Amacrine Cell Function in the Retina

描述（由申请人提供）：过去十年的工作表明，通过间隙连接的突触电传递形成了视网膜中神经元通信的重要模式。现在很清楚，间隙连接在视网膜中无处不在，由五种主要细胞类别中的每一种表达。此外，视网膜间隙连接已被证明受环境光照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）起作用。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明确哺乳动物视网膜间隙连接的分布和功能，从而确定它们在视觉信号处理中的作用。这一建议的一个具体目的是检查间隙连接在杆介导信号的传输中的作用。实验旨在研究AII腺分泌细胞之间的耦合在维持最敏感的杆信号保真度中的作用，以及杆-锥耦合在将杆介导的信号传递给水平细胞中的作用。第二个目标是研究通过利用间隙连接的电路传递给视网膜神经元的隐藏突触输入。我们最近的数据表明，一些神经节细胞亚型的杆介导的突触信号被掩盖，因为它们没有被翻译成spike代码并发送到大脑。第二种被掩盖的输入将被研究，它是由多轴突无突细胞亚型形成的间隙连接传递的ON方向选择性神经节细胞的OFF反应，通常被抑制电路隐藏。我们将确定视网膜中被掩盖的突触输入是否反映了随刺激条件变化的视觉信号的正常动态或视网膜经济线路的策略。第三个目标是研究星爆腺细胞Kv3钾通道在产生方向选择反应中的作用，这一计算机制已成为视网膜神经生物学的经典问题。最终目的是确定哺乳动物视网膜中20-30种无毛细胞亚型的结构和功能，以阐明它们在产生视网膜输出信号的过程中所起的作用，这些信号由突触后神经节细胞携带到大脑。提出的实验集中在视网膜神经元反应的电生理记录和它们的标记与间隙渗透的生物素化示踪剂。在突变小鼠模型中，间隙连接的功能将通过药理学或敲除特定的连接蛋白来评估。间隙连接与许多神经系统疾病有关，包括X连锁沙科-玛丽-图斯病、非综合征性常染色体耳聋和中风或创伤后的神经保护。尽管研究重点是哺乳动物视网膜间隙连接的功能和调节，但这项工作将为了解整个大脑中突触电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官，视觉是我们与周围世界互动的主要方式。这一提议将研究视网膜缝隙连接的作用，它是由光调节的，因此可能在光适应中起关键作用。间隙连接与许多神经缺陷有关，包括x连锁沙科-玛丽-图斯病、非综合征性常染色体耳聋和神经保护，并可能在昏暗环境光条件下与适应和视力相关的视网膜病变中发挥作用。

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.