Low cerebrospinal fluid glutamate in schizophrenic patients and a new hypothesis on schizophrenia

A review of evidence for GABergic predominance/glutamatergic deficit as a common etiological factor in both schizophrenia and affective psychoses: more support for a continuum hypothesis of "functional" psychosis

Virtually all antidepressant and antipsychotic drugs, including clozapine, rimcazole and lithium ion, are proconvulsants, and convulsive therapy, using metrazol, a known GABA-A antagonist, as well as electro-convulsive therapy, can be effective in treating both schizophrenia and affective psychoses. Many antidepressant and antipsychotic drugs, including clozapine, as well as some of their metabolites, reverse the inhibitory effect of GABA on 35S-TBPS binding, a reliable predictor of GABA-A receptor blockade. A review of relevant literature suggests that 1) "functional" psychoses constitute a continuum of disorders ranging from schizophrenia to affective psychoses with overlap of symptoms, heredity and treatments, 2) a weakening of GABergic inhibitory activity, or potentiation of counterbalancing glutamatergic neurotransmission, in the brain, may be involved in the therapeutic activities of both antidepressant and antipsychotic drugs, and 3) schizophrenia and the affective psychoses may be different expressions of the same underlying defect: GABergic preponderance/glutamatergic deficit. Schizophrenia and affective psychoses share the following: 1) several treatments are effective in both, 2) similar modes of inheritance, 3) congruent seasonal birth excesses, 4) enlarged cerebral ventricles and cerebellar vermian atrophy, 5) dexamethasone non-suppression. Both genetic and environmental factors are involved in both schizophrenia and affective psychoses, and several lines of evidence suggest that important environmental factors are neurotropic pathogens that selectively destroy glutamatergic neurons. One group of genes associated with psychoses may increase vulnerability to attack and destruction, by neurotropic pathogens, of excitatory glutamatergic neurons that counterbalance inhibitory GABergic neurons. A second group of genes may encode subunits of overactive GABA-A receptors, while a third group of genes may encode subunits of hypo-active glutamate receptors. Improved antipsychotic drugs may be found among selective blockers of GABA-A receptor subtypes and/or enhancers of glutamatergic neurotransmission. A mechanism similar to kindling, leading to long-lasting reduction of GABergic inhibition in the brain, may be involved in several treatments of psychoses.

Decreased hippocampal expression of a glutamate receptor gene in schizophrenia

A striking and specific loss of the messenger RNA that encodes a non-N-methyl D-aspartate (non-NMDA) glutamate receptor was found in hippocampal tissue obtained at necropsy from 6 patients with schizophrenia, when compared to specimens from 8 controls without neurological or psychiatric signs or symptoms. These findings support suggestions of aberrant glutamatergic function in schizophrenia. Evidence that gene expression may be abnormal in schizophrenia, with decreased production of an excitatory neurotransmitter receptor, may have therapeutic as well as pathogenetic implications.

Evidence of glutamatergic deficiency in schizophrenia

Studies of amino acid release were carried out using frozen sections from brains of schizophrenics and controls. Synaptosomes were prepared via differential centrifugation in Ficoll allowing the veratridine-induced release of aspartate, glutamate, glycine, and GABA to be measured. The release of glutamate and gamma-aminobutyric acid (GABA) was reduced in the synaptosomes from schizophrenics. This decrease could be reversed partially by pre-incubation of the synaptosomes with haloperidol. Additionally, the activity of glutamate decarboxylase was decreased and partially restored by haloperidol pre-incubation. These data are consistent with the hypothesis of a glutamatergic/GABAergic deficit in schizophrenia.

Antagonism of AP-5-induced sniffing stereotypy links umespirone to atypical antipsychotics

Blockade of glutamatergic transmission in the striatum (using the NMDA-antagonist DL-2-amino-5-phosphonovaleric acid AP-5) was recently shown to induce stereotyped sniffing in rats. Comparable stereotyped behaviour is well known to be elicited by stimulation of dopamine activity, which since long was the basis for experimental models to check for possible antipsychotic activity of new compounds. However, whereas dopamine-induced stereotypies are antagonized only by classical neuroleptics, stereotypies induced by blockade of glutamatergic transmission are antagonized by classical as well as by atypical antipsychotics. Umespirone, a novel psychotropic which has been reported to exhibit behavioural effects predictive for antipsychotic as well as anxiolytic potential was evaluated for antagonistic effects against AP-5-induced behaviour. The profile of umespirone was compared with the profile of a non-benzodiazepine anxiolytic buspirone as well as with previously published data of neuroleptics. Umespirone like clozapine specifically antagonized AP-5-induced sniffing, i.e. did not impair spontaneous sniffing but reversed AP-5-induced excessive sniffing. In contrast, buspirone impaired spontaneous and AP-5-induced sniffing to about the same extend. These results are in accordance with the glutamate hypothesis of schizophrenia and again give evidence that umespirone should have antipsychotic potential and a very low liability to exhibit unspecific sedative action.

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.

Glutamate receptor antagonism: neurotoxicity, anti-akinetic effects, and psychosis

There is evidence to suggest that glutamate and other excitatory amino acids play an important role in the regulation of neuronal excitation. Glutamate receptor stimulation leads to a non-physiological increase of intracellular free Ca2+. Disturbed Ca2+ homeostasis and subsequent radical formation may be decisive factors in the pathogenesis of neurodegenerative diseases. Decreased glutamatergic activity appears to contribute to paranoid hallucinatory psychosis in schizophrenia and pharmacotoxic psychosis in Parkinson's disease. It has been suggested that a loss of glutamatergic function causes dopaminergic over-activity. Imbalances of glutamatergic and dopaminergic systems in different brain regions may result in anti-akinetic effects or the occurrence of psychosis. The simplified hypothesis of a glutamatergic-dopaminergic (im)-balance may lead to a better understanding of motor behaviour and psychosis.

MK-801-induced stereotypy and its antagonism by neuroleptic drugs

MK-801 [(+)-5-methyl-10,11-dihydroxy-5H-dibenzo-(a,d)cyclohepten-5,10-imi ne hydrogen maleate], which blocks glutamatergic transmission at the NMDA-receptor-gated ion channel, induced stereotypies which are similar to those found after intrastriatal injections of AP-5, e.g. sniffing and locomotion. Tests in familiar or unfamiliar environment (non-stressful or stressful situation) did not qualitatively change MK-801-induced effects. Haloperidol (0.1 mg/kg, IP) delayed the onset and shortened the duration of MK-801 (0.16; 0.33 mg/kg, IP)-induced stereotypy whereas clozapine (5 mg/kg, SC) potently antagonized it. However, exact quantification of sniffing, measured in an experimental chamber designed for this purpose, revealed an antagonism by both drugs, haloperidol as well as clozapine. Stereotypy is considered to represent an animal model of schizophrenia, and the antagonism of stereotypy with classical (haloperidol) as well as with atypical (clozapine) antipsychotic drugs is in accordance with the glutamate hypothesis of schizophrenia.

Interactions between glutamatergic and monoaminergic systems within the basal ganglia--implications for schizophrenia and Parkinson's disease

Recent animal experiments suggest that dopamine plays a less crucial role than formerly supposed in the regulation of psychomotor functions. This is illustrated by the finding that even in the almost complete absence of brain dopamine, a pronounced behavioural activation is produced in mice following suppression of glutamatergic neurotransmission. This paper discusses the possibility that a deficient activity within the corticostriatal glutamatergic/aspartergic pathway may be an important pathophysiological component in schizophrenia, and that glutamatergic agonists may be beneficial in the treatment of this disease. In addition, it is suggested that glutamatergic antagonists may be valuable supplements in the treatment of Parkinson's disease.

Role of excitatory amino acid neurotransmission in synaptic plasticity and pathology. An integrative hypothesis concerning the pathogenesis and evolutionary advantages of schizophrenia-related genes

N-methyl-D-aspartate (NMDA) receptors are involved in long-term potentiation, burst firing and the generation of patterned activity in neuronal networks; in use-dependent stabilization of synaptic connectivity in developing animals; in some forms of learning in mature animals; and in pathologies as found in brain aging. A number of these characteristics are reminiscent of several manifestations of schizophrenia and therefore we present the hypothesis that one of the genes modified in schizophrenia is directly or indirectly linked to the control of excitatory neurotransmission; possibly the normal switching on of the expression of the adult form of the NMDA receptor is delayed. Alternatively the adult form of the NMDA receptor is altered, resulting in inappropriate functioning of this receptor. The delayed or faulty expression of the adult form of the NMDA receptor, in turn, should confer a series of evolutionary advantages including protection against aging-associated brain pathologies.

Quantitative autoradiographic analysis of glutamate binding sites in the hippocampal formation in normal and schizophrenic brain post mortem

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.

Beyond the dopamine hypothesis. The neurochemical pathology of schizophrenia

The dopamine hypothesis still provides a valuable approach to the study of schizophrenia and its treatment by drugs. Although the neuroleptic drugs appear to act via an inhibition of dopamine receptors, measurements of dopamine metabolites in vivo, or of the transmitter and its receptors in post-mortem brain tissue, do not provide unequivocal evidence of a hyperactivity of dopaminergic neurotransmission in the disease. Nevertheless, increased dopamine function might be a consequence of a primary neuronal abnormality in another system. Recent imaging studies and neuropathological reports suggest that, in some patients, there may be a deficit and/or disturbance of neurons in certain temporal limbic regions, and this is supported by some neurochemical investigations, particularly of neuropeptide and amino-acid transmitter systems. A loss of such neurons could conceivably lead to a disinhibition of limbic dopamine neurons, providing the means whereby neuroleptic drug treatment might ameliorate the effects of a neuronal deficit in schizophrenia.

[3H]MK-801 binding sites in postmortem brain regions of schizophrenic patients

[3H]MK-801 binding was used as a marker for the NMDA receptorion channel complex in postmortem brain samples from the frontal cortex, hippocampus, putamen, entorhinal region, and amygdala of schizophrenic patients and controls. In schizophrenia [3H]MK-801 binding levels were increased in all brain regions investigated reaching significance in the putamen.

Frontal cortical and left temporal glutamatergic dysfunction in schizophrenia

Glutamatergic mechanisms have been investigated in postmortem brain samples from schizophrenics and controls. D-[3H]Aspartate binding to glutamate uptake sites was used as a marker for glutamatergic neurones, and [3H]kainate binding for a subclass of postsynaptic glutamate receptors. There were highly significant increases in the binding of both ligands to membranes from orbital frontal cortex on both the left and right sides of schizophrenic brains. The changes are unlikely to be due to antemortem neuroleptic drug treatment, because no similar changes were recorded in other areas. A predicted left-sided reduction in D-[3H]aspartate binding was refuted at 5% probability, but not at 10%. Previously reported high concentrations of dopamine in left amygdala were strongly associated with low concentrations of D-[3H]aspartate binding in left polar temporal cortex in the schizophrenics. The findings are compatible with an overabundant glutamatergic innervation of orbital frontal cortex in schizophrenia. The results also suggest that schizophrenia may involve left-sided abnormalities in the relationship between temporal glutamatergic and dopaminergic projections to amygdala.

Release of glutamate and of free fatty acids in vasogenic brain edema

The pathophysiological potential of mediator substances in manifestations of secondary brain damage is attracting increased attention. This is particularly true of the excitatory transmitters glutamate and arachidonic acid. Noxious properties of these compounds in central nervous tissue have been demonstrated. The current study was performed to determine whether glutamate and arachidonate are released in brain tissue secondary to focal trauma. For this purpose, a cold injury of exposed cerebral cortex was induced in cats. Marked accumulation of glutamate was observed in interstitially drained edema fluid, reaching 10 to 15 times the level that was assessed in normal cerebrospinal fluid (CSF) prior to trauma. The extracellular release of glutamate was further dramatically enhanced by a critical decrease of the cerebral perfusion pressure due to a malignant increase of intracranial pressure. Under these conditions, glutamate concentrations 1000 to 1500 times normal levels accumulated in vasogenic edema fluid, demonstrating a relationship between the extent of the release of glutamate in damaged brain and the severity of the insult. Although under normal conditions glutamate concentrations in plasma were considerably higher than in the interstitial fluid, the pronounced increase of glutamate in this compartment due to trauma cannot be explained by transport of the compound together with the plasma-like edema from the intravascular space. Corresponding findings were obtained for free fatty acid concentrations in edema fluid. Almost all fatty acids that were studied had a significantly higher concentration in edema fluid than in normal CSF obtained as a control prior to trauma. However, contrary to the findings for glutamate, fatty acid concentrations in edema fluid were lower than in plasma. Accumulation of fatty acids in vasogenic edema fluid might, therefore, have resulted from uptake of the material together with edema fluid through the breached blood-brain barrier. Arachidonic acid was an exception. Its concentrations were significantly higher in edema fluid than in plasma, suggesting that it was released from cerebral parenchyma as the underlying mechanism of its extracellular accumulation. The current observations provide further support for a mediator function of glutamate and arachidonic acid in acute traumatic lesions of the brain. Quantitative assessment of the release of highly active mediator substances in brain tissue may facilitate analysis of the therapeutic efficiency of specific treatment aimed at interfering with the release or pathological function of mediators of secondary brain damage.

Schizophrenia, tardive dyskinesia, and brain GABA

We measured the contents of gamma-aminobutyric acid (GABA) and of other amino compounds in five regions of autopsied brain from 18 patients with schizophrenia and from a large group of adult control subjects dying without any neurological or psychiatric disorder. In addition, concentrations of GABA were measured in the cerebrospinal fluid (CSF) of living schizophrenic patients and control subjects. No deficiency of GABA was found in the frontal cortex, caudate nucleus, putamen, nucleus accumbens, or medial dorsal thalamus of patients dying with schizophrenia, nor were GABA concentrations low in the CSF of living schizophrenic patients. These results do not confirm our earlier report of low levels of GABA in the nucleus accumbens and thalamus of some schizophrenic patients. We do not find neurochemical evidence favoring an involvement of GABAergic neuronal hypofunction in the etiology either of schizophrenia or of neuroleptic-induced tardive dyskinesia.

Monoamine metabolites and amino acids in serum from schizophrenic patients before and during sulpiride treatment

Twenty-four acutely ill schizophrenic patients (DSM-III-R), 18-42 years old, were treated for 6 weeks with sulpiride. Sulpiride was administered in three different daily dosages (starting with 400, 800 or 1200 mg) according to a double blind randomized administration schedule. The monoamine metabolites (MAM) homovanillic acid (HVA), 5-hydroxy-indoleacetic acid (5-HIAA), 4-hydroxy-3-methoxy-phenylglycol (HMPG) and the amino acids tyrosine, tryptophan, glutamate and glutamine were measured in serum before treatment and once a week during treatment. There were no significant differences between healthy controls and schizophrenic patients in serum levels of monoamine metabolites and amino acids before treatment. There was no dose-response effect of sulpiride on serum levels of the monoamine metabolites or the amino acids. The results are therefore based on the whole group of patients. During treatment the HMPG levels were reduced at all points in time. The serum level of HVA was significantly reduced after 6 weeks. The 5-HIAA and the amino acid levels were not changed during treatment. There were no significant correlations among the monoamine metabolites before treatment. During treatment, however, significant correlations were found among MAM and amino acids. Since the biochemical findings during the treatment were not related to the dose or the concentration of sulpiride the results may be related to secondary biochemical effects of sulpiride and/or to changes in the clinical state following treatment.

An hypothesis regarding the antipsychotic effect of neuroleptic drugs

The antipsychotic effect of neuroleptic drugs appears gradually over the course of several weeks of chronic drug administration. Neuroleptic drugs are thought to act by blocking dopamine receptors; however, the dopamine-blocking effect of neuroleptics appears rapidly. One effect of dopamine antagonists which develops slowly is dopaminergic supersensitivity. It is suggested that this dopaminergic supersensitivity is related to the development of tolerance to some of the acute sedative properties of neuroleptics, but not to the antipsychotic effect. A population of glutamate receptors which are postsynaptic to the cortico-striatal afferents is located on the same neurons as striatal dopamine receptors. These glutamate synapses are located on the heads of dendritic spines of striato-nigral projection neurons, while the dopaminergic synapses are predominantly located on the necks of these same dendritic spines. Similar relationships could exist for mesolimbic and mesocortical dopamine systems. In peripheral systems, postjunctional denervation supersensitivity is known to be nonspecific; in other words, denervation of a single innervation of an excitable cell can alter the response to a range of stimuli. The antipsychotic effect of neuroleptics is therefore suggested to be due to nonspecific postjunctional subsensitivity at glutamate synapses, which develops concomitant with supersensitivity at dopaminergic synapses.

Relationships between glutamate and monoamine metabolites in cerebrospinal fluid and serum in healthy volunteers

The concentrations of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), 4-hydroxy-3-methoxyphenylglycol (HMPG), and glutamate were determined in cerebrospinal fluid (CSF) and serum in 10 healthy volunteers. The monoamine metabolites were measured by mass fragmentography and the glutamate by high-performance liquid chromatography. The level of glutamate in CSF was low (0.34 +/- 0.14 nmol/ml) in comparison with previously published values. The concentrations of monoamine metabolites in CSF were in close agreement with earlier findings. There were negative correlations between the concentrations of HVA (r = -0.82, p less than 0.01) and 5-HIAA (r = -0.77, p less than 0.01) and glutamate in CSF, but not in serum. The serum levels of HMPG and glutamate were negatively correlated (r = -0.95, p less than 0.001), but not the CSF levels. The HMPG levels in serum and CSF were positively correlated (r = 0.94, p less than 0.001), but not the HVA and the 5-HIAA levels. The serum and CSF levels of glutamate were positively correlated (r = 0.67, p less than 0.05). The results indicate relationships among the metabolism of dopamine, serotonin, and glutamate in the brain and between the metabolism of noradrenaline and glutamate in peripheral tissue.

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.

Antagonism of AP-5- and amphetamine-induced behaviour by timelotem as compared with clozapine and haloperidol

Bilateral intrastriatal injection of DL-2-amino-5-phosphonovaleric acid (AP-5), that blocks glutamatergic transmission at the N-methyl-d-aspartate preferring receptor, induces sniffing and body turns and reduces grooming in rats. Timelotem, a representative of the newly developed chemical class of anellated benzodiazepines antagonized specifically AP-5-induced sniffing and body turns. Classical (haloperidol) as well as atypical (clozapine) neuroleptics had recently been shown to antagonize AP-5-induced sniffing; clozapine, like timelotem, but not haloperidol, additionally antagonized AP-5-induced body turns. Further, timelotem antagonized amphetamine-induced stereotyped behaviour in rats, but was found less active than haloperidol in this test. Comparing the activity of drugs in both paradigms revealed that haloperidol inhibited AP-5-induced sniffing and amphetamine-induced stereotypies within the same dose range, but timelotem and clozapine were found more potent in the AP-5 test than in the amphetamine test. Thus, detailed drug profiles discriminate timelotem and clozapine from haloperidol, linking timelotem again to atypical antipsychotic compounds.

Cerebrospinal fluid amino acid concentrations in chronic schizophrenia

The concentrations of the excitatory amino acid, glutamate, the inhibitory amino acids, glycine and taurine, and the inactive amino acids, glutamine and alanine, were determined in cerebrospinal fluid samples from 12 neurological control and 17 chronic schizophrenic patients. No significant differences were observed in any amino acid between the study groups. Within the schizophrenic group, no differences were observed between paranoid and undifferentiated patients. The concentrations of these amino acids in samples obtained from six schizophrenic patients during drug-free as compared to haloperidol-treatment periods also did not differ. These results do not support the glutamate hypothesis of schizophrenia.

Plasma amino acids in relation to cerebrospinal fluid monoamine metabolites in schizophrenic patients and healthy controls

Compared to healthy controls, unmedicated schizophrenic patients had significantly higher plasma concentrations of taurine, methionine, valine, isoleucine, leucine, phenylalanine, and lysine. Except for taurine, these amino acids share the L-transport system for neutral amino acids. In the patients, homovanillic (HVA) acid levels in CSF were decreased and the plasma levels of the amino acids competing with tyrosine and tryptophan for transport into the brain, were all negatively correlated to the CSF concentrations of HVA and 5-HIAA. These findings could be explained by a change in the affinity of the L-system or by a decrease in its overall capacity in schizophrenia. Raised plasma levels of the competing amino acids may limit the brain uptake of tyrosine, leading to a diminished dopamine turnover, and resulting in a compensatory development of supersensitive dopamine receptors.

The cortico-nigral projection: reduced glutamate content in the substantia nigra following frontal cortex ablation in the rat

Unilateral ablation of the frontal cortex results in a significant reduction (19.5%) of glutamic acid in the ipsilateral compared with the contralateral substantia nigra. The GABA level in the substantia nigra and both the glutamate and GABA levels in the hippocampus remain unchanged. The results suggest that glutamate is a transmitter in the cortico-nigral fibre tract.

Chemistry, physiology and neuropsychology of schizophrenia: towards an earlier diagnosis of schizophrenia I

Data supporting the glutamate hypothesis of schizophrenia are presented. The glutamate hypothesis is linked to the dopamine hypothesis by the fact that dopamine synapses inhibit the release of glutamate in the striate and mesolimbic system. The glutamate hypothesis of schizophrenia may open a way to find better drugs for treatment. The concept of schizophrenia I is described. It consists of "negative symptoms" such as disconcentration or reduction of energy. Schizophrenia I precedes and follows schizophrenia II with "positive symptoms," e.g. hallucinations and delusions. Schizophrenia I so far cannot be diagnosed as schizophrenia unless schizophrenia II appears. Chemical, physiological or neuropsychological methods for the diagnosis of schizophrenia I would render an earlier treatment of schizophrenia possible and thus make social and occupational rehabilitation more efficient. An objective diagnosis of schizophrenia I may also elucidate the mode of genetic transmission of schizophrenia. Several neuropsychological methods distinguish schizophrenic patients as a group from normals. Some of them are based on a specific disturbance of long term concentration. The EEG also distinguishes schizophrenics from normals when analyzed during voluntary movement. For schizophrenics it takes more effort to initiate a voluntary movement, and there are several features of the EEG correlated to this. Moreover, the longer motor reaction time of schizophrenics is paralleled by a longer duration of the Bereitschaftspotential in schizophrenia. Furthermore, there is a difference in the theta rhythm between schizophrenic patients and normals in a task which requires concentration. Some of the children of schizophrenic parents show a disturbance of concentration in both reaction time tasks and the d 2 test.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased [3H]kainic acid binding in the prefrontal cortex in schizophrenia

[3H]Kainic acid binding sites were measured post mortem in the putamen and prefrontal cortex areas from 10 control subjects and 12 schizophrenic patients. A 25-50% increase in [3H]kainic acid binding was observed in the medial frontal (Brodmann areas 9, 10 and 46) and eye-movement areas (8), but not in the other regions of schizophrenic brains. No significant correlation between the binding and either age at death, storage of the brains, duration of illness or neuroleptics-free period was observed. These findings suggest that a dysfunction of cortical excitatory amino acidergic transmission may be involved in schizophrenia.

Genetic control of platelet glutaminase: a twin study

The extent of genetic determination of platelet glutaminase was evaluated by sampling 13 monozygotic and 11 dizygotic adult male twin pairs. Intraclass correlation coefficients of 0.96 for monozygotic and 0.53 for dizygotic twins together with high heritability estimates indicate a strong genetic component.

Glutamic acid diethyl ester induces catalepsy in rats. A new model for schizophrenia?

The glutamate antagonist glutamic acid diethyl ester is found to produce catalepsy in rats, when administered into the lateral ventricle. Since the cerebrospinal fluid content of glutamate is reduced in patients with schizophrenia, the central effects of glutamate antagonists are a possible experimental model for schizophrenia.

Inhibitory effects of dopamine on high affinity glutamate uptake from rat striatum

The role of dopamine (DA) input on the activity of glutamate neurons was investigated on rat striatal and cortical tissue using the measurement of sodium-dependent high affinity glutamate uptake (HAGU) as an index. Incubation of the tissue in the presence of DA, apomorphine or bromocriptine produced marked inhibition of 3H-glutamate uptake from rat striatal homogenates. No change occurred with samples from the frontal cortex. Dopaminergic inhibition of HAGU in striatal homogenates was shown to be reversed in the presence of haloperidol or domperidone which act by blocking dopaminergic receptor sites. These results are consistent with the existence of an inhibitory control of the neuronal activity of the glutamatergic neurons in the striatum by the nigro-striatal dopaminergic input. The effects could be due to the activation of D2-like DA receptors located at pre-synaptic levels on cortico-striatal glutamatergic nerve endings.

Glutamate in schizophrenics and healthy controls

Cerebrospinal fluid (CSF) glutamate levels were measured in 28 paranoid schizophrenic patients and 15 healthy individuals. From the 28 patients 15 were treated with neuroleptic drugs and 13 did not take any drugs. No significant difference was found between glutamate in patients without neuroleptics and controls. However, CSF glutamate was significantly higher in patients taking neuroleptics than in controls (P less than 0.001) or in patients without neuroleptics (P less than 0.01). This and other data from the literature indicate that enhanced levels of cerebral glutamate may be significant for the antipsychotic efficacy of neuroleptic drugs.

Normal cerebrospinal fluid and brain glutamate levels in schizophrenia do not support the hypothesis of glutamatergic neuronal dysfunction

A recently proposed hypothesis to explain schizophrenia is based on reports of reduced concentrations of glutamic acid in the cerebrospinal fluid (CFS) of schizophrenic patients. This hypothesis suggests that there may be a dysfunction of glutamatergic neurons in schizophrenia, with either a degeneration of these neurons, or their failure to release glutamate as a neurotransmitter. Direct measurement of glutamate levels in CSF and autopsied brain of schizophrenic patient showed no differences from glutamate levels in suitable adult control subjects. The data presented here do not offer support for the new hypothesis.

Synaptosomes prepared from fresh human cerebral cortex; morphology, respiration and release of transmitter amino acids

Synaptosomes prepared from fresh human cerebral cortex were shown to be morphologically similar to those from other species. On incubation, they took up oxygen at a high and linear rate and accumulated potassium against a concentration gradient. In response to depolarization by raised extracellular K+ or addition of veratrine, they showed increased respiration, lowered tissue potassium, and enhanced release of glutamate, aspartate and GABA. The preparation may be of value for studies of neurological disorders.

D-aminophosphonovalerate is 100-fold more powerful than D-alpha-aminoadipate in blocking N-methylaspartate neurotoxicity

Here we report that the D-isomers of 2-amino-5-phosphonovalerate (D-APV) and alpha-amino-adipate (D-alpha AA) protect arcuate hypothalamic neurons from the potent excitotoxic activity of N-methylaspartate (NMA). Consistent with evidence that APV is much more powerful than alpha AA in antagonizing the neuroexcitatory activity of NMA, we found D-APV nearly 100 times more powerful than D-alpha AA in preventing NMA from destroying arcuate neurons.

Effects of chronic amphetamine treatment on the glutamate concentration in cerebrospinal fluid and brain: implications for a theory of schizophrenia

In rats, chronic (12 days) amphetamine administration (5 mg/kg, s.c.) resulted in more than 30% decrease of the glutamate content in the cerebrospinal fluid (CSF) and concomitant increase of glutamate levels in the frontal cortex, striatum and hippocampus. In contrast, chronic amphetamine had no effect on the GABA contents in these areas. The data are compatible with the interpretation that amphetamine induces an increase of dopaminergic function in these brain regions which results in an enhanced inhibition of glutamate release. It is hypothesized that diminished glutamate release accompanies the amphetamine psychosis as well as schizophrenia.