Early vs. late maternal deprivation differentially alters the endocrine and hypothalamic responses to stress

Twenty-four hours of maternal deprivation results in persistent changes in the ACTH response to mild stress. These effects are dependent on the age of the neonate at the time of deprivation. Pups that were separated from the dam at postnatal days (pnd) 3-4 showed an enhanced stress-induced ACTH resp onse at age 20, while pups deprived at pnd 11-12 displayed an attenuated AC TH response to stress at that time. The present study was designed to test the hypothesis that the immediate effects of deprivation at pnd 3 vs, pnd 1 1 would provide an explanation for these paradoxical effects observed at da y 20, For this purpose, we measured the basal and the stress-induced ACTH a nd corticosterone (CORT) response at days 4 and 12, following 24 h of mater nal deprivation. Furthermore, we examined whether similar differences in c- fos and CRH mRNA expression in the paraventricular nucleus (PVN) accompanie d the differences in response characteristics of ACTH at pnd 20. The result s indicate that changes in the ACTH and CORT responses were minimal after 2 4 h of maternal deprivation at day 4, whereas these hormones were markedly elevated following deprivation at day 12. The persistent effects also showe d age-dependency: pups deprived early showed at pnd 20 an exaggerated ACTH response. Late deprived juveniles exhibited an attenuated ACTH response to stress at pnd 20 while in both conditions the CORT response was not differe nt from the non-deprived litter mates. These persistent endocrine changes w ere accompanied by the changes in the neural stress markers. The expression s of c-fos and CRH mRNA in the PVN were at pnd 20 significantly greater in their controls in early-deprived animals. The late deprived juveniles showe d a reduced response in these neural markers. In conclusion, the persistent alterations in ACTH are reflected by changes in c-fos and CRH mRNA, but th ese changes in endocrine and in neural stress markers do not appear to be r elated to any of the hormonal changes that occur at the time of maternal de privation. (C) 1998 Elsevier Science B.V. All rights reserved.