Functional analysis of retinal inhibitory processes

描述（由申请人提供）：视网膜抑制性输入在分级的、持续的光感受器信号通过视网膜时形成其动力学。在网络水平，视网膜抑制介导双极细胞感受野的拮抗性中心-环绕组织，进而介导神经节细胞的拮抗性中心-环绕组织。这个视网膜回路是对比度检测的基础，对比度检测是视网膜处理信号的基本特征。拟议研究的目标是研究针对已识别的视网膜双极细胞的抑制性输入的分布、功能特征和调节。我将利用一种从金鱼视网膜制备的独特的制备物，其中光诱发的膜电流的膜片钳记录可以从切片制备物中的ON型Mb双极细胞的索马或轴突末端进行。即使在轴突切断后，这些隔室的稳定记录也是可能的，因此可以分别研究外部或内部视网膜抑制输入。利用这些准备，我将重新讨论脊椎动物视网膜中视觉信息处理的基本问题。我的初步数据显示，光在双极细胞索马和轴突末梢引起不同的反应，这是由于它们各自的突触输入和电压门控通道的差异。第一个具体目标将表征完整Mb双极细胞中轴突末端的光诱发反应，并将研究高时间分辨率电容测量这些生理反应如何触发谷氨酸释放。第二个具体目标将集中于分离靶向Mb双极细胞的外部和内部视网膜抑制。我将确定每一种如何影响谷氨酸输出，并将它们对拮抗性周围反应的贡献分开。我记录了光诱发的抑制性突触电流从双极轴突终端切断轴突，这代表了纯粹的侧抑制。我将在不同的光适应水平下描述这些突触输入的电生理特征，并确定其潜在的突触电路。我有初步证据表明，NMDA受体提供足够的钙，直接和局部地触发GABA从无长突细胞释放，绕过电压门控钙通道。最后一个具体的目标将测试的假设，NMDA受体调节无长突细胞的影响突触触发GABA的释放，反过来，双极细胞输出。总的来说，这些实验将使用电容、膜电位/电流测量和药理学操作的组合来确定当信号通过视网膜网络时，到达神经节细胞的兴奋性视觉信息如何受到渐进的抑制水平的调节。公共卫生相关性：所有脊椎动物的视网膜，包括人类的视网膜，都以非常相似的方式将环境的图像转化为神经代码：视网膜编码轮廓，颜色和运动。拟议的研究调查的自然机制的轮廓检测。研究结果可用于指导人工视觉装置的设计，以恢复盲人的部分视力。

DESCRIPTION (provided by applicant): Retinal inhibitory inputs shape the kinetics of graded, sustained photoreceptor signals as they pass through the retina. At the network level, retinal inhibition mediates the antagonistic center-surround organization of the bipolar cell's receptive field, and in turn, that of the ganglion cell. This retinal circuit underlies contrast detection, a fundamental feature of signal processing by the retina. The goal of the proposed research is to study the distribution, functional characteristics and regulation of inhibitory inputs targeting an identified retinal bipolar cell. I will take advantage of a unique preparation made from the goldfish retina, in which patch-clamp recordings of light evoked membrane currents can be made either from the soma or the axon terminal of an ON-type, Mb bipolar cell in a slice preparation. Stable recordings from these compartments is possible even after axon severing, thus outer or inner retinal inhibitory inputs can be separately studied. Using this preparation I will revisit fundamental questions of visual information processing in the vertebrate retina. My preliminary data show that light evokes different responses at the bipolar cell soma compared to the axon terminal, due to differences in their respective synaptic inputs and voltage-gated channels. The first specific aim will characterize the light-evoked responses of the axon terminal in intact Mb bipolar cells and will study with high time-resolution capacitance measurements how these physiological responses trigger glutamate release. The second specific aim will focus on separating outer and inner retinal inhibition targeting Mb bipolar cells. I will determine how each influence the glutamate output, and separate their contributions to the antagonistic surround response. I recorded light-evoked inhibitory synaptic currents from bipolar axon terminals with severed axons, which represents pure lateral inhibition. I will characterize electrophysiologically and pharmacologically these synaptic inputs at various light adaptation levels, and determine their underlying synaptic circuitry. I have preliminary evidence that NMDA receptors provide enough calcium to trigger GABA release from amacrine cells directly and locally, bypassing voltage-gated calcium channels. The last specific aim will test the hypothesis that NMDA receptor regulation in amacrine cells influences synaptically triggered GABA release and in turn, bipolar cell output. Overall, these experiments will use a combination of capacitance, membrane potential/ current measurements and pharmacological manipulations to determine how the excitatory visual information reaching the ganglion cells is regulated by progressive levels of inhibition as the signal passes through the retinal network. PUBLIC HEALTH RELEVANCE: Images of the environment are translated into neural codes by all vertebrate retinas, including that of humans, in a very similar manner: the retina codes for contours, colors and motion. The proposed research investigates the natural mechanisms underlying contour detection. The results can be used to guide the design of prosthetic vision devices to restore some sight to blind people.