title: Reconsideration of 5-hydroxytryptamine (5-HT)(7) receptor distribution using [(3)H]5-carboxamidotryptamine and [(3)H]8-hydroxy-2-(di-n-propylamino)tetraline: analysis in brain of 5-HT(1A) knockout and 5-HT(1A/1B) double-knockout mice.
abstract: The characterization and anatomical distribution of 5-hydroxytryptamine (5-HT)(7) receptor binding sites in brain tissue has been hampered by the lack of a specific radioligand. In the present autoradiographic study, we took advantage of 5-HT(1A) knockout and 5-HT(1A/1B) double-knockout mice to revisit the pharmacological characterization and anatomical localization of 5-HT(7) binding sites in mouse brain using [(3)H]5-carboxamidotryptamine (5-CT) and [(3)H]8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT). The distribution pattern of [(3)H]5-CT binding sites (2 nM) in the brain of mice lacking the 5-HT(1A/1B) receptor was scarce and confined to the septum, globus pallidus, thalamus, hypothalamus, amygdala, cortex, and substantia nigra. The low densities of [(3)H]5-CT binding sites detected in septum, thalamus, hypothalamus, amygdala, and cortex were displaced by 10 microM of the selective 5-HT(7) receptor antagonist (R)-3-(2-(2-(4-methylpiperidin-1-yl) ethyl)pyrrolidine-1-sulfonyl) phenol (SB-269970). The SB-269970-insensitive [(3)H]5-CT binding sites detected in globus pallidus and substantia nigra of 5-HT(1A/1B) knockout mice were displaced by N-[3-(2-dimethylamino)ethoxy-4-methoxy-phenyl]-2'-methyl-4'- (5-methyl-1,2,4-oxadiazol-3-yl)-(1,1'-biphenyl)-4-carboxamide hydrochloride (SB-216641) (1 microM), demonstrating the 5-HT(1D) nature of these binding sites. In contrast to the low densities of [(3)H]5-CT binding sites, high-to-moderate densities of [(3)H]8-OH-DPAT binding sites (10 nM) were found throughout the brain of 5-HT(1A) and 5-HT(1A/1B) knockout mice (olfactory system, septum, thalamus, hypothalamus, amygdala, CA3 field of the hippocampus, cortical mantle, and central gray). These [(3)H]8-OH-DPAT binding sites were displaced by 10 microM SB-269970, risperidone, and methiothepin but not by pindolol, N-tert-butyl-3-[4-(2-methoxyphenyl)piperazin-1-yl]-2-phenylpropanamide (WAY- 100135), or citalopram. We conclude that despite its high affinity for the 5-HT(7) receptor in tissue homogenates, [(3)H]5-CT is not a good tracer for measuring 5-HT(7) receptor binding sites autoradiographically. Also, the lower affinity ligand [(3)H]8-OH-DPAT is a much better tracer for autoradiographic studies at the 5-HT(7) receptor binding sites.
authors.affiliation: Johnson & Johnson Pharmaceutical Research and Development L.L.C, 3210 Merryfield Row, San Diego, CA 92121, USA. pbonave1@prdus.jnj.com
authors.forename: Pascal
authors.initials: P
authors.lastname: Bonaventure
authors.forename: Diane
authors.initials: D
authors.lastname: Nepomuceno
authors.forename: Annette
authors.initials: A
authors.lastname: Kwok
authors.forename: Wenying
authors.initials: W
authors.lastname: Chai
authors.forename: Xavier
authors.initials: X
authors.lastname: Langlois
authors.forename: Rene
authors.initials: R
authors.lastname: Hen
authors.forename: Kimberly
authors.initials: K
authors.lastname: Stark
authors.forename: Nicholas
authors.initials: N
authors.lastname: Carruthers
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Lovenberg
mesh_terms: D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000033:anatomy & histology; D001923:Brain Chemistry / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D010636:Phenols / Q000494:pharmacology; D011869:Radioligand Assay; D044302:Receptor, Serotonin, 5-HT1B; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism*; D044263:Receptors, Serotonin, 5-HT1; D012701:Serotonin / Q000031:analogs & derivatives*; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: D010636:Phenols; D044302:Receptor, Serotonin, 5-HT1B; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; C404922:SB 269970; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D013449:Sulfonamides; C104425:serotonin 7 receptor; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C047087:5-carboxamidotryptamine