Identifying the role of NMDA receptors in STP through investigation of synaptic plasticity and discovery of novel subtype-specific antagonists

这项拟议研究的目的是制造新的化学物质，可以作为研究中枢神经系统（CNS）行使其多种功能的机制的工具。神经细胞之间的交流发生在被称为突触的特殊区域。“信息”通过释放一种叫做神经递质的化学物质在突触之间传递。突触前细胞中的神经冲动通过释放神经递质“通过”突触传递，神经递质与位于受体（或突触后细胞）表面的特殊蛋白质（称为受体）结合，当神经递质激活时产生小的电脉冲。其中一种神经递质是谷氨酸，它存在于整个中枢神经系统的突触中。我们之前的研究帮助建立了谷氨酸可以与谷氨酸受体在中枢神经系统中执行不同功能的结构相关亚型家族相互作用。目前的工作旨在设计和制造新的化学物质（药理学工具）来调节谷氨酸在特定谷氨酸受体亚型上的作用。谷氨酸受体的一种特殊亚型，n -甲基- d -天冬氨酸受体（简称NMDAR），以选择性激活它的化学物质命名，是一种由两种称为GluN1和GluN2的蛋白质亚基组成的四聚体。在中枢神经系统的大部分区域，NMDARs由两个GluN1和两个GluN2亚基组成。已知四种GluN2亚基GluN2A-D，它们可以与GluN1结合形成不同亚基组成的四聚体，在大脑中差异表达。神经细胞间突触连接的强度是可以调节的，这一过程被称为突触可塑性。突触的可塑性已经在实验中被证明存在于大脑的许多区域，包括海马体，这是大脑中已知对学习和记忆很重要的一部分。可塑性的两种主要形式是长期增强（LTP）和长期抑制（LTD），前者促进连接，从而增强神经元之间的交流，后者减少神经元之间的连接和交流。已知NMDARs参与海马LTP和LTD的机制。我们最近发现，不同的NMDAR亚型参与不同形式的突触可塑性，这可能强调特定形式的学习和记忆。不太清楚的是单个NMDAR亚型的确切作用，部分原因是缺乏能够区分具有不同GluN2亚基组成的NMDAR的特定药理学工具。我们已经开发了一系列新的抑制剂，可以通过结合与谷氨酸相同的位点（竞争性抑制剂）或结合在远离谷氨酸结合位点的受体上的一个或多个位点（变构抑制剂）来调节NMDAR的功能。我们开发的抑制剂具有不同的GluN2亚基选择性模式，并且是开发具有改进GluN2亚基选择性的新化合物的先导。我们计划开发和使用具有所需GluN2亚基选择性的NMDAR抑制剂，以研究特定NMDAR亚型在海马LTP和LTD中的具体作用。这项工作的主要重点将是研究LTP的一种早期形式，即短期增强（STP），我们假设它对短期记忆很重要。我们将与韩国的一个实验室合作，通过行为实验来验证这一假设。

The purpose of the proposed research is to make new chemicals that can be used as tools to study the mechanisms by which the central nervous system (CNS) exercises its multiple functions. Communication between nerve cells occurs at specialised zones called synapses. 'Messages' are sent across the synapse by the release of a chemical called a neurotransmitter. Nerve impulses in the pre-synaptic cell are conveyed 'through' the synapse by the release of neurotransmitter which binds to specialized proteins (called receptors) situated on the surface of the recipient (or postsynaptic cell) which generate small electrical impulses when activated by neurotransmitter. One such neurotransmitter is glutamate, which is present at synapses throughout the CNS. Our previous research helped establish that glutamate can interact with a family of structurally related glutamate receptor subtypes each performing different functions in the CNS. The present work aims to design and make novel chemicals (pharmacological tools) that modulate the action of glutamate at particular glutamate receptor subtypes. One particular subtype of glutamate receptor, the N-methyl-D-aspartate receptor (or NMDAR for short), named after the chemical that selectively activates it, is a tetramer made up of two types of protein subunit known as GluN1 and GluN2. In most areas of the CNS NMDARs are comprised of two GluN1 and two GluN2 subunits. Four GluN2 subunits are known, GluN2A-D, and they can be combined with GluN1 to form tetramers of different subunit composition, which are differentially expressed in the brain. It is now well established that the strength of synaptic connections between nerve cells can be regulated (a process known as synaptic plasticity). Synaptic plasticity has been demonstrated experimentally in many areas of the brain including the hippocampus, a part of the brain known to be important in learning and memory. Two major forms of plasticity are long-term potentiation (LTP), which facilitates connections, thereby enhancing communication between neurons and long-term depression (LTD), which decreases neuronal connections and communication between neurons. NMDARs are known to be involved in the mechanisms of LTP and LTD in the hippocampus. We have recently identified that different NMDAR subtypes are differentially involved in various forms of synaptic plasticity that may underline specific forms of learning and memory. What is less clear is the precise role of individual NMDAR subtypes, due in part to the lack of specific pharmacological tools that can discriminate between NMDARs with different GluN2 subunit composition. We have developed a series of novel inhibitors that can modulate NMDAR function either by binding to the same site as glutamate (competitive inhibitors) or binding to a site(s) on the receptor away from the glutamate binding site (allosteric inhibitors). The inhibitors that we have developed have various patterns of GluN2 subunit selectivity and are leads for the development of newer compounds with improved GluN2 subunit selectivity. We plan to develop and use NMDAR inhibitors with the desired GluN2 subunit selectivity to investigate the specific roles of particular NMDAR subtypes in LTP and LTD in the hippocampus. The major focus of this work will be to investigate an early form of LTP known as short-term potentiation (STP) which we hypothesise is important for short-term memory. We will test this hypothesis with behavioural experiments in collaboration with a laboratory in Korea.