bluuebunny/crossref_metadata_2025_split huggingface dataset:
Voltage‐dependent ‐L‐type Ca2+ channels participate in regulating neural crest migration and differentiation
Authors: Moran Denis 
Published: February 2005

AbstractGeneral models of cell activation implicate Ca2+ conductance as pivotal in conveying transmembrane signals. During embryonic development, both cell migration and differentiation are influenced by changes in Ca2+; and, as a consequence, the modulation of Ca2+ is important in the control of many morphogenetic processes. Because Ca2+ conductance may be regulated at voltage‐dependent Ca2+ channels (VDCCs), we investigated whether neural crest cells develop VDCCs and, if so, whether they function in regulating migration and establishing cytomorphology. Autoradiography indicates that neural crest cells in vitro develop‐L‐type Ca2+ channels during migration and differentiation. Blockage of these channels by verapamil, both in vivo and in vitro, leads to a dramatic and reversible inhibition of neural crest migration. Alterations are manifest in vitro in cell‐to‐cell and cell‐to‐substratum contact and in the organization of the actin cytoskeleton. In whole embryos, verapamil or nifedipine inhibits pigment pattern formation. Moreover. blockage of the ‐L‐type Ca2+ channels in whole embryos or cultures, after cells have already migrated and differentiated, results in a significant change in individual cell shape and in the overall pigment cell pattern, suggesting further that maintenance of the differentiated state also requires regulation at the ‐L‐type Ca2+ channel. Since certain aspects of neural crest adhesion and cytoskeletal function are dependent on Ca2+, it is suggested that interactions that regulate the availability of Ca2+ through the VDCC may provide coordinate control of motile and adhesive interactions at the cell‐substratum interface.
Generation of color composites for enhanced tissue differentiation in magnetic resonance imaging of the brain
Authors: Brown H. Keith , Hazelton Todd R. , Silbiger Martin L. 
Published: February 2005

AbstractCurrently, the diagnostic interpretation of magnetic resonance (MR) images requires that radiologists integrate specific tissue contrast information from several different images obtained at the same anatomic slice position. Each of these images has its own unique tissue contrast patterns which are based on the image acquisition parameters (pulse sequence) selected. The complex contrast patterns observable in these images reflect the inherent biophysical characteristics of the tissues and fluids present in the imaged section. In an effort to increase the diagnostic accuracy and efficiency of MR image interpretation, we have generated color composite images from quantitatively analyzed achromatic MR images of the brain, obtained while utilizing different pulse sequences. By using a DEC Micro VAX II computer with Interactive Digital Language (IDL), this color display method has been applied to images obtained from General Electric Signa and Siemens Magnatom imagers. For this study, our image sets included T1‐weighted, T2‐weighted, and proton density spin echo sequences as well as both high and low flip angle gradient echo sequences. Advantages of our color composite methods, in contrast to many other image processing techniques that have been described, are that minimal information is lost, computer misclassification of tissues is avoided, and the conspicuity of specific tissues is enhanced. Furthermore, with this method it is possible to produce composite images whose color renditions approach a natural anatomic tissue appearance. Availability of these color composites to radiologists may improve the efficiency and accuracy of the diagnostic interpretation of MR images.
Linkage of manchette microtubules to the nuclear envelope and observations of the role of the manchette in nuclear shaping during spermiogenesis in rodents
Authors: Russell Lonnie D. , Russell Jill A. , MacGregor Grant R. , Meistrich Marvin L. 
Published: February 2005

AbstractStructural features of the mouse and rat manchette and the role of the manchette in shaping the spermatid nucleus were investigated. Rod‐like elements about 10 nm in diameter and 40–70 nm in length were seen linking the innermost microtubules of the manchette and the outer leaflet of the nuclear envelope in step 8 through step 11 rat and mouse spermatids that either had been routinely fixed for electron microscopy or had been isolated and detergent extracted. Rod‐like linkers were also seen joining the nuclear ring to the plasma membrane and nuclear envelope. These linkers may ensure that under normal conditions the manchette remains in a defined position relative to these membranous components. A variety of compounds (taxol, cytoxan, and 5‐fluorouracil) were found to perturb the manchette and to affect nuclear shaping. In addition, sys and azh mutant mice were used to determine the consequences of defective manchette formation. These genetic conditions and chemical treatments either produced manchettes that were not in their normal position (azh, sys, and taxol) and/or caused the manchette to appear abnormal (azh, sys, cytoxan, 5‐fluorouracil, and taxol), and all resulted in a deformation of the step 9–11 spermatid nucleus. In all instances where the manchette was present, either in normal or ectopic locations, the sectioned nuclear envelope was parallel to the long axis of the microtubules of the manchette. In general, areas of the nuclear envelope where the manchette was not present, or where it was expected to be present but was not, were rounded (normal animals, sys, cytoxan). In addition, there are indications using certain compounds (cytoxan and 5‐fluorouracil) as well as in the azh and sys mouse that the manchette may exert pressure to deform the nucleus. It is suggested that the rod‐like linkages of the manchette ensure that the nuclear envelope remains at a constant distance from the manchette microtubules and that this is a major factor acting to impart nuclear shape changes on a region of the head caudal to the acrosome during the early elongation phase of spermiogenesis. The manchette microtubules, which are also known to be linked together, may act as a scaffold to deform this part of the nucleus from its spherical shape, perhaps in concert with forces initiated by other structural elements. Evidence from sys animals indicates that structural elements, such as the acrosomal complex over the anterior head (acrosome‐actin‐nuclear envelope), may affect nuclear shaping over the acrosome‐covered portion of the spermatid head. It is suggested that chromatin condensation primarily reinforces the shape changes already brought about by the manchette and other structural elements acting on the nucleus. After chromatin condensation, spermatid nuclear shape changes are minor.
Short‐term Morphological response of the rat testis to administration of five chemotherapeutic agents
Authors: Russell Lonnie D. , Russell Jill A. 
Published: February 2005

AbstractAs cancer survival rates improve, there is increasing concern about the adverse effects of chemotherapeutic agents on male fertility. Five chemotherapeutic agents (amethop‐terin, AP or methotrexate; doxorubicin, DX; cytoxan or cyclophosphamide, CP; cisplatinum, CDDP; and 5‐fluorouracil, 5‐FU) which belong to three different categories of chemotherapeutic agents (antimetabolite, antibiotic, alkylating agent, alkylating agent, antimetabolite, respectively) were given systemically to adult rats to determine the short‐term morphological patterns of response in the testis, and the testes were examined by light microscopy. Morphological patterns of response were found to be highly characteristic for each agent, and some shared morphological responses were evident. All except one chemotherapeutic agent (5‐FU) caused spermatogonial damage. Among the defects seen were probable degenerating meiotic spermatocytes (CDDP), presence of micronuclei (DX), “arrested” spermatid development (5‐FU), and abnormally shaped step 15 spermatids (5‐FU). Damage that could be due to the effect of an agent on the Sertoli cell was failure of sperm release (5‐FU, CDDP, DX, and AP), increase in the Sertoli cell lipid (5‐FU), and malorientation of step 8 spermatids (5‐FU, DX). The varied patterns of damage observed are a possible explanation of why the reproductive recovery potential in cancer patients undergoing chemotherapy is variable and drug‐specific.
Testis structure in the sys (symplastic spermatids) mouse
Authors: Russell Lonnie D. , Hikim Amiya P. Sinha , Overbeek Paul A. , MacGregor Grant R. 
Published: February 2005

AbstractTestes of mice with the recessive insertional mutation termed symplastic spermatids (sys) were assessed for structural and developmental abnormalities. Homozygous (sys/sys) males are infertile due to an abnormality in spermatogenesis leading to azoospermia. The major interruption to spermatogenesis occurs when the intercellular bridges that connect round spermatids open prematurely resulting in the formation of symplasts. Symplasts contain as many as 285 nuclei. Development of spermatids within symplasts is arrested just before, or just after, elongation of the spermatid nuclei begins. Symplasts degenerate and appear to be phagocytized by Sertoli cells and by intratubular macrophages. In addition, degeneration of young round spermatids and also spermatocytes occasionally is observed. Spermatocyte degeneration is substantial in some tubules and leaves them depleted of cells other than basal compartment cells. Sertoli cell abnormalities are prominent and include intracellular vacuolation, absence of apical processes surrounding round spermatids, degeneration, and occasional sloughing. Although reduplication and infolding of the basal lamina is also seen, this does not appear as a common phenomenon. The sys phenotype is first manifest in animals between 19 days and 22 days of age. Considerable variability is seen in testis histology of prepubertal animals; some display degenerating pachytene spermatocytes and virtually no Sertoli cell vacuoles, while others display vacuoles without apparent elevated numbers of degenerating spermatocytes. Although this study has not revealed the primary cell type(s) affected by the insertional inactivation event, it is possible that the abnormalities in the Sertoli cells are responsible for germ cell degeneration as it is generally recognized that deficits in the Sertoli cell can result in major germ cell abnormalities but not vice versa.
Reinitiation of spermatogenesis by exogenous gonadotropins in a seasonal breeder, the woodchuck (Marmota monax), during gonadal inactivity
Authors: Hikim Amiya P. Sinha , Hikim Indrani Sinha , Amador Armando G. , Bartke Andrzej , Woolf Alan , Russell Lonnie D. 
Published: February 2005

AbstractThe present study was undertaken (1) to document structural and functional changes in the testes of seasonally breeding woodchuck during active and inactive states of spermatogenesis and (2) to evaluate the ability of exogenous gonadotropins to reinitiate spermatogenesis outside the breeding season. During seasonal gonadal inactivity, there were significant (P < 0.05) reductions in volumes of several testicular features (testis, seminiferous tubules, tubular lumen, interstitial tissue, individual Leydig cells, Leydig cell nuclei, and Leydig cell cytoplasm) as compared with gonadally active animals. The diameter of the seminiferous tubules was decreased by 26%, and Leydig cell numbers also declined in the regressed testes. These changes were accompanied by a decline in testosterone (T) levels in both plasma and testis, and reduction in epithelial height of accessory reproductive organs. A hormonal regimen was developed that would reinitiate spermatogenesis in captive, sexually quiescent woodchucks. A combination of PMSG and hCG markedly stimulated testicular growth and function and restored spermatogenesis qualitatively. Quantitatively normal spermatogenesis was restored in 2 of 6 treated males. Morphometric analyses revealed substantial increases in seminiferous tubular diameter and in the volume of seminiferous tubules, tubular lumen, total Levdig cells, and individual Leydig cells in the hormone‐treated animals. These increased values corresponded to 99, 75, 68, 51, and 200%, respectively, of the values measured in naturally active woodchucks. Leydig cell numbers, however, remained unchanged and approximated only 31% of the number found in naturally active testes. Hormonal stimulation also resulted in a significant rise in serum T as well as in the total content of testicular T, and a marked increase in epithelial height in various accessory reproductive glands. The most effective hormonal protocol for stimulating spermatogenesis was treatment with 12.5 IU of PMSG twice a week for 4 weeks followed by 12.5 IU of PMSG + 25 IU of hCG twice a week for 4 weeks.
The role of hematogenous and intrinsic precursor cells in lymphocyte production in murine bone marrow and thymus
Authors: Mejino Jose L. V. , Lee Minako , Hamilton Brian L. , Rosse Cornelius 
Published: February 2005

AbstractIt is well recognized that the bone marrow contains cells that can repopulate a depleted thymus as well as cells that can be induced to express phenotypic markers characteristic of T cells. It is not known, however, to what extent thymocytopoiesis in the normal thymus relies on immigrant, bone marrow‐derived cells, nor whether some T cell precursors have entered the bone marrow from the circulation. We used the parabiotic system to test whether thymocytopoiesis relies on progenitors intrinsic to the thymus or on cells that enter the organ from the circulation. In the same system, we have also investigated whether Thy‐1− bone marrow lymphocytes that respond to phytohemagglutinin (PHA) by proliferation and Thy‐1 expression are produced by my‐elogenous or hematogenous progenitors.Syngeneic CBA/HT6 and CBA/CaJ mice were joined in parabiotic union at 4–6 weeks of age. Cross circulation between the two partners was verified by the equilibration of Evans' blue dye injected into one partner and by the equilibration of PHA‐responsive T cells in the spleen of the parabionts. Chromosome spreads were prepared from the PHA‐stimulated T cell‐depleted bone marrow and from spontaneously proliferating thymocytes as well as from thymocytes stimulated by PHA or Concanavalin A (Con A). The exchange of spleen colony‐forming units (CFU‐S) in the femoral marrow was assessed by karyotyping individual spleen colonies.Regardless of the length of parabiotic union, ranging from 4 to 20 weeks, Thy‐1−, PHA‐responsive bone marrow lymphocytes remained predominantly of the host type with only 3% being derived from the opposite partner. The same held true for CFU‐S in the femur; only around 5% of this cell population were of the nonhost type. Thus, although some Thy‐1−, PHA‐responsive lymphocytes in the bone marrow may be derived from hematogenous stem cells, the majority of them are generated by precursors resident in the bone marrow.Likewise, regardless of the length of parabiotic union, at least 95% of spontaneously proliferating cells in the thymus of each partner possessed the karyotype of the host, and this held true also for PHA‐ or Con A‐stimulated thymocytes, indicating that the small population of spontaneously proliferating immigrant cells cannot account for the production of the large number of postmitotic (mitogen‐responsive) thymocytes.Our findings, therefore, demonstrate a high degree of self‐maintenance for Thy‐1−, PHA‐reponsive lymphocytes in the bone marrow and also for intrathymic T cell precursors. In the unperturbed, postnatal thymus, thymoctye production does not rely on cell input from the circulation; the vast majority of thymoctyes are generated by an intrathymic precursor pool that is independent of immigrant myelogenous T cell precursors.
Congenitally osteosclerotic (os/os) rabbits are not cured by bone marrow transplantation from normal littermates
Authors: Popoff Steven N. , Marks Sandy C. 
Published: February 2005

AbstractThe osteopetrotic (os) rabbit is a lethal mutation of autosomal recessive inheritance characterized by hypocalcemia, hypophosphatemia, fibrosis of marrow spaces, and ultrastructural abnormalities in both osteoclasts and osteoblasts. Procedures involving the transplantation of cells from normal hemopoietic tissues, which are sources of osteoclast precursors, are known to cure osteopetrosis in several mutations including some children. We tested the ability of transplanted bone marrow and/or spleen from normal littermates to reverse the skeletal sclerosis in os rabbits. Treatment of 15 neonatal mutants consisted of immunosuppression by whole‐body irradiation followed by transplantation of normal bone marrow and/or spleen cell suspensions. This treatment failed to prolong life span or to cure osteopetrosis judged radiographically and histologically for up to 3 weeks posttreatment, the longest time of survival. These data indicate that transplantation of stem cells from multiple hemopoietic tissues, procedures known to cure osteopetrosis in other mutations, is not effective in the os rabbit. These results support the hypothesis that the skeletal microenvironment is not capable of supporting the development and function of normal osteoclasts in this mutation.
Structure‐Function relationships during preovulatory development of porcine follicles following equine chorionic gonadotropin stimulation
Authors: King G. J. , Chapeau C. , Ackerley C. A. 
Published: February 2005

AbstractPorcine follicular maturation begins by recruitment from a continually proliferating pool of small antral follicles; those receiving the appropriate stimulus differentiate rapidly through a series of structural and functional changes. Such ovarian activity can be induced in prepubertal gilts with a single injection of equine chorionic gonadotropin (eCG). Average follicular diameter in eCG treated females increased from approximately 2 mm before stimulation to 3.5 mm by 24 hr after injection, with subsequent growth to ovulatory size (8 or 9 mm) by 96 hr. Both theca and granulosa layers increased in thickness and complexity, and a prominent capillary bed evolved immediately outside the basement membrane separating the two layers. Cytoplasmic organelles associated with increased metabolic activity and steroidogenesis proliferated within the first 24 hr. Progressive changes included increasing amounts of lipid and rough and smooth endoplasmic reticulum, with the latter occurring in vesicular or lamellar forms and as lipid‐associated whorls. Bizarre mitochondrial forms also appeared, often associated with lipids.The amount and proportion of rough and smooth endoplasmic reticulum shifted dramatically as follicles matured. By 24 hr, rough endoplasmic reticulum in thecal cells increased from 4.2 to 7% of cell volume, while the amount in granulosa cells increased from less than 3.5% to more than 10%; the quantity remained relatively constant in the theca but declined to prestimulation values in the granulosa layer. Rough endoplasmic reticulum predominated over smooth in the first 24 hr following stimulation but the proportions were then reversed, so that more than 10% of both layers was composed of smooth endoplasmic reticulum by the time ovulation was imminent.Some follicles had or were in the process of ovulating by 96 hr. Their walls were collapsed into prominent folds with the two cell types beginning to mix. Slight undulations and some regions of discontinuity were observed in basement membranes of large unovulated follicles at this time. In specimens collected at 96 hr poststimulation and processed for retention of lipid, lipid‐like material was noticeable in the extracellular matrix surrounding cells that contained organelle configurations suggestive of steroidogenesis.
The vasculature of the rat penis: A scanning electron microscopic and histologic study
Authors: Fernandez Erika , Dail William G. , Walton Guy , Martinez Girard 
Published: February 2005

AbstractAs a basis for understanding the mechanism of erection in an animal model frequently used in research in reproductive biology, the angioarchitecture of the penis of the rat has been described using scanning electron microscopy. Study of the penile vasculature of the rat indicates that the corpora cavernosa penis and the corpus spongiosum are independent erectile tissues, each with its own arterial and venous vessels. The large vascular spaces and abundant smooth muscle of the penile crura are compatible with its role in regulating blood flow to more distal penile tissues. Helicine arteries of the crura, but not the parent deep penile artery or arteries elsewhere, have muscular cushions in their walls. The venous drainage of the penile crura is via subtunical veins which are thought to be compressed during erection to elevate pressure within the penis. Large, paired cavernous veins drain the shaft of the penis. A unique method for inhibiting blood flow from the penis is indicated by the division of the cavernous veins into smaller channels prior to joining the subtunical venous plexus. Erectile tissue in the bifid origins of the corpus spongiosum has abundant cavernous muscle, while in the remainder of the corpus spongiosum little smooth muscle lines the cavernous spaces. The cavernous spaces on either side of the urethra coalesce to form vessels, each of which communicates with cavernous spaces in the glans. In addition, a bypass of the glans is effected by communication of these vessels directly with the deep dorsal vein. The apparent absence of muscular pads in vessels of the spongiosum, the relative paucity of cavernous smooth muscle, and the ample venous drainage provided by the deep dorsal vein may account for the lack of a venous occlusive mechanism similar to that of the corpora cavernosa penis.
Geographic distribution of xanthine oxidase, free radical scavengers, creatine kinase, and lactate dehydrogenase enzyme systems in rat heart and skeletal muscle
Authors: Apple Fred S. , Hyde John E. , Ingersoll‐Stroubos Ann Marie , Theologides Athanasios 
Published: February 2005

AbstractThe geographic distribution of the following enzyme systems is described in the rat heart (left and right ventricles) and in different skeletal muscles (soleus, plantaris, and red and white gastrocnemius): xanthine oxidase and dehydrogenase, creatine kinase isoenzymes, lactate dehydrogenase isoenzymes, and the free radical scavenger enzymes superoxide dismutase, glutathione reductase, and glutathione peroxidase. No substantial difference in enzyme activities was observed between the left and right ventricles. Skeletal muscles showed a clear distinction between enzyme activities depending on their composition of oxidative fibers and glycolytic fibers.