Analysis of sleep-wakefulness rhythms in male rats after suprachiasmatic nucleus lesions and ocular enucleation

Abstract

To determine quantitatively characteristics of sleep-wakefulness rhythms in male albino rats, computer analysis of long term polygraphic records (24 h/day) of cortical EEG activity, neck EMG and EOG taken from 23 rats under 12:12 light-dark schedule was performed. After bilateral suprachiasmatic nucleus (SCN) lesions, the circadian rhythm in sleep-wakefulness was completely eliminated, although no attenuation or even slight enhancement of the ultradian rhythms with 2–4 h periodicity was observed. After enucleation of both eyes, the circadian rhythm was free-runing with a phase shift in the range from −12 to +22 min/day in 6 rats. A gradual decrease of the spectral value of the circadian rhythm and inverse enhancement of the ultradian rhythms with 4–7 periodicity (predominantly 6 h in 4 out of 6 rats) were also shown. In the spectral diagram, the appearance of paradoxical sleep (PS) paralleled slow-wave sleep (SWS), in the cases of the circadian rhythm and ultradian rhythms with 4–7 h periodicity. Behaviorally blind rats with bilateral primary optic tract (POT) lesions maintained the circadian rhythm in sleep-wakefulness entrained to the environmental light-dark cycle. Power spectral analysis showed no characteristic difference from normal rats. Based on these data, the role of the SCN as a pacemaker of endogenous circadian rhythm in sleep-wakefulness is discussed.