Effects of ambient light on body temperature regulation in resting and exercising rats

Abstract

We investigated the effects of environmental light and darkness on thermoregulation during both daytime and nighttime by monitoring body temperature (T_b) and physical activity of rats using a telemetry system. Experiments were performed in both resting and exercising rats. In resting rats, lights-off during the daytime resulted in an increase in both T_b and activity. Conversely, during the nighttime, T_b decreased with the lights-on stimulus despite the fact that the activity was left unchanged. Treadmill exercise (10 m/min) always increased T_b from the basal resting level. In both daytime and nighttime, exercising rats exhibited a persistent T_b-rise when lights were on. However, in the lights-off condition at nighttime, the T_b of exercising rats increased to a level significantly higher than that of exercising rats with the lights-on. Our results suggest that light at nighttime causes the suppression of T_b in both resting and exercising rats.