Electron microscopic observations on the renal caliceal wall in the rat

Summary The fine structure of the rat caliceal wall at its attachment to the renal parenchyma is described. Particular attention is paid to the smooth muscle cells and their associated nerves. A single overlapping layer of epithelial cells lines the renal papilla which changes abruptly to a layer of 3–5 cells where the calix gains attachment to the renal substance. In this region there is an associated increase in the underlying connective tissue which contains smooth muscle cells. These cells possess filaments, are surrounded by a basal lamina, and occur scattered among large bundles of collagen fibres. The muscle cells possess numerous branching processes as well as shorter projections which make close contacts with adjacent cells. Large numbers of axons and their associated Schwann cells are also observed in this region. The axons possess swellings, some of which lie within 800 Å of smooth muscle cells, and contain large and small granulated vesicles and agranular vesicles. They are therefore considered to be adrenergic effectors.Further out in the caliceal wall typical spindle-shaped smooth muscle cells are observed lying parallel to one another to form closely packes bundles and are associated with relatively few nerves.The significance of these observations is discussed.     

Immunohistochemical and ultrastructural characteristics of interstitial cells of Cajal in the rabbit duodenum. Presence of a single cilium

Santiago Ramón y Cajal discovered a new type of cell related to the myenteric plexus and also to the smooth muscle cells of the circular muscle layer of the intestine. Based on their morphology, relationships and staining characteristics, he considered these cells as primitive neurons. One century later, despite major improvements in cell biology, the interstitial cells of Cajal (ICCs) are still controversial for many researchers. The aim of study was to perform an immunohistochemical and ultrastructural characterization of the ICCs in the rabbit duodenum. We have found interstitial cells that are positive for c-Kit, CD34 and nestin and are also positive for Ki67 protein, tightly associated with somatic cell proliferation. By means of electron microscopy, we describe ICCs around enteric ganglia. They present triangular or spindle forms and a very voluminous nucleus with scarce perinuclear chromatin surrounded by a thin perinuclear cytoplasm that expands with long cytoplasmic processes. ICC processes penetrate among the smooth muscle cells and couple with the processes of other ICCs located in the connective tissue of the circular muscle layer and establish a three-dimensional network. Intercellular contacts by means of gap-like junctions are frequent. ICCs also establish gap-like junctions with smooth muscle cells. We also observe a population of interstitial cells of stellate morphology in the connective tissue that sur-rounds the muscle bundles in the circular muscle layer, usually close to nervous trunks. These cells establish different types of contacts with the muscle cells around them. In addition, the presence of a single cilium showing a structure 9 + 0 in an ICC is demonstrated for the first time. In conclusion, we report positive staining c-Kit, CD34, nestin and Ki 67. ICCs fulfilled the usual transmission electron microscopy (TEM) criteria. A new ultrastructural characteristic of at least some ICCs is demonstrated: the presence of a single cilium. Some populations of ICCs in the rabbit duodenum present certain immunohistochemical and ultrastructural characteristics that often are present in progenitor cells.     

The fine structure of smooth muscle cells and their relationship to connective tissue in the rabbit portal vein

Summary The smooth muscle of rabbit portal vein was studied by electron microscopy with particular emphasis on the mechanical linkage between the muscle cells and on the distribution of connective tissue.The media of this vein is composed of inner circular and outer longitudinal muscle layers which are orientated almost perpendicularly to each other. The muscle of the inner circular layer shows very irregular contours with much branching and anastomosing of the cytoplasmic processes, which often make membrane contacts with neighbouring cells to form an extensive network of cytoplasmic processes. The muscle cells of the outer longitudinal layer are arranged in densely packed bundles and are spindle-shaped, with no branching processes. Opposing dense areas from neighbouring cells, with variable gap distances (30–100 nm) and close membrane contacts (intermediate junctions) with a gap of 11 nm were observed in both circular and longitudinal muscle layers.In the terminal regions of muscle cells in both circular and longitudinal layers a specialized anchoring structure was present which was closely related to extracellular elastic tissue. Muscle cells in the longitudinal layer showed the most elaborate structure, the tapering end of the muscle cell showing a honeycomb-like structure penetrated by columns of connective tissue compounds. The functional implications of these structures are discussed.     

Paracloacal glands of Alligator mississippiensis: A histological and histochemical study

The histology of the paracloacal 'musk' glands of adult American alligators ( Alligator mississippiensis ) is described. The gland is a single secretory sac with a single duct and a central lumen partially occluded by a central, cylindrical conglomerate of cells and secretion product. The capsule of the gland consists of an outer layer of smooth muscle and an inner layer of connective tissue containing collagen and elastin fibres. Septa carrying blood vessels radiate from the connective tissue layer of the capsule to the border of the central conglomerate. Parenchymal cells containing lipid droplets enlarge from the periphery to the centre of the gland. Secretions formed by degeneration of cells in the central cylinder are concentrated near the secretory duct. Histochemical tests indicate lipids but not mucopolysaccharides in the glandular exudate.     

Release of biologically active TGF-beta from airway smooth muscle cells induces autocrine synthesis of collagen

In severe or chronic asthma, there is an increase in airway smooth muscle cell (ASMC) mass as well as an increase in connective tissue proteins in the smooth muscle layer of airways. Transforming growth factor-beta (TGF-beta) exists in three isoforms in mammals and is a potent regulator of connective tissue protein synthesis. Using immunohistochemistry, we had previously demonstrated that ASMCs contain large quantities of TGF-beta1-3. In this study, we demonstrate that bovine ASMC-derived TGF-beta associates with the TGF-beta latency binding protein-1 (LTBP-1) expressed by the same cells. The TGF-beta associated with LTBP-1 localizes TGF-beta extracellularly. Furthermore, plasmin, a serine protease, regulates the secretion of a biologically active form of TGF-beta by ASMCs as well as the release of extracellular TGF-beta. The biologically active TGF-beta released by plasmin induces ASMCs to synthesize collagen I in an autocrine manner. The autocrine induction of collagen expression by ASMCs may contribute to the irreversible fibrosis and remodeling seen in the airways of some asthmatics.     

Further observations on upper urinary tract smooth muscle

Summary Light and electron microscopic techniques have been employed to study the arrangement and distribution of two types of muscle in the upper urinary tract of the rat. An outer layer of cells has been identified in the wall of the renal calix and pelvis. These cells are separated by connective tissue but possess numerous processes which make close contacts with adjacent cells. A layer of similar cells has not been observed in the wall of the upper ureter. The inner layer of muscle in the calix and pelvis is composed of larger cells similar to and apparently continuous with ureteric muscle. These cells are closely related to one another without intervening connective tissue and possess numerous bundles of myofilaments which extend along the length of the cell. The two types of muscle are closely related and, in the junctional region, cells of the outer layer are arranged along the length and make close contacts with one or more of the inner smooth muscle cells. A quantitative estimation has been made of nerve bundles associated with smooth muscle forming the outer layer of the calix and pelvis and with the muscle of the ureter. The results have shown a five fold increase in nerves associated with the caliceal muscle when compared with the ureter. The results are discussed in relation to the concept of a ureteric pacemaker.The authors wish to thank Professor G. A. G. Mitchell for his useful advice and encouragement.     

Observations on the ultrastructure of the carp liver (Cyprinus carpio L.)

The paper presents information about the fine structure of the sinusoids, the space of Dissé, the development of the bile canaliculi and some compartments of the hepatocytes in the liver of the carp. The sinusoids are covered completely by flat endothel cells. The plasma of these cells contains numerous vesicles. The endothelial cells possess plasmatic processes, which extend into the space of Dissé. The fine structure of the space of Dissé corresponds to that of mammals, the existence of fibrebundles included. The bile canaliculi don't develop intracellularly as described by other authors. They run intercellularly as in mammals, but they form diverticles which reach into the plasma sideways. The rough ER was found in two types. Outwardly the liver is limited by a layer of connective tissue existing in two different layers.     

A comparative anatomical study of the mammalian uterotubal junction

Among eight species of mammals in this study (cattle, sheep, pig-tail and rhesus monkeys, rabbit, pig, rat, and dog) four basic patterns of anatomical structure at the uterotubal junction are described. The classification of types is based upon the presence or absence of an intramural portion of the oviduct and of isthmal folds or plicae projecting into the lumen of the uterine cornu. Histological variations are reported for three tissues: epithelial and connective of the mucosa and smooth muscle of the tunica muscularis. In the epithelium during the estrous cycle the differences recorded include: (a) absence of ciliated cells in the distal end of the oviduct in rat and dog; (b) variations in ciliated and nonciliated cells in (1) cell height, (2) location, shape and stainability of the nucleus, and (3) in amount and stainability of apical cytoplasm; (c) presence of lymphoblast-like cells which appear to migrate through the epithelium from the lamina propria. The connective tissue of the mucosa, as a circular layer and as cores for the mucosal folds, shows variations in thickness and in relative density of cells and fibers of the matrix. Emphasis is given to the presence of an inner longitudinal layer of smooth muscle in the tunica muscularis of the distal oviduct in six of the eight species.     

Morphological and immunohistochemical study of testicular capsule and peritubular tissue of emu (<Emphasis Type="Italic">Dromaius novaehollandiae)</Emphasis> and ostrich (<Emphasis Type="Italic">Struthio camelus</Emphasis>)

The testicular capsule and peritubular boundary tissue of the emu and ostrich, as typical representatives of ratite birds, were studied in sexually mature and active birds. The testicular capsule was much thicker (578.1±73.4 μm for the free surface of the ostrich testis, and 176.2±57.5 μm for the emu) than those of members of the Galloanserae. The cellular composition of both testicular capsule and peritubular tissue was similar generally to that of members of the previously studied Galloanserae and of mammals. The tunica albuginea of the testicular capsule mainly comprised smooth-muscle-like or myoid cells mostly running in one direction and occurring in one main mass. Unlike the Galloanserae, the tunica albuginea contained more collagen fibres than smooth muscle cells, especially in the ostrich. Peritubular tissue was similarly composed of smooth-muscle-like cells distributed in several layers. Actin microfilaments and desmin and vimentin intermediate filaments were variably immunoexpressed in these two tissue types in both birds, with a clear dichotomy in the peritubular tissue. Thus, taken together with studies of some members of the Galloanserae, avian testes clearly contain a morphological mechanism that is represented partly by the smooth muscle cells of the testicular capsule and peritubular tissue for transporting the testicular fluid, which is usually copious in birds, and its cellular content from the testis into the excurrent duct system; this mechanism is similar to that found in mammals. The authors are grateful for a University of Pretoria research grant, which aided this work. Dr Peter Ozegbe of the Department of Veterinary Anatomy, University of Ibadan is a recipient of the University of Pretoria Foreign Post-Doctoral Fellowship.     

Ultrastructural study of the heart and its relationship with the connective tissue sheath of the stomach in Rhynchonella psittacea (Tentaculata,Brachiopoda)

The fine structure of the heart and connective tissue sheath surrounding the stomach of the brachiopod Rhynchonella psittacea has been studied. The stomach wall is lined externally with peritoneal epithelium. Between the bases of the peritoneal epithelial cells and those of the stomach epithelial cells is an extracellular amorphous matrix. The exterior part of the matrix is occupied by smooth muscle cells and the interior part by fibroblasts. The heart wall shows continuity with the peritoneal epithelium covering the stomach wall and consists of three layers: an outer layer of smooth myoepithelial and epithelial cells, an intermediate thick layer of extracellular matrix, and an inner discontinuous layer of fibroblasts. In myoepithelial cells, nucleated heads protruding freely into the coelom and contractile parts embedded in the extracellular matrix can easily be distinguished. These cells contain no sarcoplasmic reticulum or any elements of a T system. The epithelial cells are non-muscular mononucleated cells scattered among the myoepithelial cells and closely associated with these basally. They possess a well-developed rough endoplasmic reticulum. In rare cases, a small amount of myofibrils occurs basally in the epithelial cells. Morphologically the epithelial cells in the myocardium are very similar to the peritoneal epithelial cells covering the stomach wall. Both epithelial and myoepithelial cells are ciliated. No nerve elements have been found in the brachiopod heart. The structure of the brachiopod heart is compared with that of other invertebrates; similarity of cellular composition of the brachiopod heart and stomach cover is considered evidence of origin of the heart cells from the cells of the connective tissue sheath of the stomach. The myogenic role of the peritoneal cells and epithelial cells of the myocardium is suggested. J. Morphol. 234:69–77, 1997. © 1997 Wiley-Liss, Inc.     

The three-dimensional microanatomy of Meissner corpuscles in monkey palmar skin

The Meissner corpuscle is a rapidly-adapting mechanoreceptor in the dermal papillae of digital skin. For an analysis of how the sensory endings detect tissue deformations, an examination of their fine structure and relationships with dermal collagen was carried out in the Japanese monkey, Macaca fuscata, using a combination of three methods: SEM of cell architecture denuded by 6N sodium hydroxide maceration, SEM of collagen networks exposed by a mild alkaline corrosion, and TEM according to a conventional procedure. Observations showed the sensory corpuscles to be represented by a stack of discoid components consisting of flattened axon terminals sandwiched between Schwann cell lamellae, as reported previously. Each corpuscle was entirely covered by a connective tissue capsule, which was linked with the basal aspect of the epidermis by dermal collagen fibers. Margins of the discoid components of the corpuscles were serrated with numerous fine projections of lamellar Schwann cells, which tightly held collagen trabeculae on the inner aspect of the pericorpuscular capsule. Central portions of the discoids, on the other hand, displayed extremely smooth surfaces, which were covered by a thick layer of basal lamina-like matrix. The former portions of the discoids appear susceptible to mechanical deformations of surrounding tissues, while the latter may follow the tissue movements rather slowly because of their indirect linkage with the dermal collagen network. The resulting distortions of the axon endings during dynamic phases of the tissue deformations will be in favor of the generation of rapidly adapting receptor potentials in the sensory corpuscle.     

The Fine Structure of the Epithelial Cells of the Mouse Prostate : II. Ventral Lobe Epithelium

The fine structure of the epithelial cells of one component of the prostatic complex of the mouse—the ventral lobe—has been investigated by electron microscopy. This organ is composed of small tubules, lined by tall simple cuboidal epithelium, surrounded by smooth muscle and connective tissue. Electron micrographs of the epithelial cells of the ventral lobe show these to be limited by a cell membrane, which appears as a continuous dense line. The nucleus occupies the basal portion of the cell and the nuclear envelope consists of two membranes. The cytoplasmic matrix is of moderately low density. The endoplasmic reticulum consists of elongated, circular, and oval profiles representing the cavities of this system bounded by rough surfaced membranes. The Golgi apparatus appears localized in a region between the apical border and the nucleus, and is composed of the usual elements found in secretory cells (3, 9). At the base of the cells, a basement membrane is visible in close contact with the outer aspect of the cell membrane. A space of varying width, which seems to be occupied by connective tissue, separates the epithelial cells from the surrounding smooth muscle fibers and the blood vessels. Bodies with the appearance of portions of the cytoplasm, mitochondria, or profiles of the endoplasmic reticulum can be seen in the lumina of the acini and on the bases of these pictures and others of the apical region the mechanism of secretion by these cells is discussed. The fine structural organization of these cells is compared with that of another component of the mouse prostate—the coagulating gland.     

Breeding and post-breeding structure of the vas deferens of the long-toed salamander Ambystoma macrodactylum

The vas deferens of Ambystoma macrodactylum is composed of a peritoneal epithelium, connective tissue layer with fibroblasts, circular smooth muscle, capillaries, cells containing lipid, and a luminal epithelium composed of a single layer of cuboidal cells covered by a net of interconnected ciliated squamous cells. The cuboidal cells have abundant rough endoplasmic reticulum, mitochondria, and PAS + secretory vesicles. Squamous cells of breeding males consistently have tufts of ～100 cilia located at one end of the long axis of each cell. These cilia may help distribute secretory products. The squamous cells, absent in post-breeding males, are apparently sloughed into the lumen. Lipid vesicles are present throughout the cytoplasm of the cuboidal and squamous epithelial cells and are also in some cells of the connective tissue layer. These vesicles increase dramatically in number during the first 4 weeks after breeding and may serve as an energy pool for the next breeding season. Enzyme-histochemical tests for testosterone synthesis were negative. In addition to the accumulation of lipid and the loss of squamous cells in the vas deferens, after breeding PAS + vesicle production is terminated. These alterations appear to represent energy conservation strategies employed by the sperm-depleted vas deferens.     

The connective tissue skeleton in the mammalian kidney and its innervation.

A special reticular basket-like system of connective tissue strips (called connective tissue skeleton - CTS) was found between the cortex and medulla in the kidney of various mammals. It enlarges the wall of the renal calyx (or pelvis) into the parenchyma. The main component of this system is collagen. A small amount of smooth muscle cells was found in one part of CTS srips situated around the papilla (the levator fornicis muscle). A dense monoaminergic and scanty cholinergic innervation was found in the whole system of the CTS. The functional importance of this system is discussed: (i) a tightly linked connection between the urine-discharging system and the kidney, (ii) 'milking' and similar effects in the papilla as well as perception of intrapelvic and intrarenal pressure, (iii) penetration of infection into the kidney and (iv) liberation of the monoaminergic transmitter.     

The Fine Structure of the Epithelial Cells of the Mouse Prostate : I. Coagulating Gland Epithelium

The fine structure of the epithelial cells of the anterior lobe, or coagulating gland, of the mouse prostate has been investigated by electron microscopy. This organ is composed of small tubules, lined by tall, simple cuboidal epithelium surrounded by connective tissue and smooth muscle. The epithelial cells are limited by a distinct plasma membrane, which covers minute projections of the cytoplasm into the lumen. The cell membranes of adjacent cells are separated by a narrow layer of structureless material of low density. The cavities of the endoplasmic reticulum are greatly dilated, and the cytoplasmic matrix is reduced to narrow strands, in which the various organelles are visible. The content of the cavities of the endoplasmic reticulum appears as structureless material of lesser density than the cytoplasmic matrix. Material which may be interpreted as secretion products can be seen in the lumina of the tubules. The possible nature of the material inside the cisternal spaces and the secretory mechanisms in these cells is discussed.     

Structural links between the renal stem/progenitor cell niche and the organ capsule

A special feature of the renal stem/progenitor cell niche is its always close neighborhood to the capsule during organ development. To explore this link, neonatal kidney was investigated by histochemistry and transmission electron microscopy. For adequate contrasting, fixation of specimens was performed by glutaraldehyde including tannic acid. The immunohistochemical data illustrate that renal stem/progenitor cells are not distributed randomly but are positioned specially to the capsule. Epithelial stem/progenitor cells are found to be enclosed by the basal lamina at a collecting duct (CD) ampulla tip. Only few layers of mesenchymal cells are detected between epithelial cells and the capsule. Most impressive, numerous microfibers reacting with soybean agglutinin, anti-collagen I and III originate from the basal lamina at a CD ampulla tip and line between mesenchymal stem/progenitor cells to the inner side of the capsule. This specific arrangement holds together both types of stem/progenitor cells in a cage and fastens the niche as a whole at the capsule. Electron microscopy further illustrates that the stem/progenitor cell niche is in contact with a tunnel system widely spreading between atypical smooth muscle cells at the inner side of the capsule. It seems probable that stem/progenitor cells are supplied here by interstitial fluid.     

Electron-microscopic study of innervation of smooth muscle cells surrounding collecting tubules of the fish kidney

Summary The fine structure of the collecting tubules of the trout and killifish kidney was studied. These tubules are surrounded by layers of smooth muscle cells which are commonly innervated. The nerve terminals contain synaptic vesicles and, occasionally, a few dense-cored granules as well. Capillaries occur in the connective tissue space between these smooth muscle cells and the collecting tubule. Epithelial cells of the collecting tubules contain abundant mitochondria and a well developed membrane system displaying parallel arrays, and were considered to be actively involved in the transport of materials. In the trout, the collecting tubules contain peculiar cells in addition to regular tubule cells. The fine structure of these peculiar cells is highly reminiscent of that of gill chloride cells. The significance of these findings may be summarized as follows: If the smooth muscles around the collecting tubule contract under neural influence, intratubular pressure may be increased and, thus affect glomerular filtration rate. The contraction of these muscles may also cause the collapse of peritubular capillaries, affecting the transport activity of tubule cells.     

Ultrastructure of sea urchin tube feet

Summary An analysis of the ultrastructure of the tube feet of three species of sea urchins (Strongylocentrotus franciscanus, Arbacia lixula and Echinus esculentus) revealed that the smooth muscle, although known to be cholinoceptive, receives no motor innervation.The muscle fibers are attached to a double layer of circular and longitudinal connective tissue which surrounds the muscle layer and contains numerous bundles of collagen fibers. On its outside, the connective tissue cylinder is invested by a basal lamina of the outer epithelium to which numerous nerve terminals are attached. These are part of a nerve plexus which surrounds the connective tissue cylinder. The plexus itself is an extension of a longitudinal nerve that extends the whole length of the tube foot. It is composed of axons, but nerve cell bodies and synapses are conspicuously lacking, suggesting that the axons and terminals derive from cells of the radial nerve. Processes of the epithelial cells penetrate the nerve plexus and attach to the basal lamina. There is no evidence that the epithelial cells function as sensory cells.On the basis of supporting evidence it is suggested that the transmitter released by the nerve terminals diffuses to the muscle cells over a distance of several microns and in doing so affects the mechanical properties of the connective tissue.Supported by the Sonderforschungsbereich 138 of the Deutsche Forschungsgemeinschaft     

Ovipositor ultrastructure of the striped bitterling Acheilognathus yamatsutae (Teleostei: Acheilognathinae) during spawning season

The ovipositor of striped bitterling Acheilognathus yamatsutae was subjected to ultrastructure and histochemical analysis during spawning season using light and electron microscopy. Although the ovipositor of A. yamatsutae is a long cylindrical tube with smooth external surface, it was possible to confirm the presence of well-developed fingerprint structure using scanning electron microscopy. Internal aspect analysis of ovipositor revealed formation of 5–8 longitudinal folds. Cross section analysis revealed that the ovipositor is composed of an outer epithelial layer, a mid connective tissue layer, and an inner epithelial layer. The outer epithelial layer contains 7–9 cell layers composed mainly of epithelial and mucous cells. Result of AB–PAS (pH 2.5) and AF–AB reaction showed that mucous cells contained mainly acidic carboxylated mucosubstances. The connective tissue layer was loose and made mainly of collagen fibers and some muscle fibers, along with blood vessels and a small number of chromatophores. The inner epithelial layer, which is a single layer, is composed of columnar epithelia. Observation under transmission electron microscope enabled distinction of the outer epithelial layer into superficial, intermediate and basal layers. Although the types of cells in the superficial tissue layer were diverse, they all shared the development of glycocalyx covered microridges. The majority of epithelial cells in the intermediate layer were cuboidal shaped, while those in the basal layer were columnar. Two types (A and B) of secretory cells were observed in the outer epithelial layer. The connective tissue layer had two types of chromatophores including xantophore and melanophore, in addition to a well-developed nerve fiber bundles. Columnar epithelial cells, mitochondria-rich cells and rodlet cells were observed in the inner epithelial layer. Microvilli were well developed on the free surface of columnar epithelial cells.     

Fine structure of the epineural connective tissue sheath of the subesophageal ganglion in Helix aspersa

Summary The epineural connective tissue sheath investing the subesophageal ganglion of Helix aspersa consists of a superficial region and a deeper region. The superficial region contains masses of globular cells intermingled with smooth muscle cells and nerve fibers all embedded in a connective tissue matrix. The histochemical and fine structural features of the globular cells show seasonal changes. During autumn to winter glycogen accumulates in their cytoplasm; this accumulation is accompanied by the appearance of dense, cytoplasmic globules which fuse together and ultimately form large pools of granular material. All the organelles and cytoplasm are displaced towards the cell periphery. Various cell-membrane invaginations containing dense material are prominent but there is no direct evidence to link these structures with the uptake of metabolites for glycogenesis. In winter there is a concentration of homogeneous, membrane-bound inclusions in the vicinity of the Golgi bodies. It is suggested that these inclusions constitute a lipid store. They decrease in number during summer. The globular cells do not bear any intimate relation to neurons and there is no reason to include these cells in the neuroglia. The muscle cells often weave around the globular cells but there is no direct contact. Nerve fibers innervate at least some of the muscle cells. The connective tissue consists of large and small diameter fibers suggesting that maturation of the fibrous components of the intercellular matrix is taking place in the superficial regions of the epineural sheath.This work has been supported by the Australian Research Grants Committee.