Pruritic and Nociceptive Sensations and Dysesthesias From a Spicule of Cowhage

• Published in: Journal of neurophysiology Vol. 101; no. 3; pp. 1430 - 1443
• Main Authors: LaMotte, R. H, Shimada, S. G, Green, B. G, Zelterman, D
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.03.2009; American Physiological Society
• Subjects: Humans; Injections, Intradermal - methods; Mucuna - chemistry; Pain Measurement; Pain Threshold - drug effects; Pain Threshold - physiology; Paresthesia - chemically induced; Paresthesia - physiopathology; Plant Structures - toxicity; Pruritus - chemically induced; Pruritus - physiopathology; Reaction Time - physiology; Skin Physiological Phenomena - drug effects; Time Factors
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.91268.2008

1 Departments of Anesthesiology, 2 Surgery (Otolaryngology), and 3 Biostatistics, School of Public Health, Yale University School of Medicine, New Haven; and 4 The John B. Pierce Laboratory, New Haven, Connecticutt Submitted 27 November 2008; accepted in final form 6 January 2009 Abstract Although the trichomes (spicules) of a pod of cowhage ( Mucuna pruriens ) are known to evoke a histamine-independent itch that is mediated by a cysteine protease, little is known of the itch and accompanying nociceptive sensations evoked by a single spicule and the enhanced itch and pain that can occur in the surrounding skin. The tip of a single spicule applied to the forearm of 45 subjects typically evoked 1 ) itch accompanied by nociceptive sensations (NS) of pricking/stinging and, to a lesser extent, burning, and 2 ) one or more areas of cutaneous dysesthesia characterized by hyperknesis (enhanced itch to pricking) with or without alloknesis (itch to stroking) and/or hyperalgesia (enhanced pricking pain). Itch could occur in the absence of NS or one or more dysesthesias but very rarely the reverse. The peak magnitude of sensation was positively correlated for itch and NS and increased (exhibited spatial summation) as the number of spicules was increased within a spatial extent of 6 cm but not 1 cm. The areas of dysesthesia did not exhibit spatial summation. We conclude that itch evoked by a punctate chemical stimulus can co-exist with NS and cutaneous dysesthesias as may occur in clinical pruritus. However, cowhage itch was not always accompanied by NS or dysesthesia nor was a momentary change in itch necessarily accompanied by a similar change in NS or vice versa. Thus there may be separate neural coding mechanisms for itch, nociceptive sensations, and each type of dysesthesia. Address for reprint requests and other correspondence: R. H. LaMotte, Dept. of Anesthesiology, Yale Univ. School of Medicine, 333 Cedar St., PO Box 208051, New Haven, CT 06520-8051 (E-mail: Robert.LaMotte{at}yale.edu )