Ancestral Adeno-Associated Viral Vector Delivery of Opsins to Spiral Ganglion Neurons: Implications for an Optogenetic Cochlear Implant

Abstract

Purpose: Optogenetics is a transformative technology based on light-sensitive microbial proteins known as “opsins” that enable precise modulation of neuronal activity with pulsed light. Optogenetics has been proposed as a means to improve auditory implant outcomes by reducing channel interaction and increasing electrode density, but the introduction of opsins into cochlear spiral ganglion neurons (SGNs) in vivo has been challenging. Here, we test opsin delivery using a synthetically-developed ancestral adeno-associated viral (AAV) vector called Anc80L65. Methods: Wild type C57BL/6 mouse pups were injected via the round window of cochlea with Anc80L65 carrying opsin Chronos under the control of a CAG promoter. Following an incubation of 6-22 weeks, mice underwent cochleostomy and pulsed blue light was delivered to cochlear SGNs via flexible optical fiber. Results: Optically-evoked auditory brainstem responses (oABRs) and multiunit activity in the inferior colliculus (IC) were observed. Post-experiment cochlear histology demonstrated opsin expression in SGNs throughout the cochlear axis (mean=74%). Amplitude of optical responses increased with intensity of light, while latency of response decreased with increased intensity. Conclusions: This study is the first to describe robust SGN transduction and optically-evoked auditory electrophysiology using opsins in postnatal mice. Ultimately, this work may provide the basis for a new generation cochlear implant based on light will and inform new inner ear gene therapy approaches that focus on SGN regeneration