Targeted spiral ganglion neuron degeneration in parvalbumin-Cre neonatal mice.

The spiral ganglion neurons (SGNs) are the primary afferent neurons in the cochlea; damage to the SGNs leads to irreversible hearing impairment. Mouse models that allow selective SGN degeneration while sparing other cell types in the cochlea are lacking. Here, we investigated a genetic ablation method of the SGN using a Cre-responsive adeno-associated virus (AAV) vector expressing diphtheria toxin subunit-A (DTA). We microinjected AAV2-retro-FLEX-DTA-mCherry driven by the EF1a or hSYN promoter in neonatal parvalbumin-Cre (PV(Cre)) and wild-type strains via the posterior semicircular canal. Apoptotic markers were observed in the degenerating SGNs as early as 3 days. After 1 week, we assessed the SGN cell density, revealing an average degeneration of 60% for AAV-DTA driven by the EF1a promoter and 61% for that driven by the hSYN promoter. By 1 month, injected ears demonstrated a nearly complete loss of SGN, while hair cell morphology was intact. The auditory brain stem response result showed significantly elevated threshold shifts at 1 month, while the distortion-product otoacoustic emissions function remained intact. Furthermore, we show that our method did not effectively ablate SGN in adult PV(Cre) mice. We generated a neonatal mouse model with primary SGN degeneration in PV(Cre) mice, mimicking auditory neuropathy phenotype using an AAV Cre-dependent expression of DTA.