Auto-inflammatory challenge of the endolymphatic sac – Cochlear damage measured by distortion product oto-acoustic emissions

Abstract

Conclusion: Twenty-five rats were challenged by an immunologic attack of the endolymphatic sac. After 6 months, distortion product oto-acoustic emissions (DPOAE) revealed a dysfunction of the outer hair cells and immunological active cells were observed in the endolymphatic sac. This information could contribute to the understanding of Ménière’s disease. Objectives: This study investigated if an autoimmune challenge of the endolymphatic sac could affect DPOAE output measurements in rats. Also, a potential autoimmune cell infiltration of the endolymphatic sac was investigated. Methods: Eighteen Lewis rats were immunized with a crude endolymphatic sac extract in complete Freund’s adjuvant. Seven control animals were injected with Freund’s adjuvant in saline. Cochlear damage was estimated by DPOAE dynamics 3 weeks and 6 months after the immunization. Infiltrative cells in the endolymphatic sac were investigated with transmission electron microscopy. Results: The hearing assessment 6 months after immunization revealed a reduction of the DPOAE, on the full range of frequencies (2–63 kHz) in an average of the mean, of 2 dB ± 1.1 in the immunized group compared to the controls (p < 0.05). The same test showed a 2.5 dB decrease from 2 to 5 kHz (p < 0.01). Immunological active cells were observed in the endolymphatic sac in most of the immunized rats.

Keywords:

• Meniere’s disease
• endolymphatic sac
• rat
• autoimmunity
• distortion product oto-acoustic emissions (DPOAE)

Acknowledgments

Zhila Nikrozi is warmly acknowledged for excellent technical assistance. Lisbeth Meyer Petersen and Michael Guldbrandsen are thanked for assistance in animal care. This study was supported by Meniere og Tinnitus Foreningen and Ørelæge Hans Skouby’s og Hustru Emma Skouby’s Fond. We acknowledge the Core Facility for Integrated Microscopy, Faculty of Health and Medical Sciences, University of Copenhagen for access to TEM.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.