Circadian and ultradian rhythms of drinking behavior of albino rats maintained in constant darkness.

The objective of the present study was to investigate the circadian and the ultradian rhythms of drinking behavior in Wistar rats maintained under conditions of constant darkness. Six mature male rats (weighing 270-350 g) were exposed to light-dark 12:12-h cycles (LD 12:12, light on at 12:00 h) for 35 days and then switched to constant darkness (DD) conditions for at least 2 weeks. Drinking behavior was monitored continuously with a standard drinkometer circuit and the data was stored in 5-min bins. A modification of Enright's periodogram technique was used to evaluate the free-running drinking behavior circadian rhythm. Ultradian rhythms in drinking behavior were estimated by the Fast Fourier Transform (FFT) technique. Two of the animals (rats 4 and 6) showed no statistically significant circadian or ultradian rhythms and the other four showed free-running drinking circadian rhythm behavior shorter than 24 h (ranging from 23.333 to 23.967 h). Ultradian rhythms of drinking behavior of 12- and 8-h periods were detected in 4 (rats 1, 2, 3 and 5) and 2 (rats 1 and 5) animals, respectively. The relation of the compound structure of the circadian and ultradian rhythms is discussed demonstrating that drinking behavior is a good marker for studies of physiology of temporal organization.