Schizophrenia, tardive dyskinesia, and brain GABA

Modulation of stimulated dopamine release in rat nucleus accumbens shell by GABA in vitro: Effect of sub-chronic phencyclidine pretreatment

Dopamine signaling in nucleus accumbens (NAc) is modulated by γ-aminobutyric acid (GABA), acting through GABA-A and GABA-B receptors: dysregulation of GABAergic control of dopamine function may be important in behavioral deficits in schizophrenia. We investigated the effect of GABA-A (muscimol) and GABA-B (baclofen) receptor agonists on electrically stimulated dopamine release. Furthermore, we explored whether drug-induced changes were disrupted by pretreatment with phencyclidine, which provides a well-validated model of schizophrenia. Using brain slices from female rats, fast-scan cyclic voltammetry was used to measure electrically stimulated dopamine release in NAc shell. Both muscimol and baclofen caused concentration-dependent attenuation of evoked dopamine release: neither effect was changed by dihydro-β-erythroidine, a nicotinic acetylcholine receptor antagonist, or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), precluding indirect mechanisms using these transmitter systems in the GABAergic actions. In slices taken from rats pretreated with phencyclidine, the attenuation of evoked dopamine release by baclofen was abolished, but the attenuation by muscimol was unaffected. Since phencyclidine pretreatment was followed by drug-free washout period of at least a week, the drug was not present during recording. Therefore, disruption of GABA-B modulation of dopamine is due to long-term functional changes resulting from the treatment, rather than transient changes due to the drug's presence at test. This enduring dysregulation of GABA-B modulation of accumbal dopamine release provides a plausible mechanism through which GABA dysfunction influences accumbal dopamine leading to behavioral changes seen in schizophrenia and may provide a route for novel therapeutic strategies to treat the condition.

The expression of long noncoding RNA NEAT1 is reduced in schizophrenia and modulates oligodendrocytes transcription

Oligodendrocyte (OLG)-related abnormalities have been broadly observed in schizophrenia (SZ); however, the etiology of these abnormalities remains unknown. As SZ is broadly believed to be a developmental disorder, the etiology of the myelin abnormalities in SZ may be related to OLG fate specification during development. Noncoding RNAs (ncRNAs) are an important part of multifaceted transcriptional complexes participating in neurogenic commitment and regulation of postmitotic cell function. The long ncRNA, NEAT1, is a structural component of paraspeckles (subnuclear bodies in interchromatin regions) that may control activity of developmental enhancers of OLG fate specification. Gene expression studies of multiple cortical regions from individuals with SZ showed strong downregulation of NEAT1 levels relative to controls. NEAT1-deficient mice show significant decreases in the numbers of OLG-lineage cells in the frontal cortex. To gain further insight into biological processes affected by NEAT1 deficiency, we analyzed RNA-seq data from frontal cortex of NEAT1^-/- mice. Analyses of differentially expressed gene signature from NEAT1^-/- mice revealed a significant impact on processes related to OLG differentiation and RNA posttranscriptional modification with the underlying mechanisms involving Wnt signaling, cell contact interactions, and regulation of cholesterol/lipid metabolism. Additional studies revealed evidence of co-expression of SOX10, an OLG transcription factor, and NEAT1, and showed enrichment of OLG-specific transcripts in NEAT1 purified chromatin isolates from human frontal cortex. Reduced nuclear retention of quaking isoform 5 in NEAT1^-/- mice shed light on possible mechanism(s) responsible for reduced expression of OLG/myelin proteins and supported the involvement of NEAT1 in oligodendrocyte function.

CSF GABA is reduced in first-episode psychosis and associates to symptom severity

Schizophrenia is characterized by a multiplicity of symptoms arising from almost all domains of mental function. γ-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the brain and is increasingly recognized to have a significant role in the pathophysiology of the disorder. In the present study, cerebrospinal fluid (CSF) concentrations of GABA were analyzed in 41 first-episode psychosis (FEP) patients and 21 age- and sex-matched healthy volunteers by high-performance liquid chromatography. We found lower CSF GABA concentration in FEP patients compared with that in the healthy volunteers, a condition that was unrelated to antipsychotic and/or anxiolytic medication. Moreover, lower CSF GABA levels were associated with total and general score of Positive and Negative Syndrome Scale, illness severity and probably with a poor performance in a test of attention. This study offers clinical in vivo evidence for a potential role of GABA in early-stage schizophrenia.

Tardive Dyskinesia Associated with Atypical Antipsychotics: Prevalence, Mechanisms and Management Strategies

All antipsychotics, including the atypical antipsychotics (AAPs), may cause tardive dyskinesia (TD), a potentially irreversible movement disorder, the pathophysiology of which is currently unknown. The prevention and treatment of TD remain major challenges for clinicians. We conducted a PubMed search to review the prevalence and etiology of and management strategies for TD associated with AAPs. TD prevalence rates varied substantially between studies, with an estimated prevalence of around 20% in patients using AAPs. The risk of TD is lower with AAPs than with typical antipsychotics (TAPs) but remains a problem because AAPs are increasingly being prescribed. Important risk factors associated with TD include the duration of antipsychotic use, age, and ethnicity other than Caucasian. Theories about the etiology of TD include supersensitivity of the dopamine receptors and oxidative stress, but other neurotransmitters and factors are probably involved. Studies concerning the management of TD have considerable methodological limitations. Thus, recommendations for the management of TD are based on a few trials and clinical experience, and no general guidelines for the management of TD can be established. The best management strategy remains prevention. Caution is required when prescribing antipsychotics, and regular screening is needed for early detection of TD. Other strategies may include reducing the AAP dosage, switching to clozapine, or administering vesicular monoamine transporter (VMAT)-2 inhibitors. In severe cases, local injections of botulinum toxin or deep brain stimulation may be considered. More clinical trials in larger samples are needed to gather valid information on the effect of interventions targeting TD.

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.

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.

Neuroleptics with differential affinities at dopamine D2 receptors and sigma receptors affect differently the N-methyl-D-aspartate-induced increase in intracellular calcium concentration: involvement of protein kinase

This study examined the effect of chronic antipsychotic treatment on the NMDA-elicited changes in intracellular free Ca2+ concentration ([Ca2+]i) in the primary culture of rat frontal cortical neurons. Antipsychotics used in the study were chosen for their differential affinities at dopamine D2 receptors and sigma receptors. The potential involvement of protein kinases in this action of antipsychotics were also examined. Chronic treatment of cells with antipsychotics (sulpiride, clozapine, and chlorpromazine) which are known to be potent dopamine D2 receptor ligands, whereas possessing low or no appreciable affinity for sigma receptors, caused a dose-dependent potentiation of the NMDA-induced increase in [Ca2+]i. On the contrary, haloperidol, which is as potent a sigma receptor ligand as a dopamine D2 receptor ligand, did not affect the NMDA-elicited increase in [Ca2+]i. Sulpiride increased the maximum effect afforded by different concentrations of NMDA and shifted the dose-response curve of NMDA to the left (EC50 value from 12.5 microM to 1.39 microM). Consistent with sulpiride's affinity at dopamine D2 receptors, this action of sulpiride was stereoselective: S(-)-sulpiride was active whereas R(+)-sulpiride was inactive. Treatment of cells with dopamine (3 microM) tends to decrease the NMDA-induced increase in [Ca2+]i. Sulpiride at 1 microM totally abolished this action of dopamine and restored its potentiating action on the NMDA-induced increase in [Ca2+]i. Haloperidol, a potent dopamine D2 and sigma receptor ligand, did not affect the sulpiride's potentiating action on the NMDA-induced responses. On the other hand, chronic treatment of cells with a sigma receptor agonist, DTG, at a concentration producing no effect of its own (10 nM), led to an enhancement of the potentiating effect of sulpiride on NMDA-induced increase in [Ca2+]i. This action of DTG was abolished by haloperidol. Further, chronic, but not acute, treatment of cells with either a protein kinase inhibitor H-7 or a cAMP-dependent protein kinase (PKA) inhibitor H-89 abolished this effect of sulpiride on the NMDA-induced [Ca2+]i changes. These results indicate that the action of NMDA in the primary cortical neurons are regulated differently by ligands with differential affinities at dopamine D2 and sigma receptors. The results with protein kinase inhibitors indicate that the potentiation of NMDA responses by sulpiride involves intracellular biochemical events.

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.

Typical and atypical neuroleptics induce alteration in blood-brain barrier and brain 59FeCl3 uptake

Long-term neuroleptic medication of schizophrenic patients induces extrapyramidal motor side effects, of which tardive dyskinesia (TD) is the most severe. The etiology of TD is still obscure. Recently, it was suggested that abnormal iron metabolism may play a crucial role in neuroleptic-induced dopamine D2 receptor super-sensitivity. The apparent relationship between neuroleptics and iron is further supported by the increase of iron in the basal ganglia of patients with TD. We now report on the ability of neuroleptic to alter the blood-brain barrier in the rat and to potentiate the normally limited iron transport into the brain. Thus, chronic treatment of rats with chlorpromazine and haloperidol facilitated 59Fe3+ uptake into brain cells. In contrast, clozapine, an atypical antipsychotic neuroleptic with little extrapyramidal motor side effects, caused iron sedimentation in brain blood vessels with no sign of detectable iron in the cells. Moreover, chronic treatment with chlorpromazine and haloperidol caused a 43% and 24% reduction, respectively, in liver nonheme iron, whereas clozapine induced an 81% increase. The apparent different potentials of chlorpromazine, haloperidol, and clozapine to increase iron transport into the brain from its peripheral stores may be linked to the severity of extrapyramidal motor side effects they induce and to the pathophysiology of TD.

Gamma-aminobutyrate aminotransferase activity in brains of schizophrenic patients

The activity of gamma-aminobutyrate aminotransferase (GABA-T) was estimated in twelve regions of brains from 22 control subjects and 6 cases with schizophrenia. In the controls, no significant correlation was found between the enzyme activity and age or postmortem interval (PMI) in any of the brain regions studied. In experiments on rat brains, the enzyme activity decreased about 20% during the first 2 hours of storage at room temperature and at 4 degrees C but remained steady thereafter. A similar initial decline in activity in the human brain material cannot be excluded. In the human brains, a slightly lower activity was found in the group below 75 years (n = 8) when compared with the group above 75 years (n = 8). A tendency to higher activities was found in female brains (n = 10) compared with male brains (n = 12). No significant difference in the enzyme activity was found between schizophrenic brains, in any of the regions studied, when compared to controls, matched for age, sex and PMI.

Regionally selective deficits in uptake sites for glutamate and gamma-aminobutyric acid in the basal ganglia in schizophrenia

In a post-mortem study of schizophrenic and control subjects, the sodium-dependent binding of D-[3H]aspartate and [3H]nipecotic acid were used to investigate uptake sites of glutamate and gamma-aminobutyric acid (GABA), respectively, in subcortical brain regions. Binding to the glutamate uptake site was substantially reduced in both the putamen and lateral pallidum of the schizophrenic subjects. Binding to the GABA uptake site was substantially reduced in the putamen; smaller reductions were apparent in the caudate nucleus and lateral pallidum. The results suggest that glutamatergic and GABAergic mechanisms in the basal ganglia are abnormal in schizophrenia. These abnormalities could be relevant to the development of psychosis but could also relate to the spectrum of mild motor disturbances often described in the disease.

Positron emission tomography and magnetic resonance imaging: a review and a local circuit neurons hypo(dys)function hypothesis of schizophrenia

A review of brain imaging (PET and MRI) studies on schizophrenia and recent data from neuroanatomy, neurophysiology, neuropathology, neurochemistry, neuropsychology, and cortical organization theory is integrated with the concept of local circuit neurons (LCNs) in a new hypothesis--the local circuit neurons hypo(dys)function hypothesis of schizophrenia--that attempts to explain the pathogenesis and pathophysiology of schizophrenia through a hypofunction (or dysfunction) of the local circuit neurons in prefrontal and limbic-temporal areas. This hypofunction (dysfunction) is then related to the neurocircuitry, neuropsychology, and psychopathology of schizophrenia.

GABA-transaminase activity in rat and human brain: regional, age and sex-related differences

The activity of 4-aminobutyrate:2-oxoglutarate transaminase (GABA-T) has been investigated in the rat and human brain. Both rat and human brain GABA-T retained its full activity for at least 2 months and with a loss of less than 10% after 6 months when frozen at -20 degrees C as tissue parts. There was a loss of activity of mouse brain GABA-T of about 15% per 24 hours postmortem. In the rat brain, GABA-T activity varied from low values in cortex and hippocampus to high in brain stem and cerebellum. There was a significant increase of GABA-T activity with age from 1 to 6 weeks and a significant reduction of the activity with age thereafter. Male rats had significant higher activity than female rats. In the human brain, GABA-T activities were measured in twelve regions of autopsied brains from 10 adult control subjects. No difference was found between the activities in the left and right sides. There is considerable variation in enzyme activity across the brain, with low activities in e.g. pons and medulla oblongata and high activities in e.g. caudatus, substantia nigra and hypothalamus. The activity of the enzyme is significantly different both between brain regions and between individuals.

Brain gamma-aminobutyrate transaminase and monoamine oxidase activities in suicide victims

The activity of gamma-aminobutyrate amino-transferase (GABA-T) and monoamine oxidase (MAO-A and -B) was measured in 42 postmortem human brains. Three brain regions (frontal cortex, cingulate cortex and hypothalamus) from 23 controls without known neurological or psychiatric disorder and from 19 suicide victims were analysed. The suicide victims were classified according to the use of violent and non-violent methods and to the presence or absence of a known history of depressive disorder. No difference was found between the series of suicide victims and the control subjects with regard to GABA-T activity. Carbon monoxide poisoning and death by drug overdose, however, were found to reduce the activity. The MAO-B activity did not differ between the groups. With MAO-A, however, a significant elevation (t = 2.01; P less than 0.05) was found in the hypothalamic region of the suicide victims. The difference seemed to be confined to the subgroup of suicides with a record of depressive disorder.

Spontaneous orofacial movements induced in rodents by very long-term neuroleptic drug administration: phenomenology, pathophysiology and putative relationship to tardive dyskinesia

While understanding of the major clinical and ethical issue of tardive dyskinesia would be greatly facilitated by the development of an isomorphic or homologous animal model, particularly in rodents, this has proved to be a highly contentious issue. The literature on orofacial function in rats administered neuroleptic drugs for substantial proportions of their adult lifespan is reviewed. It reveals the emergence of late-onset orofacial movements in a number of studies, but very early-onset movements or no effect in others. Potential explanations for these discrepancies are considered, and ways of resolving such inconsistencies are suggested. The relationship of these various orofacial phenomena to dopaminergic and non-dopaminergic function, and to clinical syndromes, is critically evaluated.