Role of the Pineal Gland in Photoperiod-Induced Changes in Hypothalamic-Pituitary Sensitivity to Testosterone Feedback in Castrated Male Hamsters*

Abstract

An exposure to short days induces testicular atrophy in intact, but not pinealectomized, golden hamsters. Since recent evidence suggests that an alteration in the sensitivity of the hypothalamic-hypophyseal system to steroid feedback may be one way in which the photoperiod acts to alter neuroendocrine- gonadal activity in seasonally breeding animals, the present investigation was designed to determine if the pineal gland is involved in this photic-induced change to steroid feedback. Castrated adult male hamsters that had been sham-pinealectomized (Sham-Px) or pinealectomized (Px) were maintained on either stimulatory long days [14 h of light, 10 h of darkness (LD 14:10)] or nonstimulatory short days (LD 6:18) for 8 weeks. The animals were then implanted with various sized testosteronefilled capsules and serum was collected 10 and 21 days later for hormone analysis. Capsules which contained 2 or 4 mm powdered testosterone maintained serum testosterone levels between about 0.8-1.5 ng/ml, and induced at leas...