Regulation of Photoreceptor Neurotransmisssion

视杆细胞和视锥细胞的光反应是通过释放充满谷氨酸的囊泡来编码的。 光感受器突触。视网膜中第一突触的突触传递因此从根本上形成了 蛋白质突变或黄斑等疾病对光感受器突触的视觉感知和损害 退化和缺血会导致视力丧失。为了了解这些突触受损的后果 而如何通过治疗手段恢复视力，需要对其正常操作有透彻的了解。 光感受器的释放涉及一种被称为突触带的板状蛋白质结构。与大多数不同 中枢神经系统(CNS)突触一次只释放一个或两个突触小泡，带状突触 在光感受器和其他感觉神经元中，神经元专门用于持续释放。除了功能区之外 带状突触的专门化能力也是由某些蛋白质的使用决定的，这些蛋白质 不同于那些更传统的突触。杆状感光器和视锥感光器的区别更大。 常规突触和其他带状突触对异常钙的胞吐钙传感器的使用 依赖。在大多数突触中，突触小泡的释放率随[Ca~(2+)]i的5次方而升高，但从 光感受器对钙离子的1-3级依赖性较弱。非典型的钙离子传感器的身份 从光感受器调节囊泡的释放是关于释放机制的一个重大悬而未决的问题 在视网膜的第一个突触。蛋白突触素(SYT)的异构体作为胞外钙离子 大多数神经元中的传感器。我们的第一个目标是鉴定控制光感受器释放的钙离子感受器 测试特定SYT蛋白从视杆细胞或视锥细胞中选择性删除的小鼠。我们的第二个目标是 为了证实小鼠视杆和视锥突触中的胞吐钙感受器保留了异常低的钙离子 在低等脊椎动物中看到的协作性。在目标3中，我们建议描述细胞内钙离子依赖性如何 释放速率由可复制的SYT、络合蛋白和SNARE蛋白的不同组合决定 快速释放机械的组件在不同的常规和带状突触上，使用独特的 可以探测单个融合毛孔的体外方法，时间分辨率低于毫秒。总而言之，这些实验 将揭示危重时神经传递的非典型钙依赖的机制 视觉中的第一个突触，并使我们能够理解特定蛋白质的表达如何塑造 释放的特性，以满足不同中枢神经系统突触的特定信号需求。

Light responses of rod and cone photoreceptors are encoded by the release of glutamate-filled vesicles at photoreceptor synapses. Synaptic transmission at the first synapse in the retina thus fundamentally shapes visual perception and damage to photoreceptor synapses by protein mutation or diseases such as macular degeneration and ischemia causes vision loss. To understand the consequences of damage to these synapses and how to restore vision by therapeutic means requires a thorough understanding of their normal operation. Release from photoreceptors involves a plate-like protein structure known as the synaptic ribbon. Unlike most central nervous system (CNS) synapses that release only one or two synaptic vesicles at a time, ribbon synapses in photoreceptors and other sensory neurons are specialized for continuous release. In addition to the ribbon itself, the specialized capabilities of ribbon synapses are also determined by the use of certain proteins that differ from those at more conventional synapses. Rod and cone photoreceptors differ further from both conventional and other ribbon synapses in their use of an exocytotic Ca2+ sensor with unusual Ca2+ dependence. At most synapses, synaptic vesicle release rate rises with the 5th power of [Ca2+]i but release from photoreceptors has a weaker 1-3rd order Ca2+-dependence. The identity of the atypical Ca2+ sensor that regulates vesicle release from photoreceptors is a major unresolved question about the mechanisms of release at the first synapse in the retina. Isoforms of the protein synaptotagmin (Syt) serve as the exocytotic Ca2+ sensors in most neurons. Our first aim is to identify the Ca2+ sensor controlling release from photoreceptors by testing mice in which specific Syt proteins have been selectively deleted from rods or cones. Our second aim is to confirm that the exocytotic Ca2+ sensors in mouse rod and cone synapses retain the unusually low Ca2+ cooperativity seen in lower vertebrates. In Aim 3, we propose to characterize how the Ca2+-dependence of release rate is shaped by different combinations of Syt, Complexin, and SNARE proteins that reproduce components of the rapid release machinery at different conventional and ribbon synapses, using unique in vitro approaches that can probe single fusion pores with sub-ms time resolution. Together, these experiments will reveal the mechanisms responsible for the atypical Ca2+-dependence of neurotransmission at the critical first synapse in vision and allow us to understand how the expression of particular proteins shapes the properties of release to meet specific signaling needs at different CNS synapses.