Visualizing Remodeling at the Retinogeniculate Synapse

描述(由申请人提供)：在发育中的中枢神经系统(CNS)中形成精确的突触连接对神经功能至关重要。在视网膜与丘脑外侧膝状核(LGN)之间的连接--视网膜原基突触上，有几个发育阶段参与了突触回路的形成、完善和成熟。在神经元与其靶点的初始映射之后，随着视网膜神经节细胞(RGC)轴突分离成眼睛特有的层，轴突的大体形态重排。在小鼠中，我们发现在RGC轴突分离到LGN的适当区域后很长一段时间(出生后第8天，p8)，有两个强大的突触可塑性和重塑时期。突触可塑性的第一阶段发生在睁开眼睛的时候(p12-14)，此时到给定LGN中继神经元的一些视网膜输入得到加强，而其他输入被修剪。第二个可塑性阶段发生在p20之后，这是以前未被检测到的，此时视网膜原基突触的强度和连接性对感觉体验变得敏感。在这里，我们建议研究与突触可塑性的两个时期相对应的视网膜轴突的形态变化。为此，我们将利用现有的转基因小鼠，并产生新的小鼠系，在这些小鼠系中，它们的RGC的稀疏子集使用不同的荧光颜色共同表达标记轴突乔木和突触前标记突触前标记的标记。利用这些小鼠，我们将检查选定的视网膜神经节细胞轴突的形态变化，以及轴突乔木区域内突触接触的相对分布。这些变化将被量化为正常发育期间的连接重建，以及在可塑性第二阶段对视觉剥夺的反应。我们将验证这样的假设，即RGC轴突茎结构比功能所需的更宽，并且在睁开眼睛的时候变得稳定。我们还将研究突触可塑性强健的时期是否代表固定的轴突支架内突触释放部位的重新排列。发现一种广泛的结构支架，其中突触接触可以形成、断裂和重排，这可能代表了一种相对新颖的神经可塑性。通过将结构与功能联系起来，我们希望对突触发育的结构机制有更清晰的理解。这个项目的目标是了解神经元之间是如何形成连接的，称为突触。我们建议可视化突触前神经元轴突终末结构在发育过程中的变化，以及轴突形态如何与突触功能相对应。了解神经系统的正常连接是如何完成的，将有助于深入了解由异常连接引起的神经疾病，如某些形式的智力低下、认知障碍和癫痫。

DESCRIPTION (provided by applicant): The formation of precise synaptic connections in the developing central nervous system (CNS) is critical for neurological function. At the retinogeniculate synapse, the connection between the retina and the lateral geniculate nucleus (LGN) of the thalamus, several developmental phases contribute to the formation, refinement and maturation of synatic circuits. After the initial mapping of a neuron to its target, there is gross morphological rearrangement of the axon arbors, as retinal ganglion cell (RGC) axons segregate into eye-specific layers. In the mouse, we have found that long after RGC axons segregate into the proper region of the LGN (postnatal day 8, p8), there are two periods of robust synaptic plasticity and remodeling. The first phase of synaptic plasticity occurs around the time of eye opening (p12-14) when some of the retinal inputs to a given LGN relay neuron strengthened while other inputs are pruned. A second, previously undetected, phase of plasticity occurs after p20, when the strength and connectivity of the retinogeniculate synapse becomes sensitive to sensory experience. Here we propose to study the morphological changes of retinal axon arbors that correspond to the two periods of synaptic plasticity. To do this, we will take advantage of available transgenic mice, and also generate new mouse lines in which a sparse subset of their RGCs co-express labels that tag axon arbors and the presynaptic marker, synaptophysin, using different fluorescent colors. Using these mice, we will examine changes in the morphology of select retinal ganglion cell axons and the relative distribution of the synaptic contacts within an axon arbor territory. These changes will be quantified as the connection remodels during normal development, and in response to visual deprivation during the second phase of plasticity. We will test the hypothesis that the RGC axon arbor structure is broader that functionally necessary and becomes stable around the time of eye opening. We will also examine whether the periods of robust synaptic plasticity represent rearrangements of synaptic release sites within a fixed axon arbor scaffold. A finding of a broad structural scaffold in which synaptic contacts can form, break and rearrange may represent a relatively novel type of neural plasticity. By relating structure to function, we hope to gain clearer understanding of the structural mechanisms that underlie synaptic development. The goal of this project is to understand the how neurons form connections, called synapses, with each other. We propose to visualize how the structure of the axon terminals of presynaptic neurons change during development and how axonal form corresponds with synaptic function. Understanding how normal wiring of the nervous system is accomplished will provide insight into neurological disorders that result from aberrant connections, such as some forms of mental retardation, cognitive disorders and epilepsy.