Patterns of weaning and adult response to stress

Early environmental effects including variation in maternal care? can modif y hypothalamic-pituitary-adrenal (HPA) axis function. One of the more overt early effects, involving maternal care, is weaning restraint. In this stud y the effects of different patterns of weaning, in the rat (Rattus norvegic us), on both adult response to restraint stress and to dexamethasone admini stration were examined. Animals that as pups experienced a gradual lengthen ing time of separation from the mother, between 21 and 30 days of postnatal age (completely separated on 30 days), showed lower levels of systemic cor ticosterone and glutamate in the sensory cortex in response to restraint st ress than seen in other groups. These animals also showed greater suppressi on of corticosterone by dexamethasone than did animals abruptly removed fro m the mother at 21 days of age. Animals left in the cage with the mother un til either 30 or 40 days of age showed the greatest levels of corticosteron e and glutamate in the sensory cortex in response to the stress and the lea st suppression by dexamethasone. These results suggest that changes in mate rnal contact at time of weaning can influence adult responsiveness to stres s. (C) 1999 Elsevier Science Inc.