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BEHAVIORAL PHARMACOLOGY

5-Hydroxytryptamine (5-HT)₂ Receptor Involvement in Acute 5-HT-Evoked Scratching but Not in Allergic Pruritus Induced by Dinitrofluorobenzene in Rats

Department of Applied Pharmacology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, Japan (H.N.); and Section of Neurobiology, Physiology, and Behavior, University of California, Davis, California (E.C.)

We investigated the role of serotonin (5-hydroxytryptamine; 5-HT)₂ and 5-HT₃ receptor subtypes in acute itch-associated scratching behavior as well as in an allergic pruritus model in rats. Intradermal 5-HT evoked hind limb scratching directed toward the injection site in naïve rats. Scratching behavior was significantly reduced by pretreatment with the 5-HT₂ receptor antagonist ketanserin. Intradermal injection of -methylserotonin, a 5-HT₂ receptor agonist, also elicited scratching behavior in a dose-dependent manner, indicating that acute 5-HT-induced scratching is mediated via peripheral 5-HT₂ receptors. To produce a model of allergic pruritus, skin was sensitized by topical application of 5% dinitrofluorobenzene (DNFB). One month later, repeated challenge of the skin with 0.2% DNFB at weekly intervals elicited scratching as part of the immediate allergic response. Scratching was not affected by ketanserin or by the 5-HT₃ receptor antagonist ondansetron, indicating that neither 5-HT₂ nor 5-HT₃ receptors is involved in itch-associated scratching behavior caused by allergic skin dermatitis in rats.

Address correspondence to: Dr. E. Carstens, Section of Neurobiology, Physiology and Behavior, University of California-Davis, 1 Shields Ave., Davis, CA 95616. E-mail address: eecarstens{at}ucdavis.edu