On the number and nature of regenerating myelinated axons after lesions of cutaneous nerves in the cat.

Abstract

Electrophysiological and anatomical techniques were used to investigate normal and regenerating sural and posterior femoral cutaneous nerve fibers in the cat. One and a half years after transection of these nerves, the regenerating neurons supported multiple sprouts in the distal stump of the nerve. The branching occurred at or beyond the level of the neuroma and some of the branched fibers innervated split receptive fields on the skin. Counts of the number of axons in the proximal stumps of transected nerves showed that the whole original population of myelinated fibers persisted for at least 18 mo. About 75% of these fibers successfully crossed the unrepaired transection site and regenerated into the distal stump of the nerve to reform functional connections in the skin. After nerve crush all the myelinated axons regenerated. None showed signs of abnormal branching. After nerve crush the conduction velocities of the regenerated axons in the distal stump of the nerve reached nearly normal values by 6 mo. After nerve transection the distal conduction velocities were reduced to 50% of normal even 18 mo. after the injury. The implications of these findings for the recovery of function after nerve injury in man are discussed.