Natural history of experimental intestinal atresia: morphologic and ultrastructural study

Involvement of the enteroendocrine system in intestinal obstruction

INTRODUCTION

Intestinal atresia, a rare congenital condition, is often associated with intestinal motility disorders despite adequate neonatal surgery. Previous studies have focused on changes in the enteric nervous system (ENS). We hypothesized that other components of the digestive tract could be involved in this condition.

MATERIAL AND METHODS

In a rat model of surgically-induced intestinal obstruction, a transcriptome analysis was performed to measure the global gene expression. Then, analyzes were focused on genes expressed in ENS and neuroendocrine cells. Rat fetus small intestines at different developmental stages (ED15, ED17, ED19 and ED21, (n = 22)) were studied as controls and compared to the upper and lower segments of small intestines from rat fetuses with surgically-induced obstruction (n = 14; ligature at ED18). The gene expression pattern was confirmed by immunohistochemistry, electron microscopy and RT-qPCR.

RESULTS

From ED15 to ED21, there was a physiological decrease in the gene expression of ENS markers and an increase in that of neuroendocrine genes. Regarding operated embryos, the changes in global gene expression were significantly higher in the proximal segment compared to the distal segment (18% vs. 9%). More precisely, a decrease in ENS gene expression and an increase in neuroendocrine gene expression were observed in the proximal segment compared to controls, indicating an accelerated maturation pattern. Immunohistochemistry and electron microscopy confirmed these findings.

CONCLUSION

Fetal intestinal obstruction seems to induce an accelerated maturation in the proximal segment. Moreover, neuroendocrine cells undergo significant unexpected changes, suggesting that ENS changes could be associated with other changes to induce intestinal motility disorders.

Reversible small bowel obstruction in the chicken foetus

BACKGROUND

Ligation of the embryonic gut is an established technique to induce intestinal obstruction and subsequently intestinal atresia in chicken embryos. In this study, we modified this established chicken model of prenatal intestinal obstruction to describe (1) the kinetics of morphological changes, (2) to test if removal of the ligature in ovo is possible in later embryonic development and (3) to describe morphological adaptations following removal of the ligature.

MATERIALS AND METHODS

On embryonic day (ED) 11, small intestines of chick embryos were ligated micro surgically in ovo. In Group 1 (n = 80) gut was harvested proximal and distal to the ligation on ED 12-19. In Group 2 (n = 20) the induced obstruction was released on day 15 and gut was harvested on ED 16-19. Acetyl choline esterase staining was used as to assess resulting morphological changes.

RESULTS

A marked intestinal dilatation of the proximal segment can be seen 4 days after the operation (ED 15). The dilatation increased in severity until ED 19 and intestinal atresia could be observed after ED 16. In the dilated proximal segments, signs of disturbed enteric nervous system morphology were obvious. In contrast to this, release of the obstruction on ED 15 in Group 2 resulted in almost normal gut morphology at ED 19.

CONCLUSION

Our model not only allows the description of morphological changes caused by an induced obstruction on ED 11 but also-more important - of morphological signs of adaptation following the release of the obstruction on ED 15.

An unusual colon atresia in a calf: at the junction of the distal loop and transverse colon. A brief overview

Congenital defects are those abnormalities present at birth. During embryogenesis, many anomalies can occur. The primitive gut tube lengthens quickly and rotates, allowing the gastrointestinal tract acquire its final position and orientation. Because the colon of large animals is complex, most changes occur in this segment. Thus, in ruminants, colon atresia is the most frequent malformation, affecting mainly ascending colon, at the level of the spiral loop. There are no previous references about a very atypical colon atresia at the junction of distal loop and transverse colon, such we have described in a 5-day-old calf, after a history of abdominal distention and absence of feces at birth, even with a patent anal opening. Atresia coli was detected at distal position of the typical colon atresia, at the junction of distal loop and transverse colon. In addition, the distal blind end was bent into a U-shape supported by the mesocolon. Besides the anatomical findings of this worthwhile atresia coli we discuss its possible etiology, in which local factors, such as a compromised blood supply during embryogenesis, are more consistent than genetic factors. Finding out the causes of atresia coli would help to reduce its incidence, lessen animal suffering and economic loss.

A novel animal model of gastrointestinal obstruction for the development of stent

BACKGROUND

The need for newer gastrointestinal (GI) stents has been continuously raised. Newly developed stents are generally tested for physical properties in vitro and directly introduced to clinical practice because there is no reliable animal model of GI obstruction. The aim of this study was to establish an animal model both that can represent obstruction of the GI tract and be used to develop new stents.

MATERIAL AND METHODS

Surgical obstruction of the descending colon by wrapping with a nonabsorbable synthetic mesh and rubber bands was made in 17 healthy mongrel dogs. Four days later, a covered self-expanding metallic stent was placed for the obstructed segment in each dog under fluoroscopic guidance. Patency and migration of the inserted stents were evaluated clinically on a daily basis and fluoroscopically on a weekly basis. After sacrifice of the dogs, the degree and extent of residual colonic obstruction were assessed fluoroscopically. The specimen of the colonic obstructed segment was examined microscopically.

RESULTS

In all 17 mongrel dogs, segmental obstruction in the descending colon was successfully created and confirmed with fluoroscopic examination using a contrast medium. The percentage of luminal narrowing ranged from 99%-100%. Stent placement was technically successful in all 17 dogs. During the follow-up period, stent migration occurred in 12 dogs and indwelling time of a stent ranged from 0-95 d (mean 29.2 ± 38.8 d). On postmortem pathologic examination, it was found that fibrosis had newly formed outside the colonic longitudinal muscle layer in all dogs.

CONCLUSIONS

Our canine colonic obstruction model is the first animal model that can be feasible for developing a new design of stent and provide in vivo data on complications, particularly stent migration.

Prenatal intestinal obstruction affects the myenteric plexus and causes functional bowel impairment in fetal rat experimental model of intestinal atresia

Background

Intestinal atresia is a rare congenital disorder with an incidence of 3/10 000 birth. About one-third of patients have severe intestinal dysfunction after surgical repair. We examined whether prenatal gastrointestinal obstruction might effect on the myenteric plexus and account for subsequent functional disorders.

Methodology/Principal Findings

We studied a rat model of surgically induced antenatal atresia, comparing intestinal samples from both sides of the obstruction and with healthy rat pups controls. Whole-mount preparations of the myenteric plexus were stained for choline acetyltransferase (ChAT) and nitric oxide synthase (nNOS). Quantitative reverse transcription PCR was used to analyze mRNAs for inflammatory markers. Functional motility and permeability analyses were performed in vitro. Phenotypic studies were also performed in 8 newborns with intestinal atresia. In the experimental model, the proportion of nNOS-immunoreactive neurons was similar in proximal and distal segments (6.7±4.6% vs 5.6±4.2%, p = 0.25), but proximal segments contained a higher proportion of ChAT-immunoreactive neurons (13.2±6.2% vs 7.5±4.3%, p = 0.005). Phenotypic changes were associated with a 100-fold lower concentration-dependent contractile response to carbachol and a 1.6-fold higher EFS-induced contractile response in proximal compared to distal segments. Transcellular (p = 0.002) but not paracellular permeability was increased. Comparison with controls showed that modifications involved not only proximal but also distal segments. Phenotypic studies in human atresia confirmed the changes in ChAT expression.

Conclusion

Experimental atresia in fetal rat induces differential myenteric plexus phenotypical as well as functional changes (motility and permeability) between the two sides of the obstruction. Delineating these changes might help to identify markers predictive of motility dysfunction and to define guidelines for post-surgical care.

Significance of abnormalities in systems proximal and distal to the obstructed site of duodenal atresia

BACKGROUND

Duodenal atresia (DA) is a well-known neonatal intestinal disease. Even after surgery, the proximal segment can continue to be severely dilated with hypoperistalsis, resulting in intestinal dysmotility problems in later life. No data have been published regarding the morphologic differences between the proximal and distal regions of obstructed sites of the intramural components in DA.

METHODS

Operative duodenal samples (N = 12) from cases with DA (age 1-3 days) were used. Age-matched controls (N = 2) were used. All of the specimens were immunohistochemically stained with antibodies to S-100 protein, α-smooth muscle actin, and c-kit protein.

RESULTS

At the proximal segments of the obstructed site in DA, the number of neuronal cells decreased in size and number. The circular musculature was moderately to severely hypertrophic. Unusual ectopic smooth muscle bundles were also identified. The innermost layer of the circular musculature was thinner. Interstitial cells of Cajal are decreased, even around the myenteric plexus. All of the staining in the distal segments in DA was similar to the control tissues.

CONCLUSIONS

Proximal and distal segments in DA differ in the neural cells, musculature, and distributions of the interstitial cells of Cajal. Based on the present study, these morphologic changes may contribute to the onset of postoperative duodenal dysmotility.

Endocrine cells in atresic chick embryo intestine: histochemical and immunohistochemical study

Intestinal motility disorders are an important problem in the postoperative management of patients with intestinal atresia. Intestinal motility could be initiated by luminal factors that activate intrinsic and extrinsic primary afferent nerves involved in the peristaltic reflex. Endocrine cells act as a key point, because they transfer information regarding the intestinal contents and intraluminal pressure to nerve fibers lying in close proximity to the basolateral surface of the epithelium. In chick embryo, experimental intestinal atresia is associated with disorders in the development of the enteric nervous system, related to the severity of intestinal dilation. Our aim was to investigate the distribution pattern of endocrine cells in the developing endocrine system of chick embryo small intestine with experimentally-induced atresia on day 12 and on day 16. Changes in enteroendocrine population were examined in gut specimens (excised proximal and distal to the atresia) from experimental embryos 19 days old and in control sham-operated chick embryos at the same age. Sections from proximal and distal bowel and control bowel were stained with Grimelius silver stain, a valuable histochemical method for detecting the argyrophil and argentophilic cells, and with an immunohistochemical procedure for detecting serotonin and neurotensin immunoreactive cells. In chick embryo proximal bowel, intestinal dilation differed in the various embryos. We found significantly higher enteroendocrine cell counts in proximal bowel than in distal and control bowel. The differences depended on the precociousness of surgery and the severity of dilation. Considering the major contribution of enteroendocrine cells to the peristaltic reflex, our data may help to explain the pathogenesis of motility disorders related to intestinal atresia.

Nervous system development in normal and atresic chick embryo intestine: an immunohistochemical study

Intestinal motility disorders are a common complication after surgery for neonatal intestinal atresia. Although intestinal atresia causes alterations in the enteric nervous system, especially in its inner structures (nervous fibers in the mucosa, submucous and deep muscular plexuses), how these alterations develop is unclear. The chick model is a useful research tool for investigating the ontogenesis of the enteric nervous system and the pathogenesis of congenital bowel diseases. More information is needed on the overlap between the developing enteric nervous system and intestinal atresia. Because vasoactive intestinal polypeptide and substance P are typical intestinal neuropeptides, and vasoactive intestinal polypeptide acts as a modulator in neurodevelopment and an inhibitor of smooth muscle cell proliferation, our aim in this study was to investigate the distribution of their immunoreactivity in the developing enteric nervous system of normal and experimental chick models. We studied gut specimens excised from normal chick embryos (aged 12-20 days) and experimental chick embryos (aged 15-20 days) that underwent surgical intervention on day 12 to induce intestinal atresia (atresic embryos) or simply to grasp the bowel loop (sham-operated embryos). In normal chick embryos we showed vasoactive intestinal polypeptide and substance P immunoreactivity from day 12 in the submucous and myenteric plexuses. The distribution of peptide immunoreactivity differed markedly in atresic and normal or sham-operated gut embryos. These differences especially affected the inner structures of the enteric nervous system of specimens proximal to atresia and were related to the severity of dilation. Because nerve structures in the gut wall mucosa and submucous and deep muscular plexuses play a role in motility control and stretch sensation in the intestinal wall, our findings in the chick embryo may help to explain how gut motility disorders develop after surgery for neonatal intestinal atresia.

The occurrence of unusual smooth muscle bundles expressing alpha-smooth muscle actin in human intestinal atresia

BACKGROUND/PURPOSE

Intestinal dysmotility is an important problem in the postoperative management of patients with intestinal atresia (IA). Changes in the intramural components have so far been histochemically and immunohistochemically examined in both the proximal and distal segments of IA, but no detailed analysis of the muscular elements has been performed. The aim of this study was to carefully examine any alterations in the muscular elements in the intestines from patients with IA.

METHODS

Resected intestines were obtained from 6 patients with ileal atresia, 4 patients with jejunal atresia, and 3 controls without gastrointestinal diseases obtained by autopsy (congenital diaphragmatic hernia). All specimens were immunochemically stained with a monoclonal antibody to alpha-smooth muscle actin (alpha-SMA) as a smooth muscle marker.

RESULTS

In the normal small intestine, almost all the enteric smooth musculature were positive for alpha-SMA antiserum, except for the bulk of the circular musculature. In the proximal segments of all cases with IA, a reduced staining intensity for alpha-SMA was observed mainly in the severely hypertrophic muscle layers. In addition, some bundles of smooth muscle also were located in the submucosal connective tissue near the border of the innermost layer of the circular musculature, in which large amounts of smooth muscle fibers extended occasionally from the innermost layer of the circular musculature to the muscularis mucosae in the proximal segments of 4 cases. In the distal segments of IA, the distribution of alpha-SMA-positive smooth muscle fibers was similar to that in the control intestines, excluding mild to moderate hypertrophy of the muscular layers.

CONCLUSIONS

Both severe hypertrophy and a reduced immunoreactivity for alpha-SMA were observed in the circular muscle layer of the proximal segments. In addition, the occurrence of alpha-SMA-positive abnormal smooth muscle fibers was recognized in the submucosal layers of the proximal segments, thus, suggesting a delay in the intestinal muscular formation or a regressive reaction secondary to dilatation. These muscular alterations in the proximal segments might be considered to contribute to the postoperative intestinal dysmotility in IA cases.