NMDA receptor regulation by Src kinase signalling in excitatory synaptic transmission and plasticity

Regulation of postsynaptic glutamate receptors is one of the main mechanisms for altering synaptic efficacy in the central nervous system. Recent studies have given insight into the upregulation of the NMDA receptor by Src family tyrosine kinases, which bind to scaffolding proteins in the NMDA receptor complex. Src acts as a common step in signalling cascades that link G-protein-coupled receptors with protein kinase C via the intermediary cell-adhesion kinase beta. This signalling to NMDA receptors is required for long-term potentiation in the CA1 region of the hippocampus.     

NMDA受体在痛觉过敏中的作用

N-甲基-D-天冬氨酸受体(NMDA受体)是中枢神经系统中兴奋性递质谷氨酸受体的一种类型,属于离子型受体。它涉及了体内许多复杂的生理和病理过程,包括wind-up、中枢敏化、长时程增强、外周敏化和内脏疼痛、细胞坏死和凋亡,除此以外,还参与了痛觉过敏的产生和维持。对NMDA受体在痛觉过敏中作用的探讨为研发新一代的镇痛药提供了广阔的思路和前景。     

Gain control of N-methyl-D-aspartate receptor activity by receptor-like protein tyrosine phosphatase alpha

Src kinase regulation of N-methyl-D-aspartate (NMDA) subtype glutamate receptors in the central nervous system (CNS) has been found to play an important role in processes related to learning and memory, ethanol sensitivity and epilepsy. However, little is known regarding the mechanisms underlying the regulation of Src family kinase activity in the control of NMDA receptors. Here we report that the distal phosphatase domain (D2) of protein tyrosine phosphatase alpha (PTPalpha) binds to the PDZ2 domain of post-synaptic density 95 (PSD95). Thus, Src kinase, its activator (PTPalpha) and substrate (NMDA receptors) are linked by the same scaffold protein, PSD95. Removal of PTPalpha does not affect the association of Src with NMDA receptors, but turns off the constitutive regulation of NMDA receptors by the kinase. Further more, we found that application of the PTPalpha catalytic domains (D1 + D2) into neurones enhances NMDA receptor-mediated synaptic responses. Conversely, the blockade of endogenous PTPalpha inhibits NMDA receptor activity and the induction of long-term potentiation in hippocampal neurones. Thus, PTPalpha is a novel up-regulator of synaptic strength in the CNS.     

成年小鼠前脑NMDA受体参与神经元的动作电位发放

谷氨酸是中枢神经系统主要的快速兴奋性递质。AMPA受体和海人藻酸受体主要参与突触传递,而NMDA受体主要参与突触可塑性。基因操作的方法增强NMDA受体的功能,可以增强动物在正常生理状态下的学习能力,及在组织损伤情况下的反应敏感性。NMDA受体参与生理功能的主要机制是长时程增强（long—term potentiation,LTP）。我们的研究表明,NMDA受体不仅参与刺激前扣带皮层的第五层细胞或刺激白质诱导的突触反应,而且参与在胞体施加去极化跃阶电流诱导的动作电位的发放。钙一钙调蛋白敏感的腺苷酸环化酶1（adenylyl cyclase 1,AC1）和cAMP信号通路可能介导了这些反应。由于扣带皮层神经元在伤害性刺激和痛中发挥重要作用,我们的结果为前脑NMDA受体参与突触传递和动作电位发放,以及与前脑相关的行为,如感受伤害性刺激和痛,提供了一个新的机制。     

The regulation of N-methyl-D-aspartate receptors by Src kinase

Src family kinases (SFKs) play critical roles in the regulation of many cellular functions by growth factors, G-protein-coupled receptors and ligand-gated ion channels. Recent data have shown that SFKs serve as a convergent point of multiple signaling pathways regulating N-methyl-d-aspartate (NMDA) receptors in the central nervous system. Multiple SFK molecules, such as Src and Fyn, closely associate with their substrate, NMDA receptors, via indirect and direct binding mechanisms. The NMDA receptor is associated with an SFK signaling complex consisting of SFKs; the SFK-activating phosphatase, protein tyrosine phosphatase α; and the SFK-inactivating kinase, C-terminal Src kinase. Early studies have demonstrated that intramolecular interactions with the SH2 or SH3 domain lock SFKs in a closed conformation. Disruption of the interdomain interactions can induce the activation of SFKs with multiple signaling pathways involved in regulation of this process. The enzyme activity of SFKs appears 'graded', exhibiting different levels coinciding with activation states. It has also been proposed that the SH2 and SH3 domains may stimulate catalytic activity of protein tyrosine kinases, such as Abl. Recently, it has been found that the enzyme activity of neuronal Src protein is associated with its stability, and that the SH2 and SH3 domain interactions may act not only to constrain the activation of neuronal Src, but also to regulate the enzyme activity of active neuronal Src. Collectively, these findings demonstrate novel mechanisms underlying the regulation of SFKs.     

Assembly and forward trafficking of NMDA receptors (Review)

N-Methyl-D-aspartate (NMDA) receptors are a subclass of the excitatory, ionotropic L-glutamate neurotransmitter receptors. They are important for normal brain function being both primary candidates for the molecular basis of learning and memory and in the establishment of synaptic connections during the development of the central nervous system. NMDA receptors are also implicated in neurological and psychiatric disorders. Their dysfunction which is primarily due to either hypo- or hyper-activity is pivotal to these pathological conditions. There is thus a fine balance between NMDA receptor-mediated mechanisms in normal brain and those in diseased states where receptor homeostasis is perturbed. Receptor activity is due in part to the number of surface expressed receptors. Understanding the assembly and trafficking of this complex, heteromeric, neurotransmitter receptor family may therefore, be pivotal to understanding diseases in which their altered activity is evident. This article will review the current understanding of the mechanisms of NMDA receptor assembly, how this assembly is regulated and how assembled receptors are trafficked to their appropriate sites in post-synaptic membranes where they are integral components of a macromolecular signalling complex.     

Assembly and forward trafficking of NMDA receptors (Review)

N-Methyl-D-aspartate (NMDA) receptors are a subclass of the excitatory, ionotropic L-glutamate neurotransmitter receptors. They are important for normal brain function being both primary candidates for the molecular basis of learning and memory and in the establishment of synaptic connections during the development of the central nervous system. NMDA receptors are also implicated in neurological and psychiatric disorders. Their dysfunction which is primarily due to either hypo- or hyper-activity is pivotal to these pathological conditions. There is thus a fine balance between NMDA receptor-mediated mechanisms in normal brain and those in diseased states where receptor homeostasis is perturbed. Receptor activity is due in part to the number of surface expressed receptors. Understanding the assembly and trafficking of this complex, heteromeric, neurotransmitter receptor family may therefore, be pivotal to understanding diseases in which their altered activity is evident. This article will review the current understanding of the mechanisms of NMDA receptor assembly, how this assembly is regulated and how assembled receptors are trafficked to their appropriate sites in post-synaptic membranes where they are integral components of a macromolecular signalling complex.     

NMDA受体参与小鼠的前额扣带回的神经突触传递

谷氨酸性突触是哺乳动物神经系统的主要兴奋性突触。在正常条件下,大多数的突触反应是由谷氨酸的AMPA受体传递的。NMDA受体在静息电位下为镁离子抑制。在被激活时,NMDA受体主要参与突触的可塑性变化。但是,许多NMDA受体拮抗剂在全身或局部注射时能产生行为效应,提示NMDA受体可能参与静息状态的生理功能。此文中,我们在离体的前额扣带回脑片上进行电生理记录,发现NMDA受体参与前额扣带回的突触传递。在重复刺激或近于生理性温度时,NMDA受体传递的反应更为明显。本文直接显示了NMDA受体参与前额扣带回的突触传递,并提示NMDA受体在前额扣带回中起着调节神经元兴奋的重要作用。     

Neurosteroid modulation of N-methyl-D-aspartate receptors: molecular mechanism and behavioral effects

Glutamate is the main neurotransmitter released at synapses in the central nervous system of vertebrates. Its excitatory role is mediated through activation of specific glutamatergic ionotropic receptors, among which the N-methyl-d-aspartate (NMDA) receptor subtype has attracted considerable attention in recent years. Substantial progress has been made in elucidating the roles these receptors play under physiological and pathological conditions and in our understanding of the functional, structural, and pharmacological properties of NMDA receptors. Many pharmacological compounds have been identified that affect the activity of NMDA receptors, including neurosteroids. This review summarizes our knowledge about molecular mechanisms underlying the neurosteroid action at NMDA receptors as well as about the action of neurosteroids in animal models of human diseases.     

NMDA receptors are movin' in

Dynamic modulation of the number of postsynaptic glutamate receptors is considered one of the main mechanisms for altering the strength of excitatory synapses in the central nervous system (CNS). However, until recently N-methyl-d-aspartate (NMDA) receptors were considered relatively stable once in the plasma membrane, especially in comparison with alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors that are internalized at a high rate. A series of recent studies has changed this viewpoint by revealing that NMDA receptors are subject to constitutive as well as agonist-induced internalization through clathrin-mediated endocytosis. Surprisingly, agonist-induced internalization is not dependent on current flow through the NMDA channel, and the receptors are primed for this type of internalization by selective stimulation of the glycine site but not of the glutamate site. Endocytosis of NMDA receptors provides a fundamental mechanism for dynamic regulation of the number of NMDA receptors at synapses, which might be important for physiological and pathological functioning of the CNS.     

Identification and characterization of two G protein-coupled receptors for neuropeptide FF

The central nervous system octapeptide, neuropeptide FF (NPFF), is believed to play a role in pain modulation and opiate tolerance. Two G protein-coupled receptors, NPFF1 and NPFF2, were isolated from human and rat central nervous system tissues. NPFF specifically bound to NPFF1 (K(d) = 1.13 nm) and NPFF2 (K(d) = 0.37 nm), and both receptors were activated by NPFF in a variety of heterologous expression systems. The localization of mRNA and binding sites of these receptors in the dorsal horn of the spinal cord, the lateral hypothalamus, the spinal trigeminal nuclei, and the thalamic nuclei supports a role for NPFF in pain modulation. Among the receptors with the highest amino acid sequence homology to NPFF1 and NPFF2 are members of the orexin, NPY, and cholecystokinin families, which have been implicated in feeding. These similarities together with the finding that BIBP3226, an anorexigenic Y1 receptor ligand, also binds to NPFF1 suggest a potential role for NPFF1 in feeding. The identification of NPFF1 and NPFF2 will help delineate their roles in these and other physiological functions.     

NMDA受体的结构及其生理作用

N-甲基-D-天冬氨酸（NMDA）受体是离子型兴奋性谷氨酸受体的一种亚型,生物体内已发现了3种NMDA受体亚基,且通过选择性剪接至少存在7种亚型,形成具有功能的多结合位点的大分子复合物。NMDA受体在中枢神经系统的突触传递、突触可塑性、学习记忆等生理过程中发挥着重要作用,且NMDA受体的异常会导致-些精神疾病及认知功能的障碍。     

Both NMDA and non-NMDA subtypes of glutamate receptors are concentrated at synapses on cerebral cortical neurons in culture.

N-methyl-D-aspartate (NMDA) and non-NMDA receptors play a key role in synaptic transmission and plasticity in the vertebrate central nervous system. Previous studies have suggested that although both receptor types are present at synapses, the NMDA receptors may be relatively uniformly distributed. We have combined iontophoretic mapping of NMDA and non-NMDA receptors with immunohistochemical localization of synaptic vesicles along dendrites of single neocortical neurons to determine the relationship between NMDA and non-NMDA receptor distribution and the location of synapses. We find that when corrections for glutamate diffusion are made, NMDA responses are concentrated at focal "hot spots" that coincide with non-NMDA hot spots and that there is an excellent correlation between these hot spots and synapses.     

Interactions between glycine transporter type 1 (GlyT-1) and some inhibitor molecules - glycine transporter type 1 and its inhibitors (review)

Glycine is a mandatory positive allosteric modulator of N-methyl-D-aspartate (NMDA)-type ionotropic glutamate receptors in the central nervous system. Elevation of glycine concentrations by inhibition of its reuptake in the vicinity of NMDA receptors may positively influence receptor functions as glycine B binding site on NR1 receptor subunit is not saturated in physiological conditions. Synaptic and extrasynaptic concentrations of glycine are regulated by its type-1 glycine transporter, which is primarily expressed in astroglial and glutamatergic cell membranes. Alteration of synaptic glycine levels may have importance in the treatment of various forms of endogenous psychosis characterized by hypofunctional NMDA receptors. Several lines of evidence indicate that impaired NMDA receptor-mediated glutamatergic neurotransmission is involved in development of the negative (and partly the positive) symptoms and the cognitive deficit in schizophrenia. Inhibitors of glycine transporter type-1 may represent a newly developed therapeutic intervention in treatment of this mental illness. We have synthesized a novel series of N-substituted sarcosines, analogues of the glycine transporter-1 inhibitor NFPS (N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)-propyl]sarcosine). Of the pyridazinone-containing compounds, SzV-1997 was found to be a potent glycine transporter-1 inhibitor in rat brain synaptosomes and it markedly increased extracellular glycine concentrations in conscious rat striatum. SzV-1997 did not exhibit toxic symptoms such as hyperlocomotion, restless movements, respiratory depression, and lethality, characteristic for NFPS. Besides pyridazinone-based, sarcosine-containing glycine transporter-1 inhibitors, a series of substrate-type amino acid inhibitors was investigated in order to obtain better insight into the ligand-binding characteristics of the substrate binding cavity of the transporter.     

The role of intracellular sodium in the regulation of NMDA-receptor-mediated channel activity and toxicity

Sodium (Na⁺) is the major cation in extracellular space and, with its entry into cells, may act as a critical intracellular second messenger that regulates many cellular functions. Through our investigations of mechanisms underlying the activity-dependent regulation of N-methyl-d-aspartate (NMDA) receptors, we recently characterized intracellular Na⁺ as a possible signaling factor common to processes underlying the upregulation of NMDA receptors by non-NMDA glutamate channels, voltage-gated Na⁺ channels, and remote NMDA receptors. Furthermore, although Ca²⁺ influx during the activation of NMDA receptors acts as a negative feedback mechanism that downregulates NMDA receptor activity, Na⁺ influx provides an essential positive feedback mechanism to overcome Ca²⁺-induced inhibition, thereby potentiating both NMDA receptor activity and inward Ca²⁺ flow. NMDA receptors may be recruited to cause excitoxicity through a Na⁺-dependent mechanism. Therefore, the further characterization of mechanisms underlying the regulation of NMDA receptors by intracellular Na⁺ is essential to understanding activity-dependent neuroplasticity in the nervous system.     

The Regulation of GluN2A by Endogenous and Exogenous Regulators in the Central Nervous System

The NMDA receptor is the most widely studied ionotropic glutamate receptor, and it is central to many physiological and pathophysiological processes in the central nervous system. GluN2A is one of the two main types of GluN2 NMDA receptor subunits in the forebrain. The proper activity of GluN2A is important to brain function, as the abnormal regulation of GluN2A may induce some neuropsychiatric disorders. This review will examine the regulation of GluN2A by endogenous and exogenous regulators in the central nervous system.     

Glutamatergic mechanisms in different disease states: overview and therapeutical implications -- an introduction

Summary.  Glutamate is the most widely distributed excitatory transmitter in the central nervous system (CNS). It is acting via large – and still growing – families of receptors: NMDA-, AMPA-, kainate-, and metabotropic receptors. Glutamate has been implicated in a large number of CNS disorders, and it is hoped that novel glutamate receptor ligands offer new therapeutic possibilites in disease states such as chronic pain, stroke, epilepsy, depression, drug addiction and dependence or Parkinson's disease. While an extensive preclinical literature exists showing potential beneficial effects of NMDA-, AMPA-, kainate- and metabotropic receptor ligands, only NMDA receptor antagonists have been characterized clinically to any appreciable degree. In these trials it has been shown that while several compounds are therapeutically active, they also produce serious side effects at therapeutic doses. Current interest largely centers on the development of receptor subtype-selective compounds, namely compounds selective for receptors containing the NR2B subunit. Preclinical findings and the first clinical results are encouraging, and it may be that such subunit-selective compounds may have a sufficiently wide therapeutic window to be safe for human use. Received July 6, 2001 Accepted August 6, 2001 Published online August 9, 2002     

Glutamate receptors and pain

Pain is an important survival and protection mechanism for animals. However, chronic/persistent pain may be differentiated from normal physiological pain in that it confers no obvious advantage. An accumulating body of pharmacological, electrophysiological, and behavioral evidence is emerging in support of the notion that glutamate receptors play a crucial role in pain pathways and that modulation of glutamate receptors may have potential for therapeutic utility in several categories of persistent pain, including neuropathic pain resulting from injury and/or disease of central (e.g., spinal cord injury) or peripheral nerves (e.g., diabetic neuropathy, radiculopathy) and inflammatory or joint-related pain (e.g., rheumatoid arthritis, osteoarthritis). This review focuses on the role of glutamate receptors, including both ionotropic (AMPA, NMDA and kainate) and metabotropic (mGlu1-8) receptors in persistent pain states with particular emphasis on their expression patterns in nociceptive pathways and their potential as targets for pharmacological intervention strategies.     

谷氨酸性突触在痛觉和记忆中的突触和分子机制

谷氨酸是哺乳动物脑中的兴奋性递质。中枢神经系统的谷氨酸性突触广泛参与痛觉传递,突触可塑性和递质的调节。谷氨酸的NMDA受体参与前脑相关的学习及功能。在这篇综述中,我们提出前脑的NMDA受体通过增强谷氨酸性突触传递导致长期性的炎痛。具有增强NMDA受体功能的小鼠会产生更多的慢性痛。NMDA NR2B受体抑制剂在未来可能被用来控制人类的慢性痛。     

NMDA受体在焦虑症发病机制的研究进展

伴随社会生活和工作压力的增大,常见精神类疾病焦虑症的发病率逐年攀升。焦虑症的发病机制非常复杂,迄今尚未完全阐明。本文概述了焦虑症发病机制与NMDA受体不同亚型的关系。NMDA受体主要广泛分布于脑、脊髓和周围神经系统。NR1广泛分布于中枢神经,在NR2D亚基敲除小鼠中,NR1和NR2D的相互影响可能参与了焦虑样行为。NR2A与NR2B是NMDA受体的两个重要亚基,NR2B的高选择性拮抗剂艾芬地尔在小鼠的高架十字迷宫实验中发挥了抗焦虑功效。将小鼠全脑的NR2C基因用NR2B替代之后,1月龄变异小鼠的高架十字迷宫实验显示有明显的非条件性焦虑行为,表明NR2B和NR2C均可能参与焦虑的发生。因此,深入阐明调控NMDA受体亚基组成的确切作用机制,将有助于探索焦虑症潜在治疗靶点的发现,并针对性地开展新药的研发。