Trophic interactions during visual system development

描述（由申请人提供）：拟议的研究将检查视网膜投射神经元与其中心靶点进行精确和功能性连接的机制。神经营养因子调节视神经轴突分支、突触形成和稳定的假设将在活的发育中的脑中进行测试。具体而言，神经营养蛋白脑源性神经营养因子（BDNF）控制轴突和树突状分支，突触形成/稳定的细胞和分子机制将在活的，麻醉蝌蚪检查。非洲爪蟾的视觉系统提供了一个独特的可访问的脊椎动物模型，其中神经元连接的发展，可以随着时间的推移，在完整的胚胎。胚胎学操作和体内成像技术（延时共聚焦显微镜和钙成像技术）将结合起来，在真实的时间，前和后突触的合作伙伴和视网膜和其目标视顶盖之间的突触连接的形成形态分化。通过对单个视神经轴突终末动脉和/或顶盖神经元树突动脉进行成像，同时观察完整动物中的突触部位，将检验以下假设： BDNF通过促进视神经轴突和目标顶盖神经元之间的突触稳定来调节发育中视网膜输入之间的活性依赖性竞争。 靶源性BDNF直接影响视神经轴突终末以调节轴突分支和突触形成。BDNF引起的视神经轴突复杂性的变化导致顶盖神经元突触复杂性的结构变化。 BDNF诱导树状视神经轴突中细胞内钙水平的局部变化，这些视神经轴突负责突触稳定和新分支的形成。 这些研究的结果将提供有价值的见解突触在活的大脑中的基本机制，并将进一步我们的视觉通路的发展，这是至关重要的维持正常的视觉功能的控制机制的理解。

DESCRIPTION (provided by applicant): The proposed studies will examine the mechanisms by which retinal projection neurons make precise and functional connections with their central targets. The hypothesis that neurotrophic factors modulate optic axon arborization, and synapse formation and stabilization will be tested in the live developing brain. Specifically, the cellular and molecular mechanisms by which the neurotrophin brain-derived neurotrophic factor (BDNF) controls axon and dendritic arborization, and synapse formation/stabilization will be examined in live, anesthetized tadpoles. The Xenopus laevis visual system offers a uniquely accessible vertebrate model in which the development of neuronal connections can be followed over time in the intact embryo. Embryologic manipulations and in vivo imaging techniques (time-lapse confocal microscopy and calcium imaging techniques) will be combined to follow, in real time, the morphological differentiation of pre- and post-synaptic partners and the formation of synaptic connections between the retina and its target optic tectum. By imaging individual optic axon terminal arbors and/or tectal neuron dendritic arbors while simultaneously visualizing synaptic sites in the intact animal, the following hypotheses will be tested: BDNF modulates activity-dependent competition between developing retinal inputs by promoting synapse stabilization between optic axons and target tectal neurons. Target-derived BDNF directly influences optic axon terminals to modulate axon arborization and synapse formation. The BDNF-elicited changes in optic axon arbor complexity lead to structural changes in tectal neuron synaptic complexity. BDNF induces localized changes in intracellular calcium levels in arborizing optic axons that are responsible for synapse stabilization and the formation of new branches. 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 visual pathways, that are critically important in the maintenance of normal visual function.