Retrograde Signaling by Intrinsically Photosensitive Retinal Ganglion Cells

传统上，光信息被认为只从杆状和锥状感光器流经双极， 水平和无长突中间神经元至视网膜神经节细胞(RGC)，它们被认为只向 大脑的高级视觉中心。出乎意料的是，PI和同事们发现RGC的一个子集， 即固有的光敏性视网膜神经节细胞(IpRGC)，传递光诱发的反应 视网膜内有几种类型的无长突细胞(ACS)。这一反直觉的功能意义 逆行信号在很大程度上是未知的。由于众所周知，ACS可以调节所有类别的 视网膜神经元，这个项目的中心假设是逆行的ipRGC信号调节 视网膜中的视觉处理，最终塑造视觉。在之前的资助期，PI的团队确定了 缝隙连接(GJ)连接是ipRGCs向ACS传递信号的一种机制。开始评估…的作用 逆行ipRGC信号，研究小组从基因上敲除了一种特定于ipRGC的GJ蛋白， 一项视动行为测试显示，小鼠追踪移动的高强度条纹的能力下降 空间频率或低对比度。因此，缝隙连接ipRGC-to-AC信号的功能意义是 它在行为层面上提高了空间敏锐度和对比敏感度。拟议中的项目将测试 缝隙连接ipRGC-to-AC信号通过三种假说机制提高视力和 对比敏感度。目标1将验证缝隙连接ipRGC-to-AC信号增强视网膜的假设 光反应。PI的团队将使用双极细胞的场电位记录和个体 当GJ介导的ipRGC到AC信号被操纵时，RGC测量这些细胞对单个光脉冲的反应是如何改变的。目标2将检验缝隙连接ipRGC-to-AC信号改善的假设 视网膜细胞解决光强度重复变化的能力。该团队将决定是否 操纵GJ介导的ipRGC-to-AC信号改变双极细胞和神经节细胞对闪烁的反应 灯。目标3将验证缝隙连接ipRGC-to-AC信号调制感受野的假设 RGC的特性。该团队将测试操纵GJ介导的ipRGC至AC信号是否改变 RGC感受野的大小和这些感受野的中心/周围拮抗强度。这个 研究团队有强有力的初步数据支持每个目标。这项研究的影响将是：1) 阐明以前被忽视但在功能上重要的视网膜信号通路的作用；2)进一步 评价ipRGCs对成像视觉的贡献，以及它们在非成像光反应中的众所周知的作用，如瞳孔反射和昼夜节律光携带；以及3)阐明 无长突细胞和神经节细胞之间的GJ偶联功能仍然知之甚少。一种潜力 了解逆行ipRGC信号的长期影响，该信号在视杆/视锥后持续存在 变性，是为光感受器营养不良患者恢复视力的新策略提供信息。

Classically, photic information was assumed to flow only from rod and cone photoreceptors through bipolar, horizontal and amacrine interneurons to retinal ganglion cells (RGCs), which were assumed to signal only to higher visual centers of the brain. Unexpectedly, the PI and colleagues discovered that a subset of RGCs, namely intrinsically photosensitive retinal ganglion cells (ipRGCs), transmit light-evoked responses intraretinally to several types of amacrine cells (ACs). The functional significance of this counterintuitive retrograde signaling is largely unknown. Since ACs are well-known to regulate the physiology of all classes of retinal neurons, the central hypothesis for this project is that retrograde ipRGC signaling serves to regulate visual processing in the retina, ultimately shaping vision. In the previous funding period the PI’s team identified gap junction (GJ) coupling as one mechanism by which ipRGCs signal to ACs. To begin to assess the roles of retrograde ipRGC signaling, the team genetically knocked out one type of GJ protein specifically in ipRGCs, and an optokinetic behavioral assay showed a reduction in the mice’s ability to track moving stripes of high spatial frequencies or low contrasts. Thus, a functional significance of gap junctional ipRGC-to-AC signaling is that it improves spatial acuity and contrast sensitivity at the behavioral level. The proposed project will test three hypothesized mechanisms by which gap junctional ipRGC-to-AC signaling could enhance acuity and contrast sensitivity. Aim 1 will test the hypothesis that gap junctional ipRGC-to-AC signaling potentiates retinal light responses. The PI’s team will use field-potential recording of bipolar cells and recording of individual RGCs to measure how these cells’ responses to single light pulses are altered when GJ-mediated ipRGC-to-AC signaling is manipulated. Aim 2 will test the hypothesis that gap junctional ipRGC-to-AC signaling improves the ability of retinal cells to resolve repetitive changes in light intensity. The team will determine whether manipulating GJ-mediated ipRGC-to-AC signaling alters bipolar and ganglion cells’ responses to flickering light. Aim 3 will test the hypothesis that gap junctional ipRGC-to-AC signaling modulates the receptive field properties of RGCs. The team will test whether manipulating GJ-mediated ipRGC-to-AC signaling alters the sizes of RGC receptive fields and the strength of center/surround antagonism in these receptive fields. The research team has strong preliminary data in support of each Aim. The impact of this study will be to: 1) illuminate the roles of a previously overlooked but functionally important retinal signaling pathway; 2) further the appreciation of ipRGCs’ contribution to image-forming vision, besides their well-known roles in nonimage-forming photoresponses such as the pupil reflex and circadian photoentrainment; and 3) elucidate the functions of GJ coupling between amacrine and ganglion cells, which remain poorly understood. A potential long-term impact of understanding retrograde ipRGC signaling, which persists following rod/cone degeneration, is to inform new strategies for restoring sight in patients suffering photoreceptor dystrophy.