title: Neuroanatomical aspects of mydriatic action of morphine in rats.
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.
authors.affiliation: Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Israel.
authors.forename: S
authors.initials: S
authors.lastname: Kamenetsky
authors.forename: R
authors.initials: R
authors.lastname: Rabinowitz
authors.forename: G
authors.initials: G
authors.lastname: Urca
authors.forename: A D
authors.initials: AD
authors.lastname: Korczyn
mesh_terms: D000701:Analgesics, Opioid / Q000627:therapeutic use*; D000818:Animals; D002375:Catalepsy / Q000139:chemically induced*; D008297:Male; D008636:Mesencephalon / Q000187:drug effects*; D009020:Morphine / Q000627:therapeutic use*; D009184:Mydriatics / Q000627:therapeutic use*; D051381:Rats
chemical_list: D000701:Analgesics, Opioid; D009184:Mydriatics; D009020:Morphine