FOOD-DEPRIVATION AND REINSTATEMENT PHASE-SHIFTS RAT ACTIVITY RHYTHMS IN CONSTANT LIGHT BUT NOT CONSTANT DARK

Three-day periods of food deprivation followed by reinstatement have produced phase shifts in the activity rhythms of the Australian marsupial, Sminthopsis macroura. However, no clear effects have been shown in rats. In the first of two experiments, rats in constant dark (DD) failed to show such phase shifts but when constant light (LL) was introduced it was possible to induce phase shifts. Because there was considerable disruption of activity rhythms, a second experiment was conducted using lower light levels which demonstrated clear phase shifts that were mainly phase delays late in the rats' inactive periods and advances late in the active periods. The size of the phase shifts was highly correlated with wheel-running activity levels and free-running period but not with proportional changes in activity associated with the food deprivation schedule. The results indicate that either the effects of food deprivation/reinstatement are augmented by LL or that the increased free-running period induced by LL produces larger phase shifts. Because no phase shifts at all were observed under DD, the former interpretation is preferred.