Isamu Takeyama

Clinical Significance of SP/AP Ratio in Inner Ear Diseases

Electrocochleogram was recorded from 28 ears affected by Ménières disease , 27 ears affected by sensorineural hearing loss resulting from hair cell damage and 22 normal ears as controls in response to tone bursts in order to evaluate diagnostic significance of the summating potential/action potential (SP/AP) ratio and the SP amplitude. The fundamental aspects of the SP/AP ratio were studied in relation to frequency, intensity and rate of tone burst stimuli. It was concluded from present results that the SP/AP ratio can be a useful indicator to detect -SP dominance, while the SP amplitude can be an indicator to detect cell damage in inner ear diseases.

Long-Term Follow-Up of Electrocochleogram in Ménière’s Disease

Serial electrochochleogram (ECochG) recordings were obtained over a long time span from 24 patients with Ménières disease showing dominant negative SP. The long-term fluctuation of responses (especially SP) was evaluated. Dominant -SP or abnormally increased SP/AP ratio has been unchanged over long periods in most operated or nonoperated patients. It is assumed that the generation of -SP dominance may chiefly result from the malfunction of hair cells, which may be caused by abnormal changes in inner ear fluids associated with endolymphatic hydrops or by other unknown disturbances in the cochlea. The mechanical factor of basilar membrane displacement can hardly be considered as a main cause of SP abnormality.

Melanocytes in Vestibular Dark Cell Areas in Human Fetuses

Melanocytes in human vestibular dark cell areas were observed to have round or spindle-shaped cell bodies with several processes. They were located below the basement membrane but the melanocyte processes were found in the dark cell epithelial layer closely adjacent to the dark cell processes or bodies without any separation from the basement membrane. Submicroscopic observations revealed melanin pigment in various stages of accumulation on the tyrosinase filaments in melanosomes. Three-dimensional stereoscopic observations clearly revealed the morphological characteristics of tyrosinase filaments, their helicoidal structure and some variations. Mature melanin granules developed from premelanosomes as the melanin pigments were gradually deposited onto the filaments. Through this progress of pigment accumulation, the melanosomes became darker. In the four mid-term fetuses used in the present investigation, few differences were seen in the mode of melanin deposition on the tyrosinase filaments. In view of the close spatial arrangement and contact of the melanocytes with the dark cells, it seems plausible that the melanocytes play some role in vestibular metabolism via the dark cells.

Retinal ganglion cells related to optokinetic nystagmus in the rat.

The nucleus of the optic tract (NOT) in the pretectum is the visuo-motor relay between the retina and preoculomotor structure in the pathway conveying signals responsible for optokinetic nystagmus (OKN) in both afoveate and foveate animals. Unilateral lesions of the NOT abolish OKN toward the side ipsilateral to the lesion. However, what parts of the retina and what kinds of retinal ganglion cells project their fibers into the NOT are still unknown. To examine this, horseradish peroxidase conjugated with wheatgerm agglutinin was injected into the NOT of the rat. Labeled retinal ganglion cells were diffusely documented in the contralateral side, whereas those situated only in the lower temporal crescent, were found in the ipsilateral side. Ganglion cells dominated in the range of small cells, i.e., W cells. Therefore, ganglion cells responsible for OKN are believed to be related to W cells. However, medium-sized and large cells were definitely labeled in the rat, suggesting possible participation of these cells in OKN.

Vestibulo-thalamic Neurons Give Off Descending Axons to the Spinal Cord

Vestibulo-thalamic (VT) neurons were physiologically studied in the anesthetized cat. Forty-seven VT neurons were recorded extracellularly. More than half of the VT neurons responded monosynaptically to vestibular nerve stimulation while the others responded polysynaptically. They were activated antidromically from one or two sites in the VPL. VPM, VL, VM, SG, and PO of the contralateral thalamus. Four fifths of the VT neurons were activated from the C1 segment of the spinal cord. Half of them were also activated from the C4 segment, but none were activated from the L5 segment. It is suggested that most VT neurons project descending axons to the cervical spinal cord. Axonal branching was shown by means of systematic microstimulation in the thalamus and the ventral horn in the C1 segment. The VT neurons were mainly located in the descending vestibular nucleus.

Role of the Dorsolateral Pontine Nucleus in Two Components of Optokinetic Nystagmus (OKN)

The anatomical features of the dorsolateral pontine nucleus (DLPN) implicate a role of the nucleus in the generation of smooth-pursuit eye movements. The DLPN receives convergent inputs from a variety of parieto-occipital cortical visual areas and projects its fibers to the flocculus and vermal lobules VI and VII. In addition to cortical afferent fibers, the DLPN receives descending fibers from the nucleus of the optic tract which is indicated as the first subcortical optokinetic nystagmus (OKN) relay. DLPN units respond not only to a discrete visual spot but also to large-field OKN stimuli. On the basis of the above anatomical and physiological features, OKN was investigated in 2 alert monkeys whose DLPN was physiologically identified and into which reversible lidocaine was injected. The present findings showed that a rapid rise in OKN velocity was reduced in both monkeys, whose lesions included the uppermost rostral part of the nucleus in the one monkey and the entire nucleus in the other, whereas optokinetic after-nystagmus velocity was affected only in the latter. Taken together with physiological data, the DLPN possibly shares the domain of low selectivity speed selection in OKN and does not play a main role in the generation of OKN.

Indications and Results of Gentamycin Injection into the Middle Ear of Patients with Meniere's Disease

Forty-six cases in whom endolymphatic drainage surgery was performed between 1986 and 1992 were followed up for more than 2 years. The results of numerical values (1985 AAOHNS) revealed complete control of definite spells in 26 cases; substantial control of definite spells in 18 cases; limited control of definite spells in 1 case; and insignificant control of definite spells in 1 case. Hence, endolymphatic drainage surgery for Meniéres disease was effective. There are, however, cases who cannot be operated on because of old age or underlying diseases. In these, we injected gentamycin sulfates mixed with prednisolone through a ventilated tube into the middle ear. The results for gentamycin injection based on numerical values showed complete control of definite spells in 12 cases; and substantial control of definite spells in 7 cases. Our treatment of choice for Meniéres disease is endolymphatic drainage surgery which resulted in 96% control of vertigo. In patients for whom operation has failed, in old patients and in those with hearing impairment more than 50 dB, gentamycin injection into the middle ear has proved to be an effective procedure to control vertigo attacks.

Retinal Ganglion Cells Projecting to the Nucleus of the Optic Tract in the Rat

The nucleus of the optic tract (NOT) has been identified as the link between the retina and the premotor nuclei in the pathway mediating the optokinetic nystagmus (OKN). However, it is still unclear from what parts of the retina and what kinds of retinal ganglion cells the NOT receives visual inputs related to OKN. In the present study, horseradish peroxidase conjugated with wheatgerm agglutinin (WGA-HRP) was injected into the NOT of hooded rats to investigate retrogradely labeled cells in the retina. A solution of WGA-HRP was injected into the NOT through a glass micropipette. Injection sites of the brain and the retina were processed by tetramethyl benzidine protocol and Hanker-Yates method. The labeled cells were observed in the whole area of the retina contralateral to the injection site, while located only in the ventral region of the retina ipsilateral to the injection site. In the retina contralateral to the injection site, a large number of small-sized cells and a few medium-sized cells were label...

EOG Findings in Patients with Lesions in Cerebellar Peduncles

EOG tests were performed in patients with lesions in either the superior or the middle cerebellar peduncle, because these patients showed cerebellar signs and symptoms and were difficult to distinguish from patients with cerebellar lesions symptomatically. EOGs of these patients showed a predominant decrease of pursuit gains and OKN velocity gains toward the lesioned side, whereas the percent reduction of fixation-suppression of caloric nystagmus decreased predominantly toward the side contralateral to the lesioned side, regardless of whether lesions were located either in the superior or the middle cerebellar peduncle. The present EOGs are best interpreted as a corresponding to a deficit of the neuronal events of the flocculus in the monkey and are solely ascribed to lesions in the cerebellar peduncles, because even well-defined cerebellar lesions on one side showed bilateral impairments of these visually induced eye movements.

Prophylaxis by Ketotifen Given Orally and by Aqueous Nasal Spray to Prevent Japanese Cedar Pollinosis.

We studied for two seasons the prophylactic and the rapeutic effect of ketotifen in patients with Japanese cedar pollinosis. We administered ketotifen orally to patients before the beginning of the dispersion of pollen. Ketotifenaqueous nasal spray (ketotifen-ANS) was administered to those with a poor-response to the prophylaxis. Of the patients examined during the season 51.4% showed a marked or moderate prophylactic effective. The poor-response patients were treated with ketotifen-ANS, and in 72.2% there was marked or moderate improvement. Thus, ketotifen-ANS was useful in patients whose symptoms were not prevented by oral ketotifen. The only side effect was sleepiness in 3 patients receiving oral ketotifen. Ketotifen-ANS caused none.Oral ketotifen and aqueous nasal spray ketotifen are considered to be excellent for the prophylaxis and therapy of Japanese cedar pollihosis.