Nobuharu Tagashira

Electron-microscopic study of the vestibular dark cells in the crista ampullaris of the guinea pig.

The ultrastructure of the vestibular dark cells in the crista ampullaris of the guinea pig was observed using both transmission and scanning electron microscopy. The dark cells had numerous vacuoles of varying size and electron density, and also characteristic well-developed basal infoldings. These findings strongly suggest that the dark cells play an important role in fluid transport. Unique meshwork structures were observed on the luminal surface of the dark cells. Otoconia showing varying degree of degeneration were occasionally recognized on and near these structures. Electron microscopy revealed that the meshwork was comprised of cytoplasmic processes in a reticular arrangement. They seem to be engaged in the metabolism of otoconia, and perhaps also in fluid transport.

Effect of gentamicin on vestibular ganglion.

The morphological changes of the vestibular ganglion induced by gentamicin (GM) were investigated using light, scanning and transmission electron microscopy. The guinea pigs were injected 4 mg of GM into the middle ear for 5 days. The vestibular ganglion was observed up to 4 weeks after the treatment. Three days after the treatment the degenerative change was first noted in the vestibular ganglion. The degenerative process started from the destruction of mitochondrial cristae and vacuolization of the cytoplasm of the Schwann cell. The cytoplasmic organelles in the ganglion cell gradually deteriorated with swelling of the endoplasmic cisterns as well as Golgi apparatus. At the later stage, the myelin sheath around the ganglion cell disappeared and the number of the cells reduced. These changes of the ganglion cell may be due to the direct action of GM.

Three-Dimensional Structures of the Vestibular Sensory Epithelia

Vestibular neurosensory epithelia of the guinea pig and the bull frog were investigated by scanning electron microscopy. The crista ampullaris or macula were freeze fractured followed by maceration with 0.1% OsO4 solution for 24-60 h (osmium-DMSO-osmium method). Following this, three-dimensional intracellular structures were observed. The mitochondria which exist in the nerve chalice surrounding the type I cell were various in shape, globular, long and slender. Golgi apparatus, endoplasmic reticulum and thin fibrous structures of the sensory cells or supporting cells were clearly demonstrated. Concerning nervous system, nerve fibre, afferent and efferent nerve endings, further synaptic structures were also observed stereoscopically.

Inner ear damage induced by Mycobacterium fortuitum

SummaryWe used electron microscopy to investigate Mycobacterium fortuitum -induced changes in the inner ears of mice. We found that the inner and outer hair cells had degenerated and disappeared in the organ of Corti. Changes in the lower turn of the cochlea were more severe than those of the upper turn while the changes of the outer hair cells were more severe than those of the inner hair cells. Disappearance, fusion and ballooning of the sensory hairs were observed in the vestibular organs. The bacterial extract also induced inner ear damage which was similar to that caused by live M. fortuitum.

Recurrent lower gingival squamous cell carcinoma spreading along the pathway of the inferior alveolar nerve

Computed tomography images showed recurrent lower gingival squamous cell carcinoma spreading from the mandibular foramen to the middle cranial fossa. This extensive tumor spread followed exactly the same anatomic pathway as the inferior alveolar nerve. Histopathologic examination revealed squamous cell carcinoma. Tumor spread was thought to be caused by perineural invasion. This case demonstrates computed tomography features of perineural tumor spread along the inferior alveolar nerve.

Action Potential of Isolated Frog Utricle

The action potential of an isolated frog utricle was recorded using a suction electrode. The utricle was stimulated with iron sand which were spread evenly on the macula. A magnetic force was employed to induce the iron sand to depress the macula lightly. Integration of the action potential resulted in a phasic component, just as observed in the isolated semicircular canal potential (Harada et al., 1969). The amplitude of the utricular phasic component was liner to the logarithm of the stimulus intensity. Similar relationship was observed between the semicircular canal action potential and the stimulus (Harada & Hirata, 1981). Phasic on-response was invaliably accompanied by an off-response. This suggests functional polarization of the utricle. It is already known that the macula is divided by the striola into two hair-cell groups having differing polarity. Since iron sand is spread evenly on the macula, all sensory cilia bend in one direction at the onset of the stimulus and one of the two cell groups ev...

Morphological Study of the Cells in the Planum Semilunatum

The fine structures of the epithelial cells in the planum semilunatum were investigated using scanning and transmission electron microscopy. The chicks and guinea pigs were used for this study. In both guinea pig and chick, the body of the planum semilunatum cell was cylindrical. Its length decreased towards the utricular and canal side, resulting in cuboid-shaped cells. In the guinea pig, the flat surfaced hexagonal cells with few microvilli were arranged like flagstones over the whole area of the planum semilunatum, while in the chick the cells with many prominent microvilli were found on both sides of the crista. The cytoplasm contained well developed endoplasmic reticula and abundant granules. Interdigitations between the neighbouring cells were well developed. Basement membrane was slightly folded but no basal infolding was observed. The morphological characteristics of the planum semilunatum cell highly suggest that these cells have some secreting function.

Anatomical and physiological characteristics of the vestibular ganglion of the bull frog.

The spatial distribution of nerve fibers from individual vestibular end organs in the vestibular ganglia (VG) was studied using horseradish peroxidase (HRP). HRP was injected into the cut end of the bull frog ampullary nerve. Stained neural elements were counted on the serial sections. Spatial distribution was also studied by recording ampullary nerve compound action potentials (AP) from VG. The anterior semicircular canal (SC) nerves were distributed in the anterior half of VG. The horizontal SC nerves were also distributed in the anterior half of VG, but tended to be posterior. The posterior SC nerves were found predominantly in the posterior half and antero-dorsal portions. These distribution patterns corresponded well with those confirmed by AP recording. There were a few neural connections between anterior and posterior SC, or horizontal and posterior SC, indicating receptor-receptor fibers.

Three-dimensional Observation of the Spiral Ganglion Cell Normal Structure and Pathological Changes

Spiral ganglia of guinea pig and mouse were investigated by scanning electron microscopy (SEM). The cochlea was freeze-fractured and then macerated with 0.1% OsO4 solution for 70-90 h (A-O-D-O method (1]. This allowed three-dimensional observation of the general view of the spiral ganglion and the intracellular structure. Two types of spiral ganglion cell, type I and type II, could be distinguished by the A-O-D-O method. Intracellular membranous structures such as mitochondria, endoplasmic reticulum (ER) and Golgi apparatus were also demonstrated stereoscopically. Furthermore, morphological changes in mouse spiral ganglion cells due to injection of Mycobacterium fortuitum were observed, using SEM. The degenerative process began as swelling of the mitochondria. When Schwann cell became affected, the myelin sheath disappeared and the ganglion cell border became indistinct. This degeneration developed rapidly, suggesting a direct influence of the bacteria on the ganglion cell. Various types of inclusion body with limiting membrane could be demonstrated stereoscopically. As Romand & Romand (4) suggested, these inclusion bodies may be remnants of cellular organellae or various type of lysosomes.

Development of the crista ampullaris in the mouse.

The process of development of the crista ampullaris has been investigated in the mouse using SEM. Cristae ampullaris of the CBA/CBA mice, from the 13.5th gestational day to the day 2 weeks by were studied. On the 13.5th gestational day, there were numerous microvilli and a primary cilium on the crista ampullaris. Sensory hairs first appeared on the 14.5th gestational day. The kinocilium and stereocilia were short and the length of the stereocilia was almost constant. The formation of the cupula, which had fine network-like structures, started on the 14.5th gestational day.