An ultrastructural study of Dirofilaria immitis infection in the Malpighian tubules of Anopheles quadrimaculatus

An ultrastructural study was conducted of the Malpighian tubules of Anopheles quadrimaculatus, both uninfected and following infection with Dirofilaria immitis. The Malpighian tubules in Anopheles are composed of primary and stellate cells. The primary cells are the predominant cell type and are characterized by the presence of membrane-bound, intracellular, mineralized concretions and large apical microvilli containing mitochondria. Following the infective blood meal, the microfilariae enter the primary cells of the Malpighian tubules and reside in the cytoplasm in a clear zone without a delimiting membrane. Cells in infected tubules differ from those in uninfected tubules in that the membranes of the vacuoles surrounding the concretions are disrupted in many specimens. The apical and basal cell membranes and the mitochondria associated with these are not disrupted during the first 6-8 days of infection. These observations differ sharply from those previously described in Aedes taeniorhynchus infected with D. immitis. The observations are consistent with the hypothesis that the extended transport capacity observed in previous physiological studies of An. quadrimaculatus infected with D. immitis are dependent on the prolonged normal ultrastructure of the apical microvilli, mitochondria, and basal membranes.     

The cytology of apocrine sweat glands

Summary The secretory cells of human apocrine sweat glands are characterized by the presence of large mitochondria, which have scant cristae and an electron opaque matrix. Electron opaque granules, presumed to be a keratin, are present in the supranuclear cytoplasm. The keratin granules contain histochemically demonstrable SH, SS, and lipid groups, and they have a typical appearance by electron microscopy. Secretory vacuoles containing mucopolysaccharide are formed in association with the Golgi apparatus and are liberated from the cytoplasm by a merocrine mechanism. The duct cells of human apocrine glands contain few organelles and are presumed to alter the secretion little, if at all. The term apocrine should be retained, although the cells secrete by a merocrine mechanism, and used in a generic sense to designate a defined group of epidermally derived glands.This investigation was supported in part by Public Health Service research grants GM-03784 and GM-10102 from the Institute of General Medical Sciences.     

STUDIES ON SMALL INTESTINAL CRYPT EPITHELIUM : I. The Fine Structure of the Crypt Epithelium of the Proximal Small Intestine of Fasting Humans

Small intestinal crypt epithelium obtained from normal fasting humans by peroral biopsy of the mucosa was studied with the electron microscope. Paneth cells were identified at the base of the crypts by their elaborate highly organized endoplasmic reticulum, large secretory granules, and small lysosome-like dense bodies within the cytoplasm. Undifferentiated cells were characterized by smaller cytoplasmic membrane-bounded granules which were presumed to be secretory in nature, a less elaborate endoplasmic reticulum, many unattached ribosomes and, in some cells, the presence of glycogen. Some undifferentiated cells at the base of the crypts contained lobulated nuclei and striking paranuclear accumulations of mitochondria. Membrane-bounded cytoplasmic fragments, probably originating from undifferentiated and Paneth cells, were frequently apparent within crypt lumina. Of the goblet cells, some were seen actively secreting mucus. In these, apical mucus appeared to exude into the crypt lumen between gaps in the microvilli. The membrane formerly surrounding the apical mucus appeared to fuse with and become part of the plasma membrane of the cell, suggesting a merocrine secretory mechanism. Enterochromaffin cells were identified by their location between the basal regions of other crypt cells and by their unique intracytoplasmic granules.     

Ultrastructure of the sexual segments of the kidney in male and female lizards,Cnemidophorus l. lemniscatus (L.)

Summary Kidneys of adult male and female lizards were studied by electron microscopy, in order to understand the ultrastructure of the collecting duct and a differentiated part thereof, the sexual segment, which is an important accessory sexual organ. First portion of sexual segment in males: The cells are filled with large secretory granules of a wide range of opacities. The granular endoplasmic reticulum is abundant; basal formations of superimposed flat cisternae are frequent. Distended vesicles and microvesicles prevail in the supranuclear, well developed Golgi apparatus. Evidences indicate that secretion of these cells is holocrine. Second portion of sexual segment in males: All of the secretory granules are apical in location and relatively electron-opaque; they show a denser core. This core is formed by a substance which, after lying in contact with ribosomes, enters the secretory vesicles of the highly developed Golgi apparatus. A lighter substance is then condensed around it. The secretion of the granules is merocrine. The granular endoplasmic reticulum is very abundant in these cells, but basal ergastoplasmic formations are lacking. Sexual segment in females: The cells show features similar to those of the male first portion, but they are smaller. Undifferentiated collecting duct: Most of the cells are mucigenic. They have small ovoid, apical secretory granules. The density of the granules varies from cell to cell; when they are electron-lucent, they exhibit laminar or dotted opaque figures. Moderately developed Golgi apparatus and granular endoplasmic reticulum, as well as elongated mitochondria, occur in mucigenic cells. Intercalated among the latter are non-secretory cells. They have very abundant mitochondria, numerous microvilli, many pinocytic and smooth-membrane vesicles, whereas the organelles participating in synthetic processes are poorly developed; their function is most likely related to active solute transport.     

Cytochemical and ultrastructural characteristics of the lining epithelium of the distal part of the epididymis in hamsters (Mesocricetus auratus)

In the terminal segment of the hamster epididymidis there was some evidence of micro-merocrine protein secretion a the level of the principal cells and clear evidence of granular secretion in the light cells, presumable of glycoproteins. The PAS and protein cytochemistry reactivities observed in both these cells, of the ductus epithelial lining, but especially in the light cells, are suggestive of mucopolysaccharides and protein complexes synthesis and secretion. This secretion is carried out to the epididymal epithelium from the lumen and luminal content. A complex of small vacuoles and vesicles appeared to form from the Golgi complex is showed in the principal cells. It was suggested that this complex may represented merocrine secretory vacuoles and vesicles in these cells. Dense granules, at the TEM level, are observed in all the cytoplasm of the light cells, with correspondence to similar PAS-positive granules observed in these cells, at the light microscope level. These granules, at the TEM level, are actually secreted to the epididymal duct lumen, by the apical cytoplasms of the light cells. Signs of absorption were suggested to the principal and light columnar cells through the ultrastructural observations of micropinocytosis, apical multivesicular bodies or great membrane-bounded vacuoles in the adluminal cytoplasms.     

Das Epithel der Tuba uterina des Neugeborenen Elektronenmikroskopische Befunde

Summary An electron microscopical study of the epithelium of the uterine tube was carried out in the newborn. Among the epithelial cells at least two morphologically well defined types can be distinguished: ciliated and non-ciliated cells.The ultrastructure of the cilia and related structures corresponds to what has been described by other authors in ciliated cells of various organs and of different species. Near the basal bodies of the cilia there is a concentration of vesicular mitochondria, which is thought to be evidence of a high metabolic activity in this region of the cell. Large opaque granules in the supranuclear zone of the ciliated cells are, it is suggested, paraplasmatic inclusions, perhaps supporting material for the ciliokinetic processes. There was no evidence of a secretory function of the ciliated cells.Among the non-ciliated cells, which in general show a straight lined luminal border with few microvilli, there are some cells containing dense granules, which are distributed throughout the cytoplasm and concentrated in the luminar side of the cell. The apical parts of these cells are protruding and sometimes digitated or branched; they contain accumulated granular materials and are separated from the rest of the cell after the formation of an intracellular plasmalemma. A similar detachment was found in an other cell type, but here the protruded apical parts of the cells are edematous and do not contain any visible secretory materials. It is uncertain if the detached cytoplasmic substances form a part of a specific secretory product; there are no secretory granules within the cytoplasm. On the contrary, the detachment of cytoplasmic parts may only accompany the excessive proliferation of cells which takes place during this period of growth.     

Invaginated apical vacuoles in the cells of the proximal convoluted tubule in the rat kidney

Summary Following perfusion fixation of the rat kidney with glutaraldehyde the proximal tubule cells display small apical vacuoles, large apical vacuoles, and apical vacuoles in which a part of the limiting membrane is invaginated into the vacuole. These invaginated apical vacuoles occur more frequently in proximal convoluted tubules than in proximal straight tubules. One tubular cell may contain apical vacuoles of different sizes and stages of invagination, ranging from larger vacuoles with a wide lumen and a small area of invaginated membrane to smaller elements with no apparent lumen and a large area of invaginated membrane. Invaginated apical vacuoles lie either singly in the cytoplasm or close to the membranes of other apical vacuoles, but never in contact with the cell membrane or the membranes of lysosomes, endoplasmic reticulum, Golgi apparatus, mitochondria and peroxisomes.These findings suggest that the invaginated apical vacuoles are not fixation artifacts, but rather develop in living state in cells of the proximal tubule from spherical endocytotic elements.Supported by the Deutsche Forschungsgemeinschaft (SFB 105)     

An electron microscopic study of the salivary gland of Rhynchosciara angelae

Summary The structure of the salivary gland of the dipteran insect Rhynchosciara angelae in a defined stage of the larval development, characterized by the synthesis and storage of secretion product, is described. Observations were made with both Nomarski optics and electron microscopy. Filiform projections extending into the lumen of the gland were observed in the apical portion of the cells. At the basal region junctions, characterized as hemidesmosomes, were observed between the membrane of the cell and the basal lamina. The plasma membrane presents numerous infoldings into the cell increasing considerably the surface area at this region. Throughout the cytoplasm of the gland cells numerous mitochondria, Golgi complexes, microtubules, profiles of endoplasmic reticulum, secretion granules and glycogen granules were observed. Carbohydrates were detected on ultrathin sections by using the periodic acid-silver methenamine and the periodic acid-thiosemicarbazide-silver proteinate techniques.     

Fluorescence Microscopic Observations on the Distribution Patterns of Actin Filaments in Stigma Cells of Eichhornia crassipes

The distribution patterns of actin filaments in the non-fixed stigma of Eichhornia crassipes (Mart) Solms were examined with fluorescence microscopy by using FITC-phalloidin as fluorescence probe. In the finger-like papillae the distribution patterns of actin filament varied greatly with actin localization. In the basal region fusiform bodies emitting intense fluorescence were scatteredly distributed. In the middle zone(often occupied by dense cytoplasm) a network composed of numerous actin filaments appeared. These filaments of various diameters lay more or less parallelly to the cell axis, extending upwards and gradually merging into some thick dense bundles . In the apical region a few actin filaments sparsely and longitudinally distrubuted in the subcortical cytoplasm,and diffuse fluorescence often appeared in the spheroidal protrusion. Furthermore,an actin network composed of very thin filaments in the periplasm of the cell was observed ;the constituent filaments were in helical arrangement and often branched and interconnected. Considering possible relationship between the actin configurations and the physiological activities and functions of the stigma cells, it is proposed that the active cytoplasmic streaming, the translocation of solutes towards the apical region ,the active secretion of exudate from the spheroidal protrusion and maintaining of the structural integrity and stability of periplasm, all these might be considered as certain physiological events being affected or regulated by the actin filament patterns described above.     

Electron microscopic study of the anterior midgut in Cenocorixa bifida Hung. (Hemiptera: Corixidae) with reference to its secretory function

The epithelium of anterior midgut of adult Cenocorixa bifida was examined with light and electron microscopy. The folded epithelium is composed of tall columnar cells extending to the lumen, differentiating dark and light cells with interdigitating apices and regenerative basal cells in the nidi surrounded by villiform ridges that penetrate deeply into the epithelium. The columnar cells display microvilli at their luminal surface. Microvilli lined intercellular spaces and basal plasma membrane infoldings are associated with mitochondria. These ultrastructural features suggest their role in absorption of electrolytes and nutrients from the midgut lumen. The columnar cells contain large oval nuclei with prominent nucleoli. Their cytoplasm is rich in rough endoplasmic reticulum, Golgi complexes and electron-dense secretory granules indicating that they are also engaged in synthesis of digestive enzymes. The presence of secretory granules in close proximity of the apical plasma membrane suggests the release of secretion is by exocytosis. The presence of degenerating cells containing secretory granules at the luminal surface and the occurance of empty vesicles and cell fragments in the lumen are consistent with the holocrine secretion of digestive enzymes. Apical extrusions of columnar cells filled with fine granular material are most likely formed in response to the lack of food in the midgut. The presence of laminated concretions in the cytoplasm is indicative of storageexcretion of surplus minerals. The peritrophic membrane is absent from the midgut of C. bifida.     

The cytology of apocrine sweat glands

Summary The apocrine sweat glands of cat and monkey have been studied by light and electron microscopy. The apocrine secretory cells of the cat are columnar cells with prominent apical cytoplasmic caps extending into the gland lumen beyond the zone of terminal bars (zonulae occludentes). Many secretory vacuoles are present in the cytoplasm, and they contain acid mucopolysaccharide demonstrable by light microscopy. These secretory vacuoles arise from prosecretory vacuoles in the region of the Golgi apparatus and are liberated from the apical cell surface as in other merocrine cells. The apocrine duct is short and the cells have scant mitochondria. The apocrine secretory cells of the monkey have secretory vacuoles similar to those of the cat but are fewer in number. The monkey apocrine cells also contain unidentified bodies similar to those seen in Langerhans cells of the epidermis. These cells liberate secretory vacuoles in a merocrine manner. Apocrine or decapitation secretion is regarded as an artifact.This investigation was supported in part by United States Public Health Service research grants GM-03784 and GM-10102 from the Institute of General Medical Sciences.     

Epithelial ultrastructure of the midgut of the horsefly, Hybomitra schineri (Tabanidae)

The study of the midgut of Hybomitra schineri by means of electron microscopy has shown that epithelial cells are of cylindrical shape. According to the electron density of cytoplasm the cells can be arranged into three subtypes. The apical surface of all the cells is covered by microvilli with filamentous glycocalyx. The peritrophic membrane of the 1st type is formed in females only during the blood digestion. Two types of secretion of digestive enzymes (merocrine and macroapocrine ones) were found, the latter being prevalent at the carbohydrate feeding.     

Respiratory portion of the lungs of intact BALB strain mice

Four male mice (1-month-old) of BALB strain have been studied. Three types of cells participate in formation of cellular lining of the terminal branchioles: ciliated, Clara cells and villose cells which are included in the neuroepithelial bodies composition. Clara cells are numerous and they are similar in their ultrastructural organization, they contain a great number of polymorphous secretory granules, single mitochondria and a poorly developed endoplasmic reticulum. A comparatively large number of pores of Khone are revealed: there are 4-8 pores per one alveole, and one pore is situated on 197.4 mcm2 of the alveolar surface. Alveolocytes of the second type of make the main actively secreting cell population of the alveolar passages and alveoles. Simultaneously, at the state of secretion there are 76% of the cells. The secretion of alveolar surfactant is realized by means of merocrine exocytosis. Relative volumetric fraction of mitochondria in alveolocytes of the II type comprises 12% and that of "cytophospholiposomes" (osmiophilic laminar bodies)--11%.     

Development of secretory activity in the seminal vesicle of the male migratory grasshopper,Melanoplus sanguinipes (fabr.) (Orthoptera : Acrididae)

This paper describes the ultrastructure of the seminal vesicle and the isoelectric focusing patterns of its secretion during sexual maturation and after allatectomy in Melanoplus sanguinipes (Fabr.) (Orthoptera : Acrididae). In epithelia from seminal vesicles of newly fledged males, the rough endoplasmic reticulum is well developed, and Golgi complexes are elaborate, which indicates the gland is metabolically active. The cells also contain large glycogen deposits and the lumen microvilli are well differentiated. These ultrastructural features are more dominant in 24-hr-old adults where the cytoplasm is clearly differentiated into basal and apical regions. Basally, the cytoplasm is dominated by rough endoplasmic reticulum, large Golgi complexes, glycogen deposits and numerous mitochondria, while the apical cytoplasm is filled with large secretory and/or lysosomal vesicles. Between days 3 and 7, the ultrastructural features change little other than the rough endoplasmic reticulum cisternae, which become vesicular. Analysis by isoelectric focusing shows that the amount of secretory protein increases with age until day 3, at which time the gland contains its full complement of secretion. In seminal vesicles from allatectomized insects, ultrastructural features of cells and isoelectric focusing patterns of the secretion arc identical to those from normal males.     

Evidence for intrarenal kallikrein storage during chromate-induced acute renal failure in rat

Summary During the course of chromate-induced acute renal failure (ARF), urinary kallikrein excretion (UKE), a serine protease of distal tubule origin in the normal animal was decreased but tissue kallikrein concentration (TK) was increased, suggesting intracellular accumulation. Severe morphological lesions were observed in proximal tubular cells which showed brush border damage, numerous vesicles, necrosis and liquefaction of cytoplasmic material. Less marked changes were also present in distal tubules: large apical vacuoles and swollen mitochondria. Compared to normal rats, using the peroxidase-anti-peroxidase (PAP) method for light microscopy, greater kallikrein immunoreactivity was detected along the apical pole in distal tubules, on the membrane and in the cytoplasm as well as in the glomerulus. By immunoelectron microscopy, kallikrein was found in the connecting apical area, along the luminal, basolateral and basement membranes, in some vesicles, in Golgi apparatus and on ribosomes bound to endoplasmic reticulum. In the glomerulus, kallikrein was observed along the luminal surface of endothelial cell. After 14 days a progressive recovery of renal function, tissue morphology and UKE towards control values was observed. The presence of immunoreactive kallikrein in the glomerulus observed only during ARF confirmed the previous demonstration of kallikrein mRNA in the glomerulus. The cellular accumulation results more likely from a dysfunction of a general secretory mechanism due to cell membrane alteration than from a specific inhibition of kallikrein production and secretion.     

Spermatogenesis and sperm structure of Acerella muscorum, (Ionescu, 1930) (Hexapoda, Protura)

The general organization of the male genital system, the spermatogenesis and the sperm structure of the proturan Acerella muscorum have been described. At the apex of testis apical huge cells are present; their cytoplasm contains a conventional centriole, a large amount of dense material and several less electron-dense masses surrounded by mitochondria. Spermatocytes have normal centrioles and are interconnected by cytoplasmic bridges. Such bridges seem to be absent between spermatid cells and justify the lack of synchronization of cell maturation. Spermatids are almost globular cells with a spheroidal nucleus and a large mass of dense material corresponding to the centriole adjunct. Within this mass a centriole is preserved. Mitochondria of normal structure are located between the nucleus and the plasma membrane. The spermatids are surrounded by a thick membrane. No flagellar structure is formed. Sperm have a compact spheroidal nucleus, a large cap of centriole adjunct material within which a centriole is still visible. A layer of mitochondria is located over the nucleus. The cytoplasm is reduced in comparison to spermatids; many dense bodies are interspersed with sperm in the testicular lumen. The sperm are small, immotile cells of about 2.5-3 μm in diameter.     

Simultaneous apocrine and merocrine secretion in the rat coagulating gland

The coagulating gland of the rat synthesizes two prevalent secretory proteins (transglutaminase and 115 K) that are discharched in a different manner, one being secreted in an apocrine fashion (transglutaminase) and the other one in a merocrine way (115 K). Differences in the intra- cellular pathway and the release of either protein were studied using immunofluorescence on semithin sections, immunoelectron microscopy of preembedding-processed chopper sections and postembedding-processed ultrathin sections of rat coagulating gland. Immunohistochemical staining using an anti-transglutaminase antibody resulted in dense labeling of the cytoplasm of secretory cells and their apical blebs, whereas the cisternae of the rough endoplasmic reticulum and the Golgi apparatus were completely unlabeled. When, on the contrary, the anti-115 K antiserum was used, dense labeling of the cisternae of the rough endoplasmic reticulum, the Golgi apparatus, and the secretory granules was seen. Intraluminal secretion was also labeled, but the secretory blebs remained unlabeled. Our findings show that, in the coagulating gland of the male rat, the two secretory proteins studied are processed in parallel, but at completely different intracellular pathways. They are released via different extrusion mechanisms. Transglutaminase is synthesized outside the endoplasmic reticulum, reaches the apical cell pole by free flow in the cytoplasm, and is released via apocrine blebs, the membranes of which appear to be derived from the apical plasma membrane. The protein 115 K, on the other hand, follows the classic route, being synthesized within the cisternae of rough endoplasmic reticulum, subsequently glycosylated in the Golgi apparatus, and released in a merocrine fashion. The mutual exclusion of the two secretory pathways and the regulation of the alternative release mechanism are still unresolved issues.     

Ultrastructure of langur monkey epididymidis prior to and following vasectomy and vasovasostomy.

The ultrastructural changes in langur monkey epididymis prior to and following vasectomy or vasovasostomy were studied. The epididymal epithelium of the intact langur monkey was found to consist mainly of principal cells and basal cells and frequently apical or mitochondria rich cells were found. Besides these cells intraepithelial lymphocytes were also a consistent feature of the epididymal epithelium. Principal cells identified by means of the tuft of the stereocilia on their apical surface, bear well developed Golgi bodies, endoplasmic reticulum, vesicles, vacuoles and multivesicular bodies. This suggests their active involvement in absorption and secretion. Basal cells present at the base of the lamina bear a few cellular organelles and strong interdigitations with the adjacent cells. Apical or mitochondria rich cells were characterized by clusters of mitochondria in the apical region of the cell and few microvilli on their apical surface. Lymphocytes with a large nucleus and a pale rim of cytoplasm were also found at the base of the epithelium. Secretory and absorptive functions of principal cells of the epididymal epithelium were found to be increased after vasectomy, as indicated by bulging of the apical portion of the principal cells and membrane bound structure in the lumen. An extensive increase in the number of lysosomes, vesicles and vacuoles was also observed. An increase in the number of macrophages with spermatozoa remnants in the lumen of epididymis suggests that the principal mechanism for spermatozoa disposal following vasectomy is intraluminal endocytosis by macrophages. Changes following vasectomy persisted in vasovasostomized animals even after 12 months of recanalization, which may contribute to the failure of functional reanastomosis.     

The ultrastructural investigation of the midgut in the quill mite Syringophilopsis fringilla (Acari,Trombidiformes: Syringophilidae)

The midgut of the females of Syringophilopsis fringilla (Fritsch) composed of anterior midgut and excretory organ (=posterior midgut) was investigated by means of light and transmission electron microscopy. The anterior midgut includes the ventriculus and two pairs of midgut caeca. These organs are lined by a similar epithelium except for the region adjacent to the coxal glands. Four cell subtypes were distinguished in the epithelium of the anterior midgut. All of them evidently represent physiological states of a single cell type. The digestive cells are most abundant. These cells are rich in rough endoplasmic reticulum and participate both in secretion and intracellular digestion. They form macropinocytotic vesicles in the apical region and a lot of secondary lysosomes in the central cytoplasm. After accumulating various residual bodies and spherites, the digestive cells transform into the excretory cells. The latter can be either extruded into the gut lumen or bud off their apical region and enter a new digestive cycle. The secretory cells were not found in all specimens examined. They are characterized by the presence of dense membrane-bounded granules, 2–4 μm in diameter, as well as by an extensive rough endoplasmic reticulum and Golgi bodies. The ventricular wall adjacent to the coxal glands demonstrates features of transporting epithelia. The cells are characterized by irregularly branched apical processes and a high concentration of mitochondria. The main function of the excretory organ (posterior midgut) is the elimination of nitrogenous waste. Formation of guanine-containing granules in the cytoplasm of the epithelial cells was shown to be associated with Golgi activity. The excretory granules are released into the gut lumen by means of eccrine or apocrine secretion. Evacuation of the fecal masses occurs periodically. Mitotic figures have been observed occasionally in the epithelial cells of the anterior midgut.