The effect of scheduled forced wheel activity on body weight in male F344 rats undergoing chronic circadian desynchronization

Abstract

To examine whether scheduled forced wheel activity counteracts the increased body weight gain in rats undergoing chronic circadian desynchronization induced by repeated 12-h shifts in the light-dark cycle. Four age- and body weight-matched groups of adult male F344 rats were subjected to 12-h intermittent forced wheel activity daily (2.2 km/day). Each group had the following schedule for 13 weeks: a fixed schedule of a daily 12:12-h light-dark cycle and activity training (WF); a fixed light-dark cycle and 12-h shifts twice a week in activity training (WS); 12-h shifts twice a week in the light-dark cycle and a fixed schedule of activity training (LSWF); and 12-h shifts twice a week in both the light-dark cycle and activity training (LSWS). Two additional age- and body weight-matched sedentary rat groups were selected from our database: one was maintained on a fixed light-dark cycle (LC) and the other was subjected to 12-h shifts twice a week in the light-dark cycle (LS). The four rat groups that were exercised showed different response patterns of the daily body temperature rhythm to different combinations of forced activity and lighting schedules. Their food intake was more than that of the two sedentary rat groups, but their body weight was comparable with that of the LC rats and less than that of the LS rats during the forced activity period. The LSWS rats were heavier than the WF and WS rats in the first and second months of the experimental treatment, but their body weight was comparable with that of the WS and WF rats in the third month. Forced activity was effective in reducing the body weight gain in chronic circadian desynchronization that was induced by repeated shifts in the light-dark cycle, although such an effect might become significant only after some time.