Abstract
A series of ten experiments on guinea pigs was performed to study the effects of NaCl crystals on the cochlear microphonics which were recorded from the basal turn with the differential electrode technique. The magnitude of the responses was determined on a cathode-ray oscilloscope for a stimulating tones of 300Hz of a certain intensity which evoked an output of 300μV of the cochlear microphonics after the application of NaCl to the round window. The NaCl crystals were equalized with the precise bolters of which meshes were 0.20mm and 0.25mm respectively, and then two pieces of right cubic crystals selected under a binocular microscope were placed directly on the round window membrane.
The results obtained were plotted in Figure 2, and the averaged curve of the cochlear microphonics after the application of NaCl crystals on the round window were shown in Figure 3 with the standard deviation at every five minutes during the recording. The variations of the cochlear microphonics of each animal were relatively small at the beginninig of the experiment and then showed remarkable increase afterwards. The course of changes of the cochlear microphonics in averaged curve are as follows; The cochlear microphonics showed an initial overshoot which was followed by a primary rapid decrease and then by a temporary recovery. A second decrease of more moderate rate was finally observed. The output of the cochlear microphonics at the peak of overshoot which occurred 1.5 minutes after the salt-application showed 7% increase of the original level and the output at the bottom of the primary decrease which was observed 15 minutes after the salt-application showed 55% of the original level. The recovery was incomplete but a marked increase (70% of original level) was observed. The cochlear microphonics decreased to a level of 205μV±72μV at 60 minites after the application of NaCl crystals on the round window.
A reversible damage of CM-generating system which is caused by the osmotic and ionic changes of the labyrinthine fluids seems to be responsible for the initial overshoot and the primary decrease of the cochlear microphonics following the salt-application. The temporary recovery of the cochlear microphonics seems to be caused by the renormalization of the ionic concentration of the perilymph and the endolymph due to production and absorption of the fluids. The second decrease of the cochlear microphonics was considered as the result of an irreversible progressive damage of the hair cells and of the fluids-production system. The permeability of the round window membrane and the metabolism of the labyrinthine fluids were considered as the factors influencing the previously mentioned changes of the cochlear microphonics after the application of NaCl crystals on the round window.
