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Biomedical subjects

E W DEMPSEY

Publications and source records attributed to E W DEMPSEY.

At least 19 recordsLinked to original sources
PubMed1956

Variations in the structure of mitochondria.

A characteristic internal structure, consisting of a double-layered outer wall enclosing a matrix-filled space through which pass double-layered membranous folds, would appear to comprise as satisfactory a definition of mitochondria for electron microscopy as their intravital affinity for Janus green affords for light microscopy. Relying for identification upon this characteristic internal structure, mitochondria appear to be pleomorphic structures which vary in size, shape, complexity, and density. They are labile also in that their number may increase or decrease under controlled conditions. The possibility therefore exists that these organelles are constantly being formed and destroyed, perhaps by their participation in metabolic processes. The problem of the origin of mitochondria is in an unsatisfactory state. New organelles unquestionably are formed in particular physiological states. The possibility that new bodies are produced by fission of ones already present does not seem adequate. On the other hand, the possible fabrication of new mitochondria out of intracellular membranes, although an attractive hypothesis, has not been adequately substantiated.

Electrons↗
PubMed1955

An electron microscopic study of the blood-brain barrier in the rat, employing silver nitrate as a vital stain.

The intravital deposition of silver in the chorioid plexuses, area postrema, intercolumnar tubercle, neurohypophysis, and pineal body of rats, given 1.5 gm. of silver nitrate per liter of drinking water for periods of up to one year, has been investigated by electron microscopy. Unlike other parts of the central nervous system, these regions store large amounts of silver. In all of these structures, silver is deposited in the form of dense granules in the basement membrane upon which the capillary endothelium rests, in and upon the connective tissue cells and fibers constituting a loose pericapillary sheath, and in an outer membrane separating this sheath from the parenchymatous cells. Parts of the central nervous system which do not store silver, for example the spinal cord, cerebellar cortex, cerebral cortex, and reticular formation, lack a connective tissue investment of the capillaries. In these locations, the glial processes or end-feet are closely applied to the walls of the capillaries. Only a narrow space, filled by an amorphous, moderately electron-dense substance, separates the plasma membranes of the endothelial cells and glial processes. The significance of these observations is discussed with respect to the questions of the Virchow-Robin perivascular spaces, the interstitial ground-substance of the brain, and the location of the hematoencephalic barrier.

Animals↗
PubMed1955

The use of silver nitrate as a vital stain, and its distribution in several mammalian tissues as studied with the electron microscope.

After chronic administration of a dilute solution of silver nitrate in drinking water to rats, mice, and guinea pigs, granular deposits of metallic silver were detected in electron micrographs of the kidney, liver, thyroid, and pancreas. The silver deposits were in the form of extremely dense, angular particles with sharp outlines. They varied from aggregates a few microns in diameter down to granules at the limit of resolution of the electron microscope. The principal sites of deposition were (1) basement membranes, especially those of the renal glomeruli, proximal convoluted tubules, and various glands, and those associated with vascular endothelium, and (2) the cytoplasm of fixed and free macrophages. Both in Kupffer cells lining hepatic sinusoids and in the wandering macrophages of other tissues, the silver was segregated in discrete vacuoles. In addition, granular deposits were observed in occasional vesicular structures in the proximal convoluted tubules of the kidney, the hepatic cells, and the pancreatic acinar cell. These structures, in favorable preparations, contained an outer double layered membrane and internal folds similar to those of mitochondria, from which they appear to have been derived. The significance of these findings in heavy metal poisoning and in cellular physiology is briefly discussed.

Animals↗