CIRCADIAN-RHYTHMS OF TEMPERATURE AND ACTIVITY IN OBESE AND LEAN ZUCKER RATS

The circadian timing system is important in the regulation of feeding and metabolism, both of which are aberrant in the obese Zucker rat. Th is study tested the hypothesis that these abnormalities involve a defi cit in circadian regulation by examining the circadian rhythms of body temperature and activity in lean and obese Zucker rats exposed to nor mal 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 cont rols in all lighting conditions. However, the circadian period of obes e Zucker rats did not exhibit differences relative to lean controls in either of the constant lighting conditions. These results indicate th at although the circadian regulation of temperature and activity in ob ese Zucker female rats is in fact depressed, obese rats do exhibit nor mal entrainment and pacemaker functions in the circadian timing system . The results suggest a deficit in the process that generates the ampl itude of the circadian rhythm.