Aging lengthens circadian period for wheel-running activity in C57BL mice

Previous reports of age effects on circadian period in rodents show a slight shortening of period with age, with the exception of house mice (Mus domesticus) where a number of studies report mixed results. The present study consists of three comparisons of circadian period for wheel-running activity in young vs. older C57BL inbred mice following entrainment to 16:8 LD, 12:12 LD and 8:16 LD photoperiods. The free-running circadian period (tau(DD)) for wheel-running activity was significantly longer in older mice following entrainment to all three photoperiods. These results support a model of heterogeneous effects of aging on circadian period among different rodent species, and suggest that the lengthening of circadian period with age in house mice is not a function of age-dependent differences in after-effects imposed by prior entrainment.