Simultaneous recording of circadian rhythms of brain and intraperitoneal temperatures and locomotor and drinking activities in the rat

In order to investigate the circadian oscillatory system, the present study performed simultaneous and continuous recordings of brain and intraperitoneal temperatures, drinking and locomotion in rats under light- dark (LD) cycles and continuous dim illumination (dim LL) for a total period of 16 days. Compared to circadian amplitudes under LD, those under dim LL were significantly reduced by 34% for drinking and 50% for locomotion, but were not for brain and intraperitoneal temperatures. On the other hand, means of steady circadian periods during last 10 days under dim LL were all within a close range between 24.2 and 24.3 h in these rhythms. Besides the steady periods, one rat exhibited weak circadian period of 23.7 and 24.6 h, but these multiple frequencies were also equally observed in the four rhythms. The similarity in the periodicities suggests that these temperature and activity rhythms might be driven by a common oscillatory system. Therefore differential reductions in the amplitudes of drinking and locomotor rhythms might be caused by a masking effect of dim LL on their rhythm output- pathways. Hence rats may temporally coordinate various physiological and behavioral functions by such clock system under time cue free environment.