Thresholds, sites, and contributions of circuit compensation following rod photoreceptorloss in mature retina

迫切需要了解细胞死亡反应的原因、程度和机制，以便可以采用最适合剩余回路状态的有效治疗，从而在部分回路持续的情况下，可以利用建设性补偿作为一种潜在的治疗方法。我们的长期目标是挽救神经元回路。在这里，我们将定义受控细胞死亡对特定电路、细胞类型、突触和蛋白质的影响，以了解导致建设性(例如，通过增加突触增益进行补偿)与破坏性(例如，破坏信号的异常自发活动)反应的条件。小鼠视网膜是这项研究的特殊平台，因为初级感觉神经元，即光感受器，可以在基因控制下进行操作；特定回路中的细胞类型是可识别和可访问的；功能读数可以解释为视觉敏感度。我们建议消融成熟视网膜中可变的视杆细胞群，并确定结构和功能对初级视杆双极细胞通路的影响，这是最敏感的视网膜通路：视杆→视杆双极细胞→AII无长突细胞→On视锥双极细胞→On持续α神经节细胞(简写为ABR)。在Alpha上)。在阿尔法神经节细胞接受最多的视杆输入，因此对视杆丢失最敏感。我们的中心假设是，视网膜对输入丢失有建设性的反应，有能力恢复正常功能，直到一个未定义的阈值；超过这个阈值，破坏性反应开始。未知的是这个临界点。我们的初步数据显示，尽管失去了一半的燃料棒，但燃料棒- 在阿尔法神经节细胞尖峰上介导的光反应与对照相当，提示代偿 在初级杆状双极细胞通路中。因此，视杆细胞丢失后视网膜内的建设性补偿具有很强的前提，我们将确定这种补偿的诱导参数、位置和对维持功能的贡献，目的如下：(1)确定导致建设性与破坏性结构和功能变化的输入损失的程度，(目的2)在明确的神经回路中定位补偿的位置(S)和机制(S)。这种方法在遗传控制视杆死亡的时间和程度方面是创新的；对明确定义的视网膜回路的突触和细胞类型的特定结构和功能的研究；以及在触发代偿机制中区分细胞消融和突触分解的分子工具。这些结果将对于(1)确定触发剩余视网膜回路进行破坏性或建设性反应的视杆死亡的程度，(2)确定结构和功能补偿对维持视网膜功能的位置和贡献，以及(3)提供对于优化和部署治疗涉及干细胞、基因和假体的功能障碍的光感受器的疗法所必需的知识，所有这些都依赖于稳定的视网膜回路和/或对存活的视网膜回路的状态的广泛了解。

There is critical need to understand the causes, extent, and mechanisms of reactions to cell death so that effective treatments most appropriate for the state of the remaining circuit can be employed, and so that constructive compensation can be harnessed as a potential treatment in conditions where a portion of the circuit endures. Our long-term goal is to salvage neuronal circuits. Here, we will define the effects of controlled cell death on specific circuits, cell types, synapses, and proteins for the purpose of understanding the conditions that result in constructive (e.g., compensation through increasing synaptic gain) vs. destructive (e.g., aberrant spontaneous activity that corrupts signal) response. The mouse retina is an exceptional platform for this study because the primary sensory neurons, photoreceptors, can be manipulated under genetic control; cell types within specific circuits are identifiable and accessible; and the functional readout can be interpreted as visual sensitivity. We propose to ablate variable populations of rods in mature retina and determine the structural and functional effects on the primary rod bipolar cell pathway, the most sensitive retinal pathway: rods→rod bipolar cells→AII amacrine cells→ON cone bipolar cells→ON sustained alpha ganglion cells (abbr. ON alpha). ON alpha ganglion cells receive the greatest number of rod inputs, thus would be the most sensitive to rod loss. Our central hypothesis is that the retina has constructive reactions to input loss with the capacity to recover normal function up to an undefined threshold; beyond this threshold, destructive reactions begin. Unknown is this tipping point. Our preliminary data show that despite loss of half the rods, rod- mediated light responses in ON alpha ganglion cell spikes are comparable to control, suggesting compensation within the primary rod bipolar cell pathway. Thus, the premise is strong for constructive compensation within the retina following rod loss, and we will determine the induction parameters, sites, and contributions of this compensation to maintaining function in the following aims: (Aim 1) to determine the degree of input loss that induces constructive vs. destructive structural and functional changes, and (Aim 2) to locate the site(s) and mechanism(s) of compensation within a well-defined neural circuit. The approach is innovative for genetic control over the timing and degree of rod death; synaptic- and cell-type specific structural and functional investigation of a well-defined retinal circuit; and molecular tools to distinguish between cell ablation and synapse disassembly in triggering compensatory mechanisms. The results will be significant for (1) determining the degree of rod death that triggers the remaining circuit to undergo destructive or constructive responses, (2) identifying the sites and contributions of structural and functional compensation to maintaining retinal function, and (3) providing knowledge essential to the optimization and deployment of therapies to treat dysfunctional photoreceptors involving stem cells, genes, and prostheses, all of which rely on a stable retinal circuit and/or extensive knowledge of the state of the surviving retinal circuit.