TROPHIC INTERACTIONS DURING VISUAL SYSTEM DEVELOPMENT

描述：（改编自申请人的摘要） 研究将检查视网膜投射神经元 与其中心目标建立精确的功能性联系。的 神经元活动和神经营养因子相互作用假说 协同调节轴突末端分支，以及 突触的形成和稳定将在活体中进行测试 大脑发育具体而言， 神经营养因子，以及动态过程中的突触前和突触后活动 视神经轴突终末支轴的加工和突触的形成 合同将在活的麻醉蝌蚪中进行检验。非洲爪蟾 LAEVIS视觉系统是唯一可访问的脊椎动物模型，其中 视网膜神经节细胞之间神经元连接的发育 它们的顶盖靶神经元可以在完整的大脑中随着时间的推移被追踪， 胚胎控制轴突生长、树枝状化和 将结合目标神经元来研究复杂性。增长 和树枝状模式的个人，荧光标记的视网膜 神经节细胞轴突将随着时间的推移使用低光水平 视频显微镜和激光扫描共聚焦显微镜。的 神经营养因子与突触前和突触后神经元之间的相互作用 轴突分支（轴突分支增加和 撤回）和轴突乔木的最终复杂性将被检查 通过干扰内源性神经营养因子水平和活性 投射或靶神经元的模式。神经营养因子水平 会被直接微量注射神经营养素改变功能 阻断抗体或对照溶液进入肝的顶盖， 麻醉的蝌蚪神经元活动的贡献， 轴突树枝化和细化的动力学将通过 选择性地改变突触前或突触后的活动， 将药理学试剂显微注射到视网膜中（钠通道 阻断剂）或直肠（谷氨酸受体激动剂或拮抗剂） 麻醉的蝌蚪体内显微成像的组合 单个视网膜神经节细胞轴突的轴突和靶向表达 以及嵌合荧光标记突触蛋白的体内成像 将被用来确定轴突形态和 突触结构这将同时提供单个细胞 观察轴突分支动力学和细化，以及突触 形成和稳定。活动和神经营养的作用 突触形成和稳定过程中的信号将通过 将神经营养因子水平的药理学扰动和 活动信号传导与轴突乔木的同时体内成像 和突触蛋白。这些研究的结果将提供 有价值的见解突触的基本机制， 活的大脑，并将进一步了解我们的机制， 控制视觉通路再生的发展， 对维持正常的视觉功能至关重要。

DESCRIPTION: (Adapted From The Applicant's Abstract) The proposed studies will examine the mechanisms by which retinal projection neurons make precise and functional connections with their central targets. The hypothesis that neuronal activity and neurotrophic factors interact synergistically to modulate axon terminal arborization, as well as synapse formation and stabilization will be tested in the live developing brain. Specifically, the roles and interactions between neurotrophins, and pre- and post-synaptic activity during the dynamic elaboration of optic axon terminal arbors and formation of synaptic contracts will be examined in live, anesthetized tadpoles. The Xenopus laevis visual system is a uniquely accessible vertebrate model in which the development of neuronal connections between retinal ganglion cells and their tecta target neurons can be followed over time in the intact embryo. The mechanisms controlling axon growth, arborization, and complexity will be studied in connections with target neurons. Growth and arborization patterns of individual, fluorescently labeled retinal ganglion cell axons will be followed over time using low-light level video microscopy and laser scanning confocal microscopy. The interactions between neurotrophins and pre- and post-synaptic neuronal activity in the dynamics of axon arborization (axon branch addition and withdrawal) and the final complexity of axonal arbors will be examined by perturbing endogenous neurotrophic factor levels and the activity patterns of projection or target neurons. Neurotrophic factor levels will be altered by direct microinjection of neurotrophins, function- blocking antibodies, or control solutions into the tecta of live, anesthetized tadpoles. The contributions of neuronal activity to the dynamics of axon arborization and refinement will be tested by selectively altering pre- or post-synaptic activity by direct microinjection of pharmacological agents into the retina (sodium channel blocks) or rectum (glutamate receptor agonists or antagonists) of the anesthetized tadpole. A combination of in vivo microscopic imaging of individual retinal ganglion cell axon arbors, and targeted expression and in vivo imaging of chimeric, fluorescently labeled synaptic proteins will be used to determine the correlates between axon morphology and synaptic structure. This will provide simultaneous, single cell observation of axon arborization dynamics and refinement, and synapse formation and stabilization. The roles of activity and neurotrophic signals during synapse formation and stabilization will be examined by combining pharmacologic perturbations of neurotrophic factor levels and activity signaling with simultaneous in vivo imaging of axonal arbors and synaptic proteins. The results of these studies will provide valuable insights into fundamental mechanisms of synaptogenesis in the living brain, and will further our understanding of the mechanisms that control the development of regeneration of the visual pathways, that are critically important in the maintenance of normal visual function.