Substance P content of the skin, neurogenic inflammation and numbers of C-fibres following capsaicin application to a cutaneous nerve in the rabbit.
The long-term effects of applying capsaicin briefly to a cutaneous nerve in the rabbit have been assessed 10 days after treatment. No changes in C-fibre numbers were seen in treated saphenous nerves and the average ratio of C-fibres to A-fibres was close to 7 in both control and treated nerves. However, the substance P content of the skin innervated by the saphenous nerve fell by 46% after capsaicin treatment compared with a fall of 65% after nerve section. Plasma extravasation in response to 7.5% mustard oil applied to the skin was also reduced following capsaicin treatment (by 43%) and following denervation (by 47%), although the response to 25% mustard oil was unaffected by previous capsaicin treatment. Thus, as in other species that have been examined (notably the rat), brief capsaicin treatment of rabbit skin nerves leads to a reduction in a neurogenic inflammatory response and in substance P content of the skin. However, unlike the rat, there is no degeneration of C-fibres. In the rabbit it is therefore possible to separate the neurotoxic, degenerative action of capsaicin from its ability to deplete substance P. The question of whether a similar dissociation between neurotoxic and other actions could be achieved in the rat by using lower capsaicin concentrations remains to be answered.
Lynn
B
B
Department of Physiology, University College London, U.K.
Shakhanbeh
J
J
D000818:Animals; D002211:Capsaicin / Q000008:administration & dosage; D005260:Female; D008297:Male; D008854:Microscopy, Electron; D009412:Nerve Fibers / Q000473:pathology*; D009443:Neuritis / Q000139:chemically induced* / Q000473:pathology; D011817:Rabbits; D012867:Skin / Q000032:analysis / Q000187:drug effects / Q000294:innervation*; D013373:Substance P / Q000032:analysis*; D013997:Time Factors
D013373:Substance P; D002211:Capsaicin