Amacrine Cell Function in the Retina

描述(申请人提供)：过去十年的研究表明，通过缝隙连接的电突触传递形成了视网膜中神经元交流的一种重要模式。现在很清楚，缝隙连接在视网膜中普遍存在，由五个主要细胞类别中的每一个表达。此外，视网膜缝隙连接已被证明受到环境照明和昼夜节律变化的动态调节，这些变化通过光激活的神经调节剂，如多巴胺和一氧化氮来发挥作用。这些数据表明，缝隙连接在光适应中起着重要作用。我们研究的长期目标是确定缝隙连接在哺乳动物视网膜中的分布和功能，从而确定它们在视觉信号处理中的作用。这项提议的一个具体目的是研究缝隙连接在杆状介导的信号传递中的作用。实验被用来研究AII无长突细胞之间的耦合在维持最敏感的视杆信号保真度中的作用，以及视杆-视锥耦合在将视杆介导的信号传递到水平细胞中的作用。第二个目标是研究由利用缝隙连接的电路传递到视网膜神经元的屏蔽突触输入。我们最近的数据表明，杆介导的某些神经节细胞亚型的突触信号被掩盖，因为它们不会被翻译成尖峰代码并发送到大脑。将被研究的第二个掩蔽输入是On方向选择性神经节细胞的OFF反应，该反应由多轴突无长突细胞亚型组成的缝隙连接传递，通常被抑制电路隐藏。我们将确定视网膜中被屏蔽的突触输入是否反映了随着刺激条件的变化而产生的视觉信号的正常动态，或者是视网膜的经济连接策略。第三个目的是研究星爆无长突细胞Kv3钾通道在产生方向选择性反应中的作用，这一计算机制已成为视网膜神经生物学中的经典问题。最终目的是确定哺乳动物视网膜中20-30个亚型的无长突细胞的结构和功能，以阐明它们在产生由突触后神经节细胞携带到大脑的视网膜输出信号中的作用。拟议的实验重点是电生理记录视网膜神经元的反应，并用间隙标记的生物素化示踪剂标记它们。在突变的小鼠模型中，缝隙连接的功能将通过选择性地去除它们，或者通过药物或敲除特定的连接蛋白来评估。缝隙连接与许多神经系统疾病有关，包括X连锁的Charcot-Marie-Tooth病、非综合征性常染色体耳聋以及中风或创伤后的神经保护。虽然这项工作的重点是哺乳动物视网膜中缝隙连接的功能和调节，但这项拟议的工作仍将为了解整个大脑中电突触传递的作用提供重要的见解。公共卫生相关性：作为人类最重要的感觉，视觉是我们主要通过它与周围世界互动的方式。这项提议将研究视网膜中缝隙连接的作用，缝隙连接受光的调节，因此可能在光适应中发挥关键作用。缝隙连接与许多神经系统缺陷有关，包括X-连锁的Charcot-Marie-Tooth病、非综合征性常染色体耳聋和神经保护，并可能在与暗环境光条件下的适应和视力相关的视网膜疾病中发挥作用。

DESCRIPTION (provided by applicant): Work over the last decade indicates that electrical synaptic transmission via gap junctions forms an important mode of neuronal communication in the retina. It is now clear that gap junctions are ubiquitous in the retina, being expressed by each of the five major cell classes. In addition, retinal gap junctions have been shown to be dynamically regulated by changes in ambient illumination and circadian rhythms acting through light-activated neuromodulators such as dopamine and nitric oxide. These data suggest that gap junctions play an important role in light adaptation. The long-term goal of our research is define the distribution and function of gap junctions in the mammalian retina so as to define their roles in the processing of visual signals. One specific aim of this proposal is to examine the role of gap junctions in the transmission of rod-mediated signals. Experiments are proposed to study the role of coupling between AII amacrine cells in maintaining the fidelity of the most sensitive rod signals and the role of rod-cone coupling in delivering rod-mediated signals to the horizontal cells. A second aim is to study masked synaptic inputs to retinal neurons, delivered by circuits that utilize gap junctions. Our recent data indicate that rod-mediated synaptic signals to some ganglion cell subtypes are masked in that they are not translated into a spike code and sent to the brain. A second masked input that will be studied is an OFF response in ON direction selective ganglion cells that is delivered by gap junctions made with a subtype of polyaxonal amacrine cells and is normally hidden by inhibitory circuitry. We will determine if masked synaptic inputs in the retina reflect normal dynamics in visual signaling with changing stimulus conditions or a strategy for economic wiring of the retina. A third aim is to study the role of starburst amacrine cell Kv3 potassium channels in generating direction selective responses, a computation whose mechanism has become a classic question in retinal neurobiology. A final aim is to define the structure and function of the 20-30 subtypes of amacrine cells in the mammalian retina to elucidate their roles in generating the output signals of the retina carried by the postsynaptic ganglion cells to the brain. The proposed experiments center on electrophysiological recording of the responses of retinal neurons and their labeling with the gap-permeant biotinylated tracers. The function of gap junctions will be assessed by selectively ablating them either pharmacologically or by knocking out specific connexin proteins in mutant mouse models. Gap junctions have been implicated in a number of neurological diseases including X- linked Charcot-Marie-Tooth disease, nonsyndromic autosomal deafness and neuroprotection following stroke or trauma. Although focused on the function and regulation of gap junctions in mammalian retina, the proposed work will nevertheless provide important insights into the roles of electrical synaptic transmission throughout the brain. PUBLIC HEALTH RELEVANCE: As the most important sense in humans, vision is the modality through which we interact mainly with the world around us. This proposal will examine the role of gap junctions in the retina, which are modulated by light and are thereby likely to play a key role in light adaptation. Gap junctions have been implicated in a number of neurological defects including X-linked Charcot-Marie-Tooth disease, nonsyndromic autosomal deafness and neuroprotection and may play a role in retinopathies related to adaptation and vision under dim ambient light conditions.