Pacing of interstitial cells of Cajal in the murine gastric antrum: neurally mediated and direct stimulation

Interstitial cells of the sip syncytium regulate basal membrane potential in murine gastric corpus

Smooth muscle cells (SMCs), Interstitial cells of Cajal (ICC) and Platelet-derived growth factor receptor α positive (PDGFRα+) cells form an integrated, electrical syncytium within the gastrointestinal (GI) muscular tissues known as the SIP syncytium. Immunohistochemical analysis of gastric corpus muscles showed that c-KIT+/ANO1+ ICC-IM and PDGFRα+ cells were closely apposed to one another in the same anatomical niches. We used intracellular microelectrode recording from corpus muscle bundles to characterize the roles of intramuscular ICC and PDGFRα+ cells in conditioning membrane potentials of gastric muscles. In muscle bundles, that have a relatively higher input impedance than larger muscle strips or sheets, we recorded an ongoing discharge of stochastic fluctuations in membrane potential, previously called unitary potentials or spontaneous transient depolarizations (STDs) and spontaneous transient hyperpolarizations (STHs). We reasoned that STDs should be blocked by antagonists of ANO1, the signature conductance of ICC. Activation of ANO1 has been shown to generate spontaneous transient inward currents (STICs), which are the basis for STDs. Ani9 reduced membrane noise and caused hyperpolarization, but this agent did not block the fluctuations in membrane potential quantitatively. Apamin, an antagonist of small conductance Ca2+-activated K+ channels (SK3), the signature conductance in PDGFRα+ cells, further reduced membrane noise and caused depolarization. Reversing the order of channel antagonists reversed the sequence of depolarization and hyperpolarization. These experiments show that the ongoing discharge of STDs and STHs by ICC and PDGFRα+ cells, respectively, exerts conditioning effects on membrane potentials in the SIP syncytium that would effectively regulate the excitability of SMCs.

Mapping the rat gastric slow-wave conduction pathway: bridging in vitro and in vivo methods, revealing a loosely coupled region in the distal stomach

Rhythmic electrical events, termed slow waves, govern the timing and amplitude of phasic contractions of the gastric musculature. Extracellular multielectrode measurement of gastric slow waves can be a biomarker for phenotypes of motility dysfunction. However, a gastric slow-wave conduction pathway for the rat, a common animal model, is unestablished. In this study, the validity of extracellular recording was demonstrated in vitro with simultaneous intracellular and extracellular recordings and by pharmacological inhibition of slow waves. The conduction pathway was determined by in vivo extracellular recordings while considering the effect of motion. Slow-wave characteristics [means (SD)] varied regionally having higher amplitude in the antrum than the distal corpus [1.03 (0.12) mV vs. 0.75 (0.31) mV; n = 7; P = 0.025 paired t test] and faster propagation near the greater curvature than the lesser curvature [1.00 (0.14) mm·s-1 vs. 0.74 (0.14) mm·s-1; n = 9 GC, 7 LC; P = 0.003 unpaired t test]. Notably, in some subjects, separate wavefronts propagated near the lesser and greater curvatures with a loosely coupled region occurring in the area near the distal corpus midline at the interface of the two wavefronts. This region had either the greater or lesser curvature wavefront propagating through it in a time-varying manner. The conduction pattern suggests that slow waves in the rat stomach form annular wavefronts in the antrum and not the corpus. This study has implications for interpretation of the relationship between slow waves, the interstitial cells of Cajal network structure, smooth muscles, and gastric motility.NEW & NOTEWORTHY Mapping of rat gastric slow waves showed regional variations in their organization. In some subjects, separate wavefronts propagated near the lesser and greater curvatures with a loosely coupled region near the midline, between the wavefronts, having a varying slow-wave origin. Furthermore, simultaneous intracellular and extracellular recordings were concordant and independent of movement artifacts, indicating that extracellular recordings can be interpreted in terms of their intracellular counterparts when intracellular recording is not possible.

Vectorgastrogram: dynamic trajectory and recurrence quantification analysis to assess slow wave vector movement in healthy subjects

Functional gastric disorders entail chronic or recurrent symptoms, high prevalence and a significant financial burden. These disorders do not always involve structural abnormalities and since they cannot be diagnosed by routine procedures, electrogastrography (EGG) has been proposed as a diagnostic alternative. However, the method still has not been transferred to clinical practice due to the difficulty of identifying gastric activity because of the low-frequency interference caused by skin-electrode contact potential in obtaining spatiotemporal information by simple procedures. This work attempted to robustly identify the gastric slow wave (SW) main components by applying multivariate variational mode decomposition (MVMD) to the multichannel EGG. Another aim was to obtain the 2D SW vectorgastrogram VGGSW from 4 electrodes perpendicularly arranged in a T-shape and analyse its dynamic trajectory and recurrence quantification (RQA) to assess slow wave vector movement in healthy subjects. The results revealed that MVMD can reliably identify the gastric SW, with detection rates over 91% in fasting postprandial subjects and a frequency instability of less than 5.3%, statistically increasing its amplitude and frequency after ingestion. The VGGSW dynamic trajectory showed a statistically higher predominance of vertical displacement after ingestion. RQA metrics (recurrence ratio, average length, entropy, and trapping time) showed a postprandial statistical increase, suggesting that gastric SW became more intense and coordinated with a less complex VGGSW and higher periodicity. The results support the VGGSW as a simple technique that can provide relevant information on the "global" spatial pattern of gastric slow wave propagation that could help diagnose gastric pathologies.

Calcium transients in intramuscular interstitial cells of Cajal of the murine gastric fundus and their regulation by neuroeffector transmission

KEY POINTS

The cells responsible for mediating enteric neuroeffector transmission remain controversial. In the stomach intramuscular interstitial cells of Cajal (ICC-IM) were the first ICC reported to receive cholinergic and nitrergic neural inputs. Utilization of a cell specific calcium biosensor, GCaMP6f, the activity and neuroeffector responses of ICC-IM were examined. ICC-IM were highly active, generating stochastic intracellular Ca²⁺ -transients. Stimulation of enteric motor nerves abolished Ca²⁺ -transients in ICC-IM. This inhibitory response was preceded by a global rise in intracellular Ca²⁺ . Individual ICC-IM responded to nerve stimulation with a rise in Ca²⁺ followed by inhibition of Ca²⁺ -transients. Inhibition of Ca²⁺ -transients was blocked by the nitric oxide synthase antagonist, L-NNA. The global rise in Ca²⁺ was inhibited by the muscarinic antagonist, atropine. Simultaneous intracellular recordings with video imaging revealed that the global rise in intracellular Ca²⁺ and inhibition of Ca²⁺ -transients was temporally associated with rapid excitatory junction potentials followed by more sustained inhibitory junction potentials. The data presented support the premise of serial innervation of ICC-IM in excitatory and inhibitory neuroeffector transmission in the proximal stomach.

ABSTRACT

Enteric neurotransmission is critical for coordinating motility throughout the gastrointestinal (GI) tract. However, there is considerable controversy regarding the cells that are responsible for the transduction of these neural inputs. In the present study, utilization of a cell-specific calcium biosensor GCaMP6f, the spontaneous activity and neuroeffector responses of intramuscular ICC (ICC-IM) to motor neural inputs was examined. Simultaneous intracellular microelectrode recordings and high-speed video-imaging during nerve stimulation was used to reveal the temporal relationship between changes in intracellular Ca²⁺ and post-junctional electrical responses to neural stimulation. ICC-IM were highly active, generating intracellular Ca²⁺ -transients that occurred stochastically, from multiple independent sites in single ICC-IM. Ca²⁺ -transients were not entrained in single ICC-IM or between neighboring ICC-IM. Activation of enteric motor neurons produced a dominant inhibitory response that abolished Ca²⁺ -transients in ICC-IM. This inhibitory response was often preceded by a summation of Ca²⁺ -transients that led to a global rise in Ca²⁺ . Individual ICC-IM responded to nerve stimulation by a global rise in Ca²⁺ followed by inhibition of Ca²⁺ -transients. The inhibition of Ca²⁺ -transients was blocked by the nitric oxide synthase antagonist, L-NNA. The global rise in intracellular Ca²⁺ was inhibited by the muscarinic antagonist, atropine. Simultaneous intracellular microelectrode recordings with video-imaging revealed that the rise in Ca²⁺ was temporally associated with rapid excitatory junction potentials and the inhibition of Ca²⁺ -transients with inhibitory junction potentials. These data support the premise of serial innervation of ICC-IM in excitatory and inhibitory neuroeffector transmission in the proximal stomach. Abstract figure legend Intramuscular interstitial cells of Cajal (ICC-IM) of the gastric fundus receive nitrergic inhibitory and cholinergic excitatory neuroeffector motor inputs. Using a genetically encoded calcium sensor we demonstrate that ICC-IM are highly active cells generating stochastic intracellular Ca2 -transients. Stimulation of enteric motor nerves abolished Ca2 -transients in ICC-IM, produced an inhibitory junction potential (IJP) and muscle relaxation that was mediated by nitric oxide (left hand side of figure). This inhibitory response was often preceded by a global rise in intracellular Ca2 in ICC-IM, a rapid excitatory junction potential (EJP) and muscle contraction, that was mediated by acetylcholine (right hand side of figure). Individual ICC-IM could respond to both excitatory and inhibitory neural inputs. These data support the premise of serial innervation of ICC-IM in excitatory and inhibitory neuroeffector transmission in the proximal stomach. This article is protected by copyright. All rights reserved.

Mathematical Modeling of Gastric Slow Waves During Electrical Field Stimulation

While neural modulation has been trialed as a therapy for functional gastric motility disorders, a computational model that guides stimulation protocol does not exist. In this work, a mathematical model of gastric slow wave activity, which incorporates the effects of neurotransmitter release during electrical field stimulation (EFS), was developed. Slow wave frequency responses due to the release of acetylcholine and slow wave amplitude responses due to the release of nitric oxide were modeled. The model was calibrated using experimental data from literature. A sensitivity analysis was conducted, which showed that the model yielded stable, periodic solutions for EFS frequencies in the range 0-20 Hz. A 25% increase in the input parameter (EFS frequency) from 5 Hz to 6.25 Hz resulted in a 5.2% increase in slow wave frequency and a 3.2 % decrease in slow wave amplitude. Simulated EFS showed that, for stimulation at 15 Hz, with blocking of the nitrergic neurotransmitter pathway the slow wave increased from the no stimulation scenario in frequency by only 2.4x compared to 2.7x when the nitrergic pathway was not blocked. A 21 % reduction in slow wave amplitude occurred when the cholinergic pathway was blocked, compared to a 46% reduction when no neurotransmitter pathways were blocked. Clinical relevance - This mathematical model is a step towards successful computational modeling of the effects ther-apeutic neural stimulation on the stomach. The model is also a tool for understanding of the physiology of neural stimulation.

Changes in interstitial cells and gastric excitability in a mouse model of sleeve gastrectomy

Obesity is a critical risk factor of several life-threatening diseases and the prevalence in adults has dramatically increased over the past ten years. In the USA the age-adjusted prevalence of obesity in adults was 42.4%, i.e., with a body mass index (BMI, weight (kg)/height (m)²) that exceeds 30 kg/m². Obese individuals are at the higher risk of obesity-related diseases, co-morbid conditions, lower quality of life, and increased mortality more than those in the normal BMI range i.e., 18.5–24.9 kg/m². Surgical treatment continues to be the most efficient and scientifically successful treatment for obese patients. Sleeve gastrectomy or vertical sleeve gastrectomy (VSG) is a relatively new gastric procedure to reduce body weight but is now the most popular bariatric operation. To date there have been few studies examining the changes in the cellular components and pacemaker activity that occur in the gastric wall following VSG and whether normal gastric activity recovers following VSG. In the present study we used a murine model to investigate the chronological changes of gastric excitability including electrophysiological, molecular and morphological changes in the gastric musculature following VSG. There is a significant disruption in specialized interstitial cells of Cajal in the gastric antrum following sleeve gastrectomy. This is associated with a loss of gastric pacemaker activity and post-junctional neuroeffector responses. Over a 4-month recovery period there was a gradual return in interstitial cells of Cajal networks, pacemaker activity and neural responses. These data describe for the first time the changes in gastric interstitial cells of Cajal networks, pacemaker activity and neuroeffector responses and the time-dependent recovery of ICC networks and normalization of motor activity and neural responses following VSG.

Analysis of Regional Variations of the Interstitial Cells of Cajal in the Murine Distal Stomach Informed by Confocal Imaging and Machine Learning Methods

Introduction

The network of Interstitial Cells of Cajal (ICC) plays a plethora of key roles in maintaining, coordinating, and regulating the contractions of the gastrointestinal (GI) smooth muscles. Several GI functional motility disorders have been associated with ICC degradation. This study extended a previously reported 2D morphological analysis and applied it to 3D spatial quantification of three different types of ICC networks in the distal stomach guided by confocal imaging and machine learning methods. The characterization of the complex changes in spatial structure of the ICC network architecture contributes to our understanding of the roles that different types of ICC may play in post-prandial physiology, pathogenesis, and/or amelioration of GI dsymotility- bridging structure and function.

Methods

A validated classification method using Trainable Weka Segmentation was applied to segment the ICC from a confocal dataset of the gastric antrum of a transgenic mouse, followed by structural analysis of the segmented images.

Results

The machine learning model performance was compared to manually segmented subfields, achieving an area under the receiver-operating characteristic (AUROC) of 0.973 and 0.995 for myenteric ICC (ICC-MP; n = 6) and intramuscular ICC (ICC-IM; n = 17). The myenteric layer in the distal antrum increased in thickness (from 14.5 to 34 μm) towards the lesser curvature, whereas the thickness decreased towards the lesser curvature in the proximal antrum (17.7 to 9 μm). There was an increase in ICC-MP volume from proximal to distal antrum (406,960 ± 140,040 vs. 559,990 ± 281,000 μm³; p = 0.000145). The % of ICC volume was similar for ICC-LM and for ICC-CM between proximal (3.6 ± 2.3% vs. 3.1 ± 1.2%; p = 0.185) and distal antrum (3.2 ± 3.9% vs. 2.5 ± 2.8%; p = 0.309). The average % volume of ICC-MP was significantly higher than ICC-IM at all points throughout sample (p < 0.0001).

Conclusions

The segmentation and analysis methods provide a high-throughput framework of investigating the structural changes in extended ICC networks and their associated physiological functions in animal models.

Antral Variation of Murine Gastric Pacemaker Cells Informed by Confocal Imaging and Machine Learning Methods

The Interstitial Cells of Cajal (ICC) are specialized gastrointestinal (GI) pacemaker cells that generate and actively propagate electrophysiological events called slow waves. Slow waves regulate the GI motility necessary for digestion. Several functional GI motility disorders have been associated with depletion in the ICC. In this study, a validated Fast Random Forest (FRF) classification method using Trainable WEKA Segmentation for segmenting the networks of ICC was applied to confocal microscopy images of a whole mount tissue from the distal antrum of a mouse stomach (583 × 3,376 × 133 μm³, parcellated into 24 equal image stacks). The FRF model performance was compared to 6 manually segmented subflelds and produced an area under the receiver-operating characteristic (AUROC) of 0.95. Structural variations of ICC network in the longitudinal muscle (ICC-LM) and myenteric plexus (ICC-MP) were quantified. The average volume of ICC-MP was significantly higher than ICC-LM at any point throughout the antral tissue sampled. There was a pronounced decline of up to 80% in ICC-LM (from 3,705 μm³ to 716 μm³) over a distance of 279.3 μm, that eventually diminished towards the distal antrum. However, an inverse relationship was observed in ICC-MP with an overall increase of up to 157% (from 59,100 μm³ to 151,830 μm³) over a distance of approximately 2 mm that proceeds towards the distal antrum.

Ca2+ transients in ICC-MY define the basis for the dominance of the corpus in gastric pacemaking

Myenteric interstitial cells of Cajal (ICC-MY) generate and actively propagate electrical slow waves in the stomach. Slow wave generation and propagation are altered in gastric motor disorders, such as gastroparesis, and the mechanism for the gradient in slow wave frequency that facilitates proximal to distal propagation of slow waves and normal gastric peristalsis is poorly understood.  Slow waves depend upon Ca2+-activated Cl- channels (encoded by Ano1). We characterized Ca2+ signaling in ICC-MY in situ using mice engineered to have cell-specific expression of GCaMP6f in ICC. Ca2+ signaling differed in ICC-MY in corpus and antrum. Localized Ca2+ transients were generated from multiple firing sites and were organized into Ca2+ transient clusters (CTCs). Ca2+ transient refractory periods occurred upon cessation of CTCs, but a relatively higher frequency of Ca2+ transients persisted during the inter-CTC interval in corpus than in antrum ICC-MY. The onset of Ca2+ transients after the refractory period was associated with initiation of the next CTC. Thus, CTCs were initiated at higher frequencies in corpus than in antrum ICC-MY. Initiation and propagation of CTCs (and electrical slow waves) depends upon T-type Ca2+ channels, and durations of CTCs relied upon L-type Ca2+ channels. The durations of CTCs mirrored the durations of slow waves. CTCs and Ca2+ transients between CTCs resulted from release of Ca2+ from intracellular stores and were maintained, in part, by store-operated Ca2+ entry. Our data suggest that Ca2+ release and activation of Ano1 channels both initiate and contribute to the plateau phase of slow waves.

Evidence for tetrodotoxin-resistant spontaneous myogenic contractions of mouse isolated stomach that are dependent on acetylcholine

Background and Purpose

Gastric pacemaker cells, interstitial cells of Cajal (ICC), are believed to initiate myogenic (non‐neuronal) contractions. These become damaged in gastroparesis, associated with dysrhythmic electrical activity and nausea. We utilised mouse isolated stomach to model myogenic contractions and investigate their origin and actions of interstitial cells of Cajal modulators.

Experimental Approach

Intraluminal pressure was recorded following distension with a physiological volume; tone, contraction amplitude and frequency were quantified. Compounds were bath applied.

Key Results

The stomach exhibited regular large amplitude contractions (median amplitude 9.0 [4.7–14.8] cmH₂O, frequency 2.9 [2.5–3.4] c.p.m; n = 20), appearing to progress aborally. Tetrodotoxin (TTX, 10⁻⁶ M) had no effect on tone, frequency or amplitude but blocked responses to nerve stimulation. ω‐conotoxin GVIA (10⁻⁷ M) ± TTX was without effect on baseline motility. In the presence of TTX, (1) atropine (10⁻¹⁰–10⁻⁶ M) reduced contraction amplitude and frequency in a concentration‐related manner (pIC₅₀ 7.5 ± 0.3 M for amplitude), (2) CaCC channel (previously ANO1) inhibitors MONNA and CaCCinh‐A01 reduced contraction amplitude (significant at 10⁻⁵, 10⁻⁴ M respectively) and frequency (significant at 10⁻⁵ M), and (3), neostigmine (10⁻⁵ M) evoked a large, variable, increase in contraction amplitude, reduced by atropine (10⁻⁸–10⁻⁶ M) but unaffected (exploratory study) by the H1 receptor antagonist mepyramine (10⁻⁶ M).

Conclusions and Implications

The distended mouse stomach exhibited myogenic contractions, resistant to blockade of neural activity by TTX. In the presence of TTX, these contractions were prevented or reduced by compounds blocking interstitial cells of Cajal activity or by atropine and enhanced by neostigmine (antagonised by atropine), suggesting involvement of non‐neuronal ACh in their regulation.

Expression of the regulated isoform of the electrogenic Na+/HCO3- cotransporter, NBCe1, is enriched in pacemaker interstitial cells of Cajal

Interstitial cells of Cajal (ICCs) generate electrical slow waves, which are required for normal gastrointestinal motility. The mechanisms for generation of normal pacemaking are not fully understood. Normal gastrointestinal contractility^- and electrical slow-wave activity depend on the presence of extracellular HCO₃^-. Previous transcriptional analysis identified enrichment of mRNA encoding the electrogenic Na⁺/HCO₃^- cotransporter (NBCe1) gene (Slc4a4) in pacemaker myenteric ICCs in mouse small intestine. We aimed to determine the distribution of NBCe1 protein in ICCs of the mouse gastrointestinal tract and to identify the transcripts of the Slc4a4 gene in mouse and human small intestinal tunica muscularis. We determined the distribution of NBCe1 immunoreactivity (NBCe1-IR) by immunofluorescent labeling in mouse and human tissues. In mice, NBCe1-IR was restricted to Kit-positive myenteric ICCs of the stomach and small intestine and submuscular ICCs of the large intestine, that is, the slow wave generating subset of ICCs. Other subtypes of ICCs were NBCe1-negative. Quantitative real-time PCR identified >500-fold enrichment of Slc4a4-207 and Slc4a4-208 transcripts ["IP3-receptor-binding protein released by IP3" (IRBIT)-regulated isoforms] in Kit-expressing cells isolated from Kit^creERT2/+, Rpl22^tm1.1Psam/Sj mice and from single GFP-positive ICCs from Kit^tm1Rosay mice. Human jejunal tunica muscularis ICCs were also NBCe1-positive, and SLC4A4-201 and SLC4A4-204 RNAs were >300-fold enriched relative to SLC4A4-202. In summary, NBCe1 protein expressed in ICCs with electrical pacemaker function is encoded by Slc4a4 gene transcripts that generate IRBIT-regulated isoforms of NBCe1. In conclusion, Na⁺/HCO₃^- cotransport through NBCe1 contributes to the generation of pacemaker activity in subsets of ICCs.NEW & NOTEWORTHY In this study, we show that the electrogenic Na+/HCO₃^- cotransporter, NBCe1/Slc4a4, is expressed in subtypes of interstitial cells of Cajal (ICCs) responsible for electrical slow wave generation throughout the mouse gastrointestinal tract and is absent in other types of ICCs. The transcripts of Slc4a4 expressed in mouse ICCs and human gastrointestinal smooth muscle are the regulated isoforms. This indicates a key role for HCO₃^- transport in generation of gastrointestinal motility patterns.

Ameliorating effects of sacral neuromodulation on gastric and small intestinal dysmotility mediated via a sacral afferent-vagal efferent pathway

BACKGROUND/AIMS

In a recent study of sacral nerve stimulation (SNS) for colonic inflammation, a possible spinal-vagal pathway was implicated. The aim of this study was to provide evidence for such a pathway by investigating the effects of SNS on dysmotility of the stomach and duodenum that are not directly innervated by the sacral efferents.

METHODS

Twenty-seven rats were chronically implanted with wire electrodes for SNS and gastrointestinal slow waves. SNS was performed in several acute sessions to investigate its effects on gastric/duodenal slow waves and emptying/transit impaired by glucagon and rectal distention (RD).

RESULTS

(a) SNS increased the percentage of normal gastric slow waves impaired by glucagon (from 53.9% to 77.0%, P < .0001) and RD (from 64% to 78%, P = .037). This improvement was abolished by atropine. (b) Similar effects were observed with SNS on duodenal slow waves, which was also blocked by atropine. (c) SNS normalized delayed gastric emptying induced by glucagon (control: 61.3%, glucagon: 44.3%, glucagon + SNS: 65.8%) and RD (control: 61.3%, RD: 46.7%, RD + SNS: 64.3%). It also normalized small intestinal transit delayed by RD (P = .001, RD + SNS vs RD; P = .9, RD + SNS vs control). (4) Both glucagon and RD induced an increase in the sympathovagal ratio (P = .007, glucagon vs baseline; P < .001, RD vs baseline) and SNS decreased the ratio (P = .006, glucagon + SNS vs glucagon; P = .04, RD + SNS vs RD).

CONCLUSIONS

Neuromodulation of the sacral nerve improves gastric and small intestinal pacemaking activity and transit impaired by glucagon and RD by normalizing the sympathovagal balance via a retrograde neural pathway from the sacral nerve to vagal efferents.

Gastric smooth muscle cells manifest an abnormal phenotype in Parkinson's disease rats with gastric dysmotility

Gastroparesis is a common symptom in Parkinson's disease (PD) and whether any change occurs in gastric smooth muscle cells (SMCs) of PD patients is unclear. We previously reported that rats with bilateral substantia nigra lesions induced by 6-hydroxydopamine (6-OHDA), referred to as 6-OHDA rats, manifest typical gastroparesis. In the present study, we further investigate the underlying mechanism. By means of an organ bath system and an implantable radiotelemetry system, both a weakened contractile force of gastric circular smooth muscle and gastric myoelectric activity were detected in the 6-OHDA rats and phasic and tonic contractions elicited by carbachol or high concentration of potassium were significantly reduced in gastric circular muscle strips. A thickened smooth muscle layer was observed under a light microscope and an ultrastructure of hypertrophic SMCs, with increased caveolae and decreased dense bodies, was observed under transmission electron microscope. Furthermore, the mRNA and protein expression levels of contractile markers (myosin light chain 20, myosin heavy chain 11 and α-smooth muscle actin) and the transcription factor serum response factor (SRF) were significantly decreased, while the TNFα and IL-1β content was increased in the 6-OHDA rats. These results suggest that the decreased contractile force in 6-OHDA rats may be associated with the phenotypic abnormality observed in SMCs, which is due to downregulated contractile proteins induced by decreased SRF expression in the inflammatory muscular microenvironment.

Phenotypic changes of interstitial cells of Cajal after intestinal obstruction in rat model

The objective was to study the effect of mechanical intestinal obstruction in rats on the phenotype of interstitial cells of Cajal (ICC). Healthy Wistar rats were randomly divided into sham-operation group (C), one day obstruction group (M1), two days obstruction group (M2), and three days obstruction group (M3), with 10 rats in each group. The expression of SCF mRNA and c-Kit protein in intestinal tissue was investigated by RT-PCR and immunohistochemistry. Compared with the sham-operation group, the relative expression of SCF mRNA and the expression of c-Kit protein in intestinal tissue were significantly decreased in both obstruction groups. Levels decreased gradually with the prolongation of obstruction time, and significantly decreased on the 3rd day after obstruction (P<0.05). Immunohistochemical staining of the small intestine showed that the number of ICC in the sham-operation group was the highest, and they were gradually decreased with the extension of obstruction time in the M1 to M3 groups. There was a significant difference between groups (P<0.05). Intestinal obstruction caused a decrease in the concentrations of SCF mRNA and c-Kit protein in ICC. With the prolongation of intestinal obstruction, the number of ICCs gradually decreased.

Phytochemicals, pharmacology, clinical application, patents, and products of Amomi fructus

Amomi fructus (A. fructus) (Sharen) is a well-known traditional Chinese medicine widely used to treat gastrointestinal diseases. It has high medical and economic values, which have been confirmed both in vitro and in vivo studies. This review highlights the phytochemicals, pharmacology, clinical application, patents, and products of A. fructus. More than 100 phytochemicals have been isolated and identified from A. fructus, mainly including volatile oils, saponins, flavonoids, organic acids, inorganic ingredients, and polysaccharides. The main pharmacology of gastrointestinal protection, anti-inflammatory activity, analgesic activity, antidiarrheal activity, antibacterial activity, anti-microbial activity and hypoglycemic activity have been confirmed. The main clinical applications include functional digestion disorder, gastritis, helicobacter pylori infection in children and treatment of mastitis. There are 23 patents and 405 different drug products of A. fructus.

The cells and conductance mediating cholinergic neurotransmission in the murine proximal stomach

KEY POINTS

Enteric neurotransmission is essential for gastrointestinal (GI) motility, although the cells and conductances responsible for post-junctional responses are controversial. The calcium-activated chloride conductance (CaCC), anoctamin-1 (Ano1), was expressed by intramuscular interstitial cells of Cajal (ICC-IM) in proximal stomach and not resolved in smooth muscle cells (SMCs). Cholinergic nerve fibres were closely apposed to ICC-IM. Conductances activated by cholinergic stimulation in isolated ICC-IM and SMCs were determined. A CaCC was activated by carbachol in ICC-IM and a non-selective cation conductance in SMCs. Responses to cholinergic nerve stimulation were studied. Excitatory junction potentials (EJPs) and mechanical responses were evoked in wild-type mice but absent or greatly reduced with knockout/down of Ano1. Drugs that block Ano1 inhibited the conductance activated by carbachol in ICC-IM and EJPs and mechanical responses in tissues. The data of the present study suggest that electrical and mechanical responses to cholinergic nerve stimulation are mediated by Ano1 expressed in ICC-IM and not SMCs.

ABSTRACT

Enteric motor neurotransmission is essential for normal gastrointestinal (GI) motility. Controversy exists regarding the cells and ionic conductance(s) that mediate post-junctional neuroeffector responses to motor neurotransmitters. Isolated intramuscular ICC (ICC-IM) and smooth muscle cells (SMCs) from murine fundus muscles were used to determine the conductances activated by carbachol (CCh) in each cell type. The calcium-activated chloride conductance (CaCC), anoctamin-1 (Ano1) is expressed by ICC-IM but not resolved in SMCs, and CCh activated a Cl- conductance in ICC-IM and a non-selective cation conductance in SMCs. We also studied responses to nerve stimulation using electrical-field stimulation (EFS) of intact fundus muscles from wild-type and Ano1 knockout mice. EFS activated excitatory junction potentials (EJPs) in wild-type mice, although EJPs were absent in mice with congenital deactivation of Ano1 and greatly reduced in animals in which the CaCC-Ano1 was knocked down using Cre/loxP technology. Contractions to cholinergic nerve stimulation were also greatly reduced in Ano1 knockouts. SMCs cells also have receptors and ion channels activated by muscarinic agonists. Blocking acetylcholine esterase with neostigmine revealed a slow depolarization that developed after EJPs in wild-type mice. This depolarization was still apparent in mice with genetic deactivation of Ano1. Pharmacological blockers of Ano1 also inhibited EJPs and contractile responses to muscarinic stimulation in fundus muscles. The data of the present study are consistent with the hypothesis that ACh released from motor nerves binds muscarinic receptors on ICC-IM with preference and activates Ano1. If metabolism of acetylcholine is inhibited, ACh overflows and binds to extrajunctional receptors on SMCs, eliciting a slower depolarization response.

Inhibitory responses mediated by vagal nerve stimulation are diminished in stomachs of mice with reduced intramuscular interstitial cells of Cajal

Intramuscular interstitial cells of Cajal (ICC-IM) are closely associated with enteric motor nerve terminals and electrically coupled to smooth muscle cells within the gastric musculature. Previous studies investigating the role of ICC-IM in motor neurotransmission have used indiscriminate electric field stimulation of neural elements within the gastric wall. To determine the role of ICC-IM in transduction of vagally-mediated motor input to gastric muscles electrical and mechanical responses to selective electrical vagal stimulation (EVS) were recorded from gastric fundus and antral regions of wild type and W/W^V mice, which lack most ICC-IM. EVS evoked inhibitory junction potentials (IJPs) in wild type muscles that were attenuated or abolished by L-NNA. IJPs were rarely evoked in W/W^V muscles by EVS, and not affected by L-NNA. EVS evoked relaxation of wild type stomachs, but the predominant response of W/W^V stomachs was contraction. EVS applied after pre-contraction with bethanechol caused relaxation of wild type gastric tissues and these were inhibited by the nitric oxide synthase inhibitor L-NNA. Relaxation responses were of smaller amplitude in W/W^V muscles and L-NNA did not attenuate relaxation responses in W/W^V fundus muscles. These data suggest an important role for ICC-IM in vagally-mediated nitrergic relaxation in the proximal and distal stomach.

Insights into the mechanisms underlying colonic motor patterns

In recent years there have been significant technical and methodological advances in our ability to record the movements of the gastrointestinal tract. This has led to significant changes in our understanding of the different types of motor patterns that exist in the gastrointestinal tract (particularly the large intestine) and in our understanding of the mechanisms underlying their generation. Compared with other tubular smooth muscle organs, a rich variety of motor patterns occurs in the large intestine. This reflects a relatively autonomous nervous system in the gut wall, which has its own unique population of sensory neurons. Although the enteric nervous system can function independently of central neural inputs, under physiological conditions bowel motility is influenced by the CNS: if spinal pathways are disrupted, deficits in motility occur. The combination of high resolution manometry and video imaging has improved our knowledge of the range of motor patterns and provided some insight into the neural and mechanical factors underlying propulsion of contents. The neural circuits responsible for the generation of peristalsis and colonic migrating motor complexes have now been identified to lie within the myenteric plexus and do not require inputs from the mucosa or submucosal ganglia for their generation, but can be modified by their activity. This review will discuss the recent advances in our understanding of the different patterns of propagating motor activity in the large intestine of mammals and how latest technologies have led to major changes in our understanding of the mechanisms underlying their generation.

Mechanisms of Electrical Activation and Conduction in the Gastrointestinal System: Lessons from Cardiac Electrophysiology

The gastrointestinal (GI) tract is an electrically excitable organ system containing multiple cell types, which coordinate electrical activity propagating through this tract. Disruption in its normal electrophysiology is observed in a number of GI motility disorders. However, this is not well characterized and the field of GI electrophysiology is much less developed compared to the cardiac field. The aim of this article is to use the established knowledge of cardiac electrophysiology to shed light on the mechanisms of electrical activation and propagation along the GI tract, and how abnormalities in these processes lead to motility disorders and suggest better treatment options based on this improved understanding. In the first part of the article, the ionic contributions to the generation of GI slow wave and the cardiac action potential (AP) are reviewed. Propagation of these electrical signals can be described by the core conductor theory in both systems. However, specifically for the GI tract, the following unique properties are observed: changes in slow wave frequency along its length, periods of quiescence, synchronization in short distances and desynchronization over long distances. These are best described by a coupled oscillator theory. Other differences include the diminished role of gap junctions in mediating this conduction in the GI tract compared to the heart. The electrophysiology of conditions such as gastroesophageal reflux disease and gastroparesis, and functional problems such as irritable bowel syndrome are discussed in detail, with reference to ion channel abnormalities and potential therapeutic targets. A deeper understanding of the molecular basis and physiological mechanisms underlying GI motility disorders will enable the development of better diagnostic and therapeutic tools and the advancement of this field.

Regulation of gastric electrical and mechanical activity by cholinesterases in mice

Background/Aims

Gastric peristalsis begins in the orad corpus and propagates to the pylorus. Directionality of peristalsis depends upon orderly generation and propagation of electrical slow waves and a frequency gradient between proximal and distal pacemakers. We sought to understand how chronotropic agonists affect coupling between corpus and antrum.

Methods

Electrophysiological and imaging techniques were used to investigate regulation of gastric slow wave frequency by muscarinic agonists in mice. We also investigated the expression and role of cholinesterases in regulating slow wave frequency and motor patterns in the stomach.

Results

Both acetycholinesterase (Ache) and butyrylcholine esterase (Bche) are expressed in gastric muscles and AChE is localized to varicose processes of motor neurons. Inhibition of AChE in the absence of stimulation increased slow wave frequency in corpus and throughout muscle strips containing corpus and antrum. CCh caused depolarization and increased slow wave frequency. Stimulation of cholinergic neurons increased slow wave frequency but did not cause depolarization. Neostigmine (1 μM) increased slow wave frequency, but uncoupling between corpus and antrum was not detected. Motility mapping of contractile activity in gastric muscles showed similar effects of enteric nerve stimulation on the frequency and propagation of slow waves, but neostigmine (> 1 μM) caused aberrant contractile frequency and propagation and ectopic pacemaking.

Conclusions

Our data show that slow wave uncoupling is difficult to assess with electrical recording from a single or double sites and suggest that efficient metabolism of ACh released from motor neurons is an extremely important regulator of slow wave frequency and propagation and gastric motility patterns.

Gastrointestinal motility and its enteric actors in mechanosensitivity: past and present

Coordinated contractions of the smooth muscle layers of the gastrointestinal (GI) tract are required to produce motor patterns that ensure normal GI motility. The crucial role of the enteric nervous system (ENS), the intrinsic ganglionated network located within the GI wall, has long been recognized in the generation of the main motor patterns. However, devising an appropriate motility requires the integration of informations emanating from the lumen of the GI tract. As already found more than half a century ago, the ability of the GI tract to respond to mechanical forces such as stretch is not restricted to neuronal mechanisms. Instead, mechanosensitivity is now recognized as a property of several non-neuronal cell types, the excitability of which is probably involved in shaping the motor patterns. This brief review gives an overview on how mechanosensitivity of different cell types in the GI tract has been established and, whenever available, on what ionic conductances are involved in mechanotransduction and their potential impact on normal GI motility.

The significance of interstitial cells in neurogastroenterology

Smooth muscle layers of the gastrointestinal tract consist of a heterogeneous population of cells that include enteric neurons, several classes of interstitial cells of mesenchymal origin, a variety of immune cells and smooth muscle cells (SMCs). Over the last number of years the complexity of the interactions between these cell types has begun to emerge. For example, interstitial cells, consisting of both interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor alpha-positive (PDGFRα(+)) cells generate pacemaker activity throughout the gastrointestinal (GI) tract and also transduce enteric motor nerve signals and mechanosensitivity to adjacent SMCs. ICC and PDGFRα(+) cells are electrically coupled to SMCs possibly via gap junctions forming a multicellular functional syncytium termed the SIP syncytium. Cells that make up the SIP syncytium are highly specialized containing unique receptors, ion channels and intracellular signaling pathways that regulate the excitability of GI muscles. The unique role of these cells in coordinating GI motility is evident by the altered motility patterns in animal models where interstitial cell networks are disrupted. Although considerable advances have been made in recent years on our understanding of the roles of these cells within the SIP syncytium, the full physiological functions of these cells and the consequences of their disruption in GI muscles have not been clearly defined. This review gives a synopsis of the history of interstitial cell discovery and highlights recent advances in structural, molecular expression and functional roles of these cells in the GI tract.

The significance of interstitial cells in neurogastroenterology

Smooth muscle layers of the gastrointestinal tract consist of a heterogeneous population of cells that include enteric neurons, several classes of interstitial cells of mesenchymal origin, a variety of immune cells and smooth muscle cells (SMCs). Over the last number of years the complexity of the interactions between these cell types has begun to emerge. For example, interstitial cells, consisting of both interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor alpha-positive (PDGFRα(+)) cells generate pacemaker activity throughout the gastrointestinal (GI) tract and also transduce enteric motor nerve signals and mechanosensitivity to adjacent SMCs. ICC and PDGFRα(+) cells are electrically coupled to SMCs possibly via gap junctions forming a multicellular functional syncytium termed the SIP syncytium. Cells that make up the SIP syncytium are highly specialized containing unique receptors, ion channels and intracellular signaling pathways that regulate the excitability of GI muscles. The unique role of these cells in coordinating GI motility is evident by the altered motility patterns in animal models where interstitial cell networks are disrupted. Although considerable advances have been made in recent years on our understanding of the roles of these cells within the SIP syncytium, the full physiological functions of these cells and the consequences of their disruption in GI muscles have not been clearly defined. This review gives a synopsis of the history of interstitial cell discovery and highlights recent advances in structural, molecular expression and functional roles of these cells in the GI tract.

Roles of interleukin-9 in the growth and cholecystokinin-induced intracellular calcium signaling of cultured interstitial cells of Cajal

Interstitial cells of Cajal (ICC) are pacemaker cells in the gastrointestinal (GI) tract and loss of ICC is associated with many GI motility disorders. Previous studies have shown that ICC have the capacity to regenerate or restore, and several growth factors are critical to their growth, maintenance or regeneration. The present study aimed to investigate the roles of interleukin-9 (IL-9) in the growth, maintenance and pacemaker functions of cultured ICC. Here, we report that IL-9 promotes proliferation of ICC, and culturing ICC with IL-9 enhances cholecystokinin-8-induced Ca²⁺ transients, which is probably caused by facilitating maintenance of ICC functions under culture condition. We also show co-localizations of cholecystokinin-1 receptor and IL-9 receptor with c-kit by double-immunohistochemical labeling. In conclusion, IL-9 can promote ICC growth and help maintain ICC functions; IL-9 probably performs its functions via IL-9 receptors on ICC.

Impairment of the proximal to distal tonic gradient in the human diabetic stomach

BACKGROUND

Little has been known about the contractile characteristics of diabetic stomach. We investigated spontaneous contractions and responses to acetylcholine in the gastric muscle in diabetic patients and non-diabetic control subjects according to the region of stomach.

METHODS

Gastric specimens were obtained from 26 diabetics and 55 controls who underwent gastrectomy at Samsung Medical Center between February 2008 and November 2011. Isometric force measurements were performed using circular muscle strips from the different regions of stomach under basal condition and in response to acetylcholine.

KEY RESULTS

Basal tone of control was higher in the proximal stomach than in the distal (0.63 g vs 0.46 g, p = 0.027). However, in diabetics, basal tone was not significantly different between the proximal and distal stomach (0.75 g vs 0.62 g, p = 0.32). The distal stomach of diabetics had higher basal tone and lower frequency than that of control (0.62 g vs 0.46 g, p = 0.049 and 4.0/min vs 4.9/min, p = 0.049, respectively). After exposure to acetylcholine, dose-dependent increases of basal tone, peak, and area under the curve (AUC) were noticed in both proximal and distal stomach of the two groups. In the proximal stomach, however, the dose-dependent increase of basal tone and AUC was less prominent in diabetics than in control.

CONCLUSIONS & INFERENCES

On the contrary to control, the proximal to distal tonic gradient was not observed in diabetic stomach. Diabetic stomach also had lower frequency of spontaneous contraction in the distal stomach and less acetylcholine-induced positive inotropic effect in the proximal stomach than control.

Ionic Conductance(s) in Response to Post-junctional Potentials

The gastrointestinal motility is regulated by extrinsic and intrinsic neural regulation. Intrinsic neural pathways are controlled by sensory input, inter-neuronal relay and motor output. Enteric motor neurons release many transmitters which affect post-junctional responses. Post-junctional responses can be excitatory and inhibitory depending on neurotransmitters. Excitatory neurotransmitters induce depolarization and contraction. In contrast, inhibitory neurotransmitters hyperpolarize and relaxe the gastrointestinal smooth muscle. Smooth muscle syncytium is composed of smooth muscle cells, interstitial cells of Cajal and platelet-derived growth factor receptor α-positive (PDGFRα(+)) cells (SIP syncytium). Specific expression of receptors and ion channels in these cells can be affected by neurotransmitters. In recent years, molecular reporter expression techniques are able to study the properties of ion channels and receptors in isolated specialized cells. In this review, we will discuss the mechanisms of ion channels to interpret the post-junctional responses in the gastrointestinal smooth muscles.

Expression of transient receptor potential channels and cholinergic muscarinic acetylcholine receptors in human gastrointestinal stromal tumors

AIM: To investigate the expression of transient receptor potential channels (TRPCs) and cholinergic muscarinic acetylcholine receptors (CHRMs) in human gastrointestinal stromal tumors (GISTs).

METHODS: Immunohistochemical method was used to detect the expression of TRPC and CHRM in GISTs.

RESULTS: GISTs expressed TRPC1, TRPC3, CHRM2 and CHRM3, and the positive rate was 57.5%, 47.5%, 22.5% and 55.0%, respectively. The expression levels of TRPC and CHRM decreased as the malignant potential grade of biological behaviors GISTs increased.

CONCLUSION: Our finding that GISTs express TRPC1, TRPC3, CHRM2 and CHRM3 provides new evidence for the origination of GIST from interstitial cells of Cajal.

Role of calcium in activation of hyperpolarization-activated cyclic nucleotide-gated channels caused by cholecystokinin octapeptide in interstitial cells of cajal

BACKGROUND

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels regulate pacemaker activity in some cardiac cells and neurons. Little is known about the effects of cholecystokinin octapeptide (CCK-8) on HCN channels and excitability of murine interstitial cells of Cajal (ICCs).

METHODS

In the present study, the effects and mechanisms of CCK-8 on HCN channels were investigated by measuring mechanical contraction of smooth muscle strips and ionic channels of ICCs in murine gastric antrum.

RESULTS

Sulfated CCK-8 (CCK-8S) was used, and we found that CCK-8S increased the contraction of smooth muscle strips in the gastric antrum, which could be suppressed by specific HCN channel blockers CsCl and ZD7288. Extracellular calcium could also intensify the contraction. Under the same conditions, when antral strips were exposed to calcium ion (Ca²⁺)-free solution, no significant changes could be recorded with CCK-8S or ZD7288. Isolated ICCs from the murine gastric antrum identified by specific c-Kit antibody primers were chosen for electrophysiological recordings. HCN current (I(h)) of cultured ICCs was studied by whole-cell patch clamp techniques. A spontaneous transient inward current was recorded in ICCs, which could be inhibited by addition of CsCl and ZD7288; the current proved to be I(h). CCK-8S-facilitated I(h) in cultured ICCs could be inhibited by CsCl and ZD7288. When cultured ICCs were exposed to Ca²⁺-free solution, no significant changes could be recorded by application of CCK-8S on I(h), which proved extracellular calcium might have an excitatory effect on HCN channels.

CONCLUSION

We demonstrate that HCN channels are present in ICCs in the murine gastric antrum; they might be an important regulator of ICC excitability and pacemaker activity and are strongly affected by CCK-8S. Extracellular calcium might be a trigger in the activation of HCN channels caused by CCK-8S in cultured ICCs.

Nesfatin-1 inhibits gastric acid secretion via a central vagal mechanism in rats

Nesfatin-1, a novel hypothalamic peptide, inhibits nocturnal feeding behavior and gastrointestinal motility in rodents. The effects of nesfatin-1 on gastrointestinal secretory function, including gastric acid production, have not been evaluated. Nesfatin-1 was injected into the fourth intracerebral ventricle (4V) of chronically cannulated rats to identify a nesfatin dose sufficient to inhibit food intake. Nesfatin-1 (2 μg) inhibited dark-phase food intake, in a dose-dependent fashion, for >3 h. Gastric acid production was evaluated in urethane-anesthetized rats. Nesfatin-1 (2 μg) was introduced via the 4V following endocrine stimulation of gastric acid secretion by pentagastrin (2 μg·kg(-1)·h(-1) iv), vagal stimulation with 2-deoxy-D-glucose (200 mg/kg sc), or no stimulus. Gastric secretions were collected via gastric cannula and neutralized by titration to determine acid content. Nesfatin-1 did not affect basal and pentagastrin-stimulated gastric acid secretion, whereas 2-deoxy-D-glucose-stimulated gastric acid production was inhibited by nesfatin-1 in a dose-dependent manner. c-Fos immunofluorescence in brain sections was used to evaluate in vivo neuronal activation by nesfatin-1 administered via the 4V. Nesfatin-1 caused activation of efferent vagal neurons, as evidenced by a 16-fold increase in the mean number of c-Fos-positive neurons in the dorsal motor nucleus of the vagus (DMNV) in nesfatin-1-treated animals vs. controls (P < 0.01). Finally, nesfatin-induced Ca(2+) signaling was evaluated in primary cultured DMNV neurons from neonatal rats. Nesfatin-1 caused dose-dependent Ca(2+) increments in 95% of cultured DMNV neurons. These studies demonstrate that central administration of nesfatin-1, at doses sufficient to inhibit food intake, results in inhibition of vagally stimulated secretion of gastric acid. Nesfatin-1 activates DMNV efferent vagal neurons in vivo and triggers Ca(2+) signaling in cultured DMNV neurons.

Progress in research of interstitial cells of Cajal

Interstitial cells of Cajal (ICCs) are a kind of cells mainly found in the gastrointestinal tract as pacemaker and signal transduction cells. They have a close connection with muscular cells and terminal neurons and can stimulate and promote gastrointestinal motility. With the help of electron microscopes, we can clearly recognize their distribution and inner structure. C-kit protein is expressed by ICCs. Besides, many disorders of gastrointestinal motility are related to ICCs. In recent years, many scholars have found the trace of ICCs in different organs such as the gastrointestinal tract, biliary tract, bladder, and uterus, and they have tried to state the relationship between abnormal ICCs and some diseases. This article will review the progress in research of ICCs in terms of their origin, morphology, receptors, function, and related diseases.

Vagal intramuscular array afferents form complexes with interstitial cells of Cajal in gastrointestinal smooth muscle: analogues of muscle spindle organs?

Intramuscular arrays (IMAs), vagal mechanoreceptors that innervate gastrointestinal smooth muscle, have not been completely described structurally or functionally. To delineate more fully the architecture of IMAs and to consider the structure-function implications of the observations, the present experiment examined the organization of the IMA terminal arbors and the accessory tissue elements of those arbors. IMA terminal fields, labeled by injection of biotinylated dextran into the nodose ganglia, were examined in whole mounts of rat gastric smooth muscle double-labeled with immunohistochemistry for interstitial cells of Cajal (ICCs; c-Kit) and/or inputs of different neuronal efferent transmitter (markers: tyrosine hydroxylase (TH), vesicular acetylcholine transporter (VAChT), and nitric oxide synthase (NOS)) or afferent neuropeptidergic (calcitonin gene-related peptide (CGRP)) phenotypes. IMAs make extensive varicose and lamellar contacts with ICCs. In addition, axons of the multiple efferent and afferent phenotypes examined converge and articulate with IMA terminal arbors innervating ICCs. This architecture is consistent with the hypothesis that IMAs, or the multiply innervated IMA-ICC complexes they form, can function as stretch receptors. The tissue organization is also consonant with the proposal that those units can operate as functional analogues of muscle spindle organs. For electrophysiological assessments of IMA functions, experiments will need protocols that preserve both the complex architecture and the dynamic operations of IMA-ICC complexes.

Use of fluoroscopy to study in vivo motility in mouse pups

OBJECTIVES

Few methods exist to noninvasively study in vivo gastrointestinal motility in animal models of enteric infections. None have been used on mouse pups, which often display more severe symptoms during enteric infections than adult mice. This study sought to determine whether digital fluoroscopy could be used to evaluate gastrointestinal motility in mouse pups as well as adult mice.

MATERIALS AND METHODS

Fluoroscopic imaging studies were performed on normal 6- to 8-week-old adult mice and 12-day-old pups to develop protocols for evaluating gastric and intestinal wall movements and changes in stomach sizes. These protocols were then applied to evaluate motility in an established rotavirus mouse model. Imaging studies were performed on adult mice at 0, 2, and 4 days postinfection and on 12-day-old pups at 2 days postinfection.

RESULTS

Fluoroscopic studies revealed postnatal differences of gastric peristalsis and rates of intestinal contractions between normal mouse pups and adult mice. Studies of the rotavirus mouse model revealed that differences in gastric function occur between rotavirus-infected and control mouse pups, but no discernible difference occurs between infected and control adult mice. In contrast, there were no detectable differences in rates of intestinal wall movements between control pups with normal stools and infected pups with loose stools.

CONCLUSIONS

These results demonstrate that fluoroscopy can evaluate in vivo motility in mouse pups and by doing so provide findings that are clinically relevant to the study of enteric infections in young.

Cannabinoid-induced reduction in antral pacemaker frequency: a telemetric study in the ferret

BACKGROUND

The gastric myoelectric activity (GMA) is the electrical pacesetter potential, which drives gastric motility. Cannabinoids have broad-spectrum antiemetic and antinauseant activity. Paradoxically, they inhibit intestinal peristalsis and reduce gastric motility but their effect on GMA remains unknown.

METHODS

Ferrets were surgically implanted with radiotelemetry transmitters to record GMA, body temperature and heart rate. The effect of WIN 55,212-2 (1 mg kg(-1), i.p.), an agonist at the cannabinoid type 1 and 2 receptors was examined in conscious, unrestrained ferrets. WIN 55,212-2 was also compared to the anandamide upregulator URB 597 (5 mg kg(-1), i.p.) for a potential to modulate the emetic response and behavioral changes induced by apomorphine (0.25 mg kg(-1), s.c.).

KEY RESULTS

WIN 55,212-2 decreased GMA frequency (8.1 ± 0.4 cpm, compared to 9.6 ± 0.1 cpm in vehicle-treated animals, n = 6, P < 0.01). Apomorphine induced 9.0 ± 1.6 emetic episodes, WIN 55,212-2 inhibited the emetic response (3.3 ± 1.0 episodes, n = 6, P < 0.05) but URB 597 had no effect (9.0 ± 1.5 episodes). Apomorphine-induced hyperactivity in vehicle-treated animals (6.5 ± 3.6-16.6 ± 4.9 active behavior counts, n = 6, P < 0.01), which was reduced by WIN 55,212-2 (5.0 ± 1.5 counts, n = 6, P < 0.05).

CONCLUSIONS & INFERENCES

WIN 55,212-2 demonstrated clear antiemetic efficacy, which extends the broad-spectrum antiemetic efficacy of cannabinoids to dopamine receptor agonists in the ferret. Our results, however, suggest a more limited spectrum of action for URB 597. WIN 55,212-2 decreased the frequency of the antral electrical pacemaker, which reveals new insights into the mechanism regulating the decrease in motility induced by cannabinoids.

Regional differences of the effects of acetylcholine in the human gastric circular muscle

The motor functions of the stomach have traditionally been regarded to have regional differences. However, to date there have been only a few data investigating whether such regional differences in motor function exist in the human stomach. The aims of the present study were to examine the spontaneous activity and responses to acetylcholine in the anatomically defined regions of human stomach. Human gastric circular muscle tissues from fundus, corpus, and antrum were obtained from 25 patients (14 men, 11 women with a mean age of 55.2 yr; 36-74 yr) undergoing gastrectomy for gastric cancers. Isometric force measurements were performed by using muscle strips from the different regions of the human stomach under basal conditions and in response to the exogenous application of acetylcholine. Spontaneous phasic contractions were observed in all human gastric smooth muscles. However, the responses to acetylcholine displayed regional differences. In the gastric antrum, there was a dose-dependent increase in the peak contraction, contractile frequency, and amplitude of contraction after acetylcholine exposure (up to 1 μM). However, there was no significant change in the basal tone. In the corpus and fundus, acetylcholine induced a dose-dependent increase in the peak contraction and basal tone. However, there was no significant change in the contractile frequency or amplitude of contraction. In conclusion, the response of human gastric circular muscle to acetylcholine displayed regional differences between the antrum and the corpus and fundus. This finding suggested the presence of distinct functional regions in human stomach.

Neuroeffector apparatus in gastrointestinal smooth muscle organs

Control of gastrointestinal (GI) movements by enteric motoneurons is critical for orderly processing of food, absorption of nutrients and elimination of wastes. Work over the past several years has suggested that motor neurotransmission is more complicated than simple release of transmitter from nerve terminals and binding of receptors on smooth muscle cells. In fact the 'neuro-effector' junction in the tunica muscularis might consist of synaptic-like connectivity with specialized cells, and contributions from multiple cell types in integrated post-junctional responses. Interstitial cells of Cajal (ICC) were proposed as potential mediators in motor neurotransmission based on reduced post-junctional responses observed in W mutants that have reduced populations of ICC. More recent studies on W mutants have contradicted the original findings, and suggested that ICC may not be significant players in motor neurotransmission. This review examines the evidence for and against the role of ICC in motor neurotransmission and outlines areas for additional investigation that would help further resolve this controversy.

C-kit-immunopositive interstitial cells of Cajal in human embryonal and fetal oesophagus

Interstitial cells of Cajal (ICC) are morphologically and functionally intercalated between the elements of the enteric nervous system and the smooth muscle cells (SMCs) in the musculature of the digestive tract. Kit immunohistochemistry reliably identifies the location of these cells and provides information on changes in ICC distribution and density. Human oesophagus specimens (7 embryos, 23 fetuses at 7-27 weeks gestational age; both sexes) were exposed to Kit antibodies to determine ICC differentiation. Enteric plexuses were examined immunohistochemically by using anti-neuron-specific enolase, whereas the differentiation of SMCs was studied with antibodies against alpha-smooth-muscle actin and desmin. By week 7, c-kit-immunopositive cells were present along the entire oesophagus in the form of an uninterrupted layer around the myenteric plexus (MP) elements. From the beginning of the 3rd month, the number of ICC progressively decreased around the MP ganglia but increased within the muscle layers. Concomitantly, differences in the number and distribution of ICC were established in the various portions of the oesophagus: specifically, ICC were abundant in the lower portion, less numerous in the middle region and rare in the upper part. By the 5th month of development, the relationship as found in later developmental stages had been established: C-kit IR ICC were present within the circular muscle layer, within the longitudinal layer and in the connective septa surrounding the muscle bundles but were completely missing around the MP ganglia.

Neurotransmission in lower esophageal sphincter of W/Wv mutant mice

To address the controversy surrounding the role of interstitial cells of Cajal (ICC) in nitrergic neurotransmission to gastrointestinal smooth muscle, circular smooth muscle from the lower esophageal sphincter (LES) of W/W(v) wild-type and mutant (ICC-deficient) mice were studied by using intracellular and tension recordings in vitro. Resting membrane potential was more negative, and the spontaneous unitary potentials diminished in mutant mice. In wild-type mice, nerve stimulation induced a biphasic inhibitory junction potential (IJP) consisting of a fast initial IJP followed by a long-lasting slow IJP (LSIJP). The IJP was markedly impaired in a significant proportion of mutant mice, whereas in others it was normal. Pharmacological studies in the mice with markedly impaired IJPs revealed that cholinergic and purinergic components of the nerve-mediated responses appeared intact. In wild-type mice, caffeine hyperpolarized smooth muscle cells, inhibited the initial fast IJP, and completely abolished the LSIJP. In mutant mice, caffeine depolarized smooth muscle cells and abolished the impaired LSIJP but did not affect the initial fast IJP. Immunohistochemical staining for c-Kit confirmed deficiency of ICC in mutant mice with a normal nitrergic IJP. Rings of LES circular smooth muscle from W/W(v) mutant mice generated significantly less spontaneous tone than controls. When tone was restored with carbachol, normal nitrergic LES relaxation was recorded. These data suggest that 1) there is significant variability in the generation of nitrergic neurotransmission in the LES of W/W(v) mutant mice, whereas purinergic and cholinergic neurotransmission are intact; 2) the altered nitrergic responses appear to be associated with abnormal Ca2+-dependent signaling initiated by spontaneous Ca2+ release from sarcoplasmic reticulum in smooth muscle cells; and 3) c-Kit-positive ICC are not essential for nitrergic neurotransmission in mouse LES smooth muscle.

Generation and propagation of gastric slow waves

1. Mechanisms underlying the generation and propagation of gastrointestinal slow wave depolarizations have long been controversial. The present review aims to collate present knowledge on this subject with specific reference to slow waves in gastric smooth muscle. 2. At present, there is strong agreement that interstitial cells of Cajal (ICC) are the pacemaker cells that generate slow waves. What has been less clear is the relative role of primary types of ICC, including the network in the myenteric plexus (ICC-MY) and the intramuscular network (ICC-IM). It is concluded that both ICC-MY and ICC-IM are likely to serve a major role in slow wave generation and propagation. 3. There has been long-standing controversy as to how slow waves 'propagate' circumferentially and down the gastrointestinal tract. Two mechanisms have been proposed, one being action potential (AP)-like conduction and the other phase wave-based 'propagation' resulting from an interaction of coupled oscillators. Studies made on single bundle gastric strips indicate that both mechanisms apply with relative dominance depending on conditions; the phase wave mechanism is dominant under circumstances of rhythmically generating slow waves and the AP-like propagation is dominant when the system is perturbed. 4. The phase wave mechanism (termed Ca(2+) phase wave) uses cyclical Ca(2+) release as the oscillator, with coupling between oscillators mediated by several factors, including: (i) store-induced depolarization; (ii) resultant electrical current flow/depolarization through the pacemaker cell network; and (iii) depolarization-induced increase in excitability of downstream Ca(2+) stores. An analogy is provided by pendulums in an array coupled together by a network of springs. These, when randomly activated, entrain to swing at the same frequency but with a relative delay along the row giving the impression of a propagating wave. 5. The AP-like mechanism (termed voltage-accelerated Ca(2+) wave) propagates sequentially like a conducting AP. However, it is different in that it depends on regenerative store Ca(2+) release and resultant depolarization rather than regenerative activation of voltage-dependent channels in the cell membrane. 6. The applicability of these mechanisms to describing propagation in large intact gastrointestinal tissues, where voltage-dependent Ca(2+) entry is also likely to be functional, is discussed.

Review article: gastric electrical stimulation for gastroparesis--physiological foundations, technical aspects and clinical implications

BACKGROUND

Application of electrical stimulation to the gut, primarily the stomach, has rapidly advanced in the last two decades, from mostly animal studies to the clinical arena. Most studies focused on the use of electrical stimulation for gastroparesis, the only approved indication for such intervention.

AIM

To review the physiological basis of gastric electrical activity and the technical aspects and clinical outcome of gastric electrical stimulation (GES) for gastroparesis.

METHODS

PubMed search from 1966 to 2009, using gastroparesis and GES as search terms. Areas in focus were systematically reviewed.

RESULTS

The literature consists of open-label studies, mostly from single centres, published in the last decade. Improvement in symptoms, quality of life and nutritional status was reported by most studies. Physiologically, stimulation parameters approved in clinical practice do not regulate gastric slow wave activity and have inconsistent effect on gastric emptying. The mechanism of action of GES is not fully known, but data support modulation of gastric biomechanical activity and afferent neural mechanisms.

CONCLUSIONS

Gastric electrical stimulation is a helpful intervention in recalcitrant gastroparesis. Controlled studies and better understanding of mechanisms of action of electrical stimulation are needed to evaluate further the clinical utility of this intervention and to exploit its therapeutic potential better.

Gastric electrical stimulation with long pulses in humans and animals: can data obtained in animals be replicated in humans?

AIMS

  The aim of this study was to investigate and compare effective parameters for gastric electrical stimulation (GES) to modulate gastric muscle functions in different species.

METHODS

  Four species: Pigs, dogs, rats, and mice implanted with two pairs of electrodes on the serosal surface of the stomach were studied, respectively. Experiment 1 was designed to entrain/pace gastric slow waves and included a series of 5-min periods with long-pulse GES of different pulse widths and frequencies. Experiment 2 was designed to induce gastric dysrhythmia with long-pulse GES of different frequencies. Gastric slow waves were recorded during the entire experiment.

RESULTS

  1) The minimum pulse width for GES to completely entrain the slow waves was similar (100-400 msec) in all four species. 2) With fixed amplitude (4 mA) and pulse width (400 msec), the highest frequency at which slow waves could be paced was similar (about 10-60% higher than the intrinsic slow wave frequency) in all species. 3) With fixed pulse width of 400 msec and amplitude of 6 mA, GES with nine to 18 cycles per min (cpm) was able to induce dysrhythmia in dogs. In addition, there was no significant difference among these frequencies of 9-18 cpm. 4) GES with 400 msec, 6 mA, and 9 cpm was able to induce dysrhythmia in all species. These effective GES parameters in results 1-4 were similar to those used in humans in the literature.

CONCLUSIONS

  There is no significant difference in stimulation parameters when GES is applied to alter gastric slow waves in different animal models. Furthermore, the effective parameters for GES to alter slow waves are similar between the humans and various animal models. These findings suggest that stimulation parameters obtained from animal studies are applicable in humans.

Cellular pathogenesis of diabetic gastroenteropathy

Gastroenteropathy manifesting in upper gastrointestinal symptoms, delayed gastric emptying, constipation, diarrhea and fecal incontinence occurs frequently in patients with diabetes mellitus and represents a significant health care burden. Current treatments are largely symptomatic and ineffective. Better understanding of the cellular and molecular pathogenesis of these disorders is required for the development of more effective therapies. Recent advances in our understanding of the inherent, high-level complexities of the control systems that execute and regulate gastrointestinal motility, together with the utilization of new experimental models and sophisticated physiological, morphological and molecular techniques have lead to the realization that diabetic gastroenteropathies cannot be ascribed to any singular defect or dysfunction. In fact, these disorders are multifactorial and involve a spectrum of metabolic and dystrophic changes that can potentially affect all key components of motor control including the systemic autonomic and enteric nervous systems, interstitial cells of Cajal and smooth muscle cells. Candidate pathomechanisms are also varied and include imbalance between pro- and anti-oxidative factors, altered trophic stimuli to mature cells and their progenitors, and, possibly, autoimmune factors. The goal of this paper is to review the cellular changes underlying diabetic gastroenteropathies and their potential causes, with particular focus on functional interactions between various cell types. It is proposed that diabetic gastroenteropathies should be considered a form of gastrointestinal neuromuscular dystrophy rather than a "functional" disorder. Future research should identify ways to block cytotoxic factors, support the regeneration of damaged cells and translate the experimental findings into new treatment modalities.

Prostaglandin regulation of gastric slow waves and peristalsis

Gastric emptying depends on functional coupling of slow waves between the corpus and antrum, to allow slow waves initiated in the gastric corpus to propagate to the pyloric sphincter and generate gastric peristalsis. Functional coupling depends on a frequency gradient where slow waves are generated at higher frequency in the corpus and drive the activity of distal pacemakers. Simultaneous intracellular recording from corpus and antrum was used to characterize the effects of PGE(2) on slow waves in the murine stomach. PGE(2) increased slow-wave frequency, and this effect was mimicked by EP(3), but not by EP(2), receptor agonists. Chronotropic effects were due to EP(3) receptors expressed by intramuscular interstitial cells of Cajal because these effects were not observed in W/W(V) mice. Although the integrated chronotropic effects of EP(3) receptor agonists were deduced from electrophysiological experiments, no clear evidence of functional uncoupling was observed with two-point electrical recording. Gastric peristalsis was also monitored by video imaging and spatiotemporal maps to study the impact of chronotropic agonists on propagating contractions. EP(3) receptor agonists increased the frequency of peristaltic contractions and caused ectopic sites of origin and collisions of peristaltic waves. The impact of selective regional application of chronotropic agonists was investigated by use of a partitioned bath. Antral slow waves followed enhanced frequencies induced by stimulation of the corpus, and corpus slow waves followed when slow-wave frequency was elevated in the antrum. This demonstrated reversal of slow-wave propagation with selective antral chronotropic stimulation. These studies demonstrate the impact of chronotropic agonists on regional intrinsic pacemaker frequency and integrated gastric peristalsis.

Distribution of the interstitial Cajal-like cells in the gallbladder and extrahepatic biliary duct of the guinea-pig

It has been suggested that interstitial Cajal-like cells (ICLC) may be involved in the spontaneous rhythmic electrical activities of the extrahepatic bile duct system. The present study investigated the distribution and characteristics of ICLC, which are immunopositive for CD117/ Kit receptor tyrosine kinase, using immunohistochemistry employing a monoclonal antibody raised against CD117/Kit on whole-mount preparations. The Kit-positive ICLC were examined using confocal laser scanning microscopy or fluorescence microscopy. ICLC, immunoreactive for Kit, were pleiomorphic and/or spindle-shaped cells with a few bipolar processes and distributed in the smooth muscle layers of the gallbladder and bile duct system. They were scattered in the hepatic duct, cystic duct and gallbladder as well as in the upper part of the common bile duct. The ICLC gradually increased in number and formed a completed cellular network in the lower part of the common bile duct and ampulla. The numbers of ICLC in the ampulla were similar to that of the duodenum and significantly much greater in number than in the gallbladder and bile ducts. The density of the ICLC in the common bile duct was significantly higher than that of other bile ducts. Our results suggested that the ICLC might contribute to the regulation of the spontaneous rhythmic contraction and development of motility disorders of the bile duct system.

A new laparoscopic technique for weight reduction with implanted gastric banding basket

BACKGROUND

Nowadays, obesity is frequently an indication for implantation of an adjustable stomach or gastric band. Among the side effects, in addition to band erosion and port chamber complications, pouch dilation in the sense of increasing enlargement of the forestomach and resulting insufficiency of initial surgical measures consistently occurs. Implantation of a soft basket band will prevent this. The objective of this study was to investigate the practical feasibility of the soft basket band.

METHODS

Ten patients were investigated in an observation study over a period from November 2006 to June 2007. Seven patients were women and three patients were men, with an average age of 43.6 years (25-66 years).

RESULTS

The average body mass index (BMI) at the time of the operation was 47.4 +/- 5.5 kg/m(2), with an average body weight of 134.5 +/- 24.6 kg. After a median follow-up period of 1 month, an average BMI of 44.9 +/- 5.8 kg/m(2) was achieved, and after 3 months, an average BMI of 41.4 +/- 4.8 kg/m(2). The excessive weight loss was 7.4 +/- 4.3 kg after 1 month and 17.9 +/- 6.4 kg after 3 months. A local wound infection occurred as a complication in one patient.

CONCLUSION

Laparoscopy procedures enable mortality to be lowered compared to bypass operations with minimal complications and substantial reduction of weight.

Are interstitial cells of Cajal plurifunction cells in the gut?

The proposed functions of the interstitial cells of Cajal (ICC) are to 1) pace the slow waves and regulate their propagation, 2) mediate enteric neuronal signals to smooth muscle cells, and 3) act as mechanosensors. In addition, impairments of ICC have been implicated in diverse motility disorders. This review critically examines the available evidence for these roles and offers alternate explanations. This review suggests the following: 1) The ICC may not pace the slow waves or help in their propagation. Instead, they may help in maintaining the gradient of resting membrane potential (RMP) through the thickness of the circular muscle layer, which stabilizes the slow waves and enhances their propagation. The impairment of ICC destabilizes the slow waves, resulting in attenuation of their amplitude and impaired propagation. 2) The one-way communication between the enteric neuronal varicosities and the smooth muscle cells occurs by volume transmission, rather than by wired transmission via the ICC. 3) There are fundamental limitations for the ICC to act as mechanosensors. 4) The ICC impair in numerous motility disorders. However, a cause-and-effect relationship between ICC impairment and motility dysfunction is not established. The ICC impair readily and transform to other cell types in response to alterations in their microenvironment, which have limited effects on motility function. Concurrent investigations of the alterations in slow-wave characteristics, excitation-contraction and excitation-inhibition couplings in smooth muscle cells, neurotransmitter synthesis and release in enteric neurons, and the impairment of the ICC are required to understand the etiologies of clinical motility disorders.

Differential expression of ionic conductances in interstitial cells of Cajal in the murine gastric antrum

Two distinct populations of interstitial cells of Cajal (ICC) exist within the tunica muscularis of the gastric antrum, and these cells serve different physiological functions. One population of ICC generates and actively propagates electrical slow waves, and the other population of ICC is innervated by excitatory and inhibitory motor neurons and mediates enteric motor neurotransmission. In spite of the key role of ICC in gastric excitability, little is known about the ionic conductances that underlie the functional diversity of these cells. In the present study we isolated ICC from the murine gastric antrum and investigated the Ca(2+)-dependent ionic conductances expressed by these cells using the patch clamp technique. Conductances in ICC were compared with those expressed in smooth muscle cells. The cells studied were identified by RT-PCR using cell-specific primers that included Myh11 (smooth muscle cells), Kit (ICC) and Uchl1 (enteric neurons) following electrophysiolgical recordings. Distinct ionic conductances were observed in Kit-positive cells. One group of ICC expressed a basal non-selective cation conductance (NSCC) that was inhibited by an increase in [Ca(2+)](i) in a calmodulin (CaM)-dependent manner. A second population of ICC generated spontaneous transient inward currents (STICs) and expressed a basal noisy NSCC that was facilitated by an increase in [Ca(2+)](i) in a CaM-dependent manner. The [Ca(2+)](i)-facilitated NSCC in ICC was blocked by the Cl(-) channel antagonists 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS), anthracene-9-carboxylate (9-AC) and niflumic acid. These data suggest that distinct NSCC are expressed in subpopulations of ICC and these conductances may underlie the functional differences of these cells within the gastric antrum.

Kit mutants and gastrointestinal physiology

There has been considerable speculation about the function of interstitial cells of Cajal (ICC) since their discovery more than 100 years ago. It has been difficult to study these cells under native conditions, but great insights about the function of ICC have come from studies of genetic models with loss-of function mutations in the Kit signalling pathway. First it was discovered that signalling via Kit (a receptor tyrosine kinase) was vital for the development and maintenance of the ICC phenotype in gastrointestinal (GI) muscles. In compound heterozygotes (W/W(V) and Sl/Sl(d) animals), where there are partial loss-of-function mutations in Kit receptors or Kit ligand (stem cell factor), ICC failed to develop in various regions of the GI tract, but no major changes in the smooth muscle layers or enteric nervous system occurred in the absence of these cells. Animals with these mutations provided an unprecedented opportunity to understand the role of ICC in GI motor function, and it is now clear from these studies that ICC serve as: (i) pacemaker cells, generating the spontaneous electrical rhythms of the gut known as slow waves; (ii) a propagation pathway for slow waves so that large areas of the musculature can be entrained to a dominant pacemaker frequency; (iii) mediators of excitatory cholinergic and inhibitory nitrergic neural inputs from the enteric nervous system, and (iv) stretch receptors that modulate membrane potential and electrical slow wave frequency. This review describes the use of genetic models to understand the important physiological role of ICC in the GI tract.

Involvement of intramuscular interstitial cells of Cajal in neuroeffector transmission in the gastrointestinal tract

Specialized cells known as interstitial cells of Cajal (ICC) are distributed in specific locations within the tunica muscularis of the gastrointestinal (GI) tract. ICC serve as electrical pacemakers, provide pathways for the active propagation of slow waves, are mediators of enteric motor neurotransmission and play a role in afferent neural signalling. Morphological studies have provided evidence that motor neurotransmission in the GI tract does not occur through poorly defined structures between nerves and smooth muscle, but rather via specialized synapses that exist between enteric nerve terminals and intramuscular ICC or ICC-IM. ICC-IM are coupled to smooth muscle cells via gap junctions and post-junctional responses elicited in ICC-IM are conducted to neighbouring smooth muscle cells. Electrophysiological studies from the stomachs and sphincters of wild-type and mutant animals that lack ICC-IM have provided functional evidence for the importance of ICC in cholinergic excitatory and nitrergic inhibitory motor neurotransmission. Intraperitoneal injection of animals with Kit neutralizing antibody or organ culture of gastrointestinal tissues in the presence of neutralizing antibody, which blocks the development and maintenance of ICC, has provided further evidence for the role of ICC in enteric motor transmission. ICC-IM also generate an ongoing discharge of unitary potentials in the gastric fundus and antrum that contributes to the overall excitability of the stomach.