PennScience Spring 2017 Issue: Radiation & Technology

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Volume 15 • Issue 2 • Spring 2017

Radiation & Technology

Galactic Cosmic Radiation

A look into the future of space travel and exploration.

Gravitational Waves Understanding ripples in the space-time continuum.

The Evolution of Medical Imaging The past, present, and future of seeing the human body.

The Evils of Radiotherapy The real risk of exposure to radiation.

Solar Technology

Penn professors explore new materials for more efficient solar power.

PennScience Spring 2017

Volume 15 Issue 2

PennScience is a peer-reviewed journal of undergraduate research published by the Science and Technology Wing at the University of Pennsylvania and advised by a board of faculty members. PennScience presents relevant science features, interviews, and research articles from many disciplines, including the biological sciences, chemistry, physics, mathematics, geological sciences, and computer sciences. PennScience is funded by the Student Activities Council. For additional information about the journal including submission guidelines, visit or email

EDITORIAL STAFF EDITORS-IN-CHIEF Jane Chuprin Richard Diurba WRITING MANAGERS Ritwik Bhatia Mia Fatuzzo EDITING MANAGERS Zoe Daniels Rachel Levinson DESIGN MANAGERS Chigoziri Konkwo Suzanne Knop BUSINESS MANAGERS Alex Wong Jici Wang TECHNOLOGY MANAGERS Rounak Gokhale Abhinav Suri FACULTY ADVISORS Dr. M. Krimo Bokreta Dr. Jorge Santiago-Aviles






Hiab Teshome Rosie Nagele Eric Teichner Xufei Huang Darsh Shah Roshni Kailar

Sarah Fendrich Aaron Zhang Sapna Nath Ila Kumar Karbi Choudhury Roshan Benefo Nikita Maheshwari Erika Harness Brian Zhong Kathleen Wang Lily Zekavat

Emily Chen Alison Weiss Abigail Szabo Grace Wu Olivia Myer Roshan Benefo Abhi Motgi

Arjun Lal Olivia Medrano Felix Shen Sitara Shirol Rekha Vegesna Donna Yoo Christopher Nicholson Tyler Larkworthy








by Xufei Huang







by Rosie Nagele


16 Mark Devlin Ph.D.

Reese W. Flower Professor of Astronomy and Astrophysics



Cytotoxic, Antibacterial and Allelopathic Properties of Select Antidiarrheal Ethnobotanical Plants Found in the Dominican Republic Tested In-Vitro

18 by Brianna Douglas

Electrophysiological Changes Following Traumatic Brain Injury in Awake Behaving Rats


23 by Robin Russo



LETTER FROM THE EDITORS Dear readers, We are excited to bring you the second issue of 15th volume of PennScience. Our theme for this Spring 2017 issue is “Radiation and Technology” and it excitingly brings together completely different fields of science such as biomedicine, physics and environmental engineering. The feature articles of this publication are roughly divided into three subsections with each writer asking the question, “How is radiation used in science.” One of these subsections covers the biomedical implications of using radiation. Roshni Kailar writes on the impact radiation therapy has on a patient’s quality life, and the risks of developing cancer. Hiab Teshome discusses the usage of radiation in medical imaging. The second subsection is how radiation is related to physics and aerospace engineering. Darsh Shah explains the efforts made by engineers and scientists to create durable spaceships that can survive the intense radiation in space. Xufei Huang provides a brief discussion of the recent discovery of gravitation waves, the radiation from intense gravitational events in space. Lastly, the third subsection is how radiation is used in environmental engineering. Alexandra (Rosie) Nagele addresses the usages of solar radiation to generate electricity using solar power, and the current problems in solar energy research being answered by researchers at Penn. Eric Teichner interviewed Dr. Mark Devlin, a scientist in the field of balloon-based telescopes for studies in Cosmology. Our two undergraduate research publications deal with different disciplines. Brianna Douglas from Cornell University studied medicinal plants in the Dominican Republic. Robin Russo from the University of Pennsylvania worked on developing a rat model for traumatic brain injuries. Our two coffee chats this semester create an engaged yet informal environment for discourse about current advances in science with Penn Undergraduates and distinguished guest speakers. We are honored to have had guest speakers Dr. Robert Dr. Hollebeek and Dr. Dennis DeTurck this semester. Dr. Hollebeek co-founded Penn’s National Scalable Cluster Project, a multi-university alliance building huge networks of medical, economic, and scientific data, and he has contributed to Penn’s Proton Therapy in cancer therapeutics. Dr. DeTurck is the Dean of the College, a Robert A. Fox Leadership Professor, and a researcher studying Partial Differential Equations and Differential Geometry. We hope you enjoy the journal just as much as we enjoyed putting it together. It has been a great and unique experience to incorporate vastly different areas of science into one theme. We hope that you enjoy reading about radiation as it found in space far away and our protons found here on Earth. Sincerely, Jane Chuprin (C’17) and Richard Diurba (C’18) Co-editors-in-chief



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Research in any scientific field will be considered, including but not limited to:

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PREVIOUS ISSUES Visit the PennScience website

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Will synthetic biology be the solution to pollution?


A look into the future of genomic editing and disease


Reprogramming metabolism in the cell

Fall 2016


How it revolutionized what was once a death sentence

Spring 2016





and the exploration of the universe By Darsh Shah “To infinity and beyond!” famously exclaimed Buzz Lightyear in Toy Story. But is it really so easy to explore the entire universe, beyond our solar system, beyond even our galaxy? What is stopping us from travelling to the unknown and back? Although space is brimming with obstacles of a myriad of shapes and sizes, there exists an almost invisible form of radiation that endangers all spaceships. Perhaps the most insidious impediment to interstellar travel, galactic cosmic radiation poses a serious threat to virtually anything we send into space. Spaceships, satellites, rovers, and even astronauts are all vulnerable to the degradation inflicted by cosmic radiation. If space exploration continues to be a fundamental human aspiration, we must create radiation-resistant technologies to allow us to safely venture into “infinity and beyond.” Cosmic rays exist everywhere in the universe and take on a number of forms depending on their energy. In particular, galactic cosmic rays, or GCRs, originate outside our solar system but within our galaxy and carry non-trivial amounts of mass.1 Consisting of high-speed atomic nuclei stripped of their electrons, GCRs are produced by a variety of violent cosmic events. Most GCRs, however, come from the shock waves generated by the debris of exploding stars, or supernovae, that rapidly surge off in all directions.2 Hurled with enormous force, GCRs accelerate to 6


speeds close to the speed of light to the speed of light or very close to it. since these cosmic rays have sizable mass, it becomes clear that our universe has a natural security system. According to Einstein’s Theory of Special Relativity, an object traveling close to the speed of light will gain tremendous kinetic energy by virtue of its mass. The more massive the object, the greater its energy As a result, man-made objects may not travel freely through space but instead must always take care that they do not collide with high-energy GCRs. The Earth’s upper atmosphere and magnetic field serve as natural protections from GCRs, by either decomposing them into showers of secondary particles that decay rapidly in the upper atmosphere or redirecting their course away from the Earth’s magnetic field.3 However, journeys outside of a low Earth orbit, where these protections do not reach, will require shielding. As explained previously, GCRs are high-energy particles that can quickly degrade the fundamental structure of any physical material with which they come into contact. In addition, GCRs are highly polarized particles whose atoms have an acute electron deficiency and heavily imbalanced nuclei with more neutrons than protons. If such ionized radiation touches astro-

FEATURES nauts, it can wreak severe or even permanent biological damage. Not unlike other forms of radiation, such as radiation from nuclear energy, cosmic radiation penetrates cells in the human body, weakens and breaks up DNA, and damages cells enough to kill them or have them mutate in ways that cause cancer.4 Contact with GCRs may even lead to Acute Radiation Syndrome (ARS), which can trigger anything from nausea and vomiting to infection and hemorrhaging. Treatments for these radiation-induced ailments are only partially effective – blood transfusions and antibiotics can offset the less serious effects of ARS, but the more serious carcinogenic effects may require much more aggressive methods that can last for years.5 Traversing into deeper arenas of space unprotected not only degrades spaceships but also mutilates living beings, giving greater reason to pursue better shielding technologies. Fortunately, the aerospace industry has been cognizant of the harmful effects of cosmic radiation and has considered alternatives to our current technologies.

Something profound. As well as something else, equally profound. Organizations like NASA, which historically have used carbon fibres and conventional metals for their equipment, are considering implementing reinforced aluminum, liquid hydrogen, and polyethylene, all of which have the potential to protect against GCRs.6 Other solutions include a repulsive electrostatic field or a magnetic field generated by superconductors to deflect charged radiation particles. Perhaps the most viable option, polyethylene, is a polymer with incredible structural properties and is the the primary building block of most plastics. Its repeated complexes of CH2 allows polyethylene to form one of the most stable chains of molecules while simultaneously remaining lightweight. As current spaceships are currently equipped with aluminum, they are vulnerable to degradation outside of Earth’s magnetic field due to its material properties.. But polyethylene, lightweight and internally sound, could strengthen the composition of our space-bound technologies and make them less prone to breaking down in the face of GCRs.7 Fitted with these high-tech gadgets, manned missions into deep space would pose far fewer risks to astronauts and equipment.

Surrounded by a vast, glimmering, and exotic universe, we stand in awe of everything we behold. Yet, our thirst for exploration is unquenchable – what about the billions of other solar systems and galaxies out there? By surmounting naturally occurring obstacles, we can move one step closer to satisfying this desire.. Although galactic cosmic radiation will always exist, our inability to bypass it is temporary. Each day, our scientists and engineers work together to invent and improve shielding technologies to help us continue our quest for discovery. Works Cited (1) NASA, “Galactic Cosmic Rays.” https://cosmicopia.gsfc.nasa. gov/gcr.html (last accessed 16 March 2017). (2) NASA, “Space Radiation Source Found.” press-release/goddard/2016/ace-cosmic-ray (last accessed 16 March 2017). (3) NOAA/NWS Space Weather Prediction Center, “Galactic Cosmic Rays.” (last accessed 17 March 2017). (4) A.K. Singh, et al., “Impact of galactic cosmic rays on Earth’s atmosphere and human health,” Atmospheric Environment 45, no. 23 (2011): 3806-3818. (5) Lawrence W. Townsend, “Implications of the space radiation environment for human exploration in deep space,” Radiation Protection Dosimetry 115, no. 1 (2005): 44-50. (6) NASA, “Understanding Space Radiation.” https://spaceflight. (last accessed 16 March 2017). (7) NASA, “Plastic Spaceships.” (last accessed 17 March 2017).





Radiation is a term commonly used to describe energy that travels as waves. In our everyday lives, especially in this day and age with our reliance on technology, it is almost impossible to escape the power of radiation. Everything from our microwaves to car speakers to cellphones emits low-levels of radiation. The powers of radiation have even entered hospitals for use in scanning and disease treatment. However, research has shown that some radiation treatments have deleterious, longterm side effects and may not effectively treat the intended condition. Although common in the treatment of cancers, radiation therapy has many limitations, which necessitate research about other treatments that could bring more optimal and personalized forms of care.1 Several studies have shown the negative effects of radiation on the body. Long-term effects, for example, were observed in survivors of the atomic bombs in Hiroshima and Nagasaki. It was found that high levels of radiation exposure increased the risk of developing cancer or cardiovascular disease. Furthermore, even those exposed to low levels of radiation had a greater risk of developing cancer and cardiovascular conditions.2 In a medical context, scanning technologies, such as computed tomography (CT), expose patients to high levels of radiation. A study by Sodickson et al. showed that patients who underwent CT scans had a higher risk of radiation-induced cancer.

By Roshni Kailar



Additionally, this risk is even more pronounced in individuals with genetic predispositions, which are aggravated by the CTassociated radiation.3 Despite the deleterious effects of radiation on the human body, radiotherapy treatments for cancer have become common because they are effective at killing cancerous cells. For example, a procedure called intensitymodulated radiation therapy (IMRT), used along with scanning technologies, such as CT scans, has become well-accepted in attempts to target tumors and decrease their size4. Despite marginal improvements in recent years, treatments such as IMRT are limited in target localization and specificity. Due to this poor localization, IMRT can be ineffective, often killing healthy cells and allowing tumors to persist.5 Because such treatments also affect healthy cells, there are many short- and long-term side effects of radiotherapy that lower quality of life and increase risks of developing other conditions. Some of the short-term side effects of radiotherapy include weakness, hair loss, loss of hearing, and memory loss. In the long-run, radiotherapy weakens the immune systems of cancer patients, making them more susceptible to relapsing or developing a new form of cancer. Additionally, radiotherapy can permanently damage brain tissue and affect the pituitary gland, which regulates the secretion of hormones such as cortisol and thyroxine in the body. These hormones are vital for the regulation of stress and endocrine function.6, 7 Due to the side effects and unreliable results of radiotherapy, doctors are switching from the use of radiation


to other therapies, including microRNA treatment and immunotherapy. MicroRNA (miRNA) treatment, in particular, shows strong promise in personalizing cancer therapies. The central dogma of biology states that DNA encodes messenger RNA (mRNA), which encodes proteins. miRNA targets the mRNA that are translated to make proteins. Therefore, miRNA treatment allows doctors to overexpress or under-express specific genes that are associated with the unregulated cell growth associated with cancer. For example, research by Cheng et al. has shown that miR155, which normally inhibits genes that regulate programmed cell death, can be inhibited to decrease lymphoma in mice, since a lack of cell death is associated with cancer.8 Because miRNA treatment is personalized to the specific genetic cause of a patient’s cancer and therefore has fewer known side effects, it is considered a safer and more effective method of treating cancer. Another treatment that has shown some promise is immunotherapy, in which the patient’s immune system is stimulated to target tumors. This type of treatment protects against specific cancer antigens and is useful due to minimal side effects and an increased degree of personalization. Immunotherapy utilizes the patient’s own antibodies to boost their immune system in an attempt to better fight the cancer. By determining the type of cancer antigen and defense mechanisms in the patient’s immune system, immunotherapy reduces problems of target localization and recurrence of the same kind of cancer because it uses immunological aspects that are inherent and unique to the patient.9 In 2017, former Vice

President Joe Biden will be launching his Cancer Moonshot Initiative at the University of Pennsylvania. Amain goal of this initiative is to search for new treatments, rather than investigating the ones that already exist. This would facilitate movement away from the use of radiotherapy in the hopes that effective treatments with minimal side effects can be found.10 This field of research could pave the way for more effective treatments that not only personalize therapy but also enhance quality of life.

Due to the side effects and unreliable results of radiotherapy, doctors are switching from the use of radiation to other therapies, including microRNA treatment and immunotherapy.

Works Cited (1) Sarpong, Y., Litofsky, M. B. and Litofsky, N. S. (2014). A Paradigm Shift in the Radiation Treatment of Brain Metastases. Journal of Tumor 2, 223–230. (2) Kamiya, K., Ozasa, K., Akiba, S., Niwa, O., Kodama, K., Takamura, N., Zaharieva E. K., Kimura, Y., and Wakeford, R. (2015). Long-term effects of radiation exposure on health. The Lancet 9992, 469 - 478. (3) Sodickson, A., Baeyens, P.F., Andriole, K.P., Prevedello, L.M., Nawfel, R.D., Hanson, R. and Khorasani, R. (2009). Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults Radiology 251, pp.175-184. (4) Schaue, D. C. B. and Mcbride, W. H. (2015). Opportunities and challenges of radiotherapy for treating cancer. Nature Reviews Clinical Oncology 12, 527–540. (5) Bindhu, J., Supe, S. and Pawar, Y.(2009). Intensity modulated radiotherapy (IMRT) the white, black and grey: a clinical perspective.Reports of Practical Oncology & Radiotherapy 14, 95–103. (6) Cancer Resources from OncoLink | Treatment, Research, Coping, Clinical Trials, Prevention(2015). Possible Side Effects of Radiation Treatment for Brain Tumors. OncoLink, University of Pennsylvania. (7) Al-Mefty, O., Kersh, J. E., Routh, A. and Smith, R. R.(1990). The long-term side effects of radiation therapy for benign brain tumors in adults. Journal of Neurosurgery 73, 502–512. (8) Cheng, C. J., Bahal, R., Babar, I. A., Pincus, Z., Barrera, F., Liu, C., Svoronos, A., Braddock, D. T., Glazer, P. M., Engelman, D. M., et al.(2015). MicroRNA Silencing For Cancer Therapy Targeted to the Tumour Microenvironment. Nature 518, 107–110. (9) Rosenberg, S. A., Yang, J. C. and Restifo, N. P.(2004). Cancer Immunotherapy: Moving Beyond Current Vaccines. Nature Medicine 10, 909–915. (10) Vice President Joe Biden Discusses Cancer Research in Weekly Address (2016). News Talk 1240 WRTA.




Gravitational Waves XUFEI HUANG

Over a billion years ago, many light years away from Earth, a pair of black holes spiralled towards one another, hurtling closer and closer until they finally collided1. Energy radiated from the collision in the form of waves and reached Earth on September 14, 2015.1 Laser Interferometer Gravitational-Wave Observatory (LIGO) picked up the incredibly faint signal and provided the first direct evidence of the existence of gravitational waves.2 Such discovery, confirming the prediction Albert Einstein made a century ago in his general theory of relativity, marked a significant leap in the field of cosmology. Einstein’s general theory of relativity described the continuum of space and time, known as spacetime, and the existence of gravitational waves.3 Gravitational waves are “ripples” in the fabric of spacetime that propagate at the speed of light, produced by extreme and violent events in the distant Universe.4 Imagine the curvature of spacetime like a giant trampoline. A trampoline remains flat and horizontal in the absence of energy and mass; however, when influenced by a massive object like Earth, it distorts similarly to how a ball distorts a trampoline when dropped. The larger the object, the greater spacetime deforms around it. Gravitational waves are produced when a pair of extremely dense objects, like black


holes or planets, circle around each other, swirling spacetime and changing the distortion of space.5 The interferometer at LIGO is a powerful instrument that can observe the ripples in space. Gravitational waves stretch space in one direction and squeeze it in the other.1 If the space between points get stretched, light takes a longer time to travel from one point to the other; if the space if squeezed,


Einstein’s general theory of relativity described the continuum of space and time, known as spacetime, and the existence of gravitational waves.

then light takes less time to travel. The interferometers, with the help of mirrors at their ends, combine sources of light to create an interference pattern that precisely measure if space has been stretched or compressed by gravitational waves.3 Although LIGO is called an observatory, it isn’t like any observatory you might imagine. It is comprised of two, widely separated L-shaped laser interferometers, one based in the state of Washington and one based in the state of Louisiana.4 LIGO’s interferometers are by far the world’s largest. With their 4 km-long arms, they can measure a change in 10-19 meters!6 Such sensitivity makes it a powerful instrument for detecting gravitational waves, which are almost inconceivable. The study of gravitational waves will open a gateway towards previously undetectable wonders and mysteries. In the past, electromagnetic radiation was the primary source for scientists to understand objects and phenomenon in the Universe. However, electromagnetic radiation interacts with matter and dust on its way to Earth, so scientists have to consider those implications in order to get the original wave.3 In contrast, gravitational waves have a small cross-section, which means they are unlikely to be absorbed or scattered by dust or other celestial objects.3 In other words, these waves contain original signals emitted from massive objects and cataclysmic

...interpretations of gravitational waves can teach us about objects like neutron stars and events like the Big Bang.

events, and scientists would be able to analyze them and learn more about the cosmos.2 Interpretations of gravitational waves can teach us about objects like neutron stars and events like the Big Bang.4 Moving on, scientists hope to enhance the performance of LIGO’s interferometers. Recently, engineers from LIGO have updated the interferometers to form a new apparatus, Advanced LIGO (aLIGO). It further reduces the amount of laboratory-caused, internal vibrations, which could interfere with aLIGO’s detection of signals from gravitational waves.1 The current interferometers of aLIGO are already 10 times more sensitive than LIGO’s interferometers.1 Over the next several decades, with more updates on aLIGO, sensitive technologies and exciting new discoveries await.

Works Cited (1) Shannon, R. M., Ravi, V., Lentati, L. T., Lasky, P. D., Hobbs, G., Kerr, M., Manchester, R. N., Coles, W. A., Levin, Y., Bailes, M., et al. (2015). Gravitational waves from binary supermassive black holes missing in pulsar observations. Science 349, 1522–1525. (2) Cho, A. (2016). Gravitational waves serve up a mystery. Science, 351, 796-797. (3) Althouse, W.E. and Zucker, M.E. (1992). LIGO: The laser interferometer gravitational-wave observatory. Science, 256, 325. (4) Abbott, B.P., Abbott, R., Abbott, T.D., Abernathy, M.R., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P., Adhikari, R.X. and Adya, V.B. (2016). Observation of gravitational waves from a binary black hole merger. Physical Review Letters, 116, 061102. (5) Tsubono, K., Fujimoto, M.K. and Kuroda, K. eds. (1997). Gravitational Wave Detection. Universal Academy Press. (6) Scientific, L.I.G.O., Abbott, B.P., Abbott, R., Abbott, T.D., Abernathy, M.R., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P. and Adhikari, R.X. (2016). Tests of general relativity with GW150914. Physical Review Letters, 116, 221101.



Nuclear Medicine The Evolution of Medical Imaging

Imagine living in the early 1800s before the discovery of X-rays and MRIs. The only way to identify if something was wrong with your body was to have a doctor perform a very high-risk and unsanitary surgery. Two hundred years later, medical imaging technology has revolutionized healthcare such that invasive surgeries are no longer needed to identify a patient’s medical issue. New medical imaging developments with radiation have bridged the gap between physics and medicine, and have granted millions of doctors the ability to not only better diagnose their patients but also personalize their healthcare. Although current medical imaging techniques have substantially improved patient care, powerful and less invasive tools are being developed today that are reshaping health-care. The broadest genre of medical imaging are X-rays. X-rays were first discovered in 1895 by Wilhelm Roentgen, who also built the first X-ray machine.1 However, credit should actually go to Penn physicist Arthur Goodspeed, who unknowingly generated X-rays in 1890 but placed the evidence of the first X-ray images in his desk, never to be seen again.2 An X-ray is a beam that passes through the body, and the portions of the X-ray that are not scattered or absorbed are transmitted to a detector for recording purposes.3 Mammograms and CT scans fall within this broad category and are the most commonly used X-rays. Mammograms can identify tiny deposits of calcium or lumps in the breast that are typically associated with tumors. The other category of X-ray imaging is computerized tomography, or CT scans. CT scans combine X-ray images from different angles in order to create a three dimensional cross sectional image of many important organs and bones in the body.4 These scans are highly detailed and quickly provide critical screening of several different bodily structures. Unlike the images produced from other X-ray techniques,


By Hiab Teshome

CT images do not show overlapping anatomical structure, therefore making it very easy and clear to distinguish bodily organs. However, X-rays and CT scans are limited and do not provide the detailed imaging necessary to successfully treat patients. The discovery of X- rays and the progressive development of CT scans and mammography represent major advancements in medicine that eventually served as the stepping stone for more complex radiation technology. After the development of the X-ray, new screening technologies were created in order to meet the demand for more complex means of looking at the body without releasing dangerous ionizing radiation. More specifically, doctors and scientists wanted a machine that could easily differentiate normal and abnormal soft tissues and organs. This need for new technology led to the development of Magnetic Resonance Imaging (MRI). In 1977 the first MRI scan of a human being was made by the first MRI prototypes. MRI is a technique that uses a magnetic field and radio waves to create detailed images of organs and tissues without using radiation.5 Inside the machine, the magnetic field aligns atoms in the body and produces signals that generate cross-sectional images of the body. Although MRI technology has been a valuable non-invasive imaging resource, there are major drawbacks to using it . Not only has MRI technology been extremely expensive in the past decade, but the procedure also takes an extremely long time. Most exams range from 50-90 minutes, and because the machine is so sensitive, any movement from the patient can distort the image and require repeated imaging procedures. These drawbacks motivated scientists to develop state-of- the-art imaging techniques that provide faster and cleaner images than those in the past. The use of radiopharmaceuticals for 3D imaging has been a pivotal stepping stone for more advanced medical imaging techniques. Nuclear medicine is a blos-

X-ray (left) and MRI (right)

FEATURES soming medical speciality that uses radioactive tracers to assess bodily functions and diagnose diseases. Radioactive tracers are made up of carrier molecules that are bound tightly to radioactive elements, and they are usually administered by injections.6 Doctors can follow the path of tracers using Single Photon Emission Computed Tomography (SPECT) or Positron Emission Tomography (PET). SPECT imaging provides a computer-generated three dimensional image of the body using gamma camera detectors that can detect gamma ray emissions from the injected tracers.6 PET imaging measures the amount of energy released in the body due to small molecules called positrons, which are positively charged antimatter versions of electrons that react with negatively charged electrons in the body. Reactions between positrons and electrons cause a small energy release that can be detected by PET scanners.6 Nuclear medicine has been a useful technique for evaluating several serious medical conditions, such as brain disorders and heart diseases. By using radioactive tracers, doctors can pinpoint the exact location of diseases and obtain very detailed

“By using radioactive tracers, doctors can identify cancers and diseases in their earliest stages, and many cancers can be treated to increase the patient’s chance of survival.” information that would otherwise be unattainable from other imaging techniques. Nuclear medicine is also cheaper and more precise than exploratory surgery- which is highly expensive and invasive - and can give doctors a better understanding of their patient’s illness or injury. This will provide doctors with the ability to administer personalized and targeted treatments. This new technology has also been very important for cancer detection because radioactive tracers can detect both benign and malignant tumors. Other imaging techniques do not provide this kind of detailed information about tumors. By using radioactive tracers, doctors can identify and treat cancers and diseases in their earliest stages, increasing the patient’s chance of survival. Currently, nuclear medicine professionals have been searching for more efficient radioactive tracers that can accurately target tumors and abnormalities in the body. At Peking Union Medical College in Beijing, China, Dr. Xiaoyuan Chen, the senior investigator of the project, and his team have documented the first in-human application of a new imaging agent, a PET radiotracer, to help diagnose cancers safely and effectively. The new agent is a gallium-68-labeled peptide, which is advantageous because it enables doctors to clearly see all aspects and details of tumors with only very miniscule amounts of radiation penetrating the patient. The radioactive tracers are only present at low concentrations and are detected by very powerful scans, therefore

substantially decreasing the radioactive input in patients. The protein tracer significantly improves the tracer’s binding affinity to abnormal tumor cells.7 The compounds have the ability to target multiple biomarkers, so the peptide can bind to both early and metastatic stages of cancer.7 This allows more accurate, precise and early diagnoses of a wide range of cancers. Last month, the new gallium-68-labeled peptide tracer was used to identify both primary and metastatic lesions that are typically associated with prostate cancer. The patients did not suffer any side effects from the procedure, demonstrating the safety of using small doses of radioactive tracers. Dr. Chen, the senior investigator of the project, even noted that the use of this tracer was not only better at diagnosing patients than previously used radioactive tracers, but was also better than other types of imaging technologies. Dr. Chen explains that the most common radioactive tracers used today are sensitive enough to detect slight irregularities in the body, but lack specificity.7 These tracers have been observed to accumulate in areas where patients have experienced traumas or infections, meaning that the tracers could sometimes identify non-tumorous injuries. The gallium-68-labeled peptide has been a significant improvement because it was synthesized to only identify specific tumorous masses, and over time can be modified to identify a broader range of tumors. Radioactive imaging has grown significantly over the past 50 years. While X-rays, CT scans, and MRIs are still popular and used today, there is a gradual increase in the use of radioactive imaging because of its less invasive procedures and large scale applications. Most people around the world have benefited from imaging, which has guided vast amount of treatments from common conditions to deadly diseases. The increase in the use of radioactive tracers has become a principal component in modern medicine and the diagnosing of diseases. Although it has its risks, the benefits of imaging have been overwhelming. Its contribution to medical imaging has not only improved healthcare outcomes, but has saved millions of lives. Works Cited (1) History of Radiography Nondestructive Testing Resources. (2) Walden, J. R. (1991). The first radiation accident in America: a centennial account of the x-ray photograph made in 1890. Radiology. (3) Center for Devices and Radiological Health Medical X-ray Imaging. U S Food and Drug Administration Home Page. (4) CT Scan Mayo Clinic. (5) Mayo Clinic Staff Print (2016). Overview. Mayo Clinic. (6) Nuclear Medicine (2017). National Institutes of Health. (7) Zhang, J., Niu, G., Lang, L., Li, F., Fan, X., Yan, X., Yao, S., Yan, W., Huo, L., Chen, L., et al. (2017). Clinical Translation of a Dual Integrin α v β 3 – and Gastrin-Releasing Peptide Receptor–Targeting PET Radiotracer, 68 Ga-BBN-RGD. Journal of Nuclear Medicine 58, 228–234. (8) Radioisotopes in Medicine World Nuclear Association.



Penn Professors Explore New Materials for Solar Technology

By Rosie Nagele The sun beats overhead as the scent of fresh grass gusts through the open car windows. Amidst the rippling fields, a flash of blue catches your eye: a solar panel, with sapphire panes elegantly tilted to greet the sun’s rays. Sharp, straight, grooves through each plate exhibit the union of detail and simplicity that epitomizes innovation. Each unit seems to have an infinite depth, though the panel can be no more than two inches thick. The blend of delicacy and strength quietly defies all of our assumptions about generating energy and power. Energy as we know it is motion, heat, and chaos. It is gears turning, a rumbling engine, exhaust filling the air. But solar panels promise something calmer, something cleaner. They promise to channel the pure and inexhaustible rays of the sun into our lights, cell phone batteries, and perhaps even cars. The blue panels, glistening under the sun, soothe our worries about the changing climate and inspire hope for the future. As innovative as this technology is, current methods of converting solar energy to electricity are dismayingly inefficient. In a single hour, the sun bestows the Earth with the amount of energy humans consume in a year, but harnessing these rays has proven quite challenging.1 Humans have been making use of the sun’s electromagnetic radiation, which can be absorbed as heat, ever since the first decision to build a home in a location and orientation to maximize sunlight. Transforming this energy into electricity, however, carries the true potential for utilizing the sun and is a much more complicated effort. Photovoltaics (PV), the process of generating electricity directly from sunlight, has been studied since the nineteenth century, though the first PV cells were not created 14 PENNSCIENCE JOURNAL | SPRING 2017

until 1954.2 Consisting of thin layers of semiconductive materials that generate electric currents, PV cells have become the cornerstone of solar technology. In these systems, light induces the semiconductive compound to release electrons, which move between the layers of material to create a current. Multiple PV cells, also known as solar cells, can be connected to form modules, which are then wired together to form an array. Grouping cells together allows for substantial electricity production, and an array is what we usually identify as a solar panel. Silicon solar cells are used in more than 85% of commercial panels.3 As a semiconductive metalloid, silicon can assume crystalline or amorphous forms. Monocrystalline arrangements of individual cylindrical crystals of silicon are the most efficient at converting solar radiation to electricity, but the manufacturing process is tedious and expensive. Polycrystalline silicon, thin slices of melted and recrystallized silicon, is less expensive but also less efficient. Although created by a simple, flexible, and low cost process of depositing silicon into thin layers onto a substrate, amorphous silicon is less efficient than both crystalline forms. Despite decades of research, no silicon panel can convert more than 25% of the solar radiation that it absorbs into electricity.4 This limited efficiency has prompted scientists to explore other materials to use in solar cells. Nanoparticles, which can be manipulated to possess specific optical and electrical properties, offer a promising new avenue of research.5 Cherie Kagan, a professor of Chemical and Electrical Engineering at the University of Pennsylvania, recently published a method to increase the efficiency of

FEATURES colloidal semiconductor quantum dot (QD) solar cells. QD solar cells are made of lead sulfide (PbS) and zinc oxide (ZnO) nanocrystals synthesized using a special process that provides precise control over their size and shape.6 Using this method, scientists can create semiconductive nanocrystals with specific bandgaps, the amount of energy required to excite electrons into the circuit. Matching the bandgap to the properties of the sun’s radiation increases the amount of solar radiation that can be converted to electricity. By manipulating the nanoparticles of the solar cell’s buffer to narrow the bandgap, Kagan’s team increased the power conversion efficiency of the solar cell by 25%. QD solar cells are just one example of using nanoparticles in solar technology. Dye-sensitized solar cells (DSSCs) present another. Thin, transparent films of titanium dioxide (TiO2) form a circuit with electrolytes, materials that can transfer charge. The TiO2 is coated in photosensitive dye, which releases electrons when exposed to light. The electrons flow continuously between the dye, the TiO2, and the electrolyte. Liquid solutions of dissolved ions are often used as electrolytes, but leakage and evaporation make them impractical in solar cells. As researchers turned to solid electrolytes, they faced the obstacle of getting a solid to completely fill the space surrounding the porous TiO2 layer. In response, Daeyeon Lee, professor of Chemical Engineering at Penn, decided to try growing a solid polymer electrolyte directly inside the pores. Using a process called initiated chemical vapor deposition (iCVD), the polymer grew to occupy 90% of pore space, greatly increasing the efficiency of the circuit.7 This technique of heating the polymer reagents

"In a single hour, the sun bestows the Earth with the amount of energy humans consume in a year" to the point of vaporization and delivering them to the surface of the pores to grow allows polymer electrolytes to be a viable alternative to liquid electrolytes in DSSCs. Lee then turned his attention to pore size and surface area. To maximize these properties, his lab created a multilayered TiO2 structure and experimented with different materials.8. 9 Both of these modifications resulted in increased DSSC efficiency. Their improvements to DSSC efficiency using manipulation of nanomaterials is promising for the future of these systems in solar technology. Also a professor of Chemistry and Engineering at Penn, Dr. Andrew Rappe has taken a different route into new solar cell materials. His lab uses ferroelectric perovskites, materials with particular crystal structures that can polarize spontaneously. They commonly involve oxygen bonded to metal and applying enough energy excites electrons from the oxygen to the metal, creating a “conduction band” of travel between metals. Since oxygen’s high electronegativity restrains it from donating electrons, the bandgap, the amount of energy required to excite

electrons of the oxygen atom to enter the conduction band of the metal atom in this case, is fairly large. To improve their efficiency, Rappe’s team created ferroelectric perovskites with lower range bandgaps. They combined a common ferroelectric perovskite with a small amount of a barium, nickel, niobium and oxygen compound (BNNO). Adding BNNO reduced the polarization of the perovskite’s bonds, which in turn lowered the bandgap. In subsequent tests, the reduced bandgap enabled up to six times more solar radiation to be absorbed. These modified ferroelectric perovskites may prove valuable to future stable, low-cost, and efficient solar cell technology. Solar power technology still has a long way to go before it will be able to replace a significant proportion of the nonrenewable and polluting sources of energy that we currently rely upon. As scientists explore new materials, setups, and methods, however, their incremental improvements will add up. A single panel’s energy depends on the contribution of many solar cells, compounding the effects of each minute detail. Though the clean efficiency anticipated by shimmering roadside panels still eludes us, scientists are steadily pushing forward towards that bright blue future. Works Cited (1) Christensen, N. L. and Leege, L. (2016). The Environment and You. Hoboken, NJ: Pearson. (2) Photovoltaic (Solar Electric)SEIA. (3) Types of Photovoltaic (PV) Cells The National Energy Foundation. (4) Crystalline Silicon Photovoltaics Research Department of Energy. (5) Talapin, D. V., Lee, J.-S., Kovalenko, M. V. and Shevchenko, E. V. (2010). Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Chemical Reviews 110, 389–458. (6) Zhao, T., Goodwin, E. D., Guo, J., Wang, H., Diroll, B. T., Murray, C. B. and Kagan, C. R. (2016). Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer. ACS Nano10, 9267–9273. (7) Effects of polymer chemistry on polymer-electrolyte dye sensitized solar cell performance: A theoretical and experimental investigation Effects of polymer chemistry on polymer-electrolyte dye sensitized solar cell performance: A theoretical and experimental investigation. (8) Park, J. T., Prosser, J. H., Ahn, S. H., Kim, S. J., Kim, J. H. and Lee, D. (2012). Enhancing the Performance of Solid‐State Dye‐Sensitized Solar Cells Using a Mesoporous Interfacial Titania Layer with a Bragg Stack. Advanced Functional Materials. (9) Park, J. T., Chi, W. S., Kim, S. J., Lee, D. and Kim, J. H. (2014). Mesoporous TiO2 Bragg Stack Templated by Graft Copolymer for Dye-sensitized Solar Cells. Nature News.


An Interview Interviewwith with

Dr. Mark MarkDevlin Devlin

CONDUCTED BY Eric Teichner (C’20) What is your research about? So what we are doing is studying the interior structure of large galaxies, these are like the milky way galaxy and 10,000 other galaxies, and they are all interacting with each other doing different things. So what we are interested in how they form, when they formed, and how they evolved. How did you get involved in this research? My father was a physicist and I went to undergraduate as a physics and math major and then I went to Berkeley thinking I was going to be high energy physics. But while I was at Wisconsin, I did research on a gamma ray telescope and I kind of enjoyed it. So when I went to Berkeley, I was basically recruited by a young faculty member there doing interesting stuff and I got hooked. What is the most exciting thing about your research? Professor Mark Devlin is a Professor of Physics and Astronomy at the University of Pennsylvania. His research is on galaxy formation and star formation using sub-millimeter telescopes. Most of his efforts are in the building of these telescopes, such as the BLAST balloonborne telescope and the ACT land-based sub-millimeter telescope in Chile. His most notable work is on BLAST, a balloon telescope, that he currently works on as principal investigator. BLAST is a telescope attached to a balloon that will eventually launch from Antarctica taking pictures of the night sky by using the thermal heat of far-off events to create images. He has a large experimental group that includes graduate students and undergraduate students working on building these cutting-edge telescopes.

Well, I mean have a great job. So, I mean exciting personally is that I can travel the world. I’ve been to Antarctica, I’ve been there three times and I’m going again this year. I’ve been to Chile.It’s not like I’m an astronomer who looks in a telescope all night long. I build the equipment and I maintain it. If you like to tinker and like to make things work, it’s a great job.” Do you have any advice for students looking to pursue research in this area? Well I think if you want to continue on a career like this, it’s a fair amount of work. There’s a lot of dedication- I was an undergrad and did research, something like 20 hours a week. It never occurred to be that I was checking off a box for graduate school. It was fun. I have a lot of students come in and I can tell they are checking off a box. They are in the same mode as then they applied to undergraduate school, the notion they need a certain level of credentials. But the bottom line is for a professional researcher, if you’re not having fun, it’s not worth it. It’s way too much work. And so, don’t kid yourself when you’re doing this. Do the research because you think it’s something you want to do, not because you have to. What is BLAST and how does it relate to your research? So BLAST stands for Balloon-borne Large Aperture Submillimeter Telescope. It was originally designed to look


at distant galaxies and find out what the star formation rate was and it was motivated by a measurement in the late 1990s, where researchers found some galaxies with incredibly bright star forming signatures. But, they couldn’t really nail it down. The problem is that from the surface of the Earth, the atmosphere absorbs most of the light from these galaxies. So there was a satellite that was designed, but while the satellite was being prepared, we built BLAST and used that. Since then, we modified it to look at the star formation of our own galaxy. When was BLAST first implemented? What was your role in its implementation? Well, I was the principal investigator the whole time through. That means I wrote a proposal and got the funding. I’m thinking we were first funded in 2002. We flew first in 2005 from Sweden to Canada. The test flight was in 2003. In 2006, we flew it in Antarctica.

What is the most interesting thing you’ve discovered about Cosmic Background Radiation? Most of the star formation has a redshift greater than two, it means that the universe is entering its middle age. The star formation rate is dropping. Years ago, you made an appearance on The Colbert Report. How fun was it going on The Colbert Report to Colbert to talk about BLAST? It was interesting, I don’t really watch TV, so I’ve never actually seen his show. So when he invited me, I watched a couple of his shows. He’s hardball on politics, but he seemed to be easier on scientists. It was a fine interview; I’ve only watched it once.

BLAST prepares for launch in Antarctica in 2012 Credit: NASA/Wallops Flight Facility SPRING 2017 | PENNSCIENCE JOURNAL 17


Cytotoxic, Antibacterial and Allelopathic Properties of Select Antidiarrheal Ethnobotanical Plants Found in the Dominican Republic Tested In-Vitro Brianna Douglas, Dr. Manuel Aregullin Cornell University, Ithaca, New York

Introduction Situated in the center of the Caribbean, the tropical climate of Hispaniola Island gives way to an eclectic array of plant life. As the most geologically diverse country in the Caribbean (Jackeline Salazar), this plant diversity is intensified in the Dominican Republic, revealing over 600 plant species, 36% of which are endemic (Jackeline Salazar). Medicinal use of native plants has long been ingrained in the culture of the Dominican Republic, dating back to the indigenous Taino peoples. The five plants selected were done so due to their ethnobotanical claims of antidiarrheal remedy. The collected plant material was then used to prepare both methanol and isopropanol organic extracts. The selected plants include: Psidium guajava, Melicoccus bijugatus, Stachytarpheta jamaicensis, Coccoloba uvifera, and Melicoccus jimenezii.

“verbena,” has long been traditionally used by the elderly in many folk medicine cultures including part of Africa and the Caribbean. Ethnobotanical claims have been made suggesting S. jamaicensis treats respiratory problems, inflammation, infectious diseases, and gastrointestinal problems including diarrhea. Research has revealed that methanol extracts of S. jamaicensis do have high antidiarrheal properties when tested in vivo on magnesium and castor oil induced diarrhea (Liew, Pearl Majorie, and Yoke Keong Yong). Antimicrobial studies have shown that the crude plant extracts in the leaves, roots and stem of the plant exhibit antimicrobial activity against Pseudomonas aeruginosa, Micrococcus luteus, and Escherichia coli. (Putera I., Anis Shazura K.). The plant material used for this research was collected in the Punta Cana area and the leaves were used to create extracts.

Psidium guajava, also known as guava or guayaba, has been used medicinally due to its claims of antihyperglycemic, anti-hyperlipidemic (íaz-de-Cerio, Elixabet et al) and anti-diarrheic activities. Recent research has revealed that P. guajava inhibits some dental caries and periodontal pathogens (Chandra Shekar, Byalakere Rudraiah et al). The fruit, husk and leaves are consumed raw to aid in the cessation of diarrhea. The leaves used in the extracts were collected from a tree in the Punta Cana area and crushed to prepare the methanol and isopropanol extracts.

Coccoloba uvifera, or commonly named Uva de Playa (sea grape) by locals is often used for decoration or consumption in the form of liquor, wine, or raw fruit. Little research has been published on potential health effects of C. uvifera, however, the veins are claimed to aid with tumors, asthma and diarrhea among others (Economic and Medicinal Plant Research). With this ethnobotany in mind, plant material was collected from the Punta Cana area and extracts were created from the dried veins of the Uva de Playa plant.

Melicoccus bijugatus, often referred to as limoncillo, is a popular fruit sold by street vendors in the Dominican Republic. The pulp, leaves, and seeds have all been used medicinally to treat ailments such as fever and diarrhea. The seeds, which are typically roasted, ground, and mixed with honey to remedy diarrhea (Economic and Medicinal Plant Research), were the part selected to prepare the extracts. Epicatechin, catechin and procyanidin B2 are phytochemicals that have been found in all parts of the seed and prevent dehydration and nutrient loss from dehydration due to chloride transport inhibition (Bystrom, L.M). Derivatives of catechin, the phytochemical found in lower quantities within the seeds, have microbe activity which is thought to inhibit some bacterial growth. A-type procyanidins, found in the seed coats, have antiadherence effects on bacteria and may be present in trace amounts of the extracts, though the coats have been removed. (Bystrom, L.M.). Specimens for the extracts were collected from the Punta Cana Ecological Foundation Fruit Garden.

Stachytarpheta jamaicensis, otherwise named


M. Jimenezii (Cotoperiz) is a fruit-bearing tree in the sapindaceae family along with M. bijugatus. M. jimenezii is a species endemic to the Punta Cana region of the Dominican Republic (Rolando Sano). Unlike the more common M. bijugatus species, the fruits of M. jimenezii are smaller and have a tough yellow rind that encases a bright orange pulp. No research could be found regarding the Punta Cana native M. jimenezii. The seeds were collected from the Punta Cana Ecological Foundation Fruit Garden and macerated to be used to create extracts, as was done with M. bijugatus. Objective The main objective for this research was to use ethnobotanical claims to identify bioactive plants in order to further assess their alternative medical value. Specific properties include their probable cytotoxic, allelopathic and antimicrobial activity. Materials and Methods Five species of plants were selected based on their ethnobotanical claims as antidiarrhoeals. Plant matter used in these claims was then collected from the Punta Cana Fruit

RESEARCH Garden in the Dominican Republic and surrounding area. This material was then laid out on the lab bench to dry for four days before being condensed. Leaf plant material (from P. guajava, S. jamaicensis) and leaf vein material (from C. uvifera) was placed in a blender to be condensed, while seed material (from M. bijugatus and M. jimenezii) was macerated with a traditional mortar and pestle. The material was then divided into glass vials, and 7.50ml of solvent were added. Both methanol and isopropanol extracts were prepared. Brine Shrimp (Artemia salina) Assay: A Cytotoxicity Test by Proxy This assay was used to determine the lethality of the plant extracts to brine shrimp (Artemia salina) as a proxy for cytotoxicity since it has been shown to have a strong correlation with results from antitumor activity against human cancer cell lines (Anderson et al., 1991; McLaughlin et al, 1995). A 24 well plate (6x4) with a capacity of 3 ml per well was used for the Brine Shrimp Assays. The plate was set up for testing as follows: Add 1 drop (25μl) of extract #1 to the first well in row A, 2 drops (50μl) of extract #1 to the first well in row B, 3 drops (75μl) of extract #1 to the first well in row C and 4 drops (100μl) of extract #1 to the first well in row D. Treat the rest of the wells (2-5) with the remaining extracts as above. To set the solvent controls: Add 1 drop of the corresponding alcohol to well 6 in row A, 2 drops of the corresponding alcohol to well 6 in row B, 3 drops of the corresponding alcohol to well 6 in row C and 4 drops of the corresponding alcohol to well 6 in row D. Allow the solvent to evaporate to dryness before introducing the brine shrimp to the wells. Add 2 ml of brine to all wells followed 10 to 15 brine shrimp per well. The number of dead brine shrimp was recorded at 24 hours under a dissecting microscope and reported as percentage mortality relative to the controls (Aregullin, Manuel). Seed Germination Assay A Whatman #1 filter paper disc (~9.5 cm in diameter) was introduced to the bottom of a Petri dish (10 cm in diameter). 0.5 ml of an isopropyl alcohol extract were deposited on the filter paper and allowed to dry before a second application of 0.5 ml of a methanol extract on the same filter paper disc was made and allow to dry. The filter paper was then moistened with 0.5 ml of water and 5 cucumber seeds were placed on the filter paper and the dish covered. Seed germination was recorded for each plant extract treatment as percentage. In addition, observations on delay in germination and root rate of elongation were recorded were appropriate (Aregullin, Manuel) Antimicrobial Test: Disc Diffusion Assay Plant extracts were tested for antimicrobial activity against Pseudomonas aeruginosa, Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Saccharomyces cerevisiae, which function as proxies for common human pathogens. The solid media used for the antimicrobial bioassays was prepared with 23 g of Nutri-

ent Agar [cat# 213000) manufactured by Difco BD, in 1 L of water. Anti-microbial experiments were conducted by first preparing filter discs of extracts by submerging them into the methanol or the isopropanol crude extracts. The saturated filter discs were left out at room temperature for 30 minutes in order for the solvent to evaporate and leave behind only the crude plant extract. Five different microorganisms were used to measure the efficacy of the crude plant extract. The five microorganisms were grown on Nutrient Agar plates and the saturated filter discs were placed on top after inoculation. The plates were incubated at 37°C for 24 hours and inspected for inhibition (Aregullin, Manuel). Results Brine Shrimp Assay (Cytotoxicity) Artemia salina (also referred to as Brine Shrimp) were used as a medium to test the cytotoxicity of the selected plants. The average survivorship rate of Artemia salina in each test well is recorded on figure 1.1 and 1.2. M. bijugatus and M. jimenezii proved to contain properties with the highest cytotoxicity. M. jimenezii had particularly potent cytotoxic effects in both the isopropanol and methanol mediums.

Figure 1.1: Comparative survival rates of Artemis salina in isopropanol plant extracts reveal the dose response in M. bijugatus and M. jimenezii has the highest cytotoxicity

Figure 1.2: Comparative survival rates of Artemis salina in methanol plant extracts reveal the dose response in M. bijugatus and the high cytotoxicity of M. jimenezii


RESEARCH Seed Germination Assay (Alleopathy) Cucumis salvis seeds were placed in petri dishes with the dried extracts and kept moist to determine alleopathy, or the ability of the plants to coexist or kill other plants. There were not separate trials for the different extracts. Percentage germination was recorded with P. guajava at 80%, M. bijugatus at 80%, S. jamaicensis at 20%, C. uvifera at 40%, and M. jimenezii at 40%. The methanol control had 100% germination and the isopropanol control had 40% germination. A relative germination key was also created to further describe the seed growth in average length of sprouts (Figure 2.2). 1cm represents weak growth, 4cm represents moderate growth, and 5cm represents strong growth. Relative growths are displayed in Figure 2.3. Disc Diffusion Assay (Antimicrobial) The organic methanol and isopropanol extracts were both tested for inhibition effects against 5 different microbes. The isopropanol extracts revealed P. guajava to inhibit the most growth with weak inhibition of S. aurens, E. coli, and S. cerevisae. S. jamaicensis also weakly inhibited E. coli and C. uvifera also weakly inhibited S. aurens. All other isopropanol extracts were ineffective on the microbes. These results are displayed in Figure 3.1. The methanol extracts inhibited more growth as a whole. The P. guajava extract inhibited growth moderately to very strongly in all of the microbes. S. jamaicensis inhibited growth in three microbes (L. monocytogenes, P.

aeruginosa, and S. cerevisae) and C. uvifera inhibited growth in P. aeruginosa. The relative inhibition was determined by the size/presence of a ring of inhibition surrounding the disk. A 0.5mm ring represents weak inhibition, 1mm represents moderate inhibition, 2mm represents strong inhibition and anything 3mm or greater represents very strong inhibition. These results are illustrated by Figure 3.2. Discussion and Conclusions Brine Shrimp Assay As can be seen by the graphs of the isopropyl alcohol extracts (Figure 1.1), the control had neither a dose effect nor significant cytotoxicity to the brine shrimp population. P. guajava extract had a weak dose effect, with the average survival rate dropping from 94.5% at 25Îź concentration to a rate of 56.2% at 100Îź. Though the trend is continuously downward, the dose effect is weak and may not be significant. Similarly, C. uvifera extract displays weak cytotoxic with no dose effect. The survival rate hovered around 50%, which may have been due to larvae viability. M. bijugatus and S. jamaicensis extracts however, both displayed dose effects with M. bijugatus revealing moderate and significant cytotoxicity with an average survival rate of 30% at 100Îź. M. jimenezii extract shows strong and significant cytotoxicity with the survival rate remaining around 25% in all concentrations. Despite this, there is no obvious dose effect.

The graph of the methanol extracts (Figure 1.2)

Figure 2.1: Germination percentages of Cucumis salvis seeds with plant extracts show S. jamaicensis is the least allopathic

Figure 2.2: Scale of relative growth lengths

Figure 2.3: Comparison of plant Cucumis salvis growth reveal P. guajava is the most allopathic



Figure 3.1: Relative microbial inhibition of isopropanol plant extracts show P. guajava inhibits the most microbes

Figure 3.2: Relative microbial inhibition of methanol extracts show P. guajava inhibits the most microbes and inhibits P. aeruginosa the best reveals a different story. Here C. uvifera had no dose effect as well as no significant cytotoxicity. S. jamaicensis also had no dose effect and weak to no significant cytotoxicity. The methanol control however, appears to have a moderate dose effect and reasonably significant cytotoxicity. The results from the other three extracts all revealed weak to very strong dose effects. The P. guajava extract showed a weak dose effect with relatively weak cytotoxicity as the survival rate dropped from 80% to about 50% in the highest (100μ) concentration. Melicoccus bijugatus and jimenezii both revealed the most dramatic changes in average survival rate. The M. bijugatus extract maintained an inverse relationship between average Artemia salina survival rate and seed extract concentration. Survival rate fell from 86.7% to 38.5%, a relatively strong dose effect and significant cytotoxicity. Increase of the concentration of M. jimenezii extract also resulted in an Artemia salina survival rate drop. With the lowest concentration (25μ) survival rate of brine shrimp was 88.5% and as concentration increased to 100μ the survival rate dropped as low as 6.7%. This revealed a strong dose response and very strong cytotoxicity levels. From the comparison of these results it appears as though neither the isopropanol nor methanol extracts revealed significant cytotoxicity or dose effects from the C. uvifera specimen, though isopropanol did reveal a better dose effect. S. jamaicensis also revealed weak to no significant cytotoxicity in either extract, though the isopropanol

S. jamaicensis did extract a relatively weak dose response. P. guajava showed very similar moderate dose responses in both solvents, though the cytotoxicity is relatively higher within the methanol extract. The plant extracts that had significant cytotoxicities were both M. bijugatus and M. jimenezii. M. bijugatus had a strong survival rate decrease of about 50% (from 25μ to 100μ) in methanol but was overall moderately more cytotoxic in isopropanol. M. jimenezii proved to be the most cytotoxic of all the tested plants with the strongest dose response in the methanol solvent. Further tests should be conducted on both the Melicoccus bijugatus seed and the Melicoccus jimenezii seed. Cross comparisons should also be done to investigate if the cytotoxicity is characteristic of the Melicoccus genus. If so, potential uses for these plants may include in the development of cancer drugs. Seed Germination Assay Because the methanol control did not have full germination it is difficult to find a clear correlation between seed germination and plant extract. However, as Figure 2.1 shows, both P. guajava and M. bijugatus exhibited 80% germination. With strong (P. guajava) to moderate (M. bijugatus) root growth over the allotted time period (Figure 2.2). It is possible that this is due to a growth promoter in either or both extracts, or no extract effect at all. C. uvifera and M. jimenezii had the same seed germination rate of 40%. Both of these plants had weak growth with all of the roots being about 1cm or less. S. jamaicensis


RESEARCH however, had the lowest germination percentage at only 20% weak growth. This appears as though it may be low enough to suggest the S. jamaicensis has allelopathic tendencies to inhibit germination. Seed viability could greatly affect these results and suggest a correlation where none exists. In order to corroborate these predictions, more trials must be performed and it must be determined whether or not the methanol does inhibit germination. Perhaps another control using water should be implemented. Disc Diffusion Assay The isopropanol seemed to be a less efficacious solvent to extract the microbe inhibitory chemistry from the plant material. Not only were fewer microbes inhibited by less plants extracts, but also the ring of inhibition was much smaller. P. guajava inhibited the most microbes (S. aurens, E. coli, and S. cerevisae) though all inhibition was weak. C. uvifera also weakly inhibited the gram-positive S. aurens while S. jamaicensis weakly inhibited gram-negative E. coli. The chemistry of the extracted alkaloids in C. uvifera and the S. jamaicensis extract must differ in a way that allows for C. uvifera to penetrate the gram positive S. aurens peptoglycan wall. Similarly, the alkaloids extracted from P. guajava must have some property that allows them to inhibit gram-negative bacteria as well as gram-positive bacteria and fungi (S cerevisae). The methanol solvent seemed to extract alkaloids with much higher anti-microbial properties. S. jamaicensis isopropanol extract revealed moderate inhibition of gram positive bacteria, L. monocytogenes, and weak inhibition of gram negative P. aeruginosa and the fungi S. cerevisae. C. uvifera extract displayed moderate inhibition of the gram-negative bacteria P. aeruginosa. P. guajava isopropanol extract revealed moderate inhibition in both grampositive bacteria as well as moderate in the gram-negative E. coli. P. guajava showed the strongest inhibition of all the trials in the gram-negative bacteria P. aeruginosa as well as strong inhibition of the fungus S. cerevisae. Isopropanol was a better solvent to extract the active antimicrobial alkaloid from P. guajava. Given the high inhibition from P. guajava, especially in the P. aeruginosa bacteria, which has been known to be the cause of infectious diarrhea (Porco and Visconte), the ethnobotanical claims of P. guajava as the best antidiarrheal could potentially be true. Especially considered its inhibition in the gram-positive bacteria (which typically possess enterotoxins responsible for diarrhea [Peterson Jw.]) as well as E. coli, another known diarrhea-causing bacterium. The lack of microbial inhibition from M. bijugatus, and M. jimenezii, though an interesting similarity, does not corroborate their claims as antidiarrheal nor prior research claims as antibacterial. In summary, this study has, particularly the facet regarding cytotoxicity, revealed evidence suggesting that M. bijugatus and the previously unexamined M. jimenezii have anticancer properties. Isopropanol appears to best extract this potential anticancer chemistry in both species overall, though the methanol medium extracted chemicals for a much stronger dose effect fin M. jimenezii. Future studies will isolate and examine the specific active compounds 22 PENNSCIENCE JOURNAL | SPRING 2017

that contributed to the cytotoxic results in each of these species and judge their potential as alternative anticancer therapies. Finally, this study also discovered evidence that may corroborate the ethnomedicinal use of P. guajava as an antidiarrheal but yielded results that may question the use of M. bijugatus as an antidiarrheal. Targeted research to examine the specific chemistry of these plants is necessary. Works Cited Aregullin, Manuel. “Re: Bioassay Protocols).” message to [Brianna Douglas]. July 15, 2016. Bystrom, Laura M. “The Potential Health Effects of Melicoccus Bijugatus Jacq. Fruits: Phytochemical, Chemotaxonomic and Ethnobotanical Investigations.” Fitoterapia 83.2 (2012): 266–271. PMC. Web. 12 Aug. 2016. Díaz-de-Cerio, Elixabet et al. “Exploratory Characterization of Phenolic Compounds with Demonstrated AntiDiabetic Activity in Guava Leaves at Different Oxidation States.” Ed. Manickam Sugumaran. International Journal of Molecular Sciences 17.5 “Economic and Medicinal Plant Research.” (1989):n. pag. Partners for Rural Health in Dominican Republic. 1989. Web. 12 Aug. 2016 Jackeline Salazar, personal communication, June 2016. Liew, Pearl Majorie, and Yoke Keong Yong. “ Stachytarpheta Jamaicensis (L.) Vahl: From Traditional Usage to Pharmacological Evidence.” Evidence-based Complementary and Alternative Medicine : eCAM 2016 (2016): 7842340. PMC. Web. 12 Aug. 2016. Peterson JW. Bacterial Pathogenesis. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 7 Porco, FV, and EB Visconte. “Result Filters.” National Center for Biotechnology Information. U.S. National Library of Medicine, 1995. Web. 15 Aug. 2016. Putera I., Anis Shazura K. Antimicrobial activity and cytotoxic effects of Stachytarpheta jamaicensis (L.) Vahl crude plant extracts [Master dissertation] Universiti Teknologi Malaysia; 2010 Rolando Sano, personal communication, June 2016


Electrophysiological Changes Following Traumatic Brain Injury in Awake Behaving Rats Robin Russo, Candidate for B.A. in Neurobiology, 2016 Department of Biology, College of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania Research Adviser: Dr. John A. Wolf Major Adviser: Dr. Marc F. Schmidt Lateral fluid percussion injury (FPI), the model of traumatic brain injury (TBI) used in the present study, produces neurobehavioral and cognitive deficits seen in patients with TBI. Our central hypothesis is that traumatic injury may disrupt the timing of theta rhythms in the hippocampus that could underlie aspects of post-TBI cognitive dysfunction. Such functional impairment after TBI may result from alteration in activity of individual hippocampal pyramidal neurons and inhibitory interneurons. To explore the representation of these spatially selective neurons, we made multiple single-unit and local field recordings using a 32-channel wireless system at a sampling rate of 32 kHz in a freely moving adult male Long Evans rat. We obtained place-specific firing fields, which are parts of the hippocampal-dependent memory, electrophysiologically mapped from a series of behavioral experiments from a rat trained to run in an open field in order to confirm spatial selectivity of place cells. Future experiments will couple the effects of injury in Long Evans rats on place cell specificity recorded in the open field with the corresponding behavioral dysfunction observed in the Morris water maze (MWM).

Introduction Traumatic brain injury (TBI) affects 1.7 million civilians (Selassie et al., 2008) and 125,000 soldiers each year with the vast majority characterized as mild in severity (Taylor et al., 2012). Mild TBI (mTBI) has been associated with subsequent occurrence of post-traumatic stress disorder (Hoge et al., 2008), and the association and overlap in symptoms suggests that mTBI could mediate or predispose an individual to post-traumatic stress disorder (PTSD), linking the two disorders as co-morbidity factors (Acosta et al., 2013). Behavioral impairments associated with TBI include disruption of nearly every level of information processing, particularly memory and information processing based in the hippocampus (Capruso and Levin, 1992; Whiting et al., 2006) The hippocampus also has an essential role in spatial memory, a type of declarative memory associated with spatial locations. Single hippocampal neurons increase firing rate whenever rats traverse a particular location, and pyramidal cells demonstrate firing patterns that also depend on location, leading to the name “place cells” for these hippocampal cells with location-dependent firing (O’Keefe and Dostrovsky, 1971). Lateral fluid percussion injury (FPI), the model of TBI used in this study, produces neurobehavioural and cognitive deficits in rats, such as difficulties with movement and memory, commonly seen in patients with TBI (Xiong et al., 2013) and has been demonstrated histopathologically to produce neuroinflammation (Acosta et al., 2013) and neuronal cell death in the hippocampus. We aim to compare hippocampal firing patterns of injured and uninjured animals in an open field task. During this project, we implanted a sham rat using a microdrive, 2-shank electrode and recorded using a wireless system and ran the same experiment in an injured animal.

Materials and Methods Subjects and Housing Conditions Adult male Harlan Sprague–Dawley and Long Evans rats (305–390 g) were used in the study. Animals arrived pair-housed before surgery and were housed individually after electrode implantation in a controlled environment (constant temperature, 20-26°C, humidity 30 – 70%, lights on 07:00 –19:00 h) with free access to food and water. All procedures were conducted in accordance with animal welfare guidelines outlined in the Guide for the Care and Use of Laboratory Animals, US Department of Health and Human Services and were approved by the Institutional Animal Care and Use Committee at the University of Pennsylvania. Open Field Task The main goal in carrying out the open field task was to understand the changes in hippocampal neural circuitry with respect to theta bursting and phase precession. The box was constructed with black acrylic with dimensions 122 cm length, 122 cm width, and 61 cm height. The Long Evans rat was trained in the open field for two ten-minute intervals daily to eat Fruit Loop pieces distributed at 10-15 s intervals with a 30-minute period between the two sessions while placed in a clear acrylic box on a pedestal in the center of the room. This intertrial interval served to acclimate the rat to feeling comfortable in an open space. Fluid Percussion Injury The fluid percussion injury (FPI) device was used to produce experimental TBI described in detail by others. Briefly, a central craniectomy is connected with luer-lock fitting to one end of a Plexiglas cylinder filled with 37°C isotonic l saline. At the other end in the cylinder is a Plexiglas cork-covered piston mounted on O-rings. Injury was produced by striking the cork with a metal pendulum


RESEARCH dropped from a specific height which results in injection of varying volumes of saline into the cranial cavity, thus producing displacement of neural tissue. The variations of cranial pressure pulses expressed in atmospheres (atm) were recorded on a storage oscilloscope with an extracranial transducer. All rats were surgically prepared for midline FPI and randomly assigned to sham or FPI group. A craniotomy was trephined over the sagittal suture midway between bregma and lambda while the rat is under a mixture of ketamine, and a luer-lock hub was placed over the exposed dura using cyanoacrylate and anchored to the skull with dental acrylic and two small nickel-plated screws. The FPI device was then fastened to the luer-lock and moderate impact was administered which correlates to a moderate degree of injury. Following injury, the luer-lock was detached, the craniotomy hole sealed with bone wax, and the scalp sutured. Sham animals were connected to the FPI device without injury delivered. Surgical Implantation of Chronic Electrode Rats were anesthetized with isoflurane and kept on a heating pad. Following fixation of the skull in the stereotaxic ear bars and a midline incision, the periosteum connective tissue adhering to the bone was removed to expose lambda and bregma points used to level the head. The craniotomy site was then marked with respect to bregma, approximately 2.4 mm posterior to bregma. Screw holes were drilled into the bone around the edge of the exposed skull and were filled with small jewelers’ screws, one of which served as a ground reference and the others as stabilization for the headcap. The craniotomy was drilled after implanting screws, taking care to avoid major blood vessels along the sagittal sinus and to hydrate the exposed dura with saline. The ground wire of the electrode was then wrapped around the ground screw and secured with dental cement. With the electrode mounted to the insertion device and the insertion rod attached to the insertion device with polyethylene glycol, the electrode was lowered to the surface of the brain(Gage et al., 2012). The sham rat was implanted with a high-resolution microdrive (Cambridge NeuroTech) designed to co-align with a small silicon probe that turns with 25 microns per turn and travels up to 6 mm. The electrode was first placed in the cortex of the brain dorsal to the hippocampus and driven down one turn per day until the hippocampus was reached, as determined by corresponding recording outputs. A 2-shank electrode (Cambridge NeuroTech and Gyorgy Buszaki) with 250 micron inter-shank spacing was used, minimizing the distance to avoid recording from the same neurons yet close enough to offer dense single-unit recordings in a target brain region, to give 32 channels total for recording. Impedance on the electrodes is 25-35 kΩ, and the width of the electrodes is 15 microns. Neuralynx Wireless Recording The Cube-64 wireless neural transmitter operates 24 PENNSCIENCE JOURNAL | SPRING 2017

at a 30 kHz sampling rate with a 5 mV input range (Neuralynx, Inc., 105 Commercial Dr, Bozeman, MT, USA). The physiological signals are digitized at the headstage and transmitted to the Digital Lynx SX via a Wi-fi access point which operates at a distance up to 10 m away from the headstage. The Cube-64 is assigned an IP address that allows it to be paired with the Digital Lynx SX. Each AD channel on the headstage is digitized using a fixed reference. The channels are AC coupled and the gain of the amplifier is fixed at 192. Two 16 bit AD converters digitize 64 AD Channel which then sends a signal to the Digitial Lynx SX. The Cube-64 is powered on and off using a magnet, and the smallest battery used lasted up to 30 minutes during a single recording session. LEDs were affixed to the headstage for video tracking, and a 32-to-64 channel reference modification was used to adjust the input connector pinout so that each bank of the 32 channels used had a unique reference. Results Behavior in Open Field and Place Cells Tracking using the LEDs on the wireless headstage monitored continuously by a camera mounted in the room allowed for tracking of the rat’s path in the open field. This task has also been used as a measure of anxiety(Sudakov et al., 2013). Given proper training, the rats should more frequently cross the center of the open field, and once the study includes open field recording from injured rats, we should expect to see a relative decrease in the amount of time FPI rats spend in the center of the open field (Moritz et al., 2014). Investigation of firing properties of neurons as correlated with the spatial location of the rat reveal place field responsiveness typical of pyramidal neurons of the rat hippocampus. A place field is a region in an environment where there is a high probability of a particular cell firing. The square image resembles the open field box with the color scale indicating the number of times a particular cell fired in a specific area normalized by time spent in the area. A place field is considered a “good” place field if there is a correlation between the firing rate of cells to the animal’s location (Venkateswaran et al., 2005), There is a region darker than other parts of the environment, representing a higher probability of the animal being in that area when the observed cell fires. This field can be contrasted with those not as selective for one region in the open field (Figure 1). Fields and Units in the Hippocampus Several units were recorded from the hippocampus of the rat, with some representing pyramidal cells and some representing inhibitory interneurons (Figure 2). Presumed pyramidal cells were distinguished from putative interneurons on the basis of spike width, average firing rate, and the presence of bursts. Inhibitory interneurons tend to have comparatively large extracellular spikes and narrower spike width (Moore and Wehr, 2014). The interactions between these neurons are likely implicated


Figure 1. Highly selective (left) and less selective (right) place cells recorded in the open field task. in generation of fast gamma oscillations, or ripples, which are important for the consolidation of learning and memory (Stark et al., 2014). The local field potential showed prominent theta oscillations and theta phase-modulated gamma oscillations. Theta is a 3-12 Hz oscillation, while gamma is a roughly 40 Hz oscillation superimposed on top of theta. As the rat approaches a specific location of place cell firing, the spiking of the place cell moves earlier in phase relative to the background theta oscillation such that the phase offset essentially measures or represents the distance. This phase shifting relative to spatial distance is called phase precession (William E. Skaggs, 1996).

wireless recording system. This system has many advantages. The relatively low impedance and size of the electrodes serve to enhance signal-to-noise ratios and minimize tissue damage, respectively. It is also physically portable, electrically stable, and has multiple uses from the open field task to more complex learning and memory tasks, such as the Morris Water Maze or fear conditioning and extinction. It provides easy linkage of behavioral changes, provides maximum freedom for the animal and the experimenter, and reduces stress to the rats, which are all important aspects in the study of animal behaviors and electrophysiological outputs.

Discussion We successfully implanted a microdrive and recorded from an awake behaving rat using the Cube-64

Some of the challenges we were presented with included earlier-than-anticipated sacrifice of the animal because the headstage fell off the animal. We also trained

Figure 2. Interneuron (left) and pyramidal cell (right) action potentials recorded in vivo.


RESEARCH the rat for several days prior to surgical implantation of the microdrive, but the rat seemed anxious in the space. This could be addressed by using a training block on the rat prior to surgery to eliminate any confounding factors of the Cube-64 on the rat’s behavior. We also tried to train Sprague Dawley rats to perform the open field task because the FPI model of TBI is better characterized in this strain, but they have limited eyesight and did not perform well, as theymainly rested in one corner, leading us to use Long Evans rats which walked around the space and ate the pieces thrown in. In the context of research on traumatic brain injury, this data provides a preliminary baseline needed to move forward with recording from chronically implanted, injured animals to understand the electrophysiological effects of injury. In past studies in the lab to verify deficits in hippocampal-dependent spatial working memory in injured animals, adult male Sprague Dawley rats were subjected to FPI (2.5 atmospheres) and were tested in the Morris water maze (MWM) 42 hours after injury. We observed significant memory dysfunction in the injured group when compared to sham animals (p<0.05). These data suggest that FPI does indeed lead to behavioral spatial learning and memory deficits. We will perform similar MWM experiments in injured and sham Long Evans rats prior to chronic implantation to confirm the behavioral effects of TBI before recording from them in vivo. Works Cited Acosta, S.A., Diamond, D.M., Wolfe, S., Tajiri, N., Shinozuka, K., Ishikawa, H., Hernandez, D.G., Sanberg, P.R., Kaneko, Y., and Borlongan, C.V. (2013). Influence of PostTraumatic Stress Disorder on Neuroinflammation and Cell Proliferation in a Rat Model of Traumatic Brain Injury. PLoS ONE 8, e81585. Capruso, D.X., and Levin, H.S. (1992). Cognitive impairment following closed head injury. Neurol. Clin. 10, 879– 893. Gage, G.J., Stoetzner, C.R., Richner, T., Brodnick, S.K., Williams, J.C., and Kipke, D.R. (2012). Surgical Implantation of Chronic Neural Electrodes for Recording Single Unit Activity and Electrocorticographic Signals. J. Vis. Exp. Hoge, C.W., McGurk, D., Thomas, J.L., Cox, A.L., Engel, C.C., and Castro, C.A. (2008). Mild Traumatic Brain Injury in U.S. Soldiers Returning from Iraq. N. Engl. J. Med. 358, 453–463. Moore, A.K., and Wehr, M. (2014). A Guide to In vivo Single-unit Recording from Optogenetically Identified Cortical Inhibitory Interneurons. J. Vis. Exp. JoVE e51757. Moritz, K.E., Geeck, K., Underly, R.G., Searles, M., and Smith, J.S. (2014). Post-operative environmental enrich26 PENNSCIENCE JOURNAL | SPRING 2017

ment improves spatial and motor deficits but may not ameliorate anxiety- or depression-like symptoms in rats following traumatic brain injury. Restor. Neurol. Neurosci. 32, 701–716. O’Keefe, J., and Dostrovsky, J. (1971). The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat. Brain Res. 34, 171–175. Selassie, A.W., Zaloshnja, E., Langlois, J.A., Miller, T., Jones, P., and Steiner, C. (2008). Incidence of long-term disability following traumatic brain injury hospitalization, United States, 2003. J. Head Trauma Rehabil. 23, 123–131. Stark, E., Roux, L., Eichler, R., Senzai, Y., Royer, S., and Buzsáki, G. (2014). Pyramidal Cell-Interneuron Interactions Underlie Hippocampal Ripple Oscillations. Neuron 83, 467–480. Sudakov, S.K., Nazarova, G.A., Alekseeva, E.V., and Bashkatova, V.G. (2013). Estimation of the level of anxiety in rats: differences in results of open-field test, elevated plusmaze test, and Vogel’s conflict test. Bull. Exp. Biol. Med. 155, 295–297. Taylor, B.C., Hagel, E.M., Carlson, K.F., Cifu, D.X., Cutting, A., Bidelspach, D.E., and Sayer, N.A. (2012). Prevalence and costs of co-occurring traumatic brain injury with and without psychiatric disturbance and pain among Afghanistan and Iraq War Veteran V.A. users. Med. Care 50, 342–346. Venkateswaran, R., Boldt, C., Parthasarathy, J., Ziaie, B., Erdman, A.G., and Redish, A.D. (2005). A motorized microdrive for recording of neural ensembles in awake behaving rats. J. Biomech. Eng. 127, 1035–1040. Whiting, M.D., Baranova, A.I., and Hamm, R.J. (2006). Cognitive Impairment following Traumatic Brain Injury. In Animal Models of Cognitive Impairment, E.D. Levin, and J.J. Buccafusco, eds. (Boca Raton (FL): CRC Press/ Taylor & Francis),. William E. Skaggs, B.L.M. (1996). Skaggs, W.E., McNaughton, B.L., Wilson, M.A. & Barnes, C.A. Theta phase precession in hippocampal neuronal populations and the compression of temporal sequences. Hippocampus 6, 149172. Hippocampus 6, 149–172. Xiong, Y., Mahmood, A., and Chopp, M. (2013). Animal models of traumatic brain injury. Nat. Rev. Neurosci. 14, 128–142.

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