Effects of ambient light an body temperature regulation in resting and exercising vats

We investigated the effects of environmental light and darkness on thermore gulation during both daytime and nighttime by monitoring body temperature ( T-b) and physical activity of rats using a telemetry system. Experiments we re performed in both resting and exercising rats. In resting rats, lights-o ff during the daytime resulted in an increase in both T-b and activity. Con versely, during the nighttime, T-b decreased with the lights-on stimulus de spite 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 exer cising rats increased to a level significantly higher than that of exercisi ng rats with the lights-on. Our results suggest that light at nighttime cau ses the suppression of T-b in both resting and exercising rats. (C) 2000 El sevier Science Ireland Ltd. All rights reserved.