Fine structure of the corpuscles of stannius in the toadfish.

The micro-anatomy of the corpuscles of Stannius of the toadfish, Opsanus tau, an aglomerular marine teleost, has been studied by light and electron microscopy. The corpuscles are composed of extensively anastomosed cords of epithelial cells which maintain intimate contact with blood capillaries. Most of the epithelial cells contain acidophilic granules which also show a positive reaction with the periodic acid-Schiff technique and aldehyde fuchsin. On the basis of fine structural criteria, three cell types can be recognized. The granular cells contain abundant quantities of granular endoplasmic reticulum, ribosomes, Golgi apparatus with prosecretory granules, coated vesicles, polymorphic mitochondria with lamellar cristae, filaments, microtubules, a cilium, a variety of lysosome-like dense bodies, glycogen particles, lipid droplets, secretory granules and intranuclear lipid-like inclusions. One variety of agranular cell (type I) is characterized by the total absence of secretory granules, but it contains large amounts of granular endoplasmic reticulum and ribosomes, conspicuous profiles of Golgi apparatus, coated vesicles and sometimes an abundance of glycogen. Another variety of agranular cell (type II) has poorly developed cytoplasmic organelles. The perivascular space between the capillary and parenchyma contains connective tissue cells and abundant nerve fibers. The different types of epithelial cells observed in the corpuscles of Stannius of this fish may represent functional stages of the secretory cycle in a single cell type.     

Granular,ciliated cells in the anterior pituitaries of immature rats

Summary In this communication we demonstrate a new type of ciliated cell in the pituitary gland of immature rats. Anterior pituitary glands of rats, 31 days of age, were examined by electron microscopy. Around the agranular cells, which lined small cavities, there were sparsely granulated cells with many cilia (granular, ciliated cells). Their small granules, which were distributed along the cell membrane, had limiting membranes. Their cilia were of 9+2 type with a central pair of micro tubules. It was suggested that the granular, ciliated cells might be an intermediate-type of cell for the different types of pituitary cells, which appear temporarily during pituitary ontogenesis.     

On the ultrastructure of follicles and isolated follicular granulosa cells of porcine ovary

Summary The endoplasmic reticulum in granulosa cells of primary, secondary, and small tertiary follicles of the porcine ovary is sparse and largely of the granular type.In granulosa cells of large tertiary follicles the endoplasmic reticulum shows distinct signs of proliferation. Some cells even contain whorls of endoplasmic reticulum membranes, essentially of the agranular variety.Direct continuity between endoplasmic reticulum membranes of the granular and agranular type as well as the continuous increase in agranular membranes suggest that these membranes may originate from the granular membranes.Granulosa cells isolated from large tertiary follicles by microdissection and keptin vitro show essentially the same ultrastructure as granulosa cells of intact large tertiary follicles.Some lipid droplets appear to be localized in cavities of the endoplasmic reticulum. It is suggested that the droplets contain precursor material for steroid hormone synthesis.Finally, the development of the agranular endoplasmic reticulum including the appearance of whorls in some granulosa cells of large tertiary follicles indicates that steroid synthesis may occur in such follicular granulosa cells.Read at the Meeting of the Swedish Society for Pathology in Umeå, September 25, 1965 (Bjersing, 1966).This investigation was supported by grants from the Swedish Medical Research Council (Projects No. 13 X-78-01, 12 X-78-02, and 12 X-78-03).     

Ultrastructural features of the nucleus and cytoplasm of rat trophoblast cells of the connective zone of the placenta and labyrinth

Ultrastructural organization of the rat trophoblast cells in the connective zone of placenta and labyrinth was investigated on the 12-14th days of gestation. A clear distinction was revealed in the cytoplasm ultrastructure of two cell subpopulations within the connective zone of placenta, i.e. glycogen and trophospongium cells. The former display a well defined network of long thin channels of granular endoplasmic reticulum situated mainly around the glycogen clusters. On the contrary, the latter are rich in the smooth endoplasmic reticulum but lacking glycogen accumulation. Differences in the nucleolar ultrastructure in these two cell subpopulations are not very considerable. A characteristic feature of glycogen cells is the presence of numerous round or oval small-fibrillar nucleolus-like bodies with the diameter of granules 20 nm. The trophoblast cells of the labyrinth are heavily laden with polysomes, which sometimes attach to short channels of the granular endoplasmic reticulum. Not often there occur short profiles of the agranular endoplasmic reticulum. Nucleolus-like bodies are found in all the cell types examined. This means that the nucleolus-like bodies may arise not only on the lampbrush chromosomes in the oocytes or polytene chromosomes, but also in the somatic cells which are capable of dividing mitotically.     

Vahlkampfia sp: structural observations of cultured trophozoites

Some structural observations on cultured Vahlkampfia sp. trophozoites are reported. Trophozoites are active and pleomorphic, producing large cell protrusions related to locomotion such as lamellipodia, filopodia and endocytic structures formed by hyaline cytoplasm, in which actin provides a framework that allows rapid changes in morphology. As observed by transmission electron microscopy, the cytoplasm is highly granular masking some cell organelles and the major cytoplasmic membrane systems. The structure of cell organelles such as the nucleus, endoplasmic reticulum, and digestive vacuoles is described. A common finding was the presence of 50 nm electron-dense round granules that are not limited by a membrane and that appear scattered in the cytoplasm, and whose function remains unknown. Apparently, the cell reserve material is glycogen, since complete trophozoites were positive to Schiff periodic-acid technique.     

Fine Structure of the Fat Body and its Bacteroids in Blattella germanica (Blattodea)

The abdominal fat body of the cockroach Blattella germanica contains three characteristic cell types—trophocytes, bacteriocytes and urate cells—which have been investigated by electron microscopy. The trophocytes are rich in lipid droplets of different sizes; glycogen, rough endoplasmic reticulum and mitochondria are also abundant. In females immediately after eclosion, the trophocytes contain a greater number of lipid droplets, some of which have different electron density; glycogen and cytoplasmic organelles are clearly reduced. The bacteriocytes hold rod-like and spherical bacteroids, which are encapsulated by a vacuolar membrane; they show a thin cytoplasmic membrane and an evident cell wall surrounded by a membrane-like outer envelope. The bacteroids appear to be dividing either by transverse partition or by budding. The urate cells, adjacent to the bacteriocytes, are characterized by complex urate vacuoles delimited by a double layer-structure.     

THE NORMAL FINE STRUCTURE OF OPOSSUM TESTICULAR INTERSTITIAL CELLS

The interstitial tissue of the opossum testis includes interstitial or Leydig cells, macrophages, and small cells which morphologically resemble mesenchymal cells. The latter are thought to give rise to mature interstitial cells. The most prominent feature of the interstitial cell cytoplasm is an exceedingly abundant agranular endoplasmic reticulum. This reticulum is generally in the form of a meshwork of interconnected tubules about 300 to 450 A in diameter, but occasionally it assumes the form of flattened, fenestrated cisternae resembling those of pancreatic acinar cells, except for the lack of ribonucleoprotein particles on the surface of the membranes. The interstitial cells vary considerably in their cytoplasmic density. The majority are quite light, but some appear extremely dense, and in addition usually have a more irregular cell surface, with numerous small pseudopodia. These differences may well reflect variations in physiological state. Cytoplasmic structures previously interpreted as "crystalloids" consist of long bundles of minute parallel tubules, each about 180 A in diameter, which seem to be local differentiations of the endoplasmic reticulum. The mitochondria are rod-shaped, and contain a moderately complex internal membrane structure, and also occasional large inclusions that are spherical and homogeneous. The prominent juxtanuclear Golgi complex contains closely packed flattened sacs and small vesicles. The results of the present study, coupled with biochemical evidence from other laboratories, make it seem highly probable that the agranular endoplasmic reticulum is involved in the synthesis of the steroid hormones produced by the interstitial cell. This finding therefore constitutes one of the first functions of the agranular reticulum for which there is good morphological and biochemical evidence.     

Mutagenic activation and carcinogenicity of aminoazo dyes ortho-aminoazotoluene and 3′-methyl-4-dimethylaminoazobenzene in experiments on suckling mice

It is found that after administration of 3′-methyl-4-dimethylaminoazobenzene (3′-Me-DAB,) which was hepatocarcinogenic to rats, in suckling mice, the number of neoplastic lesions in the liver of mice was 3 times higher than after analogous administration of equimolar dose of ortho-aminoazotoluene (OAT)). However, in the Ames test (TA-98 strain of Salmonella typhimurium) with activation by hepatic enzymes (S-9 fraction) of both intact and Aroclor-1254-induced mice and rats OAT contributed by an order of magnitude to revertant colonies compared to 3′-Me-DAB. In vivo inhibition of sulfotransferase activity, the enzyme which catalyzes the final stage of the mutagenic activation of aminoazo dyes, had no effect on carcinogenicity of 3′-Me-DAB but more than 4 times elevated that of OAT. It was concluded that the mechanism of carcinogenic action of aminoazo dyes studied is not genotoxic and that the carcinogenic potential of OAT is lost in the process of mutagenic activation.     

THE FINE STRUCTURE OF TESTICULAR INTERSTITIAL CELLS IN GUINEA PIGS

In guinea pig testes perfused with either glutaraldehyde or osmium tetroxide fixative, the cytoplasm of the interstitial cells contains an exceptionally abundant agranular endoplasmic reticulum. The reticulum in central regions of the cell is a network of interconnected tubules, but in extensive peripheral areas the reticulum is commonly organized into closely packed, flattened cisternae which are fenestrated. Occasional small patches of the granular reticulum occur in the cytoplasm and connect freely with the agranular reticulum. The mitochondria have a dense matrix and contain cristae and some tubules. The Golgi complex is disperse and shows no evidence of secretory material. The cytoplasm also contains lipid droplets. Lipofuscin pigment granules are probably polymorphic residual bodies and contain three components: (1) a dense material which at high magnification shows a 75-A periodicity; (2) a medium-sized lipid droplet; and (3) a cap-like structure. In glutaraldehyde-perfused testis the interstitial cell cytoplasm appears to have the same density from cell to cell, and the agranular reticulum is tubular or cisternal but not in the form of empty vesicles. Thus the "dark" and "light" cells and the vesicular agranular reticulum sometimes encountered in other fixations may be artifacts. Biochemical results from other laboratories, correlated with the present findings, indicate that the membranes of the agranular endoplasmic reticulum in guinea pig interstitial cells are the site of at least two enzymes of androgen biosynthesis, the 17-hydroxylase and the 17-desmolase.     

OVARIAN STEROID CELLS : I. Differentiation of the Lutein Cell from the Granulosa Follicle Cell during the Preovulatory Stage and under the Influence of Exogenous Gonadotrophins

The granulosa follicle cell of the Graafian follicle of the rabbit ovary differentiates into a lutein cell involved in steroid synthesis. Cytological events which occur within the granulosa cell of the normally stimulated follicle prior to ovulation have been duplicated by the intrafollicular injection of exogenous gonadotrophin. The luteinization of the granulosa cells involves the accumulation of 250- to 300-A, electron-opaque, spherical granules, dispersed within the cytoplasmic matrix, which have been identified as glycogen with the PAS-staining procedure. Further development of the granulosa cell following ovulation involves an increase in cell size, a decrease in the number of RNP particles, and an accumulation of an abundant system of intracellular membranes (agranular endoplasmic reticulum). Glycogen granules first appear in the granulosa cells as the separate, monoparticulate form. After follicle rupture and the formation of agranular endoplasmic reticulum, glycogen particles are present in a rosette arrangement within membrane-bounded vacuoles. The rosette arrangement of glycogen particles is also found dispersed within the cytoplasmic matrix of the lutein cell during the later stages of the cell life-span. Injection of luteinizing hormone or human chorionic gonadotrophin into a mature follicle also produces a marked accumulation of monoparticulate glycogen in the majority of granulosa cells, within 30 min. Cytoplasmic extensions which contain the glycogen masses are noticeably free of RNP particles.     

Microscopical studies on the hemocytes of bivalves and their phagocytic interaction with selected bacteria

Hemocytes represent one of the most important defense mechanisms against foreign material in Mollusca. The morphology, hematological parameters and behaviour of hemolymph cells were studied in the southern quahogMercenaria campechiensis, the eastern oysterCrassostrea virginica, and the blood arkAnadara ovalis challenged with the bacteriaVibrio vulnificus andV. anguillarum. Two general classes of hemocytes (granular and agranular) exist inC. virginica andM. campechiensis. In contrast,A. ovalis possesses 3 general classes (granular, agranular and erythrocytes). Three types of granules were identified by light microscopy. When hemolymph cells were studied by transmission electron microscopy, the cytoplasm of hemolymph cells was noted to contain many organelles, including electron dense granules. Both agranular and granular hemolymph cells were capable of colchicine-sensitive pseudopodial movement and spreading. The results indicate that marine bivalves possess hemolymph blood cells which may play a role in the internal defense paralleling mammalian phagocytes. The morphology of these cells, as determined by light, scanning and transmission electron microscopy, showed some similarity to mammalian-mononuclear phagocytes. The sub-cellular events of molluscan hemocyte phagocytosis ofV. vulnificus andV. anguillarum were studied by both scanning and transmission electron microscopy. The role of these cells and the factors which govern their behavior are of economic and public health importance.     

THE ENDOPLASMIC RETICULUM OF GASTRIC PARIETAL CELLS

An electron microscopic survey has been made of the gastric parietal or oxyntic cell of the human, cat, beaver, dog, hamster, rat, mouse, and bat, and of the corresponding cell type in two species of frog, two species of toad, and the horned lizard. A feature consistently found in the parietal cells of the mammals or their equivalent in the lower vertebrates is the agranular endoplasmic reticulum, which takes the form of branching and anastomosing small tubules approximately 200 to 500 A in diameter, sometimes expanded into flattened cisternae. In mammalian parietal cells this form of the endoplasmic reticulum is found only in limited amounts, but in the corresponding secretory cells of the amphibia and reptilia the tubular agranular reticulum is abundant. It is believed to comprise a more or less continuous system of channels, but owing to their tortuous course only short profiles are seen in thin sections. Immediately subjacent to the plasmalemma at the free surface, the cytoplasm is relatively free of organelles but is occasionally traversed by the agranular reticulum, which appears to be continuous at some points with the cell surface. The possible participation of the agranular endoplasmic reticulum in hydrochloric acid secretion is discussed.     

THE FINE STRUCTURE OF THE AXON AND GROWTH CONE OF THE DORSAL ROOT NEUROBLAST OF THE RABBIT EMBRYO

The centrally directed neurite of the dorsal root neuroblast has been described from the period of its initial entrance into the neural tube until a well-defined dorsal root is formed. Large numbers of microtubules, channels of agranular reticulum, and clusters of ribosomes are found throughout the length of the early axons. The filopodia of the growth cone appear as long thin processes or as broad flanges of cytoplasm having a finely filamentous matrix material and occasionally small ovoid or elongate vesicles. At first the varicosity is a small expansion of cytoplasm, usually containing channels of agranular reticulum and a few other organelles. The widely dilated cisternae of agranular reticulum frequently found within the growth cone probably correspond to the pinocytotic vacuoles seen in neurites in tissue culture. The varicosities enlarge to form bulbous masses of cytoplasm, which may measure up to 5 µ in width and 13 µ in length. They contain channels of agranular reticulum, microtubules, neurofilaments, mitochondria, heterogeneous dense bodies, and a few clusters of ribosomes. Large ovoid mitochondria having ribonucleoprotein particles in their matrix are common. Dense membrane specializations are found at the basal surface of the neuro-epithelial cell close to the area where the early neurites first enter the neural tube.     

The effect of prolonged dietary administration of the non-carcinogen, 4-acetylaminofluorene on the liver of the rat. An electron microscope study

A diet containing 0.05 % of the non-carcinogen 4-acetylaminofluorene (4-AAF) was fed to male Leeds strain rats for periods of up to 10 months. Some animals were killed after 8–12 weeks, 6 months and 8–10 months of 4-AAF feeding, while further groups were returned to a normal diet after 10 months of treatment and then killed 2, 5, 9 and 12 months later. The hepatic tissues were removed and prepared for electron microscopy. The main fine structural changes induced by 4-AAF were a prominent hypertrophy of the agranular endoplasmic reticulum, glycogen depletion and lipid accumulation. It was noted that these changes persisted following withdrawal of dietary 4-AAF, for the duration of the experiment. The effects of 4-AAF are compared with those of its carcinogenic isomer, 2-acetylaminofluorene (2-AAF) and the possibility is discussed that the clear differences revealed in this study may be directly related to the relative carcinogenicities of these two compounds.     

AN ANALYSIS OF COLLAGEN SECRETION BY ESTABLISHED MOUSE FIBROBLAST LINES

In vitro synthesis of collagen by established mouse fibroblast lines has been examined by electron microscopy. During rapid growth (log phase), when collagen could not be detected in the cultures, the cells lacked a well developed granular ergastoplasm and Golgi system. Upon cessation of growth (stationary phase), collagen accumulated in the cultures and the cells demonstrated highly developed granular and smooth ergastoplasm. Collagen appeared to be synthesized in the rough-surfaced endoplasmic reticulum and to be transported as a soluble protein to the cell surface by vesicular elements of the agranular ergastoplasm. Fusion of the limiting membranes of these vesicles with the cell membrane permitted the discharge of the soluble collagen into the extracellular space, where fibrils of two diameter distributions formed. The secretion of collagen is concluded to be of the merocrine type. Alternative theories of collagen secretion are discussed and the data for established lines compared with the results of other in vitro and in vivo studies of collagen fibrillogenesis.     

FINE STRUCTURE OF THE OCTOPUS RETINA

The fine structure of the visual and the supporting cells and of the blood capillaries in the octopus retina is described. Lamellated structures contained in the proximal segment of the visual cell consist of compact arrays of dense membranes each of which is quintuple-layered and divides at its margins into two thinner sheets or membranes which are connected directly with the agranular or granular endoplasmic reticulum. Proximal to the deeper extremities of the rhabdomeres, the lateral plasma membranes of two adjoining visual cells contact each other forming a quintuple-layered compound membrane, which results in occlusion of the intercellular space. The central layer of the compound membrane is of high density, so that the membrane, as a whole, appears to be a single thick layer at low magnifications. The supporting cells are connected with the neighboring visual cells by two types of junctions. Long slender processes extend from the supporting cells to the surface of the retina through narrow spaces among the distal segments of the visual cells. The capillary endothelial cells are characterized by luminal surfaces irregularly contoured and by lateral surfaces elaborately interdigitated. The functional significance of the close contact between adjoining visual cells is discussed.     

The fine structure of testicular interstitial cells in the adult golden hamster with special reference to seasonal changes

Summary The fine structure of the testicular interstitium was studied in normal adult golden hamsters sacrificed in the reproductive season (spring and summer) and in the winter. The Leydig cells in the reproductively active testes contain abundant endoplasmic reticulum (ER) and numerous mitochondria. The ER occurs in the form of flattened cisternae and tubules, the former prevailing. The cisternae are extremely extensive and are partly granular and partly agranular, their ends being continuous with the tubular reticulum. Mitochondria intervening between the cisternae are closely associated with the agranular portions of the latter. Adjacent to the Golgi complex and continuous with the centrosome a unique filamentous body with a dense laminar core is often observed. In the regressive testes, the Leydig cells show a great reduction of cytoplasmic volume and a remarkable decline of the organelles, especially agranular tubules. The possible functional significance of the tubular and cisternal ER with the associated mitochondria is discussed in relation to the biosynthesis of androgens. Macrophages appear to constitute another important population of the interstitial cell clusters.This study was supported in part by a grant from the National Science Council, the Republic of China     

Fine structure of the spiracular glands in larval Drosophila melanogaster (Meig.) (Diptera : Drosophilidae)

The spiracular glands in the third-instar larvae of Drosophila melanogaster (Diptera : Drosophilidae) were examined with light and electron microscopy. Three club-shaped, unicellular glands are associated with each spiracle. Each gland has a large nucleus with a well-developed nucleolus and polytene chromosomes. Cytoplasmic features include a prominent plasma membrane reticular system (PMRS), which contains electron-dense material and gives rise to endocytotic vesicles. Numerous lipid droplets, mitochondria, free ribosomes, glycogen, lysosomes, and vesicles are scattered throughout the cytoplasm. The smooth endoplasmic reticulum is abundant, but rough endoplasmic reticulum and Golgi complexes are sparse. Small lipid droplets appear to fuse with one another to form larger droplets. In late third-instar glands, normal mitochondria decrease in number; they appear to degenerate and become converted into dense bodies with finely granular interiors. Several microvillous channels containing lipid are present within the cytoplasm. In the lumina of most of these channels are found the distal tips of cuticular ductules. The cuticular ductules merge with one another dorsally to form the main duct that carries the lipoid secretion to the spiracle cleft. The ultrastructure of the spiracular glands is consistent with their roles in the synthesis of lipoid secretion, which is used to provide hydrophobicity of the surface and to trap small particulate matter.     

Ultrastructural analysis of the granulosa — Luteal cell transition in the ovary of the dog

The transition from ovarian granulosa to lutein cell during the estrus cycle of 60 pregnant and non-pregnant beagle bitches was analyzed by light and electron microscopy (both 100 and 1000 KV). Early proestrus was characterized by a gradual rise in serum estrogen levels, hyperplasia of the granulosa cells, the accumulation of follicular fluid, and the development of tortuous intercellular channels. During the second half of proestrus, serum estrogen levels continued to rise, but growth, division, and differentiation of the granulosa cells was minimal. Estrus was marked by the first acceptance of the male and a well-defined LH peak In the subsequent 24 hour period, the granulosa-lutein cells hypertrophy rapidly and develop a large Golgi apparatus, small profiles of granular endoplasmic reticulum, numerous microfilaments, and large gap junctions between the cells. Mitochondria also proliferate, enlarge, and elongate, but retain lamelliform cristae. Luteinization of the cells and progesterone secretion begin just after ovulation which in turn occurs about 24 hours after the LH peak. On the third and fourth day of estrus, numerous small vesicles of agranular endoplasmic reticulum fill the extoplasm and the mitochondria swell up and round off. The vesicles rapidly fuse into whorled and flattened cisternae or anastomosing tubules of agranular endoplasmic reticulum, while the mitochondria develop tubulovesicular cristae. These structures gradually become organized with respect to the basal lamina. The Golgi apparatus is centered over the pole of the nucleus that faces the pericapillary space. Stacked and whorled cisternae of agranular ER develop in the lateral margins and avascular end of the cell while mitochondria and tubular elements of agranular ER predominate in the central medial and most basal portions of the cytoplasm. Microfilaments are ubiquitous and appear to be instrumental in this orientation process. The cell surface develops three distinct regional specializations that coincide with the underlying cellular compartments: interconnecting pleomorphic folds fill the pericapillary space; long tenous microvilli project from the lateral cell surface and form tortuous intercellular channels and canaliculi; and large gap junctions form along the margins of the cell furthest removed from the basal lamina. By the sixth day of estrus, the granulosa-luteal cell transition is nearly complete and serum progesterone levels are on the rise.     

LYSOSOMES AND GERL IN NORMAL AND CHROMATOLYTIC NEURONS OF THE RAT GANGLION NODOSUM

The rat ganglion nodosum was used to study chromatolysis following axon section. After fixation by aldehyde perfusion, frozen sections were incubated for enzyme activities used as markers for cytoplasmic organelles as follows: acid phosphatase for lysosomes and GERL (a Golgi-related region of smooth endoplasmic reticulum from which lysosomes appear to develop) (31–33); inosine diphosphatase for endoplasmic reticulum and Golgi apparatus; thiamine pyrophosphatase for Golgi apparatus; acetycholinesterase for Nissl substance (endoplasmic reticulum); NADH-tetra-Nitro BT reductase for mitochondria. All but the mitochondrial enzyme were studied by electron microscopy as well as light microscopy. In chromatolytic perikarya there occur disruption of the rough endoplasmic reticulum in the center of the cell and segregation of the remainder to the cell periphery. Golgi apparatus, GERL, mitochondria and lysosomes accumulate in the central region of the cell. GERL is prominent in both normal and operated perikarya. Electron microscopic images suggest that its smooth endoplasmic reticulum produces a variety of lysosomes in several ways: (a) coated vesicles that separate from the reticulum; (b) dense bodies that arise from focal areas dilated with granular or membranous material; (c) "multivesicular bodies" in which vesicles and other material are sequestered; (d) autophagic vacuoles containing endoplasmic reticulum and ribosomes, presumably derived from the Nissl material, and mitochondria. The number of autophagic vacuoles increases following operation.