Elsevier

Physiology & Behavior

Volume 27, Issue 6, December 1981, Pages 1057-1066
Physiology & Behavior

Failure of periodic presentation of palatable diet to entrain feeding, drinking and activity rhythms under constant conditions

https://doi.org/10.1016/0031-9384(81)90370-XGet rights and content

Abstract

Feeding, drinking and activity of two groups of male laboratory rats were studied across three experimental stages: LD 12:12; LL; and LD 12:12. In the first group (Control), ordinary diet was availabel ad lib for the entire experiment. In the second group (Experimental), palatable diet was available for the first 12 hr of each day and ordinary diet for the remainder of the day in stages 2 and 3. It was found that in stage 1 all behaviors were highly nocturnal. The nocturnality of feeding was achieved by the ingestion of more meals in the D phase as compared to the L phase. Dark ingested meals were not significantly larger than meals in the L phase. In stage 2, circadian rhythms in all three variables were damped and meals became evenly spaced across the day in both groups. In the Control group, meal sizes were also of the same magnitude across the day. However, periodic presentation of palatable diet resulted in larger meals and, therefore, the ingestion of 60% of total daily food intake during the 12 hr period when palatable food was available. Total daily food intake in LL did not change compared to stage 1 and did not differ between the groups. The size and number of significant meal size/post-meal interval correlations increased over the duration of the experiment but remained relatively small. In stage 2, water intake and activity were similarly evenly distributed over the 24 hr period in both groups and were not influenced by periodic presentation of palatable diet. No marked decreases in total daily water intake, but a substantial decrease in daily activity, were found. Under LL, daily body weight increments in both groups were maintained, but subtle changes were observed. In stage 3 when the LD cycle was reinstated, both groups ate a greater number of meals in the D phase despite the availability of palatable food in the L phase for the Experimental group. These animals ate fewer but larger meals of palatable diet than ordinary food resulting in 50% of their daily intake being ingested during the L phase. Activity and water intake returned to stage 1 levels and the distributions of these behaviors were similar to those found in stage 1 in both groups. It was concluded that palatable diet influenced meal size only and that the timing of meals depended on the illumination conditions only. Further, periodic presentation of palatable diet failed to entrain the damped rhythms of feeding, drinking and activity in LL. These results do not rule out the possibility that such an entraining effect of periodic presentation of palatable diet might be found in conditions of DD.

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