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Am J Physiol Regul Integr Comp Physiol 258: R994-R1000, 1990;
0363-6119/90 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 4 994-1000, Copyright © 1990 by American Physiological Society

ARTICLES

Phase-shifting the light-dark cycle resets the food-entrainable circadian pacemaker

J. E. Ottenweller, W. N. Tapp and B. H. Natelson
Primate-Neurobehavioral Unit, Veterans Administration Medical Center, East Orange 07019.

This experiment examined coupling between two circadian pacemakers, one entrained by light and the other by food. Rats were housed in running wheels: one-half on restricted feeding from 0900 to 1100 h whereas the others were free fed. After timed-fed rats developed bursts of running before 0900 h, all rats were given free access to food. A month later, the light-dark (LD) cycles for one-half the rats in each group were delayed by 6 h. After entrainment to the new LD cycles, all rats were probed with 96-h periods of food deprivation. During these probes, unshifted timed-fed rats ran more than their free-fed controls at 0600-1200 h, but delayed timed-fed rats ran more than their controls at 1200-1500 h, i.e., 6 h later than unshifted rats. Next, the unshifted rats were subjected to a 6-h advance in their LD cycle. One month later, all rats were again probed with food deprivation. Delayed timed-fed rats continued to run more at 1200-1500 h than their free-fed controls, but timed-fed and free-fed phase-advanced rats showed similar activity patterns after the phase advance. However, when activity patterns before these probes were subtracted, timed-fed advanced rats showed greater "responses" to food deprivation at 0001-0300 h than their free-fed controls, i.e., 6 h earlier than before the phase advance. Thus LD shifts delayed and advanced the running that was previously associated with food availability and reset the food-entrainable circadian pacemaker.


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E. Challet, L. C. Solberg, and F. W. Turek
Entrainment in calorie-restricted mice: conflicting zeitgebers and free-running conditions
Am J Physiol Regulatory Integrative Comp Physiol, June 1, 1998; 274(6): R1751 - R1761.
[Abstract] [Full Text] [PDF]


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