Conduction in the lateral popliteal nerve of the baboon was studied during the course of Wallerian degeneration. Six nerves were examined. In each case the muscle response to nerve stimulation and the ascending nerve action potential were recorded daily until the nerve became inexcitable. The muscle response to nerve stimulation disappeared after four to five days, but ascending nerve action potentials could be recorded for a further two to three days. There was no change in maximal motor conduction velocity or in distal latency until the muscle response to nerve stimulation was severely reduced in amplitude. At this stage there was a consistent increase in distal latency, sometimes associated with a mild reduction in maximal motor velocity in the leg. There was no change in the velocity of ascending nerve action potentials. Histological studies confirmed the presence of degeneration in the terminal parts of the intramuscular nerve fibres at a time when the proximal parts of the same fibres were relatively normal.
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