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The effect of castration on hibernation was studied in male Turkish hamsters (Mesocricetus brandti). In the first study the animals were exposed to a long-day photoperiod from birth and throughout the period of hibernation. Hibernation was induced by exposure to cold (10 degrees C). Intact males usually hibernated for approximately 6-7 months and then became euthermic. Males which had been castrated prior to cold exposure continued to hibernate for a longer period. None of the 6 surviving castrated males terminated hibernation by 8 months. Four of these animals survived for more than 2.5 years and continued to hibernate throughout this time. In a second study, hamsters were exposed to a short-day photoperiod to induce testicular regression prior to cold exposure. Most of the intact males again hibernated for 6-7 months while castrated hamsters remained in hibernation for 8-9 months. Thus, in both studies, castration prolonged the hibernation "season." In the second study, the testes, which had regressed in response to exposure to short days, underwent recrudescence in hibernating males at 5-7 months after the initial exposure to short days. A similar time course of testicular recrudescence was displayed by males housed under short days but not exposed to cold. These latter animals remained euthermic throughout the experiment. Thus, it appears that the duration of the seasonal testicular cycle, induced by exposure to short days, was affected little, if at all, by environmental temperature or by body temperature. The testicular cycle appears to influence hibernation, probably through changes in androgen secretion.

Role of the Testis in Regulating the Duration of Hibernation in the Turkish Hamster, Mesocricetus brandti1