Mediation of mydriasis in conscious rats by central postsynaptic alpha 2-adrenoceptors

Pharmacology, Biochemistry, and Behavior
D J HealW R Buckett

Abstract

The alpha 2-adrenoceptor agonist, clonidine (0.001-1 mg/kg, IP), dose-dependently induced mydriasis in conscious rats (ED50 0.088 mg/kg). This response was maximal when measured 10 min after clonidine injection and was of about 30-min duration. The noradrenaline releasing agent, methamphetamine (0.75 mg/kg, IP), also increased pupil diameter. Clonidine (0.03 mg/kg, IP)-induced mydriasis was inhibited in a dose-related fashion by the alpha 2-adrenoceptor antagonists, idazoxan (0.03-3 mg/kg, IP) and yohimbine (0.03-3 mg/kg, IP), but was unaltered by the alpha 1- or beta-adrenergic antagonists, prazosin (1 and 3 mg/kg, IP) or pindolol (1 and 3 mg/kg, IP). Methamphetamine (0.75 mg/kg, IP)-induced mydriasis was similarly inhibited by idazoxan (1 mg/kg, IP) and yohimbine (1 mg/kg, IP). These data argued strongly that central alpha 2-adrenoceptors are involved in the mediation of mydriasis. The synaptic location of these receptors was determined using DSP-4 (50 mg/kg x 2, IP) to lesion noradrenergic neurones: this produced a 64% depletion of noradrenaline in the midbrain (containing the Edinger-Westphal nucleus responsible for mydriasis) and reduced the mydriatic effect of methamphetamine (0.75 mg/kg, IP) to a similar extent (72%), wh...Continue Reading

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Citations

Oct 15, 2009·Naunyn-Schmiedeberg's Archives of Pharmacology·Tiina LeinoRaimo Virtanen
Mar 2, 2002·European Neuropsychopharmacology : the Journal of the European College of Neuropsychopharmacology·Jean-Philippe RénéricLuis Stinus
Aug 29, 2000·Journal of Autonomic Pharmacology·A L HudsonD J Nutt
Aug 15, 2014·Journal of Psychopharmacology·C Richard ChapmanYoshio Nakamura
May 12, 2017·Dose-response : a Publication of International Hormesis Society·Joanna Raczak-GutknechtRoman Kaliszan
Jul 20, 2002·The Journal of Pharmacology and Experimental Therapeutics·Ryan K BachtellAndrey E Ryabinin
Jan 21, 2018·Applied Microbiology and Biotechnology·Narendra KumarSudhir Kumar Tomar
Jun 8, 2013·Pharmacological Reports : PR·Joanna Raczak-GutknechtRoman Kaliszan
Apr 1, 2021·British Journal of Pharmacology·James R Docherty, Hadeel A Alsufyani

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