The participation of individual SGN types in optogenetically mediated signal transfection with CatCh in Mongolian gerbils

Optogenetic stimulation of spiral ganglion neurons (SGN) may enable future optical cochlear implants (oCI), which represent a crucial advance in frequency and intensity resolution. This study investigated the extent to which different SGN types were equipped with the channelrhodopsin Calcium transporting Channelrhodopsin (CatCh) for optical excitation by AAV-mediated transduction. The viral vector AAV-PHP.B-hSyn-CatCh-EYFP was injected into the modiolus of the left cochlea of Mongolian Gerbils at the minimum age of 8 weeks. Optically evoked brainstem responses (oABRs) were derived no earlier than 4 weeks after surgery. Stimulation was performed using a 200-μm optical fiber positioned in the cochlear round window coupled with a laser. Cryosections of the harvested cochleae (left n = 13, right n = 11) were stained with antibodies against peripherin, parvalbumin and green fluorescent protein to label SGN types as well as transfected neurons. Afterwards, confocal microscopy was performed and image stacks of 10 μm depth were analyzed. In total, the viral vector transduced 10 % of SGN type I as well as 28 % of SGN type II. There was no correlation between oABR amplitude and cell density of successfully transfected SGN type II, in contrast to type I. Cell density of SGN type I, but not of type II was significantly decreased after injection compared to the control ear only in the first cell type. In conclusion, it was shown that transfection of both cell types occurs. Thereby, transfection of SGN type II had no significant effect on derived oABR amplitudes.

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Artikel online veröffentlicht:
12. Mai 2023