EFFECTS OF ENRICHMENT AND HOUSING ON CORTISOL RESPONSE IN JUVENILE RHESUS-MONKEYS

Young rhesus monkeys exposed to conditions of social restriction are s ubject to stress. The physiological indicator, plasma cortisol, can be used to measure this stress. A technique using dexamethasone suppress ion-adrenocorticotropic hormone (ACTH) challenge was used to determine whether inanimate enrichment and social housing condition affected pl asma cortisol levels in juvenile rhesus monkeys. Cortisol levels in tw o cohorts of monkeys (N = 64) were determined first while monkeys were caged singly and then while caged in pairs. Both control and enriched subjects received the dexamethasone suppression-ACTH challenge proced ure and, for each cohort, cortisol samples were obtained after 10 and 12 months of single-caging and subsequently after 2 and 4 months of pa ir-housing. Compared with controls, experimental subjects receiving in animate environmental enrichment did not show lower levels of plasma c ortisol. Although environmental enrichment may lead to behavioural imp rovements, it did not affect adrenal function in this study. Social ho using condition (single vs. pair)'also did not affect cortisol. Monkey s in most conditions responded appropriately to the dexamethasone supp ression-ACTH challenge, indicating that levels of stress were not extr eme. There were a number of significant interaction effects that were due to an atypical set of results for one of the control groups in one of the singly housed test sessions. Monkeys that spent their year of single-caging in indoor rooms showed higher activations of the hypotha lamic-pituitary-adrenal system than did monkeys that spent their year of single-caging in outdoor buildings. This suggests that aspects of t he environment outside of the cage (conspecific activity, environmenta l variation, etc.) may influence plasma cortisol. This is surprising, considering that inanimate and social enhancements within the cage had little effect.