G. Hernández-Busot, M. Rivera-López, O. Martínez-Guzmán, M. Cáceres-Chacón, D. Sierra-Mercado

Department of Anatomy and Neurobiology, University of Puerto Rico School of Medicine, San Juan, P.R. 00936


Each year 40 million people worldwide suffer from traumatic brain injury, mainly in the form of concussions. Human studies have linked concussions with the development of fear-related disorders such as post-traumatic stress disorder (PTSD). However, the relationship between concussions and fear behaviors remain unclear and animal studies show conflicting results. To evaluate the potential link between concussions and fear behaviors, a biological link must be examined using reliable injury models and behavioral tests. Given that failure to extinguish fear is a hallmark of PTSD, we hypothesized that a concussive brain injury will impair fear extinction using Pavlovian conditioning in rats. To address this gap, rats underwent fear conditioning where they learned that a tone predicts a shock, and freezing behavior is measured as an index of fear.

Freezing behavior is characterized by lack of movement save those necessary for breathing.

Afterwards, rats received a concussive-like or sham injury using a weight drop. Following recovery from concussive-like injury, rats underwent three sessions of extinction where they learn that the tone no longer predicts a shock. Results showed no significant difference (p>0.05) between concussive-like (n=9) and sham (n=8) injured groups suggesting that concussive brain injury does not affect the ability to extinguish fear. Future studies will aim at examining changes in neuronal activity in brain regions relevant to fear behaviors such as the amygdala using cFos immunohistochemistry.

Support provided by a NEURO-ID fellowship to GH-B, PRCEN-CREST graduate fellowship to MR-L and MC-C; a Young Investigator Grant from the Brain & Behavior Research Foundation (NARSAD) to DS-M; PRCTRC Pilot, RCMI8G12MD00760, NIGMS COBRE, and R21 NS119991 to DS-M.

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