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Combined effects of noise and neomycin. Cochlear changes in the guinea pig
Abstract:
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.
Insights
Neomycin combined with intense noise significantly amplifies cochlear damage in guinea pigs. This synergistic effect causes substantial hearing loss and outer hair cell destruction, highlighting combined ototoxicity risks.
Area of Science:
- Ototoxicology
- Auditory Neuroscience
Background:
- Neomycin is an aminoglycoside antibiotic with known ototoxic potential.
- Acoustic overstimulation can also damage the cochlea.
- The combined effects of neomycin and noise on cochlear integrity are not fully understood.
Purpose of the Study:
- To investigate the synergistic ototoxic effects of neomycin and acoustic overstimulation in guinea pigs.
- To quantify cochlear damage using electrophysiological and histological methods.
Main Methods:
- Guinea pigs were divided into four groups receiving daily subcutaneous neomycin or saline injections followed by exposure to either high-intensity (115 dB SPL) or low-intensity (45 dB) broadband noise for 7 days.
- Cochlear integrity was assessed after a 30-day stabilization period by measuring auditory brainstem response (ABR) thresholds and counting outer hair cells (OHCs).
Main Results:
- A significant interaction between neomycin and high-intensity noise (115 dB SPL) resulted in augmented cochlear damage.
- Group I (neomycin + 115 dB noise) exhibited an average cochlear sensitivity loss of 62 dB and nearly 100% OHC loss.
- Control groups (saline + noise or neomycin + low-intensity noise) showed significantly less damage (16-17 dB average loss and 17-26% OHC loss).
Conclusions:
- Neomycin potentiates noise-induced cochlear damage, indicating a synergistic ototoxic effect.
- Combined exposure to neomycin and intense noise leads to severe hearing impairment and outer hair cell degeneration.
- These findings underscore the critical need to consider combined exposures when assessing ototoxicity risks.