The modulation of cutaneous inflammatory reactions by peptide-containing sensory nerves

In the present experiments the role of unmyelinated sensory fibres in the mechanism of cutaneous inflammatory reactions under normal and pathological conditions has been studied in man and animals. Dye leakage responses to histamine, serotonin, compound 48/80, bradykinin and substance P were significantly reduced, while neurogenic inflammation was completely abolished in rats treated neonatally with capsaicin, as studied quantitatively by the Evans blue technique. Neurogenic inflammation could also be elicited by mustard oil in normally innervated human skin, but not in skin areas affected by herpes zoster or in a patient suffering from congenital analgesia. Repeated topical treatment of the skin with capsaicin (local desensitization) abolished the neurogenic inflammatory response for several days. Chemical pain sensitivity was strongly reduced, and thresholds for warmth and heat pain sensations were significantly elevated. Local capsaicin desensitization of the skin prevented whealing, flare and itch in patients with acquired cold and heat urticaria. The findings indicate that peptide-containing sensory nerves are involved in the mediation of chemogenic and heat pain, and possibly itch, and are responsible for initiation of the neurogenic inflammatory response. The results also provide direct evidence of the involvement of these particular sensory nerves in the modulation of the permeability-increasing effects of putative mediators of acute inflammatory reactions. It is concluded that, through modulation of cutaneous vascular reactions, peptidergic sensory nerves may play a hitherto unrecognized role in the pathomechanism of certain diseases of human skin.