bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural preservation and absolute contrast of catalase crystal sections prepared with tannic acid
Authors: Akey C.W. , Szalay M. , Edelstein S.J.
Published: June 2020

Three methods of obtaining 20 Å resolution in sectioned protein crystals have recently been described. They include tannic acid fixation, low temperature embedding and grid sectioning. To be useful for 3-dimensional reconstruction thin sections must possess suitable resolution, structural fidelity and a known contrast. Tannic acid fixation appears to satisfy the above criteria based on studies of crystals ofPseudomonascytochrome oxidase, orthorhombic beef liver catalase and beef heart F1-ATPase. In order to develop methods with general applicability, we have concentrated our efforts on a trigonal modification of catalase which routinely demonstrated a resolution of 40 Å. The catalase system is particularly useful since a comparison with the structure recently solved with x-rays will permit evaluation of the accuracy of 3-D reconstructions of sectioned crystals.

Initially, we re-evaluated the packing of trigonal catalase crystals studied by Longley. Images of the (001) plane are of particular interest since they give a projection down the 31-screw axis in space group P3121. Images obtained by the method of Longley or by tannic acid fixation are negatively contrasted since control experiments with orthorhombic catalase plates yield negatively stained specimens with conditions used for the larger trigonal crystals.
Pentamer packing in polyoma virus “hexamer” tubes analyzed by image modeling
Authors: Baker Timothy S. , Caspar D. L. D.
Published: June 2020

Polymorphic assemblies of polyoma virus capsomeres that have been called "hexamer" tubes (because the morphological units are six-coordinated) are, in fact, built of pentamers, as is the icosahedrally symmetric T=7d virus capsid. The quasi-equivalence theory of virus construction had predicted that the six-coordinated morphological units should be hexamers. We have established the pentameric form of the capsomeres in the "hexamer" tubes by Fourier analysis of low-irradiation micrographs: indexing the computed diffraction patterns and computation of the filtered image shows pentagonalshaped capsomeres arranged in a cylindrical surface lattice with p2 symmetry. Digital model building to fit averaged micrographs, summarized here, provides a sensitive means to define the packing arrangement and substructure of the pentameric units in the superimposed top and bottom layers of the tubes.

Fig. 1 shows a representative minimal exposure (∽lOe/Å2) image of a negatively stained (1% uranyl acetate) wide (Å45 nm diameter) "hexamer" tube. Metal-shadowed specimens demonstrate that the tubes are flattened and the near axial rows of capsomeres in the hexagonally packed surface lattice are inclined to the left as viewed from the outside.
Status of microcorrosion casting for SEM
Authors: Nowell J. A.
Published: June 2020

The advantage of the SEM over all other means of gaining information about a biological sample is its ability to image spatial relationships ranging from those visible to the unaided eye to those separated by a few nanometers. It is invaluable for such studies as the localization of focal lesions widely dispersed in normal tissue; the relationships between soft and hard tissue components; the identification of individual species within a large heterogeneous population of microorganisms; and, the subject of this paper, the course of vasculatures through an organ.

To date the main disadvantage of the SEM in biological research is our inability to interpret the image accurately. Our reliance on the image has decreased proportional to our understanding of the effect on the specimen of the preparation procedures. We are now aware, for instance, that ice crystals displace cellular material; that a hypertonic fixative causes shrinkage and a hypotonic one causes swelling; that unstabilized cellular constituents are extracted during solvent dehydration resulting in excessive loss of sample volume; that this volume changes during fixation, dehydration, and drying; that air drying, whether deliberate or accidental, causes structural collapse; and that sputter coating can result in thermal damage and decoration.
Ultrastructural and cell surface studies of cancer epidermal cells following reserpine administration in mice
Authors: Lupulescu A.
Published: June 2020

Recently, it was postulated that a long-term administration of reserpine as an antihypertensive drug for treatment of millions with mild hypertension increased threefold the incidence of mammary carcinoma in women. However, a considerable controversy ensued over the statistical validity of this study and the role of reserpine in carcinogenesis remains still unsolved. The present study deals with the effects of long-term administration of reserpine on the ultrastructure, cytoarchitecture and cell surface of cancer epidermal cells from squamous cell carcinomas induced by 3-methycholanthrene (MCA) in mice.

Young male Swiss mice (COBS) weighing 25 gm were used in these investigations and were divided in four groups: (1) First group was used as controls (2) Mice topically treated with 0.2 ml of 0.3% MCA sol. in acetone, twice a week for 12 months (3) Mice treated with MCA as above and simultaneously injected intramuscularly with 250 μg reserpine (serpasil), twice a week for 12 months and (4) Mice treated only with reserpine as above. Although multiple and large tumors occurred following MCA, only few small tumors were seen following reserpine and MCA treatment.
Myosin filaments localized in replicated cytoskeletons of freeze-dryed human platelets
Authors: Ruben George C. , Allen Robert D.
Published: June 2020

Spheroidal human blood platelets (2-3 μm) on contacting siliconized glass undergo a semi-stereotypicms the original spheroid into a hillock surrounded by a thin hylomere sheet. In this process, the platelet approximately doubles its diameter. Since platelets ar spreading of their margins with pseudopod and/or lamellapod extension. They also undergo a profound reorganization of their cytoskeleton in 10-15 min at 20°C which transfore 16-17% actin and 6-7% myosin and contain muscle like control proteins it is not unreasonable that platelet spreading occur by a sliding of actin filaments as in muscle. It is possible that myosin is present in platelets either as dimers or as ordered bipolar oligomeric filaments composed of 28 monomers. In the former case, filaments 165-300nm long and 2.0-4.0nm wide would be expected. In the latter case, the myosin filaments would be 325nm long and 10.7nm wide.

The cytoskeleton of demembranated platelets was investigated after an attachment interval of 20 min. or less at 20°C.
Fully correlative LM and HVEM analysis of motile fibrils and particles in the reticulopods of Allogromia sp. (protozoa, foraminiferida)
Authors: Bowser Samuel S.
Published: June 2020

The subcellular mechanism underlying the bidirectional transport of organelles in the reticulopods of foraminiferans is poorly understood. Applications of urea and colchicine suggest a role for microtubules (MT) in mediating this transport. Allen et al. have shown that intracellular transport is effected only when organelles are in contact with motile fibrils, visible by LM, and imply that such fibrils are composed of microtubules. We recently suggested that the bidirectional transport of latex particles attached to the extracellular surface of reticulopods may also be mediated by these fibrils. Since motile fibrils are an essential component of the transport mechanism, we sought to determine their ultrastructural composition and the identity of the organelles they transport.

Specimens were mounted in microperfusion chambers as described previously. Either intact organisms or isolated but functional reticulopodial networks (as illustrated here, fig 1A) may be employed. Addition of lym latex microspheres allows simultaneous study of surface motility and intracellular transport, and also provides reference marks for correlation of LM/HVEM images.
Otoconia formation in the chick embryo
Authors: Fermin C.D. , Igarashi M.
Published: June 2020

Otoconia are microscopic geometric structures that cover the sensory epithelia of the utricle and saccule (gravitational receptors) of mammals, and the lagena macula of birds. The importance of otoconia for maintanance of the body balance is evidenced by the abnormal behavior of species with genetic defects of otolith. Although a few reports have dealt with otoconia formation, some basic questions remain unanswered. The chick embryo is desirable for studying otoconial formation because its inner ear structures are easily accessible, and its gestational period is short (21 days of incubation).

The results described here are part of an intensive study intended to examine the morphogenesis of the otoconia in the chick embryo (Gallus- domesticus) inner ear. We used chick embryos from the 4th day of incubation until hatching, and examined the specimens with light (LM) and transmission electron microscopy (TEM). The embryos were decapitated, and fixed by immersion with 3% cold glutaraldehyde. The ears and their parts were dissected out under the microscope; no decalcification was used. For LM, the ears were embedded in JB-4 plastic, cut serially at 5 micra and stained with 0.2% toluidine blue and 0.1% basic fuchsin in 25% alcohol.
The human fetal pituitary: An ultrastructural analysis
Authors: Asa S. L. , Kovacs K. , Horvath E. , Laszlo F. A. , Domokos I.
Published: June 2020

An ultrastructural study was performed on 25 human fetal pituitaries to document the development of cell differentiation and hormone production in the adenohypophysis.

At 5 weeks' gestation, Rathke's cleft was lined by columnar epithelium 3-4 cells deep (Fig. 1). The cells were poorly differentiated, with abundant cytoplasmic glycogen, numerous free ribosomes and occasional secretory granules. Terminal bars were formed on the lateral cell surfaces near the luminal surface of Rathke's cleft; desmosomes formed junctions between cells.

By 6 weeks' gestation, cells resembling corticotrophs were identified (Fig. 2). They contained moderately developed, rough endoplasmic reticulum and numerous secretory granules of variable size, shape and electron density. In 8-week-old fetuses, type I microfilaments were found in those cells. Welldifferentiated somatotrophs were seen in the adenohypophyses of 8-9-week-old fetuses. They contained scattered profiles of rough-surfaced endoplasmic reticulum and spherical, evenly electron dense secretory granules, measuring 300-600 nm in diameter. Cells with dilated rough endoplasmic reticulum containing flocculent material and small, dense, round secretory granules with peripheral electron lucent halos were seen in the adenohypophysis of a 14-week-old fetus; these features are characteristic of the glycoprotein hormone cell line. Typical prolactin cells were not recognizable before 23 weeks' gestation.
Conformation of eukaryotic ribosomal RNAs
Authors: Boublik M. , Thornton G. , Oostergetel G. , Hainfeld J.F. , Wall J.S.
Published: June 2020

Understanding the structural complexity of ribosomes and their role in protein synthesis requires knowledge of the conformation of their components - rRNAs and proteins. Application of dedicated scanning transmission electron microscope (STEM), electrical discharge of the support carbon film in an atmosphere of pure nitrogen, and determination of the molecular weight of individual rRNAs enabled us to obtain high resolution electron microscopic images of unstained freeze-dried rRNA molecules from BHK cells in a form suitable for evaluation of their 3-D structure. Preliminary values for the molecular weight of 28S RNA from the large and 18S RNA from the small ribosomal subunits as obtained by mass measurement were 1.84 x 106 and 0.97 x 106, respectively. Conformation of rRNAs consists, in general, of alternating segments of intramolecular hairpin stems and single stranded loops in a proportion which depends on their ionic environment, the Mg++ concentration in particular. Molecules of 28S RNA (Fig. 1) and 18S RNA (not shown) obtained by freeze-drying from a solution of 60 mM NH+4 acetate and 2 mM Mg++ acetate, pH 7, appear as partially unfolded coils with compact cores suggesting a high degree of ordered secondary structure.
Observation of Concanavalin-A receptors on hydrated planar erythrocyte membrane film by in situ electron microscopy
Authors: He Neng-Bo , Hui S.W.
Published: June 2020

Monolayers and planar "black" lipid membranes have been widely used as models for studying the structure and properties of biological membranes. Because of the lack of a suitable method to prepare these membranes for electron microscopic observation, their ultrastructure is so far not well understood. A method of forming molecular bilayers over the holes of fine mesh grids was developed by Hui et al. to study hydrated and unsupported lipid bilayers by electron diffraction, and to image phase separated domains by diffraction contrast. We now adapted the method of Pattus et al. of spreading biological membranes vesicles on the air-water interfaces to reconstitute biological membranes into unsupported planar films for electron microscopic study. hemoglobin-free human erythrocyte membrane stroma was prepared by hemolysis. The membranes were spreaded at 20°C on balanced salt solution in a Langmuir trough until a surface pressure of 20 dyne/cm was reached. The surface film was repeatedly washed by passing to adjacent troughs over shallow partitions (fig. 1).
Identification of fluorescent analogs with antibodies specific for the fluorophore
Authors: Luby-Phelps K. , Amato P.A. , Taylor D.L.
Published: June 2020

In this study, we investigate the utility of antibodies against fluorescein as a general probe for light and electron microscopic investigations of fluoresceinated molecules. A similar rationale has recently been applied in the construction of an f-actin affinity column using acetamidofluorescein-labeled actin bound to anti-fluorescein IgG immobilized on Sepharose 4B (5,1). Possible applications of our method include electron microscopic visualization of steady state subunit exchange in mixtures of labeled and unlabeled f-actin, determination of the ultrastructural destination of fluorescent analogs injected into living cells,and controlling for damage to cellular structures during fluorescence photobleaching.

Late hyperimmune antisera are obtained from rabbits immunized with fluoresceinated bovine serum albumin (FTC-BSA). IgG is prepared by ammonium sulfate fractionation and ion exchange chromatography of DE52 (Whatman). Fab fragments are generated from IgG by digestion with papain followed by chromatography on CM32(Whatman).
Inexpensive modification of Balzers freeze-etch units for production of high resolution specimens
Authors: Steere Russell L. , Smucker Richard A. , Erbe Eric F.
Published: June 2020

Many of the early model Balzers freeze etch units are currently unused because of the unreliability of the described procedure for use of their resistance evaporators and the cost of replacement electron guns and quartz crystal monitors. The availability of a Bendix Balzers BA-510 system at no cost to us prompted our effort to modify it inexpensively and revise the operating procedure to permit perparation of high resolution replicas.

Modifications consisted of: 1) the construction of a 6 mm outside diameter brass tube 2 cm in length with a 3 mm inside diameter. The tube was split down its length so that when it was clamped into the Balzers resistance evaporator for Pt deposition a 3 mm graphite rod insert would be held in place; 2) the end of a 3 mm graphite rod was sharpened, flattened to a diameter of 1 mm and forced by the internal spring tension against the flat end of the other graphite rod (a sharpened 6 mm rod with its end flattened to 3 m m diameter.
Freeze etch of microencapsulated drugs
Authors: Rigsby W.E. , Suzuki K. , Humphreys W.J.
Published: June 2020

Microcapsules are discrete drug-containing particles formed by dispersing drug crystals or molecules in a biodegradable polymeric matrix. Such microcapsules have been designed to be administered via injection. The advantages offered by this form of drug administration would be particularly valuable in the outpatient treatment of chronic schizophrenics who cannot be relied upon to give themselves proper dosages.

In this study a model, long-acting neuroleptic was prepared by dispersing chloropromazine (CPZ) in a biodegradable polymer, poly (d, 1-lactide). Poly (d, 1-lactide) undergoes slow hydrolytic deesterification to lactic acid which is then metabolized to C02 and eliminated, thus avoiding the necessity of surgical removal of spent microcapsules. Four batches of microcapsules, differing in percentage CPZ to total capsule weight, were prepared and tested for drug release rate in an in vitro dissolution study (Fig. 1). Samples from each batch were mounted, coated and examined in a Cambridge Mark 2A SEM (Figs. 2, 3). Particle sizes ranged from 88um to 105um and were calculated from the micrographs.
Relaxation of soft-bodied aquatic and marine invertebrates for scanning electron microscopy
Authors: Rivera E. R.
Published: June 2020

Many soft bodied invertebrates contract or retract into shells upon touch stimulation. Since preparation of specimens for SEM observation requires considerable handling as well as exposure to irritating chemicals, the resulting contractions conceal many surface features that are usually seen under normal conditions. To overcome contraction during fixations (1) or surgery (2), several species of snails have been anesthetized with varying degrees of success. Several anesthetics were tested for their efficacy in relaxing soft animals for fixations and subsequent preparations for SEM observations.

From an extensive list of relaxant drugs, six anesthetics were derived for final testing based on their initial ability to anesthetize four species of contractile invertebrates in an extended condition. The following mixtures of nembutal (sodium barbital), menthol crystals, and curare (dissolved in 80% ethanol) were used: 1) nembutal, 2) menthol, 3)curare, 4)nembutal followed by menthol, 5) nembutal followed by curare, and 6) menthol followed by curare. All animals tested feed and move under fully submerged conditions.
Karnovsky/osmium as a primary fixative for electron microscopy
Authors: Buchanan Glenn M.
Published: June 2020

In general, most researchers who use electron microscopy as a research tool use sequential giutaraldehyde-osmium tetroxide as the preferred method for fixing cells or tissues. There are certain problems inherent with this technique. Glutaraldehycle serves to cross-link proteins and increase cell membrane permeability, thus making the vehicle vitally important. But the membrane mobility following the aldehyde fixation is perhaps involved in the artifactual formation of membrane blisters and seriously affects interpretation of membrane structure. Osmium was believed originally to be involved primarily with fixation of the lipid moiety. Recent evaluation of its chemistry reveals much more: it fixes and stains via the mechanism of hydrogen bonding with proteins, nucleic acids, and "the aliphatic side chains of some cellular lipids." To overcome the drawbacks of using sequential fixation, it was suggested that combined primary fixation, using glutaraldehyde/osmium, would incorporate the advantages of each. "Shrinkage effects and chromatin clumping produced by glutaraldehyde are presumably antagonized by osmium." Positive results were obtained by using this procedure in the fixation of human lymphocytes, monocytes, and neutrophils.
Structural analysis of crystalline Ca++transport ATPase vesicles
Authors: Loren Buhle E. , Knox Barry E. , Aebi Ueli
Published: June 2020

In our efforts to study the three-dimensional structure and molecular organization of ion-motive ATPases by electron microscopy and image processing we have systematically investigated conditions which induce the formation of ordered arrays of these integral membrane proteins. Among them we have explored the effect(s) of vanadate and other multi-valent ions on ATPase crystal formation by starting from published procedures [e.g. 1,2]. Here we present some preliminary results concerned with the packing and molecular organization of vanadate-induced crystalline arrays of a Ca++transport ATPase in tubular rabbit sarcoplasmic reticulum vesicles.

The Ca++activated ATPase from rabbit sarcoplasmic reticulum was purified as published. Induction of ordered tubular arrays of the protein with vanadate was basically achieved as described, except that the protein was slowly dialysed against a vanadate-containing buffer rather than directly adding the vanadate to the protein. Optimal yields of crystalline arrays were obtained after two days of dialysis at 4°C.
Stereo HVEM autoradiography of mouse taste buds
Authors: Delay R. J. , Kinnamon J. C. , Roper S. D.
Published: June 2020

The taste bud (TB) is a dynamic system in which cells are continually turning over. Although TBs have been studied for over a hundred years, disagreement still remains concerning the types of cells found in TBs and their life cycles. According to Murray, four types of cells are found in taste buds: Light cell, dark cells, gustatory cells and basal cells. While there is evidence that dark and light cells arise separately de novo from basal cells (Miller and Chaudry; Farbman Beidler and Smallman suggested that cells within the taste bud undergo considerable changes with time. We have initiated a series of experiments utilizing the technique of high voltage electron microscopy (HVEM) autoradiography to answer the following questions: 1. Where do new taste cells enter the taste bud? 2. Are dark and light cells different cell types or just various stages in the life cycle of one cell type?
Carbon tetrachloride induced surface changes in isolated rat hepatocytes
Authors: Barnard S.D. , Caldwell W.J. , Thompson D.J.
Published: June 2020

The administration of CCl4to laboratory animals produces liver toxicity detectable by both morphological and biochemical methods. Hepatocellular metabolic cleavage of CCl4creates free radicals which damage biological membranes through the process of lipid peroxidation; this process produces measurable products of peroxidative decomposition one of which is malondialdehyde (MDA). Many studies of CCl4-induced toxicity appropriately have focused on the smooth endoplasmic reticulum (SER) where the enzymatic cleavage of CCl4occurs. Reports that CCl4is also metabolized to free radicals in the plasma membrane (PM)1and that in vitro exposure to CCl4causes PM blebing and loss of microvilli2indicate a need for further study of this cellular component.

A male Sprague-Dawley rat was treated daily, i.p., with 80 mg/kg of phenobarbital in order to induce SER-associated enzymes and thereby enhance the subsequent in vitro response of the cells to CCl4. After 5 days the rat was anesthetized with pentobarbital, and the liver was perfused with collagenase solution.
The topochemistry of black spruce sulphonation: A TEM/EDXA study
Authors: Beatson R.P. , Gancet C. , Heitner C.
Published: June 2020

Pulps produced by mechanical defibration of sulphite treated black spruce wood chips contain large amounts of lignin. The degree of sulphonation of this lignin has a significant influence on the physical properties of handsheets made from the resulting pulps In earlier work we have described the factors affecting the sulphonation of black spruce.The aim of the present investigation was to determine the differences in reactivity of sulphite towards lignin in the middle lamella and cell wall of black spruce.

Black spruce wood chips were well impregnated with sodium base sulphite solutions having pH 7, and then heated at 140° and 80°C for known times. The resulting sulphonated wood chips were cut into small sticks and embedded in Vestopal. Transverse sections, 150 nm thick, were placed on a carbon grid having a single 1 mm hole bearing a collodian film which had been carbon coated. Sulphur contents in the middle lamella and cell wall were determined with a Philips 400 TEM coupled with an EDAX 9100/60 analyser. The concentration of sulphur was taken to be proportional to the x-ray counts in the sulphur Kα window after background subtraction, as shown in Figure 1.
The development of capillaries in the rat heart
Authors: Porter Glyn A.
Published: June 2020

In the adult rat, studies by others have shown that capillaries of the heart are lined by a continuous endothelial layer. Some other important mural features are : a distinct and continuous lamina densa of the basal lamina, uniformly thick lateral processes of endothelial cells, adhesive and discontinuously occluding junctions between apposing cells. In addition, coated vesicles and pits are rarely seen, while a high proportion of the endothelial luminal and abluminal surfaces, as well as the cytoplasm, is occupied by plasmalemmal vesicles. These vesicles are more frequently found in the lateral processes than in the perikaryon (Fig. 3). It was my purpose in the present study to examine those morphological features of developing heart capillaries known to be important in capillary function in the adult. The hearts of 16, 19 and 21 day fetal and of 1 and 2 day neonatal Sprague- Dawley rats were removed, diced and fixed by immersion in a dilute Karnovsky fixative and processed routinely for TEM. Several fetal hearts (16 and 19 day) were removed and processed similarly 60 seconds after carbon (Pelikan Ink) had been injected into the umbilical vein.
Glycogen in guinea pig neutrophils: Ultrastructural study of neutrophils at the intradermal site of BCG injection
Authors: Bucana Corazon D.
Published: June 2020

In the circulating blood of man and guinea pigs, glycogen occurs primarily in polymorphonuclear neutrophils and platelets. The amount of glycogen in neutrophils increases with time after the cells leave the bone marrow, and the distribution of glycogen in neutrophils changes from an apparently random distribution to large clumps when these cells move out of the circulation to the site of inflammation in the peritoneal cavity. The objective of this study was to further investigate changes in glycogen content and distribution in neutrophils. I chose an intradermal site because it allows study of neutrophils at various stages of extravasation.

Initially, osmium ferrocyanide and osmium ferricyanide were used to fix glycogen in the neutrophils for ultrastructural studies. My findings confirmed previous reports that showed that glycogen is well preserved by both these fixatives and that osmium ferricyanide protects glycogen from solubilization by uranyl acetate.I found that osmium ferrocyanide similarly protected glycogen. My studies showed, however, that the electron density of mitochondria and other cytoplasmic organelles was lower in samples fixed with osmium ferrocyanide than in samples fixed with osmium ferricyanide.
Structural analysis of the surface-layer protein of spirillum serpens by high-resolution electron microscopy
Authors: Wu W. H. , Glaeser R. M.
Published: June 2020

Spirillum serpens possesses a surface layer protein which exhibits a regular hexagonal packing of the morphological subunits. A morphological model of the structure of the protein has been proposed at a resolution of about 25 Å, in which the morphological unit might be described as having the appearance of a flared-out, hollow cylinder with six ÅspokesÅ at the flared end. In order to understand the detailed association of the macromolecules, it is necessary to do a high resolution structural analysis. Large, single layered arrays of the surface layer protein have been obtained for this purpose by means of extensive heating in high CaCl2, a procedure derived from that of Buckmire and Murray. Low dose, low temperature electron microscopy has been applied to the large arrays.

As a first step, the samples were negatively stained with neutralized phosphotungstic acid, and the specimens were imaged at 40,000 magnification by use of a high resolution cold stage on a JE0L 100B. Low dose images were recorded with exposures of 7-9 electrons/Å2. The micrographs obtained (Fig. 1) were examined by use of optical diffraction (Fig. 2) to tell what areas were especially well ordered.
Modeling connexon skewing in gap junction lattices
Authors: Baker Timothy S. , Caspar D.L.D.
Published: June 2020

Micrographs of negatively stained gap junction lattices recorded by low irradiation methods show skewed, hexameric connexons. Differences in appearance among reconstructed images illustrate variation in staining of the connexon channel and the space between connexons. Consistently observed stain concentration at six symmetrically related sites ∽3.4nm from the connexon center, 8° to the right or left of the [1,1] lattice vector outlines the skewed connexons. Fig. 1 shows that the connexon can be represented at the 2.5nm resolution of the data by a simple model with four distinct domains: 1) a circular stain excluding subunit of 1.1nm radius located ∽2.2nm from the six-fold axis at an angle of 8° to the [1,0] lattice vector; 2) a stain accessible core ∽2nm in diameter; 3) a preferential staining region centered at ∽3.4nm between the stain excluding lobes of the connexon model; 4) a variable stain excluding region on the three-fold axis. Adjustment of the weight of the stain features in this model with only small changes in dimensions can account for a wide range of image appearance. The R-factor comparing the Fourier transform of the connexon image averaged from 21 micrographs (Fig. 1a) with that of a single specimen showing a densely stained center is 33%; the models fitted to these images correspond with R-factors of about 10%.
The role of multivariate image analysis in solving the architecture of the limulus hemocyanin molecule
Authors: Frank Joachim
Published: June 2020

The detailed distribution of stain grains in contact with the stain-excluding portions of a protein molecule is random: inspection of a single image of a macromolecule reveals little below the resolution level of gross morphology (Fig 1). However, new insights can be gained by analyzing a large set of molecule images resulting from the same experiment.

Firstly, the noise reduction due to averaging allows higher-resolution detail to be retrieved. Secondly, the analysis of such a set reveals new information that is qualitatively different from information contained in a single molecule image: the patterns of variation in local stain distribution. The stain variation at any point, and the way in which stain variations at different points of the structure are correlated, reflect certain constraints that have to do with the local binding characteristics of the molecule (e.g. accessibility of charged sites) and with its detailed topography. In the past, few observations were made relating to these phenomena because they are very difficult to quantify.
Microtubule nucleation sequence studied by time-resolved x-ray scattering and electron microscopy
Authors: Mandelkow Eva-Maria , Mandelkow Eckhard , Bordas Joan
Published: June 2020

When a solution of microtubule protein is changed from non-polymerising to polymerising conditions (e.g. by temperature jump or mixing with GTP) there is a series of structural transitions preceding microtubule growth. These have been detected by time-resolved X-ray scattering using synchrotron radiation, and they may be classified into pre-nucleation and nucleation events. X-ray patterns are good indicators for the average behavior of the particles in solution, but they are difficult to interpret unless additional information on their structure is available. We therefore studied the assembly process by electron microscopy under conditions approaching those of the X-ray experiment. There are two difficulties in the EM approach: One is that the particles important for assembly are usually small and not very regular and therefore tend to be overlooked. Secondly EM specimens require low concentrations which favor disassembly of the particles one wants to observe since there is a dynamic equilibrium between polymers and subunits.
Ultrastructure of adrenal reticularis and Sertoli cells in sterile male mice
Authors: White Yvonne , Hoage Terrell , Turner Jack , Bishop Jack
Published: June 2020

Heterozygous translocations have been established as a cause of male infertility in mice. Previous studies did not establish a relationship between translocations and hormonal control of fertility in males. We examined the adrenal-zona-reticularis-cell/Sertoli cell hormonal axis in sterile male mice that had chromosomal translocations induced by triethylenemel amine (TEM). Out of 397 male offspring of TEM treated CD1 males and F1 (C57BL/6J x BALB/c) females 26 were found to be infertile and confirmed as translocation carriers by cytogenetic analysis of testicular tissue acquired by unilateral orchiectomy at 11 - 13 months of age. Radioimmunoassay of blood serum testosterone collected between 14 and 18 months of age showed the sterile males to vary from 0.96 ± 0.41 to 10.55 ± 1.65 ng/ml compared to 3.17 ± 0.55 ng/ml in fertile controls.

Adrenal and testicular tissues were collected from ether-anesthetized animals at 18 months of age. Two or three animals were selected to represent each group: non-translocation controls, and translocation groups with high serum testosterone (HT), medial serum testosterone (MT) and low serum testosterone (LT).
The internal morphology of surface zones from acid-etched caries-like lesions of enamel: An SEM study
Authors: John Hicks M. , Silverstone L.M.
Published: June 2020

The typical carious lesion of enamel is composed of four distinct histologic zones: 1) the surface zone (SZ), 2) body of the lesion (BL), 3) the dark zone and 4) the translucent zone. This study concerned only the SZ, the most superficial zone of enamel caries. Both the SZ and BL may be viewed when a carious lesion is imbibed in water and examined in polarized light (PL). The SZ has a pore volume of less than 5%; whereas the BL has a pore volume of at least 5%, representing the area of the lesion with the greatest mineral loss. Previous SEM studies have shown few differences between the morphologic characteristics of SZs and sound enamel. Remineralization of enamel caries is possible in vitro, but requires repeated, long exposures to calcifying fluids due to the intact SZ. If the intact SZ could be made slightly porous while maintaining its integrity, remineralization of the underlying BL could be facilitated.
Examination of a liver cell line tumorigenically transformed by DL-ethionine
Authors: Junker J.L. , Wilson M.J. , Munoz E.F. , Heine U.I.
Published: June 2020

A nontumorigenic cell line derived from rat hepatocytes became tumorigenic subsequent to its cultivation for 3 months in medium containing 7.5 mM DL ethionine. We used light and electron microscopy in order to observe the structural effects of this treatment. At confluence, both experimental and control cultures appeared as monolayers of contiguous polygonal cells. Subconfluent cultures of ethionine-treated cells had a minor population of elongated cells, with extended cytoplasmic processes, which were not seen in control cultures. Actin cables (visualized with a NBD-phallacidin probe), which were routinely visible in polygonal cells, were not as pronounced in elongated cells (Fig. 1). Likewise, the arrangement of microtubules (stained with FITC-antitubulin) was characteristically altered from a mainly circumferential distribution at the periphery of the cytoplasm in polygonal cells to longitudinal arrays in elongated cells.

Examination by transmission electron microscopy of confluent cell cultures revealed a marked decrease in the length of desmosomal contacts between ethionine-treated cells accompanied by an increase in extracellular fibrillar material (Fig. 2).
Altered thymic epithelial cells may be decisive for Moloney virus-induced lymphoma development
Authors: Heine U.I. , Krueger G.R.F. , Munoz E. , Karpinski A.
Published: June 2020

Infection of newborn mice with Moloney leukemia virus (M-MuLV) causes a T-cell differentiation block in the thymic cortex accompanied by proliferation and accumulation of prethymic lymphoblasts in the thymus and subsequent spreading of these cells to generate systemic lymphoma. Current evidence shows that thymic reticular epithelial cells (REC) provide a microenvironment necessary for the maturation of prethymic lymphoblasts to mature T-lymphocytes by secretion of various thymic factors. A change in that environment due to infection of REC by virus could be decisive for the failure of lymphoblasts to mature and thus contribute to lymphoma development.

We have studied the morphology and distribution of the major thymic cell populations at different stages of tumorigenesis in Balb/c mice infected when newborn with 0.2ml M-MuLV suspension, 6.8 log FFU/ml. Thymic tissue taken at 1-2 weekly intervals up to tumor development was processed for light and electron microscopy, using glutaraldehyde-OsO4fixation and Epon-Araldite embedding.
The effect of hypertension on the internal elastic lamina of rat portal vein
Authors: Sweitzer Kirby L.
Published: June 2020

Previous studies of systemic and portal hypertension have reported an increase in the elastic tissue component. However, there is no mention of conformational alterations in the elastic network beyond reduplication of the internal elastic lamina in rabbit inferior vena cava. This experiment was designed to study the configurational alterations in the internal elastic lamina (IEL) of hypertensive hepatic portal vein of the rat.

Twenty-one male Sprague-Dawley rats, approximately the same age and weight, were divided into three groups. Group A consisted of five normal controls which had not undergone surgery. Group B consisted of seven sham control rats which had a laparotomy, but the portal vein was not ligated. Group C consisted of nine experimental rats which had the portal vein partially ligated to create a stenosis. The portal vein was removed eight weeks after laparotomy. The elastic network was then exposed by removal of the nonelastic components by sonication in 0.5N sodium hydroxide and autoclaving. The tissue was fixed in Karnovsky's fluid with a phosphate buffer and routinely prepared for SEM observation.
A comparison of two indirect immune electron microscopy procedures using monoclonal antibody to localize specific African swine fever virus (ASFV) proteins in infected cells and virus
Authors: Letchworth III G. J. , Whyard T. C. , Wool S. H.
Published: June 2020

The primary purpose of this study was to devise a procedure in which a large number of monoclonal antibodies could be tested against several African swine fever virus (ASFV) preparations (virus, infected cells). The procedure had to be rapid, use a small sample and provide for some TEM.

Monoclonal antibodies were produced by standard methods using myeloma cells and lymphocytes from mice immunized against ASF viral proteins. Antibodies were characterized by immunoprecipitation of radio-labelled viral proteins (Fig 1).

The viral preparations used in this study were either infected macrophages, culture fluid supernatant from ASFV-infected macrophages or red blood cells from infected pigs. Each of the three viral preparations was tested by two indirect immune electron microscopy (IEM) methods; a grid method and a test tube method. In the grid method, formvar coated grids were floated on a viral preparation then for one hour each on the mouse monoclonal antibody and finally on ferritin tagged sheep anti-mouse IgG with washes between each step.
Structural and morphometric studies of liver in a ferret model of Reye's syndrome
Authors: Gray R. H. , Deshmukh D. R. , Maassab H. F. , Robertson D. G. , de la Iglesia F. A.
Published: June 2020

The etiology of Reye's Syndrome (RS) in children is unknown and the syndrome is preceeded by a viral infection. In addition, environmental agents, such as pesticides have been implicated as etiological factors for RS and recent epidemiological studies suggested that aspirin may predispose towards RS. In a recently developed animal model for RS, the subcellular liver changes of ferrets infected with influenza B virus, treated with aspirin and fed an arginine deficient (AD) diet have been studied.

Eight week old, male, sable-coated ferrets were used in the study. All animals were fed Purina Cat Chow until the fasting period. Experimental animals were infected intranasally with influenza B on day 1 as previously described, and on the evening of the first day, aspirin (50mg/kg) dosing was started and continued twice daily for 3 days. Control and experimental groups were fasted overnight, and on the fourth day at 9:00 AM, the controls were given Purina Cat Chow while the experimental group was given the AD diet.
Alcaligenes fecalis infected tracheal epithelium: An ultrastructural study
Authors: Renee Finer Kim
Published: June 2020

Alcaligenes fecalis is a gram negative bacterium previously thought to be nonpathogenic for humans and animals. The organism is commonly isolated in the gastrointestinal tract. In 1978 it was proven that A. fecalis was the etiologic agent of turkey coryza, an upper respiratory disease of young poults.The infectivity of A. fecalis in the upper respiratory tract suggests that the bacterium has altered its tissue tropism and developed a mechanism of adherence enabling colonization of the tracheal epithelium in spite of the muco-ciliary clearing mechanisms of the trachea. The purpose of this work was to examine the adherence of A. fecalis to the tracheal epithelium and to characterize the host cell response to infection.

One day old poults were infected intranasally with either 108 colony forming units of A. fecalis, Wampler, or, as a control, 0.5 ml of sterile brain heart infusion broth. For TEM, the cranial portion of the trachea was cut into 2 mm2 sections, fixed in 2.5% glutaraldehyde, post-fixed in 1% OsO4, dehydrated in ethanol, and embedded in Epon-Araldite. Thin sections were stained with uranyl acetate and Sato's lead. For SEM, tracheal sections were fixed in glutaraldehyde, dehydrated in ethanol, critical point dried, and coated with 250 Å of gold-palladium.
Electron microscopic studies of fiber degradation by rumen fungi
Authors: Akin Danny E.
Published: June 2020

The rumen microbial population is a complex ecosystem. Bacteria, protozoa, and fungi all play a part in degrading plant cell walls, which are a major substrate for energy and protein for the host animal. Rumen bacteria are considered to be the major degraders of forage fiber, but recent research has shown that rumen fungi are ubiquitous and are able to attack plant cell walls. Electron microscopy has been important in delineating the roles played by the various microbial types, including the fungi. The object of the present research was to assess the role of rumen fungi as degraders of particular tissues and to demonstrate that the presence of rumen fungi in the rumen can explain many of the unusual morphotypes associated with degradation of the more resistant tissues in forages.

Rumen fungi were evaluated by inoculating tubes containing leaf blade sections of Cynodon dactyl on in a semi-synthetic, anaerobic medium with rumen fluid and incubating the tubes for 48 hours at 39°C. Some of the tubes contained streptomycin (2 mg/ml) and penicillin (2 x 10 units/ml) to inhibit bacteria.
Diffraction, Imaging and the Microscopic World of Materials
Authors: Thomas G. , Clarke D. R. , Gronsky R.
Published: June 2020

Brief History - Probably no other technique has had quite the dramatic impact upon materials science and engineering as has the combination of electron diffraction and microscopy. The development of the modern electron microscope is an unusual outcome of wide and diverse series of experimental discoveries and theoretical concepts amongst which certainly the elegant Nobel Prize winning (1937) diffraction experiments of Davisson and Germer and Thomson ranks as one of the most significant.

Although the first electron microscope was developed in Berlin, a North American instrument was built in 1939 at the University of Toronto. Soon after in 1941, RCA produced the first commercial microscopes in the USA. At first, the principal technique of sample preparation was replication, until Heidenreich at Bell Labs, maintaining the electron diffraction tradition set by Davisson, and later, Heidenreich and Sturkey, paved the way for modern thin foil microscopy with their dynamical electron diffraction theory. This accounted for the interference effects observed in images of crystals.
Crystal Structure Determination of Glycerol-Containing Lipids from Electron Diffraction Data. Use of Analog Compounds Based upon Configurational Isomers of Cyclopentane-1, 2, 3-TRIOL
Authors: Dorset Douglas L. , Hancock Anthony J.
Published: June 2020

Lipids containing long polymethylene chains were among the first compounds subjected to electron diffraction structure analysis. It was only recently realized, however, that various distortions of thin lipid microcrystal plates, e.g. bends, polar group and methyl end plane disorders, etc. (1-3), restrict coherent scattering to the methylene subcell alone, particularly if undistorted molecular layers have well-defined end planes. Thus,ab initiocrystal structure determination on a given single uncharacterized natural lipid using electron diffraction data can only hope to identify the subcell packing and the chain axis orientation with respect to the crystal surface. In lipids based on glycerol, for example, conformations of long chains and polar groups about the C-C bonds of this moiety still would remain unknown.

One possible means of surmounting this difficulty is to investigate structural analogs of the material of interest in conjunction with the natural compound itself. Suitable analogs to the glycerol lipids are compounds based on the three configurational isomers of cyclopentane-1,2,3-triol shown in Fig. 1, in which three rotameric forms of the natural glycerol derivatives are fixed by the ring structure (4-7).
Microstructure of 316 Stainless Steel Cladding from a Fuel Pin Irradiated in EBR-II
Authors: Berting F. M.
Published: June 2020

Swelling of the stainless steel cladding which contains the fuel in nuclear reactors is a well-known phenomenon. Efforts to minimize the swelling and prolong the life of the fuel pins depends on understanding the mechanisms by which swelling occurs. Study of the microstructural damage caused by neutron irradiation of the 316 stainless steel currently used in cladding is an important part of the investigation of the swelling mechanisms. Most of the microstructural investigations of swelling phenomena to date have been performed on material irradiated in isothermal capsules that eliminate contact between the samples and the fuel.

This report is concerned with the steel actually used to contain the fuel pellets for a normal lifetime in-reactor. The pin cladding experienced the full range of temperatures and fluences characteristic of the 13.5" long reactor core. The conditions of irradiation for the fuel pin studied are shown in Figure 1(a), where temperature rises steadily from bottom to top of the pin and fluence reaches a peak at about core center.
Image Contrast of Dislocation Loops Near a Free Surface
Authors: Ohr S. M.
Published: June 2020

The image contrast of dislocation loops computed in the past has made use of the displacement fields which do not take into account the presence of stress- free foil surfaces. The free surface modifies the elastic fields around a dislocation loop and hence can influence the image contrast observed in the electron microscope. The effect can be significant particularly when the loops lie close to one of the foil surfaces. In general, the elasticity problem of dislocation loops that takes the free surface into account is difficult to handle mathematically. In the present paper, the method of Bastecka1 was extended to obtain explicitly the analytical expressions for the displacement fields around a pure edge circular dislocation loop lying parallel to the foil surface. In this method, the stress fields of an image dislocation loop and another axially symmetric stress system were added in order to eliminate the normal as well as shear stresses at the surface.