Effect of noise level on the Met-enkephalin content of the guinea pig cochlea.

Using a highly sensitive and specific radioimmunoassay for Met-enkephalin, we have monitored in two series of experiments the changes of the Met-enkephalin content of guinea pig cochleas following a 60 min exposure to different intensities of white noise (70 dB SPL, 90 dB SPL, 110 dB SPL). Our results indicate that the Met-enkephalin content was significantly lower after noise exposures than after exposure to the silence of a sound attenuated chamber. After a stimulation at 70 dB SPL, the levels of Met-enkephalin were 70% (series I) and 61% (series II) of those obtained after a period of silence. After a 110 dB SPL stimulation, these values fell to 41% (series I) and 55% (series II) of those in silence. These results strengthen the hypothesis that enkephalins are olivocochlear neuroactive substances. They suggest that the enkephalin-containing lateral olivocochlear system discharges with noise stimuli of moderate intensity.