Estrogen-sensitive oxytocin binding sites are differently regulated by progesterone in the telencephalon and the hypothalamus of the rat.

The localization at the cellular level and the regulation by progesterone of the estrogen-sensitive oxytocin binding sites was studied in the rat telencephalon and the hypothalamus by using quantitative film-autoradiography and histoautoradiography. Male rats (castrated or not) and ovariectomized females (estradiol supplemented or not) were used to characterize these sites and to precise their localization. They were detected in the striatal cell bridges, the olfactory tubercle, the principal nucleus of the bed nucleus of the stria terminalis and the medial nucleus of the amygdala of the telencephalon and in the medial preoptic, the ventromedial and the ventral premammillary nuclei of the hypothalamus. Estrogen administration in addition induced expression of oxytocin binding sites in the major island of Calleja, the anterior hypothalamic area and the terete nucleus. The density of the estrogen-sensitive oxytocin binding sites varied during the estrous cycle, but differently in the telencephalon and the hypothalamus. In the telencephalon it peaked at proestrus 9 h and was already decreased at proestrus 21 h, whereas in the hypothalamus it was similarly high at proestrus 9 h and proestrus 21 h, suggesting the intervention of progesterone in the regulation of the hypothalamic estrogen-sensitive oxytocin binding sites.