Predicting susceptibility and resilience in an animal model of post-traumatic stress disorder (PTSD)

Post-traumatic stress disorder (PTSD) is a psychiatric disorder whose pathogenesis relies on a maladaptive expression of the memory for a life-threatening experience, characterized by over-consolidation, generalization and impaired extinction, which in turn are responsible of dramatic changes in arousal, mood, anxiety and social behavior. Even if human subjects experiencing a traumatic event during lifetime all show an acute response to the trauma, only a subset (susceptible) of them ultimately develops PTSD, meanwhile the others (resilient) fully recover after the first acute response. The majority of the available animal models of PTSD lacks of a dynamic dissection to better understand how this acute response can turn into PTSD-related maladaptive changes. Here we have implemented the PTSD model we previously developed, to make it suitable to differentiate between susceptible (high responders, HR) and resilient (low responders, LR) rats in terms of over-consolidation, impaired extinction, enhanced anxiety and social impairment after trauma experience. Rats were exposed to inescapable footshocks paired with social isolation. One week after trauma and before starting the extinction sessions, animals were tested in the Open Field (OF) and Social Interaction (SI) tests to search for a predictive variable for HR and LR classification. We found a correlation between the number of crossings in the OF test and the cognitive and behavioral outcomes associated with PTSD-related maladaptive changes, thus suggesting that this parameter is a reliable predictive variable in term of resilience or susceptibility to develop a PTSD-like phenotype after trauma exposure in rats.