Functional analysis of retinal inhibitory processes

描述(申请人提供)：视网膜抑制输入塑造分级的、持续的光感受器信号通过视网膜时的动力学。在网络水平上，视网膜抑制调节双极细胞感受野的中心-周围拮抗性组织，进而调节神经节细胞的感受野。这个视网膜回路是对比度检测的基础，这是视网膜处理信号的基本特征。这项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输入的分布、功能特征和调节。我将利用由金鱼视网膜制成的一种独特的准备，其中光诱发的膜电流的膜片钳记录可以在切片准备中从On类型的Mb双极细胞的胞体或轴突末端进行。即使在轴突切断后，也可以从这些隔室进行稳定的记录，因此可以单独研究视网膜的外部或内部抑制输入。利用这一准备，我将重温脊椎动物视网膜视觉信息处理的基本问题。我的初步数据显示，与轴突终末相比，光在双极细胞胞体引起不同的反应，这是由于它们各自的突触输入和电压门控通道的不同。第一个具体目标将描述完整的Mb双极细胞中轴突终末的光诱发反应，并将使用高时间分辨率的电容测量来研究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在分离针对Mb双极细胞的视网膜外部和内部抑制。我将确定它们是如何影响谷氨酸输出的，并区分它们对拮抗环绕反应的贡献。我记录了来自带有切断轴突的双极轴突终末的光诱发抑制性突触电流，这代表了纯粹的侧向抑制。我将从电生理学和药理学的角度描述这些突触输入在不同的光适应水平上的特征，并确定它们潜在的突触电路。我有初步证据表明，NMDA受体提供足够的钙，绕过电压门控钙通道，直接和局部地触发无长突细胞释放GABA。最后一个具体目标将检验这样一个假设，即无长突细胞中NMDA受体的调节会影响突触触发的GABA释放，进而影响双极细胞的输出。总体而言，这些实验将结合电容、膜电位/电流测量和药物操作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逐渐抑制水平的调节。与公共健康相关：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图像翻译成神经代码：视网膜编码轮廓、颜色和运动。这项拟议的研究调查了轮廓检测的自然机制。研究结果可用于指导盲人恢复部分视力的假体视力装置的设计。

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.