Connexins and electrical synapses in the retina

描述（由申请人提供）：令人信服的证据表明，来自视杆细胞的信号使用多种途径到达神经节细胞。在经典初级通路中，视杆细胞信号通过AII无长突进入下游视锥细胞回路，AII无长突与ON锥细胞双极形成电突触（间隙连接），与OFF锥细胞双极形成甘氨酸能突触。在次级通路中，视杆细胞和视锥细胞之间的电突触为视杆细胞信号进入视锥细胞回路提供了直接入口。然而，一个可靠的直接演示杆锥耦合已经取得了只有在猴子。由于技术问题阻止了传统的方法来测量小鼠中的杆-锥耦合（即使用微电极注射连接渗透示踪剂），我们开发了一种新的方法来评估耦合。该方法基于转运蛋白的转基因细胞特异性表达，转运分子通过间隙连接运动到邻近细胞，并用特异性抗体检测该分子。这种方法消除了对活细胞的任何物理操作的需要。尽管普遍假设视杆-视锥耦合是次级通路的基础，但我们在小鼠中没有发现视杆-视锥耦合的证据。因此，我们提出了一组实验，以确定的典型的二级通路模型的一般性，通过测试杆锥耦合在兔子和评估锥锥和可能的杆棒耦合在小鼠和兔视网膜。相比之下，我们的数据强烈支持的基本原则杆主要途径。然而，虽然流行的模型假设，AII无长突表达Cx 36和锥双极表达Cx45，形成一个“异型”电突触，我们的数据表明更复杂。我们建议有两种类型的甘氨酸能无长突细胞，表达Cx45和表达Cx 36的细胞，每种细胞与表达相同连接蛋白的锥双极细胞的子集形成同型连接。我们假设不相容连接蛋白的表达是根据细胞亚型分离无长突-视锥双极相互作用的机制。我们将确定参与视杆细胞初级通路信号传导的锥状双极细胞的类型以及它们使用的连接蛋白。此外，我们将确定不同的视网膜连接蛋白是否可以在功能上相互作用。 公共卫生相关性：我们的研究解决了有关杆光感受器所采用的神经回路的基本问题，这些神经回路有助于在从接近完全黑暗到明亮月光的光输入范围内的视网膜反应。神经视网膜疾病是人类失明的主要原因，合理的治疗策略需要充分了解哺乳动物的视网膜回路。

DESCRIPTION (provided by applicant): A compelling body of evidence indicates that signals from rod photoreceptors use multiple pathways to reach ganglion cells. In the canonical primary pathway, rod signals gain access to downstream cone circuitry through the AII amacrines which form electrical synapses (gap junctions) with ON cone bipolar and glycinergic synapses with OFF cone bipolar. In the secondary pathway, electrical synapses between rods and cones provide a direct entry for rod signals into cone circuits. However, a credible direct demonstration of rod-cone coupling has been made only in monkey. Because technical issues prevent a conventional approach to measurement of rod-cone coupling in the mouse (i.e. injections of junction-permeant tracers using microelectrodes), we developed a novel method to evaluated coupling. The method is based on transgenic, cell-specific expression of a transporter, the movement of the transported molecule through gap junctions to neighboring cells and the detection of that molecule with specific antibodies. This method eliminates the need for any physical manipulation of the live cells. Despite the widely held assumption that rod-cone coupling underlies the secondary pathway, we found no evidence of rod-cone coupling in the mouse. Thus, we propose a set of experiments to determine the generality of the canonical secondary pathway model by testing rod-cone coupling in the rabbit and to evaluate cone-cone and possible rod-rod coupling in mouse and rabbit retinas. In contrast, our data strongly support the basic tenets of the rod primary pathway. However, while the prevailing model postulates that AII amacrines express Cx36 and cone ON bipolar express Cx45, forming a 'heterotypic' electrical synapse, our data indicate more complexity. We propose there are two types of glycinergic amacrine cells, those expressing Cx45 and those expressing Cx36 and that each forms homotypic junctions with a subset of cone bipolar cells expressing the same connexin. We hypothesize that the expression of incompatible connexins is mechanism to allow segregation of amacrine- cone bipolar interactions according to cell subtype. We will determine the types of cone bipolar involved in rod primary pathway signaling and which connexins they employ. In addition, we will determine if different retinal connexins can functionally interact. PUBLIC HEALTH RELEVANCE: Our studies address fundamental questions about the neural circuitry employed by rod photoreceptors, which contribute to retinal responses over a range of light inputs from near total darkness to bright moonlight. Disorders of the neural retina are a primary cause of human blindness and a rational pursuit of therapeutic strategies requires a full understand of mammalian retinal circuitry.