title: Constitutive activity of the serotonin2C receptor inhibits in vivo dopamine release in the rat striatum and nucleus accumbens.
abstract: Numerous research has pointed out that serotonin2c (5-HT2C) receptor, a subtype of 5-HT receptors belonging to the G-protein-coupled receptor superfamily, modulates the activity of mesencephalic dopamine (DA) neurons, the dysfunction of which is involved in devastating diseases such as schizophrenia, Parkinson's disease, and drug addiction. In the present study, using in vivo intracerebral microdialysis and Chinese hamster ovary (CHO) cells expressing 5-HT2C receptors to identify appropriate 5-HT2C receptor ligands, we sought to determine whether the property of 5-HT2C receptors to spontaneously activate intracellular signaling pathways in vitro (constitutive activity) participates in the tonic inhibitory control that they exert on DA release in the rat striatum and nucleus accumbens in vivo. In CHO cells, the purported antagonist 5-methyl-1-(3-pyridylcarbamoyl)-1,2,3,5-tetrahydropyrrolo[2,3-f] indole hydrochloride (SB 206553), but not 6-chloro-5-methyl-1-[6-(2-methylpiridin-3-yloxy)pyridin-3-yl carbamoyl] indoline (SB 242084), decreased basal inositol phosphate accumulation, thus behaving as a 5-HT2C inverse agonist. Its effect was prevented by SB 242084. In vivo, SB 206553 (1-10 mg/kg) elicited a dose-dependent and clear-cut increase in accumbal and striatal DA release compared with SB 242084 (1-10 mg/kg), and the 5-HT2C agonist S-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine hydrochloride (Ro-60-0175) (0.3-3 mg/kg) inhibited DA release. Pretreatment by SB 242084 reversed the change in DA release elicited by Ro-60-0175 and SB 206553. Furthermore, SB 206553-stimulated DA release was insensitive to reduction of 5-HT neuronal function induced by the 5-HT1A agonist (+/-)-8-hydroxy-2-dipropylaminotetralin or intra-raphe injections of 5,7-dihydroxytryptamine neurotoxin. The obtained results provide the first in vivo evidence that constitutive activity of the 5-HT2C receptor tonically inhibits mesencephalic DA neurons and underscore the need for a better understanding of the pathophysiological role of constitutive receptor activity.
authors.affiliation: Unité Mixte de Recherche Centre National de la Recherche Scientifique 5541-Université Victor Segalen Bordeaux 2, Boîte Postale 31, 33076 Bordeaux Cedex, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: De Deurwaerdère
authors.forename: Sylvia
authors.initials: S
authors.lastname: Navailles
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Berg
authors.forename: William P
authors.initials: WP
authors.lastname: Clarke
authors.forename: Umberto
authors.initials: U
authors.lastname: Spampinato
mesh_terms: D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005021:Ethylamines / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000493:pharmacokinetics; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008024:Ligands; D008297:Male; D017551:Microdialysis; D017072:Neostriatum / Q000187:drug effects / Q000378:metabolism*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044405:Receptor, Serotonin, 5-HT2C / Q000378:metabolism*; D058826:Serotonin 5-HT2 Receptor Agonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
chemical_list: C107820:6-chloro-5-methyl-1-((2-(2-methylpyrid-3-yloxy)pyrid-5-yl)carbamoyl)indoline; D000631:Aminopyridines; D005021:Ethylamines; D007211:Indoles; D008024:Ligands; D011725:Pyridines; D044405:Receptor, Serotonin, 5-HT2C; C103848:Ro 60-0175; D058826:Serotonin 5-HT2 Receptor Agonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D015116:5,7-Dihydroxytryptamine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C094868:SB 206553; D004298:Dopamine