N-methyl-D-aspartic Acid Receptor Research Articles

Glutamate signaling through the NMDA receptor reduces the expression of scleraxis in plantaris tendon derived cells

BackgroundA body of evidence demonstrating changes to the glutaminergic system in tendinopathy has recently emerged. This hypothesis was further tested by studying the effects of glutamate on the tenocyte phenotype, and the impact of loading and exposure to glucocorticoids on the glutamate signaling machinery.MethodsPlantaris tendon tissue and cultured plantaris tendon derived cells were immunohisto-/cytochemically stained for glutamate, N-Methyl-D-Aspartate receptor 1 (NMDAR1) and vesicular glutamate transporter 2 (VGluT2). Primary cells were exposed to glutamate or receptor agonist NMDA. Cell death/viability was measured via LDH/MTS assays, and Western blot for cleaved caspase 3 (c-caspase 3) and cleaved poly (ADP-ribose) polymerase (c-PARP). Scleraxis mRNA (Scx)/protein(SCX) were analyzed by qPCR and Western blot, respectively. A FlexCell system was used to apply cyclic strain. The effect of glucocorticoids was studies by adding dexamethasone (Dex). The mRNA of the glutamate synthesizing enzymes Got1 and Gls, and NMDAR1 protein were measured. Levels of free glutamate were determined by a colorimetric assay.ResultsImmunoreactions for glutamate, VGluT2, and NMDAR1 were found in tenocytes and peritendinous cells in tissue sections and in cultured cells. Cell death was induced by high concentrations of glutamate but not by NMDA. Scleraxis mRNA/protein was down-regulated in response to NMDA/glutamate stimulation. Cyclic strain increased, and Dex decreased, Gls and Got1 mRNA expression. Free glutamate levels were lower after Dex exposure.ConclusionsIn conclusion, NMDA receptor stimulation leads to a reduction of scleraxis expression that may be involved in a change of phenotype in tendon cells. Glutamate synthesis is increased in tendon cells in response to strain and decreased by glucocorticoid stimulation. This implies that locally produced glutamate could be involved in the tissue changes observed in tendinopathy.

Chronic Monoarthritis Pain Accelerates the Processes of Cognitive Impairment and Increases the NMDAR Subunits NR2B in CA3 of Hippocampus from 5-month-old Transgenic APP/PS1 Mice.

Many factors impact cognitive impairment; however, the effects of chronic pain and the mechanisms underlying these effects on cognitive impairment are currently unknown. Here we tested the hypothesis that chronic pain accelerates the transition from normal cognition to mild cognitive impairment (MCI) in 5-month-old transgenic APP/PS1 mice, an animal model of Alzheimer’s disease (AD), and that neurotoxicity induced by N-methyl-D-aspartic acid receptor (NMDAR) subunits may be involved in this process. Chronic monoarthritis pain was induced in transgenic APP/PS1 mice and 5-month-old wild-type (WT) mice by intra- and pre-articular injections of Freund’s complete adjuvant (FCA) into one knee joint. Pain behavior, learning and memory function, and the distribution and quantity of NMDAR subunits (NR1, NR2A and NR2B) in hippocampal CA1 and CA3 regions were assessed. Our results showed that although persistent and robust monoarthritis pain was induced by the FCA injections, only the transgenic APP/PS1 mice with chronic monoarthritis pain exhibited marked learning and memory impairments. This result suggested that chronic monoarthritis pain accelerated the cognitive impairment process. Furthermore, only transgenic APP/PS1 mice with chronic monoarthritis pain exhibited an overexpression of NR2B and an increased NR2B/NR2A ratio in the hippocampus CA3. These findings suggest that chronic pain is a risk factor for cognitive impairment and that increased neurotoxicity associated with NMDAR subunit activation may underpin the impairment. Thus, NMDARs may be a therapeutic target for the prevention of chronic pain-induced cognitive impairment.

Distinct behavioral and brain changes after different durations of the modified multiple platform method on rats: An animal model of central fatigue

The modified multiple platform method (MMPM) is a classical sleep deprivation model. It has been widely used in behavioral and brain research, due to its effects on physical and mental functions. However, different MMPM protocols can promote distinct effects in rats. Although the MMPM has been proved to induce central fatigue, the effects of different durations of subjection to the MMPM remain undetermined. This study aims to investigate the changes in behavior, N-Methyl-d-Aspartate receptor 1 (NR1) and 2A (NR2A), as well as the ultrastructural alteration in the hippocampus after different MMPM modelling, to compare the central fatigue effect induced by dynamic MMPM. Rats were randomly divided into four groups: 5-, 14- and 21- day MMPM groups, and a control group. Each MMPM group underwent a 14-hour daily MMPM modelling. After each training session, open field and elevated plus maze tests were performed. Corticosterone levels were detected by ELISA, and the hippocampal NR1 and NR2A were measured by RT-PCR and Western blot analysis. In addition, ultrastructural changes in the hippocampal cornu ammonis 1(CA1) region were determined by transmission electron microscopy (TEM). The findings showed that the 5 and 14 days of MMPM induced a high-stress state, while the 21 days of MMPM induced anxiety and degenerative alteration in the hippocampal morphology. Additionally, hippocampal NR1 and NR2A gene expression decreased in all MMPM groups, whereas the protein expression only decreased in the 21-day group. Overall, different durations of MMPM caused distinct behavioral and brain changes, and the 21 days of MMPM could induce central fatigue.

Deletion of TRPC6 Attenuates NMDA Receptor-Mediated Ca2+ Entry and Ca2+-Induced Neurotoxicity Following Cerebral Ischemia and Oxygen-Glucose Deprivation.

Transient receptor potential canonical 6 (TRPC6) channels are permeable to Na+ and Ca2+ and are widely expressed in the brain. In this study, the role of TRPC6 was investigated following ischemia/reperfusion (I/R) and oxygen-glucose deprivation (OGD). We found that TRPC6 expression was increased in wild-type (WT) mice cortical neurons following I/R and in primary neurons with OGD, and that deletion of TRPC6 reduced the I/R-induced brain infarct in mice and the OGD- /neurotoxin-induced neuronal death. Using live-cell imaging to examine intracellular Ca2+ levels ([Ca2+]i), we found that OGD induced a significant higher increase in glutamate-evoked Ca2+ influx compared to untreated control and such an increase was reduced by TRPC6 deletion. Enhancement of TRPC6 expression using AdCMV-TRPC6-GFP infection in WT neurons increased [Ca2+]i in response to glutamate application compared to AdCMV-GFP control. Inhibition of N-methyl-d-aspartic acid receptor (NMDAR) with MK801 decreased TRPC6-dependent increase of [Ca2+]i in TRPC6 infected cells, indicating that such a Ca2+ influx was NMDAR dependent. Furthermore, TRPC6-dependent Ca2+ influx was blunted by blockade of Na+ entry in TRPC6 infected cells. Finally, OGD-enhanced Ca2+ influx was reduced, but not completely blocked, in the presence of voltage-dependent Na+ channel blocker tetrodotoxin (TTX) and dl-α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) blocker CNQX. Altogether, we concluded that I/R-induced brain damage was, in part, due to upregulation of TRPC6 in cortical neurons. We postulate that overexpression of TRPC6 following I/R may induce neuronal death partially through TRPC6-dependent Na+ entry which activated NMDAR, thus leading to a damaging Ca2+ overload. These findings may provide a potential target for future intervention in stroke-induced brain damage.

Depressive-Like Behaviors Are Regulated by NOX1/NADPH Oxidase by Redox Modification of NMDA Receptor 1.

Involvement of reactive oxygen species (ROS) has been suggested in the development of psychiatric disorders. NOX1 is a nonphagocytic form of NADPH oxidase whose expression in the nervous system is negligible compared with other NOX isoforms. However, NOX1-derived ROS increase inflammatory pain and tolerance to opioid analgesia. To clarify the role of NOX1 in the brain, we examined depressive-like behaviors in mice deficient in Nox1 (Nox1-/Y). Depressive-like behaviors induced by chronic social defeat stress or administration of corticosterone (CORT) were significantly ameliorated in Nox1-/Y Generation of ROS was significantly elevated in the prefrontal cortex (PFC) of mice administrated with CORT, while NOX1 mRNA was upregulated only in the ventral tegmental area (VTA) among brain areas responsible for emotional behaviors. Delivery of miRNA against NOX1 to VTA restored CORT-induced depressive-like behaviors in wild-type (WT) littermates. Administration of CORT to WT, but not to Nox1-/Y, significantly reduced transcript levels of brain-derived neurotrophic factor (bdnf), with a concomitant increase in DNA methylation of the promoter regions in bdnf Delivery of miRNA against NOX1 to VTA restored the level of BDNF mRNA in WT PFC. Redox proteome analyses demonstrated that NMDA receptor 1 (NR1) was among the molecules redox regulated by NOX1. In cultured cortical neurons, hydrogen peroxide significantly suppressed NMDA-induced upregulation of BDNF transcripts in NR1-expressing cells but not in cells harboring mutant NR1 (C744A). Together, these findings suggest a key role of NOX1 in depressive-like behaviors through NR1-mediated epigenetic modification of bdnf in the mesoprefrontal projection.SIGNIFICANCE STATEMENT NADPH oxidase is a source of reactive oxygen species (ROS) that have been implicated in the pathogenesis of various neurological disorders. We presently showed the involvement of a nonphagocytic type of NADPH oxidase, NOX1, in major depressive disorders, including behavioral, biochemical, and anatomical changes in mice. The oxidation of NR1 by NOX1-derived ROS was demonstrated in prefrontal cortex (PFC), which may be causally linked to the downregulation of BDNF, promoting depressive-like behaviors. Given that NOX1 is upregulated only in VTA but not in PFC, mesocortical projections appear to play a crucial role in NOX1-dependent depressive-like behaviors. Our study is the first to present the potential molecular mechanism underlying the development of major depression through the NOX1-induced oxidation of NR1 and epigenetic modification of bdnf.

Autoantibodies against the N-Methyl-d-Aspartate Receptor Subunit NR1: Untangling Apparent Inconsistencies for Clinical Practice.

This viewpoint review provides an integrative picture of seemingly contradictory work published on N-methyl-d-aspartate receptor 1 (NMDAR1) autoantibodies (AB). Based on the present state of knowledge, it gives recommendations for the clinical decision process regarding immunosuppressive treatment. Brain antigen-directed AB in general and NMDAR1-AB in particular belong to a preexisting autoimmune repertoire of mammals including humans. Specific autoimmune reactive B cells may get repeatedly (perhaps transiently) boosted by various potential stimulants (e.g., microbiome, infections, or neoplasms) plus less efficiently suppressed over lifespan (gradual loss of tolerance), likely explaining the increasing seroprevalence upon aging (>20% NMDAR1-AB in 80-year-old humans). Pathophysiological significance emerges (I) when AB-specific plasma cells settle in the brain and produce large amounts of brain antigen-directed AB intrathecally and/or (II) in conditions of compromised blood–brain barrier (BBB), for instance, upon injury, infection, inflammation, or genetic predisposition (APOE4 haplotype), which then allows substantial access of circulating AB to the brain. Regarding NMDAR1-AB, functional effects on neurons in vitro and elicitation of brain symptoms in vivo have been demonstrated for immunoglobulin (Ig) classes, IgM, IgA, and IgG. Under conditions of brain inflammation, intrathecal production and class switch to IgG may provoke high NMDAR1-AB (and other brain antigen-directed AB) levels in cerebrospinal fluid (CSF) and serum, causing the severe syndrome named “anti-NMDAR encephalitis,” which then requires immunosuppressive therapy on top of the causal encephalitis treatment (if available). However, negative CSF NMDAR1-AB results cannot exclude chronic effects of serum NMDAR1-AB on the central nervous system, since the brain acts as “immunoprecipitator,” particularly in situations of compromised BBB. In any case of suspected symptomatic consequences of circulating AB directed against brain antigens, leakiness of the BBB should be evaluated by CSF analysis (albumin quotient as proxy) and magnetic resonance imaging before considering immunosuppression.

Molecular design of proneurogenic and neuroprotective compounds-allosteric NMDA receptor modulators.

N-Methyl-D-aspartic acid (NMDA) receptor is a promising target for treatment of neurodegenerative diseases and other brain disorders as well as for designing proneurogenic compounds able to stimulate neurogenesis in adult brain. We analyzed the structure of the binding site of negative allosteric modulators in the amino-terminal domain of the NMDA receptor and identified possible modes of their binding as well as performed molecular design of new modulators that significantly differ from the known ones in structure and binding mode. In addition, we formed a focused library of chemical compounds with potential neuroprotective and proneurogenic properties, desirable set of pharmacokinetic properties, and low toxicity, which can be the basis for development of new-generation drugs.

Overexpression of EphB2 in hippocampus rescues impaired NMDA receptors trafficking and cognitive dysfunction in Alzheimer model

Alzheimer’s disease (AD) is a progressive neurodegenerative disease, which affects more and more people. But there is still no effective treatment for preventing or reversing the progression of the disease. Soluble amyloid-beta (Aβ) oligomers, also known as Aβ-derived diffusible ligands (ADDLs) play an important role in AD. Synaptic activity and cognition critically depend on the function of glutamate receptors. Targeting N-methyl-D-aspartic acid (NMDA) receptors trafficking and its regulation is a new strategy for AD early treatment. EphB2 is a key regulator of synaptic localization of NMDA receptors. Aβ oligomers could bind to the fibronectin repeats domain of EphB2 and trigger EphB2 degradation in the proteasome. Here we identified that overexpression of EphB2 with lentiviral vectors in dorsal hippocampus improved impaired memory deficits and anxiety or depression-like behaviors in APPswe/PS1-dE9 (APP/PS1) transgenic mice. Phosphorylation and surface expression of GluN2B-containing NMDA receptors were also improved. Overexpression of EphB2 also rescued the ADDLs-induced depletion of the expression of EphB2 and GluN2B-containing NMDA receptors trafficking in cultured hippocampal neurons. These results suggest that improving the decreased expression of EphB2 and subsequent GluN2B-containing NMDA receptors trafficking in hippocampus may be a promising strategy for AD treatment.

Distance-dependent gradient in NMDAR-driven spine calcium signals along tapering dendrites

Neurons receive a multitude of synaptic inputs along their dendritic arbor, but how this highly heterogeneous population of synaptic compartments is spatially organized remains unclear. By measuring N-methyl-d-aspartic acid receptor (NMDAR)-driven calcium responses in single spines, we provide a spatial map of synaptic calcium signals along dendritic arbors of hippocampal neurons and relate this to measures of synapse structure. We find that quantal NMDAR calcium signals increase in amplitude as they approach a thinning dendritic tip end. Based on a compartmental model of spine calcium dynamics, we propose that this biased distribution in calcium signals is governed by a gradual, distance-dependent decline in spine size, which we visualized using serial block-face scanning electron microscopy. Our data describe a cell-autonomous feature of principal neurons, where tapering dendrites show an inverse distribution of spine size and NMDAR-driven calcium signals along dendritic trees, with important implications for synaptic plasticity rules and spine function.

Cellular protein and mRNA expression of β1 nicotinic acetylcholine receptor (nAChR) subunit in brain, skeletal muscle and placenta

The β1 nicotinic acetylcholine receptor (nAChR) subunit is a muscle type subunit of this family and as such, is found predominantly in muscle. Recent reports document its expression in other tissues and cell lines including adrenal glands, carcinomas, lung and brain. However, the majority of studies were of tissue lysates, thus the cellular distribution was not determined. This study aimed to determine the cellular distribution of the β1 nAChR subunit in the brain, at both the mRNA and protein levels, using non-radioactive in situ hybridization (ISH) and immunohistochemistry (IHC), respectively, and to compare it to two muscle tissue types, skeletal and placenta. Tissue was formalin fixed and paraffin embedded (all tissue types) and frozen (placenta) from humans. Additional control tissue from the piglet and mouse brain were also studied, as was mRNA for the α3 nAChR and N-methyl-d-aspartate receptor 1 (NR1) subunit. We found no β1 nAChR subunit mRNA expression in the human and piglet brain despite strong protein expression. Some signal was seen in the mouse brain but considered inconclusive given the probes designed were not of 100% homology to the mouse. In the skeletal muscle and placenta tissues, β1 nAChR subunit mRNA expression was prominent and mirrored protein expression. No α3 nAChR or NR1 mRNA was seen in the skeletal muscle, as expected, although both subunit mRNAs were present in the placenta. This study concludes that further experiments are required to conclusively state that the β1 nAChR subunit is expressed in the human, piglet and mouse brain.

Ionotropic glutamate receptors activate cell signaling in response to glutamate in Schwann cells.

In the peripheral nervous system, Schwann cells (SCs) demonstrate surveillance activity, detecting injury and undergoing trans-differentiation to support repair. SC receptors that detect peripheral nervous system injury remain incompletely understood. We used RT-PCR to profile ionotropic glutamate receptor expression in cultured SCs. We identified subunits required for assembly of N-methyl-d-aspartic acid (NMDA) receptors (NMDA-Rs), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, and kainate receptors. Treatment of SCs with 40-100 µM glutamate or with 0.5-1.0 µM NMDA robustly activated Akt and ERK1/2. The response was transient and bimodal; glutamate concentrations that exceeded 250 µM failed to activate cell signaling. Phosphoprotein profiling identified diverse phosphorylated proteins in glutamate-treated SCs in addition to ERK1/2 and Akt, including p70 S6-kinase, glycogen synthase kinase-3, ribosomal S6 kinase, c-Jun, and cAMP response element binding protein. Activation of SC signaling by glutamate was blocked by EGTA and dizocilpine and by silencing expression of the NMDA-R NR1 subunit. Phosphoinositide 3-kinase/PI3K functioned as an essential upstream activator of Akt and ERK1/2 in glutamate-treated SCs. When glutamate or NMDA was injected directly into crush-injured rat sciatic nerves, ERK1/2 phosphorylation was observed in myelinated and nonmyelinating SCs. Glutamate promoted SC migration by a pathway that required PI3K and ERK1/2. These results identified ionotropic glutamate receptors and NMDA-Rs, specifically, as potentially important cell signaling receptors in SCs.-Campana, W. M., Mantuano, E., Azmoon, P., Henry, K., Banki, M. A., Kim, J. H., Pizzo, D. P., Gonias, S. L. Ionotropic glutamate receptors activate cell signaling in response to glutamate in Schwann cells.

Mechanical stress activates NMDA receptors in the absence of agonists

While studying the physiological response of primary rat astrocytes to fluid shear stress in a model of traumatic brain injury (TBI), we found that shear stress induced Ca2+ entry. The influx was inhibited by MK-801, a specific pore blocker of N-Methyl-D-aspartic acid receptor (NMDAR) channels, and this occurred in the absence of agonists. Other NMDA open channel blockers ketamine and memantine showed a similar effect. The competitive glutamate antagonists AP5 and GluN2B-selective inhibitor ifenprodil reduced NMDA-activated currents, but had no effect on the mechanically induced Ca2+ influx. Extracellular Mg2+ at 2 mM did not significantly affect the shear induced Ca2+ influx, but at 10 mM it produced significant inhibition. Patch clamp experiments showed mechanical activation of NMDAR and inhibition by MK-801. The mechanical sensitivity of NMDARs may play a role in the normal physiology of fluid flow in the glymphatic system and it has obvious relevance to TBI.

Characterization of postsynaptic calcium signals in the pyramidal neurons of anterior cingulate cortex.

Calcium signaling is critical for synaptic transmission and plasticity. N-methyl-D-aspartic acid (NMDA) receptors play a key role in synaptic potentiation in the anterior cingulate cortex. Most previous studies of calcium signaling focus on hippocampal neurons, little is known about the activity-induced calcium signals in the anterior cingulate cortex. In the present study, we show that NMDA receptor-mediated postsynaptic calcium signals induced by different synaptic stimulation in anterior cingulate cortex pyramidal neurons. Single and multi-action potentials evoked significant suprathreshold Ca2+ increases in somas and spines. Both NMDA receptors and voltage-gated calcium channels contributed to this increase. Postsynaptic Ca2+signals were induced by puff-application of glutamate, and a NMDA receptor antagonist AP5 blocked these signals in both somas and spines. Finally, long-term potentiation inducing protocols triggered postsynaptic Ca2+ influx, and these influx were NMDA receptor dependent. Our results provide the first study of calcium signals in the anterior cingulate cortex and demonstrate that NMDA receptors play important roles in postsynaptic calcium signals in anterior cingulate cortex pyramidal neurons.

FAM3A Protects Against Glutamate-Induced Toxicity by Preserving Calcium Homeostasis in Differentiated PC12 Cells

Background/Aims: Stroke is the leading cause of adult disability, and glutamate-induced dysregulation of intracellular Ca²⁺ homeostasis is a key mechanism. FAM3A is the first member of the family with sequence similarity 3 (FAM3) gene family, and its biological function remains largely unknown. We have recently reported that FAM3A exerts protective effects against oxidative stress and mitochondrial dysfunction in HT22 cells. Methods: Here, we investigated the protective effects of FAM3A using a glutamate-induced neuronal injury model in nerve growth factor (NGF)-differentiated PC12 cells. The protective effects were determined by measuring lactate dehydrogenase (LDH) release, apoptosis and mitochondrial oxidative stress. Ca²⁺ imaging was performed to detect changes in intracellular Ca²⁺ concentration in PC12 cells. The related molecular mechanisms were investigated by fluorescence staining, coimmunoprecipitation (Co-IP) and western blotting. Results: Upregulation of FAM3A by lentivirus transfection markedly decreased LDH release, inhibited apoptosis and reduced mitochondrial oxidative stress, which were accompanied by alleviated intracellular Ca²⁺ levels as measured by calcium imaging. The results of western blotting showed that FAM3A significantly decreased the surface expression of metabotropic glutamate receptor 1/5 (mGluR1/5), with no effect on the expression of N-methyl-d-aspartic acid receptor (NMDAR) or α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) subunits. FAM3A overexpression also inhibited the intracellular Ca²⁺ release mediated by mGluR1/5 and inositol 1,4,5-trisphosphate receptor (IP₃R), but not the ryanodine receptor (RyR). In addition, FAM3A significantly attenuated the store-operated calcium entry (SOCE) induced by thapsigargin (Tg), but the expression of SOCE-related proteins was not altered. The results of coimmunoprecipitation (Co-IP) showed that FAM3A disrupted the interaction of stromal interaction molecule 1 (STIM1) with Orai1 triggered by glutamate. Conclusion: These results suggest that the upregulation of FAM3A protects against glutamate-induced dysfunction of Ca²⁺ homeostasis not only by inhibiting mGluR1/5-dependent endoplasmic reticulum (ER) Ca²⁺ release, but also by attenuating SOCE mediated by the STIM1-Orai1 interaction.

The Effect of Nefopam Infusion during Laparascopic Cholecystectomy on Postoperative Pain.

Background: While recovery from remifentanil is fast due to its rapid metabolism, it can induce hyperalgesia by activation of N-methyl-D-aspartic acid (NMDA) receptors. Therefore, administration of NMDA receptor antagonists such as ketamine is effective in relieving hyperalgesia caused by remifentanil. A previous study showed that nefopam administration before anesthesia combined with low-dose remifentanil reduced pain and analgesic consumption during the immediate postoperative period. We hypothesized that intraoperative infusion of nefopam during laparoscopic cholecystectomy would be as effective as ketamine in controlling pain during the acute postoperative period after sevoflurane and remifentanil based anesthesia.Methods: Sixty patients scheduled to undergo laparoscopic cholecystectomy were randomly divided into three groups. General anesthesia was maintained with sevoflurane and effect-site target concentration of remifentanil (4 ng/ml) in all patients. An intravenous bolus of nefopam (0.3 mg/kg) was given, followed by continuous infusion (65 µg/kg/h) in Group N (n=20). An intravenous bolus of ketamine (0.3 mg/kg) was administered, followed by continuous infusion (180 µg/kg/h) in Group K (n=20), and Group C received a bolus and subsequent infusion of normal saline equal to the infusion received by Group K (n=20). We compared postoperative Visual Analogue Scale (VAS) scores and analgesic requirements over the first 8 postoperative hours between groups.Results: The pain scores (VAS) and fentanyl requirements for 1 h after surgery were significantly lower in the nefopam and ketamine groups compared with the control group (p<0.05). There were no differences between the nefopam and ketamine groups. The three groups showed no differences in VAS scores and number of analgesic injections from 1 to 8 h after surgery.Conclusion: Intraoperative nefopam infusion during laparoscopic cholecystectomy reduced opioid requirements and pain scores (VAS) during the early postoperative period after remifentanil-based anesthesia.

Overexpression of βCaMKII impairs behavioral flexibility and NMDAR-dependent long-term depression in the dentate gyrus

Behavioral flexibility is in close proximity to dentate gyrus (DG) function and long-term depression (LTD), but the role of DG LTD in behavioral flexibility has hitherto been unexplored. Although the functions of alpha-Ca2+/calmodulin-dependent protein kinase II (CaMKII) have been studied extensively, the role of βCaMKII, a constituent of the CaMKII holoenzyme, in LTD and behavioral flexibility has not been investigated in vivo. Here using the βCaMKII-F90G transgenic (TG) mice, in which the inducible and reversible overexpression of βCaMKII is restricted to dentate gyrus (DG), we found that TG mice exhibited defective behavioral flexibility in two reversal tasks and seriously impaired N-methyl-d-aspartic acid receptor (NMDAR)-dependent LTD in DG medial perforant path (MPP). Consistent with the deficit in NMDAR-LTD, GluA1-Ser845, GluA1-Ser831 dephosphorylation and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) internalization were also disrupted during NMDAR-LTD in TG mice. Furthermore, these deficits were due to decreased activities of protein phosphatases (PP) 1/2A and glycogen synthesis kinase 3 beta (GSK3β), and overexpressed synaptic stargazin in TG mice. Importantly, all the deficits above could be reversed by 1-naphthylmethyl (NM)-PP1, a specific inhibitor of the exogenous βCaMKII-F90G. Taken together, our findings for the first time demonstrate that βCaMKII overexpression impairs behavioral flexibility and NMDAR-dependent LTD in DG MPP, which further confirms the close relationship between NMDAR-dependent LTD and behavioral flexibility.

Research progress in the mechanisms of the clinical effects of ketamine

Ketamine is primarily known as an effective NMDAR ( N -methyl- D -aspartic acid receptor) blocker. As one of the intravenous anesthetics, ketamine has been widely used in clinical practice for more than 50 years, exhibiting several different outcomes besides the original anesthetic effects. Recent studies provide insights into the mechanisms of the following neuropharmacological effects of ketamine: (ⅰ) Anesthesia. The anesthetic effects of ketamine are mainly due to its ability to decrease the inter-cortical communications to generate dissociative anesthesia. Besides the well-known NMDAR, another target for ketamine to show anesthetic effects has been reported to be hyperpolarization-activated cyclic nucleotide-gated channels (HCN channels). (ⅱ) Analgesia. Ketamine not only exhibits blockade on NMDAR in the central nervous system, but also reverses opioid tolerance when combined with morphine at a low dose. The affinity with sodium and potassium channels makes ketamine possible for analgesia at high doses. However, the clinical analgesic effect is currently controversial, and the algetic cases after the discontinuation of ketamine are probably caused by its metabolic product norketamine. (ⅲ) Anti-depression. Ketamine is recently regarded as a rapid antidepressant drug for its contribution to neurogenesis through several molecular processes, such as the glutamate burst by activating presynaptic NMDAR and AMPAR ( α -amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor), the synaptic protein synthesis and transportation by activating mTOR (mechanistic target of rapamycin), and the synaptic maturation by releasing BDNF (brain derived neurotrophic factor). At the circuit level, ketamine widely reconstructs circuits by dual regulation on NMDAR and AMPAR, and causes loss of phenotype of the PV GABAergic neurons (parvalbumin-positive interneurons). (ⅳ) Side effects. Ketamine is strictly constrained for its psychiatric side effects resulted from the potent disruption on neural network stability, which shares similar neuro-circuit etiology with schizophrenia. Also, the potential ketamine-induced neuroapoptosis might generate risks for anesthesia during pregnancy and childhood, which is under deep investigation. Due to the potential risks of ketamine, more attention should be paid to the development of novel anesthetics keeping the anesthetic, analgesic and antidepressant effects of ketamine, however, without the potential psychiatric side effects. Thus, exceeding novel knowledge, makes ketamine a representative example for the complexity of anesthetics due to its global targets and dose-dependent properties, which provides a breakthrough point both for the mechanism researches for the working models of general anesthetics and for exploring the state of consciousness of human beings.

MicroRNA-181c Ameliorates Cognitive Impairment Induced by Chronic Cerebral Hypoperfusion in Rats.

Chronic cerebral hypoperfusion (CCH) characterized by global cerebral ischemia is an important risk factor contributing to the development of dementia. MicroRNAs (miRNAs) play important roles in the cellular adaptation to long-term ischemia/hypoxia by turning off or on the expression of target genes. MiR-181c is widely expressed in the nervous system, and tripartite motif 2 (TRIM2) is one of its target genes. In this work, we had identified that progressive spatial memory deficiency was induced in the bilateral common carotid artery occlusion (2-VO) rat models. Meanwhile, inhibition of miR-181c expression and upregulation of TRIM2 in the hippocampus of 2-VO rats were found accompanying with reduction in the dendritic branching and dendrite spine density of the hippocampal neurons. Viral vector-mediated miR-181c delivery might improve the cognitive deficiency via TRIM2 on neurofilament light (NF-L) ubiquitination resulting in remodeling of the hippocampal neurons as well as increase in N-methyl-D-aspartate receptor 1 (NR1) subunit cell surface expression. Meanwhile, miR-181c might rescue the cellular activity from ischemia/hypoxia. These results indicated a novel miRNA-mediated mechanism involving miR-181c and TRIM2 in the cognitive impairment induced by CCH and provided a rationale for the development of miRNA-based strategies for prevention of dementia.

Centrally mediated ejaculatory response via sympathetic outflow in rats: role of N-methyl-D-aspartic acid receptors in paraventricular nucleus.

Ejaculation is mediated by a spinal generator, which integrates inputs related to the sexual activity and coordinates sympathetic, parasympathetic, and motor outflow. Previous clinical studies indicate that primary premature ejaculation is related to the hyperactivity of the sympathetic nervous system. In this study, we explored the roles of N-methyl-D-aspartic acid (NMDA) receptors in paraventricular nucleus of the hypothalamus (PVN) on ejaculatory responses and its potential mechanism in the rats. We found that microinjection of 0.20nmol NMDA into the PVN reduced the latency of intromission and facilitated ejaculation during copulation. Moreover, delayed ejaculation and intromission were observed after the rats were microinjected with NMDA receptor antagonist D (-)-2-Amino-5-phosphonopentanoic acid (AP-5). However, we discovered that microinjection of NMDA into PVN significantly increased baseline lumbar splanchnic nerve activity (LSNA), and the NMDA dose was positively correlated with the increased LSNA (r=0.875, p=0.04). Meanwhile, the plasma norepinephrine level in rats injected with NMDA was much higher than that in rats injected with saline (1453.4±136.4pg/mL vs. 492.3±36.8pg/mL, p<0.01). Additionally, AP-5 reduced the baseline LSNA and abrogated the enhancing activity of NMDA in LSNA. Thus, we propose that NMDA receptors in PVN may facilitate ejaculation through enhancing the activity of sympathetic system.

Antinociceptive effect of co-administered NMDA and histamine H4 receptor antagonists in a rat model of acute pain.

The histamine H4 receptor (H4R) has attracted a lot of attention in terms of its role in antinociception. The N-Methyl-d-aspartic acid (NMDA) receptor is a well-characterized participant in pain pathways. However, it's influence on H4R signaling is poorly understood. Thus, in the present study we investigated the effect of a selective H4R antagonist JNJ7777120 (25mg/kg) and a NMDA receptor antagonist MK-801 (0.1-10μg) on nociceptive thresholds in a rat acute pain model. The influence of intrathecally (it), intracerebroventricularly (icv) and intraplantarly (ipl) administered MK-801 co-injected with JNJ7777120 administered intraperitoneally (ip) was determined in the modified Randall-Selitto paw pressure, the tail flick and plantar tests. Both ip JNJ7777120 as well as MK-801 delivered it and ipl increased nociceptive pain thresholds. It and ipl pretreatment with MK-801 additively augmented JNJ7777120 mechanical antinociception. A weaker effect was also observed after it co-administration with MK-801 and JNJ7777120 in the tail flick test. Intracerebroventricular MK-801 failed to produce any effect nor did ipl MK-801 in the plantar test. The results show for the first time that the H4R and NMDA receptors play a significant role in antinociception in an acute non-inflammatory pain. Furthermore, the blockage of NMDA receptors at the peripheral and spinal, but not supraspinal sites produces a profound antinociceptive response upon simultaneous H4R antagonism. Thus, this study clearly demonstrates the relevance of NMDA and H4R receptors in the modulation of pain signals and that their role is not exclusively limited to their modulatory activity in inflammatory pain states.