bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructure of Melanin Formation in Curvularia sp., Alternaria sp., and Drechslera Sorokiniana
Authors: Wheeler M. H. , Tolmsoff W. J. , Bell A. A. 
Published: June 2020

(+)-Scytalone [3,4-dihydro-3,6,8-trihydroxy-l-(2Hj-naphthalenone] and 1,8-di- hydroxynaphthalene (DHN) have been proposed as intermediates of melanin synthesis in the fungiVerticillium dahliae(1, 2, 3, 4) andThielaviopsis basicola(4, 5). Scytalone is enzymatically dehydrated byV. dahliaeto 1,3,8-trihydroxynaphthalene which is then reduced to (-)-vermelone [(-)-3,4- dihydro-3,8-dihydroxy-1(2H)-naphthalenone]. Vermelone is subsequently dehydrated to DHN which is enzymatically polymerized to melanin.Melanin formation inCurvulariasp.,Alternariasp., andDrechslera soro- kinianawas examined by light and electron-transmission microscopy. Wild-type isolates of each fungus were compared with albino mutants before and after treatment with 1 mM scytalone or 0.1 mM DHN in 50 mM potassium phosphate buffer, pH 7.0. Both chemicals were converted to dark pigments in the walls of hyphae and conidia of the albino mutants. The darkened cells were similar in appearance to corresponding cells of the wild types under the light microscope.
Lipoproteins in Golgi Apparatus and GERL of Rat Hepatocytes: A CytoChemical Study
Authors: Novikoff P.M. , Yam A. 
Published: June 2020

Our laboratory has recently reported that the marked fatty liver induced in rats by feeding a purine-free diet with 1% orotic acid (OA) can be reversed by addition of ethyl chlorophenoxyiso- butyrate (clofibrate or CPIB) to the OA diet (1). Hepatocyte ultrastructure returns to normal, as do the triacylglycerol levels in liver and serum. During reversal, GERL becomes prominent, distended with particles interpreted as lipoproteins undergoing degradation.This communication reports cytochemical observations on such hepatocytes. Thiamine pyrophosphatase (TPPase) activity in hepatocytes, as in various cell types (2), is localized to the inner (trans) element of the Golgi apparatus (Figure 1). GERL, in contrast, shows no TPPase activity but displays acid phosphatase (AcPase) activity (Figure 2). Particles resembling very low density lipoproteins (VLDL) are found in both GERL and elements of the Golgi apparatus. The presence of both AcPase activity and VLDL-like particles strengthens our earlier suggestion that lipoproteins may undergo transformations in GERL.
Scanning and Transmission Electron Microscopy of Isolated Cells from the Avian Salt Gland
Authors: Thompson Ian G. 
Published: June 2020

With the advent of new techniques for isolating single cells for biochemical and physiological investigation, an important consideration is the morphological integrity of these cells after dissociation from the intact tissue. Do isolated cells retain the degree of structural differentiation that is apparent in vivo? The principal secretory cells of the avian salt gland are an example of cells that are highly differentiated in form under conditions of physiological stress. This report describes the ultrastructure of dissociated salt gland cells as visualized with the scanning and transmission electron microscope.The dissociation procedure employed here was the same as that applied to the exocrine pancreas. For transmission electron microscopy the cell suspension was centrifuged and the resultant pellet prefixed in cacodylate buffered 3% glutaraldehyde- 1% paraformaldehyde, postfixed in unbuffered 1% osmium tetroxide, and embedded in epon-araldite. An assessment of the cell surface coat following enzymatic dissociation was facilitated by the inclusion of ruthenium red (500 ppm) in both the aldehyde and osmium fixation steps.
Banded Structure in a Hepatocellular Carcinoma
Authors: Chew E. C. , Chan W. C. 
Published: June 2020

Extracellular banded structures were first reported by Luse (1) in a neural tumor and subsequently by others in many types of tissues. This subject was summerized in detail by Sun and White in 1975 (2). This communication reports observations of banded structures discovered by electron microscopy in the study of a human hepatocellular carcinoma. The tissue was fixed in 3% glutaraldehyde in 0.1 M cacodylate buffer and post-fixed in buffered osmium tetroxide. Sections were stained with uranyl acetate and lead citrate. Thick sections, about 1 - 2 μ, were stained with periodic acid-Schiff's reagent involving heating of the slides.Banded structures are observed in the connective tissue area intermingled with collagen fibrils and are usually fusiform in shape (Fig. 1). The fusiform bodies average 0.5 μ in diameter and are outlined with periodicity of 800 to 1000 A°. Each period consists of a light and a dark band. Fine filaments of about 24 A° in thickness are present in the light bands (Fig. 2). They are also found to be periodic acid-Schiff positive (Fig. 3).
Ultrastructural Effects of Mercury on the Intact Proximal Tubule of the Euryhaline TeleostFundulus Heteroclitus
Authors: Wasserman Jay , Koepp Stephen J. 
Published: June 2020

In vitro renal cytopathology has been reported for several fish species following acute exposure to mercury (1,2). Less is known about pathogenesis in kidney tissue from intact fish exposed to environmental levels of the toxicant. Prior toxicity (3) and pathological investigations (4) with the common mummi- chog (Fundulus heteroclitus) have indicated a particular susceptibility to mercury for this important estuarine inhabitant.Male fish (3.5-4.5 g) were incubated in artificial seawater containing one of three toxicologically-significant concentrations of mercuric chloride (0.25, 0.75, and 1.50 ppm). Kidney tissue cubes of survivors at 12, 36, and 96-hours exposure for each test concentration (plus controls) were fixed in cold 4% phosphate-buffered glutaraldehyde, postfixed in 1% osmium tetroxide, and subsequently embedded in Epon 812. Thin sections were doubly-stained with uranyl acetate and lead citrate.Exposure to the lowest mercury concentration (0.25 ppm) produced progressive dilatation of smooth endoplasmic reticulum and apical vesicles (Fig. 1).
Small Round Cell Tumors
Authors: Mackay B. , Garza D. 
Published: June 2020

The term "small round cell tumor" is used to designate a heterogenous group of neoplasms that have in common the fact that they are composed of small round, polygonal, or occasionally ovoid cells, compactly grouped with little or no evidence of architectural organization. Identification of tumors within this group by light microscopy can be difficult and is often not possible. Selection of a specific diagnosis by the pathologist is frequently influenced by the clinical behavior and location of the tumor, and by the age of the patient. For example, tumors with this morphology occurring in young children are usually assumed to be rhabdomyosarcoma, neuroblastoma, Ewing's sarcoma, or lymphoma.By studying these neoplasms with the electron microscope and correlating the findings with the light microscopic and clinical data, it is possible to reach a specific diagnosis in most cases. Each tumor possesses distinctive ultrastructural features that serve to identify the cell type.
Ovarian Dysfunction in Fetally Irradiated Beagles
Authors: Seed T. M. , Sanderson M. H. , Gutzeit D. L. , Fritz T. E. , Tolle D. V. , Poole C. M. , Norris W. P. 
Published: June 2020

The developing mammalian fetus is thought to be highly sensitive to ionizing radiation. However, dose, dose-rate relationships are not well established, especially the long term effects of protracted, low-dose exposure. A previous report (1) has indicated that bred beagle bitches exposed to daily doses of 5 to 35 R 60Co gamma rays throughout gestation can produce viable, seemingly normal offspring. Puppies irradiated in utero are distinguishable from controls only by their smaller size, dental abnormalities, and, in adulthood, by their inability to bear young.We report here our preliminary microscopic evaluation of ovarian pathology in young pups continuously irradiated throughout gestation at daily (22 h/day) dose rates of either 0.4, 1.0, 2.5, or 5.0 R/day of gamma rays from an attenuated 60Co source. Pups from non-irradiated bitches served as controls. Experimental animals were evaluated clinically and hematologically (control + 5.0 R/day pups) at regular intervals.
Two Investigations into Grain Boundary Structure
Authors: Humble P. 
Published: June 2020

There has been sustained interest over the last few years into both the intrinsic (primary and secondary) structure of grain boundaries and the extrinsic structure e.g. the interaction of matrix dislocations with the boundary. Most of the investigations carried out by electron microscopy have involved only the use of information contained in the transmitted image (bright field, dark field, weak beam etc.). Whilst these imaging modes are appropriate to the cases of relatively coarse intrinsic or extrinsic grain boundary dislocation structures, it is apparent that in principle (and indeed in practice, e.g. (1)-(3)) the diffraction patterns from the boundary can give extra independent information about the fine scale periodic intrinsic structure of the boundary.In this paper I shall describe one investigation into each type of structure using the appropriate method of obtaining the necessary information which has been carried out recently at Tribophysics.
Scanning transmission electron microscopy of biological macromolbcules
Authors: Tichelaar W. , Oostergetel G.T. , Haker J. , Bruggen E.F.J. Van. 
Published: June 2020

Our aim is to use Scanning Transmission Electron Microscopy (STEM) for research on biological macromolecules. Preliminary experiments have been carried out on a Philips EM 300 (equipped with a high resolution stage and normal hairpin cathode) with a STEMattachment. The elastically scattered electrons were detected on an annular detector and the images were photographed from the monitor screen. The instrumental resolution was about 15Å. The biological macromolecules were mounted on a carbon film with a thickness of about 25Å supported by a holey film; in most cases the objects were lightly (negatively) stained with uranyl acetate (UAc).Fig. 1 shows a STEM-dark field (df) image of lightly stained rooster liver (poly-) ribosomes. The mRNA can be seen; this is remarkable considering the instrumental resolution. The subunits cannot be seen; however we hope to succeed in visualizing the substructure of the ribosome by lightly negative staining.
Cryoultramicrotomy of plant protoplasts
Authors: Williamson Francis A. 
Published: June 2020

IntroductionNaked plant cells (protoplasts) have been used for the study of lectin binding to the plasma membrane, and of the initial stages of cell wall formation (2,3 and refs, therein). In this paper, I describe methods for the cryoultramicrotomy of plant protoplasts and give a general description of their ultrastructure. In addition, labelled lectins have been applied to cryo-sections to locate intracellular binding sites, and the superior resolution of the negatively stained cryo-sections has been applied to a preliminary study of cell wall fibril formation.Materials and MethodsProtoplasts were prepared from meristematic leaves of leek (Allium porrum) by enzymatic digestion (3). After washing, the cells were fixed in 1% glutaraldehyde in 0.55 M sorbitol and 1 mM CaCl2 buffered at pH 7.2 with 10 mM sodium cacodylate or HEPES. They were then washed (16 h) in 100 mM sodium cacodylate pH 7.2 and infused with 1 M sucrose in the same buffer for 3 h. A very concentrated suspension of the cells was mounted on a specimen holder and frozen in nitrogen slush (liquid nitrogen at its freezing point).
Etching of red blood cells by means of ion beam sputtering
Authors: Hojou Kiichi , Fujita Hiroshi , Ito Masamichi , Hirahata Tetsuyuki , Kanaya Koichi 
Published: June 2020

Ion etching techniques have recently been utilized in attempts to reveal subsurface cell structure in the scanning electro microscope. There has, however,been some difficulties indistingushing infracellar structure from artifacts and comtamination produced by the ion etching process.In order to avoid thermal defects caused by conventional etching processes of DC- or rf-sputtering ion beam etching can be used to study biological specimens. In this case, and in addition to using an ion beam which is well- collimated and highly accelerated, the specimen must be both cooled and rotated during processing. Using this procedure on red blood cells examined by SEM, details of their structure were revealed. However, the cone-like structures reported by several previous investigators were not consistantly observed.It is concluded that this procedure for etching may be more informative than those obtained by other ion etching processes.
High resolution experiments with a cross-hair beam-stop
Authors: Tesche B. 
Published: June 2020

Dupouy and collaborators achieved what is now known as a central beam stop with diaphragms which were partly covered by strips. The width and arrangement of these strips, however, excluded a substantial part of the Fourier spectrum, although the zero beam could readily be stopped.We succeeded in arranging a cross-hair in the center of an aperture. The three-micron thick quartz fibers are made conductive by evaporating gold onto them and also in the thin layer aperture onto which they are mounted. By this means, charging of the cross-hair and contamination of the apertures are avoided. The thin diameter of the cross-hairs permits the exclusion of the zero beam as well, yet without any great loss of the Fourier spectrum. Furthermore, small shifts of the aperture permit partial exclusion of the zero beam, which leads to very interesting contrast phenomena. It must be emphasized that the optical quality of the microscope is not impaired by such small shifts of the aperture and that the cut-off frequency remains unchanged.
Metal measured in earthworm tissue by X-ray microanalysis
Authors: Gullvåg B.M. 
Published: June 2020

Subcellular localization of polluting metals in organisms collected from the environment is an important step towards understanding the toxicological effects of environmental metal pollution.Material and MethodsLumbricid earthworms were collected from a rather trafficated road in the Trondheim area and from a supposed control area several miles from town with no traffic nearby. The earthworms were kept in a glass container for three days before fixation and given a diet of mixed cornflour and agar in order to eliminate all mineral particles from their intestine. The material which was to be used for X-ray analysis was fixed in glutaraldehyde (2.5%) for 4 hrs and no post-staining was used. Section thickness was 100 to 150 nm. Analyses were carried out with a JSTEM 200 C electron microscope combined with a side-entry goniometer and an energy dispersive X-ray spectrometer using spot size 500 Å.
Membrane alterations during thylakoid formation in rhodospirillum rubrum
Authors: Yokomura E. , Sugimoto M. , Gomi-Baba C 
Published: June 2020

Thylakoid formation in RhodospiriHum rubrum is one of the model systems adequate for studying the differentiation of the biological membranes. It is well established that thylakoids are formed from the invaginations of cell membranes. This is based on electronmicroscopic observations and biochemical studies. However, the alterations in the architecture of the cell membranes during thylakoid- forming process is ambiguous. Therefore, in the present study, thylakoid formation in R.. rubrum was investigated with freeze-fracture technique and DAB-histochemistry.For inducing thylakoid formation, the cells grown at 25° C in an aerobic-dark (AD) environment were transferred to an anaerobic-light (NL) environment. At various times after transferring from AD to NL, the cells were immersed in 30 % glycerol without any chemical prefixation and then immediately frozen in liquid Freon to be prepared for the freeze-fracture replicas. The materials were handled at 25° C throughout before freezing.
Acetylcholine receptor protein structure
Authors: Brisson A. 
Published: June 2020

The acetylcholine receptor protein plays a leading part in the synaptic transmission mechanism. The binding of the neurotransmitter, acetylcholine, to the protein triggers conformational changes, allowing the translocation of ions through the membrane. The structural relationships between the binding sites of the cholinergic ligands and the translocating part of the protein are still unknown, as the subunit composition is. A better knowledge of the structure of the acetylcholine receptor protein is the aim of the present study.Negatively stained preparations of purified cholinergic receptor protein and of membrane fragments rich in acetylcholine receptor protein are characterized by the presence of particles having a diameter of 8-9 mm, and exhibiting a doughnut like structure, with a central pit filled with stain. The variability in the stain distribution on the particle surface did'nt allow to determine the subunit structure of the protein. In the case of crystalline biological specimens, methods of averaging have allowed to overcome this problem; then, we have tried to crystallize the membrane-bound cholinergic receptor protein.
Morphometric studies of chromatin structure and nuclear organization: hepatic polyploidy and mammalian erythropoiesis
Authors: Brasch Klaus 
Published: June 2020

Morphometric techniques have seen only limited application in the establishment of quantitative parameters relating to chromatin structure and nuclear organization at the EM level. The usefulness of this approach, however, was recently demonstrated by studies on avian erythropoiesis, showing that contrary to subjective impression there is no progressive increase in the amount of condensed chromatin in developing erythrocyte nuclei. This report extends similar analysis to liver nuclei of different ploidy classes and to mammalian erythroid cells.Materials and MethodsRat liver and bone marrow from anemic rabbits were prepared for microscopy as described. Data for 2c and 4c liver nuclei were obtained using rats of appropriate ages: 28 days, >90% 2c; 400 days, >70% 4c; 8c nuclei are larger than 380 μm3. Mean nuclear volumes were calculated from the major and minor axes of at least 50 nuclei of each type measured with a micrometer using 2-3 μm thick sections. Nuclei were treated as prolate spheroids. Morphometric analysis was carried out as described, using the point counting stereological method.
Cytochemical study of nucleolar structure and formation inphysarum polycephalum
Authors: Lafontaine J.G. , Cadrin M. 
Published: June 2020

Under appropriate culture conditions the slime mold, Physarum polycephalum, can be grown in the form of multinucleated plasmodia. In view of the fact that these numerous nuclei divide in perfect synchrony, this organism offers unique advantages for studying different aspects of the cell cycle.As in other organisms studied so far, the interphase nucleolus consists of fibrillar regions surrounded by conspicuous granular zones. These fibrillar regions, however, are spherical in shape and are characterized by the presence of opaque particles. As the nucleolar mass disorganizes these spherical nucleolar portions persist in the form of bodies which migrate with the mitotic chromosomes to the nuclear poles. Prelabeling of G2nuclei with tritiated thymidine permits to demonstrate that these nucleolar remnants contain DNA and that this DNA is still present within their mass as they become integrated within the early interphase daughter nuclei. Since the G1period is lacking in this organism, both DNA and RNA synthesis are resumed soon after mitosis: the nucleus increases in size and the nucleolus is also reformed quite rap idly.
Mitochondrial DNA of acute myeloid leukemic cells
Authors: Paul Choudhury R. , Misra D. N. , Sadhukhan P. 
Published: June 2020

Mitochondrial DNA (mtDNA) of non-malignant animal tissue ceils consists of a population of covalently closed double stranded duplex circular molecules with contour lengths varying between 4.5 and 6 μ. Majority of the circles are found to be highly twisted. If they are nicked during extraction process, some molecules are fully open (Swift and Wolstenholme; Choudhury and Sadhukhan). The purpose of this paper is to describe changes in molecular configurations of mtDNA molecules of malignant cells using a model system of human acute myeloid leukemia.Peripheral blood was withdrawn aseptically from acute myeloid leukemic patients and collected in a test tube containing A.C.D. solution in the proportion of 5 : 1. The blood was allowed to settle at 4°C for 24 hr. At the end of this period buffy coat of white blood cells was drawn off and the contaminating red cells were removed by haemolysis with distilled water for 20 sec. The leukocytes were spun down at 1000g for 5 min at 4°C.
Lamella-particle complexes
Authors: Banfield William G. , Lee Cecil W. 
Published: June 2020

Lamella-particle complexes are a distinct group of morphologic structures. They have been reported in a growing number of papers often without detailed description. This could be accounted for because of the paucity of occurrence in the tissue or cells examined, the limitations inherent in preparing the tissue for electron microscopy, or because the photographs were not at a high enough magnification. We will take a closer look at these complexes, adding new information on their morphology, make correlations overlooked or not possible when initial observations were published and dispel some erroneous impressions as to the degree of similarity between complexes of different origin. Standard methods of fixation, dehydration and epon embedding were used. Staining was with lead and uranyl acetate.The lamella-particle complex is well illustrated in a lymphoma cell of the northern pike (Fig. 1). In cross section its wall is made up of a striated lamella associated with ribosome-like particles.
Formation and disintegration of lipid droplets associated with cell organelles, especially smooth-surfaced endoplasmic reticulum in the white adipose cell
Authors: Usuku G. , Iyama K. , Ohzono K. , Hirashima M. 
Published: June 2020

Although a number of ultrastructural studies on the white adipose cell have been reported, not a few unsolved problems still remain on the morphological and functional relationships between formation or disintegration of lipid droplets and cell organelles in those cells. In order to re-examine such the points, we have made electron microscopical studies on the epididymal adipose cells from normal and starved Wistar adult rats, and on these cells from rats refed ordinary animal food or given only lipid without carbohydrate after a period of starvation. Additionally, for the same purpose we have observed the ultrastructure of developing and differentiating fat cells in the epididymal adipose tissue of rats ranging from newborn to 5 weeks old.The adipose cell from normal adult rats shows that the peripheral cytoplasm which envelopes a central large lipid mass contains well-developed cell organelles and occasionally small lipid droplets. These lipid droplets have no limiting membrane, but are often observed to be closely encircled by fenestrated profiles of smooth-surfaced endoplasmic reticulum (SER) which connects with a part of rough-surfaced endoplasmic reticulum (RER) in places (Fig. 1).