Effects of noise exposure on the cochlea and neurons of the inferior colliculus

Guinea pigs were exposed for 30 or 60 min to high‐intensity stimuli (1/3‐octave band noise centered at 1 or 2 kHz tone, intensity from 130 to 145 dB SPL). Several electrophysiological measurements were made in the cochlea and in the inferior colliculus before and after the exposure. Potassium concentration in the perilymph of scala vestibuli (measured with ion‐selective double barrel microelectrodes) which was 3.07 ± 0.50 mm $K+$ in the control group of nonexposed animals, increased after the exposure to 4.70 ± 1.55 mm $K+$⁠. Threshold tuning curves for the inferior colliculus neurons were elevated by about 30–50 dB, when compared with the pre‐exposure levels. The threshold values gradually decreased, reaching the pre‐exposure level approximately after 48 hours. Similar time course was observed in the endochochlear potentials, which was decreased after the exposure. Despite the threshold elevation the excitability of neurons ot polarizing currents was not greatly affected by the exposure.