title: Recovery of otoacoustic emissions after high-level noise exposure in the American bullfrog.
abstract: The American bullfrog (Rana catesbeiana) has an amphibian papilla (AP) that senses airborne, low-frequency sound and generates distortion product otoacoustic emissions (DPOAEs) similar to other vertebrate species. Although ranid frogs are typically found in noisy environments, the effects of noise on the AP have not been studied. First, we determined the noise levels that diminished DPOAE at 2f1-f2 using an f2 stimulus level at 80 dB SPL and that also produced morphological damage of the sensory epithelium. Second, we compared DPOAE (2f1-f2) responses with histopathologic changes occurring in bullfrogs after noise exposure. Consistent morphological damage, such as fragmented hair cells and missing bundles, as well as elimination of DPOAE responses were seen only after very high-level (>150 dB SPL) sound exposures. The morphological response of hair cells to noise differed along the mediolateral AP axis: medial hair cells were sensitive to noise and lateral hair cells were relatively insensitive to noise. Renewed or repaired hair cells were not observed until 9 days post-exposure. Following noise exposure, DPOAE responses disappeared within 24 h and then recovered to normal pre-exposure levels within 3-4 days. Our results suggest that DPOAEs in the bullfrog are sensitive to the initial period of hair cell damage. After noise-induced damage, the bullfrog AP has functional recovery mechanisms that do not depend on substantial hair cell regeneration or repair. Thus, the bullfrog auditory system might serve as an interesting model for investigation of ways to prevent noise damage.
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive East, Los Angeles, CA 90095, USA.
authors: Dwayne D
authors: DD
authors: Simmons
authors: Rachel
authors: R
authors: Lohr
authors: Helena
authors: H
authors: Wotring
authors: Miriam D
authors: MD
authors: Burton
authors: Rebecca A
authors: RA
authors: Hooper
authors: Richard A
authors: RA
authors: Baird
mesh_terms: D000818:Animals; D007758:Ear, Inner / Q000503:physiopathology; D006198:Hair Cells, Auditory / Q000473:pathology*; D006317:Hearing Loss, Noise-Induced / Q000473:pathology*; D009622:Noise; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D011892:Rana catesbeiana; D020127:Recovery of Function
keywords: Active amplification; Cubic distortion product; Hair Cells; Hearing loss; Regeneration