Interaction between light- and feeding-entrainable circadian rhythms in the rat.

The interaction between light-entrainable rhythms (LER) and feeding-entrainable rhythms (FER) of wheel running was studied by maintaining 16 rats in constant darkness and on ad lib feeding for 14 days, followed by a restricted feeding schedule (2 hr food/day) for 42 days, and 25 days on ad lib feeding. In 4 rats the LER assumed the same period as food access during restricted feeding. The pre-restriction periods of the LER of these rats differed from that of the feeding schedule by 5 min or less. However, since food access did not determine the phase of the LER, food does not appear to be a true Zeitgeber for this rhythm. No synchronization was observed when the two periods differed by more than 10 min, although changes in period or phase of the LER during restricted feeding were observed in all rats. Four hour phase advances or delays of the feeding schedule did not result in consistent effects on the phase of the LER. Two hour light pulses near the onset or end of the LER resulted in phase delays and phase advances of the LER, but had no effect on the FER. In the context of a multioscillator circadian system, these results suggest that light- and feeding-entrainable circadian oscillators are only weakly coupled.