COMBINED EFFECTS OF GENTAMICIN AND NOISE ON AUDITORY BRAIN-STEM RESPONSE IN RATS

Two series of animal experiments were carried out to clarify the combi ned effect of gentamicin (GM) and noise on the auditory brainstem resp onse. In the first experiment, 64 rats were divided into eight groups: six groups for GM treatment (0, 20, 30, 40, 50 and 100 mg/kg, respect ively), one group for exposure to 110 dB SPL white noise and one for c ontrol. After four weeks of injections, no prolonged latency of peak 1 was found in the rats injected with less than 30 mg/kg GM. Prolongati on was observed in rats injected with 50 mg/kg GM. When the rats were exposed to the noise for three hours a day in the third week, the late ncy of peak 1 was temporarily prolonged in response to a four-kHz tone burst. The prolonged latency of peak 1 returned gradually to the init ial level. In the second experiment, the obvious and irreversible prol onged latencies in response to four-and 16-kHz tone bursts were found in the rats given 50 or 30 mg/kg GM for four weeks, combined with a on e-week exposure to 110 dB SPL white noise. The combined effects of GM and noise typically appeared in the latency of peak 1 in response to f our kHz and then 16 kHz. The combined effects were synergistic with a GM effect and a noise effect. The results suggest that hearing damage is easily caused by noise during GM therapy. (C) 1997 Academic Press L imited.