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Psychophysical tuning curves and auditory thresholds after hair cell damage in the chinchilla
Abstract:
Chinchillas were treated with kanamycin sulfate (150--200 mg/kg/day) to produce high-frequency hearing loss extending to about 4.0 kHz. Thresholds and psychophysical tuning curves (PTCs) were obtained before and after treatment, utilizing a shuttlebox avoidance procedure, and cochlear hair cells were evaluated under phase contrast microscopy. Hair cell loss resulting from kanamycin treatment varied from restricted lesions of the outer hair cells (OHCs) in the cochlear base, with no loss of inner hair cells (IHCs), to more extensive lesions involving both OHCs and IHCs. Threshold shift of at least 40 dB was always associated with OHC loss. PTCs obtained from frequency regions exhibiting 40--50 dB of threshold shift were normal in shape. With threshold shift in excess of 50 dB, PTCs were progressively distorted, with truncation of the tip segment and in some cases increased sensitivity of the tail segment. The results suggest that the threshold of optimally functional IHCs after kanamycin-induced OHC loss is about 40 dB higher than normal. Threshold shift in excess of 40 dB may represent IHC damage. IHCs are capable of transducing the fine-frequency information necessary for generating normally sharp PTCs in the absence of OHCs. However, with threshold shift in excess of approximately 50 dB, this frequency resolution is increasingly compromised.
Insights
Kanamycin sulfate causes hearing loss by damaging outer hair cells (OHCs), which elevates hearing thresholds by 40 dB. Inner hair cell (IHC) damage may occur with greater hearing loss, compromising frequency resolution.
Area of Science:
- Ototoxicity
- Auditory Neuroscience
- Sensory Biology
Background:
- Kanamycin sulfate is an aminoglycoside antibiotic known to cause ototoxicity.
- High-frequency hearing loss is a common side effect of aminoglycoside treatment.
- Understanding the specific roles of inner and outer hair cells in hearing loss is crucial.
Purpose of the Study:
- To investigate the effects of kanamycin-induced hearing loss on chinchilla auditory function.
- To correlate cochlear hair cell damage with changes in auditory thresholds and psychophysical tuning curves (PTCs).
- To determine the functional contribution of inner hair cells (IHCs) in the absence of outer hair cells (OHCs).
Main Methods:
- Chinchillas were treated with kanamycin sulfate to induce hearing loss.
- Auditory thresholds and PTCs were measured using a shuttlebox avoidance procedure.
- Cochlear hair cell integrity was assessed via phase contrast microscopy.
Main Results:
- Kanamycin treatment caused outer hair cell (OHC) lesions, associated with threshold shifts of at least 40 dB.
- Psychophysical tuning curves (PTCs) remained normal with 40-50 dB threshold shifts but became distorted with >50 dB shifts.
- Inner hair cell (IHC) damage was suggested with threshold shifts exceeding 40 dB.
Conclusions:
- OHC loss elevates hearing thresholds by approximately 40 dB, with IHCs still functioning.
- Threshold shifts beyond 40 dB may indicate IHC damage.
- While IHCs can support some auditory function without OHCs, significant hearing loss (>50 dB) compromises frequency resolution.