Neurotransmission at the vestibular calyx synapse

描述（由申请人提供）：本提案的目的是了解前庭I型毛细胞/花萼突触的突触传递。在羊膜嵴和胞室中描述了三类形态学传入事件。花萼单位只接触I型毛细胞（HCI），钮扣单位只接触II型毛细胞，二态单位同时接受来自钮扣和花萼纤维的神经支配（Goldberg, 2000）。这三类纤维的生理反应动态各不相同，花萼单位具有最不规则的放电模式和对旋转刺激的最低增益（Baird et al. 1988; Lysakowski et al. 1995）。这些差异的原因尚不清楚，但假设包括毛细胞机电转导（MET）特性的差异和初级前庭传入神经生物物理膜特性的差异。我们将研究HCI和相关的花萼传入，以确定这一独特末端的放电模式是如何由突触前和突触后机制形成的。在Aim 1中，膜片钳技术将用于研究一种新开发的制备中的离子电导率和递质释放，该制备与从沙鼠前厅器官中分离的HCI一起分离（Rennie & Streeter, 2006）。毛细胞递质释放引起的兴奋性突触后电流（EPSCs）将在各种条件下从花萼末端记录下来。在目标2中，我们将在整个胞体制备过程中使用硬探针记录毛束位移期间HCI的MET电流和受体电位。在Aim 3中，将采用数学建模技术来模拟HCI和花萼对谷氨酸的反应。在NEURON编程环境中，利用分段计算模型模拟花萼和附着轴突的无源电学特性。Na+、Ca2+和K+通道将使用Aims 1和2中获得的实验数据，用霍奇金-赫胥黎式速率常数进行建模。遗传算法将用于优化离子电导激活和失活的动力学参数。头晕是最常见的疾病之一。了解平衡感觉的基本细胞机制对于确定这种衰弱状况的原因和治疗奠定基础至关重要。实验和建模方法的结合将阐明感官信息是如何被HC1转换并通过它们的传入转换成神经代码的。

DESCRIPTION (provided by applicant): The goal of this proposal is to understand synaptic transmission at the vestibular type I hair cell/calyx synapse. Three classes of morphological afferents have been described in the amniote crista and utricle. Calyx units contact type I hair cells (HCI) exclusively, bouton units contact type II hair cells only & dimorphic units receive innervation from both bouton & calyx fibers (Goldberg, 2000). The physiological response dynamics of these three classes of fibers vary, with calyx units having the most irregular firing pattern & the lowest gains to rotational stimuli (Baird et al. 1988; Lysakowski et al. 1995). The reasons for these variations are unclear, but are hypothesized to include differences in hair cell mechano-electrical transduction (MET) properties & differences in the biophysical membrane properties of primary vestibular afferents. We will study HCI & associated calyx afferents to determine how firing patterns in this unique terminal are shaped by both pre- & post-synaptic mechanisms. In Aim 1, patch clamp techniques will be used to study ionic conductances & transmitter release in a newly developed preparation of calyx terminals isolated together with HCI from gerbil vestibular organs (Rennie & Streeter, 2006). Excitatory postsynaptic currents (EPSCs) resulting from hair cell transmitter release will be recorded from calyx terminals under a variety of conditions. In Aim 2 we will record MET currents & receptor potentials from HCI during displacement of the hair bundle with a stiff probe in a wholemount utricle preparation. In Aim 3, mathematical modeling techniques will be employed to simulate HCI & calyx responses to glutamate. The passive electrical properties of the calyx & attached axon will be simulated with a segmented computational model in the NEURON programming environment. Na+, Ca2+ and K+ channels will be modeled with Hodgkin-Huxley style rate constants using the experimental data obtained in Aims 1& 2. A genetic algorithm wiil be used to optimize the kinetic parameters for the activation & inactivation of ionic conductances. Dizziness is one of the most common medical complaints. Understanding the basic cellular mechanisms of balance sensation is essential to lay the groundwork for identifying causes & cures for this debilitating condition. The combination of experimental & modeling approaches will elucidate how sensory information is transformed by HC1 & converted into a neural code by their afferents.