Glutamate release and uptake at cerebellar synapses

描述(申请人提供)：神经科学的一个基本原则是，突触是大脑中的功能单位，因此在精神状态中也是如此。每个突触的作用相对独立于它的邻居，因为它主要对它自己释放的递质做出反应，而对它的邻居的递质要么根本不反应，要么更少。突触小泡的胞吐作用通常被认为只发生在超微结构定义的突触前活动区。如果这是真的，不在突触间隙内的受体必须被扩散到突触间隙外的递质激活，或者根本不被激活。然而，AMPA受体介导的由攀爬纤维释放引起的量子事件在小脑皮质的Bergmann胶质细胞中被记录下来。这些量子事件与相邻的浦肯野细胞中记录的量子不一致，这些浦肯野细胞接受来自相同攀升纤维的输入，因此似乎胞吐作用可以发生在位于Bergmann神经胶质膜正对面的异位攀升纤维释放部位。如果异位释放是一种普遍现象，异位突触和神经-胶质细胞的相互作用更有可能是这种形式的串扰导致的，而不是由于突触裂隙内释放的溢出而获得的低浓度递质。利用电生理、光学和药理学方法，我们将确定异位释放的特征，包括它的钙依赖性，哪种类型的电压依赖性钙通道提供必要的钙内流，释放概率，以及异位释放对突触前受体激活的敏感性，所有这些都与传统活动区的释放相比较。此外，我们还将确定突触外间隙高浓度递质瞬变的优势，包括AMPA受体的不同钙通透性以及对Bergmann神经胶质突起运动性的影响。

DESCRIPTION (provided by applicant): A basic tenet in neuroscience is that the synapse is the functional unit in the brain, and therefore in mentation. Each synapse acts relatively independently of its neighbors in that it primarily responds to its own released transmitter and either not at all or much less so to that of its neighbors. Exocytosis of synaptic vesicles is generally assumed to occur only at ultrastructurally defined presynaptic active zones. If this is true, receptors not located within the synaptic cleft must be activated by transmitter that diffuses out of the cleft, or not be activated at all. However, AMPA receptor-mediated quantal events resulting from climbing fiber release are recorded in Bergmann glial cells in the cerebellar cortex. These quantal events are not coincident with quanta recorded in neighboring Purkinje cells which receive input from the same climbing fiber and therefore it appears that exocytosis can occur from ectopic climbing fiber release sites located directly across from Bergmann glial membranes. If ectopic release is a general phenomenon, heterosynaptic and neural-glial interactions are more likely to result from this form of cross-talk rather than from the low concentrations of transmitter achieved by spillover from release within synaptic clefts. Using electrophysiological, optical, and pharmacological approaches, we will determine the characteristics of ectopic release including its calcium dependency, which types of voltage dependent calcium channels provide the necessary calcium influx, release probability, and the sensitivity of ectopic release to presynaptic receptor activation, all in comparison to release at conventional active zones. In addition, we will determine the advantages of high concentration transients of transmitter in the extrasynaptic space including differential calcium permeability of AMPA receptors and effects on motility of Bergmann glial processes.