The estimation of the prevalence of Meniere's Disease (M.D.) is important not only for etiology but also making medical plans for the number of beds in regional hospitals. This report describes the results of a survey of patients with M.D. conducted in Tottori prefecture in 1990. The incidence of M.D. increased with age, and the male/female ratio was about 1 : 3. Treatment was mainly ambulatory (81 %), and only 19 % were hospitalized. About 80% of the patients were treated by internist. A stratified random sampling technique showed that the estimated number of M.D. patients in Japan was 115, 881. The 95% Confidence of Interval had a wide range, from 611, 713 to 170, 588.
The diagnostic criteria for bilateral involvement of Meniere's disease delineated in our previous study were used to evaluate patients' anxieties and doctors' impressions in 135 cases of Meniere's disease with bilateral fluctuant hearing loss. These patients tended to have anxieties about disruption of their daily activities and their doctors tended to have the impression that their response to the therapy with diuretics, steroids or hospitalization was poor. Thus, the early diagnosis of bilaterality of the disease and intensive treatment such as sac op-eration or drug therapy is necessary.
In 1992, responses to a questionnaire on Meniere's disease were obtained from 39 Asean doctors. 1) Meniere's disease is not so rare in Asean countries. However, symptoms seemed less severe than in Japan or western countries. 2) Most Meniere's patients did not smoke or drink alcohol. 3) Meniere's patient seemed to occur more frequently in females than in males.
Based on the data obtained from two Japan-wide surveys of Ménière's disease (MD) conducted by the Ménière's Disease Research Committee of Japan (1975-76) and the Vestibular Disorders Research Committee of Japan (1982-84), the epidemiological characteristics of unilateral severe MD were evaluated among 810 patients with definite MD. Of these 230 had severe MD, 48 of them had with profound hearing loss (UPHL group) with a pure tone average of the affected ear at 500, 1000 and 2000Hz of 70dB or worse, and 182 had markedly disabling attacks of paroxysmal vertigo for more than 3 years (UDV group). 1) The sex ratio in the UPHL group was 1 : 1, but there were more females than males in the UDV group. 2) Age at onset of MD peaked in the third decade in the UPHL group, and in the fourth decade in the UDV group. 3) In the past history, otitis media was significantly more common in both the UPHL and UDA group than in non-severe patients. 4) Insomnia was more likely to cause vertigo attacks in the UPHL group than in non-severe patients.
The influence of a cold front (CF) on the onset of Meniere's disease was investigated. A major CF is difined by the meteorological observatory as fulfilling the following conditions: 1. falling temperature (>5 deg), 2. rising humidity, 3. strong wind more than 10 m/sec, 4. rain or snow, 5. thunder, 6. wind shifting from south to north-west. This occured 14 times in 1992. The passing of a minor CF is decided from weather maps. Major and minor CFs occured oneclench for five days in winter and for 10 days in summer. The influence of CFs on Meniere's disease was evaluated by the time n method and the results were compared with those of patients with sudden deafness and with Bell's palsy. The onset of Meniere's disease had its highest incidence just after CF passed. The histogram of the number of days between the passing of a CF and the onset of Meniere's disease indicated a normal distribution. On the other hand, in patients with Bell's palsy the onset was most frequent one day before the passing of a CF, and in those with sudden deafness no specific concentration was observed. From these results we concluded that the onset of Meniere's disease was influenced by the passing of a CF and that this influence was more specific in Meniere's disease than in Bell's palsy or sudden deafness.
An epidemiological survey of vestibular neuronitis was conducted in Japan with questionnaires. From 1988 through 1990 information was obtained from 531 patients in 71 hospitals. This paper describes the incidence of the different types of nystagmus in vestibular neuronitis. 1) Group I consisted of 473 (89%) patients who showed direction-fixed nystagmus towards the healthy side in positional and positioning nystagmus tests. Group III consisted of 27 (5%) patients who showed vertical or direction changing nystagmus in the same tests. 2) The incidences of complications and nystagmus at the last examination were higher in Group III than in Group I. Statistically significant differences weve found between the two groups. 3) It was suspected that the cause of vertical or direction-changing nystagmus in vestibular neuronitis was different from the usual cause of vestibular neuronitis.
We carried out Gd-DTPA enhanced magnetic resonance imaging (MRI) in 5 patients with vestibular neuronitis. With a fast low angle short (FLASH) method, MRI was taken before and after the intravenous administration of Gd-DTPA (0.1 mmol/Kg) using 1.5 Tesla Magnetom H15. We could not detect enhanced regions of vestibular nerve in these 5 patients. We discuss the image diagnosis of vestibular neuronitis by enhanced MRI in this preliminary investigation.
A 62-year-old female had recurrent attacks of vertigo associated with tinnitus and impaired hearing of the left ear. The findings of air CT cisternography suggested neurovascular compression syndromes (NVC) of the left eighth cranial nerve. Severe reduction of left galvanic response on the galvanic body sway test (GBST) suggested retrolabyrinthin disorder on the left. After neurovascular decompression she became free of vertigo. The galvanic response on the left side recovered 2 months after operation. It is thought that GBST is useful diagnosis of NVC of the eighth cranial nerve, and in the evaluation the progress (including the postoperative course).
To clarify an alteration of tympanic temperature (TTy) in the patient with vertigo, we evaluated bilateral TTy in a patient with Ménière's disease and 6 healthy subjects as a contral. TTy was obtained by Quick Thermo® (MC-500, Omron Matsuzaka Co Ltd), which measured infra-red rays from the tympanic membrane. There was no significant difference between the bilateral TTy in the control study. To the contrary, there existed a difference between bilateral TTy in the patient with Ménière's disease just before and after the several vertigo attacks. The results suggested that a difference between bilateral TTY might be related to cerebral blood flow which was originated from autonomic dysfunction in patient with vertigo.
In 507 patients with vertigo we examined the velocity of vertebral artery blood flow using ultrasonic blood rheography. The subjects were devided into 3 groups; laterality group, low velocity group and normal group. The differences were related to disease and aging. In 160 patients (31.5 %) abnormal results were found, such as laterality group or low velocity group. There was no difference in prognosis between the laterality group and the normal group in Meniere's disease or hypotension. However, in VBI, laterality group showed a worse prognosis than the normal group. Moreover, in 21 patients the decrease in laterality of the vertebral artery accompanied the improvement of vertigo.
Using the western blotting technique, we examined the serum of patients with sensorineural hearing loss or vertigo for the presence of inner ear autoantibodies. The SDS soluble extract was prepared as the inner ear antigen from bovine inner ear tissues. About 70% of patients had inner ear specific autoantibodies which reacted with 32kD (8.1%), 33-35kD (14.9%), 42kD (14.9%) and 68kD (9.4%) determinants. In some patients sensorineural hearing loss may result from autoimmnue reactions directed against proteins derived from the inner ear. The inner ear specific autoantibodies may also enable us to diagnose autoimmune-mediated inner ear disorders and to treat these patients more effectively. It is necessary to purify the inner ear specific antigens for exact diagonosis of inner ear disorders.
Tissues of the stria vascularis of normal rabbits were collected as cochlear antigen and injected into the foot pads of guinea pigs. Damage to the capillary endothelium and an increase in vascular permeability were found in the stria vascularis. Therefore, we studied patients with increased level of immunoglobulin G-class circulating immune complex (IgG-CIC). Hearing loss was found in 26 of 44 ears and vertigo was found in 10 of 22 patients with significantly elevated IgG-CIC levels. The relationship between inner ear disease and the presence of CIC was considered to be very significant. The possible mechanism of CIC-mediated inner ear diseases is discussed.
Glycerol test results and electrocochleographic (EcochG) findings were correlated with the plasma antidiuretic hormone (ADH) level in patients with Meniere's disease. There was no statisticaly significant correlation between the glycerol test and plasma ADH. However, the plasma ADH level tended to decrease in patients with a positive reaction to the glycerol test and tended to increase in patients with a negative reaction. There was a statisticaly significant correlation between the dominant negative SP (-SP) of EcochG and the plasma AD H level. Plasma ADH tended to increase in patients with dominant -SP. It has been reported that the plasma ADH level in patients with Meniere's disease is higher than normal. Both the positive reaction to the glycerol test and the dominant -SP of the EcochG indicate the presence of endolymphatic hydrops. In this study, however, there seems to be a discrepancy between the correlations of glycerol test result and EcochG with the plasma ADH level. These results may mean that the positive reaction to the glycerol test and the dominant -SP of EcochG may represent different conditions of endolymphatic hydrops in Meniere's disease.
Harada's disease is well known as uveoencephalitis in Europe and America. We examined a 26-year-old female who complained of a floating sensation following the sudden onset of uveitis. A diagnosis of Harada's disease was made, and she was treated with steroid. Electronystagmography showed abnormal eye movements which were suggestive of flutter-like oscillations, square wave jerks, and opsoclonus. These abnormal eye movements are observed rarely, mainly in patients with a lesion in the cerebellum and brainstem. The results of vestibular function tests suggest that the lesion of Harada's disease is located not only in peripheral vestibular organs but also in the central nervous system.
A patient with Harada's disease showed signs of cerebellar impairment such as gaze-evoked nystagmus, rebound nystagmus and vertical nystagmus. This study revealed that disorders of the central nervous system, and marked cerebellar disturbances are present in patients with Harada's disease who complain of disequilibrium. I propose that Harada's disease, which manifests cochleo-vestibular symptoms, should be divided into three subtypes, peripheral type, central type and mixed type, based on otoneurological results.
I report a rare case of the recurrent cochleo-vestibular type of Harada's disease. The patient had repeated episodes of rotatory vertigo, accompanied by cochlear signs, showed a positive response to the glycerol test, and had a dominant negative SP in the electrocochleograms, suggesting the presence of endo-lymphatic hydrops.
Unicylce riding is a sport and exercise in Japanese elementary schools. Our concern is the possibility of its effect on vestibular training. In the present experiment we examined the effects of unicycle riding on several aspects of posture-maintaining, using a stabilometer and calculating the duration of the posture-maintaining period. Twelve pupils in a Prefectural School for Deaf were selected as subjects of vestibular training with unicycles. Those subjects suffered from severe hearing impairment, and some of them also had other sensory or physical problems. Unicycle riding was taught by two physical education teachers for about two hours every day except holidays. The subjects were tested with a stabilometer while standing straight with toes and heels together, with eyes open and eyes closed. Then they were asked to keep standing with three foot positions with eyes open and eyes closed to estimate the duration of stable posture-maintaining. The 3 foot positions were 1) standing straight on one leg (one-leg standing), 2) standing with tandem Romberg's foot position (tandem-Romberg standing), and 3) standing on one leg while maintaining airplane-like posture of horizontally outstretched hands and 45 degrees forward-tilted body trunk (airplane standing). The subjects were classified into 3 groups according to the effect of train-ing: well-trained group (Group A), moderately-trained group (Group B) and poorly-trained group (Group C). Stabilometry and measurements of posture-maintaining time were performed, followed by the same tests every 3 months for 9 months. Group A and Group B obtained a significant effect of unicycle training in posture-maintaining, while Group C showed no effect in all the methods used in the present study throughout the 9 months. Vestibular training with the unicycle is very useful for the development and rehabilitation of equilibrium function.
Injection of streptomycin sulfate into the middle ear cavity was performed for treatment of frequent attacks of vertigo casused by unilateral inner ear le-sions such as Ménière's Disease (57 cases), unilateral inner ear hypofunction with unilaterally reduced caloric responses (10 cases), severe benign paroxysmal positional vertigo (BPPV) (5 cases). These 72 cases of inner ear lesions had frequent attacks of vertigo and they refused surgical therapy. After the injection of streptomycin sulfate into the middle ear cavity, the vertiginous attacks disappeared, however they needed constant trainings to regain equilibrium. These subjects were observed for 6 months to 13 years after the injection. After this treatment, their tinnitus was the same or less than before the injection. The hearing remained the same as the pre-injection in cases of unilateral inner ear hypofunction, or BPPV. However, in 2 cases of Ménière's Disease, the hearing of the lesion side was strongly impaired soon after the injection. In the other cases of Ménière's Disease, the hearing was the same as before the injection or improved. In 2 cases of Ménière's Disease, the contralateral hearing of low tone was reduced.
Sinusoidal rotational test and vestibular auto-rotation test (VAT) were per-formed on eight patients with Meniere's disease before and after vestibular nerve section. Two weeks after the operation, almost all the patients consistently showed response asymmetry toward the healthy ear at all stimulus frequencies and reduction in sensitivity to rotational stimuli at 0.01 Hz in the sinusoidal rotational test. Prior to surgery, the VOR time constant varied depending on the residual vestibular function of each patient. The time constant then dropped to a mean of 4.2 seconds 14 days afteroperation. In the VAT, almost all patients showed gain reduction at all frequencies on the seventh post-operative day. These findings suggest that the response asymmetry and the gain at 0.01Hz in the sinusoidal rotational test are valuable in evaluating the time course of compensation of the vestibular function after surgery and that the VOR time constant is useful in determining whether the vestibular nerve is cut properly.
Fifty three patients with spontaneous and traumatic perilymph fistulas (PL F) were treated in our institutions from 1988 to 1992. The presence of fistula was confirmed surgically in 20 patients (PLF-conf group). In the remaining 33, it was not found during the operation or was treated simply with bedrest and medication (PLF-susp group). Clinical features and recovery of auditory and vestibular function were compared in these two groups. No difference was noted in the clinical features of the two groups. Hearing recovery in the PLF-conf group was worse (recovery rate 30%) than in the PLF-susp group (recovery rate 69%). On the other hand, there was no significant difference in the recovery from vestibular symptoms between the two groups. Dizziness disappear-ed in all, except in two patients in the PLF-susp group. Central compensation may account for the recovery of vestibular function.
The course of recovery in 4 patients with Meniere's disease was examined with static posturography (SPG) and kinetic posturography (KPG). SPG was recorded by a stabilometer during quiet stance and KPG was recorded by PO LGON so that the angular change of the shoulder in the frontal plane was measured during stepping in the same position. The process of SPG improve-ment was concordant with that of KPG, and the abnormally high levels of SPG and KPG be came normal within 8 days. Those results differ from those of vestibular neuronitis. We consider that the mechanism of recovery from Ménière's attacks is different from vestibular compensation and is due to fluctuation of inner ear function.
Some patients with Meniere's disease undergo natural remission of their vertigo, although it is almost always difficult to establish the natural course of Me-niere's disease because of its episodic fluctuating course. In the present study, the natural course of Meniere's disease in the acute stage was examined in six patients. Their subjective and objective symptoms (frequency of spontaneous nystagmus, caloric test and pendular rotation test) were compared with the course of remission in 6 patients treated with steroids. All patients were followed every week for 8 weeks or more. The subjective effect was expressed as the "spell index" calculated by multiplying duration by number of vertigo attacks in a week in order to amalgamate both intensity and frequency into a single score. Significant decreases (p<0.05) in the "spell index" and the number of nystagmus were demonstrated during the first two weeks, and then a gradual decrease was noted. Although no difference in caloric excitability was noted between the start and the end of the trial, rotation directional preponderance was significantly (p<0.05) reduced. Subjective improvement of the "spell index" was significantly (p<0.001) associated with the improvement in the objective results of nystagmic beats. The bound effect of the drug based on natural remission was markedly demonstrated during the first period. Evaluation of the effect of treatment of vertigo should be performed on the basis of natural remission. Further examination is necessary to establish the natural course of Meniere's disease.
Isosorbide (ISO) has proved to be one of the most effective agents in the appropriate period of administration for patients taking ISO, we have done follow-up interviews and examinations of 30 Meniere's cases (48 affected ears) for one year after they had taken ISO for at least half a year. Deterioration of clinical symptoms was found in 14 patients. Our observations indicate that patients who experience vertigo attacks during the initial 6-month treatment period and have good hearing (less than 40dB) in their affected ears should continue long-term treatment with ISO.
In order to evaluate the effectiveness of various therapies for vertigo at-tacks associated with tinnitus and hearing loss in Ménière's disease, the standard of both AAOO in 1972 and AAO-HNS in 1985 for the evaluation have been used in the United States and in Japan. The efficacy of treatment to prevent or decrease vertigo attacks and the duration of observation to evaluate it are the two main points discussed because the recurrence of attacks causes great suffering and it may make a hearing loss irreversible. There is often need to evaluate conservative treatment even soon after the start of therapy in order to judge whether the treatment is suitable for the patient. The modified evaluation method of AAO-HNS, which compares the mean numbers of attacks during the same intervals before and after the start of treatment is proposed in this study. This method can be useful both for short observation times less than 2.5 years and for long times of 3 or 5 years or more.
The use of disability, a parameter that reflects the patient's subjective symptomatology, for assessment of therapeutic efficacy in peripheral vestibular dis-orders was proposed, and disability was classified into 5 stages according to AAO-HNS criteria, each of which was subdivided into categories of different grades. A series of patients followed for a long time 20 with Meniere's disease, 23 with peripheral vestibular disorders and 16 with vertebro-basilar insufficiency, was investigated by a questionnaire survey and the results were analyzed by for abnormalities of 5 fundamental elements of motion: head movement, transfer of center of gravity, gazing, solar area and passive movement. It was concluded that disturbances of these 5 fundamental elements of motion, even at the same stage of disability, varied with different disease categories and generally were disease-specific.
In order to draft the guidelines for reporting treatment results in Meniere's disease in Japan, the Committee Members were elected by the Japan Society for Equilibrium Research in 1991, and their papers were discussed in the first, second and third workshops from June 1991 to November 1992. In Septemper 1992, the Committee analyzed the preliminary criteria from the responses to a questionnaire collected from the 17 Committee Members. The preliminary draft of guidelines obtained from the analysis of the questionnaire are summarized as follows. 1) Evaluation of Symptoms: Only definitive attack of vertigo with spontaneous nystagmus should be taken into account for the evaluation of the treatment of symptoms (AAOO, 1972) (Agreement: 82 %). The degree of vertiginous spells should be noted pre-and posttreatment, and the disability should be evaluated four categories (AAOHNS 1985) (Agreement: 82 %). The parameter for the assessment of the hearing level is much better with four frequencies pure-tone average (PAT) at 250, 500Hz, IKHz and 2KHz than that of the AAOHNS's four frequencies (500Hz, 1KHz, 2KHz, and 3KHz) (Agreement: 47 %). 2) Evaluation Period: Valid results for the evaluation of vertiginous spells should be based on observation for over six months pre-treatment and over 12 months after the initiation of therapy (Agreement: 75%). If the duration of pretreatment is less than six months, the divisor is the average number of definitive spells per month for the period of observation. 3) Evaluation Criteria: In the same way as AAOHNS (1985), the formula expressing the effect of treatment on vertiginous spells should be adopted for our criteria (Agreement: 100%). 4) Global Judgment: The degree of disability should generally be evaluated in reporting the effect of therapy (Agreement: 41%). These answers to the questionnaire show that the same evaluation for medical and surgical treatment could not be adopted by all the Committee Members (Agreement: 50 %). Therefore, further discussion of these points is needed.
The present study describes a modified method of producing experimental endolymphatic hydrops in the guinea pig. The endolymphatic sac was exposed via the epidural occipital approach, and was cauterized electrically. In all of 10 animals which recieved this sac operation, slight to mild hydrops developed 1 week after the electro-cauterization of the endolymphatic sac. The endolympha-tic sac showed hypertrophic changes with increased amounts of connective tissue, but the histolgical changes did not involve the endolymphatic duct. It was noted that precipitates and macrophages were absent in the sac lumen. This epidural electro-cauterization of the sac seems to be a simple and easy method of producing the retention hydrops experimentally.
The relationship between an episode of spontaneous nystagmus and perilymph antibody levels following secondary immune reaction in the endolymphatic sac (ES) was examined in guinea pigs. Spontaneous nyztagmus was observed in 28 out of 46 animals. From day 2 to 7, the mean perilymph antiboody levels in the animals demonstrating spontaneous nystagmus were significantly higher than in animals without nystagmus. However, from day 14 to 28, no significant difference was seen in the mean perilymph antibody levels between the animals with and without spontaneous nystagmus. These results suggest that immune reaction in the ES may actually induce vestibular disorders.
Isolated living vestibular sensory cells are capable of producing self movement. After exposure to a medium containing a high concentration of potassium, type I cells show tilting of the neck portion accompanied by tilting of the hair bundle. Actin, a protein associated with the cytoskeleton and cell motility, is thought to be related to vestibular hair cell motility. The localization of F-actin in isolated vestibular hair cells has been studied with the use of FITC-labeled phallodin. In hair cells fixed by paraformaldehyde, actin filaments are distributed in the hair bundle and cuticular plate. In frozen fixed cells perfused by artificial perilymph, strong localization was found in the hair bundle and cuticular plate, as well as throughout the cytoplasm. In frozen fixed cells per-fused with artificial endolymph containing a high concentration of potassium, the staining of hair bundle and cuticular plate was less. The changes of this actin staining pattern may be closely related to the mechanism of self movement.
The present study was conducted to clarify immunocytochemically the location of neuroactive substances distributed in the vestibular efferent nerve system of various animals (chicken, pigeon, rat, guinea pig, cat and squirrel monkey). In order to compare the known efferent component with neuroactive sub-stances, the distribution of acetylcholine esterase (AChE) and choline acetyl-transferase (ChAT) were also investigated. ChAT-like immunoreactivity and ACh E-positive staining was found in alll the vestibular endorgans studied, and there were no marked species differences in the staining patterns. In contrast, the la-cation of calcitonin gene-related peptide (CGRP)-and γ-aminobutyric acid (GA BA)-like immunoreactivities varied according to the species. Numerous CGRP-like immunoreactive endings were demonstrated beneath the hair cell layer of the rat and guinea pig vestibular endorgans. However, only a few CGRP-like immunoreactive puncta were found in the chicken and pigeon vestibular periphery, and no immunoreactivity was detected in the cat and monkey vestibular en-dorgans. GABA-like immunoreactive endings and fibers were observed in the pigeon and monkey vestibular endorgans, but they were scarce in chickens, in contrast to the findings in rat, guinea pig and cat vestibular endorgans, where no GABA-like immunoreactive fibers were distributed. These differences in distribution patterns of neuroactive substances suggest that each species has a chemically (and probably functionally) distinct efferent system which may be related to the specific environment and/or evolution.
The perforating vessels in the brainstem of the Mongolian gerbil were ex-amined by India ink injection and the brainstem microvascular architecture was examined by Mercox injection. 1. Three types of perforating vessels were identified. Type 1 perforators branched into capillaries soon after penetrating the brainstem, type 2 perfora-tors changed into capillaries in the middle of the brainstem, and type 3 perfo-rators penetrated the dorsal part of the brainstem and changed into capillaries. The diameter of type 1 perforators was 10-15μm, that of type 2 was 20-25μm, and that of type 3 was 35-55μm. 2. The capillary blood vessels generally showed T-shaped or Y-shaped branching but occasional atypical configurations were observed. The blood flow may be regulated by these different configurations. 3. We observed no difference between the capillary blood vessels of the vestibular nucleus and those of the cochlear nucleus. 4. We observed that the brainstem contains a dense capillary network, and that blood flow in the perforators was regulated by the site of entry into the brainstem and by the diameter of the perforating vessel.
In the development of the model mouse with congenital vestibular disorders, the technique of "exo-utero surgery", established by Muneoka et al. (1986) was modified and applied for direct manipulation of postimplantation mouse embry-os. We conducted a basic study on the viability of exo-utero mouse embryos (Jcl: ICR) with or without injection. Hank's solution or physiological saline was injected into the telencephalic vesicle. The days of operation were from Ell to E15. The viability of exo-utero embryos was; (1) 78% (n=9) in embryos oper-ated on Ell and sacrificed on E15 (Eli-E15); (2) E12-E15: 85% (n=20), (3) E 13-E15: 80% (n=5); (4) E12-E18: 80% (n=5); (5) E14-E18: 90% (n=10); and (6) E15-E18: 100% (n=5). The viability of injected embryos was; (1) 60% (n=5) in embryos injected on Ell and sacrificed on E15 (Ell-E15); (2) E12-E15: 90% (n=10); (3) E13-E15: 100% (n=3); (4) E12-E18: 80% (n=5); (5) E14-E18: 90% (n=10); and (6) E15-E18: 100% (n=5). These results show that this method is very useful for manipulating the developing otic vesicle, and that is a possible way of developing a novel model of congenital vestibular disorders.
Viral infection has been suggested to be one of the causes of vestibular neu-ronitis. In particular the possibility that reactivation of Herpes simplex virus (H SV) in vestibular ganglia can cause vestibular neuronitis has been suggested. In this study, we inoculated HSV-I into the middle ears of rats and guinea pigs. After the inoculation, 4 rats showed nystagmus. One of them showed head deviation to the inoculated side. We administered cyclophosphamide (CP) to 11 rats and 8 guinea pigs with no clinical symptoms after inoculation to reactivate HSV- I and to induce dysequilibrium, but, none of them developed show dysequi-librium. We examined their vestibular ganglia, trigeminal ganglia, cerebrum, cerebellum and brain stem, using indirect immunofluoressence (IF) and polymerase chain reaction (PCR). Unfortunately, we could not detect HSV-I antigen by IF, but we could demonstrate HSV-I DNA by PCR in the vestibular ganglia of the rats. Reactivation of HSV-I was not shown, but latent infection with HSV-I was evident. Next, to reactivate HSV-I in vestibular ganglia and to induce dysequilibrium we will investigate the problem of the strain, the concentration of virus and the kinds of stimulation.