摘要:

AbstractThe histological and ultrastructural features of secondary neurulation in C57BL/6 mouse embryos were examined as a first step in the analysis of how this process occurs in mammalian embryos. Secondary neurulation involves two major events in mouse embryos: (1) formation of the medullary rosette (9.5‐ to 10‐day embryos) or plate (11‐ to 12‐day embryos), and (2) cavitation. These two events occur simultaneously. The medullary rosette consists of elongated tail bud cells, radially arranged around a central lumen formed by cavitation. The secondary portion of the neural tube forms in 9.5‐ to 10‐day embryos by progressive enlargement of the central lumen and addition (by cell recruitment or mitosis) of tail bud cells to the rosette. The medullary plate likewise consists of elongated tail bud cells, but these cells do not surround a central cavity. Instead, cells of the medullary plate extend ventrad from the basal aspect of the dorsal surface ectoderm to a slit‐like cavity formed by cavitation. Formation of the secondary neural tube occurs in 11‐ to 12‐day embryos, principally by the recruitment of more lateral and ventral tail bud cells into the medullary plate. Free cells and cellular debris are frequently encountered in the forming lumen of the secondary neural tube, but cells exhibiting signs of necrosis were absent in cavitating regions. Numerous small intercellular junctions form at the inner (juxtaluminal) ends of tail bud cells as the medullary rosette or plate is forming and cavitation is occurring. These observations suggest that cavitation per se (i.e., formation of a lumen) during secondary neurulation is a relatively passive phenomenon, which results principally from neighboring cells becoming polarized apicobasally and incorporated into a primitive neuroepithelium. The latter constitutes the walls of the forming seco

ISSN:0002-9106    

DOI:10.1002/aja.1001690402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe arterial pattern in chicken hatchlings was investigated by microangiography and microscopic analysis of cleared specimens. The hatchling arterial pattern was found to resemble strongly the pattern that has been described for the adult chicken. Several minor variations in this pattern were found which were probably due to species, strain, or age differences. We also investigated the arterial pattern in chicken embryos aged 4.5 to 21 days of incubation. The hatchling pattern was fully developed by approximately 8 days of incubation. Some similarities were found to exist between the embryonic pattern in the chicken embryo and that described for the human embryo.

ISSN:0002-9106    

DOI:10.1002/aja.1001690403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractLight and electron microscopic observations and biochemical analysis of the lingual cartilages from the Atlantic hagfish,Myxine glutinosa, reveal two different types of cartilage, designated types 1 and 2, respectively. The anterior and medial lingual are type 1, while the posterior lingual cartilage is type 2. Chondrocytes in type 1 cartilage are similar to those found in other vertebrate cartilages. The presence within the Golgi elements of material that resembles a component of the extracellular matrix suggests the involvement of active chondrocytes in the synthesis of the matrix. The matrix of the type 1 cartilage contains fibrils arranged to form concentric lamellae in the territorial matrix and irregularly arranged, branched fibrils in the interterritorial matrix. Biochemical analysis of the type 1 cartilage reveals that it is composed primarily of a cyanogen bromide (CNBr)‐insoluble protein of unique composition that we have termed “myxinin.” Myxinin appears to be similar, but not identical, to lamprin. Type 2 cartilage bears no resemblance to any other known vertebrate cartilage. The principal cells are hypertrophied and are characterized by masses of cytoplasmic filaments. The appearance of the organelles in smaller nest cells suggests that nest cells are active in the production of some of the matrix, which consists primarily of collagen. Microfibrils and a basal lamina‐like material are also present. Biochemical analysis of the type 2 cartilage reveals that the CNBr‐insoluble material is different from myxinin. Comparisons of lamprey and hagfish cartilages prompt the concept that these two agnathans probably followed long‐independent evolutionar

ISSN:0002-9106    

DOI:10.1002/aja.1001690404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractSeveral cell types were identified in the rat nasal respiratory epithelium using scanning electron microscopy. In addition to the previously described ciliated, nonciliated, and goblet cells, the nasal brush cell was identified based on its surface characteristics and its location between nonciliated epithelial cells. Scanning electron microscopy clearly showed the differences in distribution of cell types in the nasal mucosa. The ciliated cells increase in number from the anterior to the posterior areas of the respiratory epithelium with a corresponding decrease in nonciliated cells. However, even at a single cross‐sectional area of the nasal cavity, the various surfaces have different proportions of ciliated versus nonciliated cells, e.g., the medial surface of the nasal concha has more ciliated cells than other surfaces. Brush cells are distributed between nonciliated cells of the respiratory epithelium on most surfaces of the nasal cavity including the conchae and the lateral wall. Based on the available information, scanning electron microscopy will be useful in future studies to determine the effects that inhaled toxicants have on cells and on the location of lesion

ISSN:0002-9106    

DOI:10.1002/aja.1001690405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe amount and distribution of glycogen as well as the activity of glucose‐6‐phosphatase (G‐6‐Pase) in the livers of rats were analyzed by biochemical and/or histochemical techniques. During the first 5 hr of the light cycle, livers of rats were sampled prior to and 30 min following an injection of compound 48/80 or Ringer's solution. Glycogen decreased significantly in response to sampling; however, treatment with compound 48/80 provoked an additional significant decrease in hepatic glycogen. These differences occurred irrespective of the time during the 5 hr that this was studied. The livers of the majority of the rats treated with compound 48/80 displayed a periportal distribution of glycogen, while those treated with Ringer's showed a more uniform pattern. Hepatic G‐6‐Pase activity was unchanged in either the Ringer's or compound 48/80 treated rats. These results indicated that (1) the significant glycogenolytic response occurs independently of the amount of glycogen present, (2) G‐6‐Pase activity is not affected within 30 min following the stimulation of glycogenolysis, (3) variation in glycogen patterns during depletion depends on the nature of the stimulus and/or degree of response, and (4) the amount of glycogen available for rel

ISSN:0002-9106    

DOI:10.1002/aja.1001690406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractIn this study the human petrous bone was investigated to find out whether and in what way it is adapted to mechanical stress by inner bone structure. Three normally formed petrous bones were cut in serial sections and examined by means of microradiography and circular polarized light with respect to mineralization, distribution of bone structure, and collagen fiber arrangement over the cross section. It has been shown that the human petrous bone can be divided morphologically into four different bony layers: (1) endosteal; (2) enchrondral; (3) inner periosteal layers, which together form the labyrinthine capsule and which are characterized by a higher level of mineralization and show no clear indication of bone remodeling; and (4) outer periosteal layer, in which numerous osteons indicate appositional and resorptional growth processes. The collagen fibers in the labyrinthine capsule are arranged in an irregular web‐like pattern, whereas in the outer periosteal layer they run predominantly parallel to the surfaces of the petrous bone, probably to minimize the mechanical stress in the form of a tension band. These results support the assumption that in the human petrous bone, the outer periosteal layer is adapted to resorb elastic deformation, whereas the brittle labyrinthine capsule is better adapted to the functions of an auditory and vestibular orga

ISSN:0002-9106    

DOI:10.1002/aja.1001690407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractElectron microscopic immunostaining was used to examine the localization of type IV collagen, laminin, entactin, heparan sulfate proteoglycan, and fibronectin within the basement membranes of the rat kidney. In preliminary experiments, various methods of processing formaldehyde‐fixed kidney were compared using antilaminin antiserum and the indirect immunoperoxidase method. Little or no laminin immunostaining of the glomerular basement membrane was present in sections unless they had been frozen‐thawed; and even in this case, the immunostaining was light in comparison to that of basement membranes in adjacent tubules. However, when frozen‐thawed sections were treated with 0.5% sodium borohydride, immunostaining was then as strong in glomerular as in tubular basement membranes. Accordingly, this treatment was applied to frozen‐thawed sections before immunostaining for any of the substances under study.Immunostaining of the glomerular basement membrane for each of the five substances was fairly uniform throughout the lamina densa (also called basal lamina), but uneven in the lamina lucida interna and externa (also called lamina rara interna and externa) in which stained bands extended from the lamina densa. Similarly in the basement membranes of tubules, immunostaining for the five substances was localized to the lamina densa and bands extending into the lamina lucida.When the ultrastructure of the glomerular basement membrane was examined, three structures were found: (1) a network of 4‐nm‐thick “cords,” which seems to be the main component; the cords are closely packed in the lamina densa and more loosely arranged in the lamina lucida interna and externa; (2) straight, hollow 7–10‐nm‐thick structures referred to as “basotubules”; and (3) 3.5‐nm elements composed of minute paired rods, referred to as “double pegs.” The distribution of the cords, but not that of the other two structures, was related to the immunostaining pattern.It is concluded that (1) to fully reveal the antigenicity of the glomerular basement membrane, frozen‐thawed sections must be treated with sodium borohydride prior to immunostaining, possibly because this basement membrane is more compact than the others; and (2) in both glomerular and tubular basement membranes, type IV collagen, laminin, entactin, heparan sulfate proteoglycan and fibronectin are colocalized in the lamina densa and its extensions to the laminae lucidae. Since the distribution of the cords corresponds to that of immunostaining, it is likely that the five substa

ISSN:0002-9106    

DOI:10.1002/aja.1001690408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001690401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY