Prenatal and postnatal differentiation of the small intestine in rat

Abstract

The gastrointestinal tract in the early prenatal development is an endoblastic mesenchyme-lined tube. The endoblast differentiates and gives origin to all epithelial structures (covering epithelium, glands). The mesenchyme develops into connective tissue, blood vessels, the smooth muscle cells of lamina muscularis mucosae and muscular tunic. Neuroectoblast cells participate in these processes--individual cells with future endocrine function, nerve cells and fibers that form nerve plexuses and vegetative ganglia. AIM OF THE PRESENT STUDY: To trace the changes in the small intestine development during the prenatal period in rat embryos and fetuses, and during the postnatal period in newborn rats. We specifically studied the beta-actin expression in the cytoskeletal structures of the covering epithelium and in the contractile elements of the differentiating smooth muscle cells. The presence and localization of the enteroendocrine EC cell was studied using the immunohistochemical expression of serotonin in them.

Material and methods: Material from rat embryos and fetuses aged 8-11, 12-15, 16-20 days of gestation and small intestine fragments from newborn rats was studied using routine hematoxylin-eosin staining, enzymohistochemically for succinate dehydrogenase and immunohistochemically for beta-actin and serotonin.

Results: In the early embryogenesis (8-11 day of gestation), the primitive gut of rat embryos is an endoblastic tube of 2-3 layers of cuboidal cells covered with a thin layer of mesenchyme. In the subsequent stages of embryonic and fetal development the processes of differentiation run at different rates in the different tissues. The maturation process in the small intestine wall of one-day-old newborn rats is incomplete. The mucosa presents with shallow crypts and loosely set villi. Differentiated resorptive and enteroendocrine EC cells are found in the lining epithelium.

Conclusion: The changes we found in the beta-actin expression in the contractile elements of the differentiating smooth muscle cells and the cytoskeletal structures of the lining epithelium probably reflect the induction interference between the derivatives of the mesenchyme and endoblast.