Gentamicin uptake in the chinchilla inner ear.

Area of Science:

• Ototoxicology
• Inner Ear Physiology
• Pharmacokinetics

Background:

• Transtympanic gentamicin is used clinically, but its distribution and retention within the inner ear are not fully understood.
• Aminoglycoside ototoxicity can impact hearing and vestibular function, affecting treatment outcomes.

Purpose of the Study:

• To investigate the bilateral uptake and retention of gentamicin in inner ear structures after transtympanic administration.
• To determine the distribution pattern and cellular localization of gentamicin within the cochlea and vestibular system.

Main Methods:

• Middle ear gentamicin application in a chinchilla model via minipump or injection.
• Histological analysis using anti-gentamicin immunohistochemistry and tritiated gentamicin autoradiography.
• Examination of temporal bone sections for gentamicin distribution in inner ear cells and structures.

Main Results:

• Gentamicin was detected and retained in Scarpa's ganglion, spiral ganglion cells, stria vascularis, and vestibular dark cells of the injected ear.
• No apical to basal gradient of gentamicin staining was observed in the spiral ganglion.
• Contralateral inner ear cells showed light staining, with a gradient in the dorsal cochlear nucleus suggesting transfer via the cochlear aqueduct.

Conclusions:

• Transtympanic gentamicin leads to significant bilateral uptake and retention in specific inner ear cells.
• Findings suggest the cochlear aqueduct as a pathway for contralateral inner ear exposure.
• Implications for cochlear implantation success in aminoglycoside-deafened patients and clinical use of transtympanic gentamicin therapy.