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，来自半规管和耳石器官的传入反应有所偏离。 来自上面的附属结构所给予的连贯的机械刺激。这表明了进一步 通过毛细胞(HC)和初级传入电导以及HC-传入突触进行信号处理。 Hcs和传入神经元之间的并行突触传递模式使处理变得复杂，并且 将多个HC汇聚到单个传入。I型HC被传入的花萼包裹，形成一个 这两个元素之间有杯状的缝隙。相比之下，II型HCS突触连接到Bouton末端和/或 花萼的外表面，有相对较小的细胞贴合区域。进一步的复杂性是由三个因素引起的 HC-to-传入收敛类。在最简单的配置中，仅通过以下方式将HCS融合到传入 鲍顿的结局。在花冠末端发现了更复杂的东西，或者是简单的花萼包裹着一个 HC或AS复合体，其中传入细胞包括两个或多个HC。复杂性最高的出现在 通过Bouton和内外表面的组合接触I型和II型Hcs的二态末端 肾盏突触。先前在海龟身上的实验表明，对于肾盏末梢，快速兴奋性突触 通过谷氨酸能AMPA受体的传递，受K+、H+和Ca~(2+)积累的调节。作为对.的回应 HC去极化时，裂隙内离子浓度有动态变化。这些反过来又会影响响应 在I型HCS及其传入中，由于平衡电位和驱动力的变化 面朝缝隙的导体。因此，这些帽状触点的性能与 HC和传入电导则沐浴在体液外淋巴中。因此，现有的单电极 无论是在原地对HCs或其传入细胞进行生物物理实验，还是使用分离的细胞，都无法 剖析由独特体积产生的互惠相互作用导致的HCS和传入的贡献 联结两者的突触裂隙。我现在对孤立的前半环有了初步的生物物理结果 小白鼠的管状上皮细胞。这些实验表明，我将能够扩展和 改进一种哺乳动物制剂的开发，在这种制剂中我可以表征 突触裂隙与中枢神经系统与传入神经突触传递的生物物理特征 同时控制HC及其相关传入的膜电位的条件。 我将集中在两个方面：(1)暴露在动态环境中的I型HC导体的门控 突触裂隙；和(2)来自I型HCS的突触输入在花瓣内面和 II型HCS突触位于花萼的外表面，或在二型性传入纤维的末端。

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.