Effect of lighting on maturation of neural elements controlling biorhythm of sleep, wakefulness and paradoxical sleep in rats

Biorhythm of sleep, wakefulness and paradoxical sleep was studied in unanesthetized, freely moving, female rats. A concentric bipolar stainless steel electrode for EEG recording was placed in the dorsal hippocampus and monopolar EEG recording electrodes were placed in the formal cortex. One week after surgery, and the resumption of consecutive 4 days estrous cycles, EEG patterns were recorded for 7 consecutive days. Female rats subjected to light and dark schedule (LD) during the period of gestation and through puberty exhibited a diurnal rhythm of sleep, and paradoxical sleep; a circadian rhythm with peaks of sleep during the light phase. When these rats were transferred from LD to continous illumination (CI), circadian rhythm was annihilated and indeed all rhythms disappeared. It seems likely that light serves as synchronizer or oscillator for regulation of circadian rhythm of sleep, wakefulness and paradoxical sleep. However, in female rats subjected to CI during the period of gestation and puberty, light apparently does not serve as synchronizer or oscillator for the regulation of circadian rhythm. Further, these rats exhibit a nocturnal rhythm (12 h shift of acrophase of circadian rhythm of sleep and parodoxical sleep from rats born and reared in LD) of sleep, and paradoxical sleep; a circadian rhythm with peaks of sleep during midnight. The evidence illustrates the nature of oscillatory phenomena controlling circadian rhythm of sleep, wakefulness and paradoxical sleep in rats.