In order to study the effect of vitamin B1 derivative (O, S-dicarbethoxy-thiamine, DCET) on the kanamycin (KM) ototoxicity, the electrophysiological and phase contrast microscopical studies using rabbits with electrodes permanently implanted on the round windows were carried out. Rabbits (control group) were daily given 100mg/kg of KM intraperitoneally, and the others (experimental group) 100mg/kg of KM with 20mg/kg of DCET in the same way. The measurements of the cochlear microphonic (stimulus: 1000Hz, 80dB) and the drug administrations were daily performed until their CM could not be detected, and adout 10 days or 2 weeks after the completion of the drug administration all of the raddits were sacrificed for phase contrast microscopical examinations. As previously reported the main electrophysiological findings were the followings: After the onset of reduction of maximum CM amplitude, in the control group, the curves of CM amplitude were reduced rapidly. On the contrary, in the experimental group, the curves were reduced with a gentle slope to the lower level. There was the clear-cut difference between the curves of the two groups. The cytological findings of the outer and inner hair cells, the supporting cells (Hensen's and Deiters' cells) and pillar cells were precisely investigated. However, the cytological difference between the two groups were not observed. It may be given as a conclusion the functional effect of vitamin B1 derivative (DCET) on the KM ototoxicity was very clearly observed, but the histopathological proof on its effectiveness could not be obtained by the above-mentioned experimental procedure using light microscopy.
Distorted speech tests were performed to 10 normal subjects and to 50 patients sufferring from various kinds of hearing disturbance according to following battery of presentation of speech sounds. 1. Non- distorted speech sounds. 2. 1200Hz low pass filtered speech sounds. 3. 1700Hz high pass filtered speech sounds. 4. Monaurally mixed speech sounds of 1200Hz low pass and 1700Hz high pass filtered speech. (1200-1700Hz band eliminated filtered speech sounds.) 5. 1200-2400Hz band pass filtered speech sounds. To judge the results of these tests three methods were considered. The first was termed articulation method that the abnormality was judged by the articulation score of distorted speech sounds, the second was subtraction method which was judged by the difference between articulation score of non-distorted and of distorted speech sounds, and the third was division method which was judged by the ratio of the articulation score of distorted speech sounds to that of non-distorted speech sounds. Those who were judged as normal by the articulation method but as abnormal by the other methods were very rare, and were able to be found only among those who showed an articulation score of 90% or more in the non-distorted speech test. The authors considered to make simple the distorted speech tests, and concluded that both low pass filtered speech test and high pass filtered test were to be performed at least, otherwise the merit of the distorted speech test would decrease, because omitted cases would increase.
The objective testing method available for the orientation of the dominant cerebral hemisphere for speech using key tapping was applied to 8 patients who had been hospitalized at the dep. Neurosurgery of Tokyo Women's Medical College due to brain damage. The test procedure and the instrumentations used in the experiment were explained in a previous study (Tsunoda, T.: Contralateral shift of Cerebral Dominance for Nonverbal Sounds During Speech Perception. J. aud. Res. 3; 221, 1969). The side of the dominant cerebral hemispheres thus obtained were compared with the represented hemispheres for speech confirmed by Wada technique and the following conclusions were obtaind. The auditory testing method was considered to be able to be utilized to the detection of the represented brain for speech in normals, however, the extreme contralateral pathological shift of the cerebral dominance towards nondominant hemisphere observed in a group of unilateral brain damage involving higher auditory pathway was not able to be considered to indicate the existence of the contralateral pathological shift of the speech function.
Through examination on requirements for audio-timer used in a variety of experimental conditions revealed that the “universal” audio-timers should provide for following characteristics: 1) numbers of unit interval time (UIT) should be as many as required for the most complex sequence of the intervals and should be subject to selection neither more nor less than required, 2) UIT should have sufficiently wide time range with necessary time-analytic power 3) time setting should be performed precisely, easily and speedily and should be directly eradable on the time-calibrated dial, 4) time setting on one of the UIT should not affect the other, 5) versatility of sequence patterns of UIT should be available, 6) synchronization with the input signal phase should be provided for. Analog UIT generators such as monostable multivibrator and phantastron are capable of use for audio-timer, if their advantages are put together to use. The type of timers are available on the commercial base and widely used up to now. Digital timers, if so called, however, have many advantages over the analog timers. The Multi-Interval Digital Timer designed by the author (Fig. 5) can have the characterististics mentioned above.
The present authors injected capreomycin (CPM) 400mg/kg intramuscularly into 10 albino guinea pigs of the Hartley strain (about 300g at the start of the experiment) for 28 days and simultaneously kanamycin (KM) 400mg/kg into 11 guinea pigs of the same strain for the same period. Preyer pinna reflex test was performed before, during and after the injection of the antibiotics with audiometer for the guinea pig. All of these animals underwent intravital fixation with Wittmaack's fixative through the ascending aorta under nembutal anesthesia. Bilateral temporal bones were taken enbloc from the skull and fixed further in the same fixative for several days. These temporal bones were decalcified, rinsed under running water, dehydrated and then embedded in celloidin. The serial horizontal celloidin sections including the both cochlea (25-30 microns in thickness) were stained with hematoxylin-eosin. Histologic changes of the internal ear, especially, damages of the organ of Corti and stria vascularis were examined. 1) CPM caused the disappearance of the outer hair cells of the organ of Corti localized in the lower part of the hook (lower 1/4 of the 1 turn) of the cochlea in 40% of the 10 CPM injected guinea pigs. 2) KM induced relatively extensive loss of the outer hair cells extending from the lower end of the basal turn to the upper turn of the cochlea in 100% of the 11KM treated guinea pigs. 3) The present experimental study indicated that CPM is less ototoxic in guinea pigs than KM. 4) There was no distinct morphological evidence of vestibular damage in the guinea pigs.