NEOMYCIN INDUCES APOPTOSIS IN THE INNER EAR
Keywords:
Apoptosis, auditory hair cells, neomycinAbstract
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.
References
Adams JM, Cory S., 1998, The Bcl-2 protein family: arbiters of cell survival.
Science, 281(5381), 1322-6.
Cheng AG, Cunningham LL, Rubel EW., 2003, Hair cell death in the avian
basilar papilla: characterization of the in vitro model and caspase activation. J Assoc
Res Otolaryngol., 4(1), 91-105.
Cunningham LL, Cheng AG, Rubel EW. 2002, Caspase activation in hair cells
of the mouse utricle exposed to neomycin. J Neurosci., 22(19):8532-40.
Devarajan P, Savoca M, Castaneda MP, et al., 2002, Cisplatin-induced
apoptosis in auditory cells: role of death receptor and mitochondrial pathways. Hear
Res.; 174(1-2), 45-54.
Forge A, Li L., 2000, Apoptotic death of hair cells in mammalian vestibular
sensory epithelia. Hear Res. 139(1-2), 97-115.
Lang H, Liu C., 1997, Apoptosis and hair cell degeneration in the vestibular
sensory epithelia of the guinea pig following a gentamicin insult. Hear Res. 111(1-
,177-84.
Löwenheim H, Kil J, Gultig K., Zenner HP , 1999, Determination of hair cell
degeneration and hair cell death in neomycin treated cultures of neonatal rat cochlea
Hearing Research 128, 16-19
Matsui JI, Gale JE, Warchol ME., 2004, Critical signaling events during the
aminoglycoside-induced death of sensory hair cells in vitro. J Neurobiol., 61(2),250-
