THE EFFECT OF OVERPRODUCTION OF ENDOLYMPH ON THE INNER EAR FUNCTION

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In order to study the effect of an overproduction of the endolymph on the inner ear function, artificial endolymph was injected into the scala media in animals with the experimentally-induced endolymphatic hydrops, and the auditory and vestibular functions were examined. The results were as follows : 1) Endolymphatic hydrops was induced by electro-cauterization of the endolymphatic sac. Moderate or severe hydrops developed 2 months after the cauterization. In these animals, the positive and negative endocochlear potentials had already decreased. Artificial endolymph injection into the cochlear duct produced no significant alteration in these potentials, although the negative endolymphatic potential decreased in normal animals. 2) The compound action potentials and cochlear microphonics also decreased in animals with experimentally induced hydrops. These potentials showed no change before and after the artificial endolymph injection. The delayd CM could not be detected in the present se … More ries of experiments. 3) Transient evoked otoacoustic emission (TEOA) was detected 2 weeks after the cauterization of the sac, but disappeared after 2 months. Thus, the effect of artificial endolymph injection to TEOAE was not investigated. Distortion product otoacoustic emission (DPOAE) could be recorded, but we could not examine the influence of artificial endolymph injection on DPOAE because of its instability. 4) Artificial endolymph injection into the cochlear duct produced no alteration in spontaneous discharge of the vestibular nerve either in normal animals or in animals with experimentally induced hydrops. 5) artificial endolymph injection into the cochlear duct produced no alteration in K^+ activity in the scala tympani either in normal animals or in animals with experimentally induced hydrops.In the previous studies, cochlear and vestibular dysfunction seemed to be attributed to high concentration of K ^+ in the scala media due to the leakage of endolymph via extended Reissner's membrane. However, the present results did not favor this hypothesis. Less