Interindividual and sex differences in resilience and vulnerability to post-traumatic stress disorder (PTSD). Insights from animal models

Stress triggers many responses including behavioral strategies to cope with the environment and to maintain homeostasis. Notably, the experience of stressful events is highly subjective. In fact, in susceptible individuals, primary adaptation responses can fail leading to maladaptive mechanisms and to the subsequent development of stress-related disorders (e.g., post-traumatic stress disorder; PTSD). However, the mechanisms underlying interindividual variability in stress adaptation are still to be elucidated. Animal models are widely recognized as essential scientific tools to understand the neurobiological underpinnings of stress susceptibility/resilience, and as tools to identify novel and personalized interventions to treat (and prevent) such disorders in humans. Experimental models have however several limitations, as validity criteria can be very problematic when modeling psychiatric disorders. Also, while sex dimorphism crucially contributes to the risk for stress-related diseases, several frequently used models overlooked sex differences in the interindividual variability in response to stress. In this review, we describe the interindividual and sex differences in susceptibility and resilience in stress-related disorders, with a particular focus on PTSD. Further, we examine aspects of animal models of PTSD that can be improved to obtain higher translational value.