title: Four Possible Itching Pathways Related to the TRPV1 Channel, Histamine, PAR-2 and Serotonin.
abstract: The following four possible pathways for itching sensation have been suggested by recent reports. 1) Histaminergic TRPV1-positive pathway: Although histamine-positive nerve fibers cannot strictly be classified as "itch specific" due to their excitation also by pure algogens (making them itch-selective), the existence of a subpopulation of nociceptors responsible for itching is strongly suggested. Moreover, the TRPV1-expressing neurons have been suggested to be the main sensors and mediators of itching. 2) Histaminergic TRPV1-negative pathway: The scratching behavior caused by itching was not different between capsaicin-pre-treated and vehicle-treated (control) mast cell-rich NC mice. This result suggests the existence of a capsaicin-insensitive (TRPV1-negative) histaminergic pathway. 3) Non-histaminergic PAR-2 pathway: Protease-activated receptor 2 (PAR-2) has been shown to play a role in the itching of atopic dermatitis (AD). The itch evoked by cowhage (a non-histaminergic pruritogen that activates PAR-2) is very similar in characteristics to the itch evoked by conditions such as AD. 4) Non-histaminergic serotonin (5-HT) pathway: 5-HT alone applied to the human skin evokes an itching sensation and has been suggested to be involved in the itching associated with pruritic diseases, such as polycythemia vera and cholestasis.
authors.affiliation: Dentistry for Persons with Disability, Tokushima University Hospital, 3-18-15 Kuramoto cho, Tokushima 770, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakagawa
authors.forename: Akio
authors.initials: A
authors.lastname: Hiura
keywords: PAR-2; TRPV1; histamine; itch; serotonin
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