Circadian and ultradian motor activity rhythms under 21h and 28h lighting cycles

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.