SYNAPSE FORMATION AND REFINEMENT IN THE VISUAL SYSTEM

在哺乳动物的发育过程中，视皮层中的神经元从没有几个突起的未成熟细胞分化为能够进行复杂信息处理的网络中精心设计、相互连接的组件。在发育的关键时期，视觉皮质内数千个连接的精致精确度被建立，此时，未成熟的神经连接被视觉经验重塑，以产生成人的连接模式。尽管这种活性依赖的竞争一直是系统水平上的研究重点，但人们对突触形成初期以及随后突触强化和减弱过程中单个突触发生的细胞和分子变化知之甚少。这项建议的中心目标是研究发育中的视皮层中突触形成和细化的细胞和分子机制。具体地说，随着皮质突触的形成和加强和稳定，或者被削弱和消除，发生的分子和生理变化将被实时研究，使用荧光标记的突触蛋白的同步延时共聚焦成像和对单个已识别突触的活动的全细胞路径钳记录。这一建议的具体目的是：(1)确定在视觉皮质谷氨酸能神经元之间突触发生的细胞和分子事件的序列；(2)确定在视觉皮质神经元之间的兴奋性突触中介导活性依赖的精细的细胞和分子事件；以及(3)检验神经营养因子调节视觉皮质神经元之间谷氨酸能突触的形成和/或细化的假设。这些实验的结果对于全面了解视皮层发育的细胞和分子机制至关重要。这些结果还将为弱视的机制以及可能的治疗方法提供深入的见解。更广泛地说，突触形成的缺陷可能会导致许多神经发育障碍--从智力低下到自闭症，再到精神分裂症。了解突触形成和细化的细胞和分子机制可以彻底改变我们识别、预防和治疗这些发育障碍的能力。

During mammalian development, neurons in the visual cortex differentiate from immature cells with few processes into elaborate, richly interconnected components of a network capable of complex information processing. The exquisite precision of these thousands of connections within visual cortex is established during a critical period of development, when immature neural connections are remodeled by visual experience to generate adult patterns of connectivity. Although this activity-dependent competition has been the focus of much research at the system level, there is very little known about the cellular and molecular changes that occur at individual synapses during initial synapse formation, and then subsequently during the synaptic strengthening and weakening that underlie synaptic refinement. The central goal of this proposal is to investigate the cellular and molecular mechanisms of synapse formation and refinement in the developing visual cortex. Specifically, the molecular and physiological changes that occur as cortical synapses form and are strengthened and stabilized, or are weakened and eliminated, will be studied in real-time using simultaneous time-lapse confocal imaging of fluorescently-tagged synaptic proteins and whole-cell path-clamp recording of the activity of individual, identified synapses. These specific aims of this proposal are: (1) to define the sequence of cellular and molecular events that occurs during synaptogenesis between glutamatergic neurons from the visual cortex, (2) to identify the cellular and molecular events that mediate activity-dependent refinement at excitatory synapses between visual cortical neurons, and (3) to test the hypothesis that the hypothesis that the neurotrophins regulate the formation and/or refinement of glutamatergic synapses between visual cortical neurons. The results of these experiments will be essential for a comprehensive understanding of the cellular and molecular mechanisms underlying the development of the visual cortex. These results will also provide insight into the mechanisms responsible for amblyopia, as well as possible approaches to therapy. More generally, defects in synapse formation are likely to cause many neurodevelopmental disorders-from mental retardation, to autism, to schizophrenia. Understanding the cellular and molecular mechanisms of synapse formation and refinement could revolutionize our ability to identify, prevent, and treat these developmental disorders.