Clin Exp Otorhinolaryngol.  2008 Jun;1(2):80-85. 10.3342/ceo.2008.1.2.80.

Apoptotic Pattern of Cochlear Outer Hair Cells and Frequency-specific Hearing Threshold Shift in Noise-exposed BALB/c Mice

Affiliations
  • 1Department of Otolaryngology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea. jwchung@amc.seoul.kr

Abstract


OBJECTIVES
Apoptosis of outer hair cell (OHC) can be identified through nuclear staining by specific nuclear changes. The change of filamentous actin (F-actin) is also involved in early cell death process. The study was designed to investigate OHC death along the whole length of the organ of Corti. METHODS: BALB/c hybrid mice were used in this study. The noise group was exposed to white noise of 120 dB SPL for 3 hr per day for 3 consecutive days. The tone burst auditory brainstem response (ABR) test was conducted and cochleas from each group were obtained for the immunostaining of FITC phalloidin for F-actin and propidium iodide (PI) for nuclei. RESULTS: ABR threshold of the noise group significantly increased after noise exposure (P<0.001). No threshold shift was found in the control group. Threshold shift of the noise group constantly increased from 4 to 16 kHz, but threshold shifts at 16 kHz and 32 kHz were similar. Patterns of OHC staining were subclassified as FITC+PI- cells, FITC+ PI+ cells, FITC-PI+ cells and missing cells. Proportion of normal live OHCs (FITC+PI-) rapidly decreased from the apex to the base. In the basal turn, FITC-PI+ cells and vacancy OHC (missing cells) were observed easily. Apoptotic and missing cells were most abundant at 60% of the whole length of the Corti organ. CONCLUSION: We could subclassify morphologic changes in OHC death after noise exposure. Quantitative changes in OHCs along the whole Corti organ showed a plateau pattern similar to that of a frequency-specific threshold shift.

Keyword

Noise-induced hearing loss; Apoptosis; Auditory brainstem evoked potential; Cell death

MeSH Terms

Actins
Animals
Apoptosis
Cell Death
Chimera
Cochlea
European Continental Ancestry Group
Evoked Potentials, Auditory, Brain Stem
Fluorescein-5-isothiocyanate
Hair
Hearing
Hearing Loss, Noise-Induced
Humans
Mice
Noise
Organ of Corti
Phalloidine
Propidium
Actins
Fluorescein-5-isothiocyanate
Phalloidine
Propidium

Figure

  • Fig. 1 Images of immunoreactivity for PI and FITC-phalloidin in the organ of Corti of a noise-exposed mouse (×400). (A) Apical turn. There shows a nuclear condensation in a fluorescent image for PI (PI+, arrow, upper panel). In an image for FITC-phalloidin, the corresponding cell shows normal appearance (FITC+, arrow, lower panel). Other cells are normal live cells (FITC+, PI-). (B) Middle turn. There is a cell with no nuclear staining (arrow, upper panel) and no fluorescence for FITC-phalloidin (arrow, lower panel). This cell is considered as missing. (C) Basal turn. Nuclear condensation (PI+, arrow, upper panel) with an intact structure (FITC+, arrow, lower panel) was noted in one cell. Adjacent cells (asterisk in both panels) show nuclear condensation and a deformed structure (FITC-, PI+). The other cells (thick arrow in both panels) have no nucleus and show deformed structures (missing). Scale bar: 10 µm.

  • Fig. 2 Distribution of several OHC conditions along the whole length of the cochlear OHC layer in the noise group mice after noise exposure. Error bars represent standard deviation.

  • Fig. 3 Distribution of damaged OHCs in the noise group mice after noise exposure.

  • Fig. 4 ABR threshold of the noise and control groups. ABR threshold of noise group was significantly increased after noise exposure (P<0.001). ABR threshold of the noise group after noise exposure and that of the control group after silent condition within noise booth were significantly different (P<0.001). Error bars represent standard deviation.

  • Fig. 5 ABR threshold shift after noise exposure. Threshold shift of the noise group was constantly increased from 4 to 16 kHz, but threshold shifts at 16 and 32 kHz were similar. Error bars represent standard deviation.


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Gi Jung Im, June Choi, Ji Won Chang, Seo Jin Kim, Hye In Kim, Hak Hyun Jung
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