bluuebunny/crossref_metadata_2025_split huggingface dataset:
ON THE MECHANISMS OF BONE RESORPTION
Authors: Vaes Gilbert 
Published: May 2004

Bone resorption, characterized by the solubilization of both the mineral and the organic components of the osseous matrix, was obtained in tissue culture under the action of parathyroid hormone (PTH). It was accompanied by the excretion of six lysosomal acid hydrolases, which was in good correlation with the progress of the resorption evaluated by the release of phosphate, calcium 45 or hydroxyproline from the explants; there was no increased excretion of two nonlysosomal enzymes, alkaline phosphatase, and catalase. Balance studies and experiments with inhibitors of protein synthesis indicated that the intracellular stores of the acid hydrolases excreted were maintained by new synthesis. The release was not due to a direct disruption of the lysosomal membrane by PTH; it is presumed to result from an exocytosis of the whole lysosomal content and to involve mechanisms similar to those controlling the secretion of this content into digestive vacuoles.
The resorbing explants acidified their culture fluids at a faster rate and released more lactate and citrate than the controls; this release was in good correlation, in the PTH-treated cultures, with the resorption of the bone mineral, but the amount of citrate released was considerably smaller than that of lactate. The acid released could account for the resorption of the mineral.
It is proposed, as a working hypothesis, that the acid hydrolases of the lysosomes are active in the resorption of the organic matrix of bone and that acid, originating possibly from the stimulation of glycolysis, cares for the concomitant solubilization of bone mineral while also favoring the hydrolytic action of the lysosomal enzymes.
A Histochemical Study of Normal and Denervated Red and White Muscles of the Rat
Authors: Nachmias Vivianne T. , Padykula Helen A. 
Published: May 2004

The distribution and characterization of the fibers of normal and denervated red and white muscles of the albino rat are reported in this study. Histochemical procedures for succinic dehydrogenase, lipides, adenosinetriphosphatase, esterase, and glycogen were utilized to differentiate muscle fibers, and these methods facilitated the study of the distribution of fiber types within whole muscle.
Muscle fibers of the granular type (dark or red fibers) can be clearly distinguished from those with clearer sarcoplasm (light or white fibers) by methods for demonstrating succinic dehydrogenase, lipides, and esterase. The method for adenosine-triphosphatase reveals differences only under the special conditions described in the text. Additional fiber types are described in the cat's diaphragm and in the extrinsic ocular muscles of the rat. Succinic dehydrogenase and adenosinetriphosphatase activities of the soleus and biceps femoris were studied 14 days after denervation of these muscles. The histochemical findings are discussed principally in the light of current biochemical knowledge of these enzymes.
Observations on the Fine Structure of the Turtle Atrium
Authors: Fawcett Don W. , Selby Cecily C. 
Published: May 2004

The general fine structure of the atrial musculature of the turtle heart is described, including; the nature of the sarcolemma; the cross-banded structure of the myofibrils; the character of the sarcoplasm, and the form and disposition of its organelles. An abundant granular component of the sarcoplasm in this species is tentatively identified as a particulate form of glycogen.
The myocardium is composed of individual cells joined end to end at primitive intercalated discs, and side to side at sites of cohesion that resemble the desmosomes of epithelia. Transitional forms are found between desmosomes and intercalated discs. Both consist of a thickened area of the cell membrane with an accumulation of dense material in the subjacent cytoplasm. This dense amorphous component is often continuous with the Z substance of the myofibrils and may be of the same composition. The observations reported reemphasize the basic similarity between desmosomes and terminal bars of epithelia and intercalated discs of cardiac muscle.
Numerous unmyelinated nerves are found beneath the endocardium. Some of these occupy recesses in the surface of Schwann cells; others are naked axons. No specialized nerve endings are found. Axons passing near the sarcolemma contain synaptic vesicles, and it is believed that this degree of proximity is sufficient to constitute a functioning myoneural junction.
Electron Microscopic Observations on Spinal Ganglion Cells of Rana pipiens after Injection of Malononitrile
Authors: Anderson Everett , van Breemen V. L. 
Published: May 2004

Spinal ganglionic cells of Rana pipiens were studied with light and electron microscopes in normal animals and in animals which had received graded dosages of malononitrile intraperitoneally. After treatment no increase in the intensity of staining was noted in the Nissl substance when spinal ganglion cells were examined with the light microscope. The electron micrographs demonstrated the following in malononitrile-treated animals:
1. The cisternae of the endoplasmic reticulum composing the Nissl bodies appeared to fragment and lose their parallel orientation.
2. The microvesicular components of the Golgi complex appeared to increase in number, and the increase was apparently due to fragmentation of the membrane system of the Golgi complex.
3. The mitochondria enlarged and became pleomorphic, but displayed no alterations of internal structure.
The morphological changes may be interpreted as reflections of biochemical alterations.
Electron Microscopic Observations on the Taste Buds of the Rabbit
Authors: de Lorenzo A. J. 
Published: May 2004

An examination of the fine structure of the taste buds in the rabbit was undertaken. Gustatory epithelium was fixed in OsO4 or 1 per cent KMnO4 solution, containing polyvinylpyrrolidone (PVP). Thick sections were examined in the phase microscope and contiguous sections prepared for the electron microscope.
The bud contains two types of cells, gustatory receptors and sustentacular cells. The receptors are characterized by a dark nucleus and densely granular cytoplasm. The apical processes bear numerous microvilli which extend into the taste pore. Imbedded between the microvilli there is a dense substance, which is also present in the apical cytoplasm of the receptors. The sustentacular cells contain a large pale nucleus and less dense cytoplasm. Their basal surfaces rest upon a basement membrane.
The subepithelial nerve plexuses comprise the fibers which innervate the gustatory receptors. The nerve fibers vary in diameter from 500 A to 0.3 µ, and are ensheathed by Schwann cells. The intragemmal fibers enter the taste bud between adjacent cells, and are ensheathed by the plasma membranes of the supporting cell until they synapse upon the gustatory cell. The synaptic terminals contain synaptic vesicles, which at this junction reside in the postsynaptic element. This observation is discussed with reference to synapses described elsewhere in the nervous system.
A Cytochemical Study on the Pancreas of the Guinea Pig
Authors: Siekevitz Philip , Palade George E. 
Published: May 2004

Pancreatic tissue, (guinea pig) homogenized in 0.88 M sucrose, was fractionated by differential centrifugation into a nuclear, zymogen, mitochondrial, microsomal, and final supernatant fraction.
The components of the particulate fractions were identified with well known intracellular structures by electron microscopy.
The fractions were analyzed for protein-N and RNA, and were assayed for RNase and trypsin-activatable proteolytic (TAPase) activity.
The zymogen fraction accounted for 30 to 40 per cent of the total TAPase and RNase activities, and its specific enzymatic activities were 4 to 10 times higher than those of any other cell fraction. The zymogen fraction was cytologically heterogeneous; zymogen granules and mitochondria represented its main components.
More homogeneous zymogen fractions, obtained by successive washing or by separation in a discontinuous density-gradient, had specific activities 2 to 4 times greater than the crude zymogen fractions.
Chymotrypsinogen was isolated by column chromatography from pancreas homogenates and derived cell fractions. The largest amount was recovered in the zymogen fraction.
The final supernatant had properties similar to those of the trypsin inhibitor described by Kunitz and Northrop.
An Electron Microscopic Study of the Ductuli Efferentes and Rete Testis of the Guinea Pig
Authors: Ladman Aaron J. , Young William C. 
Published: May 2004

The ductuli efferentes and rete testis of the guinea pig were isolated by micro dissection, fixed in cold buffered osmium tetroxide, and sectioned for examination with the light and electron microscopes.
Proximal and distal segments of the ductuli efferentes were identified and their respective cytological organizations characterized. The cytological components of the rete testis are briefly described and figured.
Non-ciliated and ciliated cells are found in both segments of the ductuli efferentes. The non-ciliated cells have a microvillous border, mitochondria, a Golgi complex, an ubiquitous endoplasmic reticulum, and numerous cytoplasmic vacuoles. The ciliated cells contain more mitochondria, an endoplasmic reticulum with a relatively sparse distribution, and few, if any, cytoplasmic vacuoles. A regional difference exists in proximal and distal segments based on the distribution, size, number, and electron opacity of the cytoplasmic vacuoles. Attention was paid to the disposition of the endoplasmic reticulum and its relation to the system of cytoplasmic vacuoles. These findings are interpreted as suggesting that the continuity of the vacuolar system with elements of the endoplasmic reticulum represents a pathway for transfer of large quantities of fluid, an activity which has long been ascribed to the epithelium of the ductuli efferentes.
Periductular capillaries possess pore-like apertures in their endothelia similar to those in other tissues known to engage in fluid transfer.
Neuromuscular Junctions in Flight and Tymbal Muscles of the Cicada
Authors: Edwards George A. , Ruska Helmut , de Harven Étienne 
Published: May 2004

The tymbal muscle fiber in the cicada closely resembles the indirect flight muscle fiber in its structural detail. We agree with other authors that the tymbal muscle is a modified indirect flight muscle.
The peripheral nerve branches to the tymbal and flight muscle fibers are similar to those in the wasp leg. The axon is loosely mantled by irregular turns of the mesaxon, enclosing cytoplasm. The nerve is therefore a tunicated nerve.
The neuromuscular junction in the high frequency muscle fibers shows direct apposition of plasma membranes of axon and muscle fiber, large numbers of mitochondria and synaptic vesicles in the axon, and concentrations of mitochondria, aposynaptic granules, and endoplasmic reticulum in the postsynaptic area of the muscle fiber.
Of special interest is the multitude of intracellular, opposing membranes in the postsynaptic area. They form laminated stacks and whorls, vesicles, cysternae, and tubules. They occasionally show continuity with the plasma membrane, the outer nuclear envelope, and the circumfibrillar endoplasmic reticulum. The membrane system in this area is designated "rete synapticum." It is believed to add to the electrical capacity of the neuromuscular junction, to serve in transmission of potentials, and possibly is the site of the oscillating mechanism in high-frequency muscle fibers.
An Electron Microscope Study of Basophile Substances of Frozen-Dried Rat Liver
Authors: Finck Henry 
Published: May 2004

Small pieces of liver from rats subjected to different dietary regimes were fixed by freeze-drying, and postfixed by in vacuo heating and denaturation with alcohol. Specimens were digested with ribo- or deoxyribonuclease, and stained with gallocyanin-chromalum, azure II, the Feulgen procedure or alcoholic platinic tetrabromide. Some specimens were reserved as controls of the effects of enzyme treatment. Stained and unstained specimens were embedded in methacrylate and examined by light and electron microscopy.
Basophilic and Feulgen-positive substances, after contact with watery reagents, were found by electron microscopy to exist as small dense granules embedded in a less dense homogeneous matrix, forming the walls of submicroscopic vacuoles. These granules were absent after digestion with nucleodepolymerases. In specimens (unstained, or stained with platinic tetrabromide) which had not passed through water, the dense (basophile) substances in nuclei and cytoplasm were found to exist, not as granules, but as ill defined submicroscopic concentrates which blended imperceptibly into the homogeneous matrix of the vacuolar walls.
Objections to the use of stains for improving contrast conditions in electron microscopy of tissues are discussed, and it is concluded that the reagents do not necessarily produce the observed increases in contrast by selectively stabilizing certain structures. The concept of microsomes as pre-existing distinct morphological entities in intact (unhomogenized) cells is thought to be inconsistent with the distribution of basophile substances in frozen-dried liver.
The Two-Wavelength Method of Microspectrophotometry
Authors: Mendelsohn Mortimer L. 
Published: May 2004

In spite of a number of examples of the apparently successful application of the two-wavelength method of microspectrophotometry to biological materials, a demonstration of the effective transition from the theoretical to the practical aspects of the method has never been given. The following tests were carried out on model systems in order to confirm the practical validity of the method:
(1) Spherical droplets of Sudan blue or Sudan IV (varying in volume by as much as 400 times) were measured with the surrounding blank field included and were found to have amounts of chromophore which conformed to the estimated droplet volume to within 3 to 6 per cent.
(2) Repeated determinations on the same isolated nucleus gave results which did not vary in spite of wide variations in the area of the photometric field.
(3) The results of repeated determinations on the same droplet of dye were unaffected by gross changes in the focus of the objective.
The microspectrophotometer on which these measurements were made has been briefly described; it was designed specifically for the two-wavelength method. Some of the details of instrumentation have been discussed, in particular, the effects of non-uniform illumination and the contrasting demands of the two integral parts of this type of photometry. Although it has certain limitations, the two-wavelength method conforms to its theoretical promise and is a practical method of measuring light absorption in complex objects.
Metachromasy: An Experimental and Theoretical Reevaluation
Authors: Bergeron John A. , Singer Marcus 
Published: May 2004

Non-chromotropic substances such as fibrin and gelatin and most tissue and cellular structures stain orthochromatically with internal dye concentrations of such metachromatic dyes as methylene blue and toluidine blue which, if in solution, would be metachromatic. Therefore, at ordinary levels of staining these substances depress the natural tendency of these dyes to change color. However, at elevated levels of dye-binding metachromasy eventually occurs. This phenomenon is explained on the basis of the distribution of dye-binding sites. In these substrates, by contrast with chromotropic substances, many binding sites are too far removed for dye interaction, consequently the interaction frequency can become high enough to produce a color change only as saturation of the available sites is approached.
It is also shown that the destruction of color is a characteristic of metachromasy and that water molecules intercalated between approximated dye ions are responsible for the loss and change of color. A concept of metachromasy is proposed in which the interaction between water molecules and suitably approximated dye ions plays an essential role.
The experimental studies are described against a background of the history and evolution of ideas on metachromasy. The literature is reviewed and reassessed particularly from the physicochemical viewpoint.
The Spermatid Nucleus in Two Species of Grasshopper
Authors: Gall Joseph G. , Bjork Lois B. 
Published: May 2004

The nuclear changes accompanying spermatid elongation have been studied in two species of grasshopper, Dissosteira carolina and Melanoplus femur-rubrum. Testes were fixed in 1 per cent buffered OsO4, imbedded in butyl methacrylate, and examined as thin sections in the electron microscope.
In both species nuclear changes during spermatid development involve (1) an early period, during which the nuclear contents are predominately fibrous; (2) a middle period, characterized by the lateral association of the nuclear fibers to form plates or lamellae which are oriented longitudinally in the major axis of the elongated nucleus; and (3) a late period, involving coalescence of the lamellae into a crystalline body which eventually becomes so dense that all resolvable detail is lost.
The fibers seen in the early spermatid nucleus are about 150 A in diameter and so are similar to fibers described from other types of nuclei. The thickness of the lamellae varies from about 150 A when first formed to 70 A during the later stages. The lack of evident chromosomal boundaries in the spermatid nucleus makes it difficult to relate either the fibers or lamellae to more familiar aspects of chromosome structure. We see no apparent reason to consider that the fiber alignment described here is related to conventional chromosome pairing.
Serial Observations on Patterns of Growth, Myelin Formation, Maintenance and Degeneration in Cultures of New-Born Rat and Kitten Cerebellum
Authors: Bornstein Murray B. , Murray Margaret R. 
Published: May 2004

New-born rat and kitten cerebellum may be maintained for prolonged periods (over 5 months) in the Maximow assembly if explanted on to a coverslip previously coated with a thin gel of reconstituted rat tail collagen and fed a glucose-enriched "natural" medium.
After a 2 week period of adjustment and early outgrowth, most cultures exhibit myelin formation. Axons located within the surrounding neuroglial sheet of the explant area myelinate. The sheaths are first evident as long, unsegmented, smooth, parallel, refractile lines. Simultaneously, neuronal nuclei tend to assume central positions and powdery granules of Nissl substance and lipoid materials begin to accumulate within the cytoplasm.
During prolonged maintenance, axons may increase in width and the myelin may thicken. Some exhibit transient irregularities and swellings. Degeneration of some axons occurs manifested either by (a) progressive swellings and distortions of the myelin sheath and thinning of intervening portions of the axons which finally yield, leaving the swellings as myelin bodies, or by (b) small aneurysm-like distortions of myelin sheaths on thinning axons which become dull, irregular, and thread-like filaments beaded by the former herniations.
The observations are compared with previous studies of in vitro and in vivo myelin formation with particular reference to neuronal-neuroglial relationships.
The Fine Structure of the Interrelationship of Cells in the Human Epidermis
Authors: Obland George F. 
Published: May 2004

In the present investigation an analysis has been made of the fine structure of the interrelationships of cells in human forearm epidermis by means of the electron microscope.
The "intercellular bridges," here called attachment zones, are more complex than has previously been recognized. It is shown that dense oval thickenings, called attachment plaques, appear in apposed areas of adjacent epidermal cell membranes. The tonofibrils terminate at the internal face of the attachment plaque and do not traverse the 300 A distance between apposed plaques. Seven intervening layers of unidentified substance occupy the space between attachment plaques. The attachment zones appear in all of the classical histological layers of the epidermis.
The portions of epidermal cell membrane not involved in intercellular attachments have extensive surface area resulting from plication of the membrane, and its further modification to form microvilli. The possible functional significance of these observations is discussed. Prior observations concerning the basement membrane of epidermis are confirmed.
Identification of epidermal melanocytes is achieved, the finer morphology of their dendritic processes is described, and their relationship to epidermal cells is discussed.
The Early Changes in the Axoplasm during Wallerian Degeneration
Authors: Vial Juan D. 
Published: May 2004

Axoplasmic changes were studied in the saphenous nerve of the albino rat during the early stages of Wallerian degeneration. The axons were examined at 0, 24, and 48 hours after the surgical transection of the nerve. The material was fixed in 2 per cent OsO4 in phosphate buffer (pH 7.2–7.5) with sucrose (added to a final osmolar concentration of ∼0.37 M).
The earliest changes were seen in the endoplasmic reticulum which became fragmented into rows of small vesicles. Then, between 24 and 48 hours, the neurofilaments underwent complete disintegration and the axoplasm became filled with finely granular material which later formed irregular clumps surrounded by a structureless matrix, probably fluid in vivo.
The fragmentation of the neurofilaments was accompanied by pronounced swelling of the mitochondria.
Methods and Principles of Fixation by Freeze-Substitution
Authors: Feder Ned , Sidman Richard L. 
Published: May 2004

Freeze-substitution is based on rapid freezing of tissues followed by solution ("substitution") of ice at temperatures well below O°C. A 1 to 3 mm. specimen was thrown into 3:1 propane-isopentane cooled by liquid nitrogen to -175°C. (with precautions). The frozen tissue was placed in substituting fluid at -70°C. for 1 week to dissolve ice slowly without distorting tissue structure. Excess substituting agent was washed out, and the specimen was embedded, sectioned, and stained conventionally.
For best morphological and histochemical preservation, substituting fluids should in general contain both chemical fixing agent and solvent for ice, e.g., 1 per cent solutions of osmium tetroxide in acetone, mercuric chloride in ethanol, and picric acid in ethanol. Preservation of structure was poorer after substitution in solvent alone. Evidence was obtained that the chemical agent fixes tissue at low temperatures. The chemical mechanisms of fixation are probably similar to those operating at room temperature: new chemical cross-linkages, which contain the fixing agent, join tissue constituents together. This process is distinguished from denaturation by pure solvents.
Freeze-substitution has many advantages, particularly the preservation of structure to the limit of resolution with the light microscope, and the accurate localization of many soluble and labile substances.