Quantitative autoradiographic distribution of [3H]AF-DX 116 muscarinic-M2 receptor binding sites in rat brain.
The distribution of muscarinic-M2 receptors in rat brain was investigated by in vitro autoradiography using [3H]AF-DX 116, a putative probe for the muscarinic-M2 receptor subtype. Incubation of rat brain coronal sections with 10 nM [3H]AF-DX 116 showed highest binding site densities in discrete areas such as the superior colliculus and certain thalamic and brainstem nuclei, similar to the distribution reported for [2H]acetylcholine/M2 sites. [3H]AF-DX 116 site densities were markedly lower in forebrain areas such as cortex, striatum, and hippocampus, in contrast to the distribution seen for [3H]pirenzepine-M1 binding sites, which were concentrated in these forebrain areas; however, differential patterns of labeling were observed for the two muscarinic-M2 probes, [3H]AF-DX 116 and [3H]acetylcholine, in the hippocampal formation. Although [3H]AF-DX 116 binding was broadly distributed in multiple subfields of the hippocampus, [3H]acetylcholine binding was discretely distributed in a manner resembling that of acetylcholinesterase staining. This suggests the existence of muscarinic-M2 subtypes in the CNS, especially in the hippocampal formation.
Douglas Hospital Research Centre, Faculty of Medicine, McGill University, Verdun, Québec, Canada.
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Regenold
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Araujo
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Quirion
D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000378:metabolism*; D008297:Male; D018727:Muscarinic Antagonists; D010890:Pirenzepine / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000145:classification / Q000378:metabolism*
D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic; D010890:Pirenzepine; C048593:otenzepad