Pharmacological Characterization of Itch-Associated Response Induced by Repeated Application of Oxazolone in Mice

We investigated pharmacological characteristics of the itch-associated response to chronic dermatitis induced by 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one (oxazolone) repeated application in mice. Application of an oxazolone challenge to mice with oxazolone-induced chronic dermatitis evoked severe and transient scratching behavior for up to 1h. Thereafter, mild and continuous scratching behavior was observed for at least 8 h. Both severe and continuous scratching behaviors were suppressed by the opioid-receptor antagonist naltrexone, but not by the HI histamine receptor antagonist fexofenadine, 5-hydroxytryptamine-2 (5-HT(2))-receptor antagonist methysergide, NK(1)-receptor antagonist LY303870, cyclooxygenase inhibitor indomethacin, or the platelet-activating factor-receptor antagonist YM264. The severe scratching behavior was suppressed by the 5-lipoxygenase inhibitor zileuton and leukotriene B(4)- receptor antagonist ONO-4057, but not by the cysteinyl leukotriene-receptor antagonist montelukast. The continuous scratching behavior was suppressed by pretreatment with the non-selective muscarinic acetylcholine receptor antagonist atropine and M(3) muscarinic acetylcholine-receptor antagonist darifenacin. These results suggest that leukotriene B(4) receptor and M(3) muscarinic acetylcholine receptor are involved in the itch-associated response induced by repeated application of oxazolone in mice.