Wheel running raises body temperature and changes the daily cycle in golden hamsters

The purpose of this study was to characterize the influence of wheel-running activity on temperature circadian rhythm in golden hamsters. Amplitude of body temperature rhythm was significantly higher in animals that had access to the running wheel. Qualitatively, wheel running resulted in squaring of temperature rhythm waveform, a phenomenon that was independent of ambient illumination. When the hamsters had access to an immobilized wheel, the effect on temperature was no longer observed. Fast Fourier Transformation after subtracting 24-h sine waveforms (to rule out harmonics of the principal frequency), indicated distinct secondary components of the rhythms, i.e., a 12-h component in animals that had access to the wheels and an 8-h component in animals that did not. The rise in body temperature could be dissociated from the start of the activity period, body temperature augmenting before the time of light-dark transition, while activity increased about 12 min later. On the first night after presentation of an estrous female, the temperature cycle in male hamsters that did not access to the wheels was similar to that found in animals running on the wheels; the effect was no longer observed in subsequent nights. The results contribute to the view that the spontaneous locomotor activity in hamsters has a significant effect on temperature cycle.