Phasic events indicating presynaptic inhibition of primary afferents to the spinal cord during desynchronized sleep.

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Abstract
In unrestrained unanaesthetized cats with chronically implanted electrodes the Electrospingogram (ESG), the cord dorsumpotential (CDP) evoked by posterior biceps semitendinosus (PBST) group I fibers stimulation and iii) the antideomic la gastrocnemius soleus (GS) response to intramedullary microelectrode stimulation have been studied during wakefulness, synchronized and desynchronized sleep. The following phasic events have been observed synchronously with rapid eye movements (REM) of desynchronized sleep: high voltage ESG slow wave activity, in-crease of ESG fast background activity, reduction or disappearance of P wave of CDP, augmentation of GS antidromic spike amplitude to intramedullary stimulation of its Ia fibers. All these phasic phenomena disappeared after section of the spinal cord at T9. The simultaneous appearance in the spinal cord during REM period of the above mentioned phasic events indicates a Ia terminals depolarization i. e. presynaptic inhibition of monosynaptic reflex coming from supraspinal structures.