TORPOR SHORTENS THE PERIOD OF SIBERIAN HAMSTER CIRCADIAN-RHYTHMS

We investigated the influence of ambient and body temperature (T(a) an d T(b)) On circadian rhythms of gonadectomized male Siberian hamsters. Animals that entered torpor (T(b) < 30-degrees-C) had significantly s horter circadian periods (taus) than did nontorpid hamsters at a T(a) of 13-degrees-C (24.17 +/- 0.05 vs. 24.33 +/- 0.04 h). The taus of hom eothermic hamsters were not affected by T(a) change. Short-term decrea ses in T(b), rather than changes in T(a), appear to affect tau. Access to activity wheels inhibited expression of torpor in short daylengths and was associated with significant increases in body mass. Running w heel activity can mask or block specific short-day responses.