Abstract :
[en] Sex steroid hormones act on developing neural circuits regulating the hypothalamic-pituitary-gonadal axis and are involved in hormone-sensitive behaviours. These hormones act mainly via nuclear receptors, i.e. oestrogen receptor-alpha (ERalpha) and androgen receptor (AR). By using immunohistochemistry, we analysed the expression level of ERalpha and AR throughout perinatal life [at embryonic (E) day 19 and postnatal (P) days 5-15-25] and in adulthood in several hypothalamic nuclei controlling reproduction in both wild-type (WT) and aromatase knockout (ArKO) (which cannot convert testosterone into oestradiol) mice to determine whether there are sex differences in hypothalamic ERalpha and AR expression and if so, whether these are established by oestradiol action. As early as E19, ERalpha immunoreactivity (-ir) was observed at same expression levels in both sexes in the anteroventral periventricular nucleus (AVPv), the medial preoptic area (MPOA), the bed nucleus of the stria terminalis (BnST), the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl) and the arcuate nucleus (ARC). Sex differences (female > male) in ERalpha-ir were only observed during the prepubertal period in the BnST (P5 to P25) and the MPOA (P15), but also in adulthood in these two brain regions. Sex differences in AR-ir (male > female) were observed at P5 in the AVPv and ARC, and at P25 in the MPOA and ARC as well as in adulthood in all hypothalamic regions analysed. In adulthood, gonadectomy and hormonal treatment (oestradiol or dihydrotestosterone) also strongly modulated ERalpha-ir and AR, respectively. Taken together, sex differences in ERalpha-ir and AR-ir were observed in all hypothalamic regions analysed, but most likely do not reflect oestradiol actions since ArKO mice of both sexes showed very similar expression levels as WT mice throughout perinatal development. This article is protected by copyright. All rights reserved.
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