[Histochemical study of various lysosomal hydrolases of the intestinal epithelium during the development of the tadpole of Discoglossus pictus Otth, anuran amphibian. I. Light microscopy study]

Histology and lectin-binding patterns in the digestive tract of the carnivorous larvae of the anuran, Ceratophrys ornata

Larvae of Ceratophrys ornata are carnivorous, have relatively short digestive tracts and continue to feed during metamorphic climax, in contrast to those of more typical herbivorous anuran larvae. The present study describes both histological and histochemical changes in the stomach, small intestine, and large intestine of C. ornata prior to and during metamorphic climax. Modifications in these organs were found to be similar to but less dramatic than those in herbivorous larvae. Luminal epithelial cells in the three regions develop vacuoles, suggesting degeneration, but sloughing of this epithelium, as occurs in herbivorous larvae, was not observed in C. ornata. Multicellular tubular glands develop gradually in the gastric area during the larval stages, gastric pits appear during metamorphic climax, and mucous neck cells are first visible in the juvenile. Goblet cells in the small and large intestine increase in number during larval life, as do the number of folds in the intestinal wall. Increase in diameter and thickness of the wall occurs in the stomach as well as in the small and large intestine. Such changes result in an adult-type digestive tract characteristic of frogs in general. Staining with two horseradish peroxidase conjugated lectins, soybean agglutinin (SBA) and Ulex europaeus agglutinin I (UEA I), demonstrated specific sites along the digestive tract of glycoconjugates with terminal sugars N-acetylgalactosamine and alpha-fucose, respectively. As metamorphic climax approaches, staining intensities decrease--thus providing evidence for metamorphic changes in the sugar moieties of glycoconjugates present in the digestive tract of carnivorous larvae.

Morphological changes of the myenteric plexus neurons in the bullfrog (Rana catesbeiana) duodenum during metamorphosis

Myenteric plexus neurons of the duodenum in the bullfrog Rana catesbeiana were examined during metamorphosis by the Gros-Bielschowsky silver impregnation method and electron microscopy. Larval type neurons with slender and curved cell soma were recognized in the duodenum of the premetamorphic tadpole. They degenerate and decrease in number during early metamorphic climax through shrinkage of the cell soma and autolysis of the cytoplasm. These larval type neurons reduce to debris and then disappear. Two new cell types (adult type neurons) subsequently appear. These new neurons develop and increase in number during late climax and after metamorphosis. Those that appear first are large type A neurons each with a prominent axon and they stain darkly with silver. They enlarge during late stages. Subsequently small type B neurons appear which stain weakly with silver. They increase the number of their dendrites, change their shape, but enlarge only slightly during late development. In summary, therefore, it is concluded that during metamorphosis, the larval myenteric plexus neurons in the bullfrog duodenum are replaced by two new populations of adult neurons.

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.