Heptanol Application to the Mouse Round Window: A Novel Model for Studying Cochlear Regenerative Potential

Abstract

Objectives:

1) Introduce a novel model for studying cochlear lateral wall regeneration. 2) Describe implications of this study on research and treatment of human presbycusis. Background: Human presbycusis likely occurs secondary to senile degeneration of the stria vascularis (SV) and spiral ligament fibrocytes (SLFs). SLFs have a limited regenerative capacity. Augmenting this process may play a role in hearing preservation, recovery, or both. Few models currently exist, however, that can selectively and temporarily damage the cochlear lateral wall to study SLF regeneration.

Methods:

Heptanol, a gap junction uncoupler, was surgically applied to the round window of 25 normal hearing mice, with sacrifice at points 12 hours - 14 days post-treatment. Auditory brainstem response testing, electron microscopy, and immunostaining techniques were used to assess treatment response.

Results:

Click tone thresholds were significantly elevated (mean +40.5 dB sound pressure level) in all treated mice. Hearing loss plateaued on days 1-7, followed by near complete recovery thereafter. Ultrastructural analysis revealed selective SV injury and SLF apoptosis at the apical, middle, and basal turns. A marked reduction in ion channel immunostaining intensity occurred throughout the lateral wall but resolved by 2 weeks. 3-4 days, SLFs stained positive for EdU, a labeled thymidine analog and marker of cellular proliferation.

Conclusions:

This is one of the first models described to reliably and selectively induce lateral wall toxicity followed by full hearing recovery and SLF regeneration. Future study of the molecular and genetic expression profiles governing this process will be greatly facilitated by this technique.