Structural and functional effects of acoustic exposure in XXXX : evidence for tonotopy in the teleost saccule.

@entity1 @entity393 @entity1829 @entity2083
BACKGROUND: @entity1 and avian auditory hair cells display tonotopic mapping of frequency along the length of the @entity1829 . It is not known whether the auditory hair cells of fishes possess a similar tonotopic organization in the saccule, which is thought to be the primary auditory receptor in teleosts. To investigate this question, we determined the location of hair cell damage in the saccules of @entity2083 ( @entity2083 ) following exposure to specific frequencies. Subjects were divided into six groups of six fish each (five treatment groups plus control). The treatment groups were each exposed to one of five tones: 100, 400, 800, 2000, and 4000 Hz at 176 dB re 1  Pa root mean squared (RMS) for 48 hours. The saccules of each fish were dissected and labeled with phalloidin in order to visualize hair cell bundles. The hair cell bundles were counted at 19 specific locations in each saccule to determine the extent and location of hair cell damage. In addition to quantification of anatomical injury, hearing tests (using auditory evoked potentials) were performed on each fish immediately following sound exposure. Threshold shifts were calculated by subtracting control thresholds from post-sound exposure thresholds. RESULTS: All sound-exposed fish exhibited significant hair cell and @entity393 following sound exposure. The location of hair cell loss varied along the length of the saccule in a graded manner with the frequency of sound exposure, with lower and higher frequencies damaging the more caudal and rostral regions of the saccule, respectively. Similarly, fish exposed to lower frequency tones exhibited greater threshold shifts at lower frequencies, while high-frequency tone exposure led to @entity393 at higher frequencies. In general, both hair cell and @entity393 declined as a function of increasing frequency of exposure tone, and there was a significant linear relationship between hair cell loss and @entity393 . CONCLUSIONS: The pattern of hair cell loss as a function of exposure tone frequency and saccular rostral-caudal location is similar to the pattern of @entity393 as a function of exposure tone frequency and hearing threshold frequency. This data suggest that the frequency analysis ability of @entity2083 is at least partially driven by peripheral tonotopy in the saccule.
