Role of serotonin in the pathophysiology of the irritable bowel syndrome

Effects of serotonin 5-HT3 receptor antagonists on stress-induced colonic hyperalgesia and diarrhoea in rats: a comparative study with opioid receptor agonists, a muscarinic receptor antagonist and a synthetic polymer

In this study, we examined the effects of serotonin (5-HT)3 receptor antagonists (5-HT3RAs) including ramosetron, alosetron, and cilansetron on colonic nociceptive threshold in rats. Furthermore, we established a restraint stress-induced colonic hyperalgesia model in rats, and compared the inhibitory effects of 5-HT3RAs on restraint stress-induced colonic hyperalgesia and diarrhoea with those of loperamide, trimebutine, tiquizium and polycarbophil. The colonic nociceptive threshold was measured as the balloon pressure at the time the rat showed a nociceptive response during colonic distension by an intrarectally inserted balloon. Oral administration of ramosetron (3-30 microg kg(-1)), alosetron (30-300 microg kg(-1)), or cilansetron (30-300 microg kg(-1)) increased the colonic nociceptive threshold in a dose-dependent manner in non-stressed rats. Restraint stress for 1 h significantly decreased the colonic nociceptive threshold, but ramosetron (0.3-3 microg kg(-1)), alosetron (3-30 microg kg(-1)), cilansetron (3-30 microg kg(-1)) and trimebutine (100-1000 mg kg(-1)) significantly inhibited the decrease in the threshold. Loperamide (3-30 mg kg(-1)), tiquizium (100-1000 mg kg(-1)) and polycarbophil (1000 mg kg(-1)) did not affect the restraint stress-induced decrease in the colonic nociceptive threshold. All drugs tested in this study showed dose-dependent inhibition of restraint stress-induced diarrhoea in rats. These results indicate that, unlike existing antidiarrhoeal and spasmolytic agents, 5-HT3RAs have inhibitory effects on colonic nociception, and prevented restraint stress-induced both diarrhoea and hyperalgesia at almost the same doses in rats. This suggests that the 5-HT3RAs may be useful in ameliorating both colonic hyperalgesia and diarrhoea in patients with irritable bowel syndrome.

Effects of serotonin 5-HT(3) receptor antagonists on CRF-induced abnormal colonic water transport and defecation in rats

The effects of corticotropin releasing factor (CRF) and serotonin (5-HT)(3) receptor antagonists on intestinal water transport are not well understood. Hence, we established a CRF-induced abnormal water transport model in rat colon, and evaluated the effects of 5-HT(3) receptor antagonists including ramosetron, alosetron, and cilansetron, and the antidiarrheal agent loperamide, in this model. In addition, the effects of 5-HT(3) receptor antagonists and loperamide on abnormal defecation induced by CRF in rats were examined. Colonic water transport was measured in colonic loops in conscious rats. Centrally administered CRF (3-30 microg/kg) markedly decreased colonic fluid loss, whereas oral administration of ramosetron (3, 30 microg/kg), alosetron (300 microg/kg), cilansetron (300 microg/kg), or loperamide (3 mg/kg) significantly inhibited it. Ramosetron (1-10 microg/kg), alosetron (10-100 microg/kg), cilansetron (10-100 microg/kg), or loperamide (0.3-3 mg/kg) also showed dose-dependent inhibition of CRF-induced defecation in rats. These results suggest that 5-HT(3) receptors are involved in both abnormal colonic water transport and defecation induced by CRF, and that the inhibitory effects of 5-HT(3) receptor antagonists on CRF-induced abnormal defecation partly result from their ameliorating action on colonic water transport.

Decreased expression of serotonin in the jejunum and increased numbers of mast cells in the terminal ileum in patients with irritable bowel syndrome

AIM

To investigate if there are changes in serotonin (5-HT) levels, enterochromaffin (EC) cells and mast cells in small intestinal mucosa of patients with irritable bowel syndrome (IBS).

METHODS

Diarrhea-predominant (IBS-D, n = 20), or constipation-predominant (IBS-C, n = 18) IBS patients and healthy controls (n = 20) underwent colonoscopy and peroral small intestinal endoscopy, and mucosal samples were obtained at the descending part of the duodenum, proximal end of jejunum and terminal ileum. High-performance liquid chromatography-electrochemistry and immunohistochemical methods were used to detect 5-HT content, EC cells and mast cells.

RESULTS

(1) There were no differences in the number and distribution of EC cells between IBS patients and the normal group. (2) The mucosal 5-HT contents at the duodenum, jejunum and ileum in IBS-C patients were 182 +/- 90, 122 +/- 54, 61 +/- 35 ng/mg protein, respectively, which were all lower than those in the normal group (256 +/- 84, 188 +/- 91, and 93 +/- 45 ng/mg protein, respectively), with a significant difference at the jejunum (P < 0.05). There were no differences in the small intestinal mucosal 5-HT contents between IBS-D patients and the normal group. The mucosal 5-HT contents at the duodenum were significantly higher than those at the ileum in the three groups (P < 0.001). (3) The numbers of mast cells in patients with IBS-C and IBS-D at the ileum were 38.7 +/- 9.4 and 35.8 +/- 5.5/high power field (hpf), respectively, which were significantly more than that in the normal group (29.8 +/- 4.4/hpf) (P < 0.001). There was no significant difference in the numbers of mast cells at the other two parts between IBS patients and the normal group. The numbers of mast cells in IBS-C, IBS-D, and normal groups were all significantly higher at the ileum (38.7 +/- 9.4, 35.8 +/- 5.5, 29.8 +/- 4.4/hpf, respectively) than at the duodenum (19.6 +/- 4.7, 18.5 +/- 6.3, 19.2 +/- 3.3/hpf, respectively, P < 0.001).

CONCLUSION

The changes in the 5-HT signaling pathway at the jejunum of IBS-C patients and the increase in mast cells in patients with IBS at the terminal ileum may offer evidence to explain the pathogenesis of IBS.

Decreased expression of serotonin in the jejunum and increased numbers of mast cells in the terminal ileum in patients with irritable bowel syndrome

AIM

To investigate if there are changes in serotonin (5-HT) levels, enterochromaffin (EC) cells and mast cells in small intestinal mucosa of patients with irritable bowel syndrome (IBS).

METHODS

Diarrhea-predominant (IBS-D, n = 20), or constipation-predominant (IBS-C, n = 18) IBS patients and healthy controls (n = 20) underwent colonoscopy and peroral small intestinal endoscopy, and mucosal samples were obtained at the descending part of the duodenum, proximal end of jejunum and terminal ileum. High-performance liquid chromatography-electrochemistry and immunohistochemical methods were used to detect 5-HT content, EC cells and mast cells.

RESULTS

(1) There were no differences in the number and distribution of EC cells between IBS patients and the normal group. (2) The mucosal 5-HT contents at the duodenum, jejunum and ileum in IBS-C patients were 182 +/- 90, 122 +/- 54, 61 +/- 35 ng/mg protein, respectively, which were all lower than those in the normal group (256 +/- 84, 188 +/- 91, and 93 +/- 45 ng/mg protein, respectively), with a significant difference at the jejunum (P < 0.05). There were no differences in the small intestinal mucosal 5-HT contents between IBS-D patients and the normal group. The mucosal 5-HT contents at the duodenum were significantly higher than those at the ileum in the three groups (P < 0.001). (3) The numbers of mast cells in patients with IBS-C and IBS-D at the ileum were 38.7 +/- 9.4 and 35.8 +/- 5.5/high power field (hpf), respectively, which were significantly more than that in the normal group (29.8 +/- 4.4/hpf) (P < 0.001). There was no significant difference in the numbers of mast cells at the other two parts between IBS patients and the normal group. The numbers of mast cells in IBS-C, IBS-D, and normal groups were all significantly higher at the ileum (38.7 +/- 9.4, 35.8 +/- 5.5, 29.8 +/- 4.4/hpf, respectively) than at the duodenum (19.6 +/- 4.7, 18.5 +/- 6.3, 19.2 +/- 3.3/hpf, respectively, P < 0.001).

CONCLUSION

The changes in the 5-HT signaling pathway at the jejunum of IBS-C patients and the increase in mast cells in patients with IBS at the terminal ileum may offer evidence to explain the pathogenesis of IBS.

Postinfectious irritable bowel syndrome: a long-term consequence of bacterial gastroenteritis

Irritable bowel syndrome (IBS) is a commonly diagnosed disease characterized by gastrointestinal symptoms that may be associated with psychological illness and emotional problems. The prevalence rate worldwide for IBS ranges from 10 to 20% and is higher for women than for men. IBS imposes a substantial financial burden on both patients and employers because of increased medical costs and decreased work productivity. Recent studies indicate that inflammatory processes involving the gastrointestinal tract are strongly correlated with IBS. Acute bacterial gastroenteritis has been linked with the onset of symptoms in approximately 15% of patients diagnosed with IBS; these cases have been called postinfectious IBS. Organisms commonly associated with postinfectious IBS include the foodborne pathogens Campylobacter, Escherichia coli, Salmonella, and Shigella. The pathologic changes associated with postinfectious IBS are likely due to inflammatory reactions induced by the infecting organisms. Postinfectious IBS should be recognized as a potential long-term consequence of foodborne gastroenteritis.

Autonomic nervous system and secretion across the intestinal mucosal surface

Chloride secretion is important because it is the driving force for fluid movement into the intestinal lumen. The flow of accumulated fluid flushes out invading micro-organisms in defense of the host. Chloride secretion is regulated by neurons in the submucosal plexus of the enteric nervous system. Mechanosensitive enterochromaffin cells that release 5-hydroxytryptamine (5-HT) and activate intrinsic afferent neurons in the submucosal plexus and initiate chloride secretion. Mechanical stimulation by distention may also trigger reflexes by a direct action on intrinsic afferent neurons. Dysregulation of 5-HT release or altered activity of intrinsic afferents is likely to occur in states of inflammation and other disorders.

Tegaserod in the treatment of irritable bowel syndrome (IBS) with constipation as the prime symptom

Irritable bowel syndrome with constipation (IBS-C) as the predominant bowel symptom is a prevalent disorder, characterized by recurring abdominal pain/discomfort, bloating, and constipation, and imposes a significant socio-economic burden. Traditional treatments generally address just one of the multiple IBS symptoms. The efficacy and safety profile of tegaserod, a serotonin 5-HT(4) receptor agonist, has been demonstrated in several randomized, placebo-controlled, and open-label trials. This review discusses the major clinical trials of tegaserod, which have involved 8948 IBS patients. Overall, data reveal that tegaserod is an effective treatment for IBS-C, providing statistically significant relief of overall and multiple individual IBS-C symptoms (abdominal pain/discomfort, bloating, and constipation) in both placebo-controlled and "real-life" open-label settings. Repeat treatments with tegaserod were also shown to be effective, which is noteworthy given the chronic and episodic nature of IBS. Moreover, tegaserod was associated with improvements in patients' quality of life and work productivity. Data also indicate that tegaserod is well tolerated over the short-term (4 weeks), long-term (12 months), and repeated treatments. Diarrhea is the only adverse event consistently associated with tegaserod and was generally mild and transient. Overall, tegaserod has been demonstrated to offer effective and well-tolerated treatment of IBS-C, providing patients with meaningful symptom relief.

Comparison of 5-HT4 and 5-HT7 receptor expression and function in the circular muscle of the human colon

Serotonin receptors are potential targets for treating functional bowel disorders. This study investigated the functional roles and expression of the 5-HT4 and the 5-HT7 receptor, which coexist in human colon circular smooth muscle. 5-HT3 receptor expression was also investigated. Part of the relaxant response to 5-HT was due to activation of 5-HT4 receptors as the apparent pKB value of the selective 5-HT4 antagonist, GR 113808, was 9.36. 5-HT4 mRNA levels were low in five tissues and undetectable in four others, but all responded to 5-HT with an EC50 value of 102.54+/-19.32 nM. The contribution of 5-HT7 receptors to the response was not readily demonstrated using the selective 5-HT7 antagonist, SB-269970, as its apparent pKB value of 7.19 (5-HT4 block with 1 microM GR 113808) was lower than the value obtained using the 5-HT7 guinea pig ileum assay (8.62). Nevertheless, the 5-HT7 receptor was expressed more consistently than the 5-HT4, but at similar levels. The 5-HT(3Ashort) and 5-HT(3B) subunits were co-expressed at similar levels, but the 5-HT(3Along) subunit was detected in only five of the nine samples tested. The findings show that 5-HT4-induced relaxation occurs at low to undetectable levels of tissue mRNA, as measured by qPCR. Although 5-HT7 receptor mRNA is detected at low, but consistent levels, the functional activity of this receptor is not readily identified given the currently available drugs.

5-Hydroxytryptophan activates colonic myenteric neurons and propulsive motor function through 5-HT4 receptors in conscious mice

Serotonin [5-hydroxytryptamine (5-HT)] acts as a modulator of colonic motility and secretion. We characterized the action of the 5-HT precursor 5-hydroxytryptophan (5-HTP) on colonic myenteric neurons and propulsive motor activity in conscious mice. Fos immunoreactivity (IR), used as a marker of neuronal activation, was monitored in longitudinal muscle/myenteric plexus whole mount preparations of the distal colon 90 min after an intraperitoneal injection of 5-HTP. Double staining of Fos IR with peripheral choline acetyltransferase (pChAT) IR or NADPH-diaphorase activity was performed. The injection of 5-HTP (0.5, 1, 5, or 10 mg/kg ip) increased fecal pellet output and fluid content in a dose-related manner, with a peak response observed within the first 15 min postinjection. 5-HTP (0.5-10 mg/kg) dose dependently increased Fos expression in myenteric neurons, with a maximal response of 9.9 +/- 1.0 cells/ganglion [P < 0.05 vs. vehicle-treated mice (2.3 +/- 0.6 cells/ganglion)]. There was a positive correlation between Fos expression and fecal output. Of Fos-positive ganglionic cells, 40 +/- 4% were also pChAT positive and 21 +/- 5% were NADPH-diaphorase positive in response to 5-HTP, respectively. 5-HTP-induced defecation and Fos expression were completely prevented by pretreatment with the selective 5-HT4 antagonist RS-39604. These results show that 5-HTP injected peripherally increases Fos expression in different populations of cholinergic and nitrergic myenteric neurons in the distal colon and stimulates propulsive colonic motor function through 5-HT4 receptors in conscious mice. These findings suggest an important role of activation of colonic myenteric neurons in the 5-HT4 receptor-mediated colonic propulsive motor response.

Irritable bowel syndrome in the 21st century: perspectives from Asia or South-east Asia

Asian irritable bowel syndrome (IBS) studies not only confirm the truth of this functional disorder but also describe the current disease situation of this continent, with its variable socioeconomic backgrounds. Most Asian community IBS prevalence is within 5-10%, regardless of gender or ethnic character. As well as meeting the main Rome II criteria, Asian IBS subjects also have many minor symptoms. Thus this recommendation remains useful to diagnose Asian IBS. Also, female patients commonly express constipation-predominant (C-) symptoms. Extra-colonic symptoms are common in Asia, for example dyspepsia, insomnia and irritable urinary bladder. Asian IBS subjects do experience psychological disturbances including anxiety, depression, agoraphobia and neuroticism. Accordingly, their quality of life is poor and there is absenteeism leading to excessive physician visits. Abnormal gut motor and sensory functions have been indicated among the Asian IBS subjects. Now, there is evidence of altered colonic neuroimmune function leading to gut hypersensitivity and dysmotility. An Asia-Pacific trial also confirmed tegaserod efficacy on female C-IBS subjects. More than 90% of nurses have very limited IBS knowledge, and are unable even to explain it clearly. In conclusion, Western recommended criteria clearly diagnose Asian IBS and many factors are mutual leading to IBS. Current IBS treatments remain useful but additional reeducation for medical professionals appears to be needed.

Isolation, functional characterization, and transcriptome of Mastomys ileal enterochromaffin cells

Although the enterochromaffin (EC) cell is one of the primary neuroendocrine regulatory cells of the small intestine, the lack of a purified cell system has precluded characterization of the cell and limited precise physiological evaluation. We developed methodology to obtain a pure population of Mastomys ileal EC cells, evaluated their functional regulation, and defined the transcriptome. Mastomys ilea were everted, end ligated, pronase-collagenase digested, and Nycodenz gradient centrifuged, and EC cells were collected by fluorescence-activated cell sorting (FACS) of acridine orange-labeled cells. Enrichment was confirmed by immunostaining of tryptophan hydroxylase and chromogranin A, specific EC cell markers, serotonin content, EC cell marker gene expression, and electron microscopy. Pituitary adenylate cyclase-activating polypeptide (PACAP), somatostatin, and gastrin receptor expression was determined by real-time RT-PCR. Live post-FACS-sorted cells were cultured, and the effects of forskolin, isoproterenol, acetylcholine, GABAA, PACAP-38, and gastrin on serotonin secretion were measured by ELISA. GeneChip Affymetrix profiling of FACS-sorted cells was undertaken to obtain the EC cell transcriptome. FACS produced a >70-fold enrichment of EC cells with a serotonin content of 240 +/- 22 ng/mg protein. Preparations were 99 +/- 0.7% pure by immunostaining for tryptophan hydroxylase. Vasoactive intestinal peptide/PACAP receptor 1 (VPAC1) and somatostatin receptor 2 were present, whereas PACAP receptor 1 (PAC1) and CCK2 receptors were undetectable. Forskolin, isoproterenol, and PACAP-38 stimulated serotonin secretion at EC50 values of 5 x 10(-10), 4.5 x 10(-10), and 1.2 x 10(-9) M, respectively. Isoproterenol stimulated cAMP levels by approximately 3.5 +/- 0.62-fold vs. unstimulated cells (EC50 of approximately 10(-9) M). Octreotide, acetylcholine, and GABAA inhibited serotonin secretion with IC50 values of 3 x 10(-11), 3 x 10(-10), and 2.9 x 10(-10) M, respectively. Gastrin had no effect on serotonin secretion. The naive EC cell transcriptome revealed highly expressed EC cell marker genes, the absence of marker genes for other small intestinal cell types, and a receptor profile that included cholinergic, adrenergic, dopaminergic, serotoninergic, GABAergic, and prostaglandin receptors. We were able to isolate homogeneous preparations (>99%) of live ileal EC cells and demonstrated regulation of serotonin secretion as well as established the normal EC cell transcriptome. Application of this methodology to normal and diseased human ileum will facilitate the elucidation of the pathophysiology of EC cells.

Acute tryptophan depletion alters gastrointestinal and anxiety symptoms in irritable bowel syndrome

OBJECTIVES

To assess the effect of acute changes in serotonin (5-HT) synthesis using the acute tryptophan depletion (ATD) paradigm on gastrointestinal (GI) and mood symptoms in irritable bowel syndrome (IBS).

METHODS

In a randomized double-blind crossover study, 29 subjects (18 patients with ROME II defined IBS and 11 age-matched controls) were studied under ATD and acute tryptophan increase (ATI) conditions. GI symptoms, mood and anxiety ratings, as well as plasma tryptophan concentrations were measured.

RESULTS

Total (and free) plasma tryptophan concentrations decreased on the ATD day in patients (73%[82%]) and controls (73%[80%]), and increased on the ATI day in patients (59%[143%]) and controls (61%[381%]). Compared with the ATD day, IBS patients reported more GI symptoms on the ATI day at +210 (p < 0.001) and at +270 (p < 0.05) min post drink. IBS patients also reported less anxiety on the ATI day compared with the ATD day at +270 min (p < 0.001). ATD and ATI did not affect these ratings in control participants. IBS patients had a lower mood compared with controls (p < 0.05), but this did not differ between the ATI and ATD days in either group.

CONCLUSIONS

IBS patients' GI and anxiety responses to changes in tryptophan load differ from controls. This suggests a difference in serotonergic functioning between these two groups and provides evidence to support the hypothesis that 5-HT dysfunction is involved in IBS.

Myenteric denervation differentially reduces enteroendocrine serotonin cell population in rats during postnatal development

The enteric nervous and enteroendocrine systems regulate different processes in the small intestine. Ablation of myenteric plexus with benzalkonium chloride (BAC) stimulates epithelial cell proliferation, whereas endocrine serotonin cells may inhibit the process. To evaluate the connection between the systems and the influence of myenteric plexus on serotoninergic cells in rats during postnatal development, the ileal plexus was partially removed with BAC. Rats were treated at 13 or 21 days and sacrificed after 15 days. The cell bodies of myenteric neurons were stained by beta NADH-diaphorase to detect the extension of denervation. The number of enteroendocrine cells in the ileum was estimated in crypts and villi in paraffin sections immunostained for serotonin. The number of neurons was reduced by 27.6 and 45% in rats treated on the 13th and 21st days, respectively. We tried to establish a correlation of denervation and the serotonin population according to the age of treatment. We observed a reduction of immunolabelled cells in the crypts of rats treated at 13 days, whereas this effect was seen in the villi of rats denervated at 21 days. These results suggest that the enteric nervous system might control the enteroendocrine cell population and this complex mechanism could be correlated to changes in cell proliferation.

Review article: modulation of the brain-gut axis as a therapeutic approach in gastrointestinal disease

BACKGROUND

The importance of bi-directional brain-gut interactions in gastrointestinal illness is increasingly being recognized, most prominently in the area of functional gastrointestinal disorders. Numerous current and emerging therapies aimed at normalizing brain-gut interactions are a focus of interest, particularly for irritable bowel syndrome and functional dyspepsia.

METHODS

A literature search was completed for preclinical and clinical studies related to central modulation of gastrointestinal functions and published in English between 1980 and 2006.

RESULTS

Existing data, while sparse, support the use of different classes of antidepressant drugs, including tricyclics, and selective and non-selective serotonin reuptake inhibitors in irritable bowel syndrome. Serotonin receptor agonists and antagonists with peripheral and possibly central effects are effective in treating specific subtypes of irritable bowel syndrome. Based largely on theoretical and preclinical evidence, several novel compounds that selectively target receptors at multiple levels within the brain-gut axis such as neurokinin, somatostatin and corticotropin-releasing factor receptor antagonists are promising.

CONCLUSIONS

This review discusses the rationale for modulation of the brain-gut axis in the treatment of functional gastrointestinal disorders and highlights the most promising current and future therapeutic strategies.

A controlled crossover study of the selective serotonin reuptake inhibitor citalopram in irritable bowel syndrome

INTRODUCTION

Selective serotonin reuptake inhibitors (SSRIs) are frequently used in the treatment of irritable bowel syndrome (IBS) although evidence of their efficacy is scarce.

AIM

Twenty three non-depressed IBS patients were recruited from a tertiary care centre and included in a crossover trial comparing six weeks of treatment with the SSRI citalopram (20 mg for three weeks, 40 mg for three weeks) with placebo. IBS symptom severity was the primary outcome measure, and depression and anxiety scores were also measured. The effect of acute administration of citalopram on colonic sensitivity and on colonic response to feeding was investigated as a putative predictor of symptomatic response to the drug.

RESULTS

After three and six weeks of treatment, citalopram significantly improved abdominal pain, bloating, impact of symptoms on daily life, and overall well being compared with placebo. There was only a modest effect on stool pattern. Changes in depression or anxiety scores were not related to symptom improvement. The effect of acute administration of citalopram during a colonic barostat study did not predict clinical outcome. Analysis of the first treatment period as a double blind parallel arm study confirmed the benefit of citalopram over placebo.

CONCLUSIONS

The SSRI citalopram significantly improves IBS symptoms, including abdominal pain, compared with placebo. The therapeutic effect is independent of effects on anxiety, depression, and colonic sensorimotor function.

Enteroendocrine cell counts correlate with visceral hypersensitivity in patients with diarrhoea-predominant irritable bowel syndrome

The objective of this study was to determine whether or not the number of enteroendocrine cells (ECs) in the gut is related to visceral hypersensitivity in patients with diarrhoea-predominant irritable bowel syndrome (D-IBS). Twenty-five subjects with D-IBS (mean, 43.1 years; 16 women, nine men) were recruited into our study, along with 13 healthy controls (mean, 40.7 years; nine women, four men). Maximally tolerable pressures were evaluated via barostat testing, and the levels of ECs were immunohistochemically identified and quantified via image analysis. The numbers of ECs between the D-IBS subjects and the controls were not significantly different in the terminal ileum, ascending colon and rectum. However, the maximally tolerable pressures determined in the D-IBS subjects were significantly lower than those of the control subjects (P < 0.01), and we detected a significant relationship between the maximally tolerable pressures and the numbers of ECs in the rectum (r = -0.37, P < 0.01). Rectal sensitivity was enhanced to a greater degree in D-IBS patients exhibiting an elevated level of rectal ECs. This study provides some evidence to suggest that ECs play an important role in visceral hypersensitivity.

Electro-acupuncture attenuates stress-induced defecation in rats with chronic visceral hypersensitivity via serotonergic pathway

Acupuncture has long been used for patients with irritable bowel syndrome. However, it has remained unclear. The aim of this study was to testify the effect of electro-acupuncture(EA) on (1) visceral hypersensitivity induced by the mechanical colorectal irritation during postnatal development of rats, and (2) stress-induced colonic motility changes on rats with chronic visceral hypersensitivity. The abdominal withdrawal reflex (pain threshold and score) for visceral hypersensitivity and fecal pellet output for motor dysfunction were selected as two indexes for measurement. In addition, the effect of EA on 5-HT(4a) receptor and serotonin transporter (SERT) expression in the colon mucosa was analyzed semi-quantitatively through immunohistochemistry and 5-HT concentration in the colon tissue was observed through spectro-photo-fluorimeter detection, respectively. Our results showed that EA significantly elevated pain threshold, decreased the scores and also decreased fecal pellet output during water avoid stress. Furthermore, EA decreased 5-HT concentration in colon in rats with CVH and CVH rats with water avoidance stress, and increased the 5-HT(4a) and SERT expression in rats with CVH. Thus, it can be concluded that EA attenuates behavioral hyperalgesia and stress-induced colonic motor dysfunction in CVH rats via serotonergic pathway.

Effect of 5-HT1 agonist (sumatriptan) on anorectal function in irritable bowel syndrome patients

AIM: To evaluate the effect of sumatriptan, a selective 5-HT₁ agonist, on anorectal function in irritable bowel syndrome (IBS) patients.

METHODS: Twenty-two IBS patients selected according to the Rome II criteria (F 15, M 7; mean age 29.3±6.8, range 22-44 years) were examined. The study was blind, randomized and placebo-controlled with a crossover design. Anorectal manometry and rectal balloon distension test were performed before and after the administration of placebo and sumatriptan.

RESULTS: The administration of sumatriptan caused a significant increase in the resting anal canal pressure from 9.2±2.0 kPa to 13.1±3.3 kPa (P<0.0001) connected with the increase in the anal sphincter length and high pressure zone. After sumatriptan injection a remarkable increase in the threshold for the first sensation from 27±9 mL to 34±12 mL (P<0.05) and urge sensation from 61±19 mL to 68±18 mL (P<0.01) was observed. Sumatriptan did not affect either the volume evoking the rectoanal inhibitory reflex or the results of the straining test.

CONCLUSION: 5-HT₁ receptors participate in the regulation of anorectal function. Elucidation of the role of 5-HT₁ receptors in the pathophysiological mechanisms of IBS may have some therapeutic implications.

Gasping activity in vitro: a rhythm dependent on 5-HT2A receptors

Many rhythmic behaviors are continuously modulated by endogenous peptides and amines, but whether neuromodulation is critical to the expression of a rhythmic behavior often remains unknown, particularly in mammals. Here, we address this issue in the respiratory network that was isolated in spontaneously rhythmic medullary slice preparations from mice. Under control conditions, the respiratory network generates fictive eupneic activity. We hypothesized previously that this activity depends on two types of pacemaker neurons. The bursting properties of one pacemaker rely on the persistent sodium current (INa(p)) and are insensitive to blockade of calcium channels with cadmium (CI-pacemakers), whereas bursting mechanisms of a second pacemaker are sensitive to cadmium (CS-pacemakers) and the calcium-dependent nonspecific cation current blocker flufenamic acid. During hypoxia, fictive eupneic activity is supplanted by the neural correlate of gasping, which is proposed to depend only on CI-pacemakers. Because CI-pacemakers require endogenous activation of 5-HT2A receptors, we tested the hypothesis that 5-HT2A receptor activation is critical for gasping. Here, we demonstrate that fictive gasping and CI-pacemaker bursting were selectively eliminated by the 5-HT2A receptor antagonist piperidine or ketanserin. Neither 5-HT2A antagonist eliminated bursting by CS-pacemakers and ventral respiratory group (VRG) population activity. However, this VRG activity was very different from eupneic activity. In the presence of 5-HT2A antagonists, VRG activity was eliminated by flufenamic acid and could not be reliably restored by adding substance P. These data support the hypothesis that two types of pacemaker bursting mechanisms underlie fictive eupnea, whereas only one burst mechanism is critical for gasping.

The rationale, efficacy and safety evidence for tegaserod in the treatment of irritable bowel syndrome

A growing body of evidence implicates abnormal serotonergic regulation of gastrointestinal function in the pathogenesis of the irritable bowel syndrome (IBS). Drugs targeting this system are therefore attractive concepts. The partial 5-HT4 receptor agonist tegaserod might be predicted to have positive therapeutic effects on a constipated and uncomfortable gut. However, IBS runs a chronic, benign course and carries no associated mortality, so it is imperative that the safety profile of new pharmacological agents made available to physicians is exemplary. The authors review the evidence for 5-HT in the aetiology of IBS and its symptoms, and the data available concerning the partial 5-HT4 receptor agonist tegaserod, in terms of rationale, efficacy and safety.

The effects of an acute serotonergic challenge on brain-gut responses in irritable bowel syndrome patients and controls

BACKGROUND

Serotonin, a key denominator of the brain-gut axis is involved in the regulation of gastrointestinal function as well as cognition, mood and hypothalamic-pituitary-adrenal axis-mediated neuroendocrine responses.

AIM

To assess the effects of an acutely increased serotonergic activity, using a 20 mg intravenous citalopram challenge test on visceral perception, affective memory performance, mood and neuroendocrine responses, respectively, in diarrhoea-predominant irritable bowel syndrome patients and controls.

METHODS

In a randomized, double-blind crossover design, 14 diarrhoea-predominant irritable bowel syndrome patients and 14 matched controls were studied under citalopram and placebo conditions, respectively. Visceral perception was scored in response to rectal distensions. Affective memory performance, mood, levels of adrenocorticotropic hormone, cortisol, prolactin and biochemical parameters of serotonergic metabolism were simultaneously assessed.

RESULTS

Visceral perception did not significantly differ between the citalopram and placebo condition. Citalopram administration enhanced affective memory performance because of a bias towards positive material but no significant changes in mood. Citalopram significantly increased plasma serotonin, adrenocorticotropic hormone and cortisol levels compared with placebo. Citalopram did not differentially affect the patient or control group.

CONCLUSIONS

We have provided evidence that acutely increased serotonergic activity influences neuroendocrine responses and cognition in diarrhoea-predominant irritable bowel syndrome and controls without a significant effect on visceral perception.

Diagnosis and treatment of noncardiac chest pain

Chest pain is common: one in four of the population have an episode annually. Of those who present to hospital, nearly two-thirds have noncardiac chest pain. More than half of these cases might have gastroesophageal reflux disease. Opinion differs over what is the most appropriate application of current investigatory methods. Evidence suggests that, once cardiac disease is ruled unlikely, empiric use of a proton pump inhibitor is an option; if acid suppression fails, detailed investigations as clinically indicated can be considered. A range of esophageal investigations is available, including 24-hour or 48-hour esophageal pH testing and esophageal manometry, as well as provocative tests, but there is no consensus as to which methods are the most useful. Psychiatric evaluation is not routine, but psychiatric or psychological disorders are common. Musculoskeletal disorders are also common, but are frequently overlooked. It is possible to subject patients to a comprehensive set of investigations before empiric therapy, but recent studies have failed to demonstrate an improved outcome using this exhaustive approach. A new tactic is required, with less attention spent on absolute diagnostic accuracy and more emphasis on optimizing the long-term clinical outcome in patients with noncardiac chest pain. It is possible that the targeted use of multiple drug trials in a policy of 'therapy as investigation' might be a superior methodology.