title: Measuring nicotinic receptors with characteristics of alpha4beta2, alpha3beta2 and alpha3beta4 subtypes in rat tissues by autoradiography.
abstract: Comparison of [125I]epibatidine and 5-[125I]iodo-3-(2-azetidinylmethoxy)pyridine ([125I]A-85380) autoradiography showed evidence for nicotinic receptor heterogeneity. To identify the receptor subtypes, we performed [125I]epibatidine autoradiography in the presence of cytisine or A-85380. By comparing these results with binding data from human embryonic kidney (HEK) 293 cells stably transfected with different combinations of rat nicotinic receptor subunits, we were able to quantify three distinct populations of [125I]epibatidine binding sites with characteristics of alpha4beta2, alpha3beta2 and alpha3beta4 receptors. Although the predominant subtype in rat brain was alpha4beta2, non-alpha4beta2 binding sites were prominent in many regions. In the habenulo-peduncular system, cerebellum, substantia gelatinosa, and many medullary nuclei, alpha3beta4-like binding accounted for more than 40% of [125I]epibatidine binding, and nearly all binding in superior cervical ganglion and pineal gland. Other regions enriched in alpha3beta4-like binding included locus ceruleus, dorsal tegmentum, subiculum and anteroventral thalamic nucleus. Regions enriched in alpha3beta2-like binding included the habenulo-peduncular system, many visual system structures, certain geniculate nuclei, and dopaminergic regions. The combination of autoradiography using a broad spectrum radioligand in the presence of selective competitors, and data from binding to defined receptor subtypes in expression systems, allowed us to quantify the relative populations of these three subtypes.
authors.affiliation: Department of Pharmacology, George Washington University Medical Center, Washington, DC 20037, USA. phmdcp@gwumc.edu
authors.forename: David C
authors.initials: DC
authors.lastname: Perry
authors.forename: Yingxian
authors.initials: Y
authors.lastname: Xiao
authors.forename: Henry N
authors.initials: HN
authors.lastname: Nguyen
authors.forename: John L
authors.initials: JL
authors.lastname: Musachio
authors.forename: Martha I
authors.initials: MI
authors.lastname: Dávila-García
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Kellar
mesh_terms: D000470:Alkaloids / Q000493:pharmacokinetics / Q000494:pharmacology; D000818:Animals; D001345:Autoradiography; D001384:Azetidines / Q000493:pharmacokinetics / Q000494:pharmacology; D001392:Azocines; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000493:pharmacokinetics; D002460:Cell Line; D006801:Humans; D007457:Iodine Radioisotopes; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008024:Ligands; D008297:Male; D018733:Nicotinic Antagonists / Q000493:pharmacokinetics / Q000494:pharmacology; D009928:Organ Specificity; D010870:Pineal Gland / Q000378:metabolism; D021122:Protein Subunits; D011725:Pyridines / Q000493:pharmacokinetics; D011807:Quinolizines; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000032:analysis / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism*; D017783:Superior Cervical Ganglion / Q000378:metabolism; D014018:Tissue Distribution; D000093843:Quinolizidine Alkaloids
chemical_list: D000470:Alkaloids; D001384:Azetidines; D001392:Azocines; D019086:Bridged Bicyclo Compounds, Heterocyclic; D007457:Iodine Radioisotopes; D008024:Ligands; D018733:Nicotinic Antagonists; D021122:Protein Subunits; D011725:Pyridines; D011807:Quinolizines; D011978:Receptors, Nicotinic; C104288:A 85380; C419362:nicotinic receptor alpha3beta2; C403530:nicotinic receptor alpha3beta4; C403531:nicotinic receptor alpha4beta2; C004712:cytisine; D000093843:Quinolizidine Alkaloids; C082748:epibatidine