| Research Abstract |
1) Spontaneous itch-scratch response of NC mice : Although NC mice did not show apparent scratching under SPF conditions, they gradually and markedly increased after transfer to conventional environment. The frequency of spontaneous scratching was roughly parallel to the degree of dermatitis, but not to the plasma concentration of IgE.Histamine and substance P did not elicit scratching in NC mice. Although serotonin elicited scratching, serotonin antagonists did not inhibit spontaneous scratching of NC mice. The concentration of NO was increased in the skin with dermatitis. NO synthase inhibitors inhibited spontaneous scratching and firing of cutaneous nerve and decreased cutaneous concentration of NO in NC mice with dermatitis. Since an intradermal injection of NO donor does not elicit scratching, NO may be itch enhancer rather than pruritogen. Opioid antagonist inhibited spontaneous scratching but not spontaneous firing of cutaneous nerve in NC mice, suggesting the central inhibitory
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action. Opioid antagonist may be effective antipruritic agent for allergic and atopic dermatitis.
2) Allergic itch after mosquito bites : Although in naive mice, mosquito bites and an injection of extract of mosquito salivary gland did not apparently elicit scratching, their repetition gradually increased scratching. In mice which had been given repeated injection of the salivary gland extract, mosquito bites elicited scratching and marked plasma extravasation. The H_1 histamine receptor antagonist terfenadine (30 mg/kg) almost completely inhibited such plasma extravasation, without effect on the scratching. Thus, mosquito bites may induced itching of immediate allergy and this itching may not mediated by histamine.
3) Antipruritic effects of natural medicines : We examined antipruritic effects of 22 kampo medicines and found that Byakko-ka-ninjin-to and Kami-shoyoh-san inhibited spontaneous scratching of NC mice. Since Byakko-ka-ninjin-to decreased the surface temperature of the skin, it may be at least partly involved in the antipurititic action. Less
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