Tamotsu Morimitsu

Development of endocochlear potential and its negative component in mouse cochlea

The chronological developmental processes of endocochlear potential (EP) and negative endocochlear potential (-EP) were investigated as a function of age from birth in the basal and second cochlear turns in normal ICR-strain mice. The EP of the basal turn developed between 5 and 17 days after birth (DAB). The -EP of the basal turn attained to its mature level on 11 DAB and it increased its absolute value further between 12 and 16 DAB and then, recovered to its mature level again on 20 DAB. The developmental processes of EP and -EP of the second turn followed similar courses to those of the basal turn although they were several millivolts different on each day in detail. The results suggest that the developmental processes of the +EP and the -EP are different. The time of reaching minimum -EP during anoxia were measured and the rate of EP decline were calculated on each animal. The rate of EP decline increased rapidly on 10 DAB, almost coinciding the day which EP began to increase abruptly. Although the rate of EP decline is influenced by several processes, this result showed one of the possibility that the sensitivity of the stria vascularis to hypoxia may develop parallel to the development of the EP.

Utilization of nickel-titanium shape memory alloy for stapes prosthesis.

A new type of stapes prosthesis made of nickel-titanium shape memory alloy wire was developed and its biocompatibility was examined in 24 ears of 12 cats. The prosthesis was implanted at the long crus of the incus. The incus was examined 27-355 days after operation. In 23 ears, the prosthesis was found macroscopically well implanted at the aimed position. In one ear the prosthesis was found to be dislocated and in another the prosthesis was slightly loosened. The incudes were removed and five specimens were prepared for scanning electron microscopy and the other specimens were observed under light microscopy. Histological studies revealed severe bone resorption of the long crus in the dislocated case and moderate bone resorption in the slightly loosened case. These bone resorptions were found to be caused by the inadvertent removal of the mucosal membrane during the implant operations. In seven ears under a light microscope and in one ear under a scanning electron microscope, slight bone resorption as bone erosion was seen at the contact area of the prosthesis. This bone resorption was induced by the mechanical pressure of the prosthesis and was not progressive due to fading of the pressure of the prosthesis. With the exception of pressure induced bone erosions, there was no progressive bone resorption which was prosthesis induced. The biocompatibility of the nickel-titanium alloy stapes prosthesis with the long crus of the incus was proved. The prosthesis should be implanted loosely at the long crus of the incus without removal of the mucosal membrane.

Cochlear implantation in an intralabyrinthine acoustic neuroma patient after resection of an intracanalicular tumour

This case study describes a therapeutic strategy using a cochlear implant for a bilateral acoustic neuroma deafened patient. The cochlear nerve had previously been sacrificed on one side during tumour removal, but on the remaining side a functioning cochlear nerve was assessed by electric promontory stimulation in spite of a neuroma extending into the vestibular labyrinth. The patient was successfully stimulated with a Nucleus 22-channel implant after removal of the intracanalicular portion of the neuroma via a middle fossa approach.

Congenital cricoid stenosis.

A case of congenital cricoid stenosis in a 9‐year‐old girl was reported. The stenosis was confirmed by direct laryngoscopy and laryngotracheograms performed through the tracheostoma. The excess cartilaginous tissue was removed under a midline incision of the cricoid cartilage (cricoidplasty). Seventeen cases of cricoid stenosis reported since 1960 were studied and the clinical entity was discussed. On the basis of the embryology of the larynx, the mechanism of origin of this malformation was also discussed.

Magnetic resonance imaging in patients with sudden deafness.

Although many theories on the etiology of sudden deafness have been proposed, the main pathological focus remains uncertain. In this study, MR examinations were performed on patients with unilateral sudden deafness to study the relationship between MRI findings and response to treatments, i.e. amidotrizoate, steroid, or both. In 7 out of 30 cases, the cochlea and/or the vestibule showed higher signal intensity on proton density and T2-weighted images on the diseased side (MRI positive cases). These findings suggest changes in the chemical composition of the perilymph and/or the endolymph, since proton density and T2-weighted images reflect water content. It appears that MRI positive sudden deafness is more difficult to cure even with the use of amidotrizoate or steroid than MRI negative sudden deafness. Amidotrizoate seems to be more effective in MRI negative sudden deafness. MRI would help us to further classify the etiology of sudden deafness.

Pathogenesis of Cholesteatoma Based on Clinical Results of Anterior Tympanotomy

A new conception of the pathogenesis of cholesteatoma is proposed based on clinical results of anterior tympanotomy, a procedure developed in order to prevent recurrence of cholesteatoma following retraction pocket formation after canal-up operation. In the cholesteatomatous ear, there is always a long, thick bony septum between the epitympanum and the supratubal recess. This septum is called the anterior attic bony plate, forming the tympanic diaphragm together with the tensor tympani mucosal fold. In anterior tympanotomy, this bony plate is removed finishing intact canal wall mastoidectomy, making a new ventilating route to the eustachian tube. With this technique, the rate of recurrence was reduced from 17 to 5%. Based on these results it is proposed that the real pathogenesis of cholesteatoma is not tubal dysfunction, but the osseous tympanic diaphragm.

Effects of Kanamycin Sulfate on Cochlear Potentials and Potassium Ion Permeability through the Cochlear Partitions

The cochlear microphonics (CM), endocochlear potential (EP) and potassium ion activities in the endolymph and perilymph were measured in guinea pigs which received daily successive intramuscular injections of 500 mg/kg of body weight of kanamycin sulfate. Preyers reflex threshold at 8 kHz began to increase after the 5th day of kanamycin treatment and disappeared on the 11th day. The maximum output of CM at 8 kHz began to decrease with a time course similar to Preyers reflex. The potassium ion activities in the endolymph and perilymph and the EP did not change appreciably through all experimental days. The magnitude of the negative EP decreased in parallel with the reduction in CM and the relative potassium conductance (GK) between the endolymph and perilymph. These results lend support to the hypothesis that the site of production of the negative EP is probably in the hair cells and that the negative EP is mainly dependent on the permeability of the potassium ions in the organ of Corti.

Computed Tomographic Evaluation of Middle Ear Aeration Following Intact Canal Wall Tympanoplasty

The condition of the mastoidectomy cavity following intact canal wall tympanoplasty (ICWT) is always of great interest to the otosurgeon. We evaluated the status of postoperative aeration in a stable ear following ICWT for various types of chronic otitis media using high-resolution computed tomography (CT). The mastoidectomy cavity in all the cases of simple suppurative otitis is totally aerated and that in over 60% of the cases of adhesive otitis, attic type cholesteatoma and adhesive type cholesteatoma is obliterated by a soft tissue density mass. The size of aerated spaces in the postoperative middle ear cavity not only depends on the type of chronic otitis media but also tends to correlate with the degree of mastoid pneumatization in the opposite ear. CT is useful for the postoperative assessment of middle ear aeration.

LONG TERM EFFECTS OF INTENSE SOUND ON ENDOCOCHLEAR DC POTENTIAL

Changes in endocochlear DC potential (EP) after single and repeated intense sound exposure and negative EP induced by anoxia were observed in guinea pigs with passage of time. The intense sound used was a pure tone of 2 kHz at 145 dB SPL for 4 h. The single exposure group was divided into 8 groups of 1, 2, 5, 10, 20, 30, 45, and 60 days after sound exposure. The EP level dropped remarkably in the 1 and 2 day groups and recovered almost completely in the remaining groups. In the 60 day group, EP was significantly higher than that of the control group. The double exposure group consisted of 1, 2, 5, 10, 20, and 30 day groups after the second exposure at an interval of 30 to 40 days. EP in the 1, 2, 5, and 10 day groups was significantly lower than the control level and in the 20 and 30 day groups was almost the same as that of the controls. In all groups after single and double sound exposure, disappearance of negative EP during anoxia was observed. The EP decrease after sound exposure was apparently caused by a mechanical but reversible lesion at the stria vascularis. The disappearance of negative EP after sound exposure was thought to be induced by an irreversible lesion of Cortis organ.

Parasitogenic octavus neuropathy as a cause of mass stranding of Odontoceti

this fraction. The MW suggested for F8-200 by the standards used in the Sephadex G-200 column ranged from 13 to 17K. In a preliminary study performed in 6.5% SDS-PAGE with the active F2-50 of hemolymph and intestinal homogenate of the unconcentrated samples, only a 14-17K band was detected (data not shown). When 10-fold concentrated F2-50 of intestinal homogenate was analyzed for protein components in SDS-PAGE, the sample revealed the presence of 5 major proteins of apparent MW of 75, 59, 42, 23, and 16K, together with other minor components. The protein having a MW in the 16K band appeared to be present at the highest concentration (Fig. 2). The intestinal homogenate was prepared without protease inhibitors to avoid toxicity. Therefore, part of the major or minor proteins detected might represent degradation products. The relative contribution of each of these components to the process of differentiation is under study at present. As F250 contained components under 75K, a contamination of F2-50 samples with the inhibitory fraction was possible, but the lack of inhibitory action suggests either negligible contamination, or neutralization of its activity by some other component. This work was supported by funds of Secretaria de Estado de Ciencia y Tecnologia y Universidad de Buenos Aires, Argentina. A.M.K. and S.M.G.C. are members of the Research Career of the Consejo Nacional de Investigaciones Cientificas y Tecnicas from Argentina. roteins detected might represent