Abstract
Morphine causes mydriasis in rats. In order to investigate whether this effect is due to direct inhibition of preganglionic pupilloconstrictor neurons in the Edinger-Westphal nucleus (EWN), we injected opiate agonists into the EWN in male albino Charles River rats. Bilateral stereotactic microinjections of morphine (10, 20, 30, 40 micrograms/side) inhibited spinal nociceptive reflexes and caused pronounced catalepsy, but had no effect on pupillary size. The powerful opiate agonist, fentanyl, also elicited analgesia and catalepsy, when given in doses of 5 and 10 micrograms/side, but no dose of fentanyl up to 10 micrograms/side induced mydriasis. Naloxone (10 micrograms/side), given into the EWN, effectively antagonized inhibition of the tail-flick response induced by subcutaneously administered morphine (30 micrograms/kg), but had no effect on the cataleptic and mydriatic actions of systemic morphine. These results indicate that, in the rat, morphine-induced mydriasis is not accounted for by a direct action on the EWN.
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Schedule a callMore From: Journal of ocular pharmacology and therapeutics : the official journal of the Association for Ocular Pharmacology and Therapeutics
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