The impact of photoperiods and melatonin on gonadal development in juvenile Turkish hamsters (Mesocricetus brandti)

The reproductive response of both intact adult and juvenile Turkish hamster s has been thoroughly studied and shown to be similar, unlike the golden ha mster where juveniles remain aphotoperiodic until approximately 8 weeks of age. Unstudied to date, however, is the role of the pineal and its hormone melatonin in generating the testicular response to photoperiod in juvenile Turkish hamsters. Therefore, in this study we examined the reproductive res ponse of prepubertal male Turkish hamsters, subjected to four different pho toperiods (8L:16D, 16L:8D, 20L:4D, and 24L:OD) with altered pineal gland fu nction. At 15 days of age, long-day-born (16L:8D) hamsters were either pine alectomized, received melatonin implants, or remained untreated. Testes siz es were measured every 2 weeks. Testicular growth occurred only in untreate d and beeswax implanted groups in 16L:8D, Exposure to other photoperiods in hibited testicular development in untreated and beeswax implanted animals. Removal of the pineal gland, masking of the daily melatonin rhythm with con stant release subcutaneous melatonin implants, or eliminating the daily rhy thm of melatonin by continuous light exposure resulted in inhibition of gon adal development. These results demonstrate that juvenile Turkish hamsters respond similarly to adults on all photoperiods and under all conditions of pineal function tested.