Altered stress responsiveness and hypothalamic-pituitary-adrenal axis function in male rat offspring of socially isolated parents.

Social isolation in male rats at weaning results in reduced basal levels of the neuroactive steroid 3a,5a-tetrahydroprogesterone (3a,5a-TH PROG) in the brain and plasma as well as increased anxiety-like behavior. We now show that socially isolated female rats also manifest a reduced basal cerebrocortical concentration of 3a,5a-TH PROG as well as an anxiety-like prole in the elevated plus-maze and Vogel conict tests compared with group-housed controls. In contrast, despite the fact that they were raised under normal conditions, adult male offspring of male and female rats subjected to social isolation before mating exhibited an increased basal cerebrocortical level of 3a,5a-TH PROG but no difference in emotional reactivity compared with the offspring of group-housed parents. These animals also showed an increased basal activity of the hypothalamicpituitary- adrenal axis as well as reduced abundance of corticotropin-releasing factor in the hypothalamus and of corticotropin-releasing factor receptor type 1 in the pituitary. Moreover, negative feedback regulation of hypothalamicpituitary- adrenal axis activity by glucocorticoid was enhanced in association with up-regulation of glucocorticoid receptor expression in the hippocampus. There was also attenuation of corticosterone release induced by foot-shock stress in the offspring of socially isolated parents. The increase in the brain concentration of 3a,5a-TH PROG induced by acute stress was also blunted in these animals. Our results thus show that a stressful experience before mating can inuence neuroendocrine signaling in the next generation. Keywords: 3a,5a-tetrahydroprogesterone, glucocorticoid receptor, HPA axis, rat, socially isolated offspring, stress.