Cerebrospinal fluid amino acid concentrations in chronic schizophrenia

Glutamatergic dysfunction in Schizophrenia

The NMDA-R hypofunction model of schizophrenia started with the clinical observation of the precipitation of psychotic symptoms in patients with schizophrenia exposed to PCP or ketamine. Healthy volunteers exposed to acute low doses of ketamine experienced mild psychosis but also negative and cognitive type symptoms reminiscent of the full clinical picture of schizophrenia. In rodents, acute systemic ketamine resulted in a paradoxical increase in extracellular frontal glutamate as well as of dopamine. Similar increase in prefrontal glutamate was documented with acute ketamine in healthy volunteers with ¹H-MRS. Furthermore, sub-chronic low dose PCP lead to reductions in frontal dendritic tree density in rodents. In post-mortem ultrastructural studies in schizophrenia, a broad reduction in dendritic complexity and somal volume of pyramidal cells has been repeatedly described. This most likely accounts for the broad, subtle progressive cortical thinning described with MRI in- vivo. Additionally, prefrontal reductions in the obligatory GluN₁ subunit of the NMDA-R has been repeatedly found in post-mortem tissue. The vast ¹H-MRS literature in schizophrenia has documented trait-like small increases in glutamate concentrations in striatum very early in the illness, before antipsychotic treatment (the same structure where increased pre-synaptic release of dopamine has been reported with PET). The more recent genetic literature has reliably detected very small risk effects for common variants involving several glutamate-related genes. The pharmacological literature has followed two main tracks, directly informed by the NMDA-R hypo model: agonism at the glycine site (as mostly add-on studies targeting negative and cognitive symptoms); and pre-synaptic modulation of glutamatergic release (as single agents for acute psychosis). Unfortunately, both approaches have failed so far. There is little doubt that brain glutamatergic abnormalities are present in schizophrenia and that some of these are related to the etiology of the illness. The genetic literature directly supports a non- specific etiological role for glutamatergic dysfunction. Whether NMDA-R hypofunction as a specific mechanism accounts for any important component of the illness is still not evident. However, a glutamatergic model still has heuristic value to guide future research in schizophrenia. New tools to jointly examine brain glutamatergic, GABA-ergic and dopaminergic systems in-vivo, early in the illness, may lay the ground for a next generation of clinical trials that go beyond dopamine D2 blockade.

Glutamate in schizophrenia: Neurodevelopmental perspectives and drug development

Research into the neurobiological processes that may lead to the onset of schizophrenia places growing emphasis on the glutamatergic system and brain development. Preclinical studies have shown that neurodevelopmental, genetic, and environmental factors contribute to glutamatergic dysfunction and schizophrenia-related phenotypes. Clinical research has suggested that altered brain glutamate levels may be present before the onset of psychosis and relate to outcome in those at clinical high risk. After psychosis onset, glutamate dysfunction may also relate to the degree of antipsychotic response and clinical outcome. These findings support ongoing efforts to develop pharmacological interventions that target the glutamate system and could suggest that glutamatergic compounds may be more effective in specific patient subgroups or illness stages. In this review, we consider the updated glutamate hypothesis of schizophrenia, from a neurodevelopmental perspective, by reviewing recent preclinical and clinical evidence, and discuss the potential implications for novel therapeutics.

Glutamate and dopamine in schizophrenia: an update for the 21st century

The glutamate and dopamine hypotheses are leading theories of the pathoaetiology of schizophrenia. Both were initially based on indirect evidence from pharmacological studies supported by post-mortem findings, but have since been substantially advanced by new lines of evidence from in vivo imaging studies. This review provides an update on the latest findings on dopamine and glutamate abnormalities in schizophrenia, focusing on in vivo neuroimaging studies in patients and clinical high-risk groups, and considers their implications for understanding the biology and treatment of schizophrenia. These findings have refined both the dopamine and glutamate hypotheses, enabling greater anatomical and functional specificity, and have been complemented by preclinical evidence showing how the risk factors for schizophrenia impact on the dopamine and glutamate systems. The implications of this new evidence for understanding the development and treatment of schizophrenia are considered, and the gaps in current knowledge highlighted. Finally, the evidence for an integrated model of the interactions between the glutamate and dopamine systems is reviewed, and future directions discussed.

GABA transporter-1 deficiency confers schizophrenia-like behavioral phenotypes

The mechanism underlying the pathogenesis of schizophrenia remains poorly understood. The hyper-dopamine and hypo-NMDA receptor hypotheses have been the most enduring ideas. Recently, emerging evidence implicates alterations of the major inhibitory system, GABAergic neurotransmission in the schizophrenic patients. However, the pathophysiological role of GABAergic system in schizophrenia still remains dubious. In this study, we took advantage of GABA transporter 1 (GAT1) knockout (KO) mouse, a unique animal model with elevated ambient GABA, to study the schizophrenia-related behavioral abnormalities. We found that GAT1 KO mice displayed multiple behavioral abnormalities related to schizophrenic positive, negative and cognitive symptoms. Moreover, GAT1 deficiency did not change the striatal dopamine levels, but significantly enhanced the tonic GABA currents in prefrontal cortex. The GABA(A) receptor antagonist picrotoxin could effectively ameliorate several behavioral defects of GAT1 KO mice. These results identified a novel function of GAT1, and indicated that the elevated ambient GABA contributed critically to the pathogenesis of schizophrenia. Furthermore, several commonly used antipsychotic drugs were effective in treating the locomotor hyperactivity in GAT1 KO mice, suggesting the utility of GAT1 KO mice as an alternative animal model for studying schizophrenia pathogenesis and developing new antipsychotic drugs.

Recent advances in targeting the ionotropic glutamate receptors in treating schizophrenia

The treatment of schizophrenia has been focused on modulation of dopamine receptors for over 50 years. Recent developments have implicated other neurotransmitter systems in the pathophysiology of this illness. The discovery and characterization of glutamate receptors and their roles in the brain has lead to novel approaches for the treatment of schizophrenia. In this article, we review drugs that modulate ionotropic gluamate receptors and discuss their efficacy for the treatment of this often debilitating severe mental illness.

Different serine and glycine metabolism in patients with schizophrenia receiving clozapine

Dysfunction of the N-methyl-d-aspartate receptor, which is modulated by excitatory amino acids (EAA), is involved in the pathophysiology of schizophrenia. The effects of antipsychotics on EAA metabolism are uncertain. Positive clinical effects of treatment with antipsychotics were not always associated with changes in EAA serum levels in patients with schizophrenia in clinical trials. To examine EAA serum levels in relation to the intensity of psychotic symptoms and the type of medication received we compared these variables among patients with schizophrenia (n = 49) treated with first (FGA) or second (SGA) generation antipsychotics or clozapine. Glutamate, aspartate, glycine, total serine and d-serine serum levels were measured by High Performance Liquid Chromatography. The Positive and Negative Syndrome Scale (PANSS) and the Scale for the Assessment of Negative Symptoms (SANS) were used to assess symptoms of schizophrenia. Lower average levels of glycine and total serine were found in the serum of patients receiving clozapine when compared to the groups of patients treated with FGA or SGA. There were no differences in serum glutamate, aspartate or d-serine levels or in the intensity of schizophrenic symptoms assessed by PANSS or SANS among the groups of patients treated with FGA or SGA or clozapine. Lower glycine and total serine serum levels could be caused by the particular characteristics of the population of patients receiving clozapine rather than as an effect of the clozapine. The results suggest selective deficiency of l-serine synthesis in the patients with resistance to non-clozapine treatment. It might be an unique biochemical and pathophysiological characteristic of the treatment-resistance in schizophrenia.

Elevated gamma-aminobutyric acid levels in chronic schizophrenia

BACKGROUND

Despite widely replicated abnormalities of gamma-aminobutyric acid (GABA) neurons in schizophrenia postmortem, few studies have measured tissue GABA levels in vivo. We used proton magnetic resonance spectroscopy to measure tissue GABA levels in participants with schizophrenia and healthy control subjects in the anterior cingulate cortex and parieto-occipital cortex.

METHODS

Twenty-one schizophrenia participants effectively treated on a stable medication regimen (mean age 39.0, 14 male) and 19 healthy control subjects (mean age 36.3, 12 male) underwent a proton magnetic resonance spectroscopy scan using GABA-selective editing at 4 Tesla after providing informed consent. Data were collected from two 16.7-mL voxels and analyzed using LCModel.

RESULTS

We found elevations in GABA/creatine in the schizophrenia group compared with control subjects [F(1,65) = 4.149, p = .046] in both brain areas (15.5% elevation in anterior cingulate cortex, 11.9% in parieto-occipital cortex). We also found a positive correlation between GABA/creatine and glutamate/creatine, which was not accounted for by % GM or brain region.

CONCLUSIONS

We found elevated GABA/creatinine in participants with chronically treated schizophrenia. Postmortem studies report evidence for dysfunctional GABAergic neurotransmission in schizophrenia. Elevated GABA levels, whether primary to illness or compensatory to another process, may be associated with dysfunctional GABAergic neurotransmission in chronic schizophrenia.

Glycine serum level in schizophrenia: relation to negative symptoms

Glycine acts as an endogenous selective co-agonist at the glycine modulatory site of the NMDA (N-methyl-d-aspartate) receptor. Significantly decreased glycine serum levels were reported in patients with schizophrenia in comparison to healthy controls. Administration of glycine improved negative symptoms in patients with schizophrenia treated with antipsychotics in some clinical trials. We hypothesized that glycine serum levels might be associated with intensity of negative symptoms in schizophrenia. Fifty outpatients with the diagnosis of schizophrenia as defined by ICD-10 and fifty age- and gender-matched healthy controls were recruited into the study. Glycine serum levels were measured by high performance liquid chromatography (HPLC). We used the Positive and Negative Syndrome Scale (PANSS) and the Scale for the Assessment of Negative Symptoms (SANS) to assess the symptoms of schizophrenia in the patients. We found mean glycine serum levels to be significantly lower in patients than in controls. This difference was only caused by findings in the male study population. Glycine serum levels were negatively associated with intensity of negative symptoms assessed by the PANSS negative subscale and the SANS total scores in the patients. These data suggest a possible implication of NMDA receptor dysfunction in the pathogenesis of negative symptoms in schizophrenia.

Mice with genetically altered glutamate receptors as models of schizophrenia: a comprehensive review

Recent clinical evidence for the effectiveness of new antipsychotic drugs that specifically target glutamate receptors has rekindled interest in the glutamatergic system regarding pathophysiology and treatment of schizophrenia. The glutamatergic hypothesis of schizophrenia was triggered by the clinical/behavioural observation that NMDA receptor antagonists can induce psychosis in humans and abnormal behaviour with schizophrenia-like symptoms in animals. Initial models focused on NMDA receptor hypofunction as a potential pathogenetic mechanism. More recent genetic and pharmacological studies revealed that malfunction of other components of the glutamatergic system might also be relevant in explaining specific symptoms of this complex disease. Here, we review mutant mouse models with relevance for schizophrenia. These rodent models, in which specific glutamate receptor subtypes or various components of their intracellular transduction machinery are genetically altered, permit a detailed dissection of the contribution of different components of the glutamate system in inducing schizophrenia-like behaviours. They may provide insight into the pathophysiology of schizophrenia and prove useful in the development of new therapeutics.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Abnormal expression of glutamate transporter and transporter interacting molecules in prefrontal cortex in elderly patients with schizophrenia

Glutamate cycling is critically important for neurotransmission, and may be altered in schizophrenia. The excitatory amino acid transporters (EAATs) facilitate the reuptake of glutamate from the synaptic cleft and have a key role in glutamate cycling. We hypothesized that expression of the EAATs and the EAAT regulating proteins ARHGEF11, JWA, G-protein suppressor pathway 1 (GPS1), and KIAA0302 are altered in the brain in schizophrenia. To test this, we measured expression of EAAT1, EAAT2, EAAT3, and EAAT interacting proteins in postmortem tissue from the dorsolateral prefrontal and anterior cingulate cortex of patients with schizophrenia and a comparison group using in situ hybridization and Western blot analysis. We found increased EAAT1 transcripts and decreased protein expression, increased EAAT3 transcripts and protein, and elevated protein expression of both GPS1 and KIAA0302 protein. We did not find any changes in expression of EAAT2. These data indicate that proteins involved in glutamate reuptake and cycling are altered in the cortex in schizophrenia, and may provide potential targets for future treatment strategies.

Two distinct subtypes of serotonergic fibers classified by co-expression with vesicular glutamate transporter 3 in rat forebrain

Although virtually all of serotonin (5-HT) neurons in the midbrain raphe nuclei of rats are known to express vesicular glutamate transporter 3 (VGLUT3), VGLUT3-positive 5-HT fibers have been identified only in the cerebral cortex and hippocampus. Thus, our understanding of forebrain sites where 5-HT-glutamate interaction may be potentially managed by such possible glutamatergic 5-HT fibers themselves, is still largely fragmentary from a morphological point of view. To address this issue, we analyzed the rat forebrain by immunohistochemistry and chemical lesion experiment of 5-HT neurons by intracerebroventricular injection of a neurotoxin, 5,7-dihydroxytriptamine. Contrary to expectation, the double-label immunofluorescence staining revealed that the incidence of VGLUT3-positive 5-HT fibers is generally low over the forebrain, demonstrating occasional fibers with one or two double-labeled varicosities. The most extreme example was the nucleus of the lateral olfactory tract (LOT), which seemed to be devoid of double-labeled fibers despite high densities of 5-HT fibers and VGLUT3-positive fibers. In sharp contrast, robust plexuses of VGLUT3-positive 5-HT fibers were found in the dorsal, but not ventral, part of the lateral septum. The lesion experiment carried out to explore whether VGLUT3 exists in 5-HT fibers showed that in lesioned rats VGLUT3-positive fibers almost completely disappear from the septal region but seemed unchanged in the LOT. The present study shows that midbrain raphe-derived 5-HT fibers can be classified into two subtypes depending on co-expression with VGLUT3 staining in the forebrain.

Cerebrospinal fluid kynurenic acid in male patients with schizophrenia - correlation with monoamine metabolites

BACKGROUND

The tryptophan metabolite kynurenic acid (KYNA) is an endogenous glutamate/nicotinic receptor antagonist. Previous studies have shown that the concentration of the compound is increased in cerebrospinal fluid (CSF) of patients with schizophrenia. Furthermore, it has been found that the CSF concentration of KYNA is positively correlated to CSF concentrations of the monoamine metabolites homovanillic acid (HVA) and 5-hydroxy indoleacetic acid (5-HIAA) in healthy control subjects.

OBJECTIVES

To study the correlations between KYNA and the monoamine metabolites HVA, 5-HIAA and 4-hydroxy-3-methoxyphenylglycol (HMPG) in CSF of male patients (n= 53, ranging from 20 to 48 years of age) with verified schizophrenia.

METHODS

CSF was obtained by lumbar puncture, and KYNA analysis was performed with an isocratic reversed-phase high-performance liquid chromatography system connected to a fluorescence detector. HVA, 5-HIAA and HMPG concentrations were measured by mass fragmentography with deuterium-labelled internal standards.

RESULTS

Positive intercorrelations were found between CSF KYNA, HVA and 5-HIAA, while CSF content of HMPG did not correlate to KYNA or any of the monoamine metabolites in CSF.

CONCLUSION

The results of this study suggest that increased KYNA formation is associated with an increased dopamine and serotonin turnover in male patients with schizophrenia.

Schizophrenia-associated neural growth factors in peripheral blood. A review

In this paper we review the findings on neural growth factors in the peripheral blood of schizophrenia patients. The studies we review provide evidence for the fact that in schizophrenia the levels of growth factors in peripheral blood are disturbed. The most robust results (7 studies) are reported for S100B protein, which seems to be elevated in acute psychosis and in patients with predominant negative symptoms. We conclude that there are aberrant levels of growth factors in peripheral blood in schizophrenia patients, probably most notably in patients with negative symptoms. Large-scale longitudinal multivariate studies, investigating the levels of several growth factors at the same time might give insight in etiological processes and identify clinically useful subsets of patients within the heterogeneous schizophrenia sample.

Possible Mechanisms of Neurodegeneration in Schizophrenia

Brain morphological alterations in schizophrenic patients have led to the neurodevelopmental hypothesis of schizophrenia. On the other hand, a progressive neurodegenerative process has also been suggested and some follow-up studies have shown progressive morphological changes in schizophrenic patients. Several neurotransmitter systems have been suggested to be involved in this disorder and some of them could lead to neuronal death under certain conditions. This review discusses some of the biochemical pathways that could lead to neurodegeneration in schizophrenia showing that neuronal death may have a role in the etiology or natural course of this disorder.

Alterations of plasma and cerebrospinal fluid glutamate levels in rats treated with the N-methyl-D-aspartate receptor antagonist, ketamine

It has been reported that the repeated administration of a sub-anesthetic dose of an N-methyl-D-aspartate receptor antagonist, ketamine, can produce an animal model of schizophrenia. Since no information is available on the alterations of the amino acid levels in ketamine-treated rats, we investigated the amino acid composition in the plasma and cerebrospinal fluid of rats that were repeatedly administered with ketamine for 5 consecutive days (30 mg/kg/day). The plasma and cerebrospinal fluid amino acid compositions in the fifth week after cessation of repeated ketamine administration were determined by highperformance liquid chromatography with fluorescence detection using a pre-column fluorescence reagent, i.e. 4-fluoro-7nitro-2,1,3-benzoxadiazole. Among the amino acids investigated in the present study, the level of plasma glutamic acid increased significantly (p < 0.05), while that of the cerebrospinal fluid glutamic acid decreased significantly in the ketamine-treated rats as compared with these levels in control rats injected with saline (p < 0.05, n = 7). These alterations in the glutamic acid level in the plasma and cerebrospinal fluid resemble those in schizophrenic patients, suggesting that ketamine-treated rats may be a useful model for performing research on the pathophysiology of schizophrenia.

Glutamatergic dysfunction in OCD

The role of glutamatergic dysfunction in the pathophysiology of OCD has hardly been explored despite recent reports implicating glutamatergic dysfunction in OCD. We decided to investigate CSF glutamate levels in adult OCD probands compared to psychiatrically normal controls. In total, 21 consenting psychotropic drug-naïve adult OCD patients, diagnosed using SCID-IV-CV, and 18 consenting psychiatrically normal controls with age within 10 years of age of the patients, who did not have any history of head injury or neurological illness, were included into the study. Aseptically collected and stored CSF samples obtained from the patients and control subjects were used for glutamate estimation, which was carried out by a modification of the procedure described by Lund (1986). CSF glutamate (micromol/l) level was found to be significantly higher [F(1,31)=6.846, p=0.014] in OCD patients (47.12+/-4.25) compared to control subjects (41.36+/-3.63) on analysis of covariance. There was no effect of gender, age, duration of illness, Y-BOCS score, or CGI-S score on CSF glutamate levels. Our study provides preliminary evidence implicating glutamatergic excess in the pathophysiology of OCD, which needs to be further explored by studies from other centers involving larger sample sets from different age groups.

Effects of haloperidol and clozapine on glutamate release from nerve terminals isolated from rat prefrontal cortex

The present study was conducted to understand the effect of haloperidol, a typical antipsychotic, and clozapine, an atypical one, on the release of endogenous glutamate in nerve terminals isolated from rat prefrontal cortex using an on-line enzyme-linked fluorometric assay. We found that both haloperidol and clozapine significantly inhibited 4-aminopyridine (4AP)-evoked and veratridine-evoked but not KCl-evoked glutamate release from prefrontocortical synaptosomes. This inhibition produced by these two drugs was concentration-dependent with different potency, and associated with a reduction both in the depolarization-evoked increase in the intrasynaptosomal free Na(+) concentration ([Na(+)](i)) and in 4AP or KCl-evoked depolarization of the synaptosomal plasma membrane potential. Additionally, in the presence of calcium-free medium containing 0.2 mM EGTA, the Ca(2+)-independent component of 4AP-evoked glutamate release was also inhibited by haloperidol or clozapine. Based on these results, we suggest that haloperidol and clozapine inhibit glutamate release from rat prefrontocortical nerve terminals by affecting ion-channel activities determining nerve terminal excitability, probably as a result of Na(+) channel blockage or K(+) channel activation.

Phenotype of schizophrenia: a review and formulation

The discovery of the pathophysiology(ies) for schizophrenia is necessary to direct rational treatment directions for this brain disorder. Firm knowledge about this illness is limited to areas of phenomenology, clinical electrophysiology, and genetic risk; some aspects of dopamine pharmacology, cognitive symptoms, and risk genes are known. Basic questions remain about diagnostic heterogeneity, tissue neurochemistry, and in vivo brain function. It is an illness ripe for molecular characterization using a rational approach with a confirmatory strategy; drug discovery based on knowledge is the only way to advance fully effective treatments. This paper reviews the status of general knowledge in this area and proposes an approach to discovery, including identifying brain regions of dysfunction and subsequent localized, hypothesis-driven molecular screening.

Thalamic dysfunction in schizophrenia: neurochemical, neuropathological, and in vivo imaging abnormalities

While abnormalities of the prefrontal cortex and temporal lobe structures have typically been associated with the pathophysiology of schizophrenia, recent findings implicate thalamic dysfunction in this illness as well. The thalamus plays a critical role in processing and integrating sensory information relevant to emotional and cognitive functions. Neuropathological and in vivo imaging studies in schizophrenia have identified several structural and metabolic abnormalities in the thalamus, which may contribute to a deficit in sensory processing and be related to psychotic symptomatology. In addition to these postmortem and in vivo imaging studies indicating structural and metabolic changes in the thalamus in schizophrenia, more recent studies have examined the neurochemical substrates that accompany these changes. Much of this work to date has focused on glutamatergic abnormalities in the thalamus, in part because it is a predominant neurotransmitter used in the thalamus, and because glutamatergic dysfunction has been hypothesized to be involved in schizophrenia. Several studies, however, have also examined markers of gamma-aminobutyric acid (GABA) and dopaminergic neurotransmission in the thalamus in schizophrenia. We review these neurochemical findings, as well as the growing body of postmortem and in vivo imaging evidence that supports the hypothesis of thalamic dysfunction in schizophrenia.

High-dose glycine added to olanzapine and risperidone for the treatment of schizophrenia

BACKGROUND

Clinical trials indicate that glycine site agonists of the N-methyl-D-aspartate (NMDA) receptors may reduce negative and cognitive symptoms in treatment-resistant schizophrenia when used as adjuvants to conventional antipsychotics but possibly not to clozapine. In this study, we assessed whether high-dose glycine may also be therapeutically beneficial when added to olanzapine and risperidone treatment.

METHODS

Seventeen olanzapine- or risperidone-treated schizophrenia patients participated in a double-blind, placebo-controlled, 6-week crossover treatment trial with.8 g/kg/day glycine added to their ongoing antipsychotic medication. Clinical assessments were performed biweekly throughout the study. Clinical laboratory parameters and amino acid serum levels were monitored.

RESULTS

Glycine treatment was well tolerated and resulted in a significant (p <.0001) 23% +/- 8% reduction in negative symptoms. Significant improvements were also registered in cognitive and positive symptoms. The negative symptoms improvement remained significant even following covariation for changes in other symptom clusters and extrapyramidal side effects. High posttreatment glycine serum levels significantly predicted (r =.60) clinical response.

CONCLUSIONS

These findings indicate that the efficacy of olanzapine and risperidone may be augmented using high-dose adjuvant glycine treatment and suggest that these atypical antipsychotics may affect NMDA receptor-mediated neurotransmission differently than clozapine.

Interactions of the mGluR5 gene with breeding and maternal factors on startle and prepulse inhibition in mice

Sensorimotor gating, measured by prepulse inhibition (PPI), is a fundamental form of information processing that is deficient in schizophrenia patients and mice lacking the gene for metabotropic glutamate receptor 5 (mGluR5). Both breeding strategies and mothering behaviors are capable of influencing the behavioral phenotype of knockout (KO) mice. Previous studies found a PPI deficit and increased startle magnitudes in mGluR5 KO mice derived from homozygous matings. Here we compared the PPI of mGluR5 wildtype (WT) and KO mice derived from heterozygous matings to that seen in mice derived from homozygous matings. Possible influences of postnatal mothering behaviors were examined using two different methods of cross-fostering. The potential developmental nature of the PPI deficit of the mGluR5 KO mice was also addressed via acute administration of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) to C57BL/6J mice. The mGluR5 KO mice exhibited reduced PPI independently of breeding strategy or postnatal mothering behavior. Startle magnitude, however, varied with breeding strategy. The PPI deficit seen in the mGluR5 KO mice is not mimicked by acute administration of an mGluR5 antagonist, and is therefore most likely due to compensatory alterations in neuronal circuitry occurring during development independent of maternal behaviors in the postnatal environment.

Glutamatergic neurotransmission modulation and the mechanisms of antipsychotic atypicality

The neurotransmission mediated by the excitatory amino acids (EAA) glutamate (GLU) and aspartate is of interest to the pharmacotherapy of psychosis due to its role in neurodevelopment and neurotoxicity, its complex interactions with dopaminergic and other neurotransmitter systems and its pivotal importance in recent models of schizophrenia. Accumulating evidence indicates that modulation of glutamatergic neurotransmission may play an important role in the mechanisms of action of atypical antipsychotic drugs. The principles of the phencyclidine (PCP) model of schizophrenia suggest that conventional neuroleptics cannot counteract all aspects of schizophrenia symptomatology, while a more favorable outcome, including anti-negative and cognitive symptoms effects, would be expected with the use of treatment modalities targeting glutamatergic neurotransmission. Clozapine and other presently used atypical antipsychotics differ from conventional neuroleptics in the way they affect various aspects of glutamatergic receptors function. In this context, a specific hypothesis suggesting an agonistic role of clozapine at the N-methyl-D-aspartate (NMDA) subtype of GLU receptors has been postulated. Furthermore, the results of the first generation of clinical trials with glycine (GLY) site agonists of the NMDA receptor in schizophrenia suggest that this type of compounds (1) have efficacy and side effects profiles different than those of conventional neuroleptics and (2) differ in their synergic effects when used in addition to conventional neuroleptics versus clozapine and possibly additional atypical antipsychotics. These findings (1) bring further support to the hypothesis that glutamatergic effects may play an important role in the mechanism of action of atypical antipsychotics, (2) help explain the unique clinical profile of clozapine, and (3) suggest that GLY site agonists of the NMDA receptor may represent a new class of atypical antipsychotic medication. Future research in this area is bound to bring about a better understanding of the role of glutamatergic neurotransmission manipulation in the pharmacotherapy of psychosis and the development of novel pharmacological strategies targeting GLU brain systems.

[Glutamatergic hypothesis of schizophrenia]

Schizophrenia is a devastating psychiatric disorder whose pathophysiology has not been fully clarified yet. Although dopamine dysfunction in schizophrenia is unequivocal, there are many evidences suggesting the involvement of the glutamatergic system. This paper briefly describes some basic knowledge regarding the functioning of the glutamatergic receptors with emphasis on the N-methyl-D-aspartate (NMDA) receptors. Presents evidence for glutamatergic dysfunction in schizophrenia, more specifically NMDA receptor hypofunction. Finaly the paper discusses the interaction between the dopaminergic and the glutamatergic systems; in special how hyperdopaminergic state found in schizophrenia can be associated to glutamatergic dysfunctions.

Indirect modulation of dopamine D2 receptors as potential pharmacotherapy for schizophrenia: II. Glutamate (Ant)agonists

OBJECTIVE

To summarize the published preclinical and clinical data that suggest the possible use of glutamate receptor agonists or antagonists as novel antipsychotic agents.

DATA SOURCES

Primary and review articles were identified by MEDLINE search (from 1966 to December 1999) and through secondary sources.

STUDY SELECTION AND DATA EXTRACTION

All of the articles identified from the data sources were evaluated and all information deemed relevant was included.

DATA SYNTHESIS

The standard antipsychotic drugs, whose clinical activity correlates with affinity for dopamine D2 receptors, alleviate some of the positive symptoms of schizophrenia, but have limited impact on negative symptoms. Several lines of evidence implicate glutamate-receptor system dysfunction(s) in schizophrenia, either as causative or contributory factors. In addition, several standard antipsychotic drugs modulate glutamate or glutamate receptor activity, suggesting an alternative view of their mechanism of antipsychotic action. Preliminary studies have shown that drugs which modulate glutamate brain concentrations have positive effects in animal models of schizophrenia.

CONCLUSIONS

A role for glutamate in the pathogenesis or pharmacotherapy of schizophrenia is suggested from anatomic (interactions between glutamatergic and dopaminergic systems in relevant brain regions), physiologic (implication of glutamate-receptor dysfunction), and pharmacologic (modulation of glutamate or glutamate receptors) evidence. Therefore, compounds that function at glutamate receptors might represent a novel approach to the treatment of the disease or to the amelioration of symptoms, either as monotherapy or as an adjunct to dopamine D2 receptor antagonists.

Hippocampal pathology in schizophrenia: magnetic resonance imaging and spectroscopy studies

The hippocampus is a site of previously reported structural and functional abnormalities in schizophrenia. We used magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (MRS) to measure gray matter volumes, the neuronal marker N-acetylaspartate (NAA), and the combination of glutamate (Glu), glutamine (Gln), and gamma-aminobutyric acid (GABA), designated Glx. Measurements were obtained of the medial temporal lobe, centered on the hippocampus, in 10 male patients with schizophrenia (3 neuroleptic-medicated and 7 medication-free), and 10 matched normal volunteers. MRI volumetric measurements and MRS data obtained with short echo time (TE=20 ms) one-dimensional STEAM chemical shift imaging (CSI) on a GE 1.5 Tesla Signa system were analyzed. A laterality index ¿(L-R)/(L+R) was generated from the ratio of Glx to choline-containing compounds (Cho) to test asymmetry changes. Reliability of the MRS measures was assessed with five test-retest studies of healthy volunteers and showed coefficients of variation (CV) in the range of 36-44% for the MRS ratios and standard deviations (S.D.) of 0.15-0.17 for the laterality indices. The Glx/Cho laterality index showed a relative right-sided excess in this region in the patients (-0.23+/-0.20) compared to the controls (+0.06+/-0.20), which was not confounded by tissue composition or placement variability of the MRS voxels. Hippocampal volume deficit and asymmetry were not significant, and other MRS measures showed no differences between patients and controls. The preliminary finding of a lateralized abnormality in Glx is consistent with postmortem findings of asymmetric neurochemical temporal lobe abnormalities in schizophrenia.

Increased cerebrospinal fluid glutamine levels in depressed patients

BACKGROUND

There is increasing evidence for an association between alterations of brain glutamatergic neurotransmission and the pathophysiology of affective disorders.

METHODS

We studied the association between cerebrospinal fluid (CSF) metabolites, including glutamine, in unipolar and bipolar depressed patients versus control subjects using a proton magnetic resonance spectroscopy technique. Cerebrospinal fluid samples were obtained from 18 hospitalized patients with acute unmedicated severe depression without medical problems and compared with those of 22 control subjects.

RESULTS

Compared with the control group, the depressed patient group had significantly higher CSF glutamine concentrations, which correlated positively with CSF magnesium levels.

CONCLUSIONS

These findings suggest an abnormality of the brain glial-neuronal glutamine/glutamate cycle associated with N-methyl-D-aspartate receptor systems in patients with depression.

Differential effects of haloperidol and clozapine on ionotropic glutamate receptors in rats

Despite multiple lines of investigation the effect of neuroleptics on glutamate-mediated neurotransmission remains controversial. To study the effects of typical and atypical neuroleptics on selected parameters of glutamate-mediated neurotransmission, male Sprague-Dawley rats were randomly assigned to a 21-day oral treatment course with vehicle, haloperidol (HDL), or clozapine (CLZ). Coronal slices of rat brain were then incubated with tritiated ligands to measure NMDA, AMPA, and kainate receptor, and glutamate reuptake site density. Regions of interest included the frontal cortex, anterior cingulate cortex, dorsal striatum, ventral striatum, and the nucleus accumbens. CLZ increased the density of AMPA receptors significantly in the frontal and anterior cingulate cortices compared with normal controls. In the dorsal and ventral striatum, and nucleus accumbens as a whole, CLZ-treated rats had a higher AMPA receptor density compared with both the HDL- and vehicle-treated controls. Additionally, within the nucleus accumbens, CLZ-treated rats had a higher density of AMPA receptors compared with the HDL group in the core, and at trend level in the shell. There was a group by region interaction for NMDA receptor density, primarily reflecting the tendency of HDL treated rats to have high receptor densities in the frontal and anterior cingulate cortices. Kainate receptors and glutamate reuptake site densities did not differ significantly across groups. These results suggest a critical role for glutamate in the mediation of atypical antipsychotic drug action in anatomically-specific regions, and further encourage the investigation of glutamate neurotransmitter systems in schizophrenia.

Phencyclidine in the social interaction test: an animal model of schizophrenia with face and predictive validity

Phencyclidine (PCP) is a hallucinogenic drug that can mimic several aspects of the schizophrenic symptomatology in healthy volunteers. In a series of studies PCP was administered to rats to determine whether it was possible to develop an animal model of the positive and negative symptoms of schizophrenia. The rats were tested in the social interaction test and it was found that PCP dose-dependently induces stereotyped behaviour and social withdrawal, which may correspond to certain aspects of the positive and negative symptoms, respectively. The effects of PCP could be reduced selectively by antipsychotic drug treatment, whereas drugs lacking antipsychotic effects did not alleviate the PCP-induced behaviours. Together these findings indicate that PCP effects in the rat social interaction test may be a model of the positive and negative symptoms of schizophrenia with face and predictive validity and that it may be useful for the evaluation of novel antipsychotic compounds.

Cerebrospinal fluid glutamate inversely correlates with positive symptom severity in unmedicated male schizophrenic/schizoaffective patients

BACKGROUND

Recent hypotheses have suggested that diminished brain glutamate may be of importance in the neurochemical basis of schizophrenia.

METHODS

We assayed cerebrospinal fluid for glutamate and obtained clinical symptom ratings in 19 medication-free (except p.r.n. chloral hydrate) schizophrenic or schizoaffective (typically with significant schizophrenic qualities) male inpatients.

RESULTS

Ratings of positive symptoms were significantly inversely correlated (rs = -.457, p < .05, one-tailed test) with glutamate concentrations. Hallucinatory behavior was strongly correlated (rs = -.621, p < .01, one-tailed test) with glutamate. A subset of 11 patients consented to a second lumbar puncture (LP) after treatment with haloperidol (typically 15 or 20 mg/day) for 2-4 weeks. Haloperidol treatment did not alter glutamate concentrations. No correlations were noted between glutamate and symptoms in the medicated subsample. Though approximately half the patients received chloral hydrate during the 72 hours prior to the unmedicated LP, the correlations between positive symptoms and glutamate in the patients who received no chloral hydrate prior to the LP were quite similar to those found in the overall sample.

CONCLUSIONS

The results provide further support for the potential importance of glutamate in the neurochemical basis of schizophrenia.

Biological research on schizophrenia

Based on the biochemical analysis of postmortem brains from chronic schizophrenic patients, we found abnormalities of glutamatergic neurons as well as dopaminergic neurons. Glutamate receptors, such as the kainate receptor labeled by 3H-kainate, the N-methyl-D-aspartate (NMDA) receptor by 3H MK801, and the strychnine-insensitive glycine sites in the NMDA receptor by 3H-glycine, increased significantly in various cortical areas of schizophrenic brains. According to the animal experiments and a significant negative correlation between kainate binding values and glutamate concentrations, it is suggested that glutamate receptors increased due to hypoglutamatergic function in the brain of chronic schizophrenia. Hyperdopamine hippothesis of schizophrenia is supported by the correlation between affinity to dopamine receptor and clinical potency of antipsychotic drugs. Measurement of tyrosine hydroxylase activity and dopamine D2 receptor in the schizophrenic brain provided evidence of hyperdopaminergia. Association study of a missense variant in the dopamine D2 receptor gene (Cys311) revealed that the allele frequency of the variant was significantly higher in the schizophrenic patients than the controls. The patients carrying this variant had less severe negative symptoms and better response to antipsychotic drug treatment. Dopamine-induced sequestration of dopamine D2S receptor with Cys variant expressed in CHO cells was shown to a lesser extent than wild-type receptor. This experimental result may be consistent with better responsiveness of the patients with Cys311 to antipsychotic drugs.

Glutamatergic neurotransmission involves structural and clinical deficits of schizophrenia

BACKGROUND

Phencyclidine and ketamine induce a syndrome closely resembling schizophrenia due to their blockade of N-methyl-D-aspartate (NMDA) receptor. These findings suggested that some aspects of schizophrenia are associated with decreased NMDA--glutamatergic function. We hypothesized that structural and symptomatic deficits in schizophrenia are related to glutamatergic neurotransmission.

METHODS

We studied the relationships among cerebrospinal fluid (CSF) glutamatergic markers, clinical presentation of schizophrenia, and CT parameters of brain structure in drug-free schizophrenics.

RESULTS

We found no significant differences between patients with schizophrenia and controls in CSF glutamatergic markers. When patients with schizophrenia were considered as a group, significant negative correlations between glutamatergic markers and brain structural measures as well as clinical measures were observed. Cluster analysis reveals a group of lower indices of glutamatergic neurotransmission, and more prominent thought disorder as well as ventricular enlargement, and a group with increased glutamate level.

CONCLUSIONS

The findings support the hypothesis that altered glutamatergic neurotransmission plays a role in the brain structure and the clinical symptoms of schizophrenia.

In vivo neurochemistry of the brain in schizophrenia as revealed by magnetic resonance spectroscopy

Magnetic resonance spectroscopy (MRS), an application of the methods of nuclear magnetic resonance (NMR), is a functional imaging modality that provides a view of localized biochemistry in vivo. A number of studies applying MRS to the neurochemistry of schizophrenia have been reported, which encompass a range of patient populations, states of medication, anatomic regions, nuclear species, and MRS techniques. A brief review of the history and methodology of NMR and MRS is presented. Comparison is made of MRS capabilities with other functional imaging modalities. Aspects of the neurochemistry of schizophrenia relevant to MRS studies are reviewed, as are the reported MRS studies involving patients with schizophrenia. Areas of consistent findings include decreased phosphomonoesters and increased phosphodiesters in frontal lobes, and decreases in the putative neuronal cell marker, N-acetylaspartate, in temporal lobes. Studies of neurotransmitters such as glutamate, gamma-aminobutyric acid, and glutamine have generated inconsistent results. New insights into alterations in neurochemistry in schizophrenia have been provided by MRS. Studies of neurotransmitters have future potential with improvements in field strength and in spectral editing techniques. MRS has the potential to measure brain medication levels and simultaneous effects on neurochemistry. MRS may assist in characterizing high-risk populations, and ultimately guide medication use.

Clozapine treatment increases serum glutamate and aspartate compared to conventional neuroleptics

To examine whether serum excitatory amino acid concentrations change with clozapine treatment and whether these changes correlate with improvement in negative symptoms, serum excitatory amino acids were measured and clinical scales administered in seven subjects with schizophrenia before and after switching from conventional neuroleptics to clozapine. Clozapine treatment was associated with increased serum glutamate and aspartate concentrations. Clinical improvement was negatively correlated with baseline glycine concentrations. These results support the hypothesis that clozapine acts at least in part by increasing glutamatergic activity.

Glutamate in schizophrenia: clinical and research implications

The excitatory amino acids, glutamate and aspartate, are of interest to schizophrenia research because of their roles in neurodevelopment, neurotoxicity and neurotransmission. Recent evidence suggests that densities of glutamatergic receptors and the ratios of subunits composing these receptors may be altered in schizophrenia, although it is unclear whether these changes are primary or compensatory. Agents acting at the phencyclidine binding site of the NMDA receptor produce symptoms of schizophrenia in normal subjects, and precipitate relapse in patients with schizophrenia. The improvement of negative symptoms with agents acting at the glycine modulatory site of the NMDA receptor, as well as preliminary evidence that clozapine may differ from conventional neuroleptic agents in its effects on glutamatergic systems, suggest that clinical implications may follow from this model. While geriatric patients may be at increased risk for glutamate-mediated neurotoxicity, very little is known about the specific relevance of this model to geriatric patients with schizophrenia.

A two-process theory of schizophrenia: evidence from studies in post-mortem brain

Glutamate and GABA are the principle neurotransmitters of the cerebral cortex and are known to modulate dopaminergic function. Evidence of structural abnormalities in the cortex raises the possibility that schizophrenia involves disturbances of cortical amino-acid neurotransmission. The psychotomimetic effects of phencyclidine, a glutamate antagonist, have been taken to suggest that schizophrenia involves reduced brain glutamate function. Direct evidence for diminished glutamate function in schizophrenia is lacking. However, in polar temporal cortex and hippocampus we reported evidence of an asymmetric loss of glutamate terminals, and of reduced GABA function, which may be secondary to the loss of glutamatergic input. Glutamate cell body markers are spared in temporal lobe; the neurones which degenerate may originate in frontal cortex. A number of studies have reported increases in markers of glutamatergic cell bodies and terminals in orbital frontal cortex in schizophrenia. These findings are consistent with the presence of an abnormally abundant glutamatergic innervation, which may be the result of an arrest in the normal process of cellular and synaptic elimination which occurs during development. There is evidence that frontal abnormalities in schizophrenia are genetically determined. We suggest that glutamatergic abnormalities in anterior temporal cortex in schizophrenia are the result of the degeneration of fronto-temporal projections. Orbital frontal projections to polar temporal cortex may be prone to degeneration because they arise from an unstable frontal cortical cytoarchitecture which has not completed the normal process of post-natal remodelling. The structural abnormality of the orbital frontal region may confer vulnerability to some intrinsic or extrinsic mechanism, which brings about a progressive degeneration of projections to polar temporal lobe.

Glutamate receptor subtype expression in human postmortem brain tissue from schizophrenics and alcohol abusers

Antibodies to functional AMPA/kainate (GluR1, GluR2, GluR3), and kainate binding sites (GluR5-7) were used as probes to characterize and quantitate glutamatergic receptor subtypes in human post-mortem brain tissue from schizophrenic subjects and non-psychotic control subjects, which included normal controls and subjects with a previous history of alcohol abuse. Crude membrane fractions from human hippocampi and cingulate cortices were fractionated by SDS-PAGE, electrotransferred to nitrocellulose, and probed for the various glutamate receptor subtypes. Western blots were developed with chemiluminescence and the images analyzed by densitometry. Significant reductions were observed in the hippocampal immunoreactivity of both GluR2 and GluR3 AMPA/kainate receptor subtypes in schizophrenic subjects compared to the entire group of non-psychotic control subjects. No significant changes were observed in schizophrenic hippocampal GluR1 and GluR5 receptor subtypes or in levels of the structural control proteins, NCAM and tau. Significant increases were observed for GluR2 and GluR3 in the hippocampi of subjects with alcohol abuse histories when compared to the non-psychotic normal control group. When subjects with alcohol abuse histories were removed from the non-psychotic control pool, schizophrenics were no longer statistically different from the remaining normal controls. An analysis of GluR2 and GluR3 immunoreactivity in the cingulate cortex revealed no changes in these receptor subtypes among any of the groups. No alterations were observed in the immunoreactivity of these various proteins due to confounding factors such as age, sex, postmortem interval, or smoking history, except in the cingulate cortex were GluR3 receptor subtype levels were significantly reduced in the brains of smokers.(ABSTRACT TRUNCATED AT 250 WORDS)

Excitatory amino acids: implications for psychiatric disorders research

The hyperdopaminergic theory of schizophrenia may account for some types of schizophrenia, but schizophrenia with negative symptoms or resulting in a chronic state of deterioration after repeated relapses cannot be explained by this theory. This minireview first discusses the interactions between dopamine and excitatory amino acid (EAA) neurons to produce abnormal behavior. Secondly, it deals with the influence of the psychotropic drugs on EAA, such as the relationship between phencyclidine and the hypoglutamate theory, the involvement of EAA in behavioral sensitization induced by amphetamines, the interactions between antipsychotic, antidepressant and antianxiety drugs and EAA, considering the possibility of developing newer psychotropic drugs related with EAA. Finally, glutamate receptors measured in postmortem schizophrenic brains are tabulated and the bases of the hypoglutamate hypothesis are discussed.

Amino acids and glucose in human cerebrospinal fluid after acute ischaemic brain damage

In the search for potential biochemical markers of value for prognosis after acute hypoxic brain damage, amino acids and glucose were assessed in the cerebrospinal fluid (CSF) and glucose in blood. Samples were taken by lumbar puncture 4, 28, 76 and 172 h after resuscitation from 20 patients and once from 10 control patients. Eight of the resuscitated patients recovered neurologically but 12 remained comatose. The concentrations of alanine (P less than 0.001) and phenylalanine (P less than 0.035) differed most in 4-h samples between the groups. The concentration of alanine was higher in all patient groups with hypoxic brain damage as compared to the controls, the concentrations in patients dying within 76 h (disabled-s group) being higher than in the recovered patients. Phenylalanine in the disabled-s group was significantly higher than the control value. Furthermore, there were significant differences between various patient groups in the concentrations of glutamine, isoleucine, leucine, lysine, serine, tyrosine and valine. When taking into account the permeability of the BBB to these amino acids, alanine, valine and isoleucine most clearly represent brain amino acid metabolism. CSF glucose in the control group and in the recovered patients was lower than in patients dying within 76 h.

Deficient NMDA-mediated glutamate release from synaptosomes of schizophrenics

Previous studies from our laboratory indicated that the veratridine-induced release of glutamate and GABA from synaptosomes derived from brains of schizophrenics was decreased. In the present study, synaptosomes were prepared from frozen brain samples from schizophrenics and from controls. Stimulation by 10 mumol/L 2-amino-3-hydroxy-5-methoxylisoxazole-4-propionic acid (AMPA) produced equal glutamate release from both groups. Release induced by either 10 mumol/L kainic acid (KA) or n-methyl-d-asparate (NMDA) was reduced significantly in the preparations derived from schizophrenics. Similarly, the amount of GABA released by 50 mumol/L glutamate was also reduced in the schizophrenic-derived synaptosomes. However, in membranes derived from the crude synaptosomal pellet, no differences between the controls and schizophrenics were observed in measures of total glutamate binding or its displacement by NMDA. The data demonstrate a deficiency in NMDA (and possibly KA) receptor functioning schizophrenics and support the "second-generation" theories of schizophrenia as a glutamatergic deficiency disorder.

Phasic versus tonic dopamine release and the modulation of dopamine system responsivity: a hypothesis for the etiology of schizophrenia

A novel mechanism for regulating dopamine activity in subcortical sites and its possible relevance to schizophrenia is proposed. This hypothesis is based on the regulation of dopamine release into subcortical regions occurring via two independent mechanisms: (1) transient or phasic dopamine release caused by dopamine neuron firing, and (2) sustained, "background" tonic dopamine release regulated by prefrontal cortical afferents. Behaviorally relevant stimuli are proposed to cause short-term activation of dopamine cell firing to trigger the phasic component of dopamine release. In contrast, tonic dopamine release is proposed to regulate the intensity of the phasic dopamine response through its effect on extracellular dopamine levels. In this way, tonic dopamine release would set the background level of dopamine receptor stimulation (both autoreceptor and postsynaptic) and, through homeostatic mechanisms, the responsivity of the system to dopamine in these sites. In schizophrenics, a prolonged decrease in prefrontal cortical activity is proposed to reduce tonic dopamine release. Over time, this would elicit homeostatic compensations that would increase overall dopamine responsivity and thereby cause subsequent phasic dopamine release to elicit abnormally large responses.

Leukocyte glutamate dehydrogenase and CSF amino acids in late onset ataxias

Leukocyte glutamate dehydrogenase (GDH) activity was measured in 11 healthy control subjects, 16 neurological controls, 12 patients with dominant late onset ataxia, 15 with sporadic late onset ataxia and 8 with alcoholic cerebellar ataxia. Serum hexosaminidase activity was also determined in ataxic patients. Concentrations of free amino acids were determined in the lumbal CSF of 16 neurological controls, 8 patients with late onset ataxia and 5 with alcoholic ataxia. Mean total GDH activity was reduced significantly in dominant (p less than 0.05) and sporadic (p less than 0.01) cerebellar ataxia, while the heat-labile form was decreased significantly (p less than 0.01) only in sporadic ataxia. All GDH activities were within normal range in patients with alcoholic ataxia. The serum hexosaminidase activities were also within reference range in all patient groups. The CSF concentrations of alanine, glycine, methionine and valine were significantly elevated and those of GABA and glutamate were normal in patients with late onset ataxia as compared to neurological controls. The most significant (p less than 0.01) increase was found for methionine. The amino acid levels of patients with alcoholic ataxia did not differ from those of the controls. The results suggest that GDH activity is only partially decreased in some ataxic patients and that altered amino acid metabolism may be reflected in the CSF.

Leukocyte glutamate dehydrogenase and CSF amino acids in late onset ataxias

Leukocyte glutamate dehydrogenase (GDH) activity was measured in 11 healthy control subjects, 16 neurological controls, 12 patients with dominant late onset ataxia, 15 patients with sporadic late onset ataxia and 8 with alcoholic cerebellar ataxia. Serum hexosaminidase activity was also determined in ataxic patients. Concentrations of free amino acids were determined in the lumbal CSF of 16 neurological controls, 8 patients with late onset ataxia and 5 with alcoholic ataxia. Mean total GDH activity was reduced significantly in dominant (p less than 0.05) and sporadic (p less than 0.01) cerebellar ataxia, while the heat-labile form was decreased significantly (p less than 0.01) only in sporadic ataxia. All GDH activities were within normal range in patients with alcoholic ataxia. The serum hexosaminidase activities were also within reference range in all patient groups. The CSF concentrations of alanine, glycine, methionine and valine were significantly elevated and those of GABA and glutamate were normal in patients with late onset ataxia as compared to neurological controls. The most significant (p less than 0.01) increase was found for methionine. The amino acid levels of patients with alcoholic ataxia did not differ from those of the controls. The results suggest that GDH activity is only partially decreased in some ataxic patients and that altered amino acid metabolism may be reflected in the CSF.

Amino acid patterns in schizophrenia: some new findings

Blood concentrations of various amino acids were measured in schizophrenic patients and control subjects. Significantly higher blood concentrations of glycine, glutamate, and serine were found in the schizophrenic patients. Glycine was abnormally elevated in subjects with paranoid or undifferentiated schizophrenia, but not in disorganized patients. Since glutamate, glycine, and serine play a complex role in the regulation of N-methyl-D-aspartate (NMDA) receptors, which are important in the control of normal cognitive processes, we hypothesized that the elevated levels of these amino acids might disrupt the normal functioning of NMDA receptors and might be involved in the pathophysiology of schizophrenia.

Neurotransmitter amino acids in post-mortem brains of chronic schizophrenic patients

Neurotransmitter amino acids were measured in post-mortem caudate nucleus, nucleus accumbens, frontal cortex, amygdala, and hypothalamus of chronic schizophrenic and normal control subjects. The concentrations of upsilon-aminobutyric acid (GABA), taurine, glycine-threonine, glutamate, aspartate, glutamine, tryptophan, and alanine were similar in both groups, with the exception of decreased GABA and tryptophan in the amygdala of the schizophrenic group. Strong positive correlations were obtained between the concentration of tryptophan, a putative agonal status marker of post-mortem brain tissue, and the concentration of GABA in all brain areas. When the GABA concentrations were adjusted for tryptophan concentrations in amygdala, the difference between the schizophrenic and control samples was no longer significant, suggesting that the original difference may have been due to different agonal or post-mortem changes in the tissues. There were, however, no significant correlations between GABA and post-mortem interval. The present results do not support the aminoacidergic hypotheses of chronic schizophrenia, although a GABA deficiency cannot be entirely excluded.