Immunolocalization of plakoglobin in endothelial junctions: identification as a special type of Zonulae adhaerentes

We have characterized the junctions between endothelial cells of diverse blood vessels at the light and electron microscopic level using various antibodies to plakoglobin (polypeptide Mr 83,000) and vinculin. Endothelial cells from fenestrated and non-fenestrated capillaries to large arteries are connected to each other by extended junctions that are coated on their cytoplasmic face by plaques of loosely matted filamentous material that form a continuous belt system along the cell circumference. These plaques are devoid of desmosome-specific proteins such as desmoplakin(s) and desmoglein, but contain plakoglobin. Immunofluorescence microscopic reactions of these regions with vinculin antibodies have also been observed, although they are much weaker and less consistent. This composition, together with their association with actin microfilaments, classifies this extended plaque system as Zonulae adhaerentes. Our results also show that such endothelia may be distinguished from truly epithelial cells by the absence of desmosomes and intermediate filaments of the cytokeratin type. The relationship of the various kinds of adhering junctions and the physiological importance of these junctions are discussed.     

A blood-brain barrier without tight junctions in the fly central nervous system in the early postembryonic stage

Summary The anatomical basis of the vertebrate blood-brain barrier is a series of tight junctions between endothelial cells of capillaries in the central nervous system. Over two decades ago, tight junctions were also proposed as the basis of the blood-brain barrier in insects. Currently there is a growing understanding that septate junctions might possess barrier properties in various invertebrate epithelial cells. We now examine these two views by studying the blood-brain barrier properties of the early postembryonic larva of a dipteran fly (Delia platura) by transmission electron microscopy. Newly hatched larvae possess a functioning blood-brain barrier that excludes the extracellular tracer, ionic lanthanum. This barrier is intact throughout the second instar stage as well. The ultrastructural correlate of this barrier is a series of extensive septate junctions that pervade the intercellular space between adjacent perineurial cells. No tight junctions were located in either nerve, glial or perineurial cell layers. We suggest that the overall barrier might involve septate junctions within extensive, meandering intercellular clefts.     

Macrophages and Reticulum Cells in the Spleen of the Dogfish,Scyliorhinus canicula

The presence and ultrastructural features of reticulum cells and macrophages were studied in the spleen of the dogfish Scyliorhinus canicula. Three morphologically distinguishable regions of the spleen were identified: the white pulp, the red pulp and the ellipsoids. In all three, the splenic parenchyma was a meshwork supported by reticulum cells and fibres. Reticulum cells in both the white and the red pulp are irregular elements, the processes of which are joined by cell junctions and embrace developing reticular fibres. The ellipsoids of the dogfish spleen are terminal branches of the splenic arteries of the white pulp, with a sheath consisting of reticulum cells, reticular fibres, ground substance, macrophages and occasional lymphocytes. Isolated melanomacrophages also occur in the ellipsoid walls as well as in the red pulp. In both the white and the red pulp phagocytic reticulum cells, and macrophages appear frequently forming cell associations with surrounding blood cells, mainly lymphocytes. The functional significance of the ellipsoids and the cell-cell clusters of the white and the red pulp is discussed in relation to the immune capacities demonstrated in elasmobranchs.     

鲤鱼和鲫鱼脾脏显微结构和亚显微结构的研究

鲤鱼和鲫鱼的脾脏中都没有小梁,其红髓和白髓是混合的。脾脏中都有椭圆体,其末端向脾髓开放。脾髓的纤维网眼中缺乏血管壁,椭圆体毛细血管中的血液可直接流入脾髓网状结缔组织的腔隙中。腹腔注射墨汁的鲫鱼,2小时后即可在椭圆体的巨噬细胞中看到碳粒的积累,可见脾脏的过滤作用主要在椭圆体中进行。在注射墨汁的鲫鱼脾脏中,黑色素巨噬细胞中心比未经注射鱼的脾脏明显,且数量增多,它和哺乳动物淋巴结和脾脏中的生发中心结构和功能都不相同。       

Cytoplasmic filaments in the endothelial cells of the sheathed capillary: an ultrastructural and immunocytochemical study in the pig spleen.

Cytoplasmic filaments of the endothelial cells of sheathed capillaries in the pig spleen were identified and their ultrastructure was studied. Two types of cytoplasmic filaments were found: intermediate filaments (diameter: 10 nm) which filled most of the interior of the cells, and thin filaments (diameter: 5 nm) which were located just beneath the cell membrane and filled the lateral cytoplasmic processes. In immunocytochemical preparations, the intermediate filaments were positive for vimentin and desmin, and were negative for keratin. Staining of the thin filaments with heavy meromyosin resulted in arrowhead formations. These observations suggest that the intermediate filaments maintain the cytoarchitecture, possibly protecting the cell from structural alterations induced by blood pressure changes. Concurrently, thin filaments may facilitate the passage of red blood cells and blood platelets through the interendothelial fenestrae of the sheathed endothelial cell to the reticular meshwork in the capillary sheath.     

Structure of the spleen of the sea bass (Dicentrarchus labrax): A light and electron microscopic study

The spleen of sea bass (Dicentrarchus labrax) is composed mainly of red pulp, whereas the white pulp is poorly developed. The red pulp consists of clear reticular cells intermingled with blood cells, sinusoids, and melanomacrophage centers (MMCs). The MMCs are enclosed by an interrupted connective tissue capsule and show some areas in continuity with the adjacent pulp. The MMCs are formed by the association of free macrophages that have phagocytosed some blood cells. Sparse white pulp is diffuse, forming a cuff around the pulp arteries and MMCs, or occurring in small groups between the splenic cords. A longitudinal artery and vein, lying side by side, extend the length of the spleen. Frequently the capillaries are surrounded by a sheath of macrophages or ellipsoids. These macrophages may contain erythrocytes in varying degrees of degradation. Lymphopoiesis and plasmapoiesis occur in the sparse lymphold areas. Abundant plasma cell groups may indicate the presence of antibody production.     

The equine spleen: an electron microscopic analysis

The capacity of the equine spleen to store and rapidly release as much as half the circulating blood volume after adrenergic stimulation depends upon the size of the spleen, its muscular capsule, and the distinctive structure of its red pulp. The unit, or lobule, of red pulp is a cylinder of pulp spaces organized in a reticular meshwork, supplied by a peripheral ring of arterial capillaries, and drained by a central venule. Reticular cells, which make up the meshwork of the pulp, contain an extraordinarily large complement of microfilaments and intermediate filaments and are richly innervated by nerves containing both dense and lucent core vesicles typical of adrenergic nerves. The wall of the pulp venule contains large apertures. The capacious red pulp would thus appear capable both of large-scale blood storage and, by the contractile adrenergic innervated reticulum and open venous vasculature, of rapid expression of stored blood into the circulation. Antigen-presenting cells are present not only in B and T cell zones in white pulp but in the periarterial macrophage sheath of red pulp as well. The periarterial macrophage sheath is one of the first sites of antigen capture, and the presence of these cells confers on it an immunological role.     

Ultrastructural observations at pineal gland capillaries in four rodent species.

The fine structure of the capillaries of the pineal glands of the rat, mouse, chinchilla, and ground squirrel were investigated. The pineal endothelial cells in the rat, mouse and ground squirrel were often composed of attenuated cytoplasmic portions which contained numerous fenestrations, in contrast to pineal capillaries in the chinchilla which were lined by thick non-fenestrated endothelial cells. Marked morphological differences were also apparent in terms of the types of vesicles within the cytoplasm and abutting on the cell surface of pineal endothelial cells from the various species investigated. The interendothelial junctions exhibited remarkable species differences with the chinchilla pineal possessing typical tight endothelial junctions while those in the rat, mouse and ground squirrel lacked such endothelial cell associations. Generally, capillary lining cells in the chinchilla pineal resembled similar cells within the brain, while endothelial cells in pineal glands of rat, mouse and ground squirrel were more typical of those found in other endocrine organs. Species differences in the structure of the pineal capillaries may represent physiological differences as well.     

Ultrastructure of the jugular body of Rana pipiens

Summary The jugular bodies in adult Rana pipiens, are surrounded by a capsule of mesothelium and connective tissue, and their parenchyma consists of cell cords arranged in a sinusoidal network. The cell cords are formed by irregular reticular cells, showing numerous filaments and joined together by zonulae adhaerents. The intercellular spaces are filled by reticular fibres and free cells. These latter are small and medium lymphocytes, lymphoblasts, and developing and mature plasma cells. Additionally, free macrophages, neutrophils and acidophils also occur. Sinusoidal blood vessels show thin walls with numerous filaments and pinocytotic vesicles. They exhibit a discontinuous basement membrane, and tight junctions frequently occur between endothelial cells. Occasionally, lymphatic vessels are found and the innervation is principally vasomotor, although nerve endings appear remarkably near reticular cells and lymphocytes. The jugular bodies of adult R. pipiens are plasma cell and antibody-forming organs, whose functional significance is discussed in relation to their ultrastructural organization.     

The vasculature of the rat embryo: an electron microscope study

The ultrastructure of portions of the arterial and venous systems of the 11.5 day old Wistar rat embryos has been studied by scanning and transmission electron microscopy. The vessels at this stage of development are in the form of capillaries, and the arterial and venous types can be distinguished by the morphology of the endothelial cells by SEM. The endothelial cells of the arterial vessels gave prominent nuclear bulges and numerous microvilli apart from their spindle shape, whilst those of the veins appear flattened, are polygonal in shape, and have few microvilli. Transmission electron microscopy shows that the endothelial cells of the arteries and veins are identical in structure. The ultrastructure of these cells resembles that of endothelial cells at later stages of development including the adult type in that mature forms of cytoplasmic organelles are obtained. In studies on the intercellular junctions and fenestrations with lanthanum nitrate, the impression is formed that the vessels at this stage are impermeable to small molecular size particles, compared with adult capillaries. This suggests that cytoplasmic vesicles must play a major role in the transport of macromolecules in the 11.5 day embryonic vessels.     

Immunocytochemical studies of desmin and vimentin in pericapillary cells of chicken

The composition of intermediate filaments in pericytes was examined by immunofluorescent and immunoelectron microscopic labeling of frozen sections of various chicken microvascular beds in situ. Pericytes in capillaries of cardiac muscle, exocrine pancreas, and kidney (peritubular capillary) were found to contain both desmin and vimentin. In some capillaries where pericytes do not exist, cells apposed to endothelial cells--the Ito cell in the hepatic sinusoid and the reticular cell in the splenic sinusoid--were shown to contain both of the intermediate filament proteins. In contrast, podocytes and mesangial cells around renal glomerular capillaries contained only vimentin. The presence of desmin supports the hypothesis that pericytes may have a contractile apparatus similar to that of vascular smooth muscle cells. Our results also revealed that even in microvascular beds where pericytes are not found, cells having both desmin and vimentin exist next to endothelial cells and may assume similar functions to pericytes.     

Morphological study by scanning electron microscopy of the lymphatic vessels of the guinea pig

The purpose of this study was to describe the morphology of the whole lymphatic way: from capillaries to thoracic duct including cisterna chili using scanning electron microscopy and Evan's technique. We observed the lymph vascular wall that is: the endothelial surface, the muscular layer and the adventitial one. All these vessels were covered by an endothelial surface, with raised nuclei and long cell axes oriented parallel to the direction of flow. The borders between adjacent endothelial cell were often seen and open junctions were noted in lymphatic capillaries. The technique we used, permitted the removal of connective tissue by HC1 hydrolysis, so that smooth muscle cells could be examined. The latter showed a great variety of aspects and a very irregular course. The adventitial layer was thin in capillaries and became complex in thoracic duct where collagen fibers and connective elements were seen.     

Sensory innervation monitoring movement and position in the mandibular stylets of the aphid, Brevicoryne brassicae

The sensory innervation of the mandibular stylets of the aphid Brevicoryne brassicae (L.) has been examined by electron microscopy. Two groups of sensory neurones are present in the mandible. Each has two neurones, one with a short dendrite extending into the base of the mandible and ending in the base and another with a long microtubular process which extends 500 m? down to the distal tip of the mandible. The two neurones are enclosed by an ensheathing cell comparable to the trichogen cell enveloping the group of neurones innervating pegs and hairs. This ensheathing cell is supported by extensive electron-dense filaments to form a scolopale and is embedded in the mass of stylet-forming cells at the base of the mandible. The inner segments of the dendrites are anchored to the ensheathing cell by desmosome junctions. Desmosome junctions also bind the microtubular outer segments of the short and long dendrite to each other. There is no evidence of a dendritic sheath enclosing the distal portion of the short dendrite which ends while still in the extracellular space within the ensheathing cell. The microtubular process of the long dendrite extends down the lumen of the mandible enclosed by a close-fitting extracellular sheath which penetrates and is attached to the cuticular wall of the mandible tip. Distally this sheath is thickened on one side. Deflection of the mandible would therefore deform the dendritic membrane asymmetrically because the thin walls of the sheath would bend more than the thick walls. This would exert an unequal mechanical strain on the dendritic membrane which could result in depolarization in response to deflection in a particular direction. The arrangement of the dendrites and their sheaths within the mandible is such that deflection to the right would distort one dendrite in the same way as deflection to the left would distort the other.     

The structure of lymphatic capillaries in lymph formation.

The lymphatic vascular system consists of endothelial lined vessels which begin as blind-end tubes or saccules that are located within the connective tissue areas. This system serves as a one-way drainage apparatus for the removal of diffusible substances as well as plasma proteins that escape the blood capillaries. If permitted to accumulate, these escaped components would deplete the circulatory system of its plasma colloids and disrupt the balance of forces responsible for the control of fluid movement and the exchange of gases and fluids across the blood vascular wall. The lymphatic capillaries are strategically placed and anatomically constructed to permit a continuous and rapid removal of the transient interstitial fluids, plasma proteins, and cells from the interstitium. Structurally the lymphatic capillaries consist of a continuous endothelium that is extremely attenuated over major aspects of its diameter, except in the perinuclear region which bulges into the lumen. These vessels lack a continuous basal lamina and maintain a close relationship with the adjoining interstitium by way of anchoring filaments. The adjacent cells are extensively overlapped and lack adhesion devices in many areas. When electron-opaque tracers are injected intravenously (i.e., horseradish peroxidase and ferritin), subsequent electron microscopic examination of tissues reveals the presence of tracer particles within the interstitium and the lymphatic capillary lumen. These particles gain access into the lymphatic capillaries via two major pathways: 1) the intercellular clefts of patent junctions and 2) plasmalemmal vesicles (pinocytotic vesicles). Another salient feature of the lymphatic endothelial cell includes the presence of numerous cytoplasmic filaments, which are similar in morphology to the actin filaments observed in a variety of cell types. The ultrastructural features of the lymphatic capillaries are discussed in relation to their role in the removal of interstitial fluids and particulate matter, and in the formation of lymph.     

Tight junction of sinus endothelial cells of the rat spleen

The fine structure of the tight junctions between sinus endothelial cells of the rat spleen and the permeability of such sinus endothelial cells were examined by transmission electron microscopy, using freeze-fracture, triton extraction, and lanthanum-tracer techniques. In freeze-fracture replicas, the segmented strands and grooves of the tight junctions were frequently observed on the basolateral surfaces of the sinus endothelial cells irrespective of the location of the ring fiber. There were one or two wavy-strands or grooves which were, for the most part, oriented parallel to the long cell axis thus forming networks at places. In addition, some strands or grooves were discontinuous while some networks of the junctional strands were not closed. These strands also occasionally lacked intramembranous particles in the tight junctions. The junctional strands run apicobasically at certain sites. In the vertical sections of the sinus endothelial cells treated with lanthanum nitrate, although no tight junctions were observed wherever the endothelial cells were apposed, most of them were situated on the basal part of the lateral surfaces of the adjacent endothelial cells. Several fusions of the junctional membranes were observed in a vertical section of the lateral surfaces of the adjacent endothelial cells. The intercellular spaces of the adjacent endothelial cells except for the fusion of the junctional membranes, were electron dense and the infiltration of lanthanum nitrate was found not to be interrupted by these tight junctions. Based on these observations, the molecular 'fence' and paracellular 'gate' functions of the tight junctions in the sinus endothelial cells are discussed.     

Ultrastructure of pericytes in mouse heart

The pericytes of mouse myocardium are extensively branched cells that form an incomplete layer around the endothelium of capillaries and postcapillary venules. The membranes of pericytes and endothelial cells are connected by specialized junctions. Microtubules, intermediate (10-nm) filaments and microfilaments are oriented within circumferentially-arranged cytoplasmic processes of pericytes so as partially to encircle the endothelial cylinder. The intracellular organization of these myocardial pericytes suggests that they are smooth muscle-like cells which may be capable of influencing microvascular dynamics in the heart.     

Bovine Brain Endothelial Cells Express Tight Junctions and Monoamine Oxidase Activity in Long-Term Culture

The passage of substances across the blood-brain barrier is regulated by cerebral capillaries which possess certain distinctly different morphological and enzymatic properties compared to capillaries of other organs. Investigations of the functional characteristics of brain capillaries have been facilitated by the use of cultured brain endothelial cells, but in most studies a number of characteristics of the in vivo system are lost. To provide an in vitro system for studies of brain capillary functions, we developed a method of isolating and producing a large number of bovine brain capillary endothelial cells. These cells, absolutely free of pericyte contamination, are subcultured, at the split ratio of 1:20 (20-fold increase of the cultured surface), with no apparent changes in cell morphology up to the fiftieth generation (10 passages). Retention of endothelial-specific characteristics (factor VIII-related antigen, angiotensin-converting enzyme, and nonthrombogenic surface) is shown for brain capillary-derived endothelial cells up to passage 10, even after frozen storage at passage 3. Furthermore, we showed that bovine brain capillary endothelial cells retain, up to the fiftieth generation, some of the characteristics of the blood-brain barrier: occurrence of tight junctions, paucity of pinocytotic vesicles, and monoamine oxidase activity.     

Junctions between pericytes and the endothelium in rat myocardial capillaries: A morphometric and immunogold study

Summary Pericytes are cells of mesodermal origin which are closely associated with the microvasculature. Despite numerous studies little is known about their function. We have studied the relationship between pericytes and the endothelium in rat myocardial capillaries employing ultrastructural and immunogold techniques. 14% of the subendothelial cell membrane is covered by comparatively small pericytic cell processes. About half of these processes are completely embedded in baseement membrane material, whereas the remaining half forms closer contacts with the endothelium. These contacts are devoid of anti-laminin immunogold label, a marker for basement membranes. A small fraction of these contacts has been identified as tight junctions resembling those seen between endothelial cells in capillaries of the same tissue. The remaining majority of junctions reveals a cleft of approximately 18 nm between the apposed membranes in which a succession of cleft-spanning structures can often bedetected. It was also found that pericytic processes are preferentially located close to interendothelial junctions. We suggest that the high frequency of intimate junctions between pericytes and the endothelium and the preferential localisation near paracellular clefts may have functional significance.     

Paravascular structures of the major arteries of the cerebral hemispheres (electron microscopy study)

The ultrastructure of the paravasal formations of the magistral arteries in the brain hemispheres has been studied: the paravasal nerve trunks (components of the external nerve plexus of the arteries, running outside the adventitia and surrounded with liquor) and the artery-stabilizing constructions--strings in the human being and in the dog. The human para-arterial nerve trunks possess the vasa nervorum system, presented by blood capillaries situating at the border of endo- and perineurium, by powerfully developed perineurium, which includes into its composition a system of basal membranes and perineural cells. In the canine para-arterial nerve trunks these formation are absent. In the string composition there are collagenous-fibrillar base represented by tightly packed fasciculi of collagenous fibers, oriented in parallel to the long axis of the string, and by stellate cells. Both the paravasal nerve trunks and the strings are surrounded with flattened cells of the endothelial sheath. They are very much alike with the arachnoidendothelial cells lining the subarachnoidal space.