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PubMed1988

Peptide-containing neurons in explant cultures of guinea-pig myenteric plexus during development in vitro: gross morphology and growth patterns.

The gross morphology and growth patterns of substance P, enkephalin-, somatostatin- and vasoactive intestinal peptide-immunoreactive neurons have been studied in explant cultures of the myenteric plexus taken from beneath the newborn guinea-pig taenia coli, grown for up to 4 weeks in vitro. Substance P- and enkephalin-immunoreactive neurons were more abundant than somatostatin- and vasoactive intestinal peptide-immunoreactive neurons. The peptide-containing neuronal cell bodies were clearly visible in culture and exhibited characteristic gross morphologies similar to those described in situ, although some overlap of shape between populations containing different peptides was seen. All four types of peptide-containing fibres were found in the outgrowth and central areas of the cultures. In the case of substance P and somatostatin, the density and pattern of labelling in the central, neuronal area of the cultures resembled that previously seen in the myenteric plexus of the newborn guinea-pig caecum in situ, while the density of the enkephalin-immunoreactive fibres was greater, and that of the vasoactive intestinal peptide-immunoreactive fibres less than that seen in situ. These observations suggest that subpopulations of myenteric neurons containing different peptides may be differentially affected by the culture environment. Possible contributory factors are discussed.

Animals↗

PubMed1980

Structure of the myenteric plexus in the sphincters of cat gastro-intestinal tract. III. Character and distribution of the dense-core vesicles in the axonal varicosities.

Attempts at differentiating the axonal varicosities and the vesicular population in them in the myenteric plexus of the gastro-intestinal tract, result from the participation of these structures in the metabolism of various transmitters. The present work studies the spatial distribution of the populations of dense-core vesicles in the different axonal varicosities in the myenteric plexus of the sphincters of cat gastro-intestinal tract. It is found that the axonal varicosities are characterized by a definite number of populations of dense-core vesicles and by their respective densities. Moreover, each group of varicosities has features common for the sphincters studied and at the same time characteristics observed in only one sphincter. The changes in the densities of the different populations of dense-core vesicles in the groups of axonal varicostities after reserpine treatment suggest their connection with different transmitter systems.

Animals↗

PubMed1980

Slow synaptic potentials in neurones of the myenteric plexus.

1. Intracellular recordings were made in vitro from neurones in the myenteric plexus of the guinea-pig ileum. Potential changes were recorded in response to focal stimulation of the surface of the myenteric ganglion at a distance of 30-100 microM from the impaled cell. 2. Stimuli comprising single pulses evoked cholinergic excitatory post-synaptic potentials ('fast' e.p.s.p.s) in S cells. In a small proportion (20%) of both S and AH cells such stimuli also evoked depolarizing potentials with a time course about 1000 times slower than that of the fast e.p.s.p. 3. Stimuli comprising repeated pulses (up to 20 Hz for 2 sec) evoked the slow depolarizing potentials in a higher proporton of neurones (42%). These stimuli caused a hyperpolarizing potential change in 9% of cells, and in a very few cells biphasic changes i membrane potential were observed. 4. Both the slow depolarizing and the slow hyperpolarizing responses persisted in atropine (up to 5 microM) and hexamethonium (up to 200 microM), but were reversibly abolished by changing to calcium-free solutions. 5. Evidence is presented which suggests that the slow depolarizing response is caused by inactivation of the membrane potassium conductance, and the slow hyperpolarizing response is due to activaton of the potassium conductance.

Animals↗

PubMed1990

Distribution of GABA-like immunoreactivity in myenteric plexus of carp, frog and chicken.

The distribution of GABA-like immunoreactivity was studied by means of indirect immunocytochemical methods in some lower vertebrate species (carp, frog, chicken). An immunoreactive network was revealed in the myenteric plexus of the alimentary canal of carp. GABA-positive nerve cells were attached closely to the fibres in the stomach. In other gut regions immunostained neurons were less frequent. Immunoreactive fibres often formed baskets on the surfaces of immunonegative neurons along the whole length of the alimentary canal. The number of immunopositive nerve fibres and pericellular baskets seemed to be lower in the mid- and hingut than in the foregut region. A similar distribution of GABA-immunoreactivity was revealed in the frog myenteric plexus. The ganglionated foregut region possessed a relatively dense GABAergic innervation. This part of the gut contained immunostained nerve cells and fibres, while the mid- and hindgut possessed only a scanty fibre system. Chicken exhibited an extensive immunoreactive plexus for GABA, although the GABA-stained perikarya were restricted mainly to the duodenum. Further regions of the small intestine were poor in immunoreactive cell bodies, which suggests a segmental origin and arrangement of GABAergic innervation within the plexus. In all three species studied, GABA-positive fibres run into the circular muscle layer. The varicosity suggests their influence on the movement of the smooth muscles through modifying the transmitter release of neighbouring terminals.

Animals↗

PubMed1993

Modulation of acetylcholine release from the myenteric plexus of guinea-pig ileum by 5-lipoxygenase metabolites of arachidonic acid.

Eicosatetraenoic acid, an inhibitor of 5- and 12-lipoxygenase, and AA861, a selective inhibitor of 5-lipoxygenase, dose dependently inhibited acetylcholine release from the myenteric plexus of guinea-pig ileum induced by electrical field stimulation. Metabolites of arachidonic acid produced by the 5-lipoxygenase pathway, such as 5-hydroxyeicosatetraenoic acid (5-HETE), leukotriene C4, D4 and E4, reversed the inhibitory effect of AA861. Among them, leukotriene D4 was the most potent, having an EC50 value of about 3 nM. The present study shows for the first time that 5-lipoxygenase metabolites may have a modulatory effect on acetylcholine release in the myenteric plexus of guinea-pig ileum.

Acetylcholine↗

PubMed1999

Vasoactive-intestinal-peptide- and substance-P-immunoreactive nerve fibres in the myenteric plexus of mouse colon during the chronic phase of Trypanosoma cruzi infection.

The distribution of a tachykinin (substance P) and vasoactive intestinal peptide (VIP) and the number and morphology of the large granular vesicles (LGV) in the myenteric plexus of the colons of mice were investigated. Six of the 12 young, male, Swiss mice studied had been inoculated with the Y strain of Trypanosoma cruzi 2 months previously whereas the others were uninfected controls. Substance P (SP) and VIP were localized by light microscopy, using an immunohistochemical method, and LGV were counted in sections studied by electron microscopy. There were far fewer LGV and less intensely staining varicose VIP- and SP-positive nerve fibres in the infected mice than in the controls. Denervation of the myenteric plexus may decrease the content of tachykinins (TK) and VIP in animals infected with T. cruzi. Such reduction in TK and VIP activity could be related to the disturbances in intestinal motility observed in the chronic phase of Chagas disease.

Animals↗

PubMed1977

Muscarinic feedback inhibition of acetylcholine release from the myenteric plexus in the quinea pig ileum and its status after chronic exposure to morphine.

Atropine (10(-8)-10(-6) M) produced a dose-related increase in the release of ACh from the electrically stimulated longitudinal muscle-myenteric plexus preparation. This increase in release was frequency dependent, being greater at low frequencies of stimulation where the pulse release of ACh was greater than at high frequencies. The muscarinic agonist oxotremorine (up to 100 micrometer) did not inhibit ACh release although 100 micrometer oxotremorine did antagonize the ability of atropine to increase release. The effect of chronic exposure to morphine, both in vivo and in vitro, on the reactivity of muscarinic receptors mediating this increase was examined. Neither the control rate of ACh release nor the dose-response curve for atropine were altered by (a) an 8-day morphine injection schedule, and (b) exposure of the tissue to morphine in the bath for 90 min. The results of this study support the existence of a muscarinic feedback mechanism which controls ACh release from the myenteric plexus. Chronic exposure to morphine does not produce specific changes in the muscarinic receptor mediating this inhibition.

Acetylcholine↗

PubMed1986

Three-dimensional visualization of the intraganglionic structures of the rat myenteric plexus: scanning electron microscopy with the connective tissue digestion method.

The rat myenteric plexus was chemically microdissected and the internal structures of the ganglia were demonstrated under a scanning electron microscope. The present preparation offers a view of the three-dimensional features of ganglion cells and permits their surface structures and the size and pattern of varicosities to be observed. Numerous finger-like processes were observed on the cell bodies of the studded neurons in close relationship with the varicose axons. The intramuscular branches of the plexus were also microdissected and their running pattern was observed.

Animals↗

PubMed1981

Acetylcholine release from the myenteric plexus of guinea-pig ileum by prostaglandin E1.

Release of acetylcholine (ACh) by prostaglandin E1 from the nerve terminals of the guinea-pig longitudinal muscle strip was studied in order to reveal the effect of PGE1 on myenteric plexus activity. The ACh released was collected in the presence of physostigmine (2.1 microgram ml-1) and choline (0.1 microgram ml-1) at 38 degrees C. Five to 100 ng ml-1 PGE1 enhanced the release dose-dependently. The effect was maintained during the presence of PGE1 in the organ bath, while rapid tachyphylaxis was observed with the ACh-releasing action of nicotine. Tetrodotoxin or morphine almost completely inhibited the effect of PGE1 on ACh release. Hexamethonium, in a concentration which completely blocked the effect of nicotine, partially inhibited the effect of PGE1. In the late phase of nicotine action, the tissue was still sensitive to PGE1 despite the continued exposure to nicotine. These data suggest the presence in the myenteric plexus of PG receptors which can increase ACh release.

Acetylcholine↗

PubMed1988

Decreased response to GABA-B agonists in longitudinal smooth muscle-myenteric plexus preparations from morphine-tolerant guinea-pigs.

1) Responsiveness of guinea-pig ileal longitudinal smooth muscle-myenteric plexus preparations to drugs activating GABA-B receptors was studied in morphine-tolerant animals. For this purpose morphine pellets (75 mg each) were implanted subcutaneously in guinea-pigs and experiments were performed three days later in electrically-stimulated ileal strips. 2) Activation of GABA-B receptors with GABA (10(-6) -10(-3) M) or (-)-baclofen (10(-6)-10(-3) M) caused a dose-related inhibition of twitch response that was about 80% lower in preparations from morphine-tolerant animals than in controls. This was found both in preparations maintained in the presence of morphine (10(-6) M) and in morphine-free Krebs. The effect was evident also in ileal preparations from morphine-tolerant animals in which a withdrawal syndrome was induced by the administration of naloxone before sacrifice. 3) The phenomenon was specific since the dose-response curve of the adenosine-inhibitory effect was comparable in preparations from tolerant animals and controls. 4) The hyporesponsiveness to GABA-B receptor activation began 12 h after pellet implantation and was maximal on the third day. 5) It is concluded that during tolerance to and withdrawal from morphine there is a hyporesponsiveness of GABA-B receptors in "in vitro" guinea-pig ileal longitudinal muscle-myenteric plexus preparations.

Animals↗

PubMed1997

Muscarinic autoinhibition and modulatory role of protein kinase C in acetylcholine release from the myenteric plexus of guinea pig ileum.

The modulatory role of protein kinase C on phospholipase A2, activation of which had been suggested to result in acetylcholine release from cholinergic neurons, was studied in longitudinal muscle preparations with the myenteric plexus of guinea pig ileum. The relationship of muscarinic autoinhibition to the modulation was also examined. Phorbol-12,13-dibutyrate (PDBu), an activator of protein kinase C, dose-dependently increased spontaneous and electrical field stimulation-induced acetylcholine releases from the preparation. The inhibitors of protein kinase C, staurosporine and calphostin C, inhibited the stimulatory effects of PDBu, but neither inhibitor affected spontaneous or electrical field stimulation-induced acetylcholine release in the absence of PDBu. On the other hand, atropine significantly increased electrical field stimulation-induced release by blocking a muscarinic autoinhibitory mechanism. Under the auto-inhibition blocked condition, U73122, an inhibitor of phospholipase C, and staurosporine significantly inhibited the effect of atropine on electrical field stimulation-induced release. An inhibitor of phospholipase A2, mepacrine, inhibited PDBu-induced acetylcholine release and also inhibited the effect of atropine on electrical field stimulation-induced release. An activator of phospholipase A2, melittin, and a product of the phospholipase, arachidonic acid, increased the spontaneous and electrical field stimulation-induced releases. These results suggest that the phospholipase C-protein kinase C system modulates acetylcholine release from cholinergic neurons by activating phospholipase A2 in the myenteric plexus of guinea pig ileum, and the activation of muscarinic autoreceptor may negatively modulate acetylcholine release at a point upstream of the system.

Acetylcholine↗

PubMed1999

Topographical and electrophysiological characteristics of highly excitable S neurones in the myenteric plexus of the guinea-pig ileum.

1. Most intracellular electrical recordings from myenteric neurones have been made from the centre of large ganglia. In this study, we examined the electrophysiological properties of neurones at the corners of large ganglia close to internodal strands and in microganglia. 2. Of 150 neurones in these locations: 111 were tonic S neurones; 9 were phasic S neurones and 30 were AH neurones. 3. Tonic S neurones were characterized by: (i) low resting membrane potentials (-50 +/- 1 mV, mean +/- s.e.m.); (ii) high input impedance (522 +/- 23 MOmega); (iii) low threshold for action potential (AP) generation (0.012 +/- 0.004 nA); (iv) firing of APs throughout a depolarizing pulse (duration <= 1 s) and one to four APs following a hyperpolarizing pulse and (v) spontaneous fast excitatory postsynaptic potentials (FEPSPs). A substantial proportion of tonic S neurones (43 %) also fired APs spontaneously (7.6 +/- 0.6 Hz; range, 0.3-19 Hz). All APs were blocked by tetrodotoxin (1 microM). 4. Tonic S neurones were subclassified, according to their post-stimulus responses, as SAH or SAD neurones. Following a burst of APs, SAH neurones exhibited a prominent after-hyperpolarization (duration, 711 +/- 10 ms) and SAD neurones an after-depolarization (duration, 170 +/- 10 ms). The after-hyperpolarization was reduced in four of ten neurones by apamin (0.3 microM). 5. FEPSPs were evoked in 20 of 38 S neurones by electrical stimulation applied both oral and anal to the recording site. Repetitive stimuli evoked slow excitatory postsynaptic potentials (SEPSPs) in some tonic S neurones. 6. Three functional classes of S neurones were identified after injection of neurobiotin through the recording microelectrode: (i) longitudinal muscle motor neurones, (ii) short circular muscle motor neurones, and (iii) ascending interneurones. 7. In conclusion, there appears to be topographical organization of highly excitable, tonic S neurones within the myenteric plexus, since, in contrast to other S neurones, they can be readily impaled in myenteric ganglia close to internodal strands and in microganglia.

Action Potentials↗

PubMed1999

The GDNF-induced neurite outgrowth and neuronal survival in dissociated myenteric plexus cultures of the rat small intestine decreases postnatally.

Glial cell-line-derived neurotrophic factor (GDNF), a member of the transforming growth-factor-(TGF-) beta-family, is an essential factor for the development of the enteric nervous system (ENS) during embryogenesis. In the present study, the effects of GDNF on postnatal ENS development were investigated using cultures of myenteric plexus from the small intestine of newborn albino rats of different developmental phases (P1, P7, P14). Myenteric plexus was dissociated and cultivated as mixed cultures of enteric neurons and glial cells. After seeding, the cultures were kept for 24 h or 7 days in serum-free medium containing various doses (1, 10, 100 ng/ml) of GDNF. The effect of the neurotrophic factor was evaluated using parameters such as cell size, neuronal survival, or neurite elongation. While neither glial-cell nor neuronal size was influenced by GDNF, there was an observable effect upon neuronal survival and neurite elongation. The cultures treated with GDNF displayed increased neurite outgrowth. The promoting effect was dose- and age-dependent, decreasing clearly during the early postnatal period. Already after 24 h, neuronal survival was increased in P1 and P7, but not in P14 cultures. In long-term cultures, a marked tendency to form cell aggregates and dense fiber networks was observed when treated with GDNF. These observations suggest that GDNF plays an important role not only in pre-, but also in postnatal development of the enteric nervous system.

Animals↗

PubMed1990

Inhibition by beta-CCM of cholecystokinin-induced release of acetylcholine from the longitudinal muscle-myenteric plexus preparation in the guinea-pig ileum.

The antagonism between cholecystokinin (CCK) and methyl beta-carboline-3-carboxylate (beta-CCM) in the nervous system was studied by measuring the release of acetylcholine (ACh) from the longitudinal muscle-myenteric plexus preparation of guinea-pig. The ACh release was assessed by measuring [3H] output from the preparation preincubated with [3H] choline. Thirty mM of KCl caused a pronounced release of [3H] ACh from the preparation. Sulfated cholecystokinin octapeptide (CCK8) also increased the release of [3H] ACh in a dose-dependent manner at concentrations ranging from 10(-10)M to 10(-8)M. CCK8 at a concentration of 10(-8)M released [3H] ACh by about 300% of the 30 mM KCl-induced [3H] ACh release. In the presence of beta-CCM (10(-8)M to 10(-4)M), the release of [3H] ACh by KCl was not affected, but that by CCK8 was significantly inhibited depending on the concentrations of beta-CCM. These results show that the action of CCK8 to stimulate neurons in the myenteric plexus can be selectively antagonized by beta-CCM.

Acetylcholine↗

PubMed1983

Arrangement of the myenteric plexus throughout the gastrointestinal tract of the opossum.

Silver impregnation of the myenteric plexus of the opossum gut was used to find differences among various regions. In the esophagus, the plexus was sparse and ganglia were spaced irregularly, many being parafascicular. Ganglia were sparse in the striated-muscle region, but more frequent in the smooth-muscle region. In the stomach, uniformly spaced ganglia were large and intrafascicular; ganglia were larger in the distal stomach than in the proximal stomach. The proximal stomach contained thick fascicles, called shunt fascicles, radiating from the lesser to the greater curvatures and bypassing ganglia. A thick nerve bundle encircled the pylorus. In the small intestine, the regularly spaced ganglia were large and intrafascicular. In the cecum, they were small and intrafascicular. In the colon, they were large and intrafascicular. Shunt fascicles, like those of the proximal stomach, extended from the rectum into the distal colon. In the rectum, the plexus was sparse, and ganglia were small and distributed irregularly. Many ganglia were parafascicular. Unique knots of tangled fascicles were frequent in the rectum; these were called labyrinthine nodes. The least densely innervated regions of the gut are the lower esophageal sphincter and the rectum. Major differences in the anatomy of the plexus characterize the different regions of the gut.

Animals↗

PubMed1982

Encephalomyeloneuropathy with ganglionitis of the myenteric plexuses in the absence of cancer.

A 55-year-old woman presented with rapidly progressive brainstem dysfunction which led to death within a month. She also had constipation for three weeks, and barium enema showed ileus. Subacute encephalomyelitis predominantly involving the medulla and pons correlated with the patient's initial symptoms. In addition, ganglionitis of the myenteric plexuses explained the constipation and ileus. Ganglioradiculoneuropathy was another finding. The presence of abundant neuronophagia in the brainstem, dorsal root ganglia, and myenteric plexuses raised the speculation that a putative virus, toxic agent, or immune reaction possessed special affinity for neurons and ganglion cells. The neuropathological findings were similar to paraneoplastic changes, but no neoplasm was found.

Brain Stem↗

PubMed2006

Tolerance to cannabinoid response on the myenteric plexus of guinea-pig ileum and human small intestinal strips.

1. We studied tolerance to cannabinoid agonist action by comparing the in vitro inhibition of electrically evoked contractions of longitudinal muscle from small intestine of human and guinea-pig (myenteric plexus preparations) after 48-h incubation with the synthetic agonist (+) WIN 55,212-2. We also investigated the intrinsic response to the selective cannabinoid CB(1) receptor antagonist rimonabant in control and tolerant strips. 2. (+) WIN 55,212-2 inhibited guinea-pig (IC(50) 4.8 nM) and human small intestine (56 nM) contractions with similar potency before or after 48-h incubation in drug-free conditions; this effect was competitively antagonized by rimonabant (pA(2), 8.4, 8.2). A 48-h preincubation with (+) WIN 55,212-2, but not with (-) WIN 55,212-3, completely abolished the acute agonist response in both tissue preparations. The opiate K-receptor agonist U69593 inhibited human small intestine contractions with a similar potency in control and strips tolerant to (+) WIN 55,212-2, IC(50) 39 and 43 nM. 3. Unlike human tissue, in guinea-pig small intestine, which has a high level of endocannabinoids, rimonabant alone increased the twitches induced by the electrical field stimulation (EC(50) 100 nM) with a maximal effect of 123%. 4. In strips tolerant to (+) WIN 55,212-2, rimonabant markedly increased (155%) the electrical twitches in human ileum and in guinea-pig myenteric plexus smooth muscle (133%). 5. This study shows tolerance can be induced to the cannabinoids' action in intestinal strips of human and guinea-pig by long in vitro incubation with the agonist (+) WIN 55,212-2.

Animals↗

PubMed1980

Structure of the myenteric plexus in the sphincters of cat gastro-intestinal tract. I. Quantitative assessment of the types of dense-core vesicles.

Ultrastructural studies show that dense-core vesicles are among the most frequently occurring types of vesicles in the axonal varicosities of the myenteric plexus of the gastro-intestinal tract, and interest in them is due to their significance for the formation, storage and release of the transmitters. However, measurements so far have been made on the basis of the images of the dense-core vesicles on the electronograms, whereby the size and the type of the vesicles greatly depend on their position with respect to the surface of the sections observed. The methods applied by us made it possible to determine the spatial dimensions and the density of the dense-core vesicles in the myenteric plexus of the sphincters of cat gastrointestinal tract. Using the method of reconstruction in arranging the diameters in geometrical order, five populations of dense-core vesicles with corresponding mean diameter and small mean square deviation are differentiated.

Animals↗