Possible role of mast cells in cineole-induced scratching behavior in mice.

We examined the scratch (itch) inducing effect of 1,8-cineole (cineole), a monoterpene oxide present in many plant essential oils and the possible role of mast cells in the response. Subcutaneous injection of cineole (10, 20 and 40 microl/site) or the mast cell degranulating agent, compound 48/80 (25, 50 and 100 microg/site) into the rostral back of mice induced a scratching behavior. This response of cineole as well as that of 48/80 was markedly suppressed in mice subjected to mast cell desensitization by repeated injections of 48/80. The cineole-induced scratching was also significantly diminished in animals pretreated with diphenhydramine, the histamine H1-receptor antagonist or cyproheptadine, the dual histamine/serotonin-receptor antagonist. Furthermore, the scratch-inducing effect of cineole was greatly reduced in mice that received the opioid antagonist naloxone or the selective adenosine A1-receptor agonist, N6-cyclopentyladenosine (CPA), but not the more selective adenosine A2-receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA). The data suggest a likely role for mast cells in cineole-induced scratching behavior of mice, possibly involving adenosinergic and opioidergic mechanisms.