title: Native rat hippocampal 5-HT1A receptors show constitutive activity.
abstract: Previous studies have shown that human 5-hydroxytryptamine (5-HT)1A receptors stably expressed in transfected cell lines show constitutive G-protein activity, as revealed by the inhibitory effect of inverse agonists, such as spiperone, on basal guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]GTPgammaS) binding. In the present study, we evaluated the constitutive activity of native rat 5-HT1A receptors in hippocampal membranes. Using anti-Galphao-antibody capture coupled to scintillation proximity assay under low sodium (30 mM) conditions, we observed high basal [35S]GTPgammaS binding to Galphao subunits (defined as 100%). Under these conditions, 5-HT and the prototypic selective 5-HT1A agonist (+)8-hydroxy-2-(di-n-propylamino)tetralin [(+)-8-OH-DPAT] both stimulated [35S]GTPgammaS binding to Galphao to a similar extent, raising binding to approximately 130% of basal with pEC50 values of 7.91 and 7.87, respectively. The 5-HT1A-selective neutral antagonist [O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY100,635) could block these effects in a competitive manner with pKb values (5-HT, 9.57; (+)-8-OH-DPAT, 9.52) that are consistent with its pKi value at r5-HT1A receptors (9.33). In this native receptor system, spiperone and methiothepin reduced basal [35S]GTPgammaS binding to Galphao in a concentration-dependent manner to 90% of basal with pIC50 values of 7.37 and 7.98, respectively. The inhibition of basal [35S]GTPgammaS binding induced by maximally effective concentrations of spiperone (10 microM) or methiothepin (1 microM) was antagonized by WAY100,635 in a concentration-dependent manner (pKb, 9.52 and 8.87, respectively), thus indicating that this inverse agonism was mediated by 5-HT1A receptors. These data provide the first demonstration that native rat serotonin 5-HT1A receptors can exhibit constitutive activity in vitro.
authors.affiliation: Department of Neurobiology 2, Institut de Recherche Pierre Fabre, France. jean.claude.martel@pierre-fabre.com
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Martel
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Ormière
authors.forename: Nathalie
authors.initials: N
authors.lastname: Leduc
authors.forename: Marie-Bernadette
authors.initials: MB
authors.lastname: Assié
authors.forename: Didier
authors.initials: D
authors.lastname: Cussac
authors.forename: Adrian
authors.initials: A
authors.lastname: Newman-Tancredi
mesh_terms: D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000818:Animals; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D010879:Piperazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D044282:Receptor, Serotonin, 5-HT1A / Q000378:metabolism*
chemical_list: D010879:Piperazines; D011725:Pyridines; D044282:Receptor, Serotonin, 5-HT1A; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go