Ec. Kohler et al., EVIDENCE FOR MUSCARINIC ACETYLCHOLINE-RECEPTOR SUBTYPES IN THE PIGEONTELENCEPHALON, Journal of comparative neurology, 362(2), 1995, pp. 271-282
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.