Early deprivation, but not maternal separation, attenuates rise in corticosterone levels after exposure to a novel environment in both juvenile and adult female rats

Abstract

Separation from the maternal nest alters the hypothalamic-pituitary-adrenal (HPA) axis stress response in adult male rats, but little research has addressed how separation affects female rats. The following experiments investigated how early maternal separation from postnatal day (PND) 2 to 14 affected stress-induced corticosterone and ACTH after exposure to an open field in juvenile and adult female rats. Female rats were separated for 5 h daily from mother and littermates (early deprivation: ED), separated from mother but not littermates (maternal separation: MS), or animal facility reared (AFR). Male siblings were left with the mother rat during separation. Female rats were exposed to an open field arena either during the juvenile period (PND 30) or during adulthood (PND 80–100). Results show that ED juvenile female rats showed a lower corticosterone stress response than MS and AFR female rats when measured at 5 min post-stress, but no difference at 20 or 60 min post-stress. In adulthood, ED female rats showed comparable elevations of corticosterone as MS and AFR rats at 5 min post-stress but lower elevations at 20 min. In terms of behavior, there were no significant effects of early experience. However, in adulthood, ED and MS rats tended to show a decreased proportion of inner grid crossings of the open field compared to AFR rats, suggesting a tendency for increased anxiety in these two separation groups.