Social housing conditions around puberty determine later changes in plasma cortisol levels and behavior

A recent study found that male guinea pigs raised in large, mixed age/sex groups exhibited an unexpected suppression of their cortisol response at 4 mo of age. The present study examined the effect of social experience around the time of puberty on cortisol response suppression and social behavior at 4 mo of age. Males reared in large, mixed age/sex groups were either pair-housed with a female or moved to another large colony at 55 days of age. When tested at 4 mo, pair-housed males exhibited much higher levels of courtship and sexual behavior than did colony-housed males, and a shorter latency to begin courtship when with an unfamiliar adult female. In addition, pair-housed males showed much higher levels of agonistic behavior and a shorter latency to escalated aggression with an unfamiliar adult male. Pair-housed males also had lower basal cortisol concentrations and exhibited a greater increment in cortisol levels when isolated in a novel cage than did colony-housed males. Finally, pair-housed males showed a smaller increment in cortisol levels when with the stimulus female or male than when isolated, but colony-housed males did not. The findings demonstrate that social housing conditions around the time of puberty can have pervasive effects on social behavior and hypothalamic-pituitary-adrenal (HPA) activity in 4-mo-old males. Further, these findings are consistent with the notion that changes in HPA activity contribute to social behavior development beyond the time of sexual maturity. (c) 2006 Elsevier Inc. All rights reserved.