Understanding the neural basis of hearing function and dysfunction in vivo.

听觉系统是我们日常生活的关键，因为它允许我们感知所有不同形式的声音，从噪音到语音和音乐。这种感觉的灵敏度和动态范围是显著的，使我们能够检测到从像针掉下来一样安静到像爆炸或飞机起飞一样响亮的声音。它也是许多动物物种生存的关键，因为声音可以从身体周围的任何地方被检测到，并且处理声音信息的速度在感觉系统中是无与伦比的（这就是为什么时间紧迫的运动，如短跑比赛，以枪声开始，而不是，例如，闪光）。声音由位于内耳的极其敏感的感觉细胞检测，称为毛细胞。这些细胞的功能对于我们从声音刺激中提取信息的能力至关重要。大脑是如何发展这种能力的？当毛细胞功能失调时，例如损伤后，大脑如何适应？这些都是我们探索大脑如何工作的关键问题，以及理解听力障碍的生理基础。这项建议的目的是阐明听觉系统的复杂性是如何在发育过程中得到改善的，并确定外周感觉细胞的活动如何塑造大脑中作为听觉信息处理基础的反应。实现这一任务在技术上是不可能的在哺乳动物中，由于大脑的大尺寸和复杂性以及感觉毛细胞无法用于体内研究。因此，在这项研究中，我们建议使用较小的脊椎动物，斑马鱼。这种鱼是所谓的“听觉专家”之一，已经发展出一种与哺乳动物大致相似的听觉。这包括使用位于内耳内的感觉毛细胞，其通过称为机械电转导的过程将声学刺激转化为神经信号，该过程也发生在哺乳动物中。近年来，斑马鱼为我们理解听力和耳聋的遗传基础提供了宝贵的信息。对于这一提议至关重要的是，斑马鱼的小大脑尺寸（直径约为1 mm）和透明度使得在显微镜下观察整个大脑成为可能，同时由于遗传编码的荧光报告染料，可以解析单个细胞的声音诱导活动。这些好处，当与行为分析的可访问性相结合时，使斑马鱼成为一种理想的模式生物，以确定体内神经回路和感觉整合形成的机制。我们将使用在毛细胞和神经元中表达荧光报告染料的斑马鱼系。当毛细胞和听觉神经元受到声音刺激时，这些分子会增加它们的亮度，使我们能够在真实的时间内监测声音是如何从耳朵传递到大脑的。我们将联合收割机与斑马鱼细胞系相结合，在斑马鱼细胞系中，我们将破坏外周毛细胞的活动，通过使用一种称为光遗传学的技术使它们沉默，或者通过大声噪音破坏它们。这将使我们能够了解毛细胞如何影响大脑中听觉反应的编码，以及当毛细胞受损时这种变化如何。从长远来看，这项工作所获得的信息可以用来更好地了解听觉系统病理变化的机制，如噪声引起的听力损失。

The auditory system is key to our daily life, as it allows us to perceive sound in all of its different forms, from noises to speech and music. The sensitivity and dynamic range of this sense are remarkable, allowing us to detect sounds from as quiet as a pin drop to as loud as an explosion or an airplane taking off. It is also key for survival in many animal species, since sounds can be detected from anywhere around the body and the speed of processing sound information is unparalleled among sensory systems (this is the reason why time-critical sports such as sprint races start with a gunshot and not, for example, with a flash of light).Sound is detected by extremely sensitive sensory cells named hair cells that are located in the inner ear. The function of these cells is critical for our ability to extract information from acoustic stimuli. How does the brain develop this ability? How does the brain adapt when hair cells become dysfunctional, for example after damage? These are critical questions in our quest to understand how the brain works, as well as to understand the physiological basis of hearing disorders.The aim of this proposal is to elucidate how the complexity of the auditory system is refined during development and to determine how the activity of the peripheral sensory cells shapes the responses in the brain that underlie the processing of auditory information.Achieving this task is technically prohibitive in mammals, due to the large size and complexity of the brain and the inaccessibility of the sensory hair cells for in vivo investigation. Therefore, for this study, we propose to use a smaller vertebrate, the zebrafish. This fish is among the so called "hearing specialists", having developed a sense of hearing that works in a broadly similar way to that of mammals. This includes the use of sensory hair cells, located within the inner ear, that convert acoustic stimuli into neural signals by a process known as mechanoelectrical transduction, which also occurs in mammals. In recent years, the zebrafish has provided invaluable information towards our understanding of the genetic basis of hearing and deafness. Crucial to this proposal, the small brain size (~1 mm diameter) and transparency of the zebrafish, make it possible to observe the entire brain under a microscope, while resolving the sound-induced activity of individual cells thanks to genetically encoded fluorescent reporter dyes. These benefits, when combined with the accessibility for behavioural analysis, make the zebrafish an ideal model organism to identify the mechanisms underlying the formation of nerve circuits and sensory integration in vivo. We will use zebrafish lines which express the fluorescent reporter dyes in hair cells and neurons. These molecules increase their brightness when hair cells and auditory neurons are stimulated by sound, allowing us to monitor in real time how sound is processed from the ear to the brain. We will combine this with zebrafish lines in which will disrupt the activity of the peripheral hair cells, either by silencing them using a technique called optogenetics or by damaging them with loud noise. This will allow us to understand how hair cells influence the encoding of auditory responses in the brain and how this change when hair cells become damaged. In the long term, the information obtained with this work could be used to better understand the mechanisms underlying pathological changes in the auditory system, such as noise induced hearing loss.