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，信息由神经递质的时间特性和释放量编码。神经转运蛋白的释放受到突触前钙离子浓度变化的严格调控。突触前活动导致各种类型的钙通道的激活，因此钙从细胞外来源进入终末，此外，钙也可以以活动依赖的方式从细胞内的池中释放出来。钙浓度的动态变化使终端具有在多种释放模式下运行的能力。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。相反，在目前的提案中，我们建议检验以下假设：*通过不同类型的电压门控钙通道调节和控制神经递质释放的不同生理特性的钙内流。我们认为，突触前终末特定的电压门控钙通道(VGCC)的性质、密度和空间分布允许靶向钙内流在特定的活动模式下启动不同的神经递质释放模式。为了验证这一假说，实验计划分为三个目标：*1.VGCC在同一突触前终末的活动区之间的分布有何不同？不同类型的VGCC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来确定不同类型的VGCC在不同活动水平时对突触相互作用的贡献，而不同释放机制的性质将用定量分析来评估。我们将使用斜坡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在单个突触前终末活动区的空间分布。总之，这些实验将提供一幅复杂而全面的图景，说明在神经元活动过程中，钙是如何通过不同类型的VGCC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. **