N-methyl-D-aspartate Receptor Research Articles

Norepinephrine triggers glutamatergic long-term potentiation in hypothalamic paraventricular nucleus magnocellular neuroendocrine cells through postsynaptic β1-AR/PKA signaling pathway in vitro in rats.

Norepinephrine (NE) modulates synaptic transmission and long-term plasticity through distinct subtype adrenergic receptor (AR)-mediated-intracellular signaling cascades. However, the role of NE modulates glutamatergic long-term potentiation (LTP) in the hypothalamic paraventricular nucleus (PVN) magnocellular neuroendocrine cells (MNCs) is unclear. We here investigate the effect of NE on high frequency stimulation (HFS)-induced glutamatergic LTP in rat hypothalamic PVN MNCs in vitro, by whole-cell patch-clamp recording, biocytin staining and pharmacological methods. Delivery of HFS induced glutamatergic LTP with a decrease in N2/N1 ratio in the PVN MNCs, which was enhanced by application of NE (100 nM). HFS-induced LTP was abolished by the blockade of N-methyl-D-aspartate receptors (NMDAR) with D-APV, but it was rescued by the application of NE. NE failed to rescue HFS-induced LTP of MNCs in the presence of a selective β1-AR antagonist, CGP 20712. However, application of β1-AR agonist, dobutamine HCl rescued HFS-induced LTP of MNCs in the absence of NMDAR activity. In the absence of NMDAR activity, NE failed to rescue HFS-induced MNC LTP when protein kinase A (PKA) was inhibited by extracellular applying KT5720 or intracellular administration of PKI. These results indicate that NE activates β1-AR and triggers HFS to induce a novel glutamatergic LTP of hypothalamic PVN NMCs via the postsynaptic PKA signaling pathway in vitro in rats.

Procognitive Effects of Adjunctive D-Cycloserine to Intermittent Theta-Burst Stimulation in Major Depressive Disorder: Effets procognitifs de la D-cyclosérine en traitement complémentaire par la stimulation thêta-burst intermittente dans le trouble dépressif caractérisé.

Major depressive disorder (MDD) is associated with cognitive impairments that persist despite successful treatment. Transcranial magnetic stimulation is a noninvasive treatment for MDD that is associated with small procognitive effects on working memory and executive function. We hypothesized that pairing stimulation with N-methyl-D-aspartate (NMDA) receptor agonism would enhance the effects of stimulation and its procognitive effects. The effect of NMDA receptor agonism (D-cycloserine, 100 mg) on cognitive performance was tested in two randomized double-blind placebo-controlled trials: (1) acute effects of in the absence of stimulation (n = 20 healthy participants) and (2) a treatment study of individuals with MDD (n = 50) randomized to daily intermittent theta-burst stimulation (iTBS) with placebo or D-cycloserine for 2 weeks. Cognitive function was measured using the THINC-it battery, comprised of the Perceived Deficits Questionnaire, the Choice Reaction Time, the Trail Making Test, the Digit Symbol Substitution Test, and the 1-Back tests. D-cycloserine had no acute effect on cognition compared to placebo. iTBS + D-cycloserine was associated with significant improvements in subjective cognitive function and correct responses on the 1-Back when compared to iTBS + placebo. Improvements in subjective cognition paralleled depressive symptoms improvement, however 1-Back improvements were not attributable to improvement in depression. An intersectional strategy pairing iTBS with NMDA receptor agonism may restore cognitive function in MDD.

Effects of puerarin on gait disturbance in a 6-hydroxydopamine mouse model of Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disorder caused by dopamine (DA) neuronal dysfunction. Although DA agonists and N-methyl-D-aspartate receptor (NMDAR) antagonists are used to treat PD, chronic use causes severe side effects. Puerarin (PUE) is a natural bioactive compound that affects the DA system; however, its effect on PD-associated motor functions is unknown. Therefore, we investigated whether PUE treatment in a 6-hydroxydopamine (6-OHDA) PD mouse model affects motor dysfunction. Adult male ICR mice received unilateral 6-OHDA microinfusion into the right medial forebrain bundle. After a 2-week recovery period, PUE (20 or 50mg/kg) or the vehicle (saline, VEH) was administered intraperitoneally once daily for 21 days. Motor dysfunction was assessed using the locomotion, gait cycle, and rotation tests. Local field potentials (LFPs) were measured in the substantia nigra compacta (SNc), striatum (STR), subthalamic nucleus (STN), and primary motor cortex. 6-OHDA-lesioned PD mice showed increased gait cycle disturbance and unidirectional rotation. PUE treatment ameliorated the gait cycle disturbance, but not unidirectional rotation of PD mice. These effects differed with DA agonist treatment (which improved PD symptoms) and NMDAR antagonist treatment (which aggravated PD symptoms). Moreover, locomotion was increased only in NMDAR antagonist treatment. PUE treatment induced no changes in the attenuated LFP of the beta wave in the STR and STN, and SNc-STN delta-wave coherence was shown in PD animals. This study suggests that PUE is a beneficial co-therapeutic agent for alleviating gait cycle disturbance in PD symptoms.

Synaptic and extrasynaptic distribution of NMDA receptors in the cortex of Alzheimer's disease patients.

Synaptic and extrasynaptic distribution of N-methyl-D-aspartate receptors (NMDARs) has not been addressed in the brain from Alzheimer´s disease (AD) subjects, despite theircontribution to neurodegeneration. We have developed a protocol to isolate synaptic and extrasynaptic membranes from controls and AD frontal cortex. We characterized the distribution of the NMDAR subunits GluN2B, GluN2A, GluN1, and GluN3A, as well aspost-translational modifications, such as phosphorylation and glycosylation. Lower levels of synaptic GluN2B and GluN2A were found in AD fractions, while extrasynaptic GluN2B and GluN1 levels were significantly higher; GluN3A distribution remained unaffected in AD. We also identified different glycoforms of GluN2B and GluN2A in extrasynaptic membranes. Synaptic Tyr1472 GluN2B phosphorylation was significantly lower in AD fractions. Reduction of synaptic NMDAR subunits, particularly for GluN2B, is likely to contribute to synaptic transmission failure in AD. Additionally, the increment of extrasynaptic NMDAR subunits could favor the activation of excitotoxicity in AD. New protocol to isolate synaptic and extrasynaptic membranes from the human cortex. Low GluN2B and GluN2A levels in Alzheimer´s disease (AD) synaptic membranes. High GluN2B and GluN1 levels in AD extrasynaptic membranes. Specific glycoforms of extrasynaptic GluN2B and GluN2A. Low phosphorylation at Tyr1472 in synaptic GluN2B in AD.

Sinapinic acid as a potential therapeutic agent for epilepsy through targeting NMDA receptors and nitrite level

Epilepsy, a widespread neural ailment considered by prolonged neuronal depolarization and repetitive discharge, has been linked to extreme stimulus of N-methyl-D-aspartate receptors (NMDARs). Despite the availability of approved anti-seizure medications (ASMs) in many developed nations, approximately 30% of epilepsy patients continue to experience drug-resistant seizures. Thus, a growing interest in discovering natural compounds as potential sources for new medications is growing. Sinapinic acid, a natural derivative of cinnamic acid found in food sources, is known for its neuroprotective properties. This study investigated how sinapinic acid interacts with NMDA receptors and its potential role in providing anticonvulsant effects. Male mice were randomly allocated into nine groups: a control group receiving normal saline (1 ml/kg), groups treated with sinapinic acid at doses of 1, 3, and 10 mg/kg, a group treated with diazepam at 10 mg/kg, a group treated with an NMDA agonist at 75 mg/kg, a group treated with an NMDA antagonist at 0.5 mg/kg, a group receiving the ineffective dose of sinapinic acid (1 mg/kg) along with the NMDA antagonist, and a group receiving the effective dose of sinapinic acid (10 mg/kg) along with the NMDA agonist. Sinapinic acid and other treatments were administered intraperitoneally 30 min prior to inducing seizures with PTZ injection. Seizure onset time was recorded following PTZ injection. Blood and brain samples were collected after anesthesia to determine serum and brain nitrite levels. Real-time PCR assessed NMDAR gene expression in the prefrontal cortex (PFC). Data were analyzed using Prism software. The time seizures began was notably extended in groups treated with sinapinic acid at doses of 3 and 10 mg/kg compared to those treated with saline (P < 0.05). Additionally, in the receiving group of an ineffective dose of sinapinic acid alongside ketamine, the beginning of seizure time was significantly prolonged compared to the group that received the ineffective dose of sinapinic acid alone (P < 0.05). Serum and prefrontal cortex (PFC) nitrite levels were significantly lower in mice treated with sinapinic acid at doses of 1, 3, and 10 mg/kg compared to the saline-treated group (P < 0.05). The gene expression of the NMDAR NR2B subunit in the PFC was decreased in groups treated with sinapinic acid at 1 and 10 mg/kg compared to the saline-treated group. Furthermore, co-administration of sinapinic acid (10 mg/kg) with NMDA resulted in significantly lower NR2A gene expression than the group treated with 10 mg/kg of sinapinic acid alone. Conversely, co-administration of ketamine with sinapinic acid (1 mg/kg) significantly increased NR2B subunit gene expression compared to the group treated with sinapinic acid at 1 mg/kg alone. Sinapinic acid showed anticonvulsant effects through reduced serum and PFC nitrite and modulation of glutamatergic signaling.

Glutamate signaling and neuroligin/neurexin adhesion play opposing roles that are mediated by major histocompatibility complex I molecules in cortical synapse formation.

Although neurons release neurotransmitter before contact, the role for this release in synapse formation remains unclear. Cortical synapses do not require synaptic vesicle release for formation (Verhage et al., 2000; Sando et al., 2017; Sigler et al., 2017; Held et al., 2020), yet glutamate clearly regulates glutamate receptor trafficking (Roche et al., 2001; Nong et al., 2004) and induces spine formation (Engert and Bonhoeffer, 1999; Maletic-Savatic et al., 1999; Toni et al., 1999; Kwon and Sabatini, 2011; Oh et al., 2016). Using rat and murine culture systems to dissect molecular mechanisms, we found that glutamate rapidly decreases synapse density specifically in young cortical neurons in a local and calcium-dependent manner through decreasing N-methyl-D-aspartate receptor (NMDAR) transport and surface expression as well as co-transport with neuroligin (NL1). Adhesion between NL1 and neurexin 1 protects against this glutamate-induced synapse loss. Major histocompatibility I (MHCI) molecules are required for the effects of glutamate in causing synapse loss through negatively regulating NL1 levels in both sexes. Thus, like acetylcholine at the neuromuscular junction (NMJ), glutamate acts as a dispersal signal for NMDARs and causes rapid synapse loss unless opposed by NL1-mediated trans-synaptic adhesion. Together, glutamate, MHCI and NL1 mediate a novel form of homeostatic plasticity in young neurons that induces rapid changes in NMDARs to regulate when and where nascent glutamatergic synapses are formed.Significance Statement The role for neurotransmitter release in synaptogenesis in the central nervous system (CNS) remains unclear. Here, we reconcile conflicting results in the field by showing that glutamate plays an important role in synapse formation by acting as a dispersal signal for NMDARs that is counteracted by trans-synaptic adhesion in intact tissue, similar to the role for neurotransmitter at the NMJ. We also describe a novel form of homeostatic plasticity in young neurons that allows them to respond to changes in activity through surprisingly rapid changes in synapse density. Finally, we show that this plasticity is modulated by immune proteins-MHCI molecules-through negative regulation of NL1 levels, connecting two important synaptic signaling pathways for the first time.

Glycine Transporter 1 Inhibitors Minimize the Analgesic Tolerance to Morphine.

Opioid analgesic tolerance (OAT), among other central side effects, limits opioids' indispensable clinical use for managing chronic pain. Therefore, there is an existing unmet medical need to prevent OAT. Extrasynaptic N-methyl D-aspartate receptors (NMDARs) containing GluN2B subunit blockers delay OAT, indicating the involvement of glutamate in OAT. Glycine acts as a co-agonist on NMDARs, and glycine transporters (GlyTs), particularly GlyT-1 inhibitors, could affect the NMDAR pathways related to OAT. Chronic subcutaneous treatments with morphine and NFPS, a GlyT-1 inhibitor, reduced morphine antinociceptive tolerance (MAT) in the rat tail-flick assay, a thermal pain model. In spinal tissues of rats treated with a morphine-NFPS combination, NFPS alone, or vehicle-comparable changes in µ-opioid receptor activation, protein and mRNA expressions were seen. Yet, no changes were observed in GluN2B mRNA levels. An increase was observed in glycine and glutamate contents of cerebrospinal fluids from animals treated with a morphine-NFPS combination and morphine, respectively. Finally, GlyT-1 inhibitors are likely to delay MAT by mechanisms relying on NMDARs functioning rather than an increase in opioid efficacy. This study, to the best of our knowledge, shows for the first time the impact of GlyT-1 inhibitors on MAT. Nevertheless, future studies are required to decipher the exact mechanisms.

Exploring the Therapeutic Potential of N-Methyl-D-Aspartate Receptor Antagonists in Neuropathic Pain Management.

Neuropathic pain (NeP) is a complex and debilitating condition that impacts millions of people globally. Although various treatment options exist, their effectiveness is often limited, and they can be accompanied by significant side effects. In recent years, there has been increasing interest in targeting the N-methyl-D-aspartate receptor (NMDAR) as a potential therapeutic approach to alleviate different types of neuropathic pain. This narrative review aims to provide a comprehensive examination of NMDAR antagonists, specifically ketamine, memantine, methadone, amantadine, carbamazepine, valproic acid, phenytoin, dextromethorphan, riluzole, and levorphanol, in the management of NeP. By analyzing and summarizing current preclinical and clinical studies, this review seeks to evaluate the efficacy of these pharmacologic agents in providing adequate relief for NeP.

DTD1 modulates synaptic efficacy by maintaining D-serine and D-aspartate homeostasis.

D-serine and D-aspartate are involved in N-methyl-D-aspartate receptor (NMDAR)-related physiological and pathological processes. D-aminoacyl-tRNA deacylase 1 (DTD1) may biochemically contribute to D-serine or D-aspartate production. However, it is unclear thus far whether DTD1 regulates D-serine or D-aspartate content in neurobiological processes. In the present research, we found that DTD1 was essential to maintain the D-serine or D-aspartate homeostasis, which was consistent with the phenomenon that DTD1-deficiency resulted in changes in the quantity changes of functional NMDAR subunits in postsynaptic compartments. Moreover, DTD1 played a considerable role in regulating dendritic morphology and synaptic structure. As a consequence, DTD1 affected neurobiological events, including the synaptic strength of the CA3-to-CA1 circuit, dendritic spine density of hippocampal pyramidal neurons, and behavioral performance of mice in the Morris water maze. These findings highlight the important role of DTD1 in synaptic transmission, neuronal morphology, and spatial learning and memory and suggest an undisclosed mechanism of DTD1 that participates the regulation of D-serine or D-aspartate homeostasis in hippocampal neurons.

GlyT1 inhibition promotes neuroprotection in the middle cerebral artery occlusion model through the activation of GluN2A-containing NMDAR

Glycine Transporter Type 1 (GlyT1) inhibition confers neuroprotection against different forms of cerebral damage. This effect occurs through the elevation of synaptic glycine concentrations, which enhances N-methyl-d-aspartate receptor (NMDAR) activation by glutamate. To investigate the neuroprotective mechanism of GlyT1 inhibition, we used the Middle Cerebral Artery Occlusion (MCAO) model in male C57BL/6 mice, aged 10–12 weeks. We administered N-[3-(4′-fluorophenyl)-3-(4′-phenylphenoxy)propyl] sarcosine (NFPS), a GlyT1 inhibitor, 24 h prior to ischemia induction. NFPS pretreatment provided significant neuroprotection in the MCAO model, associated with modulation of pathways related to long-term potentiation. Specifically, GluN2A subunit expression was upregulated, while GluN2B subunit expression was downregulated in cortical areas, correlating with enhanced phosphorylation of CaMKIV and CREB proteins. Coadministration with the GluN2B antagonist Eliprodil or the CREB inhibitor C646 did not affect the neuroprotective effects of NFPS pretreatment, but TCN-201, a specific GluN2A antagonist, disrupted these effects. These findings suggest that GlyT1 inhibition mediates neuroprotection through activation of GluN2A-containing NMDARs and the GluN2A/CaMKIV/CREB signaling cascade, thereby modulating the balance between GluN2A and GluN2B subunits.

N-Methyl-d-Aspartate Receptor Antibody and Sensory Gating Deficits in Non-smoking, Minimal Antipsychotic Medication Exposure, and First-Episode Patients With Schizophrenia.

Sensory gating deficit is considered a pathophysiological feature of schizophrenia, which has been linked to N-methyl-d-aspartate receptor (NMDAR) hypofunction as one of the potential underlying mechanisms. Here, we hypothesize that higher levels of NMDAR antibody (Ab) may contribute to the sensory gating deficits in schizophrenia. We enrolled 72 non-smoking inpatients with first-episode schizophrenia (FES), most of them with only a relatively short duration of exposure to antipsychotic medications, and 51 non-smoking healthy controls (HC). Sensory gating was measured by P50 evoked potentials ratio and the difference between the two stimuli in an auditory paired-stimuli paradigm and serum NMDAR Ab levels were quantified by enzyme-linked immunosorbent assay. The FES group showed higher serum NMDAR Ab levels [(9.23 ± 4.15) ng/mL vs. (7.08 ± 2.83) ng/mL; P = .002], higher P50 ratio (P = .002), and less P50 difference (P = .001) than HC. In partial correlation analysis, serum NMDAR Ab levels were positively correlated with the P50 ratio (r = 0.36, P = .003) and negatively with the P50 difference (r = -0.39, P = .001) in the FES group. The NMDAR Ab levels mediated the diagnosis of schizophrenia and P50 sensory gating deficits (P50 ratio and P50 difference). Autoimmunity targeting NMDAR is a crucial intermediate mechanism in impaired sensory gating in patients with schizophrenia. The findings support early intervention targeting NMDAR for patients with schizophrenia.

Developmental spike timing-dependent long-term depression requires astrocyte D-serine at L2/3-L2/3 synapses of the mouse somatosensory cortex.

Spike timing-dependent plasticity (STDP) is a learning rule important for synaptic refinement and for learning and memory during development. While different forms of presynaptic t-LTD have been deeply investigated, little is known about the mechanisms of somatosensory cortex postsynaptic t-LTD. In the present work, we investigated the requirements and mechanisms for induction of developmental spike timing-dependent long-term depression (t-LTD) at L2/3-L2/3 synapses in the juvenile mouse somatosensory cortex. We found that P13-21 mice of either sex show t-LTD at L2/3-L2/3 synapses induced by pairing single presynaptic activity with single postsynaptic action potentials at low stimulation frequency (0.2 Hz) is expressed postsynaptically, and requires the activation of ionotropic postsynaptic NMDA-type glutamate receptors containing GluN2B subunits. In addition, it requires postsynaptic Ca2+, Ca2+ release from internal stores, calcineurin, postsynaptic endocannabinoid (eCB) synthesis, activation of CB1 receptors and astrocytic signalling to release the gliotransmitter d-serine to activate postsynaptic NMDARs to induce t-LTD. These results show direct evidence of the mechanism involved in developmental postsynaptic t-LTD at L2/3-L2/3 synapses, revealing a central role of astrocytes and their release of D-serine in its induction.Significance statement We show here the mechanisms and role of astrocytes and gliotransmitters in a postsynaptic spike timing dependent long-term depression (t-LTD) form defined at layer (L)2/3-L2/3 synapses of the somatosensory cortex. We have discovered that this form of plasticity involves N-methyl D-aspartate receptors (NMDAR) containing the GluN2B subunit and requires astrocytes and the gliotransmitter D-serine to co-activate (together with glutamate) postsynaptic NMDAR to mediate LTD. This can be a general mechanism in the brain to define different forms of plasticity. Defining the mechanisms of synaptic plasticity may have important implications for brain repair, sensorial recovery, the treatment of neurodevelopmental disorders and even, for educational policy.

Regulating the NMDA/NR2B signaling pathway mediates anticonvulsant, antineuroinflammation, and anti-oxidative stress effects of 1,3,benzothiazole derivative 1M in pentylenetetrazole-induced kindling in mice.

Periodic epileptic episodes are the hallmark of epilepsy, a prevalent neurological disorder. Research suggests a significant correlation between neuroinflammation and oxidative stress in a variety of neurological diseases, such as epilepsy. A substantial amount of evidence supports the role of N-methyl-D-aspartate receptors (NMDARs) in the progression of epilepsy. Although several lines of research have disclosed numerous biochemical effects of early seizures, its connection with disturbed NMDAR/NR2B subunit expression remains unclear. 2-Mercaptobenzothiazole (MBT) is a vital scaffold with several biological activities, and its various substitutes show promising anti-inflammatory potential. The current study aimed to investigate the newly synthesized 1,3-(benzothiazole-2-sulfanyl)-1-(morpholine-4-yl)ethan-1-one (1M), a substituted MBT, for its neuroprotective potential in a mice model of pentylenetetrazole-induced epilepsy (PTZ), by modulating NMDA/NR2B pathway. The compound was tested for docking and simulation analysis, demonstrating a solid and stable bond with the NR2B subunit of NMDA. To ascertain the effects of 1M, as well as to further illustrate its mechanism of neuroprotection via NMDA/NR2B in PTZ-induced kindling model, mice of either sex were given two doses of test compound, 1M (10mg/kg and 20mg/kg). The behavioral assessments were evaluated using open-field, Y-maze, and elevated-plus maze tests, which indicated improved behavioral alterations caused by PTZ after 1M treatment. The antioxidant profiling was done by estimating glutathione-S-transferase (GST), catalase (CAT), reduced glutathione (GSH), and LPO (lipid peroxidation) in hippocampal tissues, where the test compound 1M significantly restored the depleted antioxidants, showcasing its antioxidant potential. Moreover, the cellular morphological damages induced by PTZ were detected by H&E staining, which was rescued after 1M administration. Furthermore, the activation of the inflammatory pathway was confirmed by quantitative analysis of inflammatory mediators tumor necrotic factor (TNF-α), nuclear factor kappa B (NF-κB), and cylooxegenase2 (COX-2) by enzyme-linked immunosorbent assay (ELISA), where 1M administration significantly ameliorated their expression. Furthermore, to demonstrate the involvement of the NR2B pathway, NR2B-antagonist ifenprodil was employed, and results were further confirmed through RT-PCR analysis. Our results, when considered collectively, indicate that 1M may act by inhibiting the NR2B subunit of the NMDA receptor, subsequently mitigating downstream oxidative stress and inflammatory mediators through various pathways.

Cofilin linked to GluN2B subunits of NMDA receptors is required for behavioral sensitization by changing the dendritic spines of neurons in the caudate and putamen after repeated nicotine exposure

BackgroundNicotine dependence is associated with glutamatergic neurotransmission in the caudate and putamen (CPu) of the forebrain which includes alterations in the structure of dendritic spines at glutamate synapses. These changes after nicotine exposure can lead to the development of habitual behaviors such as smoking. The present study investigated the hypothesis that cofilin, an actin-binding protein that is linked to the GluN2B subunits of N-methyl-D-aspartate (NMDA) receptors regulates the morphology of dendritic spines in the neurons of the CPu after repeated exposure to nicotine.ResultsAdult male rats received subcutaneous injections of nicotine (0.3 mg/kg/day) or vehicle for seven consecutive days. DiI staining was conducted to observe changes in dendritic spine morphology. Repeated subcutaneous injections of nicotine decreased the phosphorylation of cofilin while increasing the formation of thin spines and filopodia in the dendrites of medium spiny neurons (MSN) in the CPu of rats. Bilateral intra-CPu infusion of the cofilin inhibitor, cytochalasin D (12.5 µg/µL/side), restored the thin spines and filopodia from mushroom types after repeated exposure to nicotine. Similar results were obtained from the bilateral intra-CPu infusion of the selective GluN2B subunit antagonist, Ro 25-6981 (4 µM/µL/side). Bilateral intra-CPu infusion of cytochalasin D that interferes with the actin-cofilin interaction attenuated the repeated nicotine-induced increase in locomotor sensitization in rats.ConclusionsThese findings suggest that active cofilin alters the structure of spine heads from mushroom to thin spine/filopodia by potentiating actin turnover, contributing to behavioral sensitization after nicotine exposure.

Bi-directional allosteric pathway in NMDA receptor activation and modulation

N-methyl-D-aspartate (NMDA) receptors are ionotropic glutamate receptors involved in learning and memory. NMDA receptors primarily comprise two GluN1 and two GluN2 subunits. The GluN2 subunit dictates biophysical receptor properties, including the extent of receptor activation and desensitization. GluN2A- and GluN2D-containing receptors represent two functional extremes. To uncover the conformational basis of their functional divergence, we utilize single-molecule fluorescence resonance energy transfer to probe the extracellular domains of these receptor subtypes under resting and ligand-bound conditions. We find that the conformational profile of the GluN2 amino-terminal domain correlates with the disparate functions of GluN2A- and GluN2D-containing receptors. Changes at the pre-transmembrane segments inversely correlate with those observed at the amino-terminal domain, confirming direct allosteric communication between these domains. Additionally, binding of a positive allosteric modulator at the transmembrane domain shifts the conformational profile of the amino-terminal domain towards the active state, revealing a bidirectional allosteric pathway between extracellular and transmembrane domains.

Increased serum phenylalanine/tyrosine ratio associated with the psychiatric symptom of anti-NMDAR encephalitis.

Encephalitis associated with antibodies against the N-methyl-D-aspartate receptor (NMDAR) results in a distinctive neuro-psychiatric syndrome. It has been reported that the serum phenylalanine-tyrosine (Phe/Tyr) ratio increases during infection. However, the connection between phenylalanine-tyrosine metabolism and psychiatric symptoms remains unclear. We enrolled 24 individuals with anti-NMDAR encephalitis and 18 individuals with non-inflammatory neurological diseases (OND). Chromatography was used to measure serum levels of phenylalanine and tyrosine. Serum and cerebrospinal fluid (CSF) TNF-α levels were obtained from the clinical database. The modified Rankin Scale (mRS) score and Glasgow Coma Scale (GCS) score were recorded during the acute phase. The area under the curve (AUC) of the receiver operating characteristic curve was used to assess prediction efficacy. In NMDAR patients, levels of serum Phe and the ratio of serum Phe/Tyr were higher compared to OND patients. The serum Phe/Tyr ratio was also elevated in NMDAR patients with psychiatric syndrome. Furthermore, serum Phe and Tyr levels were correlated with inflammatory indexes. The serum Phe/Tyr ratio is elevated in NMDAR patients with psychiatric syndrome and is associated with severity. Therefore, the serum Phe/Tyr ratio may serve as a potential prognostic biomarker.

Research Progress on NMDA Receptor Enhancement Drugs for the Treatment of Depressive Disorder.

Major depressive disorder (MDD) is a severe mental illness with a complex etiology. Currently, many medications employed in clinical treatment exhibit limitations such as delayed onset of action and a high incidence of adverse reactions. Therefore, there is a pressing need to develop antidepressants that exhibit enhanced efficacy and safety. The N-methyl-D-aspartate receptor (NMDAR), a distinctive glutamate-gated ion channel receptor, has been implicated in the onset and progression of depressive disorder, as evidenced by both preclinical and clinical research. The NMDAR antagonist, ketamine, exhibits rapid and sustained antidepressant effects, holding promise as a novel therapeutic approach for depressive disorder. However, its psychotomimetic impact and potential for addiction have restricted its widespread clinical application. Notably, over the past decade, studies have suggested that enhancing NMDAR functionality can produce antidepressant effects with improved safety, especially with the emergence of NMDAR-positive allosteric modulators (PAMs). We view this as a potential novel strategy for treating depression, forming the basis for the narrative review that follows.

Elevated peripheral glutamate and upregulated expression of NMDA receptor NR1 subunit in insomnia disorder.

The present study explored the serum glutamate (Glu), glutamine (Gln), glutamic acid dehydrogenase (GAD) concentrations and the mRNA expression levels of the N-methyl-D-aspartate receptor (NMDAR) NR1 subunit in the peripheral blood of patients with insomnia disorder (ID). To our knowledge, this is the first study showing an increase in the mRNA expression levels of the NMDAR NR1 subunit in patients with ID. This study included 30 ID patients and 30 matched healthy controls. We investigated the demographic and illness information and assessed subjective sleep quality using the Pittsburgh Sleep Quality Index. The Hamilton Depression Scale-17 and Hamilton Anxiety Scale were used to evaluate the patients' symptoms of depression and anxiety, respectively. The quantifications of Glu, Gln and GAD concentrations were performed by Enzyme-linked immunosorbent assay (ELISA). Real-time PCR was used to detect the mRNA expression levels of the NMDAR NR1 subunit in peripheral blood. Compared with the healthy control group, the serum Glu concentrations and the mRNA expression levels of the NMDAR NR1 subunit in the ID group were significantly higher. However, there was no significant difference in Gln and GAD between the two groups. The receiver operating characteristic (ROC) analysis showed that the mRNA expression levels of the NMDAR NR1 subunit could distinguish ID patients from healthy individuals (area under the curve: 0.758; sensitivity: 73.3%; specificity: 76.7%). A negative correlation was found between the mRNA expression levels of the NMDAR NR1 subunit for age, total duration of illness, and age of first onset in the ID group, whereas a positive correlation was detected for daytime dysfunction. Glutamatergic neurotransmission was abnormal in ID patients. Additionally, the mRNA expression levels of the NMDAR NR1 subunit appeared to have potential as a clinical biomarker for ID. However, the sample size of our study was limited, and future studies with larger sample sizes are needed to further validate and explore the mechanisms involved and to assess the reliability of the biomarker.

Biochemical Properties of Synaptic Proteins Are Dependent on Tissue Preparation: NMDA Receptor Solubility Is Regulated by the C-Terminal Tail.

Synaptic proteins are essential for neuronal development, synaptic transmission, and synaptic plasticity. The postsynaptic density (PSD) is a membrane-associated structure at excitatory synapses, which is composed of a huge protein complex. To understand the interactions and functions of PSD proteins, researchers have employed a variety of imaging and biochemical approaches including sophisticated mass spectrometry. However, the field is lacking a systematic comparison of different experimental conditions and how they might influence the study of the PSD interactome isolated from various tissue preparations. To evaluate the efficiency of several common solubilization conditions, we isolated receptors, scaffolding proteins, and adhesion molecules from brain tissue or primary cultured neurons or human forebrain neurons differentiated from induced pluripotent stem cells (iPSCs). We observed some striking differences in solubility. We found that N-methyl-d-aspartate receptors (NMDARs) and PSD-95 are relatively insoluble in brain tissue, cultured neurons, and human forebrain neurons compared to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptors (AMPARs) or SAP102. In general, synaptic proteins were more soluble in primary neuronal cultures and human forebrain neurons compared to brain tissue. Interestingly, NMDARs are relatively insoluble in HEK293T cells suggesting that insolubility does not directly represent the synaptic fraction but rather it is related to a detergent-insoluble fraction such as lipid rafts. Surprisingly, truncation of the intracellular carboxyl-terminal tail (C-tail) of NMDAR subunits increased NMDAR solubility in HEK293T cells. Our findings show that detergent, pH, and temperature are important for protein preparations to study PSD protein complexes, and NMDAR solubility is regulated by its C-tail, thus providing a technical guide to study synaptic interactomes and subcellular localization of synaptic proteins.

Association between Polypharmacy and Adverse Events in Patients with Alzheimer's Disease: An Analysis of the Japanese Adverse Drug Event Report Database (JADER).

Background and Objectives: Alzheimer's disease is a global health concern, with a rising prevalence among the elderly. Current pharmacological treatments, including acetylcholinesterase inhibitors (AChEIs) and N-Methyl D-Aspartate (NMDA) receptor antagonists, are associated with adverse events (AEs), particularly in the context of polypharmacy. This study aimed to investigate the relationship between Alzheimer's disease treatment combinations, the number of concomitant medications, and the occurrence of AEs. Materials and Methods: Data from the Japanese Adverse Drug Event Report database, spanning from April 2004 to June 2020, were analyzed. Patients aged 60 and older with Alzheimer's disease treated with AChEIs (donepezil, galantamine, and rivastigmine) or the NMDA receptor antagonist memantine were included. Logistic regression models were employed to assess the association between AEs and Alzheimer's disease drug combinations, as well as the number of concomitant medications. Results: Among 2653 patients, 47.7% were prescribed five or more drugs. The frequency of AEs was 6.4% for bradycardia, 4.6% for pneumonia, 3.6% for altered state of consciousness, 3.5% for seizures, 3.5% for decreased appetite, 3.5% for vomiting, 3.4% for loss of consciousness, 3.4% for fracture, 3.2% for cardiac failure, and 3.0% for falls. The combination of memantine with AChEIs was associated with a higher risk of bradycardia, whereas donepezil alone was linked to a reduced risk of fractures and falls. Polypharmacy was significantly correlated with an increased incidence of AEs, particularly altered state of consciousness, decreased appetite, vomiting, and falls. The adjusted odds ratios for using five or more drugs compared to no drugs was 10.45 for altered state of consciousness, 7.92 for decreased appetite, 4.74 for vomiting, and 5.95 for falls. Conclusions: In the treatment of Alzheimer's disease, the occurrence of AEs is associated with the number of concurrent medications, independently of the known AEs of Alzheimer's disease drugs and their combination patterns.