| Summary: | The hypothalamo-pituitary-adrenal (HPA) axis, a neuroendocrine pathway involved in the stress response is well studied in both human beings and rodents. Major gender-related neuroendocrine changes take place during pubcl1y (days 30 - 60 in rats) including a robust increase in the levels of gonadal steroids which are thought to underlie numerous neural and behavioural changes brought on after puberty. Evidence suggests the HPA axis undergoes significant changes over the pubertal period. This project investigated the effects of gonadal steroids on the HPA axis before and after puberty and the role of the pubertal surge in endogenous gonadal steroids in both sexes; specifically looking at the sensitivity of the resulting adult HPA axis to exogenous gonadal steroids. There was a significant effect of both age and sex on the adrenocorticotrophic hormone (ACTH) and corticosterone response to restraint stress. Sexual dimorphism in the endocrine stress response became more pronounced after puberty. Adult physiological levels of gonadal steroids reduced the corticosterone and ACTH response to restraint stress in both male and female prepubertal rats. In adult males, testosterone reduced the ACTH response to stress while in adult females, there was a s significant effect of ovariectomy (OVX) on the stress response. 1:estosterone treatment did not significantly affect overall corticosterone release over the 24hr period in adult animals castrated (CSX) before puberty. In contrast, testosterone significantly suppressed corticosterone secretion in animals CSX in adulthood. Animals CSX prepubertally displayed significantly lower glucocorticoid receptor levels in the dentate gyrus of the dorsal hippocampus than animals CSX in adulthood. [n females, prepubertal OVX did not affect the ability of oestradiol to affect basal HPA activity in adulthood. Overall, the data suggest vital roles of peripubertal gonadal steroids on the adult HPA axis; although the pubertal maturation of the female HP A phenotype appears to be independent of peripubertal oestrogens.
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