Inhibition Of NMDA Receptors Research Articles

Inhibitory effects of fucoidan on NMDA receptors and l-type Ca2+ channels regulating the Ca2+ responses in rat neurons

Context: Fucoidan, a sulphated polysaccharide extracted from brown algae [Fucus vesiculosus Linn. (Fucaceae)], has multiple biological activities.Objective: The effects of fucoidan on Ca2+ responses of rat neurons and its probable mechanisms with focus on glutamate receptors were examined.Materials and methods: The neurons isolated from the cortex and hippocampi of Wistar rats in postnatal day 1 were employed. The intracellular Ca2+ responses triggered by various stimuli were measured in vitro by Fura-2/AM. Fucoidan at 0.5 mg/mL or 1.5 mg/mL was applied for 3 min to determine its effects on Ca2+ responses. RT-PCR was used to determine the mRNA expression of neuron receptors treated with fucoidan at 0.5 mg/mL for 3 h.Results: The Ca2+ responses induced by NMDA were 100% suppressed by fucoidan, and those induced by Bay K8644 90% in the cortical neurons. However, fucoidan has no significant effect on the Ca2+ responses of cortical neurons induced by AMPA or quisqualate. Meanwhile, the Ca2+ responses of hippocampal neurons induced by glutamate, ACPD or adrenaline, showed only a slight decrease following fucoidan treatment. RT-PCR assays of cortical and hippocampal neurons showed that fucoidan treatment significantly decreased the mRNA expression of NMDA-NR1 receptor and the primer pair for l-type Ca2+ channels, PR1/PR2.Discussion and conclusions: Our data indicate that fucoidan suppresses the intracellular Ca2+ responses by selectively inhibiting NMDA receptors in cortical neurons and l-type Ca2+ channels in hippocampal neurons. A wide spectrum of fucoidan binding to cell membrane may be useful for designing a general purpose drug in future.

Agmatine preferentially antagonizes GluN2B-containing N-methyl-d-aspartate receptors in spinal cord.

The role of the N-methyl-d-aspartate receptor (NMDAr) as a contributor to maladaptive neuroplasticity underlying the maintenance of chronic pain is well established. Agmatine, an NMDAr antagonist, has been shown to reverse tactile hypersensitivity in rodent models of neuropathic pain while lacking the side effects characteristic of global NMDAr antagonism, including sedation and motor impairment, indicating a likely subunit specificity of agmatine's NMDAr inhibition. The present study assessed whether agmatine inhibits subunit-specific NMDAr-mediated current in the dorsal horn of mouse spinal cord slices. We isolated NMDAr-mediated excitatory postsynaptic currents (EPSCs) in small lamina II dorsal horn neurons evoked by optogenetic stimulation of Nav1.8-containing nociceptive afferents. We determined that agmatine abbreviated the amplitude, duration, and decay constant of NMDAr-mediated EPSCs similarly to the application of the GluN2B antagonist ifenprodil. In addition, we developed a site-specific knockdown of the GluN2B subunit of the NMDAr. We assessed whether agmatine and ifenprodil were able to inhibit NMDAr-mediated current in the spinal cord dorsal horn of mice lacking the GluN2B subunit of the NMDAr by analysis of electrically evoked EPSCs. In control mouse spinal cord, agmatine and ifenprodil both inhibited amplitude and accelerated the decay kinetics. However, agmatine and ifenprodil failed to attenuate the decay kinetics of NMDAr-mediated EPSCs in the GluN2B-knockdown mouse spinal cord. The present study indicates that agmatine preferentially antagonizes GluN2B-containing NMDArs in mouse dorsal horn neurons. NEW & NOTEWORTHY Our study is the first to report that agmatine preferentially antagonizes the GluN2B receptor subunit of the N-methyl-d-aspartate (NMDA) receptor in spinal cord. The preferential targeting of GluN2B receptor is consistent with the pharmacological profile of agmatine in that it reduces chronic pain without the motor side effects commonly seen with non-subunit-selective NMDA receptor antagonists.

Strong Inhibitory Effect, Low Cytotoxicity and High Plasma Stability of Steroidal Inhibitors of N-Methyl-D-Aspartate Receptors With C-3 Amide Structural Motif.

Herein, we report the synthesis, structure-activity relationship study, and biological evaluation of neurosteroid inhibitors of N-methyl-D-aspartate receptors (NMDARs) receptors that employ an amide structural motif, relative to pregnanolone glutamate (PAG) – a compound with neuroprotective properties. All compounds were found to be more potent NMDAR inhibitors (IC50 values varying from 1.4 to 21.7 μM) than PAG (IC50 = 51.7 μM). Selected compound 6 was evaluated for its NMDAR subtype selectivity and its ability to inhibit AMPAR/GABAR responses. Compound 6 inhibits the NMDARs (8.3 receptors (8.3 ± 2.1 μM) more strongly than it does at the GABAR and AMPARs (17.0 receptors (17.0 ± 0.2 μM and 276.4 ± 178.7 μM, respectively). In addition, compound 6 (10 μM) decreases the frequency of action potentials recorded in cultured hippocampal neurons. Next, compounds 3, 5–7, 9, and 10 were not associated with mitotoxicity, hepatotoxicity nor ROS induction. Lastly, we were able to show that all compounds have improved rat and human plasma stability over PAG.

Interaction of aquaporin 4 and N-methyl-D-aspartate NMDA receptor 1 in traumatic brain injury of rats.

Objective(s):methyl-D-aspartate NMDA receptor (NMDAR) and aquaporin 4 (AQP4) are involved in the molecular cascade of edema after traumatic brain injury (TBI) and are potential targets of studies in pharmacology and medicine. However, their association and interactions are still unknown.Materials and Methods: We established a rat TBI model in this study. The cellular distribution patterns of AQP4 after inhibition of NMDAR were determined by Western blotting and immunoreactive staining. Furthermore, the regulation of NMDA receptor 1 by AQP4 was studied by injection of a viral vector targeting AQP4 by RNAi into the rat brain before TBI.Results:The results suggest that AQP4 protein expression increased significantly (P<0.05) after TBI and was down-regulated by the NMDAR inhibitor MK801. This decrease could be partly reversed using the NMDAR agonist NMDA. This indicated that AQP4 mRNA levels and protein expression are regulated by the NMDA signaling pathway. By injection of AQP4 RNAi viral vector into the brain of TBI rat models, we found that the mRNA and protein levels of NMDAR decreased significantly (P<0.05). This suggested that NMDAR is also regulated by AQP4.Conclusion:These data suggested that the inhibition of AQP4 down-regulates NMDAR expression, which might be one of the mechanisms involved in edema after TBI.

Kaempferol Inhibits Extra-synaptic NMDAR-Mediated Downregulation of TRkβ in Rat Hippocampus During Hypoxia

Cognitive dysfunction on chronic exposure to hypobaric hypoxia has been attributed to a myriad of survival and degenerative factors. Downregulation of Trkβ and compromised survival signaling has been ascribed as a major contributing factor for hypoxic neurodegeneration. The mechanisms leading to downregulation of Trkβ in hypoxia, however, remain to be elucidated. The present study aimed at investigating the upstream signaling mechanisms leading to Trkβ downregulation in hypoxia and the potential of Kaempferol in ameliorating these changes. Our results showed a duration-dependent increase in hypoxic neurodegeneration as measured by Fluoro-Jade C staining of hippocampal CA3 neurons. Protein expression studies revealed strong correlation of Trkβ with NR1 and NR2b expression on exposure to hypoxic stress. Administration of Kaempferol during hypoxic stress revealed its neuroprotective effect and Morris Water Maze test also highlighted its efficacy in improving spatial learning and memory. Further elucidation of the signaling mechanisms using specific inhibitors and in vitro silencing experiments confirmed involvement of extra-synaptic N-methyl-d-aspartate receptor (NMDAR) i.e. NR2b receptor subunit in downregulation of Trkβ under hypoxic conditions. ChIP assay showed involvement of E47 transcription factor in NR2b mediated Trkβ downregulation. Selective inhibition of signaling intermediate MLK2 by CEP11004 and inhibition of extra-synaptic NMDAR during hypoxic stress prevented Trkβ downregulation in the hippocampus of hypoxic rats. Administration of Kaempferol also inhibited phosphorylation of E47 and hypoxia-induced downregulation of Trkβ. The present study establishes the role of extra-synaptic NMDAR in hypoxia-induced downregulation of Trkβ and the efficacy of Kaempferol in inhibiting extra-synaptic NMDAR-mediated signaling.

Mechanism underlying NMDA blockade-induced inhibition of aggression in post-weaning socially isolated mice

When faced with stressful conditions, people with a tendency toward impulsive aggression may suddenly hurt others. We have previously shown that the blockade of NMDA receptors (NMDARs) within the ventral hippocampus (VH) produces anti-aggressive effects. However, little is known about the mechanism for tamping down stress-provoked attack behavior. Here, we report that expression of brain-derived neurotrophic factor (BDNF) after inhibition of NMDARs in the VH is required for blunting stress-provoked attack behavior in post-weaning socially isolated mice. Administration of NMDAR antagonist MK-801 decreased the phosphorylated eukaryotic elongation factor 2 (p-eEF2) and increased BDNF expression in the VH. Infusion of eEF2 kinase inhibitor NH125 to the VH decreased attack behavior and increased BDNF expression. Knockdown of BDNF in the VH blocked the anti-aggressive effect of MK-801 and NH125. Furthermore, MK-801 rapidly increased the activity of protein phosphatase 2A (PP2A). Intra-VH infusion of PP2A inhibitor okadaic acid blocked the anti-aggressive effects of MK-801. These results suggest that blockade of NMDAR reduces attack behavior through increasing PP2A activity leading to dephosphorylation of eEF2 and an increase in BDNF expression. Our findings indicate that the enhancement of BDNF expression is beneficial for preventing impulsive aggression in at-risk beings.

Dopamine D1 receptor in the medial prefrontal cortex mediates anxiety-like behaviors induced by blocking glutamatergic activity of the ventral hippocampus in rats

The medial prefrontal cortex (mPFC) receives direct and indirect projections from the ventral hippocampus (VH) and plays an important role in the regulation of anxiety. However, the effect of the mPFC dopamine D1 receptor on anxiety-like behaviors induced by inhibition of glutamatergic activity in the VH has not been described. Here, we examined the effects of SKF38393, a selective dopamine D1 receptor agonist, on anxiety-like behaviors induced by NMDA receptor inhibition in the VH and neuron firing activity of mPFC. Injection of MK-801 (6 μg/0.5 μl) into the VH produced anxiety-like behaviors in the elevated plus maze and open field tests, increased the firing activity of pyramidal neurons in the mPFC, and decreased the level of dopamine in the mPFC. Injection of SKF38393 (0.5 μg/0.5 μl) into the mPFC produced anxiolytic effects, and normalized the hyperactive firing activity of mPFC pyramidal neurons induced by MK-801, whereas in both normal and anxiety-like rats caused by MK-801, injection of SKF38393 into the mPFC decreased the firing activity of mPFC interneurons but did not affect the dopamine content in the mPFC. The present data demonstrate that decreased D1 receptor activation in the mPFC may mediate anxiety-like behaviors induced by inhibition of glutamatergic activity in the VH. The balance of D1 receptor activity between pyramidal neurons and interneurons is a crucial factor in maintaining normal conditions, and inhibitory glutamatergic activity in the VH induces hyperactivity of mPFC pyramidal neurons through decreases in dopamine release and in the amount of D1 receptor activation on mPFC pyramidal neurons, which may be a critical factor for anxiety disorders.

Inhibition of GluN2A NMDA receptors ameliorates synaptic plasticity deficits in the Fmr1-/y mouse model.

Fragile X syndrome (FXS) is a genetic condition that is the most common form of inherited intellectual impairment and causes a range of neurodevelopmental complications including learning disabilities and intellectual disability and shares many characteristics with autism spectrum disorder (ASD). In the FXS mouse model, Fmr1-/y , impaired synaptic plasticity was restored by pharmacologically inhibiting GluN2A-containing NMDA receptors but not GluN2B-containing receptors. Similar results were obtained by crossing Fmr1-/y with GluN2A knock-out (Grin2A-/- ) mice. These results suggest that dampening the elevated levels of GluN2A-containing NMDA receptors in Fmr1-/y mice has the potential to restore hyperexcitability of the neural circuitry to (a more) normal-like level of brain activity. NMDA receptors (NMDARs) play important roles in synaptic plasticity at central excitatory synapses, and dysregulation of their function may lead to severe disorders such Fragile X syndrome (FXS). FXS is caused by transcriptional silencing of the FMR1 gene followed by lack of the encoding protein. Here we examined the effects of pharmacological and genetic manipulation of hippocampal NMDAR functions in long-term potentiation (LTP) and depression (LTD). We found impaired NMDAR-dependent LTP in the Fmr1-deficient mice, which could be fully restored when GluN2A-containing NMDARs was pharmacological inhibited. Interestingly, similar LTP effects were observed when the GluN2A gene (Grin2a) was deleted in Fmr1-/y mice (Fmr1-/y /Grin2a-/- double knockout). In addition, GluN2A inhibition improved elevated mGluR5-dependent LTD to normal level in the Fmr1-/y mouse. These findings suggest that GluN2A is a promising target in FXS research that could help us better understand the disorder.

Fast changes of NMDA and AMPA receptor activity under acute hyperammonemia in vitro

It was established in experiments on cell cultures of neurons and astrocytes that ammonium ions at concentrations of 4–8 mM cause hyperexcitation of the neuronal network, as a result of which there is a disturbance of calcium homeostasis, which can lead to the death of neurons. In the present study, we investigated the effect of toxic doses of ammonium (8 mM NH4Cl) on the activity of NMDA and AMPA receptors and the role of these receptors in spontaneous synchronous activity (SSA). In a control experiment in the absence of NH4Cl, SSA is not suppressed by NMDA receptor inhibitors, but is suppressed by AMPA receptor antagonists. In the presence of toxic doses of NH4Cl, SSA is completely inhibited by NMDA receptor inhibitors in 63% of neurons and by AMPA receptor inhibitors in 33% of neurons. After short-term applications of toxic doses of ammonium, the amplitude of the Ca2+ response to 10 μM NMDA increases, and decreases in response to 500 nM FW (agonist of AMPA receptors). NMDA receptor blocker MK-801 (20 μM), competitive antagonist D-AP5 (10 μM) and competitive AMPA receptor antagonist NBQX (2 μM) abolished the activating ammonium mediated effect on the NMDA receptors while only MK-801, but not NBQX, abolished the inhibiting ammonium mediated effect on AMPA receptors. These data indicate that under acute hyperammonemia, the activity of NMDA receptors increases, while the activity of AMPA receptors decreases. This phenomenon could explain such a wide range of toxic effects of ammonium ions mediated by NMDA receptors.

Chronic d-serine supplementation impairs insulin secretion

ObjectiveThe metabolic role of d-serine, a non-proteinogenic NMDA receptor co-agonist, is poorly understood. Conversely, inhibition of pancreatic NMDA receptors as well as loss of the d-serine producing enzyme serine racemase have been shown to modulate insulin secretion. Thus, we aim to study the impact of chronic and acute d-serine supplementation on insulin secretion and other parameters of glucose homeostasis. MethodsWe apply MALDI FT-ICR mass spectrometry imaging, NMR based metabolomics, 16s rRNA gene sequencing of gut microbiota in combination with a detailed physiological characterization to unravel the metabolic action of d-serine in mice acutely and chronically treated with 1% d-serine in drinking water in combination with either chow or high fat diet feeding. Moreover, we identify SNPs in SRR, the enzyme converting L-to d-serine and two subunits of the NMDA receptor to associate with insulin secretion in humans, based on the analysis of 2760 non-diabetic Caucasian individuals. ResultsWe show that chronic elevation of d-serine results in reduced high fat diet intake. In addition, d-serine leads to diet-independent hyperglycemia due to blunted insulin secretion from pancreatic beta cells. Inhibition of alpha 2-adrenergic receptors rapidly restores glycemia and glucose tolerance in d-serine supplemented mice. Moreover, we show that single nucleotide polymorphisms (SNPs) in SRR as well as in individual NMDAR subunits are associated with insulin secretion in humans. ConclusionThus, we identify a novel role of d-serine in regulating systemic glucose metabolism through modulating insulin secretion.

Monoclonal antibodies from a patient with anti-NMDA receptor encephalitis.

ObjectiveAnti‐NMDA receptor encephalitis (ANRE) is a potentially lethal encephalitis attributed to autoantibodies against the N‐methyl‐D‐aspartate receptor (NMDAR). We sought to clone and characterize monoclonal antibodies (mAbs) from an ANRE patient.MethodsWe used a hybridoma method to clone two IgG mAbs from a female patient with ANRE without teratoma, and characterized their binding activities on NMDAR‐transfected cell lines, cultured primary rat neurons, and mouse hippocampus. We also assessed their effects on voluntary locomotor activity in mice and binding to NMDAR in vivo.ResultsThe mAbs are structurally distinct and arose from distinct B‐cell lineages. They recognize different epitopes on the GluN1 amino terminal domain (ATD), yet both require amino acids important for post‐translational modification. Both mAbs bind subsets of GluN1 on cultured rat hippocampal neurons. The 5F5 mAb binds mouse brain hippocampal tissues, and the GluN1 recognized on cultured rat neurons was substantially extra‐synaptic. Antibody binding to primary hippocampal neurons induced receptor internalization. The NMDAR inhibitor MK‐801 inhibited internalization without preventing mAb binding; AP5 inhibited both mAb binding and internalization. Exposure of mice to the mAbs following permeabilization of the blood brain barrier increased voluntary wheel running activity, similar to low doses of the NMDAR inhibitor, MK‐801.InterpretationThese mAbs recapitulate features demonstrated in previous studies of ANRE patient CSF, and exert effects on NMDAR in vitro and in vivo consistent with modulation of NMDAR activity.

NMDA-receptor inhibition and oxidative stress during hippocampal maturation differentially alter parvalbumin expression and gamma-band activity

Dysfunction of parvalbumin (PV)-expressing interneurons is thought to underlie the alterations of gamma-band oscillations observed in schizophrenia. Although the pathomechanisms of this disease remain unclear, oxidative stress induced by NMDA receptor (NMDAR) hypofunction and decreased glutathione (GSH) synthesizing capacity have been shown to lead to PV-loss and aberrant oscillatory activity. However, the individual contributions of NMDAR-inhibition and GSH-depletion to the developmental alterations observed in schizophrenia are largely unknown. We therefore investigated each condition in isolation using hippocampal slice cultures wherein interneuron maturation occurs entirely in vitro. Although both treatments caused oxidative stress, NMDAR-inhibition led to an immediate reduction in gamma oscillation frequency and a delayed loss of PV. In contrast, GSH-depletion immediately decreased PV expression and increased power, without affecting frequency. Hence, although disturbances of PV-expression and gamma oscillations coexist in schizophrenia, they can arise from separate pathological processes.

Distinct Roles of NMDAR and mGluR5 in Light Exposure Reversal of Feedforward Synaptic Strength in V1 of Juvenile Mice after Binocular Vision Deprivation

In the visual cortex, sensory deprivation causes global augmentation of the amplitude of AMPA receptor-mediated miniature EPSCs in layer 2/3 pyramidal cells and enhancement of NMDA receptor-dependent long-term potentiation (LTP) in cells activated in layer 4, effects that are both rapidly reversed by light exposure. Layer 2/3 pyramidal cells receive both feedforward input from layer 4 and intra-cortical lateral input from the same layer, LTP is mainly induced by the former input. Whether feedforward excitatory synaptic strength is affected by visual deprivation and light exposure, how this synaptic strength correlates with the magnitude of LTP in this pathway, and the underlying mechanism have not been explored. Here, we showed that in juvenile mice, both dark rearing and dark exposure reduced the feedforward excitatory synaptic strength, and the effects can be reversed completely by 10–12 h and 6–8 h light exposure, respectively. However, inhibition of NMDA receptors by CPP or mGluR5 by MPEP, prevented the effect of light exposure on the mice reared in the dark from birth, while only inhibition of NMDAR prevented the effect of light exposure on dark-exposed mice. These results suggested that the activation of both NMDAR and mGluR5 are essential in the light exposure reversal of feedforward excitatory synaptic strength in the dark reared mice from birth; while in the dark exposed mice, only activation of NMDAR is required.

Intra-accumbal administration of AMN082, a metabotropic glutamate receptor type 7 allosteric agonist, inhibits the acquisition but not the expression of morphine-induced conditioned place preference in rats

The nucleus accumbens (NAc) plays a primary role in opioid reward. The actions of glutamate are mediated by the activation of ionotropic and metabotropic glutamate receptors (mGluRs). Previous documents have shown the extensive distributions of the different types of mGluRs, including mGluR7, in regions that are involved in opioid reward, such as the NAc. In this study, seventy male Wistar rats were used to investigate the role of mGluR7 receptors in the NAc on the acquisition and expression of morphine-induced conditioned place preference (CPP). In Experiment 1, to determine the effect of AMN082, a selective mGluR7 allosteric agonist, on the acquisition of morphine-induced conditioned place preference (CPP), the rats bilaterally received AMN082 (1, 3 and 5 μg/0.5 μL DMSO) during three-day conditioning by morphine (5 mg/kg). In Experiment 2, the rats bilaterally received AMN082 (5 μg/0.5 μL DMSO) 5 min prior to the post-conditioning test to investigate the effect of AMN082 on the expression of morphine-induced CPP. The results showed that the intra-accumbal injection of AMN082 prevents the acquisition of morphine-induced CPP in a dose-dependent manner. However, intra-accumbal injection of AMN082 had no effect on the expression of morphine-induced CPP. The findings propose that the mGluR7 in the NAc inhibits the acquisition of morphine-induced CPP that could be mediated by inhibition of NMDA receptors in the NAc.

Вплив модуляторів NMDA-рецепторів на біохімічні змінив сітківці при ішемічному та травматичному ураженні зорового аналізатора

Introduction. Glutamate exitotoxicity and hyperactivation of NMDA receptors play an important role in affecting the visual analyzer in cases of ischemia and trauma. It remains unexplored the influence of modulators of various sites of NMDA receptors on metabolic processes in the retina in these pathological conditions.The aim of the work – to determine the effect of NMDA receptor modulators on metabolic changes (oxidative stress, energy deficit, state of nitrogen oxide system, glutamate content) in the retina with the ischemic injury of the visual analyzer in rats and traumatic damage to the visual analyzer in rabbits.Research Methods. Experiments were conducted on 56 white male rats and 24 rabbits. Ischemic lesions of the visual analyzer in rats was caused by the creation of a one-sided ischemia-reperfusion in the a. ophthalmica.Traumatic damage of the visual analyzer in rabbits was caused by the action of a carbon dioxide stream under pressure on the cornea of the eye. NMDA receptor modulators were administered within 7 days before and 30 minutes after pathology simulation. Polyamino site blocker amantadine sulfate (5 mg/kg i/v) and phencyclidine site blocker memantine (20 mg/kg i/g) were used. The content of AT P, markers of oxidative-nitrosative stress, glutamate levels in retina, and the level of neuronspecific enolase (NSE) in serum were determined.Results and Discussion. The use of NMDA receptor inhibitors causes de-escalation of NSE levels in the blood, reduces energy deficit, oxidative-nitrosative stress, glutamate levels in the retina of ischemia-reperfusion of the eye in rats and contusion of the eye in rabbits. The polyamino site inhibitor amantadine sulfate exceeds (in 1.2-1.5 times, p&lt;0.05) the fencyclidine site inhibitor memantine by the ability to adjust the levels of ATP, MDA, oxide-modified proteins, to restore the activity of glutathione peroxidase in the retina on ischemic and traumatic lesions of visual analyzer.Conclusions. Thus, the modulators of the polyamino- and phencyclidine sites of the NMDA receptors showed a protective effect on neuroretina for both ischemic and traumatic damage of the visual analyzer in animals. The study of the effects of amantadine sulfate on reparative processes in the retina is a promising direction for further research.

Investigating the Inhibitory Effect of Fatty Acids on NMDA Receptor

&lt;p&gt;&lt;em&gt;Previous research has showed that AMPA receptor can be used as a molecular target for anti-epileptic drugs, and there is evidence of an inhibitory effect of several fatty acids on AMPA receptor, for example, &lt;/em&gt;&lt;em&gt;D&lt;/em&gt;&lt;em&gt;ecanoic &lt;/em&gt;&lt;em&gt;A&lt;/em&gt;&lt;em&gt;cid (DA), 4-&lt;/em&gt;&lt;em&gt;E&lt;/em&gt;&lt;em&gt;thyl &lt;/em&gt;&lt;em&gt;O&lt;/em&gt;&lt;em&gt;ctanoic &lt;/em&gt;&lt;em&gt;A&lt;/em&gt;&lt;em&gt;cid (4EOA) and 4-&lt;/em&gt;&lt;em&gt;B&lt;/em&gt;&lt;em&gt;utyl&lt;/em&gt;&lt;em&gt;c&lt;/em&gt;&lt;em&gt;y&lt;/em&gt;&lt;em&gt; C&lt;/em&gt;&lt;em&gt;loheaxne &lt;/em&gt;&lt;em&gt;C&lt;/em&gt;&lt;em&gt;arboxylic &lt;/em&gt;&lt;em&gt;A&lt;/em&gt;&lt;em&gt;cid (4BCCA). However, as NMDA receptor and AMPA receptor are quite similar in structures and are widely distributed in CNS, there is a concern on whether the three fatty acids also have an effect on NMDA receptor, and NMDA receptor inhibition may result in some unwanted side effects, such as hallucinations, nightmares, and memory loss. Two-electrode voltage clamp was performed on the oocytes of Xenopus Laevis expressing the NMDAR subunit GluN1/N2A, to record agonist evoked inward currents generated from oocytes exposed to different concentrations of fatty acid solutions. On further examination it was found that all of the three acids have some inhibitory effect on NMDA recceptor, and seem to act as non-competitive antagonists. The 4EOA has the strongest inhibition effect on NMDA receptor, followed by 4BCCA and DA. However, the three fatty acids only have a clear inhibitory effect when the concentration of the corresponding fatty acid is higher than 500 µM, which is considered high for clinical use. Moreover, the fatty acids tested had a stronger inhibitory effect on NMDA receptor containing the GluN1/N2B subunits.&lt;/em&gt;&lt;/p&gt;

Effects of neonatal MK-801 exposure on recognition memory and excitatory-inhibitory balance of hippocampus in adult female rats

Objective To investigate the long-term effects of repeated neonatal administration of dizocipline maleate (MK-801), the glutamate N-methyl-D-aspartate (NMDA) receptor antagonist, on recognition memory and hippocampal excitatory-inhibitory balance at the synaptic level in adult female rats. Methods Neonatal female Sprague-Dawley (SD) rats were randomly divided into model group and control group. Rats were administrated subcutaneously with MK-801 or normal saline from postnatal day (PND) 5 to PND14 (0.25 mg/kg, twice daily). (1) Object-in-context recognition test was performed on PND73-75. (2) The expression levels of vesicular glutamate transporter 1(VGLUT1) and vesicular GABA transporter(VGAT) in hippocampus were detected by immunohistochemical staining. Results (1) The preference index of model group for new objects was significantly lower than that of the control group (t=-2.762, P=0.012). (2) There was no significant difference in the expression of VGLUT1 in hippocampus of MK-801 mode group(P>0.05). Compared with control group(48.19±2.10), the VGAT level of model group in CA1(39.60±2.19) was lower. Compared with control group(CA1: (0.99±0.05), CA3: (1.28±0.02), the ratio of VGLUT1/VGAT was significantly upregulated in CA1(1.16±0.05)and CA3(1.44±0.03)(P<0.05). Conclusion Early NMDA receptor inhibition produces long-term deleterious effects on associative recognition memory and excitatory-inhibitory balance of hippocampus in female rats. These biochemical abnormalities may contribute to cognitive impairments observed in this study. Key words: MK-801; N-methyl-D-aspartate receptor; Recognition memory; Excitatory-inhibitory imbalance; Rat

Inhibition of NMDA Receptors Prevents the Loss of BDNF Function Induced by Amyloid β.

Brain-derived neurotrophic factor (BDNF) plays important functions in cell survival and differentiation, neuronal outgrowth and plasticity. In Alzheimer’s disease (AD), BDNF signaling is known to be impaired, partially because amyloid β (Aβ) induces truncation of BDNF main receptor, TrkB-full length (TrkB-FL). We have previously shown that such truncation is mediated by calpains, results in the formation of an intracellular domain (ICD) fragment and causes BDNF loss of function. Since calpains are Ca2+-dependent proteases, we hypothesized that excessive intracellular Ca2+ build-up could be due to dysfunctional N-methyl-d-aspartate receptors (NMDARs) activation. To experimentally address this hypothesis, we investigated whether TrkB-FL truncation by calpains and consequent BDNF loss of function could be prevented by NMDAR blockade. We herein demonstrate that a NMDAR antagonist, memantine, prevented excessive calpain activation and TrkB-FL truncation induced by Aβ25–35. When calpains were inhibited by calpastatin, BDNF was able to increase the dendritic spine density of neurons exposed to Aβ25135. Moreover, NMDAR inhibition by memantine also prevented Aβ-driven deleterious impact of BDNF loss of function on structural (spine density) and functional outcomes (synaptic potentiation). Collectively, these findings support NMDAR/Ca2+/calpains mechanistic involvement in Aβ-triggered BDNF signaling disruption.

GKAP Acts as a Genetic Modulator of NMDAR Signaling to Govern Invasive Tumor Growth

SummaryGenetic linkage analysis previously suggested that GKAP, a scaffold protein of the N-methyl-D-aspartate receptor (NMDAR), was a potential modifier of invasion in a mouse model of pancreatic neuroendocrine tumor (PanNET). Here, we establish that GKAP governs invasive growth and treatment response to NMDAR inhibitors of PanNET via its pivotal role in regulating NMDAR pathway activity. Combining genetic knockdown of GKAP and pharmacological inhibition of NMDAR, we implicate as downstream effectors FMRP and HSF1, which along with GKAP demonstrably support invasiveness of PanNET and pancreatic ductal adenocarcinoma cancer cells. Furthermore, we distilled genome-wide expression profiles orchestrated by the NMDAR-GKAP signaling axis, identifying transcriptome signatures in tumors with low/inhibited NMDAR activity that significantly associate with favorable patient prognosis in several cancer types.

Dexras1 is a homeostatic regulator of exercise-dependent proliferation and cell survival in the hippocampal neurogenic niche

Adult hippocampal neurogenesis is highly responsive to exercise, which promotes the proliferation of neural progenitor cells and the integration of newborn granule neurons in the dentate gyrus. Here we show that genetic ablation of the small GTPase, Dexras1, suppresses exercise-induced proliferation of neural progenitors, alters survival of mitotic and post-mitotic cells in a stage-specific manner, and increases the number of mature newborn granule neurons. Dexras1 is required for exercise-triggered recruitment of quiescent neural progenitors into the cell cycle. Pharmacological inhibition of NMDA receptors enhances SGZ cell proliferation in wild-type but not dexras1-deficient mice, suggesting that NMDA receptor-mediated signaling is dependent on Dexras1. At the molecular level, the absence of Dexras1 abolishes exercise-dependent activation of ERK/MAPK and CREB, and inhibits the upregulation of NMDA receptor subunit NR2A, bdnf, trkB and vegf-a expression in the dentate gyrus. Our study reveals Dexras1 as an important stage-specific regulator of exercise-induced neurogenesis in the adult hippocampus by enhancing pro-mitogenic signaling to neural progenitor cells and modulating cell survival.