CORTICOSTERONE RELEASE IN RESPONSE TO REPEATED, SHORT EPISODES OF NEONATAL ISOLATION - EVIDENCE OF SENSITIZATION

Repeated isolation of neonatal rats produces persistent changes in phy siology and behavior. In Experiment 1, we examined changes in plasma c orticosterone (CORT) levels asa possible mechanism for the effects of isolation. Pups that were isolated from their mother and the nest for 1 h per day on postnatal days (PND) 2-9 were compared to control litte rs of pups that were either nonhandled or handled but not isolated. On PND 2, compared to nonhandled pups, handled pups had elevated CORT le vels that returned to baseline levels within 30 to 60 min of return to the home cage. No significant elevation of CORT levels were found in handled pups on PND 9. The CORT levels of isolated pups were over twic e those of nonhandled pups on PND 2 and four times those of nonhandled pups on PND 9. In Experiment 2, we investigated whether the increased CORT release in response to isolation on PND 9 was the result of the pups' treatment on the previous six days as against an effect of matur ation. Plasma CORT levels were measured in rat pups that were either i solated, handled or nonhandled on PNDs 2-8 during the conditions of is olation, handling and nonhandling on PND 9. There were no differences among the groups in basal plasma levels of CORT. Handling on PND 9 did not result in elevated CORT levels in any of the groups. All three gr oups showed a significant increase in plasma CORT levels after isolati on on PND 9. However, the CORT response to isolation of pups previousl y isolated on PND 2-8 were significantly higher than pups that were ei ther handled or nonhandled on PNDs 2-8. Thus; daily episodes of isolat ion potentiate the hypothalamic-pituitary-adrenal response to stress. (C) 1998 ISDN. Published by Elsevier Science Ltd.