Data on the sites of the stimulatory feedback action of gonadal steroids indispensable for follicle-stimulating hormone release in the rat.

The sites of the stimulatory feedback action of gonadal steroids on FSH release were examined in estrogen-primed ovariectomized rats. Estradiol benzoate (E2) injected 72 h after E2 priming induced a significant increase in serum FSH 6 and 30 h later. However, injections of estrone failed to induce a similar significant increase. Progesterone (P) injections also increased serum FSH 6 h later. Horizontal sections placed above the medial preoptic area prevented the increase in serum FSH after E2 injections but not after P injections. Furthermore, retrochiasmatic sections or bilateral lesions in the medial basal part of the suprachiasmatic area prevented the increase after E2 injections and P injections. E2, implanted into the bed nucleus of stria terminalis and the anterior hypothalamic area in E2-primed ovariectomized rats, induced a significant increase and decrease in serum FSH, respectively, whereas P implanted into the same areas failed to induce it. On the other hand, P implantations into the diagonal band of Broca and the lateral and the medial septum were effective in increasing and decreasing serum FSH, respectively, whereas E2 implantations into these areas were ineffective. Neither E2 nor P implanted into the medial amygdala, the medial preoptic area, or the hippocampus altered serum FSH levels. These results suggest that the stimulatory feedback actions of E2 and P on FSH release are exerted at different sites in the limbic structures.