Effect of anterior deafferentation of the hypothalamus on the release of luteinizing hormone (LH) and reproductive function in sheep.

The present study was designed to determine the effects of the anterior deafferentation of the hypothalamus performed at the level of posterior border of the optic chiasm--group I and above the midline of the optic chiasm--group II, on the release of LH and reproductive function in sheep. All 13 ewes of the group I lost their estrous cycles and did not experience ovulations as well as preovulatory type of LH surge. In 8 ewes the basal LH concentration in the blood plasma remained in physiological range of the diestrous phase of the cyclic ewes. In the remaining 5 animals in which deafferentation caused some lesions of the ventromedial-infundibular area the basal plasma LH level was markedly reduced. In contrast in all 18 ewes of group II, estrous cycles occurred regularly during the whole postoperative period of the breeding season. Moreover, throughout the subsequent quiescent non-breeding season 10 of these ewes displayed regular estrous cycles, 3 ewes had irregular estrous cycles and 5 ewes became anestrous. In all the ewes of this group the basal plasma LH levels were in physiological range, but preovulatory peaks of LH were lower than in the control ones. The neuroanatomic organization of the sheep hypothalamic structure participating in the control of gonadotropin secretion and estrous cycle regulation is discussed.