The Journal of pharmacology and experimental therapeutics
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J. Pharmacol. Exp. Ther. · Sep 1985
Morphine-induced mydriasis and inhibition of pupillary light reflex and fluctuations in the cat.
Morphine has species-characteristic effects on pupillary size The effects of morphine on pupillary size, fluctuations and the light reflex were tested with an infrared video pupillometer in the gallamine-paralyzed cat. Compared with saline or base-line responses, i.v. morphine (0.06-1.5 mg/kg) caused a dose-related decrease in the light reflex and fluctuations but increased pupil size. Naloxone (1-100 micrograms/kg i.v.), injected 1 h after morphine, reversed all pupillary effects. ⋯ It was concluded that morphine disrupts parasympathetic innervation of the iris through interactions with opiate receptors, some of which are in the brain. The morphine-induced changes on the light reflex and fluctuations in the cat are opposite those reported in the rat and rabbit. These results enlarge on the familiar species-dependent effects of opiates on pupillary size.