Optogenetic Infection and Optical Stimulation: A Study on Auditory Responses in Guinea Pig Cochlear Neurons

This study aims to establish an economically viable and easily accessible adult animal model for optogenetic activation of auditory neurons using adeno-associated viruses (AAVs) carrying ChR2(H134R) to explore the potential of cochlear optogenetics as a hearing restoration technology.

Healthy adult guinea pigs were used in the experiments. The viral vector AAV2/8-ChR2(H134R)-hSyn-eYFP was administered to the right cochlea via the round window membrane. The confocal microscopy and reverse transcription polymerase chain reaction (RT-PCR) were utilized to analyze the ChR2(H134R) expression localized to spiral ganglion neurons (SGNs). The auditory pathway activation was assessed by recording the optical compound action potential (oCAP) and acoustic compound action potential (aCAP) at various laser intensities.

The ChR2(H134R)-eYFP expression was confirmed in 90% of the tested animals, localized to the SGNs of the injected ear. Higher mRNA levels of ChR2(H134R) and eYFP were observed in the injected ear compared to the non-injected ear, while actin (Actb) mRNA levels were not significantly different. The oCAP was successfully elicited by a 470 nm blue light laser stimulus, with similar amplitudes and latency periods to those of aCAPs when the oCAP was evoked by 5.80 mW blue light and the aCAP was evoked by a 40 dB SPL click. The amplitudes of oCAPs increased with increasing laser intensity.

This study demonstrates the viability of optogenetic activation of the auditory system in adult guinea pigs through the transduction of AAV-ChR2(H134R) in SGNs. Cochlear optogenetics demonstrates potential as a hearing restoration technology, providing a basis for further clinical research and opening new avenues for investigation.