Experience-dependent development of neural circuits in the Xenopus visual system

描述（由申请人提供）：了解大脑中的神经回路如何使我们形成对环境的感知并引发行为反应一直是神经科学的长期目标。在我们能够阐明中枢神经系统中哪些细胞相互连接之前，不可能理解这些复杂的过程。绘制神经回路的传统工具存在局限性，这减缓了理解哪些细胞相互连接的进展;因此，我们对神经回路的发展知之甚少，特别是神经回路连接如何响应感觉体验或突触输入活动的差异而变化。应用嗜神经病毒来绘制神经回路将对我们理解神经回路的发展做出重大贡献。本研究项目的总体目标是了解神经回路如何发展，并阐明活动在这一过程中的作用，通过应用假狂犬病病毒介导的跟踪到一个模型系统，独特的适合在体内发育研究。此外，我们可以使用假型狂犬病毒介导的追踪来绘制分子定义的神经元类型的电路，例如GABA能神经元。GABA能神经元在中枢神经系统中占相对较小的比例，但它们精确地平衡了由数量多得多的兴奋性神经元产生的兴奋。中枢神经系统兴奋与抑制平衡的紊乱被认为是自闭症和精神分裂症等神经发育障碍的基础。这项建议的具体目标是：（1）使假型狂犬病病毒跨突触追踪方法适用于非洲爪蟾蝌蚪，（2）使用假型狂犬病病毒的逆行追踪来识别视顶盖神经元的突触前伙伴，并测试视觉体验是否影响顶盖细胞连接图，以及（3）使用假型狂犬病毒跨突触追踪来测试谷氨酸能或GABA能突触输入是否影响顶盖细胞连接图的形成。这些实验将使我们能够确定尚未确定的顶盖神经元的突触前伙伴，并直接测试视觉体验或突触传递是否改变了顶盖神经元的突触前伙伴的数量和类型。这些实验将有助于阐明调节神经回路发育的机制，而这种对大脑发育的基本理解对于开发治疗大脑疾病和损伤的新方法至关重要。此外，这些实验将扩大我们对GABA能回路发育的了解，并对自闭症和精神分裂症等神经发育障碍具有重要意义。 公共卫生相关性：了解大脑中哪些细胞相互连接对于理解大脑功能和治疗大脑疾病和损伤至关重要。该提案中的实验将扩展我们对神经元连接的知识，并对我们理解和治疗自闭症和精神分裂症等神经发育障碍具有重要意义。

DESCRIPTION (provided by applicant): Understanding how neural circuits in the brain allow us to form a percept of our environment and elicit a behavioral response has been a long-standing goal in Neuroscience. An understanding of these complex processes will not be possible until we can elucidate which cells connect to one another in the central nervous system. Conventional tools to map neural circuits have limitations that have slowed progress in understanding which cells connect to one another; thus, we know relatively little about the development of neural circuits, particularly how neuronal circuit connections change in response to differences in sensory experience or synaptic input activity. Application of neurotropic viruses to map neural circuits will make a significant contribution to our understanding of neural circuit development. The overall goal of this research project is to understand how neural circuits develop and to elucidate the role of activity in this process by applying pseudotyped rabies virus-mediated tracing to a model system uniquely amenable to in vivo developmental studies. Furthermore, we can use pseudotyped rabies virus-mediated tracing to map the circuitry of a molecularly-defined neuron type, such as GABAergic neurons. GABAergic neurons comprise a relatively small proportion of neurons in the central nervous system, but they exquisitely balance out the excitation produced by the far more numerous excitatory neurons. Perturbation in this balance of excitation to inhibition in the central nervous system is thought to underlie neurodevelopmental disorders like autism and schizophrenia. The specific aims of this proposal are to: (1) adapt the pseudotyped rabies virus trans-synaptic tracing method to Xenopus tadpoles, (2) to identify the presynaptic partners of optic tectal neurons using retrograde tracing with pseudotyped rabies virus and to test whether visual experience affects tectal cell connectivity maps, and (3) to test whether glutamatergic or GABAergic synaptic inputs affect the development of tectal cell connectivity maps using pseudotyped rabies virus trans-synaptic tracing. These experiments will allow us to both determine as yet unidentified presynaptic partners of tectal neurons, and also to test directly whether visual experience or synaptic transmission alters the number and type of presynaptic partners that a tectal neuron has. These experiments will help to elucidate the mechanisms regulating the development of neural circuits and this basic understanding of brain development is critical to developing new ways to treat brain illness and injury. Furthermore, these experiments will expand our knowledge of GABAergic circuit development and can have important implications for neurodevelopmental disorders like autism and schizophrenia. PUBLIC HEALTH RELEVANCE: An understanding of which cells in the brain connect to one another is critical to understanding brain function and to treating brain illness and injury. The experiments in this proposal will expand our knowledge of neuronal connectivity and can have important implications for our understanding and treatment of neurodevelopmental disorders such as autism and schizophrenia.