Glutamate in schizophrenics and healthy controls

A Selective Review of the Excitatory-Inhibitory Imbalance in Schizophrenia: Underlying Biology, Genetics, Microcircuits, and Symptoms

Schizophrenia is a chronic disorder characterized by specific positive and negative primary symptoms, social behavior disturbances and cognitive deficits (e.g., impairment in working memory and cognitive flexibility). Mounting evidence suggests that altered excitability and inhibition at the molecular, cellular, circuit and network level might be the basis for the pathophysiology of neurodevelopmental and neuropsychiatric disorders such as schizophrenia. In the past decades, human and animal studies have identified that glutamate and gamma-aminobutyric acid (GABA) neurotransmissions are critically involved in several cognitive progresses, including learning and memory. The purpose of this review is, by analyzing emerging findings relating to the balance of excitatory and inhibitory, ranging from animal models of schizophrenia to clinical studies in patients with early onset, first-episode or chronic schizophrenia, to discuss how the excitatory-inhibitory imbalance may relate to the pathophysiology of disease phenotypes such as cognitive deficits and negative symptoms, and highlight directions for appropriate therapeutic strategies.

Blood Levels of Glutamate and Glutamine in Recent Onset and Chronic Schizophrenia

Converging evidence indicates that dysfunctions in glutamatergic neurotransmission and in the glutamate-glutamine cycle play a role in the pathophysiology of schizophrenia. Here, we investigated glutamate and glutamine levels in the blood of patients with recent onset schizophrenia or chronic schizophrenia compared to healthy controls. Compared with healthy controls, patients with recent onset schizophrenia showed increased glutamine/glutamate ratio, while patients with chronic schizophrenia showed decreased glutamine/glutamate ratio. Results indicate that circulating glutamate and glutamine levels exhibit a dual behavior in schizophrenia, with an increase of glutamine/glutamate ratio at the onset of schizophrenia followed by a decrease with progression of the disorder. Further studies are warranted to elucidate the mechanisms and consequences of changes in circulating glutamate and glutamine in schizophrenia.

High resolution crystal structures of human kynurenine aminotransferase-I bound to PLP cofactor, and in complex with aminooxyacetate

In this study, we report two high-resolution structures of the pyridoxal 5' phosphate (PLP)-dependent enzyme kynurenine aminotransferase-I (KAT-I). One is the native structure with the cofactor in the PLP form bound to Lys247 with the highest resolution yet available for KAT-I at 1.28 Å resolution, and the other with the general PLP-dependent aminotransferase inhibitor, aminooxyacetate (AOAA) covalently bound to the cofactor at 1.54 Å. Only small conformational differences are observed in the vicinity of the aldimine (oxime) linkage with which the PLP forms the Schiff base with Lys247 in the 1.28 Å resolution native structure, in comparison to other native PLP-bound structures. We also report the inhibition of KAT-1 by AOAA and aminooxy-phenylpropionic acid (AOPP), with IC50s of 13.1 and 5.7 μM, respectively. The crystal structure of the enzyme in complex with the inhibitor AOAA revealed that the cofactor is the PLP form with the external aldimine linkage. The location of this oxime with the PLP, which forms in place of the native internal aldimine linkage of PLP of the native KAT-I, is away from the position of the native internal aldimine, with the free Lys247 substantially retaining the orientation of the native structure. Tyr101, at the active site, was observed in two conformations in both structures.

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.

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.

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.

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 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.

Increased volume and glial density in primate prefrontal cortex associated with chronic antipsychotic drug exposure

BACKGROUND

Long term medication with antipsychotic drugs is known to produce changes in neurotransmitter levels and receptor sensitivity in the cortex; however, the anatomic consequences of chronic antipsychotic exposure are not well established.

METHODS

Accordingly, rhesus monkeys were given daily oral doses of typical or atypical antipsychotic drugs (TAP or AAP) or a placebo for 6 months. After treatment, a stereologic method was used to assess neuronal and glial density and cortical thickness in prefrontal area 46.

RESULTS

Neuronal density in drug-treated monkeys and controls did not differ in any cortical layer. Glial density was elevated in monkeys that received antipsychotic medications: as much as 33% in layers that receive dense excitatory afferents (layers I in TAP monkeys and IV in AAP monkeys). In addition, layer V was wider in all drug-treated monkeys.

CONCLUSIONS

Our findings indicate that glial proliferation and hypertrophy of the cerebral cortex is a common response to antipsychotic drugs. We hypothesize that these responses play a regulatory role in adjusting neurotransmitter levels or metabolic processes. Finally, the negative results with respect to neuronal density indicate that the elevated neuronal density found in the schizophrenic cortex is unlikely to be a medication effect.

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.

The role of N-methyl-D-aspartate (NMDA) receptor-mediated neurotransmission in the pathophysiology and therapeutics of psychiatric syndromes

The study of excitatory amino acids (EAAs) has recently resulted in new and fundamental concepts in neuroscience. This progress has led to a growing awareness of the crucial role that brain EAAs systems play in a variety of physiological and pathological processes. The N-methyl-D-aspartate (NMDA) receptor, presently the most well understood subtype of EAAs receptors, has been implicated in crucial physiological processes such as synaptogenesis, learning and memory. Dysfunctions of NMDA receptors seem to play a crucial role in the neurobiology of disorders such as Parkinson's disease, Alzheimer's disease, epilepsy and ischemic stroke. This paper is a review of emerging data indicating that alterations of NMDA receptor function may be pivotal to the pathophysiology of four common psychiatric syndromes: schizophrenia, major depression, posttraumatic stress disorder, and alcoholism. Special emphasis is placed on the current state of development of pharmacological strategies aiming at the modulation of NMDA receptor-mediated neurotransmission in these disorders.

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.

Mechanisms of action of atypical antipsychotic drugs: a critical analysis

Various criteria used to define atypical antipsychotic drugs include: 1) decrease, or absence, of the capacity to cause acute extrapyramidal motor side effects (acute EPSE) and tardive dyskinesia (TD); 2) increased therapeutic efficacy reflected by improvement in positive, negative, or cognitive symptoms; 3) and a decrease, or absence, of the capacity to increase prolactin levels. The pharmacologic basis of atypical antipsychotic drug activity has been the target of intensive study since the significance of clozapine was first appreciated. Three notions have been utilized conceptually to explain the distinction between atypical versus typical antipsychotic drugs: 1) dose-response separation between particular pharmacologic functions; 2) anatomic specificity of particular pharmacologic activities; 3) neurotransmitter receptor interactions and pharmacodynamics. These conceptual bases are not mutually exclusive, and the demonstration of limbic versus extrapyramidal motor functional selectivity is apparent within each arbitrary theoretical base. This review discusses salient distinctions predominantly between prototypic atypical and typical antipsychotic drugs such as clozapine and haloperidol, respectively. In addition, areas of common function between atypical and typical antipsychotic drug action may also be crucial to our identification of pathophysiological foci of the different dimensions of schizophrenia, including positive symptoms, negative symptoms, and neurocognitive deficits.

Competitive and non-competitive N-methyl-D-aspartate antagonists fail to prevent the induction of methamphetamine-induced sensitization

In order to elucidate the possible roles of the glutamate system in the mechanisms underlying behavioral sensitization, which is used as an animal model for human psychosis, we investigated the effects of 3-((+/-)-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) and MK-801 ((+)-dizocilpine), a competitive and noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, respectively, on methamphetamine-induced behavioral sensitization in rats. Administration of 0.5 mg/kg MK-801 enhanced 2 mg/kg methamphetamine-induced hyperactivity, whereas it reduced 6 mg/kg methamphetamine-induced stereotyped behavior markedly. CPP (10 mg/kg) reduced 2 mg/kg methamphetamine-induced stereotypy slightly. Repeated treatment with 2 and 6 mg/kg methamphetamine alone induced progressive augmentation of stereotypy, whereas combining either MK-801 or CPP with methamphetamine treatment abolished or attenuated this augmentation. However, when rats were challenged with methamphetamine after a 7-day period of abstinence, the intensity of stereotypy among the rats pretreated with repeated doses of methamphetamine alone or in combination with MK-801 or CPP did not differ significantly. These results indicate that competitive and non-competitive NMDA receptor antagonists modulate acute methamphetamine-induced abnormal behavior and sensitization expression, but they failed to prevent the induction of the neural mechanisms underlying behavioral sensitization.

Multidimensional analysis of the concentrations of 17 substances in the CSF of schizophrenics and controls

The concentrations of 17 substances were determined in the cerebrospinal fluid (CSF) of 28 paranoid schizophrenic patients and 16 controls. Results were standardized and simultaneously evaluated through Multidimensional Scaling (MDS). The full data set can be considered as a cloud of points consisting of the 44 subjects in the 17-dimensional parameter space. MDS seeks a two-dimensional representation of this 17-dimensional cloud of points, while retaining as much as possible the distances between the subjects. The two-dimensional reduction of the 17 CSF parameters correctly separated 15 of 16 controls from the schizophrenic subjects. This indicates that a biological heterogeneity between schizophrenic and nonschizophrenic subjects can be detected by the simultaneous analysis of the CSF concentrations of substances related directly or indirectly to the neuronal activity in the brain.

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)

Dopamine and noradrenalin in the cerebrospinal fluid of schizophrenic patients

Concentrations of both dopamine (DA) and noradrenalin (NA) were determined in the cerebrospinal fluid (CSF) of schizophrenic patients with and without neuroleptic treatment and in healthy controls. No significant differences were found between unmedicated patients and controls for either DA or NA. Patients receiving neuroleptics showed significantly higher levels of both DA and NA in the CSF. These results suggest that the reported findings of increased NA in the CSF and increased DA and NA in the brain of schizophrenic patients could be due, at least in part, to the effects of neuroleptic drugs.

Effects of subchronic treatment of methamphetamine haloperidol on the rat brain levels of GABA, glutamate and aspartate

Centrally active amino acids (GABA, glutamate, aspartate) were assayed enzyme-fluorometrically in five brain regions of the rat after a 16-day administration of methamphetamine (2.5 mg/kg, i.p.) and haloperidol (2.5 mg/kg, i.p.), or both agents together. Methamphetamine caused no statistically-significant changes in the GABA contents in any brain areas, a significant decrease in the glutamate content of the striatum, hippocampus and midbrain and an increase in the aspartate content of the hypothalamus. Haloperidol treatment resulted in no changes in the GABA content, a significant decrease in the glutamate content of the striatum and a significant increase in the aspartate content in the frontal cortex. The treatment with both agents caused a significant decrease in the GABA content of the hypothalamus. The combined administration normalized a lowering of the glutamate levels in the striatum caused by methamphetamine and haloperidol, respectively, and increased the level of aspartate in the hypothalamus caused by methamphetamine and in the frontal cortex caused by haloperidol.

Phenylethylamine and phenylacetic acid in CSF of schizophrenics and healthy controls

Phenylethylamine (PEA) is an endogenous substance with amphetamine-like stimulant properties. On the basis of this ability an abnormal brain PEA metabolism has been proposed as an etiological factor in some forms of schizophrenia. In the present study 28 schizophrenic patients and 15 healthy controls were investigated. No significant difference from control values was found in PEA concentration in cerebrospinal fluid (CSF) of either untreated of neuroleptic-treated schizophrenics. However, 2 schizophrenics with highest BPRS scores had extremely high PES concentrations. Free phenylacetic acid (PAA), the major metabolite of PEA, was significantly decreased in ummedicated but not in drug-treated schizophrenics. Because of the assumed neuromodulatory properties of PEA, it is suggested that lowered PAA concentrations and the tendency for PEA to be elevated may imply that altered central neurotransmission occurs in certain forms of schizophrenia.