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PubMedDate not supplied

Motor response secondary to the release of endogenous serotonin by tryptamine in guinea-pig ileal longitudinal muscle with adherent myenteric plexus.

The mechanism of the contractile action of tryptamine on the longitudinal smooth muscle with adherent myenteric plexus in the guinea-pig ileum was reexamined in view of new evidence that tryptamine releases the enteric neural serotonin (5-HT) and noradrenaline. The desensitization to 5-HT abolished the contractile response to tryptamine (5 and 10 microM). The contractile response to tryptamine (1-5 microM) was progressively decreased by repeated application. The progressive decrease by tryptamine was more pronounced than that by exogenous 5-HT. Tetrodotoxin and atropine significantly decreased the contraction upon the 2nd trial of tryptamine (5 microM) by about 40% and 45% of the control, respectively. However, guanethidine or cocaine did not change the contraction by tryptamine (5 microM). A 5-HT uptake inhibitor, zimelidine, which had been demonstrated to block the release of preloaded [3H]5-HT by tryptamine (Takaki et al., 1985), intensively reduced the contractile response to tryptamine to the same extent as atropine. These results are consistent with the previous finding that tryptamine releases the physiologically active 5-HT from myenteric neurons (Takaki et al., 1985). The 5-HT released by tryptamine, at least in part, acts on myenteric cholinergic neurons, resulting in the muscular contraction.

Animals↗

PubMed1984

[Ultrastructure of neurons of the myenteric plexus in the normal cat and after temporary circulatory interruption].

Ultrastructural organization of neurons in the myenteric plexus of the cat small intestine has been studied in norm and after the blood stream had been switched off for 4 hours and 1, 3, 7, 30 days after recirculation. Ultrastructural uniformity of perikaryons is noted, therefore it is impossible to reveal electron microscopically neurons with different functional qualities. Four morphological types of preterminal dilatations of axons are revealed. Some neurons demonstrate certain resistance to the four hours' ischemia of the intestine, predominance of reactive processes in most of the cells. Dynamics of destructive and reparative processes are followed in neurons and their processes after recirculation.

Animals↗

PubMed2003

Characterization of specific opioid binding sites in neural membranes from the myenteric plexus of porcine small intestine.

Delta- and kappa-opioid receptors (OPRs), but not micro-OPRs, are expressed in the myenteric plexus of the porcine distal small intestine. In a subpopulation of myenteric neurons, delta- and kappa-OPRs seem to be colocalized and may functionally interact. In this study, radioligand binding was used to characterize myenteric OPR populations in detail. The nonselective OPR antagonist [3H]diprenorphine bound to a single, high-affinity site in myenteric neural membrane homogenates. Naloxone displaced 65 and 59% of [3H]diprenorphine binding from this site in Na(+)-free Tris and Krebs-HEPES buffers, respectively. Naltrexone-derived delta- and kappa-OPR antagonists, including naltriben, 7-benzylidenenaltrexone, nor-binaltorphimine, and 5'-guanidinonaltrindole, displaced [3H]diprenorphine from two distinct binding sites to levels similar to that of naloxone. The selective delta-OPR ligands Tyr-1,2,3,4-tetrahydroisoquinoline-Phe-Phe-OH (TIPP), [D-Pen2,D-Pen5]enkephalin (DPDPE), [D-Ala2, Glu4]deltorphin II, and (+)-4-[(alphaR)-alpha((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl-3-methoxybenzyl)-N,N-diethylbenzamide (SNC-80) and the kappa-OPR agonist (D-(5alpha,7alpha,8beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxoaspiro-(4,5)dec-8-yl) benzeneacetamide (U-69,593) displaced [3H]diprenorphine from three independent binding sites; these included high-affinity delta- and kappa-OPR sites, and a residual binding site. Residual [3H]diprenorphine binding was displaced by the selective kappa-OPR antagonist nor-binaltorphimine after saturation of delta and kappa sites, respectively, with DPDPE and U-69,593. The residual binding site displayed low affinity for delta- and kappa-OPR agonists and TIPP, as well as moderate affinity for naltrexone-derived ligands, properties reminiscent of delta-/kappa-OPR heterodimers.

Animals↗

PubMed2005

Structural development of PGP9.5-immunopositive myenteric plexus in embryonic rats.

To investigate relationships between changes in the 3-dimensional structure of the myenteric plexus and the time at which functional movement of intestine begins in mammalian embryos, whole mounts of embryonic rat intestine were examined under confocal laser scanning microscopy on spacer-equipped glass slides after immunostaining with antiprotein gene product 9.5 antibody. At embryonic day 12.5, very few nerve cells were scattered throughout the small intestine, but no immunostained structures were apparent on the anal side of the large intestine. At embryonic day 13.5, immunostained fibers appeared on the oral side of the large intestine. Nerve cells and associated fiber bundles formed neuronal networks with large meshes in both intestines. Marked increases in number of nerve fibers and decreases in mesh size were seen in the small intestine between embryonic days 13.5 and 15.5. Similar changes were found in the large intestine between embryonic days 13.5 and 16.5. After embryonic day 16.5, nerve cells were arranged parallel to circular muscle fibers, and networks formed by cell fibers elongated until the neonatal period in both intestines. Meconium passed through the large intestine from embryonic day 17.5. Thin fiber bundles extended from the ganglion to the inner side of the myenteric layer, parallel (and occasionally extending) to the circular muscle fibers. Formation of nerve fiber networks and arrangement of nerve cells parallel to circular muscle fibers probably relate to movement coordination for inner circular muscle fibers in the intestinal wall, and development of this neural network may be important for acquiring intestinal movements before birth.

Animals↗

PubMed1981

Autoradiographic localization of [3H]gamma-amino-butyric acid in the myenteric plexus of the guinea-pig small intestine.

Localization of [3H]GABA in the guinea-pig myenteric plexus has been studied using light microscopic autoradiography. In the presence of beta-alanine, 10(-3) M, an inhibitor of glial cell high affinity GABA transport, [3H]GABA was transported by a high affinity uptake system into neuronal elements of the plexus. Scattered neurones accumulating [3H]GABA showed localization of silver grains over the soma and axonal processes. In addition a large population of uptake sites for [3H]GABA was found within the secondary and tertiary meshworks of the plexus so that dense accumulations of silver grains were observed localized over distinct 'tracts' within all three meshworks of the plexus. These results are considered to provide strong evidence for GABAergic neurons in the enteric nervous system.

Animals↗

PubMed1982

Histochemical study of the myenteric plexus following gastric resection on dogs.

Enzyme histochemical methods were used to follow up to changes within the myenteric plexus from 1 week to 7 months following subtotal Billroth I gastric resection in dogs. Different regions of the resected stomach were examined. The changes affected the neurons and the neuropil of the myenteric ganglia, the connecting strands and the nerve bundles and fibers within the muscle layers. The changes in size, from and enzyme activity of some myenteric neurons correspond to those observed during axon regeneration. The 2nd week showed a significant reduction of the nerve cell number in most of the examined regions of the resected stomach. Along with, the amitotic forms of cell division and immature nerve cells became more numerous. The enzyme activity of the latter increased with the time elapsed after resection, 7 months afterwards, the size of the myenteric ganglia in the resected stomach did not differ from those in the control dogs. There were some hypertrophic nerve cells with higher enzyme activity. Some changes presume the formation of new intramural ganglia. The changes in the myenteric neurons were accompanied by reactive changes in the non-neuronal elements. Hyperinnervation was observed in the gastric muscles.

Animals↗

PubMed1985

Cyclic 3',5'-adenosine monophosphate mimics slow synaptic excitation in myenteric plexus neurons.

Iontophoretic injection of cyclic adenosine monophosphate (cAMP) into the somas of ganglion cells in the myenteric plexus of guinea pig small intestine mimicked the slow excitatory postsynaptic potentials that occur in these neurons. These effects were: (1) membrane depolarization. (2) decreased membrane conductance, (3) augmented excitability with increased probability of spontaneous spike discharge and increased spike discharge during depolarizing current pulses, (4) anodal break excitation, (5) suppression of hyperpolarizing afterpotentials. The same effects were produced by application of membrane-permeable analogs of cAMP in the bathing medium. The phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, potentiated the effects of the analogs. The results suggest that the biochemical basis for long-lasting excitatory neuromodulation in myenteric neurons is activation of adenylate cyclase and elevation of intraneuronal cAMP.

1-Methyl-3-isobutylxanthine↗

PubMed1997

Effect of maternal protein deprivation on morphological and quantitative aspects of the myenteric plexus neurons of proximal colon in rats.

We have studied the morphological and quantitative aspects of the myenteric plexus neurons of the proximal colon in rats (Rattus norvegicus of Wistar strain) submitted to a protein deprivation during prenatal and lactation periods. Twenty pregnant dams were divided in four groups labeled according to the kind of nourishment they were given: Group NN, normal diet; Group DN, low protein diet during prenatal period, and normal diet during lactation period; Group ND, normal diet during prenatal period, and low protein diet during lactation period; Group DD, low protein diet during prenatal and lactation periods. Histological analyses were developed with proximal colon segments using the haematoxylin and eosin staining method. Membrane preparations were stained by Giemsa's method. The statistical analysis has demonstrated no significant difference among the means of neurons found in the four studied groups. It was noticed that the animals under protein deprivation during prenatal and lactation periods presented greater quantity of large and strongly basophilic myenteric neurons. This suggests that neurons have accumulated protein in the cytoplasm.

Animals↗

PubMed1992

Inhibitory effects of certain enantiomeric cannabinoids in the mouse vas deferens and the myenteric plexus preparation of guinea-pig small intestine.

1. The psychoactive cannabinoids (-)-delta 9-tetrahydrocannabinol ((-)-delta 9-THC) and the 1,1-dimethyl-heptyl homologue of (-)-11-hydroxy-delta 8-tetrahydrocannabinol ((-)-DMH) both inhibited electrically-evoked contractions of the mouse isolated vas deferens and the myenteric plexus-longitudinal muscle preparation of the guinea-pig small intestine. 2. Concentrations of (-)-delta 9-THC and (-)-DMH that decreased twitch heights by 50% were 6.3 and 0.15 nM respectively in the mouse vas deferens and 60 nM and 1.4 nM respectively in the myenteric plexus preparation. (-)-DMH was about 40 times more potent than (-)-delta 9-THC in both preparations, supporting the notion that their mode of action in each tissue is the same. 3. The psychically inactive cannabinoid, (+)-DMH, had no inhibitory effect in the mouse vas deferens at a concentration of 30 nM, showing it to be at least 1000 times less potent than (-)-DMH. In the myenteric plexus preparation, (+)-DMH was about 500 times less potent than its (-)-enantiomer. 4. The inhibitory effects of sub-maximal concentrations of (-)-delta 9-THC were not attenuated by 300 nM naloxone. 5. The findings that (-)-delta 9-THC and (-)-DMH are highly potent as inhibitors of the twitch response of the mouse vas deferens and guinea-pig myenteric plexus preparation and that DMH shows considerable stereoselectivity suggest that the inhibitory effects of cannabinoids in these preparations are mediated by cannabinoid receptors.

Animals↗

PubMed1988

Shapes of nerve cells in the myenteric plexus of the guinea-pig small intestine revealed by the intracellular injection of dye.

The shapes of myenteric neurons in the guinea-pig small intestine were determined after injecting living neurons with the dye Lucifer yellow via a microelectrode. The cells were fixed and the distribution of Lucifer yellow rendered permanent by an immunohistochemical method. Each of 204 nerve cells was examined in whole-mount preparations of the myenteric plexus and drawn using a camera lucida at 1250 x magnification. Four cell shapes were distinguished: (1) neurons with several long processes corresponding to type II of Dogiel; (2) neurons with a single long process and lamellar dendrites corresponding to type I of Dogiel; (3) neurons with numerous filamentous dendrites; and (4) small neurons with few processes. About 15% of the neurons could not be placed into these classes or into any single class. The type II neurons (39% of the sample) had generally smooth somata and up to 7 (average 3.3) long processes, most of which ran circumferentially. Dogiel type I neurons (34% of sampled neurons) had characteristic lamellar dendrites, i.e., broad dendrites that were flattened in the plane of the plexus. The filamentous neurons (7% of the sample), had, on average, 14 fine processes up to about 50 microns in length. Small neurons with smooth outlines and a few fine processes made up 5% of the neurons encountered. We conclude that myenteric neurons that have been injected with dye can be separated into morphologically distinct classes and that the different morphological classes probably correspond to different functional groupings of neurons.

Animals↗

PubMed1978

Muscarinic modulation of acetylcholine release evoked by dimethylphenylpiperazinium and high potassium from guinea-pig myenteric plexus.

The effects of oxotremorine and atropine on the ACh release evoked from the guinea-pig myenteric plexus by dimethylphenylpiperazinium (DMPP) or by high potassium were investigated. DMPP caused an output of ACh by stimulating nicotine receptors that are probably situated on the soma-dendritic part of the cholinergic neuron. The DMPP-induced release of ACh was dose-dependently inhibited by oxotremorine and increased by atropine. The ACh output evoked by either 45 or 108 mM potassium was enhanced by atropine. Oxotremorine did not affect the ACh release by high potassium but prevented the facilitatory effect of atropine. It is concluded that the inhibitory muscarinic mechanism modulates similarly the ACh release evoked by DMPP or high potassium and the release caused by electrical stimulation. From the experiments with high potassium it is concluded that the inhibitory muscarine receptors are localized at the site of ACh release.

Acetylcholine↗

PubMed1992

Increased levels of substance P in the myenteric plexus of Trichinella-infected rats.

Changes in immunoreactive substance P concentrations were investigated in longitudinal muscle-myenteric plexus preparations from the inflamed jejunum of Trichinella spiralis-infected rats. The substance P concentration increased within 2 days of infection and increased fivefold by day 6; in contrast, there was no significant increase in substance P in the noninflamed ileum. In vitro exposure of preparations from infected rats to scorpion venom reduced substance P levels by 88%. In addition, no increase in substance P was observed in rats that had been treated with capsaicin as neonates or as adults before infection. Treatment of infected rats with betamethasone attenuated the inflammatory response to the infection and prevented the increase in substance P. Furthermore, no significant increase in substance P concentration was seen in congenitally athymic rats infected with T. spiralis. This study is consistent with the hypothesis that inflammation increases substance P in myenteric nerves by a process that involves T lymphocytes.

Animals↗

PubMed1988

A quantitative study on the myenteric plexus of the distal end of the human esophagus.

The densities of ganglia and nerve cells in the myenteric plexus of the last distal 11 cm of the human esophagus were determined in 6 esophagi from autopsy material. The densities of ganglia and nerve cells in cresyl violet-stained stretch preparations of 11 esophageal segments, each 1 cm in length, were compared. The highest values were recorded in segments 4, 5, and 6 cm above cardiac incisura. The lowest densities of ganglia and nerve cells were found in segments 1, 2, and 3 cm above the cardiac incisura. The segments contained 659 to 3,316 perikarya/cm2 and 31 to 110 ganglia/cm2; ganglia contained 3 to 310 cells.

Esophagus↗

PubMed1989

Three-dimensional observation of the fibroblast-like cells associated with the rat myenteric plexus, with special reference to the interstitial cells of Cajal.

An extensive cellular network becomes visible over the myenteric plexus of the rat after removal of the overlying tissues under the scanning electron microscope. The cells are mainly stellate and have many slender processes via which they interconnect. They form a three-dimensional network and are closely associated with the ganglia and nerve bundles, and also extend over the smooth muscle cells. They are considered to correspond to the interstitial cells of Cajal because of their peculiar arrangement and their topography. Transmission electron-microscopic evidence demonstrates that the majority of those cells have features of fibroblasts. Gap junctions and intermediate junctions are observed between these fibroblast-like cells, and also between them and smooth muscle cells. Examination of serial thin sections reveals that single fibroblast-like interstitial cells connect to both circular and longitudinal muscle cells via gap junctions. It is suggested that the network of interstitial cells conducts electrical signals.

Animals↗

PubMed1980

Structure of the myenteric plexus in the sphincters of cat gastro-intestinal tract. IV. Light-microscopic characteristics.

The structure of the myenteric plexus in the lower esophageal, pyloric and ileo-caecal sphincters of cats is studied in semi-thin sections through impregnation and demonstration of cholinesterase. The plexus ganglia are shown to be well formed structures, with varied sizes and shapes, in the collagen between the muscle layers of the sphincters. Impregnation reveals clearly in them Dogiel's neurones of 1st and 2nd type. The neurones and the nerve bundles of the plexus manifest intensive cholinesterase activity. The morphological data obtained are discussed in view of some functional specificities of the sphincter regions.

Animals↗

PubMed1980

The action of somatostatin on neurones of the myenteric plexus of the guinea-pig ileum.

1. Intracellular recordings were made from neurones in ganglia of the myenteric plexus of the guinea-pig ileum. 2. Somatostatin (10-300 nM) was applied to the neurones by adding it to the perfusing solution or by ejecting it (charges up to 500 nC) from an ionophoresis electrode onto the soma membrane. 3. By both methods of application, somatostatin either hyperpolarized or depolarized a proportion of neurones. Depolarizing responses were more often observed with ionophoretic application, and hyperpolarizing responses were more often observed with application by perfusion. Both responses were preserved in solutions containing zero Ca and elevated (6 mM) Mg. Some cells were both hyperpolarized and depolarized, depending on the method of administration. 4. The depolarizing responses to somatostatin were associated with an increase in cell input resistance; they became larger with membrane depolarization and smaller with membrane hyperpolarization, and reversed in polarity at a potential close to the potassium equilibrium potential. The hyperpolarizing responses to somatostatin were accompanied by a fall in cell input resistance.

Animals↗

PubMed1986

Vasoactive intestinal polypeptide provokes acetylcholine release from the myenteric plexus.

Effects of vasoactive intestinal polypeptide (VIP) on the release of acetylcholine (ACh) from longitudinal muscle strips with myenteric plexus (LM) preparations were examined in the guinea pig small intestine. VIP (10(-10) to 10(-6) M) induced a concentration-dependent contraction of LM preparation. The VIP-induced contractions seem to be related to three components, the scopolamine-sensitive, the scopolamine-insensitive, the tetrodotoxin-sensitive, and the tetrodotoxin-insensitive contractions. VIP (10(-10) to 10(-6) M) induced a concentration-dependent increase in the release of [3H]ACh from LM preparations preloaded with [3H]choline. The VIP-evoked [3H]ACh release was inhibited by removal of Ca2+ from the perfusion medium and by treatment with tetrodotoxin but not by scopolamine and hexamethonium. The spontaneous and VIP-evoked [3H]ACh release was not affected by phentolamine, propranolol, methysergide, diphenhydramine, cimetidine, bicuculline, or [D-Pro2, D-Trp7,9]substance P. The result demonstrates that VIP induces contractions of longitudinal smooth muscle directly and indirectly by the stimulation of both cholinergic neurons and noncholinergic excitatory neurons.

Acetylcholine↗

PubMed1991

Electrically-induced release of opioid peptides from the guinea-pig myenteric plexus preparation.

Preparations of guinea-pig myenteric plexus-longitudinal muscle suspended in Krebs solution were stimulated electrically in the presence of cycloheximide and tetraethylammonium. The amounts of eleven endogenous opioid peptides released into the perifusing Krebs solution were determined and correlated with the decrease in the tissue contents induced by stimulation. For pro-enkephalin fragments the ratio of release to reduction in tissue contents was 29 to 43% for [Met]enkephalin, [Leu]enkephalin, [Met]enkephalyl-RF and [Met]enkephalyl-RGL. With [Met]enkephalyl-RRV-NH2 (BAM-8) the ratio was higher by 50% or more. However, it is of interest that there was no release of the probable precursor [Met]enkephalyl-RRVGRPEWWMDYQ(BAM-18). In this context it may be important that BAM-8 is the only endogenous opioid peptide having -NH2 at the C-terminal. The low tissue levels of pro-dynorphin derived peptide have made estimation of release unreliable.

Amino Acid Sequence↗