Biomedical subjects
Publications and source records attributed to K Hama.
GABAergic synapses in the granule cell layer of the rat dentate gyrus were examined light and electron microscopically with glutamate decarboxylase (GAD) immunocytochemistry. GAD-immunoreactive synaptic boutons formed synapses with axon initial segments and somatic spines as well as somata and dendritic shafts of the granule cell. Most of these synapses were symmetrical, while a few were asymmetrical.
Afferent and efferent synapses of hair cells in the organ of Corti of the guinea pig have been examined in freeze-fracture replicas. Afferent synapse. In the inner hair cells, intramembranous particles 10 nm in diameter are aggregated on the ridge on the P-face of the presynaptic membrane directly beneath the synaptic rod. In the outer hair cells, in which the synaptic rod is located in the presynaptic cytoplasm underneath the presynaptic membrane, small aggregations of intramembranous particles 10 nm in diameter can be found on the P-face of the presynaptic membrane corresponding to the site of the presynaptic dense projection. Intramembranous particles 10 nm in diameter are also densely aggregated on the P-face of the postsynaptic membrane of the outer hair cells. Efferent synapse of the outer hair cells. Large intramembranous particles 13 nm in diameter are distributed in clusters composed of four to ten particles on the P-face of the presynaptic membrane. In the P-face of the postsynaptic membrane, disc-like aggregations of intramembranous particles 9 nm in diameter are found. The subsynaptic cistern covers the cytoplasmic surface of the postsynaptic membrane of the efferent synapse; it may cover more than one postsynaptic membrane when several efferent synapses are in close proximity to one another.
A new aldose reductase inhibitor, ONO-2235 [(E)-3-carboxymethyl-5-[(2E)-methyl-3-phenylpropenylidene] rhodanine], was found to possess a potent inhibitory activity of aldose reductase, partially purified from rat lens (IC50 = 1.0 X 10(-8) M) and human placenta (IC50 = 2.6 X 10(-8) M). Against rat lens aldose reductase, ONO-2235 exhibited uncompetitive inhibition as previously observed with 7-hydroxy-4-oxo-4H-chromen-2-carboxylic acid. Sorbitol accumulation in the isolated rat lenses, sciatic nerves and human erythrocytes were all effectively inhibited during incubation with high concentrations of glucose (28-50 mM) by ONO-2235 at a concentration of about 10(-6) M. Because the accumulation of sorbitol has been reported to play an etiological role in the development of diabetic complications, the results suggest that ONO-2235 may prove to be useful in preventing and improving some diabetic complications.
The basic defect of the human chondrodystrophies with normal chondro-osseous histopathology is speculated to be quantitative decrease in the rate of ossification. Homozygous brachypodism (brp/brp), chondrodystrophic mutant in mice, is characterized by shortening long bones. The light and electron microscopic observations of the growth plate were essentially normal. The method of tritiated thymidine autoradiography showed that the rate of chondrocyte division in the mutant growth plate was decreased. These findings show that the failure of chondrocytes to divide at a normal rate can produce the growth disturbance of bone without abnormal chondro-osseous histopathology.
The mitral cell in the olfactory bulb of the goldfish was examined by means of light microscopy, high-voltage electron microscopy, and conventional electron microscopy. Mitral cells are located rather diffusely throughout the glomerular and plexiform layers. They do not make their own discrete layer. The cell bodies are rounded or triangular, and are about 10-25 micrometers in diameter. In Golgi-impregnated material, thick cylindrical dendrites can be seen arising from the cell bodies and branching in the glomerular layer. Dendritic branches of some cells make two or more rather compact tufts, while the dendrites of other cells intermingle loosely with one another. In semithin and thin sections, darkly stained nodules appear to be scattered diffusely in the glomerular layer without clustering into discrete spheres, which are characteristic of the mammalian glomerulus. Hence, instead of the glomerulus, the "glomerular area" is defined as an area consisting of darkly stained nodules with rather pale granular regions surrounding them. Branches of mitral cell dendrites in the glomerular area consist of cylindrical shafts and irregular appendages arising from them. The shafts appear in the pale granular region and the appendages are found in the darkly stained nodules. Synapses can be found on all parts of the mitral cell: the soma, axon hillock, axon initial segment, thick dendritic stems, and dendritic branches. The abundance of synapses seems to vary considerably from part to part, and is highest on the dendritic branches in the glomerular area. The mitral cell is postsynaptic to olfactory nerve terminals and granule cell dendrites, and presynaptic to granule cell dendrites and some processes of unknown origin. Olfactory nerve terminals make asymmetrical synapses specifically on the appendages of the dendritic branches. Of the synapses on the shafts of the mitral cell dendritic branches in the glomerular area, 90% are with granule cell dendrites. Of the synapses between two different kinds of processes 30% are mitral-to-granule asymmetrical synapses, 20% are granule-to-mitral symmetrical synapses, and 50% are reciprocal pairs. Gap junctions and mixed synapses are also seen on branches of mitral cell dendrites. Features of the goldfish mitral cell are compared with those of the mammal. The differences in neuronal organization between the olfactory bulbs of teleosts and mammals are discussed.
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The three-dimensional structure of the ruffed cell dendrite in the olfactory bulb of the goldfish (Carassius auratus) was studied by means of light and high-voltage electron microscopy of Golgi-impregnated material, combined Golgi-electron microscopy, and electron microscopy of serial thin sections. Ruffed cell dendrites ramify in the glomerular area with tufted branching patterns. They give rise to many appendages of various shapes and sizes: sheetlike processes, fingerlike projections, or small tuftlike appendages. These appendages, singly or together, appear to entwine or cover other neuronal processes. In thin sections ruffed cell dendritic appendages frequently look like glial processes; that is, they appear to conform in shape to the contours of surrounding neuronal elements, such as mitral and granule cell dendrites. Ruffed cell dendrites display intimate relationships with mitral cell dendrites. The former appear to coil around and cover the latter. Nothwithstanding the intimate relationship between ruffed cell dendrites and mitral cell dendrites, there seem to be no synaptic connection between them. Ruffed cell dendrites bear a rather small number of presynaptic and postsynaptic sites, most of which area with granule cell dendrites. Ruffed cell dendrites seem to receive no synapses from olfactory nerve terminals.
The relative specimen thickness obtained with an energy analyser is one of the most important parameters in electron microscopy. It has been made clear that this parameter can be applied not only to inorganic specimens, but also to organic and biological specimens. Moreover, the partial specific thickness of a critical-point-dried cultured fibroblast, that is, a net thickness converted in terms of Epon, was calculated from the relative specimen thickness. The partial specific thickness of each domain of the critical-point-dried cultured fibroblast is: CC 0.05 microns, PE 0.14 microns, ED 0.32 microns and PN 0.54 microns. As a result, it is suggested that 27% of the volume of this specimen consists of biological materials.
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The ruffed cell is present in the olfactory bulb of the catfish, Parasilurus asotus, and of the sea eel, Conger myriaster. Its morphological features have been studied by light microscopy, high-voltage electron microscopy, and conventional electron microscopy. The ruffed cell of the catfish is very similar to that of the goldfish in its location and in its structural features. It has a spheroidal or ovoid cell body about 15 to 30 micrometer in diameter. Several dendrites arise from the cell body to form a rounded dendritic field about 100 micrometer in diameter near the cell body. The initial unmyelinated portion of its axon (IP) consists of a shaft and many protrusions arising from it. The shaft, about 1 micrometers in diameter, located extends for about 100 to 200 micrometer, where it acquires a myelin sheath. The protrusions intermingle with one another in a complex manner to form a rather discrete spheroidal field about 20 to 50 micrometers in diameter, located in the vicinity of the cell body. In contrast, the ruffed cell of the sea eel differs rather significantly from that of the goldfish in its morphological features. The ruffed cell of the sea eel is of a bipolar type. One thick dendrite arises from the cell body and extends for about 50 to 100 micrometers, where it gives rise to many thread-like dendritic branches. The IP arises from the cell body as a smooth thin process. However, about 30 to 70 micrometers distant from its origin, many elaborate protrusions arise from the axonal shaft. These intermingle with one another to form a spheroidal or ovoid field about 20 to 40 micrometers in diameter. Distal to this protrusion-bearing part, the axon continues as a smooth, thin process. In spite of these differences in structural features, the ruffed cell of the catfish and that of the sea eel are very similar in their synaptic features in the nest (the special synaptic field around the ruffed cell IP, composed of its protrusions, of granule cell dendrites, and of other neuronal processes); that is, synapses between the ruffed cell IP (its shaft and protrusions) and granule cell dendrites and serial synapses made by the ruffed cell IP, granule cell dendrites, and perinest cell dendrites. These results suggest that the ruffed cell is generally present in the teleostean olfactory bulb, although its detailed structural features may vary from species to species. Moreover, the neuronal organization of the olfactory bulb seems to be fundamentally similar in various species of teleosts.
Membrane specializations at the active zone of the afferent synapse in the saccular macula of goldfish are described. Those of the presynaptic membrane consist of three to six elongated aggregates of intramembrane particles separated by particle-free furrows on the concave part of the P face and its complementary figure, that is, an alternate arrangement of elongated aggregates of pits and smooth ridges on the convex part of the E face. The size of the specialized area is about 0.5 micrometer x 0.3 micrometer. Vesicle fusion sites are situated at the margin of the particle-free furrow and ridge of the presynaptic active zone. Round pores about 30-50 nm in diameter are seen on the P face around the active zone. They are probably openings of the anastomosing tubules or coated pits. A focal aggregate of intramembrane particles is observed on the E face of the postsynaptic membrane apposing the presynaptic active zone. The P face of the postsynaptic active zone shows pits and particles. Small gap junctions are found between hair cells and adjacent supporting cells. They are frequently associated with desmosomes. The possible functional significance of these gap junctions is discussed.
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A new type of neuron was recognized in the olfactory bulb of the goldfish (Carassius auratus) by means of light and high voltage electron microscopy of Golgi-impregnated material, combined Golgi-electron microscopy, and electron microscopy of serial thin sections. The neuron is located in the layer between the olfactory nerve layer and the anterior olfactory nucleus. It has a spherical cell body, about 10--20 microns in diameter, and several dendrites which form a spherical dendritic field, about 70--100 microns in diameter, in the vicinity of the cell body. The most remarkable structural feature of this neuron is that its initial unmyelinated portion of the axon (IP) has elaborate protrusions with many synapses. The IP can be divided into three parts, parts 1, 2 and 3, based on its structural features. Part 1 is the initial part of the IP, about 20--40 microns in length. Many elaborate protrusions arise from the shaft and intermingle with one another to constitute a spherical field, about 20--40 microns in diameter, around the shaft. Part 2 is the middle part of the IP, about 10--20 microns in length. There are several collateral-like protrusions, which are scattered along the shaft and extended laterally about 5--15 microns. Part 3 is the last part of the IP, and is cylindrical without protrusions. The length of part 3 varies from 20 to more than 100 microns. The axon acquires a myelin sheath at distance of 70--250 microns from its origin. Protrusions make synaptic contacts mainly with granule cell dendrites. Some of them are of the reciprocal type. Protrusion are presynaptic in asymmetrical synapses, and postsynaptic in symmetrical synapses with granule cell dendrites. The shaft of the IP also has synapses similar to those on protrusions. The neuron described is a new type of neuron in the vertebrate central nervous system. We propose for it the name "ruffed cell."
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