Raymond Ferrand

Changes in the Digestive Tract and Feeding Behavior of Anuran Amphibians during Metamorphosis

During metamorphic climax, anuran amphibians undergo dramatic changes as they pass from aquatic to terrestrial life. In particular, the digestive tract is completely modified. The pharyngeal filtering apparatus disappears. Striking transformations take place in the gastric region. The tadpoles glandular sheath regresses and ceases protruding from the gut wall. At the same time, a large permanent stomach is formed to replace the sheath, gastric glands develop, and the muscle layer thickens. The intestine also changes greatly. An overall shortening and rearrangement of its coils occurs. The histological changes that affect the intestine are largely confined to the epithelium. Degeneration occurs in the larval epithelium, while intense proliferation of stem cells results in the development of a new epithelium that is folded. During metamorphosis, the endocrine cells of the digestive tract are also redistributed. Such changes are associated with modifications in feeding behavior. Most tadpoles are microphagous and feed on particles suspended in the water, which they retain on the surface of the gill filters and other buccopharyngeal structures. Anuran tadpoles usually stop feeding at climax because the filtering apparatus degenerates. Moreover, at climax the larval intestinal epithelium is too altered to absorb anything, and the new intestinal epithelium has not yet developed. Juveniles and adults are predators (carnivores or insect eaters). The acquisition of binocular vision permits efficient perception of prey in a terrestrial environment. The new feeding behavior is also associated with the appearance of new enzymes. The secretion of proteolytic enzymes at the pancreas (trypsin) and stomach (pepsin) levels prepares the animals to digest meat. Chitinases are secreted by the stomach as soon as it differentiates and allow the digestion of chitinous insects. Moreover, the new intestinal mucosa is well equipped for the absorption of protein hydrolysis residues. Control of the digestive secretions and feeding behavior in developing anurans is also discussed in the present article.

Detection of endocrine cells by immunofluorescence method in the gastroenteropancreatic system of the adult eel, glass-eel, and leptocephalic larva (Anguilla anguilla L.)

Five antisera against insulin (Ins), glucagon (Glu), somatostatin (SRIF), met-enkephalin (met-enk), and serotonin (5-HT) were used for immunofluorescence detection of endocrine cells in pancreas and gastrointestinal tract (GIT) of the European eel (Anguilla anguilla L.) at three stages of development (leptocephalic larva, glass-eel, and adult eel). Comparable distribution of endocrine cells was observed for adults and glass-eels. In their pancreatic islets, positive immunoreactions were obtained only for Ins, SRIF, and Glu; this later was also present in the pancreatic ducts. 5-HT cells were present throughout the GIT. SRIF cells were situated mostly in the stomach and less in the intestine. Met-enk cells were abundant in the pyloric cecum, but less frequent in the intestinal mucosa. Glu cells were present only in the intestine. No insulin-immunoreactive cells could be detected in the GIT. The pancreatic islets of leptocephalic larvae exhibited a strong reaction for SRIF, a weak reaction for Glu, and none at all for Ins, met-Enk, or 5-HT. The GIT of these larvae contained numerous met-enk cells, mainly in the foregut. In the fore- and midgut, cells exhibited a weak fluorescence after treatment with Glu antiserum. No positive immunoreactive cells were observed with 5-HT, SRIF, or Ins antisera.

Human intestine epithelial cell acetyl- and butyrylcholinesterase

The epithelial cells of the human intestine exhibit a cholinesterase activity which is restricted to the apex of the villi. This activity displays a maximum in the colon and a minimum in the jejunum. Contrary to most of the studied vertebrates, the human cells present both acetylcholinesterase and butyrylcholinesterase activities, acetylcholinesterase being predominant in all the intestinal segments: duodenum, jejunum, ileum and colon. Like in the other vertebrates, only globular forms are identified by sucrose gradient centrifugation. However, the simultaneous presence, on the one hand of three globular forms (G1, G2 and G4) and, on the other hand of soluble as well as detergent-soluble molecular species seems to be a particular feature of the human cells.

Acetylcholinesterase and butyrylcholinesterase in the gut mucosal cells of various mammal species: Distribution along the intestine and molecular forms

1. A cholinesterase activity was shown to be present in the homogenates of the gut mucosal cells from seven mammal species examined. 2. The distribution of the cholinesterase activity in the mucosal cells along the intestine differs from one species to another. This distribution is not correlated with that of the aminopeptidase which is a specific marker of the enterocyte plasma membranes. 3. Except rabbit, all the other species contain a (G4) globular tetrameric form and either a (G1) monomeric form (pig, ox) or a (G2) dimeric form (mouse, rat, sheep). Both (G1) and (G2) forms are found with the (G4) form in the mucosal cells of kitten and cat. The solubility characteristics of these various forms were studied by sucrose gradient centrifugations in the presence and the absence of 1% Triton X-100. 4. The mucosal cells from the studied species essentially possess either acetylcholinesterase (rabbit, kitten, cat) or butyrylcholinesterase (ox, pig, sheep, rat, mouse). These findings indicate that both enzymes probably present identical physiological functions in this cell type.

In vitro studies on the self-differentiating capacities of quail adenohypophysis epithelium

SummaryIsolated epithelial rudiments of 3–4 days quail embryo adenohypophysis were cultivated in vitro. Differentiation of glandular cells occured when culture conditions allowed the formation of explants characterized by the presence of a fibroblastic sheet and of an epithelial roof surrounding a central cavity. Differentiation did not occur when culture conditions did not allow the fibroblastic sheet to be established or resulted in the absence of a cavity. The importance of the explant structure in differentiation is also indicated by the location of glandular cells. In vitro they differentiate near the cavity derived from Rathkes pouch lumen while in situ they first appear at the periphery of the rudiment, near the basement membrane.The results of this study show that the adenohypophyseal primordium can differentiate without any mesenchymal influence. The observed differentiation seems to be correlated with fibroblast-secreted material, and this hypo-thesis is discussed.

Immunohistological detection of methionine-enkephalin-like and endorphin-like material in the digestive tract and in the nervous system of the mussel: Mytilus edulis L.

Using the indirect immunofluorescence technique, methionine-enkephaline-like, alpha- and beta-endorphin-like peptides were detected on whole body sections of Mytilus edulis L. Met-enkephalin-like immunoreactivity was localized in the epithelium of the digestive tract, in the hepatopancreas, and in the nervous system. The immunoreactive cell bodies were very abundant in the anterior gastric epithelium, but sparse in the terminal portion of the digestive tract. By their basal processes the immunoreactive cells were in contact with a plexus of immunoreactive cells and fibers located in the connective tissue underlying the digestive epithelium. In the principal hepatopancreatic ducts, isolated cells showing met-enkephalin-like immunoreactivity were detected between the epithelial cells and the basal lamina. A few immunoreactive cells and fibers were observed between the hepatopancreatic tubules. The three pairs of nervous ganglia contained in their cortical layer numerous met-enkephalin-like immunoreactive perikarya. Their central area possessed fluorescent immunoreactive bundles of fibers extending to the commissures, the connectives, and the nerves. Met-enkephalin-like immunoreactive fibers were detected between the smooth muscle cells. At the surface of these smooth muscle cells, immunopositive met-enkephalin-like tapered nervous endings were observed. The alpha- and beta-endorphin antisera produced a positive immunoreaction in some gastric epithelial cells, in some perikarya of the pedal ganglia, and in some nervous fibers. The endorphin-like structures were far less abundant than the met-enkephalin-like structures, but very close to them.

Investigations of endocrine cells in the gastrointestinal tract and pancreas during the metamorphosis of an anuran (Alytes obstetricans L.): histochemical detection of APUD cells

Endocrine cells were detected at premetamorphosis, prometamorphosis, climax, and juvenile stages using an amine-inducing fluorescence technique with or without previous L-3,4-dihydroxyphenylalanine (L-DOPA) treatment. At premetamorphosis, serotonin cells exhibited yellow fluorescence in the gut primary epithelium of the L-DOPA untreated animals. In the treated animals, green fluorescent APUD cells could be seen in addition to the serotonin cells. In the pancreas, numerous clusters of fluorescent APUD cells were observed. At prometamorphosis the number of fluorescent cells increased in the intestinal primary epithelium and, close to the basal membrane, numerous small regenerative buds devoid of fluorescent cells appeared. In the pancreas of L-DOPA-treated animals, two types of APUD cells could be distinguished by their different fluorescence intensities. At the climax stage, the stomach developed and APUD cells were detectable in the gastric glandular buds. The degenerated primary intestinal epithelium was progressively removed in the intestinal lumen. At this stage, the regenerative buds of the secondary epithelium exhibited APUD cells. In the disorganized pancreas, the induced fluorescence decreased strongly. At the juvenile stage, cords of APUD cells displayed a cytoplasmic green fluorescence in the pancreas. In the stomach and intestine, serotonin and APUD cells were numerous.

The differentiation of follicular-like cells from the epithelium of Rathke's pouch grown in vitro

SummaryThe epithelial rudiment of 4 day-old quail embryo adenohypophysis, cultivated in vitro under conditions allowing glandular differentiation, displays peripheral cells that progressively acquire follicular cell features. They elongate, develop numerous microvilli, junctional complexes, interlocking membranes and bundles of microfilaments.These follicular-like cells derive from peripheral epithelial cells that, in situ, become glandular. These results show that follicular cells can develop from undifferentiated cells. They undergo this pathway of development, in all likelihood, as a result of perturbations in their microenvironment.

Characterization of cholinesterase molecular forms in the mucosal cells along the intestine of the chicken

The presence of a butyrylcholinesterase (BuChE, EC 3.1.1.8) in the musocal cells of the chicken intestine was demonstrated by histochemical and biochemical methods. The study of its distribution, along the intestine from duodenum to rectum, showed that the jejuno-ileum possesses the highest activity. Sucrose gradient centrifugation revealed, in all intestinal areas, two globular forms with sedimentation coefficients of 4.3 S (G1 form) and 10.8 S (G4 form). The presence of Triton X-100 in the preparations did not modify the sedimentation profiles of these two forms which can be considered as soluble BuChE. The ratio of G1/G4-forms progressively decreases along the intestine from duodenum to rectum indicating a predominance of the G4 form in the areas where the activity is low. Our results are discussed in relation to other studies of globular forms of chicken BuChE.

Quail Rathke's pouch differentiation

SummaryAdenohypophyseal region of quail embryo has been examined by electron microscopy from stage 12 to stage 21 of Zacchei (1961).The Seessels pouch develops prior to the early stages of adenohypophysis formation, then regresses while Rathkes pouch proliferates and differentiates.From Rathkes pouch formation by stage 12 (48 h of incubation) until appearance of the first secretory granules by stage 21 (6 days of incubation), there are no major ultrastructural modifications in adenohypophyseal cells. Mitochondria, Golgi vesicles, polysomic ribosomes, pinocytotic vesicles, and mitotic figures become more numerous while nucleocytoplasmic ratio and the number of ribosomes and lipid droplets decreases. The major change is the appearance of secretory granules by day 6 of incubation. This phenomenon occurs at the same time as in chick embryo, despite an incubation period shorter for quail than for chick. Mitotic figures are mainly distributed near the pouch lumen, while secretory granules are first located in the peripheral cells of the cephalic part ofpars distalis primordium. The hypothetical role of mesenchyme and vascularization is discussed.