In order to clarify the producing mechanism of cochlear microphonics (CM), AC and DC potentials in the organ of Corti were recorded, by introducing a microelectrode through the round, window membrane to the basilar membrane of guinea-pigs. Using the cell-making method, the cell, from which the electric potentials were recorded, was identified by surface preparation technique or cross section. The results are as follows: 1) At the subtectorial space, a positive potential (ca. 60mV) is recorded. 2) By passing through the tectorial membrane, a negative potential is occasionally recorded. 3) In the hair cells, the amplitude of CM increases remarkably. 4) In the supporting cells (especially Claudius's cells and Hensen's cells), the amplitude of CM dosen't increase, but decreases. 5) In the tunnel, the DC potential is zero milli volt, and the amplitude of CM somewhat increases. From these results, it might be suggested that the variable electric potentials at the cuticular lamina, tectorial membrane and subtectorial space influences delicately on the biophysical activity of the sensory hairs, and then have a relation with the production of CM, and the increase and decrease of the amplitude.
We investigated an anoxic increase of the endocochlear potential (EP) predamaged by “loop” diuretic, bumetanide. This hypothetical, anoxiasensitive, “negative electrogenic potential” was observed both in the declining stage of EP, and in the recovery stage of EP in intoxication of bumetanide. The further study on this potential should be carried out, but, at present, two possible explanation may be suggested. The first one is that this anoxia-sensive component of EP normally presents without the effect of bumetanide. And, the other is that the pattern of active ion transport in the stria vascularis is changed by administration of bumetanide.
The reticular membrane is composed of the brush border of hair cells and the tops of their supporting apparatus. The receptor membrane is considered to have a polarizing property since the phase of cochlear microphonics (CM) is reversed in electrode penetration from one side of the reticular membrane to the other and also the amplitude of CM is increased or decreased by appling current through the membrane. The sensory hairs of hair cells face to an environment of high potassium and very low calcium concentrations. This characteristic ionic environment is necessary to the maintenance of the CM sensitivity. The role of calcium ions in the initial receptive process of hair cells is discussed.
Auditory evoked responses from the inferior colliculus of guinea pigs were obtained at 17 frequencies between 0.5 and 20.0 kHz tested. A comparison between the evoked response threshold curves from the inferior colliculus and the behavioral audiograms by conditioned-suppresion previously reported reveals a favorable correlation. The cochlear potential curve in these animals, however, appears to be a less efficient predictor of the audibility curve than the present evoked response curve. The utility of the evoked response audiometry from the inferior colliculus for quickly assessing auditory thresholds in guinea pigs is proposed.
In order to detect NITTS and NIPTS in guinea pigs, the influence on the latency of AP (N1) after white noise exposure was studied electrocochleographically. In this series, the guinea pigs were 250 grams to 500 grams of body weights with normal Preyer's reflex. Electrocochleographic recordings were repeated several times before and after white noise was exposed to the animals under general anesthesia with pentobarbital sodium (45mg/kg i. m.). The stimulation sound used in this study was click, and was given through a ear tube. A positive needle electrode was placed in the external ear canal, and a negative needle electrode in the ipsilateral ear lobe, and the ground in the ipsilateral leg. The responses were averaged 200 times and recorded on a X-Y recorder. The experimental conditions of white noise exposure were as follows: The results wére as follows: 1. Under the experimental conditions of A, B, C, D and F, the latency of AP was prolonged immediately after white noise exposure. However, one day after or one week after white noise exposure the latency of AP returned completely to the pre-exposure level. In these experimental conditions, therefore, white noise exposure were considered to induce NITTS in the guinea pigs. 2. Contrary to the above, in the experimental conditions of E and G, the latency of AP was prolonged even one week or 2.5 months after white noise exposure. Thus, these two experimental conditions were considered to have induce NIPTS in the guinea pigs. 3. From these two results, the latency of AP in electrocochleography was considered to be one of the parameters to detect NITTS and NIPTS in the guinea pigs.
In this study the cochlear microphonics were recorded from human subjects and guinea pigs on ECoG, and they were used to evaluate the relationship between two-tone suppression and the suppressor frequency and intensity. The results are as follows: 1. The amplitude of the ECoG CM suppressed not only at higher frequency but also at lower frequency. At the higher frequency as 1 or 2 octave, CM suppression was usually evident. 2. Two-tone suppression measured with ECoG was observed in human subjects, and it was concluded that the basilar membrane of the human cochlea has the nonlinear characteristics. The results of this study are consistent with the previous findings which were obtain by the use of CM, by a model of the basilar membrane and by the use of the Mössbauer effect, but some differences between our results. and the two-tone suppresion obtained from the acoustic nerve, cochlear nucleus and psychophysical observations were observed. This difference was thought to be caused by the difference of the intensity of the test and suppressing tones and by the existence of the different 2nd filter.