Acoustically induced hearing loss: intracellular studies in the guinea pig cochlea.

Intracellular recordings were made from both inner and outer hair cells (IHC, OHC) in the basal coil of the guinea pig cochlea before, during and after the animal was exposed to loud, pure tones. Following multiple loud tones both types of sensory cells demonstrate a culmulative decrease in their voltage responses to a test tone. A loss in sensitivity of the compound action potential (CAP) of the eighth nerve co-incides with a decrease in both the amplitude of the IHC receptor potential and the positive summating potential (+SP) recorded at the round window. The largest decreases in sensitivity of IHCs are found at the characteristic or best frequency (CF) of each cell and this frequency selective loss of sensitivity results in a decrease in the tuning of the hair cell. During and following a loud tone the nonlinear properties of IHCs are also reduced.