Neurotrophin and Synaptic Plasticity

描述(由申请人提供)：神经营养因子(NTS)，一种对发育中的神经元的生存和分化至关重要的蛋白质家族，已被证明参与活性依赖的突触可塑性。在这个项目中，我们建议检验这样一种假设，即在发育中的突触中，NTS的分泌是由突触活动以一种尖峰模式依赖的方式触发的，而分泌的NTS的局部突触行为反过来又产生了对发育中的突触连接的长期的功能和结构修饰。我们将结合生理学、分子生物学和光学成像方法，将注意力集中在脑源性神经营养因子(BDNF)上，它是一种在发育中的神经系统中广泛表达的神经营养因子。本研究由三部分组成。在第一部分中，我们将使用大鼠或小鼠海马神经元的培养来检测外源性应用BDNF对谷氨酸和GABA能突触的功能和可塑性以及对轴突/树突形态和突触发生的急性影响。BDNF的突触特异性局部作用和潜在的信号机制也将被研究。在第二部分中，我们将研究内源性BDNF在活性诱导的突触功能和形态改变、活性依赖的BDNF分泌以及BDNF在神经元内和神经元间转运中的作用。在本论文的第一部分中，我们将利用发育中的非洲爪哇蝌蚪，研究BDNF对视网膜顶盖突触的功能和可塑性、顶盖轴突/树突动力学和突触发生的影响，以及内源性BDNF的运输和分泌。最后，我们将探讨脑源性神经营养因子在视网膜定位图和顶盖神经元方向选择性感受野发育中的作用。综上所述，这些体外和体内研究提供了独特的机会来解决几个基本的细胞生物学问题，这些问题涉及神经营养因子在依赖活动的精细化神经连接中的调节功能，并可能产生与我们对发育中的神经系统的生理学和病理学的基本理解相关的新信息。

DESCRIPTION (provided by applicant): Neurotrophins (NTs), a family of proteins essential for the survival and differentiation of developing neurons, have been shown to participate in activity-dependent synaptic plasticity. In this project, we propose to test the hypothesis that secretion of NTs at developing synapses is triggered by synaptic activity in a spike pattern-dependent manner and localized synaptic actions of secreted NTs in turn produce long-term functional and structural modification of developing synaptic connections. We will focus our attention on brain-derived neurotrophic factor (BDNF), a NT widely expressed in the developing nervous system, using a combination of physiological, molecular biological, and optical imaging methods. The proposed research consists of three parts. In PART I, we will use cultures of rat or mouse hippocampal neurons to examine the acute pre- and postsynaptic effects of exogenously-applied BDNF on the function and plasticity of glutamatergic and GABAergic synapses and on axon/dendrite morphology and synaptogenesis. The synapse-specific local actions of BDNF and underlying signaling mechanisms will also be investigated. In PART II, we will study the role of endogenously-secreted BDNF in activity-induced modifications of synaptic function and morphology in hippocampal cultures, activity-dependent BDNF secretion, and intra- and interneuronal trafficking of BDNF. In PART Ill, using developing Xenopus tadpoles, we will examine the in vivo effect of BDNF on the function and plasticity of retinotectal synapses, axon/dendrite dynamics and synaptogenesis in the tectum, and the trafficking and secretion of endogenous BDNF. Finally, we will investigate the role of BDNF in the development of retinotopic map and direction-selective receptive field of tectal neurons. Taken together, these in vitro and in vivo studies provide unique opportunities to address several fundamental cell biological issues concerning the modulatory function of neurotrophins in activity-dependent refinement of developing neural connections, and are likely to yield new information relevant to our basic understanding of physiology and pathology of the developing nervous system.