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Evidence for and significance of the projection of VIP neurons from the myenteric plexus to the taenia coli in the guinea pig.

Immunohistochemical studies of the distribution of vasoactive intestinal polypeptide were made in the cecum from normal guinea pigs and from guinea pigs after lesions of the cecal wall had been made. These experiments were designed to determine the origin of the vasoactive intestinal polypeptide axons which supply the taenia of the cecum in order to ascertain whether the projections of the vasoactive intestinal polypeptide neurons were consistent with VIP being contained in enteric inhibitory neurons. Vasoactive intestinal peptide was found in nerve cell bodies of both the myenteric and submucous taenia and the myenteric plexus the vasoactive intestinal polypeptide fibers in the taenia disappeared, but there was no effect on these fibers if the taenia was separated from the submucous plexus or surrounding muscle while leaving connections with the myenteric plexus intact. Retrograde degenerative signs were seen in VIP fibers and nerve cell bodies of the myenteric plexus after removal of the taenia. In conclusion, VIP is contained in neurons that have the same projections as the enteric inhibitory neurons from the myenteric plexus to the taenia of the cecum.

Animals↗

Familial multiple gastrointestinal stromal tumours with associated abnormalities of the myenteric plexus layer and skeinoid fibres.

AIMS: Multiple familial gastrointestinal stromal tumours are rare. We report the third family with two cases of multiple gastrointestinal stromal tumours showing skeinoid fibres. Associated abnormalities of the myenteric plexus layer are described and new hypotheses for the histogenesis of gastrointestinal stromal tumours are formulated. METHODS AND RESULTS: Multiple gastrointestinal stromal tumours developed in the duodenum and proximal jejunum were removed from mother and son. No history of a specific syndrome or of mastocytosis was known. Light microscopy revealed typical gastrointestinal stromal tumours with skeinoid fibres. An unusual abnormality of the myenteric plexus layer, showing a diffuse spindle cell hyperplasia, was noted in the macroscopically normal digestive wall. No abnormalities of the ganglion cells were associated. Tumours and the spindle cell hyperplasia showed similar morphological and immunohistochemical features with expression of CD34 and CD117 antigens. Follow-up revealed recurrences in the mother. CONCLUSION: The morphological characteristics of these two cases of familial gastrointestinal stromal tumours and of the associated abnormalities of the myenteric plexus layer, help to better explain the histogenesis of multiple familial gastrointestinal stromal tumours. The hyperplasia of the myenteric plexus could be considered a risk factor for recurrent tumours.

Actins↗

Ultrastructure of rat duodenal myenteric plexus revealed by quick-freezing and deep-etching method.

A quick-freezing and deep-etching (QF-DE) method was employed with whole-mount strips of rat duodenal muscle walls to exhibit the cytoskeletons of the myenteric plexus. Nerve fibers in the myenteric plexus, which contained fewer neurofilaments than other types of neurons examined, had many varicosed contours, and were bundled by enteroglial cells. Cytoskeleton arrays were rarely observed in the varicosed regions, where synaptic vesicles were often seen, although other nerve regions contained many neurofilaments running almost in parallel with the nerve fiber bundle. Enteroglial cells had short cytoskeletons predominantly across the cytoplasm, becoming thinner the around varicosed regions of the nerve bundles. Such enteroglial extruded areas were often in close association with neighboring nerve fibers, indicating intercommunications between the nerve fibers. In distal parts of enteric nerve processes, there were numerous synaptic vesicles, but few neurofilaments. Smooth muscle cells were closely associated with the enteric nerve processes. Fine network structures, responsible for the extracellular matrix, were present between the smooth muscle cells and the enteric nerve processes. These specific structures of the myenteric plexus could be important for signalling or for the transportation of neurotransmitters involved in gut motility.

Animals↗

Involvement of the myenteric plexus in the cholera toxin-induced net fluid secretion in the rat small intestine.

BACKGROUND: The enteric nervous system is responsible in vivo for most of the change in fluid transport induced by cholera toxin. The aim of the present study was to investigate the importance of the myenteric plexus in the Intramural reflex responsible for this secretion. METHODS: Long-term ablation of the myenteric plexus was achieved by serosal application of benzalkonium chloride on jejunal segments in rats. RESULTS: The treated segments without functioning myenteric plexus showed a normal net fluid absorption. Cholera toxin in this segment only induced a reduction of fluid absorption, whereas in a nontreated ileal segment it concomitantly induced a conspicuous net fluid secretion. Intravenous hexamethonium did not change the cholera toxin response in the treated jejunal segments, whereas vasoactive intestinal polypeptide elicited a marked secretion. CONCLUSIONS: Benzalkonium chloride treatment eliminated the ability of cholera toxin to induce intestinal secretion. Thus, all afferent fibers in the intramural secretory reflex activated by cholera toxin are probably conveyed via the myenteric plexus, which functions as the integrating center in the enteric nervous system. The Ussing chamber technique using stripped intestinal preparations cannot be used when studying effects of luminal secretagogues.

Animals↗

Structural and chemical organization of the myenteric plexus.

The most striking characteristics of the myenteric plexus are the heterogeneity of its neuronal populations and the complexity of its organization. Myenteric neurons greatly differ in their morphological characteristics, projection patterns, and topographical arrangement within the ganglia. The discovery of histochemically distinct types of neurons together with the development of nerve-tracing techniques and specific lesions have allowed a better understanding of the relationships of enteric neurons to specific target tissues. Consequently, these techniques have contributed significantly to our knowledge of the highly ordered organization of the ENS, which represents the anatomical substrate for the neural coordination and integration of the complex functions it subserves. The existence of different types of neurons that probably use different substances as transmitters may reflect on the existence of defined functional roles for each type of neurons. To date, only ACh, NE, and probably 5-HT seem to satisfy all the criteria necessary for establishing a neurotransmitter, although there is increasing evidence that some of the other substances, such as GABA, SP, and VIP, are enteric transmitters or modulators. The functional roles of the different types of neurons in the neural circuitry that regulates gastrointestinal functions remain to be elucidated.

Animals↗

Differentiation between myenteric plexus and longitudinal muscle of the rat jejunum as the site of action of putative enteric neurotransmitters.

The contribution of the myenteric plexus in the mechanical responses of rat jejunal longitudinal muscle produced by several enteric nerve substances was evaluated. The myenteric plexus of a segment of rat jejunum was destroyed by serosal application of benzalkonium chloride (BAC). Fifteen days after BAC treatment, both the BAC-treated and an orad control jejunal segment were removed and the mechanical responses of the longitudinal muscle produced by the following substances were examined: substance P, acetylcholine (ACh), 5-hydroxytryptamine (5-HT), cholecystokinin octapeptide (CCK-8), norepinephrine, vasoactive intestinal peptide (VIP), bombesin, [Leu5]enkephalin and somatostatin. Our results indicate that: substance P and norepinephrine produce their mechanical responses by acting predominantly on the longitudinal smooth muscle; 5-HT, CCK-8, ATP, VIP and neurotensin act predominantly through the myenteric plexus; ACh possesses both direct and indirect actions; and because the responses to [Leu5]enkephalin, bombesin and somatostatin were equivocal, a conclusion as to their site of action could not be made with this preparation.

Acetylcholine↗

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.

Animals↗

Characterization of content and chromatographic forms of neuropeptides in purified nerve varicosities prepared from guinea pig myenteric plexus.

Partially purified nerve varicosities (PV) prepared from guinea pig ileal myenteric plexus were found to contain, by radioimmunoassay, gastrin-releasing polypeptide (GRP), substance P (SP), galanin, Leu-enkephalin (LE), Met-enkephalin (ME), and vasoactive intestinal polypeptide (VIP). SP was present in the highest concentration followed by, in descending order, ME, LE, VIP, GRP and galanin. On reverse-phase HPLC, SP-, LE- and ME-like immunoreactivity in the PV preparation eluted at retention times similar to their synthetic analogues, galanin-like immunoreactivity eluted at a retention time different from that of synthetic porcine galanin and VIP-like immunoreactivity eluted at the retention time of synthetic guinea pig VIP. GRP-like immunoreactivity, on reverse-phase HPLC, eluted at retention times close to that of synthetic porcine GRP-(1-27) and its major oxidized form. Evidence was obtained for the presence of an alpha-neurokinin-like immunoreactive entity and an unidentified SP-like immunoreactive entity in guinea pig myenteric plexus.

Animals↗

Evoked secretion of [3H]noradrenaline and ATP from nerve varicosities isolated from the myenteric plexus of the guinea pig ileum.

Neuronal varicosities, isolated from the myenteric plexus of guinea pig ileum longitudinal muscle, were incubated with [3H]noradrenaline to label the contents of the noradrenergic secretory vesicles. Exposure of these varicosities to KCl, nicotine, or acetylcholine resulted in the Ca2+ -dependent release of [3H]noradrenaline. Veratridine also evoked a large efflux of [3H] from this preparation, but this release was only partially Ca2+ dependent. The alpha 2-adrenoceptor agonist, clonidine, inhibited the K+-, nicotine-, and acetylcholine-induced release of [3H]noradrenaline. Similarly, exogenously administered (-)noradrenaline was an effective inhibitor of the K+ -evoked release of [3H]noradrenaline. The alpha 2-adrenoceptor antagonist, yohimbine, antagonized the inhibitory actions of both clonidine and (-)noradrenaline on the K+ -evoked release of [3H]noradrenaline from myenteric varicosities. Nicotine, acetylcholine, KCl, and veratridine also released ATP from these guinea pig ileal myenteric varicosities. However, the evoked release of ATP was unaffected by clonidine. These results indicate that myenteric varicosities can take up and release [3H]noradrenaline and that they possess presynaptic alpha 2-adrenoceptors which, when activated, inhibit the release of [3H]noradrenaline. These receptors may play a role in modulating the release of noradrenaline in the myenteric plexus in vivo. In addition, the present results suggest that ATP and [3H]noradrenaline may not be released from the same population of secretory vesicles in neuronal varicosities isolated from guinea pig ileum longitudinal muscle.

Acetylcholine↗

Activation of smooth muscle and myenteric plexus cells of jejunum via Toll-like receptor 4.

The cell types of the gut expressing Toll-like receptor 4, which recognizes specifically bacterial lipopolysaccharides, as well as the functionality of this receptor, have remained controversial. We aimed to clarify these issues. Mouse and human intestinal specimens were stained immunohistochemically to detect Toll-like receptor 4 expression. Smooth muscle and myenteric plexus cells but not enterocytes revealed receptor expression. Murine intestinal smooth muscle and myenteric plexus cells but not enterocytes showed nuclear translocation of nuclear factor-kappaB after in vivo stimulation with lipopolysaccharide. Moreover, lipopolysaccharide added to human jejunum biopsies free of epithelial cells induced release of interleukin-8 (IL-8). We can conclude that Toll-like receptor 4 is not expressed in epithelial layer, but rather on smooth muscle and myenteric plexus cells and that expression is functional. The expression of Toll-like receptor 4 on smooth muscle and myenteric plexus cells is consistent with the possibility that these cells are involved in intestinal immune defense; the low or absent expression of Toll-like receptor 4 on enterocytes might explain the intestinal epithelium hyporesponsiveness to the abundance of LPS in the intestinal lumen.

Animals↗

High density of neuropeptide Y-innervation in the myenteric plexus of the turtle midgut. An immunocytochemical study.

Using an indirect immunocytochemical method, a high density of NPY-containing neural network is revealed in the myenteric plexus of the midgut of the turtle, Pseudemys scripta elegans. The labelled elements included strongly stained small nerve cells and generally weakly labelled large ones of the plexus, as well as a substantial proportion of the nerve fibres within both the myenteric plexus and around blood vessels. Pericellular baskets around nonstained nerve cells and in some cases around weakly stained larger nerve cells were common. In the mammalian species the bulk of the NPY-immunoreactive nerve cells is found in the submucous plexus. In the turtle, however, NPY could be found in about 20-30% of the perikarya of the myenteric plexus. The layers of the circular and longitudinal musculature, on the other hand, seem to be hardly innervated by NPY-immunopositive fibres. Thus, NPY may fulfill a key role in the myenteric microcircuitry, but not in the direct regulation of smooth muscle movement, of the turtle small intestine.

Animals↗

The differential contribution of endogenous prostaglandins to the release of acetylcholine from the myenteric plexus of the guinea-pig ileum.

1. Prostaglandin E (PGE) may be essential for maintaining the sensitivity of the myenteric plexus of guinea-pig ileum to nicotine. The contributions of prostaglandins to nervous activity evoked by different stimuli have now been investigated by measuring the amount of acetylcholine (ACh) released from the myenteric plexus of the guinea-pig ileum. 2. The amount of ACh released in response to dimethylphenylpiperazinium (DMPP) or substance P was depressed to about 40% of control by 2.8 microM indomethacin (Ind), whereas the release of ACh induced by 5-hydroxytryptamine (5-HT) was not affected. The inhibitory effects of Ind were overcome by 14.3 nM PGE2. 3. Mepacrine 5 microM, an inhibitor of phospholipase A2, depressed the release of ACh in response to DMPP and substance P to the same extent as Ind. These inhibitory effects of mepacrine were overcome by arachidonic acid (10 microM), but not by arachidonic acid plus Ind. The release of ACh evoked by 5-HT or electrical field stimulation (EFS) was also inhibited to about 60% of control by mepacrine but these inhibitions were overcome by arachidonic acid (10 microM) either in the absence or the presence of Ind. 4. The results suggest that endogenous prostaglandins and arachidonic acid contribute to the maintenance of the excitability of the myenteric plexus by DMPP and substance P. By contrast, the release of ACh induced by 5-HT and EFS may be regulated by arachidonic acid and not by prostaglandins.

Acetylcholine↗

Lymphocyte-mediated regulation of beta-endorphin in the myenteric plexus.

Lymphocytes are antinociceptive and can modulate visceral pain perception in mice. Previously, we have shown that adoptive transfer of CD4+ T cells to severe combined immune-deficient (SCID) mice normalized immunodeficiency-related visceral hyperalgesia. Pain attenuation was associated with an increase in beta-endorphin release by T cells and an upregulation of beta-endorphin in the enteric nervous system. In this study, we investigated the relationship between T cells and opioid expression in the myenteric plexus. We examined opioid peptide and receptor expression in the myenteric plexus in the presence and absence of mucosal T cells. We found a positive association between T cells and beta-endorphin expression; this was accompanied by a downregulation of the micro-opioid receptor (MOR). In vitro, T helper (Th) type 1 and type 2 cytokine stimulation of CD4+ T cells or isolation of T cells from in vivo Th-polarized mice did not increase T cell release of beta-endorphin or the induction of beta-endorphin expression in the myenteric plexus. However, exogenous beta-endorphin did upregulate beta-endorphin expression, and both cycloheximide and naloxone methiodide inhibited peptide upregulation. Therefore, our results suggest that nonpolarized CD4+ T cells release beta-endorphin, which, through an interaction with MOR, stimulates an upregulation of beta-endorphin expression in the myenteric plexus. Thus, we propose that the mechanism underlying lymphocyte modulation of visceral pain involves T cell modulation of opioid expression in the enteric nervous system.

Animals↗

Expression of c-fos in gastric myenteric plexus and spinal cord of rats with cervical spondylosis.

AIM: To determine the expression of c-fos in gastric myenteric plexus and spinal cord of rats with cervical spondylosis and its clinical significance. METHODS: A cervical spondylosis model was established in rats by destroying the stability of cervical posterior column, and the cord segments C(4-6) and gastric antrum were collected 3, 4 and 5 mo after the operation. Rats with sham operation were used as controls. c-fos neuronal counter-staining was performed with an immunohistochemistry method. Every third sections from C(4-6) segments were drawn. The 10 most labeled c-fos-immunoreactive (Fos-IR) neurons were counted, and the average number was used for statistical analysis. The mean of Fos-IR neurons in myenteric plexus was calculated after counting Fos-IR neurons in 25 ganglia from each antral preparation, and expressed as a mean count per myenteric ganglion. RESULTS: There were a few c-fos-positive neurons in the cervical cord and antrum in the control group. There was an increased c-fos expression in model group 3, 4 and 5 mo after operation, whereas there was no significant increase in c-fos expression in the control group at 3, 4 and 5 mo. More importantly, there was a significant difference in c-fos expression between rats followed up for 3 mo and those for 5 mo in the model group (11.20+/-2.26 vs 27.68+/-4.36, P<0.05, for the cervical cord; and 11.3+/-2.3 vs 29.3+/-4.6, P<0.05, for the gastric antrum). There was no significant difference between rats followed up for 3 mo and those for 4 mo and between rats followed up for 4 mo and those for 5 mo in the model group. CONCLUSION: c-fos expression in gastric myenteric plexus was dramatically associated with that in the spinal cord in rats with cervical spondylosis, suggesting that the gastrointestinal function may be affected by cervical spondylosis. If this hypothesis is confirmed by further studies, functional gastrointestinal diseases such as functional dyspepsia and irritable bowel syndrome could be explained by neurogastroenterology.

Animals↗

Effects of inflammation on cell proliferation in the myenteric plexus of the guinea-pig ileum.

This study was undertaken to investigate the occurrence and identity of dividing cells within the myenteric plexus of the guinea-pig ileum and to analyze the effects of inflammation induced by trinitrobenzene sulfonic acid. The incorporation of 5-bromo-2-deoxyuridine, or BrdU, into replicating DNA was used to label proliferative cells, and immunohistochemistry was used to assess the occurrence of BrdU in specific cells of the myenteric plexus. Compared to normal tissue, inflammation is associated with increased BrdU labelling in the crypts and in the substantially thickened muscle layers. In longitudinal muscle/myenteric plexus whole-mounts, there was a significant increase in BrdU labelling of the myenteric plexus after induced inflammation. No BrdU-labelled neurons were detected in tissue double labelled with neuron-specific antibodies. Fluorescein isothiocyanate/dextran-labelled macrophages were rare or absent from the ganglia, and none were double labelled with BrdU in the muscle layers. CD3-immunoreactive T cells were substantially increased in the inflamed longitudinal muscle, but still rare or absent within the enteric ganglia. Some BrdU-labelled T cells were observed in the longitudinal muscle but not in the myenteric ganglia. Lastly, in tissues double labelled with anti-BrdU and anti-S-100, many BrdU-containing cells within the myenteric ganglia were found to be S-100-immunoreactive glial cells. We conclude that inflammation does not stimulate the appearance of new myenteric neurons but does stimulate mitosis in myenteric glia.

Animals↗

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

The 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced model of experimental colitis was used to investigate the time-course of alterations in enteric neurotransmission and/or smooth muscle function that occur in chronic inflammation. Myenteric plexus morphology (immunocytochemical markers), functional integrity of cholinergic neurons (3H-choline uptake, acetylcholine release and contractile response to electrical field stimulation) and smooth muscle integrity (contractile response to exogenous acetylcholine) were determined 2, 7, 15, and 30 days after TNBS treatment. In TNBS-treated rats extensive ulcerations of the mucosa and/or the submucosa and increase in colonic weights were accompanied by significant reduction in 3H-choline uptake, acetylcholine release and contractile response to stimulation of enteric nerves. These changes were maximal 7 and 15 days after TNBS treatment. Immunocytochemical marker (PGP 9.5, SNAP 25, synaptophysin and S100 protein) expression was absent in necrotic areas of colons removed 7 days post-injury and partially reduced in colons removed 15 days after TNBS treatment. By contrast, the contractile response to exogenous acetylcholine was significantly increased after 7 days in both inflamed and uninflamed regions and returned to control values by day 30. Likewise, an almost complete recovery of neural cholinergic function and of myenteric plexus morphology was observed 30 days after TNBS treatment. These data suggest that TNBS-induced colitis is associated with progressive and selective alterations in myenteric plexus structure and function, with consequent reduction of cholinergic neurotransmission and abnormality in colonic contractility. The reversibility of myenteric plexus disruption is a clear indication of neuronal plasticity within enteric nervous system as an adaptative mechanism against inflammatory challenges.

Animals↗

The expression of a NMDA receptor gene in guinea-pig myenteric plexus.

Muscle tension studies of guinea-pig ileum longitudinal muscle-myenteric plexus preparations suggest that the N-methyl-D-aspartate (NMDA) receptor may be present in the enteric nervous system. Therefore, we investigated the expression of a gene for the NMDA receptor in guinea-pig taenia coli. The gene product was amplified using polymerase chain reaction (PCR) and its synthesis localized using in situ hybridization. A NMDA receptor PCR product from the myenteric plexus was demonstrated with nearly identical sequence characteristics to that in the brain. In situ hybridization studies identified myenteric neurons which express NMDA receptor messenger RNA. Demonstration of the genetic expression of the NMDA receptor supports a role for glutamate as a neurotransmitter in the enteric nervous system.

Amino Acid Sequence↗

c-Fos expression in the myenteric plexus, spinal cord and brainstem following injection of formalin in the rat colonic wall.

Fos expression induced by injection of dilute formalin (50 microl, 5% in physiological saline) into the colonic wall was examined in the myenteric plexus, lumbosacral spinal cord and brainstem of the rat. The aims of this study were (i) to determine whether neurons in these regions express Fos in response to the injection of formalin into the colon and (ii) to examine whether administration of an alpha 2 adrenoceptor agonist modulates Fos expression. Tissues were removed 2 h after the injection of saline or formalin. Saline injected in the colon induced Fos in enteric glia in the myenteric plexus. The number of Fos immunoreactive nuclei significantly increased in both myenteric neurons and enteric glia after the injection of formalin. Similarly, Fos immunoreactive neuronal nuclei were significantly increased in the spinal cord, area postrema and nucleus of the solitary tract after the injection of formalin. Pretreatment of rats with the alpha 2 adrenoceptor agonist xylazine (2, 4 and 8 mg/kg) 15 min before the injection of formalin, dose-dependently reduced the number of Fos immunoreactive neuronal and glial nuclei in the myenteric plexus, and neuronal nuclei in the spinal cord and brainstem. Simultaneous administration of xylazine (8 mg/kg) and the alpha 2 adrenoceptor antagonist yohimbine (1 mg/kg) reversed the effects of xylazine in the spinal cord and brainstem, but not in the myenteric plexus. These data show that injection of formalin in the colonic wall results in Fos expression in myenteric neurons and enteric glia, and neurons in the spinal cord and brainstem. This may be due to the direct chemical stimulation of the innervation of the colon and/or the subsequent acute colitis. The observed neuronal Fos expression can be modulated by an alpha 2 adrenoceptor agonist through noradrenergic pathways and/or reduction of the excitability of the enteric neural circuitry.

Journal Article↗