Nicotine mydriasis.

In mice, nicotine produces dose-dependent mydriasis following interperitoneal or intracerebroventicular administration but not after local application through the conjunctival sac. Since mydriasis is not prevented by cervical sympathectomy, it is likely to be due to central inhibition of the parasympathetic tone. Repeated administration of nicotine over 8 h progressively diminished and finally obliterated the response to a test dose of nicotine. This acute tolerance was maintained for 24 h. Tolerance was also produced by daily administration of nicotine and lasted up to 12 days after withdrawal. The easily measurable examination of the pupillary responses provide a convenient method for the investigation of mechanisms underlying tolerance to nicotine.