The biophysical roles of hair cell and calyx afferent ion channels in synaptic transmission between vestibular receptors and afferent nerves in mammals.

项目摘要 先前的前庭研究表明，半规管和耳石器官的传入反应偏离 从由覆盖的附属结构给予的连贯的机械刺激。这进一步表明， 毛细胞（HC）和初级传入传导的信号处理，以及HC-传入突触的信号处理。 HC和传入神经之间突触传递的平行模式使处理复杂化， 多个HC会聚到单个传入上。I型毛细胞被传入萼包裹，形成一个 两个元素之间的杯状裂缝。相比之下，II型HC突触到终末和/或终末上。 一花萼的外部面，具相对小的细胞并置的区域。进一步的复杂性是由三个 类HC到传入收敛。在最简单的配置中，HC仅通过 饰扣结尾。增加的复杂性被发现在花萼的末端，或者作为简单的花萼包围一个单一的 HC或复杂的肾盏，其中传入包括两个或更多的HC。最高的复杂性发生在 通过终扣和内、外表面的组合与I型和II型HC接触的二形末端 萼突触先前在海龟身上的实验已经表明，对于花萼末梢，快速兴奋性突触 通过谷氨酸能AMPA受体的传递受到K+、H+和Ca 2+积累的调节。响应于 HC去极化时，裂隙中离子浓度有动态变化。这些反过来又影响着应对措施 由于平衡电位和驱动力的变化，I型HC和它们的传入神经中 面对裂缝的电导。因此，这些肾盏接触的性质与 那些HC和传入电导沐浴在散装外淋巴液。因此，现有的单电极 对HC或其传入神经进行的原位生物物理实验，或使用分离细胞的生物物理实验， 剖析HCs和传入神经的贡献，这些贡献来自独特体积产生的相互作用 连接两者的突触间隙我现在有了孤立性前半月板的初步生物物理结果 小家鼠耳道上皮。这些实验表明，我将能够扩展和 完善的哺乳动物制备的发展，其中我可以表征的离子环境的 突触间隙和条件下毛细胞与传入纤维之间突触传递的生物物理特性 同时控制HC及其相关传入神经的膜电位的条件。 我将集中在两个方面：（1）门控的I型HC电导暴露在动态环境的 突触间隙;和（2）来自I型毛细胞的突触输入整合在花萼的内表面上， II型毛细胞在花萼的外表面或在二形传入纤维的终末上形成突触。

Project Summary Prior vestibular research has shown that afferent responses from semicircular canals and otolith organs deviate from the coherent mechanical stimulation imparted by the overlying accessory structures. This suggests further signal processing by hair cells (HCs) and primary afferent conductances, and by the HC–afferent synapse. Processing is complicated by the parallel modes of synaptic transmission between HCs and afferents, and the convergence of multiple HCs onto single afferents. Type I HCs are enveloped by an afferent calyx, creating a cup-shaped cleft between the two elements. By contrast, type II HCs synapse onto bouton endings and/or the external face of a calyx, with relatively small areas of cellular apposition. Further complexity is conferred by three classes of HC-to-afferent convergence. In the simplest configuration, HCs converge onto an afferent solely via bouton endings. Increased complexity is found at calyceal endings, either as simple calyces enveloping a single HC or as complex calyces where the afferent encompasses two or more HCs. The highest complexity occurs at dimorphic endings that contact both type I and II HCs via a combination of bouton and inner– and outer–face calyceal synapses. Prior experiments in turtles have shown that for calyceal endings, rapid excitatory synaptic transmission, via glutamatergic AMPA receptors, is modulated by K+, H+, and Ca2+ accumulation. In response to HC depolarization, there are dynamic changes in ion concentration in the cleft. These in turn impact responses in both the type I HCs and their afferents due to changes in the equilibrium potentials and driving forces for conductances facing the cleft. As a result, properties of these calyceal contacts are significantly different from those for HC and afferent conductances bathed in the bulk perilymph. Consequently, prior single-electrode biophysical experiments on either HCs or their afferents in situ, or using isolated cells, have been unable to dissect the contributions of HCs and afferents resulting from reciprocal interactions created by the unique volume of the synaptic cleft coupling the two. I now have preliminary biophysical results on isolated anterior semicircular canal epithelia in the mouse, Mus musculus. These experiments demonstrate that I will be able to extend and refine the development of a mammalian preparation in which I can characterize the ionic environment of the synaptic cleft and the biophysical characteristics of synaptic transmission between HCs and afferents under conditions where the membrane potentials of the HC and its associated afferent are controlled simultaneously. I will focus on two areas: (1) the gating of type I HC conductances exposed to the dynamic environment of the synaptic cleft; and (2) the integration of synaptic inputs from type I HCs on the internal face of the calyx and type II HCs synapsing either on the external face of the calyx, or on bouton endings of dimorphic afferents.