[Effect of cerebral serotonin on cyclic LH release in rats]

An experimental increase in serotonin (5-HT) induced shortly before the "critical period" of ovulation control blocks the release of LH. Administration of a synthesis inhibitor of the amine p-chlorophenylalanine, (pCP) is ineffective when given during the critical period. However, pCP given in the evening of dioestrus II (18 to 24 hours before the "critical period") blocks ovulation. That 5-HT is specifically involved in this delayed effect of the drug is shown by the ability of increasing doses of 5-hydroxytryptophane (5-HTP) to induce with pCP a graded restoration of LH release when given together. This result, obtained in immature rats, has been confirmed in cyclic ones. A positive, permissive effect of 5-HT containing neurons on neural processes leading to LH release and ovulation is thus postulated. This action affects early stages of the LH release regulating mechanisms, in contrast to the classically described inhibiting effect of the amine, which blocks the actual release of LH-RH at the median eminence level during the critical period.