Social interaction, testosterone, and stress responsiveness during adolescence.

Adolescence is the transition from childhood to adulthood, including alterations in the endocrine systems, in neural circuitry and in behavior. During late adolescence, male guinea pigs living in large mixed-sex colonies exhibit a peculiar stress hyporesponsiveness compared with animals in other developmental stages or other housing conditions. In the present study, it was hypothesized that the interaction with conspecifics leads to an increase in testosterone (T) concentrations, which, in turn, reduces cortisol (C) responsiveness. To test this hypothesis, the stress response of pair- and colony-housed animals was compared with that of pair-housed animals that had limited opportunities to interact with unfamiliar animals of both sexes (social stimulation). The main findings were: (1) Social stimulation caused a significant acute increase in T levels. (2) T concentrations increased significantly in colony-housed males from early to late adolescence but not in the other groups. (3) The C response to a novel environment was significantly reduced in late adolescent colony-housed males compared with similarly aged pair-housed males; C responsiveness of socially stimulated males was intermediate. The present data support our general hypothesis that socially induced increases in T during adolescence might organize a reduction of the endocrine stress response.