Effect of artificial endolymph injection into the cochlear duct on the endocochlear potential

Area of Science:

• Otoacoustic emissions
• Inner ear physiology
• Auditory neuroscience

Background:

• Endolymphatic hydrops, characterized by excess endolymph, is implicated in inner ear disorders like Ménière's disease.
• The endocochlear potential (EP), crucial for hearing, comprises positive (+EP) and negative (-EP) components affected by endolymphatic pressure.
• Previous studies suggest chronic hydrops decreases both +EP and -EP, but acute effects remain less understood.

Purpose of the Study:

• To investigate the immediate effects of acute endolymphatic hydrops on the positive endocochlear potential (+EP) and negative endocochlear potential (-EP).
• To differentiate the direct impact of increased endolymphatic pressure from chronic hydrops effects.
• To establish a reliable animal model for studying hydrops-induced inner ear changes and hearing loss mechanisms.

Main Methods:

• Acute endolymphatic hydrops was induced in guinea pigs via injection (no outlet) or perfusion (with outlet) of artificial endolymph into the cochlear duct.
• +EP was measured during fluid manipulation.
• -EP was assessed during anoxia following the procedures.
• Control experiments excluded artificial endolymph as a direct cause of -EP decrease.

Main Results:

• Injection of artificial endolymph caused a transient increase in +EP and a significant decrease in -EP magnitude.
• Perfusion of the cochlear duct prevented the decrease in -EP, indicating artificial endolymph itself did not cause this change.
• Results support that elevated endolymphatic pressure, even below current measurement resolution, can reduce -EP during hydrops.

Conclusions:

• Acute endolymphatic hydrops has distinct effects on +EP and -EP compared to chronic hydrops.
• The transient +EP increase may relate to basilar membrane shifts, though the exact mechanism requires further study.
• The developed animal model is valuable for isolating hydrops' direct effects on the inner ear and elucidating hearing loss mechanisms in conditions like Ménière's disease.