Inhibitory influence of the nuclei of the posterior hypothalamus on the pro-oestrous surge of LH.

Abstract

The effect of transecting caudal afferents to the medial basal hypothalamus on the pro-oestrous surge of LH was studied in cyclic female rats. Rats with transverse cuts placed just in front of the mammillary bodies and caudal to the ventromedial hypothalamic nucleus showed an earlier time of onset of pro-oestrous surge of LH. Conversely, rats with transverse cuts placed 2 mm more caudally or with cuts along the lateral edges of the hypothalamus showed no altered release of LH. Advanced release of LH occurred also in rats in which the ventral premammillary nuclei or the posterior hypothalamic nuclei were bilaterally destroyed but not in those sham operated or with lesions in the dorsal premammillary nuclei. The number of ova ovulated was higher in rats bearing lesions of any of these nuclei but enhanced LH release was seen only in animals with lesions of the posterior hypothalamic nuclei. Electrochemical stimulation (anodic d.c., 100 microA, 15 s) applied at noon of pro-oestrus to the ventral premammillary nucleus, dorsal premammillary nucleus or posterior hypothalamic nucleus prevented ovulation and the preovulatory discharge of LH. It is concluded that inputs from nuclei of the posterior hypothalamus are inhibitory for LH release and could participate in determining the timing and magnitude of the pro-oestrous surge of the hormone.