VICARIOUS FEAR LEARNING MOUSE MODELS MIMIC POSTTRAUMATIC STRESS DISORDER (PTSD) SYMPTOMS

This study was undertaken to examine the effects of cue- or context-triggered fear conditioning using our vicarious fear learning paradigm and the resilience to repeated unconditioned stimulus (US)-free recall-mediated extinction of such cue- and context-conditioned fear responses in both sexes of mice. Mouse observers were individually subjected to an observational compartment next to the training compartment wherein three demonstrators received 3-days of 30-min vanilla odors contingent on the delivery of 15 pseudo-randomly-arranged footshocks (0.5 mA, 2 s in duration per shock). Vanilla odors-induced freezing response (FR) was used to indicate observers’ vicarious learning magnitude. To investigate the long-term effects of the cue- or context-triggered vicarious fear learning magnitude, we tested the fear conditioning magnitudes (vanilla odors-induced FR) in both novel environment and fear-conditioned (original training) chambers at different time point including 24 hours, 2 weeks and 1 month after the conclusion of a 3-day training sessions. Both male and female mouse observers exhibited higher vanilla odors-induced FR magnitudes in novel environment and maintained such heightened magnitudes up to 1 month after. Likewise, both male and female mouse observes displayed higher context-induced FR magnitudes in the fear-conditioned chambers and only female mouse observers maintained such magnitudes up to 2 weeks after. Moreover, female mouse observers exhibited greater fear conditioning magnitudes than male mouse observers while receiving FR test in both novel environment and fear-conditioned chambers. These results seem to provide a feasible animal model for mimicking PTSD symptoms and reveal the sex dimorphic in the cue- and context-triggered vicarious fear learning.