The superstructure of the guinea pig vestibular endorgan has been investigated using scanning electron microscopy combined with the freeze-fracturing technique. The statoconial membrane is composed of the otoconial layer, otolithic membrane and subcupular meshwork. Thecupula is composed of the cupula and subcupular meshwork. The otolithic membrane consists of closely arranged filaments with beaded appearance and densely packed globular matrix near the otoconial layer. The cupula consists of closely arranged filaments with beaded appearance. The subcupular meshwork consists of long branching filaments cross-bridged to one another. The filaments are continuous with those of the otolithic membrane or the cupula on one side and with the surface of the epithelium on the other, which fills the space between the otolithic membrane and the macular surface as well as between the cupula and the surface of the crista. The otolithic membrane or the cupula would function as a rigid plate and equally distribute the shear force of the otoconial layer or of the cupula to all the ciliary bundles. The subcupular meshwork may play an important role to transmit the shear strain of the otolithic membrane or the cupula to all the ciliary bundle and may also to exert additional damping effect to prevent from unwanted vibration.
The supporting structures in the semicircular canal of the guinea pig were investigated by using several methods as follows: transmission and scanning electron microscopy, high-voltage transmission electron microscopy and immunoelectronmicroscopy. The membranous semicircular canal formed a monolayer of epithelial cells. Transmission and scanning electron microscopy showed that numerous microfibrils, fibroblasts and their cytoplasmic processes were distributed in the perilymphatic space known as the mesh-like structures. The cytoplasmic processes were connected with each other interdigitatedly. These findings suggest that the membranous semicircular canal is supported by meshlike structures from the bony labyrinth with moderate elasticity. Immunocytochemical study revealed that microfibrils of the subepithelial connective tissues were type II collagen. Freeze-fracture study was also done in order to examine the intercellular junctions of crista ampullaris. The obtained results indicated that the tight junction of the sensory epithelium was a “very tight” type and that of the transitional and dark cells was an “intermediate to tight” type.
Reduced cochlear blood flow has been implicated in various pathologies of the inner ear, including sudden deafness, noise-induced hearing loss and Meniere's disease. We studied on the effects of the inner ear fluid on cochlear blood flow. Various factors such as inner ear pressure, perilymph fistula, and vasodilating agents in the perilymph were investigated. 1) In order to study how an increased fluid pressure in the inner ear influences cochlear blood flow, hydrostatic pressure was applied to perilymph through a glass capillary tube inserted into the scala tympani of the basal turn in guinea pigs. Nonradioactive microspheres were injected into the left ventricle, and comparison of the numbers of microspheres between the control (right) and test (left) cochleas was performed. Because of the elevation of the inner ear pressure, the cochlear blood flow decreased significantly. 2) The effect of perilymph fistula on the cochlear blood flow in guinea pigs was studied with use of nonradioactive microspheres. When the round window membrane was ruptured with a fine needle under ordinary inner ear pressure, cochlear blood flow did not change significantly. To study the effect of a persistent perilymph fistula on the cochlear blood flow, a small cannula was inserted into the scala tympani of the basal turn, and the cochlear blood flow was evaluated after one month. Two animals showed no cochlear blood-flow reduction, even if tubal patency was maintained and a perilymph leakage lasted for one month. These results suggest that a perilymph fistula, per se, causes no significant effect on the cochlear blood flow. 3) The effect of topical application of vasodilating agents on the cochlear blood flow was studied with a laser-Doppler flowmeter. Sodium nitroprusside, hydralazine and pentoxifylline were placed on the round window in mice. Nitroglycerin was placed on the round window in guinea pigs. Sodium nitroprusside, hydralazine and nitroglycerin elevated cochlear blood flow but pentoxifylline had no significant effect on cochlear blood flow.
Patch-clamp single channel recordings were made on excised apical and basolateral membrane from dark cells of the semicircular canal of the gerbil to determine if ion channels could be involved in the process of endolymphatic secretion. Dark cells are thought to secrete K+ into endolymph. Nonselective cation channels (28pS), were equally conductive for K+, Na+, Rb+, Li+, and Cs+ and 1.5 times more permeable to NH4+ but not permeable to Cl-, Ca2+, Ba2+, nor to N-methyl-Dglucamine. Maxi-K+ channels (240pS) were impermeable to Na+, Li+, NH4+, N-methyl-Dglucamine, and Cl-. They were identified in the apical membrane and might participate in K+ secretion under stimulated condition. Two types of Cl- channels (90pS and 370pS) in the basolateral membrane had linear current-voltage relations and may provide the paths for the recirculation of Cl- across the basolateral membrane.
The influence of cerebrospinal fluid (CSF) to perilymph composition in the scala tympani of the cochlea, and the difference of transport mechanism of organic anions between scala tympani and scala vestibuli ware studied to elucidate the metallic elements in the perilymph measured with a new method-an inductively-coupled plasma atomic emission spectrometer. And the effect of acoustic overstimulation and anoxia on the concentrations of these metallic elements was investigated. Results and conclusions were as follows: 1) Samples of less than 200nl taken through the round window showed relatively high glycine and alanine contents, comparable to the level found in the scala vestibuli. If a larger amount was withdrawn, lower glycine or alanine levels were observed. This is consistant with CSF which has low glycine and alanine drawn into the scala tympani through the cochlear aqueduct and contaminating the sample. 2) To investigate the transport mechanism of organic anions from blood to perilymph, the concentrations of furosemide, penicillin G and salicylate in the perilymph of the scala tympani (STP) and the scala vestibuli (SVP) were measured after intravenous administrations of these drugs. The steep gradient of furosemide and penicillin G concentrations between STP and the serum was maintained for 2 hours after administration. The maximum concentrations were observed in STP at 15min for furosemide and at 60min for penicillin G, though no elimination was observed in SVP at least for 2 hours. Moreover, high dosage of the competitive inhibitor for organic anion transport, probenecid or sulfinpyrazone, had a drastic effect on the elimination of furosemide or penicillin G in STP, i. e. the concentration in STP increased slowly for 2 hours without any elimination in animals with pretreatment of probenecid or sulfinpyrazone, which had no effect on the elimination in SVP. These results suggested a difference in the transport mechanism of furosemide and penicillin G between STP (active transport) and SVP (passive transport). On the contrary, there was no difference in the elimination of salicylate between STP and SVP. 3) The concentrations of phosphorus and eight metallic elements, i. e. calcium, copper, iron, potassium, magnesium, sodium, lead and zinc were measured simultaneously in a 2μl sample of STP. Our study is the first report on the quantitative measurement of copper, iron, lead and zinc in STP. There was no significant effect of acoustic overstimulation on the concentrations of these elements except for magnesium, which decreased significantly after the exposure to a intense sound (2kHz, 115 dBSPL) for 15min. Among these cationic elements, only iron significantly increased at 5min after anoxia (for 3min) and decreased thereafter to the steady state level in 30min. These rapid changes of iron concentration in STP after the anoxia are very interesting with respect to free radicals, though detailed mechanisms are yet to be clarified. Further biochemical, physiological and morphological studies are necessary to elucidate the roles of these metallic elements in cochlear function.
A pure tone audiometry (PTA), an impedance measurement of the tympanic membrane, tympanometry and an acoustic reflex (AR) test, which are clinically performed as the examinations for preoperative diagnosis of conductive deafness without perforation of the tympanic membrane, were theoretically reviewed. A liquid test, which is one of the clinical tests for examination of the continuity of the ossicular chain by filling the external auditory canal with liquid was investigated by the calculation using formulae. In this test, the gains of the bone conduction were calculated as 35dB, 20dB and 10dB at 250Hz, 500Hz and 1000Hz, respectively, in the case with normal middle ear function. The results of clinical tests in the pathological condition of the middle ear were theoretically summarized as follow; 1) Impedance measurement of the tympanic membrane: the reactance was always negative in value of the acoustic ohm at any frequency in the cases of ossicular fixation, which was sometimes difficult to distinguish the pathological ear (ossicular fixation) from the normal one. In the cases of ossicular discontinuity, it was positive in value of the acoustic ohm at some frequencies. 2) Liquid test: in the cases of ossicular fixation, bone conduction was slightly improved at lower frequency, though it was deteriorated at 1000Hz. No improvement of threshold of bone conduction should be recognized at any frequency in the ears with ossicular discontinuity. 3) AR test: in the AR test ipsilaterally stimulated, the “reversed pattern”, which was the artificial and mechanical response in the ear without physiological AR, should be recognized in the pathological ears. Based on the resonant frequency, “reversed pattern” should be the most remarkable at 2000Hz, 1000Hz and 500Hz in the cases of ossicular fixation, total deafness (or facial nerve palsy) or ossicular discontinuity, respectively.
The clinical examinations, including pure tone audiometry (PTA), impedance measurement of the tympanic membrane, tympanometry, liquid test and acoustic reflex test (AR), were performed for preoperative diagnosis of the conductive deafness without perforation of the tympanic membrane. The specificity and usefulness of these examinations to make a differential diagnosis between ossicular fixation and discontinuity were evaluated by the retrospective studies in 17 cases (23 ears) operated on from April 1990 to March 1993.There was no significant difference between ossicular fixation and discontinuity in air conduction hearing level in PTA. The tympanometry or impedance measurement of the tympanic membrane was not contributory to the differential diagnosis of ossicular chain anomaly. In contrast to these results, the liquid test showed a significant difference between two conditions of the ossicular chain, i. e. no improvement of bone conduction threshold at any frequency by filling the external auditory canal with fluid in all 5 ears of ossicular discontinuity, and deterioration of bone conduction at 1000Hz in 16 for 18 ears of ossicular fixation. The “reversed pattem” in the ipsilaterally stimulated AR was observed in all cases of conductive deaf. ness examined. Furthermore, the amplitude of this response was larger at higher frequency (2 kHz) in the cases of ossicular fixation and at lower frequency (0.5kHz) in those of ossicular discontinuity. This phenomenon was recognized in all 23 ears. It was concluded that AR and liquid test are the most reliable examinations for the differential diagnosis between fixation and discontinuity of the ossicles.
Middle ear and eustachian tube were studied histopathologically in 8 children (12 ears) with otitis media with effusion who had been treated with tympanostomy tubes for 3 weeks to 11 months. In the middle ear, 1) almost no effusion was seen in ears treated for longer than 6 months, 2) degree of inflammation was grossly proportional to the amount of effusion, and 3) epidermal ingrowth at the site of tube insertion was seen in both of the two ears treated for longer than 10 months. In the eutachian tube, 1) inflammation was generally more severe than that in the middle ear, but tended to subside eventually with treatment, 2) dense effusion plugged the bony portion in two ears with obstructed tympanostomy tube.
Beschitin® (W-type-T; t=0.08mm), a non-woven chitin fabric of poly-N-acetyl glucosamine extracted from the crab's shell, was applied to 10 cases with traumatic perforation of the tympanic membrane, and 15 cases with chronic otitis media. Perforation was covered by a sterilized patch of the chitin fabric. Hearing loss and ear-fullness were improved immediately after application of the chitin fabric. Nine of 10 cases showed a closure of the tympanic membrane perforation without atrophic changes. In one case, a simple myringoplasty was performed after 5 months because of chronic infection. The procedure using a patch of chitin facric was very simple, safe and effective.
Six patients with ear diseases caused by nose blowing are described. Four of them developed perilymphatic fistula. Exploratory tympanotomy was performed on the left ear of case 1 who complained of tinnitus. Leakage was identified in the area of the round window, which was covered with a piece of perichondrium. Three patients (cases 2-4) complained of tinnitus and a floating sensation, echo sound, and dizziness. All of them have the habit of nose blowing. The symptoms disappeared spontaneously after a rest. Two patients (cases 5 and 6) developed fullness of the ear after nose blowing. They were diagnosed as suffering from bullous myringitis. Nose blowing may predispose to formation of bubbles within an infected tympanic membrane.
A 43-year-old man developed a perilymphatic fistula via the explosive route of the left ear. Exploratory tympanotomy was carried out in 1989, and the perilymphatic leakage from the oval window was observed. The round and oval windows were covered with perichondrium, and the patient became subsequently symptom free for nearly three years and three months. In 1992, difficulty walking and generalized dull headache was noted. Although these symptoms were improved spontaneously, diagnostic CT of the skull demonstrated the findings consistent with hydrocephalus. Neurological examination revealed only left gaze nystagmus. No hearing deficit was evident. High resolution CT of the left temporal bone demonstrated no abnormal findings, such as congenital anomalies, widened cochlear aqueduct, widened internal auditory meatus. MRI of the left temporal area four weeks later demonstrated the findings suggestive of fluid collection in the left mastoid area. At present, this patient has no complaints. Further observation is necessary to identify any recurrence of perilymphatic fistula. The association of hydrocephalus and perilymphatic fistula suggests that perilyniphatic fistulae may develop in response to increased intracranial pressure secondary to hydrocephalus.
In recent years, we have identified certain patients with idiopathic sensorineural hearing loss for whom acute progression of the disease in one or both ears was found to be responsive to steroid administration, and for whom any recovery of hearing function thus obtained could be manintained with long term steroid administration. We named it as steroid-responsive sensorineural hearing loss. Although the pathological mechanism of sensorineural hearing loss in such patients is not as yet understood, it is possible that autoimmune disease may play a role. To investigate this possibility, studies of cellular and serological immune function were conducted for 14 patients with steroidresponsive sensorineural hearing loss or idiopathic progressive sensorineural hearing loss, including assays for immunoglobulins, lymphocyte subsets, complement, circulating immune complexes and specific autoantibodies. Quantitative assessment of immunoglobulin levels was found to be manifestly abnormal in 5 out of 10 patients (50.0%) for whom such studies were carried out. Additionally, abnormalities in ratios of various lymphocyte subsets were identified in 7 out of 14 patients (50.0%) for whom lymphocyte subsets were assessed. More particularly, several patients demonstrated depressed ratios of suppressor T cells which are known to permit or induce B cell activation, although there was no clear correlation of measured immunoglobulin level with abnormalities in suppressor T cells ratios. While there was an increased incidence of some type of immunological abnormality in the patients we studied, no obvious trend or pattern in abnormal immunological functions was identified. This may be attributable to the small number of patients studied, variation in the stage or duration of disease, as well as to variables pertaining to treatment, for example, dosage and/or duration.
A nonlinear transmission-line-analog model of the cochlea, which is a version of the onedimentional long-wave model of the cochlea, was used to simulate evoked otoacoustic emissions (EOAEs). The model produced echoes very similar to real EOAEs in respect to the latency, spectral features and saturation characteristics when highly damped points were set on the basilar membrane (BM) with equal spacing. It was concluded that EOAEs were the waves reflected from BM due to irregularities of the impedance.
Thirty cases with bilateral enlargement of the internal auditory canal demonstrated on a conventional temporal bone roentgenogramme (Stenvers projection) were clinically studied. Enlargement of the canal was defined as the vertical diameter 10 mm or more (magnificataion 1.4x). Maximal vertical diameter was 16 mm and bilateral variation within 3 mm. The shapes of the canal observed were oval in 41 ears, straight 14 and narrowed medially 5. When compared bilaterally, shape was the same in 90% of the cases. No correlation was found between the diameter of the canal and age, hearing levels and caloric test. Acoustic neurinomas were identified in 2 cases, 3 ears. In conclusion, the authors postulated that most of the bilateral enlargement of the internal auditory canal, especially symmetrical and oval one, might be a normal variant.
The time course of postoperative facial nerve function in early stage after tumor removal(up to 60 days)was investigated in 12 cases of surgically proven unilateral acoustic neuroma(AN). The simultaneous evaluations of facial nerve function by 40 points grading system(40 points system)and House and Brackmann's facial nerve grading system(House and Brackmann's system)were sequentially conducted and the results were compared. The results obtained were as follows; 1) A highly positive correlation was found between the total score in 40 points system and the grade in House and Brackmann's system(rs=0.96, Spearman rank correlation coefficient, n=202 evaluations). 2) The apparent change in postoperative facial nerve function was observed in 9 out of 12 cases during the follow-up period. Two cases did not show the postoperative facial palsy and another case did not show any recovery of facial nerve function during the follow-up period because of severe paralysis. 3) The time course of postoperative facial nerve function evaluated by two systems was found to be almost parallel in 2 out of 9 cases. The speed of change in facial nerve function in these 2 cases was relatively fast. 4) The facial nerve function evaluated by two systems showed the somewhat different time course in 7 out of 9 cases. The velocity of the change in facial nerve function in these 7 cases was relatively slow. The cause of this difference could be due to the more precise detectability of the change in facial nerve function in 40 points system than that in House and Brackmann's system. 5) Based upon these results, it was concluded that the time course of postoperative facial nerve function evaluated by two systems could differ in some cases of AN, although there was a highly positive correlation between the results evaluated by two systems in general.
Amyotrophic lateral sclerosis (ALS) is a disease of unknown etiology characterized by progressive degeneration of the neurons that give rise to the corticospinal tract and of the motor cells of the brainstem and spinal cord. Although it has been known that ALS is often associated with facial weakness or palsy during the course of the disease, little attention has clinically been paid to this symptom because the prognosis is always grave and fatal. In addition, to our knowledge, there has as yet been no postmortem report on temporal bone histopathology of patient with the disease in the literature. We examined 5 pairs of the temporal bones of patients with ALS. Histological study of the temporal bones revealed severe, bilateral degeneration of the motor neurons of the facial nerve throughout the intratemporal segments in 4 or 5 cases. In contrast, sensory components (the nervus intermedius, geniculate ganglion, greater superficial petrosal nerve and chorda tympani nerve) were well preserved and appeared normal. The pathologic feature of degeneration of the nerve was further analyzed using the special staining technique for demyelination of the motor fibers developed by Kltiver and Barrera.
The presence of carbohydrates in glycocalyx of the vestibular end organs of the guinea pig was investigated at the ultrastructural level using gold labelled lectins. The glycocalyx of both the sensory and the supporting cells has variable suger components. The glycocalyx of the sensory cells including the ciliary interconnections, contains N-acetyl-glucosamine, N-acetyl neuraminic acid, galactose and mannose.In contrast, the glycocalyx of the supporting cells has a lower amount of N-acetyl-glucosamine. The ciliary interconnections, which have been considered to be a part of the glycocalyx, have a larger amount of N-acetyl neuraminic acid, galactose and mannose than the surface glycocalyx. These findings indicate that sugar components may be closely related to the functional significance of the inner ear glycocalyx and that the functional properties of the glycocalyx may differ between the sensory and the supporting cells of the vestibular end organs.
The auditory brainstem response (ABR) and teh VIII-th nerve compound action potential (AP) were measured in guinea pigs using click stimuli to investigate the age-related changes in the neural auditory thresholds. The animals were divided into following four groups: group A (2 months of age;20 subjects), B (13 to 14 months of age; 20 subjects), C (23 to 24 months of age; 10 subjects) and D (33 to 34 months of age; 10 subjects). With advancing age, a distinct elevation of the thresholds in both the ABR and AP was obtained among the 4 groups. Ni latencies of the AP prolonged with advancing age and the difference between group A and three other groups (B, C and D) was significant. Ni amplitudes of the AP decreased with advancing age. There were singnificant differences in the Ni amplitudes of the AP between group A and three other groups (B, C and D). In selected animal subjects in groups B and C, however, similar neural auditory thresholds obtained form the ABR and AP, Ni latencies and amplitudes of the AP to those measured in younger subjects in group A were occasionally observed. This fact suggested that there were some individual differences among the animals examined.
Adenosine diphosphate (ADP) was applied to the basal turn of the cochlea in guinea pigs using iontophoresis. The following conclusions were obtained. (1) ADP iontophoresis induced thrombi in the stria vascularis of the basal turn. (2) ADP iontophoresis induced a decrease in coclear blood flow and cochlear microphonics. (3) The induction of thrombi in the stria vascularis by the ADP iontophoresis method might prove to be an animal model for certain cases of sudden deafness.
The function of the stria vascularis in the cochlea is believed to produce endolymph. The mechanisms that control or maintain the function of the stria vascularis however, remain unclear. From an anatomical viewpoint, it has already been elucidated that there is no innervation to the stria vascularis. In the present study, in order to clarify the humoral control or maintenance of stria vascularis function, we investigated the effects of one-shot reserpine administration on the ouabainsensitive, K+-dependent, p-nitrophenylphosphatase (K-NPPase) activity, the second step of Na-K ATPase activity, of the stria vascularis in guinea pigs. K-NPPase activity was shown to be completely inhibited 3-20 days after reserpine administration, and was detectable again 60 days after reserpinization. As reserpine is an adrenergic neuron blocker, these results suggested that catecholamines might play an essential role in the maintenance or control of K-NPPase activity, and that the stria vascularis might be one of the target organs of catecholamines.
It is well documented in the literature that cochlear electrical potentials such as endocochlear DC potential and cochlear microphonics are maintained normally under sufficient oxygen supply and can be disrupted by ischemic or anoxic condition. It is presumed that anoxia or prolonged hypoxia may produce functional and/or morphological deficits in the membranous labyrinth. We histopathologically studied 6 pairs of the temporal bones of the patients who died of severe respiratory distress caused by progressive respiratory paralysis resulting from amyotrophic lateral sclerosis (5 cases) and by serious restrictive ventilatory failure (1case) in order to examine whether or not long-standing hypoxic and/or hypercapnic conditions during their terminal stages might affect any histological changes in the sensory epithelia and neuronal populations in the human inner ear. Histological study of the temporal bones revealed unexpectedly good histologic preservation of the hair cell population of the organ of Corti and vestibular sense organs and of the stria vascularis, as well as the cochlear and vestibular neurons in 4 of 6 cases except for some senile changes of varying degree. In 2 of 6 cases, the histological details of the sensory epithelia could not be clearly identified because of rather severe postmortem autolysis, which seemed to be more advanced than that of the specimens with similar time lapse after death. The cochlear and vestibular neurons, however, appeared normal in the two cases. It is concluded that the sensory epithelia and neuronal population in the human inner ear appear to be considerably resistant to long-standing hypoxic and/or hypercapnic conditions, despite the fact that postmortem autolytic changes of the inner ear seem to be enhanced to some extent by hypoxia and/or hypercapnia.