INTRODUCTION: Circadian rhythms are responsible for physiological and behavioral processes coordinated in a 24-h cycle. We investigated whether untimed, long-term voluntary wheel access mitigated circadian disruption and facilitated re-entrainment.
METHODS: Thirty-five C57Bl/6J mice ( n = 21 males, n = 14 females) were used in this experiment. Long-term exercised (LTEx) mice ran from 3 wk to 12 months of age. At 12 months, animals were circadian disrupted for 14 d and then re-entrained for 7 d. Long-term sedentary (LTSed) animals were disrupted but had no access to a wheel. Another long-term sedentary group had access to a wheel only during disruption (LTSed+Ex). SubCue data loggers were used to track internal rhythm of core body temperature (Tb). RNA was extracted from skeletal muscle and RT-qPCR was used to analyze gene expression.
RESULTS: Overall, all three experimental groups had an initial entrained period lengths of ~24 h at baseline. There was a main effect of time ( P = 0.012), treatment ( P = 0.005), and time-treatment interaction ( P = 0.033) from baseline to disruption. A post hoc analysis within-group one-way ANOVA showed no difference between baseline and disruption period lengths in the LTSed+Ex treatment, yet a difference from baseline to disruption in LTSed and LTEx. Lastly, there is a difference in entrained period lengths between all three treatment groups at the re-entrainment time point ( P = 0.026) with a difference in change between disruption and re-entrainment with LTEx being lower than LTSed+Ex.
CONCLUSIONS: Our results suggest that acute-like exercise during circadian disruption aided in mitigating circadian disruption. When all treatment groups were re-entrained back to a normal rhythm, the LTEx animals that had access to a wheel before, during, and after disruption had period lengths closest to baseline values.
