Physical exercise-induced changes in the core body temperature of mice depend more on ambient temperature than on exercise protocol or intensity

The mechanisms underlying physical exercise-induced hyperthermia may be species specific. Therefore, the present study aimed to investigate the effects of exercise intensity and ambient temperature on the core body temperature (Tcore) of running mice, which provide an important experimental model for advancing the understanding of thermal physiology. We evaluated the influence of different protocols (constant- or incremental-speed exercises), treadmill speeds and ambient temperatures (Ta) on the magnitude of exercise-induced hyperthermia. To measure Tcore, a telemetric sensor was implanted in the abdominal cavity of male adult Swiss mice under anesthesia. After recovering from the surgery, the animals were familiarized to running on a treadmill and then subjected to the different running protocols and speeds at two Ta: 24 °C or 34 °C. All of the experimental trials resulted in marked increases in Tcore. As expected, the higher-temperature environment increased the magnitude of running-induced hyperthermia. For example, during incremental exercise at 34 °C, the maximal Tcore achieved was increased by 1.2 °C relative to the value reached at 24 °C. However, at the same Ta, neither treadmill speed nor exercise protocol altered the magnitude of exercise-induced hyperthermia. We conclude that Tcore of running mice is influenced greatly by Ta, but not by the exercise protocols or intensities examined in the present report. These findings suggest that the magnitude of hyperthermia in running mice may be regulated centrally, independently of exercise intensity.