Control of cochlear amplification by cellular and acellular elements of the mammalian cochlea

哺乳动物的听觉器官——耳蜗，使它们能够在巨大的频率和动态范围内以惊人的敏锐度和灵敏度听到声音。这种能力是由于哺乳动物耳蜗的新设计，它促进了感觉毛细胞、Corti感觉器官复杂细胞结构的支持细胞以及Corti器官的盖层和基底膜的细胞外基质之间的机电相互作用。支撑耳蜗的基底膜将声音分离成不同的频率成分，是耳蜗张力性的基础。充满液体的耳蜗中的粘性阻尼通过感觉运动外毛细胞的作用被抵消，外毛细胞增强并增强内耳毛细胞感知的耳蜗反应。由此产生的内毛细胞兴奋和随后的递质释放在听神经中产生信号流到大脑。毛细胞因暴露于强烈的声音、耳毒性、疾病、年龄和遗传疾病而受损时死亡。据世卫组织统计，世界人口中有5%患有无法恢复的听力损失。毛细胞再生和听力恢复令人兴奋的可能性现在变得可行。了解感觉毛细胞、支持细胞、盖层和基底膜之间复杂的体内相互作用，对于未来成功治疗听力损失至关重要，特别是那些涉及受损听力细胞的恢复或死亡感觉听力细胞的替换。因此，我们的主要目标是研究这种复杂的相互作用的耳蜗感觉上皮的元素背后的哺乳动物听觉的独特特征，使用体内测量支持的离体测量。这项研究计划的动机是我们实验室和其他地方最近的发现，表明耳蜗不同元素之间的频率和水平依赖的相互作用远比在耳蜗功能的经典模型中提出的要复杂得多，基底膜被动地分离声音的频率成分和外毛细胞放大和锐化基底膜反应，然后被视为尖锐，敏感的神经反应。为了实现我们的目标，我们记录了耳蜗的机械、声学、电和神经反应，并将它们与预测建模相结合，以验证我们的想法，并进一步了解Corti器官不同结构之间相互作用的功能意义。更具体地说，我们将确定外毛细胞兴奋输入的时间，优化其在适当的时间和地点将能量传递给耳蜗结构的运动。我们将研究细胞外电压在控制外毛细胞运动和毛细胞之间的电和机械相互作用方面的意义，这使得它们能够在具有非常高频率分辨率的超声波频率下增强耳蜗反应。因此，将对Corti器官的电学特性进行表征。被盖膜的力学特性，它们对刺激参数的依赖以及对耳蜗放大和耳蜗反应锐化的贡献将被确定。利用在支持细胞中表达通道视紫红质的光遗传学小鼠，我们将得出支持细胞调节毛细胞运作和调节Corti器官内能量纵向流动的机制。

The hearing organ of mammals, the cochlea, permits them to listen to sounds with remarkable acuity and sensitivity over enormous frequency and dynamic ranges. This ability is due to the novel design of the mammalian cochlea which facilitates electromechanical interaction between sensory hair cells, supporting cells of the sophisticated cellular architecture of the sensory organ of Corti, and the extracellular matrixes of the tectorial and basilar membranes that sandwich the organ of Corti. The basilar membrane, which supports the organ of Corti, separates sounds into constituent frequency components and underlies cochlear tonotopicity. Viscous damping in the fluid filled cochlea is counteracted through the action of sensory-motor outer hair cells, which boost and sharpen cochlear responses that are sensed by the inner hair cells. Resultant inner hair cell excitation and consequent transmitter release generates a flow of signals in the auditory nerve to the brain. Hair cells die when damaged by exposure to intense sounds, ototoxicity, disease, age and genetic disorders. According to WHO, 5% of the world population suffer from irrecoverable hearing loss. Exciting possibilities for hair cell regeneration and hearing restoration are now becoming available. Understanding of the complex in vivo interaction between the sensory hair cells, supporting cells and tectorial and basilar membranes is essential for the future development of successful treatments for hearing loss, especially those involving recovery of damaged, or replacement of, dead sensory hear cells. Therefore, our prime objective is to study this complex interaction between elements of the cochlear sensory epithelium underlying the unique features of mammalian audition using in vivo measurements supported by ex vivo measurements. This research proposal is motivated by recent discoveries from our laboratory and elsewhere showing that the frequency and level-dependent interaction between different elements of the cochlea are far more complex than is presented in classical models of cochlear function, with the basilar membrane passively separating the frequency constituents of sounds and outer hair cells amplifying and sharpening the basilar membrane responses, which are then seen as sharp, sensitive, neural responses. To achieve our goals we record mechanical, acoustic, electrical and neural cochlear responses and combine them with predictive modelling to validate our ideas and gain further insights into the functional significance of interaction between different structures of the organ of Corti. More specifically, we will determine the timing of outer hair cell excitatory input which is optimised to deliver energy to the movement of cochlear structures at the appropriate time and place. We will investigate the significance of extracellular voltage for controlling outer hair cell motility and electrical and mechanical interaction between hair cells, which permits them to boost cochlear responses at ultrasonic frequencies with very sharp frequency resolution. Accordingly, the electrical properties of the organ of Corti will be characterised. Mechanical properties of the tectorial membrane, their dependence on the stimulus parameters and contribution to the build-up of cochlear amplification and sharpening of cochlear response will be determined. Using optogenetic mice that express channel rhodopsins in supporting cells, we will derive the mechanisms by which supporting cells regulate hair cell operation and regulate the longitudinal flow of energy within the organ of Corti.