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First published online October 18, 2006
Journal of Experimental Biology 209, 4193-4202 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02490

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Anatomical and functional recovery of the goldfish (Carassius auratus) ear following noise exposure

Michael E. Smith^1,2,,*, Allison B. Coffin^1,,, Diane L. Miller¹ and Arthur N. Popper¹

¹ Department of Biology and Center for Comparative and Evolutionary Biology of Hearing, University of Maryland, College Park, MD 20742, USA
² Department of Biology, Western Kentucky University, Bowling Green, KY 42104, USA

View larger version (5K): [in a new window]   Fig. 1. The power spectra level of the 170 dB re. 1 µPa white noise stimulus (top curve) used for noise exposure experiments and control levels (bottom curve). The sounds were recorded by a hydrophone placed centrally within the noise exposure container at a depth of 23 cm under the water surface, 1 cm above the underwater speaker.

View larger version (14K): [in a new window]   Fig. 2. (A) Auditory thresholds of control and experimental goldfish at various times following 48 h of white noise exposure. Day 0, goldfish tested immediately following exposure. (B) Mean TTS (temporary threshold shift) at each frequency calculated as threshold after noise exposure (from A) minus mean control levels. Values are means ± s.e.m.; N=6 per data point.

View larger version (5K): [in a new window]   Fig. 3. Temporary threshold shift (TTS) of goldfish at various times following 48 h of white noise exposure. Day 0, goldfish were tested immediately following exposure. Values are means ± s.e.m.; N=6 per data point (one mean value of six fish for each of six frequencies). The line represents the linear regression equation for the data shown.

View larger version (20K): [in a new window]   Fig. 4. (A) Drawing showing the four 2500 µm2 regions of the saccular macula where hair bundles were quantified (see Materials and methods for details). (B) Numbers of hair bundles in each saccular region by day; day 0 is immediately following 48 h of noise exposure; B, baseline animals that were killed prior to the experiment; C, control animals that were held in the experimental set-up for 48 h without the sound stimulus. Values are means ± s.e.m.; N=6 per data point for controls and days 0-8; N=2 for baseline. Asterisks indicate significant differences from baselines and controls (P<0.05).

View larger version (58K): [in a new window]   Fig. 5. Phalloidin-labeled saccular epithelia showing evidence of hair bundle loss following exposure to noise. (A) Control tissue from the caudal end of the saccule showing normal complement of hair bundles. (B) The same region of the saccule in an animal following 48 h of noise exposure and 1 day of recovery. (C) High magnification image of the saccule in B showing a scar formation characteristic of hair cell loss (arrow) and a bundleless cuticular plate (arrowhead). Scale bars, (A,B) 20 µm, (C) 5 µm.

View larger version (14K): [in a new window]   Fig. 6. (A) Caudal saccule from a control goldfish double-labeled with phalloidin and DAPI, showing hair cell nuclei (blue) and associated hair bundles (green). (B) Caudal saccule from a goldfish exposed to 48 h of white noise and then allowed to recover for 1 day. The arrow indicates a remaining hair bundle, and the arrowhead indicates a hair cell nucleus without a hair bundle. Scale bars, 10 µm. (C-E) Numbers of hair cell bundles and nuclei counted from 2500 µm2 regions located at (C) 75% (caudal), (D) 50% (central) and (E) 25% (mid-rostral) along the rostrocaudal axis of the saccular macula following noise exposure. Values are means ± s.e.m.; N=3 (days 0-1); N=5 (controls).

View larger version (57K): [in a new window]   Fig. 7. (A) Caudal region of the saccular epithelium immediately after noise exposure (day 0). Arrows point to examples of TUNEL-labeled (apoptotic) cells visualized by brown DAB labeling. Scale bar, 50 µm. (B) TUNEL-labeled cells in the goldfish saccule (gray) and lagena (black) at specific days following 48 h white noise exposure. Labeled cells were counted for each whole-mount epithelium. Values are means ± s.e.m.; N=6 (controls + days 0-8); N=2 (baseline). Asterisks indicate significantly elevated cell counts relative to baseline (B) and control (C) values (P<0.05).