Synapse growth and elimination in mature CNS

 描述（由申请人提供）：长期目标是了解成人中枢神经系统中的突触结构如何支持学习和记忆。我们研究海马长时程增强（LTP），一种突触可塑性的形式，被视为学习和记忆的细胞基质。重点是树突棘，大脑中超过90%的兴奋性突触的微小突起，在LTP，学习和记忆过程中被修改，并在各种神经系统疾病中严重扭曲。最近，我们已经表明，最初饱和的LTP可以随后增加，如果超过1.5小时的LTP诱导事件之间的间隔，与100%的成功实现后，在成年小鼠海马4小时的间隔。这些研究结果支持了这一假设，即间隔事件的LTP从事的机制，可能是间隔的优势，集中学习。利用连续切片电子显微镜（3DEM）的3D重建，我们发现了突触结构的几个变化，随着时间的推移，LTP的初始饱和后表现出来。在体内和体外，许多突触都有新生区，动态边缘区域具有突触后密度，但缺乏通常在活动区发现的突触前囊泡。新生区迅速获得突触前囊泡，从而在30分钟内转化为活动区。新生区和活动区均扩大，最大的突触扩大发生在含有滑面内质网（SER）和多聚核糖体的棘上。我们将测试的假设，修改突触结构的能力最初是饱和的LTP，和突触需要时间来恢复或增长，为以后的增强做准备。我们将在进行更耗时的3DEM和免疫标记之前，在成熟小鼠海马中进行各种药理学和遗传操作后，用生理学验证成功的LTP诱导。我们的目标是测试以下关于增强机制的假设：1）受体和突触前对接位点必须在LTP初始饱和后扩大的突触处积累。2)依赖于SER的突触生长和棘簇形成有助于增强LTP。3)这种蛋白质合成依赖的突触生长是增强LTP所必需的。4)参与建立或稳定突触的候选分子的缺失破坏了LTP的饱和或增强。在完成这些目标后，我们将知道结构突触可塑性的哪些元素是LTP增强不可或缺的。结果将提供新的理解新生区域转换，突触生长和脊柱集群的机制，以及这些过程是否耦合到SER扩展，局部蛋白质合成和突触粘附在准备随后的增强最初饱和的LTP在成熟的小鼠大脑。这些结果最终将为修复功能失调的突触回路的新策略的开发提供信息。

 DESCRIPTION (provided by applicant): The long-term goal is to understand how synapse structure in the adult central nervous system supports learning and memory. We study hippocampal long-term potentiation (LTP), a form of synaptic plasticity that is viewed as a cellular substrate for learning and memory. The focus is on dendritic spines, the tiny protrusions that host more than 90% of excitatory synapses in the brain, are modified during LTP, learning, and memory, and are severely distorted in a variety of neurological disorders. Recently, we have shown that initially saturated LTP can be subsequently augmented if more than 1.5 hours elapse between episodes of LTP induction, with 100% success achieved in adult mouse hippocampus after a 4 hour interval. These findings support the hypothesis that spacing episodes of LTP engages mechanisms that might underlie the advantage of spaced over massed learning. Using 3D reconstruction from serial section electron microscopy (3DEM), we have discovered several changes in synapse structure that manifest over time after the initial saturation of LTP. Both in vivo and in vitro, many synapses had nascent zones, dynamic edge regions that have a postsynaptic density but lack the presynaptic vesicles normally found at active zones. Nascent zones rapidly acquired presynaptic vesicles, thereby converting to active zones however by 30 min. By 2 hr., both nascent and active zones were enlarged, and the greatest synapse enlargement occurred on spines that contained smooth endoplasmic reticulum (SER) and polyribosomes. We will test the hypothesis that the capacity to modify synaptic structure is initially saturated by LTP, and time is required for synapses to recover or grow in preparation for later augmentation. We will verify successful LTP induction with physiology following various pharmacological and genetic manipulations in mature mouse hippocampus prior to performing the more time consuming 3DEM and immunolabeling. We aim to test the following hypotheses regarding mechanisms of augmentation: 1) That receptors and presynaptic docking sites must accumulate at synapses enlarged after the initial saturation of LTP. 2) That SER-dependent synapse growth and spine clustering serve the augmentation of LTP. 3) That protein synthesis-dependent growth of synapses is required for augmentation of LTP. 4) That absence of candidate molecules involved in building or stabilizing synapses disrupts saturation or augmentation of LTP. Upon completion of these aims we will know which elements of structural synaptic plasticity are integral to the augmentation of LTP. Outcomes will provide new understanding of the mechanisms of nascent zone conversion, synapse growth, and spine clustering, and whether these processes are coupled to SER expansion, local protein synthesis, and synapse adhesion in preparation for the subsequent augmentation of initially saturated LTP in the mature mouse brain. The results should ultimately inform the development of new strategies to repair dysfunctional synaptic circuits.