The potentiation of noise-induced hearing loss by neomycin.
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Biomedical subjects
Publications and source records attributed to J Vernon.
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Cochlear damage resulting from the combination of neomycin with acoustic overstimulation was investigated in guinea pigs. Four groups of animals received subcutaneous injections and exposure to broad band noise daily for 7 days, as follows: I. Neomycin (200 mg/kg) followed by 10 hours of noise at 115 dB SPL; II. Saline followed by 115 dB noise: III. Neomycin followed by low intensity noise (45 dB as an acoustic control); or IV. Saline followed by 45 dB noise. After a 30 day stabilization period, each ear was examined electrophysiologically and histologically. Measures of cochlear integrity included AC cochlear potentials from 100 Hz through 20 kHz as well as outer hair cell (OHC) counts. A marked interaction leading to augmentation of damage was found when neomycin was combined with 115 dB noise (Group I). Losses in cochlear sensitivity, averaged across all frequencies, amounted to 62 dB in Group I, whereas the averaged losses for Groups II and III were only 16 dB and 17 dB respectively. Loss of OHC's was close to 100% in Group I, while OHC losses were only 17% in Group II and 26% in Group III.
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The major effect here has been to present two forms of treatment which have provided relief of tinnitus for some patients. Use of a properly fitted hearing aid relieves tinnitus when that tinnitus is embedded within the frequency region of the hearing loss. When the use of a hearing aid is counterindicated, then use of the tinnitus masker can bring relief for certain kinds of tinnitus. At present the only tinnitus masker available presents a band of noise of moderate frequencies, and it is capable of relieving tinnitus in that frequency region or near it. When masking of tinnitus is effective it produces a suppresion of the tinnitus which extends beyond the duration of the masker. This is termed residual inhibition, a matter about which we need to know a great deal more. For tinnitus which is intractable to medical treatment it has become a practice to instruct the patient that he must learn to live with his affliction. It is hoped that this presentation will cast doubt upon that view, for it can be seen that there are many tinnitus sufferers for whom much can be done.
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