Synaptic mechanisms in the auditory system

描述(申请人提供)：神经末梢被赋予丰富的各种递质的突触前受体，这些受体的某些类别的激活是众所周知的，以中介不同类别的药物的作用。然而，在中枢听觉系统中，这些受体的功能还没有被很好地理解。我们建议利用一个容易获得和研究得很好的听觉突触--Hold的花瓣，来探索几个新的突触前受体的作用机制、调节和生理功能。最受关注的将是突触前甘氨酸受体(GlyR)，它通过去极化肾盏神经末梢来调节兴奋性递质谷氨酸的释放增加。在使用膜片钳技术的实验中，我们将对比这些受体在花萼和突触后细胞中的生物物理性质，以获得亚基组成的证据。此外，我们还将确定这些受体在特定受体亚单位存在缺陷的小鼠突变体中的特性。其他实验将确定哪些第二信使途径调节这些受体，以及这些受体的激活如何与更知名的突触后受体协同工作。先前的数据表明，GABAA受体在GlyR表达时下调，这表明它们的表达或靶向机制存在耦合。因此，在发育研究中，我们将检查突触前GABAA受体和GlyR在突变小鼠神经末梢的协调表达，以确定GlyR功能的丧失是否对GABAA能传递有影响。最后，我们将探索花萼末端的NMDA反应的特性，它似乎具有不同于传统突触后NMDA受体的特性。总而言之，这些研究应该会显著扩大对听觉脑干中突触相互作用的理解，并有可能识别用于选择性控制听觉信号处理的新药物靶点。

DESCRIPTION (provided by applicant): Nerve terminals are richly endowed with presynaptic receptors for a variety of transmitters, and activation of some classes of these receptors are well-known to mediate the actions of diverse classes of drugs. In the central auditory system, however, the functions of these receptors is not well understood. We propose to take advantage of an accessible and well-studied auditory synapse, the calyx of Held, to explore the mechanisms of action, the modulation, and the physiological functions of several novel presynaptic receptors. Most attention will be given to the presynaptic glycine receptor (GlyR), which mediates an increase in the release of the excitatory transmitter glutamate by depolarizing the calyceal nerve terminal. In experiments using patch clamp techniques we will contrast the biophysical properties of these receptors in calyces and in postsynaptic cells to gain evidence of subunit composition. Additionally, we will determine the properties of these receptors in mouse mutants having defects in specific subunits of the receptor. Other experiments will determine what second messenger pathways modulate these receptors and how activation of these receptors function in concert with their better known postsynaptic counterparts. Previous data indicate that the GABAA receptors are down regulated upon expression of the GlyR, suggesting a coupling in the mechanisms of their expression or targeting. In developmental studies we therefore will examine the coordinate expression of presynaptic GABAA receptors and GlyR in nerve terminals of the mutant mice, to determine if loss of GlyR function has consequences for GABAergic transmission. Finally, we will explore the properties of an NMDA response in the calyx terminal, which appears to have properties distinct from conventional postsynaptic NMDA receptors. Together, these studies should significantly expand out understanding of synaptic interactions in the auditory brainstem and potentially identify new drug targets for selective control of processing of auditory signals.