Interstitial cells of Cajal mediate inhibitory neurotransmission in the stomach

Activation of outward K+ currents: effect of VIP in oesophagus

1. Electrical field stimulations (EFS) of the opossum and canine lower oesophageal sphincters (OLOS and CLOS respectively) and opossum oesophageal body circular muscle (OOBCM) induce non-adrenergic, non-cholinergic (NANC) relaxations of any active tension and NO-mediated hyperpolarization. VIP relaxes the OLOS and CLOS and any tone in OOBCM without major electrophysiological effects. These relaxations are not blocked by NOS inhibitors. Using isolated smooth muscle cells, we tested whether VIP acted through myogenic NO production. 2. Outward currents were similar in OOBCM and OLOS and NO increased them regardless of pipette Ca2+(i), from 50-8000 nM. L-NAME or L-NOARG did not block outward currents in OLOS at 200 nM pipette Ca2+. 3. Outward currents in CLOS cells decreased at 200 nM pipette Ca2+ or less but NO donors still increased them. VIP had no effect on outward currents in cells from OOBCM, OLOS or CLOS under conditions of pipette Ca2+ at which NO donors increased outward K+ currents. 4. We conclude, VIP does not mimic electrophysiological effects of NO donors on isolated cells of OOBCM, OLOS or CLOS. VIP relaxes the OLOS and CLOS and inhibits contraction of OOBCM by a mechanism unrelated to release of myogenic NO or an increase in outward current. 5. Also, the different dependence of outward currents of OOBCM and OLOS on pipette Ca2+ from those of CLOS suggests that different K+ channels are involved and that myogenic NO production contributes to K+ channel activity in CLOS but not in OLOS or OOBCM.

Parallel pathways mediate inhibitory effects of vasoactive intestinal polypeptide and nitric oxide in canine fundus

1. The gastric adaptation reflex is activated by the release of non-adrenergic, non-cholinergic (NANC) inhibitory transmitters, including nitric oxide (NO) and vasoactive intestinal polypeptide (VIP). The role of NO in this reflex is not disputed, but some investigators suggest that NO synthesis is stimulated by VIP in post-junctional cells or in nerve terminals. We investigated whether the effects of these transmitters are mediated by independent pathways in the canine gastric fundus. 2. VIP and NO produced concentration-dependent relaxation of the canine fundus. Nomega-nitro-L-arginine (L-NNA) reduced relaxation induced by electrical field stimulation (EFS; 0.5-8 Hz), but had no effect on responses to exogenous VIP and sodium nitroprusside (SNP, 10 microM). 3. Oxyhaemoglobin reduced relaxations produced by EFS and SNP. Oxyhaemoglobin also reduced relaxation responses to low concentrations of VIP (<10 nM), but these effects were non-specific and mimicked by methaemoglobin which had no effect on nitrergic responses. 4. A blocker of guanylyl cyclase, 1H-[1,2,4]oxidiazolo [4,3,-a]quinoxalin-1-one, (ODQ) inhibited responses to EFS, SNP and DETA/NONOate (an NO.donor), but had no effect on responses to VIP. cis-N-(2-phenylcyclopentil)-azacyclotridec-1en-2-amine monohydrochloride (MDL 12,330A), a blocker of adenylyl cyclase, reduced responses to EFS, VIP and forskolin, but did not affect responses to SNP. 5. Levels of cyclic GMP were enhanced by the NO donor S-nitroso-n-acetylpenicillamine (SNAP) but were unaffected by VIP (1 microM). The increase in cyclic GMP in response to SNAP was blocked by ODQ. 6. The results suggest that at least two transmitters, possibly NO and VIP, mediate relaxation responses in the canine fundus. NO and VIP mediate responses via cyclic GMP- and cyclic AMP-dependent mechanisms, respectively. No evidence was found for a serial cascade in which VIP is coupled to NO-dependent responses.

The enteric nervous system and regulation of intestinal motility

The enteric nervous system exerts local control over mixing and propulsive movements in the small intestine. When digestion is in progress, intrinsic primary afferent neurons (IPANs) are activated by the contents of the intestine. The IPANs that have been physiologically characterized are in the intrinsic myenteric ganglia. They are numerous, about 650/mm length of small intestine in the guinea pig, and communicate with each other through slow excitatory transmission to form self-reinforcing assemblies. High proportions of these neurons respond to chemicals in the lumen or to tension in the muscle; physiological stimuli activate assemblies of hundreds or thousands of IPANs. The IPANs make direct connections with muscle motor neurons and with ascending and descending interneurons. The circular muscle contracts as an annulus, about 2-3 mm in minimum oral-to-anal extent in the guinea pig small intestine. The smooth muscle cells form an electrical syncytium that is innervated by about 300 excitatory and 400 inhibitory motor neurons per mm length. The intrinsic nerve circuits that control mixing and propulsion in the small intestine are now known, but it remains to be determined how they are programmed to generate the motility patterns that are observed.

Cellular and molecular basis for electrical rhythmicity in gastrointestinal muscles

Regulation of gastrointestinal (GI) motility is intimately coordinated with the modulation of ionic conductance expressed in GI smooth muscle and nonmuscle cells. Interstitial cells of Cajal (ICC) act as pacemaker cells and possess unique ionic conductances that trigger slow wave activity in these cells. The slow wave mechanism is an exclusive feature of ICC: Smooth muscle cells may lack the basic ionic mechanisms necessary to generate or regenerate slow waves. The molecular identification of the components for these conductances provides the foundation for a complete understanding of the ionic basis for GI motility. In addition, this information will provide a basis for the identification or development of therapeutics that might act on these channels. It is much easier to study these conductances and develop blocking drugs in expression systems than in native GI muscle cells. This review focuses on the relationship between ionic currents in native GI smooth muscle cells and ICC and their molecular counterparts.

Immunohistochemical distribution of c-Kit-positive cells and nitric oxide synthase-positive nerves in the guinea-pig small intestine

Anatomical relationships between c-Kit-positive cells and nitric oxide synthase-positive nerves in the small intestine were examined by double-labeling immunohistochemistry. Cryosections and whole mount preparations of the guinea-pig small intestine were double-immunolabeled using anti-c-Kit and neuronal nitric oxide synthase antibodies, and were observed using confocal laser scanning microscopy. The c-Kit-like immunoreactivity constituted dense reticular networks in the deep muscular plexus and myenteric plexus of the intestinal wall. The nitric oxide synthase-like immunoreactivity occurred in the circular muscle layer, most densely at the deep muscular plexus, as well as within the ganglion strands or connecting strands of the myenteric plexus. Close association between c-Kit-like immunoreactivity and nitric oxide synthase-like immunoreactivity was evident in the deep muscular plexus. Specimens immunolabeled with the anti-nitric oxide synthase antibody were further examined under transmission electron microscopy. Axon profiles with nitric oxide synthase-like immunoreactivity lay closely adjacent to the interstitial cells in the deep muscular plexus as well as to smooth muscle cells of the circular muscle layer, whereas there was a considerable distance (> 500 nm) between interstitial cells and axon profiles with nitric oxide synthase-like immunoreactivity in the myenteric plexus. These results suggest that the interstitial cells in the deep muscular plexus serve as mediators of the nitrergic neurotransmission to the musculature in the small intestine, playing a role in the regulation of intestinal movement.

Voltage sensitivity of slow wave frequency in isolated circular muscle strips from guinea pig gastric antrum

In circular muscle preparations isolated from the guinea pig gastric antrum, regular spontaneous electrical activity (slow waves) was recorded. Under normal conditions (6 mM K+), the frequency and shape of the slow waves were similar to those observed in ordinary stomach smooth muscle preparations. When the resting membrane potential was hyperpolarized and depolarized by changing the extracellular K+ concentration (2-18 mM), the frequency of slow waves decreased and increased, respectively. Application of cromakalim hyperpolarized the cell membrane and reduced the frequency of slow waves in a dose-dependent manner. Cromakalim (3 microM) hyperpolarized the membrane, and slow waves ceased in most preparations. In the presence of cromakalim, subsequent increases in the extracellular K+ concentration restored the frequency of slow waves accompanied by depolarization. Also, glibenclamide completely antagonized this effect of cromakalim. In smooth muscle strips containing both circular and longitudinal muscle layers, such changes in the slow wave frequency were not observed. It was concluded that the maneuver of isolating circular smooth muscle altered the voltage dependence of the slow wave frequency.

Slow waves in circular muscle of porcine ileum: structural and electrophysiological studies

The structural and functional bases of pacemaking (slow waves) in porcine ileal circular muscle were studied. The myenteric plexus contained two, structurally distinct types of interstitial cells of Cajal (ICC) interconnected by gap junctions and connected by close contacts to muscle layers. At the deep muscular plexus, ICC were present, not regularly close to nerve axons or in gap junction contact with one another or outer circular muscle, which had many gap junctions. Slow waves (5.2 +/- 2 mV amplitude and 4.6 +/- 0.7 s duration) occurred at 9.9 +/- 1.1 counts/min. Tissue length and time constants were 2.00 +/- 0.3 mm and 111 +/- 37 ms, respectively. Large electrical field-induced hyperpolarizations or depolarizations reduced amplitudes but not frequencies or durations of slow waves; hyperpolarizations progressively reduced inhibitory junction potentials as if the K+ channel opening mediated them. In conclusion, the myenteric plexus ICC of pig ileum, which appears to pace the muscle layers, appears insensitive to voltages applied to the syncytium of circular muscle cells. Limited coupling between ICC and circular muscle or voltage-insensitive pacemaking activity may explain these findings.

c-Kit immunoreactive interstitial cells in the human gastrointestinal tract

c-Kit immunopositive cells are considered to be pacemakers and/or mediators of neurotransmission in the gastrointestinal tract. They also correspond to the interstitial cells of Cajal (ICs) in mice. The normal distribution of c-Kit positive cells and their relation to ICs in the human gastrointestinal tract remain unclear. In this study we examine the distribution of c-Kit positive cells and their ultrastructure in normal human tissue. We then classified them and examined their relationship to ICs. Thirty nine samples of gut from the esophagus to the sigmoid colon from humans (ranging in age from a 16 week old fetus to a 57 year old and without motility disorders), were processed for immunohistochemistry, electronmicroscopy and immuno-electronmicroscopy. c-Kit immunopositive cells were located in the external muscle from the lower esophagus to the sigmoid colon, wherever the external muscle was composed of smooth muscle cells, and they were classified morphologically into two groups. Cells in the first group were mainly spindle-shaped bipolar cells with few branches; these cells ran parallel to nearby smooth muscle. Ultrastructurally, they possessed many intermediate filaments and caveolae. The spindle-shaped cells were present in the esophagus, stomach and small intestine. The second group of cells were located only in the colon, and were multipolar or bipolar cells with numerous branches. Cells in the second group were also rich in caveolae and/or smooth endoplasmic reticulum, but intermediate filaments were not prominent. Although both groups of c-Kit immunopositive cells corresponded to ICs, some ICs in the human gut do not appear to express c-Kit immunoreactivity.

Searching for intrinsic properties and functions of interstitial cells of Cajal

Evidence is mounting that interstitial cells of Cajal may function as pacemaker cells and have a role in NO-mediated neurotransmission. Several colonic motor disorders may be associated with abnormal ICC function.

Modulation of cholinergic neuromuscular transmission by nitric oxide in canine colonic circular smooth muscle

This study examines the effect of nitric oxide (NO) on cholinergic transmission in strips of canine colonic circular muscle in which neural plexus-pacemaker regions had been removed. Electrical field stimulation gave rise to atropine- and TTX-sensitive excitatory junction potentials (EJPs), the amplitude of which were frequency dependent. In 47% of control muscles, the EJP was followed by an inhibitory junction potential (IJP), whereas in the presence of atropine all preparations exhibited only IJPs. The NO synthase inhibitor Nomega-nitro-L-arginine (L-NNA), the guanylyl cyclase inhibitor 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxaline-1-one (ODQ), and the protein kinase G (PKG) antagonist Rp-8-bromo-PET-cGMPS all significantly increased EJP amplitude and reduced or abolished IJPs. The potentiation of EJPs by L-NNA was reversed by the NO donors sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine in a manner blocked by ODQ. [14C]ACh overflow was also measured to evaluate the possible prejunctional effects of NO. Both norepinephrine and TTX significantly decreased [14C]ACh overflow; however, L-NNA, ODQ, and SNP were without effect. These data suggest that both cholinergic and nitrergic motoneurons functionally innervate the interior of the circular muscle layer. The inhibitory actions of NO on cholinergic transmission appear to be post- rather than prejunctional and to involve guanylyl cyclase as well as possibly PKG.

Distribution of the interstitial cells of Cajal in the human anorectum

The interstitial cells of Cajal are proposed to have a role in the control of gut motility. The aim of this study was to establish the distribution of interstitial cells of Cajal in the wall of the normal human anorectum. Interstitial cells of Cajal express the proto-oncogene c-kit. Interstitial cells of Cajal were identified in the colon by immunohistochemical staining, using a rabbit polyclonal anti-c-kit antibody. Anorectal tissue was obtained at surgical resection for carcinoma of the colorectum. Density of interstitial cells of Cajal was graded. Statistical analysis was performed using chi2 tests. In the longitudinal and circular muscle layers of the rectum interstitial cells of Cajal were seen in the bulk of the muscle layer. In the intermuscular plane interstitial cells of Cajal encased the myenteric plexus. Interstitial cells of Cajal were found at the inner margin of the circular muscle and in association with neural elements of the submuscular plexus. Within the internal anal sphincter interstitial cells of Cajal were infrequently scattered among the muscle fibres. The density of interstitial cells of Cajal in the internal anal sphincter was significantly lower than that observed in the circular muscle layer of the rectum (P = 0.014). In conclusion, interstitial cells of Cajal are evenly distributed in the layers of the muscularis propria of the rectum, but have a lower density in the internal anal sphincter.

Protein kinase G expression in the small intestine and functional importance for smooth muscle relaxation

In functional experiments, the nitric oxide (NO) donor N-morpholino-N-nitroso-aminoacetonitrile or the cGMP analog 8-(4-chlorophenylthio)-cGMP caused a concentration-dependent, tetrodotoxin-resistant relaxation of precontracted strips from rat small intestine. The inhibitory effect of both substances was completely blocked at lower concentrations and was significantly attenuated at higher concentrations by the selective cGMP-dependent protein kinase (cGK) antagonist KT-5823 (1 microM). cGK-I was identified by immunohistochemistry in circular and longitudinal muscle, lamina muscularis mucosae, and smooth muscle cells of the villi and in fibroblast-like cells of the small intestine. Additionally, there was staining of a subpopulation of myenteric and submucous plexus neurons. Double staining for neuronal NO synthase (nNOS) and cGK-I demonstrated a colocalization of these two enzymes. Western blot analysis of smooth muscle preparations and isolated nerve terminals demonstrated that these structures predominantly contain the cGK-Ibeta isoenzyme, whereas the cGK-Ialpha expression is about threefold less. The isoform cGK-II was entirely confined to mucosal epithelial cells. These results show that cGK-I is expressed in different muscular structures of the small intestine and participates in the NO-induced relaxation of gastrointestinal smooth muscle. The presence of cGK-I in NOS-positive enteric neurons further suggests a possible neuronal action site.

Oesophagitis-induced changes in capsaicin-sensitive tachykininergic pathways in the ferret lower oesophageal sphincter

Prolonged oesophageal acidification may impair lower oesophageal sphincter (LOS) function in reflux disease. The aim of this study was to investigate aspects of altered LOS innervation in a model of oesophagitis. Oesophagitis was induced by acid (HCl, 0.15 M) and pepsin (0.1% w/v) infusions in anaesthetized ferrets. LOS muscle strip responses to the following stimuli were measured in vitro from control and acid/pepsin-treated ferrets: electrical field stimulation (EFS; 1-50 Hz), potassium chloride KCl; 20 mM), substance P, [beta-Ala8]-neurokinin A 4-10, [Sar9, Met (O2)11]-substance P (all 10(-10) to 10(-6) M) and capsaicin (10(-8) to 10(-6) M). LOS relaxation occurred in response to all stimuli except [beta-Ala8]-neurokinin A 4-10, which evoked contraction. In muscle strips from acid/pepsin-treated animals there were no differences in amplitude or sensitivity of relaxation following EFS, KCl or substance P vs controls. However, the inhibitory response to capsaicin was increased four-fold (10(-8) M; P < 0.05) and an increased sensitivity of the inhibitory response to [Sar9, Met (O2)11]-substance P occurred (pD2 = 8.64 +/- 0.12 acid/pepsin-treated vs 7.94 +/- 0.24 control, P < 0.05). We conclude that in acute oesophagitis, increased sensitivity of capsaicin-activated inhibitory pathways occurs in which activation of NK-1 receptors plays an integral role in the ferret LOS.

Neural injury, repair, and adaptation in the GI tract. IV. Pathophysiology of GI motility related to interstitial cells of Cajal

Our understanding of the physiological roles played by interstitial cells of Cajal (ICC) in relation to gastrointestinal (GI) motility is still rudimentary. Nevertheless, studies into the pathophysiology of ICC are emerging at a rapid pace. Caution should be exercised, however, in assuming correlations between changes in Kit immunoreactivity, findings of ultrastructural abnormalities in ICC, and the pathophysiology and symptoms of the patients. Recent studies have revealed reduced numbers or the absence of ICC in small intestine and colon that do not exhibit normal peristaltic activity. Furthermore, important evidence is emerging that motor abnormalities in newborns may be associated with delayed maturation of the ICC network. These preliminary clinical studies provide plausible hypotheses toward the pathophysiology of certain motor disorders and strongly encourage basic scientific studies directed toward discovering the intrinsic properties of ICC as well as obtaining a deeper understanding of the physiological roles played by these cells.

The identification and chemical coding of cholinergic neurons in the small and large intestine of the mouse

BACKGROUND

The recent availability of antisera to the vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT) that demonstrate peripheral cholinergic neurons has made possible the anatomical identification of cholinergic neurons in the enteric nervous system. In this study, we localised cholinergic neurons in the mouse small and large intestine and identified which substances are found colocalised in the cholinergic neurons.

METHODS

Immunohistochemical single and double staining techniques were used on whole mount preparations and frozen sections to examine the localisation and chemical coding of cholinergic neurons in the small and large intestine of the mouse. Cholinergic neurons were identified using antisera to ChAT or VAChT.

RESULTS

In both the small and large intestine, numerous ChAT-immunoreactive nerve cell bodies were present in the myenteric and submucous ganglia, and ChAT- and VAChT-immunoreactive nerve terminals were abundant in the myenteric and submucous plexuses and the external muscle. Previous studies have identified two major classes of myenteric neurons in the small intestine of the mouse--those containing calretinin plus substance P, and those containing nitric oxide synthase (NOS) plus vasoactive intestinal peptide (VIP). Double-label studies showed that the vast majority of the calretinin/substance P neurons were cholinergic neurons, whereas only a small proportion of the NOS/VIP cells were cholinergic; the noncholinergic NOS/VIP neurons were motor neurons or interneurons, whereas the cholinergic NOS/VIP neurons appeared to be exclusively interneurons. In the small intestine, all of the 5-HT-loaded neurons and a subpopulation of the calbindin neurons were also cholinergic. In the large intestine, there was a pattern of overlaps similar to that found in the small intestine, except that in the large intestine approximately 25% of the calretinin cells were not cholinergic. Only approximately one third of the GABA-loaded neurons in the large intestine were cholinergic.

CONCLUSIONS

Large subpopulations of motor neurons and interneurons in the mouse small intestine are cholinergic neurons.

Interstitial cells of Cajal mediate enteric inhibitory neurotransmission in the lower esophageal and pyloric sphincters

BACKGROUND & AIMS

Previous studies have suggested that a specific class of interstitial cells of Cajal (ICC) act as mediators in nitrergic inhibitory neurotransmission. The aim of this investigation was to examine the role of intramuscular ICC (IC-IM) in neurotransmission in the murine lower esophageal (LES) and pyloric sphincters (PS).

METHODS

Immunohistochemistry and electrophysiology were used to study the distribution and role of IC-IM.

RESULTS

The LES and PS contain spindle-shaped IC-IM, which form close relationships with nitric oxide synthase-containing nerve fibers. The PS contains ICC within the myenteric plexus and c-Kit immunopositive cells along the submucosal surface of the circular muscle. IC-IM were absent in the LES and PS of c-kit (W/Wv) mutant mice. Using these mutants, we tested whether IC-IM mediate neural inputs in the LES and PS. Although the distribution of inhibitory nerves was normal in W/Wv animals, NO-dependent inhibitory neurotransmission was reduced. Hyperpolarizations to sodium nitroprusside were also attenuated in W/Wv animals.

CONCLUSIONS

The data suggest that IC-IM play an important role in NO-dependent neurotransmission in the LES and PS. IC-IM may be the effectors that transduce NO signals into hyperpolarizing responses. Loss of IC-IM may interfere with relaxations and normal motility in these sphincters.

Neuron density and distribution of NADPH-diaphorase positive neurons in the human stomach

Neuron density and distribution of the NADPH-diaphorase positive neurons were studied in the fundus, corpus and antrum of adult human stomach using cresyl violet staining and NADPH-diaphorase histochemistry. The submucous plexus contained significantly less neurons than the myenteric plexus. Submucous NADPH-d positive neurons were mostly located in ganglia close to the circular muscle layer. Myenteric NADPH-d positive neurons represented 50-60% of the neurons in all the three regions; their density, however, was significantly lower in the fundus. NADPH-d positive fibers formed a rich plexus in the innermost portion of the circular muscle layer of the corpus.

G protein-coupled receptors in gastrointestinal physiology. IV. Neural regulation of gastrointestinal smooth muscle

G protein-coupled receptors receive many of the neural, hormonal, and paracrine inputs to gastrointestinal (GI) smooth muscle cells. This article examines the major G protein-coupled receptors, G proteins, and effectors that mediate responses to enteric neuromuscular transmitters. Excitatory transmitters primarily couple through Gq/11 and Gi/Go proteins and elicit responses via formation of inositol trisphosphate and diacylglycerol and inhibition of adenylyl cyclase. Several inhibitory transmitters couple through Gs and activation of adenylyl cyclase. There are interesting examples, however, of inhibitory transmitters apparently using pathways regulated by Gq/11 to elicit responses by localized Ca2+ release and activation of Ca2+-dependent ion channels. G protein-coupled receptors may also be differentially expressed by smooth muscle cells and interstitial cells of Cajal, which may increase the diversity of responses and allow specialized innervation of GI muscle tissues.

The deep muscular plexus of the pig duodenum: a histochemical and ultrastructural study with special reference to the interstitial cells

The aim of the present study was to describe the deep muscular plexus of the pig duodenum and to characterize its cellular components. Numerous nerve varicosities have been detected in the deep muscular plexus using anti-synaptophysin antibodies. Nerve fibres were also detected here in the outer circular muscle layer, whereas no nerve fibres were observed in the inner circular muscle layer. In the deep muscular plexus, nerve fibres projected to interstitial cells which were characterized at the ultrastructural level. The interstitial cells were of two kinds: the interstitial fibroblastic-like cells (FLC) and the interstitial dense cells (IDC), both of which were interposed between nerve fibres and smooth muscle cells. The FLC were characterized by their elongated bipolar shape, the lack of basal lamina, a well-developed endoplasmic reticulum, a Golgi apparatus, and intermediate filaments. They were closely apposed to axon terminals containing small clear synaptic vesicles and/or dense-cored vesicles. They were frequently connected to each other and to smooth muscle cells of the inner and outer circular layer by desmosomes and more rarely by gap junctions. The IDC are myoid-like cells. They had a stellate appearance and were characterized by a dense cell body, numerous caveolae, and a discontinuous basal lamina. The IDC were always closely apposed to nerve fibres and were connected to smooth muscle cells by desmosomes and small gap junctions. The present results show the unique pattern of cellular organization of the deep muscular plexus of the pig small intestine. They suggest that the interstitial cells in the deep muscular plexus are involved in the integration and transmission of nervous inputs from myenteric neurons to the inner and outer circular muscle layers. The clear-cut distinction observed here between the two types of interstitial cells (fibroblastic and myoid-like) suggests that the interstitial cells of each type may also be involved in some other specific activity, which still remains to be determined.

Enteric neuronal plasticity and a reduced number of interstitial cells of Cajal in hypertrophic rat ileum

BACKGROUND

Partial obstruction of the ileum causes a notable hypertrophy of smooth muscle cells and enteric neurones in the proximally located intestine.

AIMS

To study the expression of neuromessengers in the hypertrophic ileum of rat as little is known about neuromessenger plasticity under these conditions. To investigate the presence of interstitial cells of Cajal (ICC) in hypertrophic ileum.

METHODS

Ileal hypertrophy was induced by circumferential application of a strip of plastic film for 18-24 days. Immunocytochemistry, in situ hybridisation, nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry, and ethidium bromide staining were used to investigate the number of enteric neurones expressing neuropeptides and nitric oxide synthase, and the frequency of ICC.

RESULTS

In the hypertrophic ileum several neuronal populations showed changes in their expression of neuromessengers. Myenteric neurones expressing vasoactive intestinal peptide (VIP), pituitary adenylate cyclase activating peptide, and galanin were notably increased in number. In submucous ganglia the number of VIP immunoreactive neurones decreased while those expressing VIP mRNA increased. NADPH diaphorase positive submucous neurones increased dramatically while the number of neuronal type nitric oxide synthase expressing ones was unchanged. The number of ICC decreased notably in hypertrophic ileum.

CONCLUSION

Enteric neurones change their levels of expression of neuromessengers in hypertrophic ileum. ICC are also affected. The changes are presumably part of an adaptive response to the increased work load.

Dissociation between electrical and mechanical responses to nitrergic stimulation in the canine gastric fundus

1. We examined the relationships between membrane potential, intracellular [Ca2+] ([Ca2+]i), and tension in muscles of the canine gastric fundus in response to nitrergic stimulation by NO donors and electrical field stimulation (EFS) of intrinsic enteric inhibitory neurons when adrenergic and cholinergic responses were blocked. 2. NO donors reduced [Ca2+]i and tension in a concentration-dependent manner. A close relationship was noted between these parameters. 3. In terms of the [Ca2+] vs. force relationship, relaxation responses to EFS differed from responses to NO donors. EFS resulted in smaller decreases in [Ca2+]i to produce a given relaxation compared with responses to NO donors. Thus, muscles stimulated with EFS were less sensitive to [Ca2+]i than muscles stimulated with exogenous NO. 4. When membrane potential, [Ca2+]i and tension were monitored simultaneously in the same muscles, a temporal dissociation was noted between the electrical responses and changes in [Ca2+]i and tension. Brief electrical responses were associated with more sustained changes in [Ca2+]i and tension. 5. Further dissociation between electrical and mechanical effects was noted. Changes in [Ca2+]i and tension caused by sodium nitroprusside and EFS were blocked by arginine analogues and by oxyhaemoglobin, but electrical responses were unaffected. 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase, also blocked the effects of nitrergic stimulation on [Ca2+]i and tension, without affecting hyperpolarization. Thus, in the presence of continued hyperpolarization, the reductions in [Ca2+]i and tension caused by nitrergic stimulation were blocked. 6. Block of hyperpolarization in response to nitrergic stimulation with tetrapentylammonium chloride (TPEA) had relatively little effect on the [Ca2+]i and tension responses. Thus, hyperpolarization is not required for nitrergic effects on [Ca2+]i and tension. 7. In summary, reduction in [Ca2+]i and tension in response to nitrergic stimulation of the canine gastric fundus does not depend upon electrical hyperpolarization. Non-electrical mechanisms such as enhanced uptake of Ca2+ by the sarcoplasmic reticulum or reduction in the Ca2+ sensitivity of the contractile apparatus may be the primary mechanisms mediating nitrergic responses in these muscles.

The identification and chemical coding of cholinergic neurons in the small and large intestine of the mouse

BACKGROUND

The recent availability of antisera to the vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT) that demonstrate peripheral cholinergic neurons has made possible the anatomical identification of cholinergic neurons in the enteric nervous system. In this study, we localised cholinergic neurons in the mouse small and large intestine and identified which substances are found colocalised in the cholinergic neurons.

METHODS

Immunohistochemical single and double staining techniques were used on whole mount preparations and frozen sections to examine the localisation and chemical coding of cholinergic neurons in the small and large intestine of the mouse. Cholinergic neurons were identified using antisera to ChAT or VAChT.

RESULTS

In both the small and large intestine, numerous ChAT-immunoreactive nerve cell bodies were present in the myenteric and submucous ganglia, and ChAT- and VAChT-immunoreactive nerve terminals were abundant in the myenteric and submucous plexuses and the external muscle. Previous studies have identified two major classes of myenteric neurons in the small intestine of the mouse--those containing calretinin plus substance P, and those containing nitric oxide synthase (NOS) plus vasoactive intestinal peptide (VIP). Double-label studies showed that the vast majority of the calretinin/substance P neurons were cholinergic neurons, whereas only a small proportion of the NOS/VIP cells were cholinergic; the noncholinergic NOS/VIP neurons were motor neurons or interneurons, whereas the cholinergic NOS/VIP neurons appeared to be exclusively interneurons. In the small intestine, all of the 5-HT-loaded neurons and a subpopulation of the calbindin neurons were also cholinergic. In the large intestine, there was a pattern of overlaps similar to that found in the small intestine, except that in the large intestine approximately 25% of the calretinin cells were not cholinergic. Only approximately one third of the GABA-loaded neurons in the large intestine were cholinergic.

CONCLUSIONS

Large subpopulations of motor neurons and interneurons in the mouse small intestine are cholinergic neurons.

Defective smooth muscle regulation in cGMP kinase I-deficient mice

Regulation of smooth muscle contractility is essential for many important biological processes such as tissue perfusion, cardiovascular haemostasis and gastrointestinal motility. While an increase in calcium initiates smooth muscle contraction, relaxation can be induced by cGMP or cAMP. cGMP-dependent protein kinase I (cGKI) has been suggested as a major mediator of the relaxant effects of both nucleotides. To study the biological role of cGKI and its postulated cross-activation by cAMP, we inactivated the gene coding for cGKI in mice. Loss of cGKI abolishes nitric oxide (NO)/cGMP-dependent relaxation of smooth muscle, resulting in severe vascular and intestinal dysfunctions. However, cGKI-deficient smooth muscle responded normally to cAMP, indicating that cAMP and cGMP signal via independent pathways, with cGKI being the specific mediator of the NO/cGMP effects in murine smooth muscle.

Immunohistochemical study of the c-kit expressing cells and connexin 43 in the guinea-pig digestive tract

The distribution of the c-kit receptor expressing cells and gap junction protein, connexin (Cx) 43 in the guinea-pig stomach (antrum), small intestine (jejunum) and colon (ascending) was studied by immunohistochemistry. The anti-c-kit protein immunopositive cells were regularly observed in the myenteric region throughout all three organs. The immunopositive cells were also sparsely distributed in the circular muscle layer of both the stomach and the colon, but not in the small intestine. They were densely located in the regions of the deep muscular plexus (DMP) of the small intestine and submuscular plexus (SMP) of the colon. In contrast, strong immunoreactivity to anti-Cx 43 antibody was observed in almost the entire thickness of the circular muscle layer of the stomach and the small intestine, but not in the colon. Dense immunoreaction deposits were observed in the region of the DMP and SMP. However, only very weak immunoreactivity to anti-Cx 43 antibody was detected in the myenteric region of all three organs. These results suggest that the c-kit receptor expressing cells or interstitial cells of Cajal (ICC) in the myenteric region of the three organs, and in the SMP of the colon, are poorly coupled with the bulk of circular muscle tissue by gap junctions, while ICC in the DMP and in the circular muscle layer of the stomach couple well with the surrounding muscle tissue.

Development of electrical rhythmicity in the murine gastrointestinal tract is specifically encoded in the tunica muscularis

1. Interstitial cells of Cajal (ICCs) have been identified as pacemaker cells in the gastrointestinal (GI) tracts of vertebrates. We have studied the development of ICCs in pacemaker regions and the onset of electrical rhythmicity in the gastric antrum, small bowel and proximal colon of the mouse. 2. ICCs, as detected by c-Kit immunofluorescence, were found during embryogenesis in regions of the GI tract that eventually become pacemaker areas. Prior to birth, these cells were organized into well-structured networks, and by the end of the embryonic period the morphology of ICC networks in pacemaker regions appeared very similar to that observed in adult animals. 3. Electrical rhythmicity was recorded prior to birth (by E18) in the proximal GI tract (stomach and jejunum), and this activity developed to adult-like behaviour within a week after birth. In the ileum and proximal colon rhythmicity developed after birth, and adult-like characteristics were apparent within the first week. 4. Post-junctional responses of smooth muscles to neural inputs could be recorded at birth, and stimulation of intrinsic nerves often led to oscillatory activity resembling slow waves for up to several minutes following brief stimuli. Nerve stimulation augmented spontaneous activity in the proximal portions of the GI tract and elicited rhythmic activity temporarily in quiescent tissues of the distal GI tract. 5. ICCs and rhythmicity developed in an apparently normal manner in tissues isolated at birth and placed in organ culture. These data suggest that the tunica muscularis provides a suitable microenvironment for the development of ICCs and rhythmicity without the need for extrinsic stimuli. 6. Treatment of small intestinal tissues taken from embryos at E15 with neutralizing c-Kit antibodies abolished ICC development and the organization of ICCs into networks that typically occurs during the late embryonic period. Treatment of muscles taken from newborn animals with c-Kit antibodies blocked postnatal development of ICCs, disrupted already established and functional ICC networks, and rendered muscles electrically quiescent. 7. In summary, ICC networks develop in the pacemaker regions of the murine GI tract before birth. Development and organization of ICCs of the myenteric plexus region into networks precedes the development of electrical rhythmicity. Post-natal development of electrical rhythmicity is mainly characterized by enhancement of the amplitude and frequency of slow waves. The development of ICCs and electrical rhythmicity persists in vitro. ICCs appear to be necessary for the initiation of electrical rhythmicity. These findings provide further evidence for the pacemaker role of ICCs.

Interstitial cells of Cajal as targets for pharmacological intervention in gastrointestinal motor disorders

Interstitial cells of Cajal (ICCs) have recently been identified as the pacemaker cells for contractile activity of the gastrointestinal tract. These cells generate the electrical 'slow-wave' activity that determines the characteristic frequency of phasic contractions of the stomach, intestine and colon. Slow waves also determine the direction and velocity of propagation of peristaltic activity, in concert with the enteric nervous system. Characterization of receptors and ion channels in the ICC membrane is under way, and manipulation of slow-wave activity markedly alters movement of contents through the gut organs. Here Jan Huizinga, Lars Thuneberg, Jean-Marie Vanderwinden and Jüri Rumessen, suggest that, as ICCs are unique to the gut, they might be ideal targets for pharmacological intervention in gastrointestinal motility disorders, which are very common and costly.

Basal release of nitric oxide induces an oscillatory motor pattern in canine colon

1. The consequences of intrinsic, basal nitric oxide release on electrical and contractile activity of canine proximal colon were examined. Membrane potential and contraction were simultaneously recorded from the circular muscle in the presence of drugs to block adrenergic and cholinergic responses. 2. Electrical slow waves were recorded from muscle cells near the submucosal surface of the circular layer. Spontaneous contractions were initiated by each slow wave. Contractile amplitude increased 1.9-fold when nerves were blocked with tetrodotoxin (TTX, 1 microM). 3. Muscle cells near the myenteric surface displayed myenteric potential oscillations (MPOs) averaging 16 cycles per minute (c.p.m.) in frequency and 10 mV in amplitude. Twenty-five per cent of muscles displayed an additional slow, neurogenic oscillation (mean frequency, 1 c.p.m.; amplitude, 14 mV) superimposed upon the MPO rhythm. 4. The nitric oxide (NO) synthase inhibitor N omega -nitro-L-arginine (L-NA, 100 microM; n = 16) abolished neurogenic oscillations, depolarized cells, and increased MPO upstroke velocity, amplitude and frequency. The actions of L-NA were mimicked by N omega-nitro-L-arginine methylester (L-NAME, 100 microM) and oxyhaemoglobin (3%). 5. Spontaneous contractions were increased 2.3-fold by L-NA, and TTX had no effect on contractions after addition of L-NA. 6. The NO-donor sodium nitroprusside (SNP, 1 microM) reversed the electrical and mechanical effects of L-NA and initiated slow oscillations similar to the neurogenic oscillations. Slow oscillations were also evoked with S-nitroso-N-acetylpenicillamine (SNAP, 1 microM). The effects of NO donors were blocked by oxyhaemoglobin. 7. Slow electrical oscillations could not be elicited by SNP after removal of a thin strip of circular muscle along the myenteric edge. 8. These data suggest that the spontaneous electrical and contractile activity of the proximal colon is tonically suppressed by basal release of NO. Basal NO causes an oscillatory pattern of electrical and mechanical activity. This activity does not require patterned firing of nerves; rather a continuous, low level release of NO would be capable of producing the neurogenic oscillatory behaviour. The slow oscillatory activity depends upon the presence of the myenteric region of the circular muscle layer, which contains cell bodies of enteric neurons and interstitial cells of Cajal.

Enteric neurons express Steel factor-lacZ transgene in the murine gastrointestinal tract

The cells that express Steel factor (SLF) in the gastrointestinal (GI) tract were studied using SLF-lacZ transgenic mice. Expression, detected by beta-galactosidase histochemistry, was evident in cells between the circular and longitudinal muscle layers in the GI tract. Double staining with antibodies specific for the neural markers, PGP 9.5, MAP2 and c-Ret, showed that SLF-lacZ positive cells were enteric neurons. Enteroglia did not express SLF-lacZ. The distribution of expressing cells was complimentary to the expression of c-Kit in myenteric interstitial cells.