Development of the hypothalamic-pituitary-adrenal (HPA) axis is influenced by external factors during early life in mammals, which optimizes adult function for predicted conditions. We have hypothesized that adolescence represents a sensitive period for the development of some aspects of adult stress response regulation. This was based on prior work showing that repeated exposure of rats to a stressor across an adolescent period increases fearfulness in a novel environment in adulthood and results in lower levels of dopamine receptor subtype-2 protein in prefrontal cortex. Here, we further our investigation of both acute and long-term effects of repeated adolescent stressor exposure on physiological (i.e., corticosterone) and behavioral (i.e., defensive behavior) measures of stress responding in male and female rats. Furthermore, we compared outcomes with those following identical manipulations administered in early adulthood and found that animals exposed to cues of predation threat during adolescence showed the most robust defensive responses to a homotypic stressor encountered in adulthood. Peer interaction during control manipulation in adolescence was identified as an important individual characteristic mediating development of adult defensive strategies.
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