Abstract
Background:
To assess and compare an effect of local cochlear ischemia (LCI) and coulomb-controlled iontophoresis (CCI) system stimulation on activity of the cochlea, with monitoring by transtympanic electrocochleography (TT-ECochG).
Method and Measures:
Young albino rabbits were used in this study. In both experimental models, the same surgical approach through the bulla to visualize the round window (RW) of the cochlea was used. The internal ear canal content was reached via a suboccipital posterior craniotomy. Laser-Doppler cochlear blood flow (LD-CBF) and TT-ECochG (cochlear microphonics [CM] and compound action potentials [CAPs]) were measured using a specially designed probe placed at the RW niche. The TT-ECochG was measured for 4, 8, and 12 KHz tone-bursts. The CCI system was connected to the same probe, and 3 minutes-effective current of no more than 25 microA was delivered. The internal auditory artery (IAA) compression inducing LCI was maintained for 3 minutes.
Results:
After the first CCI system stimulation, overshoot of CAP and CM amplitudes were observed reaching 140 to 180% of the baseline value, followed by a systemic reduction of both CAP and CM amplitudes for all test frequencies. After 5–10 minutes, CM amplitudes were reduced deeper than CAP amplitudes. The successive CCI stimulations induced regular and fast reduction of TT-EcochG, finally reaching a total or near-total reduction of CM and CAP during 20–30 minutes of observation. In all ears following IAA compression, CBF was reduced to a background level. Simultaneously monitored CM/CAP amplitudes showed systematic decrease, nearly to background values. After reperfusion, CM systematically recovered in the same way for all compressions stabilizing near the baseline. After the first ischemic/reperfusion episode, the CM amplitude for all frequencies was reduced ∼5–10%, whereas the reduction was 10–20% after subsequent episodes. At all frequencies, the CAP began to recover within several minutes and showed serious changes in waveform morphology.
Conclusions:
Both CCI and LCI affected activity of the cochlea, which was manifested by a CM/CAP amplitude reduction: CCI was found to be a more destructive factor; CM/CAP amplitude reduction for higher frequencies was deeper than for lower frequencies, revealing that the base of the cochlea is more susceptible for damage than the apex.