Effects of chronic social stress in adolescence on anxiety and neuroendocrine response to mild stress in male and female rats.

Using a rat model of adolescent social stress (SS, daily 1 h isolation and change of cage partner, 30-45 days of age), we have reported sex-specific effects on neuroendocrine function over the course of SS, and enduring effects of SS in females, and not males, on drug-related behaviour. Here, we investigated both the immediate and enduring impact of SS in adolescence on anxiety-like behaviour in the elevated plus maze (EPM) and determined the temporal pattern of corticosterone release after confinement to the open arm of the EPM. When tested as adolescents, SS decreased anxiety-like behaviour in females and had no effect in males. When tested as adults several weeks after the chronic stress, overall, SS tended to increase anxiety-like behaviour in both sexes. However, estrous cycle moderated the effect in females, in that reduced anxiety-like behaviour was observed for SS females in the estrous group. Confinement to the open arm of the EPM increased plasma corticosterone concentrations, which declined markedly upon return to home cage for all except adolescent control males for which corticosterone concentrations at 45 and 90 min were elevated compared other groups. Among controls, anxiety-like behaviour decreased in females and increased in males with age, and confinement to the open arm of the EPM led to a greater increase in corticosterone concentrations in adult males compared to adolescent males. In sum, modest effects of adolescent social stress were observable several weeks after the stress exposure, indicating that sex-specific developmental trajectories and vulnerability to anxiety may be shaped by experiences in adolescence.