SUPRACHIASMATIC NUCLEUS AND PHOTOPERIODIC REGULATION OF GONADAL DEVELOPMENT IN THE SIBERIAN HAMSTER, PHODOPUS-SUNGORUS

Photoregressed Siberian hamsters exposed at 19 days of age to constant light for 24 h manifested increased testicular development 16 days la ter. Hamsters that sustained lesions of the suprachiasmatic nucleus (S CN) 3 days after the light pulse had significantly heavier gonads than did sham-operated animals or hamsters pinealectomized at 19 days of a ge. Enhanced reproductive development after SCN ablation is not due so lely to lesion-induced elimination of melatonin secretion. SCN neural activity beginning 3 days after the light pulse is not necessary for l ight-induced gonadal growth.