The flow and fate of digestive enzymes in the field cricket,Gryllus bimaculatus

The flow of enzymes, the ratio of bound to unbound enzymes, and their inactivation in the cricket Gryllus bimaculatus was studied. The digestive enzymes are forced forward into the crop by caecal contraction and then they are mixed with freshly chewed food and saliva, forming a crop‐chyme. This chyme is blended by crop peristalsis, and periodic opening of the preproventricular valve (PPV) allows posterior movement into the proventriculus and further into the midgut. The contraction of the crop is modulated by Grybi‐AST and Grybi‐SK peptides, which are partially secreted by the caecal endocrine cells. Most of the aminopeptidase and the four disaccharidases examined are membrane bound (62–80%); the remaining (20–38%) as well all trypsin, chymotrypsin, lipase, and amylase are secreted free into the caecal lumen. Cricket trypsin loses only 30% of its activity in 4 h and very little thereafter. The presence of digestive products in the lumen appears to retard further trypsin autolysis. Cricket trypsin digests 42% of the chymotrypsin, 37% of the lipase, and 45% of the amylase in the caecal fluids over 24 h in vitro no significant difference. Without Ca ion amylase was almost completely digested. About 50% of the membrane bound and free aminopeptidase was digested in the caecal lumen, and about 30–38% of the bound and free maltase. This loss of digestive enzyme activity is possible, because enzyme secretion rates are high, the unbound enzymes are effectively recycled, and the time of nutrient passage is short.     

An ultrastructural study of alimentary tract development in the cercariae of Prosorhynchoides borealis (Digenea,Bucephalidae)

Podvyaznaya I. 2011. An ultrastructural study of alimentary tract development in the cercariae of Prosorhynchoides borealis (Digenea, Bucephalidae). —Acta Zoologica (Stockholm) 92 : 170–178. The development of digestive system in Prosorhynchoides borealis cercariae was studied using transmission electron microscopy. The foregut and caecum primordia arise in early cercarial embryos as two adjoining cellular cords. The primordial pharynx appears as a cluster of myoblasts in the mid‐part of the foregut primordium whose proximal end abuts onto the ventral embryonic tegument. Later, a lumen develops within the gut primordia and their component cells form the embryonic cellular epithelium with an essentially similar structure in the foregut and caecal regions. Subsequently, the foregut epithelial cells merge to form a syncytium. This process proceeds asynchronously and the most proximal foregut area remains cellular for the longest time. The syncytial lining of the foregut establishes syncytial connections with secretory cytons differentiating in the surrounding parenchyma. These cytons produce secretory granules, which are transported through cytoplasmic connections to the foregut syncytium. Before cercariae reach maturity, their foregut epithelium becomes anucleate and continuous with the external tegument. By the end of cercarial development, numerous short lamellae appear on the luminal surface of the caecal epithelium. The caecal cells become involved in secretory activity as indicated by the presence of Golgi‐derived secretory bodies in their cytoplasm.     

TRANSPORT OF UNCONTAMINATED AND MOLLUSCICIDE-CONTAINING FOOD IN THE DIGESTIVE TRACT OF THE SLUG DEROCERAS RETICULATUM (MULLER)

By X-ray analysis of food transport in the alimentary tractof Deroceras reticulatum it was shown that even ten hours afteringestion of a thorium sulfate-containing bait, this materialcan be detected in the crop. After 2.5 h, some parts of labelledfood passes down from the anterior to the posterior part ofthe gut. After 13 h, thorium sulfate-containing material canbe observed only in the gut. After 19 h, no more labelled materialis present in the alimentary tract of the animals. After addition of Cloethocarb, the animals feed on only smallamounts of food. The labelled material only enters the anteriorpart of the gut. After ten hours, the food does not move anymore and does not leave the crop even 19 h after feeding. After molluscicide application, the crop epithelium is moreinfolded than in control animals and the cells are elongated.After 30 h, cells protrude into the lumen of the digestive tract. (Received 11 May 1992; accepted 26 June 1992)     

Fasciola gigantica: Histology of the digestive tract and the expression of cathepsin L

The digestive tract of Fasciola gigantica is composed of the oral sucker, buccal tube, pharynx, esophagus, and caecum. The tegumental-type epithelium lines the first four parts of the digestive tract while the caecal-type epithelium lines the remaining parts from the caecal bifurcation. The caecal-epithelial cells are classified into 3 types according to their staining properties and ultrastructural characteristics, as related to the amount of food contents in the caecal lumen. All caecal-type epithelial cells synthesize and secrete cathepsin L, a major group of enzymes in the digestive tract, as detected by in situ hybridization and immunolocalization. Moreover, the secreted cathepsin L is also adsorbed on the outer surface of the tegument and the glycocalyx coating of the surface of the tegument, whereas the tegumental cells and tegumental syncytium covering the parasite’s body and lining the proximal part of the digestive tract exhibit no in situ hybridization signal and immunostaining for cathepsin L.     

Functional Morphology of the Introvert and Digestive System of Myzostoma cirriferum (Myzostomida)

Myzostoma cirriferum feeds by diverting food particles carried by the ambulacral grooves of its comatulid host Antedon bifida. When searching for food, the myzostome uses its protrusible introvert to fulfil two major functions: sensory perception and the capture of food particles. The digestive system is composed of four parts, viz. a pharynx, that is contained within the introvert, a stomach, a series of paired caeca and an intestine that lie in the myzostome's trunk. The pharynx is supplied with a thick muscle which, thanks to peristaltic movements, carries food particles from the mouth to the stomach. Both stomach and caecal cells are able to absorb dissolved nutriments and to store lipids, whereas intestinal cells are only capable of absorption. Due to the beating of their cilia, stomach cells also carry food particles into the caecal lumen, where they are subjected to endocytosis and intracellular digestion by caecal cells. Undigested food fragments eventually gather in a very large, apical vacuole, and the cell apices containing vacuoles are eliminated into the caecal lumen by an apocrinal process. Detached cell apices reach the stomach, where they are embedded in a matrix, together forming a spindle-shaped faecal mass that is expelled through the postero-ventral anus. The observed digestive process—entailing the regular elimination of the apical part of the caecal digestive cells—appears to be unique among the Spiralia.     

THE FUNCTIONAL ANATOMY OF THE GUT OF THE PROSOBRANCH GASTROPOD POMACEA CANALICULATA AND OF SOME OTHER PILIDS

The structure and functioning of the gut of Pomacea canaliculata (D'Orb.) has been investigated using living and preserved material. Anatomical studies were also carried out on preserved specimens of Pila globosa, Turbinicola saxea and Lanistes ovum bangweolicus .
The gut of pilids is specialised for a macrophagous diet, usually of aquatic angiosperms. The mid-oesophagus is a crop for storage, and the stomach has a large triturating gizzard developed from the gastric shield area. This is the site of extra-cellular digestion; there is no intra-cellular digestion in any part of the gut. The ducts of the digestive gland open into a special region of the stomach, the vestibule, which is histologically similar to them. The style sac begins the compacting of the faeces, which is completed in tho intestine. There is no evidence that absorption ocrurs in the epithelium of tho stomach or intestine; soluble products of digestion are carried into the digestive gland, which is the main site of absorption. Its activity is supplemented by amoebocytes entering the lumen of the style sac and intestine. Two types of cell occur in the gland, one type producing digestive enzymes and absorbing soluble products of digestion, the other type being excretory in function. There is no sign of phagocytosis in either. The excretory activity of the kidney is further supplemented by an anal gland.     

8种有胃真骨鱼消化道降钙素免疫活性细胞的定位及形态学研究

应用过氧化物酶标记的链霉卵白素免疫细胞化学技术对鳜、大口黑鲈、尼罗非鲫、短盖巨脂鲤、鲇、黄颡鱼、黄鳝和乌鳢等8种有胃真骨鱼消化道粘膜中降钙素免疫活性内分泌细胞进行了免疫细胞化学定位及形态学比较．结果表明,在尼罗非鲫、鳜和大口黑鲈消化道的任何部位均未见到阳性反应。另外5种鱼消化道的不同部位可不同程度地见到阳性细胞,其中黄颡鱼的整个消化道均有降钙素免疫活性的阳性反应;黄鳝和乌鳢的肠道中则无阳性反应,但在它们的胃以及黄鳝的食道中见到阳性细胞;鲇除食道中没有发现阳性细胞外,消化道各段中均有阳性细胞的存在;短盖巨脂鲤则仅在食道中发现阳性细胞。降钙素免疫活性细胞在肠道中的形态大多为长校形,胞体膨大,胞核是空油状,有两个相对的胞突分别伸向肠腔和基膜;胃中的降钙素细胞在位于胃上皮细胞之间时形状多为较短的梭形,而位于胃腺中时其形状较前者更加粗、短,胞突短小,常常呈不规则形状沿胃腺管边缘分布。     

Ultrastructural analysis of the morphology and function of the spermatheca of the pulmonate snail,Sonorella santaritana

The ultrastructure of the spermatheca of the reproductive tract in the pulmonate snail, Sonorella santaritana, was investigated. This organ has a debris-filled lumen and an outer wall which can be divided into three distinct layers. The cell layer adjacent to the lumen is comprised of two cell types, tall columnar epithelial cells with microvilli and cells lacking microvilli. The next layer also has two cell types, muscle cells and apparent pigment cells. The most distant layer is an adventitia of large glycogen-containing cells. The lumen of the spermatheca contains a core of partially digested sperm and related materials. The luminal contents and the cellular morphology of this organ suggest that the spermathecal functions are both digestive and absorptive. It is proposed that excess sperm and related materials are transported to the spermatheca, digested, and the usable products are reabsorbed.     

Schistosoma mansoni: uptake of exogenous hemeproteins by schistosomules grown in vitro

The uptake and fate of the hemeproteins horseradish peroxidase (HRPO) and hemoglobin (Hb) by schistosomules of Schistosoma mansoni maintained in vitro were studied by electron microscopy and cytochemical techniques. After administration of HRPO, reaction product was observed initially in the lumen of the digestive tract, and, after 2 hr of feeding, reaction product was also visible in the cytoplasm of the gastrodermis. There was no evidence of pinocytosis. After administration of Hb, reaction product was observed only in the lumen of the digestive tract. As is found following red blood cell feeding, digestive pigment was formed in the lumen of the gut following Hb feeding. The possible significance of these findings is discussed.     

Endosymbiotic and Host Proteases in the Digestive Tract of the Invasive Snail Pomacea canaliculata: Diversity,Origin and Characterization

Digestive proteases of the digestive tract of the apple snail Pomacea canaliculata were studied. Luminal protease activity was found in the crop, the style sac and the coiled gut and was significantly higher in the coiled gut. Several protease bands and their apparent molecular weights were identified in both tissue extracts and luminal contents by gel zymography: (1) a 125 kDa protease in salivary gland extracts and in the crop content; (2) a 30 kDa protease throughout all studied luminal contents and in extracts of the midgut gland and of the endosymbionts isolated from this gland; (3) two proteases of 145 and 198 kDa in the coiled gut content. All these proteases were inhibited by aprotinin, a serine-protease inhibitor, and showed maximum activity between 30°C and 35°C and pH between 8.5 and 9.5. Tissue L-alanine-N-aminopeptidase activity was determined in the wall of the crop, the style sac and the coiled gut and was significantly higher in the coiled gut. Our findings show that protein digestion in P. canaliculata is carried out through a battery of diverse proteases originated from the salivary glands and the endosymbionts lodged in the midgut gland and by proteases of uncertain origin that occur in the coiled gut lumen.     

Enzyme activities and pH variations in the digestive tract of gilthead sea bream

Two investigations were carried out with 150 g gilthead sea bream Sparus aurata to determine the relative activity of six digestive enzymes (pepsin, trypsin, chymotrypsin, carboxypeptidase A, carboxypeptidase B and amylase) and the pH variation in the lumen of different parts of the gut of fish fed one or two meals per day. Pepsin activity was found exclusively in the stomach, whereas activities of the other enzymes studied were found in all regions of the gut, including the stomach. The lack of localization of enzyme production in the digestive tract of S. aurata is similar to many other species as reported in the literature. The pH variations found in the different regions of the gut could be explained by general digestive physiology following the flow of digesta along the digestive tract. The range of pHs recorded in the various regions of the gut were generally outside the cited optima for many digestive proteases in this species.     

Detection and Pharmacokinetics of Alginate Oligosaccharides in Mouse Plasma and Urine after Oral Administration by a Liquid Chromatography/Tandem Mass Spectrometry (LC-MS/MS) Method

A sensitive and simple liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed for the detection of alginate oligosaccharides (AOs) in mouse plasma and urine after oral administration. In an AO mixture, dimer, trimer, and tetramer were detected by LC-MS/MS equipped with an anion-exchange column with extremely high sensitivity. By this method, we detected certain levels of AOs in samples prepared from mouse plasma and urine after a single oral administration of the AO mixture. Based on a calibration curve made with an AO trimer peak area as a standard, the maximum plasma and urine concentrations of AOs were estimated to be 24.5 μg/ml at 5 min and 425.5 μg/ml at 30 min, respectively. These results suggest that the LC-MS/MS method is well suited to pharmacokinetic analysis of AOs in an in vivo system, and that some of orally administered AOs, at least from dimer to tetramer, are absorbed by digestive organs promptly, and that unaltered, these oligomers were excreted into an urine after a single oral administration to a mouse.     

Compartmentalization of the digestive process in Abracris flavolineata (Orthoptera: Acrididae) adults

Carbohydrases predominate in the crop and their pH optima agree with pH prevailing in crop contents. Major amounts are also found in caecal contents. Aminopeptidase and trypsin are active mainly in the caeca, where they predominate in cells and contents, respectively. Aminopeptidase is partly membrane-bound. Except for trehalase, salivary glands display negligible amounts of digestive enzymes. The specific activity of digestive enzymes is high in all midgut cells and the enzyme molecules do not differ among gut compartments, as judged by polyacrylamide gel electrophoresis. Thus, it is probable that digestive enzymes are synthesized and secreted by all midgut cells (mainly in caeca) and then passed forward into the crop. Digestive enzymes are found in hindgut in concentrations similar to those in ventricular contents and, since they are stable in gut contents, they are likely excreted at a rate similar to undigested food. The data support the hypothesis that carbohydrate and protein are digested mainly in crop and caecal lumina, respectively, with part of the final digestion of proteins occurring at the surface of caecal cells. The peculiar features of the digestion of A. flavolineata grasshoppers, including the lack of midgut countercurrent fluxes, are thought to be derived from putative Polyneoptera ancestors.     

Control of the release of digestive enzymes in the caeca of the cricket Gryllus bimaculatus

Abstract In Gryllus bimaculatus, more digestive enzymes (amylase, trypsin, aminopeptidase) are secreted in the caecum of fed crickets than in unfed crickets, but the enzymes are released continuously at a basal rate in unfed animals. The rate of synthesis of the enzymes appears to parallel their rate of release. Digestive enzymes are released in response to a specific ratio of nutrients, although a high nutrient component in the food does not necessarily induce a high digestive enzyme release for that component. Rinsed flat‐sheet preparations of the caecum are incubated with specific nutrients (carbohydrates and proteins) and various concentrations of a neuropeptide (type‐A allatostatin), which affects generally the basal rates of secretion. Both maltose and glucose increase the release of amylase in vitro, but starch produces an inhibition of amylase release at lower concentrations. Bovine serum albumin (BSA), peptone and a mixture of amino acids have almost no effect on the release of aminopeptidase or carboxypeptidase, and only low concentrations of peptone increase trypsin release. High concentrations of both BSA and peptone strongly inhibit trypsin activity, perhaps by excess substrate binding to the trypsin active site. The allatostatin Grybi‐AST 5 elevates the release of amylase in vitro, but not of trypsin or aminopeptidase, in 2‐day‐old fed females. In the caeca from 1‐day‐old unfed crickets, both amylase and the trypsin release are stimulated in the presence of AST 5. The paracrine AST 5 is probably released from the gut endocrine cells and binds to the enzyme‐producing caecal cells.     

Calcitonin-immunoreactive cells of the digestive tract of the amphioxus are distributed concentrically in a restricted region of the mid-gut

In amphioxus (Branchiostoma belcheri), calcitonin‐immunoreactive cells of the digestive tract were distributed concentrically in a 1‐mm region of the latter half of the mid‐gut. In the mid‐gut caecum these cells were also present, but were dispersed throughout the length. The total number of cells in both parts ranged from 280 to 1157, varying from individual to individual, although the number in the mid‐gut caecum was only 100–200. These cells were morphologically typical gut endocrine cells. Considering their morphology and the characteristics of their distribution pattern, these cells may be related to some phenomena of digestive processes.     

Permeability and disruption of the peritrophic matrix and caecal membrane from Aedes aegypti and Anopheles gambiae mosquito larvae

In mosquito larvae, the peritrophic matrix (PM) separates the gut contents from the intestinal epithelium. This report describes a new in vivo assay for estimating PM permeability. The assay also allows for assessment of the permeability of the caecal membrane, a structure that separates each caecum from the gut lumen. Permeability was estimated by the appearance of fluorescently-labeled dextrans (size range 4,400 to 2 million Da) within the gastric caecae of mosquito larvae. While the intact peritrophic matrix was impermeable to 2 million Da dextran particles, it was permeable to dextran particles of 148 kDa and smaller. The caecal membrane appears to have considerably smaller pores, being permeable only to dextrans of 19.5 kDa and smaller. The assay was also used to devise a treatment that disrupts the PM sufficiently to allow the passage of virus-sized particles. Dithiothreitol and to a lesser extent, chitinase were effective in disrupting the PM. Cycloheximide had a small effect; Polyoxin D, Pronase and calcofluor did not alter the permeability to 2 million Da dextran particles. Disruption of the PM is discussed in the context of infecting mosquitoes with retroviral transformation vectors.     

Site‐specific profiles of biochemical properties in the larval digestive tract of Japanese rhinoceros beetle,Trypoxylus dichotomus (Coleoptera: Scarabaeidae)

The larvae of Japanese rhinoceros beetle, Trypoxylus dichotomus, feed on dead plant material in forest soils that are derived from fallen leaves broken down by basidiomycete fungi. Our previous work provided an understanding of the degradation of polysaccharides in dead plant material by T. dichotomus larvae and reported the complexity of the physicochemical and biochemical environment of the larval gut. Here, we examined ten divisions of the digestive tract of T. dichotomus larvae for physicochemical and biochemical conditions to elucidate site‐specifically functional properties along the tract. The distribution of potassium ions, pH, and acetic acid differed markedly along the length of the digestive tract with the potassium ion concentration profile closely reflecting that of pH along the length of the digestive tract. Distinct physicochemical environments were maintained in the digestive tract along with site‐specific polysaccharide degradation. Based on these findings, we suggest that there are metabolic relationships between the activities of the enzymes involved in polysaccharide degradation, the presence of intermediate metabolites and location along the digestive tract. Furthermore, we revealed that the anterior region of the gut plays an important role in the degradation of polysaccharides in the digestive tract of T. dichotomus larvae.     

Oleospheres of the cave-dwelling shrimp Troglocaris schmidtii: A unique mode of extracellular lipid storage

The cave-dwelling shrimp, Troglocaris schmidtii, has a unique mode of lipid storage. The lipid lies extracellularly in specialized compartments of the hepatopancreas, named oleospheres. The lipid is synthesized in the R-cells of the hepatopancreatic epithelium and accumulates in lipid droplets which fuse to form bigger globules. Mature lipid globules display moderately electron dense centers probably comprising triglycerides, and a broad electron dense boundary presumably consisting of lipoproteins. The globules are discharged into the lumen of the hepatopancreatic tubules by a kind of apocrine secretion. There, they coalesce to form larger masses. Finally, these lipid masses are transported into the oleospheres through a valve-like structure. The continual accumulation of lipid results in a drastic expansion of the oleospheres up to 500 μm in diameter. The absence of food in the digestive tract and the inactivity of the digestive enzyme producing F-cells indicate that digestion is suspended in the period of oleosphere formation. The curious mode of lipid storage in T. schmidtii may represent an adaptation to the extreme environmental conditions of a cave.