3D ultrastructural analysis of the subcellular organisation of inner hair cells and of their innervation during ageing.

听力随着年龄的增长而逐渐衰退。这是由于内耳耳蜗中检测声音的细胞（感觉细胞，所谓的“毛”细胞）和/或将信号传递到大脑的神经功能障碍。听力缺陷是永久性的。早期表现是在噪音中难以理解言语，然后降低听到更安静和更高频率声音的能力，随着对更大声音和更低频率的敏感性降低而逐渐减弱。据估计，超过退休年龄的人中有70%患有某种形式的听力障碍。这是降低他们生活质量的一个主要因素。目前，改善这种状况仅限于助听器和人工耳蜗等技术解决方案。没有药物治疗。为了提高这些技术的有效性并发现治疗的药理学靶点，更好地了解随着年龄的增长发生的毛细胞和神经的渐进性变化是至关重要的。最近的研究表明，导致听力随年龄下降的一个主要因素是缓慢的渐进性损失，在生命的早期就开始了，耳蜗是一种神经纤维，通常将声音信息从耳蜗传递到大脑（传入纤维），并与感觉细胞-内毛细胞（IHC）连接，将声音信号转换为刺激神经的电信号。也可能有神经（“传出”纤维）的重组，这些神经将信息从大脑传递到传入神经末梢，以调节到达大脑的听觉信号。此外，有证据表明，国际人道主义协调委员会本身的内部组织也发生了变化。在我们目前的研究中，我们应用了两种三维电子显微镜（3DEM）技术来观察IHC的内部结构和周围接触神经纤维的分布。通过这些技术，我们已经证明了IHC中以前未被认识到的结构组织程度，并且能够绘制细胞周围所有传入神经末梢的分布和内部组织，这是一项以前没有完成的壮举，但由于应用了3DEM技术而成为可能。我们发现了一个由细胞膜和细胞器组成的连续网络，它似乎在结构上与细胞的突触机制（细胞和神经之间的信号传递界面）以及神经末梢的位置相关。初步工作还显示，IHC的细胞内组织破坏似乎与衰老期间神经纤维的损失相称。在拟议的项目中，我们将这些技术扩展到完全与细胞及其神经支配相关的变化。我们还将开发使用第三个3DEM技术，阵列断层扫描，它提供了组织的常规3D分析的潜力，而不需要其他两种技术所需的专业显微镜。该项目的中心目标是在细胞和亚细胞水平上绘制老化耳蜗中IHC内部结构的变化，并研究这些变化与传入末梢丧失之间的关系。我们还将确定IHC和其余传入神经的代偿性变化，以及传出神经的重组。该项目将对听力随年龄增长而恶化的细胞基础进行全面评估，并将汇集电子显微镜和3D分析、耳蜗解剖学、耳蜗生理学以及耳聋的分子和遗传基础方面的专业研究人员。这种协调的方法旨在产生新的方法和未来的合作，以进一步研究听觉系统的生命过程。

Hearing deteriorates progressively with age. This results from dysfunction of the cells in the cochlea of the inner ear that detect sound (the sensory cells, so-called "hair" cells), and/or the nerves that carry the signals to the brain. The hearing deficits are permanent. An early manifestation is difficulty in understanding speech in noise, then reduced ability to hear quieter and higher frequency sounds that progressively worsens with decreasing sensitivity to louder sounds and lower frequencies. An estimated 70% of those over retirement age suffer some form of hearing impairment. It is a major factor in reducing their quality of life. Amelioration of the condition is currently limited to technological solutions such as hearing aids and cochlear implants. There are no drug treatments. In order to improve the effectiveness of the technologies and to discover pharmacological targets for treatments, a better understanding of the progressive changes to the hair cells and nerves that occur with ageing is essential.Recent work has suggested that a major factor contributing to the deterioration of hearing with age is a slowly progressive loss, beginning quite early in life, of the nerve fibres that normally transmit sound information from the cochlea to the brain (afferent fibres), and which connect with the sensory cell - the inner hair cell (IHC) - that converts sound signals into the electrical signals that stimulate the nerves. There may also be re-organisation of the nerves ("efferent" fibres) that carry information from the brain to the afferent nerve terminals to modulate the auditory signals reaching the brain. In addition there is evidence of changes to the internal organisation of the IHCs themselves. In our current research we have applied two techniques for three-dimensional electron microscopy (3DEM) to characterise of the internal structures of IHC and the distribution of the contacting nerves fibres around it. With these techniques, we have demonstrated a previously unrecognised degree of structural organisation in IHC and have been able to map the distribution of all the afferent nerve terminals around the cell and the internal organisation, a feat not previously accomplished but made possible by the application the 3DEM technologies. We have found a continuous network of cellular membranes and organelles that appears to be structurally related to the synaptic machinery of the cell (the interface between the cell and the nerve where signals are transmitted) and to the position of the nerve terminals. Preliminary work has also shown disruptions to intracellular organisation of IHC that appear to be commensurate with loss nerve fibre loss during ageing. In the proposed project we will extend these techniques to fully characterise age-related changes to the cells and their innervation. We will also develop the use of a third 3DEM technique, array tomography, which offers the potential for routine 3D analysis of tissues without the need for the specialised microscopes that the other two techniques require. The central aim of the project is to map at the cellular and sub-cellular levels the changes to the internal structures of IHCs in the ageing cochlea and to examine the relationship between those and the loss of afferent terminals. We will also identify the compensatory changes to IHC and to the remaining afferent nerves, and the re-organisation of the efferent nerves. The project will provide a comprehensive assessment of the cellular basis of the deterioration of hearing with age.This application also will bring together researchers with expertise in electron microscopy and 3D analysis, cochlear anatomy, cochlear physiology and the molecular and genetic bases of deafness. This co-ordinated approach is designed to generate new approaches and future collaborations to further research into the life-course of the auditory system.