Ultradian Rhythms in Albino Rats during the Light Phase

The aim of this work is to investigate the ultradian rhythms of the rest-activity cycle of albino rats during the light phase. Occurrence (time-of-day) of 11 behavioral items was registered in a portable computer (HP95-LX). Each animal was visually and continuously observed for a interval of 2 hr, 3 hr after lights-on. Spectral analysis showed rest-activity cycles with statistically significant periods of 1 hr and also in the range of 10 to 20 min. As these rats were synchronized by a light-dark cycle (LD 12:12, 350:1 lux), these results suggest that ultradian rhythms are components of the circadian rest-activity cycle. The ultradian temporal organization of rest and activity behavioral items obtained by visual inspection is similar to the cycle of REM-NREM sleep stages obtained by EEG and described earlier in albino rats.