摘要:

AbstractThe ultrastructure and the three‐dimensional cytoarchitecture of the developing murine extensor digitorum longus muscle has been studied in spaced, serial, transverse and longitudinal ultrathin sections of the muscles of 12‐, 14‐, 16‐, and 18‐dayin utero, newborn, and 5‐day‐old 129 ReJ mice. Despite the fact thatin vivomyogenesis is asynchronous (i.e., during most of the fetal period, multiple stages of myogenesis can be seen in a single developing muscle mass), a distinct temporal pattern of development can be seen across the entire width and length of the developing muscle. At 12 daysin utero, the developing extensor digitorum longus muscle consists of primary myotubes surrounded by a pleomorphic population of mononucleated cells devoid of myofilaments. At this stage, blood vessels and nerves are found peripheral to but not within the developing muscle mass. A delay of ≥ 2 days occurs between the time of formation of the primary and secondary myotubes. Clusters (consisting of one primary myotube and secondary myotubes), axon bundles, capillaries, and primitive motor endplates are found in the muscle by 16 daysin utero. Evidence is presented consistent with the hypothesis that cluster formation and cluster dispersal occur simultaneously in the developing muscle, beginning as early as 16‐daysin utero. By 18 daysin utero, many of the primary myotubes of the cluster and the independent myotubes (i.e., single myotubes enclosed in their own basal lamina) have begun to acquire the polygonal shape, fascicular arrangement, and ultrastructure characteristic of more mature myofibers. At birth, clusters are infrequently encountered, and intramuscular axons have begun to undergo myelination. At this time, the only undifferentiated, mononucleated cells present in the muscle are myosatellite cells. The first week postnatal was characterized by further maturation

ISSN:0002-9106    

DOI:10.1002/aja.1001710202

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

年代:1984

数据来源: WILEY

摘要:

AbstractA quantitative analysis of the pattern of development and growth of the fetal extensor digitorum longus muscle of the 129 ReJ mouse was carried out in spaced, serial ultrathin sections with computer‐assisted morphometry. Muscle from 12‐, 14‐, 16‐, and 18‐dayin uteromice and from newborn and 5‐day postnatal mice was analyzed to determine age‐related changes in such factors as the maximal girth and length of the muscle, the number of myotubes, the “cluster” frequency, and the diameters and lengths of the myotubes and muscle units. A distinct temporal pattern of development was established. It was quantitatively determined that a delay ≥ 2 days occurs between the formation of primary myotubes (present at 12 daysin utero, and secondary myotubes (present at 16 daysin utero)). By 16 daysin utero, groups of myotubes, consisting of one primary myotube and a variable number of secondary myotubes, form “clusters” surrounded by a common basal lamina. Morphometric analyses of diameter distributions establish that most, if not all, secondary‐generation myotubes are formed in association with larger, more mature myotubes. Quantitative data support the hypothesis (Ontell and Kozeka, 1984) that cluster formation and cluster dispersion occur simultaneously, beginning sometime between 16 and 18 daysin utero. By 18 daysin utero, the adult number of myofibers is present in the developing muscle mass. Analyses of lengths and diameters of the same fibers establish that the pattern of growth of the last‐formed myotubes of the developing muscle mass is different from that of myotubes fo

ISSN:0002-9106    

DOI:10.1002/aja.1001710203

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe distribution and structure of the putative sites where enamel matrix is secreted from the ameloblast were studied by correlating the external topography with the distribution of organelles in Tomes' process cut in various planes of section. Both the interrod and rod secretion sites are associated with deep membrane infoldings. It was found that the interrod secretion site completely surrounds each ameloblast, and the marked interdigitation of adjacent cells results in a cooperative growth front for interrod enamel. In contrast, the rod secretion site is present on only one surface of the interdigitating portion of Tomes' process. Numerous granules were observed adjacent to the membrane infoldings associated with both sites, and granules were seen fused to membrane infoldings suggesting that the matrix of enamel is a merocrine secretion product.

ISSN:0002-9106    

DOI:10.1002/aja.1001710204

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

年代:1984

数据来源: WILEY

摘要:

AbstractAtrial cardiac muscle cells enzymatically isolated from adult rats were maintained in culture for 0–17 days and examined by transmission electron microscopy (TEM). Cells were stained with conventional TEM stains as well as with osmium ferrocyanide and tannic acid. Our results show that cultured adult atrial cells are capable ofin vitroultrastructural reorganization and possess differentiated ultrastructural characteristics including specific atrial granules, sarcomerically arranged myofilaments, appropriately organized sarcoplasmic reticulum (both junctional and nonjunctional), and intercalated disc components. In addition, the cultured atrial cells also posses rare, but ultrastructurally typical, elements of the transverse tubular system. These can be identified on the basis of size, location, association with internal junctional sarcoplasmic reticulum, and accumulation of extracellular tracer. Atrial muscle cells are capable of reestablishing a myotypic ultrastructure, although they have a considerably less complex and organizedin vitroultrastructure than similarly cultured adult ventricular myocytes. This lessenedin vitroultrastructural specialization is in accord with thein vivocomparative ultrastructure of atrial vs. ventricular myocyte

ISSN:0002-9106    

DOI:10.1002/aja.1001710205

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe porosity of the epithelial basal lamina of normal rat intestine was studied by SEM. Epithelial removal was accomplished by prolonged fixation of tissue samples in OsO4or immersion in aqueous H3BO3, followed by dehydration in acetone and microdissection by ultrasonic vibration. The underlying basal lamina of intestinal epithelium reveals numerous pores of variable size. These pores are more numerous in small than in large intestine and penetrate the entire thickness of the basal lamina. Within the basal lamina overlying lymph nodules, they are numerically increased. Their occurrence is evident in fixed and unfixed, sonicated and unsonicated tissue samples. Microprojections of epithelial cytoplasm are often observed within these pores. The results of this study suggest that migrating cells or epithelial‐cell processes induce pore formation in epithelial basal laminae and that these pores may be eventually repaire

ISSN:0002-9106    

DOI:10.1002/aja.1001710206

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe thick ascending limb of Henle (TAL) in the rat until recently has been considered a morphologically homogeneous structure despite physiologic and biochemical evidence to the contrary. The present study was designed to examine the ultrastructural characteristics of the TAL in the inner cortex and the outer and inner stripes of the outer medulla using qualitative and quantitative transmission electron microscopy. Kidneys of male Sprague‐Dawley rats were preserved byin vivoperfusion with glutaraldehyde for light and electron microscopy. The peritubular diameter and cell height were determined by direct measurements on tubule cross sections. Morphometric analyses were performed on montages of tubule cross sections. The peritubular diameter of the TAl was similar in the three regions under investigation, but the TAL cells were taller in the inner stripe than in the inner cortex and outer stripe. Morphometry revealed significant differences between the three regions with respect to the mean tubular cross‐sectional area (AT), the surface density (SV), and the surface area per mm of tubule (ST) of apical and basolateral plasma membranes, and the volume density (VV) of mitochondria. The major morphologic division appeared to be between the inner stripe segment and the remainder of the TAL. These findings document the presence of significant morphologic heterogeneity of the rat

ISSN:0002-9106    

DOI:10.1002/aja.1001710207

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

年代:1984

数据来源: WILEY

摘要:

AbstractAlthough the urinary bladder ofNecturus maculosusprovides an important model system for studying the mechanisms of active Na absorption, little critical attention has been paid to the fine structure of its epithelium. Moreover, two distinct groups of urinary bladders, low and high Na transporters, have been described based on short‐circuit current or transepithelial potential difference. In the present study, over an 11‐month period, stable electrical parameters (short‐circuit current, transepithelial potential difference, and resistance) were recorded from 63 chamber‐mounted bladders. Analysis of these parameters revealed a highly significant difference between two groups (low transporters and high transporters) occurring at different times of the year. Consistent with these data, in urine collected from the bladders, the Na concentration in low transporters was significantly higher than that in high transporters. A subpopulation of these bladders was subsequently fixed and examined at the light and/or electron microscopic level. Low‐transporting bladders were characterized unequivocally by a thin, stratified squamous epithelium only 6–15 μm thick. High‐transporting bladders were composed predominantly of columnar‐shaped granular cells up to 70 μm in height, with ciliated, mitochondria‐rich, and basal cells present in small numbers. There is thus a correlation between transport activity, as measured by electrophysiological techniques and urine sodium analysis, and the structure of the tissue. Moreover, these parameters exhibit significant seasonal variation, the underlying mechanisms of w

ISSN:0002-9106    

DOI:10.1002/aja.1001710208

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.1001710201

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

年代:1984

数据来源: WILEY