Collateral Nerve Regeneration

Abstract

Experiments are reviewed which confirm Exner''s (1885) suggestion that nerve fibers have a dynamic association with their periphery which enables them to exhibit adaptive, conpensatory responses following the destruction of neighboring axons. While these responses have been more fully studied in motor neurons they are also characteristic of sensory neurons and perhaps also of autonomic neurons as well. They occur in all mammals thus far studied but are more readily demonstrable in motor axons of primates. A few days after surgical elimination of some of the fibers in a mixed nerve, and the concomitant partial de-nervation of a muscle, the residual intramusc. axons develop subterminal collateral or ultraterminal branches which enter the denervated regions and reneurotize them. The amt. of collateral regeneration is a distinct function of the degree of original denervation; as a result the affected muscle usually recovers its lost wts. Analysis of causal factors responsible for the emergence of collateral sprouts from the residual axons permits the assertion that nerve fibers have sufficient turgor to extend their terminals when not restrained from doing so by the presence of neighboring nerve fibers. Whether the guidance is primarily a matter of contact affinity or whether chemotropic effects must be admitted is undecided.