Excessive Activation Of Glutamate Receptors Research Articles

Origanum majorana L. polyphenols: in vivo antiepileptic effect, in silico evaluation of their bioavailability, and interaction with the NMDA receptor.

Introduction: Epilepsy is a chronic brain disease characterized by repeated seizures and caused by excessive glutamate receptor activation. Many plants are traditionally used in the treatment of this disease. This study aimed to evaluate the bioavailability of a polyphenolic extract obtained from Origanum majorana L. (OMP) leaves, as well as its antiepileptic activity and its potential mechanism of action. Methods: We have developed and validated a simple, rapid, and accurate stability-indicating reversed-phase liquid chromatographic method for the simultaneous determination of caffeine and quercetin in rat plasma. The OMP antiepileptic effect was evaluated with pilocarpine-induced seizures, and a docking method was used to determine the possible interaction between caffeic acid and quercetin with the N-methyl-D-aspartate (NMDA) receptor. Results and Discussion: Both compounds tested showed low bioavailability in unchanged form. However, the tested extract showed an anticonvulsant effect due to the considerably delayed onset of seizures in the pilocarpine model at a dose of 100mg/kg. The molecular docking proved a high-affinity interaction between the caffeic acid and quercetin with the NMDA receptor. Taken together, OLP polyphenols demonstrated good antiepileptic activity, probably due to the interaction of quercetin, caffeic acid, or their metabolites with the NMDA receptor.

Nobiletin as a Neuroprotectant against NMDA Receptors: An In Silico Approach.

Excitotoxicity is a type of neurodegenerative disorder. It caused by excessive glutamate receptor activation, which leads to neuronal malfunction and fatality. The N-methyl-D-aspartate (NMDA) receptors are found in glutamatergic neurons, and their excessive activation is primarily responsible for excitotoxicity. They are activated by both glutamate binding and postsynaptic depolarization, facilitating Ca2+ entry upon activation. Therefore, they are now widely acknowledged as being essential targets for excitotoxicity issues. Molecular docking and molecular dynamics (MD) simulation analyses have demonstrated that nobiletin efficiently targets the binding pocket of the NMDA receptor protein and exhibits stable dynamic behavior at the binding site. In this study, five potential neuroprotectants, nobiletin, silibinin, ononin, ginkgolide B, and epigallocatechin gallate (EGCG), were screened against the glutamate NMDA receptors in humans via computational methods. An in silico ADMET study was also performed, to predict the pharmacokinetics and toxicity profile for the expression of good drug-like behavior and a non-toxic nature. It was revealed that nobiletin fulfills the criteria for all of the drug-likeness rules (Veber, Lipinski, Ghose, Muegge, and Egan) and has neither PAINS nor structural alerts (Brenks). In conclusion, nobiletin demonstrated a possible promising neuroprotectant activities compared to other selected phytochemicals. Further, it can be evaluated in the laboratory for promising therapeutic approaches for in vitro and in vivo studies.

Akt / GSK3β / Nrf2 / HO-1 pathway activation by flurbiprofen protects the hippocampal neurons in a rat model of glutamate excitotoxicity

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates redox homeostasis of the cell through regulation of the antioxidant response element genes transcription. Nrf2 also regulates the antiapoptotic Bcl-2 gene. Nrf2 degradation and nuclear translocation is regulated by upstream kinases Akt and GSK3β. Glutamate excitotoxicity is a process of neuronal cells death due to excessive activation of glutamate receptors. Glutamate excitotoxicity participates in the pathophysiology of several acute and chronic neurological conditions. In addition, glutamate excitotoxicity interrupts the PI3K/Akt prosurvival pathway so GSK3β remains active. Active GSK3β increases Nrf2 degradation, decreases Nrf2 nuclear translocation and increases Nrf2 nuclear export which decreases the ARE genes transcription such as, SOD, GSH synthesis enzyme and HO-1. Also, Bcl-2 transcription decreases. Flurbiprofen is a COX inhibitor. Previous studies showed that it has a neuroprotective effect in neurodegeneration and in focal cerebral ischemia/reperfusion model. In our research we aimed to test the hypothesis that flurbiprofen may have a neuroprotective effect in a rat model of glutamate-induced excitotoxicity and this neuroprotection may occur through modulation of (Akt/GSK3β/Nrf2/HO-1) pathway. Rats were divided into 4 groups; control, MSG (2.5 g/Kg, i.p), low dose FB (5 mg/kg, i.p) and high dose FB (10 mg/kg, i.p). We found that low and high doses FB decreased COX-2, PGE2, NO and MDA and increased SOD and GSH in brain compared to MSG group. High dose was more effective than low dose. Western blotting analysis in hippocampus tissue showed that high dose FB increased p-Akt, p-GSK3β, nuclear Nrf2 and HO-1 and decreased cytosolic Nrf2 level in comparison with MSG group. Immunohistochemical analysis in hippocampus and cerebral cortex showed that high dose FB increased Bcl-2 and decreased Bax compared to MSG group. In addition, FB increased the number of intact neurons in hippocampus areas and cerebral cortex neurons and showed an anxiolytic-like action in OF and EPM tests. These findings suggest that FB has a neuroprotective effect in glutamate-induced excitotoxicity model through reduction of the glutamate excitotoxicity damage and activation of the survival pathway. These may occur due to modulation the survival pathway (Akt/GSK3β/Nrf2/HO-1) and inhibition of COX-2.

NADPH and Mito-Apocynin Treatment Protects Against KA-Induced Excitotoxic Injury Through Autophagy Pathway

AimPrevious research recognizes that NADPH can produce reduced glutathione (GSH) as a coenzyme and produce ROS as a substrate of NADPH oxidase (NOX). Besides, excessive activation of glutamate receptors results in mitochondrial impairment. The study aims at spelling out the effects of NADPH and Mito-apocynin, a NOX inhibitor which specifically targets the mitochondria, on the excitotoxicity induced by Kainic acid (KA) and its mechanism.MethodsThe in vivo neuronal excitotoxicity model was constructed by stereotypically injecting KA into the unilateral striatum of mice. Administrated NADPH (i.v, intravenous) 30 min prior and Mito-apocynin (i.g, intragastric) 1 day prior, respectively, then kept administrating daily until mice were sacrificed 14 days later. Nissl staining measured the lesion of striatum and survival status of neurons. Cylinder test of forelimb asymmetry and the adhesive removal test reflected the behavioral deficit caused by neural dysfunction. Determined Total superoxide dismutase (T-SOD), malondialdehyde (MDA), and GSH indicated oxidative stress. Western blot presented the expression levels of LC3-II/LC3-I, SQSTM1/p62, TIGAR, and NOX4. Assessed oxygen consumption rate using High-Resolution Respirometry. In vitro, the MitoSOX Indicator reflected superoxide released by neuron mitochondria. JC-1 and ATP assay Kit were used to detect mitochondrial membrane potential (MMP) and energy metabolism, respectively.ResultsIn this study, we have successfully established excitotoxic model by KA in vivo and in vitro. KA induced decreased SOD activity and increased MDA concentration. KA cause the change of LC3-II/LC3-I, SQSTM1/p62, and TIGAR expression, indicating the autophagy activation. NADPH plays a protective role in vivo and in vitro. It reversed the KA-mediated changes in LC3, SQSTM1/p62, TIGAR, and NOX4 protein expression. Mito-apocynin inhibited KA-induced increases in mitochondrial NOX4 expression and activity. Compared with NADPH, the combination showed more significant neuroprotective effects, presenting more neurons survive and better motor function recovery. The combination also better inhibited the over-activated autophagy. In vitro, combination of NADPH and Mito-apocynin performed better in restoring mitochondria membrane potential.ConclusionIn summary, combined administration of NADPH and NOX inhibitors offers better neuroprotection by reducing NADPH as a NOX substrate to generate ROS. The combined use of NADPH and Mito-apocynin can better restore neurons and mitochondrial function through autophagy pathway.

Excitotoxicity in the pathogenesis of neurological and psychiatric disorders: Therapeutic implications.

Neurological and psychiatric disorders are leading contributors to the global disease burden, having a serious impact on the quality of life of both patients and their relatives. Although the molecular events underlying these heterogeneous diseases remain poorly understood, some studies have raised the idea of common mechanisms involved. In excitotoxicity, there is an excessive activation of glutamate receptors by excitatory amino acids, leading to neuronal damage. Thus, the excessive release of glutamate can lead to a dysregulation of Ca2+ homeostasis, triggering the production of free radicals and oxidative stress, mitochondrial dysfunction and eventually cell death. Although there is a consensus in considering excitotoxicity as a hallmark in most neurodegenerative diseases, increasing evidence points to the relevant role of this pathological mechanism in other illnesses affecting the central nervous system. Consequently, antagonists of glutamate receptors are used in current treatments or in clinical trials in both neurological and psychiatric disorders. However, drugs modulating other aspects of the excitotoxic mechanism could be more beneficial. This review discusses how excitotoxicity is involved in the pathogenesis of different neurological and psychiatric disorders and the promising strategies targeting the excitotoxic insult.

Mechanism of Neuroprotection Against Experimental Spinal Cord Injury by Riluzole or Methylprednisolone.

Any spinal cord injury carries the potential for persistent disability affecting motor, sensory and autonomic functions. To prevent this outcome, it is highly desirable to block a chain of deleterious reactions developing in the spinal areas immediately around the primary lesion. Thus, early timing of pharmacological neuroprotection should be one major strategy whose impact may be first studied with preclinical models. Using a simple in vitro model of the rat spinal cord it is possible to mimic pathological processes like excitotoxicity that damages neurons because of excessive glutamate receptor activation due to injury, or hypoxic/dysmetabolic insult that preferentially affects glia following vascular dysfunction. While ongoing research is exploring the various components of pathways leading to cell death, current treatment principally relies on the off-label use of riluzole (RLZ) or methylprednisolone sodium succinate (MPSS). The mechanism of action of these drugs is diverse as RLZ targets mainly neurons and MPSS targets glia. Even when applied after a transient excitotoxic stimulus, RLZ can provide effective prevention of secondary excitotoxic damage to premotoneurons, although not to motoneurons that remain very vulnerable. This observation indicates persistent inability to express locomotor activity despite pharmacological treatment conferringsome histological protection. MPSS can protect glia from dysmetabolic insult, yet it remains poorly effective to prevent neuronal death. In summary, it appears that these pharmacological agents can produce delayed protection for certain cell types only, and that their combined administration does not provide additional benefit. The search should continue for better, mechanism-based neuroprotective agents.

Differential regulation of the Rac1 GTPase–activating protein (GAP) BCR during oxygen/glucose deprivation in hippocampal and cortical neurons

Brain ischemia causes oxygen and glucose deprivation (OGD) in neurons, triggering a cascade of events leading to synaptic accumulation of glutamate. Excessive activation of glutamate receptors causes excitotoxicity and delayed cell death in vulnerable neurons. Following global cerebral ischemia, hippocampal CA1 pyramidal neurons are more vulnerable to injury than their cortical counterparts, but the mechanisms that underlie this difference are unclear. Signaling via Rho-family small GTPases, their upstream guanine nucleotide exchange factors, and GTPase-activating proteins (GAPs) is differentially dysregulated in response to OGD/ischemia in hippocampal and cortical neurons. Increased Rac1 activity caused by OGD/ischemia contributes to neuronal death in hippocampal neurons via diverse effects on NADPH oxidase activity and dendritic spine morphology. The Rac1 guanine nucleotide exchange factor Tiam1 mediates an OGD-induced increase in Rac1 activity in hippocampal neurons; however, the identity of an antagonistic GAP remains elusive. Here we show that the Rac1 GAP breakpoint cluster region (BCR) associates with NMDA receptors (NMDARs) along with Tiam1 and that this protein complex is more abundant in hippocampal compared with cortical neurons. Although total BCR is similar in the two neuronal types, BCR is more active in hippocampal compared with cortical neurons. OGD causes an NMDAR- and Ca2+-permeable AMPAR-dependent deactivation of BCR in hippocampal but not cortical neurons. BCR knockdown occludes OGD-induced Rac1 activation in hippocampal neurons. Furthermore, disrupting the Tiam1–NMDAR interaction with a fragment of Tiam1 blocks OGD-induced Tiam1 activation but has no effect on the deactivation of BCR. This work identifies BCR as a critical player in Rac1 regulation during OGD in hippocampal neurons.

Mystixin-7 Peptide Protects Ionotropic Glutamatergic Mechanisms against Glutamate-Induced Excitotoxicity In Vitro.

Hyperactivation of the N-methyl-D-aspartic acid type glutamate receptors (NMDARs) causes glutamate excitotoxicity, a process potentially important for many neurological diseases. This study aims to investigate protective effects of the synthetic corticotrophin-releasing factor-like peptide, mystixin-7 (MTX), on model glutamate-induced excitotoxicity in vitro. The technique online monitoring of electrophysiological parameters (excitatory glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPAR) and NMDAR-dependent postsynaptic mechanisms) in the olfactory cortex slices was used. Application of L-glutamate in toxic concentration (20 mM) on slices evoked hyperactivation of NMDARs and weaker activation of the AMPARs. Upon further action agonist, the excessive activation of glutamate receptors was replaced by their irreversible blockade. Pretreatment of the slices using MTX in different concentrations (50 and 100 mg/mL) protected both NMDARs and AMPARs from glutamate-induced damage. An enzymatic treatment of MTX reduced hyperactivation of both NMDARs and AMPARs. The present study demonstrated that MTX minipeptide protected the functioning of both NMDARs and AMPARs against glutamate-induced damage. The MTX peptide is a prospective candidate for elaborated medication in treatment of neurological diseases.

GLUTAMATERGIC SYSTEM MODULATORS AS AGENTS IN PREVENTION AND MANAGEMENT OF CHEMOTHERAPY- INDUCED POLYNEUROPATHY

Polyneuropathy is a common and important chemotherapy-induced adverse effect which often leads to dose modifications and impact on patients’ quality of life. Limited treatment options for prevention and management of this neuropathology stimulate further research on the topic. Recent attention has been focused on downregulation of glial glutamate transporter expression observed in spinal region of rodents treated with cancer chemotherapy drugs. Consequent extrasynaptic glutamate overflow could be considered a key element in neuropathic pathogenesis resulting in excessive activation of glutamate receptors and neuronal hyper-excitability, finally contributing to develop neuropathic condition. Recently, the onset of neuropathy in bortezomib treated rats could be prevented by preemptive administration of drugs promoting glial glutamate transporter expression and antagonism at mGlur5, a metabotropic receptor which reinforces glutamatergic transmission in presence of high extracellular glutamate concentrations. These findings point to glial-glutamate system dysregulation as a main mechanism in the pathogenesis of anticancer chemotherapy induced neuropathy.

Neuroprotection induced by NMDA preconditioning as a strategy to understand brain tolerance mechanism.

Excitotoxicity refers to toxicity caused by abnormal concentrations of glutamate in the synaptic cleft that may lead to neuronal death. Since its description, the phenomenon of glutamatergic excitotoxicity has been implicated in the physiopathology of a wide range of neurological and psychiatric disorders, from acute brain damage such as traumatic brain injury, ischemia as well as chronic conditions like epilepsy, depression and neurodegenerative pathologies such as Huntington's, Parkinson's and Alzheimer's diseases. Excessive stimulation of glutamatergic receptors, mainly N-methyl-D-aspartate (NMDA) receptors (NMDAR), can have numerous adverse effects on the cell viability, including increased nitric oxide release (NO), activation of proteases, increased production of reactive oxygen (ROS) and nitrogen (RNS) species and massive influx of calcium ions (Ca2+), resulting in cell death. Thus, the use of strategies that modulate the excitotoxic cell damage represents a perspective for the treatment of diseases such as Parkinson's and Alzheimer's diseases, ischemia, traumatic brain injury (TBI) and seizures.

Investigating dynamic structural and mechanical changes of neuroblastoma cells associated with glutamate-mediated neurodegeneration.

Glutamate-mediated neurodegeneration resulting from excessive activation of glutamate receptors is recognized as one of the major causes of various neurological disorders such as Alzheimer's and Huntington's diseases. However, the underlying mechanisms in the neurodegenerative process remain unidentified. Here, we investigate the real-time dynamic structural and mechanical changes associated with the neurodegeneration induced by the activation of N-methyl-D-aspartate (NMDA) receptors (a subtype of glutamate receptors) at the nanoscale. Atomic force microscopy (AFM) is employed to measure the three-dimensional (3-D) topography and mechanical properties of live SH-SY5Y cells under stimulus of NMDA receptors. A significant increase in surface roughness and stiffness of the cell is observed after NMDA treatment, which indicates the time-dependent neuronal cell behavior under NMDA-mediated neurodegeneration. The present AFM based study further advance our understanding of the neurodegenerative process to elucidate the pathways and mechanisms that govern NMDA induced neurodegeneration, so as to facilitate the development of novel therapeutic strategies for neurodegenerative diseases.

Interleukin‐1 beta enhances endocytosis of glial glutamate transporters in the spinal dorsal horn through activating protein kinase C

Excessive activation of glutamate receptors in spinal dorsal horn neurons is a key mechanism leading to abnormal neuronal activation in pathological pain conditions. Previous studies have shown that activation of glutamate receptors in the spinal dorsal horn is enhanced by impaired glial glutamate transporter functions and proinflammatory cytokines including interleukin-1 beta (IL-1β). In this study, we for the first time revealed that spinal glial glutamate transporter activities in the neuropathic animals are attenuated by endogenous IL-1β. Specifically, we demonstrated that nerve injury results in an increased expression of IL-1β and activation of PKC in the spinal dorsal horn as well as suppression of glial glutamate uptake activities. We provided evidence that the nerve-injury induced suppression of glial glutamate uptake is at least in part ascribed to endogenous IL-1β and activation of PKC in the spinal dorsal horn. IL-1β reduces glial glutamate transporter activities through enhancing the endocytosis of both GLT-1 and GLAST glial glutamate transporters. The IL-1β induced trafficking of glial glutamate transporters is through the calcium/PKC signaling pathway, and the dynamin-dependent endocytosis, which is dependent on the integrity of actin filaments. The signaling pathway regulating glial glutamate transporters revealed in this study provides novel targets to attenuate aberrant activation of glutamate receptors in the spinal dorsal horn, which could ultimately help the development of analgesics.

Distinct Subunit-specific α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Trafficking Mechanisms in Cultured Cortical and Hippocampal Neurons in Response to Oxygen and Glucose Deprivation

Brain ischemia occurs when the blood supply to the brain is interrupted, leading to oxygen and glucose deprivation (OGD). This triggers a cascade of events causing a synaptic accumulation of glutamate. Excessive activation of glutamate receptors results in excitotoxicity and delayed cell death in vulnerable neurons. Following global cerebral ischemia, hippocampal CA1 pyramidal neurons are more vulnerable to injury than their cortical counterparts. The mechanisms that underlie this difference are unclear. Cultured hippocampal neurons respond to OGD with a rapid internalization of AMPA receptor (AMPAR) subunit GluA2, resulting in a switch from GluA2-containing Ca(2+)-impermeable receptors to GluA2-lacking Ca(2+)-permeable subtypes (CP-AMPARs). GluA2 internalization is a critical component of OGD-induced cell death in hippocampal neurons. It is unknown how AMPAR trafficking is affected in cortical neurons following OGD. Here, we show that cultured cortical neurons are resistant to an OGD insult that causes cell death in hippocampal neurons. GluA1 is inserted at the plasma membrane in both cortical and hippocampal neurons in response to OGD. In contrast, OGD causes a rapid endocytosis of GluA2 in hippocampal neurons, which is absent in cortical neurons. These data demonstrate that populations of neurons with different vulnerabilities to OGD recruit distinct cell biological mechanisms in response to insult, and that a crucial aspect of the mechanism leading to OGD-induced cell death is absent in cortical neurons. This strongly suggests that the absence of OGD-induced GluA2 trafficking contributes to the relatively low vulnerability of cortical neurons to ischemia.

Abeta(1-42) Enhances Neuronal Excitability in the CA1 via NR2B Subunit-Containing NMDA Receptors

Neuronal hyperexcitability is a phenomenon associated with early Alzheimer's disease. The underlying mechanism is considered to involve excessive activation of glutamate receptors; however, the exact molecular pathway remains to be determined. Extracellular recording from the CA1 of hippocampal slices is a long-standing standard for a range of studies both in basic research and in neuropharmacology. Evoked field potentials (fEPSPs) are regarded as the input, while spiking rate is regarded as the output of the neuronal network; however, the relationship between these two phenomena is not fully clear. We investigated the relationship between spontaneous spiking and evoked fEPSPs using mouse hippocampal slices. Blocking AMPA receptors (AMPARs) with CNQX abolished fEPSPs, but left firing rate unchanged. NMDA receptor (NMDAR) blockade with MK801 decreased neuronal spiking dose dependently without altering fEPSPs. Activating NMDARs by small concentration of NMDA induced a trend of increased firing. These results suggest that fEPSPs are mediated by synaptic activation of AMPARs, while spontaneous firing is regulated by the activation of extrasynaptic NMDARs. Synaptotoxic Abeta(1-42) increased firing activity without modifying evoked fEPSPs. This hyperexcitation was prevented by ifenprodil, an antagonist of the NR2B NMDARs. Overall, these results suggest that Abeta(1-42) induced neuronal overactivity is not dependent on AMPARs but requires NR2B.

Endogenous Interleukin-1β in Neuropathic Rats Enhances Glutamate Release from the Primary Afferents in the Spinal Dorsal Horn through Coupling with Presynaptic N-Methyl-d-aspartic Acid Receptors*♦

Excessive activation of glutamate receptors and overproduction of proinflammatory cytokines, including interleukin-1β (IL-1β) in the spinal dorsal horn, are key mechanisms underlying the development and maintenance of neuropathic pain. In this study, we investigated the mechanisms by which endogenous IL-1β alters glutamatergic synaptic transmission in the spinal dorsal horn in rats with neuropathic pain induced by ligation of the L5 spinal nerve. We demonstrated that endogenous IL-1β in neuropathic rats enhances glutamate release from the primary afferent terminals and non-NMDA glutamate receptor activities in postsynaptic neurons in the spinal dorsal horn. Myeloid differentiation primary response protein 88 (MyD88) is a mediator used by IL-1β to enhance non-NMDA glutamate receptor activities in postsynaptic neurons in the spinal dorsal horn. Presynaptic NMDA receptors are effector receptors used by the endogenous IL-1β to enhance glutamate release from the primary afferents in neuropathic rats. This is further supported by the fact that NMDA currents recorded from small neurons in the dorsal root ganglion of normal rats are potentiated by exogenous IL-1β. Furthermore, we provided evidence that functional coupling between IL-1β receptors and presynaptic NMDA receptors at the primary afferent terminals is mediated by the neutral sphingomyelinase/ceramide signaling pathway. Hence, functional coupling between IL-1β receptors and presynaptic NMDA receptors at the primary afferent terminals is a crucial mechanism leading to enhanced glutamate release and activation of non-NMDA receptors in the spinal dorsal horn neurons in neuropathic pain conditions. Interruption of such functional coupling could be an effective approach for the treatment of neuropathic pain.

Excitation BolsTORs Motor Neurons in ALS Mice

It is unclear why motor neurons selectively degenerate in amyotrophic lateral sclerosis (ALS). Saxena etal. (2013) demonstrate that excitation of motor neurons can prevent their demise in a mouse model of inherited ALS by a mechanism involving the mTOR pathway.

Synthesis of phenylalaninol-derived oxazolopyrrolidone lactams and evaluation as NMDA receptor antagonists

N-Methyl-d-aspartate (NMDA) receptor antagonists are known to rescue neuronal cell death caused by excessive activation of glutamate receptors. This phenomenon, known as excitotoxicity, is implicated in the pathogenesis of several neurodegenerative disorders including ischemia, Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Unfortunately, some NMDA receptor antagonists have shown discouraging results when tested in clinical trials. However, recent advances in the physiology and pharmacology of the NMDA receptor have kept interest alive in modulating NMDA receptors for therapeutic intervention. We present here the synthesis of a small library of phenylalaninol-derived oxazolopyrrolidone lactams and their evaluation as NMDA receptor antagonists. The compounds were easily synthesized in yields up to 92 %. In addition, one of the compounds has a 50 % inhibitory concentration (IC 50) of 62 μM and offers potential to develop more potent NMDA receptor antagonists.

The NMDA receptor subunit GluN3A protects against 3-nitroproprionic-induced striatal lesions via inhibition of calpain activation

Excitotoxicity due to excessive activation of glutamate receptors is a primary mediator of cell death in acute and chronic neurological disorders, and NMDA-type glutamate receptors (NMDARs) are thought to be involved. NMDARs assemble from heteromeric combinations of GluN1, GluN2 and GluN3 subunits, yielding a variety of receptor subtypes that differ in biophysical properties, signaling, and synaptic targeting. Inclusion of inhibitory GluN3 subunits reduces Ca2+ influx via NMDAR channels and alters their synaptic targeting, thus modifying the two hallmarks of NMDARs that are critical for their roles on neuronal death and survival. Here we evaluated the neuroprotective potential of GluN3A subunits by analyzing the susceptibility to striatal excitotoxic damage of transgenic mice overexpressing GluN3A. We found that mild GluN3A overexpression protected susceptible striatal neurons from lesions induced by the neurotoxin 3-nitropropionic acid (3-NP), an inhibitor of mitochondrial complex II/succinate dehydrogenase. GluN3A-mediated neuroprotection was dose-dependent, and correlated with the levels of transgenic GluN3A expressed by two different mice strains. Neuroprotection was associated with a potent reduction of the activation of calpain, a Ca2+-dependent protease, which was measured as a decrease in 3-NP-induced fodrin and STEP cleavage in GluN3A transgenic mice relative to controls. We further show that transgenic GluN3A subunits incorporate into extrasynaptic compartments in mouse striatum, suggesting that reductions of toxic calpain activation might be linked to inhibition by GluN3A of pathological extrasynaptic NMDAR activity.

Temperature management in central nervous infection

Temperature management in central nervous infection

Tonic NMDA receptor-mediated current in prefrontal cortical pyramidal cells and fast-spiking interneurons

Tonically activated neuronal currents mediated by N-methyl-d-aspartate receptors (NMDARs) have been hypothesized to contribute to normal neuronal function as well as to neuronal pathology resulting from excessive activation of glutamate receptors (e.g., excitotoxicity). Whereas cortical excitatory cells are very vulnerable to excitotoxic insult, the data regarding resistance of inhibitory cells (or interneurons) are inconsistent. Types of neurons with more pronounced tonic NMDAR current potentially associated with the activation of extrasynaptic NMDARs could be expected to be more vulnerable to excessive activation by glutamate. In this study, we compared tonic activation of NMDARs in excitatory pyramidal cells and inhibitory fast-spiking interneurons in prefrontal cortical slices. We assessed tonic NMDAR current by measuring holding current shift as well as noise reduction following NMDAR blockade after removal of spontaneous glutamate release. In addition, we compared NMDAR miniature excitatory postsynaptic currents (EPSCs) in both cell types. We have demonstrated for the first time that tonic NMDAR currents are present in inhibitory fast-spiking interneurons. We found that the magnitude of tonic NMDAR current is similar in pyramidal cells and fast-spiking interneurons, and that quantal release of glutamate does not significantly impact tonic NMDAR current.