title: M1 muscarinic receptor signaling in mouse hippocampus and cortex.
abstract: The five subtypes (M1-M5) of muscarinic acetylcholine receptors signal through G(alpha)(q) or G(alpha)(i)/G(alpha)(o). M1, M3 and M5 receptors couple through G(alpha)(q) and function predominantly as postsynaptic receptors in the central nervous system. M1 and M3 receptors are localized to brain regions involved in cognition, such as hippocampus and cortex, but their relative contribution to function has been difficult to ascertain due to the lack of subtype specific ligands. A functional and genetic approach was used to identify the predominant muscarinic receptor subtype(s) mediating responses in mouse hippocampus and cortex, as well as the relative degree of spare muscarinic receptors in hippocampus. The nonselective muscarinic agonist oxotremorine-M stimulated G(alpha)(q)/11-specific GTP-gamma-35S binding in a concentration dependent manner with a Hill slope near unity in wild type mouse hippocampus and cortex. Muscarinic receptor stimulated G(alpha)(q)/11-specific GTP-gamma-35S binding was virtually abolished in both the hippocampus and cortex of M1 receptor knockout (KO) mice. In contrast, there was no loss of signaling in M3 receptor KO mice in either brain region. Muscarinic receptor reserve in wildtype mouse hippocampus was measured by Furchgott analysis after partial receptor alkylation with propylbenzylcholine mustard. Occupation of just 15% of the M1 receptors in mouse hippocampus was required for maximal efficacy of oxotremorine-M-stimulated GTP-gamma-35S binding indicating a substantial level of spare receptors. These findings support a role for the M1 receptor subtype as the primary G(alpha)(q)/11-coupled muscarinic receptor in mouse hippocampus and cortex.
authors.affiliation: Lilly Research Laboratories, Neuroscience Research Division, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285-0510, USA. aporter@lilly.com
authors.forename: Amy C
authors.initials: AC
authors.lastname: Porter
authors.forename: Frank P
authors.initials: FP
authors.lastname: Bymaster
authors.forename: Neil W
authors.initials: NW
authors.lastname: DeLapp
authors.forename: Masahisa
authors.initials: M
authors.lastname: Yamada
authors.forename: Jürgen
authors.initials: J
authors.lastname: Wess
authors.forename: Susan E
authors.initials: SE
authors.lastname: Hamilton
authors.forename: Neil M
authors.initials: NM
authors.lastname: Nathanson
authors.forename: Christian C
authors.initials: CC
authors.lastname: Felder
mesh_terms: D000818:Animals; D001667:Binding, Competitive / Q000502:physiology; D002540:Cerebral Cortex / Q000378:metabolism*; D005260:Female; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006153:Guanosine Diphosphate; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D018721:Muscarinic Agonists / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D010095:Oxotremorine; D011438:Propylbenzilylcholine Mustard; D011869:Radioligand Assay; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000172:deficiency* / Q000187:drug effects / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics*; D013347:Subcellular Fractions; D009435:Synaptic Transmission / Q000235:genetics*
chemical_list: D018721:Muscarinic Agonists; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D006153:Guanosine Diphosphate; D011438:Propylbenzilylcholine Mustard; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010095:Oxotremorine; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins