Showing papers on "Apical cytoplasm published in 1979"

The terminal web. A reevaluation of its structure and function.

Abstract: The apical cytoplasm of epithelial cells of the small and large intestines has been examined by freeze-etch techniques as well as conventional and high voltage electron microscopy of sectioned material to gain a better understanding of the fine structural organization of the terminal web region. In the small intestine the terminal web exhibits a distinct stratification caused by the association of different sets of filaments with the three members of the junctional complex. Individual filaments of this network are closely associated with the sealing elements of the tight junctions, the surface of the core microfilament bundles, and the intermicrovillar plasma membrane. This region of the terminal web is the apical zone. The adherens zone appears as a band of interwoven filaments of two different diameters extending across the cytoplasm at the level of the intermediate junction. Within this region of the terminal web, individual 60-70 A actin-like filaments separate from the bundles of core microfilaments to interact with one another and with filaments of similar diameter from the zonula adherens. 100 A tonofilaments also contribute to the adherens zone, presumably stabilizing the orientation of the actin-like filaments. The basal zone which underlies the adherens zone consists of closely interwoven bundles of tonofilaments that are anchored to and interconnect the spot desmosomes. Within the large intestine the cytoplasmic microfilaments form a looser and less clearly stratified network which nevertheless retains the same basic organization found in the small intestine. Transmembrane linkers appear to originate within the cytoplasmic plaques of the spot desmosomes, pass through the plasma membranes, and meet in a staggered configuration in the intercellular space; these linkers may thus mediate the actual mechanical coupling between the cytoskeletal networks of tonofilament bundles of adjacent cells. This integrated system of cytoplasmic filaments and intercellular junctions endows the apical cytoplasm with both the flexibility and the stability necessary for the normal functioning of the epithelium.

Failure of Exogenous Androgen to Prevent Regression of the Initial Segments of the Rat Epididymis after Efferent Duct Ligation or Orchidectomy

Abstract: This investigation was undertaken to explore further the dependence of the initial segments of the epididymis upon substances in the testicular fluid. The experimental groups consisted of rats castrated, rats with ligated ductuli efferentes and sham operated controls. The epdidymides were examined by light and electron microscopy 3 and 6 weeks postoperatively. The initial segments of the duct in both ligated and castrated animals exhibited 1) striking decrease in duct diameter and epithelial height, 2) a marked decrease in endoplasmic reticulum in the apical cytoplasm, 3) evidence of diminished activity of the Golgi complex, but 4) persistence of fluid uptake by pinocytosis. Daily administration of 500 pg testosterone proprionate beginning on the first postoperative day maintained the accessory gland weights at normal or supranormal values, but was ineffective in preventing the cytological regression of the initial segments of the caput epididymidis. In an effort to achieve levels of androgen in the blood comparable to those normally found in the rete testis fluid, castrated and ligated rats were implanted s.c. with 30 cm of Silastic tubing containing testosterone, each estimated to release 4 mg/day (Berndtson et al., 1974). Plasma testosterone levels when the rats were killed were 8-10 times normal. Despite these high levels of circulating androgen, cytological dedifferentiation of the initial segments was not prevented. More distal segments of the duct were essentially normal in dimensions and appearance. It is concluded that the initial segments of the rat epididymis require high intraluminal concentrations of androgen bound to androgen binding protein. The possibility that they are dependent upon some other, as yet unidentified, constituent of testicular fluid is not ruled out.

Development of villus absorptive cells in the human fetal small intestine: A morphological and morphometric study

Abstract: We describe the sequential ultrastructural changes in villus absorptive cells of human fetal small intestine between 9 and 22 weeks of gestation. In concert with villus formation at 9 to 10 weeks, a complex membranous system designated the apical tubular system appeared in the apical cytonous system designated the apical tubular system appeared in the apical cytoplasm of absorptive cells. The apical tubular system consisted of deep invaginations of plasma membrane and membrane-bounded vesicles and tubules. Some elements of this system were characterized by linear arrays of particles on the inner (luminal) membrane leaflet. After villus formation, many lysosomal elements designated "meconium corpuscles" also appeared in the apical cytoplasm. Modified morphometric studies suggested that both the apical tubular system and the lysosomal elements were more extensively developed in the distal than in the proximal intestine, were most abundant at 15 to 17 weeks, and decreased by 18 to 22 weeks. Morhpometry also showed an inverse relationship between the relative surface density of the apical tubular system and microvillus membrane, suggesting the possible derivation of elements of the former from the apical plasma membrane. Exposure of intestine to ferritin for 8 to 40 minutes in vitro revealed ferritin in elements of the apical tubular system of 12- to 20-week fetuses. There was no evidence of transport of ferritin across absorptive cells. Distinctive membranous bodies composed of convoluted membrane-bound cisternae separated by narrow channels of cytoplasmic matrix were seen in the Golgi region and apical cytoplasm of fetal absorptive cells between 14 and 22 weeks. In a single 22-week fetus, there was marked proliferation of smooth endoplasmic reticulum, a decrease in cytoplasmic glycogen and loss of most lysosomal and apical tubular elements in the proximal but not the distal intestine. Thus, by the end of the second trimester, the structure of absorptive cells in proximal intestine was remarkably similar to absorptive cells in adult intestine.

Structure and function of the intestinal epithelial cells in the perch (perca fluviatilis l.)

Abstract: An ultrastructural study of the intestinal absorptive epithelium in perch (Perca fluviatilis) has shown that the perch intestine can be divided into three segments: the proximal segment, the middle segment and the distal segment. The enterocytes of the proximal segment are found to be concerned with lipid absorption. The adsorbed fat gives rise to the presence of two forms of inclusions: lipid particles and lipid droplets. Enterocytes of the middle segment exhibit the typical ultrastructural features of pinocytosis; these consist of extensive invaginations of the luminal surface membrane and acculation of vacuoles in the apical cytoplasm. Exogenous proteins are ingested by absorptive cells from the intestinal lumen by a process similar to that described in neonatal mammals. In the distal segment the absorptive cells have few, short microvilli. Besides the absorptive epithelial cells, goblet cells, endocrine cells, pear-shaped cells, and plasma cells are occasionally found.

Morphology of the epithelium of the extratesticular rete testis, ductuli efferentes and ductus epididymidis of the adult male rabbit.

Abstract: The fine structure of the epithelium lining the extratesticular rete testis, ductuli efferentes and ductus epididymidis of the rabbit has been investigated. In the ductuli efferentes the epithelium is composed of two cell types, principal cells and ciliated cells. The latter type is distinguished from principal cells by the presence of cilia projecting into the lumen and the position of the nucleus in the apical half of the cell. Principal cells in this segment are characterized by micropinocytotic vesicles on the surface plasma membrane and a variety of small dense bodies scattered throughout the cytoplasm. In the ductus epididymidis basal cells replace ciliated cells as the second cell type, but differences between various segments of the epididymis are related to the fine structure of the principal cells. In the proximal caput epididymidis (Nicander's region 1) the principal cells are tall with long microvilli. They typically contain a small Golgi apparatus and a cluster of dense bodies adjacent to the nucleus. In the distal caput epididymidis (Nicander's regions 2-5) the apical cytoplasm of principal cells is filled with numerous micropinocytotic vesicles and large multivesicular bodies; these features are interpreted as signs of absorptive activity. The multivesicular bodies are absent from the cytoplasm of principal cells in the corpus epididymidis (Nicander's region 6) and, instead, numerous elements of smooth endoplasmic reticulum, a large Golgi apparatus, lipid droplets and dense bodies characterize principal cells in this segment. Towards the proximal cauda epididymidis (Nicander's region 7), the number of dense bodies (lysosomes) in the cytoplasm increases considerably. In the globose cauda (Nicander's region 8), the principal cells are reduced in height, and in addition to the features described in region 7, are characterized by a concentric array of rough endoplasmic reticulum in the basal cytoplasm. These observations are discussed in relation to the role of the epididymis in promoting the maturation and survival of spermatozoa.

Ultrastructure of alimentary epithelia of lobsters,Homarus americanus andH. gammarus, and crab,Cancer magister

Abstract: The ultrastructure of the alimentary tract lining, excluding the hepatopancreas, of lobsters,Homarus americanus andH. gammarus, and Dungeness crab,Cancer magister, was investigated with transmission electron microscopy. The foregut lining consists of a cuboidal epithelium with extensive interdigitations of the lateral cell membranes and adhering junctions. The ultrastructural organization of the midgut and midgut caeca resembles that of other transporting epithelia. The cells possess a microvillous border, and the basal cytoplasm contains numerous mitochondria and an anastomosing system of smooth endoplasmic reticulum. Hemocytes, presumed neurosecretory axons, and putative endocrine cells occur within the epithelium of the midgut and midgut caeca. Hindgut epithelial cells have numerous mitochondria in the apical cytoplasm, and their basal cell membranes are elaborately infolded. These observations suggest that one of the principal functions of the midgut, midgut caeca, and hindgut epithelia is the transport of ions and water.

Synthesis of secretory and plasma membrane glycoproteins by striated duct cells of rat salivary glands as visualized by radioautography after 3H-fucose injection.

Abstract: The ability of the striated ducts of rat salivary glands to incorporate 3H-fucose into glycoprotein was studied by light and electron microscope radioautography. At 3.5 to 20 minutes after intravenous injection, the majority of the radioautographic grains in the ducts of the parotid gland were localized to the Golgi apparatus. By 40 minutes, the percentage of grains over the Golgi apparatus had decreased; a corresponding increase in grains occurred over small (0.1-0.4 micrometer) apical granules and the highly infolded basal and lateral plasma membranes. By two hours, less than 10% of the label was associated with the Golgi apparatus, while 26% and 28% were attributed to the apical granules and plasma membrane, respectively. By 8 to 12 hours after injection, the number of grains over the apical cytoplasm had decreased, suggesint luminal discharge of the apical granules. In contrast, the basal and lateral plasma membranes remained labeled up to 30 hours after injection as judged by the distribution of grains in light microscope radioautographs. Mitochondria appeared capable of independent incorporation of fucose, accounting for about 20% of the grains from ten minutes to two hours after injection. Comparable results were obtained in the striated ducts of the submandibular and sublingual glands. These results indicate that the striated duct cells readily incorporate 3H-fucose into newly-synthesized glycoproteins. A portion of these are secretory glycoproteins which are packaged and stored in the apical granules, and a portion are membrane glycoproteins which are incorporated into the extensive plasma membrane of these cells.

Fine structure of the oxynticopeptic cell in the gastric glands of an elasmobranch species (Halaelurus chilensis)

Abstract: Gastric mucosa of an elasmobranch species was examined by electron microscope. The gastric glands contain one form of cell whose fine structure is similar to the cell that secretes both hydrochloric acid and pepsinogen of the amphibian gastric glands proper. The oxynticopeptic cells are characterized by: (a) a luminal surface with long projections of cytoplasm having dilatations in their thickness; (b) a tubulo-vesicular system in the apical cytoplasm; (c) a great number of mitochondria, some of which are of great length; (d) a well developed granular endoplasmic reticulum and a conspicuous Golgi apparatus; and (e) a large nucleus with a conspicuous nucleolus. A fourth part of the cells are binucleated. Physiological implications of some of these ultrastructural features are discussed.

Pathology of proliferative haemorrhagic enteropathy in pigs.

Abstract: Examination of the small intestine of pigs with proliferative haemorrhagic enteropathy showed changes consistent with defects in vascular permeability. Early in the disease there were many eosinophils and distension of lacteals and intercellular spaces with proteinaceous material. Later the predominant features were red blood cells and exudate in tissue spaces. This was most severe and extensive at the tips of villi which were covered by a cast of cells and fibrinous exudate. Adenomatous intestinal mucosal cells contained organisms that were free within the apical cytoplasm and were morphologically identical with those seen in the related disease, porcine intestinal adenomatosis. Also these bacteria were seen free in the subepithelial mucosal area, in blood vessels and within membrane-bound vesicles in phagocytic cells in the mucosa and its blood vessels. Mast cells were prominent in some areas as were thrombosed vessels.

Fine Structural Localization of Endogeneous Peroxidase in the Endostyle of Ascidians, Ciona intestinalis

Abstract: The fine structural localization of peroxidase activity in the endostyle of Ciona intestinalis was studied by cytochemistry at electron microscopic level. Only zone 7 cells in this organ are positive for this enzyme activity. The reaction product is recognized in the external surface of the apical plasma membrane, and in the cisternae of the rough endoplasmic reticulum, of the nuclear envelope, and of the Golgi lamellae, and small vesicles of the Golgi region and of the apical cytoplasm. By electron microscopic autoradiography of 125I, the main site of iodination of thyroglobulin-like protein is considered to be the apical plasma membrane region of the zone 7 cells. The possibility of iodination of protein taking place within the endostylar lumen near the zone 7 cell cannot be ruled out. The relationship between the fine-structural localization of peroxidase activity and the site of iodination of protein is discussed.

Ependymal changes in experimental hydrocephalus

Abstract: A morphologic investigation of ependyma over gray matter (caudate nucleus) and over periventricular white matter (tapetum) of the rabbit lateral ventricle was performed four months after the induction of experimental hydrocephalus. Ependymal cells over the caudate nucleus are not modified by hydrocephalus. They remain cuboidal and heavily ciliated. Numerous microvilli cover the cell surface. The extracellular space of the neuropil is not expanded. Ependymal cells over the periventricular white matter are markedly modified. The characteristic response of these ependymal cells is to enlarge and to form lacunae in their apical cytoplasm. Their apical, horizontal cytoplasmic processes elongate as adjacent ependymal cells separate. The ex-tracellular space of the neuropil is expanded. It is proposed that the changes seen in ependymal cells over periventricular white matter are a response to enlargement of the ventricular surface permitted by the orientation of neuronal and glial fibers parallel to the ventricular surface. With expansion of the ventricular surface, overlapping apical processes become elongated and modified, containing a terminal web. With further enlargement, sliding of an overlapping apical process of one cell uncovers the apical process of its neighboring cell. By this mechanism, the ventricular surface area of any ependymal cell whose surface has been partially covered by its neighbor is increased. With further progression, this compensation fails and the neuropil is exposed to the ventricular cavity. Over caudate nucleus, expansion of ventricular surface is hindered by the disposition of fascie adherentes along intercellular clefts oriented perpendicular to the ventricular surface. Lateral sliding of horizontal apical processes does not occur as such processes are not found in ependyma over the caudate nucleus. The differential response of the ventricular surface in these two areas characteristically seen in hydrocephalus is; determined by regional differences in the morphology of their ependymal cells and underlying neuropil.

Surface morphology and functions of pharyngeal structures in the larval lamprey Petromyzon marinus.

Abstract: To gain insight into the multiple functions of a complex biological structure, the morphology of the pharynx of the larva (ammocoete) of the lamprey Petromyzon marinus was investigated with scanning electron microscopy and histochemistry (PAS and Alcian blue). Features studied include the gills, the parabranchial chambers external to the gills, intrapharyngeal ciliary tracts, the ridged pharyngeal roof, the floor, and the intrapharyngeal taste buds. Significant findings are: (1) All (nonciliated) cells lining these structures are covered with microvilli or microridges. The pattern and packing density of these membrane features vary among different pharyngeal structures. The lumenar membranes of pharyngeal lining cells overlie a mucous prosecretion in the apical cytoplasm, suggesting that the microvilli/ridges on these membranes function to anchor mucus. (2) Patterns of microvilli/ridges on the gill respiratory lamellae differ among ammocoetes of different species. (3) Pharyngeal osmo-regulatory cells (“chloride cells”) could not be identified on the basis of the microvillus/ridge pattern. (4) Two types of ciliary tracts are present within the pharynx. One has tall (x= 13 μm) and densely packed cilia, whereas the other has shorter (x= 7 μm) and less densely packed ones. Because mucus covers both types of tracts their function appears to involve the transport of mucus. (5) Food particles were found on the lateral surfaces of the gill filaments and on the surfaces of the parabranchial chambers. It appears that goblet cells in the epithelia of these regions secrete mucus in which the particles are trapped.

Ultrastructure of an exocrine dermal gland in the gills of the grass shrimp, Palaemonetes pugio: Occurrence of transitory ciliary axonemes associated with the sloughing and reformation of the ductule.

Abstract: Exocrine dermal glands, comparable to the class 3 glandular units of insects, are found in the gills of the grass shrimp, Palaemonetes pugio. The dermal glands are composed of three cells: secretory cell, hillock cell and canal cell. Originating as a complex invagination of the apical cytoplasm of the granular secretory cell, a duct ascends through the hillock and canal cells to the cuticular surface. The duct is divisible into four regions: the secretory apparatus in the granular secretory cell, the locular complex, the hillock region within the hillock cell and the canal within the canal cell. A tubular ductule is contained within the latter two regions. As the ductule ascends to the cuticular surface, its constitution gradually changes from one of a fibrous material to one which possesses layers of epicuticle. During the proecdysial period, the ductule is extruded into the ecdysial space and this is followed by the secretion of a new ductule. Temporary ciliary structures, located near the secretory apparatus of the secretory cell, are associated with the extrusion and reformation of the ductule. Characterized only by a basal body and rootlets throughout most of the intermolt cycle, the ciliary organelles give rise to temporary axonemic processes which ascend through the ductule toward the ecdysial space at the onset of proecdysis. Subsequently, the old ductule is sloughed off and a new ductule is reformed around the ciliary axonemes. Following this reformation, the ciliary axonemes degenerate. The function of cytoplasmic processes, derived from the apical cytoplasm of the secretory cell, is also discussed.

Metabolic-morphologic events in the integument of the Pacific hagfish (Eptatretus stoutii)

Abstract: Light- and electron-microscopic autoradiography were used to obtain a coordinated metabolic-morphologic view of some of the events of cellular differentiation that occur across the epidermis of the Pacific hagfish (Eptatretus stoutii) and which enable this animal to secrete copious amounts of mucus. As judged by epidermal incorporation of [3H]-thymidine in vivo, about 98 % of DNA replication is confined to the basal three layers of the total of 6–8 layers of cells. Small mucous cells (SMC), the most numerous of the three major cell types involved in mucigenesis, show in vitro and in vivo radioincorporation profiles of [3H]-L-lysine and [3H]-D-glucosamine which differ markedly from those of [3H]-L-fucose and [3H]-D-galactose. Time-course incorporation profiles (mean silver grains/cell and percentage of cells with at least one cluster of silver grains) of [3H]-L-lysine and [3H]-D-glucosamine not only reflected the metabolic activities of cell renewal and differentiation in basally-located cells but also the high mucigenic activity in cells near the epidermal surface. By contrast, [3H]-L-fucose and [3H]-D-galactose were mainly incorporated by the more mature SMC in juxtanuclear regions near Golgi complexes and newly formed secretory vesicles. The intensity of [3H]-fucose labeling appeared proportional to the intensity of histochemical staining of the apical cytoplasm. The prominent capsule, within SMC in basal and lateral regions, which arises from a tight intermingling of tonofilaments, appears to restrict secretory vesicles to apical regions while the cell progressively differentiates and migrates to the epidermal surface. The other mucigenic cell types, large mucous cells and thread cells, each show distinctive differentiation and radioincorporation patterns.

Milk lipid absorption and chylomicron production in the suckling rat.

Abstract: Structural correlates of milk lipid absorption and chylomicron production were studied in 10-day-old suckled rats. The gastric and duodenal contents and duodenal mucosae were examined with the light and electron microscopes. In the gastric lumen the milk lipid globule cores were smooth, circular and uniformly electron opaque. Many membranes and lamellar structures with a trilaminar and multilamellar appearance were adherent to the peripheries of the cores. In the central duodenal lumen the milk lipid globule cores were also smooth, circular and uniformly electron opaque. Very few milk lipid globules in the duodenal lumen showed adherent membranes or lamellae. Membrane fragments and lamellae were present in the lumen separate from the milk lipid globules. In the duodenal lumen between villi the milk lipid globules had multiple electron lucent indentations of the core. It is believed that the irregular peripheries of the milk lipid globule cores are the result of lipolysis within the duodenal lumen acting at the milk lipid globule surface. This lipolysis of triacylglycerol would produce amphiphilic lipids which may result in the electron lucent spaces at the milk lipid globule periphery. The absorptive epithelial cells along the length of the duodenal villus varied in structure relative to their position at the tip, middle, or base of the villus. Typical mid-villus epithelial cells contained lipid droplets averaging 0.3-micrometer diameter in the smooth and rough endoplasmic reticulum and in Golgi complexes in the apical cytoplasm. Villus tip and villus base cells contained large lipid droplets between 7-16 micrometers. Only a few 0.3-micrometer lipid droplets were present within these cells. These large lipid droplets appeared to be accumulations of triacylglycerol present in the apical cytoplasm associated with lamellar and membranous structures. Numerous chylomicrons were present between epithelial cells located in the middle region of the villus while significantly fewer chylomicrons were seen between epithelial cells at the tip and base of the villus. These observations suggest that the cells at the middle of the duodenal villus of suckling rats were more efficient in the production of chylomicron triacylglycerol derived from incoming milk triacylglycerol than cells at the tip and base of the villus.

Ultrastructure of the accessory glands of the Mediterranean flour moth.

Abstract: Five regions are recognized in the accessory glands of the Mediterranean flour moth, Anagasta kuehniella (Zeller), on the basis of cellular morphology and aggregates of secretory material in the lumen. Some variation is found in each of the posterior four regions, especially the third one. In the most anterior region (region 1) the epithelium is composed of a single type of cell, while in each of the other regions there are two classes of cells. The cells of region 1 and one class in each of the other four regions are fairly typical exocrine cells with extensive rough endoplasmic reticula. Secretion is primarily via Golgi-derived vesicles. Apocrine secretion in the form of sloughing off of the apical cytoplasm probably also occurs in all regions but is most prominent in the posterior two regions. One class of cells is very similar in morphology in each of the posterior four regions though their secretory products form characteristic aggregates in the lumen. The second class of cells (foliate cells) occurring in the posterior four segments is most notably characterized by elongate apical projections that extend out into the lumen. The apical projections contain large quantities of glycogen, some microtubules, and, in some cases, many minute mitochondria. The membrane content of the projections is also very high. In the anterior regions, the membranes are mostly fused in pairs and typically form multilayered whorls. Fusion and whorl formation decrease in the posterior regions. The cytoplasm of the foliate cells has a high organelle content including many lysosomes and mitochondria. The latter exhibit considerable polymorphism, with particular forms occurring in the different regions of the glands. The apical projections of the foliate cells are detached during copulation, presumably as the result of nervous stimulation, and become a part of the ejaculate. Replenishment of all secretory material, including the apical projections, occurs after copulation.

Transport of radiolabelled glycoprotein to cell surface and lysosome-like bodies of absorptive cells in clutured small-intestinal tissue from normal subjects and patients with a lysosomal storage disease.

Abstract: The transport of3H-fucose-and3H-glucosamine-labelled glycoproteins in the absorptive cells of cultured human small-intestinal tissue was investigated with light-and electron-microscopical autoradiography. The findings showed that these glycoproteins were completed in the Golgi apparatus and transported in small vesicular structures to the apical cytoplasm of these cells. Since this material arrived in the cell coat on the microvilli and in the lysosome-like bodies simultaneously, a crinophagic function of these organelles in the regulation of the transport or secretion of cell-coat material was supported. In the absorptive cells of patients with fucosidosis or Hunter’s type of lysosomal storage disease, a similar transport of cell-coat material to the lysosome-like bodies and a congenital defect of a lysosomal hydrolase normally involved in the degradation of cell-coat material, can explain the accumulation of this material in the dense bodies.

Electron microscopic observations on the yolk sac of the Indian fruit bat, Rousettus leschenaulti (Desmarest) (Pteropidae).

Abstract: The yolk sac of the Indian fruit bat Rousettus leschenaulti is unique since during the course of development it become converted into a solid, richly vascular endocrine gland-like structure with both the endodermal and mesothelial cells undergoing substantial hypertrophy. The yolk sac is progressively drawn from the abembryonic (antimesometrial side) to the embryonic pole (mesometrial side) of the chorionic sac where in late stages it comes to rest against the placental disc. The endodermal cells become grouped into clusters of acinus-like structures surrounded by the columnar mesothelial cells; the yolk-sac lumen is in most instances obliterated. Individual endodermal cells are large in comparison to mesothelial cells. The endodermal cell population varies between cells with abundant agranular ER and areas devoid of organelles to others with dense cytoplasm containing stacks of granular ER. All endodermal cells have numerous mitochondria and a few lipid droplets. The mesothelial cells are columnar with either dome-shaped, pointed or flattened apices bearing numerous elongate microvilli; within these are parallel-arranged microfilaments. While the apical cytoplasm shows the presence of absorptive tubules. coated vesicles and caveolae, the basal cytoplasm contains a few small mitochondria. Some mesothelial cells contain lipid droplets in their basal cytoplasm. On structural bases it is postulated that the mesothelial cells are absorptive in function while the endodermal cells are synthetic and secretory.

The allantoic and amniotic epithelia of the pig: SEM and TEM studies.

Abstract: The epithelial layers of the allantoamnion of pig embryos and fetuses during various gestational ages were studied utilizing SEM, TEM, and light microscopic histochemistry. The allantoic endoderm exhibits a gland-like secretory activity and thereby differs greatly from that of other mammals. On the surface of this unilaminar cuboidal epithelium, the majority of the cells exhibit characteristic short vermiform ridges, while some protruding cells display larger individual microvilli. These two cell types are also distinct in thin sections. The more common “granular cells” with short and blunt microvillous projections and a lobated nucleus are characterized by small, Golgi-derived secretory granules in the apical cytoplasm showing a positive PAS-reaction. They contain vast glycogen deposits. Extensive regions of lateral interdigitations are found. In the younger stages, membrane thickenings of the apical plasmalemma resemble those of the urinary bladder. The cytoplasm harbors many more interwoven filaments than organelles. The second cell type, the “mitochondria-rich cells”, bearing longer apical microvilli in many cases, only constitutes up to 3% of the mucosal cell population. They are frequently flask-shaped, heavily reactive to oxidoreductases, and rich in lysosomes but have smaller glycogen deposits. Mitochondria-rich cells lack secretory granules but have light apical tubules, probably of endocytotic character. These cells can be found in different functional states. The amniotic epithelium is simple squamous in the younger stages and largely resembles that in other mammals exhibiting cells with few organelles but rich in filaments. Each terminal bar consists of a zonula occludens only which may open toward the end of gestation. In older fetuses, small stratified areas of cells sloughing off into the lumen appear as blisters which contain large vacuolated cells.

Ultrastructural and morphometric studies on the rat pituitary thyrotrophs and thyroid follicular cells following administration of thyrotropin releasing hormone.

Abstract: The pituitary thyrotrophs and thyroid follicular cells of rats were studied by electron microscopy and morphometric analysis at 5, 10, 20, 30 and 60min after intravenous injection of 200μg of thyrotropin releasing hormone (TRH) and at 10min after injection of 10μg TRH.Multiple granule extrusions in a group were often observed around the pituitary thyrotrophs at 5, 10 and 20min after administration of 200μg TRH, as well as at 10min after injectiom of 10μg TRH. The number of released granules reached its maximum at 10min after 200μg TRH injection, but the total number of secretory granules in the cytoplasm of thyrotrophs did not show any significant variation throughout the experimental period. Percent area of the rough endoplasmic reticulum indicated the maximum value at 20min and that of the Golgi apparatus at 10min. These findings suggest that TRH stimulates the thyrotroph and accelerates synchronously the secretion as well as the synthesis of TSH.In the thyroid follicular cells after 200μg TRH injection, numerous small vesicles which might be secretory granules were found in the apical cytoplasm at 5 and 10min. Pseudopod formation on the luminal surface and accumulation of colloid droplets and lysosome-like granules in the apical cytoplasm were most frequently observed at 20 and 30min. The value of the mean ratio of the diameter of the colloid lumen to the cell height of follicular cells in the thyroid follicles of all experimental animals stimulated with TRH decreased much more than that of the control animals. This value may indicate the increased activity of follicular cells to reabsorb the colloid.

The fine structural effect of sialectomy on the taste bud cells in the rat

Abstract: Taste buds in the rat and other mammals share a secretory activity with their transduction function as taste receptor. The present work shows the effect of bilateral removal of the main salivary glands on taste bud cells' components related to secretion in the vallate papilla of the rat. In the sialectomized rats remarkable changes were evidence in the dark and intermediate types of taste bud cells, which are known to be the secretory components. Such changes involve hypertrophy of either the protein synthetizing machinery, the smooth endoplasmic reticulum or the Golgi complex. Lucent and coated vesicles associated to Golgi cisternae increased in number but the amount of dense-core vesicles (secretory vesicles) at the apical cytoplasm of cells decreased. Images of exocytosis of secretory products were observed. The hypertrophy of Golgi complex components was clearly detected with the OsO4 impregnation method for light and electron microscopy. Alteration in the acid phosphatase activity of taste bud cells was not observed in the sialectomized rats. These findings suggest that sialectomy stimulates the entire secretory cycle of dark and intermediate taste bud cells. The light taste bud cells, which are not engaged in secretion, are hardly affected by the treatment. Although taste buds in mammals are neuro-dependent structures, present evidence indicates that they are also sensitive to non-neural influences.

Protein transmission in the intestine of the newborn lamb: the involvement of acid and alkaline phosphatase activity.

Abstract: The localization of acid phosphatase activity was differentiated from that of alkaline phosphatase in the foregut of the newborn lamb by light and electron microscopy. The examination of samples from fed and unfed lambs indicated the presence of alkaline phosphatase activity in endocytic vesicles originating from the brushborder. These vesicles, associated with protein absorption, were particularly numerous in fed lambs and occurred throughout the cytoplasm of the enterocytes. Acid phosphatase activity was absent from vesicles in the apical cytoplasm but it was localized in most sub-nuclear vesicles, also in the Golgi apparatus and the lysosomes of macrophages.

Proliferative hemorrhagic enteropathy in swine: an outbreak and review of the literature.

Abstract: An account is given of an acute outbreak of hemorrhagic enteric disease in 34 young adult boars of primarily Yorkshire breeding at a performance testing station in Western Canada Two of the boars died A diagnosis of proliferative hemorrhagic enteropathy was made on the basis of clinical signs, gross necropsy and histopathological lesions Campylobacter-like bacteria were seen in the apical cytoplasm of epithelial cells of the ileal mucosa by Warthin-Faulkner stain on histological sections, but were not isolated on culture Treatment with several drugs simultaneously was associated with termination of the outbreak, but the therapeutic effect was not controlled by leaving some animals untreated Reported sequelae, such as porcine intestinal adenomatosis, were not present at necropsy or slaughter of pigs surviving the outbreak, but all were killed no longer than two months after the first case was observed This outbreak is discussed in the context of previously reported hemorrhagic enteric conditions of pigs

Fine structural analysis of the effect of trypan blue on the visceral endoderm of the mouse egg cylinder.

Abstract: The effects of a maternal injection of trypan blue on primitive streak mouse embryos were studied with electron microscopy. Commercial trypan blue was purified by descending paper chromatography, and pregnant females received an intraperitoneal injection of the collected blue fraction on the evening of the 7th day of gestation. Ultrastructurally, the changes in the visceral endoderm were apparent 10 min after the injection and included an increase in the number of fuzzy-coated vesicles in the apical cytoplasm. By 20 min the apical cytoplasm of the extraembryonic visceral endodermal cells was filled with many fuzzy-coated vesicles and numerous vacuoles of various size and electron density. 30 min after the injection, the extraembryonic visceral endodermal cells were relatively smooth lacking a microvillous border and evidence of endocytic activity was rare. Many embryonic visceral endodermal cells were observed in various stages of degeneration although the underlying embryonic ectoderm appeared unaffected. Morphologically, it appears that trypan blue exerts its first effect by altering the endocytic activity of the visceral endoderm.

Ultrastructural radioautography and cytochemistry of lead absorption.

Abstract: Lead is a universal environmental contaminant absorbed largely through the gastrointestinal tract by unknown mechanisms. Because lead absorption is influenced by iron content in the body and diet, we used ultrastructural radioautography and cytochemistry to study absorption of physiologic lead doses in the rat duodenal epithelial cell and compared these findings to those previously reported for iron absorption. Rat duodenal loops exposed in vivo to 210Pb for 1 minute demonstrated the majority of labels on the microvilli, terminal web, and apical cytoplasm. Specimens exposed to radiolead for 10 minutes demonstrated more abundant labeling with a relative increase in labeling of epithelial cell mitochondria, nuclei and basal cytoplasm, as well as phagocytic cells, endothelial cells, and circulating erythrocytes of the lamina propria. Timm's sulfide-silver method localized trace metals in epithelial cells. After administration of lead, a significant increase in staining was observed in microvilli, mitochondria, non-membrane-bound cytoplasm, and nuclear chromatin. The rapid appearance of absorbed lead in epithelial cell mitochondria and nuclei, as well as phagocytic cells in the lamina propria, was distinctly different from that reported for absorbed iron and suggests different mechanisms for the subcellular transport of these cations. The combination of radioautography and Timm's sulfide-silver staining provides the specificity and resolution needed for ultrastructural evaluation of lead absorption and should be useful in further studies of lead metabolism.

A dense cell in the epithelium of the gill lamellae of the brook trout, Salvelinus fontinalis (Mitchill)

Abstract: A cell was found in freshwater brook trout which was similar to a chloride cell as it was mitochondria-rich with an extensive tubular network, but differed in having a dark cytoplasm, large round vesicles in the apical cytoplasm, and large membrane-bound bodies near the nucleus. The base of the cell was separated from the basement membrane by cytoplasm from another epithelial cell. The cell was more rarely found in trout adapted to brackish water and salt water.