Secondary Degeneration of Auditory Neurons after Topical Aminoglycoside Administration in a Gerbil Model

Abstract

Hair cells in the cochlea can be damaged by various causes. Damaged hair cells can lead to additional destruction of parts of the auditory afferent pathway sequentially, which is called secondary degeneration. Recently, researches regarding cochlear implants have been actively carried out for clinical purposes; secondary degeneration in animals is a much more practical model for identifying the prognosis of cochlear implants. However, an appropriate model for this research is not established yet. Thus, we developed a secondary degeneration model using an ototoxic drug. 35 gerbils were separated into four different groups and kanamycin was applied via various approaches. ABR was measured several times after drug administration. SGCs were also counted to identify any secondary degeneration. The results showed that outer and inner HCs were damaged in all kanamycin-treated groups. Twelve weeks after kanamycin treatment, the round window membrane injection group showed severe subject differences in hair cells and SGC damage, whereas the gelfoam group showed consistent and severe damage in hair cells and SGCs. In this study, we successfully induced secondary degeneration in hair cells in a gerbil model. This model can be used for various purposes in the hearing research area either for treatment or for preservation.

Distribution and Afferent Effects of Transplanted mESCs on Cochlea in Acute and Chronic Neural Hearing Loss Models

“…Although this was not confirmed in the acute group of the current study, structure of the organ of Corti and possibly the structure of stria vascularis remained with probable survival of supporting cells which maintains the endolymphatic conditions. Conversely, KM induced SGN loss and flat epithelium, causing secondary degeneration [19]. In the present study, similar results were obtained in chronic model partially.…”

Hearing loss, stem cells, and photobiomodulation

“…As the loss of cochlear hair cell maintains, connecting neural structures consequently degenerate. 9 This secondary degeneration of neural structure is very critical for current hearing rehabilitation strategies (Fig. 1A).…”

Applications of photobiomodulation in hearing research: from bench to clinic

“…High-level noise or ototoxic drugs can trigger IHC synaptopathy, reducing the peak amplitude of the auditory brainstem response (ABR) without changing the threshold [41][42][43][44]. The auditory and spiral ganglion neurons can also be either primary or secondary targets of external insults [45,46]. Damage to the myelin or satellite cells of nerve fibers delays signal transport, triggering encoding deficits or rendering temporal processing inadequate [47].…”