Glutamate Γ-aminobutyric Acid Research Articles

Tropisetron, an Antiemetic Drug, Exerts an Anti-Epileptic Effect Through the Activation of α7nAChRs in a Rat Model of Temporal Lobe Epilepsy.

Temporal lobe epilepsy (TLE), a prevalent chronic neurological disorder, affects millions of individuals and is often resistant to anti-epileptic drugs. Increasing evidence has shown that acetylcholine (ACh) and cholinergic neurotransmission play a role in the pathophysiology of epilepsy. Tropisetron, an antiemetic drug used for chemotherapy in clinic, has displayed potential in the treatment of Alzheimer's disease, depression, and schizophrenia in animal models. However, as a partial agonist of α7 nicotinic acetylcholine receptors (α7nAChRs), whether tropisetron possesses the therapeutic potential for TLE has not yet been determined. In this study, tropisetron was intraperitoneally injected into pilocarpine-induced epileptic rats for 3 weeks. Alpha-bungarotoxin (α-bgt), a specific α7nAChR antagonist, was applied to investigate the mechanism of tropisetron. Rats were assessed for spontaneous recurrent seizures (SRS) and cognitive function using video surveillance and Morris's water maze testing. Hippocampal impairment and synaptic structure were evaluated by Nissl staining, immunohistochemistry, and Golgi staining. Additionally, the levels of glutamate, γ-aminobutyric acid (GABA), ACh, α7nAChRs, neuroinflammatory cytokines, glucocorticoids and their receptors, as well as synapse-associated protein (F-actin, cofilin-1) were quantified. The results showed that tropisetron significantly reduced SRS, improved cognitive function, alleviated hippocampal sclerosis, and concurrently suppressed synaptic remodeling and the m6A modification of cofilin-1 in TLE rats. Furthermore, tropisetron lowered glutamate levels without affecting GABA levels, reduced neuroinflammation, and increased ACh levels and α7nAChR expression in the hippocampi of TLE rats. The effects of tropisetron treatment were counteracted by α-bgt. In summary, these findings indicate that tropisetron exhibits an anti-epileptic effect and provides neuroprotection in TLE rats through the activation of α7nAChRs. The potential mechanism may involve the reduction of glutamate levels, enhancement of cholinergic transmission, and suppression of synaptic remodeling. Consequently, the present study not only highlights the potential of tropisetron as an anti-epileptic drug but also identifies α7nAChRs as a promising therapeutic target for the treatment of TLE.

Genetic predisposition of suicidal behavior: variants in GRIN2B, GABRG2, and ODC1 genes in attempted and completed suicide in two Balkan populations

AbstractCompleted suicide accounts for over 700,000 deaths worldwide annually, while attempted suicide is 20 times more frequent. Genetic background is an important factor contributing to suicidal behavior, including candidate genes in glutamate, γ-aminobutyric acid (GABA), and polyamine systems. Our aim was to differentiate genetic predispositions underlying different types of suicidal behavior, attempted and completed suicide, in two Balkan populations. Analysis of variants in the genes GRIN2B (rs2268115 and rs220557), GABRG2 (rs424740), and ODC1 (rs1049500 and rs2302614) was performed on a study sample including 173 suicide attempters with comorbid psychiatric disorders, 216 non-suicidal psychiatric patients and 172 healthy controls from Serbia, and 333 suicide completers and 356 non-suicidal autopsy controls from Slovenia. CA genotype of rs220557 in GRIN2B gene increased the risk for completed suicide (P = 0.021), and violent suicide (P = 0.037), compared to controls. In ODC1 gene, CA genotype of rs2302614 decreased the risk for completed suicide compared to suicide attempt (P = 0.012). Marginally, AC haplotype for variants rs1049500-rs2302614 in ODC1 gene decreased the risk for completed suicide compared to suicide attempt (P = 0.052). Specific genetic variants of glutamate and polyamine systems are differently distributed among diverse suicidal phenotypes, providing further information on the implication of these systems in suicidality.

Abstract 1507: Involvement of GABAergic signaling in enhanced tumor cell invasion in a mechanically dynamic tumor microenvironment

Abstract Metastasis is a major contributor to cancer morbidity and mortality. However, studying this complex, multi-step, multi-organ process is challenging. There is a pressing need to dissect the contributions of the tumor microenvironment (TME) on this process in a controlled and precise manner. Fortunately, the utilization of microfluidic “organs-on-chips” (OOC) in cancer research is facilitating such investigations. Moreover, by combining organoids and organs-on-chips we can enhance the progress of these studies in a patient specific manner. In this study, we have developed a cancer-on-chip model aimed at investigating early metastatic spread within the colon milieu. To achieve this, we employ colorectal cancer (CRC) cell lines as well as patient-derived CRC organoids chosen from our biorepository to encompass diverse representations across race/ethnicity, sex, and mutational profiles. The tumor cells are introduced into the upper chamber of the OOC model, while human microvascular endothelial cells (HIMECs) are introduced into the lower chamber to establish a tube-like structure resembling a blood vessel. These two chambers are separated by a porous membrane, and the chip is flanked by vacuum chambers to introduce stretch-like motions, simulating peristalsis in the gastrointestinal track. Creating a mechanically dynamic microenvironment facilitates the exploration of neurotransmitters and their impact on tumor cell behavior. Recent studies have suggested that tumor cells may exploit physiological processes, such as neurotransmitter signaling, to their benefit. By utilizing mass spectrometry-based metabolomics we detected dynamic and patient organoid-specific changes in neurotransmitter levels (i.e., serotonin, aspartate, glutamate, γ-aminobutyric acid (GABA)) in the effluent of our CRC-on-chip model. Coupled with live-cell imaging, we discovered tumor cell-derived GABA, a major inhibitory neurotransmitter, serves as an energy source for supporting tumor cell intravasation. This finding was most pronounced in KRAS-mutant tumor cells and further supported by analysis of CRC patient samples from The Cancer Genome Atlas (TCGA) database. We were able to reverse the GABA-mediated invasion effect by inhibiting 4-aminobutyrate aminotransferase (ABAT), the enzyme responsible for GABA catabolism. In summary, our cancer-on-chip model holds promise for exploring various aspects of the metastatic process and uncovering potential therapeutic targets, such as neurotransmitters. Citation Format: Carly Strelez, Rachel Perez, John S. Chlystek, Christopher Cherry, Bethany Haliday, Ah Young Yoon, Curran Shah, Ren X. Sun, Roy Lau, Aaron Schatz, Josh Neman, Heinz Josef-Lenz, Jonathan Katz, Shannon M. Mumenthaler. Involvement of GABAergic signaling in enhanced tumor cell invasion in a mechanically dynamic tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1507.

Neurotoxicity of the Cu(OH)2 Nanopesticide through Perturbing Multiple Neurotransmitter Pathways in Developing Zebrafish.

The copper hydroxide [Cu(OH)2] nanopesticide is an emerging agricultural chemical that can negatively impact aquatic organisms. This study evaluated the behavioral changes of zebrafish larvae exposed to the Cu(OH)2 nanopesticide and assessed its potential to induce neurotoxicity. Metabolomic and transcriptomic profiling was also conducted to uncover the molecular mechanisms related to potential neurotoxicity. The Cu(OH)2 nanopesticide at 100 μg/L induced zebrafish hypoactivity, dark avoidance, and response to the light stimulus, suggestive of neurotoxic effects. Altered neurotransmitter-related pathways (serotoninergic, dopaminergic, glutamatergic, GABAergic) and reduction of serotonin (5-HT), dopamine (DA), glutamate (GLU), γ-aminobutyric acid (GABA), and several of their precursors and metabolites were noted following metabolomic and transcriptomic analyses. Differentially expressed genes (DEGs) were associated with the synthesis, transport, receptor binding, and metabolism of 5-HT, DA, GLU, and GABA. Transcripts (or protein levels) related to neurotransmitter receptors for 5-HT, DA, GLU, and GABA and enzymes for the synthesis of GLU and GABA were downregulated. Effects on both the glutamatergic and GABAergic pathways in zebrafish were specific to the nanopesticide and differed from those in fish exposed to copper ions. Taken together, the Cu(OH)2 nanopesticide induced developmental neurotoxicity in zebrafish by inhibiting several neurotransmitter-related pathways. This study presented a model for Cu(OH)2 nanopesticide-induced neurotoxicity in developing zebrafish that can inform ecological risk assessments.

Role of ON and OFF Visual Pathways in Rod- and Cone-Driven Flicker Responses.

To evaluate the effects of various retinal neurotransmitters on temporal resolution, particularly, on the Critical Flicker Fusion Frequency (CFF), which has been previously applied in ophthalmic pathophysiologic research. A binocular physiologic electroretinogram was performed on adult mice. Animals in the control group were injected in the right eye with 1 μL of phosphate-buffered saline (PBS). Animals in the experimental group were injected in the left eye with 1 μL of PBS and in the right eye with 1 μL of PBS to which different molecules were added: 2-amino-4-phosphonobutyric acid (APB), Glutamate, γ-aminobutyric acid (GABA), 6,7-dinitroquinoxaline-2,3-dione (DNQX), Bicuculline, Glycine, and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). Initially, rod response was recorded and later the cone response. APB suppressed the rod-driven, but not the cone-driven flicker response. The other agents severely affected the lower flickering frequency response amplitude, in particular, at 3 Hz. The threshold of CFF was lowered from 50 Hz to 40 Hz after applying APB, Glycine, and HEPES. GABA remarkably enhanced rod-driven and cone-driven flicker response at 3 Hz, whereas Glutamate and GABA/Glutamate only did in rod-driven flicker response. Both ON and OFF visual pathways were implied in cone-driven response, but only the ON visual pathway appears to play a relevant role in rod-driven flicker response. Flicker response seems to be enhanced by horizontal cells both in rod-driven and cone-driven response. In addition, due to the greater sensitivity of the flicker at low frequencies, it is suggested that pathophysiological studies should be carried out at said frequencies.

In vivo evidence of differential frontal cortex metabolic abnormalities in progressive and relapsing‐remitting multiple sclerosis

The pathophysiology of progressive multiple sclerosis remains elusive, significantly limiting available disease-modifying therapies. Proton MRS (1 H-MRS) enables in vivo measurement of small molecules implicated in multiple sclerosis, but its application to key metabolites glutamate, γ-aminobutyric acid (GABA), and glutathione has been sparse. We employed, at 7 T, a previously validated 1 H-MRS protocol to measure glutamate, GABA, and glutathione, as well as glutamine, N-acetyl aspartate, choline, and myoinositol, in the frontal cortex of individuals with relapsing-remitting (N = 26) or progressive (N = 21) multiple sclerosis or healthy control adults (N = 25) in a cross-sectional analysis. Only individuals with progressive multiple sclerosis demonstrated reduced glutamate (F2,65 = 3.424, p = 0.04; 12.40 ± 0.62 mM versus control 13.17 ± 0.95 mM, p = 0.03) but not glutamine (F2,65 = 0.352, p = 0.7; 4.71 ± 0.35 mM versus control 4.84 ± 0.42 mM), reduced GABA (F2,65 = 3.89, p = 0.03; 1.29 ± 0.23 mM versus control 1.47 ± 0.25 mM, p = 0.05), and possibly reduced glutathione (F2,65 = 0.352, p = 0.056; 2.23 ± 0.46 mM versus control 2.51 ± 0.48 mM, p < 0.1). As a group, multiple sclerosis patients demonstrated significant negative correlations between disease duration and glutamate or GABA (ρ= -0.4, p = 0.02) but not glutamine or glutathione. Alone, only relapsing-remitting multiple sclerosis patients exhibited a significant negative correlation between disease duration and GABA (ρ = -0.5, p = 0.03). Taken together, these results indicate that frontal cortex metabolism is differentially disturbed in progressive and relapsing-remitting multiple sclerosis.

Metabolomic signature of the Dravet syndrome: A genetic mouse model study.

Alterations in metabolic homeostasis can contribute to neuronal hyperexcitability and seizure susceptibility. Although the pivotal role of impaired bioenergetics is obvious in metabolic epilepsies, there is a gap of knowledge regarding secondary changes in metabolite patterns as a result of genetic Scn1a deficiency and ketogenic diet in the Dravet syndrome. A comprehensive untargeted metabolomics analysis, along with assessment of epileptiform activity and behavioral tests, was completed in a Dravet mouse model. Data sets were compared between animals on a control and a ketogenic diet, and metabolic alterations associated with Dravet mice phenotype and ketogenic diet were identified. Hippocampal metabolomic data revealed complex alterations in energy metabolism with an effect of the genotype on concentrations of glucose and several glycolysis and tricarboxylic acid (TCA) cycle intermediates. Although low glucose, lactate, malate, and citrate concentrations became evident, the increase of several intermediates suggested a genotype-associated activation of catabolic processes with enhanced glycogenolysis and glycolysis. Moreover, we observed an impact on the glutamate/γ-aminobutyric acid (GABA)-glutamine cycle with reduced levels of all components along with a shift toward an increased GABA-to-glutamate ratio. Further alterations comprised a reduction in hippocampal levels of noradrenaline, corticosterone, and of two bile acids. Considering that energy depletion can predominantly compromise the function of GABAergic interneurons, the changes in energy metabolism may contribute to seizure susceptibility and ictogenesis. They may also explain the therapeutic potential of the ketogenic diet, which aims to shift energy metabolism toward a more fat-based energy supply. Conversely, the increased GABA-to-glutamate ratio might serve as an endogenous compensatory mechanism, which can be further supported by GABAergic drugs, representing the mainstay of therapeutic management of Dravet syndrome. In view of a possible neuroprotective function of bile acids, it might be of interest to explore a possible therapeutic potential of bile acid-mediated therapies, already in discussion for neurodegenerative disorders.

Cytisine Exerts an Anti-Epileptic Effect via α7nAChRs in a Rat Model of Temporal Lobe Epilepsy.

Background and Purpose: Temporal lobe epilepsy (TLE) is a common chronic neurological disease that is often invulnerable to anti-epileptic drugs. Increasing data have demonstrated that acetylcholine (ACh) and cholinergic neurotransmission are involved in the pathophysiology of epilepsy. Cytisine, a full agonist of α7 nicotinic acetylcholine receptors (α7nAChRs) and a partial agonist of α4β2nAChRs, has been widely applied for smoking cessation and has shown neuroprotection in neurological diseases. However, whether cytisine plays a role in treating TLE has not yet been determined. Experimental Approach: In this study, cytisine was injected intraperitoneally into pilocarpine-induced epileptic rats for three weeks. Alpha-bungarotoxin (α-bgt), a specific α7nAChR antagonist, was used to evaluate the mechanism of action of cytisine. Rats were assayed for the occurrence of seizures and cognitive function by video surveillance and Morris water maze. Hippocampal injuries and synaptic structure were assessed by Nissl staining and Golgi staining. Furthermore, levels of glutamate, γ-aminobutyric acid (GABA), ACh, and α7nAChRs were measured. Results: Cytisine significantly reduced seizures and hippocampal damage while improving cognition and inhibiting synaptic remodeling in TLE rats. Additionally, cytisine decreased glutamate levels without altering GABA levels, and increased ACh levels and α7nAChR expression in the hippocampi of TLE rats. α-bgt antagonized the above-mentioned effects of cytisine treatment. Conclusion and Implications: Taken together, these findings indicate that cytisine exerted an anti-epileptic and neuroprotective effect in TLE rats via activation of α7nAChRs, which was associated with a decrease in glutamate levels, inhibition of synaptic remodeling, and improvement of cholinergic transmission in the hippocampus. Hence, our findings not only suggest that cytisine represents a promising anti-epileptic drug, but provides evidence of α7nAChRs as a novel therapeutic target for TLE.

Effects of brainstem lesions on amino acid levels in the rat cochlear nucleus

There is evidence for glutamate, γ-amino butyric acid (GABA), and glycine as neurotransmitters of centrifugal pathways to the cochlear nucleus, but the quantitative extent of their contributions to amino acid neurotransmission in cochlear nucleus regions has not been known. We used microdissection of freeze-dried tissue sections of rat cochlear nucleus, with mapping of sample locations, combined with a high performance liquid chromatography (HPLC) assay, to measure amino acid levels in cochlear nucleus subregions of rats with unilateral lesions of centrifugal pathways to the cochlear nucleus. In rats with lesions transecting all or almost all pathways to the cochlear nucleus from brain stem regions, GABA, aspartate, and glutamate levels were reduced, compared to contralateral values, in almost all ipsilateral cochlear nucleus regions. The largest reductions, in dorsal (DCN), anteroventral (AVCN), and posteroventral (PVCN) cochlear nucleus regions, approached 50% for GABA, 40% for aspartate, and 30% for glutamate. In contrast, glutamine and taurine levels were typically higher in lesioned-side cochlear nucleus regions than contralaterally. Effects on glycine levels were mixed but usually included increased lesioned-side values compared to contralateral, probably reflecting a balance between increases during protein breakdown and decreases of free glycine in transected pathways. More limited lesions transecting just dorsal pathways showed much less effect on amino acid levels. Lesion of the ipsilateral trapezoid body connection plus ipsilateral superior olivary nuclei resulted in decreases of GABA, aspartate, and glutamate levels especially in ventral cochlear nucleus regions. No clear contralateral effects of this lesion could be shown. The results most strongly support centrifugal GABAergic pathways to the cochlear nucleus, providing almost half of GABAergic neurotransmission in most regions. Our results support and extend previously published measurements of lesion effects on GABA uptake and release in cochlear nucleus subdivisions.

Towards screening the neurotoxicity of chemicals through feces after exposure to methylmercury or inorganic mercury in rats: A combined study using gut microbiome, metabolomics and metallomics

Mercury (Hg) is one of the chemicals that bring serious adverse effects to the environment and human beings. Methylmercury (MeHg) is a neurotoxin while inorganic Hg (IHg) is not. Early screening of the neurotoxicity of chemicals may help reduce the occurrence of neurological disorders by minimizing chemical exposure. This work proposed the combined application of gut microbiome, metabolomics and metallomics to differentiate the neurotoxicity between MeHg and IHg in rats. It was found that MeHg caused down-regulated Bacteroides, Firmicutes and Proteobacteria, and up-regulated Actinobacteria and Verrucomicrobia at phylum level, while MeHg caused up-regulated Verrucomicrobiaceae, Desulfovibrionaceae, Helicobacteraceae, Lachnospiraceae and down-regulated Rikenellaceae, Erysipelotrichaceae, Sutterellaceae, Anaeroplasmataceae and Coriobacteriaceae in feces than IHg did at family level; Besides, MeHg brought metabolites change in activation of gut-brain axis pathway than IHg did, such as Glutamate, γ-aminobutyric acid (GABA), Dopamine (DA) and Tryptophan. These differences between MeHg and IHg were further confirmed by the distribution of Hg in the intestine, as well as the level of brain-derived neurotrophic factor (BDNF) in the intestine, brain and serum. Therefore, the difference of toxicity between MeHg and IHg can be well distinguished through feces after exposure for only 24 h, which may be used for the screening of neurotoxicity of other chemicals.

Sex differences in the neurochemistry of frontal cortex: Impact of early life stress.

Traumatic events during early life have been linked with later life psychopathology. To understand this risk factor, researchers have studied the effects of prenatal and postnatal early life stress on neurochemical changes. Here we review the rodent literature on sex differences and sex-specific impact of early life stress on frontal cortex neurochemistry. This region is implicated in regulating motivation and emotion, which are often disrupted in psychological disorders. The prefrontal cortex (PFC) in particular is one of the last brain regions to develop, and there are sex differences in the rate of this development. To draw direct comparisons between sexes, our review of the literature was restricted to studies where the effects of prenatal or postnatal stress had been described in male and female littermates. This literature included research describing glutamate, γ-amino butyric acid (GABA), corticosteroids, monoamines, and cannabinoids. We found that sex-dependent effects of stress are mediated by the age at which stress is experienced, age at test, and type of stress endured. More research is required, particularly into the effects of adolescent stress on male and female littermates. We hope that a greater understanding of sex-specific susceptibilities in response to stress across development will help to uncover risk factors for psychological disorders in vulnerable populations.

Excitatory and inhibitory responses in the brain to experimental pain: A systematic review of MR spectroscopy studies

BackgroundThe role of the brain in processing pain has been extensively investigated using various functional imaging techniques coupled with well controlled noxious stimuli. Studies applying experimental pain have also used proton magnetic resonance spectroscopy (1H-MRS). The advantage of MRS compared to other techniques is the capacity to non-invasively examine metabolites involved in neurotransmission of pain, including glutamate, γ-aminobutyric acid (GABA), glutamate ​+ ​glutamine (Glx), and glutamine. ObjectiveTo systematically review MRS studies used in the context of studying experimental pain in healthy human participants. Data sourcesPubMed, Ovid Medline, and Embase databases were searched using pre-specified search terms. Eligibility criteriaStudies investigating glutamate, GABA, Glx and/or glutamine in relation to experimental pain (e.g., heat) in healthy participants via MRS. Appraisal criteriaEach study was evaluated with a modified quality criterion (used in previous imaging systematic reviews) as well as a risk of bias assessment. ResultsFrom 5275 studies, 14 met the selection criteria. Studies fell into two general categories, those examining changes in metabolites triggered by noxious stimulation or examining the relationship between sensitivity to pain and resting metabolite levels. In five (out of ten) studies, glutamate, Glx and/or glutamine increased significantly in response to experimental pain (compared to baseline) in three different brain areas. To date, there is no evidence to suggest Glx, glutamate or glutamine levels decrease, suggesting an overall effect in favour of increased excitation to pain. In addition to no changes, both increases and decreases were reported for levels of GABA+ (=GABA ​+ ​macromolecules). A positive correlation between pain sensitivity and resting glutamate and Glx levels were reported across three studies (out of three). Further research is needed to examine the relationship of GABA+ and pain sensitivity. LimitationsA major limitation of our review was a limited number of studies that used MRS to examine experimental pain. In light of this and major differences in study design, we did not attempt to aggregate results in a meta-analysis. As for the studies we reviewed, there was a limited number of brain areas were examined by studies included in our review. Moreover, the majority of studies included lacked an adequate control condition (i.e., non-noxious stimulation) or blinding, which represent a major source of potential bias. ConclusionMRS represents a promising tool to examine the brain in pain, functionally, and at rest with support for increased glutamate, glutamine and Glx levels in relation to pain. ImplicationsResting and functional MRS should be viewed as complementary to existing neuroimaging techniques, and serve to investigate the brain in pain.Systematic review registration number- CRD42018112917.

Pyridox(am)ine 5′-phosphate oxidase (PNPO) deficiency in zebrafish results in fatal seizures and metabolic aberrations

Pyridox(am)ine 5′-phosphate oxidase (PNPO) catalyzes oxidation of pyridoxine 5′-phosphate (PNP) and pyridoxamine 5′-phosphate (PMP) to pyridoxal 5′-phosphate (PLP), the active form of vitamin B6. PNPO deficiency results in neonatal/infantile seizures and neurodevelopmental delay. To gain insight into this disorder we generated Pnpo deficient (pnpo−/−) zebrafish (CRISPR/Cas9 gene editing). Locomotion analysis showed that pnpo−/− zebrafish develop seizures resulting in only 38% of pnpo−/− zebrafish surviving beyond 20 days post fertilization (dpf). The age of seizure onset varied and survival after the onset was brief. Biochemical profiling at 20 dpf revealed a reduction of PLP and pyridoxal (PL) and accumulation of PMP and pyridoxamine (PM). Amino acids involved in neurotransmission including glutamate, γ-aminobutyric acid (GABA) and glycine were decreased. Concentrations of several, mostly essential, amino acids were increased in pnpo−/− zebrafish suggesting impaired activity of PLP-dependent transaminases involved in their degradation. PLP treatment increased survival at 20 dpf and led to complete normalization of PLP, PL, glutamate, GABA and glycine. However, amino acid profiles only partially normalized and accumulation of PMP and PM persisted. Taken together, our data indicate that not only decreased PLP but also accumulation of PMP may play a role in the clinical phenotype of PNPO deficiency.

Isocitrate Lyase and Succinate Semialdehyde Dehydrogenase Mediate the Synthesis of α-Ketoglutarate in Pseudomonas fluorescens.

Glycerol is an important by-product of the biodiesel industry and its transformation into value-added products like keto acids is being actively pursued in order to improve the efficacy of this renewable energy sector. Here, we report that the enhanced production of α-ketoglutarate (KG) effected by Pseudomonas fluorescens in a mineral medium supplemented with manganese (Mn) is propelled by the increased activities of succinate semialdehyde dehydrogenase (SSADH), γ-aminobutyric acid aminotransaminase (GABAT), and isocitrate lyase (ICL). The latter generates glyoxylate and succinate two key metabolites involved in this process. Fumarate reductase (FRD) also aids in augmenting the pool of succinate, a precursor of succinate semialdehyde (SSA). The latter is then carboxylated to KG with the assistance of α-ketoglutarate decarboxylase (KDC). These enzymes work in tandem to ensure copious secretion of the keto acid. When incubated with glycerol in the presence of bicarbonate (), cell-free extracts readily produce KG with a metabolite fingerprint attributed to glutamate, γ-aminobutyric acid (GABA), succinate and succinate semialdehyde. Further targeted metabolomic and functional proteomic studies with high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and gel electrophoresis techniques provided molecular insights into this KG-generating machinery. Real-time quantitative polymerase chain reaction (RT-qPCR) analyses revealed the transcripts responsible for ICL and SSADH were elevated in the Mn-supplemented cultures. This hitherto unreported metabolic network where ICL and SSADH orchestrate the enhanced production of KG from glycerol, provides an elegant means of converting an industrial waste into a keto acid with wide-ranging application in the medical, cosmetic, and chemical sectors.

A review on the role of γ-aminobutyric acid signaling pathway in autism spectrum disorder

The etiology and pathogenesis of autism spectrum disorder (ASD) are not yet clear. Studies have shown that there are many neurotransmitter abnormalities in children with ASD, mainly involving in glutamate, γ-aminobutyric acid (GABA), dopamine, 5-HT and oxytocin. The imbalance of excitatory glutamatergic neurotransmitters and inhibitory GABAergic neurotransmitters is closely related to the pathogenesis of ASD. Both animal model studies and clinical studies on ASD suggest that GABA signaling pathway may play an important role in the pathogenesis of ASD. This article reviews the research on the association between GABA signaling pathway and the pathogenesis of ASD to further explore the pathogenesis of ASD and provide theoretical basis for the treatment of ASD.

Alterations in the Glutamate metabolism and Aminotransferases (AAT, ALAT) during PTZ – induced Epilepsy: Protective role of Bacopa monnieri

Epilepsy, a common chronic neurological disorder characterized by repeated, spontaneous seizures, also known as seizure disorder. Seizure related neuronal injury has been assumed to be mediated by glutamate, the excitatory amino acid, in the central nervous system that causes a sudden imbalance between the inhibitory and excitatory signals in the brain with glutamate, γ-aminobutyric acid (GABA), noradrenaline, serotonin, and dopamine. Since long term usage of antiepileptic drugs cause high incidence of pharmacoresistence and untoward side effects, attention has been paid in recent years to screen bioactive compounds from natural medicinal plants for treatment of several neurological disorders including Epilepsy. Keeping in view of relative importance of natural medicinal plants, the present study is mainly focused to characterize the anti-convulsant effect of Bacopa monnieri (BM), an Indian herb which is being extensively used in Ayurvedic treatments related to neurological complications. The present study is designed to assess the neurotoxicity of Pentylene tetrazole (PTZ), an epileptic compounds, on the Glutamate metabolism and Amino transferases in different brain regions (Cerebral cortex, Cerebellum, Pons medulla and Hippocampus) of rat and to explore the possible antiepileptic effect of different extracts (Ethanol, n-Hexane, Chloroform, Ethyl acetate, n-Butanol and Aqueous extracts) of BM in comparison with Diazepam (DZ) (Reference control). The activities of glutamate dehydrogenase (GDH), glutamine synthetase (GS) and glutamine content were decreased in different regions of brain during PTZ induced epilepsy which were increased in epileptic rats pretreated with different extracts of Bacopa monnieri except EAE and AE. Glutaminase activity was increased in PTZ induced epilepsy and decreased on pretreatment with all the extracts of BM except AE. In addition aspartate (AAT) and alanine aminotransferase (ALAT) activity levels were increased during PTZ induced epilepsy when compared with normal control and levels were reversed on pretreatment with different extracts of BM. Recoveries of these parameters during antiepileptic treatment suggest that the bioactive factors present in the extracts offer neuroprotection by interrupting the pathological cascade of glutamatergic hyperexcitation that occurs during epileptogenesis.

Serotonergic transmission at Merkel discs: modulation by exogenously applied chemical messengers and involvement of Ih currents.

The Merkel disc is a main type of tactile end organ consisting of Merkel cells and Aβ-afferent endings that responds to tactile stimulation with slowly adapting type 1 (SA1) afferent impulses. Our recent study has shown that Merkel discs in whisker hair follicles are serotonergic synapses using endogenous serotonin to transmit tactile signals from Merkel cells to Aβ-afferent endings. In this study, we hypothesize that tactile sensitivity of Merkel discs can be modulated by chemical messengers. We tested this hypothesis by determining whether and how SA1 responses of mouse whisker hair follicles may be affected by exogenously applied chemical messengers. We found that SA1 responses were potentiated by serotonin at low concentration (10μM) but almost completely occluded by serotonin at high concentration (2mM). In contrast, SA1 responses were not significantly affected by ATP and its metabolically stable analog α,β-methylene-ATP, glutamate, γ-aminobutyric acid (GABA), and histamine. SA1 responses were also not affected by antagonists for P2X receptors, ionotropic glutamate receptors, and ionotropic GABA and glycine receptors. Whole-cell patch-clamp recordings reconfirm the presence of both ionotropic and metabotropic 5-HT receptors on afferent neurons and their terminals innervating whisker hair follicles. All whisker afferent neurons expressed hyperpolarization-activated inward currents (Ih ), which are potentiated by serotonin through the activation of metabotropic 5-HT receptors. Taken together, the findings substantiate the serotonergic mechanism of tactile transmission at Merkel discs and identify the involvement of Ih currents in postsynaptic excitatory actions of serotonin. In addition, the findings do not favor any significant involvement of ATP, glutamate, histamine, GABA, or glycine in tactile transmission at the Merkel discs of whisker hair follicles.

Glutamine-Glutamate Cycle Flux Is Similar in Cultured Astrocytes and Brain and Both Glutamate Production and Oxidation Are Mainly Catalyzed by Aspartate Aminotransferase

The glutamine-glutamate cycle provides neurons with astrocyte-generated glutamate/γ-aminobutyric acid (GABA) and oxidizes glutamate in astrocytes, and it returns released transmitter glutamate/GABA to neurons after astrocytic uptake. This review deals primarily with the glutamate/GABA generation/oxidation, although it also shows similarity between metabolic rates in cultured astrocytes and intact brain. A key point is identification of the enzyme(s) converting astrocytic α-ketoglutarate to glutamate and vice versa. Most experiments in cultured astrocytes, including those by one of us, suggest that glutamate formation is catalyzed by aspartate aminotransferase (AAT) and its degradation by glutamate dehydrogenase (GDH). Strongly supported by results shown in Table 1 we now propose that both reactions are primarily catalyzed by AAT. This is possible because the formation occurs in the cytosol and the degradation in mitochondria and they are temporally separate. High glutamate/glutamine concentrations abolish the need for glutamate production from α-ketoglutarate and due to metabolic coupling between glutamate synthesis and oxidation these high concentrations render AAT-mediated glutamate oxidation impossible. This necessitates the use of GDH under these conditions, shown by insensitivity of the oxidation to the transamination inhibitor aminooxyacetic acid (AOAA). Experiments using lower glutamate/glutamine concentration show inhibition of glutamate oxidation by AOAA, consistent with the coupled transamination reactions described here.

Rhizobial strains exert a major effect on the amino acid composition of alfalfa nodules under NaCl stress

Specific amino acids have protective functions in plants under stress conditions. This study assessed the effects of rhizobial strains on the amino acid composition in alfalfa under salt stress. Two alfalfa cultivars (Medicago sativa L. cv Apica and salt-tolerant cv Halo) in association with two Sinorhizobium meliloti strains with contrasting growth under salt stress (strain A2 and salt-tolerant strain Rm1521) were exposed to different levels of NaCl (0, 20, 40, 80 or 160 mM NaCl) under controlled conditions. We compared root and shoot biomasses, as well as root:shoot ratio for each association under these conditions as indicators of the salt tolerance of the symbiosis. Amino acid concentrations were analyzed in nodules, leaves and roots. The total concentration of free amino acids in nodules was mostly rhizobial-strain dependent while in leaves and roots it was mostly responsive to salt stress. For both cultivars, total and individual concentrations of amino acids including asparagine, proline, glutamine, aspartate, glutamate, γ-aminobutyric acid (GABA), histidine and ornithine were higher in Rm1521 nodules than in A2 nodules. Conversely, lysine and methionine were more abundant in A2 nodules than in Rm1521 nodules. Proline, glutamine, arginine, GABA and histidine substantially accumulated in salt-stressed nodules, suggesting an enhanced production of amino acids associated with osmoregulation, N storage or energy metabolism to counteract salt stress. Combining the salt-tolerant strain Rm1521 and the salt-tolerant cultivar Halo enhanced the root:shoot ratios and amino acid concentrations involved in plant protection which could be in part responsible for the enhancement of salt tolerance in alfalfa.

Neurotransmitter receptors on microglia

As the resident immune cells in the central nervous system, microglia have long been hypothesised to promote neuroinflammation and exacerbate neurotoxicity. However, this traditional view has undergone recent revision as...