The fine structure of the human vestibular ganglion cells was studied by serial sections under the electron microscope. Most cells were unmyelinated and bipolar but a few were myelinated. There were two types of unmyelinated ganglion cells: one, bipolar, and the other, multipolar. The unmyelinated bipolar cells consisted of two types, light and dark cells. The unmyelinated multipolar cells were subclassified into large cells without synapses and small cells with synapses. No morphological evidence has been presented as to functional correlates between different types of the vestibular ganglion cells. The length of the initial segments of the unmyelinated processes from the vestibular perikaryon was measured by serial sections. A wide range was found in the length of both the central and peripheral processes. Their functional significance has yet to be determined.

View full abstract

Dr. Kitamura is to be congratulated on his thorough electron microscopic study on the human vestibular nerve and ganglion.
Although my speciality is not the fine neuro-anatomy of the vestibular system, I would like to comment briefly on the lipofuscin granules in the human inner ear and neurosensory structures. Lipofuscin granules are distributed in the neural tissue of the human vestibular sensory organs and are especially abundant in the cells of Scarpa's ganglion, particularly in the specimen from the elderly. These results were reported by Ishii, moderator of this session, myself, Kimura and Balogh in 1967.

View full abstract

The wall cytoarchitecture and the innervation patterns of the cochlear blood vessels were examined by scanning electron microscopy. Six types of vascular segments were classified according to the overall morphology of periendothelial cells: (1) arteries with compact elongated smooth muscle cells oriented transversely; (2) arterioles with compact spindle-shaped smooth muscle cells arranged in circular fashion; (3) precapillary arterioles with less compact branched smooth muscle cells and helically oriented processes; (4) capillaries with widely scattered pericytes and longitudinally oriented primary processes which branch out fine processes in succession; (5) postcapillary venules with scattered spidery pericytes and radially oriented processes; (6) venules and veins with scattered polygonal pericytes and irregularly oriented processes. The artery and the arterioles are always innervated either densely or sparsely. But nerve fibers do not always reach the precapillary arterioles and capillaries. On the venous side, no nerve fibers are observed in association with the vessels. Such morphological differences of the wall cytoarchitecture and the innervation patterns suggest that each vascular segment has a different role in the cochlear vascular system.

View full abstract

The “Rupture theory” of Schuknecht (1963), has been proposed to explain the vertiginous attack of Meniere's disease, and the high perilymphatic potassium ion was thought to be the most important factor in this theory. In this paper, potassium ion was introduced through the round window into the perilymphatic space of guinea pig by means of iontophoresis to histochemically investigate the effect of high perilymphatic potassium concentration on the sensory epithelia in the labyrinth. After the iontophoretic procedure, spontaneous nystagmus was observed. Nystagmus directed toward the iontophoretic side (irritative nystagmus) for the first 10 minutes, and then toward the unaffected side (paralytic nystagmus) for later 24 hours. These nystagmus were quite reversible and left no morphological change of sensory cells. But, histochemical analysis revealed the increased ATPase activity during the irritative nystagmus and the decreased ATPase activity during the paralytic nystagmus in the synaptic area between the hair cells and the nerve endings of the iontophoretic side. According to these results, high perilymphatic potassium concentration was supposed to affect the synaptic area of sensory epithelia and was able to produce reversible nystagmus.

View full abstract

Tachibana M, Mizukoshi F. Ear Res Jpn 1985; Suppl: Localization of the Na⁺ K⁺-ATPase phosphatase component in the crista ampullaris of the guinea pig was examined using p-nitrophenyl phosphate (NPP) as a substrate. Activity was found in the dark cell area. Three dimensional reconstruction of the overlayed serial sections confirmed that the activity was limited to this area. The possible role of this enzyme activity in the generation of ampullar endolymphatic potential is discussed briefly.

View full abstract

Intravenously injected kanamycin sulfate (KM) and endogenous IgG was located in the endolymphatic sac (ES) of guinea pigs by an immunohistological method. KM had already passed through the capillary in the subepithelial layer and had reached the epithelial layer as early as 1 minute after the injection. The amount of KM in the epithelial layer gradually and progressively increased until 30 minutes after the injection. KM accumulated in the floating cells in the ES whereas IgG existed in the subepithelial layer of the ES. These results may indicate that the ES is rather easily permeable to systemically administered drugs, which readily get into the regional endolymph and also that ES has some functional role in defending the inner ear from diseases. In conclusion, much more attention should be paid to ES and drug ototoxity associated with drug therapy in the management of patients with inner ear disturbances.

View full abstract

The posterior semicircular canal was isolated in the frog Ringer's solution. The ampullary nerve action potentials in response to mechanical endolymphatic flow were recorded. When the entire cupula was removed, the action potential almost completely disappeared. When the cupula was replaced on the crista, the potentials were restored. These results show the importance of the cupula-crista attachment for sensory cell activation. Next, the cupula was again removed, cut in half either vertically or horizontally and the sectioned half of the cupula was replaced on the crista. After vertical sectioning, the action potentials were markedly reduced to 50.3% of the replaced entire cupula. After horizontal sectioning, potentials were 64.1%. These results indicate that the ampullary nerve responses are related to the base area and height of the cupula. Cupular movement as a swing-door deflection was compared to cupular movement as diaphragm motion, in terms of the maximum spike count and the time course of the ampullary nerve action potential. Diaphragm motion was achieved by immobilizing the entire top portion of the cupula using fine glass micropipettes. Diaphragm motion resulted in very low response increase rate, and extremely short time course as compared to swing-door deflection. These findings suggest that the swing-door deflection is physiologically more relevant in giving the optimum increase in response rate, as well as maintaining the time course of the tonic response.

View full abstract

Ouabain, a potent Na⁺K⁺-ATPase inhibitor, was found to depress endocochlear potential drastically. Using radioactive ouabain, the binding sites of perilymphatically perfused ouabain was examined. Strong binding was observed in the subepithelial region of the spiral prominence and the surrounding spiral ligament, while moderate activity was observed in the vascular stria. However, a histochemical study revealed that Na⁺K⁺-ATPase was localized mainly in the vascular stria, while moderate activity was observed in the subepithelial region of the spiral prominence and the surrounding spiral ligament. These results have two interpretations: ouabain most likely binds with Na⁺K⁺-ATPase in the lateral wall tissue of the cochlea when perilymphatically perfused and; ii) there might be a barrier for ouabain between the perilymphatic tissues (spiral ligament+spiral prominence) and the endolymphatic tissue (vascular stria).

View full abstract

1. This study revealed the distribution of paramyxovirus antigen in the cochlea of adult guinea pigs by means of immunohistochemical techniques.
2. In the animals with intralabyrinthine inoculation, viral antigen of both viruses were found in marginal cells of stria vascularis, mesothelial cells of the Reissner's membrane and supporting cells of the organ of Corti.
3. In the animals with intravascular injection, viral antigens of both viruses were found limited to endolymphatic structures, primarily in stria vascularis and occasionally in the organ of Corti. These results indicate that endolymphatic labyrinthitis may occur as a result of viremia.

View full abstract

Alternation of the perilymphatic pressure and cochlear microphonics were investigated by increasing CSF pressure (0-100 cm H₂O) in guinea pigs.
Perilymphatic pressure increased in a linear manner without any time lag as the CSF was pressurized.
Cochlear microphonics was suppressed as the CSF was pressurized to more than 30 cm H₂O, and CM suppression was greater at low frequency sounds. Endolymphatic dc potential indicated no change until the CSF pressure was increased up to 70 cm H₂O. These results indicate that CM suppression with increased CSF pressure is due to the increased basilar membrane stiffness.

View full abstract

Changes in endocochlear DC potential (EP) and potassium ion concentrations in endolymph were measured simultaneously during anoxia in normal and kanamycindeafened guinea pigs. The potassium ion conductance (Gk) through the cochlear partitions was approximately four times greater in normal guinea pigs than in kanamycindeafened guinea pigs within thirty minutes after anoxia. In the early stage of anoxia the rate of potassium ion concentration decrease in the endolymph per unit time is greater in normal guinea pigs than in kanamycin-deafened guinea pigs. These results suggest a rapid increase in the permeability of potassium ions in the organ of Corti in the early stage of anoxia might produce a large negative potassium ion diffusion potential or negative EP in normal guinea pigs, and the failure to develop the negative EP in kanamycin-deafened guinea pigs might be due to the lack of such a rapid increase in the permeability because of the loss of the hair cells.

View full abstract

The endocochlear potential (EP) of the guinea pig during systemic ischemia could be maintained by fast perilymphatic perfusion of oxygenated artificial perilymph. The perfusion of the scala vestibuli in the ischemic cochlea could maintain the EP at a level close to the original level prior to the initiation of ischemia. The ATP measurement substantiated the EP recovery was a true recovery of the strial function. The perfusion in scala tympani could only partially recover the EP.
The difference in the recovery of the EP between the two perilymphatic scalae suggests the diffusion barrier for oxygen between the scala tympani and the stria vascularis is greater than that between the scala vestibuli and the stria vascularis.

View full abstract