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PubMed1978

Properties of the enteric nervous system: limitation of access of intravascular macromolecules to the myenteric plexus and muscularis externa.

The possible presence of a blood-myenteric plexus barrier similar to the blood-nerve and blood-brain barriers was investigated. The myenteric plexus was found to be an enclosed tubular structure incompletely surrounded by a sheath of supporting cell processes. Capillaries do not enter the plexus. The capillaries which supply the myenteric layer differ in structure from capillaries of other layers of the gut and are non-fenestrated. Tracers, Evans blue labeled albumin or horseradish peroxidase, readily leak out of fenestrated capillaries, but do not readily escape from myenteric capillaries. These capillaries have impermeable junctions that prevent the passage of tracer between endothelial cells. A slow leakage of macromolecules is probably accounted for by transport through endothelial cells within plasmalemmal vesicles. A backup system of phagocytic cells removes this material and prevents the tracers leaking from the vasculature from reaching detectable concentrations in the extracellular space. Neither tracer was ever found in the myenteric plexus. Therefore, there is a blood-myenteric plexus barrier to macromolecules that resembles the blood-thymic barrier and may be functionally analogous to the blood-brain barrier.

Animals↗

PubMed1997

Morphologic and quantitative evaluation of the myenteric plexuses and neurons in the large colon of horses.

OBJECTIVE: To determine the number of myenteric plexuses and neurons in the large colon of clinically normal horses and whether the number was decreased in the large colon of horses with colon disease. DESIGN: Prospective study. SAMPLE POPULATION: Colon samples from 15 clinically normal horses and 31 horses with colon disease. PROCEDURE: Samples were obtained, fixed, and stained with H&E. The number of myenteric plexuses and neurons and longitudinal muscle thickness were determined in each segment of colon for clinically normal horses. Counts for segments were compared with each other and with counts in the same segment from horses with colon disease. RESULTS: Myenteric plexus and neuron densities and longitudinal muscle thickness in clinically normal horses were significantly greater in the pelvic flexure and left dorsal and transverse colons. Horses with chronic obstruction (> 24 hours' duration) or with previous obstruction had significantly lower neuron density in the pelvic flexure. Myenteric plexus density in horses with strangulating large colon torsion/volvulus was significantly less in the right ventral, right dorsal, and transverse colons, and neuron density in these horses was significantly less in all segments of colon, except the left ventral colon. Horses with colon strangulation that survived had significantly greater neuron density than horses with colon strangulation that died. Enteroglial cell numbers were increased in myenteric plexuses of horses with acute and chronic obstruction. CLINICAL IMPLICATIONS: Myenteric plexus and neuron densities can be estimated by evaluating linear counts of H&E-stained colon samples. Enteroglial cells may increase in number in response to myenteric plexus inflammation, which may affect bowel function.

Animals↗

PubMed1989

Spread of the single spike activity in the myenteric plexus of the guinea-pig duodenum.

The spontaneous single spikes in the myenteric plexus of the guinea-pig duodenum were recorded extracellularly. The myenteric plexus neurones in the cardiac region of the stomach also exhibited the spontaneous single spike activity. The frequency of these spikes was at low level. By the treatment with a high Mg and Ca-free Krebs solution, the single spikes were abolished. The generation of the single spikes was also inhibited by d-tubocurarine. These results suggest the presence of nicotinic neurotransmission in the myenteric plexus. The field stimulation could not evoke the single spike activity. The single spike activities of the myenteric plexus neurones were recorded by two electrodes situated in a ganglion or at two different ganglia. The simultaneous recordings by two different spots showed that there were corresponded and non-corresponded spikes. The former may be due to the conduction of excitation. The values of the correspondence ratio were calculated and the values ranged from 39.1% to 69.6% in a ganglion and ranged from 55.2% to 94.2% in different ganglia. The single spikes may spread over 10 mm in a longitudinal direction. These results suggest that the intra- and interganglionic interactions appear within the myenteric plexus and ganglia are interconnected into a functional integrative circuitry.

Action Potentials↗

PubMed1997

Morphometry and acetylcholinesterase activity of the myenteric plexus of the wild mouse Calomys callosus.

The myenteric plexus of the digestive tract of the wild mouse Calomys callosus was examined using a histochemical method that selectively stains nerve cells, and the acetylcholinesterase (AChE) histochemical technique in whole-mount preparations. Neuronal density was 1,500 +/- 116 neurons/cm2 (mean +/- SEM) in the esophagus, 8,900 +/- 1,518 in the stomach, 9,000 +/- 711 in the jejunum and 13,100 +/- 2,089 in the colon. The difference in neuronal density between the esophagus and other regions was statistically significant. The neuron profile area ranged from 45 to 1,100 microns2. The difference in nerve cell size between the jejunum and other regions was statistically significant. AChE-positive nerve fibers were distributed within the myenteric plexus which is formed by a primary meshwork of large nerve bundles and a secondary meshwork of finer nerve bundles. Most of the nerve cells displayed AChE activity in the cytoplasm of different reaction intensities. These results are important in order to understand the changes occurring in the myenteric plexus in experimental Chagas' disease.

Acetylcholinesterase↗

PubMed2000

Reaggregation of rat dissociated myenteric plexus in extracellular matrix gels.

The aim of this study was to investigate the growth behavior of freshly dissociated myenteric plexus in a three-dimensional extracellular matrix (ECM) environment with and without stimulation of glial cell line-derived neurotrophic factor (GDNF). Therefore, cell suspensions of the dissected myenteric plexus of newborn rats were cultured in freshly prepared gels of commercially available mixtures of collagen, laminin, and hepatoglycans as a first step towards mimicking the natural environment of the myenteric plexus. The cultures were kept either in chemically defined serum-free medium alone or supplemented with GDNF. Cultures on polylysinc-coated glass cover slips served as controls. Dissociated myenteric plexus grown on polylysine formed dense clusters of neurons with radially outgrowing nerve fibers, while the neurons cultured in the gel reaggregated to much smaller clusters. These contained, depending on the culture conditions, 2-10 neurons. The morphology of the network that was seen in the gels after a few days in vitro resembled very closely the in situ situation of the submucous plexus and the myenteric plexus in hypoganglionic children. Electron microscope investigations showed a high degree of organization with fiber bundles and vesicle-containing varicosities and growth cones. Independent of the method of culturing, GDNF obviously influenced the growth behavior of the dissociated plexus. The size of the ganglia was larger, and the secondary network denser when GDNF was supplemented. Moreover, the enteric neurons in the gel cultures tended to be larger in size when treated with GDNF. Three-dimensional cultures of dissociated myenteric plexus in an ECM gel might be a valuable tool towards the understanding of the formation of the enteric nervous system during development, especially considering pathological conditions such as Hirschsprung's disease or other dysganglionic diseases.

Animals↗

PubMed1977

Ultrastructural observations of the myenteric plexus of the pylorus in infantile hypertrophic pyloric stenosis.

Myenteric plexuses and smooth muscle of the pylorus obtained by biopsy at pyloro myotomy in 5 infants with hypertrophic pyloric stenosis were studied by electron microscopy. Animal controls consisted of pyloruses from 2 infant and 2 adult rabbits and 2 adult rats. The principal findings in the plexuses of the patients were moderate numbers of variably sized, swollen degenerating axons that contained dense bodies, lamellated figures, vacuoles, granular or fibrillar material, and swollen mitochondria. The significance of this alteration in the etiology and pathogenesis of this disorder is not clear. Neurons in the plexuses showed no definite abnormalities. Although these findings do not confirm previous light microscopic observation of neuronal changes in the pyloric myenteric plexuses, they do not exclude a neurogenic mechanism for this disorder. The presence of small immature neurons and large mature neurons suggests that neuronal maturation and development in infantile hypertrophic pyloric stenosis are not impaired as previously reported. No ultrastructural changes were found in interstitial cells of the myenteric plexuses. Except for hypertrophy of the circular smooth muscle layers, no specific alterations were found in muscle fibers of the pylorus.

Animals↗

PubMed2004

The myenteric plexus of the rat colon after fecal stream diversion: a morpho-quantitative study.

The myenteric plexus undergoes adaptive changes under several conditions. Mucosal and muscular alterations of the colon have been described after fecal stream diversion but studies concerning the myenteric plexus after this procedure are scarce. Therefore, 28 Wistar rats were submitted to fecal diversion and followed for different periods (30, 60, 120 and 180 days), in order to study the myenteric plexus of the excluded segments. Seven non-operated rats were employed as control. The myenteric plexus was subsequently evaluated with the NADH and NADPH histochemical techniques. The colonic area of excluded segments is significantly decreased. The density of NADH-stained neurons continuously increases during the entire postoperative period but does not match the extent of surface reduction. Neuronal area measurements suggest hypertrophy of the remaining neurons in the late postoperative period. Morphological alterations of myenteric ganglia and neurons were also evident. An important surface area reduction combined with slight density increase points toward significant neuronal loss after fecal diversion. While studies correlating neuronal loss and functional changes are still lacking, surgeons should bear in mind the modifications of the myenteric plexus when performing fecal stream diversion surgeries.

Analysis of Variance↗

PubMed2006

Effects of age on sympathetic innervation of the myenteric plexus and gastrointestinal smooth muscle of Fischer 344 rats.

Loss of myenteric neurons with age is well documented, however little is known about age-related changes of the sympathetic innervation of the myenteric plexus and gastrointestinal smooth muscle. The goal of the present study, therefore, was to evaluate the influence of age on the sympathetic innervation of the myenteric plexus throughout the gastrointestinal tract. Ad libitum fed virgin male Fischer 344 rats at 3, 15-16, 24, and 27-28 months of age were sampled. Whole mounts of the stomach, small intestine, and large intestine were processed with an antibody to tyrosine hydroxylase (TH). Additionally, some specimens labeled for TH were stained for NADPH-diaphorase to selectively label the nitrergic subpopulation of neurons in the myenteric plexus. Age-related changes in the TH-positive axons occurred as early as 15-16 months and became more pronounced by 27-28 months. Changes included markedly swollen axons and terminals and a decrease in the intensity of TH staining in some of the surviving processes. Similarly, swollen NADPH-diaphorase-positive axons were found in the myenteric ganglia and secondary plexus between ganglia in the whole mounts of rats 15-28 months of age, but swollen nitrergic axons and dystrophic TH-positive axons were never present in the same ganglion or connective. Therefore, in the aged rat, deterioration of the sympathetic innervation of the myenteric plexus could be one possible mechanism for the age-related decline in gastrointestinal motor function evidenced in the elderly.

Adrenergic Fibers↗

PubMed1989

Consecutive diaphorase-acetylcholinesterase histochemistry in the myenteric plexus of frog stomach.

An investigation was made on the frog stomach myenteric plexus with 2 different histochemical techniques. Neuronal perikarya were stained with nicotinamide-adenine-dinucleotide-diaphorase (NADHd), while the acetyl-cholinesterase (AChE) staining showed rather the axoarchitectonic arrangement of the frog myenteric plexus. In double-labelled "whole mounts", NADHd-positive cell bodies and AChE-positive nerve processes were revealed. Some of the nerve cells and neuronal processes did not exhibit AChE activity at all. Since glyoxylic acid-induced fluorescence (GIF) was not detected in the myenteric plexus, the presence of catecholamines can be excluded. As a consequence of these observations, we suggest the presence of a non-cholinergic, non-adrenergic intrinsic neuronal system in the frog stomach myenteric plexus, containing purines or peptides as transmitters.

Acetylcholinesterase↗

PubMed1989

Immunocytochemical analysis of potential neurotransmitters present in the myenteric plexus and muscular layers of the corpus of the guinea pig stomach.

Recent electrophysiological studies of neurons of the myenteric plexus of the corpus of the guinea pig stomach have revealed that slow synaptic events are extremely rare. In contrast, they are commonly encountered in similar investigations of myenteric ganglia of the guinea pig small intestine. The current immunocytochemical analysis of the myenteric plexus and innervation of the muscularis externa of the corpus of the guinea pig stomach was undertaken in order to determine whether putative neurotransmitters capable of mediating slow synaptic events are present in gastric ganglia. A major difference between the small intestine and the stomach was found in the innervation of the musculature. Whereas the longitudinal muscle layer of the small intestine contains very few nerve fibers and is innervated mainly at its interface with the myenteric plexus, the longitudinal muscle of the corpus of the stomach contained as many varicose substance P (SP)-, vasocative intestinal polypeptide (VIP)-, and neuropeptide Y (NPY)-immunoreactive axons as the circular muscle layer. These putative neurotransmitters were also present in the ganglia of the myenteric plexus, where varicose SP-, VIP-, and NPY-immunoreactive fibers encircled nonimmunoreactive neurons. Varicose 5-hydroxytryptamine (5-HT)-immunoreactive terminal axons were essentially limited to the myenteric plexus and were found both in ganglia and in interganglionic connectives, where they were particularly numerous; 5-HT-immunoreactive neurons appeared to be more abundant in the stomach than in the small intestine. Tyrosine hydroxylase (TH)- and calcitonin-gene-related-peptide (CGRP)-immunoreactive axons were also more common in the myenteric plexus than in the musculature, but of these, only the TH-immunoreactive neurites tended, like those of the other putative transmitters, to encircle neurons in myenteric ganglia. Evidence was obtained that, as in the small intestine, at least some of the SP-, VIP-, NPY-, and 5-HT-immunoreactive fibers in the stomach are derived from intrinsic gastric myenteric neurons. In contrast, unlike the small intestine, gastric myenteric ganglia appeared to lack intrinsic CGRP-immunoreactive neurons; therefore, the CGRP-immunoreactive gastric axons are probably of extrinsic origin.(ABSTRACT TRUNCATED AT 400 WORDS)

5-Hydroxytryptophan↗

PubMedDate not supplied

Morphometric assessment of Hirschsprung's disease: associated hypoganglionosis of the colonic myenteric plexus.

At present, there are no generally acceptable criteria for the evaluation of hypoganglionosis of the myenteric plexus. The aim of this morphometrical investigation was to examine the most important quantitative characteristics of hypoganglionosis. Colon specimens from 35 children with Hirschsprung's disease were assessed morphometrically. Twenty specimens with Hirschsprung's disease and proximal hypoganglionosis of the myenteric plexus were compared with 15 specimens with Hirschsprung's disease and normal innervation in the proximal myenteric plexus. All native surgical specimens were caudocranial coiled and sectioned in a cryostat. Nerve cells and ganglia were selectively stained with an enzyme-histochemical lactic dehydrogenase reaction. Morphometric measurements were done with an optic-electronic image analysis system. Hirschsprung's disease-associated hypoganglionosis of the myenteric plexus is characterized by a significant decrease in ganglion cross-sectional area (-56.2%) and in plexus area per mm colon (-53.5%). Together with these data, an increase in ganglion distance (+20%) was also determined, and the number of nerve cells per mm colon was decreased by -25.5%. The decrease in ganglion area and in the number of nerve cells per mm colon in the myenteric plexus proved to be the most characteristic parameters of a hypoganglionosis.

Acetylcholinesterase↗

PubMed1993

Chronic intestinal pseudo-obstruction in infants and children caused by diverse abnormalities of the myenteric plexus.

BACKGROUND: Chronic intestinal pseudo-obstruction is a motility disorder that leads to severe disability in infants and children. Our purpose was to study the myenteric plexus in infants and children with pseudo-obstruction METHODS: Using cross sections stained with H&E and frozen tangential sections of the myenteric plexus processed using Smith's silver technique, the myenteric plexus of the stomach, small intestine, and colon from 26 affected infants and children was analyzed quantitatively. RESULTS: Under H&E staining, there were decreased neuron scores of 34.1 +/- 7.4 and 25.3 +/- 7.1 in the jejunum and ileum (normal, 57.5 +/- 6.2 and 55.0 +/- 4; P = 0.005 for both). Using Smith's technique, the specimens had decreased argyrophilic neuron counts of 3.1 +/- 1.4, 3.6 +/- 1.1, 3.4 +/- 1.0, and 2.8 +/- 0.6 in the duodenum, jejunum, ileum, and colon, respectively (normal, 14.0 +/- 1, 14.8 +/- 1, 14.7 +/- 0.5, and 13.6 +/- 1.1; P < 0.0003). The abnormalities included (1) absence of myenteric plexus in 3 patients; (2) small numbers of neuronal structures present on H&E stains but the absence of the plexus on silver stains in 2; and (3) myenteric plexus present but decreased argyrophilic neurons and axons on silver stains in 18. The abnormalities would have been missed in 10 patients if H&E had been used alone, whereas Smith's technique identified the deficiency of argyrophilic neurons in all patients tested. CONCLUSIONS: Pseudo-obstruction in infants and children may be caused by diverse abnormalities of the myenteric plexus.

Abnormalities, Multiple↗

PubMed1976

Effect of synaptic transmission blockade on morphine action in the guinea-pig myenteric plexus.

Morphine, which inhibits release of acetylcholine from neurons in the myenteric plexus, also inhibits the spontaneous electrical activity of some myenteric neurons. To determine whether morphine acts at a site presynaptic to these neurons, we investigated this morphine effect under conditions of synaptic transmission blockade. Synaptically driven action potentials evoked by point stimulation were recorded extracellularly, and it was shown that all synaptic responses were eliminated or greatly reduced in Ca-free, high-Mg Ringer's with ethylenebis [(oxyethylenenitrilo)]-tetraacetic acid (EGTA), suggesting that synaptic transmission was blocked. Under these conditions, the ability of morphine to inhibit spontaneous electrical activity was virtually unimpaired. Assuming a single locus of narcotic action in the myenteric plexus, it is unlikely, therefore, that the primary action of opiates is to stimulate release of an inhibitory transmitter, to prevent release of an excitatory transmitter or to block the postsynaptic receptor for an excitatory transmitter. Rather, opiates may raise the membrane threshold of a class of neurons. Electric field stimulation activates myenteric neurons, resulting in a morphine-sensitive release of acetylcholine and a contraction of the longitudinal muscle. The ability of field stimulation to induce contractions and of morphine to inhibit these contractions, was virtually unchanged when the only two known excitatory inputs to the cholinergic motor neuron were eliminated by receptor blockade. These observations, taken together, suggest that opiates act directly on the cholinergic motor neuron of the myenteric plexus.

Animals↗

PubMed1996

Neuro-muscular junctions of longitudinal and circular muscle fibers of the guinea-pig esophagus and their relation to myenteric plexus.

The structure of the neuromuscular junctions (NMJs) and their relation to the myenteric plexus were studied by zinc iodide-osmic acid (ZIO) staining and by scanning electron microscopy in the guinea-pig esophagus. The esophageal muscle coat consisted of the inner circular and outer longitudinal striated muscle fibers. The myenteric plexus was located between the two muscle layers along its whole length and was characterized by a loose and irregular network. It was demonstrated that unmyelinated nerve fibers form NMJs with the muscle fibers of both layers. The NMJs in the longitudinal muscle can be classified as 'plate' type, whereas those of the circular muscle resemble the 'grape' type. The different NMJs in the two muscle layers probably correspond to different contractile properties. The whole-mount preparations with ZIO staining also demonstrated that some NMJs receive minute branches from the myenteric plexus. Therefore, it is likely that the myenteric plexus is involved in the control of striated muscles of the guinea-pig esophagus.

Animals↗

PubMed1977

Uptake of serotonin by intrinsic neurons of the myenteric plexus grown in organotypic tissue culture.

The myenteric plexus contains axons, not found elsewhere in the peripheral nervous system, which are distinguished by a specific, high affinity transport system for serotinin (5-HT). This study was undertaken to determine the location of the cell bodies of origin of these axons. Vagotomy decreased uptake of [3H]5-HT and tritiated norepinephrine ([3H]NE) by the myenteric plexus. However, while examination by histofluorescence revealed the presence of descending vagal adrenergic fibers, no evidence was found for the presence or accumulation of 5-HT above a vagal ligature. Vagus nerves thus contain adrenergic but not serotonergic axons. The gut was also denervated of all extrinsic axons by growth of intestinal explants in organotypic tissue culture for 3 weeks. Uptake of [3H]5-HT persisted while uptake of [3H]NE was lost. Light and quantitative electron microscopic radioautography revealed that, as in intact gut, the elements of the cultures responsible for uptake of [3H]5-HT were axons distinguished by varicosities containing large dense cored vesicles. In conclusion, these experiments establish that the mammalian gut contains intrinsic neurons which selectively take up 5-HT. The capacity of these neurons for 5-HT uptake may be influenced by the vagus nerves.

Animals↗

PubMed1980

The effects of dipyridamole on the guinea-pig ileal longitudinal muscle-myenteric plexus preparation.

1 The longitudinal muscle-myenteric plexus strip prepared from guinea-pig ileum has been used to study the actions of dipyridamole and its interactions with adenine derivatives. 2 Dipyridamole augmented the inhibitory effects of adenine derivatives on the twitch response induced by 0.1 Hz field stimulation of the preparation. This synergistic effect was apparent with relatively low concentrations of dipyridamole (10 to 100 nM) and after short pretreatment times (1 to 2 min) that did not inhibit the twitch response on their own. Appropriate studies suggested the dipyridamole-adenosine synergism followed a pattern of facilitative agonist competition. 3 Dipyridamole did not inhibit either uptake of [3H]-adenosine by the preparation or adenosine deaminase activity under the same conditions that it exhibited synergism with adenosine. 4 Higher concentrations of dipyridamole inhibited the twitch response, mainly by decreasing acetylcholine release but partly by a direct action on smooth muscle. The direct action of dipyridamole on muscle was not synergistic with adenosine. 5 Fluorescence microscopy showed preferential binding of dipyridamole to the myenteric plexus.

Adenosine↗

PubMed1990

Histochemical characterization of myenteric plexus in domestic fowl small intestine.

The myenteric plexus of the domestic fowl (Gallus domesticus) small intestine was studied by means of silver staining, glyoxylic acid-induced fluorescence, the modified Koelle-Friedenwald method for the detection of acetylcholinesterase, NADH-diaphorase techniques and the unlabelled antibody method involving the use of an antiserum raised against GABA conjugated by glutaraldehyde to bovine serum albumin. The majority of the perikarya were in the ganglia, with an average density of 3370 +/- 942 nerve cells/cm2. Cholinesterase-positive and a few GABA-immunoreactive nerve cell bodies were seen in the myenteric ganglia, while fluorescent ganglion cells were not observed. In addition to AChE and GABA-positive nerve fibres, a rich fluorescent network of varicose and nonvaricose nerve fibres was detected, pointing to the presence of an extrinsic aminergic system in the domestic fowl myenteric plexus. Electron microscopic observations on nerve cells, axon profiles and varicosites with various vesicle populations were in good agreement with the histochemical findings.

Acetylcholinesterase↗

PubMed1993

Myenteric plexus destruction alters morphology of rat intestine.

BACKGROUND: It has been shown previously that myenteric plexus destruction by benzalkonium chloride (BAC) increased villus height, crypt depth, and muscle thickness, suggesting that these neurons influence intestinal morphology. A nonspecific trophic effect of BAC, intraluminal stasis, and inflammation resulting from the chemical treatment could also be causes for these changes. Our goals were to (1) show that the morphological sequelae of BAC treatment are caused by myenteric plexus removal and not the factors listed above, and (2) determine whether segmental myenteric plexus removal alters morphology elsewhere in the small intestine. METHODS: Six groups of rats were studied: control, chemical denervation (3 mmol/L BAC), surgical denervation, intraluminal stasis produced by partial obstruction, chemical inflammation (5% acetic acid), and surgical inflammation (serosa removal only). Tissue for histological study was taken from the treated segment, 15-20 cm proximal to the treated segment, and 5-10 cm distal to the treated segment 28 days after treatment. RESULTS: Chemical and surgical denervation reduced the number of myenteric neurons by 94% and 98%, respectively. Denervation had a direct effect on morphology; it increased villus height, crypt depth, and muscle thickness in the treated and proximal segments, but only muscle thickness was increased in the distal segment. The other treatments had minimal morphological sequelae. CONCLUSIONS: Segmental myenteric plexus removal alters the mucosa in the treated and proximal segments but influences muscle thickness throughout the intestine.

Acetates↗