[Steroid-responsive sensorineural hearing loss with low tone loss].

Five cases of sensorineural hearing loss of sudden onset were reviewed. They were not responsive to administration of ATP and Vit. B12, but very responsive to steroid administration. All the patients were male and showed hearing loss in low frequencies in pure tone audiogram. Administration of steroid recovered hearing impairment immediately. However, cessation of steroid aggravated the recovered hearing. Serological and immunological examinations did not show any abnormal findings on all the patients. It was considered that these five patients had characteristics of both steroid-sensitive and low tone-loss type sensorineural hearing losses.

Fine structure of the human cochlear aqueduct: a light and transmission electron microscopic study of decalcified temporal bones.

The morphologic features of the human cochlear aqueduct were examined using both light and electron microscopy. The lumen of the cochlear aqueduct was observed to be filled with dense, irregular connective tissue corresponding to dura mater. At the entrance to the cerebrospinal fluid space, the dense connective tissue in the ductal lumen was covered with a thin layer of a few flattened cells, which was contiguous with the arachnoid membrane of the brain. A simple low cuboidal epithelium also separated the perilymphatic space from the lumen of the duct. Our observations confirm the presence of a barrier membrane at the opening to the perilymphatic space, and suggest that no transport occurs in the human cochlear aqueduct.

[Fine structure of the guinea pig organ of Corti revealed by a quick-freeze, freeze-substitution method].

A quick-freeze, freeze-substitution method was applied to the guinea pig organ of Corti. Many similarities were apparent between the conventionally fixed samples and the freeze-substituted samples, including the lateral membrane system of the cochlear outer hair cells consisting of the lateral plasma membrane, pillars, cytoskeletal lattice and subsurface cysternae. However, some ultrastructural differences were found in the cells prepared by the freeze-substitution method. Electron-dense mosaic structures were found in the lumen of the tubules of the subsurface cysternae. Tangential sections of the tubules of the subsurface cysternae showed spirally wound parallel rows of electron-dense materials. In a rectangularly cut membrane with a trilaminar structure, the electron-dense materials appeared to be triangular protrusions from the outer leaflet of the unit membrane. These structures suggest that the subsurface cysternae may play an important role in the contraction of cochlear outer hair cells.

Quick-freeze, deep-etch visualization of the 'cytoskeletal spring' of cochlear outer hair cells.

The lateral membrane system of the cochlear outer hair cell, consisting of the lateral plasma membrane, pillars, filamentous lattice and subsurface cisternae, is considered to be involved in the contractile movement of the isolated cochlear outer hair cell. The filamentous lattice, called the cytoskeletal spring, has been identified in the demembranated cochlear outer hair cell treated with the detergent Triton X-100. In this study, the quick-freeze, deep-etch method was applied to demonstrate the three-dimensional organization of both the filamentous and membranous structures of the lateral membrane system of cochlear outer hair cells. Treatment with saponin revealed that the inner leaflet of the lateral plasma membrane of the cochlear outer hair cell possesses more membrane particles than the outer leaflets, and that the pillars are closely associated with membrane particles in the inner leaflet of the lateral membrane. The presence of filamentous bridges between the filamentous lattice and the subsurface cisternae was also detected. We propose that the lateral membrane system in the cochlear outer hair cell may play an important role in the tuning mechanisms within the cochlea in normal hearing.

Ultrastructure of the guinea pig cochlear aqueduct. An electron microscopic study of decalcified temporal bones.

The ultrastructure of the guinea pig cochlear aqueduct was examined using semi-thin and thin sections. The lumen of the cochlear aqueduct was occupied by a sparse meshwork of fibroblasts and delicate connective tissue trabeculae. The periotic tissue lining the bony wall of the aqueduct was composed of multiple layers of both elongated cells and densely arranged laminae of collagen fibrils. These structures were identical to those of the dura mater and the arachnoid. The opening to the perilymphatic space of the scala tympani also contained connective tissue trabeculae, but the arrangement of fibroblasts was more compact here than in the main part of the duct. These structural features suggest that fluid can move freely through cochlear aqueduct, and that the effects of sudden pressure changes in the CSF may be protected against by the densely and perpendicularly arranged fibroblast at the opening to the perilymphatic space.

Computer-aided three-dimensional reconstruction of guinea pig cochlear aqueduct.

A computer-aided method of three-dimensional reconstruction was applied to the determination of the overall spatial configuration of the guinea pig cochlear aqueduct. The rotation function of the reconstructed images was useful in showing the individual small parts of the duct. A semi-translucent display of the segmental reconstruction of the duct demonstrated a difference in the density of the cellular components between the opening to the perilymphatic space and the duct portion. We propose that the cochlear aqueduct serves as a protective mechanism against a sudden change in CSF pressure in the subarachnoid space.