DISRUPTION OF ESTROUS CYCLICITY FOLLOWING ADMINISTRATION OF A LUTEINIZING-HORMONE-RELEASING HORMONE ANTAGONIST TO THE PREOPTIC AREA OF THE RAT

Experiments were designed to test the hypothesis that LHRH receptors i n the preoptic area (POA) are of physiological importance for maintain ing estrous cyclicity in the rat Bilateral cannulae were implanted jus t dorsal to the POA. Estrous cycles were monitored daily by vaginal sm ears. Antide, a long-acting LHRH antagonist, was infused bilaterally ( 2,5 mu g/side) in the POA or the hypothalamus on the mornings of diest rus I and II. As controls, at separate times, rats also received simil ar infusions of either vehicle (1:1 water:propylene glycol) or a bombe sin antagonist (#B0650; Sigma, St. Louis, MO). Collection of daily vag inal smears continued, and the number of days from the first infusion to the next day of estrus that preceded a normal cycle was recorded. A fter infusion of Antide into the POA, rats demonstrated varying durati ons of interrupted cycles ranging from 11 days to more than 100 days. These periods of disruption were characterized by either long periods of diestrus, long periods of estrus, or an extended period of diestrus followed by an extended period of estrus. After infusion of Antide in to the dorsomedial, ventromedial or anterior hypothalamic areas, rats had either a 4- or 5-day estrous cycle and continued to cycle normally . Likewise, infusions into the septum had no effect. Infusion of vehic le or bombesin antagonist into any of the hypothalamic or POA sites te sted also resulted in no interruptions in the cyclic activity of the r ats. Therefore, it appears that functional LHRH receptors in the POA a re necessary to drive the normal estrous cycle.