Elucidation of the role of kainate receptor subtypes in hippocampal synaptic function using novel pharmacological tools

这项研究的主要目标是设计和合成新的化学物质，这些化学物质可用作研究大脑行使多种功能的一些基本机制的工具。具体来说，我们的目标是提供药理学工具来阐明一个神经细胞（神经元）与大脑中其他细胞通信的机制。这种交流在神经元之间的连接点（突触）上进行。我们之前的工作已经帮助建立了神经元链或网络中的一个细胞与下一个细胞通信的主要机制之一是通过从其多个突触末端释放氨基酸谷氨酸。这种氨基酸流过突触间隙到达下一个神经元，并与位于下一个神经元表面的蛋白质（谷氨酸受体）相互作用，产生控制第二个细胞电活动的电化学和/或生物化学变化。我们已经帮助建立了谷氨酸可以与一个结构相关的蛋白质家族相互作用，这些蛋白质被称为谷氨酸受体亚型，每个亚型在中枢神经系统中执行不同的功能。目前的工作旨在合成化学品（药理学工具），阻断谷氨酸在特定谷氨酸受体亚型的作用，这些受体亚型由天然产物红藻氨酸（红藻氨酸受体）激活。红藻氨酸受体是由称为GluR 5、GluR 6、GluR 7、KA 1和KA 2的蛋白质亚基的组合组成的四聚体。而谷氨酸本身可以结合所有这些亚基，导致受体活化，目的是设计和化学合成称为拮抗剂的试剂，可以选择性地阻断GluR 6，GluR 7或KA 1/KA 2亚基的活化。我们已经产生了计算机模型的配体结合核心的GluR 6，GluR 7和KA 1的基础上，我们的X-射线晶体结构的配体结合核心的GluR 5在复杂的选择性GluR 5亚基拮抗剂。我们计划使用这些模型来设计选择性地与配体结合核心中的亚基特异性氨基酸残基相互作用的分子，从而产生选择性GluR 6、GluR 7或KA 1/KA 2拮抗剂。通过观察红藻氨酸受体亚单位的特异性阻断对中枢神经系统功能的影响，可以推断该受体亚单位在中枢神经活动的综合模式中的特定作用。红藻氨酸受体被认为在被称为海马体的大脑部分存储记忆的基本机制中发挥作用，尽管由于缺乏特定的药理学工具，每个亚基在这些过程中的作用仍然存在争议。本项目开发的亚基特异性药理学工具将使我们能够了解GluR 6，GluR 7和KA 1/KA 2在这些机制中的作用。此外，我们计划生产放射性同位素标记的亚单位选择性红藻氨酸受体拮抗剂。这将使我们能够可视化GluR 6，GluR 7或KA 1/KA 2亚基在特定大脑区域（如海马体）中的位置。

The main objective of the proposed research is to design and synthesize new chemical substances that can be used as tools to study some of the fundamental mechanisms by which the brain exercises its multiple functions. Specifically we aim to provide pharmacological tools to elucidate the mechanisms by which one nerve cell (neuron) communicates with others in the brain. This communication is effected at the junctions (synapses) between neurons. Our previous work has helped to establish that one of the main mechanisms by which one cell in a neuronal chain or network communicates with the next cell is by releasing an amino acid, glutamate from its multiple synaptic endings. This amino acid flows across the synaptic gap to the next neuron and there interacts with a protein (glutamate receptor) situated on the surface of the next neuron, to produce electrochemical and/or biochemical changes that control the electrical activity of the second cell. We have helped establish that glutamate can interact with a family of structurally related proteins known as glutamate receptor subtypes each performing different functions in the central nervous system. The present work aims to synthesize chemicals (pharmacological tools) that block the action of glutamate at particular glutamate receptor subtypes that are activated by the natural product kainic acid (kainate receptors). Kainate receptors are tetramers made up of a combination of protein subunits known as GluR5, GluR6, GluR7, KA1 and KA2. Whereas glutamate itself can bind to all of these subunits leading to receptor activation, the aim is to design and chemically synthesise agents known as antagonists that can selectively block the activation of GluR6, GluR7 or KA1/KA2 subunits. We have generated computer models of the ligand binding cores of GluR6, GluR7 and KA1 based on our X-ray crystal structures of the ligand binding core of GluR5 in complex with selective GluR5 subunit antagonists. We plan to use these models to design molecules that interact selectively with subunit specific amino acid residues in the ligand binding core, thereby producing selective GluR6, GluR7 or KA1/KA2 antagonists. By observing what the effect of specific blockade of each of the kainate receptor subunits has on the functioning of the central nervous system, one can deduce the particular roles of that receptor subunit in the integrated pattern of central nervous activity. Kainate receptors are thought to play a role in the fundamental mechanisms by which part of the brain known as the hippocampus stores memories, though the role of each individual subunit in these processes is still controversial due to the lack of specific pharmacological tools. Subunit specific pharmacological tools developed in this project will enable us to understand the role of GluR6, GluR7 and KA1/KA2 in these mechanisms. In addition, we plan to produce radioisotope labelled subunit selective kainate receptor antagonists. This will enable us to visualise the location of the GluR6, GluR7 or KA1/KA2 subunits within particular brain regions such as the hippocampus.