SEROTONIN INVOLVEMENT IN THE CONTROL OF PHASIC LUTEINIZING-HORMONE RELEASE IN THE RAT - EVIDENCE FOR A CRITICAL PERIOD

A marked surge of luteinizing hormone (LH) occurs daily at 18.00 h in oestrogen-treated ovariectomized rats maintained under regular lighting from 06.00 to 20.00 h. The administration of p-chlorophenylalanine (PCPA), p-chloroamphetamine or 5,6-dihydroxytryptamine in treatments designed to cause a severe depletion of brain serotonin abolished this daily surge. Synthesis of serotonin may be temporarily restored in PCPA-treated animals by the administration of the serotonin precursor, 5-hydroxytryptophan. The effectiveness with which restoration of synthesis resulted in restoration of the LH surge varied according to the time at which the precursor was administered, the optimal time being 10.00 h. The results suggest that there is an essential, permissive function performed by serotonin in the production of the LH surge and that this function occurs during a critical period.