Published papers

c-Fos is known to be a component of a transcription factor, activator protein-1, which is induced by oxidative stress. Guinea pigs were exposed to 4 kHz band noise of 110 dB SPL for 1 or 5 h and the expression of c-Fos in the organ of Corti was determined using Western blotting analysis and immunocytochemistry. c-Fos was expressed only after the noise exposure. The c-Fos expression was mainly found in the Hensen's cells, Claudius' cells and Deiter's cells of the basal and second turns of the cochlea. Since the threshold shift was temporary, the expression of c-Fos is therefore considered to contribute to the survival or protective function of the organ of Corti.

The quality of life of vestibular schwannoma (VS) patients after surgery was investigated. The subjects consisted of 236 unilateral VS patients who underwent tumor removal between 1990 and 1997. A questionnaire was sent to all patients regarding their hearing, tinnitus, dizziness and the changes in their daily life after surgery; 176 out of 204 patients (86%) who received the questionnaire completed and returned it. The answers were compared with recent data reported in other clinical studies. Ninety percent of the patients with postoperative class A hearing were satisfied with their hearing. However, only 30% of patients with postoperative class B hearing were satisfied. Tinnitus worsened after surgery more often in patients who underwent a labyrinthectomy than in those who did not. Dizziness improved after surgery in the majority of VS patients. However, 30% of patients had difficulty driving a car and 50% of patients could not enjoy activities such as playing sport after surgery.

Purpose of the study: Though perilymph fistula (PLF) is not a rare disease, preoperative diagnosis still remains to be established. Some new diagnostic methods are challenging, but there is still no established diagnostic method except exploratory tympanotomy that verifies the occurrence of leakage. Early diagnosis of PLF is fully depending on history taking and some clinical examinations. To know the clinical features of PLF is one of the greatest helps to make both earlier and accurate diagnosis. In spite of some innovations in clinical examinations classic diagnostic procedure is thought to be still reliable. Procedures: We investigated the clinical symptoms, basic tests results and therapeutic results in patients with PLF. Results: From 1983 to 1998 PLF was identified in 44 patients (45 ears) with exploratory tympanotomies in our hospital. With respect to clinical history the predisposing factors such as blowing the nose, lifting heavy goods, and landing in an airplane were found in almost half of the patients, while the rest of them had no clear inducing factors. Their major symptoms included hearing loss (93%), vertigo and dizziness (91%), tinnitus (76%), and aural fullness (31%). The patients who have a clear predisposing factor tended to make diagnosis easily; on the other hand the rest of the patients who do not have clear etiology had some diagnostic difficulty. Subjective positive fistula signs were observed in 71% of patients. Vestibular symptoms improved in 80% of patients after closure of PLF. Conclusions: These results suggest that the variety of clinical manifestation make diagnosis more difficult. At the moment meticulous clinical history taking and close follow-up applying repeating fistula tests are the most important for not only earlier but also accurate diagnosis.

In the present study, we investigated the presence of phosphatidylinositol-specific phospholipase C (PLC) isoforms in the cochlea of the guinea pig using Western blot analysis and immunocytochemistry. By Western blotting, PLCβ1 and δ1 were expressed in the cochlear sensory epithelia (CSE) and PLCβ1, γ1 and δ1 were expressed in the cochlear lateral wall. By immunocytochemistry of the CSE, PLCβ1-like immunoreactivity was mainly expressed in the outer hair cells (OHCs), but not in the inner hair cells (IHCs). PLCγ1 and δ1 were expressed neither in the OHCs nor in the IHCs. In the cochlear lateral wall, PLCβ1, δ1 and γ1 were expressed in the stria vascularis and the spiral ligament. In addition, PLCβ1, δ1 and γ1 were also present in type I spiral ganglion cells. Based on these results, we discussed the function of these PLC isoforms in the cochlea.

Effect of changes in stimulus levels of both lower (f1) and higher (f2) stimulus tones on phases of 2f1-f2 component of the distortion product otoacoustic emission (DPOAE) was examined in five normal hearing adults. The f2 was fixed at 4004 Hz in all of the measurements, and the stimulus frequency ratio (f2/f1) was varied from 1.15 to 1.3. Change of the level of lower stimulus tone (L1) and the level of higher stimulus tone (L2) showed different effects on the DPOAE phases. The phase lags increased with increasing L1, when f2/f1 was above 1.22, whereas the phase gains increased with increasing L1, when f2/f1 was below 1.22. On the other hand, the difference in L2 minimally affected DPOAE phase at most f1s. The previous studies about basilar membrane vibration revealed that phase lags increase with increasing stimulus level, when the stimulus frequency is below the best frequency, while phase gains increase with increasing stimulus level, when the stimulus frequency is above the best frequency, and the effect of phase change in stimulus level diminished, when the stimulus frequency was far above the best frequency. Based on the comparison between the results of the present study and the previous findings of others concerning basilar membrane vibration, the DPOAE generation site is assumed to be located at apical of the peak of the f2 traveling wave.

The aim of this study was to clarify the effects of neuropeptide Y (NPY) on cochlear blood flow (CBF) in pigmented guinea pigs. NPY was administered with or without noradrenaline (NA) by systemic perfusion or perilymphatic local perfusion, and CBF was measured using a laser Doppler flowmeter. The systemic and perilymphatic administrations of NPY with NA induced greater prolongation of the increase in and recovery of CBF than the administration of NA or NPY alone. Continuous reduction in CBF induced by NPY may play an important role in the pathogenesis of stress-induced sensorineural hearing losses, such as sudden deafness.

Purpose: We chronologically investigated whether the hearing preservation (HP) rate improved or not in vestibular schwannoma (VS) surgery. Subjects and methods: HP surgery has been attempted in 127 VS patients with pre-operative class A and B hearing from 1976 to 1999. The HP rate was chronologically compared with hearing level and tumor size. Results: The preservation rate of pre-operative class A hearing which was preserved post-operatively as class A has recently been increasing especially in patients with an intracanalicular (IC) tumor. This rate was improved to 67% from 1995, although this was 33% from 1989 to 1994. However, the preservation rate of pre-operative class B in patients with an IC tumor and that of pre-operative class A hearing which was preserved as class A in patients with a larger tumor extending into the posterior fossa, have not improved over the last 10 years. Conclusion: These results indicate that the improvement of the HP rate is mainly due to the increased number of patients with an IC tumor with class A pre-operative hearing. In patients with a tumor of 4-20 mm in size, especially in those showing pre-operative class B hearing, there may be histologically some limitations such as gliosis in the cochlear nerve in the preservation rate of good quality (class A or B) of hearing.