Runwheel activity patterns of mature-young and senescent mice: the effect of constant lighting conditions

A group of 18 5-mo.-old young and a group of 16 27-mo.-old senescent mice of the C57BL/6J strain were adapted for wheel-running under standard LD 12 : 12 cyclic illumination, after which each group was divided into three subgroups. One old and one young subgroup remained in standard lighting conditions as controls, while the two experimental subgroups received constant light followed by constant dark or constant dark followed by constant light. Rhythmic runwheel activity patterns were compared using periodicity, activity-rest ratios, and amplitude as parameters (defined in text). As expected, senescent mice were less active than young mice, although they did not always spend less time in activity than did the young. Generally, young mice were more reactive to the initial experimental conditions than were the senescent mice, whereas the reverse was observed in the final experimental conditions.