Neurotransmission at the vestibular calyx synapse

描述(由申请人提供)：本方案的目标是了解前庭I型毛细胞/花冠突触的突触传递。在羊膜突起和椭圆囊中已描述了三种形态传入。花萼单位只接触I型毛细胞(HCI)，花冠单位只接触II型毛细胞，二型单位接受来自花冠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，其中花萼单位具有最不规则的放电模式&对旋转刺激的增益最低(Baird等人。1988年；Lysakowski等人。1995年)。这些差异的原因尚不清楚，但假设包括毛细胞机械-电转导(MET)属性的差异，即初级前庭传入的生物物理膜属性的差异。我们将研究与HCI相关的花萼传入，以确定突触前和突触后机制如何塑造这一独特终末的放电模式。在目标1中，膜片钳技术将用于研究一种新开发的从沙土鼠前庭器官分离的与HCI一起分离的花萼末端的离子电导和递质释放(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终末被记录下来。在目标2中，我们将在整个椭圆囊制备中用刚性探针记录毛束移位期间来自HCI的MET电流和感受器电位。在目标3中，将使用数学建模技术来模拟HCI和花萼对谷氨酸的反应。在神经元编程环境中，将使用分段计算模型来模拟花萼附着轴突的被动电学特性。利用AIMS 1和2中的实验数据，用Hodgkin-Huxley模型模拟Na、Ca和K通道。用遗传算法优化离子电导的激活和失活的动力学参数。头晕是最常见的医疗主诉之一。了解平衡感觉的基本细胞机制对于确定这种衰弱疾病的原因和治疗方法至关重要。实验和建模方法的结合将阐明感觉信息是如何由HCl转换的，并由它们的传入转化为神经代码。

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.