SPONTANEOUS RECOVERY OF MUSCLE FOLLOWING PARTIAL DENERVATION

Abstract

Incomplete denervation of muscles in the rat was found to be followed by "spontaneous" recovery not attributable to regeneration of the severed nerve fibers. Partial denervation was effected by cutting the spinal nerves L4 and 6 or L5. The proximal stumps were prevented from regenerating by capping. The denervated portion of such a partially intact muscle atrophies less than it would if the muscle were completely denervated. Within a few wks., atrophy is checked and the muscle gradually returns to nearly its original size. Isometric tensions after stimulation of the nerve show a trend roughly parallel to the wt. changes. Histologic study showed a progressively increasing number of muscle fibers recovering normal size after some initial atrophy. Four months after the denervation of 80% of the muscle fibers, only 5% were still in an atrophic (i.e., denervated) state. At no time was there evidence of hypertrophied fibers. All observed facts lead to the conclusion that the intramuscular branches of the intact motor nerve fibers undergo additional branching and take over the supply of the denervated muscle fibers. This occurs only when intact and denervated elements lie intermingled; the stimulus for branching lies presumably in some traumatic contact action, and no "neurotropic" stimulation of branching or "attraction" of branches toward a solid denervated area has been noted. A similar phenomenon was discovered in the nerve trunk, where some of the uninjured fibers later broke down "spontaneously" and then regenerated with some branching .