The circadian rhythms of temperature and activity in obese and lean
zucker rats.
Murakami, Dean M., Barbara A. Horwitz, and Charles A. Fuller.
Section of Neurobiology, Physiology & Behavior, University of
California, Davis, CA 95616-8519
APStracts 2:0149R, 1995.
The circadian timing system is important in the regulation of feeding
and metabolism, both of which are aberrant in the obese Zucker rat.
This study tested the hypothesis that these abnormalities involve a
deficit in circadian regulation by examining the circadian rhythms of
body temperature and activity in lean and obese Zucker rats exposed
to normal light/dark cycles, constant light, and constant dark.
Significant deficits in both daily mean and circadian amplitude of
temperature and activity were found in obese Zucker female rats
relative to lean controls in all lighting conditions. However, the
circadian period of obese Zucker rats did not exhibit differences
relative to lean controls in either of the constant lighting
conditions. These results indicate that although the circadian
regulation of temperature and activity in obese Zucker female rats is
in fact depressed, obese rats do exhibit normal entrainment and
pacemaker functions in the circadian timing system. The results
suggest a deficit in the process which generates the amplitude of the
circadian rhythm.
Received 29 August 1994; accepted in final form 14 April 1995.
APS Manuscript Number R483-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 June 1995.