Development of the human gastrointestinal tract: twenty years of progress

Development of the fetal intestine in mice lacking the glucocorticoid receptor (GR)

During rodent development there are two surges of circulating corticosterone: one just prior to birth and then one in the third postnatal week. Prior studies have shown that the latter controls the rate of intestinal development in the postnatal period. To date, a role for the earlier surge in the prenatal phase of intestinal development has not been investigated. We hypothesized that the late fetal surge of circulating corticosterone is involved in both morphologic and functional maturation of the intestinal epithelium, and thus that such maturation would be delayed if glucocorticoid action was abrogated. The hypothesis was tested by studying intestinal development in mice lacking a functional glucocorticoid receptor (GR). After GR+/- mice were bred onto a C57Bl/6 background, heterozygote matings yielded the expected ratios of -/-, +/-, and +/+ offspring. Analysis of GR mRNA in intestines of +/+ and -/- fetuses confirmed expression in wild-type mice but not in the GR-null mice. Intestinal histology of GR+/+ and -/- littermates at E13.5, E15.5, and E18.5 showed no effect of GR genotype on morphologic development. Further studies at E18.5 showed that GR-/- mice have normal functional maturation of the intestinal epithelium as assessed by: lactase activity in the enterocyte lineage, normal numbers of goblet and enteroendocrine cells, and normal numbers of proliferating cells in the intestinal crypts. Neither the minerolocorticoid receptor (MR) nor the pregnane X receptor (PXR) showed compensatory up-regulation in GR-/- mice. We conclude that, in contrast to our original hypothesis, the rodent intestine passes through a phase of glucocorticoid independence (late fetal) prior to becoming responsive to glucocorticoids in the postnatal period. These findings have implications for the clinical use of corticosteroids to enhance intestinal maturation in preterm infants.

Dietary influence of kefir on microbial activities in the mouse bowel

AIMS

In this work the microflora present in kefir, a fermented milk product, was studied together with the effect of kefir administration on different groups of indigenous bacteria of mouse bowel.

METHODS AND RESULTS

Kefir microflora was composed of lactic acid bacteria, acetic acid bacteria and yeasts. Yeast population was composed of Saccharomyces cerevisiae, S. unisporus, Candida kefir, Kluyveromyces marxianus and K. lactis. The streptococci levels in kefir treated mice increased by 10-fold and the levels of sulfite-reducing clostridia decreased by 100-fold. The number of lactic acid bacteria increased significantly.

CONCLUSIONS

The administration of kefir significantly increased the lactic acid bacteria counts in the mucosa of the bowel. Ingestion of kefir specifically lowered microbial populations of Enterobacteriaceae and clostridia.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first long-term study about the effects of the kefir administration on the intestinal microflora of mice.

Preterm birth affects the intestinal response to parenteral and enteral nutrition in newborn pigs

Maturation of gastrointestinal (GI) function in neonates is stimulated by enteral nutrition, whereas parenteral nutrition induces GI atrophy and malfunction. We investigated whether preterm birth alters the GI responses to parenteral and enteral nutrition. Pigs were delivered either preterm (107 d gestation) or at term (115 d gestation) and fed total parenteral nutrition (TPN) or enteral sow's milk (ENT) for 6 d after birth. Immaturity of the preterm pigs was documented by reduced blood pH, oxygen saturation and neutrophil granulocyte function, impaired intestinal immunoglobulin G uptake from colostrum, and altered relative weights of visceral organs (small intestine, liver, spleen, pancreas, and adrenals). For both ages at delivery, increases occurred in pancreatic weight (30-75%) and amylase activity (0.5- to 13-fold) after birth, but much more in ENT than in TPN pigs (P < 0.05). Six days of TPN feeding was associated with reduced intestinal weight for both delivery groups (60% of values in ENT, P < 0.001), but only in term TPN pigs was the weight lower than at birth (-20%, P < 0.05). Likewise, it was only in term TPN pigs that intestinal maltase activity increased, compared with ENT, and the absorption of glucose and proline decreased. Only in preterm pigs did TPN feeding increase lactase activity (+50% compared with ENT, P < 0.05). For both delivery ages, the mRNA of lactase-phloridzin hydrolase and sodium-coupled glucose transporter 1 (SGLT-1) were increased in TPN, compared with ENT. In conclusion, the trophic effect of enteral vs. parenteral nutrition on the GI tract is also present after preterm birth, but the postnatal maturation of many GI functions is modified, compared with term birth. The effects of nutritional regimen on the maturation of the gut epithelium in neonates depend on gestational age at birth.

Epimorphin expression in intestinal myofibroblasts induces epithelial morphogenesis

The formation of the crypt-villus axis during gut ontogeny requires continued reciprocal interactions between the endoderm and mesenchyme. Epimorphin/syntaxin 2 (epimorphin) is a mesenchymal protein expressed in the fetal gastrointestinal tract during villus morphogenesis. To elucidate its role in gut ontogeny, the epimorphin cDNA was transfected, in sense and antisense orientations, into a rat intestinal myofibroblast cell line, MIC 216. To determine the effects of epimorphin on the epithelium, myofibroblasts were cocultured with the Caco2 cell line. Caco2 cells spread in a simple monolayer over antisense-transfected cells lacking epimorphin. In contrast, sense-transfected myofibroblasts induced Caco2 cells to form compact, round clusters with small lumens. These morphologic differences were preserved in Transwell cocultures in which cell-cell contact was prevented, suggesting that epimorphin's effects were mediated by secreted factor(s). To determine the effects of epimorphin on crypt-villus axis formation in an in vivo model, rat gut endoderm was combined with epimorphin-transfected myofibroblasts and implanted into the chick intracoelomic cavity. The grafts in which epimorphin was overexpressed revealed multiple well-formed villi with crypt-like units, whereas those in which epimorphin expression was inhibited developed into round cystic structures without crypts or villi. Of several potential secreted morphogens, only the expression of bone morphogenetic protein 4 (Bmp4) was increased in the epimorphin-transfected cells. Incubation with noggin partially blocked the transfected myofibroblasts' effects on Caco2 colony morphology. These results indicate that mesenchymal epimorphin has profound effects on crypt-villus morphogenesis, mediated in part by secreted factor(s) including the Bmp's.

Influence of diet complexity on intestinal adaptation following massive small bowel resection in a preclinical model

AIMS

To investigate the effect of dietary complexity on intestinal adaptation using a preclinical model.

METHODS

Four-week-old piglets underwent a 75% proximal small bowel resection or transection operation (control). Post-operatively, animals received either pig chow (n = 15), polymeric formula (n = 9), polymeric formula plus fiber (n = 6), or elemental formula (n = 7).

RESULTS

The weight gain of all groups was reduced compared with controls that were fed the same diet. Animals that had a resection, which were fed elemental formula, had significantly reduced weight gain compared with the other groups (4.7 4.2 vs 30.7 7.1 kg chow and 11.5 1.3 kg polymeric formula). Villus height was increased in the jejunum, ileum and terminal ileum of resected animals compared with controls in animals fed with pig chow, polymeric formula and elemental formula. The animals that had a resection had a significant reduction in the transepithelial conductance (10.4 5.5 vs 25.4 6.5 mS/cm2) and 51Chromium-EDTA flux (2.8 1.9 vs 4.8 4.9 microL/h per cm2) compared with the controls.

CONCLUSIONS

A complex diet was found to be superior to an elemental diet in terms of the morphological and functional features of adaptation following massive small bowel resection.

Hepatocyte nuclear factor-1 alpha, GATA-4, and caudal related homeodomain protein Cdx2 interact functionally to modulate intestinal gene transcription. Implication for the developmental regulation of the sucrase-isomaltase gene

Sucrase-isomaltase (SI), an intestine-specific gene, is induced in the differentiated small intestinal villous epithelium during the suckling-weaning transition in mice. We have previously identified cis-acting elements within a short evolutionarily conserved SI promoter. However, the nature and profile of expression of the interacting proteins have not been fully characterized during this developmental transition. Herein, we show that hepatocyte nuclear factor-1 alpha (HNF-1 alpha), GATA-4, and caudal related homeodomain proteins Cdx2 and Cdx1 are the primary transcription factors from the adult mouse intestinal epithelium to interact with the SIF3, GATA, and SIF1 elements of the SI promoter. We wanted to study whether HNF-1 alpha, GATA-4, and Cdx2 can cooperate in the regulation of SI gene expression. Immunolocalization experiments revealed that HNF-1 alpha is detected in rare epithelial cells of suckling mice and becomes progressively more expressed in the villous epithelial cells during the suckling-weaning transition. GATA-4 protein is expressed exclusively in villous differentiated epithelial cells of the proximal small intestine, decreases in expression in the ileum, and becomes undetectable in the colon. HNF-1 alpha, GATA-4, and Cdx2 interact in vitro and in vivo. These factors activate SI promoter activity in cotransfection experiments where GATA-4 requires the presence of both HNF-1 alpha and Cdx2. These findings imply a combinatory role of HNF-1 alpha, Cdx2, and GATA-4 for the time- and position-dependent regulation of SI transcription during development.

Physical interaction between GATA-5 and hepatocyte nuclear factor-1alpha results in synergistic activation of the human lactase-phlorizin hydrolase promoter

GATA-4, -5, and -6 zinc finger and hepatocyte nuclear factor-1alpha (HNF-1alpha) homeodomain transcription factors are expressed in the intestinal epithelium and synergistically activate the promoter of intestinal genes. Here, we demonstrate that GATA-5 and HNF-1alpha physically associate both in vivo and in vitro and that this interaction is necessary for cooperative activation of the lactase-phlorizin hydrolase promoter. Furthermore, physical association is mediated by the C-terminal zinc finger of GATA factors and the homeodomain of HNF-1alpha. Deletion of HNF-1alpha activation domains or interruption of HNF-1-binding sites in the lactase-phlorizin hydrolase promoter resulted in a complete loss of cooperativity, whereas deletion of GATA-5 activation domains or interruption of GATA-binding sites resulted in a reduction, but not an elimination, of cooperativity. We hypothesize that GATA/HNF-1alpha cooperativity is mediated by HNF-1alpha through its activation domains, which are oriented for high levels of activation through binding to DNA and physical association with GATA factors. These data suggest a paradigm whereby intestine-specific gene expression is regulated by unique interactions among tissue-restricted transcription factors coexpressed in the intestine. Parallel mechanisms in other tissues as well as in Drosophila suggest that zinc finger/homeodomain interactions are an efficient pathway of cooperative activation of gene transcription that has been conserved throughout evolution.

Developmental Issues: Physiologic Factors Affecting the Safety and Bioavailability

In this expanded overview, the development of digestive and absorptive function at birth and during the first year of life are reviewed. Concerns regarding these functions in premature will be considered. In addition, nonspecific and specific host immune function in the developing gut are considered in the context of bioavailability of dietary supplements. Having reviewed what is known about these developmental gut functions and their maturation in the first year of life, safety and bioavailability issues and recommendations are considered.

Bile acids regulate the ontogenic expression of ileal bile acid binding protein in the rat via the farnesoid X receptor

BACKGROUND & AIMS

In the rat, an increase in ileal bile acid binding protein (IBABP) expression occurs during the third postnatal week. In vitro studies suggest that bile acids (BAs) increase IBABP transcription by activating the BA receptor, farnesoid X receptor (FXR). Thus, we investigated the role of BAs on the ontogenic expression of IBABP and whether FXR may mediate these effects.

METHODS

Suckling rats were gavage-fed taurocholate for 3 days or were allowed to develop normally. Ileums were collected for Northern and Western blot analyses. Electrophoretic mobility shift assays for functional FXR were performed using nuclear extracts from ileums of both adult and developing rats.

RESULTS

Taurocholate gavage significantly elevated IBABP messenger RNA and protein levels in suckling animals. Gelshift assays using adult ileal nuclear extracts incubated with a radiolabeled consensus inverted repeat-1 oligonucleotide (response element for FXR) revealed a high-molecular weight DNA/protein complex. Cold competition and supershift assays showed that this complex is sequence specific and confirmed that FXR is a component of the complex. Gelshift assays with nuclear extracts from rat ileum at different ages revealed absence of the DNA/protein complex in the second postnatal week when there is lack of IBABP expression and presence of these complexes at later ages when there is normally high expression. Western blot analyses showed FXR and its heterodimer partner, retinoid X receptor alpha, protein levels are low in the ileum during the suckling period and increase during the third postnatal week.

CONCLUSIONS

BAs play a role in the normal developmental expression of IBABP through FXR activation, and decreased functional FXR in ileal nuclei during the suckling period may account, in part, for the lack of IBABP expression at this time.

Laminins and TGF-beta maintain cell polarity and functionality of human gastric glandular epithelium

The human gastric glandular epithelium produces a gastric lipase enzyme (HGL) that plays an important role in digestion of dietary triglycerides. To assess the involvement of extracellular matrix components and transforming growth factor-beta1 (TGF-beta1) in the regulation of this enzymic function, normal gastric epithelial cells were cultured on collagen type I, Matrigel, and laminins (LN)-1 and -2 with or without TGF-beta1. Epithelial morphology and HGL expression were evaluated using microscopy techniques, enzymic assays, Western blot, Northern hybridization, and RT-PCR. A correlation was observed between the cell polarity status and the level of HGL expression. TGF-beta1 alone or individual matrix components stimulated cell spreading and caused a downfall of HGL activity and mRNA. By contrast, Matrigel preserved the morphological features of differentiated epithelial cells and maintained HGL expression. The combination of LNs with TGF-beta1 (two constituents of Matrigel) exerted similar beneficial effects on epithelial cell polarity and evoked a 10-fold increase of HGL levels that was blunted by a neutralizing antibody against the alpha(2)-integrin subunit and by mitogen-activated protein kinase (MAPK) inhibitors PD-98059 (p42/p44) or SB-203580 (p38). This investigation demonstrates for the first time that a powerful synergism between a growth factor and basement membrane LNs positively influences cell polarity and functionality of the human gastric glandular epithelium through an activation of the alpha(2)beta(1)-integrin and effectors of two MAPK pathways.

Development of the enteric nervous system

Development of the ENS requires the function of a diverse set of genes encoding transcription factors, signaling molecules, and their receptors. Mutations of these genes result in altered ENS function in animals and humans. In particular, such mutations have been shown to contribute to many cases of Hirschsprung's disease. Elucidation of the mechanisms of ENS development and function allow the development of new approaches to the diagnosis, therapy, and prevention of human disorders of gastrointestinal motility.

Region-specific ontogeny of alpha-2,6-sialyltransferase during normal and cortisone-induced maturation in mouse intestine

Regional differences in the ontogeny of mouse intestinal alpha-2,6-sialyltransferase activities (alpha-2,6-ST) and the influence of cortisone acetate (CA) on this expression were determined. High ST activity and alpha-2,6-ST mRNA levels were detected in immature small and large intestine, with activity increasing distally from the duodenum. As the mice matured, ST activity (predominantly alpha-2,6-ST) in the small intestine decreased rapidly to adult levels by the fourth postnatal week. CA precociously accelerated this region-specific ontogenic decline. A similar decline of ST mRNA levels reflected ST activity in the small, but not the large, intestine. Small intestinal sialyl alpha-2,6-linked glycoconjugates displayed similar developmental and CA induced-precocious declines when probed using Sambucus nigra agglutinin (SNA) lectin. SNA labeling demonstrated age-dependent diminished sialyl alpha2,6 glycoconjugate expression in goblet cells in the small (but not large) intestine, but no such regional specificity was apparent in microvillus membrane. This suggests differential regulation of sialyl alpha-2,6 glycoconjugates in absorptive vs. globlet cells. These age-dependent and region-specific differences in sialyl alpha-2,6 glycoconjugates may be mediated in part by altered alpha-2,6-ST gene expression regulated by trophic factors such as glucocorticoids.

Evidence-based feeding guidelines for very low-birth-weight infants

Clinical practice guidelines (CPG) for the nutritional management of premature infants are limited. This project focused on the development of a research-based enteral feeding CPG for infants of < 1,500 g. The CPG was based on an extensive literature review and developed through a process of consensus decision making by a team of clinical researchers. Infants that weigh < 1,000 g initiate minimal enteral nutrition (MEN) at 48 hours; nutritional feedings begin on day 5 to 6 of life. For infants between 1,000 and 1,500 g, nutritional feedings begin at 48 hours and are advanced at a rate of less than 30 mL/kg per day. The benefits and risks of continuous versus intermittent nasogastric tube feeding were inconclusive; therefore, the CPG does not stipulate a feeding method. Breast milk is used preferentially, and specific guidelines for the definition and management of feeding intolerance are provided. A follow-up study testing this CPG has been completed and is published in the original research section of this issue.

Effects of radiation damage on intestinal morphology

The current flow of papers on intestinal structure, radiation science, and intestinal radiation response is reflected in the contents of this review. Multiparameter findings and changes in compartments, cells, or subcellular structure all contribute to the overall profile of the response. The well-recognized changes in proliferation, vessels, and fibrogenesis are accompanied by alterations in other compartments, such as neuroendocrine or immune components of the intestinal wall. The responses at the molecular level, such as in levels of hormones, cytokines, or neurotransmitters, are of fundamental importance. The intestine responds to localized radiation, or to changes in other organs that influence its structure or function: some structural parameters respond differently to different radiation schedules. Apart from radiation conditions, factors affecting the outcome include the pathophysiology of the irradiated subject and accompanying treatment or intervention. More progress in understanding the overall responses is expected in the next few years.

The pathogenesis of Hirschsprung disease

Hirschsprung disease is the most common congenital malformation of the enteric nervous system. Phenotypic expression is variable because of incomplete penetrance, and the pathogenesis is multifactorial. Although mutations of the RET tyrosine kinase gene remain the most commonly identified cause, there are now eight separate human gene loci identified whose mutations result in this disease. Analysis of these gene products in experimental animal models and cell systems has led to an increasing elucidation of the signaling pathways that are in operation during specific embryonic time stages and that direct the spatial arrangements and differentiation of enteric neuroblasts. Mutation analysis through in vitro cell expression studies has led to detailed descriptions of the affected microdomains of signal pathway receptors and the cellular pathogenesis of abnormal signaling that leads to apoptosis of developing neurons before the completion of enteric nervous system development. The full description of the pathogenesis of this disorder awaits the definition of new genetic loci, multiple gene interactions, and the acknowledgment of random events that may lead to aganglionosis of the distal bowel.

Morphologic and functional development of whole human fetal stomachs grafted into nude mice

To study in vivo the cellular differentiation and secretion of human developing fetal stomach, ethically and technically impossible to perform in utero, 256 fetal stomachs were xenografted. Human stomachs from 6- to 10-week-old fetuses were grafted for 1-273 days into nude mice. Biopsies for immunohistochemistry, hybridization and electron microscopy were taken and a catheter introduced into the human stomach. Macroscopic growth was fast and cells in S phase were numerous during the first 9 weeks, then the stomach size was stable and the gastric mucosa, of adult type, remained normal. In situ hybridization detected only a minute mouse mesenchymal chimerism in the graft. Chromogranin A, intrinsic factor and H+/K+ adenosine triphosphatase were immunohistolocally detected in epithelial cells 20 days after grafting, gastrin was detected after 30 days and pepsinogen after 60 days. The pH in gastric juice, which was at 8.0 +/- 0.1 from days 10-25, dropped from 4.39 +/- 1.80 at 30 days to 1.58 +/- 0.29 at 90 days. Intrinsic factor was stable and pepsin ranged from 6.8 +/- 7.8 to 134 +/- 51 units at 90 days. The differentiation of the epithelial cells in xenografts was very accelerated in comparison to that in utero.

Developmental regulation of intestinal epithelial hydrolase activity in human fetal jejunal xenografts maintained in severe-combined immunodeficient mice

Intestinal epithelial brush border hydrolases are important and sensitive enzyme markers of gastrointestinal development and function. Little is know about the mechanisms that regulate the induction of these enzymes during human fetal development, as these events occur primarily in utero. The present work used ectopically grafted human fetal jejunal xenografts (median age,13.3 wk of gestation), maintained in severe-combined immunodeficient mice, to study the differential expression of five different hydrolases after 10 wk of xenotransplantation. The spatio-temporal distribution of brush border alkaline phosphatase, aminopeptidase-N, alpha-glucosidase, lactase-phlorizin hydrolase, and dipeptidyl peptidase IV enzyme activities were measured quantitatively using scanning microdensitometry along the crypt-villus axes of fetal, xenograft, and pediatric (median age, 34 mo) biopsies. Ectopic grafting of fetal jejunum closely recapitulated the development of these enzymes in utero, with alkaline phosphatase, aminopeptidase-N, alpha-glucosidase, and dipeptidyl peptidase IV enzyme activities closely matching the spatio-temporal distribution and levels recorded in pediatric duodenal biopsies. Lactase-phlorizin hydrolase was the only enzyme not to reach values recorded in pediatric brush border membranes, although activities were significantly (5.6-fold) higher than in pretransplanted fetal bowel. Human jejunal xenografts therefore demonstrate an appropriate developmental induction of brush border hydrolase activity and may represent a useful model to study trans-acting factors that promote human epithelial differentiation and function in vivo. Characterization of such agents may be of potential therapeutic use in the treatment of diseases associated with gastrointestinal immaturity, notably necrotizing enterocolitis.

Gastrointestinal projection maps of the vagus nerve are specified permanently in the perinatal period

The vagal innervation of the proximal gastrointestinal (GI) tract is lateralized. To determine whether this pattern is specified as early as the perinatal period, neonatal rat pups were given unilateral cervical vagotomies. Separate groups received (1) transections below the left nodose ganglion, (2) left cervical resections that included removal of the nodose ganglion, or (3) sham surgeries. At 4 months of age, each animal's vagal afferent projections from the unoperated side were mapped by injecting the nodose with WGA-HRP, preparing the stomach as wholemounts, and processing the tissue with tetramethyl benzidine. The two types of vagal afferent endings in GI smooth muscle, namely intraganglionic laminar endings and intramuscular arrays, were surveyed separately, and their regional distributions were mapped. Changes in the nucleus of the solitary tract (NST) and dorsal motor nucleus of the vagus (DMNX) were assessed with cell counts and area measurements. Neonatal loss of the vagus innervating one side of the GI tract, with or without ganglionectomy, did not cause the unoperated vagus to sprout to the denervated side. In addition, removal of the projections to the one side of the target organ did not produce a reorganization of the projection maps of the unoperated vagus within its normal or ipsilateral wall of the GI tract. Although the regional patterns of the unoperated ipsilateral vagus were not affected, the packing densities of both types of afferents supplied by this trunk were moderately reduced. The DMNX of the vagotomized side displayed extensive (approximately 83%) neuronal loss; the DMNX on the unoperated side as well as the NST on both sides exhibited limited (approximately 20--25%) losses. The lack of a peripheral projection field reorganization -- except for a moderate down-regulation -- after complete unilateral denervation suggests that both the laterality and the afferent terminal phenotypes (or target tissues) of the vagus in the proximal GI tract are specified by postnatal day one in the rat. The present results, taken together with other observations, also suggest that three different combinations of signals orchestrate the commitments of vagal afferents respectively to (1) the side of the organ, (2) the region within the organ wall, and (3) the accessory and innervated tissues that complex with the fully differentiated ending.

Intestinal epithelial cell differentiation involves activation of p38 mitogen-activated protein kinase that regulates the homeobox transcription factor CDX2

The intracellular signaling pathways responsible for cell cycle arrest and differentiation along the crypt-villus axis of the human small intestine remain largely unknown. p38 mitogen-activated protein kinases (MAPKs) have recently emerged as key modulators of various vertebrate cell differentiation processes. In order to elucidate further the mechanism(s) responsible for the loss of proliferative potential once committed intestinal cells begin to differentiate, the role and regulation of p38 MAPK with regard to differentiation were analyzed in both intact epithelium as well as in well established intestinal cell models recapitulating the crypt-villus axis in vitro. Results show that phosphorylated and active forms of p38 were detected primarily in the nuclei of differentiated villus cells. Inhibition of p38 MAPK signaling by 2-20 microm SB203580 did not affect E2F-dependent transcriptional activity in subconfluent Caco-2/15 or HIEC cells. p38 MAPK activity dramatically increased as soon as Caco-2/15 cells reached confluence, whereas addition of SB203580 during differentiation of Caco-2/15 cells strongly attenuated sucrase-isomaltase gene and protein expression as well as protein expression of villin and alkaline phosphatase. The binding of CDX2 to the sucrase-isomaltase promoter and its transcriptional activity were significantly reduced by SB203580. Pull-down glutathione S-transferase and immunoprecipitation experiments demonstrated a direct interaction of CDX3 with p38. Finally, p38-dependent phosphorylation of CDX3 was observed in differentiating Caco-2/15 cells. Taken together, our results indicate that p38 MAPK may be involved in the regulation of CDX2/3 function and intestinal cell differentiation.

Role of stem cell factor and c-kit signaling in regulation of fetal intestinal epithelial cell adhesion to fibronectin

The interaction of stem cell factor (SCF) and c-kit is considered to be an important signaling event for the homeostasis of the epithelial barrier function in the intestinal tract. This study was designed to investigate the role of the SCF and c-kit signaling pathway in adhesion of intestinal epithelial cells (IECs) to fibronectin (FN) using primary cells. Fetal murine IECs were prepared from the small intestine of mouse fetus. The mRNAs coding for SCF in mesenchymes and c-kit in IECs were detected by reverse transcription-PCR. The expression of FN receptor VLA-5 on IECs was examined by flow cytometry. A cell adhesion assay showed that the stimulation of IECs with SCF increased the number of cells adhering to FN. Experiments using specific antibody against SCF indicated that this increase in cell adhesion was SCF-dependent. On the other hand, SCF did not influence the expression of VLA-5 on IECs. The IEC adhesion to FN was inhibited by specific antibody against the FN receptor (VLA-5), as well as competitive Arg-Gly-Asp (RGD) peptide. When alteration of intracellular signal transduction induced by SCF was examined, it was found that SCF stimulated a tyrosine-specific c-kit autophosphorylation cascade of IECs. Further, preincubation of IECs with an optimal concentration of genistein resulted in the inhibition of SCF-induced c-kit phosphorylation and adhesion of IECs to FN. These results suggested that adhesion of immature IECs to FN is regulated by activation of RGD-dependent VLA-5 through the SCF and c-kit signal transduction pathway. SCF, which may be produced by mesenchymes locally, is an important regulatory factor for the adhesion of immature IECs to basement membrane matrix via VLA-5 and FN interaction. This cytokine-regulated interaction between VLA-5 and FN may play an important role in the development and wound repair of the intestinal tract.

Two CCAAT boxes in a novel inverted repeat motif are required for Hlx homeobox gene expression

Hlx is a homeobox transcription factor gene required for normal intestinal and hepatic growth in development. We previously found high sequence identity and 17 conserved consensus cis-regulatory/transcription factor binding elements in the mouse and human Hlx 5' regions. A 594 bp sequence in the Hlx 5' region possessing the same activity in driving luciferase expression as larger Hlx 5' sequences had three segments each necessary but not sufficient for luciferase expression in NIH 3T3 cells (which express Hlx). Nine of the conserved putative regulatory elements are positioned within these segments, including two CCAAT boxes on opposite strands within a conserved 44 bp inverted repeat sequence. To test the hypothesis that these elements are required for promoter activity, we compared the reporter expression activity of segments containing mutations of these elements with activity of the parent Hlx promoter sequence. We found that mutation of either CCAAT box or a conserved AP-2 site resulted in a significant decrease in promoter activity. Restoration of the inverted repeat with complementary mutations of both CCAAT boxes did not restore activity. Further, mutation of other portions of the inverted repeat did not affect promoter activity. Mutation of other elements had no effect on promoter activity.

The use of 1H magnetic resonance spectroscopy in inflammatory bowel diseases: distinguishing ulcerative colitis from Crohn's disease

OBJECTIVES

The distinction between the two major forms of inflammatory bowel diseases (IBD), i.e., ulcerative colitis (UC) and Crohn's disease is sometimes difficult and may lead to a diagnosis of indeterminate colitis. We have used 1H magnetic resonance spectroscopy (MRS) combined with multivariate methods of spectral data analysis to differentiate UC from Crohn's disease and to evaluate normal-appearing mucosa in IBD.

METHODS

Colon mucosal biopsies (45 UC and 31 Crohn's disease) were submitted to 1H MRS, and multivariate analysis was applied to distinguish the two diseases. A second study was performed to test endoscopically and histologically normal biopsies from IBD patients. A classifier was developed by training on 101 spectra (76 inflamed IBD tissues and 25 normal control tissues). The spectra of 38 biopsies obtained from endoscopically and histologically normal areas of the colons of patients with IBD were put into the validation test set.

RESULTS

The classification accuracy between UC and Crohn's disease was 98.6%, with only one case of Crohn's disease and no cases of UC misclassified. The diagnostic spectral regions identified by our algorithm included those for taurine, lysine, and lipid. In the second study, the classification accuracy between normal controls and IBD was 97.9%. Only 47.4% of the endoscopically and histologically normal IBD tissue spectra were classified as true normals; 34.2% showed "abnormal" magnetic resonance spectral profiles, and the remaining 18.4% could not be classified unambiguously.

CONCLUSIONS

There is a strong potential for MRS to be used in the accurate diagnosis of indeterminate colitis; it may also be sensitive in detecting preclinical inflammatory changes in the colon.

The gastrointestinal ecosystem: a precarious alliance among epithelium, immunity and microbiota

The gastrointestinal (GI) tract is a complex ecosystem generated by the alliance of GI epithelium, immune cells and resident microbiota. The three components of the GI ecosystem have co-evolved such that each relies on the presence of the other two components to achieve its normal function and activity. Experimental systems such as cell culture, germ-free animal models and intestinal isografts have demonstrated that each member of the GI ecosystem can follow a predetermined developmental pathway, even if isolated from the other components of the ecosystem. However, the presence of all three components is required for full physiological function. Genetic or functional alterations of any one component of this ecosystem can result in a broken alliance and subsequent GI pathology. A more detailed understanding of the interactions among microbiota, GI epithelium and the immune system should provide insight into multiple human disease states.

Clonally related cells are restricted to organ boundaries early in the development of the chicken gut to form compartment boundaries

The gut organs are all derived from a simple, undifferentiated, linear gut tube. We analyzed the lineage relationships of cells derived from this gut tube in chicken embryos, determining where the progeny of a single cell are located within the gut. We find that daughter cells derived from a single progenitor can populate both the gizzard (chicken stomach) and the small intestine early in development, but that clonally related cells are restricted to a single organ by stage 12. We also find that clonally related cells can populate different mesodermal layers within the radial axis of the gut throughout all of the stages tested in these experiments. Many genes that have organ-specific expression patterns within the gut have been isolated. The onset of these restricted expression patterns correlates with the time that clonal boundaries appear to form, suggesting that these genes might be involved in the establishment of compartment boundaries, which prevent cells on one side of the boundary from intermingling with cells on the other side of the boundary.

Evolutionary relationships between the amphibian, avian, and mammalian stomachs

Although the gut is homologous among different vertebrates, morphological differences exist between different species. The most obvious variation in the guts of extant vertebrates appears in the stomach. To investigate the evolution of this structure, we compared the histology of the stomach and gastrointestinal tract in amphibian (Xenopus laevis), avian (Gallus gallus), and mammalian (Mus musculus) organisms, and defined the expression patterns of several genes within the developing guts of these lineages. In all three groups, we find that the anterior portion of the stomach has a similar glandular histology as well as a common embryonic expression of the secreted factors Wnt5a and BMP-4. Likewise, within the amniote lineages, the posterior nonglandular stomach and pyloric sphincter regions are also comparable in both histological and molecular phenotypes. The posterior stomach expresses Six2, BMPR1B, and Barx1, whereas the pyloric sphincter expresses Nkx2.5. Although the adult Xenopus stomach exhibits both glandular and aglandular regions and a distinct pyloric sphincter similar to that of the amniotic vertebrates, the histology of the Xenopus tadpole gut shows less distinct variation in differentiation in this region, which is most likely a derived condition. The molecular signature of the embryonic Xenopus gut correlates with the more derived morphology of the larval phase. We conclude that the global patterning of the gut is remarkably similar among the different vertebrate lineages. The distinct compartments of gene expression that we find in the gut be necessary for the unique morphological specializations that distinguish the stomachs from terrestrial vertebrates.

A duodenum-specific enhancer regulates expression along three axes in the small intestine

Adenosine deaminase (ADA) is expressed at high levels in the epithelium of proximal small intestine. Transgenic mice were used to characterize the regulatory region governing this activation. A duodenum-specific enhancer is located in intron 2 of the human ADA gene at the central site among a cluster of seven DNase I-hypersensitive sites present in duodenal DNA. Flanking DNA, including the remaining hypersensitive sites, is required for consistent high-level enhancer function. The enhancer activates expression in a pattern identical to endogenous ADA along both the anterior-posterior axis of the small intestine and the crypt-villus differentiation axis of the intestinal epithelium. Timing of activation by the central enhancer mimics endogenous mouse ADA activation, occurring at 2-3 wk of age. However, two upstream DNA segments, one proximal and one distal, collaborate to change enhancer activation to a perinatal time point. Studies with duodenal nuclear extracts identified five distinct DNase I footprints within the enhancer. Protected regions encompass six putative binding sites for the transcription factor PDX-1, as well as proposed CDX, hepatocyte nuclear factor-4, and GATA-type sites.

Ontogeny of the glucagon-like peptide-2 receptor axis in the developing rat intestine

Glucagon-like peptide-2 (GLP-2) is secreted by enteroendocrine cells in the small and large intestines and exerts intestinotropic effects in the gastrointestinal mucosal epithelium of the adult rodent. The actions of GLP-2 are mediated by the GLP-2 receptor, a new member of the G protein-coupled receptor superfamily. To ascertain whether the GLP-2/GLP-2 receptor axis is expressed and functional in the developing intestine, we have studied the synthesis of GLP-2 and the expression of the GLP-2 receptor (GLP-2R) in the fetal and neonatal rat gut. GLP-2 immunoreactivity (GLP-2-IR) was detected in the fetal rat intestine, and fetal rat intestinal cell cultures secreted correctly processed GLP-2(1-33) into the medium. High levels of GLP-2(1-33) were also detected in the circulation of 13-day-old neonatal rats (P < 0.001 vs. adult). Analysis of GLP-2 receptor expression by RT-PCR demonstrated GLP-2R messenger RNA transcripts in fetal intestine and in neonatal stomach, jejunum, ileum, and colon. The levels of GLP-2R messenger RNA transcripts were comparatively higher in the fetal and neonatal intestine (P < 0.05-001 vs. adult) and declined to adult levels by postnatal day 21. Subcutaneous administration of a degradation-resistant GLP-2 analog, h[Gly2]-GLP-2 once daily for 10 days increased stomach (0.009 +/- 0.0003 vs. 0.007 +/- 0.002 g/g body mass, h[Gly2]-GLP-2-treated vs. controls; P < 0.05) and small bowel weight (0.043 +/- 0.0037 vs. 0.031 +/- 0.0030 g/g body mass; P < 0.05). h[Gly2]-GLP-2 also increased both small (2.4 +/- 0.05 vs. 1.8 +/- 0.17 cm/g body mass; P < 0.05) and large bowel length (0.32 +/- 0.01 vs. 0.25 +/- 0.02 cm/g body mass, h[Gly2]-GLP-2-treated vs. saline-treated controls, respectively; P < 0.05) in neonatal rats. These findings demonstrate that both components of the GLP-2/GLP-2 receptor axis are expressed in the fetal and neonatal intestine. The ontogenic regulation and functional integrity of this axis raises the possibility that GLP-2 may play a role in the development and/or maturation of the developing rat intestine.

Functional characterization of the keratinocyte growth factor system in human fetal gastrointestinal tract

Keratinocyte growth factor (KGF) is a paracrine growth factor whose mRNA has been detected in human adult and rodent gut tissues together with its associated receptor. Our objectives were to assess the presence of immunoreactive KGF ligand and receptor proteins in human fetal gastrointestinal (GI) tract segments and to evaluate the role of exogenous KGF on cell proliferation and intestinal digestive functions. KGF (26-28 kD doublet) was identified in esophagus, stomach, small intestine, and colon by Western blot. Its receptor (135 kD) was ubiquitously detected in proliferative and differentiated epithelial cells of each GI segment by use of indirect immunofluorescence (anti-bek, anti-K-sam). The addition of KGF to explants cultured in serum-free conditions greatly stimulated DNA synthesis in all GI tract tissues. The growth factor up-regulated intestinal sucrase-isomaltase and gamma-glutamyl-transpeptidase activities in jejunal explants, whereas it down-regulated these activities in colon explants. It is suggested that the KGF system likely represents an important paracrine pathway that is able to stimulate cell proliferation in all segments of the human fetal GI tract and to differentially regulate intestinal digestive functions.

Abnormal gastrointestinal development in PDGF-A and PDGFR-(alpha) deficient mice implicates a novel mesenchymal structure with putative instructive properties in villus morphogenesis

Development of the gastrointestinal (GI) tract depends on reciprocal epithelial-mesenchymal cell signaling. Here, we demonstrate a role for platelet-derived growth factor-A (PDGF-A) and its receptor, PDGFR-(alpha), in this process. Mice lacking PDGF-A or PDGFR-(alpha) were found to develop an abnormal GI mucosal lining, including fewer and misshapen villi and loss of pericryptal mesenchyme. Onset of villus morphogenesis correlated with the formation of clusters of PDGFR-(alpha) positive cells, ‘villus clusters’, which remained located at the tip of the mesenchymal core of the growing villus. Lack of PDGF-A or PDGFR-(alpha) resulted in progressive depletion of PDGFR-(alpha) positive mesenchymal cells, the formation of fewer villus clusters, and premature expression of smooth muscle actin (SMA) in the villus mesenchyme. We found that the villus clusters were postmitotic, expressed BMP-2 and BMP-4, and that their formation correlated with downregulated DNA synthesis in adjacent intestinal epithelium. We propose a model in which villus morphogenesis is initiated as a result of aggregation of PDGFR-(α) positive cells into cell clusters that subsequently function as mesenchymal centers of signaling to the epithelium. The role of PDGF-A seems to be to secure renewal of PDGFR-(alpha) positive cells when they are consumed in the initial rounds of cluster formation.

Immunolocalization of the HNK-1 epitope in the autonomic innervation to the liver and upper digestive tract of the developing rat embryo

The immunohistochemical analysis of the HNK-1 epitope presence in the liver and upper digestive tract nerves was carried out in 12- to 18-day-old rat embryos embedded in acrylamide-agarose and observed with laser scanning confocal microscopy. The vagus and sympathetic trunk were intensely immunostained at all ages; branches of both structures were also HNK-1 positive, and ramified ventrocaudally following the course of the thoracic and abdominal aorta, caval vein, portal vein and ductus venosus. As early as day 12, some immunostained cells were seen in the mesentery that formed the enteric nervous system. Clearly immunostained HNK-1-immunoreactive fibres were detected innervating the digestive wall after day 14, forming both myenteric and submucosal plexuses. After day 16, the Glisson sheath showed streams of HNK-1-positive fibres coming from dorsal areas, lining the peritoneal surface of the diaphragm, invading the capsule, and ramifying superficially around the lobes of the liver. We saw no immunoreactive structures pervading the hepatic lobes at all ages studied, with the exception of occasional HNK-l-positive cells in the superficial parenchyma, which were visualized after 16 days of gestation. Our findings can help to understand the development of the gastrointestinal and liver innervation in the rat.

Ontogeny of intestinal nutrient transport

Children born prematurely lack the ability to digest and to absorb nutrients at rates compatible with their nutritional needs. As a result, total parenteral nutrition may need to be given. While this nutritional support may be life-saving, the baby who receives this therapy is exposed to the risks of possible sepsis, catheter dysfunction, and liver disease. The rodent model of postnatal development provides a useful framework to investigate some of the cellular features of human intestinal development. The up-regulation of intestinal gene expression and precocious development of intestinal nutrient absorption can be achieved by providing growth factor(s) or by modifying the composition of the maternal diet during pregnancy and nursing or the weaning diet of the infant. Accelerating the digestive and absorptive functions of the intestine would thereby allow for the maintenance of infant nutrition through oral food intake, and might possibly eliminate the need for, and risks of, total parenteral nutrition. Accordingly, this review was undertaken to focus on the adaptive processes available to the intestine, to identify what might be the signals for and mechanisms of the modified nutrient absorption, and to speculate on approaches that need to be studied as means to possibly accelerate the adaptive processes in ways which would be beneficial to the newborn young.Key words: absorption, adaptation, diet, peptides.

An air-liquid interface promotes the differentiation of gastric surface mucous cells (GSM06) in culture

The gastric surface epithelium is situated at an air-liquid interface because the luminal surface of the alimentary tract is in continuity with the air phase. However, the effects of this microenvironment on the gastric epithelium remain unclear. The aim of this study was to clarify the effects of an air-liquid interface on gastric epithelial cell biology. Gastric surface mucous cells (GSM06) were cultured at an air-liquid interface. Cultured cells were examined by histology, histochemistry, and transmission electron microscopy. When the cells were cultured at an air-liquid interface, the surface cells on the collagen gel became tall columnar and secreted periodic acid-Shiff-positive substances at the apical surface. These cells indicated many mucous granules in the apical cytoplasm and organized the basal lamina at the contact side with the gel. In contrast, under immersed condition, the surface cells showed immature features. This is the first report of an air-liquid interface promoting the differentiation of gastric surface mucous cells in a reconstruction culture of the gastric surface epithelial layer, suggesting that an air-liquid interface may function as a crucial luminal factor to maintain the homeostasis of gastric mucosa.

Developmental aspects of lipid and lipoprotein synthesis and secretion in human gut

This review article focuses on the ontogeny and the regulatory mechanisms involved in the modulation of the intracellular events governing the assembly and delivery of lipoproteins in human gut. The human fetal intestine organizes villi covered with well-differentiated enterocytes during the end of the first trimester in utero. One striking event is the formation of villi in the colonic mucosa similar to those of the small intestine. The small intestine exhibits very early (14-20 weeks) the capacity to absorb lipids, to elaborate most of the major lipoprotein classes (chylomicrons, very-low-density lipoproteins, low-density lipoproteins, high-density lipoproteins), and to efficiently export these lipoproteins from the intestinal cells. The ontogenic changes of lipid and lipoprotein synthesis are correlated with specific patterns of regulatory enzymes (HMG-CoA reductase, ACAT, MGAT) that are representative of key patterns such as the cholesterol pathway, cholesterol esterification, and neutral lipid pathway. The human fetal colon also has the capability to synthesize lipids, lipoproteins, and apolipoproteins. However, comapred with the small intestine, it is much less efficient at exporting these lipoproteins. Epidermal growth factor, insulin, and hydrocortisone, which are known modulators of the brush border digestive functions of the human gut, differentially modulate the synthesis and secretion of lipoproteins in the small intestine and colon. The use of human fetal gut represents a unique model to further our understanding of the complex biosynthetic molecular events essential for the formation and secretion of lipoproteins relevant to human intestine, both in normal or pathological conditions.

Human cell models to study small intestinal functions: recapitulation of the crypt-villus axis

The intestinal epithelium is continuously and rapidly renewed by a process involving cell generation, migration, and differentiation, from the stem cell population located at the bottom of the crypt to the extrusion of the terminally differentiated cells at the tip of the villus. Because of the lack of normal human intestinal cell models, most of our knowledge about the regulation of human intestinal cell functions has been derived from studies conducted on cell cultures generated from experimental animals and human colon cancers. However, important advances have been achieved over recent years in the generation of normal human intestinal cell models. These models include (a) intestinal cell lines with typical crypt cell proliferative noncommitted characteristics, (b) conditionally immortalized intestinal cell lines that can be induced to differentiate, and (c) primary cultures of differentiated villuslike cells that can be maintained in culture for up to 10 days. Each of these models should help in the investigation of the specific aspects of human intestinal function and regulation. Furthermore, taken together, these models provide an integrated system that allows an in vitro recapitulation of the entire crypt-villus axis of the normal human small intestine.

Differential expression of peroxisome proliferator-activated receptors (PPARs) in the developing human fetal digestive tract

We investigated the spatiotemporal distributions of the different peroxisome proliferator-activated receptor (PPAR) isotypes (alpha, beta, and gamma) during development (Week 7 to Week 22 of gestation) of the human fetal digestive tract by immunohistochemistry using specific polyclonal antibodies. The PPAR subtypes, including PPARgamma, are expressed as early as 7 weeks of development in cell types of endodermal and mesodermal origin. The presence of PPARgamma was also found by Western blotting and nuclease-S1 protection assay, confirming that this subtype is not adipocyte-specific. PPARalpha, PPARbeta, and PPARgamma exhibit different patterns of expression during morphogenesis of the digestive tract. Whatever the stage and the gut region (except the stomach) examined, PPARgamma is expressed at a high level, suggesting some fundamental role for this receptor in development and/or physiology of the human digestive tract.

Marked morphological differences in the myenteric plexus between the mesenteric and antimesenteric sides of small bowel in premature infants

BACKGROUND

The gastrointestinal tract appears morphologically prepared for oral feeding by the end of the second trimester, but many of the physiological processes required for efficient enteral nutrition are not developed fully until 33 to 34 weeks' gestation. Myenteric plexus is well recognized as an important regulator of peristaltic activity. Whole-mount preparation technique produces a 3-dimensional picture to better show the neuronal networks branching and interconnections. The aim of this study was to investigate neurone density and morphology of the myenteric plexus in premature infants using whole-mount technique.

METHODS

Full-thickness small and large bowel specimens were collected at autopsy from 6 premature babies (gestational age, 26 to 32 weeks) who died without evidence of gastrointestinal disease. Whole-mount preparation of the myenteric plexus was made and stained with NADPH-diaphorase and Acetylcholinesterase (AChE) histochemistry. The stained myenteric network was measured with a computer image analysis system. Controls included 4 full-term babies who died of nongastrointestinal disease.

RESULTS

In premature infants there were striking differences in neuronal density of myenteric plexus in the mesenteric and antimesenteric border of small bowel. The differences in neuronal density in mesenteric and antimesenteric border of small bowel gradually became less striking as the gestation progressed with no differences evident at gestational age 32 weeks.

CONCLUSIONS

This study shows for the first time that the neurone density of myenteric plexus is significantly higher in the mesenteric border of the small bowel compared with antimesenteric border in premature infants. The marked morphological differences observed in neurone density in the small bowel of premature infants may contribute to immature small bowel activity.

Slow transit constipation: a model of human gut dysmotility. Review of possible aetiologies

Slow transit constipation is a severe condition of gut dysmotility that predominantly affects young women and may result in surgical intervention. Current medical treatments for STC are often ineffective, and the outcome of surgery is unpredictable. STC was first described almost a century ago. Since this time, progress in improving therapy for this condition has been complicated by a lack of understanding of the aetiology, and great variation in the methods and criteria used for the study of patients with this debilitating disorder. It is difficult to find unequivocal data, and harder still to give a definitive picture of the cause or causes of STC. Here we consider the evidence for various aetiologies of STC, in the light of the physiological and pathological findings.

Establishment of culture systems of human gastric epithelium for the study of pepsinogen and gastric lipase synthesis and secretion

A main purpose of gastric secretion pertains to the digestion of dietary proteins and involves the release of pepsinogens by the fundic and antral mucosa. Over the last decade, data on human gastric physiology has expanded to equally include a significant role in fat digestion. Characteristics of human gastric lipase (HGL) such as optimum acid pH, resistance to proteolysis and non requirement of bile salts or cofactors, are advantageous in gastric lipolysis. Furthermore, the importance of HGL increases in the context of perinatal physiology and pathological situations where secretion of HGL could compensate, to some extent the depressed pancreatic activities. It is therefore important to understand the regulatory mechanisms involved in the synthesis and secretion of human gastric digestive enzymes. The establishment of an organ culture technique as well as a novel primary culture system of human gastric epithelium permitted us to demonstrate that Pg5 and HGL are colocalized in human chief cells and both digestive enzymes are efficiently synthesized and secreted in explants and primary cultures. Pepsin activity rises at the cellular level while its secretion remains constant. In contrast, cellular lipase activity drastically diminishes while being preferentially secreted. This nonparallelism supports the concept that Pg5 and HGL are differently regulated in culture. Furthermore, EGF downregulates HGL expression at the mRNA level via the p42/44(MAPK) pathway without affecting Pg5. Future studies should be designed to fully understand the cellular and molecular mechanisms involved in regulating HGL activity in normal and pathological conditions.

Digestive System 1

This chapter deals with the digestive system. The major and minor salivary glands and their secretions also represent and integral part of the protective mechanism of the oral cavity, and derangement of saliva production may lead to loss of integrity of the oral mucosa. Drug-induced abnormalities of taste sensation are also well-described phenomena occurring in man although human studies are necessary for the detection of these effects. Inflammation of the oral cavity may involve the buccal mucosa, the gingiva (gingivitis), the tongue (glossitis), and the peridontal tissues (peridontitis). Therapeutic agents can induce inflammatory lesions in the tongue. Moreover, a protective layer of mucus, a visco-elastic material containing high molecular weight glycoproteins produced by the major and minor salivary glands, covers the stratified squamous mucosa of the oral cavity. Salivary secretions also possess digestive enzyme activity although in herbivores and carnivores, it is usually low in contrast to high digestive enzyme activity in omnivorous species.

Plasticity in the enteric nervous system

Enteric ganglia can maintain integrated functions, such as the peristaltic reflex, in the absence of input from the central nervous system, which has a modulatory role. Several clinical and experimental observations suggest that homeostatic control of gut function in a changing environment may be achieved through adaptive changes occurring in the enteric ganglia. A distinctive feature of enteric ganglia, which may be crucial during the development of adaptive responses, is the vicinity of the final effector cells, which are an important source of mediators regulating cell growth. The aim of this review is to focus on the possible mechanisms underlying neuronal plasticity in the enteric nervous system and to consider approaches to the study of plasticity in this model. These include investigations of neuronal connectivity during development, adaptive mechanisms that maintain function after suppression of a specific neural input, and the possible occurrence of activity-dependent modifications of synaptic efficacy, which are thought to be important in storage of information in the brain. One of the applied aspects of the study of plasticity in the enteric nervous system is that knowledge of the underlying mechanisms may eventually enable us to develop strategies to correct neuronal alterations described in several diseases.