Prolonged injury discharge in unmyelinated nerve fibres following transection of the sural nerve in rats.

We studied the prolonged injury discharge in axotomized myelinated (A) and unmyelinated (C) nerve fibres within the first 15 min following sural nerve transection of the rat. Immediately after axotomy, 18% (22/122) of the C fibres generated action potentials, but none of 73 A fibres. This discharge ceased during the first 2 min after axotomy in most of the C fibres. The discharge frequency in the first 15 s after nerve cut varied between 0.3 and 7.2 Hz (mean 2 Hz) and decreased to a mean of 0.3 Hz 4 min after nerve lesion. C fibres displaying initial discharge frequencies of > or = 2 Hz ceased to generate action potentials significantly sooner than those with initial discharge frequencies of < 2 Hz.