SENSORY-MOTOR NERVE CROSSES IN THE RAT

Abstract

The problem of the regeneration of sensory nerve fibers into motor stumps and muscles has been re-examined in rats. Arterial sleeves prevented the intrusion of stray fibers. The sensory fibers, exhibiting no sign of selectivity, regenerated through the motor nerve with ease and pervaded the muscle with dense arborizations. After regeneration, electric stimulation of the crossed nerve in most cases caused muscle contraction. Stimulation of the dorsal and ventral roots separately, or of the de-efferented peripheral nerve, however, proved that these muscle contractions were mediated only by ventral root fibers included in the cross. No transmissive connections were formed by sensory fibers. Muscle fibers surrounded by sensory fibers exclusively underwent the same degree of atrophy and degeneration as if no nerve fibers were present. Muscles with mixed reinnerva-tion recovered wt. to a greater extent than in proportion to the ratio of motor to sensory fibers present. Evidently, each motor fiber takes on an excess load; but this expansiveness of the motor unit is limited. Histologically, the innervated muscle fiber groups are rather sharply set off against the degenerated, uninnervated ones, indicating a tendency of the motor nerve fibers to stay assembled. In no case was there any sign of resorption of functionally useless nerve fibers as late as 8 mos. post operative.