Middle-aged mice show delayed and destabilized food-anticipatory circadian activity under restricted feeding.

Mice are nocturnal and normally feed during the night; however, timed daily feeding can markedly alter behavioral and physiological rhythms. A well-known example is food-anticipatory activity (FAA), characterized by increased locomotor activity before feeding. In this study, we examined age-related effects on FAA under temporally restricted feeding (RF). Male C57BL/6 J mice aged 12 weeks and 54 weeks were maintained under a 12:12 light-dark cycle and subjected to a 4-h daily RF schedule. Wheel-running activity, feeding timing, intake, and body weight were monitored. Under ad libitum conditions, both age groups exhibited nocturnal activity and feeding. During RF, FAA emerged significantly earlier in young mice than in middle-aged mice. After returning to ad libitum feeding, daytime activity gradually merged into nocturnal rhythms, although some middle-aged mice showed unstable patterns. These results indicate that FAA reflects a circadian system distinct from the suprachiasmatic nucleus and that aging delays and destabilizes its expression.