SYNAPSE FORMATION AND REFINEMENT IN THE VISUAL SYSTEM

在哺乳动物的发育过程中，视觉皮层中的神经元从未成熟的细胞分化为具有复杂信息处理能力的复杂、相互关联的网络组成部分。在发育的关键时期，视觉皮层内数千个连接的精确程度得以建立，在此期间，未成熟的神经连接被视觉经验重塑，形成成人的连接模式。尽管这种依赖于活动的竞争在系统水平上已经成为许多研究的焦点，但在突触初始形成过程中单个突触发生的细胞和分子变化，以及随后在突触完善基础上的突触加强和减弱过程中发生的细胞和分子变化，我们知之甚少。本研究的中心目标是研究发育中的视觉皮层突触形成和完善的细胞和分子机制。具体来说，当皮层突触形成、加强和稳定，或减弱和消除时发生的分子和生理变化，将通过荧光标记突触蛋白的同步延时共聚焦成像和全细胞路径钳记录单个已识别突触的活动来实时研究。这项建议的具体目标是：(1)确定视觉皮层谷氨酸能神经元突触形成过程中发生的细胞和分子事件的序列；(2)确定视觉皮层神经元之间兴奋性突触中介导活动依赖性精细化的细胞和分子事件；(3)验证神经营养因子调节视觉皮层神经元之间谷氨酸能突触形成和/或精细化的假设。这些实验的结果对于全面理解视觉皮层发育的细胞和分子机制至关重要。这些结果也将为了解弱视的机制以及可能的治疗方法提供见解。更普遍的是，突触形成缺陷可能导致许多神经发育障碍——从智力迟钝到自闭症，再到精神分裂症。了解突触形成和完善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.