Internal Structure Of Cells Research Articles

A retina with parallel input and pulsed output, extracting high-resolution information

Animal eyes resolve images 10-100 times better than either the acceptance angle of a single photoreceptor or the center-to-center distance between neighboring photoreceptors. A new model of the fly's visual system emulates this improved performance, offering a different approach to subpixel resolution. That an animal without a cortex is capable of this performance suggests that high level computation is not involved. The model takes advantage of a photoreceptor cell's internal structure for capturing and transducing light. This organelle is a waveguide. Neurocircuitry exploits the waveguide's optical nonlinearities, namely the shoulder region of its gaussian, angular-sensitivity profile, to extract high resolution information from the visual scene. The receptive fields of optically disparate inputs overlap in space. Photoreceptor input is continuous rather than discretely sampled. The output of the integrating module is a signal proportional to the position of the target within the detector array. Input imbalance at the level of the photodiode modules is detected by circuitry connecting neighboring visual elements. A pulsed network of these connections forms a parallel array that segments edges of an object and continuously reports its position to the underlying layer of feature extractors, offering a new approach to real time processing with high resolution and reduced computational load.

Stress waves in composite materials.

The method of cells (MOC) developed by Aboudi provides a powerful means for studying the propagation of waves through systems having complicated internal cell structure [Wave Motion 9, 141 (1987)]. Laminated materials are a common example. The method can handle harmonic waves and also transient waves arising from a finite duration impulse. The method is sufficiently robust to treat impact, as we show here. Both linear and nonlinear elastic-stress-strain relations can be included. The present work generalizes the method to include viscoelastic materials (such as polymers), systems with cell structure deviating from perfect periodicity (including random), and systems simulating actual impact experiments. We test the theory by comparing our results with measurements taken from a flat-plate impact experiment. The system investigated was a bilaminate composed of unit cells of epoxy and epoxy-graphite subcells. Using known and estimated material parameters, we find that the MOC gives a reasonable representation of the data. We then address some features of the experimental data that have not yet been explained by other theoretical methods. The importance of unit cell periodicity is tested by adding a random incremental width to each unit cell. Finally, the shortcomings of the MOC caused by using a truncated series expansion for the particle displacements, and neglecting plastic flow and nonadiabatic effects are discussed.

Dielectric spectroscopy of biological cells

In this paper, we describe some applications of dielectric spectroscopy to studies of the internal structure of biological cells, monitoring of cell growth in fermentation and imaging of biological cells. The composite cell models proposed for biological cells, including intracellular organelles, successfully simulate the dielectric behavior of lymphocytes and plant protoplasts. A new electrode-less method based on electromagnetic induction has been demonstrated to be a powerful method for the dielectric monitoring of cell growth in whisky and beer fermentation. The scanning dielectric microscope is a promising tool for dielectric imaging of biological cells.

FEISEM of the cell nucleus: A consideration of parameters

The wider usage of field emission scanning instruments over recent years has demonstrated their potential to provide useful information on internal cell structure without the necessity to prepare thin specimens in such a way that allows transmission of the electron beam. Resolution of these instruments at around lnm is comparable to that routinely achieved by TEM of biological samples, allowing high resolution surface imaging of intracellular structure. Over the past five years we have been investigating structural organisation of cell nuclei using a Topcon ABT DS130F instrument with a Schottky field emission system which incorporates a Tungsten/Zirconium oxide tip of 0.4μm radius, maintained at 1800°C and 10−8 torr with an extraction voltage of 4,800 volts which generates an emission current of around 60-80 microamps. Specification resolution of this instrument is 1nm at 30kV and 4nms at 1.0kV, using the top stage ‘in lens’ specimen position.After chemical fixation and critical point drying (optimised by maintaining absolute alcohols over molecular sieve and in line filtration of high purity CO2).

A Microtome for Sectioning Critical Point Dried Tissues for SEM

In this short technical note the construction and use of a simple microtome for sectioning critical point dried (CPD) specimens mounted on stubs are outlined. The rigidity of CPD specimens allows for light microscopically controlled sectioning by which the internal structure of plant organs or individual cells becomes visible. If compared with cryo-fracturing, this sectioning technique enables repeated sectioning through any exactly chosen plane, cell or nucleus of the specimen.

Sample preparation for electron microscopy of internal cell structure.

Methods are reviewed for examination of internal cell structure by high-resolution scanning electron microscopy and compared with the rapid-freeze deep-etch replica technique used in transmission electron microscopy. Rapid freezing of fresh material, followed by freeze-fracture, provides a theoretically attractive approach in ultrastructure studies, but the high protein and solute content of most cells prevents a deep three-dimensional view for material frozen without some form of extraction. After discussion of other methods it is concluded that the most useful general approach, at least for cultured cells, is to first permeabilize or break open the cells in a medium which preserves the structure under study in a functional state as, for example, the movement of chromosomes along the division spindle, or transport of proteins within the Golgi region. After permeabilization, with attendant partial extraction, the preparation can be fixed, then viewed by either deep-etch replication, or by high-resolution scanning electron microscopy, with structure of interest revealed in deep view.

Immunohistochemical identification of mast cells in formaldehyde‐fixed tissue using monoclonal antibodies specific for tryptase

An avidin-biotin enhanced immunoperoxidase procedure using monoclonal antibodies (AA1, AA3, and AA5) prepared against human mast cell tryptase resulted in intense staining of mast cells in paraffin-embedded tissue. The distribution of mast cells observed was similar to that seen when adjacent serial sections were stained using a standard procedure with toluidine blue, though the immunoperoxidase technique permitted the identification of significantly more mast cells. With monoclonal antibody AA1, immunostaining was entirely specific for mast cell granules, and there was negligible background staining in a range of tissues including lung, tonsil, colon, gastric mucosa, skin, and pituitary. There was no staining of antibody on basophils or on any other normal blood leukocyte. The technique was effective with tissue fixed in either Carnoy's or neutral buffered formalin, though the internal mast cell structure was better preserved with formaldehyde fixation. The immunoperoxidase staining procedure with monoclonal antibody AA1 is a highly specific and sensitive means for the detection of mast cells in routinely processed tissues.

Differential cellular response ofanabaena variabilisto iron

Abstract Anabaena variabilis is a photosynthetic, oxygenic bacterium which grows in multicellular filaments. We have observed two types of differential cell activities which occur in this organism with respect to iron nutrition. In iron limited cultures, a change in cellular organization is observed by light and electron microscopy. The change, characteristic of iron starvation is a breakdown of internal membranous cell structure and a thickened, electron dense outer boundary. With prolonged iron deprivation, cell lysis is observed and all cellular structure becomes disorganized. A second response to iron was noted in stationary phase cultures where a few cells in the filaments showed no cell disorganization. Autoradiography revealed that uptake of 55Fe was not uniform but only by a few cells in each filament.

Heteromerous interactions among glycolytic enzymes and of glycolytic enzymes with F-actin: effects of poly(ethylene glycol)

Interactions of glucose-6-phosphate isomerase ( d-glucose-6-phosphate ketol-isomerase, EC 5.3.1.9), aldolase ( d-fructose-1,6-bisphosphate D-glyceraldehyde-3-phosphate lyase, EC 4.1.2.13), glyceralde-3-phosphate dehydrogenase ( d-glyceraldehyde-3-phosphate: NAD + oxidoreductase (phosphorylating), EC 1.2.1.12), triosephosphate isomerase ( d-glyceraldehyde-3-phosphate ketol-isomerase, EC 5.3.1.1), phosphoglycerate mutase ( d-phosphoglycerate 2,3-phosphomutase, EC 5.4.2.1), phosphoglycerate kinase (ATP:3-phospho- d-glycerate 1-phosphotransferase, EC 2.7.2.3), enolase (2-phospho- d-glycerate hydro-lyase, EC 4.2.1.11), pyruvate kinase (ATP: Pyruvate O 2- phosphotransferase , EC 2.7.1.40) and lactate dehydrogenase ( (S)- lactate : NAD + oxidoreductase, EC 1.1.1.27) with F-actin, among the glycolytic enzymes listed above, and with phosphofruktokinase (ATP: d-fructose-6-phosphate 1-phosphortransferase, EC 2.7.1.11) were studied in the presence of poly(ethylene glycol). Both purified rabbit muscle enzymes and rabbit muscle myogen, a high-speed supernatant fraction containing the glycolytic enzymes, were used to study enzyme-F-actin interactions. Following ultracentrifugation, F-actin and poly(ethylene glycol) tended to increase and KCl to decrease the pelleting of enzymes. In general, the greater part of the pelleting occurred in the presence of both F-actin and poly(ethylene glycol) and the absence of KCl. Enzymes that pelleted more in myogen preparations than as individual purified enzymes in the presence of poly(ethylene glycol) and the absence of F-actin were tested for specific enzyme-enzyme associations, several of which were obsereved. Such interactions support the view that the internal cell structure is composed of proteins that interact with one another to form the microtrabecular lattice.

The Disposition of Silver Released from Soviet OBLAKO Rockets in Precipitation during the Hail Suppression Experiment Grossversuch IV. Part II: Case Studies of Seeded Cells

Abstract This paper describes analyses of data collected from four seeded storms during the 1978 summer program of Grossversuch IV in Switzerland. The storms all met the Soviet criteria for hail-forming potential and were seeded with Soviet-type OBLAKO rockets. A seeding “quality” was estimated in each of the cases by observing the internal structure of the storm cells with C, S and X-band radar, and the trajectory, time of residence and dispersion of the AgI aerosols in the seeded clouds with radar and chemical techniques. The notion of “seeding coverage” is presented as the ratio of the surface area of precipitation in which the seeding chemical is found at the ground to the surface area of the rainfall (using the 40 dBZ radar reflectivity contour near the ground). The study of two cells on 30 June 1978 shows that the seeding coverages were small (7% and 25%) and that estimated residence times for AgI in those portions of the cloud colder than −5°C were too short to allow for significant ice phase modif...

Atlas of Clinical Hematology

It is 25 years since the first edition of this atlas was published. The availability to physicians and technicians of a superior reference from which to learn and to check identification of cells and patterns in blood and bone marrow is as pertinent today as it was then. The meticulous, beautifully colored drawings of cellular detail as revealed in smears give this work particular value. The artists show a feeling for the internal structure of cells, depicting it in a way usually appreciated only on continuous fine focusing of the microscope, and generally not adequately represented in photomicrographs. The principal ingredients of this atlas are full- or half-page color reproductions of these drawings, many additional color photomicrographs, a number of electron photomicrographs, and suitable expository text, including recommendations on laboratory methodology. Normal cellular morphology is considered, as well as findings in blood, marrow, lymph nodes, and spleen in various hematologic

The structure of the sinus wall of the lymph node relative to its endocytic properties and transmural cell passage.

The internal structure of cells lining the lymphatic sinus of the lymph node includes the presence of large bristle-coated vesicles, transfer tubules, and vesicular organelles for the uptake and intracellular disposition of endocytosed material. The lining cells of the sinuses phagocytose particulate material from the lymph in the same manner as the sinusoidal endothelium of the bone marrow takes up particulates from the blood and, thus, are similar in this respect to the endothelial lining of the bone marrow sinusoids. Transmission and scanning electron microscopic examination of the lymphatic sinus wall in rat lymph nodes show that the walls of the lymphatic sinuses are continuous and do not have permanent apertures allowing free communication between the extrasinusoidal and intrasinusoidal compartments in the lymph node. Migrating lymphocytes cross the lymphatic sinus wall intracellularly, i.e., through the body of the lining cell, by making a temporary migration pore, which closes after the cell has reached the lumen of the sinus. In addition there are sporadic aggregations of macrophages in transmural positions. The direction of their movement is unknown.

Detection of the vacuole of yeast cells in suspension by transmittance radiometry

In search of methods for obtaining information about the internal structure of biological cells, two types of experimental/theoretical studies were carried out on suspensions of yeast cells. Both showed cells with central vacuoles to be radiometrically different from those of cells without vacuoles. In one case the cells were osmotically preshrunken, placed in a normal medium, and transmittance was monitored as they swelled. The presence of a vacuole was determined from the manner in which transmittance varied with cell volume. In the other method, the wavelength dependence of transmittance was measured. It was found to be different for suspensions of cells with and without vacuoles. For theoretical calculations, the cells were modeled as homogeneous and hollow spheres and spheroids. The refractive index of the core was taken equal to that of the medium. Predictions based on these cell models were used to interpret-the experimental findings.

Changes in the ultrastructure of Chlamydia psittaci produced by treatment of the host cell with DEAE-Dextran and cycloheximide

The ultrastructure of two Chlamydia psittaci serotypes was investigated in infected L-cell monolayers fixed and embedded in situ . This preparation preserved the relationship of the parasite to the internal structure of the host cells. Chlamydial inclusions in cells treated with diethylaminoethyl-dextran (DEAE-D) and cycloheximide were compared to inclusions in untreated cells. C. psittaci serotype 1 had the same or larger yields of infectious progeny per infected cell in treated cells as in untreated cells. This serotype developed normal inclusions following both treatments. C. psittaci serotype 2 had decreased infectivity yields per infected cell and developed aberrant chlamydial forms in treated cell monolayers. Serotype 2 inclusions contained pycnotic chlamydial forms and numerous miniature reticulate bodies in cycloheximide-treated cells. In DEAE-Dtreated cells, some serotype 2 reticulate bodies were abnormally pleomorphic and contained amorphous material of intermediate electron density. Other reticulate bodies had lost electron density, degenerated, and contained only fragments of the reticulum. Maturation of reticulate bodies into infectious elementary bodies was greatly decreased in serotype 2 inclusions that contained aberrant forms.

A scanning electron microscopic study of normal human oxyntic mucosa using blunt dissection and freeze fracture.

Biopsies from the fundic mucosa of healthy volunteers were examined by scanning electron microscopy following blunt dissection and freeze fracture. The mucosal surface exhibited a cobblestone appearance. With increased magnification, microvilli could be demonstrated on the luminal surface of individual surface cells. Blunt dissection of the gastric mucosa revealed tubular gastric pits descending from the surface until they opened into branched tubular gastric glands. The gastric glands are irregular in outline due to the knoblike projections of individual parietal cells. The internal structure of the component cells also was examined with the scanning electron microscope following freeze fracture. Mucous granules were observed in the apical portion of surface epithelial cells. Lumina of parietal cell canaliculi were found to be continuous with the lumen of the gastric glands. Pepsinogen granules could be seen throughout the cytoplasm of chief cells. The blunt dissection-freeze fracture technique utilizing the scanning electron microscope allows, for the first time, a three-dimensional view of human gastric mucosa, including the gastric pits and glands as well as some of the internal architecture of component cells.

General considerations of membranes.

It has long been believed that a membrane separates the contents of cells from the extracellular environment. With the advent of electron microscopy, this membrane, called the plasma membrane, was for the first time visualized and in addition it became evident that the internal structure of cells also contained complex systems of membranes (1) which are components of what often are called organelles (e.g., mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, etc.) (Fig.1). In recent years it has become possible to isolate in relatively pure form many of these membranous organelles from homogenates of tissues by means of differential and density gradient ultracentrifugation. From studies utilizing these isolated membranes the biochemical nature and the functions of many of these organelles have been established.KeywordsSarcoplasmic ReticulumGranular Endoplasmic ReticulumDensity Gradient UltracentrifugationSarcoplasmic Reticulum MembraneSarcoplasmic Reticulum FunctionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Ultrastructure of rat pineal gland after preparation by freeze-etching technique.

The pineal glands of Wistar rats were fixed in glutaraldehyde and prepared by the freeze-etching technique. With regard to the form and internal structure of pineal cells this technique has revealed nothing essentially new. Synaptic ribbons are very rarely found. A regular diagonal arrangement of membrane attached particles between the Schwann cell and the axon of an autonomic nerve terminal was observed.

Scanning electron microscopy of etched Epon extraocular muscle sections.

SUMMARYThe internal fine structure of extraocular muscle cells was observed with scanning electron microscopy. One micrometre Epon sections were etched with an iodine acetone solution. When adhered to carbon coated glass, such specimens may be viewed without surface coating. Such preparations provide information about the fibrillar organization of the muscle fibre, as well as its transverse tubular system and M line.

The Influence of Heat Processing and Mechanical Disintegration on Yeast for Single‐Cell Protein

AbstractYeast was processed by means of different technical drying procedures, heating in water suspension, and mechanical disintegration. The influence on the ultrastructure, the nutritive value and on the availability of the cell nitrogen‐containing compounds to chemical extractants was studied.On micrographs no cell wall disrupture could be observed after any of the heat treatments. The internal cell structure was affected at the higher temperatures. After drum drying this structure was destroyed to a large extent. The heat treatments increased the nutritive value compared to unheated yeast cells but did not increase the availability of the cell content to chemical extractants. Mechanical disintegration increased both the nutritive value and the availability to chemical extractants.Heat processes and mechanical disintegration give high nutritive value to the yeast. Mechanical disintegration is advantageous when processing steps such as extraction with chemicals are necessary for obtaining specific protein products.

Molecular Aspects of Sickle Cell Hemoglobin: Clinical Applications

This book is welcomed because it brings under one cover the numerous recent contributions of Dr. Nalbandian and his associates relating to sickle cell diseases. The theme of the book is that the pathogenesis, diagnosis, and treatment have a molecular basis, that urea is capable of inhibiting and reversing the sickling process, and that urea is the treatment of choice. Murayama presents his hypothesis that the sickling process involves hydrophobic bonding between the hemoglobin molecules, resulting in the stacking of molecules in elongated microtubules. He discusses magnetically oriented sickled erythrocytes and the presence of a dialyzable cofactor. Marion Barnhart furnishes exquisite photographs of the three dimensional morphological features displayed by scanning electron microscopy and photographs of the internal structure of red cells revealed by high resolution transmission electron microscopy. Orten and Nalbandian present evidence that the electrophoretic mobility of sickle cell hemoglobin is not affected by urea. Henry collaborates in