2 MEALS PROMOTE ENTRAINMENT OF RAT FOOD-ANTICIPATORY AND REST-ACTIVITY RHYTHMS

Ten female rats were fed early and late in the dark period of a 12-12 h light-dark cycle and then were fed at the same times in constant dar kness. In both conditions rats were active prior to mealtimes and mani fested no free-running components of activity. When the rats were plac ed in constant darkness and either were fed early and late in the inac tive period, or had free access to food, six of the rats had rest-acti vity rhythms different from 24.0 h. Though a masking explanation could not be ruled out, two meals during the active period apparently entra ined the rest-activity rhythms of these rats. The light-entrainable os cillator appears to integrate information from cycles of both illumina tion and food availability. Multiple sources of temporal information m ay promote more stable entrainment of the rest-activity rhythm than th e light-dark cycle alone, especially in a burrow dwelling organism, li ke the rat, that can be exposed to inconsistent light-dark transitions .