Daily restricted feeding effects on the circadian activity rhythms of the stripe-faced dunnart, Sminthopsis macroura

The effect of daily restricted feeding (RF) on the circadian wheel-running activity rhythms of the stripe-faced dunnart (Sminthopsis macroura) was examined. Dunnarts were presented with a 2-h meal in the middle of the light period of a 14:10 light:dark (LD) cycle and during constant dim light (LL). No meal-anticipatory activity (AA) was observed in any of the dunnarts during the experiment. This contrasts with previous work where AA has been reported in dunnarts subjected to RF. In LL, RF acted as a weak zeitgeber for the circadian activity rhythms of the dunnart. Evidence supporting this observation was the fact that 4/8 dunnarts' activity rhythms were entrained by RF, 2 showed relative coordination, and 1 exhibited bouncing phenomenon. In other species of marsupials and in rats, it has been proposed that RF entrains a food-entrainable pacemaker, which, in turn, entrains, via coupling, the suprachiasmatic-based, light-entrainable pacemaker. The findings of the present study differ from those reported previously in that no observable AA was entrained but the light-entrainable pacemaker was entrained by RF. In the dunnart, it remains to be determined whether RF directly entrains the light-entrainable pacemaker or whether RF entrains a food-entrainable pacemaker and in turn, via coupling, the light-entrainable pacemaker.