Three-dimensional reconstruction by scanning electron microscopy from serial epoxy resin semi-thin sections after ion-etching

Three-dimensional reconstruction was performed using scanning electron micrographs of serial semi-thin sections of Epon embedded specimens. Connective tissue in a rabbit ear chamber was fixed in glutaraldehyde and osmium tetroxide, and then embedded in Epon. One-microm-thick serial sections were cut with a diamond knife, mounted on glass slides and stained with toluidine blue. After observation with a light microscope, the sections were ion-etched with an ion-spatter coater. Following double staining with uranyl acetate and lead citrate, the consecutive sections were ion-coated with platinum. Each serial section was photographed with a scanning electron microscope. Profiles of a blood vessel and fibroblasts were digitized with a computer and computer reconstruction of the blood vessel was performed. Three-dimensional reconstructions showed that the newly formed blood vessel was a cylinder-like, bare endothelial tube with a rather smooth outer surface. Fibroblasts were situated around the endothelial tube. Several openings were found in the endothelial tube, suggesting the morphological feature of high permeability and fragility in newly formed blood vessels. The availability of three-dimensional reconstruction from scanning electron micrographs of serial semi-thin epoxy resin sections was discussed; structures of interest can be reconstructed (1) quickly and easily, (2) without skilful techniques, and (3) almost at the level of ultrastructure.

A new method for detecting and localizing cell markers endocytosed by fibroblasts in epoxy resin semi-thin sections using scanning electron microscopy combined with energy dispersive X-ray microanalysis after ion-etching

Cell marking is widely used to examine cell development and differentiation in developmental biology. We developed a new method for localizing cell markers in a semi-thin epoxy section with scanning electron microscopy. Cultured fibroblasts ingesting carbon particles were autologously transplanted into a rabbit transparent ear chamber, 6 mm in diameter and 100 microm in depth. Eight days after the transplantation, tissues in the chamber were fixed and embedded in epoxy resin. Semi-thin sections were cut and stained with toluidine blue. Fibroblasts in connective tissues which contained black spots were observed with a light microscope. These sections were subsequently ion-etched with an ion-coater and coated with platinum. The same fibroblasts were then visualized by secondary electron imaging using a scanning electron microscope. A nucleus with nuclear envelope, nuclear pores, a nucleolus and heterochromatin, mitochondria with cristae and rough endoplasmic reticulum were observed in the fibroblasts. The black spots in the fibroblasts were identified as bright bodies with the scanning electron microscope. The bright bodies were found to be a lump of tiny particles less than 100 nm in diameter. In order to analyse such particles with energy dispersive X-ray microanalysis, ion-etched sections were coated with carbon. X-ray energy spectrometry clearly demonstrated that these were carbon particles, which had been endocytosed by the fibroblast. This suggests that scanning electron microscopy combined with energy dispersive X-ray microanalysis is useful for detecting carbon particles in the cytoplasm at an ultrastructural level in semi-thin epoxy sections subsequent to ion etching and that this method may be applicable to other cell markers, such as gold particles to track cells in the field of cell development and cell differentiation.

An investigation of the nature and function of module 10 in a family F/10 xylanase FXYN of Streptomyces olivaceoviridis E-86 by module shuffling with the Cex of Cellulomonas fimi and by site-directed mutagenesis

Although the amino acid homology in the catalytic domain of FXYN xylanase from Streptomyces olivaceoviridis E-86 and Cex xylanase from Cellulomonas fimi is only 50%, an active chimeric enzyme was obtained by replacing module 10 in FXYN with module 10 from Cex. In the family F/10 xylanases, module 10 is an important region as it includes an acid/base catalyst and a substrate binding residue. In FXYN, module 10 consists of 15 amino acid residues, while in Cex it consists of 14 amino acid residues. The Km and kcat values of the chimeric xylanase FCF-C10 for PNP-xylobioside (PNP-X2) were 10-fold less than those for FXYN. CD spectral data indicated that the structure of the chimeric enzyme was similar to that of FXYN. Based on the comparison of the amino acid sequences of FXYN and Cex in module 10, we constructed four mutants of FXYN. When D133 or S135 of FXYN was deleted, the kinetic properties were not changed from those of FXYN. By deletion of both D133 and S135, the Km value for PNP-X2 decreased from the 2.0 mM of FXYN to 0.6 mM and the kcat value decreased from the 20 s(-1) of FXYN to 8.7 s(-1). Insertion of Q140 into the doubly deleted mutant further reduced the Km value to 0.3 mM and the kcat value to 3.8 s(-1). These values are close to those for the chimeric enzyme FCF-C10. These results indicate that module 10 itself is able to accommodate changes in the sequence position of amino acids which are critical for enzyme function. Since changes of the spatial position of these amino acids would be expected to result in enzyme inactivation, module 10 must have some flexibility in its tertiary structure. The structure of module 10 itself also affects the substrate specificity of the enzyme.

Significant enhancement in the binding of p-nitrophenyl-beta-D-xylobioside by the E128H mutant F/10 xylanase from Streptomyces olivaceoviridis E-86

Mutagenesis studies were carried out to examine the effects of replacement of either the nucleophile Glu-236 or the acid/base Glu-128 residue of the F/10 xylanase by a His residue. To our surprise, the affinity for the p-nitrophenyl-beta-D-xylobioside substrate was increased by 10(3)-fold in the case of the mutant E128H enzyme compared with that of the wild-type F/10 xylanase. The catalytic activity of the mutant enzymes was low, despite the fact that the distance between the nucleophilic atom (an oxygen in the native xylanase and a nitrogen in the mutant) and the alpha-carbon was barely changed. Thus, the alteration of the acid/base functionality (Glu-128 to His mutation) provided a significantly favorable interaction within the E128H enzyme/substrate complex in the ground state, accompanying a reduction in the stabilization effect in the transition state.

Dorsal root ganglion neuron development in chick and rat

The aim of this study was to compare the morphological development of dorsal root ganglion neurons in embryonic and early postnatal chicks and rats. The three-dimensional architecture of neurons was observed in ganglia in situ and in dissociated neurons by scanning electron microscopy after removal of the capsule and connective tissue. The percentages of neurons at different developmental stages were determined. The general morphological changes in the chick resembled those in the rat but the timing was different. In both chick and rat, the majority of neurons were bipolar at early stages of development (embryonic day 6 in chick and day 14 in rats) and later underwent pseudo-unipolarization to become mostly unipolar neurons at hatching or birth. This maturation event started at an earlier stage in chick embryos than in rats, with 57% unipolar neurons in chick and only 7% in rat on embryonic day 14. However, just after hatching or birth, at day 22 of development, a larger proportion of immature unipolar neurons remained in chicks (13%) than in rats (3%). We conclude that these differences should be taken into consideration in designing experiments on dorsal root ganglion neurons grown in tissue culture.

Noradrenergic hyperinnervation in the caval vein of stroke-prone spontaneously hypertensive rats

1. The distribution of fluorescent noradrenergic (NA) nerve fibres in the caval vein, which originate from the coeliac ganglion, was examined by glyoxylic acid method in stroke-prone spontaneously hypertensive rats (SHRSP) aged 10, 30, 60, 90 and 180 days. The results were compared with those in age-matched normotensive Wistar Kyoto (WKY) rats. 2. The distribution pattern of NA nerve fibres in the caval vein in both strains changed from a meshwork pattern at 10 days of age to a wavelike line arrangement after 30 days of age. 3. The densities of NA fibres of the caval veins in SHRSP were significantly higher (P < 0.01, Student's t-test, 6 d.f.) than those of WKY at all ages examined. The difference in NA fibre density between SHRSP and WKY showed double peaks at 10 and 90 days of age. 4. The present study suggests that hyperinnervation of the caval vein based on the hyperfunction of the coeliac ganglion is an important factor in the development of hypertension and also may participate in increasing cardiac output because the heart of SHR causes marked hypertrophy from 90 days of age.

Application of a new morphometry system based on SEM stereo-pairs to the study of intestinal mucosa of rodents

A new morphometry system for submicroscopic three-dimensional structures was developed on the same principles as for the aerial survey using SEM stereo-pairs. This computer graphic system was applied to the analysis of the surface features of the intestinal mucosa. After removing the epithelial layer by prolonged osmication, core structures of the intestinal villi were exposed and 100 villi each from rat and mouse were measured. Average height, basal area and surface area of a single core of the rat were 188 microns, 20,200 microns2 and 93,500 microns2, respectively. Those of the mouse were 148 microns, 7,530 microns2 and 37,100 microns2, respectively. Surface amplifications by the rat and the mouse villi, after compensating for epithelial thickness, were calculated as 3.5 and 4.3, respectively; though amplifications based on the villous core were 4.6 and 4.9, respectively. These three-dimensional features of the intestinal mucosa were illustrated as submicroscopic maps by drawing their contour lines. It was demonstrated that the present morphometry system makes it possible to know not only the average features of a large sample, but also a variety of features of individual structures which were directly observed under SEM.

Morphometric study of the superior cervical and stellate ganglia of spontaneously hypertensive rats during the prehypertensive stage

To compare the functional state of the superior cervical (SCG) and stellate sympathetic ganglia (SG) of spontaneously hypertensive rats (SHR) with those of age-matched normotensive Wistar Kyoto rats (WKY), ganglion cell volume and area occupied by ganglion cells relative to each whole ganglionic area were morphometrically examined using the Texture Analyse System (TAS) in rats at 0, 10 and 30 days of age. The weight of each ganglion relative to animal weight was also measured. The ganglion cell volume and the relative area of ganglionic cells in both ganglia of SHR were significantly larger (P less than 0.05) than those of age-matched WKY at ages 0 and 10 days after birth. The relative ganglionic weights of SHR were significantly larger (P less than 0.01) compared with those of WKY at all ages examined, except for SG at 0 days after birth. These results show that the relative volume of sympathetic ganglion cells is greater in both SCG and SG of SHR than that of WKY, suggesting that hyperfunction of sympathetic ganglia occurs at the prehypertensive stage as a primary factor in the development of hypertension in SHR.

Clinical significance of mean circulatory filling pressure and cardiac preload under anesthesia

The circulatory effects of a rapid infusion of plasma substitute with intravenous administration of nitroglycerine (TNG) were investigated in low pressure systems of anesthetized patients by measuring various hemodynamic parameters. Measurements were made when the systolic blood pressure reached 70-80% of the control value after intravenous administration of TNG at 1-2 microg/kg/min and a 3.5% modified gelatin solution (Haemaccel) at a rate of 0.5 ml/kg/min. After the TNG was administered, the mean circulatory filling pressure (Pms) decreased, and the venous to arterial capacitance ratio (CV/CA) increased; however, they returned to control values after a rapid Haemaccel infusion. Changes in the pressure gradient between the X and Y valley of the right atrial pressure wave decreased to 70 +/- 14% of the control value when TNG was given and recovered to 106 +/- 22% by infusion. Pulmonary vascular resistance (PVR) decreased to 70 +/- 24% of the control value when TNG was administered and was restored to 96 +/- 40% by a rapid infusion. In the left ventricle, the mean velocity of myocardial circumferential fiber shortening (VCF) decreased in all cases when TNG was given and it recovered by a rapid infusion. In the right ventricle, VGF did not always decrease, and in a few case increased, but all cases recovered by a Haemaccel rapid infusion. We conclude that the augmentation of the right ventricular preload reserve is achieved by administration of TNG and infusion of a plasma substitute.

[Effect of mazindol on obesity induced by administration of gold thioglucose]

The present experiments were carried out to elucidate the effect of mazindol feeding on obese mice made by gold-thioglucose injection. Mazindol was added to the diet at the level of 0.5, 2, 10 mg/kg body weight. It was found that oral administration of mazindol reduced the body weight gain and perimetrial adipose tissue weights increased in GTG-obese mice. Decreased adipose tissue weights were correlated with the decreased level of size and volume of fat cells. Basal lipolytic activity and adrenaline-induced lipolysis were also significantly decreased in mazindol groups as compared to those in GTG-obese mice that were not administered mazindol. These results indicate that the weight reduction induced by mazindol administration might not be due to increase in fat mobilization. The increased level of liver and serum lipid induced by GTG-obesity was also found to be improved by mazindol. Scanning electron micrographs indicated that the villous width of the small intestine were significantly smaller in the mazindol group that those in the GTG-obese group. Sucrase and esterase activities of the small intestine were also decreased by mazindol feeding as compared to those in the GTG-obese mice. based on these results mechanisms of action of mazindol were discussed.

Role of endogenous lipid droplets of fat cells in epinephrine-induced lipolysis

Endogenous lipid droplets were prepared by subjecting fat cells to hypotonic shock and to Triton X-100 treatment. The structure of the endogenous lipid droplet fraction was examined by scanning and transmission electron microscopies. Neither intact fat cells nor disrupted cell membranes were detectable in the endogenous lipid droplet fraction. With this endogenous substrate, epinephrine elicited lipolysis with either hormone-sensitive lipase or lipoprotein lipase, but no cyclic AMP-protein kinase mediated stimulation of lipolysis was observed. On the other hand, epinephrine did not stimulate lipolysis when triolein emulsified with arabic gum was used as substrate. With the latter exogenous substrate, however, cyclic AMP-protein kinase was found to stimulate lipolysis with hormone-sensitive lipase as enzyme. These results agree with the proposal of Wise and Jungas that the epinephrine-stimulated increase of hydrolysis of endogenous fat is not mediated through cyclic AMP-protein kinase. A possible mechanism of hydrolysis of endogenous fat by induction of lipolysis by epinephrine in fat cells is discussed.

Morphometric analysis of testicular Leydig cells in normal adult mice

Stereological analysis was carried out on Leydig cells in perfusion-fixed testes of normal adult mice. In a decapsulated testis, the seminiferous tubules occupy 89.3% and the interstitial tissue makes up 10.7% of the volume of the testis parenchyma. The Leydig cells comprise 3.8% of testicular volume. There are 24.9 million Leydig cells per cm3 (or gm) of tissue. An average Leydig cell has a volume of 1,533 microns 3 and a surface area of 1150 microns 2. The smooth endoplasmic reticulum (SER) is the most prominent organelle in the Leydig cells, and has a membrane surface area of 2,428 cm2 per cm3 of fresh testis tissue, which is 8.5 times the surface area of the plasma membrane and constitutes 56.9% of the total membranes in Leydig cells. Mitochondria occupy 10.1% of the Leydig cell volume or 11.4% of cytoplasmic volume. The inner mitochondrial membrane (including tubular or vesicular cristae) provides a surface area of about 2855 microns 2/cell and is 2.26 times that of the outer membrane. There are approximately 712 cm2 of inner membranes per cm3 tissue. Mouse Leydig cells have numerous lipid droplets, which average 147 per cell and occupy 5.1% of the cell volume.

Decreased viscosity of human erythrocyte suspension due to drug-induced spherostomatocytosis

The effect of two cationic drugs (chlorpromazine and isoxsuprine) on the suspension viscosity of human erythrocytes were examined, comparing with the effect of anionic drugs. (1) As increasing the drug concentrations, the cationic drugs transformed the erythrocytes to stomatocytes, then to spherostomatocytes, while trinitrobenzene sulfonate, dehydroepiandrosterone sulfate and lysolecithin induced echinocytes, as well known. (2) The suspension viscosity decreased in parallel with the appearance of spherostomatocytes, but it increased in echinocytosis. (3) The membrane fluidity, measured by spin label method, was not a major determinant for the suspension viscosity in these cases, because of no systematic correlation. (4) The rheoscopic observation under shear force demonstrated that the spherostomatocytes deformed easily to ellipsoid with smooth cell surface, while the echinocytes less easily deformed to ellipsoid on which the small spikes persisted at higher shear. These distinct difference in deformed shape under high shear force could be related to the decreased suspension viscosity of spherostomatocytes. (5) In addition, the transformation to spherostomatocytes, thus the decreased viscosity, was primarily determined by the intramembraneous drug concentration.