Biomedical subjects
Publications and source records attributed to J L Ojeda.
Duplication of the slit diaphragms between the pedicels of the visceral and parietal podocytes of glomerular cysts induced by a single intramuscular injection of methylprednisolone acetate is reported here. These changes are not accompanied by modifications of the cell coat of the podocytes.
The microanatomy of a unique type of juxtamedullary nephrons has been studied in the rabbit kidney by means of corrosion casts, scanning electron microscopy and the air cast method. The nephrons described in this paper are located in the outer stripe of the outer medulla and are the only nephrons that are not arranged radially within the kidney. They differ from other juxtamedullary nephrons in the morphology and course followed by the proximal tubule and by the close relationship that they establish with the arcuate vessels. The glomerulus of these nephrons is supplied by a short afferent arteriole that arises directly from the arcuate artery. Because of the special characteristics of these nephrons we have named them 'arcuate nephrons'. The morphology, spatial relationships and vascularization of the arcuate nephrons suggest that these nephrons differ functionally from the other juxtamedullary nephrons. Possible developmental factors responsible for the special microanatomy of the arcuate nephrons are analyzed.
The sequential changes of cell morphology and the ratio distribution of the different types of cells which exist in tubular cysts induced by methylprednisolone acetate have been studied by light, transmission and scanning electron microscopy. We have also studied the blood levels of sodium and potassium by flame photometry. In both control and cystic ducts, at the level of the outer cortex, the first intercalated cells (IC) were not observed until the 4th postnatal day. Some intermediate cell configurations were observed during the 3rd postnatal day, suggesting that some primitive principal cells (PC) are transformed into IC. Development of IC seems to be independent of both the effects of corticoids and the blood levels of potassium. The ratio distribution and the types of IC observed throughout the period studied was similar in both normal and cystic ducts. The type of IC characterized by the presence of a huge apical process, which has gone previously undescribed with either TEM or SEM, was observed in both control and cystic ducts. We propose to name these cells as cells with surface pattern type V. During the period of regression of the tubular cysts dead and migrating cells were observed closely associated with cilia of the PC. Both types of cells do not seem to represent, based in their localization and frequency, abnormal cell types of the cyst wall. Our results support the hypothesis that renal cysts are giant collecting ducts which conserve both the morphology and the function of the epithelium.
This paper presents a study of the renal vascular architecture in polycystic kidneys induced in newborn rabbits by a single injection of methylprednisolone acetate. Ink perfusion and polyester resin corrosion casts were utilized, and the vasculature was studied by light and scanning electron microscopy. Vascular alterations were observed in the two main evolutive stages of the renal polycystosis: the stage of tubular cysts and the stage of glomerular cysts. These alterations were compared with the normal vascular pattern of control kidneys. At the tubular cyst stage the sinusoidal vascular cortical plexus persisted for a long period of time and the superficial cortical glomerular tufts were poorly developed. At the glomerular cyst stage, the vascular architecture of the superficial cortex showed numerous alterations. The glomerular tufts were small and their structural pattern was affected. Frequently the hilum was very wide and the afferent and efferent arterioles were on opposite sides of the glomerular tufts. The afferent arterioles were variable in size and length. Sometimes the glomeruli showed several afferent arterioles. There were numerous cases of double efferent arterioles in the superficial glomeruli of the polycystic kidneys. Various types of aglomerular shunts were observed regardless of the cystic stage or age. These data indicate that, in addition to the cysts, the corticoid-induced polycystic kidneys showed alterations of the renal vascular architecture which are interpreted as a malformation. We suggest, on the basis of these morphologic observations, that the pathogenesis of the polycystic kidneys is not related to the vascular alterations.
The cell surface characteristics of degenerating cells and phagocytes, as well as the participation of lysosomes in the cell death process associated with the early embryogenesis of chick lens rudiment, were studied by means of scanning electron microscopy and cytochemically using the Gomori-beta-glycerophosphate method for acid phosphatase. The prospective dying columnar epithelial cells lose their apical and basal processes and become rounded. The rounded, isolated, dying cells initially show a rough surface with some cytoplasmic constrictions followed by progressive break-up into several pitted fragments. Coincident with the loss of the columnar cell shape, acid phosphatase is localized within the Golgi apparatus and autophagic vacuoles which progressively increase in size. In contrast, the isolated dying cells and fragments do not show significant acid phosphatase activity. The role of lysosomes in this degenerative process is discussed. Neighboring epithelial cells phagocytose the dead cell fragments, becoming nonspecialized phagocytes. These consist of columnar epithelial cells and free cells which have migrated from the lens epithelium. Two mechanisms of internalization are observed. The most frequent mechanism takes place in both the columnar epithelial cells and the free cells, and consists of the progressive engulfment of the fragments into craters of the cell surface. The other mechanism is only detected in the free cells and takes place by pseudopod engulfment. We suggest that both phagocytic procedures could be related to the degree of intercellular connection. The presence of phagocytic internalization by crater formation in the epithelial cells could be a mechanism preserving the epithelial stability, which is necessary for a normal morphogenesis. Small microprocesses binding the surface of the phagocyte and the fragment are present prior to the internalization process. In the lens stalk and in the space located between the ectoderm and the lens vesicle, there are some cells displaying migratory characteristics. This fact suggests that an active migration of epithelial cells from the lens stalk could account for the process of detachment of lens vesicle from the ectoderm. The free cells appear to undergo an in situ progressive degeneration.
The role of microtubules in the early development of the chick embryo heart was studied. The microtubules were disrupted by treatment of the embryos with colchicine. The embryos were divided for study into three groups: (I) before the fusion of the paired cardiac primordia; (II) before the starting of the cardiac loop, and (III) during the formation of the looping process. Colchicine did not impair the fusion of the paired heart primordia nor the acquisition of an asymmetric C-shaped form. However, the normal counterclockwise movement of the heart loop was prevented. From these results we conclude that the formation of the tubular heart and its looping are independent of the integrity of the microtubular system. Under the effects of colchicine the developing myocytes rounded up bulging into the pericardial cavity. The cell contours became scarcely discernible and the individual cell surfaces gave rise to blebs and ruffles of different sizes. In older embryos, clefts of different sizes appeared between the myocardial cells. The effects of colchicine on the pulsatile activity of the heart were recorded. These effects, as well as those on the cell surface characteristics, were found to be age dependent. The more mature the hearts were, the more resistant to colchicine they became. The developmental significance of the results reported here is discussed.
A simple procedure for studying the microanatomy of the kidney by light microscopy is described. Specimens are dried by the critical-point method and later impregnated with a mounting medium. The retention of air within the lumen of nephrons and collecting tubules permits their visualization. The method allows the observation of renal microanatomy without the distortions produced by microdissection or the loss of structural relationships among different kidney components. It also permits observation of the same specimen by both light and scanning electron microscopy.
The spatiotemporal pattern of morphogenetic cell death during the early development of the chick retina was studied by means of the neutral red vital staining and light microscopy. A modification of the conventional procedure of vital staining, which consisted of the injection of the dye into the neural tube lumen, was used for this purpose. In addition to the two areas of cell death known from previous literature, the first located in the ventral part of the optic cup and the second located in the insertion of the optic stalk with the diencephalon, a new area of cell death was described. This third necrotic area was located in the protruding dorsal part of the optic cup rim and was present throughout the stages 15 to 18. The area consisted of dying cells, fragments and phagocytosed cells. We suggest that this dorsal area of cell death could stop the intense dorsal growth of the optic cup and/or reshape the optic cup rim. Moreover, this area may influence the production of cell degeneration in the dorsal part of the invaginating lens placode.
This paper presents a quantitative study of the position of the Golgi apparatus in the developing chick myocardium between stages 8+ and 13+. In addition we have studied the effects of colchicine on the position and structure of the Golgi apparatus. During the formation of the heart tube and loop the position of the Golgi apparatus in the myocytes situated in the vicinity of the dorsal mesocardium is related to that found in the cells of the precardiac mesoderm, but it is completely different from that found in the bulk of myocytes of the heart tube and loop. The position of the Golgi apparatus in both pre- and myocardial cells shows clear significative patterns of polarity. The possible significance of the Golgi apparatus polarity is discussed. After colchicine treatment microtubules disappear, the Golgi apparatus loses its polarization and vacuoles filled with amorphous material and/or collagen fibrils are observed. A possible role of the microtubular system in the maintenance of the structure and polarity of the Golgi apparatus and in the intracytoplasmic transport of the cardiac jelly materials is proposed.
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This paper reports an anatomical study of the vascular supply in 60 human cerebelli from subjects of both sexes, aged between 20 and 60 years, who had died of various accidental causes. The origin, branching pattern and cortical and central distributions of the cerebellar arteries have been studied by gross dissection, vascular injection and corrosion procedures. Variations of the normal pattern of the cerebellar arteries in both origin and cortical distribution are frequently found, the anterior inferior and the posterior inferior cerebellar arteries being the arteries showing the highest number of variations. The anomalies most frequently found are duplication in the origin, abnormal origin, and the presence of hypoplastic vessels. The cerebellar nuclei were supplied by the rhomboidal artery, a collateral branch of the superior cerebellar artery. The formation of a precise segmentary vascular pattern into the dentate nucleus by branches arising from the rhomboidal artery is described. The results are discussed in the light of other anatomical studies.
Newborn rabbits were injected with methylprednisolone acetate to induce polycystic kidneys. Two major types of cysts were observed: tubular cysts formed by the dilation of collecting tubules and glomerular cysts formed by the dilation of Bowman's capsular space. We examined the structure and developmental changes of the glomerular cysts of rabbits aged 2 to 75 days. Two types (I and II) of fully developed glomerular cysts were observed. Most were type I, having one small glomerulus and a parietal layer composed entirely of podocytes. Type II had one or several small glomeruli and a parietal layer composed partially of podocytes. In both types I and II cysts, the podocytes in the parietal layer were connected to various structures surrounding the cysts by a basal lamina. These cysts were first detected in the early postnatal stages. During the S-shaped body stage, the presumptive parietal layer was composed of simple columnar cells in contrast to the flat cells of normal S-shaped bodies. In the following stages, Bowman's capsular space was dilated, and podocytes were in the process of differentiation. The sequence of differentiation of the parietal podocytes was similar to that in the visceral layer in normal conditions. These data indicate that the differentiation and maturation of podocytes are not dependent upon the endothelial capillary factors. We hypothesized that an inhibitory factor that stabilizes the phenotype of the parietal cells under normal conditions is absent under conditions that cause glomerular cyst formation.
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A quantitative evaluation of the positional changes of the Golgi apparatus during the invagination of the lens placode and the presumptive neural retina of the chick embryo was carried out by silver impregnation. The Golgi apparatus is predominantly polarized in the apical process of the elongated interphasic cells; however, basal and lateral positions are also present. When the nuclei are located close to the luminal surface, basal and lateral positions increase significantly showing that a loss of Golgi apparatus polarization takes place, associated with the mitotic cycle. At the beginning of the invagination of lens and neural retina rudiments, a marked shift in orientation occurs between lateral and apical positions of the Golgi apparatus; this is associated with the nuclei located close to the luminal surface. The possible significance of these results is related to some processes concerning the invagination of these rudiments, such as interkinetic nuclear migration and secretion of extracellular materials.
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The hearts of chick embryos of stages 9-13 were subjected to SEM, TEM and histochemical studies to ascertain possible regional differences in the structure and composition of the cardiac jelly. Two distinct regions, the cardiac jelly filling the space located between the myocardium and the endocardium (MECJ) and the cardiac jelly filling the dorsal mesocardium (EECJ), were distinguished by their structural and histochemical properties. MECJ is formed by amorphous and fibrillar material arranged between the endocardial and myocardial layer. The amount of its components increases when cetylpyridinium chloride is introduced into the fixative, and it appears intensely stained by ruthenium red and alcian blue at low concentrations of MgCl2. The amount and arrangement of its components increase during the beginning of the looping process of the heart tube. The EECJ is very rich in ruthenium-red-positive basal-lamina-like material and the addition of cetylpyridinium chloride to the fixative does not modify its appearance. It also appears poorly stained by alcian blue at low concentrations of MgCl2 and its arrangment undergoes modifications closely associated with the events of endocardial fusion. The possible significance of these results in the early morphogenesis of the heart is discussed.
A metaplastic transformation of the parietal layer of the Bowman's capsule into podocytes is described in glomerular cysts induced by postnatal injection of methylprednisolone acetate to rabbits. Both the anomalous location of podocytes and their utility for the study of the biology of the cells are discussed.
Phagocytosis by neuroepithelial cells independent of the presence of pseudopodes is observed as the main mechanism of elimination of physiologically degenerating cells during the early development of the retina in the chick embryo.