Osmarie Martínez-Guzmán¹, Mauricio Cáceres-Chacón¹, Melissa Rivera-López¹, Héctor Haddock-Martínez ², and Demetrio Sierra-Mercado¹

1 Department of Anatomy & Neurobiology, University of Puerto Rico (UPR) School of Medicine;

2 University of Puerto Rico, Río Piedras Campus (UPR-RP)

The most common form of brain injury, concussion, is frequently seen in contact sports and military combat. Converging lines of evidence suggest that concussion may impair fear-related behaviors.

One type of fear-related behavior, avoidance, occurs when the need to escape from difficult situations such as an aversive stimulus (i.e. footshock) is presented in the presence of a reward (i.e. sucrose pellets). The effects of concussion on avoidance remains unknowns. Concussion can be modeled in rodents with a closed head injury (CHI). Here, a guide tube is placed above the head of anesthetized rats, and a weight is dropped through the tube. In the current study, we hypothesize that CHI will impair avoidance. One hour after CHI or Sham injury, locomotion behaviors were assessed in an open field to test for motion deficits, and CHI did not affect the distance travelled. In the platform-mediated avoidance, rats were conditioned in an operant chamber to auditory tones co-terminating with a mild footshock. An acrylic platform in the opposite corner of the sucrose-delivering bar allowed rats to avoid the shocks. Animals that underwent a CHI spent more time on the platform throughout the test session during the absence of the tone, even though they learn previously that the absence of tone was a safe period. These suggesting that brain injury results in excess avoidance (p=0.0127). The translational relevance of this work suggests that brain injury may contribute to mental health disorders, since excess avoidance is characteristic of patients with fear and anxiety disorders.

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