Partial peripheral motor nerve lesions induce changes in the conduction properties of remaining intact motoneurons

A partial injury or loss of peripheral motor axons is followed by compensatory sprouting of remaining intact motor axons in order to reinnervate muscle. Little is known, however, about the electrophysiologic properties proximally of these intact motoneurons and their axons following injury of neighboring motor axons. We studied the conduction properties of intact cat motor axons and motoneurons proximal to the site of a partial peripheral nerve section. Twelve weeks after the partial transection of the cat medial gastrocnemius motor nerve, there was a significant (7%) reduction in conduction velocity and a 13% prolongation in afterhyperpolarization half-decay time in the remaining intact motoneurons, compared with controls. Partial injury to motor nerves thus induces reactive electrophysiologic changes in the remaining intact motoneurons and their axons, perhaps associated with compensatory sprouting within partially denervated muscle.