Wheel running in female C57BL/6J mice: impact of oestrus and dietary fat and effects on sleep and body mass

Objective: To examine the impact of two diets differing in fat content and of wheel-running exercise on body mass. Methods: A total of 32 female C57BL/6J mice were assigned to either a high-fat (HF, 41% of dietary energy as fat) or low-fat (LF, 11% of dietary energy as fat) diet (16 per diet, individually housed). Eight mice from each diet group were housed with running wheels. Non-running mice were housed in similar cages, without wheels. Total cage activity (including non-exercise physical activity +wheel running) and sleep time were also measured using an infra-red-sensing device. Oestrus stage of the wheel-running mice was assessed daily for 17 days. Results: After 8 weeks, HF mice were significantly heavier than LF mice (P = 0.004), but there was no detectable difference in body fat mass. Wheel-running mice tended to have a lower body mass than non-running controls (P = 0.056). Voluntary cage activity was greater in LF control mice than HF control mice, and in wheel-running mice compared with non-wheel-running mice. HF control mice slept more than LF control mice. Stage of oestrus was significantly correlated with running distance, with mice running farthest in the immediate preoestrus phase and least immediately after oestrus. Conclusion: This study shows that HF diets in female C57BL/6J mice may increase sleep time similar to the effect of daytime sleepiness observed in obese humans.