Monoamine- and peptide-containing elements in the nemertine digestive tract

Detailed comparative-histological data on localization and morphological peculiarities of catecholamine-, serotonin-, neurotensin- and FMRFamide-containing elements in the nemertine digestive system are presented for the first time. Using fluorescent histochemistry and immunohistochemistry, pharynx, esophagus, and midgut were studied in five species from three genera of the White Sea nemertines. Described in various nemertine species are intra- and subepithelial cells of the open and closed type, containing biologically active substances. Their processes are distributed in basi- and subepithelial nerve plexuses and can make contact with lumen of the digestive tract. Species-specificity in localization of the cells containing certain biologically active substances is noticed both along the length of the tract and with respect to its epithelial layer. Peculiarities and common regularities in distribution are discussed, as well as a possible function of monoamine- and peptide-containing elements in the digestive tract of the studied nemertines and other invertebrates.     

Phylogenetic position of phylum Nemertini, inferred from 18S rRNA sequences: molecular data as a test of morphological character homology.

Partial 18S rRNA sequence of the nemertine Cerebratulus lacteus was obtained and compared with those of coelomate metazoans and acoelomate platyhelminths to test whether nemertines share a most recent common ancestor with the platyhelminths, as traditionally has been implied, or whether nemertines lie within a protostome coelomate clade, as suggested by more recent morphological analyses. Maximum-parsimony analysis supports the inclusion of the nemertine within a protostome-coelomate clade that falls within a more inclusive coelomate clade. Bootstrap analysis indicates strong support for a monophyletic Coelomata composed of a deuterostome and protostome-coelomate clade. Support for a monophyletic protostome Coelomata is weak. Inference by distance analysis is consistent with that of maximum parsimony. Analysis of down-weighted paired sites by maximum parsimony reveals variation in topology only within the protostome-coelomate clade. The relationships among the protostome coelomates cannot be reliably inferred from the partial sequences, suggesting that coelomate protostomes diversified rapidly. Results with evolutionary parsimony are consistent with the inclusion of the nemertine in a coelomate clade. The molecular inference corroborates recent morphological character analyses that reveal no synapomorphies of nemertines and flatworms but instead suggest that the circulatory system and rhynchocoel of nemertines are homologous to coelomic cavities of protostome coelomates, thus supporting the corresponding hypothesis that nemertines belong within a protostome-coelomate clade. The sequence data provide an independent test of morphological character homology.     

NADPH-diaphorase activity in the digestive system of gastropod molluscs <Emphasis Type="Italic">Achatina fulica</Emphasis> and <Emphasis Type="Italic">Littorina littorea</Emphasis>

Distribution and morphological peculiarities of nitroxidergic elements throughout the entire length of digestive tract was studied for the first time in gastropod molluscs Littorina littorea (Prosobranchia) and Achatina fulica (Pulmonata) using histochemical detection of NADPH-diaphorase (NADPHd). NO-ergic cells and fibers were revealed in all parts of the mollusc digestive system beginning from esophagus. Intensive NADPHd activity is found in a great number of intraepithelial cells of the open type and their processes in the intraand subepithelial nerve plexuses, subepithelial neurons, granular connective tissue cells, and multiple nervous fibers distributed among muscular elements of digestive tract as well as those in nerves innervating the tract. NADPHd was also revealed in receptor cells in the oral area and in the A. fulica CNS ganglia innervating the digestive tract. A. fulica has a more complicated organization of A. fulica nitroxidergic system of the digestive tract. A system of glomerular structures formed by thin NADPHd-positive neural fibers coming from epithelium is found directly beneath the epithelium in esophagus, stomach, and midgut of the mollusc. More superficially under the main groups of muscular elements there are revealed small clusters of NADPHd-positive neurons that can be classified as primitive, non-structured microganglia. The distribution pattern and a possible functional role of nitroxidergic elements in digestive tract of molluscs as compared with other invertebrate and vertebrate animals are discussed.     

Nitroxidergic elements in the digestive system of Mactra chinensis and Spisula sachalinensis (Mollusca: Bivalvia: Mactridae)

Localization and morphology of NO-ergic elements in the digestive system of bivalve molluscs Mactra chinensis and Spisula sachalinensis were studied using histochemical technique [1] for detection of NADPH-diaphorase (EC 1.6.99.1) [1]. The NO-producing elements were revealed in all parts of the digestive system of the studied animals. NADPH-diaphorase was found in cells of several morphological types as well as in nerve plexuses. The most abundant in the digestive tract parts of the studied molluscs were intraepithelial nerve cells of the “open” type, whose thin apical process is directed towards the gut lumen. Subepithelial NO-ergic neurons were revealed in stomach and crystalline style sac of Mactra chinensis. Besides, diformazan granules are present in brush-border epitheliocytes of the major and secondary ducts of the digestive gland as well as in cells of digestive tubules of this gland. All studied parts were found to contain basiepithelial and subepithelial NO-ergic nerve fibers forming networks of various densities from, most commonly, loose to dense plexuses particularly developed in labia, esophagus, and gut of the studied molluscs.     

Observations on the morphology of some North American nemertines with consequent taxonomic changes and a reassessment of the architectonics of the phylum

A majority of the nemertine species from the western North Atlantic were originally described from life in the nineteenth century. Many of these were established by A. E. Verrill who had ‘an eye for species’ no matter which phylum he was working with, and thus when living nemertines which he described are encountered, they can usually be recognized. The morphology of most of these species has never been reported; some may prove to be species described earlier from the eastern North Atlantic. Morphological observations on the nemertine species from the North East coast of the Pacific are inadequate and have prevented satisfactory comparison with species from Japan and eastern Russia. The morphology of some species collected in the Gulf of Maine and from Cape Cod, as well as a re-examination of some of the slides of type specimens of species from the west coast of North America, indicates that their generic placement must be re-examined. The architectonic plan of the heteronemertines postulated over 100 years ago can not be substantiated and is redescribed. Three new heteronemertean genera are described: Tenuilineus gen.n. Parvicirrus gen.n., Tarrhomyos gen.n.     

Light and electron microscopy studies of the oesophagus and crop epithelium in Aplysia depilans (Mollusca, Opisthobranchia)

The oesophagus and crop epithelium of Aplysia depilans consist in a single layer of columnar cells with apical microvilli, and some of them also possess cilia. Cell membrane invaginations, small vesicles, multivesicular bodies and many dense lysosomes were observed in the apical region of the cytoplasm. In most cells, a very large lipid droplet was observed above the nucleus and a smaller one was frequently found below the nucleus; glycogen granules are also present. Considering these ultrastructural features, it seems that these cells collect nutritive substances from the lumen by endocytosis, digest them in the apical lysosomes and store the resulting products. The cell bodies of mucus secreting flask-shaped cells are subepithelial in the oesophagus and intraepithelial in the crop. Histochemistry methods showed that the secretion stored in these cells contains acidic polysaccharides. Secretory vesicles with thin electron-dense filaments scattered in an electron-lucent background fill most of these cells, and the basal nucleus is surrounded by dilated rough endoplasmic reticulum cisternae containing small tubular structures. Considering the relatively low number of secretory cells, mucus production cannot be high. Moreover, since protein secreting cells were not observed in either oesophagus or crop, extracellular digestion in the lumen of these anterior segments of the digestive tract most probably depend on the enzymes secreted by the salivary and digestive glands.     

Structure and carbohydrate histochemistry of the esophagus in ten teleostean species

The histology and carbohydrate histochemistry of ten teleostean esophagi were compared. Structurally, the four layers of a typical vertebrate digestive tract were consistently present. The epithelium was always stratified and in all but one species (Ictalurus nebulosus) contained taste buds. Esophageal mucous cells were not the typical goblet cells seen in other vertebrates but appeared to be of six different types, pairs of which were associated with particular families. In esocids, poorly developed mucous acini and serous monogranular cells were present. In all species, the subepithelial connective tissue was not divided into definitive lamina propriae and submucosae due to the absence of muscularis mucosae. Variably present in this connective tissue region were argentophilic fibers and in esocids only, randomly dispersed striated muscle fibers. The arrangement of the muscularis was reverse to that of the general vertebrate plan. In mucous cells, three general types of epithelial mucosubstances were identified and in broad terms were recognized as sulfomucins, sialomucins and neutral mucosubstances. Morphological differences were accompanied by differences in carbohydrate localization, each esophageal epithelium containing at least two different mucosubstances. However, the mucosubstances identified in each mucous cell had a profile of characteristics different in some respects from any other. Thus teleostean esophagi appear to perform an integrated diversity of functions as reflected by their complex morphology and carbohydrate histochemistry.     

NEMERTINES AS POSSIBLE ANCESTORS OF THE VERTEBRATES

1. Primitive vertebrates have many characters which do not appear to be immediately represented in any obvious precursor. 2. The hypothesis is put forward that creeping, or bottom-living worms, classifiable as nemertines, attempted to recolonize the water by acquiring buoyancy, by swimming or both. 3. Some of those that succeeded were able to do so by adopting a method of filter-feeding made adequate by the development of gill slits, and then converting the proboscis rudiment into a semi-rigid structure (the notochord) essential for oscillatory swimming movements. These were the precursors of the protochordates and the vertebrates. 4. The acquisition of the ability to swim efficiently depended on the simultaneous development of distance receptors and the co-ordination of the information that they provided with that provided by proprioceptors on the one hand and with the changing motor systems on the other. This entailed the development of a far more extensive nervous system, probably by incorporating into it much more of the dorsal ectoderm, and superimposing a primarily sensori-motor system on to the more vegetative system already present in nemertines. This was achieved by elaboration of the placodal folding of the ectoderm which is characteristic of many nemertine embryos of the present day. In this manner a new central nervous system was combined and integrated with the existing more primitive ‘autonomic’ system and the cephalic ganglia of the nemertines became incorporated in the hypothalamus. 5. The hypothesis suggests likely precursor tissues from which the following vertebrate structures could plausibly have developed: olfactory organ, lateral line system, anterior and posterior pituitary, thyroid, pineal organ, chloride-secreting cells, oxyntic cells, notochord, urinogenital system, liver, and several others. 6. The possible origins of the vertebrate eye, the somitic muscles, and some other fundamental features of the vertebrates are discussed. The evidence is still equivocal. 7. The acquisition of filter-feeding and swimming by nemertine worms would be expected to bring into operation a whole new system for the selection of appropriate genes and thus inaugurate a period of very rapid and probably divergent evolution, made even more rapid by the enormous advantages gained by animals acquiring efficient form-vision together with rapid and well co-ordinated movements. It is thought likely that the rapid evolution of this group of animals, which possessed few features conducive to clear fossil remains, accounts for the apparent break in the continuity of the story of animal evolution which has until now made the origin of the vertebrates such an enigma. 8. It is suggested that studies of the proteins and secretions of the various organs of the nemertines and their comparison with those of the organs of the more primitive vertebrates might lead to the establishment of some important homologies.     

Localization of NO-Ergic Structures in Oral Lobes, Labia, and Esophagus of the Bivalve Mollusc Crenomytilus grayanus

Localization of NO-ergic elements in oral lobes, labia, and esophagus in the bivalve mollusc, mussel Crenomytilus grayanus was studied using histochemical technique [1] for detection of NADPH-diaphorase (EC 1.6.99.1). The NO-producing elements were revealed in all studied parts of the digestive system. NADPH-diaphorase was found in nerve and secretory cells as well as in nerve plexuses. Numerous NO-ergic nerve cells were observed in the basal part of epithelium of labia and of the initial part of esophagus as well as in the subepithelial area of these organs. In the middle and posterior parts of esophagus, only subepithelially located NO-ergic nerve cell are present. Basiepithelial NO-producing secretory cells are found in all the parts, but most of these cells are observed in labia and the initial part of esophagus. Subepithelial secretory cells labeled with diformazan granules are spread from the folded surface of oral lobes to the initial part of esophagus; no such cells were found on the smooth surface of the lobes. The deposit labeled basi- and subepithelial nerve plexuses in all studied organs except for oral lobes. These plexuses are the most developed in labia and the initial part of esophagus of the studied mollusc.     

Immunohistochemical detection of regulatory cells in the digestive system of leeches

The digestive system of four leech species,Glossiphonia complanata, Hirudo medicinalis, Haemopis sanguisuga, andErpobdella octoculata, was studied using, as markers, antisera to biologically active peptides, neurotensin, calcitonin, FRMF-amide, and serotonin. In the epithelium and the wall of the alimentary tract, regulatory cells were revealed. They differed in shapes and detected immunoreactivities; presumably they are elements of the diffuse endocrine system as well as of the peripheral nervous system. The data obtained show that the organization of the intestinal regulatory system in leeches basically is similar morphologically to intestinal regulatory systems of representatives of other classes of this type of invertebrate animals.     

Intestinal Regulatory Systems of Invertebrates and Their Probable Evolution in Multicellular Animals

A wide distribution of regulatory (endocrine, nerve) cells in the digestive tract epithelium has been shown in representatives of taxons at different levels of the evolutionary tree, and their brief comparative characteristics are presented. The hypothesis is put forward that the intestinal regulatory systems, on having initially appeared based on predominantly nerve elements, were subsequently complicated due to the appearance of various endocrine cells originating from the epithelial ones. In the course of evolution, the spatial separation occurred of this heterogeneous system into the intraepithelial endocrine and subepithelial nerve components, this process running in parallel in the rows of protostomian and deuterostomian animals.     

两栖类消化道嗜银细胞和5-羟色胺细胞的研究进展

嗜银细胞属于内分泌细胞类,是消化道所含各类内分泌细胞的总称,5-羟色胺是其中含量和分布范围较广的一种胃肠激素。本文总结了两栖动物消化道嗜银细胞和5-羟色胺细胞的形态学特征、分布位置和分布密度规律,概述了冬眠、禁食和不同生活史阶段与两种细胞分布密度的关系。     

Structure and Action of Nemertine Toxins

Bacq (1936, 1937) discovered two substances by pharmacologicalexperiments using whole body extracts of various nemertine species."Amphiporine," found only in hoplonemertines, stimulated nicotinicacetylcholine receptor-mediated events. "Nemertine" evoked spontaneousaction potentials in isolated crab nerves. Both substances causedconvulsions when injected into crabs. Anabaseine, a pyridinealkaloid isolated from the hoplonemertine Paranemertes peregrina,has chemical and pharmacological properties equivalent to "amphiporine."Hoplonemertines produce a wide variety of pyridine toxins dependingon the species. The heteronemertine Cerebratulus lacteus contains cytolytic(10,000 dalton) and neurotoxic (6,000 dalton) proteins. Theneurotoxic polypeptides most closely resemble "nemertine": theycause repetitive spiking in isolated crustacean axons. Severalcytolytic and neurotoxic "isotoxins" occur within Cerebratulus. Both the hoplonemertine and heteronemertine toxins are localizedin the integumentary tissues of the body wall and proboscis.So far, the pyridine alkaloid toxins are only found in the Enoplanspecies, where they probably function as both offensive anddefensive toxins. Protein toxins have only been found in Anoplanspecies; they probably serve as a chemical defense against somepredators.     

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.     

Ecological and Geographical Reasons for the Variation of Digestive Tract Length in Anurans

Changes of environmental conditions can shape organs size evolution in animal kingdoms. In particular, environmental changes lead to difference in food resources between different habitats, thereby affecting individual's energy intake and allocation. The digestive theory states that animals consuming food with low contents of digestible materials should result in increasing gut length. In this study, to test the hypothesis of digestive theory, we studied ecological and geographical reasons for variation in digestive tract length among 35 species of anurans distributing in different altitude and latitude. The results showed that ecological type significantly affected digestive tract length among species, with aquatic and terrestrial species having longer digestive tract than arboreal ones. Latitude was positively correlated with digestive tract length. However, altitude, as well as monthly mean temperature and precipitation, did not correlate with digestive tract length among species. Our findings suggest that aquatic and terrestrial species might forage less digestible materials than arboreal species, thereby displaying relatively longer digestive tract than arboreal species.     

Ultrastructural changes of the midgut epithelial cells in feeding and moulting nymphs of the tick Haemaphysalis longicornis

The midgut epithelial cells in nymphs fed on laboratory rabbits were examined during feeding and after detachment. The midgut epithelium at the unfed stage consisted of digestive cells of lower activity, containing such nutritive substances as protein, lipid and glycogen. As feeding proceeded, the cells became active in intracellular digestion. At the middle of the feeding stage, the spent digestive cells derived from the active digestive cells began to be replaced by the new digestive cells of lower activity. After detachment, the pinocytotic activity of the above cells increased greatly, and the digestive activity increased to some extent. As a result, many large endosomes were formed by fusion of numerous pinosomes. Thereafter, endosomes decreased in size as digestion proceeded and there was an increase of haematin granules. On day 7 after detachment, the new digestive cells of lower activity, belonging to the 'nutritional reserve' type, appeared adjacent to the spent digestive cells which had almost exhausted all endosomes, and these new cells had completely replaced the spent cells by day 3 after moulting.     

The digestive tract of Helicoradomenia (Solenogastres, Mollusca), aplacophoran molluscs from the hydrothermal vents of the East Pacific Rise

Abstract. Species of Helicoradomenia are constantly found at hydrothermal vent sites of the eastern and western Pacific Ocean. The digestive tract of 2 species of the genus was investigated with special focus on the ultrastructure and histochemistry of epithelia and glandular organs. The preoral cavity and foregut epithelia are composed of microvillous main cells, secretory cells producing protein-rich substances, and sensory cells with specialized cilia. The foregut bears a pair of glands with 3 types of extremely long-necked glandular cells surrounded by musculature. Each glandular cell opens directly into the radula pocket without a gland duct. The large radula apparatus consists of pairs of denticulated bars resting on a flexible radular membrane without elaboration of a subradular membrane. The midgut has a narrow, mid-dorsal tract of ciliary cells, but most of the epithelium is composed of digestive cells with a highly developed lysosomal system. The hindgut is lined by ciliated cells and free of glands. The foregut and radula seem to be highly efficient in the capture of relatively large, motile prey. Food contents within the midgut lumen and within some of the large secondary lysosomes indicate a triploblastic metazoan prey of non-cnidarian origin. The digestive tract is not adapted to microvory and there is no indication of a symbiosis with chemoautotrophic bacteria.     

Survival, physiology, and lysis of Lactococcus lactis in the digestive tract.

The survival and the physiology of lactococcal cells in the different compartments of the digestive tracts of rats were studied in order to know better the fate of ingested lactic acid bacteria after oral administration. For this purpose, we used strains marked with reporter genes, the luxA-luxB gene of Vibrio harveyi and the gfp gene of Aequora victoria, that allowed us to differentiate the inoculated bacteria from food and the other intestinal bacteria. Luciferase was chosen to measure the metabolic activity of Lactococcus lactis in the digestive tract because it requires NADH, which is available only in metabolically active cells. The green fluorescent protein was used to assess the bacterial lysis independently of death. We report not only that specific factors affect the cell viability and integrity in some digestive tract compartments but also that the way bacteria are administrated has a dramatic impact. Lactococci which transit with the diet are quite resistant to gastric acidity (90 to 98% survival). In contrast, only 10 to 30% of bacteria survive in the duodenum. Viable cells are metabolically active in each compartment of the digestive tract, whereas most dead cells appear to be subject to rapid lysis. This property suggests that lactococci could be used as a vector to deliver specifically into the duodenum the proteins produced in the cytoplasm. This type of delivery vector would be particularly appropriate for targeting digestive enzymes such as lipase to treat pancreatic deficiencies.     

A histochemical and immunohistochemical study of digestive enzymes and hormones during the larval development of the sea bream, Sparus aurata L.

Summary The distribution of different hydrolytic enzymes and the localization of the hormones which regulate glucose metabolism during development of the digestive tract of the sea bream, Sparus aurata L., were studied. The yolk sac contains trypsin, glucose-6-phosphatase, ATPases and acid and alkaline phosphatase activities. Positive insulin, glucagon and somatostatin cells were observed in the pancreas and in the lumen of the intestinal tract during endogenous feeding. From hatching until 3 days later, the digestive tract of sea bream larvae shows no enzymatic activities. During exogenous feeding, the activities of the phosphatases and trypsin generally increase, as do the amounts of the hydrolytic enzymes and trypsin, as well as the pancreatic and intestinal hormones. The enzymatic activities gradually decrease from the anterior part towards the posterior part of the digestive tract.