Abstract
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-24 h 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-24 h light cycles. The relation of the compound structure of the circadian and ultradian rhythms is discussed.
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