Inhibitory Effect of the Repeated Treatment with Unsei-in on Substance P-Induced Itch-Associated Responses through the Downregulation of the Expression of NK1 Tachykinin Receptor in Mice

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Abstract
Unsei-in, a traditional medicine, is prescribed against pruritic cutaneous diseases, but the mechanisms of antipruritic action are still unknown. In the present study, we examined the antipruritic effects of Unsei-in in mice. Single administration of Unsei-in did not inhibit substance P-induced itch-associated response (scratching) in mice. However, repeated treatment with Unsei-in for 7 d significantly inhibited substance P-induced scratching. The same repeated treatment with Unsei-in suppressed the expression of NK1 tachykinin receptors in the skin. These results suggest that Unsei-in inhibits substance P-associated itching and that the inhibition is at least partly due to the suppression of the expression of NK1 tachykinin receptors in the skin.