Differential regulation of mRNA levels encoding for the two isoforms of glutamate decarboxylase (GAD65 and GAD67) by dopamine receptors in the rat striatum

Bi-allelic GAD1 variants cause a neonatal onset syndromic developmental and epileptic encephalopathy

Developmental and epileptic encephalopathies are a heterogeneous group of early-onset epilepsy syndromes dramatically impairing neurodevelopment. Modern genomic technologies have revealed a number of monogenic origins and opened the door to therapeutic hopes. Here we describe a new syndromic developmental and epileptic encephalopathy caused by bi-allelic loss-of-function variants in GAD1, as presented by 11 patients from six independent consanguineous families. Seizure onset occurred in the first 2 months of life in all patients. All 10 patients, from whom early disease history was available, presented with seizure onset in the first month of life, mainly consisting of epileptic spasms or myoclonic seizures. Early EEG showed suppression-burst or pattern of burst attenuation or hypsarrhythmia if only recorded in the post-neonatal period. Eight patients had joint contractures and/or pes equinovarus. Seven patients presented a cleft palate and two also had an omphalocele, reproducing the phenotype of the knockout Gad1-/- mouse model. Four patients died before 4 years of age. GAD1 encodes the glutamate decarboxylase enzyme GAD67, a critical actor of the γ-aminobutyric acid (GABA) metabolism as it catalyses the decarboxylation of glutamic acid to form GABA. Our findings evoke a novel syndrome related to GAD67 deficiency, characterized by the unique association of developmental and epileptic encephalopathies, cleft palate, joint contractures and/or omphalocele.

No effect of riluzole and memantine on learning deficit following quinpirole sensitization - An animal model of obsessive-compulsive disorder

RATIONALE

Chronic quinpirole (QNP) sensitization is an established animal model relevant to obsessive-compulsive disorder (OCD) that has been previously shown to induce several OCD-like behavioral patterns, such as compulsive-like checking and increased locomotion.

OBJECTIVES

In current study we explored the effect of antiglutamatergic drugs, memantine and riluzole, on cognitive and behavioral performance of QNP sensitized rats.

METHODS

During habituation phase, the rats (N = 56) were injected with QNP (0.25 mg/kg) or saline solution (every other day up to 10 injections) and placed into rotating arena without foot shocks for 50-min exploration. Active place avoidance task in rotating arena with unmarked to-be-avoided shock sector was used during acquisition phase. Rats were injected with memantine (1 mg/kg or 5 mg/kg), riluzole (1 mg/kg or 5 mg/kg) or saline solution 30 min before the trial and with QNP (0.25 mg/kg) or saline right before they were placed inside the rotating arena with 60° unmarked shock sector. Locomotion and number of entrances into the shock sector were recorded.

RESULTS

QNP sensitization led to a robust deficit in place learning. However, neither memantine nor riluzole did reverse or alleviate the deficit induced by QNP. Contrarily, memantine significantly aggravated QNP induced deficit.

CONCLUSIONS

The exacerbation of cognitive deficit following antiglutamatergic agents could be mediated by decreased glutamate concentration in nucleus accumbens and decreased hippocampal activation in the QNP sensitization model.

Alterations in glutamatergic signaling in the brain of dopamine supersensitivity psychosis and non-supersensitivity psychosis model rats

BACKGROUND

The long-term administration of antipsychotics is known to induce dopamine supersensitivity psychosis (DSP). Although the mechanism of DSP involves mainly a compensatory upregulation of dopamine D2 receptors, the precise mechanisms underlying DSP are unknown. It is known that glutamatergic signaling plays a key role in psychosis. We thus conducted this study to investigate whether glutamatergic signaling plays a role in the development of DSP.

METHODS

Haloperidol (0.75 mg/kg/day for 14 days) or vehicle was administered to rats via osmotic mini-pump. Haloperidol-treated rats were divided into groups of DSP rats and non-DSP rats based on locomotion data. Tissue levels of glutamate, glutamine, glycine, L-serine, D-serine, and GABA and the protein expressions of N-methyl-D-aspartate receptors (NMDAR), glutamic acid decarboxylase (GAD), and serine hydroxymethyltransferase (SHMT) in the rat brain regions were examined.

RESULTS

In the DSP rats, the ratio of GABA to glutamate was significantly increased. In addition, the ratio of L-serine to glycine was increased. The striatal expressions of GAD and SHMT2 in the DSP rats were significantly increased. In contrast, the striatal expression of NMDAR2B in the non-DSP rats was significantly decreased.

CONCLUSIONS

The present study suggests that glutamatergic signaling is relatively decreased to GABA in DSP rats. Our results also showed that excessive doses of haloperidol can induce striatal NMDAR hypofunction in non-DSP rats, which could prevent the formation of tardive dyskinesia but cause treatment resistance. In view of the need for therapeutic strategies for treatment-resistant schizophrenia, further research exploring our present findings is necessary.

Progression and Persistence of Neurotoxicity Induced by MDMA in Dopaminergic Regions of the Mouse Brain and Association with Noradrenergic, GABAergic, and Serotonergic Damage

The amphetamine-related drug 3,4-methylenedioxymethamphetamine (MDMA) is known to induce neurotoxic damage in dopaminergic regions of the mouse brain. In order to characterize how the number of administrations influenced the severity of MDMA-induced dopaminergic damage and to describe the localization and persistence of this damage, we evaluated the changes in tyrosine hydroxylase (TH) and dopamine transporter (DAT) in different regions of the mouse brain. Moreover, we investigated whether dopaminergic damage was associated with noradrenergic, GABAergic, and serotonergic damage, by evaluating the changes in noradrenaline transporter (NET), glutamic acid decarboxylase-67 (GAD-67), and serotonin transporter (SERT). Mice received 14, 28, or 36 MDMA administrations (10 mg/kg twice a week) and were sacrificed at different time points (postnatal days 85, 110, 138, or 214) for immunohistochemical evaluation. Mice receiving 28 administrations showed reduced levels of DAT-positive fibers in caudate-putamen (CPu) and medial prefrontal cortex (mPFC) and reduced levels of TH-positive nigral neurons. These mice also displayed increased NET-positive hippocampal fibers, reduced GAD-67-positive neurons in CPu and hippocampus, and reduced GAD-67-positive fibers in mPFC. Similar effects of MDMA on DAT, TH, and GAD-67 were found in mice receiving 36 administrations, which also displayed reduced levels of striatal, cortical, and hippocampal TH-immunoreactive fibers. The reductions in dopaminergic markers and GAD-67 persisted at 3 months after MDMA discontinuation. Finally, MDMA never modified the levels of SERT. These results provide further insight into the localization and persistence of MDMA-induced dopaminergic damage and show that this effect may associate with GABAergic but not noradrenergic or serotonergic damage.

Evaluation of neurotransmitter receptor gene expression identifies GABA receptor changes: a follow-up study in antipsychotic-naïve patients with first-episode psychosis

A study of the gene expression levels in the blood of individuals with schizophrenia in the beginning of the disease, such as first-episode psychosis (FEP), is useful to detect gene expression changes in this disorder in response to treatment. Although a large number of genetic studies on schizophrenia have been conducted, little is known about the effects of antipsychotic treatment on gene expression. The aim of the present study was to examine differences in the gene expression in the blood of antipsychotic-naïve FEP patients before and after risperidone treatment (N = 44) and also to verify the correlation with treatment response. In addition, we determined the correlations between differentially expressed genes and clinical variables. The expression of 40 neurotransmitter and neurodevelopment-associated genes was assessed using the RT2 Profiler PCR Array. The results indicated that the GABRR2 gene was downregulated after risperidone treatment, but no genes were associated with response to treatment and clinical variables after Bonferroni correction. GABRR2 downregulation after treatment can both suggest an effect of risperidone treatment or processes related to disease progression, either not necessarily associated with the improvement of symptoms. Despite this change was observed in blood, this decrease in GABRR2 mRNA levels might be an effect of changes in GABA concentrations or other systems interplay consequently to D2 blockage induced by risperidone, for example. Thus, it is important to consider that antipsychotics or the progression of psychotic disorders might interfere with gene expression.

Gamma aminobutyric acidergic and neuronal structural markers in the nucleus accumbens core underlie trait-like impulsive behavior

BACKGROUND

Pathological forms of impulsivity are manifest in a number of psychiatric disorders listed in DSM-5, including attention-deficit/hyperactivity disorder and substance use disorder. However, the molecular and cellular substrates of impulsivity are poorly understood. Here, we investigated a specific form of motor impulsivity in rats, namely premature responding, on a five-choice serial reaction time task.

METHODS

We used in vivo voxel-based magnetic resonance imaging and ex vivo Western blot analyses to investigate putative structural, neuronal, and glial protein markers in low-impulsive (LI) and high-impulsive rats. We also investigated whether messenger RNA interference targeting glutamate decarboxylase 65/67 (GAD65/67) gene expression in the nucleus accumbens core (NAcbC) is sufficient to increase impulsivity in LI rats.

RESULTS

We identified structural and molecular abnormalities in the NAcbC associated with motor impulsivity in rats. We report a reduction in gray matter density in the left NAcbC of high-impulsive rats, with corresponding reductions in this region of glutamate decarboxylase (GAD65/67) and markers of dendritic spines and microtubules. We further demonstrate that the experimental reduction of de novo of GAD65/67 expression bilaterally in the NAcbC is sufficient to increase impulsivity in LI rats.

CONCLUSIONS

These results reveal a novel mechanism of impulsivity in rats involving gamma aminobutyric acidergic and structural abnormalities in the NAcbC with potential relevance to the etiology and treatment of attention-deficit/hyperactivity disorder and related disorders.

Aripiprazole differentially regulates the expression of Gad67 and γ-aminobutyric acid transporters in rat brain

The molecular etiology of schizophrenia comprises abnormal neurotransmission of the amino acid GABA (γ-aminobutyric acid). Neuropathological studies convincingly revealed reduced expression of glutamic acid decarboxylase (Gad67) in GABAergic interneurons. Several antipsychotics influence the expression of GABAergic genes, but aripiprazole (APZ), a partial dopaminergic and serotonergic receptor agonist, has not been involved into these studies so far. We treated Sprague-Dawley rats for 4 weeks or 4 months with APZ suspended in drinking water and doses of 10 and 40 mg per kg body weight. Gene expression of Gad67, the vesicular GABA transporter Slc32a1 (solute carrier family, Vgat), the transmembrane transporters Slc6a1 (Gat1) and Slc6a11 (Gat3) was assessed by semiquantitative radioactive in situ hybridization. APZ treatment resulted in time- and dose-dependent effects with qualitative differences between brain regions. In the 10-mg group, Slc6a1 was strongly induced after 4 weeks in the hippocampus, amygdala, and cerebral cortex, followed by an induction of Gad67 in the same regions after 4 months, while frontocortical regions as well as basal ganglia showed dose-dependent reductions of Gad67 expression after 4 months. In several frontocortical and subcortical regions, we observed a decrease of Slc32a1 and an increase of Slc6a11 expression. In conclusion, APZ modulates gene expression of GABAergic marker genes involved into pathogenetic theories of schizophrenia. APZ only partially mirrors the effects of other antipsychotics with some important differences regarding brain regions. The findings might be explained by regulatory connections between serotonergic, GABAergic, and dopaminergic neurotransmission and should be validated in behavioral animal models of psychotic disorders.

Effects of 5-HT1A receptor stimulation on D1 receptor agonist-induced striatonigral activity and dyskinesia in hemiparkinsonian rats

Accumulating evidence supports the value of 5-HT1A receptor (5-HT1AR) agonists for dyskinesias that arise with long-term L-DOPA therapy in Parkinson's disease (PD). Yet, how 5-HT1AR stimulation directly influences the dyskinetogenic D1 receptor (D1R)-expressing striatonigral pathway remains largely unknown. To directly examine this, one cohort of hemiparkinsonian rats received systemic injections of Vehicle + Vehicle, Vehicle + the D1R agonist SKF81297 (0.8 mg/kg), or the 5-HT1AR agonist ±8-OH-DPAT (1.0 mg/kg) + SKF81297. Rats were examined for changes in abnormal involuntary movements (AIMs), rotations, striatal preprodynorphin (PPD), and glutamic acid decarboxylase (GAD; 65 and 67) mRNA via RT-PCR. In the second experiment, hemiparkinsonian rats received intrastriatal pretreatments of Vehicle (aCSF), ±8-OH-DPAT (7.5 mM), or ±8-OH-DPAT + the 5-HT1AR antagonist WAY100635 (4.6 mM), followed by systemic Vehicle or SKF81297 after which AIMs, rotations, and extracellular striatal glutamate and nigral GABA efflux were measured by in vivo microdialysis. Results revealed D1R agonist-induced AIMs were reduced by systemic and intrastriatal 5-HT1AR stimulation while rotations were enhanced. Although ±8-OH-DPAT did not modify D1R agonist-induced increases in striatal PPD mRNA, the D1R/5-HT1AR agonist combination enhanced GAD65 and GAD67 mRNA. When applied locally, ±8-OH-DPAT alone diminished striatal glutamate levels while the agonist combination increased nigral GABA efflux. Thus, presynaptic 5-HT1AR stimulation may attenuate striatal glutamate levels, resulting in diminished D1R-mediated dyskinetic behaviors, but maintain or enhance striatal postsynaptic factors ultimately increasing nigral GABA levels and rotational activity. The current findings offer a novel mechanistic explanation for previous results concerning 5-HT1AR agonists for the treatment of dyskinesia.

Modeling interneuron dysfunction in schizophrenia

Schizophrenia is a debilitating neurodevelopmental disorder affecting approximately 1% of the population and imposing a significant burden on society. One of the most replicated and well-established postmortem findings is a deficit in the expression of the gene encoding the 67-kDa isoform of glutamic acid decarboxylase (GAD67), the primary GABA-producing enzyme in the brain. GAD67 is expressed in various classes of interneurons, with vastly different morphological, molecular, and physiological properties. Importantly, GABA system deficits in schizophrenia encompass multiple interneuronal subtypes, raising several important questions. First, do different classes of interneurons regulate different aspects of behavior? Second, can we model cell-type-specific GABAergic deficits in mice, and will the rodent findings translate to human physiology? Finally, will this knowledge open the door to knowledge-based approaches to treat schizophrenia?

Post-translational modification of glutamic acid decarboxylase 67 by intermittent hypoxia: evidence for the involvement of dopamine D1 receptor signaling

Intermittent hypoxia (IH) associated with sleep apnea leads to cardio-respiratory morbidities. Previous studies have shown that IH alters the synthesis of neurotransmitters including catecholamines and neuropeptides in brainstem regions associated with regulation of cardio-respiratory functions. GABA, a major inhibitory neurotransmitter in the CNS, has been implicated in cardio-respiratory control. GABA synthesis is primarily catalyzed by glutamic acid decarboxylase (GAD). In this study, we tested the hypothesis that IH like its effect on other transmitters also alters GABA synthesis. The impact of IH on GABA synthesis was investigated in pheochromocytoma 12 cells, a neuronal cell line which is known to express active form of GAD67 in the cytosolic fraction and also assessed the underlying mechanisms contributing to IH-evoked response. Exposure of cell cultures to IH decreased GAD67 activity and GABA level. IH-evoked decrease in GAD67 activity was caused by increased cAMP - protein kinase A (PKA) - dependent phosphorylation of GAD67, but not as a result of changes in either GAD67 mRNA or protein expression. PKA inhibitor restored GAD67 activity and GABA levels in IH treated cells. Pheochromocytoma 12 cells express dopamine 1 receptor (D1R), a G-protein coupled receptor whose activation increased adenylyl cyclase activity. Treatment with either D1R antagonist or adenylyl cyclase inhibitor reversed IH-evoked GAD67 inhibition. Silencing D1R expression with siRNA reversed cAMP elevation and GAD67 inhibition by IH. These results provide evidence for the role of D1R-cAMP-PKA signaling in IH-mediated inhibition of GAD67 via protein phosphorylation resulting in down-regulation of GABA synthesis.

Chronic suppression of phosphodiesterase 10A alters striatal expression of genes responsible for neurotransmitter synthesis, neurotransmission, and signaling pathways implicated in Huntington's disease

Inhibition of phosphodiesterase 10A (PDE10A) promotes cyclic nucleotide signaling, increases striatal activation, and decreases behavioral activity. Enhanced cyclic nucleotide signaling is a well established route to producing changes in gene expression. We hypothesized that chronic suppression of PDE10A activity would have significant effects on gene expression in the striatum. A comparison of the expression profile of PDE10A knockout (KO) mice and wild-type mice after chronic PDE10A inhibition revealed altered expression of 19 overlapping genes with few significant changes outside the striatum or after administration of a PDE10A inhibitor to KO animals. Chronic inhibition of PDE10A produced up-regulation of mRNAs encoding genes that included prodynorphin, synaptotagmin10, phosphodiesterase 1C, glutamate decarboxylase 1, and diacylglycerol O-acyltransferase and a down-regulation of mRNAs encoding choline acetyltransferase and Kv1.6, suggesting long-term suppression of the PDE10A enzyme is consistent with altered striatal excitability and potential utility as a antipsychotic therapy. In addition, up-regulation of mRNAs encoding histone 3 (H3) and down-regulation of histone deacetylase 4, follistatin, and claspin mRNAs suggests activation of molecular cascades capable of neuroprotection. We used lentiviral delivery of cAMP response element (CRE)-luciferase reporter constructs into the striatum and live animal imaging of 2-{4-[-pyridin-4-yl-1-(2,2,2-trifluoro-ethyl)-1H-pyrazol-3-yl]-phenoxymethyl}-quinoline succinic acid (TP-10)-induced luciferase activity to further demonstrate PDE10 inhibition results in CRE-mediated transcription. Consistent with potential neuroprotective cascades, we also demonstrate phosphorylation of mitogen- and stress-activated kinase 1 and H3 in vivo after TP-10 treatment. The observed changes in signaling and gene expression are predicted to provide neuroprotective effects in models of Huntington's disease.

GABA concentration in schizophrenia patients and the effects of antipsychotic medication: a proton magnetic resonance spectroscopy study

Gamma-amino butyric acid (GABA) is thought to play a role in the pathophysiology of schizophrenia. High magnetic field proton magnetic resonance spectroscopy ((1)H-MRS) provides a reliable measurement of GABA in specific regions of the brain. This study measured GABA concentration in the anterior cingulate cortex (ACC) and in the left basal ganglia (ltBG) in 38 patients with chronic schizophrenia and 29 healthy control subjects. There was no significant difference in GABA concentration between the schizophrenia patients and the healthy controls in either the ACC (1.36+/-0.45 mmol/l in schizophrenia patients and 1.52+/-0.54 mmol/l in control subjects) or the ltBG (1.13+/-0.26 mmol/l in schizophrenia patients and 1.18+/-0.20 mmol/l in control subjects). Among the right handed schizophrenia patients, the GABA concentration in the ltBG was significantly higher in patients taking typical antipsychotics (1.25+/-0.24 mmol/l) than in those taking atypical antipsychotics (1.03+/-0.24 mmol/l, p=0.026). In the ACC, the GABA concentration was negatively correlated with the dose of the antipsychotics (rs=-0.347, p=0.035). In the ltBG, the GABA concentration was positively correlated with the dose of the anticholinergics (rs=0.403, p=0.015). To the best of our knowledge, this is the first study to have directly measured GABA concentrations in schizophrenia patients using (1)H-MRS. Our results suggest that there are no differences in GABA concentrations in the ACC or the ltBG of schizophrenia patients compared to healthy controls. Antipsychotic medication may cause changes in GABA concentration, and atypical and typical antipsychotics may have differing effects. It is possible that medication effects conceal inherent differences in GABA concentrations between schizophrenia patients and healthy controls.

Metabotropic glutamate mGluR5 receptor blockade opposes abnormal involuntary movements and the increases in glutamic acid decarboxylase mRNA levels induced by l-DOPA in striatal neurons of 6-hydroxydopamine-lesioned rats

The present study examined the effect of a subchronic systemic administration of the glutamate metabotropic mGluR5 receptor antagonist MPEP on l-DOPA-induced dyskinesias and striatal gene expression in adult rats with a unilateral 6-OHDA lesion of dopamine neurons. The daily systemic administration of l-DOPA for 2 weeks induced a gradual increase in limb dyskinesia and axial dystonia. The subchronic systemic co-administration of MPEP reduced the severity of limb dyskinesia and axial dystonia over the whole duration of l-DOPA treatment. Subchronic l-DOPA administration was paralleled by a significant increase in mRNA levels of the two isoforms of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD67 and GAD65) and preprodynorphin (PPD). Single cell analysis on emulsion radioautographs indicated that l-DOPA-induced increases in GAD67 occurred predominantly in preproenkephalin-unlabeled striatonigral and, to a lesser extent, in preproenkephalin-labeled striatopallidal neurons. MPEP completely reversed the effects of l-DOPA on GAD67 and reduced the increases in GAD65 and PPD mRNA levels in striatonigral neurons. MPEP also reversed the small l-DOPA-induced increase in GAD67 mRNA levels in striatopallidal neurons. Altogether, the findings support the idea that the relative efficacy of mGluR5 receptor antagonists to oppose l-DOPA-induced abnormal involuntary movements involves an ability to oppose increases in GAD gene expression and GABA-mediated signaling in striatonigral and striatopallidal neurons. The results also confirm the potential usefulness of antagonists of mGluR5 receptors as adjuncts in the treatment of l-DOPA-induced dyskinesia in patients with Parkinson's disease.

Chronic psychotropic drug treatment causes differential expression of Reelin signaling system in frontal cortex of rats

Disruption of the Reelin and GABAergic signaling systems have been observed in psychiatric disorders including autism, schizophrenia, bipolar disorder, and major depression. Less is known of therapeutic interventions that may help ameliorate the effects of these disruptions. The current study investigated whether chronic administration of psychotropic medications (clozapine, fluoxetine, haloperidol, lithium, olanzapine, and valproic acid) used in the treatment of psychiatric disorders alters levels of Reelin, its receptor Vldlr, downstream molecules Gsk3 beta, Dab-1, and Gad65/67 in rat prefrontal cortex as measured by qRT-PCR and SDS-PAGE and western blotting. qRT-PCR revealed that mRNAs for Reelin, Vldlr, Dab-1, Gsk3 beta, and Gad65 were each significantly altered by at least one of the drugs tested, and in the case of Reelin, Dab-1, and Gsk3 beta, by multiple drugs. To verify our results, we also performed SDS-PAGE and western blotting experiments. Again, several of the protein products for Reelin, Vldlr, Dab-1, Gsk3 beta, Gad65, and Gad67 were also significantly altered by multiple drugs. The present results suggest that the Reelin signaling and GABAergic systems are affected by commonly used psychotropic medications. These changes may help explain the efficacy of these drugs and provide further support for the investigation of the Reelin and GABAergic signaling systems as therapeutic targets for the treatment of neuropsychiatric diseases.

A novel mechanism for GABA synthesis and packaging into synaptic vesicles

This review focuses on the recent advances that were made in understanding the fundamental mechanisms of the regulation of l-glutamic acid decarboxylase (GAD; E.C. 4.1.1.15), the enzyme responsible for the synthesis of the major inhibitory neurotransmitter gamma-amino butyric acid (GABA). In the brain, there are two isoforms of GAD- GAD67 and GAD65, where 67 and 65 refer to their respective molecular weights in kDa. A number of neurodegenerative diseases are known to occur as a result of insufficient inhibition due to failure of GABA neurotransmission. Since the rate-limiting step in GABA biosynthesis is the decarboxylation of glutamate by GAD, it is important to understand how GAD is regulated. So far, we know that GAD is regulated at the transcriptional level by alternate splicing and at the post-translational level by protein phosphorylation, palmitoylation and activity-dependent cleavage. Here, we present new evidence of the presence of GAD65 associated with mitochondria in the axon terminal and project a model in which ATP generated by mitochondrial GAD65 may serve an important function in providing energy for GAD65 mediated GABA biosynthesis and packaging into synaptic vesicles by vesicular GABA transporter (VGAT).

Time-course of SKF-81297-induced increase in glutamic acid decarboxylase 65 and 67 mRNA levels in striatonigral neurons and decrease in GABA(A) receptor alpha1 subunit mRNA levels in the substantia nigra, pars reticulata, in adult rats with a unilateral 6-hydroxydopamine lesion

Striatal projection neurons use GABA as their neurotransmitter and express the rate-limiting synthesizing enzyme glutamic acid decarboxylase (GAD) and the vesicular GABA transporter vGAT. The chronic systemic administration of an agonist of dopamine D1/D5-preferring receptors is known to alter GAD mRNA levels in striatonigral neurons in intact and dopamine-depleted rats. In the present study, the effects of a single or subchronic systemic administration of the dopamine D1/D5-preferring receptor agonist SKF-81297 on GAD65, GAD67, PPD and vGAT mRNA levels in the striatum and GABA(A) receptor alpha1 subunit mRNA levels in the substantia nigra, pars reticulata, were measured in rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion. After a single injection of SKF-81297, striatal GAD65 mRNA levels were significantly increased at 3 but not 72 h. In contrast, striatal GAD67 mRNA levels were increased and nigral alpha1 mRNA levels were decreased at 72 but not 3 h. Single cell analysis on double-labeled sections indicated that increased GAD or vGAT mRNA levels after acute SKF-81297 occurred in striatonigral neurons identified by their lack of preproenkephalin expression. Subchronic SKF-81297 induced significant increases in striatal GAD67, GAD65, preprodynorphin and vGAT mRNA levels and decreases in nigral alpha1 mRNA levels. In the striatum contralateral to the 6-OHDA lesion, subchronic but not acute SKF-81297 induced a significant increase in GAD65 mRNA levels. The other mRNA levels were not significantly altered. Finally, striatal GAD67 mRNA levels were negatively correlated with nigral alpha1 mRNA levels in the dopamine-depleted but not dopamine-intact side. The results suggest that different signaling pathways are involved in the modulation by dopamine D1/D5 receptors of GAD65 and GAD67 mRNA levels in striatonigral neurons. They also suggest that the down-regulation of nigral GABA(A) receptors is linked to the increase in striatal GAD67 mRNA levels in the dopamine-depleted striatum.

Decreased GAD67 mRNA levels in cerebellar Purkinje cells in autism: pathophysiological implications

The recent identification of decreased protein levels of glutamate decarboxylase (GAD) 65 and 67 isoforms in the autistic cerebellar tissue raises the possibility that abnormal regulation of GABA production in individual neurons may contribute to the clinical features of autism. Reductions in Purkinje cell number have been widely reported in autism. It is not known whether the GAD changes also occur in Purkinje cells at the level of transcription. Using a novel approach, the present study quantified GAD67 mRNA, the most abundant isoform in Purkinje cells, using in situ hybridization in adult autistic and control cases. The results indicate that GAD67 mRNA level was reduced by 40% in the autistic group (P < 0.0001; two-tailed t test), suggesting that reduced Purkinje cell GABA input to the cerebellar nuclei potentially disrupts cerebellar output to higher association cortices affecting motor and/or cognitive function. These findings may also contribute to the understanding of previous reports of alterations in the GABAergic system in limbic and cerebro-cortical areas contributing to a more widespread pathophysiology in autistic brains.

Toxic influence of subchronic paraquat administration on dopaminergic neurons in rats

Paraquat is a toxin suggested to contribute to pathogenesis of Parkinson's disease. The aim of the present study was to examine toxic influence of subchronic treatment with this pesticide (5 days, one injection per day, 2-3 days of withdrawal) on dopaminergic, serotonergic, noradrenergic and GABAergic neurons. Paraquat decreased the number of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the substantia nigra by 22% (measured 3 days after withdrawal). Two days after withdrawal the levels of the dopamine metabolites and dopamine turnover in the caudate-putamen, substantia nigra and prefrontal cortex were reduced by ca. 20-60%, and the binding of [(3)H]GBR 12,935 to dopamine transporter dropped by 25-40% in the caudate-putamen. Three days after paraquat withdrawal, the level of dopamine in the caudate-putamen was significantly increased, and earlier decreases in DOPAC and HVA in the substantia nigra, as well as [(3)H]GBR 12,935 binding in the caudate-putamen were reversed. Moreover, an increase in serotonin turnover in the caudate-putamen and prefrontal cortex, and noradrenaline level in the former structure was observed 2-3 days after paraquat withdrawal. Three days after the last paraquat injection 24-35% decreases in the proenkephalin mRNA levels and 5-7% reduction in glutamic acid decarboxylase (GAD)67 mRNA were found in the caudate-putamen. The present study suggests that subchronic paraquat administration triggers processes characteristic of early stages of dopaminergic neuron degeneration, and activates compensatory mechanisms involving dopaminergic, noradrenergic, serotonergic and GABAergic transmissions.

Unilateral 6-hydroxydopamine lesion of dopamine neurons and subchronic L-DOPA administration in the adult rat alters the expression of the vesicular GABA transporter in different subsets of striatal neurons and in the substantia nigra, pars reticulata

The loss of dopamine neurons combined or not with the subsequent administration of L-DOPA in patients with Parkinson's disease or in experimental models of the disease results in altered GABAergic signaling throughout the basal ganglia, including the striatum and the substantia nigra, pars reticulata. However, the molecular mechanisms involved in altered GABA neurotransmission remain poorly understood. In order to be released from synaptic vesicles, newly synthesized GABA is transported from the cytosol into synaptic vesicles by a vesicular GABA transporter. The objective of this study was to examine the hypothesis that expression of the vesicular GABA transporter (vGAT) is altered in the unilateral 6-hydroxydopamine model of Parkinson's disease. Our results provide evidence that a unilateral 6-hydroxydopamine lesion results in increased and decreased vGAT mRNA levels in striatopallidal and striatonigral neurons, respectively. These two subsets of neurons were identified by the co-expression or lack of co-expression of preproenkephalin, a marker of striatopallidal neurons, using double-labeling in situ hybridization histochemistry. Such changes occurred in the striatum ipsilateral to the 6-hydroxydopamine lesion and were paralleled by decreased vGAT protein levels in the substantia nigra, pars reticulate (SNr). On the other hand, the subchronic systemic administration of L-DOPA increased vGAT mRNA levels in preproenkephalin-negative neurons on the side ipsilateral and, to a lesser extent, the side contralateral to the 6-hydroxydopamine lesion. Systemic L-DOPA also increased vGAT protein levels in the ipsi- and contralateral SNr. As a whole, the results provide original evidence that vGAT expression is altered in the 6-hydroxydopamine model of Parkinson's disease. They also suggest that the behavioral effects induced by a subchronic administration of L-DOPA to 6-hydroxydopamine-lesioned rats involve an increase in the vesicular release of GABA by striatonigral neurons.

Molecular and cellular mechanisms of altered GAD1/GAD67 expression in schizophrenia and related disorders

The 67 and 65 kDa isoforms of glutamic acid decarboxylase, the key enzymes for GABA biosynthesis, are expressed at altered levels in postmortem brain of subjects diagnosed with schizophrenia and related disorders, including autism and bipolar illness. The predominant finding is a decrease in GAD67 mRNA levels, affecting multiple brain regions, including prefrontal and temporal cortex. Postmortem studies, in conjunction with animal models, identified several mechanisms that contribute to the dysregulation of GAD67 in cerebral cortex. These include disordered connectivity formation during development, abnormal expression of Reelin and neural cell adhesion molecule (NCAM) glycoproteins, defects in neurotrophin signaling and alterations in dopaminergic and glutamatergic neurotransmission. These mechanisms are likely to operate in conjunction with genetic risk factors for psychosis, including sequence polymorphisms residing in the promoter of GAD1 (2q31), the gene encoding GAD67. We propose an integrative model, with multiple molecular and cellular mechanisms contributing to transcriptional dysregulation of GAD67 and cortical dysfunction in psychosis.

High-dose methamphetamine acutely activates the striatonigral pathway to increase striatal glutamate and mediate long-term dopamine toxicity

Methamphetamine (METH) has been shown to increase the extracellular concentrations of both dopamine (DA) and glutamate (GLU) in the striatum. Dopamine, glutamate, or their combined effects have been hypothesized to mediate striatal DA nerve terminal damage. Although it is known that METH releases DA via reverse transport, it is not known how METH increases the release of GLU. We hypothesized that METH increases GLU indirectly via activation of the basal ganglia output pathways. METH increased striatonigral GABAergic transmission, as evidenced by increased striatal GAD65 mRNA expression and extracellular GABA concentrations in substantia nigra pars reticulata (SNr). The METH-induced increase in nigral extracellular GABA concentrations was D1 receptor-dependent because intranigral perfusion of the D1 DA antagonist SCH23390 (10 microm) attenuated the METH-induced increase in GABA release in the SNr. Additionally, METH decreased extracellular GABA concentrations in the ventromedial thalamus (VM). Intranigral perfusion of the GABA-A receptor antagonist, bicuculline (10 microm), blocked the METH-induced decrease in extracellular GABA in the VM and the METH-induced increase in striatal GLU. Intranigral perfusion of either a DA D1 or GABA-A receptor antagonist during the systemic administrations of METH attenuated the striatal DA depletions when measured 1 week later. These results show that METH enhances D1-mediated striatonigral GABAergic transmission (1), which in turn activates GABA-A receptors in the SNr (2), leading to a decrease in GABAergic nigrothalamic activity (3), an increase in corticostriatal GLU release (4), and a consequent long-term depletion of striatal DA content (5).

Differences in the cellular distribution of D1 receptor mRNA in the hippocampus of bipolars and schizophrenics

Several lines of evidence have pointed to a role of the dopamine system in the pathophysiology of schizophrenia. A recent postmortem study demonstrated a selective decrease of tyrosine hydroxylase fibers on pyramidal neurons in sector CA2 in the hippocampus of schizophrenics. Although both brain imaging and postmortem studies have examined the distribution of the D1 receptor in the prefrontal and cingulate cortex, no study to date has examined its expression of mRNA using a high-resolution autoradiographic approach. In order to further assess whether the regulation of the dopamine D1 receptor is altered in hippocampal neurons in this disorder, we used in situ hybridization (ISH) to measure the expression of messenger RNA for this receptor in the dentate gyrus and sectors CA1-4. Both the number of cells expressing D1 mRNA and the amount of expression per cell were measured in 15 schizophrenic, 15 bipolar disorder, and 15 normal control subjects. The results show a significant (21%) and selective decrease in D1 mRNA expression in sector CA3 of schizophrenic subjects. First-degree relatives of schizophrenics did not show any differences in either the expression of D1 mRNA per cell or the number of cells expressing this mRNA when compared to a separate group of normal controls matched for age and PMI. Subjects with bipolar disorder also showed a significant (25%) and selective increase of D1 mRNA expression in sector CA2. Other hippocampal sectors did not show significant changes. These findings in schizophrenics and bipolars were also associated with inverse changes in the overall number of neurons expressing D1 mRNA in sectors CA3 and CA2, respectively. This study shows diagnosis-specific changes in D1 mRNA expression in the hippocampus of schizophrenic versus bipolar subjects and suggests that this neuromodulatory system may show distinct changes in the pathophysiology of the two disorders.

Response of the GABAergic and dopaminergic mesostriatal projections to the lesion of the contralateral dopaminergic mesostriatal pathway in the rat

Although dopamine is the main neurotransmitter in the mesostriatal system, recent studies indicate the existence of two nigrostriatal GABAergic projections: one arising from neurons immunoreactive for GABA, glutamic acid decarboxylase (GAD67), and parvalbumin (PV) lying in the substantia nigra pars reticulata (nigrostriatal GABA cells) and the other arising from a subpopulation of dopaminergic neurons lying in the substantia nigra pars compacta and ventral tegmental area, which under normal conditions, contains mRNA for GAD65 (one of the two isoforms of glutamic acid decarboxylase), but which is not immunoreactive for GABA and GAD65 (nigrostriatal dopaminergic [DA]/GABA cells). With the aim of improving our knowledge about the interaction between the nigrostriatal system of both brain hemispheres, we have studied the response of these three components of the mesostriatal system (GABA, DA/GABA, and DA) to the lesion of the contralateral mesostriatal DA pathway, by using morphological and neurophysiological techniques. Our findings show that, in the side contralateral to the lesion, (1) the number of nigrostriatal GABA cells increases from 6% to 17% with respect to the total number of nigrostriatal cells, (2) the soma of DA/GABA cells becomes immunoreactive for GABA and GAD65, and (3) there is an increase in the firing rate and burst activity of DA-neurons, except in those projecting to the striatum, which may be under the action of the GABA hyperactivity. Taken together, our results suggest that the GABAergic components of the mesostriatal projection play a regulatory role on the DA component, activated or upregulated after contralateral DA lesion and are probably addressed to restoring the functional symmetry in basal ganglia and to slowing down the contralateral progression of DA-cell degeneration in Parkinson's disease.

Homozygosity for a missense mutation in the 67 kDa isoform of glutamate decarboxylase in a family with autosomal recessive spastic cerebral palsy: parallels with Stiff-Person Syndrome and other movement disorders

BACKGROUND

Cerebral palsy (CP) is an heterogeneous group of neurological disorders of movement and/or posture, with an estimated incidence of 1 in 1000 live births. Non-progressive forms of symmetrical, spastic CP have been identified, which show a Mendelian autosomal recessive pattern of inheritance. We recently described the mapping of a recessive spastic CP locus to a 5 cM chromosomal region located at 2q24-31.1, in rare consanguineous families.

METHODS

Here we present data that refine this locus to a 0.5 cM region, flanked by the microsatellite markers D2S2345 and D2S326. The minimal region contains the candidate gene GAD1, which encodes a glutamate decarboxylase isoform (GAD67), involved in conversion of the amino acid and excitatory neurotransmitter glutamate to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA).

RESULTS

A novel amino acid mis-sense mutation in GAD67 was detected, which segregated with CP in affected individuals.

CONCLUSIONS

This result is interesting because auto-antibodies to GAD67 and the more widely studied GAD65 homologue encoded by the GAD2 gene, are described in patients with Stiff-Person Syndrome (SPS), epilepsy, cerebellar ataxia and Batten disease. Further investigation seems merited of the possibility that variation in the GAD1 sequence, potentially affecting glutamate/GABA ratios, may underlie this form of spastic CP, given the presence of anti-GAD antibodies in SPS and the recognised excitotoxicity of glutamate in various contexts.

Dopamine D2-like antagonists induce chromatin remodeling in striatal neurons through cyclic AMP-protein kinase A and NMDA receptor signaling

Antipsychotic drugs regulate gene transcription in striatal neurons by blocking dopamine D2-like receptors. Little is known about the underlying changes in chromatin structure, including covalent modifications at histone N-terminal tails that are epigenetic regulators of gene expression. We show that treatment with D2-like antagonists rapidly induces the phosphorylation of histone H3 at serine 10 and the acetylation of H3-lysine 14 in bulk chromatin from striatum and in nuclei of striatal neurons. We find that, in vivo, D2-like antagonist-induced H3 phospho-acetylation is inhibited by the NMDA receptor antagonist MK-801 and by the protein kinase A (PKA) inhibitor Rp-adenosine 3c',5c'-cyclic monophosphorothioate triethylammonium salt but increased by the PKA activator Sp-adenosine 3c',5c'-cyclic monophosphorothioate triethylammonium salt. Furthermore, in dissociated striatal cultures which lack midbrain and cortical pre-synaptic inputs, H3 phospho-acetylation was induced by glutamate, L-type Ca2+ channel agonists and activators of cAMP-dependent PKA but inhibited by NMDA receptor antagonists or PKA antagonists. The dual modification, H3pS10-acK14, was enriched at genomic sites with active transcription and showed the kinetics of the early response. Together, these results suggest that histone modifications and chromatin structure in striatal neurons are dynamically regulated by dopaminergic and glutamatergic inputs converging on the cellular level. Blockade of D2-like receptors induces H3 phospho-acetylation, H3pS10-acK14, through cAMP-dependent PKA, and post-synaptic NMDA receptor signaling.

Normalization of glutamate decarboxylase gene expression in the entopeduncular nucleus of rats with a unilateral 6-hydroxydopamine lesion correlates with increased GABAergic input following intermittent but not continuous levodopa

The expression of mRNA encoding for the 67 kilodalton isoform of glutamate decarboxylase (GAD67) was examined by in situ hybridization histochemistry in the entopeduncular nucleus (EP) of adult rats with a 6-hydroxydopamine unilaterally lesion of dopamine neurons. Our results provide original evidence that continuous or intermittent levodopa administration is equally effective at reversing the lesion-induced increase in GAD67 mRNA expression in the EP when compared with vehicle controls. To characterize the GABAergic interactions that may mediate levodopa-induced alterations in the EP, double-labeling in situ hybridization was conducted with a combination of GAD67 radioactive and preproenkephalin or preprotachykinin digoxigenin-labeled complementary RNA probes in the striatum. Levels of GAD67 mRNA labeling were significantly increased by intermittent, but not continuous levodopa. Analysis at the cellular level in a dorsal sector of the striatum revealed that GAD67 mRNA levels increased predominantly in preproenkephalin-unlabeled neuronal profiles, presumably striatal/EP neurons (+99.3%). Saturation analyses of (3)H-flunitrazepam binding to GABA(A) receptors in the EP showed that the increase in GAD67 mRNA in preproenkephalin-unlabeled neurons by intermittent levodopa paralleled a significant decrease in number of GABA(A) receptors (Bmax) in the EP ipsilateral to the lesion. Continuous levodopa failed to alter striatal GAD67 mRNA levels, or the number or affinity of GABA(A) receptors when compared with vehicle-treated controls. These results suggest the normalization of GAD gene expression in the EP by intermittent levodopa involves an increase in GABAergic inhibition by striatonigral/EP neurons of the direct pathway. Conversely, the effects of continuous levodopa on GAD mRNA levels in the EP do not appear to be mediated by GABA.

Differential effects of long-term treatment with clozapine or haloperidol on GABAA receptor binding and GAD67 expression

One of the most consistent findings in postmortem studies of schizophrenia is increased GABAA receptor binding and reduced glutamic acid decarboxylase (GAD67) expression. Due to long-term antipsychotic treatment before death, these findings may reflect not only the consequences of schizophrenia but also medication effects. To differentiate between these options, we used an animal model and evaluated long-term effects of typical (haloperidol) and atypical (clozapine) antipsychotic drugs on the GABAergic system. A total of 33 adult male rats were treated in three cohorts over a period of 6 months. One cohort of 11 animals received clozapine (45 mg/kg/day), another one received haloperidol (1.5 mg/kg/day) and a third one received pH-adapted minimal concentrations of HCl in the drinking water. Receptor autoradiography of the GABAA receptor ([3H]-muscimol binding) and in situ hybridization in adjacent sections with 35S-labeled cRNA probes of the y-aminobutyric acid (GABA)-producing enzyme, GAD67, was performed. While haloperidol increased GABAA receptor binding in striatum and nucleus accumbens (NA), it suppressed GABAA receptor binding in temporal (TEMPC) and parietal (PARC) cortex. Clozapine induced GABAA receptor binding in infralimbic cortex (ILC) and similar like haloperidol in anterior cingulate cortex (ACC), two regions of the limbic cortex. In addition, either drug increased gene expression of GAD67. It is concluded that antipsychotic drugs differentially alter the GABAergic system, strongly suggesting that drug effects are partially responsible for the up-regulation of GABAA receptor binding in certain brain regions as observed in postmortem brains of schizophrenic patients. However, the reduced GAD67 expression seen in postmortem brains does not appear to reflect drug effects, since our animal model demonstrated increased gene expression.

Structural and functional characterization of mouse glutamate decarboxylase 67 gene promoter

Neuronal expression of the mouse glutamate decarboxylase 67 (mGAD67) gene occurs exclusively in neurons that synthesize and release GABA (GABAergic neurons). This gene is also expressed in pancreatic islet cells and testicular spermatocytes. In order to elucidate the molecular mechanisms underlying the regulation of mGAD67 gene expression, we isolated and characterized the 5'-flanking region of this gene. Sequence analysis of a 10.2-kb DNA fragment of this gene containing a promoter region (8.4 kb) and noncoding exons 0A and 0B revealed the presence of numerous potential neuron-specific cis-regulatory elements. Functional analysis of the 5'-flanking region of exons 0A and 0B by transient transfection into cultured cells revealed that the region -98 to -52 close to exon 0A is important for the transcriptional activity of both exons 0A and 0B. In addition, we used transgenic mice to examine the expression pattern conferred by the 10.2 kb DNA fragment of the mGAD67 gene fused to the bacterial lacZ reporter gene. Transgene expression was observed in neurons of particular brain regions containing abundant GABAergic neurons such as the basal ganglia, in pancreatic islet cells and in testicular spermatocytes and spermatogonia. These results suggest that the 10.2 kb DNA fragment of the mGAD67 gene contains regulatory elements essential for its targeted expression in GABAergic neurons, islet cells and spermatocytes.

Gene expression in dopamine and GABA systems in an animal model of schizophrenia: effects of antipsychotic drugs

We used in situ hybridization histochemistry to assess expression of dopamine receptors (D1R, D2R and D3R), neurotensin, proenkephalin and glutamate decarboxylase-67 (GAD67) in the prefrontal cortex, striatum, and/or nucleus accumbens in adult rats with neonatal ventral hippocampal (VH) lesions and in control animals after acute and chronic treatment with antipsychotic drugs clozapine and haloperidol. We also acquired these measures in a separate cohort of treatment-naïve sham and neonatally VH-lesioned rats used as an animal model of schizophrenia. Our results indicate that the neonatal VH lesion did not alter expression of D1R, D3R, neurotensin or proenkephalin expression in any brain region examined. However, D2R mRNA expression was down-regulated in the striatum, GAD67 mRNA was down-regulated in the prefrontal cortex and prodynorphin mRNA was up-regulated in the striatum of the VH-lesioned rats as compared with sham controls. Antipsychotic drugs did not alter expression of D1R, D2R or D3R receptor mRNAs but elevated neurotensin and proenkephalin expression in both groups of rats; patterns of changes were dependent on the duration of treatment and brain area examined. GAD67 mRNA was up-regulated by chronic antispychotics in the nucleus accumbens and the striatum and by chronic haloperidol in the prefrontal cortex in both sham and lesioned rats. These results indicate that the developmental VH lesion changed the striatal expression of D2R and prodynorphin and robustly compromised prefrontal GAD67 expression but did not modify drug-induced expression of any genes examined in this study.

Effects of dopaminergic cell degeneration on electrophysiological characteristics and GAD65/GAD67 expression in the substantia nigra: different action on GABA cell subpopulations

The motor disturbances occurring in Parkinson's disease have been partially attributed to a hyperactivity of gamma-aminobutyric acid (GABA)-ergic nigral cells largely in the substantia nigra pars reticulata (SNr) secondary to the degeneration of dopaminergic nigrostriatal neurons. However, some aspects of this response remain unclear. In this work, different electrophysiological and neurochemical parameters were studied in GABAergic cells of the SN after unilateral nigrostriatal dopaminergic lesion using 6-hydroxydopamine injection in rats. Our data showed that 1) the SN under normal conditions contains different subsets of GABAergic cells according to their firing pattern and glutamic acid decarboxylase mRNA levels, and 2) the response of these GABAergic cell subgroups was different after the ipsi- and contralateral dopaminergic cell degeneration. These findings indicate a complex regulation of nigral GABAergic activity after nigrostriatal dopaminergic degeneration that probably involves local mechanisms, the nigro-striato-nigral loop, as well as interhemispheric mechanisms whose anatomical basis remains unstudied.

Response of GABAergic cells in the deep mesencephalic nucleus to dopaminergic cell degeneration: an electrophysiological and in situ hybridization study

The deep mesencephalic nucleus (DMN) is a large midbrain reticular region located between the substantia nigra compacta and the superior colliculus. It contains GABAergic cells that share striatal afferents, thalamic and collicular efferents, as well as neurochemical and electrophysiological similarities, with those of the substantia nigra reticulata. In the present paper we used electrophysiological (firing rate and firing pattern) and morphological (densitometric analysis of in situ hybridization histochemical labeling for glutamic acid decarboxylase (GAD)65 and GAD67 mRNA) techniques, to study the response of DMN GABAergic cells to the degeneration of nigral dopaminergic cells. Our results showed that unilateral dopaminergic cell loss (after injection of 6-hydroxydopamine in the medial forebrain bundle) induces a bilateral and symmetrical increase in both firing rate and GAD67 mRNA levels and a decrease in GAD65 mRNA levels. These findings support the involvement of DMN GABAergic cells in the basal ganglia modifications that follow dopaminergic cell loss, also suggesting its participation in the pathophysiology of Parkinson's disease. The symmetry of effects, together with its recently reported bilateral projections to the thalamus and superior colliculus, suggest that unlike substantia nigra reticulata, DMN is involved in the interhemispheric regulation of basal ganglia, probably keeping their functional symmetry even after asymmetric lesions.

Regulation of glutamic acid decarboxylase 65 and 67 gene expression by ovarian steroids: identification of two functionally distinct populations of GABA neurones in the preoptic area

GABA neurones in the preoptic area (POA) are critical for oestradiol (E2)-dependent surge release of luteinizing hormone (LH); however, it is not clear which population(s) of POA GABA neurones is involved. The goals of the present studies were: (i) to determine whether E2 regulates GABA neurones similarly in two subdivisions of the POA that play a role in LH surge release, the rostral POA region that contains the organum vasculosum of the lamina terminalis (rPOA/OVLT), and the region containing the anteroventral periventricular nucleus (AVPV) and medial preoptic nucleus (MPN) and (ii) to determine whether GABA neurones in either or both regions exhibit temporal changes consistent with a role in the regulation of LH surge release. To accomplish these goals, we measured glutamic acid decarboxylase (GAD) 65 and 67 mRNA levels at several time points in ovariectomized (OVX), E2-treated OVX rats exhibiting LH surge release, and in E2-treated OVX rats in which LH surge release was blocked by prior administration of progesterone (P4). Our findings demonstrate that, despite their close proximity, GABA neurones in the AVPV/MPN region are regulated differently from those in the rPOA/OVLT. Only neurones in the AVPV/MPN region show temporal changes in GAD 67 mRNA expression that appear to be linked to positive-feedback effects of E2 on luteinizing hormone-releasing hormone (LHRH) and LH release. Our findings also indicate that a morning rise and an afternoon fall in GAD 67 mRNA levels marks two E2-dependent signals required for LHRH and LH surge release. Finally, our results suggest that there are distinct E2-induced signals to the rPOA/OVLT and AVPV/MPN regions and that these signals differentially regulate GAD 65 and 67 gene expression.

Acute and chronic caffeine administration differentially alters striatal gene expression in wild-type and adenosine A(2A) receptor-deficient mice

In order to assess for the respective involvement of adenosine A(1) and A(2A) receptors (A(2A)-R) in the consequences of short- and long-term caffeine exposure on gene expression, the effects of acute caffeine administration on striatal, cortical, and hippocampal expression of immediate early genes (IEG), zif-268 and arc, and the effects of long-term caffeine or 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) exposure (once daily for 15 days) on striatal gene expression of substance P, enkephalin, and glutamic acid decarboxylase isoforms, GAD65 and GAD67, were evaluated in wild-type and A(2A)-R-deficient (A(2A)-R(-/-)) mice. In situ hybridization histochemistry was performed using oligonucleotides followed by quantitative image analysis. Our results demonstrated that a biphasic response of IEG expression to acute caffeine observed in the wild-type striatum was resumed in a monophasic response in the mutant striatum. In the cerebral cortex and hippocampus, the effect of caffeine was weak in wild-type, whereas in mutant mice it induced a 2-3-fold increase in the IEG expression to restore a level similar to the wild-type basal expression. Chronic caffeine and DPCPX-mediated regulation in neuropeptide and GADs striatal gene expression typically showed the mimicking of alterations resulting from the A(2A)-R genetic deficiency in 25 mg/kg caffeine-treated wild-type mice as well as the dose-dependent normalization of substance P and enkephalin expression in A(2A)-R(-/-) mice. These results indicate that, depending on the dose, the blockade of A(2A)-R or A(1) receptors by caffeine is preferentially revealed leading to highly differential alterations in striatal gene expression and they also suggested the central role of these two receptors on the control of dopaminergic functions.

Role of glutamatergic and GABAergic systems in alcoholism

The pharmacological effects of ethanol are complex and widespread without a well-defined target. Since glutamatergic and GABAergic innervation are both dense and diffuse and account for more than 80% of the neuronal circuitry in the human brain, alterations in glutamatergic and GABAergic function could affect the function of all neurotransmitter systems. Here, we review recent progress in glutamatergic and GABAergic systems with a special focus on their roles in alcohol dependence and alcohol withdrawal-induced seizures. In particular, NMDA-receptors appear to play a central role in alcohol dependence and alcohol-induced neurological disorders. Hence, NMDA receptor antagonists may have multiple functions in treating alcoholism and other addictions and they may become important therapeutics for numerous disorders including epilepsy, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's chorea, anxiety, neurotoxicity, ischemic stroke, and chronic pain. One of the new family of NMDA receptor antagonists, such as DETC-MESO, which regulate the redox site of NMDA receptors, may prove to be the drug of choice for treating alcoholism as well as many neurological diseases.

Structure of the mouse glutamate decarboxylase 65 gene and its promoter: preferential expression of its promoter in the GABAergic neurons of transgenic mice

GABA is synthesized by glutamate decarboxylase (GAD), which has two forms, GAD65 and GAD67. To elucidate the molecular mechanisms of mouse GAD65 (mGAD65) gene expression, we isolated and characterized the mGAD65 gene. The mGAD65 gene was found to be divided into 16 exons and spread over 75 kb. The sequence of the first exon and the 5'-flanking region indicated the presence of potential neuron-specific cis-regulatory elements. We used transgenic mice to examine the expression pattern conferred by a 9.2-kb promoter-proximal DNA fragment of the mGAD65 gene fused to the bacterial lacZ reporter gene. Transgenic mice showed high beta-galactosidase activity specifically in brain and testis. They also showed characteristic patterns of transgene expression in olfactory bulb, cerebellar cortex, and spinal cord, a similar expression pattern to that of endogenous mGAD65. However, no transgene expression was observed in the ventral thalamus or hypothalamus, in which high mGAD65 gene expression levels have been observed. These results suggest that the 9.2-kb DNA fragment of the mGAD65 gene is associated with its tissue-specific expression and its targeted expression in GABAergic neurons of specific brain regions but that additional regulatory elements are necessary to obtain fully correct expression.

Developmental regulation of glutamic acid decarboxylase mRNA expression and splicing in the rat striatum by dopamine

Dopamine (DA) promotes the morphological differentiation of striatal GABAergic neurons through D(1) receptor activation and cAMP/PKA signaling. In this study, we investigated the developmental role of DA on the expression of the two GAD(65/67) genes and the alternative splicing of GAD(67) transcripts in the rat striatum. In vivo, embryonic and adult GAD(67) splice variants and GAD(65) transcripts increased until E17 and E19, respectively. Thereafter, the embryonic GAD(67) isoform disappeared, whereas GAD(65) mRNA levels remained unchanged postnatally. The hypothesis that the prenatal ingrowth and functional maturation of nigrostriatal afferents may be responsible for these developmental events through DA-dependent signaling pathways was tested in E17 rat striatal cultures. Treatment with DA and D(1) but not D(2) agonists decreased the ratio of embryonic to adult GAD(67) mRNAs and increased GAD(65) mRNA levels as well as GABA synthesis rates. Our findings demonstrate a distinct developmental switch in the regulation of GAD(65) expression and GAD(67) splicing in the rat striatum which clearly depends upon D(1) receptor but not D(2) signaling. The dopaminergic input thus appears to control the functional differentiation of GABAergic neurons not only by upregulation of expression of the two GAD genes but also by regulating GAD(67) splicing.

Decrease in striatal enkephalin mRNA in mouse models of Huntington's disease

Huntington's disease is a devastating progressive neurodegenerative illness characterized by massive neuronal loss in the striatum. It is caused by the presence of an expanded CAG repeat in the gene encoding huntingtin, a protein of unknown function. We have examined the expression of neurotransmitters and other antigens present in striatal neurons with immunohistochemistry, and the level of expression of mRNAs encoding enkephalin, substance P, and glutamic acid decarboxylases with quantitative in situ hybridization histochemistry, in the striatum of two mouse models of Huntington's disease: transgenic animals expressing exon 1 of the human huntingtin gene with 144 CAG repeats and "knock-in" mice containing a chimeric mouse/human exon 1 with 71 or 94 CAG repeats inserted by homologous targeting. Although the transgenic (but not the knock-in) mice were previously shown to display prominent huntingtin- and ubiquitin-containing nuclear inclusions in striatal neurons, in situ nick translation followed by emulsion autoradiography did not reveal any DNA damage in striatum or cortex in these mice. Immunolabeling for calbindin D 28K, enkephalin, substance P, glutamic acid decarboxylases (M(r) 65,000 or 67,000, GAD65 and GAD67), somatostatin, choline acetyltransferase, parvalbumin, and glial fibrillary acidic protein were remarkably similar in transgenic, knock-in, and wild-type mice. Both transgenic and knock-in mice, however, showed a marked decrease in the level of expression of enkephalin mRNA in striatal neurons without significant decreases in mRNAs encoding substance P, GAD65, or GAD67. The data indicate that decreased expression of enkephalin mRNA may be an early sign of neuronal dysfunction due to the Huntington's disease mutation.

Neurochemical changes in the entopeduncular nucleus and increased oral behavior in rats treated subchronically with clozapine or haloperidol

The purpose of the present experiment was to test the possibility that atypical antipsychotics and classical antipsychotics differentially regulate specific neurochemical processes within the entopeduncular nucleus. For these experiments, rats were administered clozapine (25 mg/kg), haloperidol (1 mg/kg), or Tween-80 (control) daily for 21 days. Dopamine D(1)-receptor binding was assessed with in vitro receptor autoradiographic methods and the mRNAs corresponding to the two forms of glutamate decarboxylase (glutamate decarboxylase-65 and glutamate decarboxylase-67) were analyzed using in situ hybridization histochemical methods. In addition, vacuous chewing movements (VCM) were measured throughout the drug administration period as a functional indicator of drug action and changes in striatal dopamine D(2)-receptor binding were measured as a positive control for D(2)-receptor antagonist properties of haloperidol and clozapine. In agreement with previous reports, haloperidol increased D(2)-receptor binding throughout the striatum while clozapine had a more limited impact on D(2)-receptors. Behavioral analysis revealed that both haloperidol and clozapine enhanced the display of vacuous chewing movements to a similar extent but with a different postinjection latency. In the entopeduncular nucleus, clozapine increased D(1)-receptor binding compared to controls while haloperidol was without effect. With respect to the regulation of GAD mRNAs, haloperidol increased glutamate decarboxylase-65 and glutamate decarboxylase-67 mRNA levels throughout the entopeduncular nucleus. The effects of clozapine were restricted to increases in glutamate decarboxylase-65 mRNA. These studies show that clozapine and haloperidol, both of which increase the occurrence of VCM, differentially modulate the neurochemistry of the entopeduncular nucleus.

Gene expression of the GAD67 and GAD65 isoforms of glutamate decarboxylase is differentially altered in subpopulations of striatal neurons in adult rats lesioned with 6-OHDA as neonates

The levels of mRNAs encoding for the two isoforms of glutamate decarboxylase, GAD65 and GAD67, were measured in subpopulations of striatal neurons in adult rats depleted of dopamine as neonates with 6-OHDA and chronically injected with vehicle or with the dopamine receptor agonists apomorphine or SKF-38393. In adult rats depleted of dopamine as neonates, an increase of GAD65 and GAD67 mRNA levels was measured in the striatum. These changes were paralleled by an increase in preproenkephalin (PPE) and a decrease in preprodynorphin (PPD) mRNA levels. Quantitative analysis at the cellular level indicated that GAD67 mRNA levels were increased in PPE-labeled neurons, whereas GAD65 mRNA levels were increased in PPE-unlabeled neurons. Chronic and systemic injections of apomorphine or SKF-38393 induced further increases in striatal GAD65 and GAD67 mRNA levels. These increases were only detected in the subpopulation of PPE-unlabeled neurons and were paralleled by an increase in PPD mRNA levels. The increases in GAD67, GAD65, and PPD mRNA levels induced by SKF-38393 were abolished by the administration of the D1 receptor antagonist SCH-23390. The present results provide further evidence that GAD67 and GAD65 gene expression is differentially regulated in the two subpopulations of efferent striatal neurons. They also suggest that neonatal depletions in dopamine levels induce alterations of GABA-mediated signaling in the two subpopulations of striatal efferent neurons. We speculate that these alterations are involved in the behavioral particularities exhibited by rats depleted of dopamine as neonates.

Increased striatal expression of glutamate decarboxylase 67 after priming of 6-hydroxydopamine-lesioned rats

Previous single exposure (priming) to a dopamine receptor agonist greatly enhances the contralateral turning behaviour elicited by dopamine D1 receptor agonists in unilaterally 6-hydroxydopamine lesioned rats. In the present study we have investigated the levels of glutamate decarboxylase 67 and glutamate decarboxylase 65 messenger RNA in the striatum of 6-hydroxydopamine-lesioned rats primed with L-3,4-dihydroxyphenylalanine (L-DOPA) and challenged with the D1 receptor agonist SKF 38393, three days thereafter. As previously reported, levels of glutamate decarboxylase 67 messenger RNA increased in the striatum denervated by the 6-hydroxydopamine lesion as compared with the intact one. Striatal glutamate decarboxylase 67 messenger RNA levels, measured three days after priming with L-DOPA (50 mg/kg), further increased in the lesioned striatum while were not modified in the intact one. Administration of SKF 38393 (3 mg/kg) elicited a more intense contralateral turning behaviour in primed than in drug-naive 6-hydroxydopamine-lesioned rats but did not induce any change in striatal glutamate decarboxylase 67 messenger RNA. In contrast, striatal levels of glutamate decarboxylase 65 messenger RNA were not modified by either 6-hydroxydopamine lesions or priming with L-DOPA. The results show that priming with L-DOPA induces long-lasting changes in GABAergic neurons of the 6-hydroxydopamine-lesioned striatum. These changes might play a role in the increased behavioural response of striatal D1 receptors induced by priming.

Two isoforms of glutamate decarboxylase: why?

Adults express two isoforms of glutamate decarboxylase (GAD), GAD67 and GAD65, which are encoded by different independently regulated genes, a situation that differs from that of other neurotransmitters. In this article, J-J. Soghomonian and David Martin review current knowledge on the differences between these two isoforms. Both isoforms are present in most GABA-containing neurones in the CNS, but GAD65 appears to be targeted to membranes and nerve endings, whereas GAD67 is more widely distributed in cells. Both forms can synthesize transmitter GABA, but GAD67 might preferentially synthesize cytoplasmic GABA and GAD65 might preferentially synthesize GABA for vesicular release. Several lines of evidence suggest that the two forms have different roles in the coding of information by GABA-containing neurones.

Dopamine depletion reorganizes projections from the nucleus accumbens and ventral pallidum that mediate opioid-induced motor activity

Motor activity elicited pharmacologically from the nucleus accumbens by the mu-opioid receptor agonist D-Ala-Tyr-Gly-NMePhe-Gly-OH (DAMGO) is augmented in rats sustaining dopamine depletions. GABAergic projections from the nucleus accumbens to ventral pallidum and ventral tegmental area (VTA) are involved because stimulation of GABAB receptors in the VTA (by baclofen) or GABAA receptors in the ventral pallidum (by muscimol) inhibit the motor response induced by the microinjection of DAMGO into the nucleus accumbens. The present study was done to determine which of these projections is mediating the augmented DAMGO-induced motor activity that follows 6-hydroxydopamine lesions of the nucleus accumbens. The inhibition of DAMGO-induced activation by pallidal injections of muscimol was markedly attenuated in lesioned animals, whereas the inhibition by VTA injections with baclofen was greatly enhanced. A similar switch in emphasis from pallidal to mesencephalic efferents was not observed for dopamine-induced motor activity, because muscimol microinjections inhibited the response elicited by dopamine microinjection into the nucleus accumbens in all subjects. The stimulation of mu-opioid receptors in the ventral pallidum also elicits motor activation, and this is blocked by baclofen microinjection into the VTA. However, after dopamine depletion in the nucleus accumbens, baclofen in the VTA was ineffective in blocking the motor response by DAMGO in the ventral pallidum. These data reveal that dopamine depletion in the nucleus accumbens produces a lesion-induced plasticity that alters the effect of mu-opioid receptor stimulation on efferent projections from the nucleus accumbens and ventral pallidum.

c-fos gene expression is induced in a subpopulation of striatal neurons following a single administration of a dopamine D1-receptor agonist in adult rats lesioned with 6-OHDA as neonates

The effects of the dopamine D1 receptor agonist, SKF-38393, on the levels of mRNAs encoding for the proto-oncogene c-fos and the GABA-synthesizing enzyme glutamate decarboxylase (GAD65) were measured by in situ hybridization histochemistry in the striatum of adult rats depleted of dopamine as neonates. c-fos mRNA levels exhibited a prominent increase following the acute systemic administration of SKF-38393 in dopamine-depleted but not in normal rats. Double-labeling in situ hybridization histochemistry using a radioactive c-fos probe and a digoxigenin-labeled preproenkephalin (PPE) cRNA probe indicated that c-fos mRNA levels were increased by SKF-38393 exclusively in a subpopulation of PPE-unlabeled neurons. Dopamine-depleted rats exhibited an increase in GAD65 mRNA levels relative to control rats. Acute administration of SKF-38393 did not alter GAD65 mRNA levels in control or in dopamine-depleted rats. Our results demonstrate that an acute administration of a D1-receptor agonist induces c-fos but not GAD65 gene expression in a subpopulation of presumed striato-nigral/entopeduncular neurons. They also suggest that the D1-dependent behavioral plasticity exhibited by adult rats depleted of dopamine as neonates is not the result of an altered activation of the two subpopulations of striatal efferent neurons.

Serotonergic regulation of neuropeptide and glutamic acid decarboxylase mRNA levels in the rat striatum and globus pallidus: studies with fluoxetine and DOI

The serotonergic regulation of neuropeptide and glutamic acid decarboxylase (GAD) mRNA level in the rat basal ganglia was investigated by determining the effects of chronic treatment with the serotonin uptake blocker fluoxetine and the serotonin 5-HT2 agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrobromide (DOI). Fluoxetine (10 mg/kg) induced a reduction of preproenkephalin and GAD65 mRNA levels in the caudate-putamen and nucleus accumbens core and shell after 5 days of treatment. In addition, GAD65 mRNA levels were reduced in the globus pallidus. These changes appeared to be transient as they were not found after 15 days of fluoxetine treatment. DOI (7 mg/kg), administered for 9 days, induced a decrease of preprodynorphin mRNA levels in the caudate-putamen and the nucleus accumbens core and shell. No regional differentiation in the effects of fluoxetine and DOI was observed. Based on the present results, we propose that an increased 5-HT tone may reduce enkephalin and GABA mRNA levels in striatal regions and in the globus pallidus. Our results further show that preproenkephalin mRNA is not affected by chronic 5-HT2 receptor stimulation, indicating that the fluoxetine-induced decrease in preproenkephalin mRNA levels involves other 5-HT receptors than the 5-HT2 receptor. Preprodynorphin mRNA levels, on the other hand, were found to be reduced after chronic 5-HT2 receptors than stimulation. This observation, together with our previous finding that the 5-HT2 antagonist ritanserin tends to increase preprodynorphin mRNA levels, suggests a 5-HT2-mediated tonic inhibition of preprodynorphin mRNA levels.

Glutamate decarboxylase (GAD65) gene expression is increased by dopamine receptor agonists in a subpopulation of rat striatal neurons

The mRNA levels encoding for the two isoforms of glutamate decarboxylase (GAD65 and GAD67) were measured in the adult rat striatum following systemic administration of dopamine receptor agonists. Double-labeling in situ hybridization histochemistry was used to measure GAD65 or GAD67 mRNA levels in neurons labeled or not with a preproenkephalin (PPE) cRNA probe. Chronic treatment with the D1/D2 dopamine receptor agonist apomorphine or with the D1 dopamine receptor agonist SKF-38393 induced an increase in GAD65 but not GAD67 mRNA levels in different sectors of the striatum. These effects were abolished by pre-administration of the D1 dopamine receptor antagonist SCH-23390. On double-labeled sections, GAD65 mRNA labeling was distributed in neurons labeled and unlabeled with the PPE cRNA probe. About half of all neuronal profiles labeled with the GAD65 cRNA probe were also labeled with the PPE cRNA probe. Quantification of labeling at cellular level demonstrated a significant increase of GAD65 mRNA levels in PPE-unlabeled neurons. On the other hand, no significant changes of GAD65 mRNA levels were detected in PPE-labeled neurons. Our results demonstrate a differential effect of dopamine receptor agonists on striatal GAD65 and GAD67 gene expression. In particular, we show that GAD65 mRNA levels are selectively increased in presumed striato-nigral neurons following treatments with dopamine receptor agonists. These data provide evidence that the GAD65 isoform is preferentially involved in the regulation of GABAergic neurotransmission in striato-nigral neurons.

Structure and alternative promoters of the mouse glutamic acid decarboxylase 67 gene

gamma-Aminobutyric acid is synthesized by glutamic acid decarboxylase (GAD), which has two forms, GAD65 and GAD67. Genomic clones coding mouse GAD67 (mGAD67) have been isolated. The restriction map of the overlapping clones covers a region of more than 45 kb of genomic DNA. The mGAD67 gene contains 16 translated exons in addition to an exon which is preferentially expressed in foetal brain. The rapid amplification of 5'-cDNA ends showed that mGAD67 gene transcripts have two different 5'-untranslated regions. Analysis of the genomic clones encompassing the 5'-exons revealed that the two transcripts arose from a single gene by alternative splicing using two different donor sites and a common acceptor. The exons were found 1.5 and 0.6 kb upstream of exon 1. The corresponding promoter regions of these exons have a number of putative regulatory elements, including Sp1- and Krox-24-binding sites. Analysis of mGAD67 transcripts demonstrated that each of the 5'-untranslated exons was expressed in mouse brain. In contrast, exon 0A, but not exon 0B, was expressed in mouse testis and pancreas. These results suggest that these transcripts may be regulated under the control of independent promoters.