Subtype-Specific Roles of Presynaptic-Acting NMDA Receptors

描述（由申请人提供）：人们普遍认为，在视觉发育过程中，需要激活NMDA型谷氨酸受体（NMDAR）来加强和减弱皮质突触连接。NMDAR功能障碍与多种神经疾病状态有关，例如癫痫、精神分裂症、中风和神经性疼痛。大多数研究都集中在NMDARs在突触后的作用。最近发现，视觉皮层中的神经元也表达能够改变突触前功能的NMDAR（preNMDAR）。前NMDAR在皮质发育早期表达，并通过诸如尖峰定时依赖性长期抑制的机制调节神经递质的释放。研究还表明，前NMDAR与癫痫等疾病状态有关。尽管对前NMDAR有了这些了解，但尚不清楚是什么允许它们的功能和发育调节。与突触后NMDAR不同，发育中的新皮层中的前NMDAR不需要谷氨酸和去极化的同时结合才能激活。相反，它们具有张力活性，因此能够在没有去极化的情况下增加神经递质的释放。出生后第20天，前NMDAR在新皮层中也急剧下调。我推测，一个NMDAR亚基赋予前NMDAR的能力，是紧张性的活动，是必不可少的发育调节。因此，我将决定：1）生命早期前NMDAR的NMDAR亚基组成，其允许它们的紧张活性，2）前NMDAR亚基允许紧张活性的机制，和3）这些亚基是否是时间依赖性长期抑郁和前NMDAR调节动作电位驱动的释放所需的。为了实现这一点，我将使用电生理学，电子显微镜，和缺乏特定的NMDAR亚基的小鼠的生化分馏。这些研究将证明前NMDAR的分子组成及其功能机制。因此，这些实验有望为治疗癫痫、中风、神经性疼痛和精神分裂症提供新的分子靶点，并可能阐明目前NMDAR介导的治疗作用机制。 公共卫生相关性：NMDA受体（NMDAR）对于学习和记忆至关重要，并且它们的功能障碍导致无数神经系统疾病，包括精神分裂症、癫痫、疼痛和中风。这项建议将扩大这些受体的知识，确定其组成和功能，在以前未研究的细胞室。因此，这些实验可能会揭示神经系统疾病的新治疗靶点，并可能阐明当前NMDAR介导的疗法的作用机制。

DESCRIPTION (provided by applicant): It is widely accepted that activation of NMDA-type glutamate receptors (NMDARs) is required for the strengthening and weakening of cortical synaptic connections during visual development. NMDAR dysfunction has been implicated in a wide variety of neurological disease states such as epilepsy, schizophrenia, stroke, and neuropathic pain. Most research has focused on the role of NMDARs postsynaptically. Recently it has been found that neurons in the visual cortex also express NMDARs that can modify presynaptic functions (preNMDARs). PreNMDARs are expressed early in cortical development and modulate the release of neurotransmitter through mechanisms such as spike-timing dependent long-term depression. Studies have also implicated preNMDARs in disease states such as epilepsy. Despite this knowledge about preNMDARs, it is not clear what allows for their function and developmental regulation. Unlike postsynaptic NMDARs, preNMDARs in the developing neocortex do not require the coincident binding of glutamate and depolarization to be active. Instead, they are tonically active and therefore able to increase the release of neurotransmitter in the absence of depolarization. PreNMDARs are also sharply downregulated in the neocortex following postnatal day 20. I hypothesize that a NMDAR subunit endows preNMDARs with the ability to be tonically active and is essential for their developmental regulation. I will therefore determine: 1) The NMDAR subunit composition of preNMDARs early in life which allows for their tonic activity, 2) The mechanism by which preNMDAR subunits allow for tonic activity, and 3) If these subunits are required for timing-dependent long- term depression and for preNMDARs to modulate action potential-driven release. To accomplish this, I will use electrophysiology, electron microscopy, and biochemical fractionation on mice which lack specific NMDAR subunits. These studies will demonstrate the molecular composition of preNMDARs and the mechanism by which they function. Therefore, these experiments are expected to provide new molecular targets for therapies to treat epilepsy, stroke, neuropathic pain, and schizophrenia and may clarify the mechanism by which current NMDAR-mediated therapies act. PUBLIC HEALTH RELEVANCE: NMDA receptors (NMDARs) are critically important for learning and memory, and their dysfunction contributes to a myriad of neurological disorders, including schizophrenia, epilepsy, pain, and stroke. This proposal will expand the knowledge of these receptors by determining their composition and function in a previously unstudied cellular compartment. Therefore, these experiments may reveal new therapeutic targets for neurological disorders and may clarify the mechanism by which current NMDAR-mediated therapies act.