Neural Circuits and Synapses for Early Visual Processing

这项研究计划的目标是了解视觉信息是如何通过突触相互作用进行编码的 在视网膜的神经回路中。本研究主要探讨突触抑制的机制和作用 由称为无长突细胞的视网膜中间神经元介导。无长突细胞是视网膜上最多样化的细胞类型 以及视网膜回路功能多样性的主要驱动因素：它们通过其 突触与双极细胞终端（兴奋性中间神经元），神经节细胞（投射神经元），和其他 无长突细胞尽管它们的重要性，只有少数无长突细胞类型已被详细研究。来 在上一个资助期，我们发现并研究了新的无长突细胞回路。我们还认识到， 使用单个无长突细胞类型的遗传失活来研究其在视网膜病变中的作用的理论局限性 功能基于过去的经验，我们在这里提出了研究抑制的替代方法： 在研究充分的视网膜回路中，在特定点处有条件地删除突触后抑制性受体， 质膜GABA转运蛋白（GATs）的扰动。 我们的初步数据证明了新开发的小鼠遗传工具，用于条件性敲除（KO） 功能性GABAA或甘氨酸受体（GABAAR，GlyR）所需的蛋白质。目标1将扩展这些 研究，重点是桥蛋白，这是必不可少的形成甘氨酸能突触，和β亚单位的 GABAAR是形成GABA能突触所必需的。随后的实验将评估 使用超分辨率显微镜（STochastic）对视网膜神经节细胞中蛋白质KO的结构结果进行了研究 光学重建显微术; STORM）。我们将确定蛋白质KO对细胞的功能影响。 神经节细胞生理学;这些实验将揭示可能的补偿机制， 抑制性受体缺失与抑制性受体缺失对感受野的影响。 我们的初步数据提出了一个全新的观点GAT-3在哺乳动物视网膜中的功能。可能 GAT-3在Müller神经胶质细胞上表达，似乎限制了突触前抑制， GABABRs。在目标2中，我们提出了会聚到ON Alpha或ON Alpha的抑制性突触的光遗传学研究。 方向选择性神经节细胞我们将测试从初步观察中产生的假设，即GAT-3 通过调节反馈机制来调节突触传递的强度， 抑制神经递质释放。这项规定的功能意义将通过以下研究进行评估： GAT-3依赖性调节神经节细胞回路中的感受野特性。 这些研究将促进我们对抑制性突触传递机制的理解， 的视网膜和揭示的作用，突触抑制视网膜神经节细胞的功能。结果可以告知 用于治疗视网膜疾病，包括色素性视网膜炎、糖尿病性视网膜病和青光眼的疗法， 这伴随着抑制回路功能的变化。

The goal of this research program is to understand how visual information is encoded by synaptic interactions within neural circuits of the retina. This proposal focuses on the mechanisms and roles for synaptic inhibition mediated by retinal interneurons called amacrine cells. Amacrine cells are the retina's most diverse cell class and the main drivers of functional diversity in retinal circuits: they influence visual processing through their synapses with bipolar cell terminals (excitatory interneurons), ganglion cells (projection neurons), and other amacrine cells. Despite their significance, only a few amacrine cell types have been studied in detail. Over the previous grant period, we discovered and studied novel amacrine cell circuits. We also realized practical and theoretical limitations to using genetic inactivation of individual amacrine cell types to study their roles in retinal function. Building on past experience, here we propose alternative approaches to studying inhibition: conditional deletion of postsynaptic inhibitory receptors at specific points in well-studied retinal circuits, and perturbation of plasmalemmal GABA transporters (GATs). Our preliminary data demonstrate newly-developed mouse genetic tools for conditional knockout (KO) of proteins that are required for functional GABAA or glycine receptors (GABAAR, GlyR). Aim 1 will extend these studies, focusing on gephyrin, which is essential for forming glycinergic synapses, and beta subunits of the GABAAR, which are essential for forming GABAergic synapses. Subsequent experiments will evaluate the structural consequences of protein KO in retinal ganglion cells using super-resolution microscopy (STochastic Optical Reconstruction Microscopy; STORM). We will determine the functional consequences of protein KO on ganglion cell physiology; these experiments will reveal possible mechanisms for compensation following inhibitory receptor deletion versus consequences of inhibitory receptor deletion on receptive fields. Our preliminary data present a completely novel view of GAT-3 function in the mammalian retina. Likely expressed on Müller glial cells, GAT-3 appears to limit presynaptic inhibition of transmission mediated by GABABRs. In Aim 2, we propose optogenetic studies of inhibitory synapses that converge onto ON Alpha or direction-selective ganglion cells. We will test the hypotheses arising from preliminary observations that GAT-3 regulates the strength of synaptic transmission by regulating feedback mechanisms that would otherwise suppress neurotransmitter release. The functional significance of this regulation will be assessed by studies of GAT-3-dependent modulation of receptive field properties in ganglion cell circuits. The proposed studies will advance our understanding of the mechanisms for inhibitory synaptic transmission in the retina and reveal the role of synaptic inhibition in retinal ganglion cell function. The outcome could inform therapies for treating retinal diseases, including retinitis pigmentosa, diabetic retinopathy and glaucoma, all of which are accompanied by changes in inhibitory circuit function.