Development of the bovine duodenum with reference to enterochromaffin cells

Human amniocytes regulate serotonin levels by active uptake and express genes suggestive of a wider role in facilitating neurotransmitter regulation in the fetal environment

Fetal serotonin levels, which mediate multiple developmental processes, are highly regulated. However, an incomplete picture exists on the component parts of such regulation during fetal growth. Serotonin and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) are found in the amniotic fluid, also containing significant numbers of amniocytes, previously thought to be the result of cell shedding as a byproduct of growth. The aim of the present study was to examine human amniocytes as a potentially active and dynamic component of serotonin regulation in the fetal environment. Using amniocytes derived from multiple donors of amniocentesis, we found all components necessary for serotonin metabolism. We identified a strong expression of the serotonin transporter and confirmed the high-affinity serotonin transporter-mediated uptake of serotonin (5-HT), along with uptake via the norepinephrine transporter, and an evidence of 5-HT breakdown due to the expression of the degradative enzymes monoamine oxidase A and B. Additionally, wider expression analysis for biogenic amine and cholinergic metabolism suggests a capability for cholinergic synthesis and release and for catecholamine storage. Our results shed new light on amniocytes, consistent with a role in the homeostasis of neurotransmitters during fetal development. Moreover, these results may provide clinical significance for amniocytes as new targets for uptake inhibitors such as tricyclic antidepressants, selective serotonin reuptake inhibitors, and drugs of abuse such as cocaine, with implications on their regulation during pregnancy. This work shows for the first time an inherent in vivo function of amniocytes and more broadly implicates them as a new and active component of the fetal-maternal regulatory system.

Placenta detachment: unexpected high concentrations of 5-hydroxytryptamine (serotonin) in fetal blood and its mitogenic effect on placental cells in bovine

The purpose of this study was twofold: (1) to determine whether there is a profile of 5-hydroxytryptamine (5-HT, serotonin) concentrations in fetal bovine blood and tissues during pregnancy, parturition and the early neonatal period and (2) to determine whether 5-HT has a 'mitogenic' effect on cultured placentome cells in bovine. Results revealed a 5-HT concentration profile in fetal blood. Overall concentrations of 5-HT in fetal blood were 6.6 times (P< 0.001) that of adult cows and 2.8 times (P< 0.001) that of blood collected during caesarean section (from umbilical veins) and from 18-72 h old calves. Mid-term and full-term pregnancy fetuses were not statistically different from each other. Overall concentrations of 5-HT in the intestinal wall of the fetus were 4.4 times higher (P< 0.05) than in the 24 h calf. Concentration of 5-HT in full-term muscle was 3.5 times higher than in mid-term muscle and 2.8 times higher than in 24 h old calf muscle (P< 0.05). Concentrations of 5-HT in mid-term and full-term cotyledon were 4.4 times higher (P< 0.05) than in post partum cotyledon. Characterized trophoblast cells and a heterogeneous population of bovine cotyledon cells treated with 5-HT (2.5, 5.0 and 10.0 microm) incorporated between 2.0 and 3.0 times more(3)[H]-thymidine than untreated controls, indicating a dose-dependent (r=0.94) positive mitogenic effect of 5-HT. Both groups of cultured cells responded equally. Five-HT treatment did not affect either cell number or cell size. It was concluded that a 5-HT concentration profile exists in fetal bovine blood and tissues and that 5-HT has the ability to act as a mitogen in bovine placental cells.

Ontogeny of neurohormonal peptides, serotonin, and nitric oxide synthase in the gastrointestinal neuroendocrine system of the axolotl (Ambystoma mexicanum): an immunohistochemical analysis

The ontogeny of the neurohormonal peptides vasoactive intestinal polypeptide (VIP), neurotensin (NT), substance P (SP), calcitonin gene-related peptide (CGRP), gastrin/cholecystokinin (GAS/CCK), and somatostatin (SOM) as well as serotonin (SER) and nitric oxide synthase (NOS) was investigated in the gastrointestinal tract of the urodele Ambystoma mexicanum, the axolotl, using immunohistochemical techniques. The first regulatory substances to appear were SP, SOM, and SER that could be immunohistochemically detected up from stage 1. At early stage 2, VIP immunoreactivity was observed infrequently in enteric nerve fibers. With the onset of external feeding at late stage 2, SP-immunoreactive (IR) and SER-IR endocrine cells and VIP-IR nerve fibers were present throughout the gastrointestinal tract. Furthermore, in the small intestine NT-IR and GAS/CCK-IR endocrine cells appeared. At stage 3, SER immunoreactivity was observed not only in endocrine cells but also in nerve fibers. CGRP-IR and SP-IR nerve fibers were detectable at stage 4 and stage 5, respectively. From stage 5 on, a minority of the CGRP immunoreactivity occurred in SP-IR nerve fibers. NOS immunoreactivity did not appear before stage 6 when it was found infrequently in nerve fibers. Thus, several phases of development can be distinguished: (1) at the yolk sac stages only few regulatory substances are present. (2) At the onset of external feeding, all endocrine cell types investigated were readily detectable. Thus, the onset of external feeding seems to trigger the development of the gastrointestinal endocrine system. (3) The endocrine cells are first found in the proximal part of the gastrointestinal tract and later in higher numbers in the distal parts. (4) The dually distributed neurohormonal peptides and SER first appear in endocrine cells and later additionally in nerve fibers. Thus, the nerve fibers likely set up the fine regulation of gastrointestinal blood flow and motility.

[Prenatal development of the lamina epithelialis in the phase of vacuolization of villous epithelial cells. Investigations on the intestines of cattle (Bos primigenius taurus L., 1758)]

The development of the bovine small intestine was examined in 39 embryos and fetuses by light microscopic and transmission electron microscopic methods. Special reference was paid to the histogenesis of the ephithelium. In contrast to the duodenum the epithelium of jejunum and ileum undergoes a degeneration by vacuolation of its villous epithelial cells. The demonstration of the acid phosphatase activity of these vacuoles shows their lysosomal character. This degenerative process of the small intestinal epithelium is also known in large intestine where it leads to the destruction of the intestinal villi. Both seem to be part of a 'principle of construction of the intestine of the vertebrates' (Wille, 1984).

[Early fetal development of the small intestine mucosa in cattle (Bos primigenius taurus)]

The development of the bovine small intestine was examined in 24 embryos and fetuses by light microscopic, scanning and transmission electron microscopic methods. Special reference was paid to the genesis of the epithelium and particularly of the villi intestinales. The primitive intestine consists of one layer of epithelial cells surrounded by mesenchym and tunica serosa. The fetal intestine (up to the 24th week of gestation) shows all the morphologic structures of the adult. In small intestine the development of cryptae and villi intestinales starts before the 7th week of gestation and progresses with a proximo-distal gradient. Epithelial proliferation that gives rise to primary epithelial villi makes epithelium become temporarily stratified. Finger-like secondary villi develop by proliferation of the mesenchym. In addition to this process mucosal folds occur in duodenum giving rise to villi by segmentation. At the same time the differentiation of epithelium starts. The fetal small intestine, like many other fetal tissues displays masses of glycogen.