MECHANISMS OF PARADOXICAL SLEEP AS REVEALED BY NEUROPHYSIOLOGIC AND PHARMACOLOGIC APPROACHES IN THE RABBIT.

Abstract

With the use of the Computer of Average Transients a study has been made of evoked responses in the central nervous system (CNS) of rabbits during paradoxical sleep and other stages of sleep and alertness. In “chronically implanted” animals responses evoked in the frontal cortex by stimulating the midbrain reticular formation were averaged and used as a guide to the state of wakefulness. During the alert state the averaged evoked responses show consistently a major peak at a latency of about 20–25 msec, which disappears during ordinary sleep. During paradoxical sleep (PS) the peak reappears with a latency and amplitude comparable to the response evoked during hyperalertness. Enhanced responses similar to the evoked potentials during PS are seen following treatment with amphetamine, LSD-25 and reserpine, all of which induce an aroused EEG. Reserpine also fosters PS behavior. A group of central depressant drugs including pentobarbital, morphine, chlorpromazine and atropine all markedly reduce the amplitude and increase the latency of the evoked response in dosages which prevent the appearance of PS. The conclusion is reached that PS is not a deep stage of sleep. The results suggest, rather, that PS represents a hyperactive condition of the limbic midbrain component of the brainstem reticular system and that the behavioral depression in PS results from an active inhibition of afferent synapses and/or enhanced activity in the descending bulbar inhibitory system.