N-methyl-D-aspartate Receptor Antagonist Research Articles

Facial Stimulation Induces Long-Term Potentiation of Mossy Fiber-Granule Cell Synaptic Transmission via GluN2A-Containing N-Methyl-D-Aspartate Receptor/Nitric Oxide Cascade in the Mouse Cerebellum.

Long-term synaptic plasticity in the cerebellar cortex is a possible mechanism for motor learning. Previous studies have demonstrated the induction of mossy fiber-granule cell (MF-GrC) synaptic plasticity under in vitro and in vivo conditions, but the mechanisms underlying sensory stimulation-evoked long-term synaptic plasticity of MF-GrC in living animals are unclear. In this study, we investigated the mechanism of long-term potentiation (LTP) of MF-GrC synaptic transmission in the cerebellum induced by train of facial stimulation at 20 Hz in urethane-anesthetized mice using electrophysiological recording, immunohistochemistry techniques, and pharmacological methods. Blockade of GABAA receptor activity and repetitive facial stimulation at 20 Hz (240 pulses) induced an LTP of MF-GrC synapses in the mouse cerebellar cortical folium Crus II, accompanied with a decrease in paired-pulse ratio (N2/N1). The facial stimulation-induced MF-GrC LTP was abolished by either an N-methyl-D-aspartate (NMDA) receptor blocker, i.e., D-APV, or a specific GluNR2A subunit-containing NMDA receptor antagonist, PEAQX, but was not prevented by selective GluNR2B or GluNR2C/D subunit-containing NMDA receptor blockers. Application of GNE-0723, a selective and brain-penetrant-positive allosteric modulator of GluN2A subunit-containing NMDA receptors, produced an LTP of N1, accompanied with a decrease in N2/N1 ratio, and occluded the 20-Hz facial stimulation-induced MF-GrC LTP. Inhibition of nitric oxide synthesis (NOS) prevented the facial stimulation-induced MF-GrC LTP, while activation of NOS produced an LTP of N1, with a decrease in N2/N1 ratio, and occluded the 20-Hz facial stimulation-induced MF-GrC LTP. In addition, GluN2A-containing NMDA receptor immunoreactivity was observed in the mouse cerebellar granular layer. These results indicate that facial stimulation at 20 Hz induced LTP of MF-GrC synaptic transmission via the GluN2A-containing NMDA receptor/nitric oxide cascade in mice. The results suggest that the sensory stimulation-evoked LTP of MF-GrC synaptic transmission in the granular layer may play a critical role in cerebellar adaptation to native mossy fiber excitatory inputs and motor learning behavior in living animals.

N-methyl-D-aspartate receptor antagonism impairs sensory gating in the auditory cortex in response to speech stimuli.

Deficits in early auditory sensory processing in schizophrenia have been linked to N-methyl-D-aspartate receptor (NMDAR) hypofunction, but the role of NMDARs in aberrant auditory sensory gating (SG) in this disorder is unclear. This study, conducted in 22 healthy humans, examined the acute effects of a subanesthetic dose of the NMDAR antagonist ketamine on SG as measured electrophysiologically by suppression of the P50 event-related potential (ERP) to the second (S2) relative to the first (S1) of two closely paired (500ms) identical speech stimuli. Ketamine induced impairment in SG indices at sensor (scalp)-level and at source-level in the auditory cortex (as assessed with eLORETA). Together with preliminary evidence of modest positive associations between impaired gating and dissociative symptoms elicited by ketamine, tentatively support a model of NMDAR hypofunction underlying disturbances in auditory SG in schizophrenia.

GABAB R activation partially normalizes acute NMDAR hypofunction oscillatory abnormalities but fails to rescue sensory processing deficits.

Cognitive deficits and impaired sensory processing are hallmarks of several neurodevelopmental and neuropsychiatric disorders. N-methyl-d-aspartate receptor (NMDAR) hypofunction contributes to these deficits by disrupting the excitation-to-inhibition balance in neuronal networks. Although preclinical data suggest that the activation of gamma-Aminobutyric acid B receptors (GABAB R) may restore excitation-to-inhibition balance and rescues some behavioral deficits, GABAB R agonists have failed to meet their clinical study endpoints, suggesting more complex interactions at play. Here, we studied the effects of Baclofen (a GABAB R agonist) and MK-801 (a non-competitive NMDAR antagonist) on the neurophysiology of limbic-auditory circuits in freely-moving rats. The pharmacological effects were assessed using resting-state EEG, auditory-evoked oscillation, and mismatch negativity paradigms. MK-801 elevated resting-state oscillatory power, mainly in the gamma and higher frequency ranges, and impaired auditory-evoked responses. Baclofen partially normalized resting-state oscillations but failed to rescue auditory-evoked oscillatory abnormalities. Coherence analysis indicated that NMDAR hypofunction alters the functional coupling of limbic and thalamocortical circuits in several frequency bands. Baclofen normalized only a fraction of MK-801-induced abnormalities (e.g., theta coherence between frontal cortex and amygdala) while reducing delta-theta and augmenting gamma coherence in thalamocortical circuits. Finally, we report that Baclofen intensified the MK-801-induced deficits in auditory mismatch responses. In summary, while Baclofen partially normalizes MK-801-induced gamma abnormalities, it either fails to rescue or exacerbates deficits in other phenotypes like functional coupling and auditory processing. We hope that the presented complex interactions between pharmacologically induced NMDAR hypofunction and GABABR agonism inspire a new understanding of the therapeutic potential around GABAergic modulation.

Deletion of Grin1 in mouse megakaryocytes reveals NMDA receptor role in platelet function and proplatelet formation

AbstractThe process of proplatelet formation (PPF) requires coordinated interaction between megakaryocytes (MKs) and the extracellular matrix (ECM), followed by a dynamic reorganization of the actin and microtubule cytoskeleton. Localized fluxes of intracellular calcium ions (Ca2+) facilitate MK-ECM interaction and PPF. Glutamate-gated N-methyl-D-aspartate receptor (NMDAR) is highly permeable to Ca2+. NMDAR antagonists inhibit MK maturation ex vivo; however, there are no in vivo data. Using the Cre-loxP system, we generated a platelet lineage–specific knockout mouse model of reduced NMDAR function in MKs and platelets (Pf4-Grin1−/− mice). Effects of NMDAR deletion were examined using well-established assays of platelet function and production in vivo and ex vivo. We found that Pf4-Grin1−/− mice had defects in megakaryopoiesis, thrombopoiesis, and platelet function, which manifested as reduced platelet counts, lower rates of platelet production in the immune model of thrombocytopenia, and prolonged tail bleeding time. Platelet activation was impaired to a range of agonists associated with reduced Ca2+ responses, including metabotropic like, and defective platelet spreading. MKs showed reduced colony and proplatelet formation. Impaired reorganization of intracellular F-actin and α-tubulin was identified as the main cause of reduced platelet function and production. Pf4-Grin1−/− MKs also had lower levels of transcripts encoding crucial ECM elements and enzymes, suggesting NMDAR signaling is involved in ECM remodeling. In summary, we provide the first genetic evidence that NMDAR plays an active role in platelet function and production. NMDAR regulates PPF through a mechanism that involves MK-ECM interaction and cytoskeletal reorganization. Our results suggest that NMDAR helps guide PPF in vivo.

Antillatoxin-Stimulated Neurite Outgrowth Involves the Brain-Derived Neurotrophic Factor (BDNF) - Tropomyosin Related Kinase B (TrkB) Signaling Pathway.

Voltage-gated sodium channel (VGSC) activators promote neurite outgrowth by augmenting intracellular Na+ concentration ([Na+]i) and upregulating N-methyl-d-aspartate receptor (NMDAR) function. NMDAR activation stimulates calcium (Ca2+) influx and increases brain-derived neurotrophic factor (BDNF) release and activation of tropomyosin receptor kinase B (TrkB) signaling. The BDNF-TrkB pathway has been implicated in activity-dependent neuronal development. We have previously shown that antillatoxin (ATX), a novel lipopeptide isolated from the cyanobacterium Moorea producens, is a VGSC activator that produces an elevation of [Na+]i. Here we address the effect of ATX on the synthesis and release of BDNF and determine the signaling mechanisms by which ATX enhances neurite outgrowth in immature cerebrocortical neurons. ATX treatment produced a concentration-dependent release of BDNF. Acute treatment with ATX also resulted in increased synthesis of BDNF. ATX stimulation of neurite outgrowth was prevented by pretreatment with a TrkB inhibitor or transfection with a dominant-negative Trk-B. The ATX activation of TrkB and Akt was blocked by both a NMDAR antagonist (MK-801) and a VGSC blocker (tetrodotoxin). These results suggest that VGSC activators such as the structurally novel ATX may represent a new pharmacological strategy to promote neuronal plasticity through a NMDAR-BDNF-TrkB-dependent mechanism.

NMDA receptor antagonist amantadine in treatment of neuropathic orofacial pain

Neuropathic orofacial pain caused by trauma to the distal branches of the trigeminal nerve is most often an iatrogenic complication in the practice of dentists, maxillofacial surgeons, ENT surgeons, cosmetologists and plastic surgeons. The pain is often high-intensity, persistent, and difficult to treat with pain medications. Early signs of spontaneous pain aggravate the course of the disease. There is evidence of the use of N-methyl-d-aspartate (NMDA) receptor antagonists in the treatment of neuropathic pain in the practice of oncologists and diabetologists. The present study was designed to test the efficacy of administration of the NMDA receptor antagonist amantadine (PK-Merz) in the treatment of neuropathic orofacial pain in patients with posttraumatic trigeminal neuropathy (PTN). Our task was to study the effect of amantadine (PK-Merz) on spontaneous burning and evoked types of pain.Objective.To present a treatment protocol using amantadine (PK-Merz) and evaluate the effect of a three-time infusion of the drug on the clinical manifestations of pain in patients with post-traumatic trigeminal neuropathy.Materials and methods.30 patients were examined (22 women, 8 men). The average age is 42.6 years. Patients are experiencing amantadine (PK-Merz, Merz + Co., Germany) – 200 mg (500 ml) intravenously, drip, for 2 hours with a frequency of 1 time per week. A total of three infusions were performed. Spontaneous and evoked pain was measured within 48 hours before treatment, during treatment (after 1 hour), immediately after infusion (after 2 hours), as well as after 7, 14 and 21 days from the start of therapy. The effectiveness of therapy was studied according to the highest criteria: VAS, questionnaires for neuropathic pain DN 4 and Pain DETECT. Spontaneous and induced pain were considered separately. To assess the immediate effects of treatment, spontaneous pain was measured using a visual analog scale (VAS) before, after 1 hour, and at the end of each treatment (after 2 hours), as well as at visits on days 7th, 14th, and 21st. A series of mechanical and thermal stimuli was applied to each patient before, after 1 hour, and at the end of each treatment session to study the pain evoked. Pain caused by these stimuli was also measured using VAS.Results.The patients were divided into two groups, which were formed according to the duration of the disease. Group 1 (n = 12) included patients in the acute period – the time after nerve injury ranged from 5 to 30 days. In group 2, patients were in subacute and chronic periods (time after injury ranged from 30 days to 1.5 years). The mean score of spontaneous pain according to VAS in patients of group 2 was significantly higher than in patients of group 1 (6.1 ± 2.1 vs 4.2 ± 1.6; p = 0.0001). A mean pain reduction of 71 % was reported at the end of amantadine infusion (after 2 hours) in patients in the acute period (Group 1) compared with 29 % in patients in Group 2. The difference in pain reduction between the two patient groups was statistically significant (p = 0.009). Further dynamics of pain also showed the best analgesic result in patients of group 1 – after the completion of treatment with amantadine (PK-Merz), in patients of group 1, a significant decrease in the average score of spontaneous burning pain according to VAS was demonstrated from 4.2 ± 1.6 points to 1.2 ± 1.1 points (p = 0.006; 71 ± 10 % reduction). After treatment of patients in group 2, only a slight and insignificant decrease in VAS was found from 6.1 ± 2.1 to 5.0 ± 1.7 (p = 0.400; 18.0 ± 8.5 %). Symptoms of induced pain were determined mainly among patients of the 2nd group – allodynia (n = 12), hyperalgesia to a needle prick (n = 10), thermal (cold) hyperalgesia (n = 10), "inflated" pain in response to repeated injections (n = 10). A mean decrease in allodynia of 52 % ± 8 % was found at the end of the course of treatment (3.8 ± 1.1 points at the beginning and 1.9 ± 1.1 points at the end; p = 0.006). Indicators of cold hyperalgesia (4.4 ± 1.4 points at the beginning, 2.7 ± 1.4 points at the end; p = 0.004) and ‘inflated’ pain (2.9 ± 1.1 points at the beginning, 1.5 ± 1.2 at the end; p = 0.004) before treatment and at the end of therapy (after 21 days) also differed significantly.Conclusions.We concluded that amantadine (PK-Merz) infusion is a safe and effective treatment for neuropathic pain in the acute period of KITN, and also has a positive effect on the manifestations of induced pain in patients with chronic orofacial pain. Further trials of long-term oral or parenteral treatment with amantadine should be conducted.

N-methyl-D-aspartic acid increases tight junction protein destruction in brain endothelial cell via caveolin-1-associated ERK1/2 signaling

N-methyl-D-aspartic acid (NMDA), a glutamate analog, can activate N-Methyl-D-Aspartate receptor (NMDAR) to induce vascular endothelial cell injury but the mechanisms are not fully understood. The present study intended to evaluate the role of caveolin-1 (Cav-1) in NMDA-induced dysfunction of human brain microvascular endothelial cells (HBEC-5i), and verify that endothelial NMDAR activation mediates the disruption of tight junction barrier integrity via extracellular signal-regulated kinase (ERK)1/2 pathway. The expression of NMDAR NR1 were confirmed firstly in HBEC-5i and compared with that in mouse brain by Western blot. To study the role of Cav-1 in NMDA mediated reduction of tight junction protein zonula occludens- (ZO) 1 expression, HBEC-5i were transduced with Cav-1 shRNA or Control shRNA, and the Cav-1 knockdown rate tested with qRT-PCR and Western blot is 99.98% or 87.5%, respectively. NMDA exposure decreased mRNA and protein levels of tight junction protein ZO-1 and suppressed transendothelial electrical resistance (TEER) values in HBEC-5i but blocked by NMDAR antagonist MK801. In addition, NMDA induced Cav-1 and ERK1/2 sequential phosphorylation，but these effects were attenuated by silencing the Cav-1 gene with shRNA and ERK1/2 inhibitor U0126, respectively. These results show that the functional presence of NMDAR NR1 in HBEC-5i. Endothelial NMDAR NR1 activation regulate the maintenance of HBEC-5i-constructed tight junction barrier integrity via the caveolin-1-associated ERK1/2 signaling pathway.

Perioperative Breast Analgesia: a Systematic Review of the Evidence for Perioperative Analgesic Medications

Breast surgery is common and may result in significant acute as well as chronic pain. A wide range of pharmacologic interventions is available including opioids, non-steroidal anti-inflammatory drugs (NSAIDs), N-methyl-D-aspartate (NMDA) receptor antagonists, anticonvulsants, and other non-opioids with analgesic properties. We present a review of the evidence for these pharmacologic interventions. A literature search of the MEDLINE database was performed via PubMed with combined terms related to breast surgery, anesthesia, and analgesia. Articles were limited to randomized controlled trial (RCT) design, adult patients undergoing elective surgery on the breast (not including biopsy), and pharmacologic interventions only. Article titles and abstracts were screened, and risk of bias assessments were performed. The search strategy initially captured 7254 articles of which 60 articles met the full inclusion criteria. Articles were organized according to intervention: 6 opioid agonists, 14 NSAIDs and acetaminophen, 4 alpha-2 agonists, 7 NMDA receptor antagonists, 6 local anesthetics, 7 steroids, 15 anticonvulsants (one of which also discussed an NMDA antagonist), 1 antiarrhythmic, and 2 serotonin reuptake inhibitors (one of which also studied an anticonvulsant). A wide variety of medications is effective for perioperative breast analgesia, but results vary by agent and dose. The most efficacious are likely NSAIDs and anticonvulsants. Some agents may also decrease the incidence of chronic postoperative pain, including flurbiprofen, gabapentin, venlafaxine, and memantine. While many individual agents are well studied, optimal combinations of analgesic medications remain unclear.

Effects of NMDA receptor antagonists on behavioral economic indices of cocaine self-administration

BackgroundCurrently, there are no FDA-approved medications for the treatment of psychostimulant (e.g., cocaine) use disorders. Because the GluN2B subunit of the glutamate N-methyl-D-aspartate (NMDA) receptor is an important mediator of addiction-like behaviors, the goal of the current study was to determine if the GluN2B-selective antagonist Ro 63–1908 is efficacious in attenuating cocaine self-administration. MethodsAdult Sprague Dawley rats (24 males and 11 females) were implanted with indwelling catheters and were trained to self-administer cocaine (0.75 mg/kg/inf). Rats were then trained in a threshold procedure, in which the dose of cocaine decreased across six 6-min blocks (0.75, 0.27, 0.08, 0.03, 0.01, 0.003 mg/kg/inf). This procedure allowed for the quantification of behavioral economic indices of drug self-administration. Following training in the threshold procedure, rats were treated with the GluN2B-selective antagonist Ro 63–1908 (0, 0.1, 0.3, 1.0 mg/kg; s.c.). Rats also received treatments of the NMDA receptor channel blocker MK-801 (0, 0.01, 0.03, 0.06 mg/kg; s.c.). ResultsBlocking NMDA receptors decreased initial intake (i.e., consumption during the first block), although Ro 63–1908 and MK-801 increased area under the curve (global measure of demand) and decreased demand elasticity, an effect observed primarily in males. Neither drug affected demand intensity (i.e., consumption of cocaine at a minimally constrained price). ConclusionsWhile blocking the NMDA receptor decreases initial intake of cocaine, NMDA receptor antagonists make cocaine more inelastic with increasing price. These results suggest that NMDA receptor antagonists can exacerbate addiction-like behaviors during self-administration during extinction-like conditions that are observed in later blocks of the threshold procedure.

Botulinum toxin promotes orofacial antinociception by modulating TRPV1 and NMDA receptors in adult zebrafish

The aim of the study was to evaluate the possible involvement of transient receptor potential (TRP) channels, Acid-sensing ion channels (ASIC) and N-Methyl-D-aspartate receptor (NMDAR) in the orofacial antinociceptive behaviour effect of botulinum toxin type A (BoNT/A) in adult zebrafish. Initially, the open field test was performed to evaluate the effect of BoNT/A on the locomotor activity of zebrafish. Subsequently, the animals were pretreated with BoNT/A (0.05U, 0.1U or 0.5U/masseter) and acute orofacial nociception was induced by cinnamaldehyde, capsaicin, menthol, acid saline or glutamate applied to the lip or masseter muscle. In another group of experiments, animals were pre-treated with capsazepine (TRPV1 antagonist) or ketamine (NMDAR antagonist) to investigate the mechanism of antinociception. The possible involvement of central C-fibre afferents was also investigated using capsaicin desensitized animals. A molecular docking study was performed to observe the in silico interaction of BoNT/A with TRPV1 and NMDA channels. Pretreatment with BoNT/A reduced the nociceptive behaviour induced by capsaicin and glutamate. Antinociception was effectively inhibited by capsazepine and ketamine, as well as by capsaicin-induced desensitization. Consistent with these in vivo findings, the molecular docking study indicated that BoNT/A can interact with TRPV1 and NMDAR. The results indicate the involvement of TRP and NMDAR mechanisms in the orofacial antinociceptive behaviour effect of BoNT/A. The results also confirm the pharmacological relevance of BoNT/A as an inhibitor of orofacial nociception behaviour.

Combined Antagonism of 5-HT2 and NMDA Receptors Reduces the Aggression of Monoamine Oxidase a Knockout Mice.

The enzyme monoamine oxidase A (MAOA) catalyzes the degradation of several neurotransmitters, including serotonin. A large body of evidence has shown that genetic MAOA deficiency predisposes humans and mice to aggression and antisocial behavior. We previously documented that the aggression of male MAOA-deficient mice is contributed by serotonin 5-HT2 and glutamate N-methyl-D-aspartate (NMDA) receptors in the prefrontal cortex (PFC). Indeed, blocking either receptor reduces the aggression of MAOA knockout (KO) mice; however, 5-HT2 receptor antagonists, such as ketanserin (KET), reduce locomotor activity, while NMDA receptor blockers are typically associated with psychotomimetic properties. To verify whether NMDA receptor blockers induce psychotomimetic effects in MAOA KO mice, here we tested the effects of these compounds on prepulse inhibition (PPI) of the acoustic startle reflex. We found that male MAOA KO mice are hypersensitive to the PPI-disrupting properties of NMDA receptor antagonists, including the non-competitive antagonist dizocilpine (DIZ; 0.1, 0.3 mg/kg, IP) and the NR2B subunit-specific blocker Ro-256981 (5, 10 mg/kg, IP). Since KET has been previously shown to counter the PPI deficits caused by NMDA receptor antagonists, we tested the behavioral effects of the combination of KET (2 mg/kg, IP) and these drugs. Our results show that the combination of KET and DIZ potently reduces aggression in MAOA KO mice without any PPI deficits and sedative effects. While the PPI-ameliorative properties of KET were also observed after infusion in the medial PFC (0.05 μg/side), KET did not counter the PPI-disruptive effects of Ro-256981 in MAOA KO mice. Taken together, these results point to the combination of non-subunit-selective NMDA and 5-HT2 receptor antagonists as a potential therapeutic approach for aggression and antisocial behavior with a better safety and tolerability profile than each monotherapy.

Opposing effects of NMDA receptor antagonists on early life stress-induced aggression in mice.

Rates of childhood trauma are high amongst violent offenders who frequently recidivate. Few clinical options are available to treat excessive and recurring violent aggression associated with childhood trauma. Those that do exist are largely ineffective and often replete with side effects. One promising pharmacological target is the glutamate binding N-methyl- d-aspartate receptor (NMDAR). Clinically available NMDAR antagonists have proven successful in mitigating violent and aggressive behavior associated with a host of psychiatric diseases and have both immediate and long-term effects on nervous system function and behavior. This study examined the impact of three NMDAR antagonists on long-lasting aggression brought on by early-life stress: MK-801, memantine, and ketamine. We find that social isolation early in adolescence followed by acute traumatic stress in the form of noncontingent foot shock (FS) late in adolescence works in tandem to promote long-lasting excessive aggression in mice when measured 1 week later. Systemic injections of MK-801 and memantine 30 min before FS suppressed the long-lasting attack behavior induced by our early life stress induction protocol. Systemic injections of ketamine, on the other hand, significantly enhanced the long-lasting attack behavior when injected before FS. These findings indicate that MK-801, memantine, and ketamine have distinct and opposing effects on early life stress-induced aggression, suggesting these drugs may be mechanistically distinct. This study identifies memantine as a promising pharmacological treatment for aggressive behavior associated with early life stress and demonstrates the need for greater care when using glutamate receptor antagonists to treat aggression.

Mechanisms of NMDA receptor inhibition by nafamostat, gabexate and furamidine

N‐methyl‐D‐aspartate (NMDA) receptors are affected by many pharmaceuticals. In this work, we studied the action of the serine protease inhibitors nafamostat, gabexate and camostat, and an antiprotozoal compound, furamidine, on native NMDA receptors in rat hippocampal pyramidal neurons. Nafamostat, furamidine and gabexate inhibited these receptors with IC50 values of 0.20 ± 0.04, 0.64 ± 0.13 and 16 ± 3 μM, respectively, whereas camostat was ineffective. Nafamostat and furamidine showed voltage-dependent inhibition, while gabexate showed practically voltage-independent inhibition. Nafamostat and furamidine demonstrated tail currents, implying a ‘foot-in-the-door’ mechanism of action; gabexate did not demonstrate any signs of ‘foot-in-the-door’ or trapping channel block. Gabexate action was also not competitive, suggesting allosteric inhibition of NMDA receptors. Furamidine and nafamostat are structurally similar to the previously studied diminazene and all three demonstrated a ‘foot‐in‐the‐door’ mechanism. They have a rather rigid, elongated structures and cannot fold into more compact forms. By contrast, the gabexate molecule can fold, but its folded structure differs drastically from that of typical NMDA receptor blockers, in agreement with its voltage-independent inhibition. These findings provide a better understanding of the structural determinants of NMDA receptor antagonism, while also supporting the potential clinical repurposing of these drugs as neuroprotectors for glaucoma and other neurodegenerative diseases.

Subchronic PCP effects on DNA methylation and protein expression of NMDA receptor subunit genes in the prefrontal cortex and hippocampus of female rats.

N-methyl-d-aspartate receptor (NMDAR) dysfunction is implicated in schizophrenia, and NMDAR antagonists, such as phencyclidine (PCP), can induce behaviours that mimic aspects of the disorder. We investigated DNA methylation of Grin1, Grin2a and Grin2b promoter region and NR1 and NR2 protein expression in the prefrontal cortex (PFC) and hippocampus of adult female Lister-hooded rats following subchronic PCP (scPCP) administration. We also determined whether any alterations were tissue-specific. Rats were divided into two groups that received vehicle (0.9% saline) or 2 mg/kg PCP twice a day for 7 days (n = 10 per group). After behavioural testing (novel object recognition), to confirm a cognitive deficit, brains were dissected and NMDAR subunit DNA methylation and protein expression were analysed by pyrosequencing and ELISA. Line-1 methylation was determined as a measure of global methylation. Data were analysed using Student's t-test and Pearson correlation. The scPCP administration led to Grin1 and Grin2b hypermethylation and reduction in NR1 protein in both PFC and hippocampus. No significant differences were observed in Line-1 or Grin2a methylation and NR2 protein. The scPCP treatment resulted in increased DNA methylation at promoter sites of Grin1 and Grin2b NMDAR subunits in two brain areas implicated in schizophrenia, independent of any global change in DNA methylation, and are similar to our observations in a neurodevelopmental animal model of schizophrenia - social isolation rearing post-weaning. Moreover, these alterations may contribute to the changes in protein expression for NMDAR subunits demonstrating the potential importance of epigenetic mechanisms in schizophrenia.

Does mismatch negativity have utility for NMDA receptor drug development in depression?

Rapid antidepressant effects associated with ketamine have shifted the landscape for the development of therapeutics to treat major depressive disorder (MDD) from a monoaminergic to glutamatergic model. Treatment with ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, may be effective, but has many non-glutamatergic targets, and clinical and logistical problems are potential challenges. These factors underscore the importance of manipulations of binding mechanics to produce antidepressant effects without concomitant clinical side effects. This will require identification of efficient biomarkers to monitor target engagement. The mismatch negativity (MMN) is a widely used electrophysiological signature linked to the activity of NMDA receptors (NMDAR) in humans and animals and validated in pre-clinical and clinical studies of ketamine. In this review, we explore the flexibility of the MMN and its capabilities for reliable use in drug development for NMDAR antagonists in MDD. We supplement this with findings from our own research with three distinct NMDAR antagonists. The research described illustrates that there are important distinctions between the mechanisms of NMDAR antagonism, which are further crystallized when considering the paradigm used to study the MMN. We conclude that the lack of standardized methodology currently prevents MMN from being ready for common use in drug discovery.Clinical trial registration:This manuscript describes data collected from the following National Institutes of Health (NIH) and Veterans Affairs (VA) studies: AV-101, NCT03583554; lanicemine, NCT03166501; ketamine, NCT02556606.

Reassessment of amphetamine- and phencyclidine-induced locomotor hyperactivity as a model of psychosis-like behavior in rats.

Locomotor hyperactivity induced by psychotomimetic drugs, such as amphetamine and phencyclidine, is widely used as an animal model of psychosis-like behaviour and is commonly attributed to an interaction with dopamine release and N-methyl-D-aspartate (NMDA) receptors, respectively. However, what is often not sufficiently taken into account is that the pharmacological profile of these drugs is complex and may involve other neurotransmitter/receptor systems. Therefore, this study aimed to assess the effect of three antagonists targeting different monoamine pathways on amphetamine- and phencyclidine-induced locomotor hyperactivity. A total of 32 rats were pre-treated with antagonists affecting dopaminergic, noradrenergic and serotonergic transmission: haloperidol (0.05 mg/kg), prazosin (2 mg/kg) and ritanserin (1 mg/kg), respectively. After 30 min of spontaneous activity, rats were injected with amphetamine (0.5 mg/kg) or phencyclidine (2.5 mg/kg) and distance travelled, stereotypy and rearing recorded in photocell cages over 90 min. Pre-treatment with haloperidol or prazosin both reduced amphetamine-induced hyperactivity although pre-treatment with ritanserin had only a partial effect. None of the pre-treatments significantly altered the hyperlocomotion effects of phencyclidine. These findings suggest that noradrenergic as well as dopaminergic neurotransmission is critical for amphetamine-induced locomotor hyperactivity. Hyperlocomotion effects of phencyclidine are dependent on other factors, most likely NMDA receptor antagonism. These results help to interpret psychotomimetic drug-induced locomotor hyperactivity as an experimental model of psychosis.

Magnesium sulphate within multimodal analgesia, pre-emptive, or preventive analgesia

BackgroundMagnesium (Mg) is a non-competitive N-methyl d-aspartate receptor antagonist with antinociceptive effects. Multimodal therapy is the optimal strategy for perioperative pain control to minimize the need for opioids. Inflammation caused by tissue trauma or direct nerve injury is responsible for the perioperative pain. The concept of “pre-emptive” analgesia, analgesic strategies administered prior to the stimulus, can modify the peripheral and central nervous system processing of noxious stimuli, thereby reducing central sensitization, hyperalgesia, and allodynia remains controversial. A more encompassing approach to the reduction of postoperative pain is the concept of “preventive” analgesia. The purpose of the study is to detect the proper use of MgSO4 as an analgesic being a non-competitive N-methyl d-aspartate (NMDA).ResultsThere is no statistically significant difference in the haemodynamic parameters, intraoperative (33% vs 20%) and postoperative requirement for analgesics 6.6% vs 10% among groups I and II, respectively. There is no significant difference in the numerical analogue scale, where 16 vs 17 patients with no pain, 12 vs 10 with mild pain, and 2 vs 3 with moderate pain in groups I and II, respectively.ConclusionThe use of MgSO4 in a bolus with or without infusion is comparable in the control of intraoperative and postoperative pain.

Astrocytic N-Methyl-D-Aspartate Receptors Protect the Hippocampal Neurons Against Amyloid-β142-Induced Synaptotoxicity by Regulating Nerve Growth Factor.

Soluble oligomeric amyloid-β (Aβ)-induced synaptic dysfunction is an early event in Alzheimer's disease (AD) pathogenesis. Mounting evidence has suggested N-methyl-D-aspartate receptors (NMDARs) play an important role in Aβ-induced synaptotoxicity. Originally NMDARs were believed to be expressed exclusively in neurons; however, recent two decades studies have demonstrated functional NMDARs present on astrocytes. Neuronal NMDARs are modulators of neurodegeneration, while our previous initial study found that astrocytic NMDARs mediated synaptoprotection and identified nerve growth factor (NGF) secreted by astrocytes, as a likely mediator, but how astrocytic NMDARs protect neurons against Aβ-induced synaptotoxicity through regulating NGF remains unclear. To achieve further insight into the mechanism of astrocytic NMDARs oppose Aβ-induced synaptotoxicity through regulating NGF. With the primary hippocampal neuronal and astrocytic co-cultures, astrocytes were pretreated with agonist or antagonist of NMDARs before Aβ142 oligomers application to neuron-astrocyte co-cultures. Western blot, RT-PCR, etc., were used for the related proteins evaluation. Activation of astrocytic NMDARs can significantly mitigate Aβ142-induced loss of PSD-95 and synaptophysin through increasing NGF release. Blockade of astrocytic NMDARs inhibited Aβ-induced compensatory protective NGF increase in protein and mRNA levels through modulating NF-κB of astrocytes. Astrocytic NMDARs activation can enhance Aβ-induced Furin increase, and blockade of astrocytic NMDARs inhibited Aβ-induced immunofluorescent intensity elevation of vesicle trafficking protein VAMP3 and NGF double-staining. Astrocytic NMDARs oppose Aβ-induced synaptotoxicity through modulating the synthesis, maturation, and secretion of NGF in astrocytes. This new information may contribute to the quest for specific targeted strategy of intervention to delay the onset of AD.

Serine racemase interaction with N-methyl-D-aspartate receptors antagonist reveals potential alternative target of chronic pain treatment: Molecular docking study.

ABSTRACTSerine racemase (SR) catalyzes L-serine racemization to activate the N-methyl-D-aspartate receptor (NMDAR). NMDAR activation is associated with the progression of acute-to-chronic neuropathic pain. This study aimed to investigate NMDAR antagonist interactions with SR to obtain potential chronic pain target therapy. Several NMDAR antagonist drugs were obtained from the drug bank, and malonate was used as a control inhibitor. Ligands were prepared using the open babel feature on PyRx. The SR structure was obtained from Protein data bank (PDB) (3l6B) and then docked with ligands using the AutoDock Vina. Haloperidol had a lower binding affinity than malonate and other ligands. Ethanol had the highest binding affinity than other drugs but could bind to the Adenosine triphosphate (ATP)-binding domain. Haloperidol is bound to reface that function for reprotonation in racemization reaction to produce D-serine. Halothane bond with Arg135 residues aligned negatively charged substrates to be reprotonated properly by reface. Tramadol is bound to amino acid residues in the triple serine loop, which determines the direction of the SR reaction. Several NMDAR antagonists such as haloperidol, halothane, ethanol, and tramadol bind to SR in the specific binding site. It reveals that SR potentially becomes an alternative target for chronic pain treatment.

Developmental stage-specific involvement of NMDA receptor hypofunction in risk formation for psychiatric disorders

Successful maturation of the brain relies on complex interactions between various neurotransmitter signaling. Glutamate, a major excitatory neurotransmitter in mammalian central nervous system, and an ionotropic glutamate receptor subtype, N-methyl-D-aspartate (NMDA) receptor, play essential roles in brain development. It has been reported that animals treated with an NMDA receptor antagonist during neonatal period show various behavioral abnormalities relevant to neurodevelopmental disorders in later life. We previously found that NMDA receptor blockade during neonatal period, but not adulthood, caused significant cognitive impairment in rats. Thus, the adverse effects of NMDA receptor blockade are dependent on the time when the treatment is administered. We further investigated the precise timing that NMDA receptors are involved in the development of cognitive functions, and the mechanism underlying the vulnerability of the immature brain to NMDA receptor blockade. In this symposium, we discuss the importance of the second postnatal week on the development of hippocampus-dependent learning in rats. We also discuss the involvement of NR2A-containing NMDA receptors in the formation of schizophrenia-related behavioral changes induced by neonatal NMDA receptor blockade.