Optical Stimulation of the Auditory Pathway by Blue-Shifted Photoswitchable Glutamate Receptor Agonists.

耳内螺旋神经节神经元（SGN）的光刺激为人工耳蜗植入中使用的电刺激提供了未来的替代方案。神经元活动的光遗传学操纵是基于光敏蛋白的表达，这需要基因治疗。光遗传学的另一种替代方法是生物药理学，它对内源性受体起作用，不需要遗传操作。在“光开关”中，由Pau Gorostiza开发的靶向共价光开关（TCP）主要与离子型红藻氨酸受体GluK 1反应。先前在体外海马神经元上显示，最好的第一代化合物TCP 9在紫外光（380 nm）下激活天然GluK 1受体，并且在可见光（500 nm）下使受体失活。我们进行了初步研究的新一代blueTCP 1和blueTCP 2在体内通过应用该化合物的沙土鼠耳蜗通过圆窗。通过圆窗龛电极的耳蜗电图显示声诱发耳蜗颤噪和复合动作电位（CAP）振幅的保存，表明在存在TCP和没有急性毒性的情况下耳蜗生理正常。在使用光纤（λ = 473 nm）的光刺激下，我们观察到光学诱发的CAP（oCAP）。光脉冲辐射通量低于3 mW时可诱发oCAP，oCAP振幅在80 µs光脉冲时最大，重复频率高达1 kHz。这种性能使这些化合物成为光学SGN刺激的有趣工具。该项目旨在建立和表征在开发光学人工耳蜗的背景下使用blueTCP 1和blueTCP 2的SGN的体内药理学刺激。将解决两个主要方面：i）SGN对blueTCP/光刺激的响应的生理表征，以确定两种化合物中最合适的。ii）测试blueTCP在装配有耦合到光学耳蜗植入物的慢性药物递送系统的耳聋模型中用于光学听力恢复的平移潜力。

Light stimulation of spiral ganglion neurons (SGNs) in the ear provides a future alternative to electrical stimulation used in cochlear implants. Optogenetic manipulation of neuronal activity is based on the expression of light-sensitive proteins, which requires gene therapy. An alternative to optogenetics is offered by photopharmacology which operates on endogenous receptors and does not require genetic manipulation. Among the “photoswitches”, the Targeted Covalent Photoswitches (TCP) developed by Pau Gorostiza, mainly reacts with the ionotropic kainate receptor GluK1. It was previously shown in vitro on hippocampal neurons that TCP9, the best first-generation compound, activates native GluK1 receptor upon ultraviolet light (380 nm) and a deactivates the receptor upon visible light (500 nm). We performed a preliminary study of a new generation of blueTCP1 and blueTCP2 in vivo by applying the compound to the gerbil cochlea via the round window. Electrocochleography via a round window niche electrode showed a preservation of acoustically-evoked cochlear microphonic and a compound action potential (CAP) amplitude, suggesting a normal cochlear physiology in the presence of TCPs and an absence of acute toxicity. Upon light stimulation using an optical fiber (λ = 473 nm), we observed optically evoked CAPs (oCAPs). oCAPs could be evoked by light pulse radiant flux as low than 3 mW, oCAP amplitudes were maximum in response to 80 µs light pulse and were sizable up to a repetition rate of 1 kHz. This performance makes these compounds interesting tools for optical SGN stimulation. The project aims to establish and characterize in vivo photopharmacological stimulation of SGNs using the blueTCP1 and blueTCP2 in the context of developing the optical cochlear implant. Two main aspects will be addressed: i) physiological characterization of SGN responses to blueTCP/light stimulation to identify the most suitable of the two compounds.; ii) testing the translational potential of blueTCP for optical hearing restoration in a deafness model fitted with a chronic drug delivery system coupled to an optical cochlear implant.