Neurogenic extravasation and substance P levels are low in muscle as compared to skin the rat hindlimb.

Activation of cutaneous chemosensitive afferents results in the release of substances which increase the permeability of the microcirculation, producing inflammation. That this inflammation is neurogenic is readily demonstrated by antidromic electrical stimulation of afferent fibres. In the present study we have used the technique of dye extravasation to compare both qualitatively and quantitatively neurogenic extravasation skin and skeletal muscle. Plasma extravasation has been found to occur in skeletal muscle after stimulation but only at less than 10% of the levels seen in skin. We have also found that the levels of the C-fibre markers substance P and fluoride-resistant acid phosphatase are greatly reduced in muscle compared with skin nerves. These results show that there are substantial differences in the population of C-fibres supplying muscle compared with those supplying skin.