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Results for “MYENTERIC PLEXUS”

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PubMed1997

Injury to myenteric plexus of intestinal segments after vascular pedicle interruption: an experimental study in rats and rabbits.

A study was conducted in rats and rabbits to histologically evaluate the effect of acute and late interruption of blood supply on the myenteric plexus located between the circular and longitudinal layers of the muscularis externa (Auerbach's plexus). An intestinal segment measuring 2 cm in rats and approximately 8cm in rabbits was sectioned and isolated on a mesenteric vascular pedicle. Animals in Group underwent clamping of the vascular pedicle for 1, 2, 3, 4, 5 or 6 h. There were 5 animals in each of these subgroups. Group: Intestinal segments with intact vascular pedicles were transferred from the abdominal cavity into the subcutaneous space. Groups with 5 animals in each underwent pedicle ligation immediately and at 1, 2, 3 or 4 weeks after the first operation. Three days later, histological studies were carried out. Injury to the myenteric plexus and the longitudinal muscle was observed in the viable intestinal segments when the mesenteric vascular pedicle was clamped for 4 to 5 h. Similar findings were observed when the pedicle was ligated within 1 to 2 weeks after grafting. The present results show that ischemia can cause injury to the myenteric plexus in the surviving intestine.

Animals↗

PubMed1986

Functional heterogeneity in the myenteric plexus: demonstration using cytochrome oxidase as a verified cytochemical probe of the activity of individual enteric neurons.

The cytochemical technique for the demonstration of cytochrome oxidase has been used to locate the sites of chronically active neurons in the CNS. The current experiments were undertaken to validate the use of this technique for the identification of active neurons and ganglia in the myenteric plexus of the gut. The excitotoxin veratridine was used to cause repetitive firing of action potentials and to depolarize myenteric neurons over an 8-hour test period in vitro. The effects of veratridine were monitored electrophysiologically and correlated with the ability of the drug to affect the density of the cytochrome oxidase reaction product, as well as the proportion of reactive myenteric neurons. The action of veratridine on cytochrome oxidase activity was evaluated by means of video microdensitometry and computer-assisted morphometry. Effects of veratridine were considered to be specific if they were blocked by the inclusion of tetrodotoxin (TTX), which antagonizes the action of veratridine on voltage-dependent Na+ channels. Veratridine (1.0 microM) depolarized the membranes of myenteric type II neurons and greatly increased both the average density of the cytochrome oxidase reaction product in individual neuronal cell bodies and the proportion that were reactive. The concentration-effect relationship for veratridine was biphasic. As the concentration of veratridine was raised, neurons became sufficiently depolarized such that they ceased to fire action potentials. This absence of spiking was associated with a decline in the stimulation of cytochrome oxidase activity by veratridine. At still higher concentrations of veratridine the degree of neuronal depolarization continued to increase. This further depolarization was associated with a secondary increase in cytochrome oxidase activity. All effects of veratridine were blocked by TTX. It is concluded that the cytochemical demonstration of cytochrome oxidase reflects the recent metabolic history and thus the physiological activity of myenteric neurons. In control preparations, fixed without exposure to veratridine, considerable variation in cytochrome oxidase was observed between ganglia and between individual neurons within ganglia. This suggests that there are significant differences in the activity of individual ganglia and neurons of the myenteric plexus. These observations support the hypothesis that there is a functional heterogeneity that corresponds to an anatomical heterogeneity (previously demonstrated) of the myenteric plexus.

Animals↗

PubMed1976

(3H)morphine localization in myenteric plexus.

Preferential binding of 3H-labeled morphine to satellite cells, but not to large neurons in the myenteric plexus, is demonstrated autoradiographically. Microfluorometric spectra of the plexus show nerve fibers that contain norepinephrine and impinge on satellite cells. Cells containing serotonin occur occasionally on longitudinal muscle outside the myenteric plexus.

Animals↗

PubMed1990

[Vascularization of the myenteric plexus in the small intestine of pigeons].

By means of light and electron microscopy vascularization of the myenteric plexus has been studied in the pigeon small intestine. Ganglia of the plexus, their cell composition, ultrastructure of neurons have been described. Links of the microcirculatory bed of the intramural ganglia are characterized, interrelations of capillaries with neurons are described, quantitative estimation of microhemovessels, surrounding the microcirculatory bed of the myenteric plexus in the intestinal wall in birds and mammalia.

Animals↗

PubMed2006

Selective up-regulation of NMDA-NR1 receptor expression in myenteric plexus after TNBS induced colitis in rats.

BACKGROUND: N-methyl-D-aspartic acid (NMDA) spinal cord receptors play an important role in the development of hyperalgesia following inflammation. It is unclear, however, if changes in NMDA subunit receptor gene expression in the colonic myenteric plexus are associated with colonic inflammation. We investigated regulation of NMDA-NR1 receptor gene expression in TNBS induced colitis in rats. Male Sprague-Dawley rats (150 g-250 g) were treated with 20 mg trinitrobenzene sulfonic acid (TNBS) diluted in 50% ethanol. The agents were delivered with a 24 gauge catheter inserted into the lumen of the colon. The animals were sacrificed at 2, 7, 14, 21, and 28 days after induction of the colitis, their descending colon was retrieved for reverse transcription-polymerase chain reaction; a subset of animals' distal colon was used for two-dimensional (2-D) western analysis and immunocytochemistry. RESULTS: NR1-exon 5 (N1) and NR1-exon 21 (C1) appeared 14, 21 and 28 days after TNBS treatment. NR1 pan mRNA was up-regulated at 14, 21, and 28 days. The NR1-exon 22 (C2) mRNA did not show significant changes. Using 2-D western analysis, untreated control rats were found to express only NR1001 whereas TNBS treated rats expressed NR1001, NR1011, and NR1111. Immunocytochemistry demonstrated NR1-N1 and NR1-C1 to be present in the myenteric plexus of TNBS treated rats. CONCLUSION: These results suggest a role for colonic myenteric plexus NMDA receptors in the development of neuronal plasticity and visceral hypersensitivity in the colon. Up-regulation of NMDA receptor subunits may reflect part of the basis for chronic visceral hypersensitivity in conditions such as post-infectious irritable bowel syndrome.

Animals↗

PubMed1996

Localization of endothelin ETB receptors on the myenteric plexus of guinea-pig ileum and the receptor-mediated release of acetylcholine.

1. The type of endothelin (ET) receptor located on the myenteric neurones of guinea-pig ileum was determined by receptor autoradiography and function of the receptor was examined by release experiments of acetylcholine (ACh) from the longitudinal muscle myenteric plexus (LM-MP) preparations. 2. Specific [125I]-ET-1 binding sites were distributed in muscle layers, myenteric and submucous plexuses, and mucosa layers. High-grain densities were detected in both myenteric and submucous plexuses. 3. Binding in the myenteric plexus was abolished by incubation with either IRL 1620 (endothelin ETB receptor agonist) or BQ 788 (endothelin ETB receptor antagonist), but not with BQ 123 (endothelin ETA receptor antagonist). The [125I]-IRL 1620 binding sites were evident in the myenteric plexus. Thus, the endothelin receptor located on the myenteric neurones is of the ETB type. 4. ET-1 (10(-10)-3 x 10(-8) M) and ET-3 (10(-10)-3 x 10(-8) M) evoked 3H outflow from LM-MP preparations of ileum preloaded with [3H]-choline, in a concentration-dependent manner. There was no significant difference between maximum amounts of ET-1-evoked and ET-3-evoked 3H outflow. 5. ET-1 and ET-3 evoked outflow of 3H was BQ 788-sensitive, but BQ 123-insensitive. Both evoked outflows of 3H were Ca(2+)-dependent and tetrodotoxin-sensitive. 6. These results indicate that the endothelin ETB receptor is located on the enteric cholinergic neurones and that stimulation evokes the release of ACh.

Acetylcholine↗

PubMed1980

The effects of calcium concentration on the inhibition of cholinergic neurotransmission in the myenteric plexus of guinea-pig ileum by adenine nucleotides.

1 Adenosine and the adenine nucleotides AMP, ADP, ATP, cyclic AMP, NAD, NADP and NADH produced a dose-related inhibition of the contractile response of guinea-pig ileum longitudinal muscle-myenteric plexus strips to low frequencies (less than 1 Hz) of electrical field stimulation. 2 These compounds inhibited hexamethonium-sensitive contractions induced by nicotine but did not alter the responses to exogenous acetylcholine, and the acetylcholine output from the myenteric plexus was inhibited by the adenyl compounds. These findings indicate that adenine derivatives act at a presynaptic site on postganglionic cholinergic neurones. 3 The degree of inhibition produced by adenine compounds was inversely related to the calcium concentration of the bath fluid over a range of calcium concentrations (1 to 5 mM) that had no effect on the responses of the muscle to exogenous acetylcholine. 4 The inhibition produced by adenine derivatives was antagonized by theophylline and augmented by dipyridamole. Both of these interactions were sensitive to, and synergistic with, alterations of the concentration of calcium in the bath fluid. 5 The results suggest that adenine compounds inhibit acetylcholine release from the myenteric plexus by diminishing the availability of intracellular calcium ions required for neurotransmitter release.

Adenine Nucleotides↗

PubMed1983

Release of gamma-aminobutyric acid from guinea pig myenteric plexus synaptosomes.

A crude synaptosomal preparation obtained from myenteric plexus of guinea pig small intestine was used to study the release of [3H]GABA. GABA release was elevated in response to depolarizing agents when tested in normal Krebs but was depressed in a calcium-free medium. GABA was also noted to stimulate a release of [3H]ACh from the same preparation. These data support the possible role of GABA as an enteric neurotransmitter.

Acetylcholine↗

PubMed1980

Variations in neuron size in the avian intestinal myenteric plexus.

The size of the neurons in the myenteric plexus of the duodenum, jejunum, ileum, rectum and cecum of chick and adult domestic fowl (Gallus gallus) was estimated using a histochemical technique for NADH diaphorase activity. The mean size of the neurons varied between different regions of hte gut and increased with age. In both chicks and adults the largest neurons were observed in the distal part of the cecum. The differences between the estimated neuron sizes in the chicks and adults are discussed and the data compared with similar estimates of neuron size in mammals.

Animals↗

PubMed1989

Glial cells in the guinea pig myenteric plexus are dye coupled.

Glial cells in the myenteric plexus of the guinea pig small intestine were stained intracellularly with Lucifer yellow and horseradish peroxidase. The cells were identified by both their electrophysiological characteristics and by their morphology. Injection of Lucifer yellow, which is known to cross gap junctions, resulted in the staining of many (up to about 100) glial cells. The staining pattern was comparable to the immunostaining of glia with an antiserum for S-100 protein. In contrast to Lucifer yellow, horseradish peroxidase (which does not cross these junctions), was confined to the injected cell. It is concluded that enteric glia are coupled, presumably by gap junctions. This finding indicates that in addition to structural and biochemical similarities, enteric glia may share certain physiological characteristics with central nervous system astrocytes.

Action Potentials↗

PubMed1982

[Effect of temporal disturbance of the blood flow on the structure of neurons of the myenteric plexus].

The dynamics of changes occurring in the myenteric plexus neurons have been followed in 230 mature cats from the first step up to the 120th day after 1-, 2.5-, 4-, 6-, 8-hour's disturbance in the arterial and venous blood circulation using Bielschowsky--Gros, Nissl and Nachlas techniques. Depending on duration of the ischemia and the postischemic period, various amount of unchanged neurons and neurons having certain reactive and destructive changes have been revealed. During all the periods of the investigation, certain differences are noted in the reaction both of all the ganglia and single neurons within one ganglion. Some neurons demonstrate certain resistivity to the prolonged disturbance in the blood flow. By means of the polarography method, the dynamics of changes in the oxygen strain in tissues of the experimental area of the small intestine after the arterial and mixed ischemia have been studied. An elevated oxygen strain has been revealed in the tissues under conditions of venous congestion and an attempt has been made to explain this effect.

Animals↗

PubMed1992

Evidence for two cholecystokinin receptors mediating the contraction of the guinea pig isolated ileum longitudinal muscle myenteric plexus.

In guinea pig isolated ileum longitudinal muscle myenteric plexus, cholecystokinin octapeptide (CCK-8S) produced a rapid (phasic) contraction followed by a slower tonic phase. The tetrapeptide derivative CCK-4 and pentagastrin elicited only the phasic response up to 10(-6) M, whereas the tonic phase was also apparent at higher concentrations. The rank order of potency for the effect of agonists on the tonic and phasic responses were CCK-8S much greater than gastrin greater than CCK-8US congruent to pentagastrin greater than CCK-4 and CCK-8S greater than gastrin congruent to pentagastrin greater than CCK-4 greater than CCK-8US, respectively. Phasic responses of CCK-8S and CCK-4 were sensitive to atropine, whereas the tonic response could be completely abolished with the neurokinin-1 antagonist GR82334. The CCK-A receptor antagonist L-364,718 up to 10(-7) M had little effect on the phasic contracture of CCK-4. The CCK-B/gastrin receptor antagonist L-365,260 had no effect on the CCK-8S phasic response up to 10(-7) M, but antagonized the phasic response induced by low concentrations of CCK-4 in a competitive manner with an estimated pKB of 8.51. This value is close to that of 8.53 found in a guinea pig cortical binding assay. Both the second phase of the CCK-4 phasic concentration response curve (CRC) and the tonic contraction were insensitive to L-365,260.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2003

Neuronal differentiation and myenteric plexus organization are delayed in gastroschisis: an immunohistochemical study in a rat model.

Gastroschisis is a malformation due to prenatal rupture of the abdominal wall and evisceration of the midgut. Intestinal loops are shortened, matted, and covered by a peel caused by the harmful effect of the amniotic fluid. Babies born with gastroschisis suffer from gastrointestinal dysmotility. The present aim was to verify whether the myenteric plexus is damaged in a rat model of gastroschisis. In the gastroschisis rat model fetus, the myenteric plexus was not yet organized in the well-defined ganglia and, in the most damaged loops, the neuronal cells were scattered or absent. Immunohistochemistry for alpha-internexin and peripherin (markers of neuronal maturity) gave results similar to those of earlier embryonic ages. These findings indicate a delay in neuronal differentiation and myenteric plexus organization that might play a role in the postnatal dysmotility observed in gastroschisis.

Animals↗

PubMed1986

Bremazocine is an agonist at kappa-opioid receptors and an antagonist at mu-opioid receptors in the guinea-pig myenteric plexus.

The agonist and antagonist activity of bremazocine at opioid receptors in the guinea-pig myenteric plexus preparation was determined in untreated tissues and in tissues in which either mu-9 or kappa-opioid receptors were blocked preferentially. After pretreatment of the tissue with beta-funaltrexamine for 90 min followed by washing out, the IC50 value of the selective mu-ligand [D-Ala2,MePhe4,Gly-ol5]enkephalin was increased 67 fold whereas the IC50 values of the selective kappa-ligand U-69,593 and of the non-selective kappa-ligand bremazocine were not significantly changed. In this experimental design bremazocine acted only on kappa-receptors. After pretreatment of the tissue with beta-chlornaltrexamine and 10 microM of the mu-ligand for 30 min followed by washout, the IC50 value of the mu-ligand was increased 2 fold whereas the IC50 value of the selective kappa-ligand was increased 32 fold and that of bremazocine 62 fold. Under these experimental conditions, it was shown that bremazocine is an antagonist against [D-Ala2,MePhe4,Gly-ol5]enkephalin at the mu-receptor (Ke = 1.6 nM). The residual agonist activity of bremazocine is at the kappa-receptor. In naive myenteric plexus preparations the mu-antagonist activity of bremazocine cannot be demonstrated because its potency at the kappa-receptor is very high. This dual action may be of importance for the responses of bremazocine in other peripheral and central tissues.

Animals↗

PubMed1998

The projections of 5-hydroxytryptamine-accumulating neurones in the myenteric plexus of the small intestine of the guinea-pig.

Retrograde tracing, combined with immunohistochemistry, was used to study the projections of 5-hydroxytryptamine (5-HT)-accumulating neurones within the ileum of the guinea-pig, with confocal microscopy being used to characterise further their morphology. Two classes of neurones in the myenteric plexus, capable of taking up 5-HT or analogues, were distinguished. One class had Dogiel type I morphology with lamellar dendrites, was located on the edge or in the middle of ganglia and lacked immunoreactivity for somatostatin (SOM). The other class had smooth ovoid cell bodies with multiple filamentous dendrites and a single axon and represented a subset of the SOM-immunoreactive interneurones in the myenteric plexus. Varicosities immunoreactive for 5-HT alone, 5-HT/SOM or SOM alone were present in the myenteric ganglia. Both classes of 5-HT-accumulating neurones had long aboral projections within the myenteric plexus (up to 100 mm long) and to the submucous plexus and probably function as descending interneurones.

Animals↗

PubMed2004

Basic fibroblast growth factor, neurofilament, and glial fibrillary acidic protein immunoreactivities in the myenteric plexus of the rat esophagus and colon.

The enteric nervous system consists of a number of interconnected networks of neuronal cell bodies and fibers as well as satellite cells, the enteric glia. Basic fibroblast growth factor (bFGF) is a mitogen for a variety of mesodermal and neuroectodermal-derived cells and its presence has been described in many tissues. The present work employs immunohistochemistry to analyze neurons and glial cells in the esophageal and colic enteric plexus of the Wistar rat for neurofilament (NF) and glial fibrillary acidic proteins (GFAP) immunoreactivity as well as bFGF immunoreactivity in these cells. Rats were processed for immunohistochemistry; the distal esophagus and colon were opened and their myenteric plexuses were processed as whole-mount preparations. The membranes were immunostained for visualization of NF, GFAP, and bFGF. NF immunoreactivity was seen in neuronal cell bodies of esophageal and colic enteric ganglia. GFAP-immunoreactive enteric glial cells and processes were present in the esophageal and colic enteric plexuses surrounding neuronal cell bodies and axons. A dense net of GFAP-immunoreactive processes was seen in the ganglia and connecting strands of the myenteric plexus. bFGF immunoreactivity was observed in the cytoplasm of the majority of the neurons in the enteric ganglia of esophagus and colon. The two-color immunoperoxidase and immunofluorescence methods revealed bFGF immunoreactivity also in the nucleus of GFAP-positive enteric glial cells. The results suggest that immunohistochemical localization of NF and GFAP may be an important tool in the study of the plasticity in the enteric nervous system. The presence of bFGF in neurons and glia of the myenteric plexus of the esophagus and the colon indicates that this neurotrophic factor may exert autocrine and paracrine actions in the enteric nervous system.

Animals↗

PubMed1985

Severe idiopathic constipation is associated with a distinctive abnormality of the colonic myenteric plexus.

We analyzed the clinical, radiographic, esophageal manometric, and pathologic features of 26 women with severe, idiopathic constipation. Twenty-four patients were between 19 and 39 yr of age. Stool frequency was once every 5-28 days. On barium enema examination, 9 of 24 patients had colons of increased length and 4 of these 9 patients had colons of increased width (greater than 10 cm). Radionuclide solid-meal gastric-emptying studies were normal in 23 patients tested. Esophageal manometry demonstrated high-amplitude waves in 10 of 22 patients and long-duration waves in 3 of these 10 patients. Rectal biopsy specimens showed normal submucosal neurons in all patients and melanosis coli in 6. Twelve patients underwent subtotal colectomies for constipation. Conventional light microscopy using hematoxylin and eosin serial sections showed (a) melanosis coli in 4 patients; (b) normal smooth muscle in 11; (c) thinning of the circular muscle in 1; and (d) no apparent abnormalities of the myenteric plexus in any. In contrast, silver stains of the myenteric plexus showed (a) quantitatively reduced numbers of argyrophilic neurons in 10 patients; (b) morphologically abnormal argyrophilic neurons in 11; (c) decreased numbers of axons in 11; and (d) increased numbers of variably sized nuclei within ganglia in all 12. A coded analysis of the silver stains of colons from 8 patients with constipation and 19 control cases demonstrated that the pathologic abnormalities of severe idiopathic constipation could be differentiated from controls. Thus, severe idiopathic constipation is associated with a pathologically identifiable abnormality of the myenteric plexus. This abnormality appears different from anything previously described in intestinal pseudoobstruction.

Adult↗

PubMed1984

Slow intracellular potentials in AH-neurons of the myenteric plexus evoked by repetitive activation of synaptic inputs.

In after-hyperpolarization-neurons of guinea-pig myenteric plexus, several types of slow responses to repetitive activation of synaptic inputs were recorded. There were at least two types of slow excitatory depolarizing potential, both associated with an increased input resistance, but in one there was an abolition or marked attenuation of the amplitude of the slow after-hyperpolarization of the neuron, whereas in the other type the slow after-hyperpolarization was not significantly affected. Slow depolarizing and hyperpolarizing synaptic potentials associated with a decrease input resistance were also recorded in some neurons following transmural stimulation. The neural processes responsible for these slow potentials in after-hyperpolarization-neurons showed no preferential projection within the myenteric plexus.

Animals↗