Intermittent physical stress during early- and mid-adolescence differentially alters rats' anxiety- and depression-like behaviors in adulthood.

Abstract

Prior work showed that exposing rats to stress from weaning through to late adolescence (PD23-51) increased anxiety- and depression-related responses in adulthood. In the current study, we tested the hypothesis that the outcome of adolescent stress depends on the specific timing of adversity in adolescence. Male and female rats were exposed to intermittent, physical stress during either early (PD22-33) or mid -(PD35-46) adolescence, and then their anxiety- and depression-related responses to acute stressors were tested in adulthood. Early adolescent stress decreased rats' open-arm exploration in the elevated plus-maze in both male and female rats. Early adolescent stress also increased the duration of time rats spent burying in the shock-probe test and the duration of time they spent immobile in the forced swim test, but these effects were only seen in males. Stress in mid-adolescence did not increase rats' anxiety-related responding in adulthood. Instead, we observed paradoxical increases in open-arm exploration and only modest increases in shock-probe burying that failed to reach significance. Mid-adolescent stress also tended to increase depression-related immobility in the swim test. Thus, the current findings underscore the importance of timing of adolescent adversity to long-term outcomes. It appears that stress in early adolescence leads to a broader range of outcomes in adulthood, at least in male rats. By contrast, stress in mid-adolescence might have more predominant effects on risk-taking behavior (indexed by increases in open-arm activity), a possibility that merits further investigation.