EVIDENCE FOR MUSCARINIC ACETYLCHOLINE-RECEPTOR SUBTYPES IN THE PIGEONTELENCEPHALON

At least five subtypes of muscarinic acetylcholine receptors are expre ssed in various mammalian tissue preparations. The following experimen t, through the use of direct binding assays (using tritiated quinuclid inyl benzilate), competitive binding assays (using tritiated quinuclid inyl benzilate and unlabeled pirenzepine or AF-DX 116), and autoradiog raphic techniques, examined whether two of these five putative muscari nic acetylcholine receptor subtypes can be found in avian brain. Accor dingly, autoradiographic mapping of pirenzepine-sensitive (Mi-like) an d AF-DX 116-sensitive (M2-like) muscarinic acetylcholine receptor subt ypes in the pigeon telencephalon was conducted. Although both ligands bound throughout the brain, most telencephalic regions, including the archistriatum, the neostriatum, and basal ganglia structures like lobu s paraolfactorius, nucleus accumbens, and paleostriatum, showed a high er density of Mi-like sites. The exception to this finding was the nuc leus basalis which appeared as a region where Ma-like sites predominat ed. Moreover, the telencephalic region with the largest ratio of M1-li ke to Ma-like sites was the lateral portion of the parahippocampus; a characteristic shared with the mammalian dentate gyrus. The findings r eported here are generally consistent with previous reports of mammali an M1/M2 receptor distributions. (C) 1995 Wiley-Liss, Inc.