Retrograde Signaling by Intrinsically Photosensitive Retinal Ganglion Cells

传统上，光信息被认为只从杆和锥光感受器通过双极， 水平和无长突的中间神经元到视网膜神经节细胞（RGC），这被认为是信号只向 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， 即内在光敏视网膜神经节细胞（ipRGC）， 视网膜内的几种类型的无长突细胞（AC）。这种违反直觉的功能意义 逆行信号传导基本上是未知的。由于AC是众所周知的调节生理的所有类别的 视网膜神经元，该项目的中心假设是，逆行ipRGC信号传导用于调节 视网膜中的视觉处理，最终形成视觉。在上一个资助期，PI的团队确定了 间隙连接（GJ）偶联作为ipRGC向AC发信号的一种机制。开始评估 逆行ipRGC信号传导，该团队在遗传上敲除了ipRGC中特异性的一种GJ蛋白， 一项视动行为分析显示，小鼠跟踪高强度运动条纹的能力下降， 空间频率或低对比度。因此，间隙连接ipRGC-to-AC信号传导的功能意义是 它在行为层面上提高了空间敏锐度和对比敏感度。该项目将测试 间隙连接ipRGC-to-AC信号传导可以增强敏锐度和灵敏度的三种假设机制 对比敏感度目的1将检验间隙连接ipRGC-to-AC信号转导增强视网膜神经元凋亡的假设。 光反应。PI的团队将使用双极细胞的场电位记录和单个细胞的记录。 RGC来测量当操纵GJ介导的ipRGC至AC信号传导时，这些细胞对单个光脉冲的响应如何改变。目的2将检验间隙连接ipRGC-to-AC信号传导改善细胞凋亡的假设。 视网膜细胞分辨光强度重复变化的能力。该小组将决定是否 操纵GJ介导的ipRGC-to-AC信号传导改变双极和神经节细胞对闪烁的反应 光目的3将检验间隙连接ipRGC-to-AC信号传导调节感受野的假设 RGC的特性研究小组将测试是否操纵GJ介导的ipRGC-to-AC信号转导改变了细胞的功能。 RGC感受野的大小和这些感受野中中心/周围拮抗的强度。的 研究团队拥有强大的初步数据来支持每个目标。本研究的影响将是：1） 阐明以前被忽视但功能重要的视网膜信号通路的作用; 2）进一步 ipRGC对成像视觉的贡献的评价，除了它们在非成像光反应如瞳孔反射和昼夜光诱导中的众所周知的作用之外;和3）阐明 无长突细胞和神经节细胞之间的GJ偶联的功能，这仍然知之甚少。一个潜在 了解逆行ipRGC信号传导的长期影响，其在杆/锥后持续存在 退化，是告知新的战略，恢复视力的患者患有感光细胞营养不良。

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.