title: Alpha2-adrenoceptors do not mediate reflex mydriasis in rabbits.
abstract: The aim of this study was to identify receptors that mediate reflex mydriasis in pentobarbital-anesthetized rabbits, in which the cervical sympathetic nerve was sectioned unilaterally. Voltage-response curves of pupillary dilation were generated bilaterally by stimulation of the sciatic nerve. Evoked mydriatic responses were mediated mainly by efferent parasympathetic innervation, and, to a lesser extent, by sympathetic innervation. The alpha-adrenergic antagonist, phenoxybenzamine (0.3 mg/kg, intravenously (i.v.)), antagonized mydriasis of the neurally intact eye, but not that on the sympathectomized side. The alpha2-adrenergic antagonist, RS 79948 (0.3 mg/kg, i.v.), potentiated mydriasis of the normal eye, but was without either a potentiating or inhibitory effect on the mydriasis of the sympathectomized eye. In addition, the dopamine-receptor antagonist, haloperidol (1 mg/kg, i.v.), inhibited evoked mydriasis of the sympathectomized eye. These results suggest that, unlike some other species (cats and rats), alpha2-adrenoceptors do not mediate reflex mydriasis elicited by sciatic-nerve stimulation in the rabbit, and support the previous finding in humans that dopamine receptors may mediate this response.
authors.affiliation: Department of Cell Biology, University of Oklahoma College of Medicine, Oklahoma City, OK 73190, USA. yongxin-yu@ouhsc.edu
authors.forename: Yongxin
authors.initials: Y
authors.lastname: Yu
authors.forename: Michael C
authors.initials: MC
authors.lastname: Koss
mesh_terms: D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000758:Anesthesia; D000818:Animals; D018492:Dopamine Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004558:Electric Stimulation; D006220:Haloperidol / Q000008:administration & dosage / Q000494:pharmacology; D007275:Injections, Intravenous; D007546:Isoquinolines / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D008959:Models, Neurological; D015878:Mydriasis / Q000139:chemically induced / Q000503:physiopathology*; D009287:Naphthyridines / Q000008:administration & dosage / Q000494:pharmacology; D010643:Phenoxybenzamine / Q000008:administration & dosage / Q000494:pharmacology; D011817:Rabbits; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D011954:Receptors, Dopamine / Q000502:physiology; D012025:Reflex, Pupillary / Q000187:drug effects / Q000502:physiology*; D012584:Sciatic Nerve / Q000502:physiology / Q000601:surgery; D013562:Sympathectomy
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D018492:Dopamine Antagonists; D007546:Isoquinolines; D009287:Naphthyridines; C104875:RS 79948-197; D018341:Receptors, Adrenergic, alpha-2; D011954:Receptors, Dopamine; D010643:Phenoxybenzamine; D006220:Haloperidol