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，皮质突触连接的增强和减弱需要nmda型谷氨酸受体（NMDARs）的激活。NMDAR功能障碍涉及多种神经系统疾病状态，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突触后NMDARs的作用上。近年来研究发现，视觉皮层神经元也表达可修饰突触前功能的NMDARs （preNMDARs）。PreNMDARs在皮层发育早期表达，并通过spike-timing依赖性长期抑郁等机制调节神经递质释放。研究还表明，preNMDARs与癫痫等疾病状态有关。尽管对preNMDARs有了这些了解，但尚不清楚是什么导致了它们的功能和发育调节。与突触后NMDARs不同，发育中的新皮层中的preNMDARs不需要同时结合谷氨酸和去极化才能激活。相反，它们具有紧张性活性，因此能够在没有去极化的情况下增加神经递质的释放。在出生后第20天，新皮层中的PreNMDARs也急剧下调。我假设NMDAR亚基赋予prenmdar具有张力活性的能力，并且对其发育调节至关重要。因此，我将确定：1)在生命早期，preNMDARs的NMDAR亚基组成允许它们的强亢活动，2)preNMDAR亚基允许强亢活动的机制，以及3)这些亚基是否需要时间依赖性的长期抑郁和preNMDARs调节动作电位驱动的释放。为了做到这一点，我将使用电生理学、电子显微镜和生化分离对缺乏特异性NMDAR亚基的小鼠。这些研究将证明preNMDARs的分子组成及其起作用的机制。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.