Effect of modulation of serotonergic, cholinergic, and nitrergic pathways on murine fundic size and compliance measured by ultrasonomicrometry

High temporal resolution gastric emptying breath tests in mice

BACKGROUND

Gastric emptying is a complex physiological process regulating the division of a meal into smaller partitions for the small intestine. Disrupted gastric emptying contributes to digestive disease, yet current measures may not reflect different mechanisms by which the process can be altered.

METHODS

We have developed high temporal resolution solid and liquid gastric emptying breath tests in mice using [13 C]-octanoic acid and off axis- integrated cavity output spectroscopy (OA-ICOS). Stretched gamma variate and 2-component stretched gamma variate models fit measured breath excretion data.

KEY RESULTS

These assays detect acceleration and delay using pharmacological (7.5 mg/kg atropine) or physiological (nutrients, cold exposure stress, diabetes) manipulations and remain stable over time. High temporal resolution resolved complex excretion curves with 2 components, which was more prevalent in mice with delayed gastric emptying following streptozotocin-induced diabetes. There were differences in the gastric emptying of Balb/c vs C57Bl6 mice, with slower gastric emptying and a greater occurrence of two-phase gastric emptying curves in the latter strain. Gastric emptying of C57Bl6 could be accelerated by halving the meal size, but with no effect on the occurrence of two-phase gastric emptying curves. A greater proportion of two-phase gastric emptying was induced in Balb/c mice with the administration of PYY (8-80 nmol) 60 min following meal ingestion.

CONCLUSIONS AND INFERENCES

Collectively, these results demonstrate the utility of high temporal resolution gastric emptying assays. Two-phase gastric emptying is more prevalent than previously reported, likely involves intestinal feedback, but contributes little to the overall rate of gastric emptying.

Motility Evaluation in the Patient with Inflammatory Bowel Disease

Patients with inflammatory bowel disease (IBD) suffer frequently from functional bowel diseases (FBD) and motility disorders. Management of FBD and motility disorders in IBD combined with continued treatment of a patient's IBD symptoms will likely lead to better clinical outcomes and improve the patient's quality of life. The goals of this review were to summarize the most recent literature on motility disturbances in patients with IBD and to give a brief overview of the ranges of motility disturbances, from reflux disease to anorectal disorders, and discuss their diagnosis and specific management.

Dual Alpha2C/5HT1A Receptor Agonist Allyphenyline Induces Gastroprotection and Inhibits Fundic and Colonic Contractility

BACKGROUND

Allyphenyline, a novel α2-adrenoceptor (AR) ligand, has been shown to selectively activate α2C-adrenoceptors (AR) and 5HT1A receptors, but also to behave as a neutral antagonist of α2A-ARs. We exploited this unique pharmacological profile to analyze the role of α2C-ARs and 5HT1A receptors in the regulation of gastric mucosal integrity and gastrointestinal motility.

METHODS

Gastric injury was induced by acidified ethanol in Wistar rats. Mucosal catalase and superoxide dismutase levels were measured by assay kits. The effect of allyphenyline on electrical field stimulation (EFS)-induced fundic and colonic contractions was determined in C57BL/6 mice.

RESULTS

Intracerebroventricularly injected allyphenyline (3 and 15 nmol/rat) dose dependently inhibited the development of mucosal damage, which was antagonized by ARC 239 (α2B/C-AR and 5HT1A receptor antagonist), (S)-WAY 100135 (selective 5HT1A receptor antagonist), and JP-1302 (selective α2C-AR antagonist). This protection was accompanied by significant elevation of mucosal catalase and superoxide dismutase levels. Allyphenyline (10(-9)-10(-5) M) also inhibited EFS-induced fundic contractions, which was antagonized by ARC 239 and (S)-WAY 100135, but not by JP-1302. Similar inhibition was observed in the colon; however, in this case only ARC 239 reduced this effect, while neither selective inhibition of α2C-ARs and 5HT1A receptors nor genetic deletion of α2A- and α2B-ARs influenced it.

CONCLUSIONS

Activation of both central α2C-ARs and 5HT1A receptors contributes to the gastroprotective action of allyphenyline in rats. Its inhibitory effect on fundic contractions is mediated by 5HT1A receptors, but neither α2-ARs nor 5HT1A receptors take part in its inhibitory effect on colonic contractility in mice.

Establishment and evaluation of animal models of functional dyspepsia

Functional dyspepsia (FD) is a group of persistent or recurrent dyspepsia syndrome in which the organic matter has not been found. According to the different symptoms of FD, it belongs to "Weipi" or "stomachache" in Chinese medicine. At present, there are many different methods for the establishment and evaluation of FD animal models. This paper summarizes the existing FD animal models from two aspects: establishment and evaluation.

Fabrication and implantation of miniature dual-element strain gages for measuring in vivo gastrointestinal contractions in rodents

Gastrointestinal dysfunction remains a major cause of morbidity and mortality. Indeed, gastrointestinal (GI) motility in health and disease remains an area of productive research with over 1,400 published animal studies in just the last 5 years. Numerous techniques have been developed for quantifying smooth muscle activity of the stomach, small intestine, and colon. In vitro and ex vivo techniques offer powerful tools for mechanistic studies of GI function, but outside the context of the integrated systems inherent to an intact organism. Typically, measuring in vivo smooth muscle contractions of the stomach has involved an anesthetized preparation coupled with the introduction of a surgically placed pressure sensor, a static pressure load such as a mildly inflated balloon or by distending the stomach with fluid under barostatically-controlled feedback. Yet many of these approaches present unique disadvantages regarding both the interpretation of results as well as applicability for in vivo use in conscious experimental animal models. The use of dual element strain gages that have been affixed to the serosal surface of the GI tract has offered numerous experimental advantages, which may continue to outweigh the disadvantages. Since these gages are not commercially available, this video presentation provides a detailed, step-by-step guide to the fabrication of the current design of these gages. The strain gage described in this protocol is a design for recording gastric motility in rats. This design has been modified for recording smooth muscle activity along the entire GI tract and requires only subtle variation in the overall fabrication. Representative data from the entire GI tract are included as well as discussion of analysis methods, data interpretation and presentation.

Gastric body cholinergic contractile signal transduction in M2 and M3 receptor knockout mice

Although most smooth muscles express a greater density of M2 than M3 muscarinic receptors, based on the potency of subtype selective muscarinic receptor antagonists, the M3 subtype predominantly mediates contraction. The effect of inhibitors of putative contractile signal transduction pathway enzymes on carbachol-induced contractions was determined in wild-type (WT) mice and mice lacking either the M2 (M2KO) or the M3 (M3KO) receptor subtype. Contractile responses to KCl, then increasing carbachol concentrations in the presence and absence of enzyme inhibitors was determined. The KCl-induced contraction was not different between strains. The carbachol response was unaffected in the M2KO strain but decreased 42% in M3KO mice (p < 0.01). Darifenacin potency was high in both WT and M2KO strains, indicating M3-mediated contractions, and low in the M3KO strain, suggesting M2-mediated contractions. The phosphatidyl inositol-specific phospholipase C (Pi-PLC) inhibitor ET-18-OCH3 had no effect. Inhibition of phosphatidyl choline-specific phospholipase C (PC-PLC) and sphingomyelin synthase with D609 decreased maximal contraction in all strains. M3-mediated contractions in the M2KO strain were decreased 54% by the protein kinase C (PKC) inhibitor chelerythrine. M2-mediated contractions in the M3KO and WT strains were decreased by the Rho kinase (ROCK) inhibitor Y27632 as well as the ROCK, PKA and PKG inhibitor H89. The M3 subtype activates PKC and either PC-PLC or sphingomyelin synthase, while the M2 subtype activates ROCK and either PC-PLC or sphingomyelin synthase. These studies suggest that multiple parallel pathways mediate cholinergic contractions in stomach body smooth muscle.

Influence of the 5-HT3 receptor antagonist ondansetron on gastric sensorimotor function and nutrient tolerance in healthy volunteers

BACKGROUND

Serotonin is believed to be involved in the regulation of the gastric accommodation reflex in man however which receptor subtype(s) are involved remains to be elucidated.

METHODS

Eleven healthy subjects (nine men, age 19-30) underwent a gastric barostat and a drinking test after treatment with either placebo or ondansetron (8 mg intravenously). During the barostat protocol an intragastric flaccid bag was stepwise distended (2 mmHg increments 2 min) to determine gastric compliance and sensitivity to distention. Subsequently, the pressure level was set at intra-abdominal pressure +2 mmHg while volume was followed before and after administration of a liquid meal (200 mL; 300 kcal). During the drink test volunteers drank at a rate of 15 mL min(-1) until maximal satiation. Results (mean ± SEM) were compared using t-tests and mixed model analysis.

KEY RESULTS

Gastric compliance was not significantly altered by ondansetron (51.5 ± 5.6 vs 49.2 ± 5.2 mL mmHg(-1)), neither were the pressure thresholds for first perception or discomfort. Ondansetron treatment did not affect basal gastric tone (173 ± 14 vs 156 ± 12 mL), neither did it affect the amplitude of the meal-induced relaxation (160 ± 52 vs 131 ± 43 mL) or the maximum volume increase after the meal (264 ± 54 mL vs 234 ± 51 mL). During the drinking test the amount of liquid meal ingested at maximum satiation was significantly increased by ondansetron (784 ± 74 vs 907 ± 64 mL, P < 0.05).

CONCLUSIONS & INFERENCES

These data suggest that 5-HT acting at 5-HT(3) receptors is not involved in the control of gastric sensorimotor function, but contributes to the regulation of hunger and satiation in man.

A novel method for study of gastric mechanical functions in conscious mice

A novel method has been developed for simultaneous study of gastric emptying, antral motility, and gastric muscle tone in conscious mice. Intragastric pressure was measured during infusion of an X-ray-opaque, viscous meal through a chronically implanted gastric fistula (0.25 ml/min). Compared with vehicle treatment, molsidomine (nitric oxide donor) and atropine (muscarinic receptor antagonist) treatment significantly reduced the area under the intragastric pressure curve (AUC) by 37 +/- 4% and 35 +/- 3%, respectively, (mean +/- S.E.M.) whereas N (G)-nitro-L-arginine methyl ester (L-NAME; nitric oxide synthase inhibitor) significantly increased the AUC by 20 +/- 3%. Atropine also significantly reduced the frequency and amplitude of stomach contraction-induced intragastric pressure waves while molsidomine only reduced the frequency. Gastric emptying, as assessed by X-ray imaging, was significantly delayed after L-NAME and atropine treatment. This methodology is the first to enable simultaneous assessment of gastric emptying, antral motility, and gastric tone in conscious mice and confirmed the important role of nitrergic and cholinergic innervation.

Influence of buspirone on gastric sensorimotor function in man

BACKGROUND

Previous studies have suggested involvement of 5HT(1) receptors in the control of gastric tone.

AIM

To study the effect of buspirone, a 5HT(1A) agonist, on gastric sensorimotor function in healthy volunteers.

METHODS

Ten healthy volunteers (six males and four females, ages 20-29 years) participated in a barostat study evaluating the influence of single oral doses of buspirone (5, 10, 20, 30 and 40 mg) on tone and sensitivity of the proximal stomach. In addition, the effect of placebo or the three lowest doses of buspirone on gastric emptying was assessed using a solid and liquid gastric emptying breath test.

RESULTS

Compared to preadministration volumes, buspirone increased proximal stomach volumes in a dose-dependent manner, with significant fundic relaxation after 30 and 40 mg doses (intra-balloon volume increases of respectively 258 +/- 80 mL and 273 +/- 49 mL, P < or = 0.05). Pressure thresholds during gastric distention were not altered, but corresponding intraballoon volumes were significantly increased after 30 and 40 mg doses (respective discomfort volumes 596 +/- 73 vs. 791 +/- 87 mL and 630 +/- 73 vs.741 +/- 60 mL, both P < 0.05). Buspirone significantly slowed solid and liquid gastric emptying at the 20-mg dose.

CONCLUSION

Buspirone dose-dependently relaxes the proximal stomach in the fasting state and decreases the gastric emptying rate in healthy volunteers.

Serotonergic modulation of murine fundic tone

Fundic tone is maintained through a balance of excitatory and inhibitory input to fundic smooth muscle. The aim of this study was to determine the role of serotonin (5-HT) and 5-HT receptors in modulating murine fundic tone. Muscle strips were prepared from the murine fundus. Intracellular recordings were made from circular smooth muscle cells, and the effects of 5-HT on tone and excitatory and inhibitory junction potentials evoked by electrical field stimulation (EFS) were determined. 5-HT induced a concentration-dependent contraction and smooth muscle depolarization that was tetrodotoxin resistant. The 5-HT(1B/D) receptor antagonists GR-127935 and BRL-155172 significantly inhibited 5-HT-induced contractions. The 5-HT(1B/D) agonist sumatriptan contracted murine fundic muscle. The 5-HT(1A) receptor agonist buspirone relaxed fundic smooth muscle, and the relaxation was inhibited by WAY-100135 but not by N(omega)-nitro-l-arginine or tetrodotoxin. 5-HT enhanced both the excitatory and inhibitory responses to EFS. The 5-HT(3) receptor antagonist MDL-72222 partly inhibited both the excitatory and inhibitory response elicited by EFS, whereas the 5-HT(4) receptor antagonist GR-113808 partly inhibited the EFS-evoked inhibitory response. The 5-HT reuptake inhibitor fluoxetine contracted smooth muscle strips, a contraction that was partially inhibited by GR-127935 and abolished by tetrodotoxin. In conclusion, the data suggest that 5-HT modulates murine fundic contractile activity through several different receptor subtypes. Sustained release of 5-HT maintains fundic tone through postjunctional 5-HT(1B/D) receptors. 5-HT(3) receptors modulate excitatory neural input to murine fundic smooth muscle, and both 5-HT(3) and 5-HT(4) receptors modulate inhibitory neural input to murine fundic smooth muscle.