TRANSMISSION AND SCANNING ELECTRON MICROSCOPIC STUDIES OF SNAKE PANCREATIC ISLETS
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概要
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The fine structure of the pancreatic islets of the snake (Elaphe climacophora) was studied by means of transmission and scanning electron microsopies, immunocytochemistry and computer simulation. The snake pancreatic islets were occasionally quite large in size, and such large islets usually appeared in the pancreatic tissues close to the spleen. In the islet tissues, at least 4 cell types were identified. (1) Glucagon-secreting A-cells contained electron-dense spherical granules, which reacted to anti-glucagon antisera. (2) Insulin -secreting B-cells contained usually less electron-dense crystalline granules, Some of these granules showed a three-dimensional crystalline structure, when observed by scannig electron microscopy. Examination by computer simulation indicated that the structure was a rhombic dodecahedron. Some of such crystalline granules were found to be excreted by the mode of emiocytosis. The B-cells were also exmined by the use of anti-insulin antisera to ascertain the real cell type. (3) The third islet cell type was found to be somatostatin-secreting D-cells, which were primarily located in the periphery of the islet tissues. These cells were rather few in number and contained less amount of electron-dense granules than those of other cell types. (4) The fourth cell type was PP-cell. These cells were small in population, distributed in every part of the islet tissues, and contained tiny electron-dense granules. In the snake pancreatic islets, nerve terminals were frequently detected. The first of these was the cholinergic type, which contained so-called synaptic vesicles together with large- cored vesicles, and were usually in contact with B- or D-cells. The latter cell type was surrounded by a number of nerve terminals. The second type of nerve terminals was the adrenergic type containing small-cored vesicles, and was distributed usually in the periphery of the islets, or in contact with the walls of blood vessels.
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