be combined with exposure therapy to make extinction more relapse-resistant. Similarly, Haaker et al (2013)5 administered a single dose of the dopamine precursor, L-dopa, and found that it makes extinction memories context-independent, thereby preventing fear renewal in both rats and humans. They predicted that extinction memory may be dopamine-dependent, so increasing dopamine levels may be promising for future anxiety therapies5. Thus, a plethora of previous studies have shown multiple factors that seem to be implicated in the retrieval of original fear memories and subsequent relapse of fear. Specific receptors and neurotransmitters involved in these processes need to be researched further. We will begin this review with a discussion of Stephen Maren’s experiments on hippocampus-mediated fear renewal. 178


Research Overview

Summary of Major Results

Maren used non-invasive experimental methods in this study through the injection of the drug muscimol, instead of employing mass lesions of the brain. Rats were first fear conditioned with a tone-shock pair, then learned to extinguish the fear a day later. Then they were injected with either the GABAA agonist muscimol or saline (control). Following the injection, rats were given a retrieval test in either the same or different context from extinction training. The researchers also presented a novel or familiar tone to the rats in a subsequent experiment. It was hypothesized that blocking the hippocampal pathway that detects associative novelty would inhibit fear renewal in rats. In experiment one (where the context was manipulated), saline-injected rats showed higher levels of freezing in the novel context compared to the context where the extinction occurred during the retrieval test. In contrast, the muscimol-injected rats had consistently low freezing behaviour in both contexts. In experiment two (where the conditioned stimulus was manipulated), saline-injected rats showed higher levels of freezing when the new conditioned stimulus was presented compared to the familiar one. The muscimol-injected rats showed similar behaviour but to a much lesser degree. In both cases, musicmol inactivated the hippocampal pathway that mediates fear renewal following extinction.

Figure 1. The visuals above indicate the extent to which rats retrieve previously extinguished fears in either the same or novel conditions. Since the muscimol injected rats can no longer detect novelty, they should have impaired memory for previously learned fears in the novel conditions, as shown in Figures A) and B).

Conclusions and Discussion The results of Marenâ&#x20AC;&#x2122;s experiment fall in line with those of the previously discussed studies, since they all involve blocking receptors and signaling pathways in the hippocampus to prevent the renewal of fear. Rats will respond strongly to novelty, but the GABAA agonist, muscimol, inhibits the normally heightened response to novel stimuli. Therefore, there seems to be a strong correlation between the hippocampusâ&#x20AC;&#x2122; detection of novelty and fear renewal, because when the hippocampus is inactivated the fear response declines or disappears entirely. Since the hippocampus is very important for spatial memory, it is no surprise that it has a preference for detecting novelty of context compared to stimuli. Both the dorsal and ventral hippocampus seem to be involved in fear renewal, as previous studies have found relevant receptors and pathways in both areas2,8. As mentioned in the background, fear extinction is most likely an inhibition or down regulation of processes rather than the erasure of fear memories. Therefore, research should continue to focus on long-lasting suppression of fear renewal pathways rather than find ways to eliminate fear memories10. Studies on inhibition of fear renewal are extremely important to understand if we want to help patients with anxiety cope with their unwanted feelings of worry. One of the most salient pieces of information we intake when we encounter a traumatic experience is the place or context where it took place. This is why people with PTSD and other anxiety disorders feel overwhelmed when they come across situations similar to the context they originally encountered the aversive experience in. Essentially, they experience a fear renewal, and this response is very difficult to eliminate once the individual has gone through a panic attack. In fact, the failure to inhibit fear is a triggering factor in the development of PTSD1. Although much progress has been made in this field of research, more studies need to be done to investigate the details of the fear renewal pathways. Determining the underlying mechanisms of fear renewal can help us develop treatments that weaken or completely erase learned fears and memories of traumatic experiences in the future.

Table 1. The two graphs above show the freezing behaviour of saline vs. muscimol injected rats with a familiar (white) or novel (grey) stimulus/context. The first graph shows results from experiment 1, while the second graph depicts results from experiment 2. The differences in behaviour for the familiar conditions were not statistically significant.

179


Criticisms and Future Directions Further research should prompt experimenters to look at how the time of muscimol administration affects the renewal of fear memories. Wang et al (2014)14 did a study where rats were given high doses of corticosterone, and this resulted in an inhibition of the renewal of fear by reducing anxiety levels. They examined the temporal context of injecting corticosterone by using different time delays, such as 1 or 24 hours after the fear conditioning, and in both cases there was reduced renewal of fear. Also, one of the limitations of Maren’s paper was that the researchers only studied short term effects of muscimol on renewal of fear. On the other hand, Wang et al. looked at long term effects of inhibition by assessing anxiety levels in rats a week later through an elevated arm maze task, which continued to result in inhibition of fear renewal. In future studies, the researchers should test how long the hippocampal inactivation lasts by doing more trials over a week or two, so that even if the fear is inhibited in the initial trial, they will know how long it will resist renewal despite various changes in stimulus/context. Although Maren’s paper studied dorsal hippocampal inactivation in suppressing the return of fear, they could study other areas of the brain that are involved in fear renewal. For example, Sharpe and Killcross (2015)12 studied how inactivation of the prelimbic cortex can also inhibit the renewal of fear in novel contexts. They used muscimol and saline injections as well, and varied the time of injection (during or after extinction). They found that rats with lesions in the prelimbic cortex exhibited less freezing in the novel context, similar to the dorsal hippocampal inactivation in the original paper by Maren. Parallel studies by Orsini et al (2011)9 looked at the how projections of the ventral hippocampus and prelimbic cortex to the basolateral amygdala mediate context-dependent fear renewal. They used a retrograde tracer for c-Fos expression in this pathway and found high expression of c-Fos when fear is renewed in a new context. However, inhibiting projections to the basolateral amygdala eliminated this fear renewal. Finally, many neurobiological methods such as stereotactic lesion and pharmacological drug injections have been discussed as non-invasive ways of exploring the renewal of extinguished fear memories; however there are other approaches that can be used to study this issue as well. For example, Drexel et al (2014)4 used a psychological viewpoint to study inhibition of fear renewal through exposure therapy, by exposing the aversive stimuli to the patient on a regular basis so that they get used to it and no longer perceive it as a threat. This kind of method can be used in future studies by exposing the rats to the previously conditioned fear stimulus and different variations of that stimulus or the context it was in after the extinction phase. In this way, even if the context changes or there’s a slight change in the stimulus itself, the rats will longer be affected by it, and there won’t be a renewal in extinguished fear response.

Figure 2 This figure from the paper by Jingji & Maren (2015)6 shows the injection of various dyes and markers in the brain where BA-projecting neurons are red, PL-projecting neurons are green, and Fos-positive neurons are blue. You can see from the merge that Fos is being expressed in the PL to BA projection pathway, and the same results are seen in the VH to BA pathway.

References 1. Baker-Andresen, D. et al. Learn Mem 20, 237-240 (2013). 2. Cole, S. et al. PLos ONE 8: e58701. doi:10.1371/journal. pone.0058701 (2013). 3. Delamater, A.R. et al. J Exp Psychol Anim Behav Process 35, 224-237 (2009). 4. Drexler, S. M. et al. Behav Neurosci 128, 474-481 (2014). 5. Haaker, J. et al. Proc Natl Acad Sci 110: e2428-2436. doi:10.1073/pnas.1303061110 (2013). 6. Jingji, J. & Maren, S. Scientific Reports 5: 8388. doi:10.1038/srep08388 (2015). 7. Lebron, K. et al. Learn Mem 11, 544-548 (2004). 8. Maren, S. Neurobiol Learn Mem 108, 88-95 (2014). 9. Orsini, C.A. et al. J Neurosci 31, 17269-17277 (2011). 10. Palomares-Castillo, E. et al. Brain Res 1476, 211-234 (2012). 11. Sah, P. & Westbrook, R.F. Nature 454, 589-590 (2008). 12. Sharpe, M. & Killcross, S. Neurobiol Learn Mem 118, 20-29 (2015). 13. Walker, D.L. & Davis, M. Pharmacol Biochem Be 71, 379-392 (2002). 14. Wang, H. et al. Pharmacol Biochem Be 124, 188-195 (2014). 15. Zelikowsky, M. et al. Biol Psychiat 73, 345-352 (2013). This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Divya Mamootil, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Divya Mamootil, Human Biology Department, University of Toronto, Toronto, CA Email: divya. mamootil@mail.utoronto.ca Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program

180


Bridging the Gap in Traumatic Brain Injury: The promise of the Collagen Matrix

Catherine B. Matolcsy

Traumatic brain injury (TBI) is a multifaceted pathophysiology that kills or leaves millions of individuals with mental deficits worldwide each year. TBI affects more men than women, which is typically attributed to its association with impulsive decision-making and behaviour. TBI can be classified as a dual-insult pathology, whereby the primary injury occurs due to mechanical force being applied to the head as a whole or a localized region, and a temporally delayed and spatially more diffuse inflammatory and metabolic insult to cells in surrounding and functionally connected areas. Current treatment options for traumatic brain injury focus on preventing further deterioration, aiming to inhibit the action of the secondary metabolic insult, such as ensuring adequate blood flow, oxygenation, and scanning for stray skull fragments or foreign objects. Very little can be done currently to reverse or rehabilitate deficits resulting from primary impact. Current animal model studies focus on anti-inflammatory based minimization of tissue loss, as well as neurotrophic and stem cell therapies to promote migration and reintroduce new cells into the lesioned area to conceivably improve behavioural and cognitive abilities post-trauma. Exogenous collagen matrix grafting has proven to be a promising mechanism to promote recovery of endogenous cells in many somatic systems, including bone, teeth, liver and bladder. Most recently, collagen grafts have been employed following brain injury in rodents and have resulted in encouraging outcomes including cognitive improvement. Key words: collagen matrix graft, traumatic brain injury (TBI), controlled cortical impact (CCI), spatial memory, Morris water maze (MWM), spatial learning, motor function, neurotrophic factors, glial scar, induced pluripotent stem cells-(iPSCs) Background TBI is a top cause of death in individuals under 35 years of age in developed countries, yet very few treatment options are available. TBI, which encompasses penetrating and non-penetrating occurrences of severe mechanical force applied to the head, is often characterized by neuronal loss, inflammation, and neurological deficits both acutely and long-term.1 Researchers have focused on providing a steppingstone for neuronal tissue to repair itself and to allow the tissue to potentially reform connections that were lost due to injury. Some have focused on purely structural models2, whereas others have integrated known neurotrophic factors and or stem cells into their constructs.2,3,4,5 Alternative approaches include noninvasive anti-inflammatories, beta-adrenoreceptor antagonists, and even cognitive-rehabilitation.6,7,8,9 Shin et al. elucidate the benefits of an exogenous bovine collagen scaffold in a rodent model following controlled cortical impact (CCI), which is used as a model of TBI.1 The results suggest a decrease in injury size due to increased neuronal survival, and ameliorated spatial learning in treated vs. non-treated TBI mice.1 Collagen has intrinsic abilities to aid in neuronal survival, and cellular migration, yet whether this is the means of action of collagen in ameliorating outcome is yet to be confirmed.2 No exogenous growth factors are used to promote regeneration in this study. These findings demonstrate a progressive advance in the field, they give hope that matrix grafts are beneficial in TBI, but leave many questions unanswered. Shin et al. have managed to answer the ‘what’ of the effects of collagen matrices in TBI but have not yet tackled the ‘how’. The field must work to elucidate the mechanisms underlying these benefits and seek further ways to ameliorate the efficacy of the grafts, potentially incorporating other therapeutics or technologies. 181

Research Overview

Summary of Major Results and Discussion

Experiments were carried out in male rats. Four cohorts were used; TBI rats with collagen matrix graft treatment (IC), sham surgery rats with collagen matrix graft treatment (SC), TBI rats with no treatment (IN) and sham rats with no treatment (SN). TBI was induced under anesthesia using craniectomy CCI procedure; CCI exposes brain tissue by disrupting the meninges; thus facilitating collagen matrix graft implantation.1 II.i MOTOR FUNCTION In beam balance and beam walking tests for motor function, IN and IC performed equally poorer than both SC and SN rats.1 However, no significant difference between IN and IC, or SC and SN, confirming that collagen implantation does not intrinsically alter motor function in days 1-5 post injury. Beam time was normalized to a pre-treatment trial time on an individual basis.1 Further precautions to ensure equivalent motor capabilities between groups included measurement of swim speeds, which were similar in all cohorts. Other treatment approaches have accomplished amelioration not limited to cognitive function but also including motor function. Introduction of an enriching environment versus a standard environment during recovery promotes cognitive & motor rehabilitation. Furthermore, introducing iPSCs into lesion site one week post trauma have proven more effective than collagen grafts in promoting motor function recovery aswell.8 II.ii SPATIAL MEMORY & RETENTION Amelioration in spatial memory and retention was observed with collagen implantation, as was assessed by a hidden platform Morris water maze. IC rats localized a submerged platform in reduced time versus IN


rats (Figure 1).1 A probe trial, whereby animals were placed in the MWM from which the platform had been removed, was used as a measurement of memory retention, where longer time spent in the correct quadrant equates to better retention. IN and IC spent equally less time in the correct quadrant versus both SC and SN rats.1 Spatial memory retention is distinct from spatial memory not only temporally but also by the structural and anatomical cortical connectivities being employed. Retention relies on a more expansive circuitry within the hippocampus, meaning on a crude level, it requires more functionally intact hippocampi than spatial memory formation alone. Specific areas of the hippocampus, especially the CA3 and longitudinal axons of these cells connecting them to one another in CA3-CA3 networks, as well as in connecting CA3-CA1 neurons are essential for spatial memory retention.10 These details indicate that potentially not only cell number should be considered but also the functionality of their connections, as the number of cells present does not fully encompass the function of the hippocampus. Swim speed tests were revisited to confirm differences in MWM performance were not due to motor capability disparities.1 No significant variations in speed were noted between groups, eliminating ability to swim as an explanation of differences in performance.

both reduced versus SN and SC, as expected (Figure 3).1 The improvements in cell numbers are significant yet remain substantially reduced versus sham-surgery mice, being that IC remained approximately 35-40% below sham levels in hippocampal neuron count. To ensure lesion volume reduction did not result due to increased glial scarring, GFAP staining of astrocytes at injury site was performed. No differences in IN versus IC astrocyte number or morphology were observed in the pericontusional regions indicating that no extensively abnormal glial scaring was visible due to collagen graft impantation.1 This however, does not dismiss the potential involvement of astrocytes or other glial cells in the recovery and increased rehabilitation in collagen graft treated rats. Ensuring that glial scaring, which is typically known to contain injuries within boarders in the central nervous system, did not increase following collagen graft implantation does not eliminate their possible involvement, as it only measures their level and morphology at a distinct time point well into the recovery process (19d). It can be postulated that potentially collagen provides a means of attracting and promoting scar formation more quickly and efficiently, resulting in less penumbral damage and less spread of injury.11,12 Therefore, not necessarily resulting in any heterogeneity of the glial scar at 19 days post-trauma yet, variations may be visualizable at an earlier time point in recovery. Further studies with earlier sacrifice would allow the definitive rejection of astrocytes as an involved party in the differences in recovery between IN and IC groups. Finally, trichrome staining of lesion site slices was used to visualize remnants of exogenous collagen. No collagen matrix remained bordering the CCI site. Many other studies have provided similar reductions in lesion volume and increased neuronal survival employing both collagen and other ECM molecules in various cortical injury models including stroke and surgical brain trauma .7,9 Conclusions and Discussion

Conclusions Figure 1. Spatial memory assay using MWM task. Collagen matrix treatment rats locate hidden platform in less time than non-treated rats, demonstrating better spatial memory in IC versus IN cohorts..1

II.iii LESION SITE PROPERTIES Post-mortem dissections were fixed, sliced and coverslipped for lesion volume studies using light microscope. Lesion volume was significantly reduced in IC versus IN rats (Figure 2). Although lesion volume reduction seems triumphant at first appraisal, it is possible that scar tissue, or non-functional cell types have infested the penumbral region of the injury, resulting it what appears to be a less extensive lesion. However, this maintenance of tissue correlated to enhanced neuronal survival/migration as CA1 and CA3 hippocampal neuron numbers were significantly higher in IC versus IN, yet

Improvements in spatial memory, hippocampal cell number and reduced lesion volume have all been attained using collagen matrix grafting in a rat model following TBI.1 Stem cells and environmental stimulation have proven advantageous in motor function recovery.8 The field of TBI treatment is divided by multiple approaches which seek therapeutics stemming from various disciplines including, cellular, molecular, behavioural and pharmacological strategies. Historically, medicine has demonstrated that a unification of methodologies typically proves superior to any single approach alone, this should be considered in future studies.

Criticisms and Future Directions

Much potential exists in the field of TBI treatment for question and explanation that must be addressed by future research. Firstly as mentioned throughout the literature, head injury leading to TBI is not typically predicted, and is typically not treated immediately after 182


Figure 2. Tissue lesion after sacrifice,19 days post-injury. Collagen graft treatment (B) resulted in reduced lesion volume versus non-treatment group (A). Quantified lesion volume differences are significant (C).1

Figure 3. Hippocampal CA1 and CA3 neuronal cell numbers. Both CA1 (A) and CA3 (B) neuronal counts were significantly less diminished in IC versus IN cohorts, however cell number remained significantly decreased in IC verus SN.1

the injury occurs. Shin et al. used an experimental design whereby the grafts were implanted immediately following controlled cortical impact (CCI), which would be highly unlikely to replicate in clinical application of the technique.1,2 This time delay in implantation would foreseeably affect the efficacy of the treatment. Certain studies have allowed between 24 hours and 7 days time between injury and surgical implantation.2,5 183

Future experiments should allow a reasonable time delay, congruent with what would be observed in human clinical application, before treatment application. Secondly, as data regarding cell numbers and growth was only measured at one time point, which was considered the end of the study, the progression of the cellsâ&#x20AC;&#x2122; migration and integration into the


grafted area was not fully tracked. The Shin et al. study investigated only the absolute number of neurons present after the allotted time post-injury had passed, others have used multiple staining and visualization techniques to localize exact cell types at and around the lesion and graft site.2 Factors such as von Willebrand factor(vWf), NeuN, DCX and Tau-1 have been utilized by other members of the field to visualize endothelial cells, neurons, neural progenitors and axons respectively.2 Capturing only the final result of implantation of this graft fails to explain the progression of how cells came to be more numerous in the case of a collagen graft implantation. Additionally the study failed to explain why collagen was so efficacious as a matrix for minimizing injury in TBI. The authors hypothesized that this could be attributed to collagenâ&#x20AC;&#x2122;s intrinsic tendency to stimulate neurogenesis through its degradation by other cell types, which other applications of collagen have demonstrated in the past.1,4,7 Using techniques that allow the elucidation of interactions between collagen and the surface receptors on the cells interacting with collagen would allow for a more conclusive argument regarding its function in this model. The effect of collagen in this study however, due to itâ&#x20AC;&#x2122;s immediate introduction post trauma, could possible be due to an inherent anti-inflammatory property that would not prove clinically relevant, as immediate implantation is not realistic. Comparison of the effects of collagen scaffold graft to the effects observed by a known substance that prevents inflammation, and immune system mediated propagation of damage, such as statins, progesterone, PPAR agonists, or minocycline would aid in explicating the effects of collagen.11 Finally, the world of regenerative medicine is becoming increasingly more focused on stem cell therapy and an inter-disciplinary approach. Past research has demonstrated that the benefits of incorporating more pro-growth factors in the injury site along with a graft.2,4, as well as stem cell treatment in combination with collagen scaffolding results in lesser inflammation and cytokine response.5 Future investigations regarding graft implantation with neural and perivascular stem cells, and potential neurotrophic factors would aid to bridge the gap between cellular and molecular therapeutics.3,5,11

5. De Freitas, H.T. et al. (2015) Effect of the treatment of focal brain ablation in rat with bone marrow mesenchymal stromal cells on sensorimotor recovery and cytokine production. J Neurol Sci. 348(1-2):166-73. doi: 10.1016/j. jns.2014.11.032 6. Park, H.Y., Maitra, K., Martinez, K.M. (2015) The Effect of Occupation-based Cognitive Rehabilitation for Traumatic Brain Injury: A Meta-analysis of Randomized Controlled Trials. Occup Ther Int. [Epub ahead of print] doi: 10.1002/oti.1389. 7. Huang, K.F., Hsu, W.C., Chiu, W.T., Wang, J.Y. (2012). Functional improvement and neurogenesis after collagen-GAG matrix implantation into surgical brain trauma. Biomaterials. 33(7): 2067-75. doi: 10.1016/j.biomaterials.2011.11.040. 8. Dunkerson, J. et al. (2014) Combining enriched environment and induced pluripotent stem cell therapy results in improved cognitive and motor function following traumatic brain injury. Restor Neurol Neurosci. 32(5):675-87. doi: 10.3233/RNN-140408. 9. Ning, R. et al. (2014) Neamine induces neuroprotection after acute ischemic stroke in type one diabetic rats. Neurosci. 257:76-85. doi: 10.1016/j.neuroscience.2013.10.071. 10. Steffenach, H.A., Sloviter, R.S., Moser, E.I., Moser, M.B. (2002) Impaired retention of spatial memory after transection of longitudinally oriented axons of hippocampal CA3 pyramidal cells. Proc Natl Acad Sci. 99(5):3194-8. 11. Kumar, A., Loane, D.J. (2012) Neuroinflammation after traumatic brain injury: opportunities for therapeutic intervention. Brain, Behaviour, and Immunity. 26(8):1191-1201. doi: 10.1016/j.bbi.2012.06.008 12. Burda, J.E., Bernstein, A.M., Sofroniew, M.V. (2015) Astrocyte roles in traumatic brain injury. Exp Neurol. [Epub ahead of print] doi: 10.1016/j.expneurol.2015.03.020. This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise.

References 1. Shin, S.C., et al. (2015) Neuroprotective effects of collagen matrix in rats after traumatic brain injury. Restorative Neurology and Neuroscience. [Epub ahead of print] doi: 10.3233/RNN-140430 2. Elias, P.Z., Spector, M. (2012) Treatment of penetrating brain injury in a rat model using collagen scaffolds incorporating soluble Nogo receptor. Journal of Tissue Engineering and Regenerative Medicine. 9:137-150. doi: 10.1002/term.1621 3. Crapo, P.M., Tottey, S., Silvka, P.F., Stephen, F. (2014) Effects of biological scaffolds on human stem cells and implications for CNS tissue engineering. Tissue Engineering. 20(1-2):312-23. 4. Han, S. et al. (2015) The linear-ordered collagen scaffoldBDNF complex significantly promotes functional recovery after completely transected spinal cord injury in canine. Biomaterials. 41:89-96. doi: 10.1016/j.biomaterials.2014. 11.031.

184


The potential for epigenetic treatment of neuropsychological disorders. Lucy McPhee

Epigenetics are a rising area of research for neuropsychological disorders such as depression, Alzheimerâ&#x20AC;&#x2122;s Disease and Huntingtonâ&#x20AC;&#x2122;s Disease. Hypermethylation of genes can lead to reduced expression by the formation of heterochromatin. By determining which genes of interest are differentially methylated from the average, it is possible to determine which genes are being underexpressed leading to the disordered phenotype. This leads to the potential for epigenetic treatments for neurological disorders. The most studied and most promising of these is histone deacteylase inhibitors, which are currently most commonly studied in cancer research. Other treatments which warrant more research include DNMT inhibitors and non coding RNAs. Key words: neuropsychological disorders; epigenetics; methylation; Histone deacetylases (HDAC); HDAC inhibitors Background Neuropsychological disorders are often discussed in psychology and neuroscience through changes in structure and activation, or neurotransmitter levels seen in the brain of disordered individuals, but it is not clear why or when these changes occur (Schwartz and Monk, 2014). With an average age of onset of 12 years, anxiety disorders are likely rooted in childhood, but much more research still needs to be done to determine the real cause. A promising epigenetics study of the amygdalas of young, anxious temperament disorder rhesus monkeys opens up the possibility that methylation of genes in development may be a factor in ATD and later anxiety disorders (Alisch et al., 2014). Epigenetics are not a part of the actual genetic code, but can be maintained through mitotic division, and can therefore affect an entire cell type or area (Mensaert, et al. 2014). DNA methylation is the most commonly studied variety of epigenetic modification, and it also the area examined in the aforementioned paper. In general, hypermethylation leads to reduced gene expression which is more often the cause of disorder than hypomethylation. This is a fairly new area of study when it comes to mental disorders, but several other studies have also implicated that epigenetics are involved. It is difficult because brain tissue is required to run epigenetic tests, so most work is done in animal models. However there have been human twin studies that implicate epigenetics in major depressive disorder (Davies et al., 2014), and other human studies have suggested that changes in genetic methylation are related to schizophrenia diagnosis (Chase et al., 2013). The current gold standard of determining epigenetic modifcations is whole genome bisulphite sequencing (WGBS), which detects hydroxymethylation of cytosines in the genome with good resolution. Analysis involved comparison of CpG regions to the average to determine whether they are hyper- or hypo-methylated (Mensaert, et al. 2014). The drawbacks of this technique are that it is very expensive and not very efficient. However it does provide a chance to identify epigenetic areas for risk for mental illness, which could lead to pharmacological treatments. The main treatment focus currently is on histone deacetylase (HDAC) inhibitors, which can reverse hypermethylation. These molecules reduce DNA methylation and 185

can open up chromatin structure leading to enhanced gene expression (Narayan & Dragunow, 2009). Research Overview

Summary of Major Results

Anxious temperament (AT) rhesus monkeys were analyzed for differential methylation of the amygdala using reduced representation bisuphate sequening by Alisch et al. AT phenotype was associated with hypermethylation and reduced gene expression of BCL11A and JAG1 genes. BCL11A is a downstream glutamate receptor effector that plays a role in neurite branching. JAG1 is a NOTCH receptor which is involved in plasticity and the formation of spatial memories. Sites on these genes with the most statistically different methylation patters look as though they will impact binding sites, or noncoding RNA regulatory sites (Alisch et al, 2014). Using immunoprecipitation and ultra-deep sequencing, Davies et al discovered that the gene ZBTB20 is hypermethylated in individuals with major depressive disorder. It normally plays a role in the development of the hippocampus, long term potentiation and NMDA receptor functioning. This method is not as reliable as the gold standard of bisulphate sequencing, but it uses periphery blood samples instead of brain tissue and can therefore be used in living patients (Davies, 2014). Schizophrenia is the mental illness which is most commonly associated with gene transcription errors. Using post mortem immunoblotting, Chase et al found increased methylation of the gene H3K9 in individuals with schizophrenia compared to controls. H3K9me2 can lead to formation of even more heterochromatin, further silencing genes in the parietal cortex, which could be an explanation for the disordered thought and disrupted sensory perception observed in many individuals with schizophrenia (Chase et al, 2013). Low transcription levels of reelin is one of the most commonly found signs in post mortem analysis of schizophrenia patients, which is important in cortical development and hippocampal functioning via interaction with NMDA receptors. Hypermethylation of the reelin promoter has been observed in schizophrenia patients, which is thought to be the cause of the low


expression of reelin, suggesting it may be a potential cause of schizophrenia itself (Grayson, et al., 2006). As reduced gene expression due to hypermethylation seems to be a possible cause for neuropsychological disorder, new treatment theories are emerging which attempt to reverse harmful methylation and return gene expression to normal. One of the most popular mechanisms for this is HDAC inhibitors, such as valproic acid (VPA), which reduce the removal of methyl groups from histones (Figure 1), allowing increased access to transcription factors (Fuchikami et al, 2015). HDAC expression increases with age, and inhibitors have demonstrated the ability to help protect aging axons from damage and ischemic injury in the optic nerves of mice (Baltan, 2012). They have also been used as a treatment for transgenic Huntington Disease mice. This study found that the HDAC inhibitor treatment led to beneficial changes in cognition and motor function compared to controls (Figure 2). The main systems affected seem to the related to ubiquitin, which is important in homeostasis, division, and neuronal functioning (Jia et al, 2012). In mouse models, HDAC inhibitors have been shows to have antidepressant effects, even more so when combined with SSRI treatment (Schroeder, et al., 2007). Conclusions and Discussion

Conclusions

These preliminary studies suggest that hypermethylation of genes related to neuronal growth and differentiation may be responsible for part of the pathology of neuropsychological disorders. Methylation levels in general or for specific genes are correlated with affect in all of the discussed disorders. Following from this theory, demethylation of genes is a possible novel treatment for these disorders. Histone deacetylase inhibitors have been suggested as a possible method through which this could be achieved, but

Figure 1: DNA methylation and histone acetylation (Narayan & Dragunow, 2010)

there is still much to be learned. However this field holds the potential to understanding the genetic and molecular causes of neuropsychological disorders, which are currently very much in the dark. The most popular area of epigenomic research right now is in cancer treatment, where the goal of the treatment is to kill off the cancer cells to treat the patient (Minucci & Pelicci, 2006). This method does not translate well to neuropsychological disorder treatment, because neuronal death is much more likely to be the cause of the disorder than any helpful treatment. Therefore new methods must be created in order to use epigenetics to treat neurological disorders.

Criticisms and Future Directions

While there is increasing research into the theory that hypermethylation may be a cause of these disorders, there is a dearth of research related to possible treatments if this is the case. Most studies indicating promising

Figure 2: Treatment with HDAC inhibitor improved open field test activity in HD mice (Jia, et al., 2012). 186


effects use animal models, but a clinical study treating Alzheimer’s Disease patients with valproic acid showed a worsening of aggressive symptoms compared to a control. However AD is a very complex disease with many molecules involved, this one trial does not mean that HDAC inhibitors will never work for any neurological disorder (Narayan & Dragunow, 2010). Further trials are needed, both animal and human, for all neuropsychological disorders before this can be considered as a useful therapy possibility. A recurring problem with HDAC inhibitor treatments is that they often have trouble bypassing the blood brain barrier (BBB). One recent study addresses this problem by developing BBB permeable HDAC inhibitors, which would reduce the doses needed for effective treatment if this does become a neuropsychological therapy in future (Seo et al., 2014). DNA methyltransferase (DNMT) inhibitors are also an area of interest in epigenetic treatments. They have been shown to stop apoptosis in cultured mouse motor neurons, which is promising, but there is very little research on their potential for neurological disorder treatment (Chestnut, et al., 2011). DNMTs have been implicated in the GABA hypothesis of major depression, but no studies have been done investigating antidepressant effects of DNMT inhibitors (Luscher, et al., 2011). Non coding RNAs are also being developed, which can help stop pathological mRNA expression, but this is an even newer field which needs further exporation as well (Qureshi & Mehler, 2013). References 1. Alisch RS., Chopra, P., Fox AS., Chen K., White ATJ., Rosebloom PH., Keles S., Kelin NH. (2014). Differentially Methylated Plasticity Genes in the Amygdala of Young Primates are Linked to Anxious Temperament, an at Risk Phenotype for Anxiety and Depressive Disorders. The Journal of Neuroscience, 34(47), 15548-15556. 2. Baltan S. (2012) Histone deacetylase inhibitors preserve function in aging axons. J Neurochem. 123(S2):108-115. 3. Chase KA., Gavin DP., Guidotti A., Sharma RP. (2013) Histone methylation at H3K9: evidence for restrictive epigenome in schizophrenia. Schizophren Res. 149(1-3):15-20. 4. Chestnut BA., Chang Q., Price A., Lesuisse C., Wong M., Martin LJ. (2011) Epigenetic regulation of motor neuron cell death through DNA methylation. J Neurosci. 31(46):1661916636. 5. Davies MN., Krause L., Bell JT., Gao F., Ward KJ., Wu H et al. (2014) Hypermethylation in the ZBTB20 gene is associated with major depressive disorder. Genome Biol. 15(4):R56 6. Fuchikami M., Yamamoto S., Morinobu S., Okada S., Yamawaki Y., Yamawaki S. (2015) The potential use of histone deacetylase inhibitors in treatment of depression. Prog Neuro-Psychopharmacol Biol. Psychiatry. In press S02785846(15) 7. Grayson DR., Chen Y., Costa E., Dong E., Guidotti A., Kundakovic M., et al. (2006) The human reelin gene: Transcription factors (+), repressors (-), and the methylation 187

switch (+/-) in schizophrenia. Pharmacol Ther. 111(1):272286. 8. Jia H., Kast RJ., Steffan JS., Thomas EA. (2012) Selective histone deacetylase (HDAC) inhibition imparts beneficial effects in Huntington’s disease mice: implications for the ubiquitin – proteasomal and autophagy systems. Human Molecular Genetics. 21(24):5280-5293 9. Luscher B., Shen Q., Sahir N. (2011) The GABAergic deficit hypothesis of major depressive disorder. Mol Psychiatry. 16(4):383-406. 10. Melucci S., Pelicci PG. (2006) Histone deacetylase inhibitors and the promise of epigenetic (and more) treatments for cancer. Nat Rev Cancer. 6(1):38-51. 11. Mensaert, K., Denil S., Trooskens G.,Van Criekinge W., Thas O., De Meyer T. (2014) Next-Generation Technologies and Data Analytical Approaches for Epigenomics. Environmental and Molecular Mutagenesis. 55:155-170. 12. Narayan P., Dragunow N. (2009) Pharmacology of epigenetics in brain disorders. British Journal of Pharmacology. 159:285-303. 13. Qureshi IA., Mehler MF. (2013) Developing epigenetic diagnostics and therapeutics for brain disorders. Trends Mol Med. 19(12):online. 14. Schroeder FA., Lin CL., Crusio WE., Akbarian S. (2007) Antidepressant-like effects of the histone deacetylase inhibitor, sodium butyrate, in the mouse. Biol Psychiatry. 62(1):55-64.


Distinguishing the neurobiological features of resilient cognition in Alzheimer’s Disease

Amaara Mohammed

The presence of neuropathological plaques and tangles in the aging population has long been associated with Alzheimer’s Disease (AD). Yet, this pathology does not always result in impaired cognition. This article reviews the neurobiological differences found in the resilient cognition of those with AD pathology. Several synaptic, cellular and biochemical features were found to be distinct in those with resilient cognition and those with AD Dementia. Key words: Alzheimer’s Disease; Synaptophysin; Synaptopodin; Cognition Background The neurodegenerative disorder Alzheimer’s Disease (AD) is currently the most common cause of dementia and affects millions of people around the world.¹ There are multiple risk factors associated with AD, including genetic factors, hypertension, diet and most significantly, age. Individuals over the age of 65 are most vulnerable to the disease and at this point, the risk increases every 5 years.¹ Alzheimer’s Disease was first described over 100 years ago by Alois Alzheimer in Germany, characterising the first case with memory impairments and the presence of neuropathological plaques and tangles, which today, are major indications of the disease.² Progressive memory loss is the clinical trademark of AD but eventually, cognitive function also deteriorates.³ The neuropathological trademarks of AD involve the accumulation of β amyloid (Aβ) proteins expressed as plaques and the phosphorylation of tau proteins expressed as neurofibrillary tangles.³ The formation of these plaques and tangles are estimated to begin 20 years before clinical symptoms arise.² MRI studies have shown the association of AD with hippocampal atrophy, however, it remains difficult to distinguish from other forms of dementia.⁴ However, this pathology is also known to be present without the impairment of cognitive function.⁵ Recently, there has been a number of studies investigating this incongruity between pathology and cognition, all of which reported similar dissonance, remarkably in older individuals.⁶⁻⁸ It was found that one third of older individuals have plaques and tangles that meet the National Institute on Aging criteria for the likelihood of developing AD, despite them having normal cognition.⁹⁻¹⁰ There is evidently a spectrum or range of brain pathology that occurs amidst cognitive function: there are those with healthy cognition with no signs of neurodegeneration, those with intact cognition despite evidence of AD pathology and those with impaired cognition with AD pathology.¹¹ While this inconsistency between pathology and cognition has been recognised for many years, there has been little postmortem examination into the the neurobiological factors responsible. Arnold et al. (2013) describe and identify the cellular, biochemical and synaptic composition that distinguishes resilient cognition in the presence of AD pathology.

Research Overview

Summary of Major Results

After characterising cognition levels and clinical diagnoses of participants annually, brain autopsies and neuropathological diagnoses of AD were made. Participants were grouped according to pathology and cognition including those with high cognition but highest quartile for pathology were categorised as “AD Resilient”, those with low cognition and high pathology as “AD Dementia” and those with high cognition scores and low pathology as “Normal Comparison” (NC). After measuring the densities of Aβ plaques and PHF-tau tangles in the mid frontal gyrus cortex, it was found that these densities were considerably larger in the AD-Resilient and AD-Dementia groups than in the NC. While the differences were not very significant, overall brain weight of AD-Dementia group were lower than the others, and NeuN neuron density of NC group was lower than that of the other two groups. The densities of GFAP astrocyte in AD-Resilient was greater than those of AD-Dementia and NC groups. The AD-Dementia group showed low measures of postsynaptic spine count densities and presynaptic vesicle synaptophysin immunoreactivity while they were retained in the AD-Resilient and NC groups (Fig. 1). In an attempt to investigate the relation between the pathologic lesions with neurons, astrocytes and synapses, Aβ plaques were also positively correlated with GFAP astrocytes but negatively correlated with NeuN neurons, synaptopodin spines and synaptophysin immunoreactivity. PHF-tau tangles were negatively correlated, most significantly with synaptopodin spines and positively correlated with GFAP astrocytes. The antibody microarray analysis showed a clear distinction between the groups. There was a tight congregation of proteins in the NC group while it was more dispersed in the other groups, suggesting a clear distinction in the protein expression profile of healthy brain tissue from those with AD pathology. 16 proteins were identified, distinguishing the AD-Resilient and AD-Dementia groups. These results indicate a clear distinction of the cellular, synaptic and biochemical features of resilient cognition in AD pathology from dementia and controls. 188


Fig 1. Photomicrographs illustrating the immunostained appearance of typical case from each group. Graphs representing the means along with standard of error bars. A: Aβ plaques, B: tau neurofibrillary tangles, C: NeuN neurons, D: glial fibrillary acidic protein astrocytes, E: Synaptopodin spines, and F: Synaptophysin spines in AD-Resilient (AD-R), AD-Dementia (AD-D) and Normal Comparison (NC).

Conclusions and Discussion Understanding the neurobiological foundations of expression in Alzheimer’s disease may be what is essential in developing new advances in maintaining cognitive function. Cellular and synaptic features Astrocytes play an important role in the repair and maintenance of a healthy brain by providing biochemical, structural, detoxifying and nutritional support to endothelial cells and neurons.¹¹ The observed increase of GFAP astrocytes in the AD-Resilient group suggests that cognition is rectified in AD pathology through these functioning’s. The severity of dementia in AD is often correlated to synaptic loss and has been associated with the collection of Aβ plaques and PHF- tau tangles.¹² Synaptophysin is an extensively studied synaptic vesicle membrane protein present in the presynaptic terminals whose normal expression demonstrates intact connectivity. This is consistent with the findings of normal synaptophysin expression in the AD-Resilient group, showing conserved connectivity while the AD-Dementia group showed a reduction of synaptophysin expression, indicating severed connectivity. Dendritic spines are postsynaptic membrane with specialised roles and are important to the connectivity of neurons in the brain. Using synaptopodin to label dendritic spines, it was found that spine densities were reduced in the AD-Dementia group indicating reduced connectivity while the AD-Resilient group showed normal densities. This preservation of both postsynaptic synaptopodin and presynaptic synaptophysin in AD-Resilient supports the notion of conserved synaptic connectivity. Synaptic connectivity plays an important role in neurotransmission, signal transduction, longterm potentiation, learning, and memory¹, all of which are severely comprised in dementia.¹³ 189

Biochemical- protein expression The tight congregation of protein expression in the NC suggests a coherent profile while the dissipated protein expression in AD-Resilient and AD-Dementia indicates pathology. Proteins distinguishing AD-Resilient from AD-Dementia were identified, including the Aβ precursor binding protein, which is shields against memory loss and interleukin-3 which inhibits neuron death brought about by Aβ, were increased in the AD-Resilient group. This explains the preservation of cognition in this group. However, proteins involved in phosphorylation of tau (Serine/threonine protein phosphatase) and apoptosis (tumour necrosis factor receptor) were expressed more in the AD-Dementia group, resulting in impairment of cognition.

Criticisms and Conclusions

Like every experiment, it is essential to take into account the strength and weaknesses. The sample classifications functioned to enhance the contrast of pathology and cognition between the AD-Resilient and AD-Dementia groups. The participants were part of the Religious Orders Study (ROS), making them quintessential due to their consistency in nutrition, education, health care and other lifestyle factors. These factors may cause generalisation among other populations but for this study, a more divergent lifestyle factors may pose to confound the experiment. While postmortem neuropathology continues to be the leading method in studying brain diseases and its neurobiology, it only provides information about pathology near the time of death and postmortem changes can alter the brain chemically and cellularly. Finally, the use of two-dimensional profile counting, optical density and an automated computer-assisted analyses of fractional area determination resulted in a minimisation of operator bias and finding betweengroup differences. However, it may have also formed


systematic inaccuracies that could have been avoided using a reference volume-based approach instead. Regardless, the findings of this study clearly shows that the resilient brain can be distinguished on a cellular and biochemical level that can form the foundation in the development of prevention and treatment procedures for dementia.

Future Directions

The identification of the candidate proteins, (interleukin-3, β-amyloid precursor binding protein, and serine/threonine protein phosphotase) found in AD-Resilient and AD-Dementia require further analysis, but these findings have provided a framework in which diagnostic, prevention, and treatment methods for dementia can be developed. These proteins can serve as potential biomarkers in the diagnoses in early stages of AD. There has been evidence which showed a significant increase in the concentrations of interleukin-3, and interleukin-11 in the serum of AD patients when compared to controls and decreased interleukin-3 in the the CSF of AD patients.¹⁴ This suggests that interleukin-3 can be a strong candidate for a biomarker in Alzheimer’s Disease. Evidence also shows that the treatment of metal ionophores (PBT2, Prana Biotechnology) on transgenic mice resulted in a decrease of Aβ plaques and PHF tau tangles, which significantly improved learning and memory performance on the Morris water maze.¹⁵ A follow up study analysed the proteins associated in the synaptic conditions involved with the PBT2 treatment.¹⁶ LTP, which involves the strengthening of dendritic spines are dependent on NMDA receptors and CaMKII. Both these proteins were increased consistently with the increase of spine density after PBT2 treatment. In addition, there was an increase in the elements involved in the BDNF pathway which is responsible for the health of dendritic spines, including pro-BDNF and TrkB after treatment. The discovery of the proteins that distinguishes resilient cognition in AD pathology is only a stepping stone as to what can be accomplished in the future. As it currently stands, by the age of diagnosis, the brain is already severely damaged, therefore improvement and development of early diagnostic methods are essential. Recognising and establishing the neurobiological differences between AD-Dementia and AD-Resilient can lead to boundless opportunities in the evolution of new and early prevention and treatment options for AD. References 1. Oboudiyat, C., Glazer, H., Seifan, A., Greer, C. & Isaacson, R. Alzheimer’s Disease. Seminars in Neurology 33, 313-329 (2013). 2. Blennow, K., J de Leon, M. & Zetterberg, H. Alzheimer’s Disease. Lancet 368, 387-403 (2006). 3. Bennett, D. et al. Epigenomics of Alzheimer’s disease. Translational Research 165, 200-220 (2015). 4. Frisoni, G. et al. Hippocampal and entorhinal cortex atrophy in frontotemporal dementia and Alzheimer’s disease.

Neurology 52, 91-91 (1999). 5. Hyman, B. et al. National Institute on Aging–Alzheimer’s Association guidelines for the neuropathologic assessment of Alzheimer’s disease. Alzheimer’s & Dementia 8, 1-13 (2012). 6. O’Brien, R.J., Resnick, S.M., Zonderman, A.B., Ferrucci, L., Crain, B.J., Pletnikova, O., Rudow, G., Iacono, D., Riudavets, M.A., Driscoll, I., Price, D.L., Martin, L.J., Troncoso, J.C. Neuropathologic studies of the Baltimore Longitudinal Study of Aging (BLSA). J. Alzheimers Dis. 18, 665–675 (2009). 7. White, L. Brain lesions at autopsy in older JapaneseAmerican men as related to cognitive impairment and dementia in the final years of life: a summary report from the HonoluluAsia Aging Study. J. Alzheimers Dis. 18, 713–725 (2009). 8. Haroutunian, V., Schnaider-Beeri, M., Schmeidler, J., Wysocki, M., Purohit, D.P., Perl, D.P., Libow, L.S., Lesser, G.T., Maroukian, M., Grossman, H.T. Role of the neuropathology of Alzheimer disease in dementia in the oldest-old. Arch. Neurol. 65, 1211–1217 (2008). 9. Bennett, D.A., Schneider, J.A., Arvanitakis, Z., Kelly, J.F., Aggarwal, N.T., Shah, R.C., Wilson, R.S. Neuropathology of older persons without cognitive impairment from two community-based studies. Neurology 66, 1837–1844 (2006). 10. Schneider, J.A., Arvanitakis, Z., Bang, W., Bennett, D.A. Mixed brain pathologies account for most dementia cases in community dwelling older persons. Neurology 69, 2197–2204 (2007). 11. Arnold, S. et al. Cellular, synaptic, and biochemical features of resilient cognition in Alzheimer’s disease. Neurobiology of Aging 34, 157-168 (2013). 12. Arendt, T. Synaptic degeneration in Alzheimer’s disease. Acta Neuropathol. 118, 167–179 (2009). 13. Alvarez, V.A., Sabatini, B.L. Anatomical and physiological plasticity of dendritic spines. Annu. Rev. Neurosci. 30, 79–97 (2007). 14. Bahl JMC, Simonsen AH, Larsen SO, Skogstrand K, Waldemar G, et al. Putative Biomarkers For Alzheimer’s Disease; Interleukin- 3, Interleukin-11 and Macrophage Inflammatory Protein-1 Delta in Serum and Cerebrospinal Fluid. Supplement 4(6): 34 (2010). 15. Adlard PA, Cherny RA, Finkelstein DI, Gautier E, Robb E, et al. Rapid restoration of cognition in Alzheimer’s transgenic mice with 8-hydroxy quinoline analogs is associated with decreased interstitial Abeta. Neuron 59: 43–55 (2008). 16. Adlard PA, Bica L, White AR, Nurjono M, Filiz G, et al. Metal Ionophore Treatment Restores Dendritic Spine Density and Synaptic Protein Levels in a Mouse Model of Alzheimer’s Disease. PLoS ONE 6(3): e17669 (2011). Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program

190


Musical experience enhances cognitive performance among the aging population Arinda Muntean

Activities such as playing an instrument can have some serious implications on enhancing the brain as we age. It can improve our memory, speech perception and cognitive performance. It is important to begin developing these skills at an earlier age as it is easier to take up new interests and learn quickly and practice should be continued even until adulthood in order to attain the aforementioned result. This will only become more crucial as the population shifts towards higher life expectancy rates so that declines in cognition function due to agerelated causes can be mitigated. The purpose of this study was to investigate if adults from ages 45-65 that have had previous musical experience show an enhanced overall performance in three areas related to cognition: speech in noise perception, auditory and visual working memory, and auditory acuity. Various tests have been conducted for each of the previous assessments and results have shown that musically experienced older adults do exhibit improved results in some of the tasks. Further research must be conducted in this growing area of study in order to understand the underlying mechanisms that drive cognitive functioning. Key words: Auditory memory, Auditory acuity, Age, Hearing in noise, Musical experience, Speech in noise perception. Background As we age, it becomes increasingly difficult to understand what is being said as background noise makes it harder to pay attention. Some of these conditions that we are aware of vary from the simple increase in volume in background noise, to mechanisms within the brain affiliated with the reduction of memory and attention. This study focused on how the understanding of speech in noise (SIN) differed between aging musicians and non-musicians, specifically if there were significant brain changes that have eventually come to adapt to noise, thus making it easier to hear in this type of environment (Parbery-Clark, et al., 2011). This topic becomes especially relevant to how effective communication can be as people age and as the average lifespan is extended due to technological advances, suggesting that musical experience can mitigate the effects of age-related cognitive decline. A previous study by Jentschz et al., has indicated that among a younger cohort, musical experience provides an advantage in improving behavioral responses in the frontal cortex as cognitive conflict appears. Not only are various brain structures affected during ageing (Huang et al., 2010), life experiences such as physical activity and any other activities that engage the brain, have an impact on cognitive abilities, which should be taken into effect for future studies (Anderson et al., 2013). Bugos et al. specified that musical practice for an extensive amount of time (i.e. six months) even for amateurs have led to an increased and effective performance in working memory, though the results were not sustained after several months of delay, suggesting that practice is key when cognitive responses are in focus. It is already known that the strength of auditory processing can be enhanced through time and that the amount of musical experience can actually increase cognitive functioning; however, Parbery-Clark et al. aimed to test these findings on an older group of adults between the ages of 45 and 65, which is not specifically unique among this type of study (Bugos et al., 2007). Various studies have aimed at a wide range of ages in order 191

to compare their results pertaining to age, as well as maintaining a consistent method (Strait et al., 2010). A study focused on a specific age range is significant because much of previous research has only focused on a younger cohort of musicians, providing evidence that there is in fact an enhancement in cognitive functioning due to musical experience; however, research on older adults can answer questions in regards to being able to extend this cognitive performance as musical experience continues throughout oneâ&#x20AC;&#x2122;s lifetime. It is important to understand what is happening in older adults, considering that as the average length of life increases, one will inevitably experience decline in cognitive function for a longer amount of time. Thus, this is one of many fields of studies that can aid in improving the aging populationâ&#x20AC;&#x2122;s lifestyle. Research Overview

Summary of Major Results

Approximately half of the participants that were considered musicians played an instrument for most of their lives and were asked to continue practicing at least thrice a week, while the rest of the participants had either never played an instrument or had less than 3 years of musical experience. There were 3 parameters of the brain in which participants were asked to engage in various tasks: speech perception in noise, working memory, and auditory temporal acuity. 3 different tests were used to determine the perception of speech in noise. The first test was called the Hearing in Noise Test (HINT) which played varying intensity level sentences in conjunction with a preset intensity level noise, and repeated the task. Similarly, the next test, QuickSIN, also appointed the task of repeating sentences through varying levels of noise. Sentences were played at 70 dB and had a signal to noise ratio of 25dB which then decreased as the task progressed. The last test was called the Words in Noise Test (WIN) was similar to QuickSIN but started at a different signal to noise ratio. For all three tests, a better performance


was portrayed by obtaining a low score based on the signal to noise ratio. Results showed that musicians did achieve a lower score than non-musicians (Figure 1). SIN results correlated with auditory memory and the backward masking task. The three SIN tests were also analyzed among each other where QuickSIN and HINT showed no correlation while no significant relationship was observed between HINT and WIN. Parbery-Clark et al. suggested that this may be due to the difference in the mechanism these tests target. Auditory memory was assessed through the WoodcockJohnson III test of Cognitive Abilities which consisted of spoken words and numbers that were then recalled in the same order or reversed order. Visual working memory was assessed through the Visual Working Memory subtest (VWM). There were 8 boxes that changed colour and participants were asked to click on the boxes in the order that they changed colour, either in the forward or reverse order. Higher scores were indicative of better performances on both tests. The correlation found between the SIN results and the auditory memory tests were analyzed between musicians and non-musicians in Table 1. Figure 2 presents findings that show that while auditory working memory in musicians produced higher results, visual working memory did not have an impact on musicians or non-musicians. In order to test for auditory acuity, a backward masking task from the IHR Multi-center Battery for Auditory Processing was used to determine to what degree the participants’ hearing can pinpoint certain changes in noise perception. Musicians demonstrated a better performance for this task, in which a lower dB target sound and therefore, a lower threshold signified the enhanced ability to perceive sounds amid various noises. Correlations were also analyzed between musicians and age of when they began practicing; however, since this study particularly looked at a specific age range (3-8 years), there was not significant correlation observed. Additionally, the researchers analyzed whether years of musical experience among musicians had an impact on cognitive function and found that there was no significant relationship as well. While comparing musicians and non-musicians exclusively, results indicated that musicians did have better cognitive performance, which is a result that is in line with previous studies on this subject.

Figure 1. Musicians demonstrated improved performance (i.e. a lower score) among the SIN tests (QuickSIN, HINT, and WIN) as well as the backwards masking task that assessed auditory temporal acuity. Source: doi:10.1371/journal.pone.0018082.g001

Figure 2. Results indicate that participants with musical experience had an increase in efficacy of auditory working memory, though no change was observed among the two groups when assessed for visual working memory. Source: doi:10.1371/ journal.pone.0018082.g002

Discussion The authors concluded that among an older cohort, participants with extensive amounts of musical experience had improved SIN results and auditory working memory and acuity compared to non-musicians (Parbery-Clark et al., 2011). SIN perception has not only been tested on older adults, but also young adults in order to compare results and see if there is in fact a decline due to age. This type of perception test is a good assessor of auditory cognition function as the participant must be able to focus on a sentence being read while distracted by various background noise thresholds (Parbery-Clark et al., 2011). The effects of the SIN perception test are almost equivocal to situations involving communication with others in one’s daily life. Other studies such as, Zendel et al., have shown enhanced auditory performance not only in SIN perception but also gap detection among musicians, suggesting that musical experience may have other positive advantages over those who haven’t practiced music. Parbery-Clark et al. indicate in their study that SIN perception can be slightly dependent on auditory working memory. For example, example, musicians had better SIN scores due to an increased auditory working memory capacity targeted by musical training. It was also discussed that SIN perception was modulated by an extensive period of musical training (Parbery-Clark et al., 2011). A strength found within this study was that the researchers aimed to focus their question towards an older cohort, considering that musical experience could have a potential long-term effect rather than studying the effects only on young adults. This information can provide essential knowledge for mitigating the hearing impairments that come with a decline in age. Additionally, this study provided further evidence that cognitive function can be strengthened through the practice of musical instruments , which was the subject of another study done by Wong et al. Their results demonstrated that musicians had enhanced cortical responses within the brainstem and of auditory information processing (Wong et al., 2007). The results of this study can be an indication that having musical experience can be beneficial and could compensate for the decline in hearing due to age. By taking a simple aspect in everyone’s daily life (communication amid background noise) this study was able to demonstrate that there was a positive relationship between musical experience and better performance on the various auditory tasks. 192


Table 1. Performance at auditory and visual tasks for musicians and non-musicians. HINT, QuickSIN, and WIN were the SIN perception tests. The backward masking test (BM) assessed auditory acuity. A lower score in the previous four tests indicates better performance. If scores were higher for auditory working memory (AWM) and visual working memory (VWM), this indicated better performance as well. The most significant results regarding improved cognitive function in musicians was observed in BM and AWM tasks. Source: doi:10.1371/journal.pone.0018082.t003

Conclusions

Although this study found a positive correlation, the results demonstrate that this was incremental knowledge gained because many previous studies have already determined that having some sort of musical experience enhances cognitive performance, despite the age range. In addition the correlation between musical experience and enhanced performance did not seem strong enough to determine that musical experience can aid in adapting to the aging process; however, it is important to note that this could be due to age-related impairments that could already setback cognitive performance. Even through there is still more research to be done in this field, the new knowledge coming from this investigation and multiple others can aid in ways to treat and mitigate the effects of decline in hearing and can be further extended to how strong the impact could be compared with learning music at different ages.

Criticisms and Future Directions

A limitation to this study was that the correlation between the age the musician began practicing an instrument and measuring cognitive skills was a weak relationship because all musiciansâ&#x20AC;&#x2122; starting age ranged from 3-8, which presented a limited set of values to analyze. Thus, future studies could investigate whether picking up an instrument at various ages, such as during early and late adolescence, or early and late adulthood, could impact cognitive and auditory performance. One study by Bugos et al. focused on the older adult cohort, ranging from ages 60 to 85, to determine whether training in piano practice could improve working memory for those that havenâ&#x20AC;&#x2122;t had much musical experience throughout their lifetimes. The results provided evidence that those participants that di d engage in Individualized Piano Instruction or the IPI program showed an improved attention and concentration for cognitive tasks over a sustained amount of time (Bugos et al., 2007). What could be extrapolated from this study is the IPI program, which not only provides instruction in musical theory and literacy, it also included dexterity exercises as soon as the participant was ready to play an instrument. Therefore, an extension to Parbery-Clark et al. study is to apply this method to other age groups and investigate its effect on cognitive skills. 193

In the Parbery-Clark et al. study, attention was not a primary parameter measured, however, it is important to note that the simple task of paying attention to a speaker aids in the overall understanding of speech during communication in daily life. Strait et al. investigated the effect that experience in music had on auditory and visual attention. An experimental method that could be incorporated for future studies include tasks that were computer simulated based and compared reactions times of various cues (Strait et al., 2010). For example, the task that measured visual attention required the participants to observe a character and to respond by pressing a button if the character moved (Strait et al., 2010). The task eventually became difficult when participants were asked not to respond to certain cues that occurred before characterâ&#x20AC;&#x2122;s movement. The auditory attention task was the same as the visual task, though the cues were sounds instead. Finally, in the current study, how there was no correlation between musical experience and an improvement in visual working memory. With no valid reason to explain this, there leaves no room but to further investigate the cause. Perhaps there is no true correlation found in older adults, but a study by Huang et al. demonstrated that when young adult, musically experienced participants were asked to perform a verbal memory task, there was activation in the visual cortex compared to no activation in non-musicians (Huang et al., 2010). Parbery-Clark et al. measured visual memory through computer-based visual exercises; however, there could be a link to inducing the visual cortex by another area of the brain. As a result, an experimental method that could be used consists of various tasks in which participants were asked to listen to 20 simple words (that were related to fruits, animals, tools, and landscapes) and remember as many words as possible as well as categorize the words as natural or artificial objects (this would induce stronger encoding) (Strait et al., 2010). Then, they were asked to retrieve as many words as they can silently while pressing a button each time a word was remembered. The recalling process was done in an MRI scanner in order to visualize what was occurring in the brain. This method could be employed on older adults as well, whether they were musicians or not, for activations in the visual cortex.


References 1. Anderson, S., White-Schwoch, T., Parbery-Clark, A., & Kraus, N. (2013). A dynamic auditory-cognitive system supports speech-in-noise perception in older adults. Hearing Research. 300:18-32. 2. Bugos, J. A., Perlstein, W.M, McCrae, C.S., Brophy, T.S., & Bedenbaugh, P.H. (2007) Individualized Piano Instruction Enhances Executive Functioning and Working Memory in Older Adults. Aging & Mental Health. 11:464-71. 3. Huang, Z., Zhang, J.X., Yang, Z., Dong, G., Wu, J., Chan, A.S., & Weng, X. (2010) Verbal Memory Retrieval Engages Visual Cortex in Musicians. Neuroscience 168: 179-89. 4. Jentzsch, I., Mkrtchian, A., & Kansal, N. (2014). Improved effectiveness of performance monitoring in amateur instrumental musicians. Neuropsychologia, 52:117-124. 5. Parbery-Clark, A., Strait, D.L., Anderson, S., Hittner, E.,& Kraus, N. (2011) Musical Experience and the Aging Auditory System: Implications for Cognitive Abilities and Hearing Speech in Noise. PLoS One 6. 6. Strait, Dana L., Kraus, N., Parbery-Clark, A., & Ashley, R. (2010) Musical Experience Shapes Top-Down Auditory Mechanisms: Evidence from Masking and Auditory Attention Performance. Hearing research. 261: 22-29. 7. Wong, P., Skoe, E., Russo, N.M., Dees, T., & Kraus, N. (2007). Musical Experience Shapes Human Brainstem Encoding of Linguistic Pitch Patterns. Nature neuroscience. 10(4): 420-422. 8. Zendel, B.R., & Alain, C. (2012). Musicians Experience Less Age-related Decline In Central Auditory Processing. Psychology and Aging, 27(2), 410-417. This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright Š 2015 Dr. Bill JU, Neurosciences, Human Biology Program

194


Visualizing anxiety through mGlu7 receptor immunocytochemistry Jena, L Niceforo

Anxiety is a disorder which is thought to decrease the afflictedâ&#x20AC;&#x2122;s quality of life through compromised mental functioning. It can associate with comorbidities like diabetes and hypertension, and become a significant economical burden. Estimated to cause around 97.4 billion dollars in losses globally due to individualâ&#x20AC;&#x2122;s inability to function correctly. Not only are anxiety disorders very difficult to diagnose, but it is thought that about two thirds of cases are misdiagnosed due to either overlapping symptoms with depression or individuals not seeking help when they need it. In addition, it is known that if left untreated, anxiety can lead to suicidal thoughts and behaviors1. Some physical manifestations and symptoms of anxiety include problems sleeping, cold or sweaty hands and feet, shortness of breath, heart palpitations, an inability to be still or calm, dry mouth, numbness or tingling in the hands or feet, nausea, muscle tension, and dizziness. While its cause is unknown, A general study by Meszaros et al. associated negative life events with increased anxiety symptoms these studies used questionnaires to find that the symptoms of anxiety manifested themselves when many negative life events occurred2. These symptoms are believed to come from molecular changes in mGlu7 receptors in the hippocampus. An understanding of anxiety at the molecular level could lead to pharmacological treatments which will dramatically increase the quality of life for those suffering from anxiety. Through some of the molecular techniques mentioned in this review, we will be able to visualize anxiety through immunocytochemistry. We will then extrapolate the results to mouse models and perform tests for anxious behaviors once knockouts have been performed. Key words are : Anxiety, immunocytochemistry, mice models, mGlu7 receptors, adenyl-cyclase Background Currently scientists have developed drug targets for mGlu2 and mGlu5 receptor subunits, however mGlu7 receptor subunits have not been examined pharmacologically. It is thought that these specific subunits play a large role in causing anxious behaviors in individuals that suffer from the condition. When mGlu7 receptors are activated, they trigger downstream effects in the hippocampus that cause anxious behaviors in people. Finding the mechanisms of this pathway has significant implications for treatment of CNS disorders, not just anxiety and depression, but the sensation of pain, and even types of brain tumors, can be treated by finding a specific blocker for mGlu7 receptors3. The pathway in which glutamate acts to bind to ionotropic NMDA and AMPA receptors is the same in which it effects metabotropic glutamate receptors (mGlur). Available today are antidepressants or antianxiety medication that act as NMDAR agonists, which have significant adverse side effects like memory dysfunction, ataxia, neurodegeneration and drug dependence. This receptor is ineffective for attempting to alleviate symptoms of depression and anxious behaviors, attention has been shifted from NMDARs to mGlurs because of their specific role in causing anxious behaviors. When attempting to target mGlurs pharmacologically you can create safer neuropharmacological drugs free of negative side effects4. mGlu7 receptors are coupled to G1/G0 proteins and when they are activated they are known to play a role in anxiety and depression. It is known that presynaptic mGlu7 autoreceptors control glutamate release in the CNS, while heteroreceptors control GABA release in the hippocampus. What scientists have inferred from immunohistochemistry performed on mGlu7 receptors in hippocampal slices is that mouse GABAergic nerve terminals have presynaptic mGlu7 heteroreceptors, and when they are activated it inhibits GABA exocy195

tosis. It was found that most nerve endings that had mGlu7 receptors were negatively coupled to adenyl cyclase activity5. When mGlu7 inhibits adenyl cyclase it effects glutamate release, it was also found that when mGlu7 receptors were exposed to agonists they facilitate glutamate release. In addition it is known that a genetic deletion of mGlu7 receptors reduces anxiety and depression by causing an increase in BDNF levels in the hippocampus6. This has significant implications for individuals who suffer from anxiety, studies in the past have showed that when mGlu7 knockouts in mice were performed it alleviated anxious behaviors. If a specific enzyme can be targeted to treat anxiety and depression than a pharmacological solution to anxiety can be presented without negative side effects, you can effectively prevent an individual from continuing to suffer from anxiety, depression panic attacks etc Research Overview

Summary of Major Results

Lacovelli et al. discovered that through the use of monoclonal anti-HA antibodies to bind to HEK293 cells that mGlu7 proteins are coupled to Gi and activate multiple signaling pathways, in addition it was found that adenyl cyclase activity was inhibited along with MAPK stimulation. When mGlu7 receptor expressing cells were given an agonist (L-AP4), the agonist stimulated cAMP formation, but when the blocker PTX was given to the cells it was found that inhibition of adenyl cyclase was prevented. Confirming that mGlu7 receptors were coupled to Gi proteins Suggesting that the Gi coupled protein is independent when it activates mGlu7 receptors. The researchers transfected cells with mGlu7 cDNA, it was found that cells that had inhibition of adenyl cyclase when the blocker L-AP4 was applied, its effect was neutralized


by cells expressing GRK4. In mGlu7 expressing cells L-AP4 stimulated ERK1/2 phosphorylation was fully desensitized. These couplings are shown on immunoblots. In addition it was discovered that β-arrestins could amplify ERK1/2 phosphorylation, and that the naturally occurring β-arrestin is required for the coupling of mGlu7 receptors to ERK1/2 activation6. These results are consistent with the fact that there is a presence of mGlu7 receptors in the hippocampus, mice were tested using immunohistochemistry where mGlu7 receptors were thought to appear in the brain by using a specific antibody for them in rat brains. It was detected that the most abundant mGlu7 receptors were found in parts of the brain that were correlated with GABAergic synapses6.

Figure 1. Shows that when JNK is applied to mGlu7 coupled to β-arrestin knockouts that mGlu7 receptors are not as effectively activated6.

glutamate to be released instead7. In their 2010 study Weironska et al. found that when mGlu7 receptors were knocked out in mice GABAergic neurons could not function as well, which lead to some significant conclusions about mGlu7 receptors. That as the level of GAD proteins associated with mGlu7 receptors decreased in the hippocampus that the level of GABA enzymes also decreased8. This study filled in the gaps from the past, it monitored presynaptic GABAergic nerve terminals to visualize mGlu7 receptors mediating GABA release. mGlu7 receptors were found to inhibit GABA release and modulate NMDA receptors as well. This has a significant impact for the rest of the brain because of 5-HT receptors and NMDA agonists effect on controlling GABA outflow to the nerves6. It is significant if mGlu7 receptors play a role in modulating these GABAergic nerve terminals as well, not only would we have another target for treating dysfunction in the brain but we could specifically target mGlu7 receptors, in this pathway to attempt to develop a drug that has minimal amount of side effects while still targeting the specific over reactive receptor in your brain that causes you to experience anxiety. Not only are mGlu7 receptors affected by GABA release in the brain but other mGlu receptors found in that family too. Each specific mGlu is responsible for a different type of behavior, what is specific about the mGlu7 receptor is that it is abundant in the brain and is responsible for the antidepressant quality of drugs in neurons that express GABA. When mGlu7 gets activated since it is coupled to Gi proteins that two cascade pathways are initiated by the same molecule, such that when knockouts are performed in mGlu7 pathway you have to be very specific which molecule you target. By specifically targeting a downstream effect of something initiated by the mGlu7 receptor (like β-arrestin) vs the Gi coupled protein. An individual would be able to theoretically eliminate what causes the symptoms of anxiety. The next step would be to extrapolate these results from cell cultures into mouse models and perform knockouts of each downstream effect from the pathway, and determine the phenotype of each mouse. Perform tests for anxious behaviors and if the mouse cannot experience anxiety based on which molecule is knocked out, finally design a specific inhibitor for that molecule, which would be defined as a drug to cure anxiety or depression.

Criticisms and Future Directions Figure 2. Shows that when GRKs were added in mGlu7 receptors, ERK decreases, when L-AP4 is added, it strengthens mGlu7 receptors, the ERK response is stronger.

Research Overview

Conclusions and Discussion

Studies before this one have inferred that mGlu7 receptors exist presynaptically on GABAergic neurons, and because of that it was thought that mGlu7 receptors played a role in inhibiting GABA release, causing

The study showed that mGlu7 receptors are coupled to Gi proteins, yet a main criticism is that there was no inhibition of Gi protein at all, only mGlu7 receptors were inhibited in the study. Leaving a fairly wide gap, since Gi are coupled to mGlu7 receptors, once the receptors become activated that also turns on the pathway which the Gi proteins are coupled to. The researchers could have attempted to knock out the Gi coupled proteins using miRNA or a specific inhibitor for them. To see which effects of the pathway would still be viable. You could also attempt to visualize, once the Gi pathway has been neutralized using immunocytochemistry if only the mGlu7 receptors still produced downstream effects and where the effects would be. If the entire pathway can be silenced from using an 196


inhibitor for Gi proteins, you need to target something farther downstream of mGlu7 receptors, you could act on β-arrestin. The next step after immunocytochemistry is performed is that you would want to extrapolate the results to mice models. You could silence any of the genes associating with mGlu7 like ERK1/2 and JNK using miRNA, you would have to sequence the gene in mice, then create a miRNA complementary to it, inject the mouse and then perform tests for anxious behaviors9. Some commonly used tests for anxious behaviors in mice would be the elevated plus maze or the open field test. If the mouse is feeling anxious it will tend to run along the walls of the maze, but if it is feeling relaxed it will run in the center. Ideally should the pathway be specific for anxiety, if you perform a knockout of the pathway in a mouse model you would have the mouse running throughout the maze regardless of what stimulus you present it with. The mouse will not be able to feel anxiety anymore once you silence the mGlu7 pathway. You could also delete a gene in a mouse that is specific for β-arrestin and see how that will effect the phenotype of the mouse, if the mouse will still be able to feel anxiety. Ideally if the science is sound behind these models, you could one day design a specific inhibitor for this mGlu7 pathway, in a pill form and give it to a person, to completely erase all anxious behaviors without negative side effects. Which would have huge implications for any individual that suffers from anxiety to one day be free from their disease permanently and to be able to lead a normal life, is what any person would want. References 1. Olariu E, Forero CG, Castro-Rodriguez JI, Rodrigo-Calvo MT, Alvarez P,Martin-Lopez LM, Sanchez-Toto A, Adroher ND, Blasco-Cubedo MJ, Vilagut G, Fullana MA, Alonso J(2015) Detection of anxiety disorders in primary care: A Meta-analysis of assisted and unassisted diagnoses. Depress Anxiety. [Epub ahead of print] 2. Meszaros V, Ajtay G, Fodor K, Komlosi S, Boross V, Barna C, Udvardy-Meszaros A, Perczel Forintos D. From life events to symptoms of anxiety and depression: the role of dysfunctional attitudes and coping. Neurological Review. 67:397-408 3. Nicoletti F, Bruno V, Ngomba RT, Gradini R, Battaglia G, Metabotropic glutamate receptors as drug targets: What’s new. Current Opinion in Pharmacology. 20:89-94 4. Weironska JM, Lequtko B, Dudys D, Pilc A. Olfactory Bulbectomy and amitriptyline treatment influences mGlu receptors expression in the mouse brain hippocampus. Pharmacological Reports. 6:844-55 5. Summa M, Di Prisco S, Grillir M, Usai C, Marchi M, Pittaluga A. Presynaptic mGlu7 receptors control GABA release in mouse hippocampus. Neuropharmacology.66:215-24 6. Lacovelli L, Felicioni M, Nistico R, Nicoletti F, De Blasi A. Selective Regulation of recombinantly expressed mGlu7 receptors metabotropic glutamate receptors by G-protein coupled receptor kinases and arrestins. Neuropharmacology. 77:303-312 7. Schoepp D. Unveiling the functions of presynaptic metabotropic glutamate receptors in the central nervous system. Journal of Pharmacological Experimental Theory. 299:12-20 197

8. Weironska M, Branski P, Siwek A, Dybala M, Nowak G, Pilc A. GABAergic dysfunction in mGlu7 receptor-deficient mice as reflected by decreased levels of glutamic acid decarboxylase 65 and 67kDa and increased reelin proteins in the hippocampus. Brain Research. 1334:12-14 9. Y, Zhang. Y, Wang. L, Wang. M, Bai. X, Zhang. X, Zhu. Dopamine receptor D2 and associated microRNAs are involved in stress susceptibility and resistance to escitalopram treatment. 2015. Int. J. Neuropsychopharmacology.[EPub Ahead of Print]. This work was supported by The Association for the Development of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program


The Next Step in Antidepressant Therapy: BDNF Oscillation Patterns as a Potential Early Predictor for Therapy Response

Yuki Nishimura

Numerous studies have shown evidence for the critical role that brain-derived neurotrophic factors (BDNF) play in the development of stress-related mood ailments like major depressive disorders. Due to its association with potential antidepressant qualities, BDNF has been targeted in treatments for depression. One such method of antidepressant therapies includes partial sleep deprivation (PSD), which has been shown to cause a rapid increase in BDNF levels, and a short lived positive effect on patients suffering from depression. Giese et al. (2014) treated 28 patients suffering from major depressive disorders using PSD, and evaluated blood serum levels of each patient before, during, and after antidepressant treatment. They found that after a 2-week follow up of these patients, all patientsâ&#x20AC;&#x2122; BDNF levels increased immediately after treatment, though the overall therapy response was short-lived. More importantly, they found that patients who had higher levels of diurnal BDNF prior to treatment had more significant increases in serum BDNF levels post-treatment, and that these patients reported better treatment responses than those patients who had lower, more un-responsive BDNF levels. These results not only show that PSD treatments result in a boost in the BDNF levels, but also that pretreatment levels of BDNF in each patient could potentially predict therapy response. However, further studies are needed in order to examine whether stress hormone deregulation and pre-treatment cortisol levels could also be playing a role in antidepressant treatment responses. Key words: BDNF; Major Depressive Disorder (MDD); Partial Sleep Deprivation; Antidepressant Therapy Response; Early Predictor. Background Fluctuating levels of neurotrophic factors, such as BDNF levels in the hippocampal region of the brain, have been correlated with many stress-induced mood disorders (Duman and Monteggia, 2006). For example, when placed in a stressful environment where rats were subject to randomized foot shocks, BDNF levels decreased rapidly, suggesting a link between high stress levels and declined BDNF levels (Rasmussen et al., 2002). Furthermore, prenatal maternal deprivation of BDNF led to the birth of rats that had more trouble adjusting to stressful environments like the swim stress test (Roceri et al., 2002). This suggests that depriving BDNF during critical periods of fetal brain development could lead to drastic functional deficiencies and increased susceptibility to stress-related mood disorders like generalized anxiety (Cutuli et a., 2015). Yet many of these deficiencies are changeable, as shown by the studies done in which boosting BDNF levels led to varying degrees of reversal or recovery of decreased brain function and stress management. One major application of this comes in the form of antidepressant treatments for major depressive disorder (MDD) patients. Many patients with depression show inherently lowered levels of BDNF (Shimizu et al., 2003), and antidepressant therapies have started to shift their focus towards increasing these BDNF levels as a potential method of treatment. For example, classical antidepressant therapies like monoamine oxidase inhibitors (MAOIs) and selective serotonin reuptake inhibitors (SSRIs) have both been shown to result in a slow increase of BDNF levels in patients (Nibuya et al, 2003; Coppell et al 2003). Although MDD does not necessarily result as a response to stressful environments, it has been well recognized that stress exacerbates MDD incidents (Gold

and Chrousos, 2002), and further studies have shown that MDD patients suffer not only a decreased BDNF level, but also a subsequent decrease in hippocampal size (Phillips et al., 2015). Because of the growing consensus that BDNF has a critical role in many stress-related mood disorders like MDD, BDNF has been proposed as a potential biomarker for both diagnosing depression, and gauging antidepressant therapy efficacy (Karege et al., 2002). Although most studies have shown that post-treatment levels of BDNF rise in patients, some studies have also reported a group of non-responder patients, who show little to no evidence of increased BDNF levels (Molendijk et al., 2011). These nonresponder patients were also shown to have less success in antidepressant therapies. These studies suggested that the presence of an immediate surge in BDNF levels after antidepressant treatment was strongly correlated to treatment success. Although this allows clinicians to predict antidepressant therapy success, it can only be done after such treatment has been performed, which ultimately does little to help the already burdensome healthcare system. Instead, being able to predict whether antidepressant therapy will be effective prior to actual treatment will allow clinicians to make more economical and less timeconsuming treatment choices. Research Overview

Summary of Major Results

In order to find an earlier predictor for antidepressant therapy treatment, Giese et al. (2014) examined patient serum BDNF levels prior to treatment admin198


istration to see whether predisposal to higher or lower BDNF levels resulted in improved treatment success. In order to have rapid BDNF increase results, Giese et al. (2014) used partial sleep deprivation (PSD) treatments on 28 patients suffering from MDD, and all participants were evaluated using the Hamilton Depression Rating Scale (HDRS) prior to treatment. The researchers collected blood serum from these patients for seven time periods, because BDNF is known to follow a daily circadian rhythm oscillation pattern in which BDNF levels are the highest in the morning and lowest during midnight (Begliuomini et al., 2008). During Day 0 (before PSD treatment was performed), they collected blood at 8am, 2pm, and 8pm to assess the baseline BDNF oscillation patterns for each patient. Then, during PSD (Day 1), they collected blood serum at 1:30am (right after patients were awoken for PSD), 8am, 2pm, and 8pm. Two weeks after PSD treatment, all 28 patients were evaluated again using the HDRS scale in order to see how successful the treatment response was. Results showed that all of the participants’ BDNF oscillation patterns on Day 0 prior to PSD treatment showed the highest levels in the morning (8am) and lowest at midnight (Day 1--1:30am), which was expected because previous studies found that BDNF levels oscillate in accordance with the circadian rhythm. After PSD treatment (Day 1), mean BDNF levels increased 10.4% (8am), 16.2% (2pm), and 20.7% (8pm) when compared to pre-treatment levels, showing that PSD resulted in rapid BDNF level increases. This result is in keeping with other similar studies done in which PSD treatments led to transient increases in BDNF levels (Beck et al., 2010). However, two weeks after PSD, all participants took the HDRS questionnaire and those who scored lower on it, and therefore had better antidepressant results from the PSD, were classified as “long-term responders” (n=10), whereas those who did not show lasting treatment effects and scored higher HDRS scores were classified as “non-responders” (n=18). Long-term responders not only had higher post-PSD

Figure 1. Diurnal serum BDNF levels. (A) Mean BDNF levels for all participants showed highest levels in the morning that steadily declined and reached its minimum levels around midnight, as was expected. (B) Post PSD treatment (Day 1) mean BDNF levels were higher than pre-PSD treatment (Day 0), showing that PSD treatment results in rapid BDNF level upsurges. (Giese et al., 2014)

(Day 1) BDNF levels than their counterparts, but also had higher serum BDNF levels pre-PSD treatment (Day 0), and had a general predisposition to higher levels of BDNF prior to any antidepressant treatment. Conclusions and Discussion Partial sleep deprivation (PSD) is effective in inducing rapid increase in BDNF levels and garnering some relief from depressive episodes, yet both of these outcomes are short-lived, as was also seen in other studies done using PSD as the choice of antidepressant therapy (Giedke and Schwarzler, 2002). Furthermore, similarly to other studies conducted by Lee and Kim (2008), Giese et al. found that antidepressant therapy resulted in some patients who had less obvious increases in BDNF levels (“nonresponder” patients), and that these patients had less success in antidepressant therapy effectiveness, as evidenced in the lack of significant difference in HDRS ratings before and after two weeks of treatment. More importantly, however, Giese et al. showed that patient predisposition to stable BDNF circadian rhythms

Figure 2. Post-PSD Treatment serum BDNF levels. (A) Day 1 (after treatment) BDNF levels show little diurnal patterns. (B) Responder patients who had shown significant HDRS rating scale improvement after two weeks of treatment show that their BDNF levels oscillate in a more noticeable fashion than their counterpart, non-responder patients. (C) Relationship between HDRS improvement and posttreatment BDNF levels. The higher the BDNF level was after treatment, the more likely the PSD treatment effects would last. 199


in which BDNF levels show clear signs of levels being highest in the morning and lowest at midnight, as well as a generally higher BDNF level prior to therapy are good predictors of antidepressant treatment efficacy and patient response to therapy. In short, clear diurnal BDNF oscillation patterns, coupled with higher levels of BDNF prior to treatment are good predictors of certain antidepressant therapy success. Therefore, BDNF’s role in neurogenesis and long-term potentiation are critical to mood disorders like major depressive disorder, and targeted studies into BDNF activity can prove worthwhile in Neuroscience and Psychiatry.

Criticisms and Future Directions

Although Giese et al. (2014) were not the first to posit that BDNF levels play a central role in antidepressant therapy efficacy, their study further supports that BDNF circadian rhythms could be an early predictor for how effective partial sleep deprivation treatment (and potentially other antidepressant therapies) will be. This study not only enhances the growing literature on the relationship between antidepressant therapy and BDNF levels, but also adds a new perspective by suggesting the potential of BDNF as a biomarker for early treatment efficacy predictor. Unlike the SSRI study conducted by Wolkowitz et al. (2011) that found similar BDNF potential as an early predictor of SSRI success, Giese et al.’s study was effective because it measured serum BDNF levels more frequently and allowed a thorough investigation into the patients’ diurnal patterns of BDNF prior to PSD treatment. However, the number of patients in this study was much lower in comparison to most other studies done on antidepressant therapies, and Giese et al. themselves saw the need for the same study to be conducted on a much wider patient scale. Prior studies like Tardic et al. (2011) have already suggested that post-treatment lack of increase in BDNF levels predict treatment ineffectiveness, so Giese et al. should focus their study on earlier, pre-treatment predictors of treatment efficacy, by collecting more data and blood samples prior to the beginning of treatment. Furthermore, because sleep deprivation has been linked to stress hormone deregulation by the hypothalamic-pituitary-adrenal (HPA) axis (Schule et al., 2001), further studies could be performed to see whether the patterns of cortisol levels relate to daily BDNF levels, and see whether pre-treatment cortisol levels and/or BDNF levels better predict the effectiveness of antidepressant treatments. By studying the HPA stress hormone regulation patterns, Giese et al. will better be able to explain the essential mechanisms underlying how to make antidepressant therapies more effective for patients. References 1. Beck J et al. (2010) Modafinil reduces microsleep during partial sleep deprivation in depressed patients. J Psychiatr Res 44:853-64. 2. Begliuomini S et al. (2008) Plasma brain-derived neurotrophic factor daily variations in men: correlation with cortisol circadian rhythm. J Endorinol 197: 429-35.

3. Coppell A et al. (2003) Bi-phasic change in BDNF gene expression following antidepressant drug treatment. Neuropharmaology 44: 903-10. 4. Cutuli A et al. (2015) Pre-reproductive maternal enrichment influences rat maternal care and offspring developmental trajectories: behavioral performances and neuroplasticity correlates. Front Behav Neurosci 12:66-72. 5. Duman RS, Monteggia LM (2006) A neurotrophic model for stress-related mood disorders. Biol Psychiatry 12: 1116-27. 6. Giedke H, Schwarzler F (2002) Therapeutic use of sleep deprivation in depression. Sleep Med Rev 6: 361-77. 7. Giese M. et al. (2014) Fast BDNF serum level increase and diurnal BDNF oscillations are associated with therapeutic response after partial sleep deprivation. J Psychiatr Res 59: 1-7. 8. Gold PW, Chrousos GP. Organization of the stress system and its dysregulation in melancholic and atypical depression: high vs low CRH/NE states. Mol Psychiatry 7:254-75. 9. Karege F et al. (2002) Postnatal developmental profile of brain-derived neurotrophic factor in rat brain and platelets. Neurosci Lett 328: 261-4. 10. Lee HY, Kim YK (2008) Plasma BDNF as a peripheral marker for the action mechanism of antidepressants. Neuropsychobiology 57: 194-9. 11. Molendijk et al. (2011) Serum levels of BDNF in MDD: State-trait issues, clinical features and pharmacological treatment. Mol Psychiatry 16: 1088-95. 12. Nibuya et al. (1995) Regulation of BDNF and trkB mRNA in rat brain by chronic electroconvulsive seizure and antidepressant drug treatments. J Neurosci 15: 7539-47. 13. Phillips JL et al. (2015) A prospective, longitudinal study of the effect of remission on cortical thickness and hippocampal volume in patients with treatment-resistant depression. Int J Neuropsychopharmacol. 14. Rasmussen A et al. (2002) Down-regulation of BDNF mRNA in the hippocampal dentate gyrus after re-axposure to cues previously associated with footshock. Neuropsycho 27: 133-42. 15. Roceri et al. (2002) Early maternal deprivation reduces the expression of BDNF and NMDA receptor subunits in rat hippocampus. Mol Psychiatry, 2: 609-16. 16. Schule C et al. (2001) Attenuation of HPA axis hyperactivity and simultaneous clinical deterioration in a depressed patient treated with mirtazapine. World J Biol Psychiatry 2: 103-5. 17. Shimizu et al. (2003) Alterations of serum levels of brainderived neurotrophic factor (BDNF) in depressed patients with or without antidepressants. Biol Psychiatry 54: 70-75. 18. Tardic A et al. (2011) The early non-increase of serum BDNF predicts failure of antidepressant treatment in patients with major depression: a pilot study. Prog Neuropsychopharmacol Biol Psychiatry 35: 415-20. 19. Wolkowitz OM et al. (2011) Serum BDNF levels before treatment predict SSRI response in depression. Prof Neuropsychopharmacol Biol Psychiatry 35: 1623-30. Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program 200


Further Insight on Using Mean Diffusivity as a Potential Biomarker to Identify Mild Cognitive Impairment Converters to Alzheimer’s Disease Original Article: Changes in White Matter Integrity Before Conversion From Mild Cognitive Impairment to Alzheimer’s Disease Miranda Nong

Alzheimer’s disease is a progressive neurodegenerative disease that causes memory and cognitive degeneration which eventually leads to dementia. Differences of gray matter and white matter has been studied in individuals with mild cognitive impairment that eventually develops Alzheimer’s Disease and those who do not. Analysis techniques such as voxel-based morphometry allows for brain volumes to be examined and compared between the different groups. The apparent diffusion technique allows for mead diffusivity values to be obtained and once again compared with the different groups since it is a good indication of neuronal loss in brain structures. It can potentially be a biomarker for diagnosing individuals with Alzheimer’s disease years before clinical symptoms occur and can provide an early treatment for those individuals. Key words: Alzheimer’s Disease (AD); white matter (WM); gray matter (GM); mean diffusivity (MD); mild cognitive impairment (MCI); voxel-based morphometry (VBM); apparent diffusion technique (ADC) Background Alzheimer’s disease (AD) is a progressive neurodegenerative disease that is a very common cause of dementia1. AD symptoms are not limited to memory loss, but also plays a role in the decline of many cognitive dependent components such as language dysfunction, loss of sight, decrease of attention, visuospatial difficulty, and personality changes usually associated with depression2. The neuropathology of AD is biochemically characterized to be due to the β amyloid and tau protein accumulation in the brain2, however there are still many other processes that underlies the pathology if AD. Through neuroimaging techniques, it has been found that AD is associated with the loss and atrophy of gray matter (GM) in many cortical and subcortical structures as well as the loss of white matter (WM) in the brain3. These processes and molecular changes within the brain could potentially act as a biological marker to identify those that have an onset of AD. Since AD is a progressive disease, there are different classifications of stages until it fully develops. Mild cognitive impairment (MCI) is a clinically identified early determinant stage of which an individual may or may not continue to develop AD4. MCI individuals has some cognitive impairment, but it is not enough to be identified as dementia and typically has memory deficit that is greater than their average age group5. Individuals who exhibit MCI and continue on to developing AD are called converters, and those who do not, are called non-converters4. Studies distinguished that MCI converters show greater GM atrophy in the parietal and left temporal lobe6 and more WM lesions in periventricular brain regions7. If individuals with AD onset can be identified at the MCI stage, then an earlier treatment can be provided since it is estimated that AD pathology occurs 10 to 20 years before clinical symptoms show2. Clark et al. used florbetapir-PET imaging was used to look at the density of β amyloid protein within the brain. This techniques allows the protein aggrega201

tion plaques to be identified in individuals that are approaching the end of their life. The purpose of this technique was to see the consistency of β amyloid plaques that are found in autopsies of AD individuals. The identification of β amyloid aggregation in the brain could potentially be a biomarker to find individuals with AD onset. However this study was limited to a small sample size and the use of individuals that are capable of providing the data instead of MCI individuals. As previously mentioned, GM and WM lesions differences has been observed in previous research, thus in the paper by Defrancesco et. al4, they focused on identifying the differences of MCI converters, MCI non-converters, and healthy individuals through neuroimaging techniques. The data obtained from different analyses based from neuroimaging could provide further insight on identifying individuals with early onset of AD. Research Overview Data from fifty five German speaking patients aged 62 or older were collected. They included 13 MCI converters, 14 MCI non-converters, and 28 healthy individuals. All patients were categorized into groups based on an interview and multiple psychological assessments which include the MMSE and CERAD battery tests to determine cognitive function levels. The main method to attain the neuroimaging was through diffusion weighted imaging and T1-weighted MRI scans for each patient. A comparison between the scans would then be done through a voxel-based morphometry (VBM) analysis, which is a technique to compare brain volume4. Apparent diffusion Coefficient (ADC) maps were also constructed to reflect the mean diffusivity (MD) values. MD values are a scalar measurement3 of the total amount of diffusion within a VBM analysis. High MD values suggests neuronal loss and increased brain water content3.


Summary of Major Results and Discussion

Multiple Regression Analysis A multiple regression analysis is a comparison of variables. Figure 1 is a comparison between the neuropsychological tests taken by the participants and GM atrophy within the brain in a T1-weighted image of all participants. A positive correlation was found between worse test results for MMSE and verbal memory with higher GM atrophy of the left putamen/sublobar and left inferior frontal gyrus, respectively. MMSE8 is a psychological test that grades the cognitive state, a low test score suggests cognitive impairment which is in accordance with lesions of the brain structures.

Figure 1. The yellow is an indication of a positive correlation between low psychological test scores (MMSE and verbal memory) and high GM atrophy4.

VBM Analysis VBM analysis is a method to look at the brain volume and do a comparison between the three different groups: MCI converters, MCI non-converters, and healthy individuals. Figure 2 indicates that there is more GM atrophy in MCI converters in the left parietal lobe, the left putamen, the left insula, the right parahippocampal gyrus, the frontal lobe, and the left temporal lobe. Based on a comparison between MCI non-converters and normal healthy individuals, no difference between the brain volumes were seen.

Analysys of ADC Maps and Mean Diffusivity A comparison analysis is done with the MD values reflected from ADC maps from diffusion weighted images of the three group of patients. MD values are measured using gradient labelling techniques of water protons. An increase in MD value indicates atrophy of brain areas. A comparison between MCI converters and nonconverters (Figure 3, left) showed a significant increase in MD values of GM in the left limbic lobe, right middle temporal lobe, basal ganglia, and increased MD values of WM in the parietal, frontal, and temporal lobe. The lesions of both GM and WM of MCI converters are very wide spread. A comparison between MCI converters and healthy individuals (Figure 3, right) presented similar data, although the increase of MD values was slightly higher, it was not significant. Which can conclude that the difference between MCI non-converters and healthy individuals are not significant. An overlap between the VBM analysis where brain volume is measured and ADC maps where MD values are calculated, there is overlap seen. Increase MD values and GM volume loss occur in most of the same structures. This suggests that volume loss is associated with neurodegeneration of the structure. Conclusions Defrancesco et al. showed the differences between MCI converters, MCI non-converters, and healthy individuals using a neuroimaging technique that can potentially be used to diagnose the early onset of AD in the population. From this study it showed that changes in MD values reflected neuronal loss, thus can be used as an indication of neurodegeneration in different areas of the brain. From the difference of GM and WM lesions within the brain seen between MCI converters versus non-converters, it can be used as a biomarker to accurately identify the early onset of AD to allow for earlier treatment of AD. Criticisms and Future Directions

Figure 2. This is a T1 MRI scan that is superimposed to show the different areas (in yellow) where GM is lost in MCI converters versus MCI non-converters. GM loss is seen in the bilateral frontal lobe, the left parietal lobe, left temporal lobe, the left putamen, the left insula, and the right parahippocampal gyrus4.

Defrancesco et al provided solid results on the difference between MCI converters and non-converters based on neuroimaging analysis techniques. However, the paper still does not provide the rate at which MCI converters will develop a full onset of AD later in life. With this, a long term analysis of current participants should be followed to show the growth of increasing GM and WM lesions as the disease progresses. This paper provides substantial evidence on the widespread lesions of WM seen in the parietal, frontal, and temporal lobes by measure MD values, but these lesions could also be attributed to other neurodegenerative diseases that is not necessarily AD. Based on research by Nowrangi et al.10, they examined the fornix, which is a region of WM that connects the medial temporal lobes to the hypothalamus. The fornix also plays a role in semantic and episodic memory and is shown to have an altered structure from normal 202


Figure 3. The left side shows an increase in MD values between MCI converters and MCI non-converters. The right side shows an increase in MC values between MCI converters and healthy individuals.

in MCI and AD patients11. Diffusion tensor imaging is a preferred type of neuroimaging for examining WM and can be used to do a comparison between MCI converters, non-converters, and healthy individuals to look at specific regions of WM differences. References 1. Barker, W. et al. Relative Frequencies of Alzheimer Disease, Lewy Body, Vascular and Frontotemporal Dementia, and Hippocampal Sclerosisin the State of Florida Brain Bank. Alzheimer Dis Assoc Disord 16, 203-212 (2002). 2. Holtzman, D., Morris, J. & Goate, A. Alzheimer’s Disease: The Challenge of the Second Century. Sci Transl Med 77, 1-17 (2011). 3. Gold, B.T., Johnson, N.F., Powell, D.K. & Smith, C.D. White matter integrity and vulnerability to Alzheimer’s disease: preliminary findings and future directions.Biochimica et Biophysica 1822, 416-422 (2012). 4. Defrancesco, M. et al. Changes in White Matter Integrity before Conversion from Mild Cognitive Impairment to Alzheimer’s Disease. PLoS ONE 9, e106062. (2014). 5. Petersen, R. C. Mild cognitive impairment as a diagnostic entity. Journal of internal medicine 256, 183–194 (2004). 6. Karas, G, Sluimer, J & Goekoop, R. Amnestic mild cognitive impairment: structural MR imaging findings predictive of conversion to Alzheimer disease.American Journal 10, 944-949 (2008). 7. Defrancesco, M & Marksteiner, J. Impact of white matter lesions and cognitive deficits on conversion from mild cognitive impairment to Alzheimer’s disease. Journal of Alzheimer’s Disease 34, 665-672 (2013). 8. Folstein, M. F., Folstein, S. E. & McHugh, P. R. Mini-mental state: a practical method for grading the cognitive state of patients for the clinician. Journal of psychiatric research12, 189–198 (1975). 9. Nowrangi M.A. & Rosenberg P.B. The fornix in mild cognitive impairment and alzheimer’s disease. Front Aging Neurosci 7. 1-7 (2015) 203

10. Kehoe E.G. et al. Fornix white matter is correlated with resting-state functional connectivity of the thalamus and hippocampus in healthy aging but not in mild cognitive impairment – a preliminary study. Front Aging Neurosci 7. 1-10 (2015)

This work was supported by The Association for the Development

of Undergraduate Neuroscience Education (SRA & RLN), The Endowment for Science Education (EA), and The Synaptic State Faculty Research Foundation (EA). The authors thank Mr. Spine L. Cord, Dr. Amy G. Dala, and the students in Neuroscience 101 for technical assistance, execution, and feedback on this lab exercise. Address correspondence to: Dr. Rita L. Neurotrophin, Biology Department, 123 Growth Cone Avenue, Action Potential College, Hillock, IL 60101 Email: rln@apc.edu Copyright © 2015 Dr. Bill JU, Neurosciences, Human Biology Program


Don’t Stress About it: 5HTT Genotype and Epigenetics Daria Pacurariu

Kumsta et al (2010) examined the relationship between 5HTT genotype, post-natal stress, and emotion regulation abilities in 127 participants. Their results show that s allele carriers are more susceptible to stress and have more emotion regulation difficulties. Early life stressors caused by institutional deprivation result in neurobiological alterations which impede proper affective processing, leading to emotional problems and possibly increasing the carrier’s vulnerability to developing psychopathologies. These neurobiological alterations may include epigenetic mechanisms such as methylation of the promoter region of the 5HTT gene. The field of epigenetics has recently been gaining importance due to its ability to provide a link between early life adversity and later depression-associated behavior (Dalton et al. 2014). Key words: early life adversity, institutional deprivation, emotional regulation, 5HTT polymorphism, epigenetics Ba