Neural Circuits and Synapses for Early Visual Processing

这个研究项目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。这项建议侧重于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中最多样的一类细胞 视网膜回路功能多样性的主要驱动力：它们通过它们的 与双极细胞终末(兴奋性中间神经元)、神经节细胞(投射神经元)等的突触 无长突细胞。尽管它们具有重要意义，但只有几种无长突细胞类型被详细研究过。超过了 在之前的资助期间，我们发现并研究了新的无长突细胞电路。我们也意识到了实用和 用个体无长突细胞类型的遗传失活来研究它们在视网膜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： 有条件地删除研究良好的视网膜回路中特定点处的突触后抑制受体，以及 血浆GABA转运蛋白(GATs)的微扰。 我们的初步数据表明，新开发的小鼠遗传工具可用于条件基因敲除(KO) 功能GABAA或甘氨酸受体(GABAAR、GlyR)所需的蛋白质。目标1号将延长这些 研究的重点是对形成甘氨酸能突触所必需的地理卟啉，以及 GABA是形成GABA能突触所必需的。后续的实验将评估 用超分辨显微镜观察视网膜神经节细胞中蛋白KO的结构结果(随机 光学重建显微镜；STORM)。我们将确定蛋白质KO在以下方面的功能后果 神经节细胞生理学；这些实验将揭示下列可能的代偿机制 抑制性受体缺失与感受野中抑制性受体缺失的后果。 我们的初步数据对GAT-3在哺乳动物视网膜中的功能提出了一个全新的观点。似然 表达于Müller神经胶质细胞的GAT-3似乎限制了突触前对传递的抑制 GABR。在目标2中，我们建议对汇聚到Alpha或On上的抑制性突触进行光遗传学研究 方向选择性神经节细胞。我们将检验从GAT-3初步观察到的假设 通过调节反馈机制来调节突触传递的强度 抑制神经递质的释放。这项规定的功能意义将通过以下研究进行评估 神经节细胞回路中依赖于GAT-3的感受场特性的调制。 建议的研究将促进我们对抑制性突触传递机制的理解。 并揭示突触抑制在视网膜神经节细胞功能中的作用。结果可能会告诉我们 治疗视网膜疾病，包括视网膜色素变性、糖尿病视网膜病变和青光眼，所有 伴随着抑制回路功能的改变。

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.