Structure of the epithelial - mesenchymal interface during early morphogenesis of the chick duodenum.

During the period of early morphogenetic folding of the intestinal epithelium, changes in the epithelial-mesenchymal interface were observed by light microscopy, scanning and transmission electron microscopy. The epithelium in cross-section, appears first as a circle, then an ellipse and finally by a triangle prior to the formation of the first three previllous ridges. The bases of all epithelial cells are flat at the circular stage. At the ellipse and triangle stages the bases of the epithelial cells occupying the sides possess lobopodia that do not penetrate the basal lamina. The immediate mesenchymal cells subjacent to those epithelial cells on the sides of the ellipse and triangle alter their orientation to being rounded-up or perpendicular to the plane of the basal lamina. Large numbers of fine mesenchymal pseudopodia in addition to many extracellular fibrils are revealed by transmission and scanning electron microscopy at the epithelial-mesenchymal interface. The fine mesenchymal pseudopodia come into close contact but do not penetrate the ruthenium red-staining basal lamina. The possible roles of close contact between epithelium and mesenchyme, the alteration in orientation of mesenchyme cells, and of the basal lamina in tissue interaction are discussed.     

Nonolfactory surface epithelium of the nasal cavity of the bonnet monkey: a morphologic and morphometric study of the transitional and respiratory epithelium

The purpose of the present study was to characterize ultrastructurally the nonolfactory nasal epithelium of a nonhuman primate, the bonnet monkey. Nasal cavities from eight subadult bonnet monkeys were processed for light microscopy, and scanning and transmission electron microscopy. Nonolfactory epithelium covered the majority of the nasal cavity and consisted of squamous (SE), transitional (TE), and respiratory epithelium (RE). Stratified SE covered septal and lateral walls of the nasal vestibule, while ciliated pseudostratified RE covered most of the remaining nasal cavity. Stratified, nonciliated TE was present between SE and RE in the anterior nasal cavity. This epithelium was distinct from the other epithelial populations in abundance and types of cells present. TE was composed of lumenal nonciliated cuboidal cells, goblet cells, small mucous granule (SMG) cells, and basal cells, while RE contained ciliated cells, goblet cells, SMG cells, basal cells, and cells with intracytoplasmic lumina lined by cilia and microvilli. TE and RE contained similar numbers of total epithelial cells and basal cells per millimeter of basal lamina. TE was composed of more SMG cells but fewer goblet cells compared to RE. We conclude that nonolfactory nasal epithelium in the bonnet monkey is complex with distinct regional epithelial populations which must be recognized before pathologic changes within this tissue can be assessed adequately.     

A case of multiloculated, intracranial epidermoid cyst in a beagle dog

An intracranial epidermoid cyst was identified within the fourth ventricle of a male 10-month-old beagle dog. The cyst, which exhibited a multilocular structure, was lined by a stratified squamous epithelium and filled with desquamated keratin. In the region of the roof of the fourth ventricle, choroid plexus adherent to the cyst wall and secondary compression of the cerebellum were also seen.     

Fine structure of the rhombencephalic tela of the bullfrog,Rana catesbeiana

Summary The posterior rhombencephalic tela choroidea of the bullfrog was examined by electron microscopy. This membrane, the pia-ependymal roof of the caudal hindbrain, contains a large central region characterized by cuboidal ependymal cells which surround sizable microscopic apertures — the interependymal pores.Ultrastructurally ependymal cells of this area are characterized by infrequent apical microvilli and cilia. They contain irregularly shaped nuclei and few cytoplasmic organelles that are largely apical in position. The most striking feature is an abundance of cytoplasmic filaments forming an extensive cytoskeleton. Laterally these cells are joined by numerous elaborate desmosomes. The majority of the ependymal cells have a basal lamina consisting of single, double, or triple laminae lying parallel to the basal plasma membrane.Several unusual specializations are seen at the margins of the interependymal pores. The ependymal cells have lateral cytoplasmic processes that form the actual border of each pore. These processes originate from the apical surface of the cell and partially enclose an elaborate network of basal lamina associated with the interependymal pores.These findings demonstrate microscopic apertures in the roof of the fourth ventricle in the bullfrog that are associated with an unusual form of supportive ependyma.     

Continuity between the ventricular and subarachnoid cerebrospinal fluid in an amphibian,Rana pipiens

Summary Continuity between the ventricular and subarachnoid cerebrospinal fluid has been investigated in Rana pipiens. The structure of the posterior tela, a deficient membrane situated at the extreme caudal end of the roof of the fourth ventricle, has been studied using whole membrane mounts and by light microscopy of resin embedded tissue. The ependymal component consists of columnar and rounded cells which form a regular syncytium enclosing round and oval fenestrations. Small fenestrations are covered on the subarachnoid side by elongated pial cells and thus do not give total continuity between the fourth ventricle and the subarachnoid space. Large fenestrations, on the other hand, are accompanied by equivalent pial fenestrations giving direct access between the fluid compartments. Towards the caudal end the fenestrations break up and the numbers of ependymal and pial cells decrease, the caudal end itself being characterised by a small remaining clump of ependyma and pia or of pia alone.Flow through the tela has been studied using fluorescein-labelled dextran placed in the intraventricular space. Infusion into the lateral ventricle and subsequent localisation by fluorescence microscopy shows the marker to be in the fourth ventricle, in the fenestrations of the posterior tela and in the subarachnoid space overlying the tela. Infusion of the marker followed by freezing and examination of the cut heads on a freezing microtome, shows fluorescence throughout the ventricular system, in the subarachnoid space adjacent to the posterior tela and also along the dorsal subarachnoid space of the spinal cord.     

The roof of the fourth ventricle in amphibian brains

The structure of the roof of the fourth ventricle in 10 amphibian species has been examined histologically using serial sections of complete skulls containing the brain and intact meninges. The caudal end of the roof, the posterior tela, consists of a single layer of epithelial cells which are continuous with the ependymal cells which line the walls of the fourth ventricle. The structure of the posterior tela varies according to the species: in the urodele amphibians and Xenopus it consists of a complete and continuous layer of cells, whereas the anurans, excluding Xenopus , have a posterior tela consisting of cells arranged in clumps and short strings. The discontinuous structure of the posterior tela in the anurans gives apparent communication between the ventricular system and the subarachnoid space and this area may be a site for exchange of cerebrospinal fluid between the two compartments.     

Fine Structure of Heart,Pericardium and Glomerular Vessel in Cephalodiscus gracilis M'Intosh, 1882 (Pterobranchia,Hemichordata)

Heart, pericardium and glomerular vessel of Cephalodiscus gracilis have been studied with the electron microscope. The lumen of the heart is lined by a basal lamina and an associated epithelium, composed of myoepithelial cells with well developed thin and thick myofilaments. The heart is located in the pericardial cavity, which is deliminated by the pericardium. The latter is composed of two flat layers of myoepithelia with fused basal laminae. The outer layer of the pericardium is the protocoelomic lining, and the inner layer is the ‘parietal’ pericardial epithelium. The myoepithelium forming the heart wall can be considered to represent the ‘visceral’ pericardial epithelium. The spacious glomerular vessel is lined by a basal lamina, on which typical podocytes rest. These cells indicate that ultrafiltration takes place through the wall of the glomerular vessel. The lumen of the vessel contains fine granular material (presumably precipitated blood proteins), fibrils with a faint cross striation, suggesting that they represent collagen, and stellate cells, which in part line the vessel. Since ultrafiltration requires hydrostatic pressure, it is inferred that the blood flow is from the dorsal region then through the heart and into the glomerular vessel.     

Fine structure of the lateral areas of the rhombencephalic tela of the bullfrog,Rana catesbeiana

Summary The lateral areas of the rhombencephalic tela of the bullfrog contain long, irregular islands of ependymal cells that are similar in fine structure to the epithelium of the rhombencephalic choroid plexus. These cells are characterized by apical microvilli, numerous mitochondria and pinocytotic vesicles, and basal infoldings of the plasma membrane. Dorsally a basal lamina and varying amounts of collagen occur. The pia mater associated with this ependyma includes two cell types. Fibroblast-like, loosely arranged cells without organized junctions line the subarachnoid space. The most abundant cells of the pia in this area, however, contain numerous intermediate filaments and frequent desmosomes. Caveolae lie along their plasma membranes. Closely organized sheets of similar filament-containing cells are also seen in the arachnoid mater of this animal.These findings demonstrate ependymal cells in the lateral areas of the rhombencephalic tela of the bullfrog that have the essential features of choroid plexus epithelium, with ultrastructural characteristics that suggest transport function. They are, however, usually separated from neighboring, nonfenestrated vessels by several layers of leptomeningeal cells joined by desmosomes. The relationship between structure and function of these cells is enigmatic.     

Fine structure of the excretory system of the deep posterior (Ebner's) salivary glands of the human tongue

Human deep posterior lingual glands (von Ebner's glands) are located beneath the circumvallate papillae. They are formed by tubuloalveolar adenomeres, intercalated ducts and excretory ducts coming together in the main excretory duct. The tubuloalveolar cells, pyramid-shaped, show large and dense secretory granules (clear cored) throughout the cytoplasm, rare basal folds and packed cisternae of rough endoplasmic reticulum (RER) at the basal pole. The columnar cells of the intercalated ducts are arranged in a monolayer. They are characterized by dense, clear-core secretory granules (mostly in the apical cytoplasm), a basal nucleus, well-developed RER and Golgi apparatus, and thin filaments distributed in supra- and perinuclear cytoplasm. Striated ducts are absent. Excretory ducts, coming together in the main duct, are lined by a bistratified epithelium. The inner layer consists of columnar cells showing bundles of tonofilaments with scarce secretory activity. The outer layer is composed of basal cells lying on the basal lamina. The main excretory duct, which opens at the bottom of the vallum, shows a stratified epithelium. The outer side is composed of 2-3 layers of malpighian cells lying on the basal lamina. The inner side consists of a single layer of cuboidal-columnar cells with dense apical granules and well-developed organelles synthesizing and condensing secretions. These cells interpolate with goblet cells, rare mitochondria-rich cells, ciliated cells and numerous small globous cells showing a clear matrix and lacking secretory granules. The cilia show a 9 + 2 microtubular structure with basal bodies provided with striated rootlets. Myoepithelial cells surround with their processes the basal portions of the secretory cells and the intercalated ducts. The conclusions concern some comparative aspects and some hypothesis on the functional role of goblet cells, ciliated cells and epithelial cells lining the different ducts, also in relation to the final secretory product.     

The study of the ultrastructure of the female reproductive system in a parasite of bats Allassogonoporus amphoraeformis (Digenea: Allassogonoporidae)

The morphology and fine structure of the female reproductive system of allassogonoporid trematode Allassogonoporus amphoraeformis have been described for the first time. The ovary consists of the germ cells being at various developmental stages and supporting cells of two types. The oviduct, seminal receptacle with its short duct and the proximal portion of Laurer's canal are lined by flattened cellular epithelium with lamellae and cilia on its luminal surface and well-developed basal infoldings. The distal part of Laurer's canal and metraterm are tegumental in structure and are characterized by sparse secretory inclusions and lacking of spines. Mehlis' glands of two types open into ootype. The uterus wall is composed of highly flattened epithelial cells surrounded by basal lamina and sparse muscle bundles. Vitelline lobules consist only of the vitelline cells at various developmental stages. The mature vitelline cells contain two types of inclusions: vitelline droplets and rarely scattered lipids. Vitelline ducts are lined by cellular epithelium with highly folded luminal surface and devoid of cilia. Presented results are compared with earlier obtained data on other lecithodendrioiden trematode Prosthodendrium ascidia ([symbol: see text], 1990).     

Ultrastructural features of degeneration of the gallbladder during lamprey biliary atresia

Thin sections and freeze-fracture replicas were used to examine the fine structural features of degeneration of the gallbladder during lamprey biliary atresia. The cells of the epithelium undergo a progressive accumulation of dense bodies and vacuoles, loss of glycogen, condensation of the filamentous ectoplasm, fragmentation of microvilli, and dilation of cisternae of rough endoplasmic reticulum but eventually disappear by stage 4 of metamorphosis. Zonulae occludentes in the epithelium show a progressive increase in apical-basal depth as the junctional strands fragment. The possibility of an influence of transformed, subepithelial cells on degeneration of epithelial cells is suggested by close contact of the former with the thickened, highly pleated, epithelial basal lamina. The smooth muscle cells of the larval gallbladder are believed to transform during lamprey metamorphosis into these subepithelial cells which shed their external lamina, become intimately associated with collagen and other microfibrils, and which may be capable of phagocytosis. The events of gallbladder degeneration during lamprey metamorphosis show features of apoptosis.     

Intercellular channels in the pars tuberalis of the rat hypophysis and their relationship to the subarachnoid space

Summary A system of intercellular channels is described in the pars tuberalis (PT) of the female rat. These spaces are lined by all types of cells found in the PT and are not sealed off by tight junctions. Ventrally and dorsally, the intercellular spaces open toward the basement membranes separating the PT from (i) the subarachnoid space, and (ii) the perivascular space of the portal capillaries, respectively. These intercellular channels differ from the follicles, which are also found in the PT, being lined by a particular type of cell.In a second group of female rats an epoxy mixture was injected into the third ventricle; 10 min thereafter horseradish peroxidase was infused into the cisterna magna. After processing the brain for the demonstration of exogenous peroxidase, it was found that the tracer had reached the subarachnoid space adjacent to the hypothalamus and entered into all ventricular cavities with the exception of the infundibular recess. Under these experimental conditions it was found that the tracer fills all intercellular channels of the PT, thus indicating that there is no barrier between the subarachnoid space and the PT. It is suggested that the subarachnoid space should be regarded as a probable route for the transport of trophic factor(s) and/or secretory product(s) of the PT.Supported by Grant S-80-13 from Directión de Investigaciones, Universidad Austral de Chile     

Histology and ultrastructure of the gut epithelium of the neotenic cave salamander, Proteus anguinus (Amphibia, Caudata)

Histological, histochemical, and ultrastructural features of the gut of the European endemic cave salamander Proteus anguinus were studied. The gut is a relatively undifferentiated muscular tube lined with a simple columnar epithelium containing numerous goblet cells. The mucosa and underlying lamina propria/submucosa are elevated into a number of high longitudinal folds projecting into the lumen. The enterocytes are covered apically with uniform microvilli. Irregularity in the arrangement of microvilli was observed. Occasionally, irregular protrusions of the cytoplasm appear between groups of microvilli. Pinocytotic activity occurs at the bases of the intermicrovillous space. Mitochondria are numerous in the apical cytoplasm and basally beneath the nuclei. The supranuclear cytoplasm contains most of the cell organelles. The lateral plasma membranes of adjacent cells interdigitate and are joined by junctional complexes. The periodic acid-Schiff (PAS) reaction, indicating neutral mucosubstances, is positive only in the apical brush border of enterocytes and in goblet cells. The goblet cells also stained with Alcian blue (AB), at pH 2.5, thus revealing the presence of carboxylated glycosaminoglycans. Compact aggregations of AB- and PAS-negative cells are situated directly below the epithelium. Mitotic figures are present in individual clusters of cells. The fine structure of cells in these clusters indicated that these cells could be responsible for renewal of intestinal epithelium. Numerous endocrine-like cells could also be seen. The closely packed smooth muscle cells and amorphous extracellular material with collagen fibrils constitute a net-like structure under the basal lamina that is very closely associated with the epithelium. There are numerous acidophilic granular cells between epithelial cells, in the lamina propria/submucosa, and between cells aggregations. They seem to be associated with nematode infections and possibly constitute a humoral defense mechanism.     

Affiliation of large numbers of fibroblasts with larval muscle fibers

Muscle fibers from fourth and fifth instar caterpillars were examined with scanning and thin section electron microscopy. Scanning micrographs showed that early fifth instar specimens had a population of cells lying beneath the basal lamina over the surface of the muscle fiber and in conjunction with tracheoles and nerves. At least two cell types were present. One type could be categorized as tracheoblasts of their close association with the tracheoles and the presence of taenidia within the tracheoblast cytoplasm in sectioned material. A second cell type, characterized by long filamentous processes, contained extensive rough endoplasmic reticulum and cisternae swollen with an electron-dense substance similar in appearance to the basal lamina. This ultrastructural appearance is characteristic of vertebrate fibroblasts and certain types of insect hemocytes. Early and late fourth instar specimens had few cells on their muscle fiber surfaces. Measurements of the basal lamina thickness were taken from thin sections of nondigested muscle fibers of early fourth, late fourth, and early fifth instar animals. The results showed that the basal lamina underwent a large increase in thickness between the fourth and fifth instars. The proliferation of cells which appeared to be in an actively synthesizing state paralleled the increase in basal lamina thickness. This suggests the hypothesis that these cells are active in connective tissue formation, and contribute to the formation of the basal lamina that lies over both them and the muscle fiber.     

Fenestration of the epithelium lining the roof of the fourth cerebral ventricle in amphibia

Summary Scanning electron microscopy of the caudal end of the roof of the fourth cerebral ventricle in four amphibian species shows that numerous pores occur between the ependymal cells. These pores have diameters ranging from 5–100 m; they permit bulk flow of cerebrospinal fluid out of the ventricular system into the subarachnoid space.     

Histochemical and immunohistochemical adaptations on the gastroesophageal tube of the blue-fronted parrot (Amazona aestiva Linnaeus, 1758)

Amazona aestiva Linnaeus, 1758 is known as the blue-fronted parrot. These animals are considered seed dispersion, contributing to ecological balance. Despite its ecological importance, A. aestiva is listed as an imminent danger of becoming extinct, as it is one of the most illegally traded native species in Brazil, besides losing its habitat due to deforestation and forest fires. The cranial oesophagus mucosa is lined with a non-keratinized stratified squamous epithelium, and the basal layer presents melanocyte accumulation. No mucous glands were observed in the lamina propria/submucosa. The ingluvium two different muscular layer patterns were observed, one internal and circular and one very thick, external and longitudinal. The proventriculum submucosa consists of polygonal proventricular glands and contents into a broad central duct lined with simple columnar epithelium Periodic acid-reactive Schiff positive (PAS+) and Alcian blue positive (AB+). The 5-HT cells are dispersed in the proventricular glands located at base and apex. The ventricle mucous layer contains numerous branched folds lined by a simple columnar epithelium. The epithelium was negative reaction for PAS and positive for AB only on the fold surfaces. The 5-HT cells were scarce and observed only at the base of the ventricular gland, as well as in the adjacent connective tissue.     

Ultrastructural diagnosis of facial nerve schwannoma using fine needle aspiration

In a 14-year-old boy presenting with left facial nerve paralysis, physical examination revealed a soft, round mass in the floor of the left external auditory canal. A fine needle aspiration biopsy was performed to obtain material for light and electron microscopy. Several small groups of uniform, spindle-shaped neoplastic cells were present on the slides; a malignant mesenchymal tumor was considered, but a definite diagnosis could not be established under light microscopy. The ultrastructural examination revealed spindle-shaped and stellate cells with multiple parallel cytoplasmic processes lined with a well-developed basal lamina; these features are highly characteristic of a benign schwannoma.     

Response of epithelial and mesenchymal cells to culture on basement lamella observed by scanning microscopy

The basement lamella of Xenopus tadpole skin has been viewed in situ by scanning microscopy, then isolated by trypsin treatment and used as a substrate for cell culture. The basal lamina may also be viewed after EDTA treatment. Responses of epithelial and mesenchymal cells to the lamella have been compared. Mesenchymal cells from chick skin and heart ventricle flatten and attach between the plies of the lamella, then infiltrate it. Myoblasts appear to move less readily within the lamella. Embryonic Xenopus skin epithelium spreads over the surface. Isolated chick skin epithelial cells first begin to spread, then round up and eventually attach to each other in clusters which form a flat basal surface above the lamella. Thus epithelial and mesenchymal cells cultured on this isolated extracellular material mimic aspects of normal tissue organization.     

Radiation-induced changes of fibroblasts in the squamous cell carcinoma of the head and neck

The regrowth of mesenchymal tissue (stroma) surrounding the malignant epithelium is an important step in tissue remodelling during and after irradiation. The radiation-induced fibroblastic changes were studied on tissue samples taken before, during and after the radical irradiation of the squamous cell carcinoma of the head and neck. Elongated fibroblasts with large amount of rough endoplasmic reticulum were seen around the tumor epithelium before radiation. The fibrosis increased during irradiation and at the same time the shape of the fibroblasts changed so that they became more triangular and nuclear structures became more prominent together with hyperchromasia. The amount of cell organelles declined although there was a large amount collagen present. Epithelial cells invaded through the basal lamina. In most samples the basal lamina could not be seen at all and the tumor cells were dispersed between stromal elements. On the other hand there were close contacts between epithelial and mesenchymal cells throughout the study in places where the basal lamina was broken, which might indicate epithelio-mesenchymal interaction. Also the connective tissue formed by fibroblasts and collagen might be part of the radiation induced healing and destruction of the tumor cells.     

Effect of anatomical fine structure on the dispersion of solutes in the spinal subarachnoid space

The dispersion of a solute bolus is calculated for cerebrospinal fluid undergoing oscillatory flow in the subarachnoid space of the spine. The fine structure of the subarachnoid space (nerves and trabeculae) enhances both longitudinal and transverse dispersions five to ten times over a simple model with an open annular space. Overall, dispersion is >10(3) times simple molecular diffusion. The result of enhanced dispersion is rapid spread and dilution of the bolus, effectively stirred by fluid movement around the fine structure.