title: Neuron-type specific cannabinoid-mediated G protein signalling in mouse hippocampus.
abstract: Type 1 cannabinoid receptor (CB1) is expressed in different neuronal populations in the mammalian brain. In particular, CB1 on GABAergic or glutamatergic neurons exerts different functions and display different pharmacological properties in vivo. This suggests the existence of neuron-type specific signalling pathways activated by different subpopulations of CB1. In this study, we analysed CB1 expression, binding and signalling in the hippocampus of conditional mutant mice, bearing CB1 deletion in GABAergic (GABA-CB1-KO mice) or cortical glutamatergic neurons (Glu-CB1-KO mice). Compared to their wild-type littermates, Glu-CB1-KO displayed a small decrease of CB1 mRNA amount, immunoreactivity and [³H]CP55,940 binding. Conversely, GABA-CB1-KO mice showed a drastic reduction of these parameters, confirming that CB1 is present at much higher density on hippocampal GABAergic interneurons than glutamatergic neurons. Surprisingly, however, saturation analysis of HU210-stimulated [(35) S]GTPγS binding demonstrated that 'glutamatergic' CB1 is more efficiently coupled to G protein signalling than 'GABAergic' CB1. Thus, the minority of CB1 on glutamatergic neurons is paradoxically several fold more strongly coupled to G protein signalling than 'GABAergic' CB1. This selective signalling mechanism raises the possibility of designing novel cannabinoid ligands that differentially activate only a subset of physiological effects of CB1 stimulation, thereby optimizing therapeutic action.
authors.affiliation: Institute of Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany.
authors.forename: Frauke
authors.initials: F
authors.lastname: Steindel
authors.forename: Raissa
authors.initials: R
authors.lastname: Lerner
authors.forename: Martin
authors.initials: M
authors.lastname: Häring
authors.forename: Sabine
authors.initials: S
authors.lastname: Ruehle
authors.forename: Giovanni
authors.initials: G
authors.lastname: Marsicano
authors.forename: Beat
authors.initials: B
authors.lastname: Lutz
authors.forename: Krisztina
authors.initials: K
authors.lastname: Monory
mesh_terms: D000818:Animals; D002186:Cannabinoids / Q000378:metabolism*; D059330:GABAergic Neurons / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D006624:Hippocampus / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011485:Protein Binding / Q000502:physiology; D043884:Receptor, Cannabinoid, CB1 / Q000172:deficiency / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D002186:Cannabinoids; D043884:Receptor, Cannabinoid, CB1; D019204:GTP-Binding Proteins