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

The sites of the stimulatory feedback action of gonadal steroids on LH release were investigated in estrogen-primed ovariectomized rats. Either estradiol benzoate (E2) or estrone (E1) injections 72 h after E2 priming induced a significant increase in serum LH 30 h later, whereas injections of progesterone (P) did so 6 h later. Horizontal sections placed above the medial preoptic area prevented the increase after E2 injections but not after E1 and P injections. Retrochiasmatic sections or bilateral lesions placed in the medial-basal part of the suprachiasmatic area prevented any increases in serum LH induced by steroid injections. Intracerebral implantations of E2 and P in E2-primed ovariectomized rats induced a similar significant increase in serum LH when E2 was implanted into the bed nucleus of stria terminalis (BST), the lateral septum (l-SEPT) and the preoptic suprachiasmatic area (POSC), and when P was implanted in to the medial amygdala, the diagonal band of Broca (DBB), the POSC, the l-SEPT and the anterior hypothalamic area (AHA). These results suggest that the stimulatory feedback effect of E2 is exerted on the limbic structures, especially the BST and the l-SEPT, while the main sites of the stimulatory feedback action of P are located in the DBB, the POSC, and the AHA.