Intradermal cholinergic agonists induce itch-associated response via M3 muscarinic acetylcholine receptors in mice.

In the present study, we examined whether cholinergic agonists would elicit an itch-associated response in mice. When mice were given an intradermal injection of carbachol (1-10 nmol) or bethanechol (0.3-100 nmol) into the rostral back, they showed the dose-dependent increase of scratching. Nicotine (1-10 nmol) showed no effect. Pretreatment with naloxone, but not with terfenadine, significantly suppressed the carbachol-induced scratching. When intradermally co-injected with carbachol, atropine and 4-DAMP but neither methoctramine nor pancuronium significantly inhibited the carbachol-induced scratching. Muscarinic agonists are suggested to produce itch through activation of M3 muscarinic receptors in the skin.