Morphological and functional alterations of the myenteric plexus in rats with TNBS-induced colitis

Differential responses of intrinsic and extrinsic innervation of smooth muscle cells in rat colitis

Intestinal smooth muscle cells receive neural input from axons that originate within the intestine, as well as from axons of extrinsic origin. In the inflamed intestine, altered motility may arise from damage to the axon/smooth muscle cell relationship, but the extent of change is unknown. Western blotting, histology and immunocytochemistry were used in the TNBS model of colitis in the rat to evaluate intrinsic and extrinsic axon numbers, which were then correlated with circular smooth muscle cell (CSMC) number during the time course from the acute onset of colitis to apparent recovery, at Day 35 post TNBS. Total axon profiles in the circular smooth muscle layer were reduced by nearly 50% on Day 4 of colitis, to 428 +/- 82 axons/section from 757 +/- 125 in control (n = 8-14 animals). The intrinsic innervation density (axon number per CSMC) dropped sharply by Day 2 to less than 30% of control. Although CSMC number nearly tripled during colitis, innervation density was restored to control levels by Day 6 due to a coordinated three-fold increase in axon number. The subpopulation of extrinsic axons expressing tyrosine hydroxylase showed a unique pattern during colitis, with no initial decrease in axon number, followed by axonal proliferation between Days 6 and 16 post-TNBS. We conclude that loss of intrinsic axons is an early event in colitis, and although reversed by axonal proliferation, transient denervation may promote CSMC hyperplasia as seen in earlier work in vitro. Axonal proliferation of both intrinsic and extrinsic axons is identified as a major homeostatic mechanism, with distinct patterns of damage and repair suggesting a structural basis for the altered motility seen in the inflamed colon.

Indiscriminate loss of myenteric neurones in the TNBS-inflamed guinea-pig distal colon

This investigation was conducted to establish whether guinea-pig trinitrobenzene sulfonic acid (TNBS)-colitis was associated with a change in the number of neurones of the myenteric plexus, and, if so, whether select subpopulations of neurones were affected. Total neurones were quantified with human (Hu) antiserum, and subpopulations were evaluated with antisera directed against choline acetyltransferase, nitric oxide synthase, calretinin, neuronal nuclear protein or vasoactive intestinal peptide (VIP). Colitis was associated with a loss of 20% of the myenteric neurones, most of which occurred during the first 12 h past-TNBS administration. During this period, myenteric ganglia were infiltrated with neutrophils while lymphocytes appeared at a later time-point. The neuronal loss persisted at a 56-day time-point, when inflammation had resolved. The decrease in myenteric neurones was not associated with a decrease in any given subpopulation of neurones, but the proportion of VIP-immunoreactive neurones increased 6 days following TNBS administration and returned to the control range at the 56 days. These findings indicate that there is an indiscriminant loss of myenteric neurones that occurs during the onset of TNBS-colitis, and the loss of neurones may be associated with the appearance of neutrophils in the region.

Effects of acupuncture at GV01 on experimentally induced colitis in rats: possible involvement of the opioid system

Oriental medicine uses acupuncture at the GV01 acupoint with great success to treat diarrhea. It significantly reduced the colonic motility and inflammation in colitic rats. Naloxone pretreatment blocked these effects. The therapeutic effects of acupuncture at GV01 in colitis may involve endogenous opioid pathways.

Myenteric plexus injury and apoptosis in experimental colitis

Intestinal inflammatory conditions are associated with structural and functional alterations of the enteric nervous system (ENS). While injury to the enteric nervous system is well described, the mechanisms of neuronal injury and neuronal cell loss remain unclear. The aim of the present study was to examine the neural consequences of distal colitis and to assess the role of neutrophil granulocytes in mediating these changes. Colitis was induced in C3H/HEN female mice with dinitrobenzene sulfonic acid. The mice were then sacrificed at 0.5, 1, 1.5, 2, 3, 4, 6, 12, 24, 120 h post instillation of dinitrobenzene sulfonic acid. The inflammatory response was assessed by macroscopic damage score, myeloperoxidase activity and histology. HuC/D and PGP 9.5 immunostaining was used to examine myenteric plexus density and structure, neural cell body numbers and distribution in cross-section and whole mount preparations. Apoptosis was investigated in whole mount preparations double stained with HuC/D and activated caspase-3 or cleaved poly (ADP-ribose) polymerase (PARP). Dinitrobenzene sulfonic acid-induced colitis was associated with a rapid and significant loss of HuC/D immunoreactive myenteric plexus neuronal cell bodies (42% decrease relative to control) that remained unchanged between 6 and 120 h. No change in myenteric plexus density was observed with PGP 9.5 immunostaining. Neuronal apoptosis was evident between 0.5 and 3 h. PARP immunoreactive neurons ranged between 1% and 2.5%. Colitis was associated with significant impairment in colonic propulsive function. Pre-treatment of mice with anti-neutrophil serum attenuated the inflammatory response and partially reduced the extent of myenteric plexus neuronal cell loss. Taken together, these data suggest that acute colitis is associated with loss of myenteric plexus neurons that is partly mediated by neutrophil granulocyte infiltration and is accompanied by impairment of colonic motility.

Nogo A expression in the adult enteric nervous system

Neuronal plasticity plays an important role in physiological and pathological processes within the gastrointestinal (GI) tract. Nogo A is a major contributor to the negative effect central nervous system (CNS) myelin has on neurite outgrowth after injury and may also play a role in maintaining synaptic connections in the healthy CNS. Nogo A is highly expressed during neuronal development but in the CNS declines postnatally concomitantly with a loss of regenerative potential while ganglia of the Peripheral Nervous System (PNS) retain Nogo A. The enteric nervous system shares a number of features in common with the CNS, thus the peripheral distribution of factors affecting plasticity is of interest. We have investigated the distribution of Nogo in the adult mammalian gastrointestinal tract. Nogo A mRNA and protein are detectable in the adult rat GI tract. Nogo A is expressed heterogeneously in enteric neurons throughout the GI tract though expression levels appear not to be correlated with neuronal sub-type. The pattern of expression is maintained in cultured myenteric plexus from the guinea-pig small intestine. As is seen in developing neurons of the CNS, enteric Nogo A is present in both neuronal cell bodies and axons. Our results point to a hitherto unsuspected role for Nogo A in enteric neuronal physiology.

Enteric P2X receptors as potential targets for drug treatment of the irritable bowel syndrome

The irritable bowel syndrome (IBS) is a gastrointestinal motility disorder affecting millions of patients. IBS symptoms include diarrhea, constipation and pain. The etiology of IBS is due partly to changes in the function of nerves supplying the gastrointestinal tract, immune system activation and to psychological factors. P2X receptors are multimeric ATP-gated cation channels expressed by neuronal and non-neuronal cells. Sensory nerve endings in the gastrointestinal tract express P2X receptors. ATP released from gastrointestinal cells activates P2X receptors on sensory nerve endings to stimulate motor reflexes and to transmit nociceptive signals. Antagonists acting at P2X receptors on sensory nerves could attenuate abdominal pain in IBS patients. Primary afferent neurons intrinsic to the gut, and enteric motor- and interneurons express P2X receptors. These neurons participate in motor reflexes. Agonists acting at enteric P2X receptors may enhance gastrointestinal propulsion and secretion, and these drugs could be useful for treating constipation-predominant IBS. Antagonists acting at enteric P2X receptors would decrease propulsion and secretion and they might be useful for treating diarrhea-predominant IBS. Current knowledge of P2X receptor distribution and function in the gut of laboratory animals provides a rational basis for further exploration of the therapeutic potential for drugs acting at P2X receptors in IBS patients. However, more information about P2X receptor distribution and function in the human gastrointestinal tract is needed. Data on the distribution and function of P2X receptors on gastrointestinal immune cells would also provide insights into the therapeutic potential of P2X receptor agents in IBS.

Alterations of enteric nerve plexus in experimental gastroschisis: is there a delay in the maturation?

BACKGROUND/PURPOSE

After surgical correction of gastroschisis, intestinal transitory hypoperistalsis usually occurs. Long-term parenteral nutrition often is necessary leading to a higher morbidity associated with this malformation. The etiology of this transitory intestinal hypomotility is unknown. It may be caused by a reversible inflammatory process in the intestinal wall or other causes, including an alteration of the maturation of intestinal neural plexus, because the disturbance disappears spontaneously after a variable period. The aim of this work was to study the neuronal cells of the myenteric plexus of the fetal intestine in experimental gastroschisis. The main hypothesis was that the transitory intestinal dismotility seen in gastroschisis could be secondary to alteration in the maturation of the enteric nervous plexus.

METHODS

Twenty-seven time-mated rabbits, on gestational day 25, were submitted to a midline laparotomy; the gravid bicornuate uterus was exposed and opened, and the more distal fetuses relative to the vaginal opening had the abdominal wall opened by a small incision to produce gastroschisis (n = 29). The fetuses not submitted to gastroschisis were used as controls (n = 12). The amniotic fluid was carefully aspirated from the opened uterus and saved for later repositions. On gestational day 30, the does were again submitted to general anesthesia, and the fetuses were delivered by cesarean section. The fetal intestine was removed, the adjacent mesentery excised, and intestinal specimens were harvested for histologic studies. The specimens were stained for acetyl-cholinesterase activity (AChE) to assess the maturity of the nervous enteric cells and for lactate dehydrogenase (LDH) that identify specifically immature nervous cells. The histologic sections stained by LDH were submitted to histomorphometric analysis of the nervous cells through an image system analysis (Kontron 300). The results were submitted to statistical analyses (P <.05).

RESULTS

Macroscopic alterations of the fetal gastroschisis intestine are similar to the human findings: shortening of the intestine, intestinal wall thickening, and a hypertrophied muscular layer. In the gastroschisis group, histologic AChE activity was decreased in comparison with control intestines. The histomorphometric assessment in slices stained with LDH, which identify immature nervous cells, showed that the neuronal intestinal cells of the gastroschisis group were significantly smaller and more numerous relative to the control group.

CONCLUSIONS

There were significant differences in the nervous plexus of the intestine of fetuses with gastroschisis relative to the controls. The observed morphologic changes may be caused by alteration in the maturation of the intestinal neuronal in gastroschisis. This alteration may explain the transitory intestinal hypomotility observed in infants after surgical correction of gastroschisis.