Unpredictable chronic stress in juvenile or adult rats has opposite effects, respectively, promoting and impairing resilience

We evaluated the effects of early maternal deprivation (MD; age 714 days) alone or in combination with unpredictable chronic stress (UCS; MDUN; 2884 days) on anxiety and learning in 90 days old adult rats. We hypothesized that exposure to both stressors (MDUN) would be more detrimental than exposure to one or neither. Unexpectedly, adult rats from the MDUN group did not differ from control animals, whereas adult MD animals exhibited impaired avoidance learning. We next investigated the effect of juvenile-onset (3090 days) versus adult-onset (6090 days) stress on avoidance learning in adulthood (90 days). We found that adult-onset chronic stress impaired avoidance learning and memory whereas juvenile-onset stress did not. Thus, the results again indicate that juvenile exposure to UCS induces resilience rather than impairment.