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TRACKING CIRCADIAN RHYTHM: CORE TEMPERATURE VERSUS RUNNING WHEELS

Abstract

Circadian rhythmicity has been extensively studied to understand physiological and metabolic processes that happen throughout the day. A mouse model has commonly been used to track circadian processes. The exercise of the mice have been used as a marker of circadian rhythmicity to track patterns during circadian disruption. However, it is now known exercise itself is a zeitgeber, a cue to promote circadian rhythms. PURPOSE: We propose that using exercise as a marker of circadian rhythmicity is incorrect and that core temperature is the best marker. METHODS: We tracked circadian rhythmicity of four groups: adult wheel running (n=6), aged wheel running (n=6), adult core temperature (n=3) and aged core temperature (n=6). Data from each group was analyzed with ClockLab. RESULTS: There is no difference between ages with the same measurement marker. However, aged mice tracked with wheel running have a longer period length than those tracked with core temperature (p=0.0529). Adult mice have an overall increase of circadian expression than aged mice (p=0.0065, p=0.0360). CONCLUSION: Tracking core temperature is a reliable way to track circadian rhythmicity. Using wheel running is detrimental to tracking rhythmicity as it is a zeitgeber, when the mice run they are influencing their circadian production, contradictory to using it as a marker. Rather, it becomes an expression and production of circadian processes. Tracking period length with wheel running becomes highly variable, but tracking with core temperature reliably shows 24 hour period lengths.

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