bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lamina lucida of basement membrane: An artefact
Authors: Chan Franky L. , Inoue Sadayuki 
Published: February 2005

AbstractIn tissues prepared with chemical fixation followed by conventional dehydration, basement membranes have been observed to be laminated structures composed of a lamina lucida and lamina densa as well as a poorly limited transitional zone referred to as the pars fibroreticularis. Scattered attempts in the application of new techniques of tissue preparation such as cryofixation or freeze substitution for the study of the basement membrane structure have been made in recent years. From these studies, the possibility has arisen in which basement membranes are composed of only the lamina densa without a lamina lucida. In recent studies in this laboratory, the attempt was made to determine whether or not this lamina lucida is an artefact, and if so, which step in the conventional method of tissue preparation is responsible for its formation. Basement membranes from diverse sources in the mouse and rat including the testis, ductus epididymis, eye, thyroid, kidney, and skin, were observed after either cryofixation by slam freezing followed by freeze substitution, or aldehyde fixation followed by freeze substitution. The basement membranes after preservation with either of these two methods were composed of only the lamina densa with no lamina lucida. It indicates that an artefactual formation of the lamina lucida occurs during dehydration in conventional tissue preparation rather than during chemical fixation. In view of the well known superiority of freeze substitution over conventional dehydration, the lamina lucida of the basement membrane is likely to be an artefact. Therefore, it is concluded that the lamina lucida is an artefact formed during conventional tissue preparation, and in its original condition in the living state, the basement membrane is composed of a single layer made up of lamina densa material. © 1994 Wiley‐Liss, Inc.
Ultrastructure of developing kidney glomerular basement membranes: Temporal changes in binding of anti‐laminin lgG and cationized ferritin
Authors: Abrahamson Dale R. , John Patricia L. St. 
Published: February 2005

AbstractIn vivo labeling of infant rat and mouse glomerular basement membranes (GBMs) with polyclonal anti‐laminin IgGs results in binding across the full widths of GBMs at all stages of development. These stages include the pre‐fusion, double basement membranes found beneath endothelial cells and podocytes in early glomeruli, and the subepithelial matrix outpockets where newly synthesized GBM is spliced into fused basement membrane during glomerular maturation. Identical binding results are obtained either with peroxidase or post‐embedding immunogold techniques. Although injected cationized ferritin also binds abundantly to all developing GBMs, it quickly disappears and, 24 hours after injection, is generally absent from GBMs but remains within mesangial matrices. Injection of newborn mice with monoclonal anti‐laminin IgGs results in dense labeling of pre‐fusion GBMs but post‐fusion GBMs and subepithelial outpockets are weak‐negative. Although masking can not be excluded, these results indicate that laminin epitopes are removed during GBM fusion and splicing, either by isoform substitution or proteolytic processing. The loss of bound cationized ferritin is believed to occur mainly through rapid turnover of GBM proteoglycans. © 1994 Wiley‐Liss, Inc.
Morphology of the basement membrane
Authors: Merker Hans‐Joachim 
Published: February 2005

AbstractThe aim of this contribution is to summarize our knowledge of the morphology of the basement membrane (BM). The first step in this direction is the attempt to define this term. The BM is composed of the Lamina lucida, densa, and fibroreticularis. Subsequently, the historical development of this term is discussed. Our main interest is, of course, focused on the description of the BM‐structure up to the macromolecular level and the special forms of this structure. This is supplemented by discussing its chemical composition and establishing a relationship between morphology and biochemistry. The obtained findings yielded some indications as to the molecular composition of the BM which may serve for the construction of “models.” The composition of the Lamina lucida (L.l.) and the Lamina or Pars fibroreticularis (L.f.) must be discussed separately, since, if present, they show a different and strongly varying structure (L.f.). An important aspect is the function of this extracellular layer which comprises mechanical tasks up to inductive effects. Finally, the concepts of the formation of the BM, especially of the Lamina densa (L.d.), are summarized. It obviously consists of a sequence of individual steps which starts with expression and secretion of the L.d.‐components and is followed by an induction of integrin expression. © 1994 Wiley‐Liss, Inc.
Quantitative X‐ray microanalysis of P, Ca, and S in the mucus secretory granules of the cryofixed frog palate epithelium
Authors: Wagner Denis , Puchelle Edith , Hinnrasky Jocelyne , Girard Pascal , Balossier GéRard 
Published: February 2005

AbstractIn respiratory epithelium, the mucus is densely packed inside the secretory granules (SG) of secretory cells (SC) before being released by exocytosis in the airway lumen. We have previously shown that the frog palate is a representative model of respiratory epithelium and that rapid cryofixation is a very effective technique in preserving the integrity of the mucus SG. The concentration of phosphorus (P), sulphur (S), and calcium (Ca) were analysed inside the SG of the SC of frog palate after quick freezing, cryosubstitution, and embedding in Lowicryl resin at low temperature. The experiments were carried out using X‐ray microanalysis conducted with energy dispersive spectrometry (EDS) at 100 kV. The quantitation was carried out using the continuum method with reference to Agar standards. The cryofixation permitted us to distinguish two types of SG depending on whether they were electron dense (serous cells) or electron‐lucent (mucous cells). A significant (P < 0.001) difference in the S concentration was observed between the individual serous (239 ± 79 mmol.kg−1) and the mucous SG (161 ± 48 mmol.kg−1). No significant difference could be identified in the Ca concentration between the two SG phenotypes. In the serous SG, the P content was high (41 ± 17 mmol.kg−1) compared with the mucous SG where it was not measurable. The comparison of the three element concentrations in each type of secretory cells showed that significant differences in concentration of S and Ca concentration could be observed from one SC cell to another. A significant correlation (r = 0.76, P < 0.01) was observed between the S concentration and the topographical position of the SG inside the SC, the more proximal to the lumen, the higher the S concentration, suggesting that the maturation of the SG involves an increase in the protein content possibly due to a maturation process before the mucus exocytosis. Therefore, these results suggest that the elemental composition of granules varies according to the phenotype of the secretory cells and that changes in the S content from one SG to another or even inside the same cell may reflect a differential state in the functional activity of the secretory cells. © 1994 Wiley‐Liss, Inc.
Role of the basement membrane in neurogenesis and repair of injury in the central nervous system
Authors: Choi Ben H. 
Published: February 2005

AbstractAlthough remarkable progress has been made during the last two decades concerning the biosynthesis, expression and assembly of extracellular matrix (ECM) macromolecules in nonneural cells, we are still far from a complete understanding of the role and function of the ECM and the basement membrane (BM) in the central nervous system (CNS). With the aid of correlative light and electron microscopic, Golgi and immunohistochemical studies of the developing neural tube of both early human fetus and mouse, we have shown that the establishment of the pial‐glial barrier (PGB) is one of the earliest histogenetic events in neurogenesis. This is accomplished by coordinated interaction among the processes of radial glia, various ECM components, and mesenchymal cells at the pial surface, with the formation of a BM that tightly abuts the glia limitans. The PGB and the BM appear to be critical to the migration and final positioning of neurons and to the differentiation of the laminar cortical pattern within the developing neopallium. This hypothesis is further supported by our study of the brain of a human newborn infant in whom multiple sites of disruption of the BM and PGB resulted in abnormal neuronal migration and massive ectopia of neurons within the subarachnoid space, with abnormal cortical lamination. Finally, studies of the experimental cryogenic injury to the neonatal rat cerebrum have shown that the final positioning of neurons within the developing cortical plate appears to depend largely on the reconstitution of the BM and PGB, which presumably provide crucial positional signals for migrating neurons. Also, one of the essential reparative features seen following cryogenic injury to the adult rat cerebrum is an orderly and dynamic interaction between various ECM components and neural cells, resulting in the formation of the BM. © 1994 Wiley‐Liss, Inc.
Surface expression and distribution of Fc receptor III (CD 16 molecule) on human natural killer cells and polymorphonuclear neutrophils
Authors: Fernández‐Segura E. , García J. M. , López‐escámez J. A. , Campos A. 
Published: February 2005

AbstractHuman natural killer cells and polymorphonuclear neutrophils constitutively express the low‐affinity IgG Fc receptor (FcγRIII, CD16 molecule). To investigate cell surface morphology, antigenic receptor density, and topographical distribution of FcγRIII on the plasma membrane of natural killer cells and polymorphonuclear neutrophils, conventional scanning electron microscopy (SEM), flow cytometry, and immunoscanning electron microscopy were used. FcγRIII was detected with an indirect immunogold labeling procedure, and receptors were visualized in the backscattered and secondary electron imaging mode of SEM. Natural killer cells showed a cell surface morphology compatible with lymphocytic differentiation characterized by microvilli and microridges. Polymorphonuclear neutrophils showed surface features characterized by ridges with folds and scattered short microvilli. Natural killer cells displayed a lower cell labeling density, whereas polymorphonuclear neutrophils showed a high level of expression of FcγRIII on the plasma membrane by quantitative analysis with SEM in the backscattered electron imaging mode. Flow cytometry analysis confirmed these findings. Analysis of the topographical distribution of FcγRIII antigenic receptor sites by SEM in the backscattered and secondary electron imaging modes showed that FcγRIII on natural killer cells are randomly distributed, whereas FcγRIII are located on ridges and folds of the plasma membrane of polymorphonuclear neutrophils. These observations suggest that natural killer cells and polymorphonuclear neutrophils differ in their levels of expression and topographic distribution of FcγRIII on the plasma membrane. This different spatial distribution of FcγRIII would provide morphological evidence of certain cellular functions mediated by natural killer cells and polymorphonuclear neutrophils. © 1994 Wiley‐Liss, Inc.
Endocytosis of three serum proteins of a multigene family and of arachidonic acid in human lectin‐stimulated T lymphocytes
Authors: Geuskens M. , Torres J. M. , Esteban C. , Uriel J. 
Published: February 2005

AbstractAlpha‐fetoprotein (AFP), serum albumin (SA), and vitamin D binding protein (DBP) are members of a multigene family of proteins showing high structural homology. AFP and SA exhibit a reciprocal relation during development and carry mostly fatty acids, while DBP carries vitamin D and its metabolites in the plasma. Covalent conjugates of these proteins with horseradish peroxidase (HRP) were used to follow by cytochemistry, at the electron microscope level, the protein uptake and intracellular pathways in peripheral blood human lymphocytes stimulated to blast formation by phytohemagglutinin (PHA). Transferrin (Tf), an iron‐binding plasma protein, was used as a control.Combined with the results of competition and saturability experiments reported elsewhere, the ultrastructural observations are in favour of a specific endocytosis of the four proteins through cell surface receptors. Tf and AFP enter the cells via small vesicles and endosomes and move to multivesicular bodies (MVBs) and tubular vesicular elements located in the Golgi‐centrosphere region to be finally recycled back into the medium. A noncovalent conjugate of AFP‐HRP with 3H arachidonic acid [3H‐(20:4)] is strongly internalized at 37°C in PHA‐stimulated lymphocytes; the autoradiographic labelling, localized in cellular membranes and mostly in lipid droplets, was only occasionally associated with organelles where the presence of AFP‐HRP was cytochemically detected.SA, which competes with AFP for a common binding site on the surface of activated T cells, is endocytosed through small vesicles, endosomes, and MVBs before being released in a degraded form from the cells, in agreement with the localization of SA‐HRP in lysosome‐like organelles. DBP‐HRP is poorly internalized through noncoated vesicles, endosomes, and MVBs and is finally routed to lysosomes.The physiological role of AFP and SA would be to mediate the transfer of fatty acids into cells, while that of DBP would be to facilitate the intracellular delivery of vitamin D. © 1994 Wiley‐Liss, Inc.
Scanning and transmission electron microscopy of clonal peripheral blood lymphocytes in low grade non‐Hodgkin's B‐cell lymphomas with predominant splenomegaly
Authors: Soligo Davide , Quirici Nadia , Caneva Lorenza , Baldini Luca , Cro Lilla , Deliliers Giorgio Lambertenghi 
Published: February 2005

AbstractPeripheral blood mononuclear cells (PBLs) from 14 patients with low grade non‐Hodgkin's B‐cell lymphomas with predominant splenomegaly were studied by means of scanning (SEM) and transmission electron microscopy (TEM). All patients had peripheral blood and bone marrow involvement, the absence of lymphoadenopathy, and, except in one case, immunophenotypic features of a malignant proliferation of mature spleen B‐cells arising from outside the germinal center, but not consistent with CLL or HCL. Several distinctive cytological features were observed in PBLs of the different subgroups. The SEM surface features of PBLs in patients with intermediate differentiation lymphocytic lymphoma (IDL) (five cases), lymphoplasmacytoid immunocytoma (LP‐IC) (two cases), and mixed small and large cells malignant lymphoma (one case) were characterized by the presence of numerous well‐developed microvilli. Some distinctive TEM ultrastructural features were also seen in the different cases. In the two cases of splenic lymphoma with villous lymphocytes (SLVL), SEM revealed large and elongated surface microvilli generally arising from two or three poles of the cells. This surface morphology, confirmed by TEM analysis, may be pathognomonic of this disease. Four additional cases, tentatively classified as small lymphocytic lymphoma on the basis of immunophenotypic data, were extremely heterogeneous at both SEM and TEM analysis. The ultrastructural features revealed by SEM and TEM may be useful for the more precise characterization of this heterogenous group of diseases, which is generally difficult to define even when immunophenotypic and molecular approaches are used. © 1994 Wiley‐Liss, Inc.
Calculation of overall tilt angles for a double tilt holder in a TEM
Authors: Kelly Patrick M. , Wauchope Corinna J. , Zhang Xuezhi 
Published: February 2005

AbstractA simple formula has been derived for the tilt angle of a specimen in terms of the two tilt angles of a side entry, double tilt holder in a transmission electron microscope. An expression for calculating the direction of the apparent tilt axis in relation to the observed diffraction pattern has also been derived. The accuracy and reproducibility of specimen tilting has been assessed experimentally. © 1994 Wiley‐Liss, Inc.
Proteoglycan synthesis by cultured human chondrocytes
Authors: Aulthouse Amy Lynn , Becker Konrad , Beck Michael 
Published: February 2005

AbstractIliac crest biopsies are important in the detection of human skeletal dysplasias. Therefore, culture of these cells may serve as a valuable method for studying proteoglycan metabolism in chondrocytes of individuals with skeletal abnormalities. Morphological and biochemical studies were performed on human iliac crest chondrocytes grown in monolayer and in agarose gels. Two proteoglycan populations of different hydrodynamic size and glycosaminoglycan composition were synthesized by cells grown in monolayer. Chondrocytes cultured in an agarose gel for 2 weeks synthesized proteoglycans identical to those of the native tissue with respect to hydrodynamic size and glycosaminoglycan chain length. However, the ratio of chondroitin‐6‐sulfate to chondroitin‐4‐sulfate was higher than in the native tissue. This ratio was not influenced by different sulfate concentrations in the medium. Moreover, treatment with ascorbic acid did not influence proteoglycan synthesis; however, there was a pericellular accumulation of proteoglycans. © 1994 Wiley‐Liss, Inc.
Preservation and contrast without osmication or section staining
Authors: Locke Michael 
Published: February 2005

AbstractConventional treatment of tissues for sectioning and transmission electron microscopy uses aldehyde fixation and osmium tetroxide postfixation. Although the result is aesthetically pleasing, osmication destroys some cell components and reduces the chemical activity of others, such as reactions with antibodies and lectins. We have found that aldehyde fixation followed by uranyl acetate preserves and contrasts most structures and visualizes some that are not easily seen after osmication. Aldehyde/UA treated tissues have enough contrast to be observed without section staining while retaining some of the chemical activity that is lost through osmication. Sections of tissues with good preservation and contrast can be used for immunogold and lectin‐gold labelling of at least some molecules. © 1994 Wiley‐Liss, Inc.
A negative contrast stain for ultra‐thin frozen sections
Authors: Himmelhoch Stanley 
Published: February 2005

AbstractUltra‐thin frozen sections are ideal substrates for immunolabeling in high resolution electron microscopy. However, visualization of subcellular structures is inferior to that obtained with corresponding plastic sections. Although negative staining is generally effective and even superior to positive staining, the accumulated stain is often too heavy, obscuring morphology and markers used for immunocytochemical localization of antigens. This paper describes the development of a modified negative contrast staining technique in which a high concentration of uranyl acetate is mixed with methyl cellulose at a low pH. Application of this stain to cryosections of cells and tissue resulted in improved visualization of morphological structures characterized by negative images of membranes and cell organelles. Use of this stain is advantageous for morphological and immunocytochemical studies involving ultra‐thin frozen sections. © 1994 Wiley‐Liss, Inc.
Correlated alkaline phosphatase histochemistry and quantitative backscattered electron imaging in the study of rat incisor ameloblasts and enamel mineralization
Authors: Gomez Santiago , Boyde Alan 
Published: February 2005

AbstractThe different functional conditions of pre‐ameloblasts, secretory ameloblasts, and maturation ameloblasts in 9 day rat incisors were recognized using high resolution light microscopic alkaline phosphatase histochemistry: Digital backscattered electron imaging was performed using the block surfaces from which thin sections were taken for histochemical study. It was possible to correlate exact locations in histochemical sections with positions in the block face at all stages of enamel mineralization from early secretion through late maturation. The first steep increase in the rate of mineralization of completed enamel matrix occurs after the first transition from smooth ended ameloblasts to ruffle ended ameloblasts. In the 9 day rat incisors used for this purpose, there are only two smooth to ruffle cyclical transitions, and the width of successional smooth ended bands of ameloblasts in the maturation cycling process is always narrow. Nevertheless, there seems to be a good correlation between mineralization increase and the acquisition of the high alkaline phosphatase activity in the deeply enfolded distal cytoplasm of the ruffle‐ended maturation stage ameloblasts. © 1994 Wiley‐Liss, Inc.
Nitric oxide synthase‐containing neurons in the pig large intestine: Topography, morphology, and viscerofugal projections
Authors: Barbiers Martine , Timmermans Jean‐Pierre , Scheuermann Dietrich W. , Adriaensen Dirk , Mayer Bernd , De Groodt‐Lasseel Marie H. A. 
Published: February 2005

AbstractThe distribution of neurons that are capable of synthesizing nitric oxide (NO) has been demonstrated in the porcine large intestine by means of NO synthase (NOS) immunocytochemistry and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry. An overall colocalization of NOS immunoreactivity and NADPHd staining was observed. Nitrergic neurons were abundant in the myenteric and outer submucous plexus of the caecum, colon, and rectum. Only a few nitrergic perikarya were seen in the inner submucous plexus of the colon and caecum, whereas a substantially larger number was observed in the rectum. Nitrergic nerve fibers were present in the three ganglionic nerve plexuses. Contrary to the outer longitudinal muscle layer and the mucosal region, the circular muscle layer received a dense nitrergic innervation. The nitrergic nerve cells were variable in size and shape, and several displayed vasoactive intestinal polypeptide (VIP) immunoreactivity (IR). Retrograde tracing studies revealed the existence of nitrergic neurons that project to the caudal (inferior) mesenteric ganglion. They were observed in the myenteric and outer submucous plexus of the transverse and descending colon and the rectum. These observations strongly suggest that several subpopulations of NO‐synthesizing neurons, namely, motor neurons and interneurons, should be distinguished in the porcine large intestine, thereby emphasizing the importance of NO as a biologically active mediator. © 1994 Wiley‐Liss, Inc.