Review article: the hypersensitive gut--peripheral kappa agonists as a new pharmacological approach

Molecular Genetics of Kappa Opioids in Pain and Itch Sensations

The opioid peptides and their receptors have been linked to multiple key biological processes in the nervous system. Here we review the functions of the kappa opioid receptor (KOR) and its endogenous agonists dynorphins (Goldstein A, Tachibana S, Lowney LI, Hunkapiller M, Hood L, Proc Natl Acad Sci U S A 76:6666-6670, 1979) in modulating itch and pain (nociception). Specifically, we discuss their roles relative to recent findings that tell us more about the cells and circuits which are impacted by this opioid and its receptor and present reanalysis of single-cell sequencing data showing the expression profiles of these molecules. Since the KOR is relatively specifically activated by peptides derived from the prodynorphin gene and other opioid peptides that show lower affinities, this will be the only interactions we consider (Chavkin C, Goldstein A, Nature 291:591-593, 1981; Chavkin C, James IF, Goldstein A, Science 215:413-415, 1982), although it was noted that at higher doses peptides other than dynorphins might stimulate KOR (Lai J, Luo MC, Chen Q, Ma S, Gardell LR, Ossipov MH, Porreca F, Nat Neurosci 9:1534-1540, 2006). This review has been organized based on anatomy with each section describing the effect of the kappa opioid system in a specific location but let us not forget that most of these circuits are interconnected and are therefore interdependent.

Effect of oral naloxone hydrochloride on gastrointestinal transit in premature infants treated with morphine

BACKGROUND

Opioids are common drugs for pain treatment in preterm newborn infants, in spite of several adverse effects. Constipation is a frequent problem when opioids are used in both adults and neonates. Although several studies indicate that the oral administration of naloxone hydrochloride (NH) improves intestinal motility during opioid therapy, there is still a lack of evidence in newborns.

AIM

The aim of this study was to assess the efficacy of NH against reduced intestinal motility during opioid treatment.

METHODS

A retrospective cohort study was performed. We analysed the medical records of fifteen infants (Group 1) treated with continuous morphine (MO) infusion and fourteen infants (Group 2) treated with both oral NH (3 microg/kg 4 times daily) and MO.

RESULTS

There was no statistically significant difference in the total MO dose. Infants treated both with NH and MO had a tendency to improve their mean stool frequency/day. A statistically significant improvement was observed in the mean total food intake (mL/kg/day) of the infants treated with NH (p = 0.014). No difference in the mean food retention between the two groups was observed.

CONCLUSION

Orally administrated NH seems to improve intestinal motility resulting in increased food intake/day and improved stool frequency/day in premature newborn infants treated with MO. Further studies are needed to corroborate these findings.

Nanoparticles of cationic chimeric peptide and sodium polyacrylate exhibit striking antinociception activity at lower dose

The current study investigates the performance of polyelectrolyte complexes based nanoparticles in improving the antinociceptive activity of cationic chimeric peptide-YFa at lower dose. Size, Zeta potential and morphology of the nanoparticles were determined. Size of the nanoparticles decreases and zeta potential increases with concomitant increase in charge ratio (Z(+/-)). The nanoparticles at Z(+/-)12 are spherical with 70+/-7 nm diameter in AFM and displayed positive surface charge and similar sizes (83+/-8 nm) by Zetasizer. The nanoparticles of Z(+/-) 12 are used in this study. Cytotoxicity by MTT assay on three different mammalian cell lines (liver, neuronal and kidney) revealed lower toxicity of nanoparticles. Hematological parameters were also not affected by nanoparticles compared to normal counts of water treated control group. Nanoparticles containing 10 mg/kg YFa produced increased antinociception, approximately 36%, in tail-flick latency test in mice, whereas the neat peptide at the same concentration did not show any antinociception activity. This enhancement in activity is attributed to the nanoparticle associated protection of peptide from proteolytic degradation. In vitro peptide release study in plasma also supported the antinociception profile of nanoparticles. Thus, our results suggest of a potential nanoparticle delivery system for cationic peptide drug candidates for improving their stability and bioavailability.

Peripherally acting opioid antagonists in the treatment of opiate-related constipation: a systematic review

Many patients treated with opioids suffer from constipation. Opiate- or opioid-related constipation is not only a frequent but also a distressing symptom and difficult to treat. There is emerging evidence regarding a novel approach to the management of opiate-related constipation. The aim of this paper is to collect, critically appraise, and summarize the evidence on the effectiveness of recently developed peripherally acting micro-receptor antagonists in the treatment of opiate-related constipation. A comprehensive search of 11 computerized databases was conducted and efforts were made to identify unpublished and ongoing research. Twenty studies were identified; 13 were randomized controlled trials (RCTs) and 7 were Phase II studies assessing toxicity. Studies were mainly executed in healthy volunteers or members of methadone programs with opioid-induced constipation as a model to mimic the condition of patients on opioids. Two RCTs were conducted in hospice patients. Quality of study design and validity of the findings was assessed in all studies. Data show proof of concept but do not allow a definitive answer concerning the effectiveness of the peripherally acting micro-opioid antagonists methylnaltrexone and alvimopan in managing opiate-related constipation. Further research is needed. If future Phase III trials provide supportive data, opioid antagonists may become a standard therapeutic option for the treatment of opiate-related constipation in patients with advanced cancer.

Novel developments with selective, non-peptidic kappa-opioid receptor agonists

Despite the recent introduction of a number of new compounds, there has of late been a cooling of interest by pharmaceutical companies in the development of centrally-active, selective kappa opioid agonists for therapeutic purposes. This is reflected in the discontinuation of a number of clinical trials, for reasons that are often not completely clear to outside observers. Spiradoline and enadoline have apparently been abandoned as potential analgesics because they induce dose-limiting central side-effects (i.e., dysphoria) in models of post-surgical pain. The development of niravoline as an aquaretic for the treatment of cirrhosis with ascites and other hyponatraemic disorders has also been halted. Enadoline may yet find some application against ischaemic stroke and severe head injury, presumably in comatose patients in whom psychiatric side-effects are taken to be immaterial, while apadoline and TRK 820 remain in Phase II clinical testing against cancer pain. The peripherally-selective kappa agonists, asimadoline, and the atypical compound, fedotozine, are well-tolerated in man. Results of Phase III trials of fedotozine against irritable bowel syndrome and dyspepsia have, however, ultimately been disappointing, whereas asimadoline is currently in Phase II clinical trials against pain of rheumatic and osteoarthritic origin. The results of these trials are eagerly awaited.

Preclinical studies of opioids and opioid antagonists on gastrointestinal function

Opioid receptors in the gastrointestinal (GI) tract mediate the effects of endogenous opioid peptides and exogenously administered opioid analgesics, on a variety of physiological functions associated with motility, secretion and visceral pain. The studies reviewed or reported here describe a range of in vivo activities of opioid receptor antagonists upon GI function in rodents, focusing on mu receptors. Naloxone, and the peripherally acting mu-opioid receptor antagonists alvimopan and methylnaltrexone, reverse morphine-induced inhibition of GI transit in mice and rats, and morphine- or loperamide-induced inhibition of castor oil-induced diarrhoea in mice. At doses producing maximal reversal of morphine-induced effects upon GI transit, only the central nervous system (CNS) penetrant antagonist naloxone was able to reverse morphine-induced analgesia. Both central and peripheral opioid antagonists may affect GI function and/or visceromotor sensitivity in the absence of exogenous opioid analgesics, suggesting a constitutive role for endogenous opioid peptides in the control of GI physiology. Furthermore, in contrast to naloxone, alvimopan does not produce hypersensitivity to the visceromotor response induced by nociceptive levels of colorectal distension in a rodent model of post-inflammatory colonic hypersensitivity, suggesting that in the periphery endogenous mu-opioid receptor-mediated mechanisms do not regulate colonic sensitivity. The data support the hypothesis that peripherally acting opioid antagonists may be able to selectively block opioid receptors in the GI tract, thereby preserving normal GI physiology, while not blocking the effects of endogenous opioid peptides or exogenous opioid analgesics in the CNS. These findings suggest that the primary sites of action of mu-opioid agonists with respect to inhibition of GI function are in the periphery, whereas analgesic activity resides primarily in the CNS.

Opioids and the gut: pharmacology and current clinical experience

This article reviews the pharmacology and physiology of opiate receptors and the current and potential uses of opioid agonists and antagonists in clinical gastroenterology. Mu-receptors are involved in motor and sensory functions, and their modulation is established for treatment of diarrhea. Mu-antagonists have potential to reverse endogenous (e.g., postoperative ileus) or iatrogenic dysmotility (e.g., opioid bowel dysfunction). Modulation of the function of kappa-receptors may be a novel approach to control visceral pain in functional gut disorders. Results of formal testing of novel opioid modulators are keenly awaited.

New developments in the treatment of functional dyspepsia

Functional dyspepsia is a clinical syndrome defined by chronic or recurrent pain or discomfort in the upper abdomen of unknown origin. Although generally accepted, investigators differently interpret this definition and clinical trials are often biased by inhomogeneous inclusion criteria. The poorly defined multifactorial pathogenesis of dyspeptic symptoms has hampered efforts to develop effective treatments. A general agreement exists on the irrelevant role played by Helicobacter pylori in the pathophysiology of functional dyspepsia. Gastric acid secretion is within normal limits in patients with functional dyspepsia but acid related symptoms may arise in a subgroup of them. Proton pump inhibitors appear to be effective in this subset of patients with dyspepsia. Non-painful dyspeptic symptoms are suggestive of underlying gastrointestinal motor disorders and such abnormalities can be demonstrated in a substantial proportion of patients. Postprandial fullness and vomiting have been associated with delayed gastric emptying of solids, and early satiety and weight loss to postcibal impaired accommodation of the gastric fundus. Prokinetics have been shown to exert beneficial effects, at least in some patients with dyspepsia. In contrast, drugs enhancing gastric fundus relaxation have been reported to improve symptoms, although conflicting results have also been published. An overdistended antrum may also generate symptoms, but its potential pathogenetic role and the effects of drugs on this abnormality have never been investigated formally. Visceral hypersensitivity plays a role in some dyspeptic patients and this abnormality is also a potential target for treatment. Both chemo- and mechanoreceptors can trigger hyperalgesic responses. Psychosocial abnormalities have been consistently found in functional digestive syndromes, including dyspepsia. Although useful in patients with irritable bowel syndromes (IBS), antidepressants have been only marginally explored in functional dyspepsia. Among the new potentially useful agents for the treatment of functional dyspepsia, serotonin 5-HT(4) receptor agonists have been shown to exert a prokinetic effect. Unlike motilides, 5-HT(4) receptor agonists do not appear to increase the gastric fundus tone and this may contribute to improve symptoms. 5-HT(3) receptor antagonists have been investigated mainly in the IBS and the few studies performed in functional dyspepsia have provided conflicting results. Also, kappa-opioid receptor agonists might be useful for functional digestive syndromes because of their antinociceptive effects, but available results in functional dyspepsia are scanty and inconclusive. Other receptors that represent potential clinical targets for antagonists include purinoceptors (i. e., P2X2/3 receptors), NMDA receptors (NR2B subtype), protease-activated receptor-2, the vanilloid receptor-1, tachykinin receptors (NK(1)/NK(2)) and cholecystokinin (CCK)(1) receptors.

Management of opioid-induced gastrointestinal effects in patients receiving palliative care

Opioid-induced gastrointestinal side effects, namely, nausea and constipation, are bothersome yet often easy to manage. Due to their widespread frequency, it is imperative that prophylactic and treatment modalities be understood. Although many pharmacotherapeutic agents are available with which to prevent or treat these side effects, few randomized, placebo-controlled studies have been conducted in terminally ill patients, thus limiting most treatment decisions to empiric therapies based on extrapolated data. A strong understanding of the pathophysiology of the sequelae is therefore paramount. Common agents administered for nausea are butyrophenones, phenothiazines, metoclopramide, and serotonin-receptor antagonists. Those given to manage constipation are stimulant laxatives and stool softeners, individually or in combination.

Emerging treatments for irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional GI disorder that is associated with abdominal discomfort and altered bowel habits. It accounts for up to 28% of patients presenting to a gastroenterology practice and poses a significant personal, societal and economic burden internationally. The Manning, Rome I and Rome II criteria were developed to identify appropriate IBS patients for entry into IBS studies in a consistent manner. Refinements in the understanding of the physiology of the enteric nervous system (ENS), which controls motility, secretion and sensation, provided the basis for our comprehension of the pathophysiology of IBS. Visceral hypersensitivity and neurotransmitter imbalance currently receive the most attention as possible mechanisms of IBS. This article outlines conventional treatments and reviews the data on emerging and experimental therapies for IBS. Emerging therapies for IBS using 5-HT mediation include 5-HT(3) antagonists, such as ondasetron, granisetron and alosetron, as well as 5-HT(4) agonists such as tegaserod and prucalopride. In addition to opioid agonists (e.g. fedotozine) several other drugs that act on other ENS receptors are being studied. In spite of significant progress in IBS research, these emerging therapies require more studies before they can be utilised as clinical treatments.

Chronic narcotic use in inflammatory bowel disease patients: prevalence and clinical characteristics

BACKGROUND

Narcotic addiction can be a significant problem in inflammatory bowel disease (IBD). However, there are few published reports about this problem.

METHODS

All patients prescribed narcotics chronically in the absence of demonstrable organic pathology were identified on the computerized Brisbane IBD Research Group database (n=332 patients with informative data as of 1 January 1999). Individual case records were reviewed with regard to clinical, psychiatric and social characteristics of these patients, and the prevalence of psychiatric disorders were compared with a control group of IBD patients.

RESULTS

Eleven patients were identified. Nine had complete datasets, eight with Crohn's disease (CD), of which six had previous stricturing ileal disease, and one patient had ulcerative colitis, making a prevalence of 2.7% of IBD patients and 5.1% of CD patients. A 67% prevalence of a psychiatric disorder in narcotic users was significantly greater than the 8% prevalence in the control group of IBD patients (odds ratio 22, 95% CI 3.24-177).

CONCLUSIONS

A significant proportion of IBD patients without demonstrable organic pathology were chronic narcotic users. Psychiatric disorders are common in this subgroup, as with chronic functional abdominal pain syndromes. It is suggested that inappropriate narcotic use in IBD patients can be reduced by appreciating that narcotics are a temporary therapy only for IBD patients, and awareness of pre-existing social and psychiatric disorders, which not only impact on clinical presentation of pain, but also help define the subgroup of patients who are at risk of narcotic misuse.

Drug treatment options for irritable bowel syndrome: managing for success

Irritable bowel syndrome (IBS) is a functional gut disorder the diagnosis of which is based on clinical symptoms as set forth by the Rome criteria. As the population ages, especially with the population of patients >75 years of age expanding greatly over the next 10 years, IBS is becoming one of the most common diseases of the elderly. Thus far, developing treatment strategies for patients with IBS has been difficult because of the lack of pharmacological targets and the wide range of symptomatology. Additionally, demonstration of a therapeutic benefit is difficult in the presence of a high placebo response observed regardless of the therapy employed. Fibre, antidiarrhoeals and antispasmodics all play some role in the symptomatic treatment of IBS. With the evolution of IBS as a disorder of visceral hypersensitivity, new drugs have been developed that target the enteric nervous system. Tricyclic antidepressants (TCAs) have been found to target the enteric neurons and play a role in pain modulation. Currently, the TCAs are recommended only for severe cases of IBS pain. The newest class of drugs to be approved for use in IBS are the serotonin (5-hydroxytryptamine; 5-HT) antagonists. Specifically, the 5-HT3 receptor antagonists have been shown to decrease symptoms in female patients with IBS. A related class of drugs, the 5-HT4 receptor agonists, is being developed for the treatment of constipation-predominant IBS. Further investigation into the role of spinal afferent neurons in visceral hypersensitivity is at the forefront of IBS research. Several experimental drug therapies for IBS are also discussed in this review including N-methyl-D-aspartate receptor antagonists, neurokinin-1 receptor antagonists, octreotide, clonidine and the selective M3 receptor antagonist, zamifenacin.

Chronic Functional Abdominal Pain (CFAP)

Patients with chronic functional abdominal pain (CFAP) present particularly challenging management issues for primary care physicians and gastroenterologists. A major objective in the care of patients with CFAP is to develop an understanding of this condition as a biopsychosocial disorder where symptoms can be attributed to "brain-gut" dysfunction rather than to a missed structurally based condition. The foundation of any therapeutic strategy is the patient-physician partnership, probably the hardest element of treatment for most physicians. All treatment programs should be based on a multi-component strategy, with the patient as a full partner. Realistic expectations should be agreed upon for "care" rather than "cure." The patient's preferences should be a major factor in the decision as to whether to recommend pharmacologic or psychological treatment, or a combination of the two. Antidepressant drugs are increasingly being used in CFAP, and well-designed studies are emerging to confirm their clinical effectiveness. Patients' understanding of the indications for and effects of antidepressants must be reframed in order to address barriers and achieve adherence to therapy. The clinical effectiveness of antidepressants can often only be assessed after 3 to 6 weeks of therapy. The side effects, which appear early, are usually transient and often disappear within 1 to 2 weeks. There is no conclusive evidence that one antidepressant drug is more effective than others, although most studies have tested tricyclic agents. The most important factors in the choice of antidepressant medication are side-effect profile, physician familiarity and comfort with the drug, and cost.

Local administration of mu or kappa opioid agonists attenuates capsaicin-induced thermal hyperalgesia via peripheral opioid receptors in rats

RATIONALE

By acting on peripheral opioid receptors, opioid agonists can attenuate nociceptive responses induced by a variety of agents.

OBJECTIVES

This study was conducted to characterize capsaicin-induced thermal hyperalgesia in rats and to evaluate the hypothesis that local administration of either mu or kappa opioid agonists (fentanyl and U50,488, respectively) can attenuate capsaicin-induced nociception.

METHODS

Capsaicin was administered s. c. in the tail of rats to evoke a nociceptive response, which was measured by the warm-water tail-withdrawal procedure. Either fentanyl or U50,488 was co-administered with capsaicin in the tail to evaluate local antinociceptive effects. In addition, the local antagonism study was performed to confirm the site of action of both opioid agonists.

RESULTS

Capsaicin (0.3-10 microg) dose dependently produced thermal hyperalgesia manifested as reduced tail-withdrawal latencies in 45 degrees C water. Co-administration of either fentanyl (0.32-3.2 microg) or U50,488 (10-100 microg) with capsaicin (3 microg) attenuated capsaicin-induced hyperalgesia in a dose-dependent manner. Furthermore, this local antinociception was antagonized by small doses (10-100 microg) of an opioid antagonist, quadazocine, applied s.c. in the tail. However, the locally effective doses of quadazocine, when applied s.c. in the back (i.e., around the scapular region), did not antagonize either fentanyl or U50,488.

CONCLUSIONS

In this experimental pain model, activation of peripheral mu or kappa opioid receptors can attenuate capsaicin-induced thermal hyperalgesia in rats. It supports the notion that peripheral antinociception can be achieved by local administration of analgesics into the injured tissue without producing central side effects.

Functional gut disorders: from motility to sensitivity disorders. A review of current and investigational drugs for their management

Functional gut disorders include several clinical entities defined on the basis of symptom patterns (e.g., functional dyspepsia, irritable bowel syndrome, functional abdominal pain, functional abdominal bloating), for which there is no established pathophysiological mechanism. Because there is no well-defined pathophysiological target, treatment should be aimed at symptom improvement. Prokinetics and antispasmodics have been widely used in the treatment of functional gut disorders on the assumption that disordered motility is the underlying cause of symptoms, and symptom improvement is indeed achievable with these compounds in some, but not all, patients with features of hypo- or hypermotility, respectively. In the first part of this review, we cover the basic pharmacology and discuss the rationale for the clinical use of prokinetics and antispasmodics. On the other hand, in the past few years, the explosive growth in the research focusing on visceral sensitivity and visceral reflexes has suggested that at least some patients with functional gut disorders have altered visceral perception. Thus, the second part of the review covers these developments and focuses on studies addressing the issue of drugs modulating visceral sensitivity.

Regional quantitation of preprodynorphin mRNA in guinea pig gastrointestinal tract

The endogenous opioid peptide dynorphin has been shown by immunochemical studies to be widely distributed in the gastrointestinal tract. The aim of this study was to determine basal levels of preprodynorphin (ppDyn) mRNA in different regions of the gastrointestinal tract of the guinea pig. A modified sensitive and specific solution hybridization RNase protection assay was used to quantitate ppDyn mRNA, with confirmation by gel analysis of the RNase protected hybrids and PCR amplified cDNA. This method combines high sensitivity and sufficient throughput to analyze large number of samples in a single assay. Low but measurable amounts of ppDyn mRNA were detected in fundus, duodenum, jejunum, ileum, cecum, and rectum. The rectum contained significantly more ppDyn mRNA than the stomach, small bowel, and cecum. The muscularis/myenteric plexus layer of both ileum and rectum contained a higher concentration of ppDyn mRNA per microg total RNA compared to the mucosa/submucosa/submucosal plexus. However, a greater absolute amount of ppDyn mRNA (80-85%) localized to the mucosal layer. The greater absolute amount of ppDyn mRNA in the mucosal layer may indicate the presence of dynorphin in the endocrine cells of the mucosa.

Review article: colonic sensorimotor physiology in health, and its alteration in constipation and diarrhoeal disorders

AIM

To review the physiology of colonic motility and sensation in healthy humans and the pathophysiological changes associated with constipation and diarrhoea.

SOURCE

Medline Search from 1965 using the index terms: human, colonic motility, sensation, pharmacology, neurohormonal control, gastrointestinal transit, constipation, diarrhoea and combinations of these.

RESULTS

In health, the ascending and transverse regions of colon function as reservoirs to accommodate ileal chyme and the descending colon acts as a conduit; the neuromuscular functions and transmitters control colonic motility and sensation and play pivotal roles in disorders associated with constipation and/or diarrhoea. Disorders of proximal colonic transit contribute to symptoms in idiopathic constipation, diarrhoea-predominant irritable bowel syndrome and carcinoid diarrhoea. Colonic function in patients presenting with constipation is best assessed clinically by colonic transit time using radiopaque markers ingested orally. Measurements of colonic contractility are less useful clinically but they can help identify motor abnormalities including colonic inertia; in some patients with irritable bowel syndrome, abdominal pain, urgency and diarrhoea are temporally associated with high amplitude contractions, which originate in the proximal colon and traverse the distal conduit at very high propagation velocities. Visceral hypersensitivity contributes to the urgency and tenesmus in irritable bowel syndrome and inflammatory bowel disease. Colonic motility and sensation can be reduced by anticholinergic agents, somatostatin analogues and 5HT3 antagonists.

CONCLUSION

Physiological and pharmacological studies of the human colon have provided new insights into the pathophysiology of colonic disorders, and offer possibilities of novel therapeutic approaches for constipation or diarrhoea associated with colonic motor or sensory dysfunction.

Fedotozine blocks hypersensitive visceral pain in conscious rats: action at peripheral kappa-opioid receptors

The effect of fedotozine on visceral hypersensitivity was evaluated in conscious rats. One hour after colonic irritation (0.6% acetic acid intracolonically), a 30 mmHg colonic distension was applied for 10 min. Irritation increased the number of abdominal contractions induced by colonic distension (23.4 +/- 4.1 versus 4.8 +/- 1.4 in saline-treated rats, P < 0.001). Facilitation of colonic pain was reversed in a dose-dependent manner by fedotozine ((+)-(-1R1)-1-phenyl-1-[(3,4,5-trimethoxy)benzyloxymethyl]-N ,N-dimethyl-n-propylamine), (+/-)-U-50,488H (trans-(+/-)-3,4-dichloro-N-methyl-N-(2-1-pyrrolidinyl]cyclohexyl)benzen eacetamide) and morphine (respective ED50 values 0.67, 0.51 and 0.23 mg/kg s.c.). The kappa-opioid receptor antagonist, nor-binaltorphimine, abolished the effects of fedotozine and (+/-)-U-50,488H but not those of morphine. Low doses of naloxone (30 microg/kg s.c.) blocked the effect of morphine but not of fedotozine or (+/-)-U-50,488H. After intracerebroventricular administration, morphine was very potent (ED50 1.7 microg/rat), (+/-)-U-50,488H poorly active (58% of antinociception at 300 microg/rat) and fedotozine inactive up to 300 microg/rat. These results show that fedotozine blocks hypersensitive visceral pain by acting on peripheral kappa-opioid receptors in animals.

Gastrointestinal sensation. Mechanisms and relation to functional gastrointestinal disorders

This article reviews the basic anatomy and physiology of visceral afferent function and its application to a clearer understanding of visceral pain and symptoms in patients with functional gastrointestinal disorders. Recent investigations have focused on the potential role of visceral tone, different afferent (A delta and C) fibers, dorsal column neurons, and supraspinal modulation in the elicitation of visceral perception of noxious and nonnoxious stimuli arising in the gut. Greater understanding of these pathomechansims and their pharmacologic manipulation offers an opportunity for future therapeutic strategies for these disorders.