Time course of apoptotic cell death in guinea pig cochlea following intratympanic gentamicin application.
CONCLUSIONS
The present study showed that the molecular signal that promotes the death of cochlear hair cells (HCs) induced by intratympanic gentamicin application is significant before the manifestation of morphological and functional changes.


OBJECTIVE
The effect of agents that protect the HCs from aminoglycoside ototoxicity is influenced by the timing of their administration. However, morphological, functional and molecular changes in the cochlea in the early stage following aminoglycoside application have rarely been studied. Therefore, we examined the chronological changes in the cochlea following intratympanic gentamicin application.


METHODS
Small pieces of gelatin sponge soaked with gentamicin (40 mg/ml) were placed on the round window membrane of mature guinea pigs, and the tympanic bulla was filled with gentamicin solution. They were euthanized at 6, 12, 18, 24, and 48 h following gentamicin application. Auditory brainstem responses (ABRs) were measured before gentamicin application and immediately before euthanasia, and the extent of missing and TUNEL-positive HCs was evaluated.


RESULTS
ABR thresholds significantly increased 18 h or later following gentamicin application, and the loss of HCs was seen at 24 and 48 h. While functional and morphological changes were not evident until 18 h after gentamicin application, substantial amounts of TUNEL-positive HCs appeared at 12 h.
Suzuki
Mitsuya
M
Department of Otolaryngology Head and Neck Surgery, University of Tokyo, Tokyo, Japan. misuzuki-tky@umin.ac.jp
Ushio
Munetaka
M
Yamasoba
Tatsuya
T
D000287:Administration, Topical; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival; D053938:DNA Fragmentation; D004195:Disease Models, Animal; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D005500:Follow-Up Studies; D005839:Gentamicins / Q000008:administration & dosage*; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000473:pathology*; D020287:In Situ Nick-End Labeling; D011500:Protein Synthesis Inhibitors / Q000008:administration & dosage*; D014432:Tympanic Membrane
D005839:Gentamicins; D011500:Protein Synthesis Inhibitors