A histological and dynamic study of the gastric region of Discoglossus pictus larvae, cultured with or without thyroxine

Abstract

The organotypic culture of the gastric region is carried out on premetamorphic Discoglossus pictus larvae. Adding thyroxine to the culture medium provokes various transformations. On the cytological level, the reactions observed, which are variable depending on the cell category concerned, can be divided into two types of phenomena: histolytic and histogenetic. Autophagia linked to lysosome intervention is frequently found among the histolytic processes. Autophagic vacuoles and residual bodies are observed. The gastric lumen is filled with deteriorated cells that probably come from the degeneration of the tadpole epithelium (primary epithelium). The incorporation of tritiated thymidine makes it possible to study the evolution of cell proliferation in the control and in the thyroxinated cultures. After a 1-2 day latency period, possibly due to the adjustment of the tissue to the culture environment, the incorporation of the radioprecursor H3-thymidine into the epithelium and the tunica muscularis of thyroxine-treated gut tissue increased on day 3, reached a maximum on day 5, and then dropped slightly on day 7. In the control cultures H3-thymidine incorporation showed the same pattern but lower levels on the same days. The histolytic phenomena induced by thyroxine in vitro are comparable to those of natural metamorphosis. On the other hand, the histogenetic phenomena are incomplete. Proliferating and transitional phases occur but neoformated (or secondary) epithelium does not replace the degenerated primary epithelium, whatever the culture time.

Cytological and Morphological Changes during Amphibian Metamorphosis

“…At higher levels of T4 (10-7 g/ml), acid phosphatase activity is recognized in lysosomes, the Golgi apparatus, and occasionally in other regions of the cell. Necrotic cells are extruded into the lumen of the explant, in a manner similar to that occurring in vivo (Pouyet and Hourdry, 1977).…”

“…Islet cells A and B have granules, probably originating from Golgi saccules. So-called D cells identified in the larval pancreas are not seen in the cultured tissue (Pouyet and Beaumont, 1975).…”

Thyroid hormone-induced apoptosis of larval cells and differentiation of pepsinogen-producing cells in the stomach of Xenopus laevis in vitro

“…In the anuran stomach, however, there have been, to our knowledge, no successful in vitro studies of organspecific differentiation of the adult epithelial cells. Although TH-induced degeneration of the larval epithelial cells and proliferation of the adult epithelial cells have previously been reported in vitro [29], it still remains unclear whether differentiation of Pg-producing cells can be induced by TH. To address this question, we cultured stomach fragments isolated from X. laevis tadpoles according to the organ culture method we have previously established for X. laevis intestine [13].…”

Effect of triiodothyronine on the growth and survival of larval striped bass (Morone saxatilis)

“…In mammals, thyroid hormones promote development of the intestine in neonates (Yeh and Moog 1974;Celano et al 1977;Henning 1981;Raul et al 1983). In amphibians, under in vitro conditions, thyroxine (T4) increases the proliferation of gastric epithelium of premetamorphic Discoglossus pictus (Pouyet et al 1983). The ability of thyroid hormones to induce metamorphosis of flounder (Paralichthys olivaceus) (Inui and Miwa 1985;Miwa and Inui 1987) suggests that thyroid hormones might be involved in structure organization.…”