title: Selective labelling of 5-HT7 receptor recognition sites in rat brain using [3H]5-carboxamidotryptamine.
abstract: The aim of the present study was to establish a radioligand binding assay to selectively label the native 5-HT7 receptor expressed in rat brain. In rat whole brain (minus cerebellum and striatum) homogenate, (+/-)-pindolol (10 microM)-insensitive [3H]5-CT ([3H]5-carboxamidotryptamine; 0.5 nM) specific binding (defined by 5-HT, 10 microM) displayed a pharmacological profile similar to the recombinant 5-HT7 receptor, although the Hill coefficients for competition curves generated by methiothepin, ritanserin, sumatriptan, clozapine and pimozide were significantly less than unity. In homogenates of rat hypothalamus, (+/-)-pindolol (10 microM)-insensitive [3H]5-CT recognition sites also resembled, pharmacologically, the 5-HT7 receptor, although pimozide still generated Hill coefficients significantly less than unity. Subsequent studies were performed in the additional presence of WAY100635 (100 nM) to prevent [3H]5-CT binding to residual, possibly, 5-HT1A sites. Competition for this [3H]5-CT binding indicated the labelling in whole rat brain homogenate of a homogenous population of sites with the pharmacological profile of the 5-HT7 receptor. Saturation studies also indicated that (+/-)-pindolol (10 microM)/WAY 100635 (100 nM)-insensitive [3H]5-CT binding to homogenates of whole rat brain was saturable and to an apparently homogenous population of sites which were labelled with nanomolar affinity (Bmax=33.2+/-0.7 fmol mg(-1) protein, pKd=8.78+/-0.05, mean+/-S.E.M., n=3). The development of this 5-HT7 receptor binding assay will aid investigation of the rat native 5-HT7 receptor.
authors.affiliation: Department of Pharmacology, The Medical School, University of Birmingham, Edgbaston, UK. RLS551@bham.ac.uk
authors.forename: R L
authors.initials: RL
authors.lastname: Stowe
authors.forename: N M
authors.initials: NM
authors.lastname: Barnes
mesh_terms: D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D003024:Clozapine / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010869:Pindolol / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000032:analysis / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012701:Serotonin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D014316:Tritium
chemical_list: D007211:Indoles; D010879:Piperazines; D011725:Pyridines; D011985:Receptors, Serotonin; D011994:Recombinant Proteins; D013449:Sulfonamides; C104425:serotonin 7 receptor; D014316:Tritium; D012701:Serotonin; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C047087:5-carboxamidotryptamine; D010869:Pindolol; D003024:Clozapine; C082871:GR 113808