Organization of intestinal pacemakers

Absence of the interstitial cell of Cajal network in mitochondrial neurogastrointestinal encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal-recessive multisystemic disorder with predominant gastrointestinal involvement, presenting with variable degrees of gut dysmotility up to frank chronic intestinal pseudoobstruction. Despite major advances in understanding its basic molecular pathogenesis in recent years, the distinct mechanisms and pathoanatomical substrate underlying MNGIE-associated gastrointestinal dysmotility are still widely unknown. As yet, though their critical role in proper gastrointestinal transit in terms of spontaneous pacemaker activity and enteric neurotransmission is well established, the population of the interstitial cells of Cajal (ICC) has not been investigated in MNGIE. Therefore, we examined small bowel samples of a well-characterized MNGIE patient by using conventional histology and immunohistochemistry techniques. The ICC network was studied by immunohistochemistry for the tyrosine kinase Kit (CD117), known to reliably detect ICCs, while mucosal mast cells served as an internal and normal small bowel specimen as external controls. At a light microscopic level, no gross structural alteration of the bowel wall composition and its neuromuscular elements was noted. However, a complete absence of Kit immunoreactive cells could be demonstrated in regions where ICCs are normally abundant, while internal and external controls retained strong Kit positivity. In conclusion, our preliminary results provide a first evidence for an alteration of the ICC network in MNGIE, and support the notion that ICC loss might be an early pathogenetic event in MNGIE-associated gut motor dysfunction before significant myopathic and/or neuropathic structural changes occur.

Absence of peristalsis in the ileum of W/W(V) mutant mice that are selectively deficient in myenteric interstitial cells of Cajal

It is well known that the enteric nervous system plays a key role in the generation of gastrointestinal peristaltic movements. Recently, the networks of interstitial cells of Cajal (ICC) have been found to be essential in the generation of spontaneous gastrointestinal movements. However, the role of ICC in the mechanisms involved in the generation of peristaltic movements is still controversial. The aim of the present study was to reveal how pacemaker myenteric ICC (ICC-MY) and the enteric nervous system contribute to the mechanisms involved in the generation of intestinal peristalsis. We compared spontaneous peristaltic movements of the ileum in wild type (WT) mice with those in W/W(V) mutant mice which are selectively deficient in ICC-MY. Simultaneous recordings were made from both the circular and longitudinal muscle of a 4-cm long segment of ileum under hydrostatic pressure of 0--0.5 cm H(2)O. Mechanical activity and continuous video-images of the ileum were compared between WT and W/W(V) mutant mice under control conditions, in the presence of N-nitro-L-arginine methyl ester (L-NAME) and after tetrodotoxin (TTX). In the WT mouse ileum, peristaltic waves to propagate from the oral to the anal end were frequently observed. The frequency of these peristaltic waves and their associated synchronous longitudinal and circular muscle contractions was increased by L-NAME. The peristaltic waves were abolished by TTX. In the W/W(V) mutant mouse ileum, no peristaltic waves to propagate from the oral to the anal end were observed in control and even after L-NAME, although the local spontaneously generated longitudinal and circular muscle contractions were enhanced by L-NAME. These local contractions were not abolished by TTX. The results presented here suggested that ICC-MY are essential for the generation of spontaneous intestinal peristaltic movements. It is conceivable that ICC-MY may determine the polarity of the excitation of the intestine such that longitudinal and circular muscle contractions propagate from the oral to the anal end of the intestinal segments, although the question of why ICC-MY are necessary for the neural pathways remains unresolved.

Different modulation of spontaneous activities by nitrergic inhibitory nerves between ileum and jejunum in W/Wv mutant mice

We compared the spontaneous electrical and mechanical activities between the jejunum and ileum in the W/Wv mutant mouse, where ICC in the myenteric region (ICC-MY) are deficient. Electrical slow waves (SWs) superimposed with spike potentials, and synchronous circular and longitudinal muscle mechanical activities at a regular rhythm under approximately 1 cm H2O were recorded in the jejunum and ileum of wild-type mice. However, in the jejunum and ileum of W/Wv mice, irregular electrical and mechanical activities without discernable SWs were recorded. N-nitro-L-arginine methyl ester (L-NAME) significantly decreased the mean interval of longitudinal muscle contractions from 4.43+/-3.39 to 2.50+/-1.23 s in the ileum of W/W(V) mice. L-NAME also significantly decreased mean coefficient of variance (decreased irregularity) in the intervals from 2.59+/-0.84 to 0.48+/-0.46 in the ileum. Tetrodotoxin also significantly decreased mean interval and coefficient of variance in the ileum. Neither L-NAME nor tetrodotoxin affected contractile activity in the jejunum. These results suggest that enteric nitrergic nerves in the ileum, but not the jejunum, mediate a steady-state inhibition of myogenic activity in W/Wv mice.