Compound structure of rodents activity rhythm.

In the present study an attempt to determine the fine structure of rodents activity rhythm was carried out. To eliminate masking effects which are produced by the active influence of the monitoring system on the behavior of the animal (e.g., running wheel) we designed a passive infra red detection system. Rats were exposed to light-dark 12:12 [LD(12:12)] cycles and mice to LD(12:12), LD(8:16) and LD(16:8) cycles. Multiwave patterns of activity were observed in both rodents genera which differ from each other in the number of activity bouts and the periods of the activity rhythm components. In LD(12:12), rats exhibited 2 bouts of activity and 1 bout of rest which were attributed to the presence of 24 and 8 h components. Mice, exposed to the three varying ratios of L to D regimens exhibited 3 bouts of activity and one bout of rest which were attributed to the presence of 24 and 6 h components. The relation of the compound structure to the 24 h rhythm is discussed.