The mRNA expression of enkephalin precursor PPE was promoted by topical application of IMQ (Fig. 4d), which supports the findings of Slominski et al. reported that naltrexone, an opioid antagonist, and olopatadine, a histamine H1 receptor antagonist, have suppressed pruritus in their mouse model of psoriasis [6], indicating that histamine and opioid pathways are involved in pruritus induction in psoriasis. The gene discussed is HRH1; the disease is psoriasis.