Effects of perilymph collected during auditory fatigue on cochlear electrophysiology

Previously we reported the release of auditory nerve activation substance (ANAS) into perilymph during sound stimulation [Soc. Neurosci. III, 11 (1977)]. Recently, experiments designed to increase the output of ANAS were carried out using more intense sound stimuli during the perilymphatic collection periods. In these experiments, compound VIIIth nerve action potentials and cochlear microphonics were measured. The more intense auditory stimuli caused reductions in these potentials reminiscent of auditory fatigue. Perilymph, collected during periods of auditory fatigue, when infused back into the guinea pig cochlea during silence caused reductions in cochlear potentials similar to those seen during auditory fatigue. Such cochlear electrical changes are not seen with perilymph collected during quiet periods. These results suggest that ANAS and/or another substance released during sound stimulation may be responsible for the changes in cochlear electrical activity seen during auditory fatigue. These results may point to a chemical basis for auditory fatigue and such related phenomena as temporary threshold shift. [Supported by NS ♯11647, The Veterans Administration Research Service and The John A. Hartford Foundation.]