Learning under stress in the adult rat is differentially affected by 'juvenile' or 'adolescent' stress

Epidemiological studies suggest that childhood trauma is associated with a predisposition to develop both mood and anxiety disorders, while trauma during adolescence is associated mainly with anxiety disorders. We studied in the rat the long-term consequences of 'juvenile' stress, namely stress experienced in a period in which substantial remodelling occurs across species in stress-sensitive brain areas involved in emotional and learning processing. In adulthood, 'juvenile' stressed rats exhibited reduced exploration in a novel setting, and poor avoidance learning, with 41% learning mainly to escape while 28% exhibited learned helplessness-like behaviours. In adult rats that underwent 'adolescent' stress, learned helplessness-like behaviours were not evident, although decreased exploration and poor avoidance learning were observed. This suggests that in the prepubertal phase juvenility may constitute a stress-sensitive period. The results suggest that juvenile stress induces lasting impairments in stress-coping responses. The 'juvenile' stress model presented here may be of relevance to individuals' reported predisposition to anxiety and depression following childhood trauma, and their increased susceptibility only to anxiety disorders following adolescent stress.