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，对这些复杂过程的理解是不可能的。绘制神经回路图的传统工具存在局限性，这减慢了了解哪些细胞彼此连接的进展；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官体验或突触输入活动的差异而变化。应用嗜神经病毒绘制神经回路图将对我们理解神经回路的发育作出重大贡献。本研究项目的总体目标是了解神经回路是如何发展的，并通过将伪狂犬病毒介导的追踪应用于一个独特的适合体内发育研究的模型系统来阐明活动在这一过程中的作用。此外，我们可以使用伪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只占相对较小的比例，但它们能很好地平衡大量兴奋性神经元产生的兴奋。在中枢神经系统中，这种兴奋到抑制的平衡被扰动，被认为是自闭症和精神分裂症等神经发育障碍的基础。这项建议的具体目的是：(1)将伪狂犬病毒跨突触示踪方法应用于爪蟾蝌蚪；(2)利用伪狂犬病毒逆行示踪方法识别视觉顶叶神经元的突触前伙伴，并测试视觉体验是否影响顶叶细胞连接图；(3)利用伪狂犬病毒跨突触示踪方法测试谷氨酸能或gaba能突触输入是否影响顶叶细胞连接图的形成。这些实验将使我们既可以确定尚未确定的顶叶神经元突触前伙伴，也可以直接测试视觉体验或突触传递是否会改变顶叶神经元突触前伙伴的数量和类型。这些实验将有助于阐明神经回路发育的调节机制，对大脑发育的基本理解对于开发治疗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能回路发育的认识，并对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.