NMDA RECEPTOR IN LEAD INDUCED COGNITIVE DEFICIT

描述：本项目的目标是通过以下方式了解这些机制： 铅（Pb 2+）在中枢神经系统中发挥神经毒性作用 (CNS)特别是在发育中的大脑中。 N-甲基-D-天冬氨酸（NMDA） 受体离子通道（nAChR）对Pb 2+的抑制非常敏感。 而Pb ~（2+）对NMDA受体的抑制作用则是由于 它对受体上的Ca 2+位点的作用，Pb 2 + 抑制携带α 7的nAChR的激活仍然是未知的， 将在本提案中进行调查。 因为NMDA受体和 携带α 7的nAChR参与记忆和学习以及其他神经元的功能。 神经可塑性和发育的形式，很可能， Pb 2+对这些受体的抑制作用，特别是在 神经元成熟，可能与严重的学习 这种重金属造成的残疾。 考虑到远端树突状细胞 海马神经元的发育对 Pb 2+的毒性作用，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， 这就提出了一个问题：铅敏感的NMDA是否 受体和nAChR在发育过程中限制在特定的神经元 不同海马区的顶树突和基底树突 (CA1、CA 3或齿状回）？ 为了回答这些问题，我们将使用 最先进的红外显微镜（其允许轴突的可视化， 树突和树突棘）与计算机驱动的机器人 显微操作系统（使我们能够控制 贴片电极和药物输送系统， 神经元表面）。 然后记录可以由全细胞制成， 来自神经元的单通道电流，无论是在视觉上还是在急性 从不同年龄的大鼠的大脑中分离出来，我们将能够 绘制Pb 2+敏感的烟碱和NMDA受体在 海马神经元的胞体、树突和树突棘。 我们 初步研究还表明， 海马神经元自发释放递质。 考虑 考虑到NMDA受体和α-BGT敏感的nAChR存在于 CNS神经元的突触前末梢可以调节许多 神经递质，这是至关重要的，以确定是否Pb 2+改变 通过作用于这些突触前受体释放递质。 因此，我们认为， Pb 2+对自发和诱发递质释放的影响将 在海马神经元的单个突触水平上进行研究， 在不同的发育阶段会严重分离 我们有 开发了一种技术，通过这种技术， 机械方法（无酶处理）， 不同年龄 这些神经元具有许多突触末端， 功能性的并且可以被电刺激。 所有这些研究 应该为理解以下因素的净影响提供基础： Pb 2+对神经元受体功能、突触激活和成熟的影响 发展CNS。

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.