INTRACELLULAR RECORDING IN EXTENSOR MOTONEURONS OF SPASTIC CATS

The intracellular effect of stimulation of afferent extensor, flexor, and cutaneous nerves on ipsilateral extensor (gastrocnemius) motoneurons of unanesthetized normal and spastic cats was studied. In normal animals, stimulation of group I afferents of the gastrocnemius nerves produced monosynaptic EPSP; when group II was stimulated, polysynaptic IPSP were recorded; the stimulation of group II and III fibers in flexor (BST) and cutaneous (SUR) nerves produced either excitatory or inhibitory polysynaptic reactions. In the spastic animals, 8-16 weeks after lesion of the sensory motor cortex, most of the gastrocnemius motoneurons responded with a monosynaptic EPSP to afferent stimulation of group I fibers of the gastrocnemius nerves; other motoneurons, however, exhibited polysynaptic EPSP before the appearance of any monosynaptic potential. Polysynaptic EPSP appeared when activation of group II fibers of the gastrocnemius nerves was obtained. The effect evoked by flexor and cutaneous nerve stimuli were also modified in spastic cats, their excitatory action being more frequent than in the controls. It is tentatively concluded that the predominance of the polysynaptic facilitatory action of group I and II extensor muscle afferents in spastic animals is caused by the long-lasting enhancement of extensor activity which increases the facilitatory action of interneurons upon extensor motoneurons. © 1969.