Characteristics of cholinergic neuroeffector transmission of ganglionic and aganglionic colon in Hirschsprung's disease

Abnormally elevated expression of ACTA2 of circular smooth muscle leads to hyperactive contraction in aganglionic segments of HSCR

BACKGROUND

Actin Alpha 2 (ACTA2) is expressed in intestinal smooth muscle cells (iSMCs) and is associated with contractility. Hirschsprung disease (HSCR), one of the most common digested tract malformations, shows peristaltic dysfunction and spasm smooth muscles. The arrangement of the circular and longitudinal smooth muscle (SM) of the aganglionic segments is disorganized. Does ACTA2, as a marker of iSMCs, exhibit abnormal expression in aganglionic segments? Does the ACTA2 expression level affect the contraction function of iSMCs? What are the spatiotemporal expression trends of ACTA2 during different developmental stages of the colon?

METHODS

Immunohistochemical staining was used to detect the expression of ACTA2 in iSMCs of children with HSCR and Ednrb-/- mice, and the small interfering RNAs (siRNAs) knockdown technique was employed to investigate how Acta2 affected the systolic function of iSMCs. Additionally, Ednrb-/- mice were used to explore the changes in the expression level of iSMCs ACTA2 at different developmental stages.

RESULTS

The expression of ACTA2 is higher in circular SM in the aganglionic segments of HSCR patients and Ednrb-/- mice than in normal control children and mice. Down regulation of Acta2 weakens the contraction ability of intestinal smooth muscle cells. Abnormally elevated expression of ACTA2 of circular smooth muscle occurs since embryonic day 15.5 (E15.5d) in aganglionic segments of Ednrb-/- mice.

CONCLUSIONS

Abnormally elevated expression of ACTA2 in the circular SM leads to hyperactive contraction, which may cause the spasm of aganglionic segments in HSCR.

Altered neurotransmitter expression profile in the ganglionic bowel in Hirschsprung's disease

PURPOSE

Despite having optimal pull-through (PT) surgery for Hirschsprung's disease (HSCR), many patients experience persistent bowel symptoms with no mechanical/histopathological cause. Murine models of HSCR suggest that expression of key neurotransmitters is unbalanced proximal to the aganglionic colonic segment. We aimed to investigate expression of key enteric neurotransmitters in the colon of children with HSCR.

METHODS

Full-length PT specimens were collected fresh from children with HSCR (n=10). Control specimens were collected at colostomy closure from children with anorectal malformation (n=8). The distributions of neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT), vasoactive intestinal peptide (VIP), and substance P (SP) were evaluated using immunofluorescence and confocal microscopy. Neurotransmitter quantification was with Western blot analysis.

RESULTS

ChAT expression was high in aganglionic bowel and transition zone but reduced in ganglionic bowel in HSCR relative to controls. Conversely, nNOS expression was markedly reduced in aganglionic bowel but high in ganglionic bowel in HSCR relative to controls. VIP expression was similar in ganglionic HSCR and control colon. SP expression was similar in all tissue types.

CONCLUSION

Imbalance of key excitatory and inhibitory neurotransmitters in the ganglionic bowel in HSCR may explain the basis of bowel dysmotility after an optimal pull-through operation in some patients.

Benzalkonium chloride-treated anorectums mimicked endothelin-3-deficient aganglionic anorectums on manometry

BACKGROUND/PURPOSE

The anorectal spasticity in Hirschsprung disease may be caused by the absence of enteric ganglia and/or the presence of hypertrophic nerves. Anorectal manometry of chemically denervated rectums was compared with that of congenital aganglionic rectums that also possessed hypertrophic nerves.

METHODS

Aganglionic and ganglionic littermates were produced from breeding heterozygous lethal-spotted mice. Benzalkonium chloride was endorectally injected into ganglionic rectums to ablate the neural elements. Anorectal manometry was performed before the injection and on day 14 postinjection. The anorectal resting pressure was calculated based on the manometric tracing. Rectums were retrieved on day 14 for histologic evaluations.

RESULTS

Benzalkonium chloride injection successfully ablated the rectal ganglia. Although ganglionic littermates exhibited regular slow waves on anorectal manometry, aganglionic lethal-spotted mice showed irregular waves. Similar to lethal spotted mice, benzalkonium chloride-treated mice exhibited significantly higher anorectal resting pressure than that of ganglionic mice. The slow waves were absent in benzalkonium chloride-treated mice.

CONCLUSION

Benzalkonium chloride treatment produced aganglionic rectums that had higher resting pressure similar to the congenital aganglionic rectums. This suggests that hypertrophic nerves in congenital aganglionosis are not necessary to produce the anorectal spasticity.

Hirschsprung disease

Hirschsprung disease is a relatively common condition managed by pediatric surgeons. Significant advances have been made in understanding its etiologies in the last decade, especially with the explosion of molecular genetic techniques and early diagnosis. The surgical management has progressed from a two- or three-stage procedure to a primary operation. More recently, definitive surgery for Hirschsprung disease through minimally invasive techniques has gained popularity. In neonates, the advancement of treatment strategies for Hirschsprung disease continues with reduced patient morbidity and improved outcomes.

Chromogranin A and B in neuronal elements in Hirschsprung's disease: an immunocytochemical and radioimmunoassay study

Chromogranin A and B (CAB) occur in several peptide hormone-producing cells and in neurons of the brain. The aim of the present study was to investigate the possible neuronal localization of these chromogranins in the ganglionic and aganglionic bowel in Hirschsprung's disease by immunocytochemistry and radioimmunoassay, using antibodies recognizing either chromogranin A or both chromogranin A and B. Further, the coexistence of chromogranins and other neuronal constituents was studied. CAB were found in nerve fibers and occasionally in nerve cell bodies of submucous and myenteric ganglia in the ganglionic bowel, indicating that at least a population of chromogranin-immunoreactive nerve fibers is intrinsic in origin. CAB-immunoreactive fibers were numerous in the muscle layers of the aganglionic segment. These fibers contained tyrosine hydroxylase (TH), which indicates that they are adrenergic, in both ganglionic and aganglionic bowel. In the muscle layers of aganglionic (but not ganglionic) bowel, chromogranin A coexisted with galanin, neuropeptide Y (NPY), and vasoactive intestinal peptide (VIP). The concentration of CAB in smooth muscle specimens was higher in the aganglionic bowel than in the ganglionic bowel. Thus, chromogranins are present in the human enteric gut hyperinnervating the aganglionic bowel of Hirschsprung's disease.

Effect of nitric oxide on the colonic smooth muscle of patients with Hirschsprung's disease

Hirschsprung's disease results in bowel obstruction because of a failure of smooth muscle relaxation in both the aganglionic segment of bowel and the internal anal sphincter (IAS). Nonadrenergic noncholinergic (NANC) nerves, which use nitric oxide (NO) as their chemical messenger, are responsible for relaxing smooth muscle in normal bowel and the IAS. Previous work indicates that the cause of the aganglionic colon's inability to relax may be a lack of NANC nerves. To test this hypothesis, the authors compared the effect of an exogenous source of NO, S-nitroso-N-acetylpenicillamine (SNAP), on the isometric tension of smooth muscle strips taken from the ganglionic colon, aganglionic colon, and IAS of patients with Hirschsprung's disease. Exposure of ganglionic and aganglionic colon specimens to SNAP (10(-3) to 10(-5) mol/L) resulted in up to 70% reduction of resting tension. This relaxation occurred in a dose-dependent fashion and could be promptly reversed by the addition of the NO antagonist methylene blue. However, SNAP had no demonstrable effect on the smooth muscle strips taken from the IAS of patients with Hirschsprung's disease. This finding suggests that, in the aganglionic colon, a deficiency of NANC nerves contributes to the development of bowel obstruction. However, the failure of the IAS to relax in Hirschsprung's disease appears to be unrelated to NO and the NANC nervous system.

Secondary effects of prolonged intestinal obstruction on the enteric nervous system in the rat

Motility disturbances following prolonged intestinal obstruction have been attributed to secondary effects. This study aimed to demonstrate the effects of incomplete obstruction on the enteric nervous system (ENS) of a rat model. Surgical placement of a nonstrangulating ligature encircling the distal bowel was performed in 41 freshly weaned rats. Anesthetic protocol included Ketamine, ether, or Xylazine (an alpha 2-adrenergic agonist). Histological evaluation was by ganglion cell morphology, histochemical staining for acetylcholinesterase (AChE) and tyrosine hydroxylase (TOH) immunocytochemistry. Forty-one freshly weaned LE rats were divided into controls (8), sham procedures (8), intestinal obstruction (16), and a group of rats with colonic biopsy performed prior to and following experimental obstruction (9). The rats were sacrificed at periods varying between 14 and 45 days post experimental obstruction (median survival, 27 days). Histological changes included elongation of ganglion cells and a decrease in the number per 5-mm slide in obstructed animals. No other obstruction specific differences were detected. A significant (P < .01) increase in AChE in the submucous plexus was recorded in Xylazine-anesthetized animals. No obstruction-specific effects could be demonstrated in the ENS, suggesting that prolonged obstruction without ischemia does not result in any significant alterations in the ENS. Pharmacological stimulation of the alpha 2-adrenergic receptor appeared to result in an increase in AChE. This mechanism may help to explain a possible role for the adrenergic system in the increased AChE levels in affected bowel in patients with Hirschsprung's disease.

Hirschsprung's disease: clinical and experimental observations

Hirschsprung's disease (HD) is a relatively common cause of intestinal obstruction in the newborn. It is characterized by an absence of ganglion cells in the distal bowel beginning at the internal sphincter and extending proximally for varying distances. The etiology of HD-associated enterocolitis remains a complex issue. This study has provided further support for a possible infectious etiology of enterocolitis complicating HD.

A novel neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), in human intestine: evidence for reduced content in Hirschsprung's disease

A novel neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), exhibits sequence homology with vasoactive intestinal polypeptide (VIP) and occurs in the mammalian brain, lung and gut. The distribution of PACAP in ganglionic and aganglionic portions of the large intestine of patients with Hirschsprung's disease was examined by immunohistochemistry and radioimmunoassay. PACAP-immunoreactive nerve fibers were distributed in all layers of the ganglionic and aganglionic segments of the intestine, although they were less numerous in the latter, and PACAP-immunoreactive nerve cell bodies were seen in the ganglionic portion of the intestine. The concentration of immunoreactive PACAP was lower in the aganglionic than in the ganglionic segment of the intestinal wall. PACAP and VIP were found to coexist in both ganglionic and aganglionic segments of the intestine. Apparently, PACAP participates in the regulation of gut motility. The scarcer PACAP innervation of the aganglionic segment may contribute to the defect in intestinal relaxation seen in patients with Hirschsprung's disease.