Abstract
Restricted daily feeding schedules entrain circadian oscillators that generate food anticipatory activity (FAA) rhythms in nocturnal rodents. The location of food-entrainable oscillators (FEOs) necessary for FAA remains uncertain. The most common procedure for inducing circadian FAA is to limit food access to a few hours in the middle of the light period, when activity levels are normally low. Although light at night suppresses activity (negative masking) in nocturnal rodents, it does not prevent the expression of daytime FAA. Nonetheless, light could reduce the duration or magnitude of FAA. If so, then neural or genetic ablations designed to identify components of the food-entrainable circadian system could alter the expression of FAA by affecting behavioral responses to light. To assess the plausibility of light as a potential mediating variable in studies of FAA mechanisms, we quantified FAA in rats and mice alternately maintained in a standard full photoperiod (12h of light/day) and in a skeleton photoperiod (two 60 min light pulses simulating dawn and dusk). In both species, FAA was significantly and reversibly enhanced in the skeleton photoperiod compared to the full photoperiod. In a third experiment, FAA was found to be significantly attenuated in rats by pinealectomy, a procedure that has been reported to enhance some effects of light on behavioral circadian rhythms. These results indicate that procedures affecting behavioral responses to light can significantly alter the magnitude of food anticipatory rhythms in rodents.
Highlights
Restricted daily feeding schedules in rats, mice and other species induce daily rhythms of food anticipatory activity (FAA) that exhibit formal properties of a circadian clock controlled process [1,2,3]
The results indicate that daytime FAA in nocturnal rodents can be altered by procedures that affect light
In Experiment 1, rats entrained to a skeleton photoperiod, with no light during the middle of the day when food was available, showed markedly enhanced FAA by comparison with rats exposed to daytime light in a full photoperiod
Summary
Restricted daily feeding schedules in rats, mice and other species induce daily rhythms of food anticipatory activity (FAA) that exhibit formal properties of a circadian clock controlled process [1,2,3]. Circadian clock genes exhibit daily rhythms of expression in cells in many brain regions and in most peripheral organs and tissues, and in most cases, these cycles are shifted or entrained by daily feeding schedules [4,5,6,7,8]. Some lesions and gene mutations have been found to attenuate or enhance food anticipatory activity, but a convincing case for necessity has not yet been made [9,10,11] One interpretation of these results is that food anticipatory circadian rhythms are regulated by an anatomically distributed system involving multiple oscillators, modulating factors and entrainment pathways
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