NMDA RECEPTOR IN LEAD INDUCED COGNITIVE DEFICIT

铅引起的认知缺陷中的 NMDA 受体

• 批准号: 2608506
• 负责人: Edson X. Albuquerque
• 金额: $ 20.86万
• 依托单位: UNIVERSITY OF MARYLAND BALTIMORE
• 依托单位国家: 美国
• 财政年份: 1992
• 资助国家: 美国
• 起止时间: 1992-06-01 至 1999-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2608506
• 关键词: NMDA receptors; aminoacid inhibitor; cerebrospinal fluid; cognition disorders; excitatory aminoacid; extracellular; hippocampus; inhibitor /antagonist; laboratory rat; lead; lead poisoning; neurotoxicology; nicotinic receptors; receptor expression; synapses

DESCRIPTION: The goal of this project is to understand the mechanisms by which lead (Pb2+) exerts neurotoxic effects in the central nervous system (CNS) particularly in the developing brain. N-methyl-D-aspartate (NMDA) receptor-ion channels (nAChRs) are very sensitive to inhibition by Pb2+. Whereas the inhibitory effect of Pb2+ on NMDA receptors is apparently due to its action on a Ca2+ site on the receptor, the mechanisms by which Pb2+ inhibits the activation of the alpha7-bearing nAChRs is still unknown and will be investigated in this proposal. Because NMDA receptors and alpha7-bearing nAChR are involved in memory and learning as well as in other forms of neuronal plasticity and development, it is very likely that inhibition of these receptors by Pb2+, particularly during early stages of neuronal maturation, could be associated with the severe learning disabilities caused by this heavy metal. Considering that distal dendritic development of the hippocampal neurons is particularly sensitive to the toxic effects of Pb2+, and that dendritic development(with formation and maturation of dendritic spines) is associated with learning and memory, the following question is raised: Is the expression of Pb2+-sensitive NMDA receptors and nAChRs restricted during development to particular neuronal regions, such as apical and basal dendrites, in distinct hippocampal areas (CA1, CA3, or dentate gyrus)? To answer this questions we will use state-of-the-art infrared microscopy (which allows visualization of axons, dendrites, and dendritic spines) combined with a computer-driven, robotic system of micromanipulators (which enables us to control the positions of patch electrodes and drug-delivery systems at precisely defined regions on the neuronal surfaces). Recordings can then be made of whole-cell and single-channel currents from neurons either visualized in or acutely dissociated from hippocampi of rats at different ages, and we will be able to map the distribution of Pb2+-sensitive nicotinic and NMDA receptors on cell bodies, dendrites, and dendritic spines of hippocampal neurons. Our preliminary studies also indicate that Pb2+ substantially increases spontaneous transmitter release from hippocampal neurons. Taking into account that NMDA receptors and alpha-BGT-sensitive nAChRs present on presynaptic terminals of CNS neurons can modulate the release of a number of neurotransmitters, it is critical to determine whether Pb2+ alters transmitter release by acting at these presynaptic receptors. Therefore, the effects of Pb2+ on spontaneous and evoked transmitter release will be investigated at the level of single synapses on hippocampal neurons, which will be acutely dissociated at various stages of development. We have developed a technique by which neurons can be acutely dissociated by mechanical means (without enzyme treatment) from hippocampi of rats at various ages. These neurons bear many synaptic terminals that are functional and can be electrically stimulated. Altogether these studies should provide the foundation for an understanding of the net effects of Pb2+ on receptor function, synaptic activation and maturation in the developing CNS.

描述：这个项目的目标是通过 铅(Pb2+)对中枢神经系统有神经毒性作用 (中枢神经系统)，特别是在发育中的大脑。N-甲基-D-天冬氨酸(NMDA) 受体离子通道(NAChRs)对Pb2+的抑制非常敏感。 而Pb2+对NMDA受体的抑制作用显然是由于 它对受体上钙离子位点的作用，Pb2+的作用机制 抑制携带α7的nAChRs的激活尚不清楚 将在这份提案中进行调查。因为NMDA受体和 携带α7的nAChR参与记忆和学习以及其他 神经可塑性和发育的形式，很可能是 Pb2+对这些受体的抑制作用，特别是在早期阶段 神经元成熟，可能与严重的学习有关 由这种重金属造成的残疾。考虑到远端树突 海马神经元的发育对 Pb2+的毒性效应，以及树突状细胞的发育(形成和 树突棘的成熟)与学习和记忆有关， 提出了以下问题：Pb2+敏感的NMDA的表达 受体和nAChRs在发育过程中受限于特定神经元 在不同的海马区，如顶端和基底部的树突等区域 (CA1、CA3或齿状回)？为了回答这个问题，我们将使用 最先进的红外显微镜(它允许轴突的可视化， 树突和树枝刺)与计算机驱动的机器人 微操作器系统(它使我们能够控制 贴片电极和药物输送系统在精确定义的区域 神经元表面)。然后，录制可以由全蜂窝和 来自神经元的单通道电流，可见或锐利 从不同年龄大鼠的海马区分离出来，我们将能够 对Pb2+敏感的烟碱受体和NMDA受体的定位 海马神经元的胞体、树突和树突。我们的 初步研究还表明，Pb2+显著增加 海马神经元自发释放递质。考虑到 考虑到NMDA受体和α-BGT敏感的nAChRs存在于 中枢神经系统神经元的突触前终末可调节多个神经元的释放 神经递质，关键是要确定Pb2+是否改变 通过作用于这些突触前受体来释放递质。因此， Pb2+对自发和诱发的递质释放的影响将是 在海马神经元单个突触的水平上进行了研究， 会在发育的不同阶段急剧分离。我们有 开发了一种技术，通过这种技术，神经元可以通过 大鼠海马区机械方法(不加酶处理) 不同年龄的人。这些神经元承载着许多突触终末，它们是 功能齐全，可电刺激。总的来说，这些研究 应为理解以下方面的净影响提供基础 铅对大鼠脑内受体功能、突触激活和成熟的影响 发展中枢神经系统。