Imaging Synaptic Transmission of Individual Active Zones

描述（由申请人提供）：我们建议使用果蝇作为模型系统，以确定如何在各个活动区神经递质释放的调节。我们将在单个活动区成像突触囊泡融合，以定义释放概率、释放模式（自发与诱发）和释放可塑性在突触能突触中如何调节。神经递质可以通过动作电位后的诱发融合释放，或者在没有神经刺激的情况下通过囊泡的自发融合（称为“小囊泡”）释放。囊泡释放的两种模式已经在大多数突触中被发现，并且被认为发生在相同的活动区群体中，尽管这很难使用经典方法来定义。研究神经递质释放的一个主要技术限制是无法检查单个活性区的囊泡融合。突触传递的电生理学研究测量了大量释放位点上神经递质释放的突触后效应，排除了单个活性区如何参与和调节突触囊泡融合的分析。我们已经开发了转基因工具，允许Ca2+成像突触后谷氨酸受体激活后，单个囊泡融合空间可视化所有发生的胞吐事件，通过自发和诱发释放途径在果蝇NMJ，使我们能够定义一般规则囊泡融合事件在单个活动区。使用这些工具，我们已经开始表征自发发生或响应于动作电位的胞吐事件的空间和时间动态。我们也已经开始分析这两种融合模式在单一释放位点之间的关系。目前的数据表明，大多数活跃区参与这两种模式的融合，虽然释放概率是不相关的两种模式之间的释放，并在整个人口是高度可变的。事实上，一个子集的活动区是专门致力于自发释放，表明人口的突触后受体是唯一的激活这种模式的囊泡融合。使用这些新的转基因工具来可视化单个活性区胞吐，我们将描述单个释放位点如何工作，它们如何进行可塑性，以及它们如何促进诱发和自发融合。

DESCRIPTION (provided by applicant): We propose to use Drosophila as a model system for determining how neurotransmitter release at individual active zones is regulated. We will image synaptic vesicle fusion at single active zones to define how release probability, release mode (spontaneous versus evoked) and release plasticity is regulated at glutamatergic synapses. Neurotransmitters can be released through evoked fusion following an action potential, or by spontaneous fusion of vesicles (termed "minis") in the absence of nerve stimulation. The two modes of vesicle release have been found at most synapses and are assumed to occur across the same population of active zones, though this has been difficult to define using classical approaches. A major technical limitation for the study of neurotransmitter release has been the inability to examine vesicle fusion at individual active zones. Electrophysiological studies of synaptic transmission measure the postsynaptic effect of neurotransmitter release over a large population of release sites, precluding an analysis of how individual active zones participate in and regulate synaptic vesicle fusion. We have developed transgenic tools that allow Ca2+ imaging of postsynaptic glutamate receptor activation following single vesicle fusion to spatially visualize all exocytotic events occurring through both spontaneous and evoked release pathways at Drosophila NMJs, allowing us to define general rules for vesicle fusion events at single active zones. Using these tools, we have begun to characterize the spatial and temporal dynamics of exocytotic events that occur spontaneously or in response to an action potential. We have also begun analyzing the relationship between these two modes of fusion at single release sites. Current data indicate a majority of active zones participate in both modes of fusion, although release probability is not correlated between the two modes of release and is highly variable across the population. Indeed, a subset of active zones is specifically dedicated to spontaneous release, indicating a population of postsynaptic receptors is uniquely activated by this mode of vesicle fusion. Using these new transgenic tools to visualize single active zone exocytosis, we will characterize how single release sites work, how they undergo plasticity, and how they contribute to both evoked and spontaneous fusion.