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 postsynaptic 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. Conclusion-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.