An analysis of factors that induce hibernation in Syrian hamsters

Factors that induce hibernation of Syrian hamsters were analyzed in young adults and older adults under two photoperiodic conditions (i.e., a long photoperiod and a natural photoperiod). The experiment was performed from September 1st, 1992 to March 24th, 1993. The older hamsters entered earlier into and spent longer in hibernation than the young ones. Water deprivation caused more torpor than free access to water in the older hamsters as well as in the young ones. As the ambient temperature dropped, not only the number of animals entering hibernation but also the number of days in hibernation increased. Long photoperiod in the cold environment tended to induce torpor in the older animals but not in the young ones. An examination of testicular weight at the end of the experiment revealed that the regressed testes were well correlated with the induction and maintenance of hibernation regardless of age and photoperiod.