Circadian clocks for all mealtimes: anticipation of multiple daily meals in rats

Behavioral studies show that rodents can anticipate a daily mealtime by entrainment of a circadian oscillator separate from the circadian clock responsible for light-dark entrained rhythms. Less is known about how rats anticipate more than one daily meal. The objective of the experiments reported here is to gain insight into the formal mechanisms by which multiple meal anticipation is achieved. Rats were maintained on two daily meals, 7 h or 10 h apart in the light period, and anticipation of each meal was measured during meal omission, meal shift and constant dark tests. The results rule out interval timing as a means for predicting mealtimes, and provide some support for the proposal that separate food-entrainable oscillators may control each bout of anticipatory activity. Characterizing the strategies employed by rats under scheduled access to multiple daily meals may yield important insights into the mechanisms underlying anticipatory behaviour.