title: Low-frequency 'conditioning' provides long-term protection from noise-induced threshold shifts in chinchillas.
abstract: Studies have shown that loss of auditory sensitivity caused by exposure to high-level acoustic stimuli can be significantly reduced by pre-exposing the subject to moderate-level acoustic stimuli. Although the protective effects of such 'conditioning' exposures have been well documented, very little is known about the persistence of conditioning-induced protection, or about the biological mechanisms underlying it. In the present study, the persistence of conditioning-induced protection was examined in chinchillas by imposing either a 30- or 60-day recovery period between conditioning (10 days of exposure to 0.5 kHz noise at 90 or 95 dB, 6 h/day) and high-level (0.5 kHz noise at 106 dB for 48 h) exposures. Comparisons of threshold shifts between conditioned animals and control animals exposed only to high-level noise indicated that conditioning provided significant protection from noise-induced threshold shifts for at least 2 months. Conditioned animals sustained outer hair cell losses similar to controls, ranging from 15 to 30% in the apical half of the cochlea. The results suggest that low-frequency conditioning can trigger long-lasting changes in cochlear homeostasis rather than temporary changes in physiology or reductions in susceptibility to hair cell loss in chinchillas.
authors.affiliation: Hearing Research Laboratories, State University of New York, Buffalo 14214-3007, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: McFadden
authors.forename: D
authors.initials: D
authors.lastname: Henderson
authors.forename: Y H
authors.initials: YH
authors.lastname: Shen
mesh_terms: D000161:Acoustic Stimulation; D000222:Adaptation, Physiological; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology*; D002682:Chinchilla / Q000502:physiology*; D006199:Hair Cells, Auditory, Inner / Q000293:injuries / Q000473:pathology; D018072:Hair Cells, Auditory, Outer / Q000293:injuries / Q000473:pathology; D006317:Hearing Loss, Noise-Induced / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control; D006801:Humans; D009622:Noise / Q000009:adverse effects*; D013997:Time Factors