| To investigate the effects of exogenous melatonin (7MT) on circadian rhythm of temperature and motor activity in rats, MT was injected to rats subcutaneously at different times of a day under normal light-dark (LD12:12) condition and constant darkness (DD). Circadian change of c- fos expression in suprachiasmatic nucleus (SCN) and in biochemical parameters in rat blood were also examined to explore mechanisms in regulation of physiological rhythms by the SCN and the pineal. (1) The temperature and motor activity of rats were recorded continually for 24 h as MT was administered with different doses and in different times of the day. Results showed that under integrity condition of SCN and pineal body, both at LD and DD regimen, circadian rhythms of temperature and motor activity of rats were confirmed. The parameters of circadian rhythms, however, were found altered with different treatments. Under the LD condition ,MT showed greater effect on motor activity than on temperature. The effect on amplitude was bidirectionary: that of temperature decreased as motor activity amplitude increased. While under DD, MT reduced the mesors of motor activity more than temperature. (2) Effects of exogenous MT on blood biochemical parameters most occurred at time period of CT4-T12. In control group, ALT and TP showed evident circadian rhythms, while others did not(P>O.05). (3) The expression of c-fos in SCN showed circadian rhythm under LD as well as DD. In the LD group, the circadian rhythm changed more evidently than in the DD group. In both the LD and DD group, the mesors of circadian rhythm increased significantly compared with the control group. The results suggested that the circadian rhythm of temperature and motor activity could remain after exogenous MT treatment. MT could affect and modulate the parameters of the circadian rhythm of temperature and motor activity. In regulation of physiological rhythm of the motor activity, the pineal seems to play a more important role than the SCN. |
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