Histopathological effects of larval digenea on the digestive epithelia of the marine prosobranch Cerithidea californica: Fine structural changes in the digestive gland

The effects of natural infections by rediae of the heterophyid Euhaplorchis californiensis on the digestive gland cells of Cerithidea californica (Gastropoda: Prosobranchiata) were studied through the use of light and electron microscopy. Pathological changes in secretory and digestive cells, including the disruption of digestive vacuoles and cell-cell junctions, the deformation of lumenal microvilli, the lysis of distal plasma membranes, and nuclear polymorphism, usually accompany the migration of larval trematodes into the digestive gland. Degenerating secretory cells are further characterized by Golgi complexes which assume an inflated appearance and a reduction of rough endoplasmic reticulum in the cell's perinuclear region. Finally, an increase in excretory and autophagic activities in the digestive gland cells of infected snails may be considered possible mechanisms by which the host is able to compensate for adverse metabolic or nutritional stresses of trematode parasitism.     

The Ultrastructure of the Digestive Glands in Pinguicula vulgaris L. (Lentibulariaceae) Relative to their Function. I. The Changes During Maturation

The digestive glands of Pinguicula vulgaris become fully maturewhilst still enclosed in the bud. All the gland cells remainintact on the fully expanded unstimulated leaves. As the secretoryhead cells mature, a special layer forms between the plasmalemmaand the cell wall. This layer is shown to be different fromthe typical labyrinthine wall of transfer cells and serves forthe storage of digestive enzymes. Ultrastructural analysis,including morphometry, indicates that the digestive enzymesare synthesized on the RER of the head cells and transferredinto the cell wall, particularly into the slime layer, and vacuoles.This transfer is achieved firstly through continuity of theendoplasmic reticulum with vacuoles (static) and the periplasmicspace (dynamic) and, secondly, into the latter through exocytosisof coated Golgi vesicles and of some vacuoles filled with enzymes. Pinguicula vulgaris L., carnivorous plant, digestive glands, ultrastructure, protein synthesis secretion     

Ultrastructural localization of esterase and acid phosphatase in digestive gland cells of fed and starvedCepaea nemoralis (L.) (Mollusca: Helicidae)

Summary The ultrastructural localizations of thiolacetic acid esterase, indoxyl acetate esterase and acid -glycerophosphatase have been studied in the digestive gland cells of fed and starvedCepaea nemoralis. In fed snails the major localization of all three enzymes was in the green granule vacuoles of digestive cells. In addition, the cytoplasm of calcium cells and the Golgi apparatus and GERL (?) of all cell types were acid phosphatase positive. Many digestive cells of starved snails showed a similar enzyme distribution to that found in fed snails but other digestive cells showed a very high cytoplasmic activity of all three enzymes. It is suggested that these cells are in the process of autolysis. New light is also thrown on the process by which food is transported from the digestive gland lumen to the phagosomes of digestive cells.     

The distribution of some hydrolytic enzymes in the cells of the digestive gland of certain lamellibranchs and gastropods

Five hydrolytic enzymes (acid phosphatase, aryl sulphatase, β-glucuronidase, N-acetyl-β-glucosaminidase, and non-specific esterase) have been studied histochemically in the cells of the digestive gland of Mytilus edulis, Helix aspersa , and certain other lamellibranchs and gastropods. All the enzymes studied have basically similar distributions.
In the digestive cells, the enzymes occur in cytoplasmic granules which are believed to be primary lysosomes; in vacuoles which contain phagocytosed food material; and in vacuoles containing lipofuscin granules, which are the residues of digestive activity.
In the basiphil cells of M. edulis , most of the enzymes are localized in a few cytoplasmic granules; non-specific esterase, however, is found throughout the cytoplasm. In the calcium cells of H. aspersa and the other pulmonate gastropods studied, the enzymes are either in cytoplasmic granules, or distributed diffusely throughout the cytoplasm. Acid phosphatase is also found in the calcium spherules, especially in H. aspersa.
In the excretory cells of H. aspersa and the other pulmonates studied, the enzymes are found in granules in the cytoplasm, and in the lipofuscin granules which lie in the vacuoles of these cells.     

Ultrastructure of the rotifer Brachionus plicatilis

The ultrastructural study of digestive organs andintegument of the rotifer, Brachionusplicatilis, was performed by transmission of electronmicroscopy to elucidate the relationship between theirstructure and function. The integument of the rotiferis composed of a thick external and a thin internallayer, in which many pores are regularly distributed.The contents of secretory bulb are excreted throughthose pores to the external surface. The inner surfaceof the digestive tract is lined with relatively denseand regularly spaced cilia for propelling food along.The cells of stomach and the intestine contains manyendocytotic vesicles, digestive vacuoles, and lipidinclusions, indicating its active endocytoticfunction. The gastric gland cells have abundant roughendoplasmic reticulum, Golgi complexes and secretorygranules for producing digestive enzymes. Thisultrastructural study clarifies the morphologicalcharacters of the integument and the digestive organsthat are closely related to its function.     

The digestive gland of the Southern Dumpling Squid (Euprymna tasmanica): structure and function

The cephalopod digestive gland plays an important role in the efficient assimilation of nutrients and therefore the fast growth of the animal. The histological and enzymatic structure of Euprymna tasmanica was studied and used in this experiment to determine the dynamics of the gland in response to feeding. The major roles of the digestive gland were secretion of digestive enzymes in spherical inclusions (boules) and excretion of metabolic wastes in brown body vacuoles. High levels of trypsin, chymotrypsin and α-amylase, low levels of α-glucosidase and negligible carboxypeptidase activity were produced by the gland. There was no evidence of secretion of digestive enzymes in other organs of the digestive tract. Within 60 min of a feeding event, the gland produced increasing numbers of boules to replace those lost from the stomach during the feeding event. Initially, small boules were seen in the digestive cells, they increased in size until they are released into the lumen of the gland where they are transported to the stomach. There was no evidence of an increase in activity of digestive enzymes following a feeding event, despite structural changes in the gland. However, there was large variation among individuals in the level of digestive enzyme activity. A negative correlation between boule and brown body vacuole density suggested that the large variation in enzyme activity may be due to the digestive gland alternating between enzyme production and excretion.     

Fine structure and absorption of ferritin in the digestive organs of Loligo vulgaris and L. Forbesi (Cephalopoda,Teuthoidea)

The digestive organs possibly involved in food absorption in Loligo vulgaris and L. forbesi are the caecum, the intestine, the digestive gland, and the digestive duct appendages. The histology and the fine structure showed that the ciliated organ, the caecal sac, and the intestine are lined with a ciliated epithelium. The ciliary rootlets are particularly well developed in the ciliated organ, apparently in relation to its function of particle collection. Mucous cells are present in the ciliated organ and the intestine. Histologically, the digestive gland appears rather different from that of other cephalopods. However, the fine structure of individual types of squid digestive cell is actually similar to that of comparable organs in other species, and the squid cells undergo the same stages of activity. Digestive cells have a brush border of microvilli, and numerous vacuoles, which sometimes contain “brown bodies.” However, no “boules” (conspicuous protein inclusions of digestive cells in other species) could be identified in their cytoplasm; instead only secretory granules are present. In the digestive duct appendages, numerous membrane infoldings associated with mitochondria are characteristic features of the epithelial cells in all cephalopods. Two unusual features were observed in Loligo: first, the large size of the lipid inclusions in the digestive gland, in the caecal sac, and in the digestive duct appendages; and second, the large number of conspicuous mitochondria with well-developed tubular cristae. When injected into the caecal sac, ferritin molecules can reach the digestive gland and the digestive duct appendages via the digestive ducts, and they are taken up by endocytosis in the digestive cells. Thus, it appears that the digestive gland of Loligo can act as an absorptive organ as it does in other cephalopods.     

The subcellular localisation of certain crop-juice esterases in the digestive gland ofCepaea (Mollusca: Helicidae)

Summary Three methods have been used to localise specific crop-juice esterases within the cells of the digestive gland ofCepaea nemoralis andC. hortensis. A comparison withHelix aspersa has also been made. Autolysis experiments showed that Est. 1 and Est. 9 were very resistant to denaturation and might therefore be of lysosomal origin. Ultracentrifugation of digestive gland homogenates suggests that these same esterases are within vacuoles and this is confirmed by histochemical studies at the electron microscope level using thiolacetic acid as a substrate. It is shown electrophoretically that only esterases within set 1 (Oxford, 1977), which includes Est. 1 and Est. 9, hydrolyse this substrate to any marked extent. Thiolacetic acid esterase activity is found within the phagolysosomes and endoplasmic reticulum of digestive cells. It is suggested that at least some of the digestive enzymes present in the crop juice originate within phagolysosomes and are specifically released from digestive cells.     

Morphofunctional changes in the midgut of tick nymphs of the genus Ixodes (Acarina: Ixodidae) during and after feeding

The midgut epithelium of feeding nymph is represented by the digestive cells of larval phase. Digestion of the main part of feed is performed by the one generation of digestive cells of nymphal phase after detachment, during moult. This period precedes the apolysis. The generation of secretory cells is absent on the nymphal phase. Secretory vacuoles are formed in the digestive cells of larval phase. All functioning cells form a peritrophic matrix on their apical surface. The replacement of the digestive cells of larval phase by the digestive cells of nymphal phase proceeds gradually, during the first 5-10 days after detachment. The beginning of the accumulation of digestive inclusions in the young digestive cells of nymphal phase takes place in the 10-15 days after detachment.     

The fine structural localization of acid phosphatase in the gut epithelial cells of the slug,Avion ater (L.)

Summary Acid phosphatase, generally thought of as a lysosomal enzyme and indeed widely employed as a lysosomal marker, has been found associated with the Golgi complex of all cell types from the crop, intestine and digestive gland ofArion ater. Reaction product was also detected within the multivesicular bodies and cytoplasm of columnar cells from the crop and the multivesicular bodies of mucous cells from the intestine. A vacuolar localization was obtained in the digestive cells of the intestine and digestive gland. Secretory protein granules in the calcium cells of the same gland and apical vacuoles in the so-called thin cells also showed a positive reaction.This work was undertaken as part of a slug research project under the direction and co-ordination of Dr. D. K.Roach, supported by A.R.C. Assistance was given by Mr. T. R.Mainwaring in the preparation of tissue for electron microscopy.I would like to thank Professor J.Brough and Professor D.Bellamy for providing facilities and encouragement.     

The Digestive Glands of Pinguicula: Structure and Cytochemistry

The digestive glands of the carnivorous genus Pinguicula havethree functional compartments, (a) a basal reservoir cell, (b)an intervening cell of endodermal character and (c) a groupof secretory head cells. The gland complex is derived from asingle epidermal initial. The reservoir cell, which is richin Cl^– ions, is highly turgid before discharge; it islinked by plasmodesmata to the surrounding epidermal cells,and is ensheathed by a pectin-rich inner wall layer. The endodermalcell is bounded by a Casparian strip to which the plasmalemmais tightly attached; it contains abundant storage lipid andnumerous mitochondria. The head cells of the developing glandhave labyrinthine radial walls of the transfer-cell type, theingrowths being composed of pectic polysaccharides. The boundingcuticle is discontinuous, although lacking well-formed pores.Mitochondria are numerous, with well-developed cristae; theplastids are large and ramifying, and invested by ribosomalendoplasmic reticulum. Dictyosomes are sparse, and where theyoccur, are associated with coated vesicles. Ribosomal endoplasmicreticulum is moderately abundant in the head cells, and so alsoare free ribosomes. Optical and electron microscopic localizationmethods indicate that the digestive enzymes are synthesizedin the head cells and transferred both into the vacuoles andinto the walls. There is no evidence of a granulocrine modeof secretion, and the transfer seems to be initially by directperfusion through the plasmalemma. During the final phase ofmaturation of the head cells they suffer a form of autolysis,vacuoles, cytoplasm and wall becoming confluent as all of themembranes of the cell undergo dissolution. The gland head isthus, in effect, simply a sac of enzymes at the time of theultimate discharge. Pinguicula, carnivorous plant, insectivorous plant, enzyme secretion, digestive gland     

Timing of perialgal vacuole membrane differentiation from digestive vacuole membrane in infection of symbiotic algae Chlorella vulgaris of the ciliate Paramecium bursaria

Each symbiotic Chlorella of the ciliate Paramecium bursaria is enclosed in a perialgal vacuole derived from the host digestive vacuole to protect from lysosomal fusion. To understand the timing of differentiation of the perialgal vacuole from the host digestive vacuole, algae-free P. bursaria cells were fed symbiotic C. vulgaris cells for 1.5min, washed, chased and fixed at various times after mixing. Acid phosphatase activity in the vacuoles enclosing the algae was detected by Gomori's staining. This activity appeared in 3-min-old vacuoles, and all algae-containing vacuoles demonstrated activity at 30min. Algal escape from these digestive vacuoles began at 30min by budding of the digestive vacuole membrane into the cytoplasm. In the budded membrane, each alga was surrounded by a Gomori's thin positive staining layer. The vacuoles containing a single algal cell moved quickly to and attached just beneath the host cell surface. Such vacuoles were Gomori's staining negative, indicating that the perialgal vacuole membrane differentiates soon after the algal escape from the host digestive vacuole. This is the first report demonstrating the timing of differentiation of the perialgal vacuole membrane during infection of P. bursaria with symbiotic Chlorella.     

Symbiotic Chlorella sp. of the ciliate Paramecium bursaria do not prevent acidification and lysosomal fusion of host digestive vacuoles during infection

Summary. Each symbiotic Chlorella sp. of the ciliate Paramecium bursaria is enclosed in a perialgal vacuole derived from the host digestive vacuole, and thereby the alga is protected from digestion by lysosomal fusion. Algae-free cells can be reinfected with algae isolated from algae-bearing cells by ingestion into digestive vacuoles. To examine the timing of acidification and lysosomal fusion of the digestive vacuoles and of algal escape from the digestive vacuole, algae-free cells were mixed with isolated algae or yeast cells stained with pH indicator dyes at 25 ± 1 °C for 1.5 min, washed, chased, and fixed at various time points. Acidification of the vacuoles and digestion of Chlorella sp. began at 0.5 and 2 min after mixing, respectively. All single green Chlorella sp. that had been present in the host cytoplasm before 0.5 h after mixing were digested by 0.5 h. At 1 h after mixing, however, single green algae reappeared in the host cytoplasm, arising from those digestive vacuoles containing both nondigested and partially digested algae, and the percentage of such cells increased to about 40% at 3 h. At 48 h, the single green algae began to multiply by cell division, indicating that these algae had succeeded in establishing endosymbiosis. In contrast to previously published studies, our data show that an alga can successfully escape from the host’s digestive vacuole after acidosomal and lysosomal fusion with the vacuole has occurred, in order to produce endosymbiosis. Correspondence and reprints: Biological Institute, Faculty of Science, Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8512, Japan.     

Phosphatase activity in the hepatopancreas of Helix aspersa

• 1.1. Phosphatase acid (PhA) activity in the digestive gland (hepatopancreas) of the common garden snail Helix aspersa has been investigated using cytochemical methods.
• 2.2. All the cells composing this gland show PhA activity, the distribution pattern differing according to the cell type.
• 3.3. The digestive cells show the most widely distributed reaction product (brush border, phagolysosomes, multivesicular bodies and autophagic vacuoles).
• 4.4. In the excretory cells this activity appears in large sacs, while in the calcium cells the reaction product is abundant in the calcium granules.
• 5.5. Cellular digestion processes performed by each of these cell types is discussed together with their role in the detoxification of heavy elements derived from the environment.

     

Histological and morphological evaluations of the digestive tract and associated organs of haddock throughout post-hatching ontogeny

At hatching, the oesophagus of haddock Melanogrammus aeglefinus lacks goblet cells, the intestine is a simple undifferentiated tube, the liver is present as a rounded mass caudal to the heart, and numerous zymogen granules are present in the pancreas. The first intestinal convolution appears at day 2, at the posterior end of the digestive tract. The oesophagus displays alcian blue and PAS positive mucus secreting cells on day 12, which become numerous by day 15. By day 18, epithelial cells of the posterior intestine show evidence of protein absorption in the form of supranuclear vacuoles. The swimbladder inflates in 50% of the larvae by day 22, although inflation rate is highly variable. By day 35, or 10 mm, a pyloric caecal ridge appears which separates the presumptive stomach, which is now showing evidence of gastric gland formation, from the intestine. This marks the beginning of digestive features characteristic of the juvenile stage.     

Golgi associated acid phosphatase in muscle and nerve cells fromArion ater (L.)

Summary Golgi associated acid phosphatase has been demonstrated within muscle and nerve cells from the sub-epithelial layers of the crop, intestine, and digestive gland ofArion ater. Enzyme activity was detected in the saccules, vacuoles, and vesicles of the Golgi apparatus of both nerve ganglia and muscle cells. Other vacuolar sources of acid phosphatase could also be distinguished within the cytoplasm of these cells.     

Endocytosis,digestive vacuolar movement and exocytosis on refeeding starvedTetrahymena pyriformis GL-9

Summary Evidence is presented in support of the hypothesis that the contents of digestive vacuoles in refed starvedTetrahymena pyriformis GL-9 are egested from the cell in approximately the sequence of their order of formation. The investigations involved measurements of the rates of disappearance of digestive vacuoles from the cells and the subsequent appearance of egested globules in the surrounding medium using both cultures and individual cells. The cells were first fed peptone and latex particles for a period and then this type of vacuole formation was suppressed by the addition of excess carmine particles (or the process was repeated with the particles in reverse order). Thus two types of morphologically distinct digestive vacuoles could be produced and observed microscopically. These observations suggest that the temporal nature of the movement of the digestive vacuoles through the cell result in the temporal nature of egestion and that no selective mechanism occurs at egestion. Thus digestive vacuoles are thought to pass through the cell from cytopharynx to cytoproct in approximately the order formed and at approximately constant rate. Under conditions of excess nutrients, where the cells become filled with digestive vacuoles, they seem to be able to maintain an approximately uniform number of digestive vacuoles within themselves by maintaining approximately constant and equal rates of vacuole formation and egestion. The maximum rates of latex or carmine vacuole formation or egestion found in single cells were approximately 0.3–0.4 vacuoles per cell per minute. The results are discussed.     

Ultrastructure and histochemistry,of the stomach of Asplanchna sieboldi

Stomach cells of female Asplanchna sieboldi are specialized for absorption and intracellular digestion of nutrients. Evidence is presented to show that electron-opaque colloidal substances, present in the medium and within digestive vacuoles of the prey (Paramecium), are taken up by the stomach cells at the apical cell membrane and sequestered within food vacuoles which contain hydrolases working in both the acid and alkaline pH range. The stomach cells are also implicated in the absorption of molecules below the resolving power of the electron microscope. In rotifers possessing a complete digestive tract, this task is presumed to be handled by the intestine.     

Surface characteristics of isopod digestive gland epithelium studied by SEM

The structure of the digestive gland epithelium of a terrestrial isopod Porcellio scaber has been investigated by conventional scanning electron microscopy (SEM), focused ion beam–scanning electron microscopy (FIB/SEM), and light microscopy in order to provide evidence on morphology of the gland epithelial surface in animals from a stock culture. We investigated the shape of cells, extrusion of lipid droplets, shape and distribution of microvilli, and the presence of bacteria on the cell surface. A total of 22 animals were investigated and we found some variability in the appearance of the gland epithelial surface. Seventeen of the animals had dome-shaped digestive gland “normal” epithelial cells, which were densely and homogeneously covered by microvilli and varying proportions of which extruded lipid droplets. On the surface of microvilli we routinely observed sparsely distributed bacteria of different shapes. Five of the 22 animals had “abnormal” epithelial cells with a significantly altered shape. In three of these animals, the cells were much smaller, partly or completely flat or sometimes pyramid-like. A thick layer of bacteria was detected on the microvillous border, and in places, the shape and size of microvilli were altered. In two animals, hypertrophic cells containing large vacuoles were observed indicating a characteristic intracellular infection. The potential of SEM in morphological investigations of epithelial surfaces is discussed.     

Changes of the cell surface and of the digestive apparatus of dictyostelium discoideum during the starvation period triggering aggregation

The effects of starvation on the cell morphology of Dictyostelium discoideum were studied with different cytochemical techniques, and with a morphometric method by which the surface areas of the cell membrane and of the digestive system can be determined. During the first 2 h, the cell membrane becomes very wrinkled and many phagocytic cups and filopods are formed. These changes are in accord with the 40 percent increase in the cell surface area to cytoplasmic volume ratio observed, which is mainly due to a strong decrease in the cytoplasmic volume. At this time of starvation, cells are able to ingest twice as many yeast as during growth. Afterwards, while the phagocytic ability decreases, the phagocytic cups disappear, and all the cells become bristled with many thin filopods. In spite of these morphological changes, no quantitative or topological differences have been observed concerning the polysaccharide content of the plasma membrane, whether it was stained with phosphotungstic acid, silver proteinate, or ruthenium red. During this time, the digestive vacuoles imbricate one into the other. Part of the vacuoles are degraded by this process, thus leading to an atrophy of the digestive apparatus. The digestive apparatus is progressively replaced by an autophagic system. Polysaccharide stainings and morphological observations show that the cytosegresomes seem to originate from the food vacuoles which flatten and sequester portions of cytoplasm. After 5 h of starvation, the digestive system is entirely transformed into an autophagic apparatus. The cell population appears to be homogeneous with respect to these changes. Therefore, potential precursors of prestalk and prespore cells were not observed.