Dynamic distribution of ototoxic gentamicin entry into inner hair cells of mice

Conclusion: Dynamic distribution of ototoxic gentamicin entry into inner hair cells (IHCs) may cause an interruption of cochlear ribbon synapse. Objective: To explore the pattern of uptake of gentamicin into IHCs, as well as its possible contribution to hearing loss. Methods: Adult C57 mice were injected intraperitoneally with gentamicin (100 mg/kg, conjugated with Texas Red ester) continuously for 14 days. The hearing thresholds were detected by auditory brainstem response (ABR) examinations. Immunostaining and confocal microscopy were utilized to trace gentamicin distribution, as well as the expression of RIBEYE/CtBP2 in mouse IHCs. Scanning electron microscopy (SEM) observation was used to find possible alterations of stereocilia. Results: The distribution of gentamicin in IHCs was first found on the 4th day and the accumulation of gentamicin was increased significantly on the 7th day after treatment, corresponding to the maximal elevation of the hearing threshold. However, the accumulation of gentamicin on the 14th day did not show significant differences compared with the level found on the 7th day. In addition, the uptake of gentamicin was excessively identified at or near the synaptic ribbons of IHCs throughout the 4th, 7th, and 14th days after the treatment, suggesting that cochlear ribbon synapses could be affected by ototoxic gentamicin exposure.