Regulation by gonadal steroids of the mRNA encoding for a type I receptor for TGF-β in the female rat hypothalamus

We have recently shown that the mRNA encoding for a type I receptor for transforming growth factor beta and activin - named B1 - is expressed in hypothalamic areas implicated in gonadotropin-releasing hormone regulation, particularly in estrogen-receptive regions. In the present study, we examined whether ovarian steroids may regulate expression of B1 mRNA in the hypothalamus. Comparing relative levels of 131 mRNA expression in ovariectomized (OVX), OVX + estradiol-treated, and OVX + estradiol + progesterone-treated female rats, we observed that estrogen significantly (p < 0.05) downregulated B1 mRNA levels in the anteroventral periventricular nucleus (by 12.5%), medial preoptic nucleus (by 27.5%), and arcuate nucleus (by 29.5%). In contrast, no effects of gonadal steroids were observed in the median preoptic nucleus. We next examined whether cells expressing B1 mRNA may be direct targets for the action of estrogen. Using an in situ hybridization coupled to immunohistochemical labeling, we found that many B1-mRNA-expressing cells also exhibited estrogen receptor alpha immunoreactvity in anteroventral periventricular nucleus, medial preoptic nucleus, and arcuate nucleus. Taken together, these results reveal that estrogen may directly modulate expression of B1 mRNA in the hypothalamus and support the idea that transforming growth factors beta play an important role in the hypothalamic control of gonadotropin-releasing hormone function. Copyright (C) 2002 S. Karger AG, Basel.