bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphological studies of the embryonic rabbit thymus: The in situ epithelial versus the extrathymic derivation of the initial population of lymphocytes in the embryonic thymus
Authors: Ackerman G. Adolph , Hostetler Jeptha R. 
Published: February 2005

AbstractThe present morphological investigation of the developing thymus of the rabbit during early embryogenesis differs with our previous studies concerning thymus lymphopoiesis in the chick and hamster which suggested that embryologically the first lymphocytes appearing in the thymus arise in situ by the direct transformation of undifferentiated epithelial cells comprising the organ parenchyma. Significantly, in the rabbit and in contrast with the chick and hamster, a few cells morphologically resembling but not completely identical to medium‐size and large lymphocytes were evident in the mesenchyme near the thymus at a time just prior to the appearance of lymphocytes or lymphocytic precursors within the thymus parenchyma (twelve and one‐half days of gestation). Within a few hours after the appearance of these extrathymic lymphocytic cells both medium‐size and large lymphocytic cells were observed both in the thymus parenchyma and in the mesenchyme (thirteen and one‐half days of gestation); these cells remain more numerous in the mesenchyme than in the thymus during the next several days. In some instances, only a thin basement membrane separated the lymphocytic cells within the thymus from the surrounding mesenchyme. In contrast with our earlier studies, several examples have been encountered between the fifteenth and seventeenth days of gestation of lymphocytic cells extending through the basement membrane seperating the thymus parenchyma from the surrounding capsular connective tissue. Morphologically cellular modulations between thymus undifferentiated epithelial cells and lymphocytic precursors have not been as convincing in the developing rabbit thymus as in the chick and hamster. In contrast with thymus development in the chick few mature or developing granulocytes are found near the embryonic rabbit thymus indicating that the primitive extrathymic lymphocytic cells are not myeloblasts.The morphological evidence of this investigation is consistent with the thesis that the first lymphocytes present in the embryonic thymus probably are derived from the invasion of extrathymic lymphocytic cells into the organ parenchyma rather than forming in situ from modulating undifferentiated epithelial cells. The presence of rare lymphocytic cells observed in the small vascular channels near the time of appearance of the lymphocytic cell population in the mesenchyme and within the thymus primordium would be consistent with the view that these primitive lymphocytic cells immigrate to the region of the thymus via the blood vascular system.
Specialized intercellular junctions in tumor cells—An electron microscope study of mouse sarcoma cells
Authors: Clarke Michael A. 
Published: February 2005

AbstractSpecialized intercellular junctions have been observed in 3‐methylcholanthrene‐induced mouse sarcomas. These junctions are of two morphologic types and appear to be focal in nature. The first type consists of an approximation of the plasma membranes of adjacent cells to within 200 Å of one another. In the junctional region the intercellular space and the adjacent cytoplasm are of increased density. The second type of junction is more complex, the intercellular space being of greater width and containing a dense central plaque. The intercellular space and the adjacent cytoplasm are of increased density. Such junctions may serve a role in structural support of the tumor mass.
The histology and rate of tooth eruption with and without temporary impaction in the dog
Authors: Cahill Donald R. 
Published: February 2005

AbstractEruption was studied by experimentally impacting and releasing permanent premolars in puppies. Eruption rates of both normal and experimentally delayed teeth were calculated from weekly radiographs. The rate of normal eruption is triphasic and similar to a normal growth curve. It has an initial slow exponential rate which changes to a more rapid exponential rate followed in turn by a terminal plateau. All of the teeth released from impaction erupted and their rates exceeded or equaled the normal rate.The morphology of the bony trabeculae beneath the erupting teeth and the relative amount of soft tissue between the bone and teeth are expressions of the eruptive rate. The trabeculae around rapidly erupting teeth are thinner, more delicate and more widely separated from one another than those of slowly erupting teeth. Trabecular orientation aligns with the direction of eruption, showing not only its vertical component, but also whether the tooth moved mesially or distally during eruption.
Fenestrated venules of the large salivary glands
Authors: Takada Mitsuya 
Published: February 2005

AbstractEndothelial fenestrations have been observed in the venules of the large salivary glands of mice. The structure of the fenestrations is similar to those of capillaries. The fenestrations are frequently demonstrated in the endothelium of the transitional portions from a capillary to a venule. They are also seen in overlapping thin cytoplasm located on either the blood or tissue front of the endothelial cells of the venules at cell junctions.
Ultrastructural study of rat mammary gland during pregnancy
Authors: Murad Tariq M. 
Published: February 2005

AbstractVirgin female Sprague‐Dawley rats were mated, and after the appearance of vaginal plugs were placed in individual cages. The animals were sacrificed at different intervals from the second day of gestation until delivery. Breast tissue was studied with the light and electron microscope.The study suggests that breast tissue undergoes changes as early as four days after fertilization and continues throughout pregnancy. The changes start with accumulation of many ribosomes and polysomes within the epithelial cell cytoplasm. Lipid droplets appear early and increase in number as pregnancy advances. Two types of proteinaceous particles appear within the cytoplasm on the seventh day of gestation, and are totally secreted into the lumina before parturition. The particles are believed to play a role in colustrum composition. The Golgi apparatus plays no role in the formation of the proteinaceous particles. The particles are formed in relation to rough surfaced endoplasmic reticulum.The changes seen are limited to the ductular epithelium and are not seen in the large ducts. In animals treated with colchicine, mitoses are seen in the ductular epithelium very early in pregnancy and continue throughout the gestation period.
Volumetric composition of the rabbit skeleton
Authors: Gong J. K. , Ries W. 
Published: February 2005

AbstractFour rabbit skeletons were completely analyzed for marrow contents by means of a volumetric technique developed previously in a study of the dog skeleton (Gong and Arnold, 1965). The distribution of the marrow in various skeletal areas as well as the relative contents of the three marrow components (water, fat and non‐fatty organic fraction) were determined.It was found that more than two‐thirds of the rabbit marrow was located in the various flat bones and one‐third in the long bones. In spite of this, almost half of the skeletal marrow fat was located in the long bones. The nonfatty organic fraction of the marrow in the long bones, on the other hand, constituted only one‐sixth of that found in the whole animal skeletal marrow. In terms of total marrow, about 51% of the rabbit skeletal volume was marrow. Based on the concept that fat‐free marrow is a more adequate index of active marrow than the red marrow (Gong and Arnold, 1965), the distribution of the various centers of marrow activity was described and discussed.
The vascular stiffening mechanism in the tongue of the echidna (Tachyglossus aculeatus)
Authors: Doran G. A. , Baggett H. 
Published: February 2005

AbstractAn extensive vascular arrangement resembling erectile tissue is described in the tongue of an anteating Monotreme, the Echidna. Its possible function as a stiffening mechanism is discussed in relation to observations on living animals.
Electron microscopy of chromosomal changes in ambystomal somatic cells during the mitotic cycle
Authors: Bloom William 
Published: February 2005

AbstractThis sequence of electron micrographs shows the progressive changes undergone by the dispersed chromosomal fibrils of the interphase nucleus as they begin to condense, in early prophase, into clumps centered on three types of small nuclear structures. These bodies do not seem to have been described previously in detail in connection with mitosis, although they were mentioned as a group in a preliminary note by Bloom (1963). In the present report they are divided into three groups indicated as F1, F2 and F3 and are labelled 1, 2 or 3 in the accompanying electron micrographs.The clumps enlarge by continued accretion of more and more fibrils concentrated about these three types of bodies until the chromosomes of metaphase are formed. The inference that the bodies depicted here form focal points for the condensation of dispersed chromosomal filaments rests solely on the repeated finding of the progressive aggregation of the fibrils about them. Further studies are in progress on factors mediating these changes and on the nature of the F bodies.
Fine structure of the alveolar macrophage of the cat and modifications of its cytoplasmic components during phagocytosis
Authors: Collet A. J. 
Published: February 2005

AbstractThe alveolar macrophage of the cat shares some features with the alveolar macrophages of ordinary laboratory mammals and man, mainly a voluminous Golgi zone exhibiting evidence of secretory activity. The very numerous typical lysosomes appear to be a secretory end product. They increase in size by a fusion process. At some stage of this process dense periodic structures, crystal‐like, become visible in intermediate size lysosomes, which later form heterogeneous crystal‐like granules characteristic of the cat's alveolar macrophage.The crystal‐like granules are bounded by a unit‐membrane pattern and contain a dense periodic parallel lamellar material (crystal‐like) mixed with fluffy amorphous substance and surrounded by a clear homogeneous material. Based on its structure as observed at a high magnification, and its behavior during phagocytosis, this crystal‐like material appears to be composed of lipid.Intra‐pulmonary injection of red blood cells was carried out in order to observe the fate of the crystal‐like granules during phagocytosis as compared to that of typical lysosomes. Like typical lysosomes the crystal‐like granules become reduced in number and undergo incorporation to the phagocytic vacuoles, demonstrating their lysosomal nature.
On the occurrence of microtubules within mature astrocytes
Authors: Raine Cedric S. , Wiśniewski Henryk 
Published: February 2005

AbstractMicrotubules have been described to occur frequently within the subpial fibrous astrocytes of the adult spinal cord of three species. This finding is related directly to perfusion fixation by glutaraldehyde. Immersion fixation produced no or fewer tubules in this area. It is suggested that the presence of microtubules in these cells might reflect a specific skeletal function. Astrocytes from other locations within the central nervous system displayed fewer microtubules within their cytoplasm.
Selective effects of testosterone and isoproterenol upon regenerating submandibular gland isografts in BALB/c mice
Authors: Hoshino Kazumasa , Lin C. D. 
Published: February 2005

AbstractSingle submandibular glands were isografted intraperitoneally to normal BALB/c mice. From the day following transplantation, 20 mg testosterone enanthate fortnightly, or daily intraperitoneal injections of 0.25 mg per gram body weight of isoproterenol‐HCl were given. Control mice were untreated. The grafts were removed from five mice in each group 1, 2, 4, or 8 weeks after grafting. Regardless of treatments, only ductal cells were observed one week after transplantation. With testosterone treatment for longer than two weeks, their remaining ductal cells tended to accumulate secretory granules. Some appeared to be secretory tubules resembling those in the glands of normal adult male mice. When the glands were transplanted from females to male hosts, surviving grafts responded to endogenous androgen of the hosts, and some secretory tubules reappeared without testosterone treatment. Contrarily, with isoproterenol treatment for longer than two weeks, acinar cells reappeared in the grafts, but no secretory tubules were observed. The remaining ductal cells often underwent hyperplastic changes with reappearing tubules or acinar cells amongst them corresponding to post‐transplantational treatment. Mechanisms of differentiation of these three different components of submandibular glands were found to be different and each had specific affinity to testosterone or isoproterenol. Grafts were removed from hosts treated with testosterone for two months, and when 4 or 8 of these grafts were retransplanted into each new host, they demonstrated a lethal effect.
Fine structure of a third epithelial component of the thyroid gland of the rat
Authors: Calvert R. , Isler H. 
Published: February 2005

AbstractDuct‐like structures made of cells different from follicular or light cells were observed with the electron microscope in the thyroid glands of 16 rats. The wall of most of the ducts was made of two types of cells: (1) the lumen‐bordering cells, mostly cuboidal or columnar, with short microvilli, and (2) the subjacent squamous cells, arranged in one or several layers of cells displaying numerous desmosomes and dense bundles of tonofilaments. Both cell types showed intricate folding of the plasma membrane at sites of cell‐to‐cell contact, an abundance of free ribosomes and nuclear indentations. In one occasion mucous‐like cells were found. The lumen contained a finely granular homogeneous material as well as cell remnants. The ducts were located among the follicles, and were ususally discrete from them; but on four occasions the epithelium of the duct was seen in direct continuity with that of a thyroid follicle. Only one case of a light cell associated with a duct was observed while many of these cells were associated with thyroid follicles.
Correlation of ovarian abnormalities in young golden hamsters with ovarian estrogens and progesterone
Authors: Kent Harry A. , Mandel Jeffrey A. 
Published: February 2005

AbstractA correlation between ovarian steroids and ovarian abnormalities is demonstrated. The decrease in levels of ovarian estrogen and progesterone is correlated, one week later, with an increase in polyovular follicles and then in multinucleate ova. The time sequence of the onset of ovarian abnormalities, as correlated with levels of estrogens and progesterone are an indication of the possibility of hormonal control of the ovarian abnormalities.
Morphological‐histochemical comparison of dog and cat splenic ellipsoid sheaths
Authors: Jacobsen Glenn 
Published: February 2005

AbstractInvestigations were made on the morphological and histochemical nature of the ellipsoid sheaths of two different types of spleens, sinusal and non‐sinusal, as found in the dog and cat respectively.Ellipsoid cells of dog and cat spleens respond similarly with Marshall's silver impregnation method as well as demonstrate activity for the hydrolytic enzyme, acid phosphatase. Both technics substantiate ellipsoid involvement in the reticuloendothelial system. Nonspecific esterase, another hydrolytic enzyme commonly found in phagocytic cells, was demonstrated in the cat ellipsoid cells but not in similar cells of the dog spleen indicating a basic difference in the physiological activity of the dog and cat ellipsoid cells.
Fine structure of the interstitial cells of leydig in the squirrel monkey during seasonal regression
Authors: Belt W. D. , Cavazos L. F. 
Published: February 2005

AbstractThe fine structure of the interstitial cells of Leydig has been examined in the squirrel monkey, Saimiri sciureus, during the non breeding portion of the year when the testes are essentially azoospermic. Interstitial cells are present in abundance as a layer, several cells thick, on the inner aspect of the tunica albuginea. Cytologically, the cells possess the characteristics usually associated with cells which synthesize and secrete steroid hormones: an abundant agranular endoplasmic reticulum in the form of anastomotic tubules; mitochon‐chondria with both lamellar and tubular cristae; only a few strands of granular endoplasmic reticulum; a Golgi apparatus and associated vesicles, some of which are of the coated variety; a varying population of lipid droplets and dense bodies. Some of the dense bodies appeared to be lipofuscin pigment. A previously undescribed inclusion was frequently encountered which consisted of arrays of a honeycomb like structure. Most frequently these structures were present near the cell periphery or in blunt protrusions of the cytoplasm.
The ultrastructure of the human adrenal medulla: With comparative studies of white rat
Authors: Brown W. Jann , Barajas Luciano , Latta Harrison 
Published: February 2005

AbstractThere is wide support for the concept that there are two types of secretory cells in adrenal medulla of various species. One cell is filled with electron dense bodies believed to contain norepinephrine; the other cell's lesser stained bodies contain epinephrine. This differential density may be seen by fixation in osmium tetroxide after glutaraldehyde.The two cell types have not been clearly shown in human tissues. Such a failure may be related to fixation. In consideration of this, fresh human adrenal was fixed in cold 1% glutaraldehyde, then 1% osmium tetroxide — a procedure known to give satisfactory differentiation in other species. A parallel study with rat tissue was then done.Electron microscopy revealed two types of cells in rats, while in man an obvious cell difference was not found. There is, however, a clear difference in human chromaffin granule density, which implies that the human cells have random numbers of both light and dark granules. The morphologic difference of the cell types in man may be less distinct than in the rat. Another possibility is that in cells with predominantly dark granules, there are co‐mingled lighter granules with the coexistence of cells of opposite dominance. Both hormones then would occur in the same cell in varying proportions according to functional demand. It seems highly unlikely that two distinct cell types would have been overlooked with wide sampling, however, in a study of three adrenal glands, one cannot rule out their existence.
Distribution of cell web‐containing epithelial reticular cells in the rat thymus
Authors: Pereira G. , Clermont Y. 
Published: February 2005

AbstractIn sections of thymus stained with the tannic acid‐phosphomolybdic acid‐amido black (TPA) technique, the epithelial reticular cells can readily be identified by the well‐stained tonofibrils in their cytoplasm. In the cortex, flattened epithelial reticular cells form a continuous layer on the inner surface of the capsule and along the interlobular septa. Within the cortex proper, stellate epithelial reticular cells are widely dispersed as a loose network. In the medulla, two zones, referred to as “outer” and “inner” medulla, are distinguished. The outer medulla, like the cortex, contains epithelial reticular cells, but these are more voluminous, are more richly provided with tonofibrils and form a denser network than in the cortex. In the inner medulla no epithelial reticular cells can be seen but instead connective tissue cells and fibers make up the supporting framework. A layer of flattened epithelial reticular cells demarcates the outer from the inner medulla. This layer of cells also extends along the outer surface of blood capillaries seen in the outer medulla and cortex. Around the larger blood vessels, this layer of epithelial reticular cells is separated from the vessel wall by a connective tissue perivascular space. Hence, the inner medulla is continuous with the perivascular spaces and, like them, is supported by connective tissue. Thus, the epithelial reticular cells constitute the supporting framework of the cortex and outer medulla and separate these regions from the connective tissue of the capsule, interlobular septa, blood vessels and inner medulla.
A study of some histochemical and phagocytic reactions of the reticuloendothelial system of the rabbit spleen
Authors: Snodgrass Michael J. , Snook Theodore 
Published: February 2005

AbstractQuestions concerning the nature of the intermediary vascular pattern make up a considerable portion of the literature concerning splenic morphology. Evidence indicates there is a special association between the reticuloendothelial system (RES) and the intermediary capillary terminations. This study was undertaken to characterize the distribution of the RES in the rabbit spleen and to correlate this with the vascular pattern described by Snook ('58). Like cells of the RES throughout the animal body, splenic RE cells can be demonstrated by several histochemical and functional methods. They are metalophilic (argyrophilic), possess several hydrolytic enzymes, and phagocytose injected particulate matter. Cells demonstrated by these methods are found in the marginal zone, and in the lumen of the red pulp sinuses but most are localized in the red pulp cords. This distribution corresponds closely to the termination of arterial capillaries in the marginal zone and pulp cords in the rabbit spleen and supports the general hypothesis that there is a unique and intimate relationship between the vascular system and the RES at these points.The sinus lining cells react characteristically to the techniques employed. They are sporadically metalophilic, strongly positive for nonspecific esterase (endoplasmic reticulum), negative for acid phosphatase (lysosomal), and occasionally contain small particles of injected matter. They probably represent a functionally distinct cell population.
Intercellular bridges between follicle cells and oocyte in the lizard, Anolis carolinensis
Authors: Neaves William B. 
Published: February 2005

AbstractCertain cells in the follicular epithelium of lizard (Anolis caro‐linensis) ovaries are connected to the oocyte by true intercellular bridges. Unlike other known intercellular bridges, these may form by secondary cell contact and membrane fusion rather than by incomplete cytokinesis. These intercellular bridges are abundant in previtellogenic tertiary follicles, and they contain glyco‐gen, ribonucleoprotein particles, and a dense, fibro‐granular material which may be exchanged between the two cells. Prior to the onset of yolk accumulation in the oocyte, the intercellular bridges and the pyriform cells from which they originated disappear from the follicular epithelium. The abundance of intercellular bridges in previtellogenic follicles suggests that they may be involved in the maintenance of dormant oocytes during periods of suspended reproductive activity and in the preparation of these oocytes for ensuing periods of intense metabolic activity associated with yolk accumulation.