Pinealectomy prevents short photoperiod inhibition of male hamster sexual behavior.

The role of the pineal gland in mediating photoperiodic influences on copulatory behavior (CB) of male hamsters (Mesocricetus auratus) was assessed in the presence and absence of testosterone (T). The results demonstrate that the pineal gland is necessary for short photoperiod exposure to alter CB. Sexually experienced males were exposed to either long (14L:10D; LP) or short (8L:16D; SP) photoperiods for 13 weeks; after the first 2 weeks of exposure, all animals were castrated and then either pinealectomized (PINX) or sham operated (SHAM PINX). CB tests over an 8-week period following surgery indicated that copulatory impairments developed in all animals, but deficits occurred more rapidly among short photoperiod males with intact pineal glands (SP-SHAM PINX), compared to pinealectomized males housed in either the long (LP-PINX) or short photoperiod (SP-PINX). LP-PINX and SP-PINX animals were not statistically different on any of the CB measures examined. Nine weeks after castration (11 weeks of photoperiod exposure), all hamsters were given a T-filled Silastic capsule to restore CB. Restoration of sexual behavior was less rapid and less complete among SP-SHAM PINX hamsters. Additionally, males in this group took longer to initiate copulation relative to the pinealectomized hamsters. These findings are compared to other reports suggesting that photoperiodic effects on the sexual behavior of female hamsters do not require an intact pineal gland.