Glutamate Transporter Research Articles

Salidroside ameliorates cerebral ischemic injury and regulates the glutamate metabolism pathway in astrocytes

Background and AimSalidroside (SA) is the main active component of Rhodiola rosea L., with potential in treating cardiovascular and cerebrovascular diseases and cerebral ischemia. However, its efficacy and mechanism in cerebral ischemia remain unclear, particularly regarding its effect on glutamate (Glu) metabolism. In this paper, we aimed to investigate the efficacy of SA in treating cerebral ischemia and its pharmacological mechanism.Experimental procedureWe studied the effects of SA on SD rats with cerebral ischemia, evaluating neurobehavior, cerebral water content, infarct size, and brain microstructure. We also assessed its impact on glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and glutamate transporter 1 (GLT-1) proteins using immunohistochemistry and Western blot. Additionally, we used SVGp12 cells to simulate cerebral ischemia and measured Glu levels and used Western blot to observe the level of GS and GLT-1.ResultsSA improved neural function, reduced infarct size, and regulated GSH and Glu levels in rats. In cell experiments, SA increased cell viability and decreased Glu concentration after ischemia induction. It also regulated the expression of GFAP, GS, and GLT-1.ConclusionSA alleviates cerebral ischemia-induced injury by acting on astrocytes, possibly through regulating the glutamate metabolic pathway.

Inhibition of IRAP Enhances the Expression of Pro-Cognitive Markers Drebrin and MAP2 in Rat Primary Neuronal Cells

The insulin-regulated aminopeptidase (IRAP; oxytocinase) is part of the M1 aminopeptidase family and is highly expressed in many tissues, including the neocortex and hippocampus of the brain. IRAP is involved in various physiological functions and has been identified as a receptor for the endogenous hexapeptide Angiotensin IV (Ang IV). The binding of Ang IV inhibits the enzymatic activity of IRAP and has been proven to enhance learning and memory in animal models. The macrocyclic compound 9 (C9) is a potent synthetic IRAP inhibitor developed from the previously reported inhibitor HA08. In this study, we have examined compound C9 and its effects on cognitive markers drebrin, microtubule-associated protein 2 (MAP2), and glial fibrillary acidic protein (GFAP) in primary hippocampal and cortical cultures. Cells from Sprague Dawley rats were cultured for 14 days before treatment with C9 for 4 consecutive days. The cells were analysed for protein expression of drebrin, MAP2, GFAP, glucose transporter type 4 (GLUT4), vesicular glutamate transporter 1 (vGluT1), and synapsin I using immunocytochemistry. The gene expression of related proteins was determined using qPCR, and viability assays were performed to evaluate toxicity. The results showed that protein expression of drebrin and MAP2 was increased, and the corresponding mRNA levels were decreased after treatment with C9 in the hippocampal cultures. The ratio of MAP2-positive neurons and GFAP-positive astrocytes was altered and there were no toxic effects observed. In conclusion, the IRAP inhibitor compound C9 enhances the expression of the pro-cognitive markers drebrin and MAP2, which further confirms IRAP as a relevant pharmaceutical target and C9 as a promising candidate for further investigation.

Decreased Expression of the EAAT5 Glutamate Transporter at Photoreceptor Synapses in Early, Pre-Clinical Experimental Autoimmune Encephalomyelitis, a Mouse Model of Multiple Sclerosis

Background: Multiple sclerosis is a frequent neuroinflammatory and neurodegenerative disease of the central nervous system that includes alterations in the white and gray matter of the brain. The visual system is frequently affected in multiple sclerosis. Glutamate excitotoxicity might play a role in disease pathogenesis. Methodology: In the present study, we analyzed with qualitative and quantitative immunofluorescence microscopy and Western blot analyses whether alterations in the EAAT5 (SLC1A7) glutamate transporter could be involved in the previously observed alterations in structure and function of glutamatergic photoreceptor ribbon synapses in the EAE mouse model of MS. EAAT5 is a presynaptic glutamate transporter located near the presynaptic release sites. Results: We found that EAAT5 was strongly reduced at the photoreceptor synapses of EAE retinas in comparison to the photoreceptor synapses of the respective control retinas as early as day 9 post-immunization. The Western blot analyses demonstrated a decreased EAAT5 expression in EAE retinas. Conclusions: Our data illustrate early alterations of the EAAT5 glutamate transporter in the early pre-clinical phase of EAE/MS and suggest an involvement of EAAT5 in the previously observed early synaptic changes at photoreceptor synapses. The precise mechanisms need to be elucidated by future investigations.

FREE FATTY ACIDS INHIBIT AN ION-COUPLED MEMBRANE TRANSPORTER BY DISSIPATING THE ION GRADIENT

Glutamate is the main excitatory transmitter in the mammalian central nervous system; glutamate transporters keep the synaptic glutamate concentrations at bay for normal brain function. Arachidonic acid (AA), docosahexaenoic acid (DHA), and other unsaturated fatty acids modulate glutamate transporters in cell- and tissue slices-based studies. Here, we investigated their effect and mechanism using a purified archaeal glutamate transporter homolog reconstituted into the lipid membranes. AA, DHA, and related fatty acids irreversibly inhibited the sodium-dependent concentrative substrate uptake into lipid vesicles within the physiologically relevant concentration range. In contrast, AA did not inhibit amino acid exchange across the membrane. The length and unsaturation of the aliphatic tail affect inhibition, and the free carboxylic headgroup is necessary. The inhibition potency did not correlate with the fatty acid effects on the bilayer deformation energies. AA does not affect the conformational dynamics of the protein, suggesting it does not inhibit structural transitions necessary for transport. Single-transporter and membrane voltage assays showed that AA and related fatty acids mediate cation leak, dissipating the driving sodium gradient. Thus, such fatty acids can act as cation ionophores, suggesting a general modulatory mechanism of membrane channels and ion-coupled transporters.

Role of cholesterol in modulating brain hyperexcitability.

Cholesterol is a critical molecule in the central nervous system, and imbalances in the synthesis and metabolism of brain cholesterol can result in a range of pathologies, including those related to hyperexcitability. The impact of cholesterol on disorders of epilepsy and developmental and epileptic encephalopathies is an area of growing interest. Cholesterol cannot cross the blood-brain barrier, and thus the brain synthesizes and metabolizes its own pool of cholesterol. The primary metabolic enzyme for brain cholesterol is cholesterol 24-hydroxylase (CH24H), which metabolizes cholesterol into 24S-hydroxycholesterol (24HC). Dysregulation of CH24H and 24HC can affect neuronal excitability through a range of mechanisms. 24HC is a positive allosteric modulator of N-methyl-D-aspartate (NMDA) receptors and can increase glutamate release via tumor necrosis factor-α-dependent pathways. Increasing cholesterol metabolism can lead to dysfunction of excitatory amino acid transporter 2 and impair glutamate reuptake. Finally, overstimulation of NMDA receptors can further activate metabolism of cholesterol, leading to a vicious cycle of overactivation. All of these mechanisms increase extracellular glutamate and can lead to hyperexcitability. For these reasons, the cholesterol pathway represents a new potential mechanistic target for antiseizure medications. CH24H inhibition has been shown to decrease seizure behavior and improve survival in multiple animal models of epilepsy and could be a promising new mechanism of action for the treatment of neuronal hyperexcitability and developmental and epileptic encephalopathies.

Inhibitory Potential of the Truncated Isoforms on Glutamate Transporter Oligomerization Identified by Computational Analysis of Gene-Centric Isoform Maps.

Glutamate transporters play a key role in central nervous system physiology by maintaining excitatory neurotransmitter homeostasis. Biological assemblies of the transporters, consisting of cyclic homotrimers, emerge as a crucial aspect of glutamate transporter modulation. Hence targeting heteromerization promises an effective approach for modulator design. On the other hand, the dynamic nature of transcription allows for the generation of transporter isoforms in structurally distinct manners. The potential isoforms were identified through the analysis of computationally generated gene-centric isoform maps. The conserved features of isoform sequences were revealed by computational chemistry methods and subsequent structural analysis of AlphaFold2 predictions. Truncated isoforms were further subjected to a wide range of docking analyses, 50ns molecular dynamics simulations, and evolutionary coupling analyses. Energetic landscapes of isoform-canonical transporter complexes suggested an inhibitory potential of truncated isoforms on glutamate transporter bio-assembly. Moreover, isoforms that mimic the trimerization domain (in particular, TM2 helices) exhibited stronger interactions with canonical transporters, underscoring the role of transmembrane helices in isoform interactions. Additionally, self-assembly dynamics observed in truncated isoforms mimicking canonical TM5 helices indicate a potential protective role against unwanted interactions with canonical transporters. Our computational studies on glutamate transporters offer insights into the roles of alternative splicing on protein interactions and identifies potential drug targets for physiological or pathological processes.

Drug developmental strategies based on functional analysis of pain-regulating molecules in astrocytes under chronic pain

Spinal cord astrocytes are activated in chronic pain models, especially under conditions of prolonged pain. Hence, targeting spinal cord astrocytes for the development of useful analgesics has attracted much attention. In the CNS, connexin43 (Cx43), a membrane protein expressed and functioning exclusively in astrocytes, is well known to be involved in intercellular signaling as a component of gap junction, but also interacts with intracellular molecules via its characteristically long C-terminal region, thereby affecting cellular function. Previously, we found that Cx43 expression was markedly reduced in spinal dorsal horn astrocytes from a mouse model of neuropathic pain. In order to investigate the relationship between reduced Cx43 expression in spinal astrocytes and the onset of pain, we showed that reduced Cx43 expression altered the expression of pain-related molecules such as the glutamate transporter GLT-1 and the pro-inflammatory cytokine interleukin-6 (IL-6). In particular, we focused on the regulation of IL-6 expression by reduced Cx43 expression in both in vivo and in vitro analyses, and found that IL-6 expression is increased through the Akt- glycogen synthase kinase-3β (GSK-3β) signaling system driven by reduced Cx43 expression during neuropathic pain, which in turn triggers pain. These findings suggest that astrocyte Cx43 is involved in pain prolongation by regulating gene expression of nociceptive factors through interactions with intracellular signaling molecules, which is different from its previously known function, and thus raises expectations for its potential as a new drug target for chronic pain.

Time course analysis of changes in neuronal loss, oxidative stress, and excitotoxicity in gerbil hippocampus following ischemia and reperfusion under hyperthermic conditions.

Oxidative stress and excitotoxicity are the major causes of neuronal death/loss in the brain following ischemia and reperfusion (IR). Hyperthermia is known to exacerbate ischemic neuronal damage; however, the underlying mechanisms remain unclear. This study investigated the mechanisms underlying neuronal damage caused by IR injury (IRI) under hyperthermic conditions in the gerbil hippocampal CA1 region. Gerbils were controlled at normothermia (37.5±0.2°C) or hyperthermia (39.5±0.2°C). After temperature control for 30 min, the animals received IRI (following 5 min of transient forebrain ischemia) or sham ischemia, and were subsequently sacrificed at 0, 3, 6, 12, 24, 48, and 120h after IRI. Neuronal death was examined using neuronal nuclear antigen immunohistochemistry and Fluoro-Jade B histofluorescence. Oxidative stress was analyzed by immunohistochemistry for 8-Hydroxy-2'-deoxyguanosine (8OHdG) and superoxide dismutase 2 (SOD2). Excitotoxicity was investigated by immunohistochemistry and western blotting for glutamate transporter 1 (GLT1). Immunohistochemical staining for glial fibrillary acidic proteins (GFAP) was performed to detect reactive astrogliosis. Loss of pyramidal neurons was detected earlier (48h post-IRI) in the hyperthermia-IRI group than in the normothermia-IRI group (120h post-IRI). Further, 8OHdG and SOD2 immunoreactivity in the hyperthermia-IRI group was significantly higher than that in the normothermia-IRI group. Changes in GLT1 immunoreactivity in both groups were biphasic, indicating that the immunoreactivity and protein levels were significantly lower in the hyperthermia-IRI group. GFAP immunoreactivity was enhanced following neuronal loss, indicating that the immunoreactivity was significantly higher in the hyperthermia-IRI group. Taken together, these results suggest that brain IR under hyperthermic conditions can aggravate neuronal damage in the hippocampal CA1 region through severe oxidative stress and excitotoxicity.

Morphine self-administration is inhibited by the antioxidant N-acetylcysteine and the anti-inflammatory ibudilast; an effect enhanced by their co-administration.

The treatment of opioid addiction mainly involves the medical administration of methadone or other opioids, aimed at gradually reducing dependence and, consequently, the need for illicit opioid procurement. Thus, initiating opioid maintenance therapy with a lower level of dependence would be advantageous. There is compelling evidence indicating that opioids induce brain oxidative stress and associated glial activation, resulting in the dysregulation of glutamatergic homeostasis, which perpetuates drug intake. The present study aimed to determine whether inhibiting oxidative stress and/or neuroinflammation reduces morphine self-administration in an animal model of opioid dependence. Morphine dependence, assessed as voluntary morphine self-administration, was evaluated in Wistar-derived UChB rats. Following an extended period of morphine self-administration, animals were administered either the antioxidant N-acetylcysteine (NAC; 40 mg/kg/day), the anti-inflammatory ibudilast (7.5 mg/kg/day) or the combination of both agents. Oxidative stress and neuroinflammation were evaluated in the hippocampus, a region involved in drug recall that feeds into the nucleus accumbens, where the levels of the glutamate transporters GLT-1 and xCT were further assessed. Daily administration of either NAC or ibudilast led to a mild reduction in voluntary morphine intake, while the co-administration of both therapeutic agents resulted in a marked inhibition (-57%) of morphine self-administration. The administration of NAC or ibudilast markedly reduced both the oxidative stress induced by chronic morphine intake and the activation of microglia and astrocytes in the hippocampus. However, only the combined administration of NAC + ibudilast was able to restore the normal levels of the glutamate transporter GLT-1 in the nucleus accumbens. Separate or joint administration of an antioxidant and anti-inflammatory agent reduced voluntary opioid intake, which could have translational value for the treatment of opioid use disorders, particularly in settings where the continued maintenance of oral opioids is a therapeutic option.

Proportion and distribution of neurotransmitter-defined cell types in the ventral tegmental area and substantia nigra pars compacta

Most studies on the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) have focused on dopamine neurons and their role in processes such as motivation, learning, movement, and associated disorders such as addiction and Parkinson's disease. However there has been increasing attention on other VTA and SNc cell types that release GABA, glutamate, or a combination of neurotransmitters. Yet the relative distributions and proportions of neurotransmitter-defined cell types across VTA and SNc has remained unclear. Here, we used fluorescent in situ hybridization in male and female mice to label VTA and SNc neurons that expressed mRNA encoding the canonical vesicular transporters for dopamine, GABA, or glutamate: vesicular monoamine transporter (VMAT2), vesicular GABA transporter (VGAT), and vesicular glutamate transporter (VGLUT2). Within VTA, we found that no one type was particularly more abundant, instead we observed similar numbers of VMAT2+ (44 %), VGAT+ (37 %) and VGLUT2+ (41 %) neurons. In SNc we found that a slight majority of neurons expressed VMAT2 (54 %), fewer were VGAT+ (42 %), and VGLUT2+ neurons were least abundant (16 %). Moreover, 20 % of VTA neurons and 10 % of SNc neurons expressed more than one vesicular transporter, including 45 % of VGLUT2+ neurons. We also assessed within VTA and SNc subregions and found remarkable heterogeneity in cell-type composition. And by quantifying density across both anterior-posterior and medial-lateral axes we generated heatmaps to visualize the distribution of each cell type. Our data complement recent single-cell RNAseq studies and support a more diverse landscape of neurotransmitter-defined cell types in VTA and SNc than is typically appreciated.

The Mechanism and Inflammatory Markers Involved in the Potential Use of N-acetylcysteine in Chronic Pain Management

N-acetylcysteine (NAC) has established use as an antidote for acetaminophen overdose and treatment for pulmonary conditions and nephropathy. It plays a role in regulating oxidative stress and interacting with various cytokines including IL-1β, TNFα, IL-8, IL-6, IL-10, and NF-κB p65. The overexpression of reactive oxygen species (ROS) is believed to contribute to chronic pain states by inducing inflammation and accelerating disease progression, favoring pain persistence in neuropathic and musculoskeletal pain conditions. Through a comprehensive review, we aim to explore the mechanisms and inflammatory pathways through which NAC may manage neuropathic and musculoskeletal pain. Evidence suggests NAC can attenuate neuropathic and musculoskeletal pain through mechanisms such as inhibiting matrix metalloproteinases (MMPs), reducing reactive oxygen species (ROS), and enhancing glutamate transport. Additionally, NAC may synergize with opioids and other pain medications, potentially reducing opioid consumption and enhancing overall pain management. Further research is needed to fully elucidate its therapeutic potential and optimize its use in pain management. As an adjuvant therapy, NAC shows potential for chronic pain management, offering significant benefits for public health.

Regulation Mechanisms of the Glutamate Transporter in the Response of Pacific Oyster upon High-Temperature Stress.

Glutamate transporters (GLTs) are integral to the glutamatergic system, modulating glutamate homeostasis to enhance resilience and resistance against environmental stress. There are six GLTs identified in the Pacific oyster (Crassostrea gigas), which were categorized into two subfamilies: excitatory amino acid transporters (CgEAATs) and vesicular glutamate transporters (CgVGLUTs). The CgEAATs harbor a GltP domain, while CgVGLUTs feature an MFS domain, both with conserved sequence and structural characteristics. The expression of CgGLTs is elevated during the planktonic larval stage compared to the fertilized egg stage and is constitutively expressed in various tissues of adult oysters, suggesting its critical role in both larval development and the physiological processes of adult oysters. Transcriptomic analysis revealed diverse expression patterns of GLTs in oyster gills after 7 days of high-temperature stress, with CgEAAT3 showing a significant upregulation. A KEGG pathway enrichment analysis identified glutathione metabolism and ferroptosis as prominently enriched pathways. At 48 h after high-temperature stress, the expression levels of Glutathione Peroxidase 4 (CgGPX4) and CgEAAT3, along with elevated Fe content in the gills, significantly increased. Moreover, the RNAi-mediated the inhibition of CgEAAT3 expression under high-temperature stress, resulting in a significant reduction in CgGPX4 expression and a further increase in Fe accumulation in oyster gills. These results indicate that CgEAAT3 contributes to the regulation of ferroptosis and redox homeostasis by modulating CgGPX4 expression. This study provides new insights into the adaptive mechanisms of bivalves to environmental stress.

Dopamine loss alters glutamate synapses and transporters in the medial prefrontal cortex and anxiety-related behaviour in a male MPTP rodent model of Parkinson's disease.

Anxiety is a prominent non-motor symptom of Parkinson's disease (PD). Changes in the B-spectrum recordings in PD patients of the prefrontal cortex correlate with increased anxiety. Using a rodent model of PD, we reported alterations in glutamate synapses in the striatum and substantia nigra following dopamine (DA) loss. We hypothesize that DA loss will result in increased anxiety-related behaviours and that this will be associated with alterations in glutamate synapses and transporters within the medial prefrontal cortex (mPFC). Following 4weeks of progressive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, there was an increase in anxiety-related behaviours and a 78% decrease in plasma corticosterone levels versus the vehicle (VEH)-treated mice. This was associated with a 30% decrease in the density of dendritic spines in Layers Il/Ill, and a 53% decrease in the density of glutamate immuno-gold labelling within vesicular glutamate transporter 1 (Vglut1)-labelled nerve terminals and spines, with no change within vesicular glutamate transporter 2 (Vglut2) positive terminals/spines in the MPTP versus VEH groups. Our prior work determined that a decrease in striatal glutamate terminal density was associated with an increase in extracellular glutamate levels. There was an increase in protein expression of Vglut1 (40%), Vglut2 (37%) and glutamate aspartate transporter (GLAST) (225%), and a decrease in glutamate transporter 1 (GLT-1) (50%) and excitatory amino acid carrier 1 (EAAC1) (51%), in the MPTP versus VEH groups within the mPFC. These data suggest that the decrease in dendritic spines within the mPFC following nigrostriatal DA loss may be due to increased extracellular glutamate levels (decrease in glutamate transporters), leading to an increase in anxiety-related behaviours.

PS1/gamma-secretase acts as rogue chaperone of glutamate transporter EAAT2/GLT-1 in Alzheimer’s disease

The recently discovered interaction between presenilin 1 (PS1), a subunit of γ-secretase involved in amyloid-β (Aβ) peptide production, and GLT-1, the major brain glutamate transporter (EAAT2 in the human), may link two pathological aspects of Alzheimer’s disease: abnormal Aβ occurrence and neuronal network hyperactivity. In the current study, we employed a FRET-based fluorescence lifetime imaging microscopy (FLIM) to characterize the PS1/GLT-1 interaction in brain tissue from sporadic AD (sAD) patients. sAD brains showed significantly less PS1/GLT-1 interaction than those with frontotemporal lobar degeneration or non-demented controls. Familial AD (fAD) PS1 mutations, inducing a “closed” PS1 conformation similar to that in sAD brain, and gamma-secretase modulators (GSMs), inducing a “relaxed” conformation, respectively reduced and increased the interaction. Furthermore, PS1 influences GLT-1 cell surface expression and homomultimer formation, acting as a chaperone but not affecting GLT-1 stability. The diminished PS1/GLT-1 interaction suggests that these functions may not work properly in AD.

Prelimbic cortex perineuronal net expression and social behavior: Impact of adolescent intermittent ethanol exposure

Adolescent intermittent ethanol (AIE) exposure in rats leads to social deficits. Parvalbumin (PV) expressing fast-spiking interneurons in the prelimbic cortex (PrL) contribute to social behavior, and perineuronal nets (PNNs) within the PrL preferentially encompass and regulate PV interneurons. AIE exposure increases PNNs, but it is unknown if this upregulation contributes to AIE-induced social impairments. The current study was designed to determine the effect of AIE exposure on PNN expression in the PrL and to assess whether PNN dysregulation contributes to social deficits elicited by AIE. cFos-LacZ male and female rats were exposed every other day to tap water or ethanol (4 g/kg, 25% w/v) via intragastric gavage between postnatal day (P) 25–45. We evaluated neuronal activation by β-galactosidase expression and PNN levels either at the end of the exposure regimen on P45 and/or in adulthood on P70. In addition, we used Chondroitinase ABC (ChABC) to deplete PNNs following adolescent exposure (P48) and allowed for PNN restoration before social testing in adulthhod. AIE exposure increased PNN expression in the PrL of adult males, but decreased PNNs immediately following AIE. Vesicular glutamate transporter 2 (vGlut2) and vesicular GABA transporter (vGat) near PNNs were downregulated only in AIE-exposed females. Gene expression of PNN components was largely unaffected by AIE exposure. Removal and reestablishment of PrL PNNs by ChABC led to upregulation of PNNs and social impairments in males, regardless of adolescent exposure. These data suggest that AIE exposure in males upregulates PrL PNNs that likely contribute to social impairments induced by AIE.

Influence of Chronic Social Stress on the Expression of Genes Associated with Neurotransmitter Systems in the Hypothalamus of Male Mice

Chronic social stress caused by repeated negative experiences in agonistic interactions induces depressive-like behavior in male mice. The aim of the study was to study changes in the expression of genes encoding proteins involved in the metabolism, reception, and transport of catecholamines, opioids, glutamate, and GABA under the influence of chronic stress. Hypothalamic samples were sequenced using RNA-Seq. It was shown that the expression of the catecholaminergic genes Adra1b, Adrbk1, Comtd1, Ppp1r1b, Sncb, Sncg, and Th in depressed animals is increased, while the expression of the Maoa and Maob genes is reduced. The expression of the opioidergic and cannabinoidergic genes Pdyn, Penk, Pomc, Pnoc, Ogfr, and Faah was upregulated, while that of the Oprk1, Opcml, Ogfrl1, and Cnr1 genes was downregulated. The expression of the glutamatergic genes Grik3, Grik4, Grik5, Grin1, Grm2, and Grm4 was increased, while the expression of the Gria3, Grik1, Grik2, Grin2a, Grin3a, Grm5, Grm8, and Gad2 genes was reduced. The expression of the GABAergic genes Gabre, Gabbr2, and Slc6a11 was higher, while the expression of the Gabra1, Gabra2, Gabra3, Gabrb2, Gabrb3, Gabrg1, Gabrg2, and Slc6a13 genes was lower in depressed animals. The data suggest that gene products that interact with other neurotransmitter systems (Th, Gad2, Gabra1, Gabrg2, Grin1, and Pdyn) may be of interest as potential targets for pharmacological correction of the consequences of social stress.

Advances in Plant GABA Research: Biological Functions, Synthesis Mechanisms and Regulatory Pathways.

The γ-aminobutyric acid (GABA) is a widely distributed neurotransmitter in living organisms, known for its inhibitory role in animals. GABA exerts calming effects on the mind, lowers blood pressure in animals, and enhances stress resistance during the growth and development of plants. Enhancing GABA content in plants has become a focal point of current research. In plants, GABA is synthesized through two metabolic pathways, the GABA shunt and the polyamine degradation pathway, with the GABA shunt being the primary route. Extensive studies have investigated the regulatory mechanisms governing GABA synthesis. At the genetic level, GABA production and degradation can be modulated by gene overexpression, signaling molecule-induced expression, transcription factor regulation, and RNA interference. Additionally, at the level of transporter proteins, increased activity of GABA transporters and proline transporters enhances the transport of glutamate and GABA. The activity of glutamate decarboxylase, a key enzyme in GABA synthesis, along with various external factors, also influences GABA synthesis. This paper summarizes the biological functions, metabolic pathways, and regulatory mechanisms of GABA, providing a theoretical foundation for further research on GABA in plants.

Schizophrenia-associated changes in neuronal subpopulations in the human midbrain.

Dysfunctional GABAergic and dopaminergic neurons are thought to exist in the ventral midbrain of patients with schizophrenia, yet transcriptional changes underpinning these abnormalities have not yet been localized to specific neuronal subsets. In the ventral midbrain, control over dopaminergic activity is maintained by both excitatory (glutamate) and inhibitory (GABA) input neurons. To further elucidate neuron pathology at the single-cell level, we characterized the transcriptional diversity of distinct NEUN+ populations in the human ventral midbrain and then tested for schizophrenia-associated changes in neuronal subset proportions and gene activity changes within neuronal subsets. Combining single nucleus RNA-sequencing with fluorescence-activated sorting of NEUN+ nuclei, we analysed 31,669 nuclei. Initially, we detected 18 transcriptionally distinct neuronal populations in the human ventral midbrain, including 2 "mixed" populations. The presence of neuronal populations in the midbrain was orthogonally validated with immunohistochemical stainings. "Mixed" populations contained nuclei expressing transcripts for vesicular glutamate transporter 2 (SLC17A6) and Glutamate Decarboxylase 2 (GAD2), but these transcripts were not typically co-expressed by the same nucleus. Upon more fine-grained subclustering of the 2 "mixed" populations, 16 additional subpopulations were identified that were transcriptionally classified as excitatory or inhibitory. In the midbrains of individuals with schizophrenia, we observed potential differences in the proportions of two (sub)populations of excitatory neurons, two subpopulations of inhibitory neurons, one "mixed" subpopulation, and one subpopulation of TH-expressing neurons. This may suggest that transcriptional changes associated with schizophrenia broadly affect excitatory, inhibitory, and dopamine neurons. We detected 99 genes differentially expressed in schizophrenia compared to controls within neuronal subpopulations identified from the 2 "mixed" populations, with the majority (67) of changes within small GABAergic neuronal subpopulations. Overall, single-nucleus transcriptomic analyses profiled a high diversity of GABAergic neurons in the human ventral midbrain, identified putative shifts in the proportion of neuronal subpopulations, and suggested dysfunction of specific GABAergic subpopulations in schizophrenia, providing directions for future research.

Astrocytic HIV-1 Nef expression decreases glutamate transporter expression in the nucleus accumbens and increases cocaine-seeking behavior in rats.

Cocaine use disorder is an intersecting issue in populations with HIV-1, further exacerbating the clinical course of the disease, contributing to neurotoxicity and neuroinflammation. Cocaine and HIV neurotoxins play roles in neuronal damage during neuroHIV progression by disrupting glutamate homeostasis in the brain. Even with cART, HIV-1 Nef, an early viral protein expressed in approximately 1% of infected astrocytes, remains a key neurotoxin. This study investigates the relationship that exists between Nef, glutamate homeostasis, and cocaine in the NAc, a critical brain region associated with drug motivation and reward. Using a rat model, we compared the effects of astrocytic Nef and cocaine by molecular analysis of glutamate transporters in the NAc. We further conducted behavioral assessments for cocaine self-administration to evaluate cocaine-seeking behavior. Our findings indicate that both cocaine and Nef independently decrease the expression of the glutamate transporter GLT-1 in the NAc. Additionally, rats with astrocytic Nef expression exhibited increased cocaine-seeking behavior but demonstrated sex dependent molecular differences after behavioral paradigm. In conclusion, our results suggest the expression of Nef intensifies cocaine-induced alterations in glutamate homeostasis in the NAc, potentially underlying increased cocaine-seeking. Understanding these interactions better may inform therapeutic strategies for managing cocaine use disorder in HIV-infected individuals.

Differential Effects of Intrahippocampal Administration of Ceftriaxone on Morphine Dependence and Withdrawal Syndrome in Rats.

Glutamate is a key factor in opiate addiction. Glial glutamate transporter-1 (GLT-1) plays a prominent role in glutamate homeostasis. Therefore, different regimens of ceftriaxone as a GLT-1 activator were prescribed to determine whether modulating GLT-1 prevents morphine dependence or withdrawal syndrome. Rats received 10 mg/kg morphine subcutaneously for ten consecutive days. Intrahippocampal ceftriaxone (0.5 μL of 0.5 mM solution) was injected 30 min before morphine administration to assess its effect on dependence process. In the next experiment, after the animals became dependent, ceftriaxone was injected before or after the last morphine administration, and its effect on withdrawal symptoms was evaluated. The reversibility of developed dependence was evaluated in the conditions when morphine and ceftriaxone were administered simultaneously. Two hours after the last morphine injection, naloxone hydrochloride (1.5 mg/kg) was administered, and morphine withdrawal syndrome was recorded for 25 min. Ceftriaxone administration before each morphine injection caused a decrease in the occurrence of withdrawal symptoms. Single dose of ceftriaxone after or before the last dose of morphine did not change the withdrawal symptoms significantly. Ceftriaxone injection for 5 days after becoming dependent could decrease the occurrence of some withdrawal symptoms. Modulation of glutamate with ceftriaxone during morphine injection may be able to prevent dependence. However, a single dose of ceftriaxone after becoming dependent could not decrease withdrawal syndrome. More prolonged administration of ceftriaxone could alleviate the induced dependence.