Alterations in hypothalamic serotonin metabolism in male hamsters with photoperiod-induced testicular regression.

Transfer of adult male golden hamsters to a short photoperiod (SD; 8L:16D) resulted in a significant decrease in testicular weight and plasma luteinizing hormone (LH) and prolactin (Prl) levels as compared to animals maintained in a long photoperiod (LD; 16L:8D). These changes were accompanied by significant increases in serotonin (5-HT) synthesis in the medial basal hypothalamus (MBH) as determined by measuring 5-hydroxytryptophan accumulation after inhibition of aromatic amino acid decarboxylase with NSD-1015. Serotonin synthesis in the median eminence, anterior hypothalamus and olfactory bulbs was not different in SD vs LD animals. Transfer of SD gonadally regressed hamsters to LD restored MBH 5-HT synthesis to control levels.