Electrophysiological study of consecutive changes of feline ventral root reflexes during degeneration and regeneration following peripheral nerve section

Abstract

Electrophysiological data which record the consecutive changes of monosynaptic and polysynaptic ventral (L7) root reflexes during retrograde degeneration and axon regeneration are presented. In cats the left posterior tibial nerve was subjected to a 1-cm resection. In one series of animals the surgical procedure included tubulation of the nerve stumps with a Millipore tube for repair; in the second series of animals nerve regeneration was prevented. Significant changes, characterized by monosynaptic failure and enormous preponderance of the polysynaptic reflex component on the operated side, dominated the reflex picture during the stages of muscle denervation. As soon as neuromuscular connections for afferent and efferent alpha fibers could be demonstrated (at 6 weeks after surgery), gradual restitution of the abnormal motoneuron reflex activity commenced. Return of normal motoneuron reflex function was seen between the twelfth and sixteenth postoperative weeks. Transient similar changes of the reflex activity in ipsilateral segmental peroneal (antagonistic) motoneurons, not directly affected by the procedure of posterior tibial nerve section, was commonly seen during the period of the gastrocnemius and scleus muscle denervation. Ventral root reflexes elicited from the regenerating nerve stump distal to the original lesion revealed abnormalities of the myotatic reflex action which lasted long after refunctioning large fiber components of the nerve could be demonstrated. The proprioceptive spike component on the operated side was never equally restituted to that obtained on the control side in terms of virtual synchrony and amplitude, even in experiments continuing up to 58 weeks after surgery. The demonstrated dysfunction of ventral root reflexes during the period of neuromuscular regeneration leading to a deficiency in the myotatic reflex action is discussed as one among other factors, which temporarily is likely to interfere with proper muscle function long after axonal continuity between nerve and muscle has been established.