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  • 1995-1999  (829)
  • 1980-1984  (3.198)
  • Physics  (3.228)
  • Ultrastructure
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Sexual plant reproduction 12 (1999), S. 99-109 
    ISSN: 1432-2145
    Schlagwort(e): Key words Arabidopsis thaliana ; Megasporogenesis ; Meiosis ; Ultrastructure ; Cellular polarity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  In this study, megasporogenesis of the plant model Arabidopsis thaliana was investigated by electron microscopy for the first time. The data described here could constitute a reference for future investigations of Arabidopsis mutants. During the beginning of meiosis the megaspore mother cell shows a polarity created by unequal distribution of organelles in the cytoplasm. Plastids accumulate in the chalazal region and long parallel saccules of endoplasmic reticulum, small vacuoles and some dictyosomes are found in the micropylar region. Plasmodesmata are abundant in the chalazal cell wall. The nucleus is almost centrally localized and contains a prominent excentric nucleolus and numerous typical synaptonemal complexes. After the second division of meiosis the four megaspores are separated by thin cell walls crossed by numerous plasmodesmata and do not show significant cellular organization. The young functional megaspore is characterized by a large nucleus and a large granular nucleolus. The cytoplasm is very electron dense due to the abundance of free ribosomes and contains the following randomly distributed organelles: mitochondria, a few short saccules of endoplasmic reticulum, dictyosomes and undifferentiated plastids. However, there is no apparent polarity, except for the distribution of some small vacuoles which are more abundant in the micropylar region of the cell. The degenerating megaspores are extremely electron dense and do not show any substructure.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Virchows Archiv 435 (1999), S. 13-19 
    ISSN: 1432-2307
    Schlagwort(e): Key words Inflammation of the lung ; Biopsy ; Ultrastructure ; Laser therapy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Examination of 127 biopsy specimens from 45 patients with inflammatory lung diseases showed changes consistent with increased permeability of the capillary endothelial cells as an initial stage in the development of the inflammatory reaction. Associated interstitial oedema, deformation of the interalveolar septa, and structural disorganization of alveolar epithelium cells occur, and local microcirculatory problems result in tissue hypoxia and fibrosis. The ultimate morphological picture is determined largely by the intensity of repair. Laser biostimulation minimizes the inflammation and stabilizes fibroplastic process.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Virchows Archiv 435 (1999), S. 58-61 
    ISSN: 1432-2307
    Schlagwort(e): Key words Capillary basement membrane ; Inflammatory myopathy ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  The capillary basement membranes from 16 skeletal muscle biopsies from patients with a clinical and histological diagnosis of inflammatory myopathy and from six controls were analysed ultrastructurally and morphometrically. Resin sections from 244 endomysial capillaries were examined by light microscope, and the results were correlated with findings seen in electron micrographs of these capillaries. The ultrastructural morphometric measurements and the statistical analysis showed that the capillary basement membrane was thick and multilaminated in 87% specimens affected by inflammatory myopathy. No thick or multilaminated basement membrane was observed in controls. In inflammatory myopathy the endomysial space next to the capillaries contained an increased amount of collagen fibrils and showed signs of a chronic reparative process. It is suggested that the thick multilaminated basement membrane in inflammatory myopathy represents an advanced stage of vascular regeneration.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1432-0533
    Schlagwort(e): Key words Polyglucosan body ; Periodic ; acid-Schiff-positive granules ; Mouse brain ; Immunohistochemistry ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Periodic acid-Schiff-positive granules (PGs) appear in the mouse brains in relation to advancing age. The exact location and pathophysiological significance of PGs, however, are not fully understood. The incidence, staining properties, and topographical distributions of PGs in the brains of 17 AKR mice ranging in age from 7 to 18 months were examined histochemically and immunohistochemically using antibody KM279 raised against a polyglucosan. In addition, to define the precise site of PG formation, we investigated the brains of 4 AKR mice of 24 months of age using conventional and immunoelectron microscopy. PGs were seen in all mice examined and the levels were increased with age. The PGs were located predominantly in the hippocampus and, to a lesser extent, in the cerebellum and olfactory bulb. Immunohistochemically, PGs in the hippocampus and cerebellum were labeled uniformly with KM279. On immunoelectron microscopy with this monoclonal antibody, the fibrillar or membranous structures corresponding to PGs seen using light microscopy were labeled specifically with gold particles. With conventional electron microscopy, fibrillar or membranous structures were seen along with synaptic vesicles and dense-core granules. Moreover, around the cells containing PGs, a few synaptic junctions with neighboring cells were observed, indicating that the cells contributing to formation of PGs were neuronal cells. The positive immunoreactivity of AKR mouse PGs for the antibody KM279 suggests that the PGs and similar structures in other species may share a common antigenicity. Thus, it is assumed that PGs in AKR mice might result from some abnormalities in glucose metabolism.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1432-0533
    Schlagwort(e): Key words Amyloid precursor protein ; immunoreactivity ; Axonal injury ; Microwave antigen retrieval ; Traumatic brain injury ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Antibodies to the amyloid precursor proteins (APP) have become routine markers for detecting traumatically induced axonal injury (AI) in animals and man. Unfortunately, the techniques used to visualize these proteins are not compatible with routine electron microscopic (EM) analysis. In the current communication, we describe a method for the ultrastructural visualization of antibodies to APP and, using this method, we identify a previously unrecognized population of traumatically injured axons. Rats were subjected to an impact acceleration traumatic brain injury and allowed to survive 30 min to 3 h postinjury. The animals were then perfused, their brains sectioned on a vibratome and the sections prepared for immunocytochemistry using a computer-controlled microwave capable of temperature regulation. The use of temperature-controlled microwave energy unmasked APP antigenic epitopes without sacrificing ultrastructural detail. The APP antibody was found in two distinct populations of reactive axons that differed in size, morphology, location, and temporal progression. Comparable to previous descriptions, one population showed traumatically related reactive changes that led to swelling and disconnection. The other population, however, revealed unanticipated changes reflected in nodal and paranodal swelling of small continuous fibers that showed no evidence of disconnection during the time periods assessed. These studies provide new insight into the complexity of the pathobiology of AI, while describing a novel approach for enhancing APP immunoreactivity at the EM level.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1432-0568
    Schlagwort(e): Key words Intrinsic laryngeal motoneurons ; Cholera toxin HRP ; Ultrastructure ; Swallowing ; Respiration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  The laryngeal motoneurons innervating the cricothyroid muscle (CT) are located in the semicompact formation just ventral to the rostral part of the compact formation of the nucleus ambiguus. The motoneurons innervating the posterior cricoarytenoid muscle (PCA) are located in the loose formation. We retrogradely labeled the CT and the PCA motoneurons using cholera toxin subunit B-conjugated horseradish peroxidase, and determined the ultrastructure and synaptic organization of these neurons. The CT and the PCA motoneurons had the appearance of α-motoneurons, i.e., large, oval or polygonal cells containing well-developed organelles and a prominent spherical nucleus. Two kinds of neurons were recognized among the PCA motoneurons. The one (PCA-A) was significantly smaller than the other (PCA-B). The average number of axosomatic terminals in a section was significantly largest in the PCA-B (56.6), smaller in the PCA-A (36.0), and smallest in the CT (32.3) neurons. Most of the axosomatic terminals (64.7%) contained pleomorphic vesicles and made symmetric synaptic contacts (Gray’s type II) with the PCA-A neurons, while more than 60% contained round vesicles with asymmetric synaptic contacts (Gray’s type I) in the CT (69.5%) and the PCA-B (60.6%) neurons. A few terminals associated with subsurface cisterns were present on all laryngeal motoneurons. These results indicated that the CT motoneurons may receive mostly excitatory terminals, whereas the PCA muscle may be regulated by neurons having many inhibitory terminals, and neurons having many excitatory terminals.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1432-0533
    Schlagwort(e): Key words Amyotrophic lateral sclerosis ; Bunina body ; Guam ; Immunohistochemistry ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract An investigation of Bunina bodies is important when studying the pathoetiology and pathomechanisms involved in amyotrophic lateral sclerosis (ALS). It may serve as a clue essential for the study of the pathogenesis of Guamanian amyotrophic lateral sclerosis (ALS-G), and it may provide a means of answering the question of whether ALS-G is the same disease as classical ALS or a different entity. In ALS-G, however, no precise histochemical, immunohistochemical, or detailed ultrastructural examination has been published to date. To elucidate the pathological differences/similarities of Bunina bodies between classical ALS and ALS-G, we performed histochemical, immunohistochemical, topographic and ultrastructural examinations. Histochemically, hematoxylin and eosin, Masson’s trichrome, methylgreen-pyronin, phosphotungstic acid-hematoxylin, Klüver-Barrera, Bodian and periodic acid-Schiff staining were utilized. Immunohistochemical examination was performed using antibodies for cystatin C, ubiquitin, Tau-2, Cu/Zn superoxide dismutase, phosphorylated neurofilament and glial fibrillary acidic protein. Histochemical findings were consistent with those previously described for classical ALS. The immunohistochemical study showed that in ALS-G Bunina bodies were intensely labeled by an anti-cystatin C antibody. Topographic examination demonstrated that Bunina bodies were distributed in the spinal anterior horns and Clarke’s column in the spinal cord. Ultrastructurally, Bunina bodies were composed of electron-dense amorphous/ granular material accompanied by vesicular structures and neurofilaments. The results of the present study have revealed that the pathological features of Bunina bodies in ALS-G are identical to those seen in classical ALS. These findings strongly suggest that a similar degenerative process occurs in the spinal anterior horn cells in both ALS-G and classical ALS.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1432-0533
    Schlagwort(e): Key words Ischemia ; Protein synthesis ; Translation ; Ultrastructure ; Hippocampus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract During post-ischemic brain reperfusion there is a substantial reduction of protein synthesis in selectively vulnerable neurons. Normal protein synthesis requires a functional translation initiation complex, a key element of which is eukaryotic initiation factor 2 (eIF2), which in a complex with GTP introduces the met-tRNAi. Phosphorylation of Ser51 on the α subunit of eIF2 [eIF2α(P)] generates a competitive inhibitor of eIF2B, thereby preventing the replenishment of GTP onto eIF2, thus blocking translation initiation. It has been shown that the conditional expression of an eIF2α mutant (Asp substituted for Ser51) imitating the negative charge of Ser51 (P) induces apoptosis. During the first 10 min of post-ischemic reperfusion, there is an approximately 20-fold increase in eIF2α(P) seen in the cytoplasm of CA1 hippocampal neurons, and, by 1 h, there is also accumulation of eIF2α(P) in the nucleus. We utilized post-embedding electron microscopical immunogold methods to examine the localization of eIF2α(P) during reperfusion. Immunogold particles (10 nm) were concentrated chiefly along the rough endoplasmic reticulum and in association with the membranes of the nuclear envelope in CA1 neurons. Aggregations of gold particles in the nucleus were concentrated: (1) within and around the nucleolus, (2) associated to strands of heterochromatin, and (3) along putative nuclear filaments. The presence of eIF2α(P) in the nucleolus probably reflects its association with nascent ribosomal subunits. The β-subunit of eIF2 has a zinc finger and polylysine blocks analogous to those on other proteins that affect transcription. The association of eIF2α(P) with chromatin may have important implications for transcription.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 199 (1999), S. 407-418 
    ISSN: 1432-0568
    Schlagwort(e): Key words Placenta ; Vascular wall ; Smooth muscle cell ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  The vascular wall structure in the human full-term placental villi of normal pregnancy was studied by means of light and electron microscopy with an improved technique of perfusion fixation and tissue preparation. We observed 81 sections of stem villi that showed cross-sectional profiles of paired vessels in their center. Both vascular walls contained a large amount of extracellular matrix and no elastic lamina between smooth muscle cells of the media, making identification of the artery and the vein quite difficult at first sight. We then noted that the density of the smooth muscle cell population was always considerably higher in one than the other, and identified the former as artery and the latter as vein on the basis of their connection with larger arteries and veins running on the chorionic plate. Between the paired vessels, the artery had a smaller caliber than the vein, and the ratio of venous to arterial caliber was distributed from 1.0 to 2.5. The thickness of media was usually thicker in the vein than in the artery. Clusters of elastic fibers were found occasionally in the media of arteries and veins, and basement membrane-like materials were associated frequently with the elastic fibers and were distributed widely in the media as well as in the adventitia. In the veins, the smooth muscle cells of the most superficial part of the media contained well-developed rough endoplasmic reticulum and Golgi apparatus, indicating differentiation to secrete extracellular matrices. The present study revealed the difference of wall structure between arteries and veins in the placental stem villi for the first time at the ultrastructural level, and suggested differentiation of venous smooth muscle cells, possibly by some influence from the luminal side.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 200 (1999), S. 81-90 
    ISSN: 1432-0568
    Schlagwort(e): Key words Elastic fibre system ; Microfibrils ; Collagen type IV ; Ultrastructure ; Immunocytochemistry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  This study deals with the examination of the elastic fibre system as well as collagen fibrils and collagen type IV in the amnion of the human chorionic plate of uncomplicated pregnancies at term. In organs other than placenta, the elastic fibre system comprises elastic fibres, elaunin and oxytalan microfibrils. The investigation was performed by light and electron microscopy and immunocytochemistry. Abundant oxytalan fibres were present in all amnionic layers, while no elastic fibres were found. Oxytalan microfibrils formed a broad subepithelial layer and were intermingled with collagen fibrils in the subjacent compact layer and in the amnionic mesoderm. Light microscopically, bunches containing orcein-stained oxytalan and collagen-type-IV-immunostained microfibrils were seen rising from the amnionic mesoderm perpendicularly towards the epithelial layer, where they obviously inserted. It can be assumed that the subepithelial microfibrillar layer and the following compact layer form an anchoring zone between the amnionic mesoderm and the epithelium that may contribute to the maintenance of strength. The ultrastructure of the bunches clearly showed collagen fibrils mixed with oxytalan microfibrils. No collagen type I-immunostaining was found in the bunches. After pretreatment of cryostat sections with elastase, oxytalan-orcein-staining was absent, but collagen type IV-immunoreactivity was not altered. Furthermore, after oxytalan-orcein-staining resp. anti-collagen type IV incubation, all positive fibres revealed an identical morphological pattern. We propose that oxytalan and collagen type IV may represent further members of the microfibril complex.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Acta neuropathologica 97 (1999), S. 509-514 
    ISSN: 1432-0533
    Schlagwort(e): Key words Hereditary inclusion body myopathy ; Desmin storage myopathy ; Ultrastructure ; Immmunocytochemistry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We report two adult familial cases of inclusion body myopathy (IBM) with desmin storage in skeletal muscle. Clinically, both patients presented late-onset, progressive, symmetrical, both proximal and distal muscle weakness. Muscle biopsy findings were identical in both cases and consisted of marked variability in fiber size, increased number of central nuclei and vacuolation involving 10% of fibers. Single or multiple vacuoles were located subsarcolemmally or in the center, and were rimmed by basophilic material. At the ultrastructural level, tubulofilamentous nuclear and cytoplasmic inclusions of 16–21 nm in diameter were frequently observed. In addition, large subsarcolemmal and central deposits composed of electron-dense granular material were present in many fibers. Immunocytochemistry revealed staining for desmin, vimentin and ubiquitin within both inclusions and vacuolated fibers. Possible structural and functional associations between these two types of muscle changes remain unclear. They may either represent two coexistent disease processes or merely reflect an abnormal form of muscle fiber degradation, with unidentifiable specificity.
    Materialart: Digitale Medien
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  • 12
    ISSN: 1432-041X
    Schlagwort(e): Key words Imaginal disc ; Axonal trajectories ; Ultrastructure ; Chaoborus (Insecta ; Diptera)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  In one of his classical studies on insect metamorphosis, Weismann compared the imaginal anlagen of the ancestral phantom midge, Chaoborus, with those of advanced brachycerans. We have expanded his findings on the relationships between larval and imaginal organs using electron microscopy and cobalt backfilling of the antenna and leg anlagen and the axonal trajectories of corresponding larval sensilla. We show that both primordia are confluent with the larval antennae and ”leg” sensilla (an ancestral Keilin organ), respectively. These fully developed larval organs represent the distal tips of the imaginal anlagen rather than separate cell clusters. The axons of the larval antenna and leg sensilla project across the corresponding anlagen to their target neuromeres within the central nervous system (CNS). Within the discs, nerves composed of these larval axons, developing afferent fibres and efferences ascending from the CNS are found. Both the structure of the primordia and the axonal trajectories thus relate the situation found in advanced brachycerans with that seen in more ancestral insects. In addition, the larval antennae, legs, wings and even the eyes possess very similar afferent pioneer trajectories supporting the idea that the described pattern is generally used in the ontogeny of sensory systems.
    Materialart: Digitale Medien
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  • 13
    ISSN: 1432-072X
    Schlagwort(e): Key wordsClostridium xylanolyticum ; Cinnamic acid ; Esterase ; Lignocellulose ; Sporogenesis ; Ultrastructure ; Cell envelope
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Microorganisms that hydrolyse the ester linkages between phenolic acids and polysaccharides in plant cell walls are potential sources of enzymes for the degradation of lignocellulosic waste. An anaerobic, mesophilic, spore-forming, xylanolytic bacterium with high hydroxy cinnamic acid esterase activity was isolated from the gut of the grass-eating termite Tumilitermes pastinator. The bacterium was motile and rod-shaped, stained gram-positive, had an eight-layered cell envelope, and formed endospores. Phylogenetic analysis based on 16S rRNA indicated that the bacterium is closely related to Clostridium xylanolyticum and is grouped with polysaccharolytic strains of clostridia. A wide range of carbohydrates were fermented, and growth was stimulated by either xylan or cellobiose as substrates. The bacterium hydrolysed and then hydrogenated the hydroxy cinnamic acids (ferulic and p-coumaric acids), which are esterified to arabinoxylan in plant cell walls. Three cytoplasmic enzymes with hydroxy cinnamic acid esterase activity were identified using non-denaturing gel electrophoresis. This bacterium possesses an unusual multilayered cell envelope in which both leaflets of the cytoplasmic membrane, the peptidoglycan layer and the S layer are clearly discernible. The fate of all these components was easily followed throughout the endospore formation process. The peptidoglycan component persisted during the entire morphogenesis. It was seen to enter the septum and to pass with the engulfing membranes to surround the prespore. It eventually expanded to form the cortex, verification for the peptidoglycan origin of the cortex. Sporogenic vesicles, which are derived from the cell wall peptidoglycan, were associated with the engulfment process. Spore coat fragments appeared early, in stage II, though spore coat formation was not complete until after cortex formation.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 124 (1999), S. 89-99 
    ISSN: 1432-1106
    Schlagwort(e): Key words Microglial culture ; Brain macrophages ; Isolectin ; Ultrastructure ; Intracellular pathway
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  The present study examined the lectin labeling of diverse morphological forms of microglia in culture. Similar to amoeboid microglial cells in vivo, polymorphic microglia showed lectin labeling at their plasma membranes, as well as in a few cytoplasmic vesicles and vacuoles. This labeling pattern was observed in cultured microglia incubated with isolectin at 4°C for 30 min. Five minutes after the temperature was raised to 37°C, the surface lectin receptors appeared to be internalized, as shown by the occurrence of many subsurface lectin-labeled vesicles, vacuoles and tubule-like structures. With longer incubation (up to 1–2 h at 37°C), many lysosomes and a few trans-Golgi saccules and associated lysosome-like structures became labeled. Concomitant with these changes was a reduction of lectin labeling at the plasma, with labeling having vanished in most of the cells after 1–2 h of incubation. By 24 h, only a few cells retained surface lectin labeling. It appears, therefore, that irrespective of morphology, lectin labeling (including its intracellular pathway) of microglia in culture parallels that of amoeboid microglia in vivo. This would offer a useful model for the study of lectin turnover in microglia and help to explain the roles of such receptors in microglial differentiation and function.
    Materialart: Digitale Medien
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  • 15
    ISSN: 1432-069X
    Schlagwort(e): Key words p75 nerve growth factor receptor ; (p75 NGFr) ; Immunoreactivity ; Ultrastructure ; Prurigo nodularis ; Nerve fiber
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Prurigo nodularis is an inflammatory skin disease characterized by neurohyperplasia. Neurotrophins and their receptors play a critical role in nerve growth, differentiation, maturation and maintenance, including cutaneous nerve fiber growth and innervation. They may also be responsible for events related to the growth and differentiation control of keratinocytes. To explore the exact distribution of the p75 low-affinity nerve growth factor receptor (p75 NGFr) in the cutaneous nerve components, p75 NGFr immunofluorescence as well as ultrastructural immunohistochemical studies were performed on prurigo nodularis lesional skin and normal human skin samples. The immunofluorescence results revealed that nerve fibers and bundles were increased in number and size in lesional upper dermis with stronger p75 NGFr immunoreactivity than in the corresponding normal tissue. At the ultrastructural level, a lot of nerve fibers clustered together in the prurigo nodularis dermal tissue. The axons were enlarged and branched, but the axons themselves seldom showed any NGFr immunoreactivity. The Schwann cell bodies were extended and irregularly shaped, and tended to separate into many branches enveloping the axons. The Schwann cell membrane showed strong p75 NGFr immunoreactivity. The perineurium cells also revealed strong p75 NGFr immunoreactivity. The Schwann cells inside the perineurium were less p75 NGFr-immunoreactive than those outside the perineurium. The membrane of certain basal keratinocytes showed NGFr immunoreactivity as well. The present results indicate that overexpression of p75 NGFr in Schwann cells and perineurium cells could contribute to the neurohyperplasia in prurigo nodularis.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Urological research 27 (1999), S. 454-461 
    ISSN: 1434-0879
    Schlagwort(e): Key words Cold-restraint stress ; Urinary bladder ; Interstitial cystitis ; Mast cell ; Urothelium ; Ultrastructure ; Ruthenium red ; Flow cytometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Stress is associated with many diseases of unknown aetiology. This study demonstrates the effects of cold-restraint stress on the morphology of the urinary bladder. Additionally, it compares the results obtained with the morphology of the interstitial cystitis. The animals were subjected to three hours of cold-restraint stress and then starved for 48 h. The morphology and histochemistry of the urinary bladder was investigated with light and electron microscopy. The proliferative activity was analysed via flow cytometry. Increased and degranulated mast cells in the mucosa, leucocyte infiltration in the lamina propria, vacuole formation in the urothelial cells, loose tight junction, dilated intercellular spaces and altered proliferative activity were observed in the stress group when compared with the control. The increase in the number of mast cells and especially degranulated mast cells and vacuole formation and the loose tight junction of the urothelium correlated with the histopathological findings of interstitial cystitis.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Protoplasma 206 (1999), S. 57-72 
    ISSN: 1615-6102
    Schlagwort(e): Anatomy ; Floral nectary ; Modified stomata ; Phloem ; Pisum sativum ; Stereology ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The floral nectary ofPisum sativum L. is situated on the receptacle at the base of the gynoecium. The gland receives phloem alone which departed the vascular bundles supplying the staminal column. Throughout the nectary, only the companion cells of the phloem exhibited wall ingrowths typical of transfer cells. Modified stomata on the nectary surface served as exits for nectar, but stomatal pores developed well before the commencement of secretion. Furthermore, stomatal pores on the nectary usually closed by occlusion, not by guard-cell movements. Pore occlusion was detected most frequently in post-secretory and secretory glands, and less commonly in pre-secretory nectaries. A quantitative stereological study revealed few changes in nectary fine structure between buds, flowers secreting nectar, and post-secretory flowers. Dissolution of abundant starch grains in plastids of subepidermal secretory cells when secretion commenced suggests that starch is a precursor of nectar carbohydrate production. Throughout nectary development, mitochondria were consistently the most plentiful organelle in both epidermal and subepidermal cells, and in addition to the relative paucity of dictyosomes, endoplasmic reticulum, and their associated vesicles, the evidence suggests that floral nectar secretion inP. sativum is an energy-requiring (eccrine) process, rather that granulocrine.
    Materialart: Digitale Medien
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  • 18
    ISSN: 1615-6102
    Schlagwort(e): Cumulus oophorus ; Ovarian follicle ; Fertilization ; Ultrastructure ; Immunocytochemistry ; Human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The fine structure of the human cumulus oophorus has been reviewed on the basis of scanning and transmission electron microscopic observations as well as of immunofluorescence data. Tissues sampled from preovulatory ovarian follicles and cumulus-enclosed oocytes and fertilized eggs (collected from the oviduct or obtained during in vitro fertilization procedures) have been evaluated from a microtopographic and morphodynamic point of view in order to better clarify the possible role of this population of cells. In particular, the following aspects have been studied and discussed: the presence of multiple close contacts (modulated by the interposition of the zona pellucida) between the oocyte surface and the long microvillous evaginations projecting from the inner aspect of corona cells surface (through these structures the intraovarian cumulus oophorus may control oocyte growth and metabolism up until the time of ovulation); the occurrence of different subpopulations of cells (steroid-synthetic cells, cells producing adhesive proteins, leukocytes, macrophages) in the postovulatory, extraovarian cumulus oophorus surrounding oocytes, zygotes and early developing embryos. All these elements found in the cumulus mass may positively act, through their paracrine activities, on the chemical composition of the microenvironment in which fertilization occurs.
    Materialart: Digitale Medien
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  • 19
    ISSN: 1615-2573
    Schlagwort(e): Endomyocardial biopsy ; Dilated cardiomyopathy ; Children ; Ultrastructure ; Basal lamina layering of capillary
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary We analyzed the electron-microscopic features of endomyocardial biopsy from pediatric patients with dilated cardiomyopathy (DCM). The specimens examined were taken from the right ventricle of ten patients aged from 2 to 15 years (mean 9.7 years). Biopsy specimens from eight patients with congenital heart disease (tetralogy of Fallot), aged from 3 to 12 (mean 7.3 years), and ten adult patients with DCM, aged from 32 to 60 (mean 45 years), were also examined. Patients considered to have endocardial fibroelastosis, arrhythmogenic right ventricular cardiomyopathy, specific cardiomyopathy, or coronary heart disease were excluded from this study. Specimens from pediatric patients with DCM showed various degrees of ultrastructural abnormalities of myocytes, including myofibrillar fragmentation, mitochondrial abnormalities, and intracellular edema. The ultrastructurally determined contractility failure index based on the severity of myocardial degeneration at the electronmicroscopic level was 4.9 ± 1.1. This value was significantly higher than that in patients with tetralogy of Fallot (0.9 ± 0.6,P 〈 0.001) but was not significantly different from that in adult patients with DCM (6.1 ± 2.6). The index of pediatric patients with DCM who died within 3 years was high (6.0 ± 0.8). Basal lamina layering of a capillary (BLL) in the myocardium was revealed in 1 of the 10 (10%) pediatric patients with DCM and in 6 of the 10 (60%) adult patients with DCM (P 〈 0.05). No BLL was noted in the patients with tetralogy of Fallot. These findings may be related to the pathogenesis of DCM in children and adults.
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  • 20
    ISSN: 1432-0878
    Schlagwort(e): Key words Neuromelanin ; Neuron ; Peroxidase ; Oxygen metabolism ; High-definition light microscopy ; Electron microscopy ; Ultrastructure ; Cytochemistry ; Substantia nigra ; Lumbricusterrestris (Annelida)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Histochemical examination of 1-μm tissue sections from the dorsal nerve plexus of the earthworm, Lumbricus terrestris, reveals multiple brown intraneuronal granules. These granules contain material morphologically and histochemically consistent with neuromelanin. When viewed with transmission electron microscopy, these were seen as single membrane-enclosed biphasic granules with diameters of 370–730 nm. Exposure of L. terrestris to high-level environmental oxygen resulted in an increase in the number of neuromelanin-like pigment granules within the neurons of the circular muscle layer. As measured by ortho-phenylenediamine hydrochloride, the endogenous peroxidase activity of extracts from worms incubated in high-level environmental oxygen was 51% more than controls. The endogenous peroxidase activity was localized in situ with 3,3-diaminobenzidine (DAB) and was found to increase in and around the neuromelanin-like pigment-containing neurons within the circular muscle layer. These studies suggest that the nerve net of L. terrestris may serve as a model to study the role of neuromelanin production in oxidative stress and its relationship to endogenous peroxidases.
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Parasitology research 85 (1999), S. 999-1006 
    ISSN: 1432-1955
    Schlagwort(e): Key wordsEchinococcus granulosus ; Praziquantel ; Metacestode ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The efficacy of praziquantel against the metacestode of Echinococcus granulosus was studied by means of in vitro incubations or in vivo experiments. The results of in vitro incubations indicated that the effectiveness of praziquantel was higher when the parasite material comprised cysts from cyst masses than in the case of intact cysts that retained their adventitial layer. Ultrastructural alterations in the germinal layer of collapsed cysts incubated in vitro were detected. The results obtained in mice after 4 months of treatment demonstrated no significant difference between the control and treated groups with regard to the number and wet weight of developed cysts. However, ultrastructural alterations were detected in the cyst tissue that were similar to those described in the in vitro experiment. In contrast, the effect of chemoprophylaxis on the number and the wet weight of developed cysts was extremely significant as compared with the control value, the efficacy being 99.41% and 98.32%, respectively. Moreover, ultrastructural observations of the cyst tissue revealed loss of its integrity, and no intact cyton was observed in the germinal layer of the developed cyst.
    Materialart: Digitale Medien
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  • 22
    ISSN: 1432-1955
    Schlagwort(e): Key words Monogenea ; Capsalidae ; Benedenia rohdei ; B. lutjani ; Ectoparasites ; Lutjanus carponotatus ; Glands ; Ultrastructure ; Adhesion ; Attachment
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The anterior adhesive areas of Benedenia rohdei from the gills and B. lutjani from the pelvic fins of Lutjanuscarponotatus at Heron Island, Australia, were studied using scanning and transmission electron microscopy. All specimens were fixed when detached from host tissue. Both monogenean species have two disc-like anteroventral attachment organs, each of which has an anterolateral adhesive area divided into three adjacent zones by tegument from the ventral surface of the attachment organ. A rod-shaped secretion and a smaller, roughly spherical secretion are associated with the anterior adhesive areas in both species; a third type of secretion occurs anteriorly but outside these adhesive areas. The electron-dense spherical secretory bodies released onto the anterior adhesive zones in these Benedenia spp. are of a single type and differ ultrastructurally from those previously reported in monogeneans living on teleost hosts. A correlation, therefore, between secretion morphology and host type is not supported. No relationship was found between parasite microhabitat and secretion morphology.
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Journal of comparative physiology 169 (1999), S. 351-359 
    ISSN: 1432-136X
    Schlagwort(e): Key words Freeze tolerance ; Sciatic nerve ; Cryoinjury ; Dehydration ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract We investigated function and ultrastructure of sciatic nerves isolated from wood frogs (Rana sylvatica) endemic to the Northwest Territories, Canada, following freezing at −2.5 °C, −5.0 °C, or −7.5 °C. All frogs frozen at −2.5 °C, and most frogs (71%) frozen at −5.0 °C, recovered within 14 h after thawing began; however, frogs did not survive exposure to −7.5 °C. Sciatic nerves isolated from frogs frozen at −7.5 °C were refractory to electrical stimulation, whereas those obtained from frogs surviving exposure to −2.5 °C or −5.0 °C generally exhibited normal characteristics of compound action potentials. Frogs responded to freezing by mobilizing hepatic glycogen reserves to synthesize the cryoprotectant glucose, which increased 20-fold in the liver and 40-fold in the blood. Ultrastructural analyses of nerves harvested from frogs in each treatment group revealed that freezing at −2.5 °C or −5.0 °C had little or no effect on tissue and cellular organization, but that (lethal) exposure to −7.5 °C resulted in marked shrinkage of the axon, degeneration of mitochondria within the axoplasm, and extensive delamination of myelin sheaths of the surrounding Schwann cells.
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  • 24
    ISSN: 1861-387X
    Schlagwort(e): Meningioma ; Intranuclear inclusion ; Immunohistochemistry ; Ultrastructure ; Intermediate filament
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We describe a case of meningothelial meningioma with a large number of intranuclear inclusions. Morphologically, these are divided into cytoplasmic inclusions and nuclear vacuoles. The cytoplasmic inclusion has a limiting membrane with cell organelles and filaments. Inclusions of this type are generally eosinophilic, like the cytoplasm. However, there are many inclusions that are more eosinophilic than the cytoplasm or that have a ground-glass appearance. Some of them may contain fine or coarse granules. On the other hand, the nuclear vacuole lacks a limiting membrane and appears empty. In most of the inclusions of this type, there is a faintly basophilic substance in the margin. Generally, the cytoplasmic inclusions are as immunopositive as cytoplasm with vimentin, but some of these cytoplasmic inclusions are more reactive. Under the electron microscope, abnormal aggregation of intermediate filaments is recognized in the cytoplasmic inclusions. It is considered that a strong reaction of cytoplasmic inclusions with vimentin immunostaining is due to abnormal aggregation of intermediate filaments. The present study distinctly demonstrates abnormal localization of intermediate filaments in the cytoplasmic inclusions, and it is suggested that the cytoskeleton participates in the evolution of the cytoplasmic inclusions.
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  • 25
    ISSN: 1432-0878
    Schlagwort(e): Key words Chondrocyte ; Synoviocyte ; Co-culture ; Proliferation ; Lipid peroxidation ; Cytotoxicity ; Ultrastructure ; Rat (Wistar)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  Objective: A new co-culture system of rat articular chondrocytes and synoviocytes (HIG-82; cell line) was incubated with phorbol myristate acetate (PMA), H2O2 or a combination of Fe2+ and ascorbic acid to simulate inflammation-like radical attacks in articular joints. Methods: Chondrocytes were characterized by immunocytochemistry against collagen type II, transmission electron (TEM) and light microscopy. Lipid peroxidation was investigated by measuring thiobarbituric-acid-reactive material in the supernatants, cytotoxicity by determining release of lactate dehydrogenase and proliferation by measuring [3H]thymidine incorporation, culture protein and DNA. Results: PMA or Fe2+ and ascorbic acid induced lipid peroxidation in chondrocytes and synoviocytes that was decreased significantly in co-cultures. PMA and H2O2 dose dependently induced release of lactate dehydrogenase in chondrocytes, which was lowered in co-cultures or in previously co-cultured chondrocytes to a nearly basal level. In contrast, conditioned media of synoviocyte cultures showed no lowering effect on the radical-induced toxicity. Protection against H2O2-induced damage of cellular membranes by co-culturing was also shown by TEM. Synoviocytes released chondrocyte-stimulating growth factors spontaneously without previous interaction. Conclusion: Chondrocytes establish protective mechanisms against reactive oxygen species via an interaction with synoviocytes. Our co-culture model presents a possible way to study mechanisms of inflammation in articular joints under defined conditions.
    Materialart: Digitale Medien
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  • 26
    ISSN: 1437-773X
    Schlagwort(e): Key words KSHV ; HHV-8 ; TPA ; Ultrastructure ; Primary effusion lymphoma
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The ultrastructure of Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus-8 (HHV-8) has not yet been fully elucidated, although some findings have been reported using primary effusion lymphoma (PEL) cell lines, KS-1, harboring no Epstein–Barr virus (EBV) coinfection. In the present study, detailed fine structural examination of KSHV/HHV-8 was performed after stimulation of the PEL-derived cell line KS-1 with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in vitro. While unstimulated KS-1 cells contained a small number of intranuclear virus particles associated with no extracellular mature particles, KS-1 cells stimulated with TPA produced many extracellular mature particles as well as intranuclear particles, in addition to interesting tubulo-reticular structures and aggregated tubular structures in vesicles. The induced intranuclear particles were empty, doughnut shaped, and dense cored, with outer and inner diameters of 100–110 nm and 60–70 nm, respectively. Dense-cored extracellular mature particles were 150–160 nm in diameter, and some contained doughnut-shaped cores, together with a few megaloviruses, 260 nm in outer diameter. These findings indicate that KS-1 cells treated with TPA can produce extracellular mature particles as well as intranuclear particles, which were proven to be KSHV/HHV-8.
    Materialart: Digitale Medien
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  • 27
    ISSN: 1437-773X
    Schlagwort(e): Key words pHGF ; HGF ; Acute liver injury ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The protective effect of hepatocyte growth-promoting factor (pHGF) against CCl4-induced acute hepatitis in rats was examined by light and electron microscopy. Hepatocyte growth-promoting factor, purified from infant pig liver in an active form, has been used clinically in patients with hepatitis in China. Four hours after administration of CCl4, a single dose of pHGF was administered intraperitoneally. Six hours after administration of CCl4, inhibition of CCl4-induced hepatic necrosis and hepatocytes with severely dilated endoplasmic reticula were evident in rats treated with pHGF. At 48 h post administration, most hepatocytes had recovered, and not only mitotic hepatocytes (10–13 mitotic cells/100) but also mitotic Kupffer cells were observed. At 72 h, it was evident that the differentiation of hepatic stellate cells (Ito cell) into myofibroblast-like cells and the development of fibrosis around the central veins was prevented by pHGF. These results suggested that (1) pHGF may stabilize cell membranes, (2) pHGF acts as a mitogen not only for hepatocytes but also for Kupffer cells, and (3) pHGF prevents fibrogenesis in the case of CCl4-induced liver injury by preventing the differentiation of hepatic stellate cells.
    Materialart: Digitale Medien
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  • 28
    ISSN: 1437-773X
    Schlagwort(e): Key words Heart ; Ultrastructure ; Capillaries ; Endothelium ; Stereology ; Cardioplegic solutions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract In open heart surgery and transplantation, sufficient structural preservation of the myocardium immediately following cardioplegic arrest is a precondition for overcoming ischemia and for resumption of postischemic function. Therefore, we compared the protective effect of three clinically applied cardioplegic solutions with fibrillating and beating hearts using structural criteria. Left ventricular samples were taken from (1) beating, or (2) fibrillating or arrested hearts following coronary perfu-sion with (3) St. Thomas' Hospital solution, (4) histidine tryptophane ketoglutalate (HTK) (Custodiol), or (5) University of Wisconsin (UW) solution and fixed by immersion. Ultrastructural differences in the swelling of capillary endothelial cells and myocytes were quantitatively evaluated using stereological methods. Endothelial cells were somewhat more swollen after St. Thomas perfusion than those in beating and fibrillating hearts. HTK-arrested hearts showed significantly lower values for cellular edema than beating hearts. UW perfusion resulted in the (significantly) lowest degree of endothelial cell edema. Edematous changes in myocytes were significantly greater in St. Thomas-arrested hearts than in UW- or HTK-arrested hearts. Cardiomyocyte edema in beating and fibrillating hearts was comparable to that in St. Thomas-perfused hearts. Thus, the stereol-ogical analysis revealed significant differences between cardioplegic solutions in structural preservation of myocardial ultrastructure.
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Medical electron microscopy 32 (1999), S. 175-183 
    ISSN: 1437-773X
    Schlagwort(e): Key words Cerebral blood flow ; Blood–brain barrier ; Repeated brief cerebral ischemia ; Hippocampal CA1 ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Neuronal damage and changes in cerebral blood flow (CBF) and the permeability of the blood–brain barrier (BBB) following repeated brief periods of ischemia were studied in Mongolian gerbils. The cerebral ischemia was produced by three repeated occlusions of bilateral common carotid arteries for 3 min at 1-h intervals. CBF and permeability of the BBB were examined with tracers (China ink and silver nitrate) at 1, 3, and 7 days post ischemia using light and electron microscopy. Three days after the reperfusion, significant extravasation of tracers, consequential reduction of CBF, extensive neuronal destruction, and intravascular platelet aggregation were observed. Such vascular changes in the CA1 region were more severe than those in the frontal cortex. These findings strongly support the view that microcirculatory disturbance may be a mechanism responsible for delayed neuronal death in the CA1 region of the hippocampus.
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  • 30
    ISSN: 1437-773X
    Schlagwort(e): Key words: Secretory carcinoma ; Breast ; Intracytoplasmic lumina ; Immnohistochemistry ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We report a rare case of secretory carcinoma of the breast in a 50-year-old Japanese woman. The patient had been aware of a right breast tumor for 8 years, but had left it untreated. The tumor enlarged in size and became painful, and she visited our hospital. Breast carcinoma was diagnosed, and mastectomy was performed. Histopathological examination revealed features of a secretory carcinoma characterized by prominent secretory activity in the glandular and microcystic spaces, with some areas showing a follicular pattern resembling the thyroid gland. The secretory material was PAS-positive and immunohistochemically α-lactalbumin-positive. Ultrastructurally, the tumor cell contained many secretory vacuoles in the cytoplasm. In addition, extracellular and intracytoplasmic lumina were conspicuous; these were lined by microvilli projection and contained secretory material. By flow cytometric analysis, the DNA index was 1.14, which was diploid, showing relatively low proliferative activity.
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  • 31
    ISSN: 1432-0878
    Schlagwort(e): Key words Melanin-concentrating hormone neurons ; Lateral hypothalamic slice culture ; Immunocytochemistry ; Ultrastructure ; In situ hybridization ; Competitive RT-PCR ; Leptin assay ; Rat (Sprague Dawley)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  Hypothalamic slices containing the lateral hypothalamic area (LHA) were prepared from 6- to 8-day-old rats and maintained in stationary culture for up to 35 days in order to analyse how well the melanin-concentrating hormone (MCH) neurons survived. As previously reported for other brain areas, this method yielded a long-term well-preserved organotypic organization. Light- and electron-microscopic investigations showed that differentiation continued and that synaptic contacts developed in vitro. After a period of elimination of damaged cells and fibres, most of the remaining neurons and glial cells retained a normal morphology throughout the culture period. MCH neurons, in particular, survived well as attested by the strong immunocytochemical and in situ hybridization signals still observed after several weeks. In a comparison with the day of explantation, competitive reverse transcription/polymerase chain reaction demonstrated the remarkable stability of the level of MCH mRNA at least until the 20th day in culture; after 30 days, the clear decrease in this level seemed to be correlated with a loss of MCH neurons, rather than with a decrease in MCH expression. After 10 days of culture, the incubation of slices in the presence of the hormone leptin (50 ng/ml) resulted in a strong decrease of MCH gene expression, suggesting that MCH neurons retained their physiological properties. Thus, the LHA slice stationary culture, especially between one and three weeks (i.e. after tissue stabilization and before extensive cell loss), appears to be a suitable method for physiological and pharmacological studies of these neurons.
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  • 32
    ISSN: 1432-0878
    Schlagwort(e): Key words Mechanoreceptors ; Synaptic proteins ; Histochemistry ; Ultrastructure ; Slit sensilla ; Hair sensilla ; Cupiennius salei (Chelicerata)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Indirect immunocytochemical tests were used at the light- and electron-microscopic levels to investigate peripheral chemical synapses in identified sensory neurons of two types of cuticular mechanosensors in the spider Cupiennius salei Keys.: (1) in the lyriform slit-sense organ VS-3 (comprising 7–8 cuticular slits, each innervated by 2 bipolar sensory neurons) and (2) in tactile hair sensilla (each supplied with 3 bipolar sensory cells). All these neurons are mechanosensitive. Application of a monoclonal antibody against Drosophila synapsin revealed clear punctate immunofluorescence in whole-mount preparations of both mechanoreceptor types. The size and overall distribution of immunoreactive puncta suggested that these were labeled presynaptic sites. Immunofluorescent puncta were 0.5–6.8 μm long and located 0.5–6.6 μm apart from each other. They were concentrated at the initial axon segments of the sensory neurons, while the somata and the dendritic regions showed fewer puncta. Western blot analysis with the same synapsin antibody against samples of spider sensory hypodermis and against samples from the central nervous system revealed a characteristic doublet band at 72 kDa and 75 kDa, corresponding to the apparent molecular mass of synapsin in Drosophila and in mammals. Conventional transmissionelectron-microscopic staining demonstrated that numerous chemical synapses (with at least 2 vesicle types) were present at these mechanosensory neurons and their surrounding glial sheath. The distribution of these synapses corresponded to our immunofluorescence results.Ultrastructural examination of anti-synapsin-stained neurons confirmed that reaction product was associated with synaptic vesicles. We assume that the peripheral synaptic contacts originate from efferents that could exert a complex modulatory influence on mechanosensory activity.
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  • 33
    ISSN: 1615-6102
    Schlagwort(e): Plasmalemmic cord ; Pollen grain ; Ultrastructure ; Magnolia ×soulangeana
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary InMagnolia ×soulangeana pollen grains the generative cell (GC) does not become totally free within the vegetative cell (VC), at least until the pollen tube emergence. Due to a deviation in its detachment process from the sporoderm, the opposing ends of the VC plasmalemma do not fuse themselves when the GC moves away from the intine. Consequently, the interplasmalemmic space surrounding the GC does not become isolated but rather maintains continuity with the sporoderm through a complex formation that we have called plasmalemmic cord. The real existence of this formation was confirmed through serial sectioning showing the plasmalemmic cord to consist of the VC plasmalemma. In its initial portion it is occupied by a reasonably accentuated wall ingrowth of the inner layer of the intine (intine 3). In the remainder portion, neither of the cytochemical tests used in this work have revealed the presence of a significant amount of wall material. However, ultrathin sections of samples processed either chemically or by cryofixation showed the existence of an intricate system of tubules and vesicles, some of which are evaginations of the VC plasmalemma. The hypothesis that the plasmalemmic cord may have a role in the complex interactions between the two pollen cells is discussed.
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  • 34
    ISSN: 1615-6102
    Schlagwort(e): Endosymbiont ; Mycetocyte ; Mycetome ; Oocyte ; Transovarial transmission ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary All anoplurans live symbiotically with prokaryotic microorganisms hosted in specialized cells, termed mycetocytes. In nymphs and males mycetocytes are distributed between midgut epithelial cells. In females, besides the midgut, mycetocytes are found in the reproductive organs where they are located at the base of ovarioles in contact with lateral oviducts. The mycetocyte-associated symbionts are transmitted from one generation to the next transovarially. Here, the results of histological and ultrastructural studies on the distribution and transmission of symbiotic microorganisms within the ovaries of the anopluranHaematopinus suis are presented. Interestingly, during advanced oogenesis (i.e., choriogenesis) of this species all symbionts are localized extracellularly and form a tight mass located at the posterior pole of the oocyte just below the hydropyle. In insects studied so far, such localization of transovarially transmitted microorganisms has been reported only in the closely related speciesHaematopinus eurysternus.
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  • 35
    ISSN: 1432-0878
    Schlagwort(e): Key words Teleost fish ; Puberty ; Testes ; Sex steroids ; Ultrastructure ; Steroidogenesis ; Clarias gariepinus (Teleostei)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The present report focuses on the mechanism(s) involved in the steroid-induced decrease of androgen production in immature African catfish testes that was observed in previous studies. Juvenile animals were implanted with Silastic pellets containing different 11-oxygenated androgens (11-ketotestosterone, KT; 11β- hydroxyandrostenedione, OHA; 11-ketoandrostenedione, KA), testosterone (T) or estradiol-17β (E2). Control groups received steroid-free pellets. Two weeks later, testis tissue fragments were either incubated with increasing concentrations of catfish luteinizing hormone (LH), or incubated with [3H]-pregnenolone ([3H]-P5) or [3H]-androstenedione ([3H]-A). Tissue fragments were also prepared for the quantitative assessment of Leydig cell morphology. Most of the parameters studied were not affected significantly by implantation of E2. Implantation of all androgens inhibited both the basal and the LH-stimulated androgen secretory capacity in vitro. This was associated with a reduced size of the Leydig cells and loss of half of their mitochondria. The studies on the metabolism of tritiated steroid hormones indicated that steroidogenic steps prior to 11β-hydroxylation, probably C17–20 lyase activity, were affected by all androgens. Although the effects of 11-oxygenated androgens and T on Leydig cells were mostly similar, previous work showed that only the 11-oxygenated androgens stimulated spermatogenesis, suggesting that distinct mechanisms of action are used by 11-oxygenated androgens and T. These mechanisms, however, seem to merge on the same target(s) to impair Leydig cell androgen production. Such a negative feedback mechanism may be of relevance in the context of the decline in androgen secretion per milligram testis tissue that accompanies the first wave of spermatogenesis in pubertal African catfish.
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  • 36
    ISSN: 1432-0878
    Schlagwort(e): Key words Chloride cells (mitochondria-rich cells) ; Teleost larvae ; Osmoregulation ; Immunohistochemistry ; Quantification ; Ultrastructure ; Oreochromis mossambicus (Teleostei)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  Integumental and branchial chloride cells of tilapia larvae (Oreochromis mossambicus) were studied at the light-microscopical and ultrastructural level. Total numbers and distribution of chloride cells were quantified after immunostaining of cross sections of the entire larvae with an antibody against the α-subunit of Na+/K+-ATPase. The majority (66%) of Na+/K+-ATPase-immunoreactive (ir) cells, i.e. chloride cells, of freshwater tilapia larvae were located extrabranchially up to 48 h after hatching. Five days after hatching, the majority (80%) of chloride cells were found in the buccal cavity. Transfer of 24-h-old larvae to 20% sea water speeded up this process; 24 h after transfer (i.e. 48 h after hatching), the majority (59%) of chloride cells were located in the buccal cavity. The branchial chloride cell population of 24-h- and 120-h-old larvae consisted of immature, mature, apoptotic and necrotic chloride cells. However, relatively more immature chloride cells were observed in freshwater larvae (42–63%) than in (previously studied) freshwater adults (21%), illustrating the developmental state of the gills. After transfer to sea water, the incidence of degenerative chloride cells did not change. Furthermore, the incidence of immature cells had decreased and a new subtype of chloride cells, the ”mitochondria-poor” cells, appeared more frequently. These mitochondria-poor chloride cells were characterised by an abundant tubular system and relatively few mitochondria, which were aligned at the border or concentrated in one part of the cytoplasm. Most of these cells did not contact the water. The function of their enhanced appearance after seawater transfer is unknown.
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  • 37
    ISSN: 1432-0878
    Schlagwort(e): Key words ECL cells ; Gastrin ; Reserpine ; Organelles ; Ultrastructure ; Rat (Sprague-Dawley)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The histamine-storing ECL cells in the stomach play a key role in the control of acid secretion. They contain granules, secretory vesicles and microvesicles, and sustained gastrin stimulation results in the additional formation of vacuoles and lipofuscin bodies. The cells are rich in the vesicle monoamine transporter type-2 (VMAT-2), which can be inhibited by reserpine. The present study examines the effect of reserpine on ECL-cell ultrastructure and histamine compartmentalization. Rats received reserpine and/or gastrin. Reserpine was given twice by the intraperitoneal route (25 mg/kg once daily). Gastrin-17 was given by subcutaneous infusion (5 nmol/kg/h), starting at the time of the first reserpine injection and continuing for 4 days when the rats were killed. At this stage, histamine in the oxyntic mucosa was unaffected by reserpine but elevated by gastrin. Immunocytochemical analysis (confocal microscopy) showed ECL-cell histamine in control and gastrin-treated rats to be localized in cytoplasmic organelles (e.g., secretory vesicles). After treatment with reserpine alone or reserpine+gastrin, ECL-cell histamine occurred mainly in the cytosol. Planimetric analysis (electron microscopy) of ECL cells showed reserpine to increase the number, size and volume density of the granules and to reduce the size and volume density of the secretory vesicles. Gastrin reduced the number and volume density of granules and secretory vesicles, increased the number and volume density of microvesicles and caused vacuoles and lipofuscin bodies to appear. Reserpine+gastrin increased the number, volume density and size of the granules. Reserpine prevented the effects of gastrin on secretory vesicles, vacuoles and microvesicles, but did not prevent the development of lipofuscin. Our findings are in line with the views: (1) that preformed cytosolic histamine is taken up by granules/secretory vesicles via VMAT-2, that histamine is instrumental in the transformation of granules into secretory vesicles and in their consequent enlargement and (2) that vacuoles are formed by the fusion of large secretory vesicles.
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Cell & tissue research 295 (1999), S. 151-158 
    ISSN: 1432-0878
    Schlagwort(e): Key words Class II MHC-positive cells ; Human leukocyte antigen-DR ; Dental pulp ; Dendritic cells ; Macrophages ; Ultrastructure ; Human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The distribution and ultrastructure of class II major histocompatibility complex (MHC)-positive cells were investigated in human dental pulp, employing immunohistochemistry using an anti-human leukocyte antigen (HLA)-DR-monoclonal antibody. HLA-DR-immunopositive cells, appearing spindle-like or dendritic in profile, were densely distributed throughout the dental pulp. Under the electron microscope, these cells exhibited various sizes of vesicles containing clear or opaque contents, multivesicular bodies and characteristic fine tubulovesicular structures in their cytoplasm. Some reactive cells possessed coated pits and vesicles including electron-dense materials, indicating an active endocytosis. At the periphery of the pulp tissue, the HLA-DR-immunopositive cells were predominantly situated in the subodontoblastic layer, with some located in the odontoblast layer and/or predentin and extending their cytoplasmic processes into the dentinal tubules. Cell processes of these cells occasionally made contact with several odontoblast processes in the same way as the nerve fibers in the predentin. These cells never contained the typical phagosomes frequently observed in the HLA-DR-immunoreactive macrophages in the subodontoblastic layer and the pulp core. The results suggest that the HLA-DR-immunopositive cells in the odontoblast layer and/or predentin have some regulatory function on the odontoblasts under physiological conditions, in addition to their involvement in the initial defense reaction after tooth injury.
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Sexual plant reproduction 11 (1998), S. 121-130 
    ISSN: 1432-2145
    Schlagwort(e): Key words Egg cell ; Parthenogenesis ; Synergid ; Ultrastructure ; Wheat ; Zygote
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The ultrastructure of the egg apparatus of the sexual (aestivum)-Salmon line (aS) and the isogenic but alloplasmic (kotschyi)-Salmon line (kS) of the Salmon system of wheat was studied by transmission electron microscopy 3 days before and during anthesis. Additionally, the zygotic stage of aS, 17 h after pollination, was included. Metabolic activity of egg cells from the sexual line aS was low 3 days before anthesis and increased dramatically after pollination and fertilization. This timing of increased activity was evident because of changes occurring in the egg cell nucleus and nucleolus, polysomes, endoplasmic reticulum and Golgi apparatus, and the completion of the cell wall around the zygote. In contrast to the sexual line, the egg cell of the parthenogenetic line showed high activity 3 days before anthesis. The metabolic and ultrastructural characters observed in the nucleus and cytoplasm of the kS line 3 days before and during anthesis corresponded with those of the isogenic sexual line aS during anthesis and 17 h after pollination, respectively. High metabolic activity observed in the persistent synergid of kS may be connected with the occurrence of additional embryos in seeds (twins) of this line.
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  • 40
    Digitale Medien
    Digitale Medien
    Springer
    Sexual plant reproduction 11 (1998), S. 284-291 
    ISSN: 1432-2145
    Schlagwort(e): Key words Abies ; Egg cell ; Plastid inheritance ; RFLP ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The ultrastructure of egg cells in Abies alba was examined to elucidate the lack of maternal inheritance of plastids. Before fertilization, maternal plastids are absent in the perinuclar zone containing mainly mitochondria and smooth endoplasmic reticulum. During egg cell development the maternal plastids are transformed into large inclusions which are situated mostly towards the periphery of the egg cell, and finally disintegrate. As a consequence, they do not participate in zygote formation. RFLP analysis of cpDNA of parental trees and their F1 interspecific hybrids (A. alba×A. numidica, A. alba×A. nordmanniana, A. nordmanniana×A. Alba) using HindIII and BamHI showed a paternal mode of cpDNA inheritance. Paternal inheritance has also been found with PCR/RFLP analysis of cpDNA from parental trees and their hybrids (A. alba×A. pinsapo, A. pinsapo×A. alba, A. pinsapo×A. numidica) using ApaI and HaeIII digests, as well as in the crosses of A. cephalonica×A. nordmanniana, A. nordmanniana×A. cephalonica, A. cephalonica×A. numidica using TagI digests.
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Virchows Archiv 433 (1998), S. 443-447 
    ISSN: 1432-2307
    Schlagwort(e): Key words Apoptosis ; Crescent-shaped spaces ; Ultrastructure ; Nivalenol ; Thymus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  There have been many reports on the formation of apoptotic bodies, but little is known about the cellular pathological processes and the morphological changes involved. We induced apoptotic cell death by administering nivalenol (NIV), a trichothecene mycotoxin produced by Fusarium species, and investigated the ultrastructural process of formation of apoptotic bodies. The thymus was examined by electron microscopy 6, 12, and 18 h after administration. Apoptotic cell death was induced in the thymus of NIV-treated mice. The nuclei became invaginated and pinched off to give fragments, and crescent-shaped spaces (CSS) were found around the nuclear envelopes of these cells at quite an early stage. In some of these spaces, myelin figures were observed. We divided the process of formation into four stages and characterized each of them. These are easily recognized in morphological stages and are also useful for clarifying the apoptotic mechanism.
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Der Pathologe 19 (1998), S. 373-378 
    ISSN: 1432-1963
    Schlagwort(e): Schlüsselwörter Metaplastische Brustdrüsenkarzinome ; Plattenepithelmetaplasie ; Plattenepithelkarzinom ; Immunhistologie ; Elektronenmikroskopie ; Zytophotometrie ; Key words Pure squamous cell carcinoma ; Mammary gland ; Squamous metaplasia ; Immunohistology ; Cytophotometry ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary Squamous metaplasia can be demonstrated in about 4% of all invasive carcinomas of the breast. Primary squamous cell carcinomas of the breast are rare, since they occur in less than 1% of all primary invasive breast carcinomas. In order to classify a breast tumor as a primary squamous cell carcinoma one must exclude an epidermal origin, especially from the nipple region and the possibility of metastatic infiltration of the breast by a squamous cell carcnoma from a different location. Causative and formal pathogenesis of primary squamous cell carcinoma of the breast is not clear. A pluripotent embryonal stem cell origin is discussed, considering the phylogenetic descent of the mammary gland from skin appendages. Squamous metaplasia is also suggested to be a precursor of squamous cell carcinoma. Here endocrine stimulation and chronic inflammation may both play an inductive role. The number of published cases of squamous cell carcinomas developing years and decades after implantation of silicon prostheses has increased in recent years. These tumors probably develop on top of squamous metaplasia induced by the inflammatory pseudocapsule. Estimating the prognosis and therapeutic management in patients with squamous cell carcinoma of the breast should follow the same guidelines as for other squamous cell cancers.
    Notizen: Zusammenfassung Plattenepithelmetaplasien werden bei etwa 4% aller invasiven Brustdrüsenkarzinome beschrieben. Reine Plattenepithelkarzinome der weiblichen Brustdrüse sind mit einem Anteil von wahrscheinlich unter 1% an allen invasiven epithelialen Tumoren der Mamma selten. Von einem primären Plattenepithelkarzinom der Brustdrüse darf nur gesprochen werden, wenn zum einen der Ursprung von der Epidermis, insbesondere auch im Bereich des Mamillentrichters ausgeschlossen ist und zum anderen keine metastatische Infiltration in die Brustdrüse durch ein Plattenepithelkarzinom anderer Organlokalisation vorliegt. Die kausale und formale Pathogenese der primären Plattenepithelkarzinome der Brustdrüse ist unklar. Zum einen wird ein Ursprung von pluripotenten embryonalen Stammzellen diskutiert, wobei bedacht wird, daß die Brustdrüse entwicklungsgeschichtlich ein Hautanhangsgebilde darstellt. Zum anderen werden Plattenepithelmetaplasien als Vorstufe der Plattenepithelkarzinome diskutiert, wobei neben einer endokrinen Induktion auch länger bestehende Entzündungsreize eine Rolle spielen sollen. In den letzten Jahren wird immer häufiger darüber berichtet, daß oft Jahrzehnte nach Implantation von Silikonprothesen periprothetische Plattenepithelkarzinome entstehen, die wahrscheinlich über die Stufe einer Plattenepithelmetaplasie der entzündlichen Prothesenpseudokapsel entstehen. Die Abschätzung der Prognose und therapeutische Maßnahmen bei primären Plattenepithelkarzinomen der Brustdrüse sollten an den Erfahrungen mit Plattenepithelkarzinomen anderer Organlokalisation ausgerichtet werden.
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    Acta neuropathologica 96 (1998), S. 97-101 
    ISSN: 1432-0533
    Schlagwort(e): Key words Brittany Spaniel dog ; Immunocytochemistry ; Purkinje cell ; Spinocerebellar degeneration ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Eight Brittany Spaniel dogs, seven females and one male, between 7 and 14 years old presented with clinical neurological signs of spinocerebellar disease of about 6 months to 4 years duration. Clinically the dogs had a dramatic forward “saluting” movement of the thoracic limbs, hypermetria of the pelvic limbs, cerebellar ataxia and intention tremors. Terminally, dogs crawled in a crouched thoracic posture with neck extension. Lesions were confined to cerebellum, medulla oblongata and spinal cord. The most severe lesion was diffuse Purkinje cell loss with massive neurofilament accumulation in degenerating cells. There was some bilateral neuronal degeneration in the dorsal horns of the spinal cord and in the gracilis and cuneate nuclei. There was bilateral sporadic axonal degeneration in the dorsal columns and lateral and ventromedial areas of the spinal cord. The etiology of this syndrome was not determined.
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  • 44
    ISSN: 1432-0533
    Schlagwort(e): Key words Dentatorubral-pallidoluysian atrophy ; Nuclear inclusion ; Ubiquitin ; Immunohistochemistry ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We examined the brains and spinal cords of seven patients with clinicopathologically and genetically confirmed hereditary dentatorubral-pallidoluysian atrophy (DRPLA) using an antibody against ubiquitin, and found small, round immunoreactive intranuclear inclusions in both neurons and glial cells in various brain regions. Ubiquitinated neuronal intranuclear inclusions (uNIIs) were consistently found in the striatum, the pontine nuclei, the inferior olivary complex, the cerebellar cortex and the dentate nucleus. Ubiquitinated glial intranuclear inclusions (uGIIs) were found less frequently than uNIIs. Most of the inclusion-bearing nuclei were of an astrocytic nature. Immunostaining with an antibody against DRPLA protein revealed similar immunoreactive neuronal and glial intranuclear inclusions, but in much smaller in numbers compared with uNIIs and uGIIs. Electron microscopy showed that such inclusions were composed of granular and filamentous structures. These findings strongly suggest that, in DRPLA, the occurrence of uNIIs and uGIIs is directly related to the causative gene abnormality (an expanded CAG repeat encoding polyglutamine), that neurons are affected much more widely than previously recognized and that glial cells are also involved in the disease process.
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  • 45
    ISSN: 1432-0533
    Schlagwort(e): Key words Congenital myopathy ; morphometry ; Ultrastructure ; Fetal myogenesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Centronuclear myopathy (CNM) is a congenital myopathy which manifests itself as a severe neonatal (also termed myotubular myopathy), early-onset, or adult form. The histological pattern of each is marked by a considerable number of nuclei of muscle fibers being internally placed. Owing to their remote resemblance to myotubes, and their expression of developmentally regulated proteins, most authors now favor the concept that myogenesis is arrested or delayed in this disease. We here present two muscle biopsy specimens of a patient with early-onset CNM, taken at the age of 5 months and 14 years, respectively. The first biopsy sample contained internally placed nuclei in 7% of the muscle fibers, abundant minute myotubes, and hypertrophic muscle fibers. The second biopsy sample showed internally placed nuclei in 40% of the muscle fibers, and hypotrophic fibers. We suggest that the histological findings in early-onset CNM are the result of a complex dynamic process, which includes a delay in maturation.
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  • 46
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 197 (1998), S. 135-141 
    ISSN: 1432-0568
    Schlagwort(e): Key words Interstitial cells of Cajal ; Ultrastructure ; Gap junction ; Intestine ; Motility
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Interstitial cells forming many large gap junctions in the region of the deep muscular plexus of the rat small intestine were studied by electron microscopy and by three-dimensional cell models reconstructed from serial ultrathin sections. Two different profiles of cells were observed. Cells of the first profile are characterized by an elongated cell shape and by less electron-dense cytoplasm, containing many mitochondria, well-developed Golgi apparatus and free ribosomes. They mainly connect with smooth muscle cells of the main circular layer. In a three-dimensional cell model, the total area of the gap junctions occupies 1.3% of the cell surface. Cells of the second profile are characterized by the frequent occurrence of slender cytoplasmic processes, higher electron-dense cytoplasm, containing mitochondria, Golgie apparatus and well-developed rough endoplasmic reticulum, and numerous caveolae on the cell membrane. In this cell model, gap junctions occupy 0.8% of the cell surface. The ratio of gap junctions with the same profile of cells to the total gap junction area is 37.7%, which is more than three times greater than the 9.9% in cells of the first profile. These cells were closely associated with nerve terminals. It is likely that these cells with different profiles constitute subtypes with each other and cooperate for regulation of intestinal motility via the transmission of nerve signals.
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  • 47
    ISSN: 1432-0568
    Schlagwort(e): Key words Adult-type Leydig cells ; Endothelium ; 3β-HSD ; Ultrastructure ; Differentiation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  In the biosynthesis of steroid hormones 3β-hydroxysteroid dehydrogenase (3β-HSD) is a key enzyme. The present report describes the subcellular localization of the enzyme in the fetal-type Leydig cells, the fibroblast-like precursors of adult-type Leydig cells and in endothelial cells of interstitial capillaries. Histochemical methods for light microscopy and ultracytochemical methods for electron microscopy were used on rat testes of postnatal day 15. 3β-HSD reactivity was located at subcellular levels by means of the ferricyanide method. A specific, distinct localization of reaction product in the form of copper ferrocyanide precipitates was observed on the membranes of the smooth endoplasmic reticulum not only in the fetal-type Leydig cells and the fibroblast-like precursors of adult-type Leydig cells, but also focally in the endothelial cells of interstitial blood capillaries. Topographically, the 3β-HSD-positive precursors were most often found in the outer layer of the boundary tissue and surrounding interstitial blood vessels. The capillaries with 3β-HSD-positive endothelial cells were usually located in the vicinity of 3β-HSD-positive Leydig cells. For the first time, 3β-HSD has been located at the subcellular level in precursors of adult-type Leydig cells and focally in capillary endothelial cells associated with them. Due to the close association between 3β-HSD-positive vascular endothelial cells and Leydig cells a paracrine relationship between the two cell types may be involved in the acute regulation of steroidogenesis by blood-borne luteinizing hormone.
    Materialart: Digitale Medien
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  • 48
    ISSN: 1432-069X
    Schlagwort(e): Key words Barrier function ; pH ; Stratum corneum ; Lamellar body ; Lipid content ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Epidermal permeability barrier homeostasis requires the postsecretory processing of polar lipid precursors into nonpolar lipid products within the stratum corneum (SC) interstices by a family of lipid hydrolases. A specific requirement for β-glucocerebrosidase (β-GlcCer’ase), which exhibits a distinct acidic pH optimum, is particularly well documented. Therefore, we sought to determine whether the recovery of the barrier after acute insults requires acidification of the SC. We examined permeability barrier recovery by assessing changes in transepidermal water loss (TEWL), SC membrane ultrastructure utilizing ruthenium tetroxide (RuO 4 ) postfixation, and β-GlcCer’ase activity by in situ zymography at an acidic vs neutral pH. Barrier recovery proceeded normally when acetone-treated skin was exposed to solutions buffered to an acidic pH. In contrast, the initiation of barrier recovery was slowed when treated skin was exposed to neutral or alkaline pH, regardless of buffer composition. In addition, enhancement of the alkaline buffer-induced delay in barrier recovery occurred with Ca 2+ and K + inclusion in the buffer. Moreover, the pH-dependent alteration in barrier recovery appeared to occur through a mechanism that was independent of Ca 2+ - or K + -controlled lamellar body secretion, since both the formation and secretion of lamellar bodies proceeded comparably at pH 5.5 and pH 7.4. In contrast, exposure to pH 7.4 (but not pH 5.5) resulted in both the persistence of immature, extracellular lamellar membrane structures, and a marked decrease in the in situ activity of β-GlcCer’ase. These results suggest first that an acidic extracellular pH is necessary for the initiation of barrier recovery, and second that the delay in barrier recovery is a consequence of inhibition of postsecretory lipid processing.
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  • 49
    ISSN: 1432-0533
    Schlagwort(e): Key words Aging ; Blood-brain barrier ; Horseradish peroxidase ; Senescence-accelerated mouse ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The ultrastructural features of microvessels showing increased permeability to intravenously injected horseradish peroxidase (HRP) were examined in the olfactory bulbs of senescence-accelerated prone mice (SAMP8), which showed age-related deficits in learning and memory, and senescence-accelerated resistant mice (SAMR1), which did not show the age-related deficits. HRP was visualized with tetramethyl benzidine (TMB) and diaminobenzidine (DAB) for light and electron microscopic examination, respectively. In the olfactory bulbs of 13-month-old SAMP8 mice, the staining reaction with TMB for HRP appeared in the neuropil of central area (granule cell layer and subependymal layer), in the pia mater and in the vascular wall. Some vessels located in the central area showed several changes observed at the ultrastructural level. The cytoplasm of the endothelial cells, especially in the arterioles, was segmentally thickened and contained numerous vesicles and vacuoles, some of which were HRP positive. The endothelial cell surface was occasionally undulated with microvillous protrusions. Membranous inclusions within the basal lamina, suggesting the cellular (presumably pericytal) degeneration, were frequently observed, especially in venules. The collagen deposits were occasionally observed in the subendothelial space of some vessels. Perivascular cells with vacuolated inclusions or lipid-like droplets were present around some vessels in the central area of the olfactory bulbs of aged SAMP8 mice. On the other hand, in the microvessels located in the areas negative for HRP-TMB reaction, except the vessel walls, the cytoplasm of the endothelial cells with smooth luminal surface was flattened and some vesicles located there contained HRP-DAB reaction product. Weak staining reaction with TMB for HRP appeared also in the central area of the olfactory bulbs of 3-month-old SAMP8 mice and 3- and 13-month-old SAMR1 mice. The cytoplasm of the endothelial cells in the olfactory bulbs of these mice was focally thickened and contained some cytoplasmic vesicles. Occasionally, the endothelial cell surface was moderately undulated with few microvillous protrusions. Membranous inclusions within the basal lamina were not observed in these animals. These findings indicate that the endothelial cells and pericytes in some vessels located in the central area of the olfactory bulb of aged SAMP8 mice, which show staining reaction with TMB for HRP, are ultrastructurally changed, suggesting their altered functions.
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  • 50
    ISSN: 1432-0533
    Schlagwort(e): Key words Anorexia nervosa ; Myopathy ; Muscle biopsy ; Ultrastructure ; Protein-energy malnutrition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Protein-energy malnutrition in anorexia nervosa is an under-recognised cause of muscle dysfunction. To characterise the skeletal myopathy that occurs in patients with severe anorexia nervosa, muscle function and structure were comprehensively examined in eight young adult female patients with severe (40%) self-induced weight loss. All of the patients showed impaired muscle function on strength and exercise measurement. The maximum voluntary contraction force for the patient group was significantly less than predicted values. Electromyography revealed myopathy in five of the patients, four of whom also had electro-physiological evidence of neuropathy. However, muscle biopsy specimens consistently showed myopathic changes with severe type 2 fibre atrophy but with no evidence of neuropathic changes. Ultrastructurally, there was separation and segmental loss of myofibrils and most biopsy samples contained abundant glycogen granules; we have previously reported that one of the most consistent biochemical abnormalities in these patients is impaired ischaemic lactate responses to forearm exercise. The result of severe protein-energy malnutrition on the musculo-skeletal system is a metabolic myopathy. Although the patients admitted to a variety of abnormal dieting behaviours, such as over-exercising and self-induced vomiting, no association was found between any of these and quantitative histological changes in the muscle biopsy samples. It is recommended that myopathy in anorexia nervosa be treated by instituting an appropriate refeeding programme.
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  • 51
    Digitale Medien
    Digitale Medien
    Springer
    Acta neuropathologica 95 (1998), S. 367-372 
    ISSN: 1432-0533
    Schlagwort(e): Key words Amyotrophic lateral sclerosis ; Heterotopic neuron ; Alpha motor neuron ; Immunocytochemistry ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract This report concerns a comparative immunocytochemical, ultrastructural and morphometric investigation on heterotopic neurons in the white matter of the spinal cords of 19 patients with amyotrophic lateral sclerosis (ALS) and 18 age-matched neurologically normal individuals. The study revealed that the heterotopic neurons were scattered in the white matter, often adjacent to gray matter, that they immunoreacted with the antibody to synaptophysin, and that there were synaptic apparatuses on the surface of their somata and their neuronal processes. Bunina bodies and ubiquitin-positive inclusions such as Lewy body-like inclusions and skein-like inclusions, characteristic of anterior horn neurons of ALS, were present in the cytoplasm of the patients’ heterotopic neurons in the anterior or lateral column of the white matter. These findings suggest that heterotopic neurons in the anterior or lateral column have the characteristics of alpha motor neurons. The average number of heterotopic neurons observed in ALS patients was generally less than in normal subjects. This reduction was correlated with the severity of neuronal loss. The heterotopic neurons in ALS were less susceptible to the degenerative process as compared with spinal cord anterior horn cells. We assume that in this disease the heterotopic neurons may be degenerated and their number diminished after or concomitantly with the depletion of anterior horn neurons.
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  • 52
    ISSN: 1432-0533
    Schlagwort(e): Key words Congenital myopathy ; Muscle fibers ; Ultrastructure ; Myofibrillar disarray
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract A 44-year-old man presenting with dyspnoic attacks was found to be affected with congenital myopathy, rigid spine, restrictive respiratory insufficiency and cardiomyopathy. Muscle biopsy showed type 1 fiber predominance (65.7%) and hypotrophy, and characteristic changes in 43.9% of the type 1 fibers, consisting in alternating pale and dark staining on alkaline ATPase reacted sections in a mosaic pattern. Ultrastructural examination demonstrated bands of myofibrils at right angles or skew to the remaining myofibrils transversing the fibers. Myofibrillar disarray was always associated with loss of the Z-discs and actin filaments, and often with aggregation of mitochondria. The muscle biopsy findings in this patient suggest a new entity of congenital myopathy with clinical features of rigid spine, cardiomyopathy and restrictive respiratory insufficiency, characterized by peculiar abnormalities of ATPase staining in a mosaic pattern and, ultrastructurally, by zones of disorientation of the sarcomeres.
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  • 53
    Digitale Medien
    Digitale Medien
    Springer
    Zeitschrift für Lebensmittel-Untersuchung und -Forschung 206 (1998), S. 38-43 
    ISSN: 1431-4630
    Schlagwort(e): Key words Starch ; Gels ; Kamaboko ; Surimi ; Gelatinization ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract  The purpose of this work was to study the changes undergone by starch during heat-induced surimi gel preparation either with or without added egg white, and their effects on the structure of gels using light and scanning electron microscopy. Gels were made from SA-grade Alaska pollack (Theragra chalcogramma) surimi with: (1) salt (3%, w/w); (2) salt and waxy corn starch (3% and 5%, respectively w/w); or (3) salt, waxy corn starch and egg white (3%, 5% and 5%, respectively, w/w). Final moisture was adjusted to 73% or 83%. The gels were prepared by prior setting (40°C, 30 min, followed by 90°C, 30 min) or cooking (90°C, 30 min). The prepared gel was frozen and stored at –20°C (±1°C) until analysis. Samples were observed by light and scanning electron microscopy. The results show that the starch granules alter according to the processing conditions, with the predominance of crystalline or amorphous morphology depending upon the availability of heat and water. Large cavities formed in the protein gel matrix during setting can trap water; as a result, water availability is limited for starch to swell and gelatinize even in the high-moisture gel.
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  • 54
    Digitale Medien
    Digitale Medien
    Springer
    European radiology 8 (1998), S. 849-857 
    ISSN: 1432-1084
    Schlagwort(e): Key words: Ultrasound ; Physics ; Vascular studies ; Vascular pathologies ; Ultrasonic contrast agents ; Clinical applications
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. The choice of the optimal ultrasonic frequency for vascular studies is determined by the required resolution and penetration. Anatomical real-time two-dimensional imaging and blood flow studies provide complementary information. Intravascular scanning allows high-frequency ultrasound to be used, with correspondingly good spatial resolution. Contrast resolution is degraded by beam side lobes and the limited dynamic range of the ultrasonic pulse. The physics of ultrasonic scattering by blood, pulsed Doppler and duplex scanning and colour flow imaging performances determines the limits of clinical applications. Contrast agents enhance the echogenicity of blood, improving sensitivity and, through second harmonic detection, suppressing solid tissue echoes. Three-dimensional display, with segmentation by the presence of the flow signal, facilitates spatial perception. Clinical applications in vascular pathologies are summarised.
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  • 55
    ISSN: 1432-072X
    Schlagwort(e): Key words Magnetic bacteria ; Biomineralization ; Magnetite ; 16S rRNA ; In situ hybridization ; Ultrastructure ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Natural enrichments of magnetic bacteria from the Itaipu lagoon near Rio de Janeiro were dominated by coccoid-to-ovoid morphotypes that produced unusually large magnetosomes. To determine the phylogenetic position of these unusual microorganisms, 16S rRNA genes were retrieved from bacteria magnetically separated from sediment of the Itaipu lagoon by in vitro amplification and cloning of PCR products into a plasmid vector. Partial sequencing of the obtained clones revealed two clusters of closely related sequences affiliated to a distinct lineage consisting exclusively of magnetic bacteria within the α-subclass of Proteobacteria. For a detailed phylogenetic analysis, several almost complete sequences of the 16S rRNA genes were determined. One representative clone of each cluster provided a PCR template for the in vitro transcription of group-specific polynucleotide probes complementary to a variable region of the 16S rRNA molecule. At least three different morphotypes of magnetic bacteria were reliably identified by post-embedding hybridization of ultra-thin sections. Electron microscopic analyses of hybridized cells enabled for the first time a detailed description of the morphological variety and ultrastructure of phylogenetically identified, uncultured magnetic bacteria. Two distinct coccoid bacteria were identified by the transcript probe complementary to the 16S rRNA sequence mabrj12, whereas the probe complementary to the sequence mabrj58 allowed the identification of an ovoid morphotype that displayed magnetosomes with the largest volumes observed to date.
    Materialart: Digitale Medien
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  • 56
    Digitale Medien
    Digitale Medien
    Springer
    Protoplasma 201 (1998), S. 101-109 
    ISSN: 1615-6102
    Schlagwort(e): Kinetochore ; Kinetoplastida ; Intranuclear microtubules ; Mitosis ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The three-dimensional ultrastructural organization of the mitotic apparatus ofDimastigella mimosa was studied by computer-aided, serial-section reconstruction. The nuclear envelope remains intact during nuclear division. During mitosis, chromosomes do not condense, whereas intranuclear microtubules are found in close association with six pairs of kinetochores. No discrete microtubule-organizing centers, except kinetochore pairs, could be found within the nucleus. The intranuclear microtubules form six separate bundles oriented at different angles to each other. Each bundle contains up to 8 tightly packed microtubules which push the daughter kinetochores apart. At late anaphase only, midzones of these bundles align along an extended interzonal spindle within the narrow isthmus between segregating progeny nuclei. The nuclear division inD. mimosa can be described as closed intranuclear mitosis with acentric and separate microtubular bundles and weakly condensed chromosomes.
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  • 57
    ISSN: 1615-6102
    Schlagwort(e): Spore balls ; Germ areas ; Ultrastructure ; Phylogeny
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Special features of teliospores in smut fungi are described, including teliospore connections, appendages, and germ pores. Balls of teliospores in species of many different genera cohere by remnants of hyphal walls, sheaths, and sometimes interlocking ornamentation. Teliospores are connected in pairs in species ofMycosyrinx andGeminago by special local structures. Appendages can be formed locally by persistent material from the sheath (Cintractia, Anthracoidea, Sphacelotheca), thickened parts of the spore wall (e.g.,Georgefischeria, Jamesdicksonia, Rhamphospora, Tolyposporella), or persistent walls of sporogenous hyphae (Rhamphospora, genera of the Tilletia relationship). Species ofGeorgefischeria, Jamesdicksonia, andTolyposporella have teliospore walls composed of more than three layers of different electron density. “Germ areas” corresponding to thinner parts of the spore wall are known, e.g., for species ofAnthracoidea, Cintractia, andUstilago infecting members of the family Poaceae, while distinct germ pores, one per teliospore, are found in some species ofThecaphora, “Tolyposporium”, andSporisorium. Teliospores ofMycosyrinx cissi have a germination ring. Characteristics of teliospores are used to discuss the phylogeny of smut fungi. A phylogenetic tree in accordance with teliospore characteristics is compared to those obtained from ultrastructural characteristics of host-parasite interaction, of septal pores, and from sequence data. Aspects of teliospore development help to define taxa at a high systematic level (Entorrhizales, Ustilaginales, Tilletiales/Entylomatales, Microbotryaceae), while details of ornamentation ontogeny delimit groups of genera (e.g., genera related toUstilago on members of the Poaceae andSporisorium, Cintractia andAnthracoidea, Tilletia) or single genera (e.g.,Melanopsichium, Dermatosorus, Mycosyrinx, Doassinga, Rhamphospora). Types of ornamentation (warty, reticulate), middle layers, teliospore balls, and germ pores evolved repeatedly by convergence. The smut teliospore itself probably evolved independently at least twice, or perhaps three (or more) times, in the Microbotryales, in the Entorrhizales, and in a common ancestor of the remainder of the Ustilaginomycetes.
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  • 58
    Digitale Medien
    Digitale Medien
    Springer
    Protoplasma 204 (1998), S. 155-169 
    ISSN: 1615-6102
    Schlagwort(e): Spores ; Ultrastructure ; Entorrhiza ; Microbotryum ; Tilletia ; Ustilago
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The concept and nomenclature for the elements of teliospore walls in smut fungi are presented and a survey of teliosporogenesis is given, as seen by light and transmission electron microscopy. Four developmental types are distinguished: the Ustilago, Microbotryum, Tilletia, and Entorrhiza type. In the Ustilago type, sporogenous hyphae are completely segmented into teliospore initials which are embedded in a hyaline matrix formed by gelatinised hyphal walls (found in species ofAnthracoidea, Cintractia, Heterotolyposporium, Kuntzeomyces, Macalpinomyces, Melanopsichium, Sporisorium, Testicularia, Tolyposporium junci, Trichocintractia, and species ofUstilago infecting members of the family Poaceae). In the Microbotryum type, septate sporogenous hyphae are also completely segmented into teliospore initials, however, they are not surrounded by a hyaline matrix (Microbotryum, Sphacelotheca, Ustilago spp. infecting dicotyledons). A yeast-like budding of teliosporogenic cells is observed for some species ofMicrobotryum, Sphacelotheca, andUstilago infecting dicotyledons. In the Tilletia type, teliospores differentiate locally in the sporogenous hyphae, in an apical or intercalary position, without a hyaline matrix (Conidiosporomyces, Doassinga, Entyloma, Erratomyces, Ingoldiomyces, Neovossia, Oberwinkleria, Rhamphospora, Tilletia). In all these types, the teliospore initials first develop a hyaline sheath under which the ornamentation, the exosporium, sometimes a middle layer, and the endosporium are successively deposited by the fungal cell. In the Entorrhiza type, the teliospores develop inside vital host cells with the wall of the sporogenous hypha included into the teliospore wall. The fungus develops a middle layer and an electron-transparent endosporium inside the hyphal wall while a layer forming the ornamentation is deposited onto the hyphal wall, probably by vesicles of dictyosomes of the host cell.
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  • 59
    ISSN: 1615-6102
    Schlagwort(e): Neck cell proliferation ; Binucleate ; Douglas fir ; Conifers ; Genetic instability ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary To study the effect of culturing on megagametophytes of Douglas fir (Pseudotsuga menziesii) and hybrid larch (Larix × eurolepis), cones were collected at the time of fertilization and the megagametophytes were removed, then placed on medium. We used a modified Murashige and Skoog medium supplemented with 5% lactose and 10% polyethylene glycol 4000. A variety of cell types proliferated including prothallial, neck, and jacket cells. Some of these multiplying cells showed a binucleate condition. The prothallial cells of the apex divided and expanded. The neck cells formed clusters composed of more cells than normally found in situ; though otherwise they showed ultrastructural similarity to neck cells in situ. These neck cells had large numbers of active Golgi complexes, numerous large and small vacuoles, coated vesicles, smooth vesicles, a well-developed endoplasmic reticulum, and thickened cell walls. These are the first reports of neck cell multiplication and induction of a binucleate state for gymnosperm megagametophyte cells in vitro.
    Materialart: Digitale Medien
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  • 60
    ISSN: 1860-1499
    Schlagwort(e): Restitution ; Ultrastructure ; Cell migration ; Colon ; Saponin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The superficial colonic epithelia of rats were exposed to 1.0% saponin solution for 3 min and fixed at various periods thereafter. The repair or restitution process was observed by light as well as by transmission and scanning electron microscopy. The exposure of the luminal surface to saponin resulted in uniform and extensive damage to the superficial epithelial cells without affecting the cells in the crypts. At 3 min after saponin treatment, the damaged epithelial cells exfoliated from the mucosa and the basal lamina was exposed. Within 15 min, most of the exposed basal lamina was covered by squamous to low-cuboidal epithelial cells, probably migrating from the crypts. These epithelial cells extended large lamellipodia over the denuded basal lamina. After 15 min the damaged surface was completely covered with epithelial cells, which became columnar at 1 h. Tight junction protein ZO-1 became positive along the restituted epithelium. Proliferating-cell nuclear antigen (PCNA) staining showed that proliferation of epithelial cells occurred after the restitution. These results suggest that saponin treatment serves as a good model system to study colonic restitution, which is carried out by rapid migration from the remaining crypt cells, followed by cellular proliferation. Rapid formation of tight junctions spanning the damaged regions allows rapid restoration of the barrier function of the colonic epithelium.
    Materialart: Digitale Medien
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  • 61
    ISSN: 1860-1499
    Schlagwort(e): Pancreas ; Peripheral nerve ; Cancer ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Nerve invasion is one of the biological features of pancreatic cancer, and its mechanism remains to be determined. In this paper, we report on 37 pancreatic cancer specimens observed by immunohistochemical and electron microscopical techniques. The results showed that pancreatic cancer directly invaded and destroyed the perineurium. At the early stage of disease, the peripheral nerve and synaptic membrane were easily destroyed by cancer cells, and invasion and metastasis continuously advanced along the perineural space and central side of nerves. These results suggest that the soft tissue and nerve plexus on the dorsal region of the pancreas may contribute to the recurrence of pancreatic cancer after duodenopancreatectomy.
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  • 62
    ISSN: 1860-1499
    Schlagwort(e): Solitary fibrous tumor of the pleura ; Mesenchymal cell ; Immunohistochemistry ; CD 34 ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract A solitary fibrous tumor of the pleura (SFTP) in a 37-year-old woman was reported as a rare pleural tumor based on morphological, immunohistochemical, and electron microscopic studies. The results showed that the tumor was composed of spindle-shaped cells forming fascicular and interlacing patterns with a mixture of mature collagen. The tumor cells coexpressed vimentin and CD34 and lacked cytokeratin reactivity. Ultrastructurally, there were abundant collagenous fibrillae surrounding spindle-shaped cells in which the junctional complex, basement membrane-like structure, and microvilli were not seen. From literature review and observation of the morphological features around the tumor, we consider that the tumor originated from the stromal cells subjacent to the mesothelium.
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  • 63
    Digitale Medien
    Digitale Medien
    Springer
    Medical molecular morphology 31 (1998), S. 151-155 
    ISSN: 1860-1499
    Schlagwort(e): Serous adenocarcinoma ; Peritoneal neoplasm ; Immunohistochemistry ; Ultrastructure ; Case report
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Two cases of serous surface carcinoma of the peritoneum (SSCP) are discussed. The first patient was a 48-year-old Japanese woman with abdominal pain and fullness. The second patient was a 66-year-old Japanese woman with abdominal fullness. In both patients, laparotomy revealed many tumor nodules on the peritoneal surface. However, the ovaries, the uterus, and other intraperitoneal organs were free from tumors. The serum levels of CA125 were excessively elevated. The tumor cells were arranged in a papillotubular pattern. Mitoses were frequent. Diastaseresistant PAS-positive, and hyaluronidase-resistant alcian blue-positive materials were observed. In immunohistochemistry, the tumor cells showed positive reactions for cytokeratin, EMA, CA125, and HBME-1, and, in contrast, negative reactions for CEA, thrombomodulin, vimentin, and HHF35. In analysis for Ber-EP4, all tumor cells of case 1 were negative, and a few tumor cells of case 2 were positive. Ultrastructurally, hobnail-shaped tumor cells rested on a continuous basal lamina. Each cell was attached to short desmosomes. Microvilli were slender, straight, and short, and some had core rootlets. Many primary lysosomes were aggregated in the basal portion of the cytoplasm. A few well-differentiated ciliated cells were present. These two cases were diagnosed as SSCP.
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  • 64
    Digitale Medien
    Digitale Medien
    Springer
    Medical molecular morphology 31 (1998), S. 185-192 
    ISSN: 1860-1499
    Schlagwort(e): Rat fetal heart ; Capillary angiogenesis M ; Myocardial cleft ; Fibroblast ; Desmosome-like structure ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract To determine the course of capillary angiogenesis in the rat fetal heart, transmission electron microscopy was used to examine the development of both capillaries and cardiomyocytes. In the 15-day-old embryo, the coronary vessels had spread into the superficial space. In the 16-day-old embryo, the coronary vessels began to enter the myocardium. In the 17-day-old embryo, the terminal vascular bed had developed and a marked increase in the population of myocytes was evident. In capillaries entering the myocardium, the outgrowth of endothelial cells into the myocardial cleft was evident. These clefts were formed by intercalated disk and desmosome-like structures. The fibroblasts were always found close to the capillaries or in contact with endothelial cells during the fetal stage to the first neonatal week. In the interstition period, the fibroblasts were not found close to the capillaries. These results are discussed in relation to the role of myocardial clefts and the role of fibroblasts in fetal capillary angiogenesis.
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  • 65
    ISSN: 1860-1499
    Schlagwort(e): Malignant myoepithelioma ; Oral palate ; Immunohistochemistry ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Malignant myoepithelioma arising in the palatal gland is extremely rare. The present study demonstrated ultrastructural and immunohistochemical features of malignant myoepithelioma transformed from long-standing benign myoepithelioma occurring in the palatal gland. Microscopically, the tumor mass was composed of plasmacytoid cells and epitheloid cells. The malignant feature was seen only at the area adjacent to the bone. Immunohistochemically, most of the cells were S-100 positive, whereas vimentin and keratin were only partially positive. Glial fibrillary acid protein (GFAP) was positive at the peripheral cells of the solid nests and epitheloid cells with myxoid stroma. Ultrastructurally, filament-rich cells, tonofilament-rich cells, and filament-poor cells were observed. At the area adjacent to the bone, the cells implying malignancy were filament-poor cells in which the luminal structures could be detected. From these findings, a scarcity of filaments in myoepitheliomatous components may imply a malignancy.
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    Springer
    Plant systematics and evolution 210 (1998), S. 25-39 
    ISSN: 1615-6110
    Schlagwort(e): Cyanophyta ; Cyanobacteria ; Cyanothece ; Synechococcus ; Cyanobium ; Ultrastructure ; nucleoids ; taxonomy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The fine structure of the type species of the genusCyanothece Komárek 1976,C. aeruginosa, is described and compared with the main cytological characteristics of morphologically related members of the generaCyanobium, Cyanobacterium andSynechococcus. Several morphological features, such as cell walls with thick outer layers containing a special type of vesicles, position of thylakoids, “keritomy” (net-like appearance of protoplast caused by arrangement of thylakoids, net-like nucleoids and/or by tendency to form intrathylakoidal spaces) and a special structure of mucilaginous envelopes were found to be characteristic of this genus, supporting its separate position among coccal cyanoprokaryotes (cyanobacteria, cyanophytes). The taxonomic significance of ultrastructural features in all mentioned genera is discussed.
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  • 67
    Digitale Medien
    Digitale Medien
    Springer
    Protoplasma 201 (1998), S. 30-37 
    ISSN: 1615-6102
    Schlagwort(e): Cell-to-cell communication ; Plasmodesmata ; Ultrastructure ; Wounding ; 2-Deoxy-D-glucose
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The transport of ions and metabolites through plasmodesmata has been thought to be controlled at the neck region where the cytoplasmic annulus is constricted and where callose has also been localised. In order to determine the possible structural and functional effects of callose, its deposition was inhibited through incubation of the plant tissue with 2-deoxy-D-glucose (DDG) for 1 h prior to fixation in 2.5% glutaraldehyde. The inhibition of callose formation was monitored through aniline blue-induced fluorescence of callose. The neck region of the plasmodesmata fromAllium cepa L. roots treated with DDG exhibited a funnel-shaped configuration. This is in contrast to the plasmodesmata from tissue not incubated with DDG, which exhibited constricted necks similar to those previously reported. Both initial dissection and glutaraldehyde fixation induced neck constriction in plasmodesmata, however, dissection of tissue increased the frequency of constrictions. The inhibition of callose formation by chemical means showed that the neck constrictions and raised collars in this area are artefacts due to physical wounding and glutaraldehyde fixation. The external electron-dense material observed when tannic acid is included in the primary fixative appears to be unrelated to the deposition of callose at the neck region.
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  • 68
    Digitale Medien
    Digitale Medien
    Springer
    Protoplasma 202 (1998), S. 23-37 
    ISSN: 1615-6102
    Schlagwort(e): Chloroplast development ; Cotton ; Fluorescence induction kinetics ; Ultrastructure ; Immunocytochemistry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Many of the studies of chloroplast ontogeny in higher plants have utilized suboptimal conditions of light and growth to assess development. In this study, we utilized structural, immunological, and physiological techniques to examine the development of the chloroplast in fieldgrown cotton (Gossypium hirsutum cv. “MD 51 ne”). Our youngest leaf sample developmentally was completely folded upon itself and about 0.5 cm in length; leaves of this same plastochron were followed for three weeks to the fully expanded leaf. The chloroplasts at the earliest stage monitored had almost all of the lamellae in small, relatively electron-opaque grana, with relatively few thylakoids which were not appressed on at least one surface. During the development of the thylakoids, the membranes increase in complexity, with considerable stroma lamellae development and an increase in the number of thylakoids per granum. Besides the increase in complexity, both the size and numbers of the chloroplast increase during the development of the leaf. Developmental changes in six thylakoid proteins, five stromal proteins, and one peroxisomal protein were monitored by quantitative immunocytochemistry. Even at the earliest stages of development, the plastids are equipped with the proteins required to carry out both light and dark reactions of photosynthesis. Several of the proteins follow three phases of accumulation: a relatively high density at early stages, a linear increase to keep step with chloroplast growth, and a final accumulation in the mature chloroplast. Photosystem-II(PS II)-related proteins are present at their highest densities early in development, with an accumulation of other parts of the photosynthetic apparatus at a latter stage. The early accumulation of PS-II-related proteins correlates with the much lower ratio of chlorophylla tob in the younger leaves and with the changes in fluorescence transients. These data indicate that some of the conclusions on chloroplast development based upon studies of intercalary meristems of monocots or the greening of etiolated plants may not be adequate to explain development of chloroplasts in leaves from apical meristems grown under natural conditions.
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  • 69
    Digitale Medien
    Digitale Medien
    Springer
    Cell & tissue research 291 (1998), S. 549-559 
    ISSN: 1432-0878
    Schlagwort(e): Key words Endolymphatic sac ; Ultrastructure ; Fluid transport ; Otoconia ; Newt ; Cynops pyrrhogaster (Urodela)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The ultrastructure of the endolymphatic sac (ES) of the late stage larva of the Japanese red-bellied newt, Cynops pyrrhogaster (stage 57), was examined by light and transmission electron microscopy. The two endolymphatic sacs are located at the dorsal-medial side of the otic vesicle on the dorsal-lateral side of the midbrain in the cranial cavity. The wall of the sac is composed of a layer of cubical epithelial cells with loose, interposed intercellular spaces. The sac contains a large luminal cavity, in which endolymph and numerous otoconia are present. The epithelial cells of different portions of the sac have a similar structure. These cells contain an abundance of cytoplasmic organelles, including ribosomes, Golgi complexes, and numerous vesicles. Two types of vesicles are found in the epithelial cells: the “floccular” vesicle and the “granular” vesicle. The floccular vesicles are located in the supra- and lateral-nuclear cytoplasm and contain flocccular material. The granular vesicles have a fine granular substance and are usually situated apposed to the apical cell membrane. The granular vesicles are suggested to be secreted into the lumen, while the floccular vesicles are thought to be absorbed from the lumen and conveyed to the intercellular spaces by the epithelial cells. The apical surfaces of the epithelial cells bear numerous microvilli. Apparently floating cells, which bear long microvilli on the free surfaces, are observed in the lumen of the ES. Based on the fine structure, the function of the endolymphatic sac of the newt Cynops pyrrhogaster is discussed.
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  • 70
    Digitale Medien
    Digitale Medien
    Springer
    Cell & tissue research 293 (1998), S. 165-171 
    ISSN: 1432-0878
    Schlagwort(e): Key words Muscle injury ; Cytoskeleton ; Sarcomere organisation ; Immunohistochemistry ; Ultrastructure ; Rabbit (New Zealand White)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Immunohistochemical and electron-microscopic techniques were used to analyze the extensor digitorum longus muscles of New Zealand White rabbits 1 h, 1 day, 3, 7, and 28 days after repetitive eccentric contractions. Loss of the cytoskeletal protein desmin was the earliest manifestation of injury. Apart from 1 h post-exercise, all desmin-negative fibers stained positively with antibody to plasma fibronectin, indicating loss of cellular integrity accompanying cytoskeletal disruption. Fiber sizes were significantly increased from 1–7 days after exercise. The large (hyaline) fibers found in histological sections after repetitive eccentric contractions resulted from segmental hypercontraction of the fiber. This phenomenon occurred proximally and distally to plasma membrane lesions of the muscle fiber and necrosis and manifested itself as very short sarcomere lengths. Thus, in serial sections, staining characteristics, sizes and shapes of one and the same fiber often varied dramatically. We conclude that the following sequence of events occurs: cytoskeletal disruptions, loss of myofibrillar registry, i.e., Z-disk streaming and A-band disorganization, and loss of cell integrity as manifested by intracellular plasma fibronectin stain, hypercontracted regions, and invasion of cells. When a fiber is disrupted, the remaining intact fibers apparently take up the tension put on the muscle and later fewer fibers are subjected to eccentric contractions.
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  • 71
    Digitale Medien
    Digitale Medien
    Springer
    Cell & tissue research 293 (1998), S. 253-269 
    ISSN: 1432-0878
    Schlagwort(e): Key words Septate junctions ; Ultrastructure ; Permeability ; Ions ; Epithelium ; Photoreceptor ; Hirudo medicinalis (Hirudinea)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The leech photoreceptor forms a unicellular epithelium: every cell surrounds an extracellular “vacuole” that is connected to the remaining extracellular space via narrow clefts containing pleated septate junctions. We analyzed the complete structural layout of all septa within the junctional complex in elastic brightfield stereo electron micrographs of semithin serial sections from photoreceptors infiltrated with colloidal lanthanum. The septa form tortuous interseptal corridors that are spatially continuous, and open ended basally and apically. Individual septa seem to be impermeable to lanthanum; interseptal corridors form the only diffusional pathway for this ion. The junctions form no diffusion barrier for the electron-dense tracer Ba2+, but they hinder the diffusion of various hydrophilic fluorescent dyes as demonstrated by confocal laser scanning microscopy (CLSM) of live cells. Even those dyes that penetrate gap junctions do not diffuse beyond the septate junctions. The aqueous diffusion pathway within the septal corridors is, therefore, less permeable than the gap-junctional pore. Our morphological results combined with published electrophysiological data suggest that the septa themselves are not completely tight for small physiologically relevant ions. We also examined, by CLSM, whether the septate junctions create a permeability barrier for the lateral diffusion of fluorescent lipophilic dyes incorporated into the peripheral membrane domain. AFC16, claimed to remain in the outer membrane leaflet, does not diffuse beyond the junctional region, whereas DiIC16, claimed to flip-flop, does. Thus, pleated septate junctions, like vertebrate tight junctions, contribute to the maintenance of cell polarity.
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  • 72
    ISSN: 1432-0878
    Schlagwort(e): Key words Angiogenesis ; Capillary growth ; Prazosin ; Shear stress ; Skeletal muscle ; Ultrastructure ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  Chronic vasodilatation represents a stimulus for capillary growth associated with increased luminal shear stress. We have examined the ultrastructure of more than 2000 capillaries to establish whether the sequence of angiogenesis in response to this stimulus is similar to that described during development and under pathological circumstances. Administration of the α1-blocker prazosin to rats for 2 weeks led to a greater capillary length density in extensor hallucis proprius muscles without any change in capillary tortuosity: J v(c,f)=262±54 compared with 350±17 mm–2, control compared with prazosin (P〈0.002). There were obvious signs of endothelial cell (EC) activation after prazosin treatment, including an increased proportion of capillaries with rough endoplasmic reticulum, large cytoplasmic vacuoles, thickened endothelium and an irregular luminal surface. Capillaries from control muscles had a maximum of three ECs in cross section, whereas four ECs were noted in 0.8+0.5% of capillaries after 1 week (n.s.) and 2.5±0.9% after 2 weeks (P〈0.01) of treatment. This could be due to elongation and/or migration of ECs, as cell proliferation has not been described at these time points. There was also an increase in the proportion of capillaries having a narrow, slit-like lumen (1.7±0.8% of controls; 7.1±1.9% at 1 week; 8.8±2.5% at 2 weeks; P〈0.02), some of which were smaller in size (less than 2 μm diameter) than in controls (3–5 μm) and/or “seamless”, i.e. lacking EC junctions. These may represent newly formed vessels. Focal discontinuity of the basement membrane and abluminal EC processes were rarely seen, and capillary growth by abluminal sprouting appeared to be very infrequent (less than 0.001% of profiles). Of more importance was growth starting from the luminal side. Significantly more thin cytoplasmic processes were observed protruding into the lumen of capillaries after 1 week (47.5±6.2%, P〈0.001) and 2 weeks of prazosin (34.2±5.5%, P〈0.05) than in control vessels (16.7±3.9%). Some of these traversed the entire lumen and connected with endothelium of the opposite side, probably involving membrane fusion, resulting in the appearance of a double lumen. Individual capillaries with a complete double lumen were observed after 2 weeks’ prazosin but comparatively rarely, in only four out of six muscles. These findings indicate a pattern of luminal growth which is completely different from intussusceptive growth previously described during development, and from the abluminal capillary sprouting seen under pathological circumstances.
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  • 73
    Digitale Medien
    Digitale Medien
    Springer
    Cell & tissue research 292 (1998), S. 275-282 
    ISSN: 1432-0878
    Schlagwort(e): Key words Interstitial cells (Cajal) ; Large intestine ; Fluorescent dyes ; Vital staining ; Ultrastructure ; Mouse (BALB/c)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  Interstitial cells of Cajal (ICCs) are believed to be a major element in generating the spontaneous rhythm of the gastrointestinal tract. A prominent problem in the study of these cells has been the difficulty in observing them in intact tissues. We used the lipophilic dye DiI to stain ICCs in the submucosal-circular muscle border of freshly dissected mouse colon. The placement of small DiI crystals in this area resulted in the labeling of ICC-like cells. Two main morphological cell types, viz., bipolar and multipolar, were noted. Bipolar cells had two primary processes emerging from the poles of an elongated soma. The mean length of these processes was 78.7 μm. These cells constituted 42.3% of the sample (n=105). Multipolar cells (54.3% of total) had a less elongated soma and extended 3–6 main processes whose mean length was 56.3 μm. These processes showed no preferred direction. The length of the primary processes of bipolar cells was 40% greater than that of multipolar cells (P〈0.02). Three cells (2.9%) had only one primary process. The DiI stain could be converted into a stable electron-opaque product. Electron-microscopic observations showed that these cells had the typical appearance of ICCs reported in previous studies. This staining method should be useful for physiological investigations of ICCs in gastrointestinal tissues.
    Materialart: Digitale Medien
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  • 74
    ISSN: 1615-6102
    Schlagwort(e): Spores ; Ultrastructure ; Microbotryum ; Tilletia ; Tolyposporium ; Ustilago
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The walls of mature teliospores and the development of ornamentation, as seen by transmission electron microscopy, are described for 37 genera of smut fungi, based on observations of ca. 120 species and on literature. Structural diversity of mature teliospore walls is due to differences in spore wall layers forming the spore wall (endosporium, middle layer, exosporium, ornamentation) and to different elements forming the ornamentation (exosporium, ornaments, sheath, hyphal wall, adjacent fungal cells, material of the host). During teliosporogenesis the outer layers are usually deposited first. At the beginning of the formation of the ornamentation the plasma membrane may be smooth or undulated carrying the developing ornaments on its tips or in its depressions. The ornamentation of some genera appears similar when seen by scanning electron microscopy, but can be the product of different developmental patterns (e.g., warts of species ofFarysia, Tilletia, andUstilago), however, warty and reticulate ornamentation can both be produced by similar developmental processes (shown, e.g., for species ofCintractia andTilletia). Typical structures of the mature teliospore wall and developmental patterns based on homologous similarities are described for the following groups of genera or species:Macalpinomyces, Melanopsichium, Sporisorium, andUstilago infecting members of the family Poaceae;Kuntzeomyces, Testicularia, andTrichocintractia; Anthracoidea, Cintractia, Heterotolyposporium piluliforme, andTolyposporium junci; Glomosporium, Sorosporium, andThecaphora; Conidiosporomyces, Erratomyces, Ingoldiomyces, Neovossia, Oberwinkleria, andTilletia; Entyloma, and genera of the Doassansia group;Liroa, Microbotryum, Sphacelotheca, Ustilago infecting dicotyledons, andZundeliomyces; Aurantiosporium, Fulvisporium, andUstilentyloma. Special characteristics of the teliospore wall were observed for the generaDermatosorus, Doassinga, Entorrhha, Farysia, Mycosyrinx, Rhamphospora, and some species ofTolyposporium.
    Materialart: Digitale Medien
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Cell & tissue research 294 (1998), S. 253-260 
    ISSN: 1432-0878
    Schlagwort(e): Key words P2X1 receptor ; Ultrastructure ; Cerebellum ; Rat (Wistar)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The distribution of the P2X1 subtype of purinoceptors associated with the extracellular activities of ATP was studied in the rat cerebellum at the electron-microscope level. Receptors were labelled with peroxidase-antiperoxidase and the avidin-biotin-peroxidase complex for immunocytochemistry. Immunoreactivity to P2X1 receptors was localized in subpopulations of synapses between varicosities of parallel fibres of granule cells and dendritic spines of Purkinje cells. Unlabelled varicosities of parallel fibres formed asymmetric synapses with labelled dendritic spines, whereas labelled varicosities of parallel fibres formed asymmetric synapses with unlabelled dendritic spines. P2X1 immunoreactivity was also localized in some astrocyte processes. The functional significance of these findings is discussed.
    Materialart: Digitale Medien
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  • 76
    Digitale Medien
    Digitale Medien
    Springer
    Cell & tissue research 294 (1998), S. 367-375 
    ISSN: 1432-0878
    Schlagwort(e): Key words Neurons ; Glia ; Tracheae ; Wing ; Ultrastructure ; Moth ; Manduca sp.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  This ultrastructural examination of sensory nerves of the Manduca wing has revealed that extensive remodeling occurs among insect sensory neurons and their associated glial cells between pupation and adult emergence. Systematic counts of axons in particular wing nerves throughout adult development have shown that a decrease in axon number per nerve occurs after day 6. The neurons and glial cells that die are believed to be cells present at pupation that have no apparent sensory function but that probably function as guidance scaffolding for neurons and glia that are born after pupation. Despite the loss of several axons from each wing nerve, these nerves continue to grow in diameter during the latter half of adult development as some of the surviving axons increase severalfold in diameter. Each growing wing nerve in turn apparently functions as a scaffold for the proximal to distal growth of adult tracheae. A correspondence exists between adult nerve pathways and adult tracheal pathways, with each trachea maintaining intimate contact with a wing nerve along its entire length.
    Materialart: Digitale Medien
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  • 77
    ISSN: 1432-0878
    Schlagwort(e): Key words Cutaneous scent glands ; Apocrine glands ; Myoepithelial cells ; Holocrine glands ; Ultrastructure ; Lectins ; Cytokeratins ; Impala ; Aepyceros melampus (Artiodactyla)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The cutaneous glands of the forehead and the metatarsus were studied by histological and histochemical methods and electron microscopy in adult male and female impalas in various seasons of the year. All glandular areas consist of apocrine and holocrine glands, which, however, occur in different proportions. Our findings in the apocrine gland cells suggest (1) the synthesis and exocytosis of a glycoproteinaceous secretory product stored in secretory granules, (2) typical apocrine secretion of the transformed apical cytoplasm, and (3) transepithelial fluid transport. The Golgi apparatus and apical membrane have binding sites for several lectins (PNA, HPA, RCA I, WGA). Cytokeratins 7, 14 and 19 are expressed at various intracellular localizations, suggesting an active role in the secretory mechanisms. The glands of the male forehead show marked seasonal changes in activity that are correlated with the main phases of the reproductive cycle, with the highest cellular activity occurring during the rut in April/May. The female forehead glands are only moderately developed and do not undergo seasonal changes. The metatarsal glands are of equal size in males and females and show no seasonal changes in activity. This study supports the hypothesis that (1) forehead glands in the male have a signaling role in the rut and (2) the metatarsal glands have a more general, probably social role maintaining and restoring contact between herd members.
    Materialart: Digitale Medien
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  • 78
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 919-930 
    ISSN: 0887-6266
    Schlagwort(e): α-relaxation ; cold crystallization ; poly(aryl-ether-ether-ketone) (PEEK) ; poly(ether-imide) (PEI) ; vitrification ; devitrification ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: We have established time-temperature transformation and continuous-heating transformation diagrams for poly(ether-ether-ketone) (PEEK) and PEEK/poly(ether-imide) (PEI) blends, in order to analyze the effects of relaxation control on crystallization. Similar diagrams are widely used in the field of thermosetting resins. Upon crystallization, the glass transition temperature (Tg) of PEEK and PEEK/PEI blends is found to increase significantly. In the case of PEEK, the shift of the α-relaxation is due to the progressive constraining of amorphous regions by nearby crystals. This phenomenon results in the isothermal vitrification of PEEK during its latest crystallization stages for crystallization temperatures near the initial Tg of PEEK. However, vitrification/devitrification effects are found to be of minor importance for anisothermal crystallization, above 0.1°C/min heating rate. In the case of PEEK/PEI blends, amorphous regions are progressively enriched in PEI upon PEEK crystallization. This promotes a shift of the α-relaxation of these regions to higher temperatures, with a consequent vitrification of the material when crystallized below the Tg of PEI. The data obtained for the blends in anisothermal regimes allow one to detect a region in the (temperature/heating rate) plane where crystallization proceeds in the continuously close proximity of the glass transition (dynamic vitrification). These experimental findings are in agreement with simple simulations based on a modified Avrami model coupled with the Fox equation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 919-930, 1998
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 79
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 977-982 
    ISSN: 0887-6266
    Schlagwort(e): compressed gases ; polymer ; plasticization ; high-pressure DSC ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A high-pressure differential scanning calorimetric technique is described for studying polymer plasticization by compressed gases at pressures to 100 atm. The in situ measurements avoid problems due to gas desorption encountered with conventional DSCs, thus providing an accurate way to determine the change in glass transition temperature, Tg, with pressure, p. The entire Tg-p curve can be established in less than 2 days. The glass transition was observed as a sharp step in the case of 100-200-μm thin samples, whereas thicker samples gave a broad transition; highly reproducible results were obtained for the thin samples. For PS-CO2, the measured Tgs under various pressures were found to be in good agreement with literature values. Results for the systems PS-HFC134a, PVC-CO2, and PC-CO2 are also reported. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 977-982, 1998
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 80
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1025-1035 
    ISSN: 0887-6266
    Schlagwort(e): polymer thin films ; thermosets ; microelectronics ; moisture ; physical aging ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: In polymers for microelectronics applications, moisture is known to have a deleterious effect upon device reliability. In this paper, the moisture transport behaviors of a newly developed family of all-aromatic and aromatic/aliphatic copolyester thermosetting films were described. The moisture uptake as a function of temperature, relative humidity, sample thickness, and processing conditions were presented via conjugate moisture sorption tests.1 It was found that the post curing near but below Tg resulted in an increase in both total moisture uptake and diffusion coefficient due to the effect of physical aging and the generation of sample defect volume. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1025-1035, 1998
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1061-1080 
    ISSN: 0887-6266
    Schlagwort(e): polymer blends ; dilatometry ; free volume ; specific volume ; excess volume ; compressibility ; thermal expansivity ; equation of state ; scaling parameters ; crystallinity ; glass transition ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Melt-miscible polymer blends of poly(ethylene oxide)/atactic poly(methyl methacrylate (PEO/a-PMMA)) were prepared by melt-mixing and characterized by pressure-volume-temperature (PVT) dilatometry in the pressure and temperature range of 0 to 200 MPa and 20 to 200°C, respectively. The PVT data were analyzed in terms of two equations of state (EOS). The empirical Tait EOS was applied in the glassy, semicrystalline, and equilibrium melt state, and the Simha-Somcynsky EOS theory was applied in the equilibrium melt and glassy state. The Simha-Somcynsky EOS theory contains a free volume function. The temperature, pressure, and composition dependence of the free volume fraction h calculated from the Simha-Somcynsky EOS theory was studied. As a function of blend composition we observe that the free volume fraction, thermal expansivity, and compressibility all deviate mainly positively from linearity while the specific volume deviates mainly negatively from linearity. These findings are reconciled with composition-dependent free volume parameters, the free volume and cell volume as well as with self- and cross-interaction parameters derived from the Simha-Somcynsky EOS theory as applied to polymer mixtures. Moreover, the pressure dependence of glass and melting transitions as well as crystallization kinetics have been investigated. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1061-1080, 1998
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
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  • 82
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1129-1139 
    ISSN: 0887-6266
    Schlagwort(e): polymer diffusion ; ambient temperature ; fluorescence ; latex films ; poly(butyl methacrylate) ; poly((acetoacetoxy)ethyl methacrylate-co-ethylhexyl methacrylate) ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polymer diffusion across interfaces at room temperature (21°C) was analyzed by direct nonradiative energy transfer (DET) in labeled latex films. Two modellatex polymers were examined: poly(butyl methacrylate) [PBMA, Mw = 3.5 × 104, Tg (dry) = 21°C] and a copolymer of 2-ethylhexyl methacrylate with 10 wt % (acetoacetoxy)-ethyl methacrylate [P(EHMA-co-AAEM), Mw = 4.8 × 104, Tg (dry) = -7°C]. Little energy transfer due to polymer diffusion was detected for the P(EHMA-co-AAEM) latex samples in the dispersed state or dried to solids content below ca. 90%, but above 90% solids, diffusion occurs among particles. For PBMA, diffusion occurs only after the film is dried (〉97% solids) and aged. In the dry PBMA films, it requires 4-5 days at 21°C to reach a significant extent of mixing (fm = 0.3-0.4). This corresponds to an estimated penetration depth dapp of 30-40 nm and a mean apparent diffusion coefficient (Dapp) of 5 × 10-4 nm2/s. The corresponding Dapp value for the dry P(EHMA-co-AAEM) sample is 5 × 10-2 nm2/s, and it takes about 25-40 min for this polymer to reach fm of 0.3-0.4 with dapp of 20-30 nm. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1129-1139, 1998
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 83
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1201-1209 
    ISSN: 0887-6266
    Schlagwort(e): polymer electrolytes ; NMR ; conductivity ; glasses ; Arrhenius and VTF dependences ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: We have studied the temperature variation of conductivity and 1H NMR linewidth of (PEG)xNH4ClO4 (x = 20, 30, 46, 100, 200, & 1000) polymer electrolyte systems. The temperature dependence of the conductivity shows two distinct behaviors, the low temperature VTF dependence crossing over to Arrhenius dependence at higher temperatures. The departure from the VTF behavior is found to be composition dependent. NMR spectra indicate the presence of large fractions of crystalline regions that start to melt around the crossover temperature. We understand the deviation from the VTF behavior as a consequence of this crystalline to elastomer transition. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1201-1209, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 84
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1227-1233 
    ISSN: 0887-6266
    Schlagwort(e): FTIR spectroscopy ; isotactic polystyrene ; crystallization process ; induction period ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The melt crystallization process of isotactic polystyrene (i-PS) was studied by means of in situ Fourier transform infrared (FTIR) spectroscopy, with a focus on the conformational changes during the induction period. The spectra obtained during the induction period suggested the occurrence of some ordered structure that is characterized by higher regularity and packing of the helical moieties than observed in the melt. This ordered structure was clearly different from the amorphous structure, and close to the crystal structure. The Avrami analysis indicated that the formation process of the ordered structure at the late stage of the induction period is similar to the growth process of the crystallites after the induction period. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1227-1233, 1998
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 85
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2327-2337 
    ISSN: 0887-6266
    Schlagwort(e): surface tension ; surface energy ; contact angle ; liquid crystalline polymers ; thermotropic polymers ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: We have determined the surface energies (γs) of two liquid crystalline polyesters (Vectra™ A-950 [Hoechst Celanese, NJ] and Xydar™ [Amoco, GA]) and one polyesteramide (Vectra™ B-950 [Hoechst Celanese, NJ]) using contact angle techniques at room temperature. These LCPs were dissolved in bis-trifluoromethyl phenol and spin coated upon glass slides to form thin films. The contact angle measurements were carried out employing a Ramé-Hart Contact Angle Goniometer (Ramé-Hart, NJ). Pure water, glycerol, formamide, and diiodomethane were chosen as the testing liquids. Various surface energy calculation models were utilized to analyze the surface energies of these LCP films. Experimental data suggest that surface energy values did match between two-liquid geometric and three-liquid acid-base approaches if the correct combinations of testing liquid were used. However, the three-liquid Lifshitz-van der Waals acid-base method is more suitable for the surface energy calculation of these three LCPs, and provides much more information (e.g., acidity and basity of LCP surfaces). The average surface energies of Vectra™ A-950, Vectra™ B-950, and Xydar™ are 41.0, 41.9, and 42.3 mJ/cm2, respectively. In addition, all these three LCPs should be classed as monopolar Lewis bases because their Lewis acid components, γ+, are negligible. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2327-2337, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 86
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2355-2369 
    ISSN: 0887-6266
    Schlagwort(e): fracture ; fatigue ; polyethylene ; molecular weight distribution ; short chain branch content ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Stepwise fatigue crack propagation in a range of polyethylene resins, some of which are candidates for use in pipes for natural gas distribution, was studied. Examination of the effect of molding conditions on fatigue crack propagation in a pipe resin indicated that fast cooling under pressure produced specimens with the same crack resistance as specimens taken from a pipe extruded from this resin. The mechanism of stepwise crack propagation in fatigue was the same as reported previously for creep loading. Observations of the region ahead of the arrested crack revealed a complex damage zone that consisted of a thick membrane at the crack tip followed by a main craze with subsidiary shear crazes that emerged from the crack tip at an angle to the main craze. The effects of molecular parameters, such as molecular weight, comonomer content, and branch distribution, on the kinetics of fatigue crack propagation were examined. Correlation of creep and fatigue crack resistance made it possible to relate fatigue fracture toughness to molecular parameters by invoking concepts of craze fibril stability developed for creep. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2355-2369, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 87
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2379-2391 
    ISSN: 0887-6266
    Schlagwort(e): block copolymer ; thermoplastic elastomer ; physical gel ; polymer micelle ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Thermoplastic elastomer gels (TPEGs) composed of a poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and a low-volatility, midblock-compatible mineral oil have been investigated at different oil concentrations to ascertain the effect of composition on TPEG morphology and mechanical properties. The impact of thermal processing is also examined by comparing gels thermally quenched to 0°C or slowly cooled to ambient temperature. Transmission electron micrographs reveal that gels with 70 to 90 wt % oil exhibit styrenic micelles measuring ca. 24 nm in diameter. Variation in composition or cooling rate does not have any perceivable effect on micelle size or shape, whereas the rate at which the gels are cooled influences the extent of microstructural order and the time to rupture (tR) at constant strain. Dynamic rheological testing confirms the presence of a physically crosslinked network at TPEG compositions ranging from 70 to 90 wt % oil, independent of cooling rate. Results presented here suggest that the dynamic elastic shear modulus (G′) scales as tαR where α varies from 0.41 to 0.59, depending on cooling rate. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2379-2391, 1998
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 88
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2423-2433 
    ISSN: 0887-6266
    Schlagwort(e): gelation theory ; nonlinear polymerization ; nonrandom crosslinking ; molecular weight distribution ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: On the basis of the first-order Markovian statistics, we propose a general matrix formula for the weight-average molecular weight of crosslinked polymer systems, explicitly given by M̄w = M̄w,0 + WX0 (I - X)-1 Sf. This equation is valid for both step and chain-growth polymerizations, including those in a nonequilibrium state irrespective of the reactor types used. In the context of the present theory, the onset of gelation is simply stated as a point at which the largest eigenvalue of the matrix X reaches unity (i.e., det(I - X) = 0). The present theory provides a unified point of view for various types of gelling systems. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2423-2433, 1998
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 89
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2461-2470 
    ISSN: 0887-6266
    Schlagwort(e): dielectric relaxation spectroscopy ; thermosets ; interpenetrating polymer networks ; curing reaction ; temperature-modulated differential scanning calorimetry ; glass transition ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Dielectric relaxation spectroscopy (3 kHz ≤ ƒ ≤ 3 MHz), differential scanning calorimetry, and temperature-modulated calorimetry have been performed during isothermal curing of an epoxy network (diglycidylether of bisphenol A crosslinked with diaminodiphenyl methane), and of two thermoplast modified epoxy resins (semi-interpenetrating polymer networks) consisting of the epoxy network component and different amounts (10 and 20 wt %) of a linear high Tg polymer (polysulfone or polyethersulfone). During reaction, the homogeneous-mixtures phase separate into an epoxy-rich and a linear polymer-rich phase with different mobilities of the electrical dipoles. The complex dielectric permittivity is composed of a contribution from the ionic dc-conductivity and a contribution from relaxations of the permanent electrical dipoles in the two phases. The decrease of the dc-conductivity in the initial stage of cure is related to the time for gelation or vitrification. The contribution of the dipole relaxations to the dielectric permittivity reflects an increase of the relaxation times with curing time for both phases. The time-dependent changes in the complex dielectric permittivity are described by a simple two-phase model based on two Havriliak-Negami functions combined with Vogel-Fulcher equations for the description of the curing-time dependence of the relaxation times. The increase of the relaxation times in the phases during isothermal curing is incorporated by time-dependent Vogel temperatures. The latter are related to the time evolution of the glass-transition temperatures in the two phases measured independently by calorimetry. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2461-2470, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 90
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2483-2492 
    ISSN: 0887-6266
    Schlagwort(e): low-density polyethylene ; surface modification of polymers ; scanning force microscopy ; self-assembled monolayer of thiols ; chemical force microscopy ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: In this article, we present the results of a study on the surface properties of chromic acid-oxidized low-density polyethylene (LDPE) by scanning force microscopy (SFM) and contact angle measurements. LDPE films were surface modified by a chromic acid treatment with subsequent annealing in argon and reconstruction in boiling water as described by Rasmussen, Stedronsky, and Whitesides [J. Am. Chem. Soc., 99, 4736 (1977)]. The LDPE oxidation in chromic acid was monitored in situ by contact mode SFM. Initially stacks of lamellae became exposed, and at later stages a granular morphology was observed. By tapping mode SFM, the sample roughness was shown to increase during the first 10 min of oxidation from initially ca. 20 nm to ca. 50 nm. Gold-coated SFM probes (tips) functionalized with self-assembled monolayers were used to determine the pull-off force characteristics in ethanol. Variations in the contact area between SFM tips and polymer surfaces that exposed sharp crystalline features were shown to obscure the results of pull-off force measurements. However, on annealed and subsequently reconstructed samples with lower roughness, the results of force measurements correlated well with the measured contact angles. Over the range of surface energies studied, the normalized pull-off force between carboxylic acid-modified tips and these smooth samples was shown to depend approximately linearly on the cosine of the contact angle. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2483-2492, 1998
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  • 91
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    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2499-2511 
    ISSN: 0887-6266
    Schlagwort(e): heat capacity ; poly(trimethylene terephthalate) ; entropy ; enthalpy ; free enthalpy ; heats of transition ; glass transition ; melting ; crystallinity ; rigid-amorphous fraction ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The heat capacity of poly(trimethylene terephthalate) (PTT) has been measured using adiabatic calorimetry, standard differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC). The heat capacities of the solid and liquid states of semicrystalline PTT are reported from 5 to 570 K. The semicrystalline PTT has a glass transition temperature of 331 K. Between 340 and 480 K, PTT can show exothermic ordering depending on the prior degree of crystallization. The melting endotherm of semicrystalline samples occurs between 480 and 505 K, with a typical onset temperature of 489 K (216°C). The heat of fusion of the semicrystalline samples is about 15 kJ mol-1. For 100% crystalline PTT the heat of fusion is estimated to be 30 ± 2 kJ mol-1. The heat capacity of solid PTT is linked to an approximate group vibrational spectrum and the Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations (θ1 = 550.5 K and θ2 = θ3 = 51 K, Nskeletal = 19). The calculated and experimental heat capacities agree to better than ±3% between 5 and 300 K. The experimental heat capacities of liquid PTT can be expressed by: \documentclass{article}\pagestyle{empty}\begin{document}$ C^L_p(exp) $\end{document} = 211.6 + 0.434 T J K-1 mol-1 and compare to ±0.5% with estimates from the ATHAS data bank using contributions of other polymers with the same constituent groups. The glass transition temperature of the completely amorphous polymer is estimated to be 310-315 K with a ΔCp of about 94 J K-1 mol-1. Knowing Cp of the solid, liquid, and the transition parameters, the thermodynamic functions enthalpy, entropy, and Gibbs function were obtained. With these data one can compute for semicrystalline samples crystallinity changes with temperature, mobile amorphous fractions, and resolve the question of rigid-amorphous fractions.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2499-2511, 1998
    Zusätzliches Material: 8 Ill.
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  • 92
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2551-2562 
    ISSN: 0887-6266
    Schlagwort(e): polytetrafluoroethylene ; virgin powder ; two-stage draw ; morphology ; tensile properties ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polytetrafluoroethylene (PTFE) virgin powder was ultradrawn uniaxially by a two-stage draw. A film, compression molded from powder below the melting temperature (Tm), was initially solid-state coextruded to an extrudate draw ratio (EDR) of 6-20 at an established optimum extrusion temperature of 325°C, near the Tm of 335°C. These extrudates from first draw were found to exhibit the highest ductility at 45-100°C for the second-stage tensile draw, depending on the initial EDR and draw rate. The maximum achievable total draw ratio (DRt, max) was 36-48. Such high ductility of PTFE, far below the Tg (125°C) and Tm, is in sharp contrast to other crystalline polymers that generally exhibit the highest ductility above their Tg and near Tm. The unusual draw characteristics of PTFE was ascribed to the existence of the reversible crystal/crystal transitions around room temperature and the low intermolecular force of this polymer, which leads to a rapid decrease in tensile strength with temperature. The structure and tensile properties of drawn products were sensitive to the initial EDR, although this had no significant influence on DRt,max. The most efficient and highest draw was achieved by the second-stage tensile draw of an extrudate with the highest EDR 20 at 100°C, as evaluated by the morphological and tensile properties as a function of DRt. The efficiency of draw for the cold tensile draw at 100°C was a little lower than that for solid-state coextrusion near the Tm. However, significantly higher tensile modulus and strength along the fiber axis at 24°C of 60 ± 2 GPa and 380 ± 20 MPa, respectively, were achieved by the two-stage draw, because the DRt,max was remarkably higher for this technique than for solid-state coextrusion (DRt,max = 48 vs. 25). The increase in the crystallite size along the fiber axis (D0015), determined by X-ray diffraction, is found to be a useful measure for the development of the morphological continuity along the fiber axis of drawn products.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2551-2562, 1998
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2597-2605 
    ISSN: 0887-6266
    Schlagwort(e): positron annihilation ; open space ; relaxation ; subsurface ; polyethylene ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Open spaces in the subsurface region (〈10 μm) of very low density polyethylene were probed by a monoenergetic positron beam. From measurements of Doppler broadening spectra measurements of the annihilation radiation and the lifetime spectra of positrons as a function of incident positron energy, the size of the open spaces in the region of 0-3 μm was found to be larger than that in the deeper region. This was attributed to the cooperative motion of large segments of molecules which is activated near the surface. After the freezing in of such motions (below 230 K), although the lineshape parameter S in the bulk was almost constant, S in the region of 0-3 μm decreased with decreasing temperature. This discrepancy was associated with the presence of the open spaces with an excess content and the resultant contraction of amorphous structure near the surface. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2597-2605, 1998
    Zusätzliches Material: 5 Ill.
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  • 94
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 755-761 
    ISSN: 0887-6266
    Schlagwort(e): positron annihilation lifetime spectroscopy ; free volume ; transition temperatures ; poly(silylenemethylene)s ; dynamic mechanical analysis ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Amorphous and crystalline poly(silylenemethylene)s with the repeating PhRSiCH2 (R : Me or Ph) units were characterized by positron annihilation lifetime spectroscopy (PALS) to gain insights into the molecular motions of these polymers. The temperature dependence of the ortho-positronium lifetime (τ3) and intensity (I3) was examined from 50 to 470 K for each sample. The glass transition temperature of each polymer was easily distinguished by a change in the slope of τ3 spectrum. Both polymers exhibited a steep drop of I3 at 130-140 K being probably assignable to the transition arising from the motions of phenyl groups, which was almost undetectable by means of differential scanning calorimetry or dynamic mechanical analysis. Several other transitions of these polymers detected by PALS are also discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 755-761, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 763-781 
    ISSN: 0887-6266
    Schlagwort(e): random copolyesters ; copolymers ; crystallization ; melting ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The melting behavior of poly(ethylene terephthalate co-1,4-cyclohexylene dimethylene terephthalate) [PET/CT] random copolyesters has been studied. The basis of this analysis was the triple melting behavior of PET homopolymers, which is commonly observed after a period of isothermal crystallization followed by linear heating in a differential scanning calorimeter. Both ET and CT homopolymers are able to crystallize, and as a consequence, the copolymer morphology depends on the ET/CT ratio. It has been reported that at low CT concentrations, the ET units can crystallize with complete rejection of the CT units and that at high CT concentrations, the CT units can cocrystallize with the ET units. In the present work, low CT concentrations were selected, as they are completely rejected from the ET crystals. The purpose was to further test the hypothesis that in the triple melting behavior of PET homopolymers, the second DSC melting endotherm is related to secondary species crystallized by material rejected from the primary crystals. This concept arose from our previous work, where it was speculated that increasing the average molecular-weight of PET would enhance molecular entanglement and increase secondary crystallization. This process would give rise to a higher amount of species being rejected from the main crystals, i.e., an increase of secondary crystallization would occur, and as a consequence the second melting endotherm would be enhanced. Similar to the effect of molecular weight, such behavior has been observed as a function of rejected copolymer content. This gives support to our previously proposed step-like crystallization and melting mechanism for PET homopolymers, and has the potential to be extended to other high temperature semicrystalline polymeric systems. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 763-781, 1998
    Zusätzliches Material: 26 Ill.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 357-371 
    ISSN: 0887-6266
    Schlagwort(e): gelation theory ; nonlinear polymerization ; molecular weight distribution ; branched polymers ; polymer modification ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A Markovian model is proposed for nonrandom branching reactions, by using free-radical polymerization that involves chain transfer to polymer as an example. Free-radical polymerizations are kinetically controlled; therefore, each primary polymer molecule experiences different history of branched structure formation. By assuming that the primary chains with the identical birth time conform to the same chain connection probabilities, the nonlinear structural development can be viewed as a system in which the primary chains formed at different birth times are combined into nonlinear polymers in accordance with the first-order Markov chain statistics. An explicit formula for the weight-average chain length is derived in a matrix form. The onset of gelation is simply stated as a point at which the largest eigenvalue of the transition matrix X reaches unity, i.e., det(X - I) = 0. This criterion for the onset of gelation can be considered as an extension of the Flory/Stockmayer theory to a nonequilibrium reaction system. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 357-371, 1998
    Zusätzliches Material: 11 Ill.
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  • 97
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 495-517 
    ISSN: 0887-6266
    Schlagwort(e): crystallization ; DSC ; multiple melting ; nascent morphology ; polyethylene ; synchrotron ; UHMW PE ; WAXS ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The nascent morphology of UHMW PE exhibits high melting point, high crystallinity, and increased WAXS line breadth relative to samples formed by melt crystallization. Different empirical relationships between crystal size and melting point are observed for nascent and molded samples. This differentiation is removed following nitric acid treatment of the nascent flake. Solid-state annealing behavior is differentiated by several regimes. Regime I is characterized by increasing crystallite dimensions and crystallinity at low annealing temperatures. Regime II[a] and II[b] is identified by double melting in DSC scans of moldings and nascent flake, respectively. The double melting is due to partial melting with incomplete recrystallization. Regime II[a] of moldings is differentiated from Regime II[b] of flake by an increase in melting point of the higher melting endotherm. Within Regime II[b], the partial melting of the nascent structure is sensitive to the distribution of morphological stability. Regime III is initiated at annealing temperatures approaching the zero heating rate melting point, and shows melting kinetics by DSC or time-resolved WAXS using synchrotron x-ray radiation. The superheat, partially associated with Regime III behavior, is sensitive to morphological heterogeneity and annealing history. Morphological models are discussed which highlight the role of noncrystalline regions and melting kinetics on the melting behavior of nascent form crystallinity. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 495-517, 1998
    Zusätzliches Material: 29 Ill.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 567-572 
    ISSN: 0887-6266
    Schlagwort(e): surface ; interfaces ; diffusion ; polystyrene ; polyphenylene oxide ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Symmetric polydisperse (Mw = 23 × 104, Mw/Mn = 2.84) and monodisperse (Mw = 21 × 104, Mw/Mn 〈 1.05) polystyrene (PS), and asymmetric polydisperse PS/poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) interfaces have been bonded in the vicinity of the glass transition temperature (Tg) of PS. In a lap-shear joint geometry, strength develops in all cases with time to the fourth power, which indicates that it is diffusion controlled. Strength developing at short times at the polydisperse PS/PS interface, at 90°C, is higher than that at the monodisperse interface, at 92°C (at Tg - 13°C in both cases), presumably due to the contribution of the low molecular weight species. The decrease of strength at the PS/PPO interface when the bonding temperature decreases from 113 to 70°C, i.e., from Tg + 10°C to Tg - 33°C of the bulk PS, indicates a high molecular mobility at the surface as compared to that in the bulk, and can be expressed by a classical diffusion equation, which is valid above Tg (of the surface layer). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 567-572, 1998
    Zusätzliches Material: 4 Ill.
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  • 99
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 629-640 
    ISSN: 0887-6266
    Schlagwort(e): poly(acrylonitrile) ; two-stage draw ; morphology and tensile properties ; effect of molecular weight ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Ultradrawing of atactic poly(acrylonitrile) (PAN) was investigated for a Mv series, ranging 8.0 × 104-2.3 × 106. Samples for the draw were prepared from 0.5-30 wt % solutions of PAN in N,N′-dimethylformamide. The solutions were converted to a gel by quenching from 100 to 0°C. The dried gel films were initially drawn uniaxially by solid-state coextrusion (first-stage draw) to an extrusion draw ratio (EDR) of 16, followed by further tensile draw at 100-250°C (second-stage draw). The maximum total draw ratio (DRt,max) and tensile properties achieved by two-stage draw increased remarkably with sample Mv. Other factors affecting ductility were the solution concentration from which gel was made and the second-stage draw temperature. The effects of these variables became more prominent with increasing Mv. The temperature for optimum second-stage draw increased with sample Mv. Both the initial gel and the drawn products showed no small-angle X-ray long period scattering maximum, suggesting the absence of a chain-folded lamellae structure, which had been found in our previous study on the drawing of nascent PAN powder. The chain orientation function (fc) and sample density (ρs) increased rapidly with DRt in the lower range (DRt 〈 30) and approached constant values of fc = 0.980-0.996 and ρs = 1.177-1.181 g/cm3, respectively, at higher DRt 〉 30-100. The tensile modulus also showed a similar increase with DRt. The tensile strength increased linearly with DRt, reaching a maximum, and decreased slightly at yet higher DRt. The highest modulus of 28.5 GPa and strength of 1.6 GPa were achieved with the highest Mv of 2.3 × 106. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 629-640, 1998
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 681-692 
    ISSN: 0887-6266
    Schlagwort(e): high-density polyethylene ; nonisothermal crystallization kinetics ; plateau temperature ; regime transition ; crystallinity ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The quiescent nonisothermal bulk crystallization kinetics of two high-density polyethylene resins were investigated by a modified light-depolarizing microscopy (LDM) technique. The technique allows studies at average cooling rates up to 2500°C/min. The polymer was found to crystallize at a pseudo-isothermal temperature even at these very high cooling rates. The overall bulk crystallization rate increased rapidly as the cooling rate and supercooling increased. Crystallization kinetics was analyzed by Avrami analysis. Avrami exponents near 3 suggested spherical growth geometry and instantaneous nucleation at predetermined sites. Observation of spherulites by optical microscopy together with a number density of spherulites that changed little with increase in cooling rate or supercooling supported this model of crystallization behavior. Analysis of the half-time of crystallization based on the Lauritzen and Hoffman secondary nucleation theory indicated that the regime II-III transition was found to occur at a degree of supercooling of approximately 22°C. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 681-692, 1998
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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