bluuebunny/crossref_metadata_2025_split huggingface dataset:
UNE FORME MICROTUBULAIRE ET PARACRISTALLINE DE RETICULUM ENDOPLASMIQUE DANS LES PHOTOCYTES DES ANNELIDES POLYNOINÆ
Authors: Bassot J. M. 
Published: May 2004

Luminous cells of polynoid worm elytra have been examined by methods of electron microscopy, with special attention focused on the fine structure of photogenic grains. These cells send apical prolongations into the mid-part of the elytra. The plasma membrane is very sinuous, and a special kind of desmosome links two portions of the same membrane. In addition to all the organelles which can be found in nonluminescent epithelial cells of the elytra, numerous photogenic grains are contained in their cytoplasm. These grains are composed of undulating microtubules measuring 200 A in diameter; their disposition in the grain is highly regular, and the grains appear as paracrystals. At the borders of the grains, the walls of the microtubules are often in continuity with those of the endoplasmic reticulum and with the external membrane of the nuclear envelope. Because of this fact, the microtubules of the grains may be considered a cytoplasmic organelle, representing a specialized form of the endoplasmic reticulum. The microtubules permit the repartition, inside and outside their walls, of two different products, one being forty-three times more abundant than the other; thus, the contact surface, in comparison to the volume, is greatly increased. The induction of the luminous reaction by change in the permeability of the microtubule walls, allowing contact between the two substances, is suggested as a working hypothesis.
There is an evolution of the grains along the axis of the photocytes. The grains are often surrounded by progressively increasing amounts of glycogen. Their paracrystalline disposition is altered at the apex of the luminous cells.
Electron Microscopy of Peripheral Nerves and Neuromuscular Junctions in the Wasp Leg
Authors: Edwards George A. , Ruska Helmut , de Harven Étienne 
Published: May 2004

The peripheral nerve branch innervating the femoral muscles of the common yellow jacket (Vespula carolina) has been found to possess a thick lemnoblast basement membrane and a complex mesaxon. The term "tunicated nerve" is proposed to designate the type of peripheral nerve in which one or several axons are loosely mantled by meandering, cytoplasm-enclosing membranes of the lemnoblast.
The peripheral axon courses longitudinally in a groove in the muscle fiber between the plasma membrane of the muscle fiber and a cap formed by lemnoblast and tracheoblast. The junction is characterized by apposition of plasma membranes of axon and muscle fiber, abundant mitochondria, and synaptic vesicles in the axon, and aggregates of "aposynaptic granules" plus mitochondria and endoplasmic reticulum on the muscle side of the synapse. Unlike the vertebrate striated muscle fiber, no complex infolding of the synapsing plasma membrane of the muscle fiber occurs.
The "connecting tissue" of the insect is formed by tracheoblasts, their basement membranes, and the basement membranes of other cells. Further mechanical support is given by the ramifying tracheoles.
The physiologic roles of the specialized structures are considered.
A Histochemical Method for the Demonstration of Diphosphopyridine Nucleotide Diaphorase
Authors: Nachlas Marvin M. , Walker Donald G. , Seligman Arnold M. 
Published: May 2004

The present investigation concerning the histochemical demonstration of DPN diaphorase follows the development of a new reagent, Nitro-BT, which has already been used successfully for the cytochemical localization of the succinic dehydrogenase system. The most consistently favorable results were obtained with the lactate-lactic dehydrogenase system buffered at pH 7.4. Using sections of rat kidney and stomach, it was found that the intensity of stain was optimal after 15 minutes incubation at 37°C., conducted aerobically.
By appropriate variations in the substrate mixture it was possible to selectively demonstrate the histochemical distribution of certain DPN-linked dehydrogenases in addition to DPN diaphorase. This was made possible by the special distribution of some of these dehydrogenases which distinguished them from one another. Of the dehydrogenases studied the distribution pattern of ß-hydroxybutyric dehydrogenase was the most singular. In the gastric mucosa ß-hydroxybutyric dehydrogenase was restricted to the cells of the mucous lining epithelium and the gland necks; and in the kidney the enzyme was limited to the cells of the proximal convoluted tubule and thick limbs of Henle's loop. In contrast, lactic dehydrogenase like DPN diaphorase was demonstrable in almost all cytologic elements of both the stomach and the kidney.
The Ultrastructure of Schmidt-Lanterman Clefts and Related Shearing Defects of the Myelin Sheath
Authors: Robertson J. David 
Published: May 2004

Schmidt-Lanterman clefts in frog sciatic nerves have been studied in thin sections by electron microscopy utilizing permanganate fixation and araldite embedding. It is shown that they are shearing defects in myelin in which the lamellae are separated widely at the major dense lines. Each lamella consisting of two apposed Schwann cell unit membranes ∼ 75 A across traverses the cleft intact. The unit membranes composing each lamella sometimes are slightly (∼ 50 to 100 A) separated in the clefts. The layers between the lamellae contain membranous structures which may be components of the endoplasmic reticulum. These layers are continuous with the outer layer of Schwann cytoplasm and the thin and inconstant cytoplasmic layer next to the axon (Mauthner's sheath). Each of these layers in perfect clefts constitutes a long helical pathway through the myelin from the axon. One of these is connected with Schwann cytoplasm and the other directly with the outside. A type of cross-sectional shearing defect, not hitherto recognized, is described and shown to be a kind of Schmidt-Lanterman cleft.
Incomplete clefts are seen and interpreted as representing stages in a dynamic process whereby the myelin lamellae may be constantly separating and coming together again in life.
Evidence for Two Metabolically Distinct Types of Ribonucleic Acid in Chromatin and Nucleoli
Authors: McMaster-Kaye Rachel , Taylor J. Herbert 
Published: May 2004

Patterns of radioisotope incorporation are useful characteristics in describing cellular RNA fractions, and have indicated a distinctive "nuclear" RNA.
In order to characterize the RNA fractions of the two nuclear components, nucleoli and chromatin, and to determine thereby the precise localization of the RNA typical of isolated nuclei, time-courses of P32 incorporation into nucleolar, chromosomal, and cytoplasmic RNA of Drosophila salivary glands have been determined from autoradiograms. Two experiments are reported which cover 12 and 18 hour periods, including an initial 2 hour feeding on P32. Concentrations of RNA-P32 (identified by ribonuclease digestion) were determined by grain counts.
After 1 hour only the nucleolar RNA is labelled. Activity is detectible in chromosomal and cytoplasmic RNA after the 2nd hour. The nucleolar fraction reaches its maximum activity shortly after transfer of the larvae to non-radioactive food, the other fractions several hours later. Maximum activities persist in the chromosomal and cytoplasmic fractions; nucleolar activity decreases after the 9th hour.
The observed differences in times at which incorporation begins and maximum activities are reached, and in maintenance of maximum activities indicate that chromosomal and nucleolar RNA are distinct fractions. The metabolic characteristics which have been ascribed to "nuclear" RNA apply only to the nucleolar fraction.
Autoradiographic Studies of the Utilization of Ca45 by the Chick Embryo
Authors: Johnston Perry M. 
Published: May 2004

Calcium-45 was injected into the dense albumen of fertile hen's eggs, to the extent of 25 µc. per egg. The eggs were incubated under standard conditions and three or more embryos removed daily and fixed in 10 per cent neutral formalin. Stripping-film autoradiograms were prepared from paraffin sections of the tibiofibulae. Exposure varied with the isotope concentration. The tissue sections with their autoradiograms in place were stained with dilute Giemsa, while other sections were stained with hematoxylin-azure-eosin and by von Kossa to demonstrate bone salt.
At about 9 days, Ca45 is found in the cartilage template both intra- and extracellularly. Between 9 and 11 days, a primary diaphyseal lamella is deposited which is largely acellular. The lamella is eroded by capillaries from the periosteum and a resorption center is established in the cartilage. New lamellae of bone are deposited centrifugally in an imbricated pattern. Bone matrix formation precedes calcification by about 1 to ½ days, and calcification in a particular lamella is not uniform. Endochondral bone formation is described, as well as calcification of the epiphyseal/diaphyseal cartilage. Calcium-45 occurs intracellularly in the osteocyte during bone formation.
An Electron Microscope Study of the Contractile Vacuole in Tokophrya infusionum
Authors: Rudzinska Maria A. 
Published: May 2004

Contractile vacuoles are organelles that collect fluid from the cytoplasm and expel it to the outside. After each discharge (systole), they appear again and expand (diastole). They are widely distributed among Protozoa, and have been found also in some fresh water algae, sponges, and recently in some blood cells of the frog, guinea pig, and man.
In spite of the extensive work on the contractile vacuole, very little is known concerning its mode of operation. An electron microscope study of a suctorian Tokophrya infusionum provided an opportunity to study thin sections of contractile vacuoles, and in these some structures were found which could be part of a mechanism for the systolic and diastolic motions the organelle displays.
In Tokophrya, as in Suctoria and Ciliata in general, the contractile vacuole has a permanent canal connecting it with the outside. The canal appears to have a very elaborate structure and is composed of three parts: (1) a pore; (2) a channel; and (3) a narrow tubule located in a papilla protruding into the cavity of the contractile vacuole. Whereas the pore and channel have fixed dimensions and are permanently widely open, the tubule has a changeable diameter. At diastole it is so narrow (about 25 to 30 mµ in diameter) that it could be regarded as closed, while at systole it is widely open.
It is assumed that the change in diameter is due to the contraction of numerous fine fibrils (about 180 A thick) which are radially disposed around the canal in form of a truncated cone, with its tip at the channel, and its base at the vacuolar membrane. It seems most probable that the broadening of the tubule results in discharge of the content of the contractile vacuole.
In the vicinity of the very thin limiting vacuolar membrane, small vesicles and canaliculi of the endoplasmic reticulum, very small dense particles, and mitochondria may be found. In addition, rows of closely packed vesicles are present in this region, and in other parts of the cytoplasm. It is suggested that they might represent dictyosome-like bodies, responsible for withdrawing fluids from the cytoplasm and then conveying them to the contractile vacuole, contributing to its expansion at diastole.
Surface Responses in Cultured Fibroblasts Elicited by Ethylenediaminetetraacetic Acid
Authors: Dornfeld Ernst J. , Owczarzak Alfred 
Published: May 2004

Cultures of chick heart fibroblasts were perfused with the chelating agent ethylenediaminetetraacetic acid (EDTA). Cellular responses were observed under phase optics and recorded by time-lapse cinemicrography.
In interphasic fibroblasts, EDTA induces cellular contraction followed by continuous protrusion and retraction of ectoplasmic blebs ("surface bubbling"), formation of motile vermiform processes, and production of rotatory ectoplasmic swellings. The contraction and surface bubbling closely resemble the metaphase contraction and "anaphase bubbling" normally displayed by cultured fibroblasts.
In dividing cells, EDTA does not affect metaphases, but anaphase bubbling appears and persists; telophasic expansion and migration of daughter cells are prevented. Initiation of new mitoses occurs during and after exposure to EDTA.
No cellular responses are induced by calcium, magnesium, or ferrous chelates of EDTA. The EDTA elects are completely reversible on removal of the chelating agent, resulting in the restoration of the normal interphasic cell form and the normal expansion and migration of mitotic products.
The EDTA effects are interpreted to result from the chelation and removal of divalent cations from the cell surface. Possible relations to surface activities observed in normal mitosis are considered, and an hypothesis is presented regarding the role of the developing spindle in cation transfer.
Mitochondria Isolated from Rat Brown Adipose Tissue and Liver
Authors: Lever J. D. , Chappell J. B. 
Published: May 2004

Mitochondrial fractions, relatively free from contamination by other cytoplasmic structures, have been isolated by differential centrifugation from homogenates of brown adipose tissue from starved rats. It was possible in such fractions to distinguish two types of mitochondria in this tissue.
Type I mitochondria, when morphologically intact, are limited by a bilaminar membrane and show regular parallel cristae. In isolated fractions, a proportion of these mitochondria are swollen, vacuolation occurring within the cristae between their limiting membranes.
Type II mitochondria are distinguished from the more numerous type I bodies by the opaque appearance of their matrix. They are limited by a membrane which is in part single, and in part double. They show a few, but crisply outlined internal membranes. Vacuolation of this type of mitochondrion has not been observed.
Vacuolation comparable to that in brown fat mitochondria was also observed between the two laminae of the enclosing membrane and within the cristae of liver mitochondria.
Factors Limiting the Number of Radiation-Induced Chromosome Exchanges
Authors: Wolff Sheldon , Atwood K. C. , Randolph M. L. , Luippold H. E. 
Published: May 2004

Soaked seeds of Vicia faba were exposed to fractionated doses of x-rays or x-rays and fast neutrons. When the two-hit (exchange) chromosome aberrations were scored at the first mitosis of the root tip, it was observed that with short fractionation times the radiation-induced breaks from the two x-ray doses could rejoin with one another to form exchanges in proportion to the square of the total dose. If, however, one dose was x-rays and the second neutrons, then no quantitatively determinable interaction occurred between the breaks induced by each of the doses, and the aberration yield was simply the sum of that induced by each fraction.
The phenomenon of non-interaction as observed by these dose fractionation studies and also by the linear dose response curve for two-break aberrations induced by neutrons has led to calculations of the distance over which two breaks can rejoin. The distance is evidently much smaller than the previously accepted value of 1 µ.
An Anterior-Posterior Gradient of Refractive Index in the Ameba and Its Significance in Ameboid Movement
Authors: Allen R. D. , Roslansky J. D. 
Published: May 2004

Sustained locomotion in Amoeba proteus and Amoeba dubia results in the establishment of a measureable gradient of refractive index along the anterior-posterior axis of the cell, provided thickness of the specimens is kept constant by even compression under a selected coverglass supported by quartz beams of uniform diameter.
The tail region of the ameba develops a higher refractive index, indicative of from 6 to 40 per cent more organic matter (expressed as protein) there than present in the front. This gradient fades on cessation of movement. The average protein concentrations in the crystal-free tails and fronts of 15 A. proteus were 3.9 and 3.4 per cent, respectively. In individual experiments, the tail-front difference ranged from one to eight times the accuracy of the method.
Since the gradient of refractive index was shown not to result from extraction of water from the tail by the contractile vacuole, it was interpreted as displacement of water toward the anterior part of the cell during movement. It is suggested that contraction of the ectoplasm drives forward a "tide" of syncretic fluid, the anterior border of which is visible as the hyaline cap, which contains less than 1 per cent protein. The movement of the granular endoplasm into the hyaline cap would then complete the cycle by imbibition of the fluid tide. The theoretical positions of Pantin and of Dellinger have been combined in the proposal that ameba cytoplasm consists of a network of a contractile phase which is able to expel (by syneresis) a highly mobile fluid phase. Some other possible interpretations are discussed.
Colorimetric Analysis with N,N-Dimethyl-p-phenylenediamine of the Uptake of Intravenously Injected Horseradish Peroxidase by Various Tissues of the Rat
Authors: Straus Werner 
Published: May 2004

1. A method is described for the colorimetric determination of peroxidase with N,N-dimethyl-p-phenylenediamine. The amount of red pigment formed by peroxidase is proportional to the concentration of enzyme and to the time of incubation during the first 40 to 90 seconds. The influence of the concentration of enzyme, N,N-dimethyl-p-phenylenediamine, H2O2, the time of incubation, pH, the temperature, and the possible interference by oxidizing and reducing agents of tissues has been tested.
2. The method has been used to follow the uptake of intravenously injected horseradish peroxidase by 18 different tissues of the rat over a period of 30 hours. The highest concentration of the injected tracer enzyme was found in extracts of kidney, liver, bone marrow, thymus, and spleen. Considerable amounts were taken up by pancreas, prostate, epididymis, and small intestine. Lower concentrations were found in extracts of lung, stomach, heart, and skeletal muscle, aorta, skin, and connective tissue. No uptake was observed by brain and peripheral nerve tissue.
3. Tissue homogenates containing high concentrations of the injected peroxidase, in general also showed high or average activity of acid phosphatase.
4. Six hours after intravenous administration, the liver contained 27 per cent, the kidney 12 per cent, and the spleen, 1.4 per cent of the injected dose.
5. Approximately 20 per cent of the injected peroxidase was excreted in the urine during the first 6 hours, and the concentration of peroxidase in blood serum and urine fell exponentially during this time. After 6 hours, only low concentrations were excreted in the urine but low enzyme activity was still detectable after 30 hours. Approximately 6 per cent of the injected dose was excreted in the feces from 6 to 20 hours after administration.
6. After feeding through a stomach tube, low concentrations of peroxidase were found in blood serum and urine. Considerable variations in the extent of absorption from the gastrointestinal tract were observed in individual rats.
A Cytochemical Study on the Pancreas of the Guinea Pig
Authors: Siekevitz Philip , Palade George E. 
Published: May 2004

DL-leucine-1-C14 was administered by intracardiac injection to guinea pigs and its in vivo incorporation into the proteins of various pancreatic cell fractions followed over a period of 2 hours.
The pancreas was homogenized in 0.88 M sucrose and fractionated by differential centrifugation to give nuclear, zymogen, mitochondrial, microsomal, postmicrosomal, and final supernatant fractions. The proteins of these fractions, obtained by precipitation with trichloroacetic acid followed by washing, were counted.
The proteins of the microsomal fraction showed the highest early specific activity and were followed by those of the zymogen and mitochondrial fractions.
The microsomal fraction was broken up into two subfractions: one consisting of detached RNP particles, the other representing mainly the microsomal content and membranes.
The incorporation of labelled leucine into the proteins of microsomal subtractions and in those of postmicrosomal fractions was studied comparatively in the pancreas of fasted and fed guinea pigs as well as in the liver and pancreas of fasted animals.
A tentative cytological picture of protein synthesis and transport based on these findings is presented.
The Fine Structure of the Adipose Cell of the Leech Glossiphonia complanata
Authors: Bradbury S. , Meek G. A. 
Published: May 2004

The two distinct types of cytoplasm seen with the light microscope in the adipose cell of the leech Glossiphonia complanata have been identified in the electron microscope image of this cell.
One of these, the basophil cytoplasm, contains many well oriented, paired membranes which are much more clearly evident when calcium ions are added to the fixative. The membranes sometimes appear as concentric arrays of lamellae and are thought to represent sections through a phospholipide-containing body. The paired membranes and the concentric lamellae have granules attached to them and resemble in size and structure the membranes of the endoplasmic reticulum encountered in many mammalian cells.
Small dense cytoplasmic particles are present throughout the cell; they may be ferritin molecules, derived from the breakdown of haemoglobin taken in as food.
On the basis of a previous histochemical study and the present electron microscope investigation, it is suggested that these paired membranes are similar to the organized type of mammalian ER and the results seem to confirm the belief that these membranes are composed of layers of phospholipoprotein together with attached particles of ribonucleoprotein.
Cellular Mechanism of Myelination in the Central Nervous System
Authors: De Robertis Eduardo , Gerschenfeld Hersch M. , Wald Flora 
Published: May 2004

A study of myelination with electron microscopy has been carried out on the spinal cord of young rats and cats. In longitudinal and transverse sections the intimate relationship of the growing axons with the oligodendrocytes was observed. Early naked axons appear to be embedded within the cytoplasm and processes of the oligodendrocytes from which they are limited only by the intimately apposed membranes of both elements (axon-oligocytic membrane). In a transverse section several axons are observed to be in a single oligodendrocyte.
The process of myelination consists in the laying down, within the cytoplasm of the oligodendrocyte and around the axon, of concentric membranous myelin layers. The first of these layers is deposited at a certain distance (200 to 600 A or more) from the axon-oligocytic membrane. This and all the other subsequently formed membranes have higher electron density and are apparently formed by the coalescence and fusion of vesicles (of 200 to 800 A) and membranes found in large amounts within the cytoplasm of the oligodendrocytes.
At an early stage the myelin layers may be discontinuous and some vesicular material may even be trapped among them or between the myelin proper and the axon-oligocytic membrane. Then, when the 8th to 10th layer is deposited, the complete coalescence and alignment of the lamellae leads to the characteristic orderly multilayered organization of the myelin sheath.
Myelination in the central nervous system appears to be a process of membrane synthesis within the cytoplasm of the oligodendrocyte and not a result of the wrapping of the plasma membranes as postulated in Geren's hypothesis for the peripheral nerve fibers. The possible participation of Schwann cell cytoplasm in peripheral myelination is now being investigated.