The use of scanning electron microscopy and fixation methods to evaluate the interaction of blood with the surfaces of medical devices

Testing the hemocompatibility of medical devices after their interaction with blood entails the need to evaluate the activation of blood elements and the degree of their coagulation and adhesion to the device surface. One possible way to achieve this is to use scanning electron microscopy (SEM). The aim was to develop a novel SEM-based method to assess the thrombogenic potential of medical devices and their adhesiveness to blood cells. As a part of this task, also find a convenient procedure of efficient and non-destructive sample fixation for SEM while reducing the use of highly toxic substances and shortening the fixation time. A polymeric surgical mesh was exposed to blood so that blood elements adhered to its surface. Such prepared samples were then chemically fixed for a subsequent SEM measurement; a number of fixation procedures were tested to find the optimal one. The fixation results were evaluated from SEM images, and the degree of blood elements' adhesion was determined from the images using ImageJ software. The best fixation was achieved with the May-Grünwald solution, which is less toxic than chemicals traditionally used. Moreover, manipulation with highly toxic osmium tetroxide can be avoided in the proposed procedure. A convenient methodology for SEM image analysis has been developed too, enabling to quantitatively evaluate the interaction of blood with the surfaces of various medical devices. Our method replaces the subjective assessment of surface coverage with a better-defined procedure, thus offering more precise and reliable results.

A preparation of bacterial outer membrane with osmium tetroxide and uranyl acetate co-stain enables improved structural determination by transmission electron microscopy

Biological nanoparticles, such as bacterial outer membrane vesicles (OMVs), are routinely characterized through transmission electron microscopy (TEM). In this study, we report a novel method to prepare OMVs for TEM imaging. To preserve vesicular shape and structure, we developed a dual fixation protocol involving osmium tetroxide incubation prior to negative staining with uranyl acetate. Combining osmium tetroxide with uranyl acetate resulted in preservation of sub-50 nm vesicles and improved morphological stability, enhancing characterization of lipid-based nanoparticles by TEM.

A conventional fixation volume electron microscopy protocol for plants

Volume electron microscopy techniques play an important role in plant research from understanding organelles and unicellular forms to developmental studies, environmental effects and microbial interactions with large plant structures, to name a few. Due to large air voids central vacuole, cell wall and waxy cuticle, many plant tissues pose challenges when trying to achieve high quality morphology, metal staining and adequate conductivity for high-resolution volume EM studies. Here, we applied a robust conventional chemical fixation strategy to address the special challenges of plant samples and suitable for, but not limited to, serial block-face and focused ion beam scanning electron microscopy. The chemistry of this protocol was modified from an approach developed for improved and uniform staining of large brain volumes. Briefly, primary fixation was in paraformaldehyde and glutaraldehyde with malachite green followed by secondary fixation with osmium tetroxide, potassium ferrocyanide, thiocarbohydrazide, osmium tetroxide and finally uranyl acetate and lead aspartate staining. Samples were then dehydrated in acetone with a propylene oxide transition and embedded in a hard formulation Quetol 651 resin. The samples were trimmed and mounted with silver epoxy, metal coated and imaged via serial block-face scanning electron microscopy and focal charge compensation for charge suppression. High-contrast plant tobacco and duckweed leaf cellular structures were readily visible including mitochondria, Golgi, endoplasmic reticulum and nuclear envelope membranes, as well as prominent chloroplast thylakoid membranes and individual lamella in grana stacks. This sample preparation protocol serves as a reliable starting point for routine plant volume electron microscopy.

Staining Methods for Normal and Regenerative Myelin in the Nervous System

Histochemical and fluorescence-based techniques enable the specific identification of myelin by bright-field or fluorescence microscopy. In this chapter, we describe four histological methods for the evaluation of myelin on peripheral nerve tissue sections. The first method combines the Luxol fast blue (LFB) technique with a modified Picrosirius staining contrasted with Harris hematoxylin, called MCOLL. This method simultaneously stains myelin, collagen fibers, and cell nuclei, thus giving an integrated overview of the histology, collagen network, and myelin content of the tissue in paraffin-embedded or cryosectioned samples. Secondly, we describe the osmium tetroxide method, which provides a permanent positive reaction for myelin as well as other lipids present in the tissue. The third method is the immunofluorescence-based detection of myelin proteins that allows to combine information about their expression status with other proteins of interest. Finally, the FluoroMyelin™ stains enable a fast detection of the myelin content that can be easily implemented in immunofluorescence staining panels for cryosectioned tissues. Together, this chapter provides a variety of methods to accurately identify myelin in different experimental approaches.

Osmium-Resistant Fluorescent Proteins and In-Resin Correlative Light-Electron Microscopy of Epon-Embedded Mammalian Cultured Cells

Postfixation with osmium tetroxide and Epon embedding are essential for the preservation and visualization of subcellular ultrastructures via electron microscopy. These chemical treatments diminish the fluorescent intensity of most fluorescent proteins in cells, creating a problem for the in-resin correlative light-electron microscopy (CLEM) of Epon-embedded mammalian cultured cells. We found that two green and two far-red fluorescent proteins retain their fluorescence after chemical fixation with glutaraldehyde, osmium tetroxide-staining, dehydration, and polymerization of Epon resins. Consequently, we could observe the fluorescence of fluorescent proteins in ultrathin sections of Epon-embedded cells via fluorescence microscopy, investigate ultrastructures of the cells in the same sections via electron microscopy, and correlate the fluorescent image with the electron microscopic image without chemical or physical distortion of the cells. In other words, referred as "in-resin CLEM" of Epon-embedded samples. This technique also improves the Z-axis resolution of fluorescent images. In this chapter, we introduce the detailed protocol for in-resin CLEM of Epon-embedded mammalian cultured cells using these fluorescent proteins.

Chemical and cryo-collection of muscle samples for transmission electron microscopy using Methacarn and dimethyl sulfoxide✰

Muscle samples are commonly chemically fixed or frozen immediately upon collection for biochemical and morphological analysis. Certain fixatives such as glutaraldehyde and osmium tetroxide are widely used for transmission electron microscopy (TEM) and lead to adequate preservation of muscle ultrastructure, but do not preserve the molecular features of samples. Methacarn is suggested to be a preferable chemical fixative for light microscopy because it maintains immunohistological features of samples. However, the efficacy of methacarn to preserve ultrastructural features as a primary chemical fixative for TEM is currently unclear. Additionally, cryo-preservation of samples for TEM analysis involves freezing processes such as plunge freezing, slam freezing, or high pressure freezing. High pressure freezing is the considered the gold standard but requires costly equipment and may not be a viable option for many labs collecting tissue samples from remote locations. Dimethyl sulfoxide (DMSO) is a commonly used cryoprotectant that may allow for better structural preservation of samples by impairing ice damage that occurs during plunge/snap freezing. We aimed to assess the effectiveness of methacarn as a primary chemical fixative and determine the effect of pre-coating samples with DMSO before plunge/snap freezing tissues to be prepared for TEM. The micrographs of the methcarn-fixed samples indicate a loss of Z-disk integrity, intermyofibrillar space, mitochondria structure, and lipids. Ultimately, methacarn is not a viable primary fixative for tissue sample preparation for TEM. Similarly, liquid nitrogen freezing of samples wrapped in aluminum foil produced non-uniform Z-disk alignments that appeared smeared with swollen mitochondria. DMSO coating before freezing appears to lessen the alterations to contractile and mitochondrial morphological structures. DMSO appears to be useful for preserving the ultrastructure of sarcomeres if samples are covered before freezing.

Recyclable Periodic Nanostructure Formed by Sublimable Liquid Crystals for Robust Cell Alignment

We demonstrate a facile method to fabricate a recyclable cell-alignment scaffold using nanogrooves based on sublimable liquid crystal (LC) material. Randomly and uniaxially arranged smectic LC structures are obtained, followed by sublimation and recondensation processes, which directly produce periodic nanogrooves with dimensions of a couple of hundreds of nanometers. After treatment with osmium tetroxide (OsO₄), the nanogroove can serve as a scaffold to efficiently induce directed cell growth without causing cytotoxicity, and it can be used repeatedly. Together, various cell types are applied to the nanogroove, proving the scaffold's broad applicability. Depending on the nanotopography of the LC structures, cells exhibit different morphologies and gene expression patterns, compared to cells on standard glass substrates, according to microscopic observation and qPCR. Furthermore, cell sheets can be formed, which consist of oriented cells that can be repeatedly formed and transferred to other substrates, while maintaining its organization. We believe that our cell-aligning scaffold may pave the way for the soft material field to bioengineering, which can involve fundamentals in cell behavior and function, as well as applications for regenerative medicine.

OUP accepted manuscript

Precise immunolocalization of molecules in relation to ultrastructural features is challenging, especially when the target is small and not frequent enough to be included in tiny ultrathin sections randomly selected for electron microscopy (EM). Glucose transporter 1 (GLUT1) is in charge of transporting glucose across brain capillary endothelial cells (BCECs). Paraformaldehyde-fixed floating sections (50 μm thick) of mouse brain were immunolabeled with anti-GLUT1 antibody and visualized with fluoronanogold. Fluorescent images encompassing the entire hemisphere were tiled to enable selection of GLUT1-positive BCECs suitable for subsequent EM and landmark placement with laser microdissection to guide trimming. Sections were then fixed with glutaraldehyde, gold enhanced to intensify the labeling and fixed with osmium tetroxide to facilitate ultrastructural recognition. Even though a region that contained target BCECs was successfully trimmed in the resin block, it was only after observation of serial ultrathin sections that GLUT1 signals in coated vesicles on the same cross section corresponding to the cross section preidentified by confocal laser microscope. This is the first ultrastructural demonstration of GLUT1 molecules in coated vesicles, which may well explain its functional relevance to transport glucose across BCECs. Successful ultrastructural localization of molecules in relation to well-preserved target structure in native tissue samples, as achieved in this study, will pave the way to understand the functional relevance of molecules and their relation to ultrastructural details.

Transmission Electron Microscopy and Morphometry of the CNS White Matter

Transmission electron microscopy of central nervous system white matter has provided unparalleled access to the ultrastructural features of axons, their myelin sheaths, and the major cells of white matter; namely, oligodendrocytes, oligodendrocyte precursors, astrocytes, and microglia. In particular, it has been invaluable in elucidating pathological changes in axons and myelin following experimentally induced injury or genetic alteration, in animal models. While also of value in the examination of human white matter, the tissue is rarely fixed adequately for the types of detailed analyses that can be performed on well-preserved samples from animal models, perfusion fixed at the time of death. In this chapter we describe methods for obtaining, processing, and visualizing white matter samples using transmission electron microscopy of perfusion fixed tissue and for unbiased morphometry of white matter, with particular emphasis on axon and myelin pathology. Several advanced electron microscopy techniques are now available, but this method remains the most expedient and accessible for routine ultrastructural examination and morphometry.

Plant tissues in 3D via X-ray tomography: simple contrasting methods allow high resolution imaging

Computed tomography remains strongly underused in plant sciences despite its high potential in delivering detailed 3D phenotypical information because of the low X-ray absorption of most plant tissues. Existing protocols to study soft tissues display poor performance, especially when compared to those used on animals. More efficient protocols to study plant material are therefore needed. Flowers of Arabidopsis thaliana and Marcgravia caudata were immersed in a selection of contrasting agents used to treat samples for transmission electron microscopy. Grayscale values for floral tissues and background were measured as a function of time. Contrast was quantified via a contrast index. The thick buds of Marcgravia were scanned to determine which contrasting agents best penetrate thick tissues. The highest contrast increase with cytoplasm-rich tissues was obtained with phosphotungstate, whereas osmium tetroxide and bismuth tatrate displayed the highest contrast increase with vacuolated tissues. Phosphotungstate also displayed the best sample penetration. Furthermore, infiltration with phosphotungstate allowed imaging of all plants parts at a high resolution of 3 µm, which approaches the maximum resolution of our equipment: 1.5 µm. The high affinity of phosphotungstate for vasculature, cytoplasm-rich tissue, and pollen causes these tissues to absorb more X-rays than the surrounding tissues, which, in turn, makes these tissues appear brighter on the scan data. Tissues with different brightness can then be virtually dissected from each other by selecting the bracket of grayscale to be visualized. Promising directions for the future include in silico phenotyping and developmental studies of plant inner parts (e.g., ovules, vasculature, pollen, and cell nuclei) via virtual dissection as well as correlations of quantitative phenotypes with omics datasets. Therefore, this work represents a crucial improvement of previous methods, allowing new directions of research to be undertaken in areas ranging from morphology to systems biology.

Heavy metal staining, a comparative assessment of gadolinium chloride and osmium tetroxide for inner ear labyrinthine contrast enhancement using X-ray microtomography

CONCLUSION

The use of both gadolinium chloride (GdCl(3)) and osmium tetroxide (OsO(4)) allowed for the visualization of the membranous labyrinth and other intralabyrinthine structures, at different intensities, as compared with the control sample. This initial comparison shows the advantages of GdCl(3) in radiological assessments and OsO(4) in more detailed anatomical studies and pathways of labyrinthine pathogenesis using X-ray microtomography (microCT).

OBJECTIVE

To assess an improved OsO(4) staining protocol and compare the staining affinities against GdCl(3).

METHODS

Guinea pig temporal bones were stained with either GdCl(3) (2% w/v) for 7 days or OsO(4) (2% w/v) for 3 days, and scanned in a microCT system. The post-scanned datasets were then assessed in a 3D rendering program.

RESULTS

The enhanced soft tissue contrast as presented in the temporal bones stained with either GdCl(3) or OsO(4) allowed for the membranous labyrinth to be visualized throughout the whole specimen. GdCl(3)-stained specimens presented more defined contours of the bone profile in the radiographs, while OsO(4)-stained specimens provided more anatomical detail of individual intralabyrinthine structures, hence allowing spatial relationships to be visualized with ease in a 3D rendering context and 2D axial slice images.

A useful method for observing intracellular structures of free and cultured cells by scanning electron microscopy

Scanning electron microscopy (SEM) using osmium-maceration methods has been used for analyzing the three-dimensional structure of cell organelles in tissue samples, but it has been quite difficult to observe free and cultured cells with this technique. The present study was performed to develop a method that can be applied to free and cultured cells for SEM studies of intracellular structures after osmium maceration. The method was also applied to light microscopy (LM) and to transmission electron microscopy (TEM). HeLa cells and human leukocytes were fixed with a mixture of 0.5% paraformaldehyde and 0.5% glutaraldehyde followed by an additional fixation with 1% osmium tetroxide. These cells were embedded in low-melting-point agarose. A temperature-responsive dish was also used for collection of cultured cells before embedding. For LM and TEM, the cell-embedded agarose was further embedded in epoxy resin, and semi- and ultrathin sections were examined conventionally. For SEM, the agarose was freeze-fractured in 50% dimethyl sulfoxide, processed for osmium maceration and observed in a high-resolution SEM. Low-melting-point agarose was useful as an embedding medium for SEM, because it was well preserved during prolonged osmication for SEM. Thus, the fine structure of cell organelles was clearly analyzed by SEM after osmium-maceration treatment. These SEM images could also be compared with those of LM and TEM of the agarose-embedded tissues.

The fusion of lipid droplets is involved in fat loss during cooking of duck "foie gras"

Fat loss during cooking of duck "foie gras" is the main quality issue in processing plants. To better understand this phenomenon, a histological and ultrastructural study was conducted. The aim was to characterize changes in lipid droplets of duck "foie gras" related to fat loss during cooking. Ten fatty livers were sampled before and after cooking and prepared for optical and transmission electron microscopy. In raw livers, the lipid droplets were nearly spherical while after cooking, they were larger and lost their spherical shape. We also observed a decrease in the number of droplets after cooking, probably due to droplet fusion caused by the heat treatment. Before cooking, there were fewer lipid droplets and a higher osmium tetroxyde staining intensity in the fatty liver, which later gave a lower technological yield. Fat loss during cooking was higher when there was more fusion of lipid droplets before cooking.

Imaging plasmodesmata

At only 50 nm in diameter, plasmodesmata (PD) are below the limit of resolution of conventional light microscopy. Consequently, much of our current interpretation of the substructure of PD is derived from transmission electron microscopy. However, PD can be imaged with alternative techniques, including field emission scanning electron microscopy and 'super-resolution' imaging approaches such as 3D-structured illumination microscopy. This review considers the methods currently available for studying PD and focuses on the boundary between light- and electron-based imaging approaches.

Osmic acid staining of myelin sheath in normal and regenerated peripheral nerves

OBJECTIVE

To introduce a practical, economical, and time-saving method to stain (with osmic acid) the myelin sheath in normal and regenerated peripheral nerves.

METHODS

A total of 12 Sprague Dawley rats, weighing 250-320 g (mean equal to 276 g+/-38 g), were divided into two groups: a normal nerve group (n equal to 6) and a regenerated nerve group (n equal to 6). In the normal nerve group, the ventral and dorsal roots of L(4) to L(6) and their sciatic nerves were harvested for histological analysis. While in the regenerated nerve group, the right sciatic nerves were severed and then repaired with an epineurial microsuture method. The repaired nerves were harvested 12 weeks postoperatively. All the specimens were fixed in 4% paraformaldehyde and transferred to 2% osmic acid for 3-5 days. Then the specimens were kept in 75% alcohol before being embedded in paraffin. The tissues were cut into sections of 3 micromolar in thickness with a conventional microtome.

RESULTS

Under a light microscope, myelin sheaths were clearly visible at all magnifications in both groups. They were stained in clear dark colour with a light yellow or colorless background, which provided high contrast images to allow reliable morphometric measurements. Morphological assessment was made in both normal and regenerated sciatic nerves. The ratios of the myelin area to the fibre area were 60.28%+/-7.66% in the normal nerve group and 51.67%+/-6.85% in the regenerated nerve group, respectively (P less than 0.01).

CONCLUSIONS

Osmic acid staining is easy to perform and a very clear image for morphometrical assessment is easy to obtain. Therefore, it is a reliable technique for quantitative evaluation of nerve morphology.

Visualization of neutrophil extracellular traps in TEM

Neutrophil extracellular traps (NETs) have recently been described as an important innate defence mechanism in inflammation. However, routine electron microscopic staining techniques faintly stain NETs and are therefore insufficient for enabling a distinction between these and the host cell debris as well as proteins regularly present at the site of inflammation. In order to test suitable electron microscopic staining techniques, NETs induced ex vivo via phorbol myristate were absorbed on formvar. Four types of drop-on-grid positive staining were used: osmium tetroxide (Os), osmium tetroxide-uranyl acetate-lead citrate (Os-U-Pb), ruthenium red-osmium tetroxide (RR-OsO4), and cuprolinic blue enhanced by sodium tungstate (CB-WO4). We observed no staining of NETs using Os, faint staining with Os-U-Pb, better but still weak staining with CB-WO4 and outstanding staining with RR-OsO4. Furthermore, RR-OsO4 staining also enables the observation of bacterial fimbriae-mediated adhesion, which is possibly responsible for the ability of NETs to bind bacteria. Thus, the offered RR-OsO4 staining technique may facilitate the study of the NETs-bacterial interactions.

“Multicolor” Electrochemical Labeling of DNA Hybridization Probes with Osmium Tetroxide Complexes

Labeling of oligonucleotide reporter probes (RP) with electroactive markers has frequently been utilized in electrochemical detection of DNA hybridization. Osmium tetroxide complexes with tertiary amines (Os,L) bind covalently to pyrimidine (predominantly thymine) bases in DNA, forming stable, electrochemically active adducts. We propose a technique of electrochemical "multicolor" DNA coding based on RP labeling with Os,L markers involving different nitrogenous ligands (such as 2,2' -bipyridine, 1,10-phenanthroline derivatives or N,N,N',N'-tetramethylethylenediamine). At carbon electrodes the Os,L-labeled RPs produce specific signals, with the potentials of these differing depending on the ligand type. When using Os,L markers providing sufficiently large differences in their peak potentials, parallel analysis of multiple target DNA sequences can easily be performed via DNA hybridization at magnetic beads followed by voltammetric detection at carbon electrodes. Os,L labeling of oligonucleotide probes comprising a segment complementary to target DNA and an oligo(T) tail (to be modified with the osmium complex) does not require any organic chemistry facilities and can be achieved in any molecular biological laboratory. We also for the first time show that this technology can be used for labeling of oligonucleotide probes hybridizing with target DNAs that contain both purine and pyrimidine bases.

Visualization of three-dimensional nephron structure with microcomputed tomography

The three-dimensional architecture of nephrons in situ and their interrelationship with other nephrons are difficult to visualize by microscopic methods. The present study uses microcomputed X-ray tomography (micro-CT) to visualize intact nephrons in situ. Rat kidneys were perfusion-fixed with buffered formalin and their vasculature was subsequently perfused with radiopaque silicone. Cortical tissue was stained en bloc with osmium tetroxide, embedded in plastic, scanned, and reconstructed at voxel resolutions of 6, 2, and 1 microm. At 6 microm resolution, large blood vessels and glomeruli could be visualized but nephrons and their lumens were small and difficult to visualize. Optimal images were obtained using a synchrotron radiation source at 2 microm resolution where nephron components could be identified, correlated with histological sections, and traced. Proximal tubules had large diameters and opaque walls, whereas distal tubules, connecting tubules, and collecting ducts had smaller diameters and less opaque walls. Blood vessels could be distinguished from nephrons by the luminal presence of radiopaque silicone. Proximal tubules were three times longer than distal tubules. Proximal and distal tubules were tightly coiled in the outer cortex but were loosely coiled in the middle and inner cortex. The connecting tubules had the narrowest diameters of the tubules and converged to form arcades that paralleled the radial vessels as they extended to the outer cortex. These results illustrate a potential use of micro-CT to obtain three-dimensional information about nephron architecture and nephron interrelationships, which could be useful in evaluating experimental tubular hypertrophy, atrophy, and necrosis.

Microwave-assisted processing and embedding for transmission electron microscopy

Microwave processors can provide a means of rapid processing and resin embedding for biological specimens that are to be sectioned and examined by transmission electron microscopy. This chapter describes a microwave-assisted protocol for processing, dehydrating, and embedding biological material, from living specimens to blocks embedded in sectionable resin in 4 h or less.

DNA damage induced nucleotide excision repair in Saccharomyces cerevisiae

Nucleotide excision repair (NER) is the most versatile and universal pathway of DNA repair that is capable of repairing virtually any damages other than a double strand break (DSB). This pathway has been shown to be inducible in several systems. However, question of a threshold and the nature of the damage that can signal induction of this pathway remain poorly understood. In this study it has been shown that prior exposure to very low doses of osmium tetroxide enhanced the survival of wild type Saccharomyces cerevisiae when the cells were challenged with UV light. Moreover, it was also found that osmium tetroxide treated rad3 mutants did not show enhanced survival indicating an involvement of nucleotide excision repair in the enhanced survival. To probe this further the actual removal of pyrimidine dimers by the treated and control cells was studied. Osmium tetroxide treated cells removed pyrimidine dimers more efficiently as compared to control cells. This was confirmed by measuring the in vitro repair synthesis in cell free extracts prepared from control and primed cells. It was found that the uptake of active (32)P was significantly higher in the plasmid substrates incubated with extracts of primed cells. This induction is dependent on de novo synthesis of proteins as cycloheximide treatment abrogated this response. The nature of induced repair was found to be essentially error free. Study conclusively shows that NER is an inducible pathway in Saccharomyces cerevisiae and its induction is dependent on exposure to a threshold of a genotoxic stress.

Use of Anti-fluorophore Antibody to Achieve High-sensitivity Immunolocalizations of Transporters and Ion Channels

We have discovered that the immunoreactivity of the fluorophore Alexa Fluor 488 survives glutaraldehyde and osmium tetroxide fixation and epoxy resin embedding and etching. We have developed new localization methods that for the first time take advantage of this property. The antigen is localized in cryosections using suitable primary antibody and an Alexa Fluor 488-conjugated secondary antibody. Cryosection fluorescence can be photographed for later correlation with electron microscopy (EM) findings. The sections are then further fixed with glutaraldehyde and OsO4, if desired and flat-embedded in epoxy resin. Semi-thin sections are etched completely with sodium ethoxide, whereas thin sections are partially etched. Alexa Fluor 488 is then localized with rabbit anti-Alexa Fluor 488 and goat anti-rabbit conjugated to Alexa Fluor 488 [light microscopy (LM)] or to colloidal gold (EM). A second antigen may also be localized using Alexa Fluor 568. When used without postfixation, these methods produce high-resolution semi-thin, or even thin, sections that retain a high level of fluorescence for LM observations. These methods allow highly sensitive immunolocalizations in tissue while preserving cell fine structure through traditional fixation and epoxy embedding. In demonstration of the methods, we describe the localization of the thiazidesensitive sodium/chloride cotransporter and the epithelial sodium channel in rat kidney.

Integral lipid in human hair follicle

On the hair surface, cells are covered with a thin lipid layer (LL) covalently bonded to hair proteins. This integral hair lipid is different from sebaceus lipid. We conducted this study to examine the lipid distribution in human hair follicle. Transmission electron microscopy was performed to observe the ultrastructure of the LL. Hair follicles were cut and observed longitudinally along the hair axis. For transmission electron microscopy, new fixative (Lee's fixative: composed of OsO4 and RuO4) was designed as the conventional fixatives such as OsO4 or RuO4 alone were not appropriate for staining for hair follicle lipid. In addition, we measured the chemical composition of integral hair lipid by high-performance thin-layer chromatography. From the above experimental procedure, it was discovered that the lipid in the hair follicle was mainly distributed in hair cuticle and keratinized inner root sheath. A multitude of lamellar granule is observed in the vicinity of the above LL. The chemical composition of integral hair lipid was different from those of epidermal or sebaceous lipids. It is assumed that the LL in the hair follicle is similar to the epidermal LL playing an important role as a skin barrier in the stratum corneum. We proposed here the new terminology "hair barrier" from this point of view.

Fine ultrastructure of chromaffin granules in rat adrenal medulla indicative of a vesicle-mediated secretory process

Observation by transmission electron microscopy, coupled with morphometric analysis and estimation procedure, revealed unique ultrastructural features in 25.94% of noradrenaline (NA)-containing granules and 16.85% of adrenaline (A)-containing granules in the rat adrenal medulla. These consisted of evaginations of the granule limiting membrane to form budding structures having different morphology and extension. In 14.8% of NA granules and 12.0% of A granules, outpouches were relatively short, looked like small blebs emerging from the granule surface and generally contained electron-dense material. A proportion of 11.2% of NA granules and 4.9% of A granules revealed the most striking ultrastructural features. These secretory organelles presented thin, elongated, tail-like or stem-like appendages, which were variably filled by chromaffin substance and terminated with spherical expansions of different electron density. A cohort of vesicles of variable size (30-150 nm in diameter) and content was found either close to them or in the intergranular cytosol. Examination of adrenal medullary cells fixed by zinc iodide-osmium tetroxide (ZIO) revealed fine electron dense precipitates in chromaffin granules, budding structures as well as cytoplasmic vesicles. These data indicate that a common constituent is revealed by the ZIO histochemical reaction in chromaffin cells. As catecholic compounds are the main tissue targets of ZIO complexes, catecholamines are good candidates to be responsible for the observed ZIO reactivity. This study adds further to the hypothesis that release of secretory material from chromaffin granules may be accomplished by a vesiclular transport mechanism typical of piecemeal degranulation.

Cytochemical characterization of the endomembranous system during the oocyte primary growth in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae)

The morphophysiological changes that occur during oocyte primary growth in Serrasalmus spilopleura were studied using ultrastructural cytochemical techniques. In the previtellogenic oocytes endoplasmic reticulum components, Golgi complex cisternae and vesicles, lysosomes, multivesicular bodies and some electron-dense vesicles react to acid phosphatase (AcPase) detection. The endoplasmic reticulum components, Golgi complex cisternae and vesicles also react to osmium tetroxide and potassium iodide impregnation (KI). These structures, except for the Golgi complex cisternae, are strongly contrasted by osmium tetroxide and zinc iodide impregnation (ZIO). Some electron-dense vesicles are ZIO-stained, while microvesicles in the multivesicular bodies and other large isolated cytoplasmic vesicles are contrasted by KI. At primary oocyte growth, the activity of the endomembranous system and the proliferation of membranous organelles are intense. The biosynthetic pathway of the lysosomal proteins such as acid phosphatase, involves the endoplasmic reticulum, Golgi complex, vesicles with inactive hydrolytic enzymes and, finally, the lysosomes. The oocyte endomembranous system have reduction capacity and are involved in the metabolism of rich in SH groups.

Modulation of smooth muscle cell function: Morphological evidence for a contractile to synthetic transition in the rat ventral prostate after castration

In this study, we evaluated the involvement of rat ventral prostate smooth muscle cells (SMC) in secretory activity and whether this function is modulated after castration. Cell morphology was examined at both light and electron microscopy levels and the organelles involved in secretory function were labeled by the zinc-iodide-osmium (ZIO) method at the ultrastructural level and their volume density was determined by stereology. Castration resulted in marked changes of the SMC, which adopted a spinous aspect and abandoned the layered arrangement observed in the prostates of non-castrated rats. The volume density of ZIO reactive organelles increased progressively after castration, reaching significantly higher levels 21 days after castration. Since previous studies have demonstrated that SMC express SMC markers (even 21 days after castration) and are able to respond to adrenergic stimulation, we concluded that differentiated SMC are able to shift from a predominantly contractile to a more synthetic phenotype without changing their differentiation status.

Low pressure mode combined with OsO4 vapor fixation and sputter-coating for the preservation of delicate aerial hyphae and conidia in the ESEM

The newer generation of environmental scanning electron microscopes (ESEMs) allows samples to be viewed under a range of different vacuum conditions. No specific sample preparation protocols are required with the ESEMs, as fresh, unfixed samples are used and discarded later. We have worked out a method that preserves aerial hyphae on biltong that closely resemble fresh specimens and may be stored for viewing at a later date. Another advantage is that fixed samples are more resilient to the variable vacuum encountered in the ESEM. When biltong samples with fungal growth were first studied, we observed that vacuum-related artifacts were induced unless vacuum conditions and changes in pressure were carefully controlled. Damage readily occured in conidia and its delicate hyphae. Fresh, unfixed samples are very vulnerable to these artifacts. In addition, biltong proved to be a problematic study sample because of its high salt content, its hygroscopic nature as well as being laden with spices. To eliminate these artifacts, the preservation of specimens by OsO4 vapor fixation combined with a special sputter-coating technique is described. Previous studies confirmed that OsO4 vapor fixation is superior to traditional immersion fixation methods for the examination of hyphae and conidia of various fungi in a conventional SEM. However, both preparation methods induce sample shrinkage. We observed that OsO4 vapor fixation followed by Au coating under strictly controlled vacuum conditions induced fewer artifacts and gave the best images with minimum distortion in low pressure (LP) mode. The proposed method allows samples to be viewed both in ESEM and LP mode. There are however some disadvantages inherent to ESEM mode. Even when viewing fixed, coated samples, care should be taken to maintain a pressure of not lower than 0.2 Torr in the specimen chamber. It is critical that different samples have the same vacuum exposure history, as shrinkage and collapse were found to be directly related to the lowest pressure the samples were subjected to, both in the sputter coater chamber and in the electron microscope specimen chamber.

Distribution of the pores of epithelial basement membrane in the rat small intestine

The distribution and diameter of the pores of epithelial basement membrane in the intestinal villi and the lymph nodules of ileal Peyer's patches were investigated in the rat small intestine by scanning electron microscopy after the removal of the overlying epithelial cells with OsO(4) maceration. In the duodenum, jejunum and ileum, the pores were mainly distributed at the upper three fourths of the villi, but were scarce around the top of the villi. The diameter of some of the pores in the upper three fourths of the villi was larger than that of those in the lower portion. The protrusion of lymphocytes and the cytoplasmic processes of macrophages were also seen at the orifices of the pores. In ileal Peyer's patches, in contrast, pores were densely distributed in the lower one third of the follicle-associated epithelium (FAE) where M cells were mainly seen. Furthermore, these pores were larger than those found in the upper two thirds. Lymphocytes or cytoplasmic processes of macrophages were frequently seen in the lower one third of FAE. These results suggest that the pores at the basement membrane correspond to the passage of the immunocompetent cells which are in contact with M cells or villous columnar epithelial cells and that the abundance of pores is a sign of aggressive interaction between the particular epithelial cells and the immunocompetent cells at the upper three fourths of intestinal villi and the lower one third of FAE in the rat small intestine.

Simultaneous fixation using glutaraldehyde and osmium tetroxide or potassium ferricyanide-reduced osmium for the preservation of monogenean flatworms: An assessment forMerizocotyle icopae

Simultaneous fixation was investigated for a marine organism: the monogenean flatworm ectoparasite Merizocotyle icopae. Four protocols for primary fixation were compared: 3% glutaraldehyde alone in 0.1M cacodylate buffer for a minimum of 2 hours; 1% glutaraldehyde in combination with 1% osmium tetroxide, both in 0.1M cacodylate buffer, until tissues darkened (5-20 minutes); 1% glutaraldehyde in 0.1M cacodylate buffer in combination with 0.5% potassium ferricyanide-reduced osmium until tissues darkened (5-20 minutes); 1% glutaraldehyde in combination with 1% osmium tetroxide, both in 0.1M cacodylate buffer, for 30 minutes. The study confirms that the standard method for transmission electron microscopic fixation (first listed protocol) routinely applied to platyhelminths is optimal for ultrastructural preservation, but some simultaneous fixation methods (second and third listed protocols) are acceptable when rapid immobilization is needed. Scanning electron microscopic preparations may be improved using simultaneous primary fixation.

The problematic issue of Kufs disease diagnosis as performed on rectal biopsies: a case report

Kufs disease, the late-onset form of a group of neurodegenerative disorders, known as the neuronal ceroid-lipofuscinoses, is characterized by intraneuronal/extraneuronal accumulation of proteins that are visible as fingerprint inclusions and granular osmiophilic deposits (GRODs) at the ultrastructural level. A problematic case of Kufs disease in a 53-year-old female affected by progressive gait disturbances, myoclonus, epilepsy, and profound dementia is presented. Laboratory, biochemical, and molecular genetic tests were unremarkable. A magnetic resonance imaging of the brain revealed a moderate atrophy over both hemispheres with no white matter changes. Ultrastructural examination of rectal mucosa biopsies showed fingerprint inclusions in perivascular smooth muscle cells. Pathological examination of autoptic tissues showed numerous intraneuronal PAS-positive, diastase-resistant inclusions corresponding to GRODs at the ultrastructural examination, but no fingerprint inclusions. Cerebellum, skeletal, and cardiac muscles, skin, and liver were unaffected. The present case illustrates the diagnostic difficulties encountered while examining Kufs disease pathological samples. Main problematic issues include (1) specificity and diagnostic value of fingerprint inclusions when found exclusively in perivascular smooth muscle cells; (2) safe distinction of GRODs from lipofuscin inclusions in cerebral tissue; and (3) reliability in using extraneural tissues and, in particular, rectal mucosa biopsies for diagnostic purposes.

Cryo-sectioning and chemical-fixing ultramicrotomy techniques for imaging rubber latex particle morphology

Two methods adapted from biological microscopy are described for a new application in imaging the morphology of rubbery latex particles. In the first method, a drop of latex is frozen in liquid nitrogen, sectioned with a diamond knife and vapour-stained with osmium tetroxide, then viewed by transmission electron microscopy. When applied to latexes made by emulsion polymerization of methyl methacrylate in a natural rubber latex seed, inclusions are clearly visible. A chemical fixation method is then described for imaging the morphology of such rubbery latex particles. Glutaraldehyde is added to the latex, followed by osmium tetroxide. The sample is then dehydrated in ethanol, epoxy resin added, and the sample cured, ultramicrotomed, and imaged with transmission electron microscopy. An inclusion morphology is again clearly seen.

Structure of long bones in mammals

Techniques for staining (silver, osmium, metal sulfides, ink) and microphotography (epi-illumination) of polished bone surfaces have been developed to visualize the three-dimensional structure of the shafts of mammalian long bones. Bone is a two-compartment system with capillaries and some kinds of connective tissue in one compartment separated from fibers of bone collagen, often forming lamellae, in the other. Laminar bone consists of stacks of lamellae separated by vascular spaces containing capillary network sheets. It is deposited at the periosteal and endosteal surfaces. Osteonic bone, well described in the literature, consists of cylinders of lamellae with central vascular spaces. The primary structure of the shafts of mammalian long bones is laminar and laminae often remain as the main component. Secondary osteons are a replacement within laminae. As laminar bones mature, some of the irregular longitudinal capillary spaces in the network sheets enlarge and become less crooked to form secondary osteons. Parts of the random networks become ordered longitudinal ones, resulting in collapse of those network spaces not converted to osteons. The residual capillaries become bloodless, making the surviving network spaces difficult to resolve. This may account for them being overlooked in descriptions of bone structure. For example, laminar bone occurs with osteonic bone in the human femur, although it is rarely figured. Nearly mature bones switch the kind of primary bone deposited at the peripheral (periosteal) surface from laminar to primary osteonic.

Synthesis of a thymine glycol building block and its incorporation into oligonucleotides

A phosphoramidite building block of thymine glycol, a major oxidative base damage in DNA, was synthesized in four steps from protected thymidine. The two hydroxyl functions of the oxidized base were protected with the tert-butyldimethylsilyl group. Using this building block, oligonucleotides containing this damage were synthesized.

Malachite green and phthalocyanine-silver reactions reveal acidic phospholipid involvement in calcification of porcine aortic valves in rat subdermal model

Subdermal implant models are helpful in the study of calcification "in vivo" and for testing anticalcific treatments. After implantation of porcine aortic valve leaflets in rat subcutis, we previously found that glutaraldehyde-Cuprolinic blue reactions (GA-CB) at low pH induce favourable tissue unmasking from mineral deposits, and visualize peculiar, electrondense layers that outline the calcifying cells and matrix vesicle-like structures. The layer-forming material seemed to consist of acidic phospholipids because of its anionic nature and differential susceptibility to chemical/enzymatic extractivity. In the present investigation, pre-embedding glutaraldehyde-Malachite green (GA-MG) reactions and subsequent osmium post-fixation were compared with pre-embedding GA-CB reactions, combined with post-embedding von Kossa silver staining (GA-CB-S), to assess whether the layer-forming material is actually composed of acidic phospholipids and exhibits calcium-binding properties. After lowering standard pH, GA-MG reactions also caused sample demineralization and the appearance of pericellular osmium-MG-reactive layers comparable to CB-reactive ones. Moreover, GA-CB-S reactions showed that major silver precipitation was superimposed to the CB-reactive layers, whereas minor metal extra-precipitation occurred at three distinct, additional sites. These results demonstrate that a unique process of cell degeneration occurs in this calcification model, in which acidic phospholipids accumulate at cell surface, replacing cell membrane and acting as major apatite nucleator. However, the overall observations are consistent with the hypothesis that certain phases are common to the various types of normal and/or abnormal calcification.

Hyperthermia triggers apoptosis and affects cell adhesiveness in human neuroblastoma cells

Hyperthermia is a known apoptotic inducer and has been recently utilized in combination with chemo-and/or radiotherapy in cancer treatment. In this study we have described its effect on SK-N-MC human neuroblastoma tumor cells, a line which grows as a double adherent and floating population. Considering this particular culture behavior, we also investigated the relationship between hyperthermia and cell adhesiveness by evaluating integrin expression, namely CD11a, which is, as known, closely correlated to cell adhesion properties. By a multiple, ultrastructural and flow cytometrical approach, we have demonstrated that hyperthermia, while triggering apoptosis, also determines a CD11a surface expression decrease in apoptotic and living cells. We thus suggest a further role for this treatment, which, affecting adhesion mechanisms, could down-regulate metastatic diffusion.

An alternative technique to reveal polysaccharides in Toxoplasma gondii tissue cysts

Ultrathin sections of tissue cysts isolated from the brain of Toxoplasma gondii infected mice were submitted to two different methodologies derived from the periodic acid - Schiff's reagent (PAS) technique. The use of osmium tetroxide vapor as a developing agent of the aldehyde oxidation to reveal polysaccharides with periodic acid resulted in positive reaction in amylopectin granules in bradyzoites, as well as in the wall and matrix of the cysts, with excellent increment of the ultrastructural morphology. This technique can be used for study of T. gondii-host cell intracellular cycle, the differentiation tachyzoite-bradyzoite, and also for the formation of cysts into the host cells.

Lipase TL-mediated kinetic tesolution of 5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol at low temperature: concise asymmetric synthesis of both enantiomers of a piperazic acid derivative

Lipase TL-mediated kinetic resolution of (+/-)-5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol (5) at low temperature proceeded to give the corresponding (S)-alcohol 5 and (R)-acetate 6 in quantitative yields with high enantiomeric purity. The addition of bases such as pyridine, DMAP, 2,4- and 2,6-lutidines, or triethylamine considerably enhanced the rate of kinetic resolution. The alcohol (S)-5 and the acetate (R)-6 were converted to piperazic acid derivatives (R)- and (S)-3, respectively, via the intramolecular Mitsunobu reaction as a key step.

Shape and position of the sarcoplasmic reticulum and the Golgi apparatus in the sole plate and remaining subsarcolemmal muscle region of the mouse using imidazole-osmium staining

By means of thin (< or =150 nm) and thick (>150 nm) sections, the shape and position of the sarcoplasmic reticulum and of the Golgi apparatus in the sole plate and in the remaining subsarcolemmal sarcoplasmic region were investigated. For this purpose the membranes were stained by means of imidazole-osmium postfixation and unstained sections analyzed under the electron microscope. Both in the sarcoplasma of the sole plate and around the muscle fiber nuclei, a network of tubules is visible after imidazole-osmium staining which can be identified as the sarcoplasmic reticulum solely on the basis of its contacts with the perinuclear cistern and the cisterns of the triads. Findings in literature on the position of the Golgi apparatus are confirmed and similar spatial relationships and vesiculations between the perinuclear cisterns and the Golgi apparatus of the sole plate nuclei and the other subsarcolemmal fiber nuclei are also demonstrated using this new staining method.

Zone between plaque and attached periodontal tissues on chronic periodontitis-affected teeth: an SEM study

The zone between plaque and attached periodontal tissues on chronic periodontitis-affected teeth was examined by a combined macroscopic and scanning electron microscopy (SEM) approach. Examined were 27 teeth with chronic periodontitis (chronic periodontitis-affected group) and three healthy teeth with no evidence of periodontal disease (control group). Both groups were collected immediately after extraction, fixed in 2% glutaraldehyde, and post-fixed in 1% osmium tetroxide. Then, teeth were macroscopically examined to identify their stained zones. Teeth were dehydrated, critical-point dried, gold coated, and examined in an SEM. Both healthy and chronic periodontitis-affected teeth showed a very similar staining pattern on their surfaces. An unstained band with a belt-like appearance was observed around the teeth, delimited by two osmium-stained zones. Some weakly stained areas were frequently observed inside the unstained band. The SEM examination showed four different regions in both groups. These regions appeared in the following coronoapical sequence: dental plaque, plaque-free zone, junctional epithelium, and attached periodontal tissues. A dental cuticle covering the cementum surface from the plaque border to the junctional epithelium was detected on chronic periodontitis-affected teeth. Some aspects of this particular zone may be involved in the pathogenesis of inflammatory periodontal disease and therefore may have some influence on treatment for chronic periodontitis-affected teeth.

Dichloroketene-chiral olefin-based approach to pyrrolizidines: highly stereocontrolled synthesis of (+)-amphorogynine A

[reaction: see text] A highly stereoselective route to (+)-amphorogynine A, a novel pyrrolizidine recently isolated from the New Caledonian plant Amphorogynine spicata, has been realized. The key step in the approach is a diastereoselective [2 + 2] dichloroketene-chiral enol ether cycloaddition (dr >or= 93:7) to access a dichlorocyclobutanone intermediate, which is converted into the alkaloid natural product via a pyrrolidinone derivative.

Lens formation in the absence of optic cup in rat embryos irradiated with soft X-ray

In order to investigate the effect of soft X-ray irradiation on ocular development, pregnant rats were exposed to a single 12.5 Gy irradiation on embryonic day 9 (ED 9). The embryos obtained by laparotomy on ED 12 and 21 were examined for ocular abnormalities under a binocular stereo-microscope and a light microscope. The ED 12 embryos were stained with osmium tetroxide to facilitate the observation. The stereo-microscopic examination on ED 12 and 21 revealed various types of ocular abnormalities characterized primarily by aplasia or hypoplasia of the optic cup and invaginated lens placode. The light microscopic examination further confirmed these findings histomorphologically, and the hypoplastic abnormalities were classified into three types: (1) hypoplasia of the optic cup and invaginated lens placode, (2) complete malformation of the optic cup and hypoplasia of the invaginated lens placode, and (3) complete malformation of the optic cup and invaginated lens placode. Because the lens was formed in the complete absence of the retina, the development and differentiation of the retina and lens do not seem to be tightly synchronized. Thus, this sequential analysis on ocular abnormalities during the early stage of development supports the notion that the presence of the retina is not always necessary for the development of the lens.

The preparation of (S)-aspartate semi-aldehyde appropriate for use in biochemical studies

We report two three-step syntheses of (S)-aspartate semi-aldehyde, an important synthetic and biosynthetic precursor, from diprotected aspartic acid. The first synthesis proceeds via a thioester, the second via a Weinreb amide. Each route yields pure (S)-aspartate semi-aldehyde in excellent yield. (S)-Aspartate semi-aldehyde prepared in this manner has proved appropriate as a substrate for detailed enzyme studies.

High-resolution scanning electron microscopy of immunogold-labelled cells by the use of thin plasma coating of osmium

The feasibility of plasma coating of a thin osmium layer for high-resolution immuno-scanning electron microscopy of cell surfaces was tested, using Drosophila embryonic motor neurones as a model system. The neuro-muscular preparations were fixed with formaldehyde and labelled with a neurone-specific antibody and 10 or 5 nm colloidal gold-conjugated secondary antibodies. The specimens were post-fixed with osmium tetroxide and freeze-dried. Then they were coated with a 1-2 nm thick layer of osmium using a hollow cathode plasma coater. The thin and continuous coating of amorphous osmium gave good signals of gold particles and fine surface structures of neurites in backscattered electron images simultaneously. This method makes it possible to visualize the antigen distribution and the three-dimensionally complex surface structures of cellular processes with a resolution of several nanometres.

Examination of the rat eye at the early stage of development with osmium tetroxide staining

This communication describes the benefit of osmium tetroxide (OsO4) staining on the examination of the eye during the early stage of organogenesis of rat embryos. The embryos were obtained by laparotomy on embryonic day 12 (ED 12) and were stained with OsO4 for examination of the ocular tissues with a binocular stereo-microscope, light microscope and scanning electron microscope. At the binocular stereo-microscopic level, the invaginated lens placode, lens pit and optic cup were clearly distinguished. The osmium-stained lens placode and the optic cup were light brown and dark brown in color, respectively. Light microscopic examination revealed that OsO4 postfixation could provide superior paraffin-embedded embryonic sections. Scanning electron microscopic examination revealed the lens pit as a round opening between the lateral nasal prominence and maxillary prominence. Thus, a rapid technique by which the ocular tissues of rat embryos can be examined under a binocular stereo-microscope was developed. This OsO4 staining method will provide a useful tool for research on organogenesis and ocular development.