Pinealectomy and lesions of the suprachiasmatic nucleus affect the castration response in hamsters exposed to short photoperiods.

Castration of male hamsters that have been exposed to a nonstimulatory photoperiod (e.g., LD 6:18) results in an attenuated increase in serum LH and FSH levels when compared to the increase observed following castration of hamsters exposed to a stimulatory photoperiod (e.g., LD 14:10). The short-day-induced inhibition of pituitary gonadotropin release, which is not dependent on the negative feedback effects of gonadal steroid hormones, is abolished if (1) the animals are transferred to LD 14:10; (2) the suprachiasmatic nuclei are lesioned at the time of castration; or (3) pinealectomy accompanies castration. These results indicate that both the pineal gland and the SCN mediate the steroid-independent inhibition of pituitary gonadotropin release that occurs during exposure to short days.