Background Histamine is one of the most common chemical mediators causing pruritus, and H1 receptor antagonists have been used as a first choice in its treatment. On the other hand, although the presence of H3 receptors has been identified in the skin, few studies have investigated the involvement of H3 receptors on pruritus.
Objective The purpose of this study was to examine whether H3 receptor agonist or antagonist influences the incidence of scratching behaviour in ICR or mast cell-deficient WBB6F1-W/WV mice.
Methods The mice were given an intradermal injection of H3 receptor agonist or antagonist into the rostral part of the back, and the occurrence of scratching behaviour at the injected site by the hind paws was counted over 60 min.
Results H3 receptor antagonists, thioperamide and AQ0145 significantly increased the incidence of scratching behaviour in ICR mice. H3 receptor agonist, (R)-alpha-methylhistamine, had no effect. On the other hand, (R)-alpha-methylhistamine significantly inhibited thioperamide or AQ0145-induced scratching behaviour. In addition, both thioperamide and AQ0145 elicited scratching behaviour in mast cell-deficient WBB6F1-W/WV mice.
Conclusion From these results, it may be concluded that H3 receptors are involved in the modulation of pruritus in the skin, and mast cells are not essential in this response. In addition, H3 receptor agonists can be useful as a novel therapeutic approach against pruritus.