Cochlear sensitivity, essential for communication and exploiting the acoustic environment, results from sensory-motor outer hair cells (OHCs) operating in a structural scaffold of supporting cells and extracellular cortilymph within the organ of Corti (OoC). Cochlear sensitivity control is hypothesized to involve interaction between the OHCs and OoC supporting cells (e.g., Deiters' cells [DCs] and outer pillar cells [OPCs]), but this has never been established in vivo. Here, we conditionally expressed channelrhodopsins (ChR2) specifically in male and female mouse DCs and OPCs. Illumination of the OoC activated the nonselective ChR2 cation conductance and depolarized DCs when measured in vivo and in isolated OoC. Measurements of sound-induced cochlear mechanical and electrical responses revealed that OoC illumination suppressed the normal functions of OoC supporting cells transiently and reversibly. OoC illumination blocked normally occurring continuous minor adjustments of tone-evoked basilar membrane displacements over their entire dynamic range and OHC voltage responses to tones at levels and frequencies subject to cochlear amplification. OoC illumination altered the OHC mechanoelectrical transduction conductance operating point, which reversed the asymmetry of OHC voltage responses to high level tones. OoC illumination accelerated recovery from temporary loud sound-induced acoustic desensitization. We concluded that DCs and OPCs are involved in both the control of cochlear responses (which are essential for normal hearing) and the recovery from temporary acoustic desensitization. This is the first direct in vivo evidence for the interdependency of the structural, mechanical, and electrochemical arrangements of OHCs and OoC supporting cells that together provide fine control of cochlear responses.

SIGNIFICANCE STATEMENT A striking feature of the mammalian cochlear sensory epithelium, the organ of Corti, is the cellular architecture and supporting cell arrangement that provides a structural scaffold for the sensory-motor outer hair cells. The role of the supporting cell scaffold, however, has never been elucidated in vivo, although in vitro and modeling studies indicate the scaffold is involved in exchange of forces between the outer hair cells and the organ of Corti. We used in vivo techniques, including optogenetics, that do not disrupt arrangements between the outer hair cells and supporting cells, but selectively, transiently, and reversibly interfere with supporting cell normal function. We revealed the supporting cells provide continuous adjustment of cochlear sensitivity, which is instrumental in normal hearing.

耳蜗敏感性对于沟通和利用声学环境至关重要，是由感觉运动外毛细胞 (OHC) 在柯蒂氏器 (OoC) 内支持细胞和细胞外皮质淋巴的结构支架中运行而产生的。假设耳蜗敏感性控制涉及 OHC 和 OoC 支持细胞（例如 Deiters 细胞 [DC] 和外柱细胞 [OPC]）之间的相互作用，但这从未在体内得到证实。在这里，我们在雄性和雌性小鼠 DC 和 OPC 中特异性表达视紫红质通道蛋白 (ChR2)。当在体内和分离的 OoC 中测量时，OoC 的照明激活了非选择性 ChR2 阳离子电导和去极化 DC。声诱导耳蜗机械和电反应的测量表明，OoC 照明短暂且可逆地抑制了 OoC 支持细胞的正常功能。 OoC 照明阻止了音调诱发的基底膜位移在其整个动态范围内正常发生的连续微小调整，以及 OHC 电压对受耳蜗放大影响的水平和频率的音调的电压响应。 OoC 照明改变了 OHC 机电转导工作点，从而扭转了 OHC 电压对高电平音调响应的不对称性。 OoC 照明加速了暂时性大声音引起的声脱敏的恢复。我们得出的结论是，DC 和 OPC 参与耳蜗反应的控制（这对于正常听力至关重要）和暂时声脱敏的恢复。 这是第一个直接的体内证据，证明 OHC 和 OoC 支持细胞的结构、机械和电化学排列之间的相互依赖性，这些细胞共同提供了对耳蜗反应的精细控制。

意义声明哺乳动物耳蜗感觉上皮（柯蒂氏器）的一个显着特征是细胞结构和支持细胞排列，为感觉运动外毛细胞提供结构支架。然而，支持细胞支架的作用在体内从未得到阐明，尽管体外和建模研究表明支架参与外毛细胞和柯蒂氏器之间的力交换。我们使用了包括光遗传学在内的体内技术，这些技术不会破坏外毛细胞和支持细胞之间的排列，而是选择性地、短暂地、可逆地干扰支持细胞的正常功能。我们发现支持细胞可以持续调节耳蜗敏感性，这对于正常听力至关重要。