Modification of paradoxical sleep following transections of the reticular formation at the pontomedullary junction.

Abstract

A retractable wire knife was employed to transect the reticular formation at the pontomedullary junction in order to assess the respective importance of pontine and medullary reticular neurons and their pathways in paradoxical sleep. Thirteen cats were implanted with a standard array of electrodes for polygraphic recording of sleep-wakefulness states during 3 days in baseline condition and during 21 days after transections. Average electroencephalographic (EEG) amplitude, average electromyographic (EMG) amplitude, and ponto-geniculo-occipital (PGO) spike rate were measured per 1-min epoch for each day. A trivariate computer graphics display of 1 day's data revealed three major clusters of points that corresponded to wakefulness, slow wave sleep, and paradoxical sleep in baseline. (a) After transections through the entire reticular formation at the pontomedullary junction, paradoxical sleep was no longer evident in the trivariate computer graphics or polygraphic record, either by the presence of a high PGO spike rate or by that of muscle atonia in association with a low-amplitude EEG. These results indicated that the reticular fibers that pass through the pontomedullary junction and interconnect the pontine tegmentum and the medullary reticular formation are necessary for generating the cluster of electrographic variables that normally characterizes paradoxical sleep. (b) After transections through the dorsal half of the reticular formation, paradoxical sleep was still evident, though with a reduced PGO spike rate, and muscle atonia was normal. These results indicated that the descending noradrenaline locus coeruleus fibers and the "longitudinal catecholamine bundle," which course through the dorsal tegmentum, are not necessary for the generation of muscle atonia or the state of paradoxical sleep. (c) After transections through the ventral half of the reticular formation, paradoxical sleep was still apparent by the association of a moderate, though reduced, rate of PGO spiking in association with low-amplitude EEG activity and a high-amplitude EMG, indicating a loss of muscle atonia. The duration of the PS episodes, however, was greatly reduced. These results indicated that the descending "tegmentoreticular" and ascending reticulotegmental pathways, which course ventrally through the pontomedullary junction and interconnect the dorsolateral pontine tegmentum and the ventromedial medullary reticular formation, are essential for the muscle atonia of paradoxical sleep and important for the normal cyclic generation and maintenance of the state of paradoxical sleep.