Stress vulnerabilities in an animal model of post-traumatic stress disorder

We have studied the effects of inescapable electric foot shocks (ISs) on rats by using a subsequent avoidance/escape task performed in a shuttle box as an animal model of post-traumatic stress disorder (PTSD). In this study, the behavioral differences and the effects of chronic stress exposure prior to IS were examined among male rats of the Wistar, Fischer 344, and Lewis strains. In concordance with our previous report on the Wistar rats, we observed the characteristic features of PTSD in all three rat strains tested, that is, the hyperactive and hypoactive bidirectional behavioral changes that are associated with hypervigilant and hyperarousal behavior, and the numbing and avoidant behavior, respectively. The induction of hypoactive behaviors after IS was most exaggerated in the Fischer and Lewis strains. Although the count of hyperactive behaviors was maximal in the Fischer strain both at basal levels without IS and after IS, the increase in the rate of hyperactive behaviors by IS was the most prominent in the Lewis strain. In addition, preloaded chronic variable stress (CVS) enhanced the degree of hyperactive behavioral changes in the Wistar strain. Thus, we consider that the present study further validates the use of shuttle box paradigm as an animal model of PTSD by demonstrating the vulnerability due to genetic background and environmental preloaded stress.