Although prominent sex differences exist in the hypothalamic-pituitary-adrenal axis's response to stressors, few studies of its regulation in the hypothalamic paraventricular nucleus (PVN) have compared both male and female subjects. In this study, we sought to explore sex differences in the acute regulation of PVN neuropeptide expression following glucocorticoid (GC) removal and the underlying role of gonadal hormones. We first examined the effects of short-term adrenalectomy (ADX) on PVN Crh and arginine vasopressin (Avp) expression in mice using in situ hybridization. ADX increased PVN AVP mRNA levels in both sexes. In contrast, PVN CRH mRNA was increased by 2 days after ADX in males only. Both sexes showed increases in CRH mRNA after 4 days. To determine if gonadal hormones contributed to this sex bias, we examined adrenalectomized (ADX'd) and gonadectomized (GDX'd) mice with or without gonadal hormone replacement. Unlike the pattern in intact animals, 2 days following ADX/gonadectomy, CRH mRNA levels did not increase in either sex. When males were given DHT propionate, CRH mRNA levels increased in ADX'd/GDX'd males similar to those observed following ADX alone. To determine a potential mechanism, we examined the coexpression of androgen receptor (AR) immunoreactivity and CRH neurons. Abundant colocalization was found in the anteroventral bed nucleus of the stria terminalis but not the PVN. Thus, our findings reveal a sex difference in PVN Crh expression following the removal of GC-negative feedback that may depend on indirect AR actions in males.
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