79 Behavioral Effects of Trauma Recruit Separate Populations of Ventral Hippocampal Neurons

Faculty Mentor: Moriel Zelikowsky (Neurobiology, University of Utah)

Trauma has been reported to affect over 70% of all adults worldwide. This includes, but is not limited to, physical and sexual violence, injury, threat of death, and natural disasters. Experiencing one or more traumatic events can lead to post-traumatic stress disorder, depression, and anxiety. These symptoms and disorders can negatively affect interpersonal relationships, confidence, aggression, and other aspects of daily behavior. Exactly how these traumatic events are encoded in the brain is poorly understood. Extensive research has been done on the hippocampus with regard to its central role in learning and memory, but only recently has research been done to uncover its role in emotional responses. This research has found distinct functional differences between the dorsal and ventral subregions of the hippocampus. Recent studies suggest that the ventral hippocampus (VH) plays an important role in emotional response. The VH projects to other emotional processing areas of the brain that modulate fear, aggression, and social processing. This project aims to test the hypothesis that distinct populations of neurons in the VH encode individual behavioral effects of trauma as well as discover the extent of overlap between neuronal cells activated by trauma-induced aggression (TIA) vs. trauma-altered sociability (TAS). To test this hypothesis, both male and female mice were injected with an hM4D inhibitory DREADD virus to chemogenetically silence VH. Later the mice underwent either no trauma or a foot shock trauma consisting of 10 1mA foot-shocks randomly applied over 60 minutes. They were then tested for aggression and social response using two distinct behavioral assays known as Resident Intruder and 3-Chamber. Half the mice received DCZ, a ligand used to activate DREADDs, while the other half received a control vehicle prior to each behavioral assay. Our findings show that silencing of the VH led to attenuated TIA and TAS when compared to control groups. Next, using retrograde viral tracing, activity-dependent neuronal tagging, and immunohistochemistry, we examined the existence and extent of overlapping neuron populations in the VH. These findings suggest the VH plays an important role in encoding and responding to trauma. They also highlight the importance of continued research into how behavioral changes are manifested in the brain and how these experiences are studied.