BackgroundThe general or spontaneous motor activity of animals is a useful parameter in chronobiology. Modified motion detectors can be used to monitor locomotor activity rhythms. We modified a commercial microwave-based detection device and validated the device by recording circadian and ultradian rhythms.MethodsMovements were detected by microwave radar based on the Doppler effect. The equipment was designed to detect and record simultaneously 12 animals in separate cages. Radars were positioned at the bottom of aluminium bulkheads. Animal cages were positioned above the bulkheads. The radars were connected to a computer through a digital I/O board.ResultsThe apparatus was evaluated by several tests. The first test showed the ability of the apparatus to detect the exact frequency of the standard moving object. The second test demonstrated the stability over time of the sensitivity of the radars. The third was performed by simultaneous observations of video-recording of a mouse and radar signals. We found that the radars are particularly sensitive to activities that involve a displacement of the whole body, as compared to movement of only a part of the body. In the fourth test, we recorded the locomotor activity of Balb/c mice. The results were in agreement with published studies.ConclusionRadar detectors can provide automatic monitoring of an animal's locomotor activity in its home cage without perturbing the pattern of its normal behaviour or initiating the spurt of exploration occasioned by transfer to a novel environment. Recording inside breeding cages enables long-term studies with uninterrupted monitoring. The use of electromagnetic waves allows contactless detection and freedom from interference of external stimuli.
Numerous works show a circadian rhythm of activity in several species of animals; the ultradian rhythms have not received much interest. This study investigated whether the circadian motor activity rhythm would be synchronized to two non-24h light cycles and explored the effects of these light-dark cycles on different ultradian rhythms. We used a radar-doppler detection system. Inbred strains of mice BALB/C and C57BL/6 were exposed to a 24LD cycle and then to a shorter (10.5:10.5 LD) or longer (14:14 LD) cycle. Time series corresponding to observation periods of seven days were analysed by Discrete Fourier Transform and Chi-Square periodogram. BALB/C synchronized to T21 and T28 cycles, whereas C57BL/6 did not. In both strains the motor activity showed ultradian components. Some ultradian rhythm was affected from the synchronization of the circadian rhythm to the non-24h light cycles. The relation of the compound structure of the circadian and ultradian rhythms is discussed
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