Muscularis inflammation and the loss of interstitial cells of Cajal in the endothelin ETB receptor null rat

Abstract

Endothelin receptor null rats [ETB(-/-)] are a model for long-segment Hirschsprung's disease. These animals have significant intestinal distension (megaileum) proximal to a constricted region of the gastrointestinal tract lacking enteric ganglia. Experiments were performed to determine the pathophysiological changes that occur in these animals and to examine the tunica muscularis as a unique, immunologically active compartment. We observed abnormal intestinal flora in ETB(-/-) rats, which included a marked increase in gram-negative aerobes (Enterobacteriaceae) and anaerobes (Bacteroidaceae) in the distended region of the small intestine. Histochemical observations showed that neutrophilic infiltration was rarely or not observed, but the number of ED2 positive macrophages was increased in the tunica muscularis. Expression of IL-1beta and IL-6 mRNA was also significantly increased, and the level of CD14 (LPS receptors) were increased significantly in the tunica muscularis. Spontaneous phasic contractions were irregular in the distended intestinal regions of ETB(-/-) rats, and this was associated with an increased number of macrophages and damage to interstitial cells of Cajal (ICC) as revealed by using Kit-like immunoreactivity and electron microscopy. These results suggest that ED2-positive resident macrophages may play an important role in the inflammation of tunica muscularis in ETB(-/-) rats. Increased numbers and activation of macrophages may result in damage to ICC networks leading to disordered intestinal rhythmicity in regions of the gut in which myenteric ganglia are intact.

Phagocytotic Activation of Muscularis Resident Macrophages Inhibits Smooth Muscle Contraction in Rat Ileum

“…In the murine bone marrow-derived macrophages, phagocytosable size of latex beads (1.1-µm) stimulated the release of PGE 2 , whereas these macrophages did not respond to nonphagocytosable particles (≥ 40-µm) [24]. In the present study, we demonstrated that the injected FITC-dextran was phagocytosed by muscularis resident macrophages in rat small intestine same as previous reports [15,20,26]. The confocal microscopic study for FITC-dextran uptake and immunohistochemical study based on the results of double staining of dextran and COX-2 protein suggest that FITC-dextran-positive resident macrophages became immunoreactive to COX-2 antibody (Figs.…”

“…In the animal models for inflammatory bowel disease (IBD) or Hirschsprung's disease, the inflammation of intestinal muscularis is accompanied with the increase in the number of resident macrophage at the level of myenteric plexus layer [10,26]. In the present results, however, the number of ED2 positive cells was not changed in the dextran injected rat (Fig.…”

“…On the other hand, PGE 2 which is released from peritoneal macrophages has been demonstrated to produce hyperalgesia [4] and increased vascular permeability [11]. We have previously reported that the injected dextrans, phagocytosed by resident macrophages reside in the intestinal muscle layer [20,26,28]. However, the possible changes in the macrophages and smooth muscle functions after the phagocytotic stimulation have not been elucidated.…”

Network of Gut Pacemaker Cells: Spatio-Temporal Evaluation of Electrical Activity by Use of Microelectrode Array

“…MEA has also been applied to investigate spontaneous electrical activity between ileal musculature preparations from WT and W/W v mice. This comparison provides a model to evaluate impairment of the ICC network, because it is well known that the latter has a largely reduced population of ICC-MyP due to a partial loss-of-function mutation of Kit receptors (Reith, 1990;Ward et al 2004;Iino et al 2007). Analyses with power spectrum and potential mapping successfully distinguished electrical properties of these musculature preparations, indicating that network-forming ICC-MyP not only generates pacemaker potentials but also co-ordinates basal electrical activities.…”

“…and W/ W v mice as a model to evaluate the impairment of ICC, because it is well known that the latter has a largely reduced population of ICC in the myenteric region due to partial loss-of-function mutation of Kit receptors (Reith, 1990;Ward et al 2004;Iino et al 2007). Fig.…”