Functional Circuitry of Long-Range Connections in the Retina

我们的主要目标是了解视网膜中的神经回路如何执行视觉计算， 健康的视力我们在这个建议中的具体目标是揭示宽视野无长突细胞（WAC）在 视网膜处理WAC是一类GABA能中间神经元，是视网膜中最大的细胞，并且在视网膜中是最大的细胞。 它们可以跨越近一半的视网膜区域。传统模型提出WAC编码 在其中央树突上局部对比，然后通过动作电位（尖峰）将抑制扩散到全局- 依赖性信号传递到毫米长的轴突。这种整体GABA能抑制将调节兴奋性 （双极细胞→神经节细胞）视网膜回路，从而形成神经节细胞对基于局部特征的响应 视觉场景的全球统计数据。系统地评价WAC功能一直是一个难点， 然而，因为该领域缺乏针对特定WAC类型进行功能和结构研究的工具。 在这里，我们通过开发交叉遗传策略来标记不同的WAC家族来解决这个问题 在小鼠视网膜中表达转录因子Bhlhb 5。使用Flp和Cre的组合 重组酶表达，结合双报告等位基因，我们开发了鉴定Bhlhb 5- 表达WAC（B5 WAC）亚型，其共同构成所有无长突细胞的约20%。 我们的初步研究挑战了传统的WAC函数模型。具体来说，我们发现了一个子集， B5 WAC是非尖峰细胞。Ca 2+指示剂成像表明，非加标B5 WAC表现出 树突隔室中[Ca 2 +]的局部变化可以被调节为刺激性质（例如，取向 调谐），导致假设，尽管它们的大小，这些细胞主要参与局部 在其宽的乔木内的多个点处处理视觉特征。拟议的实验将确定 基于遗传、结构和功能标准的加标和非加标B5 WAC类型， 揭示了这些中间神经元在视网膜功能中的新作用。我们将测试关于B5 WAC的具体假设 使用交叉光遗传学实验结合高分辨率扫描的突触组织 块面电子显微镜（SBEM）和随机光学重建显微镜（STORM）。我们 多学科的方法，从四个实验室的独特贡献，将产生新的见解， 视网膜最大神经元的电路功能。

Our broad goal is to understand how neural circuits in the retina perform the visual computations that generate healthy vision. Our specific goal in this proposal is to reveal the role of wide-field amacrine cells (WACs) in retinal processing. WACs, a class of GABAergic interneuron, are the largest cells in the retina, and in the mouse they can span nearly half of the retinal area. A conventional model proposes that WACs encode contrast locally over their central dendrites and then spread inhibition globally by action potential (spike)- dependent signaling down millimeter-long axons. This global GABAergic inhibition would tune excitatory (bipolar cell → ganglion cell) retinal circuits and thereby shape ganglion cell responses to local features based on the global statistics of the visual scene. It has been difficult to evaluate WAC function systematically, however, because the field lacks tools for targeting specific WAC types for functional and structural studies. Here, we solve this problem by developing intersectional genetic strategies to label a diverse family of WACs that express the transcription factor Bhlhb5 in the mouse retina. Using a combination of Flp and Cre recombinase expression, in conjunction with dual-reporter alleles, we developed methods to identify Bhlhb5- expressing WAC (B5 WAC) subtypes, which together comprise ~20% of all amacrine cells. Our preliminary studies challenge the conventional model of WAC function. Specifically, we identified a subset of B5 WACs that are non-spiking cells. Ca2+ indicator imaging demonstrates that non-spiking B5 WACs exhibit localized changes in [Ca2+] in dendritic compartments that can be tuned to stimulus properties (e.g., orientation tuning), leading to the hypothesis that despite their large size, these cells are involved primarily in local processing of visual features at multiple points within their wide arbors. Proposed experiments will identify spiking and non-spiking B5 WAC types based on combined genetic, structural and functional criteria and reveal novel roles for these interneurons in retinal function. We will test specific hypotheses about B5 WAC synaptic organization using intersectional optogenetic experiments combined with high-resolution Scanning Block-face Electron Microscopy (SBEM) and STochastic Optical Reconstruction Microscopy (STORM). Our multidisciplinary approach, with unique contributions from four laboratories, will yield new insights into the circuit functions of the retina's largest neurons.