Yoshiro Yazawa

Cortical and subcortical vestibular response to caloric stimulation detected by functional magnetic resonance imaging

The posterior insula, central sulcus, and inferior parietal lobule including the intraparietal sulcus have been considered the vestibular cortex based on functional brain mapping in humans as well as experiments in lower primates. The same regions receive optokinetic, visual, and proprioceptive projections. We examined the cortical and subcortical projection of vestibular activity with visual and proprioceptive input eliminated during caloric stimulation (CS), using functional magnetic resonance imaging (fMRI). Single-shot gradient-echo echoplanar image (EPI) volumes were sensitive to BOLD contrast in oblique orientation. We adopted a pharmacokinetic model for analysis of imaging data from 10 subjects as a group. The insular gyrus, intraparietal sulcus, superior temporal gyrus, hippocampus, cingulate gyrus, and thalamus showed activation by CS. Cortical and subcortical activation during CS in the present study was observed within regions less precisely delineated by other methods. As intraparietal sulcus activation showed right hemispheric dominance, this region may have an oculomotor projection as well as the vestibular input.

Presence of Autoantibodies in the Sera of Meniere's Disease

We examined the sera of patients with Menieres disease for the presence of antibodies against 8 inner ear antigens by enzyme-linked immunosorbent assay (ELISA). One hundred eight patients with Menieres disease and 28 control subjects were studied. The antibodies against chicken type II collagen, bovine type II collagen, the cyanogen bromide cleaved peptide 11 (CB11) of each, type IX and XI collagens, C-Raf, and tubulin were measured by ELISA. The sensitivity of each antigen was between 37% and 60% individually, and was 91% when all 8 inner ear antigens were combined. These results showed that 91% of Menieres disease sera have antibody activities to 1 or more of these inner ear antigens. The results suggest that performing ELISA for these 8 inner ear antigens was useful as a diagnostic tool for Menieres disease. Further study is required for elucidating the role of these antigens in the pathogenesis of Menieres disease, which might eventually result in better therapy.

Antibodies against Inner-Ear Proteins in the Sera of Patients with Inner-Ear Diseases

Sera from patients with various inner-ear diseases, especially Meniere’s disease, were investigated by Western blot against guinea pig inner-ear proteins. Of 45 patients, 24 (53%) with various inner-e

Experimental Study on Meniere's Disease

Experimental hydrops caused by underabsorption of endolymphatic fluid is a model of remissional stage of Menieres disease. In this study, another type of model, ie, hydrops caused by overproduction of endolymphatic fluid, was accomplished by applying various pressures into scala media through a micropipette via stria vascularis. This type of hydrops could be a model of attacks of Menieres disease. By using two types of the model, effects of glycerol administration and of opening the endolymphatic sac were discussed.

Vasopressin and oxytocin receptor mRNAs are expressed in the rat inner ear.

THE cause of endolymphatic hydrops, a characteristic finding in Menières disease, is not known. To study the possible involvement of the neurohormones vasopressin and oxytocin in this condition, we investigated whether transcripts of the genes encoding the arginine vasopressin (AVP) and oxytocin receptors are expressed in the rat inner ear. Utilizing the reverse transcription-polymerase chain reaction (RT-PCR) method, primers specific for each receptor showed a single message band of the expected size in the rat inner ear. When the PCR products were cloned, the sequences were identical to those of the real-type (V2) AVP receptor and oxytocin receptor transcripts. The finding of vasopressin and oxytocin receptor mRNAs in the inner ear suggests that these neurohypophyseal hormones may have roles in the regulation of inner ear fluid. In particular, the presence of vasopressin receptor mRNA in the inner ear supports the hypothesis of a relationship between high plasma vasopressin levels and endolymphatic hydrops.

Studies of Cochlear Blood Flow in Guinea Pigs with Endolymphatic Hydrops

Laser Doppler flowmetry was used to assess cochlear blood flow (CoBF) in guinea pigs with experimental endolymphatic hydrops following intravenous infusion of 5 types of drugs: 50% glycerol, 70% isosorbide, 20% mannitol, 7% sodium bicarbonate, and 1% diphenidol. The magnitude of the CoBF changes following infusion tended to be smaller in the hydropic ears than in the normal control ears. A significant reduction in CoBF changes was observed in hydropic ears infused with isosorbide and sodium bicarbonate. These results suggest that the cochlear microvascular sensitivity to various stimuli such as drug infusion is reduced in hydropic ears. This may result from atrophy of the stria vascularis which is often observed in the hydropic ears of guinea pigs. Thus it seems likely that the same reaction occurs in the inner ear of patients with Ménière’s disease in whom atrophy of the stria vascularis is also presumed to exist in conjunction with extensive endolymphatic hydrops. Therefore, it seems probable that the function of the microvasculature of the stria vascularis is impaired in the inner ear of patients with Ménière’s disease, resulting in the slow progressive deterioration of the inner ear with time.

Regulation of inner ear fluid in the rat by vasopressin.

The anti-diuretic hormone vasopressin has been shown to be important in regulating inner ear fluid. The diuretic hormone, CNP, and its receptor, ANP-B receptor, may also function in the regulation of inner ear fluid. To determine whether vasopressin directly affects the fluid level, we infused this hormone to rat and assay of V2-AVP receptor mRNA by semiquantitative RT-PCR demonstrated a significantly lower level of this transcript in vasopressin-infused animals than in saline-infused animals. The levels of CNP and ANP-B receptors mRNA, however, were the same in both groups of rats. Results suggest that high plasma levels of vasopressin may be a principal causal factor of endolymphatic hydrops in Menieres disease, perhaps by down-regulating the number of vasopressin receptors.

Bilateral Endolymphatic Hydrops in Meniere's Disease: Review of Temporal Bone Autopsies

The wide range in incidence rates reported for bilateral Menieres disease results mainly from the lack of established clinical criteria for bilaterality, and from follow-ups of varying duration. In order to help determine a reasonable bilateral involvement rate, we examined histologic reports of temporal bones with endolymphatic hydrops. We reviewed the literature on temporal bone autopsies from 1938 to 1988, and selected 72 cases for histologic examination. Of the 72 cases, 67 (93%) showed endolymphatic hydrops, 2 (2.8%) showed collapse, and 3 (4.2%) showed membranous labyrinths of normal appearance. Twenty of the 67 endolymphatic hydrops cases (29.9%) displayed bilateral involvement, suggesting a rate of bilaterality in Menieres disease of approximately 30%.

Bilateral Meniere’s Disease

A survey of 265 Japanese patients with Menieres disease revealed bilateral involvement in approximately 29% of all these patients. Somatic and psychiatric aspects of bilateral Menieres disease were as follows. (1) The duration of the disease in cases of bilateral involvement was significantly longer than cases of unilateral involvement. (2) An abnormal general condition, a more extensive degree of hearing loss and neurotic type were frequently diagnosed in cases of bilateral involvement. Based on these results, it was concluded that psychiatric management and prevention of aggravation of deafness should be part of the management of treatment in bilateral Menieres disease.

Treatment of Ménière’s Disease with Isosorbide

The effects of isosorbide – a dehydric alcohol formed by the abstraction of two molecules of water from one of sorbitol – on Meniere’s disease were examined, first using a model and then clinically. (