Functional Changes in Motor Endplates of the Target Muscle after Amputation of the C7 Nerve Root

Abstract

There are limited data on structural and functional changes in motor endplates and muscle fibers in the target muscle following amputation of the 7th cervical nerve root, a transplantation-related procedure in surgical treatment in the case of avulsions of the brachial plexus roots. We examined functional changes in these structures using stimulated single-fiber electromyography (sSF-EMG) in an animal model. Unilateral amputation of the 7th cervical nerve root was performed in 36 male rats, and the m. triceps brachii muscle was tested by sSF-EMG at different time points. We observed significant differences in the jitter (mean consecutive difference, MCD, of the latencies between adjacent muscle fibers) at post-amputation weeks 1, 2, 4, and 6. The post-operation fiber density (FD) values within the zone of effective stimulation also gradually increased. At post-amputation weeks 8 and 12, the jitter values returned to normal levels, whereas FD values continued to rise. Our results indicate that the post-amputation compensatory processes in the target muscles of the 7th cervical nerve root are mostly completed at 9-12 weeks after amputation.