The Pineal Gland Mediates the Inhibition of Proestrous Luteinizing Hormone Surge and Ovulation in Rats Resulting from Stimulation of the Medial Raphe Nucleus or Injection of 5-HT into the Third Ventricle.

Abstract In cycling rats, electrochemical stimulation of the medial raphe nucleus or injection of 5-HT into the third ventricle on the day of proestrus blocked the preovulatory surge of luteinizing hormone and inhibited ovulation. The inhibitory effect of these procedures on gonadotropin secretion failed to occur in rats that had been pinealectomized a few weeks earlier. In contrast, sham-pinealectomized rats exhibited a response similar to that of intact rats. Luteinizing hormone release and ovulation in pinealectomized rats were not different from that in the controls. The results of the present work indicate that inhibition of gonadotropin secretion induced by activation of the serotonergic system requires the presence of the pineal gland.