Korean J Otorhinolaryngol-Head Neck Surg.  2014 Sep;57(9):589-595. 10.3342/kjorl-hns.2014.57.9.589.

Damage of Spiral Ganglion Cell Induced by Ouabain Application in Cat

• Kim BY
• Bae WY
• Kim JR
• Lee TH

• KMID: 1726625
• DOI: http://doi.org/10.3342/kjorl-hns.2014.57.9.589

Abstract

BACKGROUND AND OBJECTIVES
Auditory neuropathy is a hearing disorder characterized by the absence or the marked impairment of the auditory brainstem responses with the preservation of the cochlear microphonics (CMs) and otoacoustic emissions. This suggests that outer hair cell (OHC) function is normal but proximal auditory function to OHCs is impaired. It is assumed that the lesion is localized at the level of the inner hair cells (IHCs), auditory nerve fibers, or the synapse between them. This study was aimed to observe the change of hearing threshold and pathology of spiral ganglion cell induced by ouabain application, and present basic data to explain the auditory neuropathy. MATERIALS AND METHOD: Twenty ears of twenty normal hearing cats were used in this study. Cats were treated with 100 microL ouabain (1 mM) applied on the round window. After three days, compound action potential (CAP) and CM were measured and the cochlea was obtained. Pathologic change of spiral ganglion cell was evaluated under light microscope after H&E stain. Normal saline was injected for the control group.
RESULTS
In the ouabain group, CAP threshold was increased in all tested frequencies (p<0.001) and the difference of CM threshold was not significant in all frequencies (p>0.05). There was significant difference between CAP and CM threshold shift (p<0.001). In the control group, there was no significant difference in CAP and CM thresholds. Light microscopic findings show that the condensed chromatin and nuclear fragments of spiral ganglion cells of an ear was exposed to ouabain, and outer hair cell and inner hair cell were not damaged.
CONCLUSION
This study shows that the CAP threshold was significantly increased but the CM threshold was not changed in the ouabain group. Ouabain induced damage of spiral ganglion cells. This study is not sufficient to explain auditory neuropathy because threshold shift of CAP is not obvious, but it would be helpful to explain that selective damage of spiral ganglion cell would be the mechanism of auditory neuropathy.

Keyword

Auditory neuropathy; Ouabain; Spiral ganglion cell

MeSH Terms

Action Potentials
Animals
Cats*
Chromatin
Cochlea
Cochlear Nerve
Ear
Evoked Potentials, Auditory, Brain Stem
Hair
Hearing
Hearing Disorders
Ouabain*
Pathology
Spiral Ganglion*
Synapses
Chromatin
Ouabain