5-HT receptors on interstitial cells of Cajal, smooth muscle and enteric nerves

5-Hydroxytryptamine Enhances the Pacemaker Activity of Interstitial Cells of Cajal in Mouse Colon

We examined the localization of the 5-hydroxytryptamine (5-HT) receptor and its effects on mouse colonic interstitial cells of Cajal (ICCs) using electrophysiological techniques. Treatment with 5-HT increased the pacemaker activity in colonic ICCs with depolarization of membrane potentials in a dose-dependent manner. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blockers blocked pacemaker activity and 5-HT-induced effects. Moreover, an adenylate cyclase inhibitor inhibited 5-HT-induced effects, and cell-permeable 8-bromo-cAMP increased the pacemaker activity. Various agonists of the 5-HT receptor subtype were working in colonic ICCs, including the 5-HT4 receptor. In small intestinal ICCs, 5-HT depolarized the membrane potentials transiently. Adenylate cyclase inhibitors or HCN blockers did not show any influence on 5-HT-induced effects. Anoctamin-1 (ANO1) or T-type Ca2+ channel blockers inhibited the pacemaker activity of colonic ICCs and blocked 5-HT-induced effects. A tyrosine protein kinase inhibitor inhibited pacemaker activity in colonic ICCs under controlled conditions but did not show any influence on 5-HT-induced effects. Among mitogen-activated protein kinase (MAPK) inhibitors, a p38 MAPK inhibitor inhibited 5-HT-induced effects on colonic ICCs. Thus, 5-HT's effect on pacemaker activity in small intestinal and colonic ICCs has excitatory but variable patterns. ANO1, T-type Ca2+, and HCN channels are involved in 5-HT-induced effects, and MAPKs are involved in 5-HT effects in colonic ICCs.

Torreya grandis Kernel Oil Alleviates Loperamide-Induced Slow Transit Constipation via Up-Regulating the Colonic Expressions of Occludin/Claudin-1/ZO-1 and 5-HT3R/5-HT4R in BALB/c Mice

SCOPE

Torreya grandis kernel has traditionally been used to remove intestinal parasites and increases intestinal motility. However, the effect of Torreya grandis kernel oil (TKO) on constipation has not yet been investigated. Therefore, mouse model is used to investigate the effect of TKO on slow transit constipation (STC) and its possible mechanism.

METHODS AND RESULTS

The effects of TKO on intestinal motility of STC mice are evaluated by fecal weight, fecal water content, colon length, defecation test, and intestinal propulsion test. The mechanism of TKO alleviating STC is explored by detecting biochemical analysis, histological analysis, western blot, qRT-PCR, immunohistochemistry, and gut microbiota analysis. The results reveal that TKO effectively promotes defecation and intestinal motility, increases the level of endothelin-1, and restores the histopathological morphology of the colon under LOP pretreatment. The expression levels of occludin, claudin-1, and zonula occludens-1 (ZO-1) mRNA and protein are up-regulated in mice receiving TKO treatment. The colonic 5-hydroxytryptamine 3R/4R (5-HT3R/5-HT4R) expressions are also increased by TKO supplementation. Additionally, TKO rescues LOP-caused disorders of the gut microbiota.

CONCLUSION

Consumption of TKO is beneficial to STC recovery, and it can alleviate LOP-induced STC by up-regulating the colonic expressions of Occludin/Claudin-1/ZO-1 and 5-HT3R/5-HT4R.

Xiao Cheng Qi Decoction, an Ancient Chinese Herbal Mixture, Relieves Loperamide-Induced Slow-Transit Constipation in Mice: An Action Mediated by Gut Microbiota

Xiao Cheng Qi (XCQ) decoction, an ancient Chinese herbal mixture, has been used in treating slow-transit constipation (STC) for years. The underlying action mechanism in relieving the clinical symptoms is unclear. Several lines of evidence point to a strong link between constipation and gut microbiota. Short-chain fatty acids (SCFAs) and microbial metabolites have been shown to affect 5-HT synthesis by activating the GPR43 receptor localized on intestinal enterochromaffin cells, since 5-HT receptors are known to influence colonic peristalsis. The objective of this study was to evaluate the efficacy of XCQ in alleviating clinical symptoms in a mouse model of STC induced by loperamide. The application of loperamide leads to a decrease in intestinal transport and fecal water, which is used to establish the animal model of STC. In addition, the relationship between constipation and gut microbiota was determined. The herbal materials, composed of Rhei Radix et Rhizoma (Rhizomes of Rheum palmatum L., Polygonaceae) 55.2 g, Magnoliae Officinalis Cortex (Barks of Magnolia officinalis Rehd. et Wils, Magnoliaceae) 27.6 g, and Aurantii Fructus Immaturus (Fruitlet of Citrus aurantium L., Rutaceae) 36.0 g, were extracted with water to prepare the XCQ decoction. The constipated mice were induced with loperamide (10 mg/kg/day), and then treated with an oral dose of XCQ herbal extract (2.0, 4.0, and 8.0 g/kg/day) two times a day. Mosapride was administered as a positive drug. In loperamide-induced STC mice, the therapeutic parameters of XCQ-treated mice were determined, i.e., (i) symptoms of constipation, composition of gut microbiota, and amount of short-chain fatty acids in feces; (ii) plasma level of 5-HT; and (iii) expressions of the GPR43 and 5-HT4 receptor in colon. XCQ ameliorated the constipation symptoms of loperamide-induced STC mice. In gut microbiota, the treatment of XCQ in STC mice increased the relative abundances of Lactobacillus, Prevotellaceae_UCG_001, Prevotellaceae_NK3B31_group, Muribaculaceae, and Roseburia in feces and decreased the relative abundances of Desulfovibrio, Tuzzerella, and Lachnospiraceae_ NK4A136_group. The levels of SCFAs in stools from the STC group were significantly lower than those the control group, and were greatly elevated via treatment with XCQ. Compared with the STC group, XCQ increased the plasma level of 5-HT and the colonic expressions of the GPR43 and 5-HT4 receptor, significantly. The underlying mechanism of XCQ in anti-constipation could be related to the modulation of gut microbiota, the increase in SCFAs, the increase in plasma 5-HT, and the colonic expressions of the GPR43 and 5-HT4 receptor. Our results indicate that XCQ is a potent natural product that could be a therapeutic strategy for constipation.

Intestinal tryptophan metabolism in disease prevention and swine production

Tryptophan (Trp) is an essential amino acid that cannot be synthesized by animals. It has been characterized into two different isomers, levorotation-Trp (L-Trp) and dextrorotation-Trp (D-Trp), based on their distinct molecule orientation. Intestinal epithelial cells and gut microbiota are involved in metabolizing L-Trp in the gut via the activation of the kynurenine, serotonin, and indole pathways. However, knowledge regarding D-Trp metabolism in the gut remains unclear. In this review, we briefly update the current understanding of intestinal L/D-Trp metabolism and the function of their metabolites in modulating the gut physiology and diseases. Finally, we summarize the effects of Trp nutrition on swine production at different stages, including growth performance in weaned piglets and growing pigs, as well as the reproduction performance in sows.

Flavonoids in Amomum tsaoko Crevost et Lemarie Ameliorate Loperamide-Induced Constipation in Mice by Regulating Gut Microbiota and Related Metabolites

Amomum tsaoko (AT) is a dietary botanical with laxative properties; however, the active ingredients and mechanisms are still unclear. The active fraction of AT aqueous extract (ATAE) for promoting defecation in slow transit constipation mice is the ethanol-soluble part (ATES). The total flavonoids of ATES (ATTF) were the main active component. ATTF significantly increased the abundance of Lactobacillus and Bacillus and reduced the dominant commensals, such as Lachnospiraceae, thereby changing the gut microbiota structure and composition. Meanwhile, ATTF changed the gut metabolites mainly enriched in pathways such as the serotonergic synapse. In addition, ATTF increased the serum serotonin (5-HT) content and mRNA expression of 5-hydroxytryptamine receptor 2A (5-HT_2A), Phospholipase A2 (PLA2), and Cyclooxygenase-2 (COX2), which are involved in the serotonergic synaptic pathway. ATTF increased Transient receptor potential A1 (TRPA1), which promotes the release of 5-HT, and Myosin light chain 3(MLC3), which promotes smooth muscle motility. Notably, we established a network between gut microbiota, gut metabolites, and host parameters. The dominant gut microbiota Lactobacillus and Bacillus, prostaglandin J2 (PGJ2) and laxative phenotypes showed the most significant associations. The above results suggest that ATTF may relieve constipation by regulating the gut microbiota and serotonergic synaptic pathway and has great potential for laxative drug development in the future.

Metabotropic 5-HT receptor-mediated effects in the human submucous plexus

BACKGROUND

Serotonin (5-HT) is an important mediator in the gastrointestinal tract, acting on different neuronal 5-HT receptors. The ionotropic 5-HT₃ receptor mediates immediate but transient spike discharge in human enteric neurons. We studied the role of the metabotropic 5-HT_1P , 5-HT₄ , and 5-HT₇ receptors to activate human submucous neurons.

METHODS

Neuroimaging using the voltage sensitive dye Di-8-ANEPPS was performed in submucous plexus preparations from human surgical specimens of the small and large intestine. We synthesized a new, stable 5-HT_1P agonist, 5-benzyloxyhydrazonoindalpine (5-BOHIP).

KEY RESULTS

5-HT evoked a fast and late-onset spike discharge in enteric neurons. The fast component was blocked by the 5-HT₃ receptor antagonist cilansetron, while the remaining sustained response was significantly reduced by the 5-HT_1P receptor antagonist 5-hydroxytryptophanyl-5-hydroxytryptophan amide (5-HTP-DP). The newly synthesized 5-HT_1P agonist 5-BOHIP induced a slowly developing, long-lasting activation of submucous neurons, which was blocked by 5-HTP-DP. We could not demonstrate any 5-HT₇ receptor-induced spike discharge based on the lack of response to 5-carboxamidotryptamine. Similarly, the 5-HT₄ agonists 5-methoxytryptamine and prucalopride evoked no immediate or late-onset spike discharge.

CONCLUSIONS & INFERENCES

Our work demonstrated for the first time the presence of functional 5-HT_1P receptors on human submucous neurons. Furthermore, we found no evidence for a role of 5-HT₄ or 5-HT₇ receptors in the postsynaptic activation of human submucous neurons by 5-HT.

Role of Ion Channels in the Chemotransduction and Mechanotransduction in Digestive Function and Feeding Behavior

The gastrointestinal tract constantly communicates with the environment, receiving and processing a wide range of information. The contents of the gastrointestinal tract and the gastrointestinal tract generate mechanical and chemical signals, which are essential for regulating digestive function and feeding behavior. There are many receptors here that sense intestinal contents, including nutrients, microbes, hormones, and small molecule compounds. In signal transduction, ion channels are indispensable as an essential component that can generate intracellular ionic changes or electrical signals. Ion channels generate electrical activity in numerous neurons and, more importantly, alter the action of non-neurons simply and effectively, and also affect satiety, molecular secretion, intestinal secretion, and motility through mechanisms of peripheral sensation, signaling, and altered cellular function. In this review, we focus on the identity of ion channels in chemosensing and mechanosensing in the gastrointestinal tract.

A Randomized, Double-Blinded, Placebo-controlled Study to Evaluate the Efficacy and Safety of DA-9701 (Motilitone) in Patients With Functional Dyspepsia and Constipation-type Irritable Bowel Syndrome Overlap: A Pilot Study

Background/Aims

To assess the effects and safety of DA-9701 in patients with constipation-type irritable bowel syndrome (IBS-C) which frequently accompany functional dyspepsia (FD).

Methods

FD and IBS-C were diagnosed based on the Rome III criteria. Randomized subjects were administered 30 mg of DA-9701 (Motilitone) or placebo 3 times a day for 4 weeks. The study endpoints were evaluated the percentage of responders in the overall symptom evaluation of IBS-C and FD.

Results

Thirty IBS-C patients and 30 placebos were prospectively enrolled. The proportion of responders with improvement in overall symptoms of IBS-C was 53.33% in the DA-9701 group and 40.00% in the placebo group (P = 0.301). Compared to the placebo group, the decrease of abdominal pain score in the DA-9701 group was significantly higher at week 3 in the DA-9701 group (0.96 ± 0.77 vs 0.55 ± 0.79, P = 0.042) but no significance at week 4. There was no significant difference in total IBS quality of life score at week 4 between the 2 groups (P = 0.897). Among patients with IBS-C accompanied by FD, the proportion of responders in the DA-9701 group was 50.00% (15/30), which was higher than 31.03% (9/29) of the placebo group (P = 0.138).

Conclusions

DA-9701 showed trend of treatment efficacy in patients with FD and IBS-C overlap including overall improvement, and safety, compared to placebo but without significance probably due to small numbers. It is suggested the need for a large-scale clinical trial to confirm this preliminary effect of DA-9701.

Tapping into 5-HT3 Receptors to Modify Metabolic and Immune Responses

5-hydroxytryptamine type 3 (5-HT₃) receptors are ligand gated ion channels, which clearly distinguish their mode of action from the other G-protein coupled 5-HT or serotonin receptors. 5-HT₃ receptors are well established targets for emesis and gastrointestinal mobility and are used as adjunct targets in treating schizophrenia. However, the distribution of these receptors is wider than the nervous system and there is potential that these additional sites can be targeted to modulate inflammatory and/or metabolic conditions. Recent progress in structural biology and pharmacology of 5-HT₃ receptors have provided profound insights into mechanisms of their action. These advances, combined with insights into clinical relevance of mutations in genes encoding 5-HT₃ subunits and increasing understanding of their implications in patient's predisposition to diseases and response to the treatment, open new avenues for personalized precision medicine. In this review, we recap on the current status of 5-HT₃ receptor-based therapies using a biochemical and physiological perspective. We assess the potential for targeting 5-HT₃ receptors in conditions involving metabolic or inflammatory disorders based on recent findings, underscoring the challenges and limitations of this approach.

Interstitial cells of Cajal and human colon motility in health and disease

Our understanding of human colonic motility, and autonomic reflexes that generate motor patterns, has increased markedly through high-resolution manometry. Details of the motor patterns are emerging related to frequency and propagation characteristics that allow linkage to interstitial cells of Cajal (ICC) networks. In studies on colonic motor dysfunction requiring surgery, ICC are almost always abnormal or significantly reduced. However, there are still gaps in our knowledge about the role of ICC in the control of colonic motility and there is little understanding of a mechanistic link between ICC abnormalities and colonic motor dysfunction. This review will outline the various ICC networks in the human colon and their proven and likely associations with the enteric and extrinsic autonomic nervous systems. Based on our extensive knowledge of the role of ICC in the control of gastrointestinal motility of animal models and the human stomach and small intestine, we propose how ICC networks are underlying the motor patterns of the human colon. The role of ICC will be reviewed in the autonomic neural reflexes that evoke essential motor patterns for transit and defecation. Mechanisms underlying ICC injury, maintenance, and repair will be discussed. Hypotheses are formulated as to how ICC dysfunction can lead to motor abnormalities in slow transit constipation, chronic idiopathic pseudo-obstruction, Hirschsprung's disease, fecal incontinence, diverticular disease, and inflammatory conditions. Recent studies on ICC repair after injury hold promise for future therapies.

Action Mode of Gut Motility, Fluid and Electrolyte Transport in Chronic Constipation

Chronic constipation is a common gastrointestinal disorder, with a worldwide incidence of 14–30%. It negatively affects quality of life and is associated with a considerable economic burden. As a disease with multiple etiologies and risk factors, it is important to understand the pathophysiology of chronic constipation. The purpose of this review is to discuss latest findings on the roles of gut motility, fluid, and electrolyte transport that contribute to chronic constipation, and the main drugs available for treating patients. We conducted searches on PubMed and Google Scholar up to 9 February 2021. MeSH keywords “constipation”, “gastrointestinal motility”, “peristalsis”, “electrolytes”, “fluid”, “aquaporins”, and “medicine” were included. The reference lists of searched articles were reviewed to identify further eligible articles. Studies focusing on opioid-induced constipation, evaluation, and clinic management of constipation were excluded. The occurrence of constipation is inherently connected to disorders of gut motility as well as fluid and electrolyte transport, which involve the nervous system, endocrine signaling, the gastrointestinal microbiota, ion channels, and aquaporins. The mechanisms of action and application of the main drugs are summarized; a better understanding of ion channels and aquaporins may be helpful for new drug development. This review aims to provide a scientific basis that can guide future research on the etiology and treatment of constipation.

Cholesterol gallstones: Focusing on the role of interstitial Cajal-like cells

Cholesterol gallstone (CG) is a common, frequent biliary system disease in China, with a complex and multifactorial etiology. Declined gallbladder motility reportedly contributes to CG pathogenesis. Furthermore, interstitial Cajal-like cells (ICLCs) are reportedly present in human and guinea pig gallbladder tissue. ICLCs potentially contribute to the regulation of gallbladder motility, and aberrant conditions involving the loss of ICLCs and/or a reduction in its pacing potential and reactivity to cholecystokinin may promote CG pathogenesis. This review discusses the association between ICLCs and CG pathogenesis and provides a basis for further studies on the functions of ICLCs and the etiologies of CG.

The Enteric Nervous System and Its Emerging Role as a Therapeutic Target

The gastrointestinal (GI) tract is innervated by the enteric nervous system (ENS), an extensive neuronal network that traverses along its walls. Due to local reflex circuits, the ENS is capable of functioning with and without input from the central nervous system. The functions of the ENS range from the propulsion of food to nutrient handling, blood flow regulation, and immunological defense. Records of it first being studied emerged in the early 19th century when the submucosal and myenteric plexuses were discovered. This was followed by extensive research and further delineation of its development, anatomy, and function during the next two centuries. The morbidity and mortality associated with the underdevelopment, infection, or inflammation of the ENS highlight its importance and the need for us to completely understand its normal function. This review will provide a general overview of the ENS to date and connect specific GI diseases including short bowel syndrome with neuronal pathophysiology and current therapies. Exciting opportunities in which the ENS could be used as a therapeutic target for common GI diseases will also be highlighted, as the further unlocking of such mechanisms could open the door to more therapy-related advances and ultimately change our treatment approach.

Post-natal Growth Retardation Associated With Impaired Gut Hormone Profiles, Immune and Antioxidant Function in Pigs

The factors that cause post-natal growth retardation (PGR) in pigs are complicated; however, metabolic and immune system impairment seem to be involved. The purpose of this study was to investigate the changes of blood parameters, hormone profiles, antioxidant capacity, and immune responses in PGR pigs. Blood and small intestinal mucosa samples were collected from 42-days-old PGR and healthy pigs. The results showed that compared with the healthy group, the relative weight of spleen and kidney were greater, but the liver was lighter in PGR pigs (P < 0.05). The PGR pigs had increased serum alanine transaminase, urea nitrogen, blood ammonia, IgG, and complement 4, but decreased glucose and albumin (P < 0.05). The higher levels of serum leptin (LEP) and thyroxin (T4), and the lower levels of insulin-like growth factor-1 (IGF-1), 5-hydroxytryptamine (5-HT), somatostatin (SS), and agouti gene-related protein (AgRP) were observed in PGR pigs (P < 0.05). Consistent with the serum levels of hormones, the mRNA levels of gut hormones and their receptors were also altered in intestinal mucosa from PGR pigs (P < 0.05). The PGR pigs exhibited higher plasma concentrations of interleukin-1β (IL-1β), IL-6, IL-8, and transformed growth factor beta (TGFβ) (P < 0.05). However, the mRNA expressions of several cytokines were lower in the small intestinal mucosa of PGR pigs (P < 0.05). Abnormal antioxidant indexes in serum of PGR pigs were observed, which was in accordance with the reduced mRNA expression of several anti-oxidative genes in the small intestinal mucosa of PGR pigs (P < 0.05). These data demonstrate that an abnormal gut hormone system, immune dysfunction, and decreased antioxidant capacity may contribute to PGR in pigs. These changes could provide a valuable target in the regulation of post-natal growth retardation in animals and humans.

Phytotherapeutic effects of the fruits of Poncirus trifoliata (L.) Raf. on cancer, inflammation, and digestive dysfunction

Poncirus trifoliata (L.) Raf. belongs to the family Rutaceae in the genus Poncirus. Its fruits are widely used to alleviate symptoms of various disorders. The mature fruit (MF) possesses anticancer and antiinflammatory activities. Extracts of the dried, immature fruit, Poncirus fructus (PF) are widely used as a traditional medicine for ameliorating symptoms of digestive dysfunction in East Asia. Molecular and cellular mechanisms underlying the effects of MF and PF extracts on cancer, inflammation, and gastrointestinal disorders have been extensively studied in the past decade. This review summarizes recent findings on the anticancer and antiinflammatory effects of MF and the prokinetic effects of PF. Although the therapeutic effects of MF and PF have been clearly elucidated, in-depth further clinical studies are still required to completely verify the clinical efficacy and safety of the fruits of P. trifoliata (L.) Raf.

Hwangryunhaedok-tang induces the depolarization of pacemaker potentials through 5-HT3 and 5-HT4 receptors in cultured murine small intestine interstitial cells of Cajal

AIM

To investigate the effects of a water extract of Hwangryunhaedok-tang (HHTE) on the pacemaker potentials of mouse interstitial cells of Cajal (ICCs).

METHODS

We dissociated ICCs from small intestines and cultured. ICCs were immunologically identified using an anti-c-kit antibody. We used the whole-cell patch-clamp configuration to record the pacemaker potentials generated by cultured ICCs under the current clamp mode (I = 0). All experiments were performed at 30 °C-32 °C

RESULTS

HHTE dose-dependently depolarized ICC pacemaker potentials. Pretreatment with a 5-HT₃ receptor antagonist (Y25130) or a 5-HT₄ receptor antagonist (RS39604) blocked HHTE-induced pacemaker potential depolarizations, whereas pretreatment with a 5-HT₇ receptor antagonist (SB269970) did not. Intracellular GDPβS inhibited HHTE-induced pacemaker potential depolarization and pretreatment with a Ca²⁺-free solution or thapsigargin abolished the pacemaker potentials. In the presence of a Ca²⁺-free solution or thapsigargin, HHTE did not depolarize ICC pacemaker potentials. In addition, HHTE-induced pacemaker potential depolarization was unaffected by a PKC inhibitor (calphostin C) or a Rho kinase inhibitor (Y27632). Of the four ingredients of HHT, Coptidis Rhizoma and Gardeniae Fructus more effectively inhibited pacemaker potential depolarization.

CONCLUSION

These results suggest that HHTE dose-dependently depolarizes ICC pacemaker potentials through 5-HT₃ and 5-HT₄ receptors via external and internal Ca²⁺ regulation and via G protein-, PKC- and Rho kinase-independent pathways.

Diverse Effects of Gut-Derived Serotonin in Intestinal Inflammation

The gut is the largest producer of serotonin or 5-hydroxytryptamine (5-HT) in the human body, and 5-HT has been recognized as an important signaling molecule in the gut for decades. There are two distinct sources of enteric 5-HT. Mucosal 5-HT is predominantly produced by enterochromaffin (EC) cells of the gastrointestinal (GI) tract, and neuronal 5-HT in the gut is produced by serotonergic neurons of the enteric nervous system (ENS). The quantity of mucosal 5-HT produced vastly eclipses the amount of neuronal 5-HT in the gut. Though it is difficult to separate the functions of neuronal and mucosal 5-HT, in the normal gut both types of enteric 5-HT work synergistically playing a prominent role in the maintenance of GI functions. In inflammatory conditions of the gut, like inflammatory bowel disease (IBD) recent studies have revealed new diverse functions of enteric 5-HT. Mucosal 5-HT plays an important role in the production of pro-inflammatory mediators from immune cells, and neuronal 5-HT provides neuroprotection in the ENS. Based on searches for terms such as "5-HT", "EC cell", "ENS", and "inflammation" in pubmed.gov as well as by utilizing pertinent reviews, the current review aims to provide an update on the role of enteric 5-HT and its immune mediators in the context of intestinal inflammation.

Serotonin-induced contractile responses of esophageal smooth muscle in the house musk shrew (Suncus murinus)

BACKGROUND

Serotonin (5-hydroxytryptamine, 5-HT) is a regulatory factor in motility of the gastrointestinal tract including the esophagus. Although we proposed that vagal cholinergic and mast cell-derived non-cholinergic components including serotonin coordinately shorten the esophagus, the precise mechanism of serotonin-induced contractions in the suncus esophagus is still unclear. Therefore, the aims of this study were to determine characteristics of contractile responses induced by serotonin and to identify 5-HT receptor subtypes responsible for regulating motility in the suncus esophagus.

METHODS

An isolated segment of the suncus esophagus was placed in an organ bath, and longitudinal or circular mechanical responses were recorded using a force transducer.

KEY RESULTS

Serotonin evoked contractile responses of the suncus esophagus in the longitudinal direction but not in the circular direction. Tetrodotoxin did not affect the serotonin-induced contractions. Pretreatment with a non-selective 5-HT receptor antagonist or double application of 5-HT₁ and 5-HT₂ receptor antagonists blocked the serotonin-induced contractions. 5-HT₁ and 5-HT₂ receptor agonists, but not a 5-HT₃ receptor agonist, evoked contractile responses in the suncus esophagus.

CONCLUSION & INFERENCES

The findings suggest that serotonin induces contractile responses of the longitudinal smooth muscle in the muscularis mucosae of the suncus esophagus that are mediated via 5-HT₁ and 5-HT₂ receptors on muscle cells. The serotonin-induced contractions might contribute to esophageal peristalsis and emetic response.

The effect of levosulpiride on in vitro motor patterns in the human gastric fundus, antrum, and jejunum

BACKGROUND

Levosulpiride is a 5HT4 agonist/D2 antagonist prokinetic agent used to improve gastric emptying in patients with functional dyspepsia or gastroparesis. The aim of this study was to characterize its effect on the main in vitro motility patterns in the human fundus, antrum, and jejunum.

METHODS

Circular muscle strips from human stomach (antrum and fundus) and jejunum, obtained from 46 patients undergoing bariatric surgery, were studied using organ baths. Enteric motor neurons (EMNs) were stimulated by electrical field stimulation (EFS).

KEY RESULTS

Levosulpiride, caused an increase in the EFS-induced cholinergic contractions in the gastric antrum (+37 ± 15.18% at 100 μM, pEC50 = 4.46 ± 0.14; p < 0.05, n = 8) and jejunum (+45.4 ± 22.03% at 100 μM, pEC50 = 3.78 ± 6.81; p < 0.05, n = 5), but not in the gastric fundus. It also caused a slight decrease in tone and frequency of spontaneous contractions in the jejunum, but did not have any major effect on tone or spontaneous contractions in the stomach. It did not have any effect on EFS-induced relaxations mediated by nitric oxide (NO) in the stomach (antrum and fundus) and by NO and ATP in the jejunum.

CONCLUSIONS & INFERENCES

Our results suggest that the prokinetic effects of levosulpiride in humans are mainly due to the facilitation of the release of acetylcholine by enteric motor neurons in the gastric antrum and the jejunum.

Nitric oxide regulation of migrating motor complex: randomized trial of N(G)-monomethyl-L-arginine effects in relation to muscarinic and serotonergic receptor blockade

AIM

The migrating motor complex (MMC) propels contents through the gastrointestinal tract during fasting. Nitric oxide (NO) is an inhibitory neurotransmitter in the gastrointestinal tract. Little is known about how NO regulates the MMC. In this study, the aim was to examine nitrergic inhibition of the MMC in man using N(G)-monomethyl-L-arginine (L-NMMA) in combination with muscarinic receptor antagonist atropine and 5-HT3 receptor antagonist ondansetron.

METHODS

Twenty-six healthy volunteers underwent antroduodenojejunal manometry for 8 h with saline or NO synthase (NOS) inhibitor L-NMMA randomly injected I.V. at 4 h with or without atropine or ondansetron. Plasma ghrelin, motilin and somatostatin were measured by ELISA. Intestinal muscle strip contractions were investigated for NO-dependent mechanisms using L-NMMA and tetrodotoxin. NOS expression was localized by immunohistochemistry.

RESULTS

L-NMMA elicited premature duodenojejunal phase III in all subjects but one, irrespective of atropine or ondansetron. L-NMMA shortened MMC cycle length, suppressed phase I and shifted motility towards phase II. Pre-treatment with atropine extended phase II, while ondansetron had no effect. L-NMMA did not change circulating ghrelin, motilin or somatostatin. Intestinal contractions were stimulated by L-NMMA, insensitive to tetrodotoxin. NOS immunoreactivity was detected in the myenteric plexus but not in smooth muscle cells.

CONCLUSION

Nitric oxide suppresses phase III of MMC independent of muscarinic and 5-HT3 receptors as shown by nitrergic blockade, and acts through a neurocrine disinhibition step resulting in stimulated phase III of MMC independent of cholinergic or 5-HT3 -ergic mechanisms. Furthermore, phase II of MMC is governed by inhibitory nitrergic and excitatory cholinergic, but not 5-HT3 -ergic mechanisms.

Toll-like receptors 2 and 4 modulate the contractile response induced by serotonin in mouse ileum: analysis of the serotonin receptors involved

BACKGROUND

Microbiota through toll-like receptors (TLR) may regulate gastrointestinal motility by activating neuroendocrine mechanisms. We evaluated the influence of TLR2 and TLR4 in the spontaneous contractions and serotonin (5-HT)-induced motor response in mouse ileum, and the 5-HT receptors involved.

METHODS

Muscle contractility studies to evaluate the spontaneous intestinal motility and the response to 5-HT were performed in the ileum from wild type (WT), TLR2(-/-), TLR4(-/-), and TLR2/4 double knockout (DKO) mice. 5-HT receptor expression was determined by real-time PCR.

KEY RESULTS

The amplitude of spontaneous contractions in ileum was higher in TLR2(-/-), TLR4(-/-), and TLR2/4 DKO mice with respect to WT. 5-HT evoked concentration-dependent contractile responses in the ileum from TLR2(-/-) and TLR4(-/-) mice similar to WT. However, in ileum from TLR2/4 DKO, 5-HT did not induce any contractile response. Expression of 5-HT2A, 5-HT2B, 5-HT2C, and 5-HT3 receptors resulted increased in ileum from TLR4(-/-) and TLR2/4 DKO. Expression of the 5-HT4 receptor was diminished in TLR2(-/-) and TLR2/4 DKO. High levels of 5-HT7 receptor expression were found in TLR2/4 DKO but not in TLR2(-/-) or TLR4(-/-). In WT and TLR4(-/-), 5-HT2, 5-HT3, 5-HT4, and 5-HT7 receptor antagonists reduced the contractile response evoked by 5-HT. In TLR2(-/-) mice, 5-HT4 antagonist did not reduce the 5-HT response. In TLR2/4 DKO mice, only 5-HT4 and 5-HT7 receptor antagonists reduced the relaxing response induced by 5-HT.

CONCLUSIONS & INFERENCES

TLR2 and TLR4 signaling may modulate the spontaneous contractions and the serotonin contractile response by acting on 5-HT2, 5-HT3, 5-HT4, and 5-HT7 receptors.

Involvement of 5-HT3 and 5-HT4 receptors in colonic motor patterns in rats

BACKGROUND

Colonic migrating motor complexes in the rat constitute two distinct propulsive motor patterns, pan-colonic rhythmic long distance contractions (LDCs), and rhythmic propulsive motor complexes (RPMCs) occurring primarily in the mid/distal colon. Interstitial cells of Cajal govern their rhythmicity, but their occurrence is dependent on neural programs. Our aim was to investigate the involvement of 5-HT3 and 5-HT4 receptors in the generation and pharmacological control of the motor patterns.

METHODS

Effects of 5-HT-related drugs on colonic motor patterns were analyzed through spatio-temporal maps created from video recordings of whole organ motility.

KEY RESULTS

5-HT3 antagonists abolished RPMCs and LDCs. 5-HT4 agonists inhibited LDCs; they promoted RPMCs, which was blocked by the 5-HT4 antagonist GR 125487. 5-HT and the 5-HT3 agonist m-CPBG strongly inhibited LDCs and RPMCs.

CONCLUSIONS & INFERENCES

The generation of LDCs involves ongoing 5-HT release acting on 5-HT3 and 5-HT4 receptors. The spontaneous generation of RPMCs involves ongoing 5-HT release acting on 5-HT3 but not 5-HT4 receptors. Prucalopride and mosapride promote RPMCs, an effect that is inhibited by the 5-HT4 receptor antagonist GR 125487. A 5-HT3 agonist does not promote RPMCs. Segmentation, including a pattern of sequential segmental activity not previously described, can occur without significant involvement of 5-HT3 and 5-HT4 receptors. 5-HT and a 5-HT3 agonist are strongly inhibitory indicating that 5-HT receptors are present in inhibitory pathways which are normally not involved in the generation of spontaneous or distention-induced motor patterns.

Distribution of 5-HT3, 5-HT4, and 5-HT7 Receptors Along the Human Colon

Background/Aims

Several disorders of the gastrointestinal tract are associated with abnormal serotonin (5-HT) signaling or metabolism where the 5-HT₃ and 5-HT₄ receptors are clinically relevant. The aim was to examine the distribution of 5-HT₃, 5-HT₄, and 5-HT₇ receptors in the normal human colon and how this is associated with receptor interacting chaperone 3, G protein coupled receptor kinases, and protein LIN-7 homologs to extend previous observations limited to the sigmoid colon or the upper intestine.

Methods

Samples from ascending, transverse, descending, and sigmoid human colon were dissected into 3 separate layers (mucosa, longitudinal, and circular muscles) and ileum samples were dissected into mucosa and muscle layers (n = 20). Complementary DNA was synthesized by reverse transcription from extracted RNA and expression was determined by quantitative or end point polymerase chain reaction.

Results

The 5-HT₃ receptor subunits were found in all tissues throughout the colon and ileum. The A subunit was detected in all samples and the C subunit was expressed at similar levels while the B subunit was expressed at lower levels and less frequently. The 5-HT₃ receptor E subunit was mainly found in the mucosa layers. All splice variants of the 5-HT₄ and 5-HT₇ receptors were expressed throughout the colon although the 5-HT₄ receptor d, g, and i variants were expressed less often.

Conclusions

The major differences in 5-HT receptor distribution within the human colon are in relation to the mucosa and muscular tissue layers where the 5-HT₃ receptor E subunit is predominantly found in the mucosal layer which may be of therapeutic relevance.

Genetic and Non-genetic Factors Associated With Constipation in Cancer Patients Receiving Opioids

Objectives:

To examine whether the inter-individual variation in constipation among patients receiving opioids for cancer pain is associated with genetic or non-genetic factors.

Methods:

Cancer patients receiving opioids were included from 17 centers in 11 European countries. Intensity of constipation was reported by 1,568 patients on a four-point categorical scale. Non-genetic factors were included as covariates in stratified regression analyses on the association between constipation and 75 single-nucleotide polymorphisms (SNPs) within 15 candidate genes related to opioid- or constipation-signaling pathways (HTR3E, HTR4, HTR2A, TPH1, ADRA2A, CHRM3, TACR1, CCKAR, KIT, ARRB2, GHRL, ABCB1, COMT, OPRM1, and OPRD1).

Results:

The non-genetic factors significantly associated with constipation were type of laxative, mobility and place of care among patients receiving laxatives (N=806), in addition to Karnofsky performance status and presence of metastases among patients not receiving laxatives (N=762) (P<0.01). Age, gender, body mass index, cancer diagnosis, time on opioids, opioid dose, and type of opioid did not contribute to the inter-individual differences in constipation. Five SNPs, rs1800532 in TPH1, rs1799971 in OPRM1, rs4437575 in ABCB1, rs10802789 in CHRM3, and rs2020917 in COMT were associated with constipation (P<0.01). Only rs2020917 in COMT passed the Benjamini–Hochberg criterion for a 10% false discovery rate.

Conclusions:

Type of laxative, mobility, hospitalization, Karnofsky performance status, presence of metastases, and five SNPs within TPH1, OPRM1, ABCB1, CHRM3, and COMT may contribute to the variability in constipation among cancer patients treated with opioids. Knowledge of these factors may help to develop new therapies and to identify patients needing a more individualized approach to treatment.

Herbal medicines for the treatment of cancer chemotherapy-induced side effects

Accumulating evidence suggests that Japanese herbal medicines, called Kampo, have beneficial effects on cancer chemotherapy-induced side effects. Rikkunshito ameliorates cisplatin-induced anorexia through an antagonistic effect on the 5-HT receptors and by increasing the serum ghrelin levels. Hangeshashinto improves irinotecan-induced diarrhea and chemotherapy-induced mucositis by inhibiting the activity of β-glucuronidase as well as the synthesis of prostaglandin E2. Goshajinkigan prevents oxaliplatin-induced neurotoxicity, possibly through suppressing functional alterations of the transient receptor potential channels. In this review, we will summarize the currently available literature regarding the clinical efficacy and potential mechanisms of Kampo medicines in the treatment of cancer chemotherapy-induced side effects.

Evaluation of the relation between interstitial cells of cajal (CD117) and serotonin receptor (5HT-3A) with postfundoplication dysphagia

OBJECTIVE

The aim of the present study is to investigate the effect of Nissen fundoplication to the pacemaker cells of an intestinal system and the serotonin receptors on an ICC membrane.

METHODS

Sixteen adult male rats were taken into study. Rats were divided in to the following two groups. Nissen fundoplication was performed to study group (Group 1) and no surgical procedures were applied to control group (group 2). The rats who were subjected to surgery and the rats without surgery were sacrificed on to postoperative 14 days. Specimens for the pathologic analysis were obtained from upper esophagus (group A) and esophagogastric junction (EGJ) (group B). Distribution of ICC and 5HT-3A were evaluated separately.

RESULTS

There was a significant difference (p=0.01, p=0.02, respectively) regarding number of cells stained with CD117 between the group 1B-2B and group 2A-2B. Also there was a significant difference between (p=0.01, p=0.01 respectively) number of cells stained with 5HT-3A in groups 1A-1B and 2A-2B. However, no correlation was detected between group 1B-2B for 5HT-3A.

CONCLUSION

A reduction in the number of ICC was observed in esophagogastric junctions of the fundoplication group but 5HT-3A distribution did not show a significant difference. A decrease in the number of ICC may be effective at postfundoplication dysphagia.

Perivascular Interstitial Cells of Cajal in Human Colon

BACKGROUND & AIMS

Interstitial cells of Cajal (ICC) closely associate with nerves and smooth muscles to modulate gut motility. In the ICC microenvironment, although the circulating hormones/factors have been shown to influence ICC activities, the association between ICC and microvessels in the gut wall has not been described. We applied three-dimensional (3D) vascular histology with c-kit staining to identify the perivascular ICC and characterize their morphologic and population features in the human colon wall.

METHODS

Full-thickness colons were obtained from colectomies performed for colorectal cancer. We targeted the colon wall away from the tumor site. Confocal microscopy with optical clearing (use of immersion solution to reduce scattering in optical imaging) was performed to simultaneously reveal the ICC and vascular networks in space. 3D image rendering and projection were digitally conducted to illustrate the ICC-vessel contact patterns.

RESULTS

Perivascular ICC were identified in the submucosal border, myenteric plexus, and circular and longitudinal muscles via high-definition 3D microscopy. Through in-depth image projection, we specified two contact patterns-the intimate cell body-to-vessel contact (type I, 18% of ICC in circular muscle) and the long-distance process-to-vessel contact (type II, 16%)-to classify perivascular ICC. Particularly, type I perivascular ICC were detected with elevated c-kit staining levels and were routinely found in clusters, making them readily distinguishable from other ICC in the network.

CONCLUSIONS

We propose a new subclass of ICC that closely associates with microvessels in the human colon. Our finding suggests a functional relationship between these mural ICC and microvessels based on the morphologic proximity.

Predominant mucosal expression of 5-HT4(+h) receptor splice variants in pig stomach and colon

AIM: To investigate cellular 5-HT_4(-h/+h) receptor distribution, particularly in the epithelial layer, by laser microdissection and polymerase chain reaction (PCR) in porcine gastrointestinal (GI) tissues.

METHODS: A stepwise approach was used to evaluate RNA quality and to study cell-specific 5-HT₄ receptor mRNA expression in the porcine gastric fundus and colon descendens. After freezing, staining and laser microdissection and pressure catapulting (LMPC), RNA quality was evaluated by the Experion automated electrophoresis system. 5-HT₄ receptor and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expressions were examined by endpoint reverse transcription (RT)-PCR in mucosal and muscle-myenteric plexus (MMP) tissue fractions, in mucosal and MMP parts of hematoxylin and eosin (HE) stained tissue sections and in microdissected patches of the epithelial and circular smooth muscle cell layer in these sections. Pig gastric fundus tissue sections were also stained immunohistochemically (IHC) for enterochromaffin cells (EC cells; MAB352); these cells were isolated by LMPC and examined by endpoint RT-PCR.

RESULTS: After HE staining, the epithelial and circular smooth muscle cell layer of pig colon descendens and the epithelial cell layer of gastric fundus were identified morphologically and isolated by LMPC. EC cells of pig gastric fundus were successfully stained by IHC and isolated by LMPC. Freezing, HE and IHC staining, and LMPC had no influence on RNA quality. 5-HT₄ receptor and GAPDH mRNA expressions were detected in mucosa and MMP tissue fractions, and in mucosal and MMP parts of HE stained tissue sections of pig colon descendens and gastric fundus. In the mucosa tissue fractions of both GI regions, the expression of h-exon containing receptor [5-HT_4(+h) receptor] mRNA was significantly higher (P < 0.01) compared to 5-HT_4(-h) receptor expression, and a similar trend was obtained in the mucosal part of HE stained tissue sections. Large microdissected patches of the epithelial and circular smooth muscle cell layer of pig colon descendens and of the epithelial cell layer of pig gastric fundus, also showed 5-HT₄ receptor and GAPDH mRNA expression. No 5-HT₄ receptor mRNA expression was detected in gastric LMPC-isolated EC cells from IHC stained tissues, which cells were positive for GAPDH.

CONCLUSION: Porcine GI mucosa predominantly expresses 5-HT_4(+h) receptor splice variants, suggesting their contribution to the 5-HT₄ receptor-mediated mucosal effects of 5-HT.

Neurogenic and myogenic properties of pan-colonic motor patterns and their spatiotemporal organization in rats

Background and Aims

Better understanding of intrinsic control mechanisms of colonic motility will lead to better treatment options for colonic dysmotility. The aim was to investigate neurogenic and myogenic control mechanisms underlying pan-colonic motor patterns.

Methods

Analysis of in vitro video recordings of whole rat colon motility was used to explore motor patterns and their spatiotemporal organizations and to identify mechanisms of neurogenic and myogenic control using pharmacological tools.

Results

Study of the pan-colonic spatiotemporal organization of motor patterns revealed: fluid-induced or spontaneous rhythmic propulsive long distance contractions (LDCs, 0.4–1.5/min, involving the whole colon), rhythmic propulsive motor complexes (RPMCs) (0.8–2.5/min, dominant in distal colon), ripples (10–14/min, dominant in proximal colon), segmentation and retrograde contractions (0.1–0.8/min, prominent in distal and mid colon). Spontaneous rhythmic LDCs were the dominant pattern, blocked by tetrodotoxin, lidocaine or blockers of cholinergic, nitrergic or serotonergic pathways. Change from propulsion to segmentation and distal retrograde contractions was most prominent after blocking 5-HT₃ receptors. In the presence of all neural blockers, bethanechol consistently evoked rhythmic LDC-like propulsive contractions in the same frequency range as the LDCs, indicating the existence of myogenic mechanisms of initiation and propulsion.

Conclusions

Neurogenic and myogenic control systems orchestrate distinct and variable motor patterns at different regions of the pan-colon. Cholinergic, nitrergic and serotonergic pathways are essential for rhythmic LDCs to develop. Rhythmic motor patterns in presence of neural blockade indicate the involvement of myogenic control systems and suggest a role for the networks of interstitial cells of Cajal as pacemakers.

Luminal melatonin stimulates pancreatic enzyme secretion via activation of serotonin-dependent nerves

BACKGROUND

Serotonin (5-HT) is released from enterochromaffin cells in the gastrointestinal tract. 5-HT, via the activation of 5-HT2 and 5-HT3 receptors on vagal fibers, mediates pancreatic secretion through the mechanism independent from cholecystokinin. Melatonin (5-HT derivative) or L-tryptophan (melatonin or 5-HT precursor) given systemically or intraduodenally to the rats stimulate amylase secretion, but the mechanism is not clear. The aim of this study was to investigate the involvement of 5-HT in the pancreatostimulatory effect of melatonin or L-tryptophan, administered intraduodenally.

METHODS

Wistar rats were surgically equipped with silicone catheters; inserted into pancreato-biliary duct and into the duodenum. Melatonin, L-tryptophan or 5-HT were given to the rats as a bolus. Combination of 5-HT2 or 5-HT3 receptor antagonists: ketanserin (100 μg/kg) and MDL72222 (250 μg/kg) was given intraperitoneally to the animals, 15 min. prior to the administration of the examined substances. The role of the vagal nerve, sensory fibers and CCK in the control of pancreatic exocrine function were determined. Blood samples were taken for the determination of 5-HT.

RESULTS

Melatonin, 5-HT or L-tryptophan increased pancreatic amylase secretion. The stimulatory effect of the above substances was decreased by pretreatment of the rats with ketanserin and MDL72222. Bilateral vagotomy completely abolished the increase of amylase output caused by 5-HT, while capsaicin deactivation of sensory nerves or blockade of CCK1 receptor only partially reversed the stimulatory effect of 5-HT on the pancreas. Intraduodenal L-tryptophan, but not melatonin, increased plasma 5-HT concentrations in a dose- and time-dependent manner.

CONCLUSION

Stimulation of pancreatic exocrine function caused by intraluminal administration of melatonin, or L-tryptophan is modified, at least in part, by serotoninergic mechanisms and vagal nerves.

Submucous rather than myenteric neurons are activated by mucosal biopsy supernatants from irritable bowel syndrome patients

BACKGROUND

We previously showed that colonic mucosal biopsy supernatants from patients with irritable bowel syndrome (IBS) activate neurons of the human submucous plexus, an area with densely packed immune cells. Based on the concept that mucosa-nerve signaling is altered in IBS, we tested in this study whether the nerve sensitizing effect of IBS mucosal biopsy supernatants is more prominent in the submucous than myenteric plexus.

METHODS

Fast neuroimaging with the voltage-sensitive dye Di-8-ANEPPS was used to record activity of guinea-pig submucous and myenteric neurons after application of constipation (C)- and diarrhea (D)-IBS supernatants (three each) and four supernatants from healthy control subjects. Results are based on recordings from 4731 neurons.

KEY RESULTS

Control supernatants did not evoke significant responses in submucous or myenteric neurons. In contrast, all IBS supernatants evoked a significant spike discharge (median 3.6 Hz) in 46% of submucous neurons. This activation was significantly stronger than in the myenteric plexus where even twice the amount of supernatants evoked a lower spike frequency (median 2.1Hz) in only 8.5% of neurons. Pharmacological studies revealed serotonin, histamine, and proteases as components mediating neuronal activation. Individual application of these components revealed that only serotonin evoked a significantly stronger activation of submucous compared with myenteric neurons.

CONCLUSIONS & INFERENCES

Direct neuronal activation by IBS mucosal biopsy supernatants is primarily a feature of submucous rather than myenteric neurons. This is associated with a stronger excitation of submucous neurons by serotonin. The plexus-specific effects support the concept that altered mucosa-nerve signaling underlies disturbances in IBS.

Disturbed development of the enteric nervous system after in utero exposure of selective serotonin re-uptake inhibitors and tricyclic antidepressants. Part 1: Literature review

The increase in selective serotonin re-uptake inhibitor (SSRI) use during pregnancy, questions concerning abnormal development of the enteric nervous system (ENS), increase in laxative use in children and the association of fluoxetine with infantile hypertrophic pyloric stenosis (IHPS) gave rise to this pharmacological literature review. The role of 5-HT and the NE uptake in ontogeny of the ENS and the effects SSRIs and TCAs might have on the development of the ENS were investigated. The literature study showed that SSRIs may influence the development of the ENS in two ways. Blockage of the serotonin re-uptake transporter (SERT) during foetal development could influence migration, differentiation and survival of cells. This could lead to abnormal development in the first trimester of pregnancy. The other way is that 5-HT seems to be a growth factor in the primitive ENS. This growth factor like action is mediated through the 5-HT(2B) receptor and stimulation of this receptor by SSRIs influences the fate of late-developing enteric neurons. This could lead to abnormal development in the second and third trimester. TCAs could influence the development of the ENS, besides through inhibition of the SERT, through inhibition of the norepinephrine transporter (NET). Expression of the NET seems to be essential for a full development of enteric neurons and especially for serotonergic neurons. In addition the NET was detected early in ontogeny and precedes neuronal differentiation, which suggests that TCAs might influence development of the ENS when exposed early in pregnancy. The insights of this study gave rise to hypotheses which will be tested in an epidemiological cohort study.

Effect of jatrorrhizine on delayed gastrointestinal transit in rat postoperative ileus

OBJECTIVES

Postoperative ileus is major cause of postoperative complication and prolonged hospitalization. Jatrorrhizine, which is a protoberberine alkaloid isolated from the medicinal plants Berberis aristata and Coptis chinensis, has been found to increase contractility of gastric antral and ileum smooth muscles of rat gastrointestinal tract. We have investigated whether jatrorrhizine could offset gastrointestinal transit in rat with postoperative ileus.

METHODS

Postoperative ileus was induced by laparotomy with intestinal manipulation under anaesthesia. Gastrointestinal transit was evaluated by measurement of gastric emptying, geometric centre and the migration of Evans blue.

KEY FINDINGS

Postoperative ileus significantly delayed gastric emptying and intestinal transit. Jatrorrhizine dose-dependently (0.1, 0.3 and 1 mg/kg) offset delayed gastric emptying and intestinal transit (geometric centre and the migration of Evans blue) in postoperative ileus. Pretreatment of animals with atropine inhibited the action of jatrorrhizine on gastric emptying and intestinal transit, but pretreatment of animals with SB204070 did not influence the effect of jatrorrhizine on gastric emptying and intestinal transit in postoperative ileus.

CONCLUSIONS

Jatrorrhizine offset postoperative ileus-induced delayed gastric emptying and intestinal transit in rats, an action mediated via the cholinergic pathway, but not involving activation of 5-HT(4) receptors.

Detailed knowledge of cellular expression of G protein-coupled receptors in the human enteric nervous system is essential for understanding their diverse actions

G protein-coupled receptors (GPCRs) comprise a large and diverse superfamily of transmembrane receptors that mediate the functions of an extraordinarily large number of extracellular ligands. They control many major physiological processes and are involved in diverse pathological processes, including gastrointestinal diseases. G protein-coupled receptors are one of the most targeted classes in pharmaceutical drug research. At present, much of our knowledge concerning the expression, distribution and function of GPCRs in the gut has been gleaned from studies performed in experimental models. Data obtained in the human digestive tract, especially in the enteric nervous system, are sparse and incomplete, although enteric neurons have a key position in almost all physiological and pathophysiological processes in the gut. Knowledge of cellular distribution of GPCRs, of regional differences in GPCR expression, and of altered GPCR expression during pathophysiological conditions in the human gut, will lead to a better understanding of GPCR activity, but will also contribute to the development of new drugs. In the current issue of the Journal, Harrington et al. describe the presence and cellular localization of muscarinic receptors in the human colon. Morphologically, orientated studies on the cellular expression of GPCRs in the human gut have to be encouraged, because these studies will yield data that are of therapeutic relevance.

Recent advances in studies of spontaneous activity in smooth muscle: ubiquitous pacemaker cells

The general and specific properties of pacemaker cells, including Kit-negative cells, that are distributed in gastrointestinal, urethral and uterine smooth muscle tissues, are discussed herein. In intestinal tissues, interstitial cells of Cajal (ICC) are heterogeneous in both their forms and roles. ICC distributed in the myenteric layer (ICC-MY) act as primary pacemaker cells for intestinal mechanical and electrical activity. ICC distributed in muscle bundles play a role as mediators of signals from autonomic nerves to smooth muscle cells. A group of ICC also appears to act as a stretch sensor. Intracellular Ca2+ dynamics play a crucial role in ICC-MY pacemaking; intracellular Ca2+ ([Ca2+](i)) oscillations periodically activate plasmalemmal Ca2+-activated ion channels, such as Ca2+-activated Cl(-) channels and/or non-selective cation channels, although the relative contributions of these channels are not defined. With respect to gut motility, both the ICC network and enteric nervous system, including excitatory and inhibitory enteric neurons, play an essential role in producing highly coordinated peristalsis.

Different stimulatory effects of methylisogermabullone on the spontaneous contractility of rat gastrointestinal segments

Using rat gastrointestinal (GI) strips, this study investigated the stimulatory effects of methylisogermabullone (MIGB) purified from radish on the spontaneous contractility of GI smooth muscles and pharmacological mechanisms involved in the MIGB-induced GI contraction. MIGB at 30 microM differently regulated the tone and amplitude of spontaneous GI contractility according to the region (fundus through distal colon) and orientation (longitudinal and circular) of smooth muscles: a significant increase in both tone and amplitude of spontaneous contraction in the ileum longitudinal and distal colon circular muscles and in amplitude only in the fundus, jejunum and distal colon longitudinal muscles. Pretreatment of ileum longitudinal muscles with atropine (0.5 microM) or 4-DAMP (0.5 microM) significantly inhibited the acetylcholine (ACh, 1 microM)- and MIGB (30 microM)-stimulated contraction, and methoctramine (0.5 microM) also obviously reduced the tone and amplitude increased by ACh and MIGB, respectively. In the presence of methysergide (1 microM), pretreatment of ileum longitudinal muscles with both ondansetron (0.1 microM) and GR113808 (0.1 microM) significantly inhibited the contraction stimulated by 5-HT (10 microM), but not by MIGB. Taken together, it is concluded that MIGB differently regulates the spontaneous contractility (tone and/or amplitude) of GI segments according to the region of gut and orientation of smooth muscles, and these contractile responses of GI tracts to MIGB are likely mediated, at least, by activation of acetylcholinergic M2 and M3 receptors.

Selective stimulation of intrinsic excitatory and inhibitory motor pathways in porcine lower oesophageal sphincter

The mechanisms of stimulation of inhibitory and excitatory motor neurons (MNs) in the lower oesophageal sphincter (LOS) are not fully understood. The aim of this study was to assess the effect of selective stimulation of inhibitory and excitatory MNs in porcine LOS through nicotinic acetylcholine receptors (nAChRs), 5-HT(3) and P2X receptors. Circular LOS strips from adult pigs were studied in organ baths. We compared the effects of stimulation of MNs by electrical field stimulation (26 V, 0.3-20 Hz); nicotine (1-300 micromol L(-1)); 5-HT and 2-Me-5-HT (1 nmol(-1)-30 micromol L(-1)); and alpha,beta-methylene ATP (alpha,beta-meATP 1-100 micromol L(-1)); in standard Krebs solution; a non-adrenergic non-nitrergic non-purinergic (NANNNP) solution; and a non-adrenergic non-cholinergic (NANC) solution. Electrical stimulation of inhibitory MNs caused an intense LOS relaxation (-78.94 +/- 4.50% of LOS tone); and of excitatory MNs, a strong contraction (17.89 +/- 1.96 g). Nicotine 100 micromol L(-1) relaxed LOS (-84.67 +/- 3.98%) in standard Krebs solution, an effect reduced by Tetrodotoxin (TTX) 1 micromol L(-1). Nicotine induced a weak TTX-sensitive contraction (1.64 +/- 0.4 g) in NANNNP solution. 5-HT 10 micromol L(-1) and 2-Me-5-HT 30 micromol L(-1) contracted LOS in standard, NANC and NANNNP conditions, maximal responses (7.30 +/- 1.52 g, 3.50 +/- 0.18 g respectively) being reduced by TTX. alpha,beta-meATP 100 micromol L(-1) caused a LOS relaxation (-17.45 +/- 6.62%) unaffected by TTX in NANC solution, and a contraction (6.7 +/- 0.85 g) antagonized by TTX in NANNNP solution. Our results suggest selective mechanisms for stimulation of intrinsic excitatory and inhibitory motor pathways in porcine LOS. Inhibitory MNs are strongly stimulated by nAChRs and do not respond to stimulation of 5-HT(3) and P2X receptors. By contrast, excitatory MNs are stimulated through 5-HT(3) and P2X receptors, stimulation through nACRs being difficult and causing a weak response.

Protein kinase C{gamma} mediates regulation of proliferation by the serotonin 5-hydroxytryptamine receptor 2B

Activation of the 5-hydroxytryptamine receptor 2B (5-HT(2B)), a G(q/11) protein-coupled receptor, results in proliferation of various cell types. The 5-HT(2B) receptor is also expressed on the pacemaker cells of the gastrointestinal tract, the interstitial cells of Cajal (ICC), where activation triggers ICC proliferation. The goal of this study was to characterize the mitogenic signal transduction cascade activated by the 5-HT(2B) receptor. All of the experiments were performed on mouse small intestine primary cell cultures. Activation of the 5-HT(2B) receptor by its agonist BW723C86 induced proliferation of ICC. Inhibition of phosphatidylinositol 3-kinase by LY294002 decreased base-line proliferation but had no effect on 5-HT(2B) receptor-mediated proliferation. Proliferation of ICC through the 5-HT(2B) receptor was inhibited by the phospholipase C inhibitor U73122 and by the inositol 1,4,5-trisphosphate receptor inhibitor Xestospongin C. Calphostin C, the alpha, beta, gamma, and micro protein kinase C (PKC) inhibitor Gö6976, and the alpha, beta, gamma, delta, and zeta PKC inhibitor Gö6983 inhibited 5-HT(2B) receptor-mediated proliferation, indicating the involvement of PKC alpha, beta, or gamma. Of all the PKC isoforms blocked by Gö6976, PKCgamma and micro mRNAs were found by single-cell PCR to be expressed in ICC. 5-HT(2B) receptor activation in primary cell cultures obtained from PKCgamma(-/-) mice did not result in a proliferative response, further indicating the requirement for PKCgamma in the proliferative response to 5-HT(2B) receptor activation. The data demonstrate that the 5-HT(2B) receptor-induced proliferative response of ICC is through phospholipase C, [Ca(2+)](i), and PKCgamma, implicating this PKC isoform in the regulation of cellular proliferation.

Distribution of serotonin receptors and interacting proteins in the human sigmoid colon

This study aimed to examine the distribution of 5-HT receptors in the human colon. 5-HT induces desensitization of the circular muscle and as this is facilitated by G-protein coupled receptor kinases (GRKs) and other proteins, we also examined their distribution. Human sigmoid colon samples were dissected into three separate layers (mucosa, taeniae coli and intertaenial strips) and RNA was amplified by RT-PCR. The 5-HT(2B) receptor and all 5-HT(7) receptor splice variants were expressed in all tissues. 5-HT(4) a,b,c and n splice variants were also expressed in all tissues and 5-HT(4d), 5-HT(4g) and 5-HT(4i) were only detected in some samples. The 5-HT(2A) receptor was seen predominantly in the intertaenial strips of the colon. Only one transcript of the serotonin transporter (SERT) was detected in the muscle layers. Variation was seen in GRK expression with GRK2 and 3 predominantly expressed in the mucosa, while GRK5 and 6 were found more commonly in the taeniae coli. PDZ (named after postsynaptic density protein, Drosophila disc large tumour suppressor and tight junction protein ZO-1) domain containing proteins, which may be involved in 5-HT receptor trafficking, were also detected throughout the sigmoid colon. The 5-HT(3A) subunit was expressed in all tissues, whereas the 5-HT(3E) subunit was mainly found in the mucosa layer while the 5-HT(3B) subunit was more common in the muscle layers. Receptor interacting chaperone (RIC-3), which is involved in transporting 5-HT(3) receptor subunits, is expressed less in mucosa compared to muscle layers. In conclusion, these results show that there is variation in distribution of 5-HT receptors and interacting proteins within the sigmoid colon that may contribute to colonic function.

Serotonin pharmacology in the gastrointestinal tract: a review

Serotonin (5-hydroxytryptamine or 5-HT) plays a critical physiological role in the regulation of gastrointestinal (GI) function. 5-HT dysfunction may also be involved in the pathophysiology of a number of functional GI disorders, such as chronic constipation, irritable bowel syndrome and functional dyspepsia. This article describes the role of 5-HT in the enteric nervous system (ENS) of the mammalian GI tract and the receptors with which it interacts. Existing serotonergic therapies that have proven effective in the treatment of GI functional disorders and the potential of drugs currently in development are also highlighted. Advances in our understanding of the physiological and pathophysiological roles of 5-HT in the ENS and the identification of selective receptor ligands bodes well for the future development of more efficacious therapies for patients with functional GI disorders.