Morphology of nylon 6 spherulites in bulk

A method of obtaining good quality ultrathin sections from nylon 6 bulk samples has been developed by using a special embedding technique and cryo-ultramicrotomy. The morphologies of nylon 6 processed by compression and injection molding and of reaction injection molded nylon 6 were studied in ultrathin sections of bulk samples by means of transmission electron microscopy. It was established that the spherulites of nylon 6 in bulk are built up from long flat ribbonlike lamellae. The thickness of the lamellae is in the range 50–60 Å. The width varies from 150 to 600 Å and depends on the type of nylon 6 and the method of processing. The length of the lamellae is relatively large approaching spherulite radii, extending often from the point of their origin up to the spherulite borders. Three or four neighboring lamellae within spherulites usually show similar orientation of their flat faces and form domains which can easily be mistaken for fibrils in light microscopy or low resolution electron microscopy.     

Fixation of cells in tissue culture by microwave irradiation

Summary A novel method employing in situ microwave fixation for cells cultured in monolayer is described. This method, which avoids the cell loss associated with chemical fixation, is useful for cells intended for immunofluorescence studies, for prefixation of cells for electron microscopy, and for other situations requiring cell fixation.     

Disseminated histoplasmosis in a badger (Meles meles) in Denmark.

We report the first case of disseminated histoplasmosis in an animal in Scandinavia. Yeast cells compatible with those of Histoplasma capsulatum var. capsulatum were found in the skin, liver, spleen, a kidney, and a lymph node of a wild badger (Meles meles). The diagnosis was confirmed by electron microscopy and immunofluorescence staining of the yeast cells in tissue sections.     

A Monte Carlo track structure code for electrons (approximately 10 eV-10 keV) and protons (approximately 0.3-10 MeV) in water: partitioning of energy and collision events

An event-by-event Monte Carlo simulation code for track structure studies is described. In the present form the code transports protons (approximately 0.3-10 MeV) and electrons (approximately 10 eV-10 keV) in a water medium in the gas phase approximation. For the type of particles and energy range considered, ionization, electronic excitation and electron elastic scattering are the most important collision events accounted for in the transport simulation. Efforts were made to ensure that the analytic representation of the various interaction cross sections rests on well established experimental data and theory. For example, the secondary-electron spectrum as well as partial and total ionization cross sections are represented by a semitheoretical formulation combining Bethe's asymptotic expansion and binary-encounter theory. Binding effects for five levels of ionization and eight levels of electronic excitation of the water molecule are explicitly considered. The validity of the model cross sections is examined against available experimental data and theoretical predictions from other similar studies. Results pertaining to the partitioning of energy loss and interaction events for the first-collision probability and nanometre-size track segments are presented.     

Ultracytochemical charactrization of non-specific acid phosphatase activities in Saccharomyces cerevisiae

Glutaraldehyde prefixation causes a considerable inactivation of the acid phosphatase of yeast protoplasts in dependence on the duration of aldehyde influence. Lead ions necessary for ultracytochemical demonstration effect a still stronger inhibition of enzymatic activity. Prefixation, however, protects the enzyme from further inhibition by lead. At pH 4.4 in intact cells acid phosphatase activities are mainly localized in the periplasmic space and in vesicles fused with the plasma membrane. The cell wall and cytoplasm usually remain free of reaction products. On the cell surface activities are found in form of globular lead deposits. At pH 5.2 and 6.3 the periplasmic activity appears decreased compared to that at lower pH values and the intracellular activity is increased. The plasma membrane of protoplasts is completely free of precipitates. The intracellular activity sites of protoplasts (cisternae of endoplasmic reticulum and/or Golgi-like system, small vesicles, central vacuole, nuclear envelope) are the same as for intact cells. The occurrence of at least two forms of acid phosphatase in S. cerevisiae is deduced.     

Electron microscopic autoradiography on semithin sections (author's transl)]

The present study applies semithin sections for electron microscopic autoradiography. Due to (a) the decrease of exposition time, and (b) lower intensity of isotope labelling, low power electron microscopic autoradiography on semithin sections is favoured in comparison with conventional (ultrathin section high power) electron microscopic autoradiography, and due to (c) more precise localization of silver granules, and (d) ease of quantitative evaluation of autoradiography, it is superior to ordinary (thick section) light microscopic autoradiography.     

A scanning electron microscope study of the interstitial tissue of the canine testis

Scanning electron microscopy (SEM) is a potent tool that is especially valuable in interpreting the three-dimensional relationships of cells within tissues. This type of information is obtainable from thin sections in transmission electron microscopy (TEM) only by reconstructions of serial sections. The arrangement of the interstitial cells of the testis in relation to the capillaries and lymphatic channels, in particular, is easier to visualize in SEM than in TEM. Cytoplasmic constituents, as well as cell surface modifications, are demonstrable by this technique. The presence of droplets, presumably lipid droplets, both within and on the Leydig cells and the lymphatic endothelial cells, is quite evident. Other cytoplasmic structures are also apparent. For example, the possible functional significance of “openings” that are seen by SEM on the septa that surround lipid droplets is discussed relative to the appearance of the same area as seen in thin sections or in freeze-fracture replicas. SEM should become a very useful method for studying cytological and morphological alterations that occur in testicular tissue that is subjected to physical or chemical manipulation.     

Gap junctions on GABAergic neurons containing the calcium-binding protein parvalbumin in the rat hippocampus (CA1 region)

Summary Gap junctions were identified for the first time on chemically defined neurons in the central nervous system. Gap junctions were thus demonstrated on GABAergic neurons containing the calcium-binding protein parvalbumin (PV) in the rat hippocampus. Thin and semithin (0.5 m thick) sections were cut alternately and consecutively from osmium-fixed tissue which was embedded in epoxy resin and usable for conventional electron microscopic studies. The semithin sections were processed for postembedding immunocytochemistry using an anti-PV serum. Structures corresponding to the PV-immunoreactive (PV-I) profiles on the semithin sections were easily identified on electron micrographs from the adjacent thin sections. Using this technique gap junctions were found (1) between PV-I dendrites, (2) between PV-I dendrites and PV-I somata and (3) between PV-I dendrites and small processes whose origin could not be identified. Despite a systematic search, we did not find gap junction between PV-negative processes.     

Specificity of the histochemical determination of sorbitol dehydrogenase--comparative indicator and immunohistochemical studies on the rat kidney

We have investigated the distribution of sorbitol dehydrogenase by comparative indicator- and immunohistochemical technique in rat kidney. In this connection we have tested some parameters which influence the histochemical demonstration of SoDH-activity by tetrazolium salt indicator technique (e.g. prefixation of tissue sections, elution behaviour of SoDH, influence of different dialysis membranes, composition of incubating medium). According these studies, the enzyme was demonstrated in native cryostate sections by membrane incubating method. For the immunohistochemical demonstration of SoDH specific antibodies were prepared against this enzyme in rabbits, and were used for indirect immunofluorescence method and for the unlabelled antibody enzyme (PAP) technique. A good agreement of sorbitol dehydrogenase localization was obtained with all the tested methods, but also some discrepancies was observed in enzyme topic (e.g. glomeruli). The results are discussed under methodical aspects in connection with the specifity of the used methods to localize the enzyme.     

Phage-like structures (SE-particles) in cells of the unstable and stable spheroplast type L-form of Proteus mirabilis D 52

In cells of the stable and unstable spheroplast type L-form of Proteus mirabilis D 52 small ellipsoidal particles (SE-particles) could be found after investigation of ultrathin sections. The SE-particles have diameters of 220–260 and 280–320 Å. They are composed of an electron lucent centre, an internal electron deanse layer, an electron lucent line and an outer electron dense layer. There is a porus of about 25 Å in the internal electron dense layer. The SE-particles may be arranged in chains up to 10 particles. It seems that the particle formation starts near the cytoplasmic membrane at one or more sites in a cell. Comparing electron microscopic observations with data from literature it seems certain that SE-particles are bacteriophage-like structures. However, it is not clear until now, whether they are intact tail-less phages or defect phage structures.     

Indium (III)-hematoxylin as a staining and contrasting agent for light and electron microscopy

A deeply violet indium (III)-hematoxylin complex is formed when indium trichloride is added to an aqueous solution of oxidized hematoxylin. Treatment of glutaraldehyde fixed and Araldite embedded sections of rat seminiferous tubules with indium-hematoxylin revealed a definite staining and contrasting pattern. Semithin sections showed chromatin and nucleoli in violet-blue. Under the electron microscope, chromatin, nucleoli, ribosomes, synaptonemal complexes, chromatoid bodies, membranous components, and microtubules from sperm tails presented high electron opacity, while the acrosome and basement membrane appeared with a lower contrast. This performed indium-hematoxylin complex, which shows an absorption peak at lambda = 560 nm with shoulders at about lambda = 440 and 400 nm, could be valuable as a new staining and electron contrasting agent.     

Ultrastructural demonstration of serotonin-immunoreactivity in the nervous system of an insect (Calliphora erythrocephala)

Serotonin (5-HT) immunocytochemistry, was performed on the whole dissected nervous system of the blowfly. Employing the peroxidase-antiperoxidase technique and osmium postfixation, it was possible to examine 5-HT-immunoreactive neuronal elements first light microscopically in 25 microns sections, and, after re-embedding, to analyze the same sections electron microscopically in ultrathin sections. We describe the ultrastructure of 5-HT-positive terminals in the neural sheath of peripheral nerves and in the optic lobes. The immunoreactivity was observed in large (100 nm) granular vesicles, on membranes of clear vesicles, along neurotubules, and along the internal surface of the plasmalemma.     

Morphogenesis of sandfly viruses (Bunyaviridae family)

The events occurring in the morphogenesis of sandfly fever viruses have been examined by thin-section electron microscopy and by an analysis of the association of virus-specific polypeptides with membranes of infected cells. Two representative sandfly fever viruses have been studied, Karimabad virus (KV) and Punta Toro virus (PTV), which appeared indistinguishable both in terms of virion structure, as monitored by negative staining, and morphogenesis, as observed in thin sections of infected Vero cells. Ammonium molybdate negative staining of purified, glutaraldehyde-fixed virions revealed essentially spherical particles, 87 nm in diameter, in which the surface proteins were constructed into closely packed, hollow, cylindrical subunits measuring 10–11 nm in diameter and 9–10 nm in length. These surface units are located peripherally to a 7-nm membrane bilayer which surrounds a nucleoid of variable electron density. As seen in thin sections of infected cells, the assembly of these particles was first detected at 12 hr after infection, occurred exclusively at smooth membrane vesicles, and predominantly at membranes in, or adjacent to, Golgi cisternae. Morphologically mature particles were formed by continuous involution (budding) of modified membrane segments into the lumen of these vesicles. Viral ribonucleoprotein (RNP), which was not observed free in the cytoplasm, condensed at the cytoplasmic face of these vesicles at areas at which viral spike structures could be observed at the contralateral (luminal) face. Neither RNP nor spike structures could be observed on adjacent sections of the vesicular membrane, or other membranes, which were not directly involved in the assembly of a budding virion. Analysis of the viral polypeptides in unfractionated membrane vesicles prepared from infected cells demonstrated that KV-specific envelope and nucleocapsid proteins rapidly became membrane bound, whereas a nonstructural polypeptide was found only in cytoplasmic fractions. Chymotrypsin treatment of these vesicles has indicated that at least one viral glycoprotein is inserted into cellular membranes such that approximately 12% of its sequence remains at the cytoplasmic membrane face. Proteolytic removal of this sequence generated an immunoprecipitable, glycosylated fragment which was protected from further proteolysis by its orientation within the vesicle. These morphologic and biochemical data have been used to construct a model for the assembly of these viruses. Virus particles are released from infected cells by exocytosis, a process which does not appear to result in significant modification of cell surface membranes with viral antigens.     

Insight into the ultrastructural organisation of sporulated oocysts of Eimeria nieschulzi (Coccidia, Apicomplexa)

Sporulated oocysts of Eimeria contain four sporocysts with two sporozoites each and a sporocyst residuum. The developing sporozoites are protected by the sporocyst wall and the robust double-layered oocyst wall. Because of problems with conventional fixatives, high-pressure freezing, followed by freeze substitution was used to achieve optimal ultrastructural preservation of oocysts, sporocysts and sporozoites. After embedding in Epon?, ultrathin sections were examined by electron microscopy to select specific oocyst regions for further investigation by electron tomography (ET). ET allows high-resolution three-dimensional views of subcellular structures within the oocysts and sporocysts. Analysis of several 300?nm sections by ET revealed a network of small tubular structures with a diameter of 70–120?nm inside the sporocysts which is decribed here for the first time. This network connects the residual body in a sporocyst with the endoplasmic reticulum (ER) of the surrounding sporozoites. The network consists of membrane-bound tubules that contain vesicles but no larger organelles like mitochondria. These tubules, named “sporocord”, may have a function similar to an “umbilical cord” providing the sporozoites with metabolites for long-term survival. Small vesicular structures inside the ER of the sporozoites, multivesicular structures inside the residual bodies and vesicles in the tubules support this hypothesis.     

Pathology of important diseases of endocrine organs (excluding the thyroid)

Basic principles of classification of tumors of the pituitary, parathyroid glands, adrenals, paraganglionic system and endocrine pancreas and the differential diagnosis from non-endocrine tumors are presented. There are no uniform criteria of malignancy and common neuroendocrine immunohistological markers for unequivocal identification, as each organ has its own criteria. For pituitary tumors invasive growth is not a sign of malignancy, but only metastases. For tumors of the adrenal cortex a histopathological score has to be used for proving dignity. For pheochromocytomas, structural criteria (mitoses, angioinvasion) and immunostaining (S-100 protein, p53, Ki-67) are important. Endocrine tumors of the pancreas behave differently if they are angioinvasive or if they show more than two mitoses per 10 HPF, more than 2% Ki-67 positive nuclei or a size of more than 2 cm in diameter. They are malignant if gross local invasion or metastases are demonstrable. Clinical data have to be included in pathohistological reports. In many cases immunostaining in addition to structural analysis will be necessary.     

Poly(4‐hexyl‐1,2,4‐triazole‐4H): An Electron Semiconducting Analogue to Regioregular Poly(hexylthiophene)

Summary: For the development of n‐channel field‐effect transistors it is indispensable to look for semiconducting polymers with electrons as majority charge carriers (n‐type). In addition high electron mobility values are of significant advantage in these compounds. Polymers with electron transporting properties have been rarely investigated. Main chain polymers with strong acceptor units like 1,2,4‐triazoles‐4H are potential candidates for electron transporting materials in electronic devices. Therefore, a synthetic pathway leading to an organo‐soluble polymer consisting only of 4‐hexyl‐1,2,4‐triazole‐4H units in the main chain is presented in this work. We will report the synthesis using modified classical polycondensation. The chemical and electronic properties of the polytriazole have been investigated in detail. The material has been used to prepare “electron‐only” devices for the calculation of the electron mobility.

The suggested chemical structure of poly(4‐hexyl‐1,2,4‐triazole‐4H) (PHTA).     

Phase separation in poly(methyl methacrylate)-block-poly(2,3-dibromopropyl methacrylate) copolymers

AB block copolymers poly(methyl methacrylate)-block-poly(2,3-dibromopropyl methacrylate) were prepared by a two-stage process involving the sequential anionic polymerization of methyl methacrylate and allyl methacrylate followed by bromination of the pendant allylic groups. Transmission electron microscopy of thin sections of cast films revealed phase separation, the morphology depending upon composition of the block. In particulate form these copolymers gelled with methyl methacrylate to form doughs that could be moulded and heat cured to produce hard X-ray opaque copolymers.     

Differences in the width of the intercellular spaces in the epithelial basal infolding and the renal glomerular filtration site between freeze-substitution and conventional fixation

After aldehyde prefixation, pretreatment with cryoprotectant and subsequent freeze-substitution with OsO₄ in acetone (AC-FS), extensive gap junction-like close membrane appositions are frequently found in the basal infolding of the salivary gland epithelium, although the desmosomal intercellular space had the same width as with conventional electron microscopy. The intercellular space between podocyte pedicles and endothelial cells at the renal glomerular filtration site was narrower by the total width of 2 laminae lucidae following AC-FS than with conventional electron microscopy and was occupied by a homogeneous lamina densa without a lamina lucida, although no marked difference was discernable in the thickness of the lamina densa itself between the 2 preparative procedures. In addition, a decrease in the thickness of the glycocalyx was evident in the intestinal epithelial microvilli following AC-FS. It is thus likely that osmication in acetone at freezing temperatures remove the glycocalyx and related structures to a variable extent, and that this loss is responsible for reducing the intercellular spaces at some of the simple appositions narrower to the dimensions of the gap junction. It is also responsible for disappearance of the lamina lucida of the basement membrane.     

Induced cross-protection responses against Cr(III) and Fe(III) ions in Saccharomyces cerevisiae

Stress tolerance of yeast Saccharomyces cerevisiae was examined after exposure to iron and chromium, which are essential minerals in low concentrations but can be toxic if present in high concentrations. Induction of possible cross-protection responses was performed with the yeast pre-treatment at the start of cultivation with low concentrations of Fe(III) or Cr(III) ions, which slightly inhibit the growth and the subsequent exposure to sub-lethal concentrations of Fe(III) or Cr(III) ions in the mid-exponential phase. No cross-protection was found if yeasts were pre-treated with 0.1 mM Cr(III) and subsequent exposure to 2.5 mM Fe(III) ions took place. If pre-treated with 0.1 mM Fe(III) Saccharomyces cerevisiae conferred protection to subsequent challenges with a sub-lethal concentration of 2.5 mM Cr(III) ions resulting in higher biomass formation and higher relative cell viability in comparison to cells without pre-treatment. It is shown for the first time that iron pre-treatment enhanced yeast condition against chromium related stress via cross-protection mechanism.