Modulation of striatal dopamine release by glycine transport inhibitors.
Traditional models of schizophrenia have focused primarily upon dopaminergic (DA) dysregulation. In contrast, more recent models focus on dysfunction of glutamatergic systems, acting particularly through N-methyl-D-aspartate (NMDA) receptors. NMDA receptors in brain are regulated by glycine, acting via a strychnine-insensitive regulatory site, and by glycine (GlyT1) transporters that maintain low glycine levels in the immediate vicinity of the NMDA receptor complex. The present study investigates the role of NMDA receptors in the modulation of striatal dopamine release in vitro, and of glycine transport inhibitors (GTIs) as potential psychotherapeutic agents in schizophrenia. In striatum, NMDA receptors exert dual excitatory/inhibitory effects, with inhibition reflecting activity of local GABAergic feedback regulation. We have previously demonstrated effectiveness of glycine in regulating [3H]DA release both in vivo and in vitro, consistent with its beneficial clinical effects. In the present study, similar effects were observed for the high-affinity GTI (+)N[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy-)propyl]sarcosine (NFPS), and for a range of high-affinity GTIs with appropriate rank order of potency. In addition, (+)NFPS significantly stimulated NMDA-induced [3H]GABA release. Effects, of GTIs, were blocked by the glycine-site antagonists L689,560 and HA-966, and the GABA(B) antagonists phaclofen and CGP 52432, confirming the roles of both the NMDA-associated glycine-site and presynaptic GABA(B) receptors in NMDA receptor-mediated regulation of striatal DA release in vitro. Endogenous DA hyperactivity is associated with prominent positive symptoms in schizophrenia. The present results are consistent with recent clinical studies showing significant effectiveness of glycine-site agonists and GTIs in reduction of persistent positive, as well as negative, symptoms in schizophrenia.
Javitt
Daniel C
DC
Department of Neurochemistry, Nathan S Kline Institute for Psychiatric Research/NYU School of Medicine, Orangeburg, NY, USA. javitt@nki.rfmh.org
Hashim
Audrey
A
Sershen
Henry
H
D026921:Amino Acid Transport Systems, Neutral / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology*; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D058788:GABA-B Receptor Antagonists; D005998:Glycine / Q000378:metabolism*; D050487:Glycine Plasma Membrane Transport Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D016202:N-Methylaspartate / Q000494:pharmacology; D009924:Organ Culture Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D018080:Receptors, GABA-B / Q000378:metabolism; D018009:Receptors, Glycine / Q000037:antagonists & inhibitors / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism; D012521:Sarcosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D012559:Schizophrenia / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
C502339:ALX5311; D026921:Amino Acid Transport Systems, Neutral; D001713:Biphenyl Compounds; D018690:Excitatory Amino Acid Agonists; D018756:GABA Antagonists; D058788:GABA-B Receptor Antagonists; D050487:Glycine Plasma Membrane Transport Proteins; C435025:N-(3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)-3-(4'-phenylphenoxy)propyl)sarcosine; D018080:Receptors, GABA-B; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; C493267:Slc6a9 protein, mouse; D016202:N-Methylaspartate; D005998:Glycine; D004298:Dopamine; D012521:Sarcosine