title: Differential effects of low versus high doses of apomorphine on retinal dopamine metabolism in light- and dark-adapted rabbits.
abstract: Previous electrophysiologic results from this laboratory indicate that apomorphine exerts a differential dose-related effect on rabbit electroretinograms, with low doses increasing the b-wave and higher doses decreasing this parameter. Results were interpreted as reflecting apomorphine's agonistic properties at two different receptors: 1.0 mg/kg acting at the postsynaptic site, and the lower dose, 0.01 mg/kg, preferentially stimulating inhibitory autoreceptors. The purpose of this experiment was to investigate further this hypothesis by determining retinal levels of dopamine, dihydroxyphenylacetic acid, and homovanillic acid in retinas of light- or dark-adapted rabbits treated with saline, 1.0, 0.1, or 0.01 mg/kg apomorphine intravenously. Results indicate that in dark-adapted rabbits only the highest dose tested, 1.0 mg/kg, decreased dopamine concentrations. In animals exposed to light, the lowest dose tested, 0.01 mg/kg, significantly reduced dopamine and metabolite levels, whereas the highest dose unexpectedly increased retinal dopamine turnover. Results are discussed in terms of receptor sites and the influence of lighting conditions.
authors.affiliation: Department of Psychiatry and Pharmacology, Faculty of Medicine, University of Sherbrooke, Québec, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Drumheller
authors.forename: H
authors.initials: H
authors.lastname: Henni
authors.forename: G
authors.initials: G
authors.lastname: Lafond
authors.forename: J R
authors.initials: JR
authors.lastname: Brunette
authors.forename: F B
authors.initials: FB
authors.lastname: Jolicoeur
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D001058:Apomorphine / Q000008:administration & dosage / Q000494:pharmacology*; D003623:Dark Adaptation / Q000502:physiology; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D006719:Homovanillic Acid / Q000378:metabolism; D007275:Injections, Intravenous; D008027:Light; D011817:Rabbits; D012160:Retina / Q000187:drug effects / Q000378:metabolism*
chemical_list: D015102:3,4-Dihydroxyphenylacetic Acid; D001058:Apomorphine; D004298:Dopamine; D006719:Homovanillic Acid