Nicotinic Synaptic Mechanisms in Chick Ciliary Ganglion

描述（由申请人提供）：我们工作的长期目标是了解烟碱受体如何参与神经系统中的信号传导。烟碱受体存在于外周和中枢神经系统中，它们对于多种功能都很重要，包括运动控制、兴奋性控制、认知、记忆、麻醉、镇痛和奖励。当前提案的具体目标是结合实验和建模方法来探索烟碱受体参与毫秒级信号传导的基本机制。这些实验将在胚胎鸡睫状神经节的高度可访问的模型突触中进行。快速突触通常通过胞吐作用在神经末梢上高度特化的位点释放递质量子，并与这些位点相对的突触后膜中的高密度簇受体相互作用来发挥作用。然而，在睫状神经节中，有大量受体并不位于已知释放递质的特定位点对面。这些受体在释放后被激活的快速时间过程表明，递质必须直接释放到它们上；因此，这种释放是异位的，或非突触的。最近的一项建模研究基于对突触体积 (MCell) 的精确三维表示进行的数值模拟，支持了该系统中异位释放的可能性。在当前的提案中，我们将使用免疫电子显微镜获得的几何形状和受体分布的各种测量来完善 MCell 模型，并对异位模型和传统模型进行越来越严格的测试，以检验其重现使用全细胞记录方法获得的实际数据集的能力。我们还将测试该系统中的递质释放是否具有最近被证明通过异位释放操作的另一个突触的特征。这些研究应该增加我们对神经细胞上烟碱受体参与快速时间尺度信号传导的基本过程的理解。这些研究也可用于了解受体功能丧失或改变引起或加剧的病理状态的基础（例如癫痫发作、神经退行性疾病）。

DESCRIPTION (provided by applicant): The long term objective of our work is to understand how nicotinic receptors participate in signaling in the nervous system. Nicotinic receptors are found in both the peripheral and central nervous systems, where they are important for a variety of functions, including control of movement, control of excitability, cognition, memory, anesthesia, analgesia, and reward. The specific aim of the current proposal is to explore, using a combination of experimental and modeling approaches, fundamental mechanisms by which nicotinic receptors participate in millisecond time scale signaling. These experiments will be done in a highly accessible model synapse in the embryonic chicken ciliary ganglion. Fast synapses generally operate by the release of quanta of transmitter, via exocytosis, at highly specialized sites on a nerve terminal and their interaction with high-density clusters receptors in the postsynaptic membrane opposite those sites. In the ciliary ganglion, however, there are large numbers of receptors not located opposite specialized sites from which transmitter is known to be released. The rapid time course with which these receptors are activated following release suggests that transmitter must be released directly on them; such release is therefore ectopic, or non-synaptic. A recent modeling study, based on numerical simulations performed on accurate three-dimensional representations of the synaptic volume (MCell), has supported the possibility of ectopic release in this system. In the current proposal we will refine the MCell model, using a variety of measurements on geometry and on receptor distribution, obtained using immuno electron microscopy, and will subject ectopic and conventional models to increasingly demanding tests of their ability to recapitulate actual data sets obtained using whole cell recording methods. We will also test whether transmitter release in this system has the characteristics found for another synapse that has been recently shown to operate by ectopic release. These studies should increase our understanding of the fundamental process by which nicotinic receptors on nerve cells participate in rapid time scale signaling. These studies may also be of use in understanding the basis of pathological states brought about, or exacerbated by, loss or alteration of receptor function (e.g., seizure disorders, neurodegenerative disease).