EFFECT OF INCREASED MATERNAL CORTICOSTERONE DURING LACTATION ON HIPPOCAMPAL CORTICOSTEROID RECEPTORS, STRESS-RESPONSE AND LEARNING IN OFFSPRING IN THE EARLY STAGES OF LIFE

The influence of maternal corticosterone during lactation on the devel opment of the hippocampal corticosteroid receptor system, hypothalamus -pituitary-adrenal axis activity and spatial learning/retention perfor mance was investigated in the rat during postnatal days Il to 30. We i ncreased the plasma levels of corticosterone by adding the hormone (20 0 mu g/ml) to the drinking water of the dams. When compared to control s corticosterone-nursed offspring displayed: i) higher number of hippo campal type I and type II corticosteroid receptors at 30 days of life, but no changes at 11 and 16 days; ii) higher plasma levels of cortico sterone in the basal condition and after 15 min of maternal separation at ii but not at 16 days; iii) lower adrenal weights at 11 and 16 day s, but which were no longer present at the age of 30 days; iv) no diff erence in performance in the place learning version of the Morris wate r task and T aquatic maze at 16 days. The present results, together wi th our previous findings showing that 90-day-old corticosterone-nursed rats have lower basal and restraint stress corticosterone levels and improved learning performance, indicate that the effects of maternal t reatment appears only after weaning, thereby suggesting that increased corticosteroid receptors may be responsible, at least partially, for the endocrine and learning modifications induced by pre-weaning cortic osterone exposure. The role played by maternal circulating corticoster one during the period of lactation in shaping the characteristics of t he hypothalamus-pituitary-adrenal axis and brain of the offspring is o utlined. (C) 1997 IBRO. Published by Elsevier Science Ltd.