Extrasynaptic transmission: investigating synaptic vesicle fusion at non-conventional release sites in hippocampal neurons

概述：哺乳动物的大脑可以说是所有生物结构中最复杂的，科学家们非常有动力详细了解它是如何工作的。当我们谈论大脑活动时，其本质是单个脑细胞之间的信息交流，或者说“神经元”。尽管对这一过程有很多了解，但新的实验发现不断涌现，这些发现增加了我们对大脑功能的理解。这项提议将研究一个重要的，也是最近才发现的神经元对神经元通信的一个方面，它影响我们对大脑操作的知识。为了研究这一现象，将采用最先进的方法，使人们能够直接观察活着的脑细胞中分子的运动。这样的研究极大地增加了我们对大脑如何在最基本层面上工作的知识，并可能对理解大脑疾病的形式，甚至启发新的、更复杂的计算机技术的设计产生重要影响。细节：大多数神经元到神经元的信息传递依赖于从源神经元到靶神经元的化学“递质”的释放。递质释放是一个复杂的过程，需要许多不同类型的特定分子。它们集中在神经元中被称为突触前终末的特殊位置，因此公认的观点是，这些终末是脑细胞中唯一可以释放递质的位置。然而，最近，研究人员发现这种想法是不准确的：在某些类型的神经元中，递质可以在来源神经元内的其他“非专门化”位置释放。这被称为“超突触释放”，字面意思是“从突触前终末释放”。然而，允许这一过程发生的机制尚不清楚。对于突触外释放是如何实现的，最可能的解释是，释放递质所需的分子机器可以很容易地从正常的突触前终末转移到神经元的新部分。然而，对这一想法的确认、对其进行控制的方式以及实际上需要哪些类型的机器仍有待确定。了解这一点将极大地扩展我们对化学神经传递的必要和充分组成部分的理解，并将在本提案中进行研究。实验将依赖于研究递质释放的一个重要系统：生长在玻璃上的神经元形成微型大脑电路。有了这个系统，可以用显微镜和灵敏的相机在活细胞中观察到突触前分子。第二种类型的实验方法甚至将允许以超出光学显微镜限制的分辨率观察神经元，以便获得有关突触外释放部位结构的详细信息。使用这些方法，实验将集中于研究释放部位是如何构建的，表征它们的特性，并将它们与正常的突触前终末进行比较。突触外释放的概念是神经生物学中的一个新兴主题，在促进脑细胞之间的交流方面具有重要的潜在作用。这使得它成为一个非常值得研究的领域。此外，对递质释放机制的不正确控制被认为与一些与大脑相关的疾病有关；因此，了解这一基本过程甚至可能为治疗各种形式的大脑疾病提供线索。

Overview: The brain of a mammal is arguably the most sophisticated of all biological structures and scientists are very motivated to understand, in detail, how it works. When we talk about brain activity, the essence of this is the communication of information between individual brain cells, or 'neurons'. Although a great deal is known about this process, new experimental findings which add to our understanding of brain function are emerging all the time. This proposal will examine an important and only recently identified aspect of neuron-to-neuron communication which impacts on our knowledge of brain operation. To investigate this phenomenon, state-of-the-art methods will be employed which allow movements of molecules in living brain cells to be directly observed. Research like this adds greatly to our knowledge of how the brain works at the most fundamental level and could have important implications for understanding forms of brain disease or even inspiring the design of new and more sophisticated computer technology. Detail: Most neuron-to-neuron information transfer relies on release of a chemical 'transmitter' from a source neuron to a target neuron. Transmitter release is a complex process requiring lots of different types of specific molecules. These are concentrated at specialized sites in neurons known as presynaptic terminals, and the established view is that these terminals are therefore the only location within a brain cell where transmitter release can occur. Recently, however, researchers have found this idea to be inaccurate: in certain types of neuron, transmitter can be released at other 'non-specialized' sites within a source neuron. This is called 'extrasynaptic' release, meaning literally 'release away from the presynaptic terminal'. The mechanism allowing this process to occur, however, is not understood. The most likely explanation for how extrasynaptic release is achieved is that molecular machines needed for transmitter release can be readily moved from normal presynaptic terminals to new parts of the neuron. Confirmation of this idea, the manner in which it is controlled and what types of machinery are actually necessary, though, remains to be established. A knowledge of this would greatly expand our understanding of the necessary and sufficient components of chemical-neurotransmission, and will be investigated in this proposal. Experiments will rely on an important system for studying transmitter release: neurons grown on glass to form miniature brain circuits. With this system, presynaptic molecules can be visualized in living cells with microscopes and sensitive cameras. A second type of experimental approach will even allow neurons to be viewed at a resolution beyond the limits of a light microscope so that detailed information about the structure of extrasynaptic release sites can be obtained. Using these methods, experiments will focus on investigating how release sites are constructed, characterizing their properties, and comparing them to normal presynaptic terminals. The idea of extrasynaptic release is an emerging theme in neurobiology and has important potential roles in contributing to the communication between brain cells. This makes it a very worthwhile area of study. Moreover, incorrect control of transmitter release machinery is thought to be associated with some brain-related diseases; therefore, understanding this fundamental process may even offer clues about the treatment of forms of brain-disorders.