UMLS:C0036341 - FACTA Search

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Query: UMLS:C0036341 (schizophrenia)
60,220 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cortical GABAergic dysfunction, a hallmark of both schizophrenia (SZ) and bipolar (BP) disorder pathophysiologies may relate to the hypermethylation of GABAergic gene promoters (i.e., reelin and GAD67). Benefits elicited by a combination of atypical antipsychotics with valproate (VPA) (a histone deacetylase inhibitor that may also activate brain DNA demethylation) in SZ or BP disorder treatment prompted us to investigate whether the beneficial action of this association depends on induction of a putative DNA demethylase activity. To monitor this activity, we measured the ratio of 5-methyl cytosine to unmethylated cytosine in reelin and GAD67 promoters in the mouse frontal cortex and striatum. We compared normal mice with mice pretreated with l-methionine (5.2 mmol/kg s.c. twice a day for 7 days) to hypermethylate promoters, including reelin and GAD67. Clinically relevant doses of clozapine (CLZ) (3.8 to 15 micromol/kg twice a day s.c. for 3 days) and sulpiride (SULP) (12.5 to 50 micromol/kg twice a day for 3 days) but not clinically relevant doses of haloperidol (HAL) (1.3 to 4 micromol/kg twice a day s.c. for 3 days) or olanzapine (OLZ) (4 to 15 micromol/kg twice a day for 3 days) exhibited dose-related increases in the cortical and striatal demethylation of hypermethylated reelin and GAD67 promoters. These effects of CLZ and SULP were dramatically potentiated by a clinically relevant VPA dose (0.5 mmol/kg twice a day for 3 days). By activating a DNA demethylase, the association of CLZ or SULP with VPA may facilitate a chromatin remodeling that normalizes the GABAergic gene expression down-regulation detected in the telencephalic regions of SZ and BP patients.
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PMID:Clozapine and sulpiride but not haloperidol or olanzapine activate brain DNA demethylation. 1875 38

A small experimental cryolesion to the right parietal cortex of juvenile mice causes late-onset global brain atrophy with memory impairments, reminiscent of cognitive decline, and progressive brain matter loss in schizophrenia. However, the cellular events underlying this global neurodegeneration are not understood. Here we show, based on comprehensive stereological analysis, that early unilateral lesion causes immediate and lasting bilateral increase in the number of microglia in cingulate cortex and hippocampus, consistent with a chronic low-grade inflammatory process. Whereas the total number of neurons and astrocytes in these brain regions remain unaltered, pointing to a non- gliotic neurodegeneration (as seen in schizophrenia), the subgroup of parvalbumin-positive inhibitory GABAergic interneurons is increased bilaterally in the hippocampus, as is the expression of the GABA-synthesizing enzyme GAD67. Moreover, unilateral parietal lesion causes a decrease in the expression of synapsin1, suggesting impairment of presynaptic functions/neuroplasticity. Reduced expression of the myelin protein cyclic nucleotide phosphodiesterase, reflecting a reduction of oligodendrocytes, may further contribute to the observed brain atrophy. Remarkably, early intervention with recombinant human erythropoietin (EPO), a hematopoietic growth factor with multifaceted neuroprotective properties (intraperitoneal injection of 5000 IU/kg body weight every other day for 3 weeks), prevented all these neurodegenerative changes. To conclude, unilateral parietal lesion of juvenile mice induces a non- gliotic neurodegenerative process, susceptible to early EPO treatment. Although the detailed mechanisms remain to be defined, these profound EPO effects open new ways for prophylaxis and therapy of neuropsychiatric diseases, e.g. schizophrenia.
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PMID:Uncoupling of neurodegeneration and gliosis in a murine model of juvenile cortical lesion. 1898 36

The epigenetic down-regulation of genes is emerging as a possible underlying mechanism of the GABAergic neuron dysfunction in schizophrenia. For example, evidence has been presented to show that the promoters associated with reelin and GAD67 are down-regulated as a consequence of DNA methyltransferase (DNMT)-mediated hypermethylation. Using neuronal progenitor cells to study this regulation, we have previously demonstrated that DNMT inhibitors coordinately increase reelin and GAD67 mRNAs. Here, we report that another group of epigenetic drugs, histone deacetylase (HDAC) inhibitors, activate these two genes with dose and time dependence comparable with that of DNMT inhibitors. In parallel, both groups of drugs decrease DNMT1, DNMT3A, and DNMT3B protein levels and reduce DNMT enzyme activity. Furthermore, induction of the reelin and GAD67 mRNAs is accompanied by the dissociation of repressor complexes containing all three DNMTs, MeCP2, and HDAC1 from the corresponding promoters and by increased local histone acetylation. Our data imply that drug-induced promoter demethylation is relevant for maximal activation of reelin and GAD67 transcription. The results suggest that HDAC and DNMT inhibitors activate reelin and GAD67 expression through similar mechanisms. Both classes of drugs attenuate, directly or indirectly, the enzymatic and transcriptional repressor activities of DNMTs and HDACs. These data provide a mechanistic rationale for the use of epigenetic drugs, individually or in combination, as a potential novel therapeutic strategy to alleviate deficits associated with schizophrenia.
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PMID:The reelin and GAD67 promoters are activated by epigenetic drugs that facilitate the disruption of local repressor complexes. 1902 85

Post-mortem studies suggested a disturbance of the GABAergic system in schizophrenia. Neonatal ventral hippocampal-lesioned (NVHL) rats were used as a neurodevelopmental model of schizophrenia. Here, we characterized the GABAergic system, focusing on the GABA-synthesizing enzyme, GAD67, GABAergic interneuron characteristic proteins, and the GABA transporter, gat-1. As the GABAergic system is crucial to brain excitability, the sensitivity to pentylenetetrazol (PTZ) administration, an antagonist of GABAA receptors, was also evaluated in such rats. Male pups were lesioned with ibotenic acid at postnatal day 7. As adults, they were submitted to standard behavioural tests, i.e. prepulse inhibition of the startle reflex and increased locomotion under apomorphine, to assess the effectiveness of the lesions and the PTZ infusion test before immunohistochemistry of the GABAergic neuron markers. We found a widespread perturbation of the enzyme responsible for GABA synthesis, GAD67 and a decrease of specific interneurons, restricted to the hippocampus, entorhinal and prefrontal cortex, but no alteration of gat-1-positive fibres. The usual behavioural properties of the model, such as hyperlocomotion under apomorphine and a deficit in sensorimotor gating were confirmed. NVHL rats showed changes in cortical excitability reflected by higher susceptibility than sham-operated rats to spike wave discharges and decreased susceptibility to clonic seizures, induced by increasing the dose of PTZ. These findings indicate that a neonatal lesion of the ventral hippocampus elicits alterations in the GABAergic system leading to functional consequences on brain excitability, lending support to the idea that GABAergic systems could be involved in the pathophysiology of schizophrenia.
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PMID:Selective reorganization of GABAergic transmission in neonatal ventral hippocampal-lesioned rats. 1926 57

The role of methylation in the history of psychiatry has traversed a storied path. The original trans-methylation hypothesis was proposed at a time when chlorpromazine had been synthesized but not yet marketed as an antipsychotic (Thorazine). The premise was that abnormal metabolism led to the methylation of biogenic amines in the brains of schizophrenia patients and that these hallucinogenic compounds produced positive symptoms of the disease. At the time, some psychiatrists were interested in drugs such as mescaline and lysergic acid diethylamide that replicated clinical symptoms. They understood that these compounds might provide a biological basis for psychosis. The amino acid methionine (MET) was given to patients in the hopes of confiriming the transmethylation hypothesis. However with time, many realized that the hunt for an endogenous psychotropic compound would remain elusive. We now believe that the MET studies may have produced a toxic reaction in susceptible patients by disrupting epigenetic regulation in the brain. The focus of the current review is on the coordinate regulation of multiple promoters expressed in neurons that may be modulated through methylation. While certainly the identification of genes and promoters regulated epigenetically has been steadily increasing over the years, there have been few studies that examine methylation changes as a consequence of increased levels of a dietary amino acid such as methionine (MET). We suggest that the MET mouse model may provide information regarding the identification of genes that are regulated by epigenetic perturbations. In addition to our studies with the reelin and GAD67 promoters, we also have evidence that additional promoters expressed in select neurons of the brain are similarly affected by MET administration. We suggest that to expand our knowledge of epigenetically-responsive promoters using MET might allow for a better appreciation of global methylation changes occurring in selected brain regions.
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PMID:From trans-methylation to cytosine methylation: evolution of the methylation hypothesis of schizophrenia. 1939 59

NRG1 and ERBB4 have emerged as some of the most reproducible schizophrenia risk genes. Moreover, the Neuregulin (NRG)/ErbB4 signaling pathway has been implicated in dendritic spine morphogenesis, glutamatergic synaptic plasticity, and neural network control. However, despite much attention this pathway and its effects on pyramidal cells have received recently, the presence of ErbB4 in these cells is still controversial. As knowledge of the precise locus of receptor expression is crucial to delineating the mechanisms by which NRG signaling elicits its diverse physiological effects, we have undertaken a thorough analysis of ErbB4 distribution in the CA1 area of the rodent hippocampus using newly generated rabbit monoclonal antibodies and ErbB4-mutant mice as negative controls. We detected ErbB4 immunoreactivity in GABAergic interneurons but not in pyramidal neurons, a finding that was further corroborated by the lack of ErbB4 mRNA in electrophysiologically identified pyramidal neurons as determined by single-cell reverse transcription-PCR. Contrary to some previous reports, we also did not detect processed ErbB4 fragments or nuclear ErbB4 immunoreactivity. Ultrastructural analysis in CA1 interneurons using immunoelectron microscopy revealed abundant ErbB4 expression in the somatodendritic compartment in which it accumulates at, and adjacent to, glutamatergic postsynaptic sites. In contrast, we found no evidence for presynaptic expression in cultured GAD67-positive hippocampal interneurons and in CA1 basket cell terminals. Our findings identify ErbB4-expressing interneurons, but not pyramidal neurons, as a primary target of NRG signaling in the hippocampus and, furthermore, implicate ErbB4 as a selective marker for glutamatergic synapses on inhibitory interneurons.
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PMID:Selective expression of ErbB4 in interneurons, but not pyramidal cells, of the rodent hippocampus. 1979 84

Brain injury during the last trimester to the first 1-4 years in humans is now thought to trigger an array of intellectual and emotional problems later in life, including disorders such as schizophrenia. In adult schizophrenic brains, there is a specific loss of neurons that co-express glutamic acid decarboxylase-parvalbumin (GAD67-PV). Loss of this phenotype is thought to occur in mature animals previously exposed to N-methyl-D: -aspartate receptor (NMDAR) antagonists during late gestation or at postnatal day 7 (P7). However, in similarly treated animals, we have previously shown that GAD67 and PV are unaltered in the first 24 h. To more precisely define when changes in these markers first occur, we exposed rat pups (P7 or P6-P10) to the NMDAR antagonist MK801 and at P11 co-stained brain sections for GAD67 or PV. In the cingulate cortex, we found evidence for a reduction in PV (GAD67 levels were very low to undetectable). In contrast, in the somatosensory cortex, we found that expression of GAD67 was reduced, but PV remained stable. Further, repeated but not single doses of MK801 were necessary to see such changes. Thus, depending on the region, NMDAR antagonism appears to influence expression of PV or GAD67, but not both. These observations could not have been predicted by previous studies and raise important questions as to how the GAD67-PV phenotype is lost once animals reach maturity. More importantly, such differential effects may be of great clinical importance, given that cognitive deficits are seen in children exposed to anesthetics that act by blocking the NMDAR.
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PMID:Postnatal exposure to MK801 induces selective changes in GAD67 or parvalbumin. 1988 53

Neurodevelopmental disorders, such as schizophrenia and autism, have been associated with disturbances of the GABAergic system in the brain. We examined immediate and long-lasting influences of exposure to the GABA-potentiating drug vigabatrin (GVG) on the GABAergic system in the hippocampus and cerebral cortex, before and during the developmental switch in GABA function (postnatal days P1-7 and P4-14). GVG induced a transient elevation of GABA levels. A feedback response to GABA enhancement was evident by a short-term decrease in glutamate decarboxylase (GAD) 65 and 67 levels. However, the number of GAD65/67-immunoreactive (IR) cells was greater in 2-week-old GVG-treated mice. A long-term increase in GAD65 and GAD67 levels was dependent on brain region and treatment period. Vesicular GABA transporter was insensitive to GVG. The overall effect of GVG on the Cl(-) co-transporters NKCC1 and KCC2 was an enhancement of their synthesis, which was dependent on the treatment period and brain region studied. In addition, a short-term increase was followed by a long-term decrease in KCC2 oligomerization in the cell membrane of P4-14 hippocampi and cerebral cortices. Analysis of the Ca(2+) binding proteins expressed in subpopulations of GABAergic cells, parvalbumin and calbindin, showed region-specific effects of GVG during P4-14 on parvalbumin-IR cell density. Moreover, calbindin levels were elevated in GVG mice compared to controls during this period. Cumulatively, these results suggest a particular susceptibility of the hippocampus to GVG when exposed during days P4-14. In conclusion, our studies have identified modifications of key components in the inhibitory system during a critical developmental period. These findings provide novel insights into the deleterious consequences observed in children following prenatal and neonatal exposure to GABA-potentiating drugs.
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PMID:A sensitive period of mice inhibitory system to neonatal GABA enhancement by vigabatrin is brain region dependent. 2004 3

Cortical GABA deficits that are consistently reported in schizophrenia may reflect an etiology of failed normal postnatal neurotransmitter maturation. Previous studies have found prefrontal cortical GABA(A) receptor alpha subunit alterations in schizophrenia, yet their relationship to normal developmental expression profiles in the human cortex has not been determined. The aim of this study was to quantify GABA(A) receptor alpha-subunit mRNA expression patterns in human dorsolateral prefrontal cortex (DLPFC) during normal postnatal development and in schizophrenia cases compared to controls. Transcript levels of GABA(A) receptor alpha subunits were measured using microarray and qPCR analysis of 60 normal individuals aged 6weeks to 49years and in 37 patients with schizophrenia/schizoaffective disorder and 37 matched controls. We detected robust opposing changes in cortical GABA(A) receptor alpha1 and alpha5 subunits during the first few years of postnatal development, with a 60% decrease in alpha5 mRNA expression and a doubling of alpha1 mRNA expression with increasing age. In our Australian schizophrenia cohort we detected decreased GAD67 mRNA expression (p=0.0012) and decreased alpha5 mRNA expression (p=0.038) in the DLPFC with no significant change of other alpha subunits. Our findings confirm that GABA deficits (reduced GAD67) are a consistent feature of schizophrenia postmortem brain studies. Our study does not confirm alterations in cortical alpha1 or alpha2 mRNA levels in the schizophrenic DLPFC, as seen in previous studies, but instead we report a novel down-regulation of alpha5 subunit mRNA suggesting that post-synaptic alterations of inhibitory receptors are an important feature of schizophrenia but may vary between cohorts.
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PMID:Prefrontal GABA(A) receptor alpha-subunit expression in normal postnatal human development and schizophrenia. 2010 Jun 21

Gamma-aminobutyric acid (GABA)-ergic transmission is critical for normal cortical function and is likely abnormal in a variety of neuropsychiatric disorders. We tested the in vivo effects of variations in two genes implicated in GABA function on GABA concentrations in prefrontal cortex of living subjects: glutamic acid decarboxylase 1 (GAD1), which encodes GAD67, and catechol-o-methyltransferase (COMT), which regulates synaptic dopamine in the cortex. We studied six single nucleotide polymorphisms (SNPs) in GAD1 previously associated with risk for schizophrenia or cognitive dysfunction and the val158met polymorphism in COMT in 116 healthy volunteers using proton magnetic resonance spectroscopy. Two of the GAD1 SNPs (rs1978340 (p=0.005) and rs769390 (p=0.004)) showed effects on GABA levels as did COMT val158met (p=0.04). We then tested three SNPs in GAD1 (rs1978340, rs11542313, and rs769390) for interaction with COMT val158met based on previous clinical results. In this model, rs11542313 and COMT val158met showed significant main effects (p=0.001 and 0.003, respectively) and a trend toward a significant interaction (p=0.05). Interestingly, GAD1 risk alleles for schizophrenia were associated with higher GABA/Cre, and Val-Val homozygotes had high GABA/Cre levels when on a GAD1 risk genotype background (N=6). These results support the importance of genetic variation in GAD1 and COMT in regulating prefrontal cortical GABA function. The directionality of the effects, however, is inconsistent with earlier evidence of decreased GABA activity in schizophrenia.
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PMID:Genetic modulation of GABA levels in the anterior cingulate cortex by GAD1 and COMT. 2035 58

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