Sleep-waking cycle in chronic rat preparations with brain stem transected at the caudopontine level

The brain stem of rats was transected at the middle of the nucleus reticularis pontis caudalis. The preparations were maintained 2-9 days, and their EEG activity and behavior were studied. Maintained EEG activity and EEG arousal to visual and olfactory stimuli indicated the presence of sleep-waking cycle. Three stages were identified. Two of them corresponded to waking with hippocampal theta rhythm and to slow wave sleep in intact rats. The third stage (absent in intact rats) was characterized by slow waves and spindles of low amplitude in the cortex and low frequency theta rhythm, and it was considered as "drowsiness." Waking without theta rhythm, paradoxical sleep, and its forerunner intermediate stage were never found. Paroxystic-like EEG episodes were frequently observed. Thus, although present, the sleep-waking cycle is severely impaired in the caudopontine rats. The impairment is similar to that found previously in rats transected at the intercollicular or pretrigeminal level. The preparations were able to crawl abortively and to swallow liquid. Their respiratory rhythm was normal, but the heart rate increased. Thus, the caudal part of the preparations showed remarkable ability in controlling motor and vegetative functions.