Presynaptic calcium dynamics during short-term plasticity

神经元之间的交流是通过突触接触进行的，信息是由时间特性和神经递质释放量编码的。神经递质释放受到突触前钙浓度变化的严格调节和控制。突触前活动导致各种类型钙通道的激活，因此钙从细胞外来源进入末梢，此外钙也可以以活动依赖的方式从细胞内池释放。钙浓度的动态变化赋予终端在多种释放模式下运作的能力。长期以来，人们一直认为这些不同的突触前操作模式可以用钙浓度的变化来解释。相比之下，在目前的提案中，我们提出测试以下假设：***钙通过不同类型的电压门控钙通道进入调节和控制神经递质释放的不同生理特性。我们认为，突触前末端特定电压门控钙通道（vgcc）的特性、密度和空间分布允许靶向钙内流在特定活动模式下启动不同模式的神经递质释放。***为了检验这一假设；实验计划分为三个目标：****1。在同一突触前末端的不同活动区中，vgc的分布有何不同？不同类型的vgc在神经递质释放中起什么作用？* * * 2。重复活动如何调节钙微域以形成神经递质释放的短期促进？* * * 3。钙的升高是如何以及在什么情况下全球化的？***我们将使用药理学方法确定不同类型的vgc在不同活动水平下对突触相互作用的贡献，并通过定量分析评估不同释放机制的性质。我们将使用RAMP显微镜来确定钙微域的大小和分布，以及它们在突触活动增加时如何变化。最后，我们将使用电子显微镜来确定不同类型的vgcc在单个突触前末端活动区的空间分布。总之，这些实验将提供一个复杂而全面的画面，在神经元活动期间，钙是如何通过不同类型的vgc影响神经递质释放的。**

Communication between neurons occurs via synaptic contacts, information is coded by the temporal properties and the quantity of neurotransmitter release. Neurotramsitter release is tightly regulated and controlled by changes in presynaptic calcium concentration. Presynaptic activity leads to the activation of various types of calcium channels and hence calcium entry to the terminal from extracellular sources, in addition calcium can also be released from intracellular pools in an activity-dependent fashion. Dynamic changes in calcium concentration endow the terminal with the ability to operate at a wide variety of release modes. It has been long believed that that these various modes of presynaptic operation can be explained by changes in calcium concentration. In contrast, in the current proposal we propose to test the following hypothesis: ***Calcium entry via different types of voltage gated calcium channels regulate and control distinct physiological properties of neurotransmitter release. We propose that the properties, the density, and the spatial distribution of specific voltage-gated calcium channels (VGCCs) in presynaptic terminals allows targeted calcium influx to initiate the different modes of neurotransmitter release under specific patterns of activity. ***In order to test this hypothesis; the experimental plan is divided into three objectives:****1. How does the distribution of VGCCs differs between active zones in the same presynaptic terminal? What role do different types of VGCCs play in neurotransmitter release? ***2. How does repetitive activity modulate calcium microdomains to shape short-term facilitation of neurotransmitter release? ***3. How and under what circumstances are calcium elevations globalized? ***We will use pharmacological approaches to determine the contribution of various types of VGCCs to synaptic interactions during various levels of activity, while properties of different release mechanism will be evaluated with quantal analysis. We will use RAMP microscopy to determine the size and distribution of calcium microdomains and how they change during increased synaptic activity. And finally we will use electron microscopy to determine the spatial distribution of various types of VGCCs in relation to the active zones in single presynaptic terminals. Altogether these experiments will provide a complex and comprehensive picture on how calcium entry during neuronal activity via different types of VGCCs shape neurotransmitter release. **