05-920 Sigma-AldrichAnti-NR2B Antibody, clone BWJHL

N-methyl-D-aspartate receptors (NMDARs) are a subtype of ionotropic glutamate receptors and are expressed throughout the central nervous system (CNS). Their activity is required for excitatory synaptic transmission, the developmental refinement of neural circuits and for the expression of many forms of synaptic plasticity. NMDARs are obligate heterotetramers and the expression of their constituent subunits is developmentally and anatomically regulated. In rodent cortex and hippocampus, the GluN2B subunit is expressed at high levels early in development and decreases to plateau levels later while expression of the GluN2A subunit has a concomitant increase. Regulation of GluN2A and GluN2B expressions are incompletely understood. Here, we showed the influence of miRNAs in this process.Two miRNAs, miR-19a and miR-539 can influence the levels of NMDARs subunits, as they target the mRNAs encoding GluN2A and GluN2B respectively. MiR-539 also modified the expression of the transcription factor REST, a known regulator of NMDAR subunit expression.miR-19a and miR-539, in collaboration with REST, serve to set the levels of GluN2A and GluN2B precisely during development. These miRNAs offer an entry point for interventions that affect plasticity and a novel approach to treat neurodegenerative diseases.

The MET receptor tyrosine kinase (RTK), implicated in risk for autism spectrum disorder (ASD) and in functional and structural circuit integrity in humans, is a temporally and spatially regulated receptor enriched in dorsal pallial-derived structures during mouse forebrain development. Here we report that loss or gain of function of MET in vitro or in vivo leads to changes, opposite in nature, in dendritic complexity, spine morphogenesis, and the timing of glutamatergic synapse maturation onto hippocampus CA1 neurons. Consistent with the morphological and biochemical changes, deletion of Met in mutant mice results in precocious maturation of excitatory synapse, as indicated by a reduction of the proportion of silent synapses, a faster GluN2A subunit switch, and an enhanced acquisition of AMPA receptors at synaptic sites. Thus, MET-mediated signaling appears to serve as a mechanism for controlling the timing of neuronal growth and functional maturation. These studies suggest that mistimed maturation of glutamatergic synapses leads to the aberrant neural circuits that may be associated with ASD risk.

Prolonged calpain activation is widely recognized as a key component of neurodegeneration in a variety of pathological conditions. Numerous reports have also indicated that synaptic activation of NMDA receptors (NMDARs) provides neuroprotection against a variety of insults. Here, we report the paradoxical finding that such neuroprotection involves calpain activation. NMDAR activation in cultured rat cortical neurons was neuroprotective against starvation and oxidative stress-induced damage. It also resulted in the degradation of two splice variants of PH domain and Leucine-rich repeat Protein Phosphatase 1 (PHLPP1), PHLPP1α and PHLPP1β, which inhibit the Akt and ERK1/2 pathways. Synaptic NMDAR-induced neuroprotection and PHLPP1 degradation were blocked by calpain inhibition. Lentiviral knockdown of PHLPP1 mimicked the neuroprotective effects of synaptic NMDAR activation and occluded the effects of calpain inhibition on neuroprotection. In contrast to synaptic NMDAR activation, extrasynaptic NMDAR activation had no effect on PHLPP1 and the Akt and ERK1/2 pathways, but resulted in calpain-mediated degradation of striatal-enriched protein tyrosine phosphatase (STEP) and neuronal death. Using μ-calpain- and m-calpain-selective inhibitors and μ-calpain and m-calpain siRNAs, we found that μ-calpain-dependent PHLPP1 cleavage was involved in synaptic NMDAR-mediated neuroprotection, while m-calpain-mediated STEP degradation was associated with extrasynaptic NMDAR-induced neurotoxicity. Furthermore, m-calpain inhibition reduced while μ-calpain knockout exacerbated NMDA-induced neurotoxicity in acute mouse hippocampal slices. Thus, synaptic NMDAR-coupled μ-calpain activation is neuroprotective, while extrasynaptic NMDAR-coupled m-calpain activation is neurodegenerative. These results help to reconcile a number of contradictory results in the literature and have critical implications for the understanding and potential treatment of neurodegenerative diseases.

To test whether memantine can prevent methotrexate-induced cognitive deficits in a preclinical model.After noting that methotrexate exposure induces prolonged elevations of the glutamate analog homocysteic acid (HCA) within cerebrospinal fluid, we tested whether intrathecal injection of HCA would produce memory deficits similar to those observed after intrathecal methotrexate. We then tested whether memantine, an antagonist of the N-methyl-d-aspartate (NMDA) subclass of glutamate receptors, could protect animals treated with clinically relevant doses of intrathecal methotrexate against developing memory deficits. Finally, we asked whether memantine affected this pathway beyond inhibiting the NMDA receptor by altering expression of the NMDA receptor or affecting concentrations of HCA or glutamate within the central nervous system.Four intrathecal doses of methotrexate induced deficits in spatial memory, persisting at least one month following the final injection. Intrathecal HCA was sufficient to reproduce this deficit. Concurrent administration of memantine during the period of methotrexate exposure was protective, decreasing the incidence of methotrexate-induced spatial memory deficits from 56% to 20% (P less than 0.05). Memantine neither altered expression of NMDA receptors within the hippocampus nor blunted the methotrexate-induced increases in glutamate or HCA.Excitotoxic glutamate analogs including HCA contribute to cognitive deficits observed after intrathecal methotrexate. Memantine, an NMDA receptor antagonist, reduces the incidence of cognitive deficits in rats treated with intrathecal methotrexate, and may therefore benefit patients with cancer receiving similar treatment.

The N-methyl-D-aspartate (NMDA) receptor has long been associated with learning and memory processes as well as diseased states, particularly in schizophrenia (SZ). Additionally, SZ is increasingly recognized as a neurodevelopmental disorder with cognitive impairments often preceding the onset of psychosis. However, the cause of these cognitive deficits and what initiates the pathological process is unknown. Growing evidence has implicated the glutamate system and, in particular, N-methyl-D-aspartate receptor (NMDAR) dysfunction in the pathophysiology of SZ. Yet, the vast majority of SZ-related research has focused on NMDAR function in adults leaving the role of NMDARs during development uncharacterized. We used the prenatal methylazoxymethanol acetate (MAM, E17) exposure model to determine the alterations of NMDAR protein levels and function, as well as associated cognitive deficits during development. We found that MAM-exposed animals have significantly altered NMDAR protein levels and function in the juvenile and adolescent hippocampus. Furthermore, these changes are associated with learning and memory deficits in the Morris Water Maze. Thus, in the prenatal MAM-exposure SZ model, NMDAR expression and function is altered during the critical period of hippocampal development. These changes may be involved in disease initiation and cognitive impairment in the early stage of SZ.

The development of diet-induced obesity (DIO) can potently alter multiple aspects of dopamine signaling, including dopamine transporter (DAT) expression and dopamine reuptake. However, the time-course of diet-induced changes in DAT expression and function and whether such changes are dependent upon the development of DIO remains unresolved. Here, we fed rats a high (HFD) or low (LFD) fat diet for 2 or 6 weeks. Following diet exposure, rats were anesthetized with urethane and striatal DAT function was assessed by electrically stimulating the dopamine cell bodies in the ventral tegmental area (VTA) and recording resultant changes in dopamine concentration in the ventral striatum using fast-scan cyclic voltammetry. We also quantified the effect of HFD on membrane associated DAT in striatal cell fractions from a separate group of rats following exposure to the same diet protocol. Notably, none of our treatment groups differed in body weight. We found a deficit in the rate of dopamine reuptake in HFD rats relative to LFD rats after 6 but not 2 weeks of diet exposure. Additionally, the increase in evoked dopamine following a pharmacological challenge of cocaine was significantly attenuated in HFD relative to LFD rats. Western blot analysis revealed that there was no effect of diet on total DAT protein. However, 6 weeks of HFD exposure significantly reduced the 50 kDa DAT isoform in a synaptosomal membrane-associated fraction, but not in a fraction associated with recycling endosomes. Our data provide further evidence for diet-induced alterations in dopamine reuptake independent of changes in DAT production and demonstrates that such changes can manifest without the development of DIO.

NMDA receptors (NMDARs) are critical to synaptogenesis, neural circuitry and higher cognitive functions. A hallmark feature of NMDARs is an early postnatal developmental switch from those containing primarily GluN2B to primarily GluN2A subunits. Although the switch in phenotype has been an area of intense interest for two decades, the mechanisms that trigger it and the link between experience and the switch are unclear. Here we show a new role for the transcriptional repressor REST in the developmental switch of synaptic NMDARs. REST is activated at a critical window of time and acts via epigenetic remodeling to repress Grin2b expression and alter NMDAR properties at rat hippocampal synapses. Knockdown of REST in vivo prevented the decline in GluN2B and developmental switch in NMDARs. Maternal deprivation impaired REST activation and acquisition of the mature NMDAR phenotype. Thus, REST is essential for experience-dependent fine-tuning of genes involved in synaptic plasticity.

We studied the effects of water deprivation (WD) on the phosphorylation of tyrosine kinase B (TrkB) and NMDA receptor subunits in the supraoptic nucleus (SON) of the rat. Laser capture microdissection and quantitative reverse transcriptase polymerase chain reaction was used to demonstrate brain-derived neurotrophic factor (BDNF) and TrkB gene expression in vasopressin SON neurones. Immunohistochemistry confirmed BDNF staining in vasopressin neurones, whereas staining for phosphorylated TrkB was increased following WD. Western blot analysis of brain punches containing the SON revealed that tyrosine phosphorylation of TrkB (pTrkBY(515)), serine phosphorylation of NR1 (pNR1S(866) or pNR1) and tyrosine phosphorylation of NR2B subunits (pNR2BY(1472) or pNR2B) were significantly increased in WD animals compared to controls. Access to water for 2 h reduced pTrkBY(515) content to control levels without affecting pNR1 or pNR2B. Four hours of rehydration was needed to reduce pNR1 and pNR2B to control levels. To test whether increased phosphorylation of TrkB in the present study is mediated by BDNF, a group of animals were instrumented with right SON cannula coupled to mini-osmotic pumps filled with vehicle or TrkB-Fc fusion protein, which prevents BDNF binding to TrkB. In the left SON contralateral to the cannula, TrkB phosphorylation was significantly enhanced following WD. Separate analysis of the right SON, which received TrkB-Fc, showed that the TrkB receptor phosphorylation following WD was significantly attenuated. Although increased pNR1S(866) following WD was not affected by local infusion of TrkB-Fc, pNR2BY(1472) was significantly reduced. Co-immunoprecipitation revealed an increased physical interaction between Fyn kinase and NR2B and TrkB in the SON following WD. Thus, activation of TrkB in the SON following WD may affect cellular excitability through the phosphorylation of NR2B subunits.

The N-methyl-D-aspartate receptor (NMDAR) requires both NR1 and NR2 subunits to form a functional ion channel. Despite the recent advances in our understanding of the contributions of these different subunits to both the function and pharmacology of the NMDAR, the precise subunit stoichiometry of the receptor and the regions of the subunits governing subunit interactions remain unclear. Since NR2 subunits are not transported to the cell surface unless they associate with NR1 subunits, cell-surface expression of NR2A can be used to monitor the association of the different subunits in cells transfected with N- and C-terminally truncated NR1 subunits. By combining measurements of cell-surface expression of NR2A with co-immunoprecipitation experiments, and by using Blue Native gel electrophoresis to determine the oligomerization status of the subunits, we have shown that regions of the N-terminus of NR1 are critical for subunit association, whereas the truncation of the C-terminus of NR1 before the last transmembrane region has no effect on the association of the subunits. Evidence from the Blue Native gels, sucrose-gradient centrifugation and size exclusion of soluble NR1 domains suggests that NR1 subunits alone can form stable dimers. Using a cell line, which can be induced to express the NMDAR following exposure to dexamethasone, we have shown that NMDARs can be expressed at the cell surface within 5 h of the recombinant gene induction, and that there appears to be a delay between the first appearance of the subunits and their stable association.

N-Methyl-D-aspartate receptor (NMDAR)-mediated excitotoxicity has been proposed to play a role in Huntington disease (HD), caused by expansion of a polyglutamine tract in the protein huntingtin. HD is characterized by selective neurodegeneration most severely affecting striatal medium-sized spiny projection neurons (MSNs), where expression of the NMDAR subunit NR2B is increased relative to other NR2 subunits. Here, we review our data that NR2B-type NMDAR currents are selectively potentiated by mutant huntingtin in transfected non-neuronal cells and acutely dissociated striatal MSNs from the YAC72 transgenic mouse model of HD. As well, we report increased striatal MSN NMDAR-mediated synaptic currents in corticostriatal slice recordings from YAC72 compared with wild-type mice. This effect was associated with a larger NMDAR- to AMPAR-mediated current ratio, suggesting specific potentiation of postsynaptic NMDARs. Enhanced NMDAR current likely involves increased surface receptor numbers or activity, since we observed no differences between genotypes in striatal NR2B expression. Potentiation of NR2B-containing NMDAR current in striatal MSNs expressing mutant huntingtin may help explain the exquisite vulnerability of these neurons to degeneration in HD.