Study protocol: Assessing brain region-specific connectivity and anatomy in rats after stress inoculation training

Stress inoculation is a form of prevention approach prior to exposure to an acute stressor. Thus, it is commonly employed in occupations involving exposure to life-threatening situations, such as in the military, firefighting, and law enforcement. It shares similar features with exposure therapy involving intermittent exposure to mild stressors. Stress inoculation in mice has been adapted from the well-established chronic social defeat paradigm, although the intermittent and milder nature of stress exposure promotes behavioral and endocrine signatures associated with resilience (Ayash et al. 2020; Brockhurst et al., 2015;). Here we report for the first time the effects of employing social stress for stress inoculation in rats. This involved exposing a male Sprague-Dawley rat intruder into the home cage of a novel aggression-screened male Long-Evans resident for a 15-min session every two days over 20 days. During each exposure, a divider was used to prevent the intruder and resident from physical contact but still allowed for sensory contact. In the present study, we will use magnetic resonance imaging (MRI) and diffusion MRI (dMRI) to investigate brain region-specific connectivity and morphometric changes associated with stress inoculation. We will then correlate imaging data with the resultant behavioral and hypothalamo-pituitary-adrenal (HPA) phenotypic changes response in male stress inoculated and control rats.