Optical Studies of Single Hippocampal Synapses

描述(申请人提供)：人脑包含10^10个神经元，由10^13个突触连接成一个令人惊叹的网络，该网络是神经计算和认知功能的基础。人们普遍认为，突触构成了认知及其功能障碍的重要方面的底物。例如，依赖经验的可塑性，如记忆，可能会在单个突触的属性中表现出来。为了支持这些认知功能，个体突触被认为是自主运行的，具有不同的属性。因此，解开突触功能的基本方面需要对单个突触的研究。然而，突触是大脑中最小的功能单位(大小约1微米)，只包含少数给定类型的信号转导分子，对单个突触的功能分析仍然具有挑战性。因此，突触功能和可塑性的基本方面仍然存在争议。这项应用的目标是利用最近发展起来的基于脊椎双光子[钙]成像的光学技术来探索突触功能和可塑性的基本方面。这些技术具有检测啮齿动物脑片中海马区皮质突触的单个钙通透通道和受体开放的敏感性。由突触激活的NMDA-R介导的[Ca~(2+)]积聚是可以测量的，这一事实允许确定突触传递过程中打开的NMDA-R的数量和突触上的受体数量。这一问题对突触传递的噪声源和突触传递的动态范围具有重要的影响。NMDA-R的激活也可以用来检测谷氨酸在细胞外空间的扩散。因此，可以确定单个突触是否是独立的，或者一个突触释放的谷氨酸是否溢出以激活相邻突触的受体。这个问题对神经网络的记忆能力和突触可塑性的机制有重要的影响。最后，NMDA-R激活的成像可以用来开发一种在单个突触上进行光学量化分析的方法，从而可以直接测试单泡假说，并剖析突触短期可塑性的机制。我们希望以单个突触的功能和可塑性的核心描述结束。

DESCRIPTION (provided by applicant): The human brain contains >10^10 neurons connected by > 10^13 synapses into an awesome network that underlies neural computation and cognitive function. It is widely believed that synapses form the substrate of important aspects of cognition and its dysfunctions. For example, experience-dependent plasticity, such as memory, may express itself in the properties of individual synapses. To support these cognitive functions individual synapses are thought to function autonomously and have heterogeneous properties. Unraveling basic aspects of synaptic function therefore demands the study of individual synapses. However, synapses are the smallest functional units of the brain (size about 1 micrometer), containing only a handful of signal transduction molecules of a given type, and functional assays for single synapses have remained challenging. As a consequence, fundamental aspects of synaptic function and plasticity have remained controversial. The goal of this application is to explore fundamental aspects of synaptic function and plasticity using recently developed optical techniques based on 2-photon [Ca2+] imaging in spines. These techniques have the sensitivity to detect the opening of single Ca2+ permeable channels and receptors at hippocampal cortical synapses in rodent brain slices. The fact that [Ca2+] accumulations mediated by synaptically activated NMDA-Rs can be measured allows the determination of the number of NMDA-Rs opened during synaptic transmission and the number of receptors at synapses. This issue has important consequences for the sources of noise in synaptic transmission and the dynamic range of synaptic transmission. NMDA-R activation can also be used to detect the spread of glutamate in the extracellular space. Hence it is possible to determine if individual synapses are independent or if glutamate released at one synapse spills over to activate receptors at neighboring synapses. This issue has important consequences for the memory capacity of neural networks and the mechanisms of synaptic plasticity. Finally, imaging of NMDA-R activation can be used to develop a method of optical quantal analysis at single synapses, allowing a direct test of the univesicular hypothesis and a dissection of the mechanisms of short-term synaptic plasticity. We hope to end up with a core description of the function and plasticity of single synapses.