Identification of the unmyelinated sensory nerves which evoke plasma extravasation in response to antidromic stimulation.

Antidromic stimulation of single polymodal nociceptive C fibres in the rat's hind leg evoked a localized (about 6 m2) increase in vascular permeability of the skin as shown by the leakage of Evan's blue dye from the circulation. This effect was not observed with stimulation of single C low threshold mechanosensitive or warm-sensitive fibres, or of single C fibres for which a peripheral receptive field could not be identified.