EFFECTIVENESS OF CYCLIC INTRAGASTRIC FEEDING AS A CIRCADIAN ZEITGEBER IN THE SQUIRREL-MONKEY

To investigate the mechanism of circadian synchronization by oral food consumption, the effectiveness of cyclic intragastric feeding in synchronizing squirrel monkeys to a 24-h schedule was tested. Five monkeys were prepared with intragastric catheters and were studied free-ranging within a cage in an environmentally controlled chamber with continuous monitoring of body temperature (every 15 min) and locomotor activity (every 30 min). A balance mixture of dextrose, amino acids, fat emulsion, vitamins and minerals was infused from 0800-2000 each day via the gastrostomy, first during a 12-h light and 12-h dark cycle (lights on 0800-2000 h) and then subsequently in constant illumination. Serial phase analysis was performed by computing cycle-by-cycle acrophases of best-fitting sinusoids. One animal was synchronized by the feeding regimen while 4 others exhibited relative coordination. The timing of intragastric feeding may have only a weak synchronizing effect on primate circadian rhythms and pre-gastric cues associated with oral food ingestion contribute to entrainment by feeding schedules.