耳鸣的产生与听皮层结构图谱的研究

Tinnitus is a common auditory disease and for which there is no effective medication or medical treatment. The most common cause of tinnitus is hearing loss due to aging, noise exposure and drug abuse. Currently the field is focusing on understanding the underlying mechanism of how tinnitus develops from the peripheral towards the central nerve system, but required structural information of the key neuronal circuit is still missing. In this study we set out to induce tinnitus in rats by salicylate treatment and combine positron-emission tomography (PET) and state-of-the-art high throughput 3-dimensional electron microscopy (3d EM) for functional and structural mapping of the auditory cortex. First, we will locate tinnitus-specific brain region in the cortex based on in vivo functional PET imaging, and then use the brain ultrastructural information obtained from 3d EM to determine tinnitus-specific synaptic plasticity changes, type of the synapses (excitatory or inhibitory), the region on post-synaptic cells (cell body, apical dendrite or basal dendrite), type of post-synaptic cell (pyramidal or stellate) as well as connectivity pattern, providing a neuronal circuit model of tinnitus. The study will reveal the underlying mechanism of tinnitus generation at neuronal circuit level. Gained knowledge will not only provide strong theoretical support for pathological and clinical researches of tinnitus but also inspire novel therapy for auditory dysfunction.

耳鸣是听觉神经系统的常见和多发病，目前仍缺乏有效的药物以及治疗方法。衰老、噪音以及药物滥用所引起的听功能障碍是诱发耳鸣最主要的因素。现有的研究主要聚焦于揭示耳鸣从外周到中枢神经系统完整的产生机制，但在关键神经环路方面仍缺乏必要的结构信息。本项目将以水杨酸盐诱导的大鼠耳鸣模型为研究对象，结合正电子发射断层扫描活体影像和最新的高通量三维电子显微镜技术对听皮层进行动态功能及超微结构成像。首先通过活体功能成像确定耳鸣在听皮层中发生的特征区域，再通过超微结构成像确定耳鸣特征神经突触的可塑性变化以及突触的类型（兴奋或抑制型），其在受体神经元上的位点（细胞体、顶树突或基树突），受体神经元的细胞类型（锥体细胞或星状细胞）以及相互连接方式等重要结构信息，并有望建立起耳鸣特征神经环路模型。以此初步揭示耳鸣产生的神经生物学机制，为耳鸣的新诊断方法、疗法和新药物的靶点提供强有力的理论支撑。

耳鸣是常发的听觉功能紊乱，其本质可能是听觉神经通路中关键核团的突触可塑性改变，但目前缺乏确凿和定量的结构学证据。针对这一现状，项目通过连续切片三维扫描电镜对小鼠听觉神经通路中的重要核团（包括耳蜗、耳蜗核以及听皮层）进行了突触尺度的神经解剖学分析。首先团队建立了完整耳蜗电镜样品制备方法（丁旭等, 听力学及言语疾病杂志, 2020）;并完成了国际首个成年小鼠耳蜗神经回路的大尺度电镜重构，并对耳蜗毛细胞神经编码带状突触的形态以及听神经上的突触支配进行了分类和量化（Hua et al., Cell Reports, 2021）;此外在项目研究过程中，为了更高效和客观的评价对象的听力阈值，团队还开发了自动化算法识别听性脑干反应的特征波形（Wang et al., iScience 2021）。这些成果为后续耳鸣相关的听觉神经通路的突触可塑性研究具有长远的影响。