TROPHIC INTERACTIONS DURING VISUAL SYSTEM DEVELOPMENT

描述：(改编自申请人摘要)建议的 研究将检查视网膜投射神经元的机制 与他们的中心目标建立精确和有效的联系。这个 神经元活动和神经营养因子相互作用的假说 协同调节轴突终末分支，以及 将在活体中测试突触的形成和稳定 发育中的大脑。具体地说，角色和相互作用 神经营养因子与动态过程中突触前、后的活动 视轴突终茎的细化与突触的形成 合同将在活体麻醉的蝌蚪身上进行检查。非洲爪哇 Levis视觉系统是一种唯一可访问的脊椎动物模型 视网膜神经节细胞间神经元连接的发育 他们的顶盖靶神经元可以随着时间的推移在完整的 胚胎。控制轴突生长、树枝形成和 复杂性将在与目标神经元的联系中进行研究。生长 以及个体荧光标记的视网膜的树枝状图案 神经节细胞轴突将随着时间的推移使用弱光进行追踪 视频显微镜和激光扫描共聚焦显微镜。这个 神经营养因子与突触前、后神经元的相互作用 轴突树枝形成动力学中的活动(轴突分支增加和 撤退)和轴突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活体顶盖， 麻醉的蝌蚪。神经元活动对脑功能的影响 轴突分枝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 视网膜内微量注射药物(钠通道 阻断)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分枝及其靶向表达 以及嵌合的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。这将提供同时的、单电池 轴突分枝动力学和细化及突触的观察 形成和稳定。活性与神经营养的作用 突触形成和稳定过程中的信号将通过 结合神经营养因子水平和神经营养因子的药理学扰动 轴突乔木同时活体成像的活动信号传递 和突触蛋白。这些研究的结果将提供 对脑内突触发生基本机制的有价值的见解 活的大脑，并将进一步加深我们对 控制视觉通路再生的发展，即 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.