摘要:

AbstractThe ultrastructure of nucleoli was examined in developing rat spermatocytes and spermatids, with the help of serial sections. In addition, the radioautographic reaction of nucleoli was examined in rats sacrificed 1 hr after intratesticular injection of3H(5′)‐uridine and taken as an index of the rate of synthesis of ribosomal RNA (rRNA).Primary spermatocytes from preleptotene to zygotene have small nucleoli typically composed of fibrillar centers, a fibrillar component, and a granular component, within which are narrow interstitial spaces. During early and mid‐pachytene, nucleoli enlarge to about nine times their initial size, with the fibrillar and granular components forming an extensive network of cords—a nucleolonema—within which are wide interstitial spaces. Meanwhile, there appear structures identical to the granular component but distinct from nucleoli; they are referred to asextranucleolar granular elements.Finally, from late pachytene to the first maturation division, nucleoli undergo condensation, as shown by contraction of fibrillar centers into small clumps, while fibrillar and granular components condense and segregate from each other, with a gradual decrease in interstitial spaces. In secondary spermatocytes, nucleoli are compact and rather small, while in young spermatids they are also compact and even smaller. Nucleoli disappear in elongating spermatids.In3H‐uridine radioautographs, nucleolar label is weak in young primary spermatocytes, increases progressively during early pachytene, is strong by the end of mid pachytene, but gradually decreases during late pachytene up to the first maturation division. In secondary spermatocytes and spermatids, there is no significant nucleolar label.In conclusion, rRNA synthesis by nucleoli is low in young spermatocytes. During pachytene, while nucleoli enlarge and form a lacy nucleolonema, rRNA synthesis increases gradually to a high level by the end of mid pachytene. However, during the condensation and segregation of nucleolar components occurring from late pachytene onward, the synthesis gradually decreases and disappears. The small, compact spermatids arising from the second maturation division do not synt

ISSN:0002-9106    

DOI:10.1002/aja.1001890102

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn addition to chromosomes and nucleoli, three structures, i.e., round body, coiled body, and nubecula, are encountered in the nucleus during the meiotic prophase in male rats. These structures have been examined by electron microscopy in random and serial sections.Theround bodyis a finely fibrillar, proteinaceous structure closely associated with the granular component of a nucleolus in rat spermatocytes and young spermatids. A similar structure has been observed in man, the monkeyMacaca mulatta, the gastropodAchatina fulica, and the insectLocusta migratoria.Together with evidence from the literature, these results support the view that the round body is of general occurrence in the male meiocytes of eukaryotes and may, therefore, play a role in meiosis.Thecoiled bodyis a group of electron‐dense elements called “coils”, which average 35 nm in width, except after mid‐pachytene when their size almost doubles. The coils are composed of 2‐nm‐wide filaments and 8 to 10‐nm‐wide granules, both of which are ribonucleoprotein. The coiled bodies are interpreted to be groups of “spliceosomes”, that is, structures containing heterogeneous RNA and small nuclear RNA. A remarkable feature of the coiled body is its temporary disappearance at early pachytene and its reappearance at late pachytene, possibly due to drastic changes in the turnover rate of its component RNAs.Thenubeculais a newly identified nuclear inclusion, composed of weakly staining threads loosely organized into a 560nm‐wide spheroid. It has been observed only in e

ISSN:0002-9106    

DOI:10.1002/aja.1001890103

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

年代:1990

数据来源: WILEY

摘要:

AbstractBronchus‐associated lymphoid tissue (BALT) in normal turkeys of ages 1 day and 1, 2, 3, 4, 8, and 18 weeks was examined by light microscopy and by scanning and transmission electron microscopy. Turkey BALT resembled other mucosa‐associated lymphoid tissues; it was made up of a population of lymphocytes covered by a specialized epithelium different from typical pseudostratified ciliated columnar bronchial epithelium. There were distinct age‐related differences in BALT structure. Bronchus‐associated lymphoid nodules were larger and more numerous in older turkeys. In 1‐day‐ to 2‐week‐old turkeys, the primary cell type of BALT epithelium was nonciliated cuboidal; in 2‐week old turkeys it was squamous; and in turkeys older than 4‐weeks of age, the epithelium was primarily ciliated columnar. In 1‐ to 4‐week old turkeys, large numbers of intraepithelial lymphocytes disrupted the normal organization of the epithelium. In older turkeys, epithelial and lymphoid cells were in discrete compartments separated by connective tissue. Lymphocytes in 1‐day‐old turkeys were found in loose aggregates around venules and within the epithelium. In 1‐week old turkeys, lymphocytes were organized into compartments of morphologically similar cells. By 3‐weeks of age, lymphocytes were present in distinct germinal centers. Epithelial cells of BALT did not have large numbers of apical vesicles and thus were not structurally specialized for antigen uptake by endocytosis. However, the epithelial barrier appeared to be disrupted over lymphoid nodules, suggesting that antigen would be readily available to lymphocytes and phagocytes in BALT. Age‐related differences in turkey BALT structure may have functional consequences with respect t

ISSN:0002-9106    

DOI:10.1002/aja.1001890104

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

年代:1990

数据来源: WILEY

摘要:

AbstractMale Fischer rats were fed a low‐iodine diet containing thiouracil for 21 days to produce hyperplastic thyroid glands, and then fed a high‐iodine diet for various time intervals, from 5 hr to 180 days, in order to study the morphological changes that occur during involution. Thyroids were fixed by perfusion fixation and embeded in Epon. Sections were examined by light microscopy. Initially at 0 days of involution (at the time of the change to the high‐iodine diet), follicular lumens were very narrow and capillary lumens were verywide. The capsule was thick and infiltrated with mononuclear leukocytes. No obvious changes occurred for 1 day after the change in diet, but shortly thereafter capillary lumens began to narrow. By 4 days, most capillary lumens began to narrow. By 4 days, most capillary lumens were close to normal size; capillaries formed a more or less normal bed except that many were embedded in a relatively thick or wide interfollicular matrix. This matrix was largely gone by 21 days. Between 1 and 21 days, follicular lumens dilated progressively as colloid accumulated. The density of staining of the accumulated colloid varied from follicle to follicle, and this variation was also observed in older controls. Inflammatory cells gradually disappeared from the capsule and most were gone by 15 days. Starting at approximately 15 days and continuing to 180 days, one or more disintegrating cells were found in some lumen profiles. Colloid goiters were not observed in these rats even after several months of involution. Some lumens were rather large, however, and small fractions of the follicles, both small and large, were bounded by flat cells and resembled “cold” follicles morpho

ISSN:0002-9106    

DOI:10.1002/aja.1001890105

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe ultrastructure of the thyroid epithelial cell was examined at various time intervals after induction of involution of the hyperlastic thyroid gland. Thyroids were made hyperplastic by the feeding of thiouracil in a Remington low‐iodine diet to male Fischer rats for 3 weeks. Involution was induced by replacing the thiouracil‐containing diet with Purina Laboratory Chow, a high‐iodine diet. During involution, organelles that play a role in the synthesis and secretion of thyroglobulin, such as the rough endoplasmic reticulum, Golgi apparatus, and apical vesicales, were well preserved and prominent features of the epithelial cell. The apical plasma membrane of many cells was highly irregular for approximately 2 weeks with signs suggesting rapid discharge of apical‐vesical contents into the lumen of the follicle. Pseudopods and colloid droplets were present but were not very prominent features of the cell. No signs of extensive autophagy or obvious increased incidence of lysosomes were present, although there was an elevation in the incidence of small dense bodies starting about day 8, and prominent by 15 days. Some of these may be phagosomes formed from luminal debris. The observations indicate that in volution of the hyperplastic thyroid in which there is maintenance of the protein synthetic apparatus and little sign of autophagy or death of the epithelial cells is remarkably different from phenomena occurring during involution of prostate or mammary

ISSN:0002-9106    

DOI:10.1002/aja.1001890106

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn male Fischer rats, a class of follicles with flat epithelium is present as a minor component of thyroid glands in which most of the follicles have cuboidal epithelium. These follicles occur in thyroids that have been made hyperplastic by feeding the rats thiouracil for 21 days and then allowing involution for 21 days or more. They also occur in older control rats. The follicles resemble in morphology, at the light‐microscope level, the so‐called “cold” follicles that occur in aged mice. We have examined the ultrastrucutre of the flat cells in these follicles and compared it with that of the flat cells occurring in the thyroid follicles of hypophysectomized rats. The cells in involution have abundant rough endoplasmic reticulum (RER) and few lysosomes and, in these respects, differ markedly from cells in hypophysectomized rats. The follicles with flat cells are surrounded by a normal incidence of blood capillaries, so that the cells do not appear to be deprived of access to an adequate supply of materials necessary to satisfy their metabolic requirements. Their abundant RER suggests that they have thyroid‐stimulating hormone (TSH) receptors, so that the flat cell may be the result of some process occurring at a step distal to receptor coupling with TSH. Their occurrence in young rats after the induction of hyperplasia may be a consequence of cell multiplication producing a clone of neighboring abnormal cells that have an abnormally small ce

ISSN:0002-9106    

DOI:10.1002/aja.1001890107

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

年代:1990

数据来源: WILEY

摘要:

AbstractMale and female Fischer 344 rats of three different ages (12, 18, and 25 months) have been examined for the presence of photoreceptor (PR) cell loss and for occurrence of scleral cartilage and bone formation. In addition, male and female rats, aged 11 months at the beginning of the experiments, were exposed to chronic stress for either 0.5, 2, 4, or 6 months. Photoreceptor cell death gradually increases during the aging process and is exacerbated by exposure to chronic stress. It is more severe in the peripheral than the central retina and exposure to stress increases this pattern of cell loss. The superior retina is more severely affected than the inferior hemisphere in aging and during stress. The incidence of scleral cartilage or bone formation increases with age in male and female rats, but with stress exposure an increase is seen in males only. Bone formations occur more frequently in male than in female animals and are almost always (97%) located in the superior hemisphere of the eye. Although there appears to be a direct relationship between photoreceptor cell death and the occurrence of scleral ossifications in group data, in individual eyes the bone formations are not always associated with severity of PR cell loss. The relationship of PR cell death and incidence of scleral ossification to gender and to exposure to stress supports a hypothesis for an endocrine basis of ocular aging.

ISSN:0002-9106    

DOI:10.1002/aja.1001890108

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn this study measurements were obtained from 359 vertebrae and 215 intervertebral discs in an attempt to classify discs by their size. At the cervical and thoracic levels, this attempt was unproductive because of extensive variations. In the lumbar spine, discs were allocated to six size‐matched groups. The breadth of marginal rims were also measured with a view to provide surgeons operating on the spine with precise data on disc morphology to facilitate dise replacemen

ISSN:0002-9106    

DOI:10.1002/aja.1001890109

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

年代:1990

数据来源: WILEY

摘要:

AbstractUltrastructural alterations in duced by colchicine were investigated to determine the secretory activities of odontogenic cells during formation of tooth enameloid matrix in skates. Treated skate inner dental epithelial (IDE) cells did not display dilated cisternae of the granular endoplasmic reticulum (GER) nor accumulate Golgi‐associated secretory granules at any dose level or time interval examined. This response was markedly different from that observed in teleost IDE cells synthesizing the enameloid collagen matrix. Treated skate IDE cells did show increased accumulations of glycogencontaining vesicles and intercellular glycogen associated with amorphous material, compared to controls. Additionally, the aberrant occurrence of large intracellular glycogen pools and amorphous material suggested that carbohydrate processing was a major function of skate IDE cells.Treated odontoblasts associated with enameloid matrix formation sometimes showed dilated GER cisternae, but procollagen secretory granules were not obsered. Instead, electron dense material was present within the Golgi cisternae, tubular granules, and large granules. Some elecron‐dense material appeared to be shunted to a resorptive pathway via multivesicular bodies in treated odontoblasts. The continuity of tubular granules with the enameloid matrix suggested that they contained precursors of the enameloid matrix, and possibly the periodic, 17.5‐nm crossstriated, “giant” fibers.Treated odontoblasts associated with predentin collagen matrix deposition showed dilated GER cisternae and accumulations of procollagen secretory granules, features consistent with the function of active collagen synthesis and secretion.The findings indicate that (1) skate IDE cells do not synthesize enameloid collagen as found in bony fish tooth development; (2) skate IDE cells do process glycogen for secretion into the enameloid matrix; (3) collagen, although present, is not a major constituent of skate enameloid matrix; (4) enameloid “giant” fibers are unique to elasmobranchs; and (5) odontoblasts synthesize and secrete proteins other than collagen into the ena

ISSN:0002-9106    

DOI:10.1002/aja.1001890110

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

年代:1990

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001890101

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

年代:1990

数据来源: WILEY