Comparison of synchronization of primate circadian rhythms by light and food

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Abstract
Several circadian rhythms in squirrel monkeys (Saimiri sciureus) entrained by 2 different agents were studied to compare their mode of coupling with the environmental zeitgebers. Synchronization was accomplished either by light-dark [LD] cycles consisting of 12 h of 600 lx followed by 12 h of > 1 lx (LD 12:12), or by eat-fast [EF] cycles in which the animals could eat for 3 h, then had to fast for the remaining 21 h each day (EF 3:21). The rhythms of drinking, colonic temperature and urinary K and water excretion were measured in chair-acclimatized monkeys. The drinking and urinary rhythms were more reproducible (smaller mean variance) and more stable (smaller SD of the timing of a phase reference point) in EF than in LD cycles; the temperature rhythm was more tightly controlled by LD cycles than by EF cycles. In constant light and 8 h phase delay in the EF cycle caused the drinking and urinary rhythms to resynchronize to the EF cycle within 1 day; the temperature rhythm required about 6 days to resynchronize. Previously published data for a similar phase delay in the LD cycle with food available ad lib show that the drinking and temperature rhythms resynchronized more rapidly than the urinary rhythms. Separate mechanisms may be involved in transducing temporal cues from LD and ED cycles in the circadian timekeeping system of these nonhuman primates.

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