Failure of neuromuscular transmission after complete nerve section in the dog.

After the ulnar nerve was surgically transected, nerve conduction velocity in the distal segment and the evoked motor unit potential (EMUP) from the interosseous muscle were recorded until neuromuscular transmission failed. In five of the six dogs in the experiment, functional conduction ceased by 4.8 days, as determined by failure of both proximal and distal stimulation of the distal segment to evoke a muscle response. From the time of section until neuromuscular failure, the nerve conduction velocity remained unchanged. The amplitude of the EMUP from the interosseous muscle, however, decreased markedly during this time. Changes in other features of the EMUP are also presented. Fibrillation (denervation) potentials did not appear until the first day that muscle response could not be detected by stimulating the nerve. These data present a principle which would enable a determination of relative extent and progression of peripheral nerve damage.