Changes in motor activity during the development of the circadian rhythm in the rat

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Abstract
Evolutive aspects of motor activity circadian rhythm have been studied in rats born and reared under LL, from the day of weaning. Motor activity was recorded by means of an optical detecting system that uses crossed infra‐red beams. Data were recorded every 30 min. A graphic method based in smoothing the double plotted chronograms by means of a moving average has been developed. Using this method, a decrease in motor activity is clearly seen while the circadian rhythm is appearing. This fact was confirmed (p<0.0001) by developing a statistical method, that consisted of the calculation of one statistic specially defined to test this hypothesis. Results show that the development of the motor activity rhythm of the rats is composed of three periods: The first one, where the rhythm is basically ultradian; the second one, characterized by a considerable decrease in the daily motor activity; and the third one where motor activity recovers its initial values and the circadian rhythm is well established. This decrease in motor activity could be related with the mechanisms of synchronization amongst the oscillators which drive the motor activity rhythm.