Response of Alpha Motoneurones to Direct Electrical Stimulation during Desynchronized Sleep

Abstract

THE homonymous monosynaptic reflex, as well as the polysynaptic reflex, elicited by single-shock stimulation of the primary afferents of a muscular nerve is tonically depressed during desynchronized sleep in the cat¹. The depression of these reflexes, however, is not complete. A phasic enhancement of inhibition frequently occurs in relation to the rapid eye movements during deep sleep¹. An analysis was made of the mechanisms responsible for the tonic and phasic inhibitory influences impinging on the spinal cord during desynchronized sleep by taking electromyographical recordings of the recurrent discharge of the α-motoneurones in deafferented limbs of unanaesthetized, free-moving cats². It was found that this response is depressed throughout desynchronized sleep, but that no further reduction of the recurrent discharge occurs during the bursts of rapid eye movements³. A more direct way of evaluating the excitability of the α-motoneurones is to record their response to direct electrical stimulation. The best method would be, of course, to inject the testing current through an intracellular microelectrode. Because this technique cannot be adopted in experiments on free-moving, unanaesthetized cats, an attempt was made in stimulate extracellularly the pools of motoneurones to the ventral horn.