Sensitivity of human scalp skin to pruritic stimuli investigated by intradermal microdialysis in vivo.

Abstract

Although pruritus is common in scalp skin, the forearm has been the main site for investigation in previous experimental studies. Our purpose was to compare the sensitivity to pruritic stimuli in human scalp and forearm skin. Four microdialysis fibers were inserted intradermally into scalp (n = 10) or forearm skin (n = 10) of healthy male subjects and were perfused with histamine (0.01%) or compound 48/80 (C48/80; 0.05%) for 20 minutes. Total protein content in the dialysate was assessed at 10-minute intervals. Intensity of itching and pain sensation were measured psychophysically. Histamine- and C48/80-induced protein extravasation was significantly lower in scalp skin. Histamine and C48/80 invariably provoked an itching sensation in the forearm but only in 4 of 10 applications in the scalp. Despite the high prevalence of pruritus, scalp skin is less sensitive to histamine-induced experimental itching. A lower innervation density of pruritic nociceptors and/or different central processing of itching might account for this difference.