Increase In Glutamate Concentration Research Articles

Enzyme-modified Pt nanoelectrodes for glutamate detection.

We present here a glutamate oxidase (GluOx)-modified platinum (Pt) nanoelectrode with a planar geometry for glutamate detection. The Pt nanoelectrode was characterized using electrochemistry and scanning electron microscopy (SEM). The radius of the Pt nanoelectrode measured using SEM is ∼210 nm. GluOx-modified Pt nanoelectrodes were generated by dip coating GluOx on the Pt nanoelectrode in a solution of 0.9% (wt%) bovine serum albumin (BSA), 0.126% (wt%) glutaraldehyde, and 100 U mL-1 GluOx. An increase in current was observed at +0.7 V vs. Ag/AgCl/1 M KCl with adding increasing concentrations of glutamate. Two-sample t-test results showed that there is a significant difference for current at +0.7 V between the blank and the added lowest glutamate concentration, as well as between adjacent glutamate concentrations, confirming that the increase in current is related to the increased glutamate concentration. The experimental current-concentration curve of glutamate detection fitted well to the theoretical Michaelis-Menten curve. At the low concentration range (50 μM to 200 μM), a linear relationship between the current and glutamate concentration was observed. The Michaelis-Menten constants of Imax and Km were calculated to be 1.093 pA and 0.227 mM, respectively. Biosensor efficiency (the ratio of glutamate sensitivity to H2O2 sensitivity) is calculated to be 57.9%. Enzact (Imax/H2O2 sensitivity, an indicator of the amount of enzyme loaded on the electrode) of the GluOx-modified Pt nanoelectrode is 0.243 mM. We further compared the sensitivity of a GluOx-modified Pt nanoelectrode with a GluOx-modified carbon fiber microelectrode (7 μm diameter and a sensing length of ∼350 μm). Glutamate detection on the GluOx-modified carbon fiber microelectrode fitted well to a Michaelis-Menten like response. Based on the fitting, the GluOx-modified carbon fiber microelectrode exhibited an Imax of 0.689 nA and a Km of 301.2 μM towards glutamate detection. The best linear range of glutamate detection on the GluOx-modified carbon fiber microelectrode is from 50 μM to 150 μM glutamate. The GluOx-modified carbon fiber microelectrode exhibited a higher potential requirement for glutamate detection compared to the GluOx-modified Pt nanoelectrode.

Effects of Dietary Glutamate on the Growth Performance and Antioxidant Capacity of Juvenile Chinese Mitten Crab (Eriocheir sinensis)

In order to explore the effects of glutamate on the growth performance, antioxidant capacity and protein metabolism of juvenile Chinese mitten crab, 0%, 1% and 2% glutamate were supplemented to low protein (30%) and normal protein (35%) diets, respectively. There were 5 parallel tanks in each treatment, and the feeding duration was 8 weeks. The results showed that dietary glutamate did not significantly affect the weight gain of Chinese mitten crab. Diets supplemented with 2% glutamate significantly decreased the crude protein of crabs. The T-AOC of crabs fed the 30% protein diets was significantly lower than crabs fed the 35% protein diets. At 30% protein level, the superoxide dismutase (SOD) activity significantly increased with the increase in glutamate content. Dietary glutamate significantly down-regulated the relative expressions of mTOR, PI3K, S6K1 and 4EBP at 35% protein level. In conclusion, dietary glutamate cannot significantly increase the growth of Chinese mitten crab, but it can improve the antioxidant capacity in Chinese mitten crab under low protein conditions.

Neuronal small extracellular vesicles carrying miR-181c-5p contribute to the pathogenesis of epilepsy by regulating the protein kinase C-δ/glutamate transporter-1 axis in astrocytes.

Information exchange between neurons and astrocytes mediated by extracellular vesicles (EVs) is known to play a key role in the pathogenesis of central nervous system diseases. A key driver of epilepsy is the dysregulation of intersynaptic excitatory neurotransmitters mediated by astrocytes. Thus, we investigated the potential association between neuronal EV microRNAs (miRNAs) and astrocyte glutamate uptake ability in epilepsy. Here, we showed that astrocytes were able to engulf epileptogenic neuronal EVs, inducing a significant increase in the glutamate concentration in the extracellular fluid of astrocytes, which was linked to a decrease in glutamate transporter-1 (GLT-1) protein expression. Using sequencing and gene ontology (GO) functional analysis, miR-181c-5p was found to be the most significantly upregulated miRNA in epileptogenic neuronal EVs and was linked to glutamate metabolism. Moreover, we found that neuronal EV-derived miR-181c-5p interacted with protein kinase C-delta (PKCδ), downregulated PKCδ and GLT-1 protein expression and increased glutamate concentrations in astrocytes both in vitro and in vivo. Our findings demonstrated that epileptogenic neuronal EVs carrying miR-181c-5p decrease the glutamate uptake ability of astrocytes, thus promoting susceptibility to epilepsy.

Metabolic engineering of Shewanella oneidensis to produce glutamate and itaconic acid

Shewanella oneidensis is a gram-negative bacterium known for its unique respiratory capabilities, which allow it to utilize a wide range of electron acceptors, including solid substrates such as electrodes. For a future combination of chemical production and electro-fermentation, the goal of this study was to expand its product spectrum. S. oneidensis was metabolically engineered to optimize its glutamate production and to enable production of itaconic acid. By deleting the glutamate importer gltS for a reduced glutamate uptake and pckA/ptA to redirect the carbon flux towards the TCA cycle, a ∆3 mutant was created. In combination with the plasmid pG2 carrying the glutamate dehydrogenase gdhA and a specific glutamate exporter NCgl1221 A111V, a 72-fold increase in glutamate concentration compared to the wild type was achieved. Along with overexpression of gdhA and NCgl1221 A111V, the deletion of gltS and pckA/ptA as well as the deletion of all three genes (∆3) was examined for their impact on growth and lactate consumption. This showed that the redirection of the carbon flux towards the TCA cycle is possible. Furthermore, we were able to produce itaconic acid for the first time with a S. oneidensis strain. A titer of 7 mM was achieved after 48 h. This suggests that genetic optimization with an expression vector carrying a cis-aconitate decarboxylase (cadA) and a aconitate hydratase (acnB) along with the proven redirection of the carbon flux to the TCA cycle enabled the production of itaconic acid, a valuable platform chemical used in the production of a variety of products.Key points•Heterologous expression of gdhA and NCgl1221_A111V leads to higher glutamate production.•Deletion of ackA/pta redirects carbon flux towards TCA cycle.•Heterologous expression of cadA and acnB enables itaconic acid production.

Protective effects of Embelin in Benzo[α]pyrene induced cognitive and memory impairment in experimental model of mice

Alzheimer's disease (AD) is a neurodegenerative disease that affects the neurons in the hippocampus, resulting in cognitive and memory impairment. The most prominent clinical characteristics of AD are the production of amyloid-beta (Aβ) plaques, neurofibrillary tangles, and neuroinflammation in neurons. It has been proven that embelin (Emb) possesses antioxidant, anti-inflammatory, and neuroprotective properties. Therefore, we assessed the therapeutic potential of Emb in Benzo [α]pyrene (BaP)-induced cognitive impairment in experimental mice. BaP (5 mg/kg, i. p) was given to mice daily for 28 days, and Emb (2.5, 5, and 10 mg/kg, i. p) was given from 14 to 28 days of a protocol. In addition, locomotor activity was evaluated using open-field and spatial working, and non-spatial memory was evaluated using novel object recognition tasks (NORT), Morris water maze (MWM), and Y- maze. At the end of the study, the animal tissue homogenate was used to check biochemicals, neuroinflammation, and neurotransmitter changes. BaP-treated mice showed a significant decline in locomotor activity, learning and memory deficits and augmented oxidative stress (lipid peroxidation, nitrite, and GSH). Further, BaP promoted the release of inflammatory tissue markers, decreased acetylcholine, dopamine, GABA, serotonin, and norepinephrine, and increased glutamate concentration. However, treatment with Emb at dose-dependently prevented biochemical changes, improved antioxidant levels, reduced neuroinflammation, restored neurotransmitter concentration, and inhibited the NF-κB pathway. The current study's finding suggested that Emb improved cognitive functions through antioxidant, anti-inflammatory, and neuroprotective mechanisms and inhibition of acetylcholinesterase (AChE) enzyme activities and Aβ-42 accumulation.

Alterations in glutamate and nitric oxide metabolism in the RdS mice

Aims/Purpose: Nitric oxide (NO) is an essential signalling molecule, with gaseous nature. NO is synthesized by the conversion of L‐arginine to L‐citrulline. This reaction is catalysed by the enzyme nitric oxide synthase (NOS). There are three NOS isoforms, but nNOS reflects most of the production of NO in the retina. Although NO is employed in the retina to maintain ocular function, it has also been related to different visual diseases. Increased levels of NO have been associated with ocular diseases involving increased glutamate concentrations, ischaemia, oxidative stress and inflammation (such as retinitis pigmentosa (RP)). The main purpose of this work was to determine glutamate retinal concentrations at different stages of the retinal degeneration that occurs in the rds mice and to study possible NO metabolism alterations.Methods: Rds mice were treated in accordance with the ARVO statement for the use of animals in ophthalmic and vision research. Mice were sacrificed at different postnatal days (11, 17, 21 and 28). Retinal glutamate concentrations were determined by high pressure liquid chromatography (HPLC). The expression of different enzymes related with NO metabolism (nNOS, guanylate cyclase (GC) and arginase) was determined by histochemistry.Results: Glutamate as well as nNOS was observed to be increased in the retina of rds mice mainly between the peak of rods and cones death. GC was observed to be decreased in the rds mice compared to control ones and no significant changes were observed in arginase expression when we compared rds and control mice.Conclusions: There are alterations in the expression of glutamate, nNOS and GC in rds mice retina compared to control mice. RP is a disease with no effective treatment to date and NO metabolism may be a new target in RP treatment.

Leat-associated seizures the possible role of EAAT2, pyruvate carboxylase and glutamine synthetase

BackgroundDrug-resistant epilepsy is a common condition in patients with brain neoplasms. The pathogenesis of tumor-associated seizures is poorly understood. Among the possible pathogenetic mechanisms, the increase in glutamate concentration has been proposed. Glutamate transporters, glutamine synthetase and pyruvate carboxylase are involved in maintaining the physiological concentration of glutamate in the intersynaptic spaces. In our previous research on angiocentric gliomas, we demonstrated that all tumors lacked the expression of the main glutamate transporter EAAT2, while the expression of glutamine synthetase and pyruvate carboxylase was mostly preserved. MethodsIn the present study, we evaluated the immunohistochemical expression of EAAT2, glutamine synthetase and pyruvate carboxylase in a heterogeneous series of 25 long-term epilepsy-associated tumors (10 dysembryoplastic neuroepithelial tumors, 7 gangliogliomas, 3 subependymal giant cell astrocytomas, 3 rosette forming glioneuronal tumors, 1 diffuse astrocytoma MYB- or MYBL1-altered and 1 angiocentric glioma). In order to evaluate the incidence of variants in the SLC1A2 gene, encoding EAAT2, in a large number of central nervous system tumors we also queried the PedcBioPortal. ResultsEAAT2 protein expression was lost in 9 tumors (36 %: 3 dysembryoplastic neuroepithelial tumors, 1 ganglioglioma, 3 subependymal giant cell astrocytomas, 1 diffuse astrocytoma MYB- or MYBL1-altered and 1 angiocentric glioma). Glutamine synthetase protein expression was completely lost in 2 tumors (8 %; 1 ganglioglioma and 1 diffuse astrocytoma MYB- or MYBL1-altered). All tumors of our series but rosette forming glioneuronal tumors (in which neurocytic cells were negative) were diffusely positive for pyruvate carboxylase. Consultation of the PedcBioPortal revealed that of 2307 pediatric brain tumors of different histotype and grade, 20 (< 1%) had variants in the SLC1A2 gene. Among the SLC1A2-mutated tumors, there were no angiocentric gliomas or other LEATs ConclusionsIn conclusion, unlike angiocentric gliomas where the EAAT2 loss is typical and constant, the current study shows the loss of EAAT2 expression only in a fraction of the LEATs. In these cases, we may hypothesize some possible epileptogenic role of the EAAT2 loss. The retained expression of pyruvate carboxylase may contribute to determining a pathological glutamate excess unopposed by glutamine synthetase that resulted expressed to a variable extent in the majority of the tumors. Furthermore, we can assume that the EAAT2 loss in brain tumors in general and in LEATs in particular is more conceivably epigenetic.

Chinese Tuina remodels the synaptic structure in neuropathic pain rats by downregulating the expression of N-methyl D-aspartate receptor subtype 2B and postsynaptic density protein-95 in the spinal cord dorsal horn.

To investigate whether the Chinese massage system, Tuina, exerts analgesic effects in a rat model of chronic constriction injury (CCI) by remodeling the synaptic structure in the spinal cord dorsal horn (SCDH). Sixty-nine male Sprague-Dawley rats were randomly and evenly divided into the normal group, sham group, CCI group, CCI + Tuina group, CCI + MK-801 [an -methyl D-aspartate receptor subtype 2B (NR2B) antagonist] group, and CCI + MK-801 + Tuina group. The neuropathic pain model was established using CCI with right sciatic nerve ligation. Tuina was administered 4 d after CCI surgery, using pressing manipulation for 10 min, once daily. Motor function was observed with the inclined plate test, and pain behaviors were observed by the Von Frey test and acetone spray test. At 19 d after surgery, the L3-L5 spinal cord segments were removed. Glutamate, interleukin 1β (IL-1β), and tumor necrosis factor-α (TNF-α) levels were detected by enzyme-linked immunosorbent assay. The protein expression levels of NR2B and postsynaptic density protein-95 (PSD-95) were detected by Western blot, and the synaptic structure was observed by transmission electron microscopy (TEM). CCI reduced motor function and caused mechanical and cold allodynia in rats, increased glutamate concentration and TNF-α and IL-1β levels, and increased expression of synapse-related proteins NR2B and PSD-95 in the SCDH. TEM revealed that the synaptic structure of SCDH neurons was altered. Most of these disease-induced changes were reversed by Tuina and intrathecal injection of MK-801 ( < 0.05 or < 0.01). For the majority of experiments, no significant differences were found between the CCI + MK-801 and CCI + MK-801 + Tuina groups. Chinese Tuina can alleviate pain by remodeling the synaptic structure, and NR2B and PSD-95 receptors in the SCDH may be among its targets.

Glutamate Chemical Exchange Saturation Transfer (GluCEST) MRI to Evaluate the Rapid Antidepressant Effects of Ketamine in the Hippocampus of Rat Depression Model.

Ketamine is a quick acting antidepressant drug, and an accurate detection method is lacking. Ketamine's effects in a rat depression model have not previously been well explored using glutamate chemical exchange saturation transfer (GluCEST). To investigate the GluCEST changes of chronic unpredictable mild stress (CUMS) rats after receiving either ketamine or saline injection. Randomized animal model trial. 12 CUMS and 6 Sprague-Dawley rats. Divided into three groups: ketamine (N = 6), saline (N = 6), and control (N = 6). 7.0 T/the sequence is GluCEST and 1 H MR spectroscopy (MRS). The CUMS rats were exposed to different stress factors for 8 weeks. The glutamate concentration in the hippocampus was assessed by the GluCEST,1 H MRS, and the high-performance liquid chromatography (HPLC). The t-test, Mann-Whitney U test, and Pearson's correlation. In depression conditions, GluCEST signals were lower in the bilateral hippocampus than in control group. Thirty minutes after ketamine injection, the GluCEST signals in the bilateral hippocampus were higher compared with the saline group (left: 2.99 ± 0.34 [Control] vs. 2.44 ± 0.20 [Saline] vs. 2.85 ± 0.11 [Ketamine]; right: 2.97 ± 0.28 [Control] vs. 2.49 ± 0.25 [Saline] vs. 2.86 ± 0.19 [Ketamine]). In 1 H MRS, significant changes were only observed in the left hippocampus (2.00 ± 0.16 [Control] vs. 1.81 ± 0.09 [Saline] vs. 2.04 ± 0.14 [Ketamine]). Furthermore, HPLC results showed similar trends to those observed in the GluCEST results (left: 2.32 ± 0.22 [Control] vs. 1.96 ± 0.11 [Saline] vs. 2.18 ± 0.11 [Ketamine]; right: 2.35 ± 0.18 [Control] vs. 1.87 ± 0.16 [Saline] vs. 2.09 ± 0.08 [Ketamine]). GluCEST can sensitively evaluate the ketamine's antidepressant effects by detecting the fast increase in glutamate concentration. 1 TECHNICAL EFFICACY STAGE: 1.

Bisphenol-A Neurotoxic Effects on Basal Forebrain Cholinergic Neurons In Vitro and In Vivo.

The widely used plasticizer bisphenol-A (BPA) is well-known for producing neurodegeneration and cognitive disorders, following acute and long-term exposure. Although some of the BPA actions involved in these effects have been unraveled, they are still incompletely known. Basal forebrain cholinergic neurons (BFCN) regulate memory and learning processes and their selective loss, as observed in Alzheimer's disease and other neurodegenerative diseases, leads to cognitive decline. In order to study the BPA neurotoxic effects on BFCN and the mechanisms through which they are induced, 60-day old Wistar rats were used, and a neuroblastoma cholinergic cell line from the basal forebrain (SN56) was used as a basal forebrain cholinergic neuron model. Acute treatment of rats with BPA (40 µg/kg) induced a more pronounced basal forebrain cholinergic neuronal loss. Exposure to BPA, following 1- or 14-days, produced postsynaptic-density-protein-95 (PSD95), synaptophysin, spinophilin, and N-methyl-D-aspartate-receptor-subunit-1 (NMDAR1) synaptic proteins downregulation, an increase in glutamate content through an increase in glutaminase activity, a downregulation in the vesicular-glutamate-transporter-2 (VGLUT2) and in the WNT/β-Catenin pathway, and cell death in SN56 cells. These toxic effects observed in SN56 cells were mediated by overexpression of histone-deacetylase-2 (HDAC2). These results may help to explain the synaptic plasticity, cognitive dysfunction, and neurodegeneration induced by the plasticizer BPA, which could contribute to their prevention.

Andrographis paniculata protects against brain hippocampus and cerebellum from mercury chloride induced damage by attenuating oxidative stress.

Mercury chloride (HgCl2) is a neurotoxicant that remains a health hazard despite numerous efforts to reduce its levels in the environment. The use of medicinal plants in treating various diseases and other toxic agents has grown popular owing to their effectiveness and affordable rates. Andrographis paniculata (A. paniculata) is a plant with astringent and detoxifying characteristics and is widely used worldwide for its medicinal and antioxidant benefits. This study aimed to investigate the possible protective effects of A. paniculata aqueous extract against HgCl2-induced memory impairment, oxidative stress, and brain damage. Twenty-five adult Wistar rats were randomly divided into five groups: control, HgCl2 0.5 mg/kg, HgCl2+AP 250 mg/kg, HgCl2+AP 500 mg/kg, or HgCl2+Ascorbic acid 200 mg/kg. For 28 days, administrations were given through oral gavage once a day. HgCl2 injection resulted in memory impairment, increased glutamate concentrations in the brain, and the production of oxidative stress. Memory impairment was prevented in A. paniculata-treated groups by balancing the levels of AChE and dopamine activities, which then lowered glutamate concentration, avoided oxidative stress, and improved histopathological alterations in the brain. A. paniculata alleviated HgCl2-induced memory impairment in Wistar rats by increasing the memory index, regulating neurotransmitter levels, and reducing oxidative stress.

Tongqiao Mingmu formula alleviates retinal ganglion cell autophagy through PI3K/AKT/mTOR pathway.

Glaucoma is a severe blindness-causing optic nerve disease characterized by a loss of retinal ganglion cells (RGCs). Previous studies have shown that the Tongqiao Mingmu (TQMM) formula can reduce retinal and optic nerve damage, but its mechanism of action requires further elucidation. In this study, an RGC injury model was prepared using glutamate and then treated with serum-containing drug from the TQMM formula (hereafter called "TQMM formula serum"). In the glutamate-induced RGC injury model, cell viability decreased with an increase in glutamate concentration, whereas the expression of autophagy-related biomarkers LC3 and Belicin-1 increased. An adenovirus transfection experiment revealed that glutamate markedly promoted autophagic flux in RGCs. Notably, TQMM formula serum inhibited the expression of autophagy-related biomarkers, reduced autophagy flux, and reversed the damage caused by glutamate to RGCs. Furthermore, the PI3K inhibitor LY294002 was used to intervene in the RGC autophagy model and was found to suppress the PI3K/AKT/mTOR pathway and enhance RGC autophagy. However, TQMM formula serum could generate an opposite effect and upregulate the expressions of the PI3K/AKT/mTOR pathway genes and proteins. In conclusion, the TQMM formula can prevent glutamate-induced autophagy in RGCs, possibly by activating the PI3K/AKT/mTOR pathway and reducing the expression of autophagy-related biomarkers LC3 and Belicin-1 to attenuate autophagy and maintain RGC viability.

Cardiopulmonary Resuscitation May Not Stop Glutamate Release in the Cerebral Cortex.

Cardiopulmonary resuscitation (CPR) may not be sufficient to halt the progression of brain damage. Using extracellular glutamate concentration as a marker for neuronal damage, we quantitatively evaluated the degree of brain damage during resuscitation without return of spontaneous circulation. Extracellular cerebral glutamate concentration was measured with a microdialysis probe every 2 minutes for 40 minutes after electrical stimulation-induced cardiac arrest without return of spontaneous circulation in Sprague-Dawley rats. The rats were divided into 3 groups (7 per group) according to the treatment received during the 40 minutes observation period: mechanical ventilation without chest compression (group V); mechanical ventilation and chest compression (group VC) and; ventilation, chest compression and brain hypothermia (group VCH). Chest compression (20 min) and hypothermia (40 min) were initiated 6 minutes after the onset of cardiac arrest. Glutamate concentration increased in all groups after cardiac arrest. Although after the onset of chest compression, glutamate concentration showed a significant difference at 2 min and reached the maximum at 6 min (VC group; 284±48 μmol/L vs. V group 398±126 μmol/L, P =0.003), there was no difference toward the end of chest compression (513±61 μmol/L vs. 588±103 μmol/L, P =0.051). In the VCH group, the initial increase in glutamate concentration was suddenly suppressed 2 minutes after the onset of brain hypothermia. CPR alone reduced the progression of brain damage for a limited period but CPR in combination with brain cooling strongly suppressed increases in glutamate levels.

Molecular Mechanism of Tetramethylpyrazine Ameliorating Neuroexcitotoxicity through Activating the PKA/CREB Signaling Pathway.

Background Excitotoxicity plays a key role in nervous system disease and can trigger a critical cascade of reaction which affects cell viability and promotes neuronal death. Tetramethylpyrazine (TMP) reveals its effect in the treatment of neurovascular diseases by antiapoptosis. Recently, there were several studies that demonstrated that the PKA/CREB signaling pathway played a role in neural disease because of excitotoxicity, such as stroke, AD, and Parkinson's disease. In this study, we wanted to focus on the protective effect of tetramethylpyrazine against excitotoxicity through the PKA/CREB signaling pathway. Methods In order to verify whether tetramethylpyrazine can attenuate excitotoxicity through the PKA/CREB signaling pathway, we first used molecular docking technology to predict the combinational strength and mode of tetramethylpyrazine with the proteins in the PKA/CREB signaling pathway. Then, we determined the optimal concentration and time according to the model effect of glutamate (Glu) with different concentration gradients and action times in PC12 cells. After the determination of concentration and time of glutamate in the previous step as the model way, tetramethylpyrazine was added to determine its influence on the cell viability under different doses and times. The TUNEL assay and flow cytometry were used to detect apoptosis. RT-PCR was used to detect the expression of Bcl-2, Bax, PKA, and 5CREB genes, and Western blot was used to detect the expression of these factors. Result Tetramethylpyrazine had a good docking score (-5.312) with PKA and had a moderately docking score (-3.838) with CREB. The CCK-8 cell activity assay showed that the activity of PC12 cells decreased gradually with the increase in glutamate concentration and time, and PC12 cells were treated with 10 mM/L glutamate (the half of the inhibitory concentration (IC50)) for 12 hours. Then, the cell viability increased gradually following the increased concentration of tetramethylpyrazine. When PC12 cells were treated with 0.1 mM/L tetramethylpyrazine, the cell viability was increased significantly compared with the control group (P < 0.05). The TUNEL assay and flow cytometry also showed that tetramethylpyrazine could decrease the apoptosis induced by glutamate. In the result of RT-PCR, the transcriptional levels of Bcl-2, PKA, and CREB were increased and Bax was decreased. Meanwhile, Western blot showed that expression levels of Bcl-2, PKA, CREB, and p-CREB were increased and Bax was decreased. Conclusions This study provided evidence that tetramethylpyrazine can protect against apoptosis caused by neuroexcitotoxicity and the protective mechanism is closely related to the activation of the PKA/CREB signaling pathway.

36.5 A Systemic Review of 1H-MRS Studies Investigating Brain Glutamate Level on High-Risk Adolescents for Psychosis

The glutamate hypothesis of schizophrenia highlights disturbances in the N-methyl-D-aspartate receptor (NMDAR) glutamate-gated cation channel, and there have been increasing interests in this receptor as a new target for drugs. A large body of studies reported increased glutamate concentrations in patients with schizophrenia specifically in the frontal region; however, there have been limited reports in high-risk adolescents for psychosis (HR).

Systemic oxytocin increases glutamate efflux in the nucleus accumbens core of cocaine-experienced male and female rats but only increases dopamine efflux in males

Oxytocin attenuates cocaine-seeking when administered both systemically and directly into the nucleus accumbens core. This effect is blocked by intra-accumbens antagonism of mGlu2/3 and, together with our finding that intra-accumbens oxytocin increases glutamate concentrations in this brain region, indicates that pre-synaptic regulation of glutamate release by oxytocin influences cocaine relapse. However, mGlu2/3 receptors also regulate dopamine release in the nucleus accumbens. Here we aimed to determine whether systemic oxytocin increases glutamate and dopamine concentrations in the nucleus accumbens core of cocaine-experienced and cocaine-naïve male and female rats. A subset of rats self-administered cocaine (0.5 mg/kg/infusion) and then underwent extinction training for 2–3 weeks. Rats were implanted with microdialysis probes in the accumbens core and samples were collected for a baseline period, and following saline (1 mL/kg), and oxytocin (1 mg/kg, IP) injections. Locomotion was assessed during microdialysis. In cocaine-experienced rats, oxytocin increased glutamate concentrations in the accumbens core to the same extent in males and females but only increased dopamine concentrations in male rats. Oxytocin did not alter glutamate levels in cocaine-naïve rats. Oxytocin did not produce sedation. These results extend previous findings that systemic oxytocin increases nucleus accumbens dopamine in a sex-specific manner in cocaine-experienced rats. These data are the first to find that systemic oxytocin increases nucleus accumbens glutamate after cocaine experience, providing a mechanism of action by which oxytocin attenuates the reinstatement of cocaine seeking in both male and female rats.

Glutamate connectivity associations converge upon the salience network in schizophrenia and healthy controls

Alterations in cortical inter-areal functional connectivity, and aberrant glutamatergic signalling are implicated in the pathophysiology of schizophrenia but the relationship between the two is unclear. We used multimodal imaging to identify areas of convergence between the two systems. Two separate cohorts were examined, comprising 195 participants in total. All participants received resting state functional MRI to characterise functional brain networks and proton magnetic resonance spectroscopy (1H-MRS) to measure glutamate concentrations in the frontal cortex. Study A investigated the relationship between frontal cortex glutamate concentrations and network connectivity in individuals with schizophrenia and healthy controls. Study B also used 1H-MRS, and scanned individuals with schizophrenia and healthy controls before and after a challenge with the glutamatergic modulator riluzole, to investigate the relationship between changes in glutamate concentrations and changes in network connectivity. In both studies the network based statistic was used to probe associations between glutamate and connectivity, and glutamate associated networks were then characterised in terms of their overlap with canonical functional networks. Study A involved 76 individuals with schizophrenia and 82 controls, and identified a functional network negatively associated with glutamate concentrations that was concentrated within the salience network (p < 0.05) and did not differ significantly between patients and controls (p > 0.85). Study B involved 19 individuals with schizophrenia and 17 controls and found that increases in glutamate concentrations induced by riluzole were linked to increases in connectivity localised to the salience network (p < 0.05), and the relationship did not differ between patients and controls (p > 0.4). Frontal cortex glutamate concentrations are associated with inter-areal functional connectivity of a network that localises to the salience network. Changes in network connectivity in response to glutamate modulation show an opposite effect compared to the relationship observed at baseline, which may complicate pharmacological attempts to simultaneously correct glutamatergic and connectivity aberrations.

Angiocentric glioma-associated seizures: The possible role of EATT2, pyruvate carboxylase and glutamine synthetase

PurposeOur purpose was to better understand the pathogenesis of seizures associated with angiocentric glioma. Angiocentric glioma is an indolent and rare low-grade glioma. Its typical clinical presentation is with epileptic seizures. The pathogenesis of tumor-associated seizures is poorly understood. Among the possible pathomechanisms, the increased neurotoxic concentrations of the glutamate has been proposed. Glutamate transporters, pyruvate carboxylase and glutamine synthetase are involved in maintaining the physiological concentration of glutamate in the inter synaptic spaces. MethodsWe evaluated the immunohistochemical expression of EAAT2 (the most important glutamate transporter), pyruvate carboxylase and glutamine synthetase in 17 angiocentric gliomas. ResultsEAAT2 was never expressed (0%) in the neoplastic cells in none of the cases studied. Pyruvate carboxylase was expressed in the cytoplasm of the neoplastic cells in 16/17 cases (94 %). Glutamine synthetase was expressed in the cytoplasm of the neoplastic cells in 15/17 cases (88 %). ConclusionThe net result of this enzymatic expression, in particular considering the loss of EAAT2, could be an increased glutamate concentration in the synaptic clef, which might increase local network excitability initially involving intratumoral neurons. The observation that the angiocentric glioma-associated epilepsy might be at least in part related to EAAT2 deficiency opens up interesting therapeutic perspectives.

Disturbance of the Glutamate-Glutamine Cycle, Secondary to Hepatic Damage, Compromises Memory Function.

Glutamate fulfils many vital functions both at a peripheral level and in the central nervous system (CNS). However, hyperammonemia and hepatic failure induce alterations in glutamatergic neurotransmission, which may be the main cause of hepatic encephalopathy (HE), an imbalance which may explain damage to both learning and memory. Cognitive and motor alterations in hyperammonemia may be caused by a deregulation of the glutamate-glutamine cycle, particularly in astrocytes, due to the blocking of the glutamate excitatory amino-acid transporters 1 and 2 (EAAT1, EAAT2). Excess extracellular glutamate triggers mechanisms involving astrocyte-mediated inflammation, including the release of Ca2+-dependent glutamate from astrocytes, the appearance of excitotoxicity, the formation of reactive oxygen species (ROS), and cell damage. Glutamate re-uptake not only prevents excitotoxicity, but also acts as a vital component in synaptic plasticity and function. The present review outlines the evidence of the relationship between hepatic damage, such as that occurring in HE and hyperammonemia, and changes in glutamine synthetase function, which increase glutamate concentrations in the CNS. These conditions produce dysfunction in neuronal communication. The present review also includes data indicating that hyperammonemia is related to the release of a high level of pro-inflammatory factors, such as interleukin-6, by astrocytes. This neuroinflammatory condition alters the function of the membrane receptors, such as N-methyl-D-aspartate (NMDA), (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) AMPA, and γ-aminobutyric acid (GABA), thus affecting learning and spatial memory. Data indicates that learning and spatial memory, as well as discriminatory or other information acquisition processes in the CNS, are damaged by the appearance of hyperammonemia and, moreover, are associated with a reduction in the production of cyclic guanosine monophosphate (cGMP). Therefore, increased levels of pharmacologically controlled cGMP may be used as a therapeutic tool for improving learning and memory in patients with HE, hyperammonemia, cerebral oedema, or reduced intellectual capacity.

The razor clam Sinonovacula constricta uses the strategy of conversion of toxic ammonia to glutamine in response to high environmental ammonia exposure.

High ammonia can inhibit the survival and growth, and even cause mortality of razor clam (S. constricta). The accumulation of ammonia to lethal concentrations in some invertebrates may be partially prevented by converting some of the ammonia into glutamine (Gln). Glutamine dehydrogenase (GDH) and glutamine synthetase (GS) have been widely implicated a central role in response to ammonia stress. However, the molecular and physiological response of GDH and GS to ammonia alterations has not yet been determined in clams. To investigate the possible participatory role of GDH and GS genes in altered ammonia conditions, we have cloned their gene sequences and examined the mRNA expression and western blotting under ammonia exposure in S. constricta (ScGDH and ScGS), and detected the levels of GS and GDH, and the content of glutamate (Glu) and Gln. The full-length cDNA of ScGDH was 3924bp, with a 1629bp open reading frame (ORF) encoding a 542 amino-acid polypeptide. The complete cDNA sequence for ScGS had 2739bp with an ORF of 1110bp encoding 369 amino acids. To investigate ammonia detoxification strategies, the clams were exposed to ammonia for 96h at four different concentrations (0, 100, 140, and 180mg/L). Exposure to ammonia resulted in a significant increase of glutamate concentration and Gln in the haemocytes. GDH activity, GDH relative mRNA and protein expression, GS activity, GS relative mRNA and protein expression increased significantly and showed a pronounced time and dosage interaction in the liver. The results suggested that the protective strategies of Gln formation existed in S. constricta, which could convert ammonia to non- or less toxic nitrogenous compounds on the exposure of ammonia. Glutamate content in the haemocytes increased significantly, which is to ensure sufficient Glu to meet the needs for GS to catalyze the conversion of ammonia to Gln. We proposed that the induction of Glu synthesis-related genes and the subsequent formation of the active protein occurred in preparation for the increased capacity of the body to convert ammonia, into Gln. The results of this study suggested that GDH and GS play an important role in the synthesis of Gln, emphasizing, the protective strategies of Gln formation in S. constricta convert ammonia to nontoxic or less toxic nitrogenous compounds upon exposure to ammonia.