Charm City Science #4

This image is provided by Mira Swartzlander, a PhD student in Johns Hopkins School of Medicine’s department of neuroscience. It shows cells collected from the vaginal canal of a mouse.

In many animals, ovulation - the release of an oocyte, or egg cell, from the ovaries, where it is produced, to the oviduct, where it is ready to be fertilized - occurs at regular intervals. In most female mammals (with a few exceptions, including both humans and several species of bats), this takes place in the context of the estrous cycle, a series of physical and behavioral changes that prepare the animal to reproduce.

There are 4 stages of the mouse estrus cycle (proestrus, estrus, diestrus, and metestrus), each lasting one to two days. During each stage, different kinds of cells are found in the vaginal lining. By collecting and looking at the cells under a microscope, scientists can identify what stage of the cycle a mouse is currently in. Based on the abundant nucleated epithelial cells observed in this sample, we know that it was collected during the mouse’s proestrus stage. During proestrus, estrogen levels rise in preparation for ovulation and the animal becomes more willing to mate.

Throughout the estrous cycle, dramatic changes to synaptic plasticity - flexibility of the connections between neurons - can occur as well. While these changes likely affect some aspects of behavior, such as willingness to mate, animal behavior remains otherwise mostly stable across stages of the cycle. Monitoring how the brain changes during different stages of the estrous cycle can help us better understand how dramatic synaptic plasticity is balanced with relative stability of general brain function.