Interactions between nocturnal feeding and wheel running patterns in the rat

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The purpose of this experiment was to investigate the relationship between daily patterns of wheel running activity and feeding behavior. Wheel running and bar pressing for food were continuously recorded from rats which had concurrent access to both wheels and food. In a second condition, wheel running and (non-reinforced) bar pressing were recorded during food deprivation. In a third condition, bar pressing for food was recorded while wheel running was prevented. During ad lib access to wheels and food, both behaviors occurred primarily during the dark phase of the light-dark cycle. However, the nocturnal distribution of these responses differed: the early dark hours were primarily devoted to running, while feeding occurred in small, frequent meals. Maximal food intake occurred during the late dark hours, when meals were larger and less frequent, and there was little running. During three days of complete food deprivation, both wheel running and meal initiation attempts (as indicated by non-reinforced bar pressing) maintained their normal daily patterns. However, during wheel deprivation, changes occurred in the temporal distribution of meals which equalized early and late dark food intake. These results show that the availability of an alternative activity, like wheel running, can be an important determinant of daily feeding patterns. However, the daily pattern of wheel running is not influenced by food availability. Different behaviors may show differential plasticity in the coordination of an overall daily behavioral program.