摘要:

AbstractAmelogenesis in the tooth germs of the frogRana pipienswas examined by electron microscopy at different stages of tooth development. Cellular changes in secretory ameloblasts during this process showed many basic similarities to those in mammalian amelogenesis.Amelogenesis can be divided into three stages based on histological criteria such as thickness of enamel and the relative position of the tooth germ within the continuous succession of teeth. These stages are early, transitional and late. The fine structure of the enamel‐secreting cells reflects the functional role of these ameloblasts as primarily secretory in the early stage, possibly transporting in the late stage and reorganizing between the two functions in the transitional stage. In early amelogenesis the cell exhibits well‐developed granular endoplasmic reticulum, Golgi complex, microtubules, dense granules, smooth and coated vesicles, lysosome‐like bodies in supranuclear and distal portions of the cell and mitochondria initially concentrated in the basal part of the cell. Numerous autophagic vacuoles are observed concomitant with the loss of some cell organelles at the transitional stage. During late amelogenesis the ameloblasts exhibit numerous vesicles, granules, convoluted cell membranes, junctional complexes and widely distributed mitochondria. Toward the end of amelogenesis, cells become oriented parallel to the enamel surface and the number of organelles is reduced.Amelogenesis in the frog is an extracellular process and mineralization seems to occur simultaneously with matrix form

ISSN:0002-9106    

DOI:10.1002/aja.1001480202

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe objectives were to (a) determine the age in development when GnRH is first detectable in the brain and (b) observe the distribution of GnRH throughout the fetal and early postnatal period. GnRH was localized immunohistochemically in fetal (15, 16, 17 and 19 days of gestation) and early postnatal (1‐ and 7‐day‐old) mice with the peroxidase‐antiperoxidase (PAP) method of Sternberger.In the organum vasculosum of the lamina terminalis (OVLT) and in the median eminence of the fetus, GnRH was first detected at 17 days of gestation. In the OVLT, GnRH was found ventral to the preoptic recess of the third ventricle near the ventral surface of the brain. In addition, GnRH was located adjacent to the superficial portal capillaries near the surface of the median eminence. At 19 days of gestation, the distribution of GnRH was similar to that observed at 17 days and there was a marked increase in amount.In the newborn mouse, GnRH was undetectable in the OVLT and its content in the median eminence was decreased as compared to that observed in the fetus. By the seventh postnatal day, a considerable accumulation of GnRH had occurred in the OVLT and median eminence. In the OVLT, it was associated with capillaries ventral to the preoptic recess, and its distribution in the median eminence was similar to that in the adult mouse.In both the OVLT and median eminence of the fetal and early postnatal mouse GnRH appeared to be stored in axons and axon endings, but was not detectable in nerve cell bodies or ependymal cells. These observations suggest that the potential for neuroendocrine control of gonadotropin secretion exists in the fetal mouse as early as 17 days of ge

ISSN:0002-9106    

DOI:10.1002/aja.1001480203

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe objectives were to (a) describe the cytology and distribution of mammotropes in the human pituitary gland, (b) determine whether the mammotrope is a distinctive secretory cell type and (c) ascertain when it first appears in the fetal hypophysis. Identification of mammotropes was based primarily on the Sternberger peroxidase‐antiperoxidase immunocytochemical method used with an antiserum to human prolactin. Hypophyses from 25 male and 6 female adults, and 21 fetuses ranging in gestational age from 6 to 23 weeks were studied.In the adult two morphological forms of mammotropes were observed. Mammotrope I possessed a small perikaryon that commonly was located centrally in parenchymal cell cords. From the perikaryon long cytoplasmic processes extended toward neighboring capillaries. Mammotrope I reached its highest incidence in the posterolateral zones of the pars distalis. Mammotrope II possessed a larger perikaryon with short processes; cells of this form were fewer and occurred chiefly in the anteromedian zone. Mammotropes with intermediate morphological features that prevented classification into categories I or II were common in some hypophyses.Both forms of mammotropes were present prepuberally (one 6‐week and one 9‐year‐old male) and in adult males and females. Mammotropes were only slightly more prominent in females than males. Regression of mammotropes was evident in old age. Mammotropes were distinctly different from somatotropes, corticotropes, gonadotropes and thyrotropes. In the fetal hypophysis mammotropes appeared first at 14 weeks of gestational age and remained few through 16.5 weeks. Their number increased greatly at 2

ISSN:0002-9106    

DOI:10.1002/aja.1001480204

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe formation and turnover of the glycoproteins of the plasma membrane have been investigated by quantitative radioautography in the kidney tubules of young rats and adult mice killed at various time intervals after an intravenous injection of3H‐fucose.In young (40 g) rats killed five to ten minutes after the injection, radioautographs ofdistal tubule cellsshow that the Golgi apparatus contained about 85% of the cell label. By 30 hours, only 8% of the label remained in this organelle, whereas 67% was in the plasma membrane, indicating that most of the label had migrated from Golgi apparatus to this membrane. Similarly, inproximal tubule cells, about 82% of the label was initially in the Golgi apparatus, but less than 2% remained at 30 hours, at which time 78% was in the plasma membrane. In the latter cells, the apical tubules and vacuoles became heavily labeled before the apical microvilli did and, therefore, may be involved in the transit of label from the Golgi apparatus to the microvillous membrane.The results are interpreted to mean that, in kidney tubule cells, the Golgi apparatus is the site of a continuous incorporation of fucose into glycoproteins and that these migrate to the plasma membrane. In fully formed cells, such a conclusion would imply a continuous turnover of plasma membrane glycoproteins. However, in the rapidly growing kidney of young rats many new cells are added daily, the growth of which might involve net addition as well as turnover of glycoproteins. Accordingly, the experiment has been repeated in adult mice, in which the cells are assumed to be fully formed. Furthermore, since turnover implies eventual decrease of incorporated label, some of the animals have been killed at longer intervals, up to 27 days after injection. In these adult mice, as in young rats, prompt Golgi uptake and subsequent migration of label to the plasma membrane were observed in distal and proximal tubule cells. With time the label content of the plasma membrane decreased gradually, and by 27 days had virtually disappeared. From grain counts, it is concluded that the mean half‐life of glycoproteins in the apical membrane of distal tubule cells is about two days, whereas in both the apical and basal membranes of proximal tubule cells, it is slightly over three d

ISSN:0002-9106    

DOI:10.1002/aja.1001480205

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

年代:1977

数据来源: WILEY

摘要:

AbstractUltrastructural modifications of type II pneumocytes (PNM‐II) in mice were analysed 125 and 155 minutes after puromycin treatment (12 mg/100 gm at 0, 30, 60 and 90 minutes). A quantitative evaluation of the cell compartments was carried out and the inhibition of protein synthesis in PNM‐II was monitored by light microscopic radioautography, following3H‐leucine injection.In electron micrographs, following a 125‐minute puromycin treatment, the number and size of lamellar bodies, the precursors of lung surfactant material, appeared markedly reduced. The multivesicular bodies (MVB), which are normally very frequent in PNM‐II, had almost completely disappeared, as had composite bodies. Golgi saccules were dilated, while the area occupied by Golgi vesicles was enlarged. Observations following the 155‐minute puromycin treatment showed a strong enhancement of these modifications. Smooth and coated vesicles of the Golgi area, as well as peroxisomes, did not appear modified by puromycin. Elongated zones of autophagy were more prevalent after 125‐minute treatment than after the 155‐minute one.Small bodies were frequently observed in the cytoplasm, near the Golgi zone. They were bounded by a smooth membrane and contained tiny vesicles and/or electron‐dense lamellae similar to those present within the lamellar bodies. Parallel membranes formed folds, some of them in continuity with lamellar bodies, thus encircling portions of cytoplasm. These structures, which were few in number in controls, were very frequently observed in treated cells, mainly after the 125‐minute treatment.These extensive alterations of PNM‐II morphology appeared to be related to a disturbed production of

ISSN:0002-9106    

DOI:10.1002/aja.1001480206

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

年代:1977

数据来源: WILEY

摘要:

AbstractReplicas of freeze‐fractured rat carotid body chief (Type I) cells reveal the normal complement of cytoplasmic organelles.En facefractures of the chief cell plasmalemma exhibit occasional sites of fusion of the amine‐containing vesicles which characterize the carotid body. The endothelial cells lining the capillary network of the carotid body display numerous pinocytotic vesicles often oriented in linear arrays, and occasional fenestrae. The endothelial cells are joined together by tight junctions which appear as grooves (B face) forming a continuous network over the membr

ISSN:0002-9106    

DOI:10.1002/aja.1001480207

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

年代:1977

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001480201

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

年代:1977

数据来源: WILEY