Spatial distribution and pattern of extrinsic nerve strands in the aganglionic segment of congenital aganglionosis: stereoscopic analysis in spotting lethal rats

Mesenteric Neural Crest Cells Are the Embryological Basis of Skip Segment Hirschsprung's Disease

BACKGROUND & AIMS

Defective rostrocaudal colonization of the gut by vagal neural crest cells (vNCCs) results in Hirschsprung's disease (HSCR), which is characterized by aganglionosis in variable lengths of the distal bowel. Skip segment Hirschsprung's disease (SSHD), referring to a ganglionated segment within an otherwise aganglionic intestine, contradicts HSCR pathogenesis and underscores a significant gap in our understanding of the development of the enteric nervous system. Here, we aimed to identify the embryonic origin of the ganglionic segments in SSHD.

METHODS

Intestinal biopsy specimens from HSCR patients were prepared via the Swiss-roll technique to search for SSHD cases. NCC migration from the neural tube to the gut was spatiotemporally traced using targeted cell lineages and gene manipulation in mice.

RESULTS

After invading the mesentery surrounding the foregut, vNCCs separated into 2 populations: mesenteric NCCs (mNCCs) proceeded to migrate along the mesentery, whereas enteric NCCs invaded the foregut to migrate along the gut. mNCCs not only produced neurons and glia within the gut mesentery, but also continuously complemented the enteric NCC pool. Two new cases of SSHD were identified from 183 HSCR patients, and Ednrb-mutant mice, but not Ret^-/- mice, showed a high incidence rate of SSHD-like phenotypes.

CONCLUSIONS

mNCCs, a subset of vNCCs that migrate into the gut via the gut mesentery to give rise to enteric neurons, could provide an embryologic explanation for SSHD. These findings lead to novel insights into the development of the enteric nervous system and the etiology of HSCR.

Interstitial Cells in the Musculature of the Gastrointestinal Tract: Cajal and Beyond

Expression of the receptor tyrosine kinase KIT on cells referred to as interstitial cells of Cajal (ICC) has been instrumental during the past decade in the tremendous interest in cells in the interstitium of the smooth muscle layers of the digestive tract. ICC generate the pacemaker component (electrical slow waves of depolarization) of the smooth musculature and are involved in neurotransmission. By integration of ICC functions, substantial progress has been made in our understanding of the neuromuscular control of gastrointestinal motility, opening novel therapeutic perspectives. In this article, the ultrastructure and light microscopic morphology, as well as the functions and the development of ICC and of neighboring fibroblast-like cells (FLC), are critically reviewed. Directions for future research are considered and a unifying concept of mesenchymal cells, either KIT positive (the "ICC") or KIT negative "non-Cajal" (including the FLC and possibly also other cell types) cell types in the interstitium of the smooth musculature of the gastrointestinal tract, is proposed. Furthermore, evidence is accumulating to suggest that, as postulated by Santiago Ramon y Cajal, the concept of interstitial cells is not likely to be restricted to the gastrointestinal musculature.

Extrinsic nerve strands in the aganglionic segment of Hirschsprung's disease

BACKGROUND/PURPOSE

The distributions and pathways of the extrinsic enteric nerves in the aganglionic segment in Hirschsprung's disease (HD) have not been delineated completely. The authors have clarified the major pathways and the details of fine distribution of the extrinsic nerves in the aganglionic segment of a congenital aganglionosis rat. Further investigation was extended to apply those findings in human materials.

METHODS

Five HD patients, eight fetuses, and two postmortem neonates with normally innervated colon were examined. Specimens were observed by histochemical technique using light microscopy in whole-mount preparations.

RESULTS

Two sets of extrinsic nerve strands were observed in the distal aganglionic colon; one consisted of a continuous network located between the longitudinal and circular muscle coats, and the other involved branches that mainly coursed along the blood vessels in the submucosal layer originating from the nearby mesentery. These two sets of nerve strands were similar to those of aganglionosis rats. Also, thick nerve strands were found running longitudinally in the myenteric layer in the normally ganglionated colon of 18- and 21-week-old fetuses. These nerve strands were unclear in a 32-week-old fetus.

CONCLUSIONS

This study showed the following: (1) the origin of the nerve strands in the myenteric layer is mainly the pelvic nerve plexus and (2) the number of ascending extrinsic nerve strands decreases from the proximal colon in cases of long-segment aganglionosis, which may be caused by the same process that occurs in the normally innervated bowel.

Unique spindle cells in the involved ileal segment of rats with congenital aganglionosis

Protein gene product (PGP) 9.5 is a newly characterized brain-specific protein originally detected by high-resolution two-dimensional electrophoresis of soluble human brain proteins. Immunoreactivity for PGP9.5 was investigated in the small and large intestine of aganglionic mutant and control rats with light microscopy, electron microscopy, and confocal laser scanning microscopy. Immunoreactive spindle-shaped cells were seen in the inner circular muscle layer of the aganglionic ileal segment. The long axes of these spindle cells paralleled the inner circular muscle fibers. PGP9.5-positive spindle cells were positive for enteric actin, and some of them were also positive for vimentin, a relatively specific marker for the special smooth muscle (pacemaker cells). These cells may prove to be a maldeveloped microenvironment of aganglionic segment. However, it is necessary to investigate expression of PGP9.5 in embryonal tissue with an abnormal environment to test this hypothesis. This study showed PGP9.5-positive pacemaker cells in the aganglionic ileal segment in the first time.