Nitric oxide induces apoptosis of the hair cells of cochlea.
OBJECTIVE
Nitric oxide (NO) has a toxic effect on neuronal cells related to glutamate receptors. NO released from post-synaptic cells with glutamate receptors can induce nearby cell death. In this experiment, we examined the effect of NO on cochlear hair cells.


METHODS
Two concentrations, 0.5 and 0.1 molar concentration (MC) of 1-hydroxy-2-oxo-3-(3-aminopropyl)-3-isopropyl-1-triazene (NOC-5), which is a NO donor, were placed on the round window of the guinea pig cochlea and its morphological changes were investigated at 12, 28, 72 h after the treatment.


RESULTS
By the trypan blue dye extrusion method, the cell death was recognized in the outer hair cells at the percentage 0, 36.0+/-6.6, 4.9+/-1.2% at 12, 28, 72 h after treatment respectively in the group 0.5 MC NOC-5, but no inner hair cell death was recognized. In the group of 0.1 MC NOC-5 and control any cell death was not detected. Transmission electron microscopy revealed this cell death was characteristic of apoptosis.


CONCLUSIONS
The findings that apoptosis was induced in the outer hair cells of the organ of Corti by NO suggests the possibility that the cochlea is affected when extra NO release occurs there, leading to cochlear dysfunction.
Yamane
Hideo
H
Department of Otolaryngology and Head & Neck Surgery, Osaka City University Graduate School of Medicine, Osaka, Japan. ent-yamane@med.osaka-cu.ac.jp
Takayama
Masahiro
M
Sunami
Kishiko
K
Iguchi
Hiroyoshi
H
Kanazawa
Akimori
A
Tokuhara
Yasutake
Y
Nishiura
Hiroshi
H
Nishimura
Keizou
K
Tao
Shu Dong
SD
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D003051:Cochlea / Q000473:pathology / Q000648:ultrastructure; D016166:Free Radical Scavengers / Q000633:toxicity*; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000166:cytology* / Q000187:drug effects* / Q000648:ultrastructure; D008854:Microscopy, Electron; D009569:Nitric Oxide / Q000633:toxicity*; D012405:Round Window, Ear; D014226:Triazenes / Q000008:administration & dosage / Q000378:metabolism
C114535:1-hydroxy-2-oxo-3-(3-aminopropyl)-3-isopropyl-1-triazene; D016166:Free Radical Scavengers; D014226:Triazenes; D009569:Nitric Oxide