A scanning electron microscope study of human cerebral arteries.

Human cerebral arteries were obtained from autopsy, fixed under pressure, cut open, and tacked onto pieces of cork. For one artery the intima was partly teased away, exposing the media, and treated with a silver nitrate process. For another artery the adventitia was exposed. Both arteries were processed through graded ethanols and coated with gold paladium for the scanning electron microscope. The collagen fibers of the adventitia were approximately 5 mum in diameter and consisted of a bundle of microfilaments, each of which had a diameter of 800-1000 A (1 A = 10(-10) m). The collagen fibers were oriented parallel to the long axis of the artery. The muscle cells of the media had a diameter of 2-5 mum and were arranged circumferentially with a pitch of approximately 20 degrees. The collagen fibers of the media travel perpendicular to the muscle cells, and parallel to the long axis of the artery. The fibrillar components of the elastin in the intima had a diameter of approximately 700-1000 A and were arranged parallel to the long axis of the artery. It was postulated that the fibrillar part of the elastin was the elastic component of the elastin.     

The organization of the mammalian kinetochore: a scanning electron microscope study

Summary A procedure has been developed for scanning electron microscopy that enables the visualization of kinetochores along the surface of isolated chromosomes of the Indian muntjac. Indirect immunofluorescence and thin section analysis of the kinetochores of those isolated chromosomes verified that these structures retained in vivo composition and morphology during the isolation procedure. In scanning electron micrographs the outer surface of the outer kinetochore plate can be visualized as a series of fibers 25–30 nm in diameter that are arranged across the plate. These images are comparable to those obtained by whole mount transmission electron microscopic procedures (Rattner 1986) and are compatible with a model of the kinetochore in which chromatin fiber from the body of the chromosome extend to the outer kinetochore plate.     

A scanning electron microscope study of microvascular anastomoses.

The abdominal aortas of 30 rats were sutured under an operating microscope. The results were studied under a scanning electron microscope at 8 different periods after operation, ranging from 3 minutes to one month. The observations are presented.     

A scanning electron microscope study of mouse peritoneal mesothelium.

As seen in the scanning electron microscope, peritoneal mesothelial cells of the mouse diaphragm, anterior abdominal wall and intestinal serosa carry numerous microvilli. These microvilli are absent over certain areas of the cell surface and are sometimes, interlocked in meshwork patterns or coronal formation. The apical cell membranes of the mesothelium at the base of the microvilli, are invaginated by many plasmalemmal vesicles and vacuoles and carry a number of protruding spherical structures. Deep circular craters, giving the impression of stomata, are also visible.     

The sub-membrane reticulum of the human erythrocyte: A scanning electron microscope study

A web-like reticulum underlying the human erythrocyte membrane was studied at a resolution of 5–10 nm by means of a scanning electron microscope. The network was visualized in isolated membranes (ghosts) torn open to reveal their interior space and in residues derived from ghosts extracted with Triton X-100. It formed a continuous (rather than patchy) cover over the entire cytoplasmic surface, except where lifted off or torn away. Filaments (5–40 nm in diameter), annular figures (40–60 nm in diameter), and nodes (30–100 nm in diameter) were prominent in different networks. The dimensions of the filaments and the interstices in the reticulum varied with conditions, suggesting that the network has elastic properties. This reticulum is probably related to the erythrocyte membrane proteins spectrin and actin.     

Cosmos pollen ontogeny: A scanning electron microscope study

Summary Ontogenetic data concerning pollen not only clarifies the mode of deposition of the elaborate walls but has considerable functional and taxonomic relevance. Hitherto such studies have used optical or transmission electron microscopy but here a recently devised preparative technique has enabled pollen development inCosmos bipinnatus to be studied using the scanning electron microscope. The technique involves freeze-fracturing of osmium fixed, cryoprotected anthers, maceration in dilute osmium tetroxide, critical point drying, sputter coating and examination. The processes of pollen wall development can then be observed in three dimensions, an important aid to understanding the spatial relationships involved in the determination of ornamentation and apertures. Details of the pollen and tapetum are described at various stages between meiosis and anthesis. A close conformity is demonstrated between the results obtained and those of earlier transmission electron microscopic studies of the same and related species although very different interpretations are made.     

A scanning electron microscope study of early sea urchin reaggregation

Sea urchin embryos were observed with SEM during the first 2 h of reaggregation, following dissociation of the 16-cell stage. A dense meshwork, composed of elongated microvilli embedded in the hyaline layer, surrounds the egg during early development. The dissociation procedure strips off some of the meshwork layer leaving fewer and smaller microvilli on the cell surface. Shortly after reaggregation has begun, several types of cell extensions are formed, including filopodia, which anchor the cells to the substrate, and ruffles and pseudopods, which enable the cells to move. Possible factors involved in the behavior of dissociated cells are discussed with regard to (1) the source of additional membrane in the formation of new cell extensions; (2) the ability of the cells to move.     

A study of human root cementum surfaces as prepared for and examined in the scanning electron microscope

Summary The morphology of the cementum surface of human teeth was studied directly by scanning electron microscopy of 50 freeze-dried and 170 anorganic specimens. Extrinsic (Sharpey) fibres were found to occupy almost 100% of the surface in acellular cement, about 40% of the surface in cement with intrinsic fibres but no cells, and 15–40% in cellular cement, and averaged 6 m diameter. Some areas with no extrinsic fibres resembled adult lamellar bone. The mineral front of the intrinsic fibres generally was similar to forming and resting lamellar bone; that of the extrinsic fibres varied according to the activity of the surface, but was normal to the axis of the fibre, even where these entered the surface at a sharp angle. Resorption bays were either small and isolated, often seen in newly erupted teeth; or, more rarely, large and quite deep where excessive force must have occurred.This work has been supported by grants from the Medical Research Council and the Science Research Council.We would like to thank Mr. P. S. Reynolds and Mr. T. Brett for invaluable technical assistance and Mrs. J. Mills for secretarial assistance.     

Long-term results of deep defects in articular cartilage. A scanning electron microscope study.

Core defects produced in the medial femoral condyle of the rabbit were studied by scanning electron microscopy and light microscopy over a period of 2 years. In some cases the defect was filled by hyaline articular cartilage with a fairly smooth surface, but in others the tissue was markedly fibrillated and resembled fibrous tissue and fibrocartilage. Appearances suggesting disintegration of the newly formed cartilage were seen in some cases. It would appear that a continuation of this process can lead to the exposure of subchondral bone. In one instance no repair tissue or new cartilage could be identified but the surrounding old cartilage had formed a shelf over the defect. The cartilage surrounding the defect was either normal or showed superficial fibrillation, and/or flow formation, and/or fissures.     

A scanning electron microscope technique for restoring deformed fossils

Deformed fossils which originally had a regular geometric outline, such as crinoid columnals, can be restored using a scanning electron microscope technique called tilt correction. This magnifies the specimen in one direction only. It is unsuitable for specimens where deformation has occurred unevenly and can also distort small structures while restoring the whole specimen. D Crinoid columnals, scanning electron microscope, tilt correction.     

An electron microscope study of the DNA sequence organization of the human genome

The arrangements of inverted-repeated and repeated DNA sequences in the human genome have been investigated by an electron microscope method. The arrangement of the interspersed repeated DNA sequences is found to be similar to the corresponding arrangement found in Xenopus. This arrangement consists of 300-nucleotide-long repeated DNA sequences interspersed with roughly gene-size single-copy DNA sequences. The inverted-repeated sequences are also 300 nucleotides in length and are interspersed with the other DNA sequence classes.Most inverted-repeated sequences (64%) are spaced by another sequence which is recognized by electron microscopy as a single-stranded loop in a hairpin structure. The average length of this spacer loop is 1.6 kilobases. Although some pairs of inverted-repeated sequences are clustered, most seem to be randomly distributed throughout the genome. The average distance separating two pairs of inverted-repeated sequences is 10 to 20 kilobases. The interspersed repeated sequences and inverted-repeated sequences are arranged simultaneously in a portion of the human genome resulting in an interspersion of all three sequence classes.     

Red cell fragmentation in human disease (a light and scanning electron microscope study)

Although the mechanism of schizocyte formation has been amply documented in animal experiments and in in-vitro models, the fragmentation encounter between flowing red cells and fibrin strands has not previously been successfully demonstrated in human, microangiopathic disease. If blood flow is restored briefly in vitro immediately prior to tissue fixation, the instant of red cell fragmentation can be captured. Examination of tissue specimens fixed in this manner shows a pathophysiologic process that amplifies the findings previously described in other studies. In the patient under study, the microangiopathic process was widespread in all specimens of pulmonary and renal tissue that had been fixed after brief restoration of blood flow. Small arteries as well as the true microcirculation of both organs were involved. The microangiopathic process in the small arteries and arterioles presented as a partially occlusive thrombus of characteristic histology. The pulmonary capillaries contained linear fibrin microclots festooned with distorted and partially fragmented red cells. The microcirculation of the kidney showed the same findings as well as amorphous, sludged, occlusive red cell masses, particularly in the renal medulla.     

Plant-microbial interaction under gnotobiotic conditions: A scanning electron microscope study

Inoculation of canola seeds withPseudomonas putida GR12-2 stimulates root elongation under gnotobiotic conditions. Transformation ofP. putida GR12-2 with the broad-host-range plasmid pGSS15 abolishes the enhancement of root elongation. With scanning electron microscopy it was found that both transformed and nontransformedP. putida GR12-2 are capable of binding to canola seed coats. In addition, it was observed that 4 days after the initial inoculation the roots of bothP. putida GR12-2- and GR12-2/pGSS15-treated seedlings were free of adhering bacteria despite the fact that it was subsequently shown that both bacterial strains are capable of binding to roots. Thus, adhesion to roots is not necessary for the initial phase of enhanced root elongation that is induced byP. putida GR12-2 under gnotobiotic conditions.     

The prism pattern of rat molar enamel: a scanning electron microscope study.

Rat molar enamel has been studied by sectioning the enamel along various planes, and observing the etched surfaces in the SEM. It was found that the prism pattern was much more variable than in rat incisor enamel. Regions without prism decussation seemed to dominate in the occlusal half of the molars. Where present, prism decussation was of the uniserial lamellar type, but it varied considerably in distribution, extent, and distinctness. Prism decussation seemed to have a predilection for the cervical enamel, and was almost absent in the enamel on the occlusal surface. The interprismatic substance showed a characteristic configuration: In the inner enamel it appeared in the form of radially oriented sheets, which tended to delimit radially directed, single lines of prisms. In regions with prism decussation these single lines of prisms encompassed prisms belonging to different prism lamellae. In the outer part of the enamel the interprismatic substance exhibited a honeycomb appearance. The similarities and differences between the prism patterns of rat incisor and molar enamel may be of importance for understanding the mechanisms of amelogenesis, especially for the recognition of factors controlling the movement of ameloblasts.