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，NMDA型谷氨酸受体(NMDAR)的激活是加强和削弱皮质突触连接所必需的。NMDAR功能障碍与多种神经疾病状态有关，如癫痫、精神分裂症、中风和神经病理性疼痛。大多数研究都集中在NMDAR在突触后的作用上。最近发现，视皮层中的神经元也表达可以改变突触前功能的NMDAR(PreNMDARs)。前NMDAR在皮质发育早期表达，并通过棘波时序依赖的长期抑郁等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NMDARs有了这样的了解，但还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，发育中的新皮质中的前NMDAR不需要谷氨酸和去极化的同时结合才能激活。相反，它们在音调上是活跃的，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在新皮质中的表达也急剧下调。我推测，NMDAR亚单位赋予前NMDAR具有紧张性活动的能力，对它们的发育调节是必不可少的。因此，我将确定：1)生命早期允许其紧张性活动的前NMDAR亚基的组成，2)前NMDAR亚基允许紧张性活动的机制，以及3)这些亚基是否对时序依赖性的长期抑郁和前NMDAR调节动作电位驱动的释放是必需的。为了做到这一点，我将在缺乏NMDAR亚基的小鼠身上使用电生理学、电子显微镜和生化分级。这些研究将证明前NMDAR的分子组成和它们发挥作用的机制。因此，这些实验有望为癫痫、中风、神经病理性疼痛和精神分裂症的治疗提供新的分子靶点，并可能阐明当前NMDAR介导的治疗的作用机制。

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.