On the fate of sympathetic and sensory neurons projecting into a neuroma of the superficial peroneal nerve in the cat.

Cell bodies of sympathetic and sensory axons projecting via the superficial peroneal (SP) nerve supplying hairy skin of the distal hindlimb have been labeled retrogradely with horseradish peroxidase (HRP) on both sides of three cats in which the left SP nerve had been cut and ligated about 5 months previously. Three SP nerves from unoperated cats have also been studied. The location, size, and numbers of labeled somata have been determined from serial sections of lumbosacral dorsal root and sympathetic chain ganglia after standard histochemical processing. The numbers of myelinated fibers in each nerve have also been counted. The segmental distributions of both sympathetic and sensory cell bodies were identical bilaterally in each operated animal, but the number of labeled neurons was reduced on the lesioned side. There were only about 31% of sympathetic and about 51% of sensory somata relative to the numbers on the contralateral side. The average total number of neurons labeled from SP nerves in unoperated animals was about 8% higher than on the control side of operated animals. The average number of myelinated fibers in the neuromatized nerves was not reduced with respect to that in the contralateral nerve and both of these were not significantly different from the number in unoperated animals. The dimensions of samples of labeled sympathetic and sensory somata were reduced on the side with the neuroma, both in comparison with the contralateral side and with unlabeled neurons at the same levels. The mean cross-sectional area of profiles of sympathetic ganglion cells was 76% of the control; of sensory ganglion cells, 65% of the control. Assuming that HRP labeling was not impaired, we conclude that large numbers of neurons with unmyelinated axons had degenerated in the neuromatized cutaneous nerves.