NEOMYCIN INDUCES APOPTOSIS IN THE INNER EAR

Abstract

Objectives: to study the apoptotic response of auditory hair cells in the organ of Corti after exposure to neomycin within the first 6 hours. Materials and methods: auditory hair cells harvested on the postnatal day 7 from the cochleae of C57BL6 wild type mice were cultured in vitro in the presence (neomycin group, n= 59 cochleas) or absence of neomycin (control group, n= 31 cochleas). Apoptotic cells were evaluated within 6 hours of incubation for the expression of active caspases (8, 9 or 3) in the cytoplasm and counterstained using propidium iodide to highlight apoptotic nuclei. Cells were statistically quantified using average and standard deviation. The differences between the averages were tested with the help of Student T test (threshold p< 0,05). Results: The statistic comparison between the different caspase types (caspase 3, 8 and 9), the average and dispersion inside the cell groups, permitted us to detect the first step of apoptosis taking place in the cytoplasm. The comparison of the cell group where propidium iodide was accumulated in the nucleus with the cell group where both the caspase and propidium iodide appeared, permitted us to detect the initiation and development of the second step of apoptosis, the one where the nucleus has already been affected. Conclusions: Neomycin is initiating, right after 6 hours of incubation, the process of apoptosis in auditory hair cells, determining the activation of cytoplasm caspases.

Keywords

• apoptosis
• auditory hair cells
• neomycin