Entrainment and phase shifting of circadian rhythms in mice by forced treadmill running.
Daily schedules of spontaneous, drug-, or novelty-induced running can entrain circadian rhythms in rodents. Forced running, by contrast, has been reported to have weak or no effects, although a thorough comparative study in a single species is lacking. To fill this gap, drinking or activity rhythms were monitored in C57 mice subjected to daily, 3-h bouts of forced treadmill running or to 3-h daily access to home cage running wheels. Entrainment to treadmill running was observed in 17/27 mice, and to restricted wheel access in 11/20 mice. Entrainment was affected by availability of a home cage wheel (e.g., 14/16 mice with no wheel entrained to treadmill running). Phase angle of entrainment was related to prior circadian period (tau), and tau following entrainment exhibited aftereffects. No mice entrained to a 3-h daily schedule of water access, suggesting that entrainment to scheduled running was not related to water or associated food intake. Phase shifts in response to single 3-h bouts of treadmill running or wheel access were small and not reliably induced. The entrainment paradigm is thus recommended for further study of behavioral effects on the mouse circadian system; forced running, in particular, offers several methodological advantages. The results do not support prior suggestions that forced and voluntary activity differ in value as nonphotic zeitgebers.
Marchant
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EG
Department of Psychology, Simon Fraser University, Burnaby, B.C., Canada.
Mistlberger
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RE
D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D004326:Drinking / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009043:Motor Activity / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*