6-cyano-7-nitroquinoxaline-2-3-dione and Schizophrenia

Decreased expression of the GABA synthetic enzyme glutamate decarboxylase 67 (GAD67) in a subset of GABAergic neurons, including parvalbumin (PV)-expressing neurons, has been observed in postmortem brain studies of schizophrenics and in animal models of schizophrenia. However, it is unclear whether and how the perturbations of GAD67-mediated GABA synthesis and signaling contribute to the pathogenesis of schizophrenia. To address this issue, we generated the mice lacking GAD67 primarily in PV neurons and characterized them with focus on schizophrenia-related parameters. We found that heterozygous mutant mice exhibited schizophrenia-related behavioral abnormalities such as deficits in prepulse inhibition, MK-801 sensitivity, and social memory. Furthermore, we observed reduced inhibitory synaptic transmission, altered properties of NMDA receptor-mediated synaptic responses in pyramidal neurons, and increased spine density in hippocampal CA1 apical dendrites, suggesting a possible link between GAD67 deficiency and disturbed glutamatergic excitatory synaptic functions in schizophrenia. Thus, our results indicate that the mice heterozygous for GAD67 deficiency primarily in PV neurons share several neurochemical and behavioral abnormalities with schizophrenia, offering a novel tool for addressing the underlying pathophysiology of schizophrenia.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Actins; Action Potentials; Animals; Dendrites; Disease Models, Animal; Excitatory Amino Acid Antagonists; Exploratory Behavior; GABAergic Neurons; Glutamate Decarboxylase; Hippocampus; Male; Maze Learning; Mice; Mice, Transgenic; Parvalbumins; Phenotype; Reflex, Startle; Schizophrenia; Somatostatin; Valine

Group II mGlu receptor agonists (eg LY379268 and LY354740) have been shown to reverse many of the behavioral responses to PCP as well as glutamate release elicited by PCP and ketamine. In the present set of experiments, we used in vivo microdialysis to show that, in addition to reversing PCP- and ketamine-evoked glutamate release, group II mGlu receptor stimulation also prevents ketamine-evoked norepinephrine (NE) release. Pretreating animals with the mixed 2/3 metabotropic glutamate (mGlu2/3) receptor agonist LY379268 (0.3-10 mg/kg) dose-dependently inhibited ketamine (25 mg/kg)-evoked NE release in the ventral hippocampus (VHipp). Ketamine hyperactivity was also reduced in a similar dose range. Following our initial observation on NE release, we conducted a series of microinjection experiments to reveal that the inhibitory effects of LY379268 on VHipp NE release may be linked to glutamate transmission within the medial prefrontal cortex. Finally, we were able to mimic the inhibitory effects of LY379268 on ketamine-evoked NE release by using a novel mGlu2 receptor selective positive modulator. (+/-) 2,2,2-Trifluoroethyl [3-(1-methyl-butoxy)-phenyl]-pyridin-3-ylmethyl-sulfonamide (2,2,2-TEMPS, characterized through in vitro GTPgammaS binding) at a dose of 100 mg/kg significantly reduced the NE response. Together, these results demonstrate a novel means to suppress noradrenergic neurotransmission (ie by activating mGlu2 receptors) and may, therefore, have important implications for neuropsychiatric disorders in which aberrant activation of the noradrenergic system is thought to be involved.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Analysis of Variance; Animals; Area Under Curve; Binding Sites; Bridged Bicyclo Compounds, Heterocyclic; Chromatography, High Pressure Liquid; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glutamic Acid; Guanosine 5'-O-(3-Thiotriphosphate); Hippocampus; Humans; Hyperkinesis; In Vitro Techniques; Ketamine; Male; Microdialysis; Motor Activity; Norepinephrine; Prefrontal Cortex; Rats; Rats, Sprague-Dawley; Rats, Wistar; Receptors, Metabotropic Glutamate; Schizophrenia; Serotonin; Sulfur Isotopes; Time Factors; Trifluoroethanol; Xanthenes

Previous research indicated an increased binding of AMPA receptor ligand [(3)H]CNQX at 50 nM in the caudate nucleus of schizophrenics and suicides relative to normal and neuroleptic-treated controls. The current work aimed to replicate this finding in a larger, independent sample of schizophrenics and controls. In addition to neostriatal structures, the hippocampal region and amygdala were also studied. Postmortem frozen sections from 15 schizophrenics (four suicides), 15 normal controls, 15 bipolars (eight suicides), and 15 unipolar nonpsychotic depressed (seven suicides) subjects were studied with quantitative autoradiographic procedures at 5, 20, and 50 nM [(3)H]CNQX in the striatum and at 20 nM in medial temporal structures. [(3)H]KA (kainic acid) binding was also examined. Instead of an expected increase, schizophrenics in this sample have a lower degree of [(3)H]CNQX binding in caudate and nucleus accumbens at 20 nM and in the nucleus accumbens at 50 nM, with suicided schizophrenics having higher binding than nonsuicided schizophrenics at the 20 nM concentration of [(3)H]CNQX in the caudate. [(3)H]CNQX binding was uniform across diagnostic categories at 5 nM in the striatum and at 20 nM in amygdala and hippocampal structures. KA receptor binding also did not differ among groups in any structures examined. These assays in a larger sample at three different concentrations do not support the previously reported increase in binding to AMPA receptors in schizophrenia but rather indicate an abnormal decrease in binding to this receptor in this sample. Possible explanations for the disparity in results between the two studies are considered. The data continue to indicate pathology of AMPA glutamate receptors in striatal structures in schizophrenia; however, it may be variable and its precise nature remains to be clarified.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Adult; Aged; Amygdala; Autoradiography; Bipolar Disorder; Brain; Caudate Nucleus; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Hippocampus; Humans; Kainic Acid; Male; Middle Aged; Radioligand Assay; Receptors, AMPA; Schizophrenia; Suicide; Tritium

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Brain; Catecholamines; Dizocilpine Maleate; Dopamine; Humans; Kainic Acid; Motor Activity; Neurons; Nucleus Accumbens; Quisqualic Acid; Rats; Receptors, N-Methyl-D-Aspartate; Schizophrenia; Serotonin; Stereotyped Behavior; Tegmentum Mesencephali

Previous postmortem studies of glutamate receptors and uptake sites have shown decreased D-aspartate (D-Asp) (a marker for the high affinity glutamate uptake site) and elevated (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine maleate (MK-801) binding in the putamen in schizophrenia and elevated alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor binding in the caudate nucleus of schizophrenics who committed suicide. The relative effects of schizophrenia, suicide, and neuroleptic treatment in these findings is unclear. This study further explores binding to glutamate receptors (NMDA, kainic acid, and AMPA) and uptake sites in postmortem striatal structures in schizophrenics relative to three control groups (normal controls, neuroleptic-treated controls, and nonpsychotic suicides).. We compared the binding densities of tritium-labeled ligands 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), kainic acid (KA), MK-801, and D-Asp, which target the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), KA, and N-methyl-D-aspartic acid (NMDA) ionotropic receptor sites and the glutamate uptake site, respectively, in postmortem striatal/accumbens tissue from six DSM-III-R schizophrenics, eight normal controls, eight neuroleptic-treated controls, and eight suicide victims using standard receptor autoradiographic methods.. Binding of [3H] CNQX (AMPA receptors) was significantly different among the four groups across the subdivisions of the striatum: caudate, putamen, and nucleus accumbens (ANOVA P = .0007, .002, and .004, respectively). The schizophrenia group had higher mean CNQX binding in the caudate nucleus than normal (P = .005) and neuroleptic controls (P = .006) but not suicides (P = .6), who were also higher than normals and neuroleptic-treated controls (P = .05). The binding densities of tritiated MK-801, KA, and D-Asp were not significantly different among the four groups of subjects in any of the striatal regions examined.. The data suggest there may be an increased density of AMPA receptor sites in the caudate nucleus in schizophrenia that is not apparently due to neuroleptic treatment. A similar increase was also seen the suicide group. Although these data do not confirm previous reports of an increase in [3H]MK-801 or a decrease in [3H]D-Asp binding in the basal ganglia in schizophrenia, the increased caudate AMPA binding observed here could reflect decreased cortical glutamatergic innervation of the caudate. Its implication for suicide is unclear.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Antipsychotic Agents; Aspartic Acid; Autoradiography; Basal Ganglia; Brain Chemistry; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Female; Humans; Kainic Acid; Male; Middle Aged; Neostriatum; Receptors, AMPA; Receptors, Glutamate; Schizophrenia; Suicide

Using quantitative autoradiography, the anatomical distribution of the binding sites (kainate, N-methyl-D-aspartate and quisqualate) for the excitatory neurotransmitter glutamate has been established in the hippocampal formation from control and schizophrenic brains, post mortem. There is a loss of the kainate subtype particularly in schizophrenic hippocampi mainly from the CA4/CA3 mossy fibre termination zone of the cornu ammonis (CA4 and CA3; control and schizophrenic left hippocampus, respectively, 54.2 and 66.6 pmol/g; 18.3 and 17.9 pmol/g), as well as bilateral losses in the dentate gyrus (left 14.2 pmol/g and right 28.0 pmol/g; left 9.5 pmol/g and right 7.9 pmol/g, control and schizophrenic, respectively) and parahippocampal gyrus (left 50.8 pmol/g and right 41.7 pmol/g, left 27.7 pmol/g and right 25.3 pmol/g, control and schizophrenic, respectively). There is complete preservation of N-methy-D-aspartate sites in schizophrenic hippocampi, and a marginally significant loss of the quisqualate binding site in CA4/CA3 regions (left 249 fmol/g and right 306 fmol/g, left 157 fmol/g and right 148 fmol/g, control and schizophrenic, respectively). These findings reflect the possible importance of glutamate in the pathophysiology of schizophrenia and represent novel targets for therapeutic manipulation in schizophrenia.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Adult; Aged; Autoradiography; Female; Glutamates; Hippocampus; Humans; Kainic Acid; Male; Middle Aged; N-Methylaspartate; Pyramidal Tracts; Quinoxalines; Receptors, Glutamate; Receptors, Neurotransmitter; Reference Values; Schizophrenia; Tritium