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建立精确和功能性连接的机制。神经营养因子调节视神经轴突树突和突触形成和稳定的假设将在活的发育中的大脑中得到验证。具体来说，神经营养因子脑源性神经营养因子（BDNF）控制轴突和树突树突形成以及突触形成/稳定的细胞和分子机制将在麻醉的蝌蚪中进行研究。非洲爪蟾的视觉系统提供了一个独特的脊椎动物模型，在这个模型中，神经元连接的发育可以在完整的胚胎中随着时间的推移而被跟踪。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）将结合在一起，实时跟踪突触前和突触后伙伴的形态分化以及视网膜与其目标光学顶盖之间突触连接的形成。通过成像单个视神经轴突末端和/或顶突神经元树突，同时观察完整动物的突触部位，将测试以下假设：

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.