Structure and Function of Mammalian Ganglion Cells

描述(申请人提供)：固有的光敏性视网膜神经节细胞(IpRGCs)表达光色素黑素。它们曾经被认为是一种单细胞类型，将光强度(辐照度)信息传递到用于昼夜节律、瞳孔和神经内分泌调节的非成像(NIF)中心。然而，ipRGC已被证明是多样化的，有一些亚型对皮质视觉机制起作用。了解这种与视觉行为和感知相关的多样性是该项目的主要长期目标。我们的第一个目标是开发两种新的ipRGC类型，M5和M6细胞的详细结构和功能描述。两者都有较小的视野和不同寻常的功能特性，可能有助于皮质视觉。M5细胞可能是光谱对立的，而M6细胞表现出可变的 以及令人惊讶的特征，如瞬时反应或对比抑制反应。实现这一目标将在很大程度上完成ipRGC类型的清单，并推进对小鼠神经节细胞类型的全面计算，目前该模型是视网膜研究的首选模型。尽管ipRGC多种多样，但它们中的大多数都有一个显著的特性--报告环境光线水平的能力。这适合许多NIF反射对编码全局光强度的信号的要求，而不是对空间对比度、颜色或运动的要求。我们的第二个目标是揭示这种辐照度编码能力的机制基础。是什么细胞、回路和突触机制允许ipRGC编码辐射，而传统的神经节细胞不能？我们将关注连接视杆和视锥感光细胞与ipRGC的双极细胞，询问这些细胞如何将原始辐射信息传递给ipRGC，而供给传统RGC的双极细胞过滤掉这些信息，主要编码强度的变化(时空亮度对比度)。IpRGCs的树突在内丛状层的两个特定的亚层中分离，仅构成ON亚层的一部分。这意味着它们从专门用于辐照度编码的ON双极单元的子集接收输入。抑制回路的差异似乎也可能起到一定作用。我们建议确定哪些ipRGC类型实际上编码辐射，追踪通过特定突触前双极类型和突触传递辐射信息的过程，并将这些与驱动RGC的双极电路进行对比，而不能报告辐射。我们将评估视网膜外突触机制、从双极到神经节细胞的谷氨酸能信号以及无长突细胞抑制对双极输出编码辐射能力的相对贡献。为了回答这些问题，我们将扩大我们现有的技术库(小鼠遗传模型、膜片钳记录、光刺激、药理操作、细胞内染料填充和共聚焦显微镜)，提供强大的新工具，包括病毒跨突触跟踪、双光子显微镜和令人兴奋的新成像技术，用于监测IPL中特定深度的双极终端向已识别的ipRGC释放谷氨酸。

DESCRIPTION (provided by applicant): Intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin. They were once viewed as a single cell type conveying light-intensity (irradiance) information to 'non-image-forming' (NIF) centers for circadian, pupillary and neuroendocrine regulation. However, ipRGCs have proved to be diverse, with some subtypes contributing to cortical visual mechanisms. Understanding this diversity in relation to visual behavior and perception is major long-term goal of this project. Ou first aim is to develop detailed structural and functional descriptions of two novel ipRGC types, the M5 and M6 cells. Both have small fields and unusual functional properties and may contribute to cortical vision. M5 cells may be spectrally opponent, while M6 cells exhibit variable and surprising features such as transient or suppressed-by-contrast responses. Fulfilling this aim will largely complete the inventory of ipRGC types and advance a full accounting of ganglion cell types in the mouse, now the premiere model for retinal studies. Though ipRGCs are diverse, most of them share a striking property - the ability to report environmental light levels. This suits the requirement of many NIF reflexes for a signal encoding global light intensity, rather than spatial contrast, color or movement. Our second aim is to reveal the mechanistic basis of this irradiance-coding capacity. What are the cells, circuits, and synaptic mechanisms that permit ipRGCs to encode irradiance, while conventional ganglion cells cannot? We will focus on the bipolar cells that link rod and cone photoreceptors to ipRGCs, asking how these convey raw irradiance information to the ipRGCs while bipolars that feed conventional RGCs filter out such information to encode mainly changes in intensity (spatiotemporal luminance contrast). Dendrites of ipRGCs are segregated in two specific sublaminae of the inner plexiform layer, comprising only part of the ON sublayer. This implies that they receive inputs from subsets of ON bipolar cells specialized for irradiance coding. Differences in inhibitory circuits also appear likely to contribute. We propose to determine which ipRGC types actually encode irradiance, to trace the transmission of irradiance information through specific presynaptic bipolar types and synapses, and to contrast these with the bipolar circuits driving RGCs than cannot report irradiance. We will assess the relative contributions of outer-retinal synaptic mechanisms, glutamatergic signaling from bipolar to ganglion cells, and amacrine-cell inhibition to the capacity of ON bipolar outputs to encode irradiance. To answer these questions, we will augment our established technical arsenal (mouse genetic models, patch clamp recording, light stimulation, pharmacological manipulation, intracellular dye-filling, and confocal microscopy), with powerful new tools, including viral transsynaptic tracing, two-photon microscopy and an exciting new imaging technique for monitoring glutamate release from bipolar terminals at specific depths in the IPL onto identified ipRGCs.