AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 4 951-R956, Copyright © 1993 by American Physiological Society

ARTICLES

Torpor shortens the period of Siberian hamster circadian rhythms

E. M. Thomas, M. E. Jewett and I. Zucker
Department of Psychology, University of California, Berkeley 94720.

We investigated the influence of ambient and body temperature (Ta and Tb) on circadian rhythms of gonadectomized male Siberian hamsters. Animals that entered torpor (Tb < 30 degrees C) had significantly shorter circadian periods (tau s) than did nontorpid hamsters at a Ta of 13 degrees C (24.17 +/- 0.05 vs. 24.33 +/- 0.04 h). The tau s of homeothermic hamsters were not affected by Ta change. Short-term decreases in Tb, rather than changes in Ta, 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 wheel activity can mask or block specific short-day responses.

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