title: N-[3H]methylscopolamine labeling of non-M1, non-M2 muscarinic receptor binding sites in rat brain.
abstract: Radioligand binding and quantitative autoradiographic techniques were used to characterize the pharmacological profile and anatomical distribution of N-[3H]methylscopolamine [( 3H] NMS)-labeled sites under assay conditions in which radioligand binding to M1 and M2 muscarinic receptors was blocked by addition of pirenzepine and AF-DX 116 (11[[2-[(diethylamino)methyl]-1-piperidinyl] acetyl]-5,11-dihydro-6H-pyrido[2,3-b] [1,4]benzodiazepine-6-one) to the incubation buffer. Nonlinear regression analysis of saturation data demonstrated that a large proportion of atropine-displaceable [3H]NMS binding persisted in the presence of saturating concentrations of M1 and M2 blockers. The residual [3H]NMS [( 3H]NMSb) sites were widely distributed throughout rat brain and represented the predominant muscarinic receptor population. The autoradiographic distribution of [3H]NMSb sites did not correspond to that of [3H]pirenzepine or [3H]AF-DX 116, indicating that [3H]NMSb labeled non-M1, non-M2 muscarinic sites. Moreover, the pharmacological profile of [3H]NMSb differed from that of [3H]pirenzepine at M1 sites, and was inconsistent with that of M2 receptor binding sites. Although we were unable to pharmacologically distinguish subpopulations of non-M1, non-M2 binding sites, the anatomical distribution of [3H]NMSb sites corresponded to that of the combined mRNA distributions for m3 and m4.
authors.affiliation: Department of Pharmacology, College of Medicine, University of California, Irvine.
authors.forename: T D
authors.initials: TD
authors.lastname: Smith
authors.forename: S J
authors.initials: SJ
authors.lastname: Annis
authors.forename: F J
authors.initials: FJ
authors.lastname: Ehlert
authors.forename: F M
authors.initials: FM
authors.lastname: Leslie
mesh_terms: D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D004347:Drug Interactions; D008297:Male; D019832:N-Methylscopolamine; D010276:Parasympatholytics / Q000378:metabolism*; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D012602:Scopolamine Derivatives / Q000378:metabolism*
chemical_list: D010276:Parasympatholytics; D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D010890:Pirenzepine; C048593:otenzepad; D019832:N-Methylscopolamine