Effect of amantadine on pupillary diameter in mice

Amantadine, injected into mice, produces dose-dependent mydriasis. The pupillary dilation caused by amantadine is not abolished by pretreatment with reserpine, or by combined pretreatment with reserpine and α-methyl-p-tyrosine, although the mydriasis is reduced by approximately 25%. Thus, release of catecholamines from nerve terminals can account for only 25% of amantadine-produced mydriasis. Haloperidol and phentolamine can partially block the effect of amantadine, but, when given after reserpine, neither of the antagonists increases the blockade produced by reserpine alone. We conclude that the catecholaminergic system contributes only partially to the pupillary effect of amantadine, and that other mechanisms appear to be involved.