Synaptic mechanisms underlying vestibular nerve fiber activity

描述（由申请人提供）：内耳的前庭器官将有关头部运动的信号传递给大脑，导致维持凝视和平衡以及平衡和方向感知的运动反射。因此，前庭系统的功能障碍会严重影响我们日常生活的能力。周围前庭功能障碍，如良性阵发性位置性眩晕（BPPV）和梅尼埃病，导致眩晕和其他症状的致残发作。为了分析这些疾病的病理生理学，了解头部运动信号如何在前庭外周器官中处理是至关重要的。在嵴，半规管的感觉器官，感觉毛细胞，响应头部旋转与偏转的毛束，激活毛细胞受体电位。I型毛细胞接近于完全被传入前庭神经纤维的突触后萼末端包被，这是前庭外周的独特特征，而II型毛细胞与具有更常规的终末的纤维接触。这些毛细胞类型的神经支配模式是相当复杂的，但遵循特定的形态生理模式，并且导致传入纤维在其响应特性方面存在差异，例如在其静息放电的规律性、其对外部刺激的响应特性方面 和传出输入。在这里，我们调查在高度专业化的I型毛细胞/萼突触的突触传递，目的是了解的机制，背后的放电模式的萼传入纤维。我们已经开发了一种2-4周龄啮齿动物的离体嵴的制备方法，用于同时进行I型毛细胞和花萼传入的电生理记录，以解决一些问题。使用共聚焦分析，我们还表征了花萼传入神经的形态特征，并使用抗体标记或荧光偶联标记物实时成像评估特定突触蛋白的定位。目的1：研究毛细胞膜电位与传入放电频率的关系。我们已经发现，谷氨酸积累和溢出的突触间隙诱导缓慢的膜电位变化和随后的调制传入放电率。我们研究了释放特性和突触能传递对突触后反应模式形成的贡献。目的2探讨是否存在从毛萼到I型毛细胞的胆碱能反馈回路，可能调节传入传递。在这里，我们提出了一个新的概念，包括一个花萼毛细胞反馈回路，可以解释一些在体内记录的反应模式的花萼传入放电。总之，我们研究了花萼传入放电特性的细胞机制。这些研究旨在更好地了解可能的前庭外周功能障碍，这是开发此类损伤治疗方法的先决条件。

DESCRIPTION (provided by applicant): The vestibular organs of the inner ear convey signals about head motions to the brain, resulting in motor reflexes that maintain gaze and balance as well as the perception of balance and orientation. Dysfunction of the vestibular system can therefore substantially affect the ability to lead our everyday lives. Peripheral vestibular dysfunctions, like benign paroxysmal positional vertigo (BPPV) and Meniere's disease, lead to disabling episodes of vertigo and other symptoms. To analyze the pathophysiology of such diseases, it is crucial to understand how head motion signals are processed in the vestibular peripheral organs. In the crista, the sensory organ of the semicircular canals, the sensory hair cells, respond to head rotations with a deflection of their hair bundles, activating hair cell receptor potentials. Type I hair cells are close to completely ensheathed by a postsynaptic calyx ending of the afferent vestibular nerve fiber, a unique feature of the vestibular periphery, and type II hair cells are contacted by fibers with the more conventional bouton endings. The innervation pattern of these hair cell types is quite complex, yet follows a specific morpho-physiological pattern, and results in afferent fibers with differences in their response properties for example in their regularity of resting discharge, their response properties to external stimuli and efferent inputs. Here we investigate synaptic transmission at the highly specialized type I hair cell/calyx synapse with the aim to understand the mechanisms that underlie firing patterns of the calyx afferent fibers. We have developed a preparation of excised cristae from 2-4 week old rodents to perform electrophysiological recordings from type I hair cells and calyx afferents, for some questions simultaneously. Using confocal analysis, we also characterize the morphological features of calyx afferents and assess the localization of specific synaptic proteins using antibody labeling or live imaging with fluorescently coupled markers. In Aim 1, we characterize the relation of hair cell membrane potential and afferent firing rate. We have found that glutamate accumulation and spillover in the synaptic cleft induces slow membrane potential changes and subsequent modulation of the afferent firing rate. We investigate the contribution of release properties and glutamatergic synaptic transmission to shaping the postsynaptic response pattern. Aim 2 investigates whether a cholinergic feedback loop from the calyx to the type I hair cell exists that may modulate afferent transmission. Here we put forward a new concept, including a calyx to hair cell feedback loop that may explain some of the in vivo recorded response patterns of calyx afferent firing. In Summary, we investigate the cellular mechanisms underlying calyx afferent firing properties. These studies are designed to gain a better understanding of possible vestibular peripheral dysfunctions, a prerequisite for developing treatments for such impairments.