Analysis of NR3A receptor subunits in human native NMDA receptors

The t-N-methyl-d-aspartate receptor: Making the case for d-Serine to be considered its inverse co-agonist

The N-methyl-d-aspartate receptor (NMDAR) is an enigmatic macromolecule that has garnered a good deal of attention on account of its involvement in the cellular processes that underlie learning and memory, following its discovery in the mid twentieth century (Baudry and Davis, 1991). Yet, despite advances in knowledge about its function, there remains much more to be uncovered regarding the receptor's biophysical properties, subunit composition, and role in CNS physiology and pathophysiology. The motivation for this review stems from the need for synthesizing new information gathered about these receptors that sheds light on their role in synaptic plasticity and their dichotomous relationship with the amino acid d-serine through which they influence the pathogenesis of neurodegenerative diseases like temporal lobe epilepsy (TLE), the most common type of adult epilepsies (Beesley et al., 2020a). This review will outline pertinent ideas relating structure and function of t-NMDARs (GluN3 subunit-containing triheteromeric NMDARs) for which d-serine might serve as an inverse co-agonist. We will explore how tracing d-serine's origins blends glutamate-receptor biology with glial biology to help provide fresh perspectives on how neurodegeneration might interlink with neuroinflammation to initiate and perpetuate the disease state. Taken together, we envisage the review to deepen our understanding of endogenous d-serine's new role in the brain while also recognizing its therapeutic potential in the treatment of TLE that is oftentimes refractory to medications.

Extrasynaptic NMDA receptors in acute and chronic excitotoxicity: implications for preventive treatments of ischemic stroke and late-onset Alzheimer's disease

Stroke and late-onset Alzheimer's disease (AD) are risk factors for each other; the comorbidity of these brain disorders in aging individuals represents a significant challenge in basic research and clinical practice. The similarities and differences between stroke and AD in terms of pathogenesis and pathophysiology, however, have rarely been comparably reviewed. Here, we discuss the research background and recent progresses that are important and informative for the comorbidity of stroke and late-onset AD and related dementia (ADRD). Glutamatergic NMDA receptor (NMDAR) activity and NMDAR-mediated Ca²⁺ influx are essential for neuronal function and cell survival. An ischemic insult, however, can cause rapid increases in glutamate concentration and excessive activation of NMDARs, leading to swift Ca²⁺ overload in neuronal cells and acute excitotoxicity within hours and days. On the other hand, mild upregulation of NMDAR activity, commonly seen in AD animal models and patients, is not immediately cytotoxic. Sustained NMDAR hyperactivity and Ca²⁺ dysregulation lasting from months to years, nevertheless, can be pathogenic for slowly evolving events, i.e. degenerative excitotoxicity, in the development of AD/ADRD. Specifically, Ca²⁺ influx mediated by extrasynaptic NMDARs (eNMDARs) and a downstream pathway mediated by transient receptor potential cation channel subfamily M member (TRPM) are primarily responsible for excitotoxicity. On the other hand, the NMDAR subunit GluN3A plays a "gatekeeper" role in NMDAR activity and a neuroprotective role against both acute and chronic excitotoxicity. Thus, ischemic stroke and AD share an NMDAR- and Ca²⁺-mediated pathogenic mechanism that provides a common receptor target for preventive and possibly disease-modifying therapies. Memantine (MEM) preferentially blocks eNMDARs and was approved by the Federal Drug Administration (FDA) for symptomatic treatment of moderate-to-severe AD with variable efficacy. According to the pathogenic role of eNMDARs, it is conceivable that MEM and other eNMDAR antagonists should be administered much earlier, preferably during the presymptomatic phases of AD/ADRD. This anti-AD treatment could simultaneously serve as a preconditioning strategy against stroke that attacks ≥ 50% of AD patients. Future research on the regulation of NMDARs, enduring control of eNMDARs, Ca²⁺ homeostasis, and downstream events will provide a promising opportunity to understand and treat the comorbidity of AD/ADRD and stroke.

Pathogenesis of sporadic Alzheimer's disease by deficiency of NMDA receptor subunit GluN3A

The Ca²⁺ hypothesis for Alzheimer's disease (AD) conceives Ca²⁺ dyshomeostasis as a common mechanism of AD; the cause of Ca²⁺ dysregulation, however, is obscure. Meanwhile, hyperactivities of N-Methyl-D-aspartate receptors (NMDARs), the primary mediator of Ca²⁺ influx, are reported in AD. GluN3A (NR3A) is an NMDAR inhibitory subunit. We hypothesize that GluN3A is critical for sustained Ca²⁺ homeostasis and its deficiency is pathogenic for AD. Cellular, molecular, and functional changes were examined in adult/aging GluN3A knockout (KO) mice. The GluN3A KO mouse brain displayed age-dependent moderate but persistent neuronal hyperactivity, elevated intracellular Ca²⁺ , neuroinflammation, impaired synaptic integrity/plasticity, and neuronal loss. GluN3A KO mice developed olfactory dysfunction followed by psychological/cognitive deficits prior to amyloid-β/tau pathology. Memantine at preclinical stage prevented/attenuated AD syndromes. AD patients' brains show reduced GluN3A expression. We propose that chronic "degenerative excitotoxicity" leads to sporadic AD, while GluN3A represents a primary pathogenic factor, an early biomarker, and an amyloid-independent therapeutic target.

GluN3A NMDA receptor subunits: more enigmatic than ever?

Non-conventional N-methyl-d-aspartate receptors (NMDARs) containing GluN3A subunits have unique biophysical, signalling and localization properties within the NMDAR family, and are typically thought to counterbalance functions of classical NMDARs made up of GluN1/2 subunits. Beyond their recognized roles in synapse refinement during postnatal development, recent evidence is building a wider perspective for GluN3A functions. Here we draw particular attention to the latest developments for this multifaceted and unusual subunit: from finely timed expression patterns that correlate with plasticity windows in developing brains or functional hierarchies in the mature brain to new insight onto presynaptic GluN3A-NMDARs, excitatory glycine receptors and behavioural impacts, alongside further connections to a range of brain disorders.

Computational modeling and biomarker studies of pharmacological treatment of Alzheimer's disease (Review)

Alzheimer's disease (AD) is a complex and multifactorial disease. In order to understand the genetic influence in the progression of AD, and to identify novel pharmaceutical agents and their associated targets, the present study discusses computational modeling and biomarker evaluation approaches. Based on mechanistic signaling pathway approaches, various computational models, including biochemical and morphological models, are discussed to explore the strategies that may be used to target AD treatment. Different biomarkers are interpreted on the basis of morphological and functional features of amyloid β plaques and unstable microtubule‑associated tau protein, which is involved in neurodegeneration. Furthermore, imaging and cerebrospinal fluids are also considered to be key methods in the identification of novel markers for AD. In conclusion, the present study reviews various biochemical and morphological computational models and biomarkers to interpret novel targets and agonists for the treatment of AD. This review also highlights several therapeutic targets and their associated signaling pathways in AD, which may have potential to be used in the development of novel pharmacological agents for the treatment of patients with AD. Computational modeling approaches may aid the quest for the development of AD treatments with enhanced therapeutic efficacy and reduced toxicity.

Expression of NMDA receptor subunits in human blood lymphocytes: A peripheral biomarker in online computer game addiction

Background and aims Repeated performance of some behaviors such as playing computer games could result in addiction. The NMDA receptor is critically involved in the development of behavioral and drug addictions. It has been claimed that the expression level of neurotransmitter receptors in the brain may be reflected in peripheral blood lymphocytes (PBLs). Methods Here, using a real-time PCR method, we have investigated the mRNA expression of GluN2A, GluN2D, GluN3A, and GluN3B subunits of the NMDA receptor in PBLs of male online computer game addicts (n = 25) in comparison with normal subjects (n = 26). Results Expression levels of GluN2A, GluN2D, and GluN3B subunits were not statistically different between game addicts and the control group. However, the mRNA expression of the GluN3A subunit was downregulated in PBLs of game addicts. Discussion and conclusions Transcriptional levels of GluN2A and GluN2D subunits in online computer game addicts are similar to our previously reported data of opioid addiction and are not different from the control group. However, unlike our earlier finding of drug addiction, the mRNA expression levels of GluN3A and GluN3B subunits in PBLs of game addicts are reduced and unchanged, respectively, compared with control subjects. It seems that the downregulated state of the GluN3A subunit of NMDA receptor in online computer game addicts is a finding that deserves more studies in the future to see whether it can serve as a peripheral biomarker in addiction studies, where the researcher wants to rule out the confusing effects of abused drugs.

NMDA Receptors in the Central Nervous System

NMDA-type glutamate receptors are ligand-gated ion channels that mediate a major component of excitatory neurotransmission in the central nervous system (CNS). They are widely distributed at all stages of development and are critically involved in normal brain functions, including neuronal development and synaptic plasticity. NMDA receptors are also implicated in the pathophysiology of numerous neurological and psychiatric disorders, such as ischemic stroke, traumatic brain injury, Alzheimer's disease, epilepsy, mood disorders, and schizophrenia. For these reasons, NMDA receptors have been intensively studied in the past several decades to elucidate their physiological roles and to advance them as therapeutic targets. Seven NMDA receptor subunits exist that assemble into a diverse array of tetrameric receptor complexes, which are differently regulated, have distinct regional and developmental expression, and possess a wide range of functional and pharmacological properties. The diversity in subunit composition creates NMDA receptor subtypes with distinct physiological roles across neuronal cell types and brain regions, and enables precise tuning of synaptic transmission. Here, we will review the relationship between NMDA receptor structure and function, the diversity and significance of NMDA receptor subtypes in the CNS, as well as principles and rules by which NMDA receptors operate in the CNS under normal and pathological conditions.

Ionotropic glutamate receptors: Which ones, when, and where in the mammalian neocortex

A multitude of 18 iGluR receptor subunits, many of which are diversified by splicing and RNA editing, localize to >20 excitatory and inhibitory neocortical neuron types defined by physiology, morphology, and transcriptome in addition to various types of glial, endothelial, and blood cells. Here we have compiled the published expression of iGluR subunits in the areas and cell types of developing and adult cortex of rat, mouse, carnivore, bovine, monkey, and human as determined with antibody- and mRNA-based techniques. iGluRs are differentially expressed in the cortical areas and in the species, and all have a unique developmental pattern. Differences are quantitative rather than a mere absence/presence of expression. iGluR are too ubiquitously expressed and of limited use as markers for areas or layers. A focus has been the iGluR profile of cortical interneuron types. For instance, GluK1 and GluN3A are enriched in, but not specific for, interneurons; moreover, the interneurons expressing these subunits belong to different types. Adressing the types is still a major hurdle because type-specific markers are lacking, and the frequently used neuropeptide/CaBP signatures are subject to regulation by age and activity and vary as well between species and areas. RNA-seq reveals almost all subunits in the two morphofunctionally characterized interneuron types of adult cortical layer I, suggesting a fairly broad expression at the RNA level. It remains to be determined whether all proteins are synthesized, to which pre- or postsynaptic subdomains in a given neuron type they localize, and whether all are involved in synaptic transmission. J. Comp. Neurol. 525:976-1033, 2017. © 2016 Wiley Periodicals, Inc.

ER to synapse trafficking of NMDA receptors

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. There are three distinct subtypes of ionotropic glutamate receptors (GluRs) that have been identified including 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptors (AMPARs), N-methyl-D-aspartate receptors (NMDARs) and kainate receptors. The most common GluRs in mature synapses are AMPARs that mediate the fast excitatory neurotransmission and NMDARs that mediate the slow excitatory neurotransmission. There have been large numbers of recent reports studying how a single neuron regulates synaptic numbers and types of AMPARs and NMDARs. Our current research is centered primarily on NMDARs and, therefore, we will focus in this review on recent knowledge of molecular mechanisms occurring (1) early in the biosynthetic pathway of NMDARs, (2) in the transport of NMDARs after their release from the endoplasmic reticulum (ER); and (3) at the plasma membrane including excitatory synapses. Because a growing body of evidence also indicates that abnormalities in NMDAR functioning are associated with a number of human psychiatric and neurological diseases, this review together with other chapters in this issue may help to enhance research and to gain further knowledge of normal synaptic physiology as well as of the etiology of many human brain diseases.

Triheteromeric N-methyl-D-aspartate receptors differentiate synaptic inputs onto pyramidal neurons in somatosensory cortex: involvement of the GluN3A subunit

N-methyl-D-aspartate receptors (NMDARs) are glutamatergic by virtue of glutamate-binding GluN2 subunits and glycinergic by virtue of glycine-binding GluN1 and GluN3 subunits. The existence, location, and functional-significance of NMDARs containing both GluN2 and GluN3 subunits have as yet remained unelucidated. Here we report on the discovery and characterization of a novel type of NMDARs, found at layer (L)1/primary whisker-motor-cortex inputs onto L5 pyramidal neurons in somatosensory cortex, that are distinct in structure and function from conventional GluN2A-containing NMDARs at thalamic/striatal (Str) inputs onto the same neurons. These receptors had a threshold-like activation at hyperpolarized holding-potentials with strong outward rectification of their current-voltage relationships unlike any known GluN1/GluN2-containing NMDARs. Pharmacology revealed a triheteromeric-receptor with features common to glutamate-activated GluN1/GluN2-containing and glycine-activated GluN1/GluN3-containing diheteromeric NMDARs. However, unlike GluN1/GluN3 receptors, NMDARs at L1 inputs were activated by glutamate and blocked by d-AP5, Ca(2+)-permeable, and more efficient at integrating and potentiating EPSPs selectively over Str inputs during high-frequency stimulation while obviating the need for AMPAR-mediated depolarization.

Neurotransmitter receptors and cognitive dysfunction in Alzheimer's disease and Parkinson's disease

Cognitive dysfunction is one of the most typical characteristics in various neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease (advanced stage). Although several mechanisms like neuronal apoptosis and inflammatory responses have been recognized to be involved in the pathogenesis of cognitive dysfunction in these diseases, recent studies on neurodegeneration and cognitive dysfunction have demonstrated a significant impact of receptor modulation on cognitive changes. The pathological alterations in various receptors appear to contribute to cognitive impairment and/or deterioration with correlation to diversified mechanisms. This article recapitulates the present understandings and concepts underlying the modulation of different receptors in human beings and various experimental models of Alzheimer's disease and Parkinson's disease as well as a conceptual update on the underlying mechanisms. Specific roles of serotonin, adrenaline, acetylcholine, dopamine receptors, and N-methyl-D-aspartate receptors in Alzheimer's disease and Parkinson's disease will be interactively discussed. Complex mechanisms involved in their signaling pathways in the cognitive dysfunction associated with the neurodegenerative diseases will also be addressed. Substantial evidence has suggested that those receptors are crucial neuroregulators contributing to cognitive pathology and complicated correlations exist between those receptors and the expression of cognitive capacities. The pathological alterations in the receptors would, therefore, contribute to cognitive impairments and/or deterioration in Alzheimer's disease and Parkinson's disease. Future research may shed light on new clues for the treatment of cognitive dysfunction in neurodegenerative diseases by targeting specific alterations in these receptors and their signal transduction pathways in the frontal-striatal, fronto-striato-thalamic, and mesolimbic circuitries.

GluN3 subunit-containing NMDA receptors: not just one-trick ponies

The two GluN3 subunits were the last NMDA receptor subunits to be cloned some 15 years ago. Strikingly, despite the steadily growing interest in their function, their physiological role remains elusive. The original billing as dominant-negative modulators of classical NMDA receptors composed of GluN1 and GluN2 subunits has given way to proposals of much more complex functions, including roles in synaptogenesis and synaptic plasticity. In addition, GluN3 subunits in the absence of GluN2 surprisingly assemble with GluN1 into excitatory glycine receptors. This review provides an overview of the unique spatial and temporal expression patterns of the GluN3 subunits, discusses proposed functions and physiological roles for receptors comprising these subunits, and briefly summarizes their putative involvement in several neural diseases.

Simvastatin prevents dopaminergic neurodegeneration in experimental parkinsonian models: the association with anti-inflammatory responses

BACKGROUND

In addition to their original applications to lowering cholesterol, statins display multiple neuroprotective effects. N-methyl-D-aspartate (NMDA) receptors interact closely with the dopaminergic system and are strongly implicated in therapeutic paradigms of Parkinson's disease (PD). This study aims to investigate how simvastatin impacts on experimental parkinsonian models via regulating NMDA receptors.

METHODOLOGY/PRINCIPAL FINDINGS

Regional changes in NMDA receptors in the rat brain and anxiolytic-like activity were examined after unilateral medial forebrain bundle lesion by 6-hydroxydopamine via a 3-week administration of simvastatin. NMDA receptor alterations in the post-mortem rat brain were detected by [³H]MK-801(Dizocilpine) binding autoradiography. 6-hydroxydopamine treated PC12 was applied to investigate the neuroprotection of simvastatin, the association with NMDA receptors, and the anti-inflammation. 6-hydroxydopamine induced anxiety and the downregulation of NMDA receptors in the hippocampus, CA1(Cornu Ammonis 1 Area), amygdala and caudate putamen was observed in 6-OHDA(6-hydroxydopamine) lesioned rats whereas simvastatin significantly ameliorated the anxiety-like activity and restored the expression of NMDA receptors in examined brain regions. Significant positive correlations were identified between anxiolytic-like activity and the restoration of expression of NMDA receptors in the hippocampus, amygdala and CA1 following simvastatin administration. Simvastatin exerted neuroprotection in 6-hydroxydopamine-lesioned rat brain and 6-hydroxydopamine treated PC12, partially by regulating NMDA receptors, MMP9 (matrix metalloproteinase-9), and TNF-a (tumour necrosis factor-alpha).

CONCLUSIONS/SIGNIFICANCE

Our results provide strong evidence that NMDA receptor modulation after simvastatin treatment could partially explain its anxiolytic-like activity and anti-inflammatory mechanisms in experimental parkinsonian models. These findings contribute to a better understanding of the critical roles of simvastatin in treating PD via NMDA receptors.

Foxa1 and Foxa2 maintain the metabolic and secretory features of the mature beta-cell

Foxa1 and Foxa2 play both redundant and distinct roles in early pancreas development. We demonstrate here that inducible ablation of both transcription factors in mature mouse beta-cells leads to impaired glucose homeostasis and insulin secretion. The defects in both glucose-stimulated insulin secretion and intracellular calcium oscillation are more pronounced than those in beta-cells lacking only Foxa2. Unexpectedly, in contrast to the severe reduction of beta-cell-enriched factors contributing to metabolic and secretory pathways, expression of a large number of genes that are involved in neural differentiation and function is significantly elevated. We further demonstrate that expression of carbohydrate response element-binding protein (ChREBP or Mlxipl), an important transcriptional regulator of carbohydrate metabolism, is significantly affected in compound Foxa1/a2 mutant beta-cells. ChREBP expression is directly controlled by Foxa1 and Foxa2 in both the fetal endocrine pancreas as well as mature islets. These data demonstrate that Foxa1 and Foxa2 play crucial roles in the development and maintenance of beta-cell-specific secretory and metabolic pathways.

MAP1B binds to the NMDA receptor subunit NR3A and affects NR3A protein concentrations

Incorporation of the N-methyl-d-aspartate receptor (NMDAR) subunit NR3A into functional NMDARs results in reduced channel conductance and Ca(2+) permeability. To further investigate the function of NR3A, we have set out to characterize its intracellular binding partners. Here, we report a novel protein interaction between NR3A and microtubule associated-protein (MAP) 1B, which both are localized to dendritic shafts and filopodia. NR3A protein levels were increased in MAP1B deficient (-/-) mice, with a corresponding decrease in NR1 levels, but the fraction of filopodia immunoreactive for NR3A was equal in cells from -/- and wild type (WT) mice. NR3A has previously been shown to interact with another member of the MAP1 family, MAP1S. We showed that MAP1S binds to microtubules in a similar manner as MAP1B, and suggest that MAP1S and MAP1B both are involved in regulating trafficking of NR3A-containing NMDAR.

Significant association of glutamate receptor, ionotropic N-methyl-D-aspartate 3A (GRIN3A), with nicotine dependence in European- and African-American smokers

The glutamate receptor gene, ionotropic N-methyl-D-aspartate 3A (GRIN3A), is one of the seven that code for subunits of N-methyl-D-aspartate receptors, which play an essential role at many synapses in the brain, regulating ion flow across membranes in response to glutamate signaling. In this study, we analyzed 25 single nucleotide polymorphisms (SNPs) within GRIN3A for association with nicotine dependence (ND), which was assessed by smoking quantity, heaviness of smoking index, and the Fagerström test for ND. Both individual SNP and haplotype association tests were performed in African-American (AA) and European-American (EA) samples as well as in the pooled sample consisting of 2,037 individuals from 602 nuclear families. Individual SNP analysis revealed significant associations of 5, 5, and 4 SNPs with at least one ND measure in the pooled, EA, and AA samples, respectively. Of them, SNPs rs17189632 and rs10121600 in the pooled sample and rs11788456 in the EA sample remained significant after correction for multiple testing. On the basis of the blocks determined with Haploview, we performed haplotype-based association analysis and found 2, 4, and 1 haplotype(s) that are significantly associated with at least one ND measure in the pooled, EA, and AA samples, respectively. Some of them remained significant after correction for multiple testing. We concluded that GRIN3A represents a strong candidate for involvement in the etiology of ND and warrants further investigation in independent samples.

Influence of the NR3A subunit on NMDA receptor functions

Various combinations of subunits assemble to form the NMDA-type glutamate receptor (NMDAR), generating diversity in its functions. Here we review roles of the unique NMDAR subunit, NR3A, which acts in a dominant-negative manner to suppress receptor activity. NR3A-containing NMDARs display striking regional and temporal expression specificity, and, unlike most other NMDAR subtypes, they have a low conductance, are only modestly permeable to Ca(2+), and pass current at hyperpolarized potentials in the presence of magnesium. While glutamate activates triheteromeric NMDARs composed of NR1/NR2/NR3A subunits, glycine is sufficient to activate diheteromeric NR1/NR3A-containing receptors. NR3A dysfunction may contribute to neurological disorders involving NMDARs, and the subunit offers an attractive therapeutic target given its distinct pharmacological and structural properties.

Exomic sequencing of the ionotropic glutamate receptor N-methyl-D-aspartate 3A gene (GRIN3A) reveals no association with schizophrenia

BACKGROUND

Growing evidence suggests that dysregulation of N-methyl-D-aspartate receptor (NMDAR)-mediated glutamate neurotransmission may be involved in the pathophysiology of schizophrenia. The NMDAR is a heteromeric protein complex consisting of subunits from three subfamilies (NR1, NR2A, 2B, 2C, 2D and NR3A, 3B). The unique ability of NR3A to modulate the NMDAR function makes it an attractive candidate gene of schizophrenia. The purpose of this study was to investigate the involvement of the gene encoding the human NR3A subunit (GRIN3A) in the liability to schizophrenia.

METHODS

We searched for genetic variants in the putative core promoter region and all the exons (including UTR ends) of the GRIN3A gene in 333 Han Chinese patients with schizophrenia and 369 control subjects from Taiwan using direct polymerase chain reaction (PCR) autosequencing, and assessed their association with schizophrenia.

RESULTS

We identified 22 single nucleotide polymorphisms (SNPs) in the GRIN3A gene in this sample. SNP- and haplotype-based analyses showed no association of these 22 SNPs with schizophrenia. Nevertheless, we identified two missense mutations (D133N and Q1091H), one nonsense mutation (R1024X), and two synonymous mutations (Y873Y and E889E) of the GRIN3A gene in 6 out of 333 (1.8%) patients, while no rare mutations were found in 369 control subjects (p=0.011, Fisher's exact test, one-tailed). In silico analysis showed that the R1024X and Q1091H mutations are possibly damaging.

CONCLUSIONS

Although the functional significance of these mutations remains to be characterized, our study indicates that rare mutations in the GRIN3A gene may contribute to the pathogenesis of schizophrenia in certain patients.

High dose of simvastatin induces hyperlocomotive and anxiolytic-like activities: The association with the up-regulation of NMDA receptor binding in the rat brain

Statins are widely being used for the treatment of a variety of conditions beyond their original indication for lowering cholesterol. We have previously reported that simvastatin affected the dopaminergic system in the rat brain. This study aims to investigate locomotor and anxiety effects along with the regional changes of N-methyl-d-aspartate (NMDA) receptors in the rat brain after 4-week administration of simvastatin. Hyperlocomotive and anxiolytic-like activities in the rat were observed after chronic administration of high dose simvastatin (10 mg/kg/day). Distributions and alterations of NMDA receptors in the post-mortem rat brain were detected by [(3)H] MK-801 binding autoradiography. Simvastatin increased [(3)H] MK-801 binding, predominantly in the prefrontal cortex (20%, p=0.003), primary motor cortex (20%, p<0.001), cingulate cortex (28%, p<0.001), hippocampus (41%, p<0.001), caudate putamen (30%, p=0.029), nucleus accumbens (27%, p=0.035) and amygdala (45%, p<0.001) compared to controls. Significant positive correlations were identified between hyperlocomotive as well as anxiolytic-like activities and the upregulation of NMDA receptors in different brain regions. Our results also provide strong evidence that chronic high dose simvastatin administration is to exhibit NMDA antagonist-like effects, which would partially explain the anxiolytic and hyperlocomotor activities. These findings contribute to a better understanding of the critical roles of simvastatin in modulating psycho-neurodegenerative disorders, via NMDA receptors.