Interstitial cells of cajal are involved in neurotransmission in the gastrointestinal tract

Pilot study for in vivo cellular imaging of the muscularis propria and ex vivo molecular imaging of myenteric neurons (with video)

BACKGROUND

It is challenging to optimally sample the muscularis propria endoscopically for the diagnosis of muscle layer diseases, especially for motility disorders resulting from neuroenteric dysfunction.

OBJECTIVES

Ultramagnification in vivo imaging of the muscularis mucosa and ex vivo identification of myenteric neuronal elements by confocal microscopy.

DESIGN

Ex vivo and in vivo porcine animal studies.

SETTING

Short-term study in an animal laboratory.

INTERVENTIONS

The muscularis propria in the stomach and esophagus was accessed by resecting the mucosal layer with endoscopic submucosal dissection or cap EMR techniques or by creating a submucosal space by the submucosal endoscopy with mucosal flap technique. The muscularis propria was stained with Nissl stains and 2 types of neuronal molecular stains. The muscular layer was imaged with the endocytoscope in vivo. The muscularis stained with molecular-based stains was also evaluated with a confocal microscope.

RESULTS

Cellular microstructures resembling spindle-shaped smooth muscle cells were visualized by endocytoscopy in vivo. Confocal endoscopic microscopy demonstrated that in vivo topical application of neuronal molecular stains successfully stained the muscularis and specifically highlighted neuron-like cells.

LIMITATION

Animal model pilot study.

CONCLUSIONS

In vivo endoscopic histologic evaluation of the muscularis propria is technically feasible and easy. Minimally invasive advanced endoscopic imaging may be useful for the diagnosis and study of neuroenteric disorders at the level of the muscularis propria, avoiding surgical full-thickness tissue sampling.

c-Kit-negative fibroblast-like cells express platelet-derived growth factor receptor alpha in the murine gastrointestinal musculature

Platelet-derived growth factor receptors (PDGFRs) belong to the same kinase group as c-Kit receptor tyrosine kinase that is specifically expressed in the interstitial cells of Cajal (ICC) in the gastrointestinal tract. In this study, we examined PDGFRalpha immunoreactivity in the murine gastrointestinal tract. PDGFRalpha-immunopositive (PDGFRalpha-ip) cells were observed in the musculature in all parts of the gastrointestinal tract. Although PDGFRalpha-ip cells were distinct from ICC and neurons, these cells were closely associated with intramuscular ICC and enteric nerve fibers. In the myenteric layer, PDGFRalpha-ip cells formed a cellular network with their ramified processes and encompassed myenteric ganglia. Numerous PDGFRalpha-ip cells were observed in the subserosal plane and showed a multipolar shape. The distribution pattern of the PDGFRalpha-ip cells in the ICC-deficient W(v)/W(v) mutant mice was the same as that in normal mice. PDGFRalpha-ip cells that showed intense immunoreactivity of SK3 potassium channel were considered to correspond to fibroblast-like cells or non-Cajal interstitial cells. Our observations suggest that PDGFRalpha-ip cells are basic cellular elements throughout the gastrointestinal musculature and are involved in the gastrointestinal functions.

Interstitial cells of Cajal are innervated by nitrergic nerves and express nitric oxide-sensitive guanylate cyclase in the guinea-pig gastrointestinal tract

Nitric oxide (NO) is a major signaling molecule in the gastrointestinal tract, and released NO inhibits muscular contraction. The actions of NO are mediated by stimulation of soluble guanylate cyclase (sGC, NO-sensitive GC) and a subsequent increase in cGMP concentration. To elucidate NO targets in the gastrointestinal musculature, we investigated the immunohistochemical localization of the beta1 and alpha1 subunits of sGC and the distribution of neuronal NO synthase (nNOS) -containing nerves in the guinea-pig gastrointestinal tract. Distinct immunoreactivity for sGCbeta1 and sGCalpha1 was observed in the interstitial cells of Cajal (ICC), fibroblast-like cells (FLC) and enteric neurons in the musculature. Double immunohistochemistry using anti-c-Kit antibody and anti-sGCbeta1 antibody revealed sGCbeta1 immunoreactivity in almost all intramuscular ICC throughout the entire gastrointestinal tract. Immunoelectron microscopy revealed that sGCbeta1-immunopositive cells possessed some of the criteria for intramuscular ICC: presence of caveolae; frequently associated with nerve bundles; and close contact with smooth muscle cells. sGCbeta1-immunopositive ICC were closely apposed to nNOS-containing nerve fibers in the muscle layers. Immunohistochemical and immunoelectron microscopical observations revealed that FLC in the musculature also showed sGCbeta1 immunoreactivity. FLC were often associated with nNOS-immunopositive nerve fibers. In the myenteric layer, almost all myenteric ganglia contained nNOS-immunopositive nerve cells and were surrounded by myenteric ICC and FLC. Myenteric ICC in the large intestine and FLC in the entire gastrointestinal tract showed sGCbeta1 immunoreactivity in the myenteric layer. Smooth muscle cells in the stomach and colon showed weak sGCbeta1 immunoreactivity, and those in the muscularis mucosae and vasculature also showed evident immunoreactivity. These data suggest that ICC are primary targets for NO released from nNOS-containing enteric neurons, and that some NO signals are received by FLC and smooth muscle cells in the gastrointestinal tract.