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Stabilization Of The Wheel Running Phenotype In Mice: Importance Of An Acclimation Period

Hypokinetic diseases are at epidemic levels in the human population. Increased physical activity can improve health and wellness and can decrease the prevalence of several types of chronic diseases. Rodent wheel running behavior can be used as a surrogate model for daily physical activity in humans. Initial exposure to a running wheel can elicit different responses in mice that can confound the normal activity patterns exhibited in this otherwise repeatable phenotype. To account for this differential response, a seven-day_or greater_acclimation period is used to allow phenotypic stabilization. Although a prolonged acclimation period does appear to allow adequate time for stabilization, data does not exist to support a seven-day acclimation period. PURPOSE: The purpose of this project is to evaluate the wheel running response in C57BL/6j mice immediately following running wheel exposure for fourteen days. METHODS: Twenty-eight male C57BL/6j mice (Jackson Laboratory, Bar Harbor, ME) were acquired at eight weeks of age and were immediately housed individually in cages with free access to running wheels. Wheel running distance (km·day), duration (min), and speed (m·min) were tracked for fourteen days following initial housing. Twenty-six mice completed the full fourteen-day protocol. Separate one-way ANOVAs were used to evaluate day-to-day differences in each wheel running character. RESULTS: Wheel running distance (F=5.653, p=2.14x10), duration (F=2.613, p=0.001), and speed (F=7.803, p=1.22x10) all exhibited day-to-day differences. Tukey HSD post-hoc testing indicated major differences between very early wheel running periods (days 1-3) and later wheel running periods (days > 3) in distance and speed. Duration only exhibited an anomalous difference between wheel running on day 13 and wheel running on days 1 through 4. CONCLUSION: Although it is common practice in research to allow a prolonged (≥ seven day) acclimation period prior to recording wheel running data, the current study suggests that phenotypic stabilization of all three indices is achieved by the beginning of the fourth day after running wheel exposure. As research animal housing and care costs increase, reducing utilization of animal husbandry resources by shortening the wheel running acclimation period could invariably cut facility-operating expenses while maintaining robust phenotypic control.