Effects of restricted feeding schedules on circadian organization in squirrel monkeys.
Free running circadian rhythms of motor activity, food-motivated lever-pressing, and either drinking (N = 7) or body temperature (N = 3) were recorded from 10 squirrel monkeys maintained in constant illumination with unlimited access to food. Food availability was then restricted to a single unsignaled 3-hour interval each day. The feeding schedule failed to entrain the activity rhythms of 8 monkeys, which continued to free-run. Drinking was almost completely synchronized by the schedule, while body temperature showed a feeding-induced rise superimposed on a free-running rhythm. Nonreinforced lever-pressing showed both a free-running component and a 24-hour component that anticipated the time of feeding. At the termination of the schedule, all recorded variables showed free-running rhythms, but in 3 animals the initial phase of the postschedule rhythms was advanced by several hours, suggesting relative coordination. Of the remaining 2 animals, one exhibited stable entrainment of all 3 recorded rhythms, while the other appeared to entrain temporarily to the feeding schedule. These results indicate that restricted feeding schedules are only a weak zeitgeber for the circadian pacemaker generating free-running rhythms in the squirrel monkey. Such schedules, however, may entrain a separate circadian system responsible for the timing of food-anticipatory changes in behavior and physiology.
Department of Physiology and Biophysics, Harvard Medical School, Boston, MA 02115.
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Boulos
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Frim
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Dewey
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Moore-Ede
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001831:Body Temperature; D002940:Circadian Rhythm; D003463:Cues; D004326:Drinking; D005247:Feeding Behavior / Q000502:physiology*; D007858:Learning / Q000502:physiology; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D012453:Saimiri; D013997:Time Factors