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Relation between outer hair cell loss and hearing loss in rats exposed to styrene.

Authors
Chen-GD; Tanaka-C; Henderson-D
Source
Hear Res 2008 Sep; 243(1-2):28-34
NIOSHTIC No.
20034700
Abstract
The relationship between outer hair cell (OHC) loss and cochlear sensitivity is still unclear, because in many animal models there exist surviving but dysfunctional OHCs and also injured/dead inner hair cells (IHC). Styrene is an ototoxic agent, which targets and destroys OHCs starting from the third row to the second and first rows depending on the exposure level. The remaining cells may be less affected. In this experiment, rats were exposed to styrene by gavage at different doses (200-800 mg/kg/day) for varying periods (5 days/week for 3-12 weeks). An interesting finding was that the cochlear sensitivity was not affected in a few rats with all OHCs in the third row being destroyed by styrene. A further loss of OHCs was usually accompanied with a linear input/output (I/O) function of cochlear compound action potentials (CAP), indicating the loss of cochlear amplification. However, normal CAP amplitudes at the highest stimulation level of 90 dB SPL were often observed when all OHCs were destroyed, indicating normal function of the remaining IHCs. The OHC-loss/hearing-loss relation appeared to be a sigmoid-type function. Initially, styrene-induced OHC losses (<33%) did not result in a significant threshold shift. Then CAP threshold shift increased dramatically with OHC loss from 33% to 66%. Then, CAP threshold changed less with OHC loss. The data suggest a tri-modal relationship between OHC loss and cochlear amplification. That is, under the condition that all surviving OHCs are ideally functioning, the cochlear amplifier is not affected until 33% of OHCs are absent, then the gain of the amplifier decreases proportionally with the OHC loss, and at last the amplifier may fail completely when more than 67% of OHCs are lost.
Keywords
Hearing-loss; Biomarkers; Styrenes; Auditory-system; Ototoxicity; Organic-chemicals; Cell-damage; Exposure-assessment; Exposure-levels; Dose-response
Contact
Guang-Di Chen, Center for Hearing and Deafness, SUNY at Buffalo, 137 Cary Hall, 3435 Main Street, Buffalo, NY 14214
CODEN
HERED3
CAS No.
100-42-5
Publication Date
20080901
Document Type
Journal Article
Email Address
gchen7@buffalo.edu
Funding Type
Grant
Fiscal Year
2008
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-R01-OH-008113
Issue of Publication
1-2
ISSN
0378-5955
Source Name
Hearing Research
State
NY
Performing Organization
State University of New York at Buffalo
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