Pilocarpine Mydriasis in Mice

In several rodent species pilocarpine and oxotremorine produce mydriasis, rather than the miosis which is characteristic of most other species. We have established that pilocarpine is a mydriatic drug in mice, a species in which the action has previously not been described, and that this effect occurs after local ocular, intraperitoneal (IP) or intracerebroventricular (ICV) application. Arecoline produces miosis or mydriasis (depending on dose) following direct ocular application but mild mydriasis after IP or ICV injection. Atropine also produces mydriasis in mice, and the effect of pilocarpine is additive with that produced by atropine and is not antagonized by antihistamines. Direct ICV pilocarpine injection produces mydriasis at doses equivalent to those used systemically. Pilocarpine mydriasis probably results from inhibition of parasympathetic activity.