Presynaptic NMDA receptors in the CNS

CNS 中的突触前 NMDA 受体

• 批准号: 7697612
• 负责人: CRAIG E JAHR
• 金额: $ 33.39万
• 依托单位: OREGON HEALTH & SCIENCE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-16 至 2011-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7697612
• 关键词: Accounting; Action Potentials; Address; Affect; Agonist; Axon; Calcium; Calcium Channel; Cessation of life; Diffuse; Distal; Electrophysiology (science); Elements; Event; Excitatory Synapse; Glutamates; Image; Ion Channel; Ischemia; Learning; Location; Measures; Mediating; Memory; Microscopy; N-Methyl-D-Aspartate Receptors; N-Methylaspartate; Neocortex; Neuraxis; Neurons; Pathway interactions; Permeability; Physiological; Play; Postsynaptic Membrane; Potassium Channel; Probability; Process; Property; Purkinje Cells; Pyramidal Cells; Receptor Activation; Regulation; Relative (related person); Reporting; Role; Secondary to; Side; Signal Transduction; Site; Sodium Channel; Spinal Cord; Synapses; Synaptic Transmission; Synaptic plasticity; Testing; Time; Varicosity; Work; cell type; density; millisecond; neocortical; nervous system disorder; neurotransmitter release; postsynaptic; presynaptic; receptor; response; stellate cell; two-photon; voltage

NMDA receptors (NMDARs) are one of two major types of ion channels located in the postsynaptic membrane at the vast majority of excitatory synapses in the CNS. They not only mediate excitation but, because of their permeability to calcium, raise intracellular calcium concentrations and thus trigger a variety of intracellular pathways leading to short and long term changes in synaptic strength. They also contribute to neuronal death in pathological conditions. Recent studies suggest that NMDARs are located not only at postsynaptic sites but also at presynaptic release sites and can modify the likelihood of vesicular release. As these receptors are important in both physiological and pathological conditions, determining where they are located will help define their effects. We will test whether NMDARs are expressed presynaptically with a combination of calcium imaging using two photon microscopy and electrophysiology to measure pre- and postsynaptic responses to global and local applications of NMDAR agonists and antagonists. We have chosen two types of neurons for this study: cerebellar stellate cells and neocortical layer 5 pyramidal cells. It is clear that NMDAR activation alters transmitter release from these two cell types but it is unclear if the same mechanisms are involved. Whether these receptors alter release by directly increasing intracellular calcium at release sites or rather by depolarizing release sites is not clear. If the former is true, NMDARs would have to be located very close to sites of release because calcium does not diffuse far intracellularly. If the regulation of release by NMDARs is secondary to their depolarizing influence, however, they need not be located near release sites because depolarizations can spread electrotonically for hundreds of micrometers. These two mechanisms are not mutually exclusive and could be mutually reinforcing. NMDAR-mediated depolarization by itself may have multiple effects on vesicular release by 1) directly activating voltage-sensitive calcium channels (VSCCs) and thereby increasing release by elevating baseline calcium concentrations, 2) inactivating axonal Kv1-type potassium channels leading to a broadening of action potentials, enhanced activation of VSCCs and thus greater release, 3) a calcium-independent, though uncharacterized, regulation of the release process and 4) inactivation of voltage-dependent sodium channels and/or VSCCs and therefore a blockade of action potential propagation to release zones and decreased calcium influx leading to decreased neurotransmitter release. We will determine whether NMDARs are located at presynaptic release zones and whether somatic depolarizations alter release by one or a combination of these mechanisms.

NMDA受体（NMDAR）是位于中枢神经系统中绝大多数兴奋性突触的两种主要类型的离子通道之一。它们不仅介导了激发，而且由于它们对钙的渗透性，还会提高细胞内钙浓度，从而触发各种细胞内途径，从而导致突触强度的短期和长期变化。它们还导致病理状况下的神经元死亡。最近的研究表明，NMDAR不仅位于突触后部位，而且位于突触前释放部位，并且可以改变囊泡释放的可能性。由于这些受体在生理和病理条件下都很重要，因此确定它们所在的位置将有助于定义其影响。我们将使用两种光子显微镜和电生理学的钙成像结合结合钙成像，以测量NMDAR对NMDAR激动剂和拮抗剂的全球和局部应用的结合。我们为这项研究选择了两种类型的神经元：小脑星状细胞和新皮层5锥体细胞。显然，NMDAR激活改变了从这两种细胞类型中释放发射机，但尚不清楚是否涉及相同的机制。这些受体是通过直接增加释放位点上的细胞内钙还是通过去极化释放位点来改变释放。如果前者是正确的，则NMDAR必须非常靠近释放部位，因为钙不会细胞内扩散。但是，如果NMDARS释放的释放是其去极化影响的继发的，那么它们不必位于释放位置附近，因为去极化可能会以数百微米的电量传播。这两种机制不是相互排斥的，并且可以互相加强。 NMDAR介导的去极化本身可能对囊泡释放产生多种影响。未表征，对释放过程的调节以及4）电压依赖性钠通道和/或VSCC的灭活，因此会阻断动作电位传播以释放区域并减少钙涌入，从而导致神经递质释放减少。我们将确定NMDAR是否位于突触前释放区域，以及体细胞去极化是否会通过一种或结合这些机制改变释放。