SOCIAL REARING EFFECTS ON HPA AXIS ACTIVITY OVER EARLY DEVELOPMENT AND IN RESPONSE TO STRESS IN RHESUS-MONKEYS

Previous studies have found evidence of behavioral and psychophysiolog ical differences between nonhuman primates reared in different social environments, however, few of these have employed longitudinal study o f the animals over early development. In this study, HPA axis activity was assessed via measurement of ACTH and cortisol values over the fir st 6 months of life and in response to two stressful housing transitio ns in 48 infant rhesus monkeys that were either mother- or peer-reared . ACTH and cortisol values declined over the first 6 months in both re aring groups. Peer-reared monkeys showed lower levels of ACTH over the Brst 6 months of life than mother-reared, but the rearing groups did not differ in basal cortisol values over this period. Mother-reared an imals showed a greater ACTH response to the mild stress of being moved to a new cage, and male monkeys showed higher values than females. Mo ther-reared animals showed the largest cortisol increase in response t o the caging transition. Both groups showed increases in ACTH and cort isol in response to the more severe stress of separation from their re aring partners and housing with unfamiliar agemates. Mother-reared ani mals again showed the largest increase in ACTH in response to these ev ents, but increases in cortisol were similar among both sexes and rear ing groups. These results suggest an interaction of sex and rearing hi story in response to stressful events. (C) 1993 John Wiley & Sons, Inc .