Sensory SystemResearch PaperDifferential expression of apoptosis-related genes in the cochlea of noise-exposed rats
Section snippets
Animals
Young Sprague–Dawley rats (210–300 g, male, Charles River Laboratories, Wilmington, MA, USA) were used. The procedures involving use and care of animals were reviewed and approved by the State University of New York at Buffalo Institutional Animal Care and Use Committee. The procedure minimized the number of animals used in this study as well as the suffering experienced by the animals.
Noise exposure
Rats were exposed for 2 h to a continuous noise (1–7 kHz) at 115 dB SPL (re 20 μPa). This noise level was
ABR threshold shifts
The average ABR thresholds measured pre-exposure and 4 h and 7-day post-exposure are presented in Fig. 1. The pre-exposure ABR thresholds varied from 30 to 45 dB between 5 and 40 kHz consistent with a previous study (Chen and Fechter, 2003). ABR thresholds at 4 h post-exposure were elevated significantly relative to pre-exposure thresholds (P<0.01). The average threshold shift across the frequency range was 50±9.3 dB (mean±SD). At 7 days post-exposure, thresholds had partially recovered leaving
Discussion
We exposed rats for 2 h to broadband noise at 115 dB SPL. The exposure caused a 40–60 dB hearing loss over a wide frequency range 4 h post-exposure. Morphological assessment of the cochlea at this time revealed a small portion (approximately 1% of the total hair cell population) of hair cells with apoptotic features, specifically condensed nuclei and TUNEL positive staining. At 7 days post-exposure, the hearing loss had decreased to 20–30 dB. Few hair cells with apoptotic features were seen at
Acknowledgments
The research was supported by R01DC00909101, R01DC006630, R03DC006181-03 and New Faculty Startup funds from College of Arts and Sciences, University at Buffalo. Presented in part at the 38th annual meeting of the Society for Neuroscience, held November 15–19, 2008, in Washington, DC.
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