Membrane potential and input resistance in alpha motoneurons of hindlimb extensors during isolated and clustered episodes of phasic events in REM sleep

Abstract

The function of motoneurons during the phasic events of REM sleep was investigated in cats. The membrane potential, synaptic activity, input resistance and rheobase were measured in hindlimb extensor motoneurons during periods of concentrated phasic events (Type II) in REM sleep in undrugged, minimally restrained cats. During Type II episodes in REM sleep, motoneurons depolarized 3 mV on the average, reduced in input resistance by 20%, and had distinct increases in spontaneous synaptic activity, as compared with periods of REM sleep between episodes (i.e. Type I). This constillation of properties is explained by increases frequencies of both unitary EPSPs and IPSPs in motoneurons. Myoclonic jerks in Type II episodes do not appear to arise because of a temporary withdrawal of the tonic motoneuron inhibition found in REM sleep. Instead, large increases in excitatory synaptic activity overcome the inhibition, giving rise to motoneuron discharges.