Treatment of nausea and vomiting: gaps in our knowledge

Varenicline for smoking cessation: nausea severity and variation in nicotinic receptor genes

This study evaluated association between common and rare sequence variants in 10 nicotinic acetylcholine receptor subunit genes and the severity of nausea 21 days after initiating the standard, FDA-approved varenicline regimen for smoking cessation. Included in the analysis were 397 participants from a randomized clinical effectiveness trial with complete clinical and DNA resequencing data (mean age = 49.2 years; 68.0% female). Evidence for significant association between common sequence variants in CHRNB2 and nausea severity was obtained after adjusting for age, gender, and correlated tests (all P_ACT<.05). Individuals with the minor allele of CHRNB2 variants experienced less nausea than did those without the minor allele, consistent with previously reported findings for CHRNB2 and the occurrence of nausea and dizziness as a consequence of first smoking attempt in adolescents, and with the known neurophysiology of nausea. As nausea is the most common reason for discontinuance of varenicline, further pharmacogenetic investigations are warranted.

Guamanian Suncus murinus responsiveness to emetic stimuli and the antiemetic effects of 8-OH-DPAT

The Japanese Suncus murinus, the house musk shrew, is a small insectivore commonly used in emetic research. The Guamanian S. murinus has not had extensive testing as an emetic model, but it is readily available for use in emetic experiments in the United States, unlike the Japanese Suncus. This study determined that Guamanian S. murinus is an acceptable model for emesis research and its differences from the Japanese strain were examined. Motion and nicotine were used as emetic stimuli and comparable doses of 8-OH-DPAT were used to compare emetic susceptibility to the Japanese strain. The Guamanian strain had decreased susceptibility to motion and increased susceptibility to nicotine as compared to the Japanese, as well as increased sensitivity to 8-OH-DPAT, with lower doses of the recovery drug eliminating retching episodes. The study also determined that Guamanian S. murinus are smaller and more aggressive than the Japanese strain, but just as effective as a model for emetic research.

Autonomic nerve function in adult patients with cyclic vomiting syndrome

BACKGROUND

Cyclic vomiting syndrome (CVS) in adults is a disorder characterized by recurrent and stereotypic episodes of severe nausea and vomiting separated by symptom-free periods. Autonomic dysfunction has been a postulated mechanism for the pathogenesis of this disorder in children but has not been explored in adults.

METHODS

Our goals were to investigate autonomic nerve function in adult patients with CVS. The sympathetic nervous system was evaluated through postural changes in heart rate and blood pressure and sympathetic skin response in the hand and foot. The parasympathetic nervous system was tested through heart rate response to deep breathing [expiration/inspiration (E/I)], Valsalva and postural indices (30 : 15 ratio). All patients had a 4-h standard isotope labeled egg beater meal gastric emptying test (GET).

KEY RESULTS

Twenty-two adult (18 female), mean age 35 ± 11 (range 19-61 years), who met Rome III criteria for CVS were included. History of migraine headache was reported in three patients. Five (23%) had pediatric onset. Of 21 patients who completed the test, nine patients had 21 abnormalities detected in their autonomic nerve testing profile and the remaining 12 had normal autonomic function results. Orthostatic tachycardia was observed in two (mean heart rate increase 39 beats min(-1)) and a decline in blood pressure (BP) in three patients (mean BP drop 30/14 mmHg). Parasympathetic abnormalities were elicited in six patients with an abnormal response to deep breathing and E/I index <1.25. Sympathetic nerve dysfunction was reported in seven patients with absent sympathetic skin response in the foot and/or hand. Twelve (57%) of CVS group had rapid GET (<50% retention at 1 h). The frequency of abnormal autonomic nerve function was not significantly higher in rapid GET subgroup.

CONCLUSIONS & INFERENCES

(i) Autonomic nerve dysfunction is common in adult CVS patients, being observed in 43% of our cohort; (ii) Sympathetic abnormalities dominate; and (iii) Rapid gastric emptying, present in 57% of patients, did not correlate with autonomic testing results. These new data provide more insight into the pathophysiology of CVS in adults and help explain the spectrum of clinical manifestations observed in this entity.

The translational value of rodent gastrointestinal functions: a cautionary tale

Understanding relationships between gene complements and physiology is important, especially where major species-dependent differences are apparent. Molecular and functional differences between rodents (rats, mice, guinea pigs) and humans are increasingly reported. Recently, the motilin gene, which encodes a gastrointestinal hormone widely detected in mammals, was found to be absent in rodents where the receptors are pseudogenes; however, actions of motilin in rodents are sometimes observed. Although ghrelin shares common ancestry with motilin, major species-dependent abberations are not reported. The apparently specific absence of functional motilin in rodents is associated with specialised digestive physiology, including loss of ability to vomit; motilin is functional in mammals capable of vomiting. The exception is rabbit, the only other mammal unable to vomit, in which motilin might be conserved to regulate caecotrophy, another specialised digestive process. Motilin illustrates a need for caution when translating animal functions to humans. Nevertheless, motilin receptor agonists are under development as gastroprokinetic drugs.

[Postoperative nausea and vomiting and opioid-induced nausea and vomiting: guidelines for prevention and treatment]

Postoperative nausea and vomiting (PONV) causes patient discomfort, lowers patient satisfaction, and increases care requirements. Opioid-induced nausea and vomiting (OINV) may also occur if opioids are used to treat postoperative pain. These guidelines aim to provide recommendations for the prevention and treatment of both problems. A working group was established in accordance with the charter of the Sociedad Española de Anestesiología y Reanimación. The group undertook the critical appraisal of articles relevant to the management of PONV and OINV in adults and children early and late in the perioperative period. Discussions led to recommendations, summarized as follows: 1) Risk for PONV should be assessed in all patients undergoing surgery; 2 easy-to-use scales are useful for risk assessment: the Apfel scale for adults and the Eberhart scale for children. 2) Measures to reduce baseline risk should be used for adults at moderate or high risk and all children. 3) Pharmacologic prophylaxis with 1 drug is useful for patients at low risk (Apfel or Eberhart 1) who are to receive general anesthesia; patients with higher levels of risk should receive prophylaxis with 2 or more drugs and baseline risk should be reduced (multimodal approach). 4) Dexamethasone, droperidol, and ondansetron (or other setrons) have similar levels of efficacy; drug choice should be made based on individual patient factors. 5) The drug prescribed for treating PONV should preferably be different from the one used for prophylaxis; ondansetron is the most effective drug for treating PONV. 6) Risk for PONV should be assessed before discharge after outpatient surgery or on the ward for hospitalized patients; there is no evidence that late preventive strategies are effective. 7) The drug of choice for preventing OINV is droperidol.

Acute gastroenteritis: from guidelines to real life

Acute gastroenteritis is a very common disease. It causes significant mortality in developing countries and significant economic burden to developed countries. Viruses are responsible for approximately 70% of episodes of acute gastroenteritis in children and rotavirus is one of the best studied of these viruses. Oral rehydration therapy is as effective as intravenous therapy in treating mild to moderate dehydration in acute gastroenteritis and is strongly recommended as the first line therapy. However, the oral rehydration solution is described as an underused simple solution. Vomiting is one of the main reasons to explain the underuse of oral rehydration therapy. Antiemetics are not routinely recommended in treating acute gastroenteritis, though they are still commonly prescribed. Ondansetron is one of the best studied antiemetics and its role in enhancing the compliance of oral rehydration therapy and decreasing the rate of hospitalization has been proved recently. The guidelines regarding the recommendation on antiemetics have been changed according to the evidence of these recent studies.

Cisplatin-induced gastrointestinal dysmotility is aggravated after chronic administration in the rat. Comparison with pica

BACKGROUND

Chemotherapy induces nausea/emesis and gastrointestinal dysmotility. Pica, the ingestion of non-nutritive substances, is considered as an indirect marker of nausea/emesis in non-vomiting species, like the rat. Cisplatin is the most emetogenic antitumoral drug. In the rat, acute cisplatin induces pica and gastric dysmotility in a temporally related manner, but the effects of chronic cisplatin are not well known. This study analyzed the effects of chronic cisplatin on pica and on gastrointestinal motor function in the rat, using radiographic, non-invasive methods.

METHODS

Rats received saline or cisplatin (1-3 mg kg(-1), i.p.) once a week for four consecutive weeks. Serial X-rays were taken 0-8 h after administration of barium sulfate, which was given intragastrically immediately after the first and last cisplatin administrations and 1 week after treatment finalization. Pica (i.e., kaolin intake) was measured in isolated rats.

KEY RESULTS

Cisplatin delayed gastric emptying and induced acute (during the 24 h following each administration) pica. Upon chronic administration, these effects were exacerbated. In addition, basal kaolin intake was enhanced (facilitated) and gastric distension induced. Delayed gastric emptying and gastric distension were not apparent 1 week after treatment, but basal kaolin intake was still elevated.

CONCLUSIONS & INFERENCES

Whereas gastric dysmotility induced by cisplatin is parallel to the development of acute pica and might underlie facilitation of pica throughout chronic treatment, it does not explain its long-term maintenance. These findings should be taken into account in the search for new antiemetic strategies.

Enhanced tolerability of the 5-hydroxytryptophane challenge test combined with granisetron

A recently developed oral serotonergic challenge test consisting of 5-Hydroxytryptophane (5-HTP, 200 mg) combined with carbidopa (CBD, 100 mg + 50 mg) exhibited dose-related neuroendocrine responsiveness and predictable pharmacokinetics. However, its applicability is limited by nausea and vomiting. A randomized, double-blind, placebo-controlled, four-way crossover trial was performed in 12 healthy male volunteers. The 5-HTP/CBD-challenge was combined with two oral anti-emetics (granisetron, 2 mg or domperidone, 10 mg) to investigate its reliability when side-effects are suppressed. The neuroendocrine response (serum cortisol and prolactin), the side-effect profile [Visual Analogue Scale Nausea (VAS)] and vomiting subjects per treatment were the main outcome measures. Compared to 5-HTP/CBD/placebo, 5-HTP/CBD/ granisetron had no impact on cortisol [% change with 95% confidence interval: -7.1% (18.9; 6.5)] or prolactin levels [-9.6% (-25.1; 9.1)]; 5-HTP/CBD/domperidone increased cortisol [+13.0% (-4.2; 33.4)], and increased prolactin extensively [+336.8% (245.7; 451.9)]. Compared to placebo, VAS Nausea increased non-significantly with granisetron [+7.6 mm (-1.3; 16.5)], as opposed to domperidone [+16.2 mm (7.2; 25.2)] and 5-HTP/CBD/placebo [+14.7 mm (5.5; 23.8)]. No subjects vomited with granisetron, compared to two subjects treated with 5-HTP/CBD/placebo and five subjects with domperidone. Compared with 5-HTP/CBD/placebo, granisetron addition decreased C(max) of 5-HTP statistically significantly different (from 1483 to 1272 ng/ml) without influencing AUC(0- infinity). Addition of granisetron to the combined 5-HTP/CBD challenge suppresses nausea and vomiting without influencing the neuroendocrine response or pharmacokinetics, enhancing its clinical applicability in future psychiatric research and drug development.

Food restriction, refeeding, and gastric fill fail to affect emesis in musk shrews

Nausea and emesis are common side effects of gastrointestinal disease. Reports indicate that ghrelin and endocannabinoids, agents that stimulate appetite, also reduce emesis evoked by chemotherapy treatment, which suggests that stimulation of feeding inhibits the emetic system. In the following study we conducted a more direct test of this hypothesis by determining the impact of manipulating the motivation to eat on emesis, using food restriction and refeeding. Emesis was induced in musk shrews, a commonly used animal model for emesis research, using the cancer chemotherapy agent cisplatin (20 mg/kg ip), nicotine (2 mg/kg sc), or motion (1 Hz, horizontal, 4-cm displacement), because these treatments are known to target separate emetic pathways: gut vagal afferents, area postrema, and vestibular pathways, respectively. Twenty-four hours of food restriction was sufficient to stimulate food intake, and 1 h of refeeding filled the stomach. The results indicate that food restriction, refeeding, and gastric fill had no significant effects on the amount of emesis produced by any of the emetic treatments tested here. This suggests that, although activation of the emetic system might have prominent effects on food intake, neural controls for feeding behavior do not significantly affect the neural pathways for emesis. These results may have implications for how we treat patients who experience a constellation of side effects, including nausea and emesis, since stimulating appetite may not necessarily inhibit emetic pathways.

Emesis in dogs: a review

Emesis is a common presenting sign in small animal practice. It requires a rational approach to management that is based upon a sound understanding of pathophysiology combined with logical decision making. This review, which assesses the weight of available evidence, outlines the physiology of the vomiting reflex, causes of emesis, the consequences of emesis and the approach to clinical management of the vomiting dog. The applicability of diagnostic testing modalities and the merit of traditional approaches to management, such as dietary changes, are discussed. The role and usefulness of both traditional and novel anti-emetic drugs is examined, including in specific circumstances such as following cytotoxic drug treatment. The review also examines areas in which common clinical practice is not necessarily supported by objective evidence and, as such, highlights questions worthy of further clinical research.

Childhood periodic syndromes

This review focuses on so-called "periodic syndromes of childhood that are precursors to migraine," as included in the second edition of the International Classification of Headache Disorders. Presentation is characterized by an episodic pattern and intervals of complete health. Benign paroxysmal torticollis is characterized by recurrent episodes of head tilt, secondary to cervical dystonia, with onset between ages 2-8 months. Benign paroxysmal vertigo presents as sudden attacks of vertigo lasting seconds to minutes, accompanied by an inability to stand without support, between ages 2-4 years. Cyclic vomiting syndrome is distinguished by its unique intensity of vomiting, affecting quality of life, whereas abdominal migraine presents as episodic abdominal pain occurring in the absence of headache. Their mean ages of onset are 5 and 7 years, respectively. Diagnostic criteria and appropriate evaluation represent the key issues. Therapeutic recommendations include reassurance, lifestyle changes, and prophylactic as well as acute antimigraine therapy.

Electrophysiology of vagal afferents: amino acid detection in the gut

The alimentary canal includes the mouth, stomach, and intestines, and is connected to the brain by thousands of chemosensory neurons. In contrast to the understanding of the lingual taste system, there is little insight into the chemosensory function of other regions of the alimentary canal. The presence of known taste receptors in the gastrointestinal tract suggests a similarity to taste mechanisms present in the oral cavity. Afferent fibers of the vagus play a prominent role in signaling the chemical contents of the gastrointestinal tract to the hindbrain and this information can be used to elicit defensive responses, such as vomiting or nutritional responses. A host of amino acids are likely detected by vagal afferent fibers, but the initial sensory transduction of these stimuli and functional significance remains a mystery. Several problems with recording the electrophysiological signals of vagal afferents are discussed, with particular reference to sampling the afferent signals from the duodenum and liver region.

Chemotherapy-induced kaolin intake is increased by lesion of the lateral parabrachial nucleus of the rat

Anticancer agents, such as cisplatin, stimulate nausea, vomiting, and behaviors indicative of malaise. Rats and mice do not possess a vomiting response, and, therefore, in these species, the ingestion of kaolin clay (a pica response) has been used as an index of malaise. In the rat, cisplatin-induced kaolin intake is inhibited by antiemetic treatments. In addition, cisplatin activates vagal afferent fibers in the gut, and kaolin intake induced by cisplatin is largely dependent on an intact vagus. Nevertheless, little is known about the brain pathways controlling pica. We investigated the role of the lateral parabrachial nucleus (lPBN), a major visceral afferent link between the hindbrain and forebrain, in cisplatin-induced c-Fos expression and pica. Injection of cisplatin (6 mg/kg ip) produced c-Fos expression in the ventrolateral (external) lPBN, a region receiving viscerosensory input. In rats with bilateral ibotenic acid lPBN lesions, cisplatin treatment substantially increased kaolin intake compared with controls ( approximately 30 g vs. approximately 5 g, respectively, over 24 h). Food intake was reduced by cisplatin treatment and by apomorphine, an emetic agent that acts centrally. Unlike cisplatin, however, apomorphine stimulated kaolin intake to a similar degree in both the lesioned and control rats, suggesting that lPBN damage neither produces nonspecific effects nor enhances malaise in general. These data suggest that lPBN-lesioned animals not only demonstrate pica after cisplatin treatment, but, in fact, show an exaggerated response that is greatly in excess of any treatment known to produce kaolin intake in rats.

Opportunities for the replacement of animals in the study of nausea and vomiting

Nausea and vomiting are among the most common symptoms encountered in medicine as either symptoms of disease or side effects of treatments. Developing novel anti-emetics and identifying emetic liability in novel chemical entities rely on models that can recreate the complexity of these multi-system reflexes. Animal models (especially the ferret and dog) are the current gold standard; however, the selection of appropriate models is still a matter of debate, especially when studying the subjective human sensation of nausea. Furthermore, these studies are associated with animal suffering. Here, following a recent workshop held to review the utility of animal models in nausea and vomiting research, we discuss the limitations of some of the current models in the context of basic research, anti-emetic development and emetic liability detection. We provide suggestions for how these limitations may be overcome using non-animal alternatives, including greater use of human volunteers, in silico and in vitro techniques and lower organisms.

Novel promoter and alternate transcription start site of the human serotonin reuptake transporter in intestinal mucosa

Selective serotonin-reuptake inhibitors are therapies for psychological and bowel disorders, but produce adverse effects in the non-targeted system. To determine whether human serotonin-selective reuptake transporter (SERT) transcripts in the intestine are different from the brain, rapid amplification of cDNA ends, primer extension and RT-PCR assays were used to evaluate SERT transcripts from each region. Potential SLC6A4 gene promoter constructs were evaluated with a secreted alkaline phosphatase reporter assay. A novel transcript of the human SLC6A4 gene was discovered that predominates in the intestine, and differs from previous transcripts in the 5'-untranslated region. The distinct transcriptional start site and alternate promoter suggest that gastrointestinal SERT can be differentially regulated from brain SERT, may explain why the polymorphism in the previously identified promoter is associated with affective disorders, but not associated with gastrointestinal dysfunction, and suggest the intriguing possibility of the development of site-specific therapeutics for SERT regulation in the treatment of multiple disorders.

Chemotherapy agent cisplatin induces 48-h Fos expression in the brain of a vomiting species, the house musk shrew (Suncus murinus)

Cancer chemotherapy drugs, such as cisplatin, potently produce nausea and vomiting. Acute effects of these treatments are partly controlled by antiemetic drugs, but the delayed effects (>24 h), especially nausea, are more difficult to treat. It is unknown what brain pathways produce this delayed sickness. Our prior data show that brain Fos expression is increased for at least 48 h after cisplatin treatment in the rat, a nonvomiting species. Here, we extend these observations by using house musk shrews (Suncus murinus), a species with an emetic response. Compared with saline injection, cisplatin treatment (30 mg/kg ip) induced Fos expression in hindbrain areas known to play a role in the generation of emesis, the dorsal motor nucleus (DMN), the area postrema, and the nucleus of the solitary tract (NTS), for up to 48 h. Cisplatin also stimulated Fos expression in the parabrachial nucleus (PBN) of the midbrain and the central nucleus of the amygdala (CeA) for at least 48 h after treatment. When animals were pretreated with the antiemetic palonosetron, a long-term serotonin type 3 (5-HT(3)) receptor antagonist, cisplatin-induced Fos expression was significantly attenuated in the NTS, DMN, and CeA at 6 h but not at 48 h. These results indicate that cisplatin activates a neural system that includes the dorsal vagal complex and forebrain in the musk shrew, which is partially suppressed by a 5-HT(3) receptor antagonist. Our findings suggest the existence of an extensive neural system that could be targeted to reduce nausea, vomiting, and malaise in cancer patients receiving chemotherapy.

Association between migraine and a functional polymorphism at the dopamine beta-hydroxylase locus

Migraine is a common neurological disorder with a significant genetic component. Although a number of linkage and association studies have been undertaken, the number and identity of all migraine susceptibility genes has yet to be defined. The existence of dopaminergic hypersensitivity in migraine has been recognised on a pharmacological basis and some studies have reported genetic association between migraine and dopamine-related gene variants. Our laboratory has previously reported association of migraine with a promoter STR marker in the dopamine beta hydroxylase (DBH) gene. In the present study, we analysed two additional DBH markers in two independent migraine case-control cohorts. These two markers are putative functional SNPs, one within the promoter (-1021C-->T) and another SNP (+1603C-->T) in exon 11 of the DBH gene. The results showed a significant association for allelic and genotypic frequency distribution between the DBH marker in the promoter and migraine in the first (P = 0.004 and P = 0.012, respectively) and the second (P = 0.013 and P = 0.031, respectively) tested cohorts. There was no association observed between either genotype and/or allelic frequencies for the DBH marker located in exon 11 and migraine (P > or = 0.05). The promoter DBH marker, reported associated with migraine in this study, has been shown to affect up to 52% of plasma DBH activity. Varying DBH activity levels have been postulated to be involved in migraine process with an increase of dopamine, resulting from a lower DBH activity shown positively correlated with migraine severity. It is plausible that the functional promoter variant of DBH may play a role in the migraine disorder.

The first demonstration that a subset of women with hyperemesis gravidarum has abnormalities in the vestibuloocular reflex pathway

OBJECTIVE

The vestibular system is a major pathway to nausea and vomiting, and the vestibuloocular reflex (VOR) is a central component; its function can be studied using the vestibular autorotation test (VAT). We hypothesize that women with hyperemesis gravidarum (HG) may have VOR abnormalities.

STUDY DESIGN

Women with HG were compared with women without HG using the VAT. Horizontal and vertical VOR gains and phases were evaluated at 3 frequency ranges: low (2.0 to 3.5 Hz), medium (greater than 3.5 to 5.0 Hz), and high (greater than 5.0 to 6.0 Hz) during pregnancy and postpartum.

RESULTS

Twenty women with HG and 48 unaffected women were evaluated in early pregnancy. Women with HG had higher horizontal gains at all 3 frequency ranges. Horizontal phase differences were also observed at medium frequencies. No VAT differences were noted postpartum.

CONCLUSION

Women experiencing HG had a higher mean VOR horizontal gain and lower horizontal phase when compared with unaffected women.

Polymorphisms within the adenosine receptor 2a gene are associated with adverse events in RA patients treated with MTX

Objective. To examine the role of adenosine receptor 2a gene (ADORA2a) polymorphisms on outcome of MTX treatment in RA.

Methods. Subjects included 309 RA patients with a defined response to MTX. Patients were included if they were (i) good responders (n = 147) (ESR <20 for >6/12 on stable dose of MTX) (ii) inefficacy failures (n = 101) (physician statement and failure to reduce ESR/CRP by 20%) or (iii) adverse event (AE) failures (n = 61) (verified by medical record review). AEs were sub-divided into gastrointestinal (GI) (n = 24), abnormal LFTs (n = 20) or other (n = 17). 8 single nucleotide polymorphisms (SNPs) within ADORA2a were genotyped using the Sequenom MALDI-TOF platform.

Results. Five SNPs within ADORA2a were associated with stopping MTX for AEs (OR 2.1–3.07, P < 0.05 for all). Analysis by AE type showed that the association was specific for GI toxicity. No association was observed between ADORA2a and inefficacy outcomes.

Conclusion. Genetic variation within ADORA2a is significantly associated with AEs on MTX, specifically GI AEs. Knowledge of the ADORA2a genotype may help to improve identification of patients at high risk of GI toxicity with MTX.

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.

Cyclic vomiting syndrome in adults

Cyclic vomiting syndrome (CVS) was initially described in children but can occur in all age groups. Cyclic vomiting syndrome is increasingly recognized in adults. However, the lack of awareness of CVS in adults has led to small numbers of diagnosed patients and a paucity of published data on the causes, diagnosis and management of CVS in adults. This article is a state-of-knowledge overview on CVS in adults and is intended to provide a framework for management and further investigations into CVS in adults.

Hormones of the gut-brain axis as targets for the treatment of upper gastrointestinal disorders

The concept of the gut forming the centre of an integrated gut-brain-energy axis - modulating appetite, metabolism and digestion - opens up new paradigms for drugs that can tackle multiple symptoms in complex upper gastrointestinal disorders. These include eating disorders, nausea and vomiting, gastroesophageal reflux disease, gastroparesis, dyspepsia and irritable bowel syndrome. The hormones that modulate gastric motility represent targets for gastric prokinetic drugs, and peptides that modify eating behaviours may be targeted to develop drugs that reduce nausea, a currently poorly treated condition. The gut-brain axis may therefore provide a range of therapeutic opportunities that deliver a more holistic treatment of upper gastrointestinal disorders.

Development of drugs for gastrointestinal motor disorders: translating science to clinical need

Only a small number of new drugs have recently become available for gastrointestinal (GI) disorders. This is partly because we await outcomes of research into functional bowel disorder aetiology (e.g., role of microbiota) and of trials to control stress- related or painful GI symptoms (e.g., via CRF(1) receptors or beta(3) adrenoceptors). Nevertheless, only the ClC-2 channel activator lubiprostone has recently reached the clinic, joining the 5-HT(3) antagonist alosetron and the long-established 5-HT(4) agonist and D(2) antagonist metoclopramide; tegaserod, a non-selective ligand, was withdrawn. Interestingly, each has shortcomings, providing opportunities for molecules with 5-HT(4) or motilin receptor selectivity, and for new biology via guanylate cyclase C or ghrelin receptor activation. For translation into new drugs, the molecule must have appropriate efficacy, selectivity and pharmacodynamic properties. It is argued that the compound must then be evaluated in conditions where changes in motility are known to exist, before considering more difficult symptomatic conditions such as irritable bowel syndrome (IBS) or functional dyspepsia (FD), where relationships with disordered motility are unclear. Thus, it may be better to begin studying a gastric prokinetic in diabetics requiring improved glucose control, rather than in FD. Notably, new 5-HT(4) receptor agonists are being evaluated firstly as treatments of constipation, not IBS. New antidiarrhoeal agents should be developed similarly. Thus, progression of new drugs may require initial studies in smaller patient populations where clinical outcome is better defined. Only then can disease-related ideas be properly tested and drugs brought forward for these disorders (with high clinical need) and then, if successful for IBS and FD.

Endocannabinoids and the gastrointestinal tract: what are the key questions?

Cannabinoid (CB1) receptor activation acts neuronally, reducing GI motility, diarrhoea, pain, transient lower oesophageal sphincter relaxations (TLESRs) and emesis, and promoting eating. CB2 receptor activation acts mostly via immune cells to reduce inflammation. What are the key questions which now need answering to further understand endocannabinoid pathophysiology? GPR55. Does this receptor have a GI role? Satiety, Nausea, Vomiting, Gastro-Oesophageal Reflux, Gastric Emptying. Endocannabinoids acting at CB1 receptors can increase food intake and body weight, exert anti-emetic activity, reduce gastric acid secretion and TLESRs; CB2 receptors may have a small role in emesis. Question 1: CB1 receptor activation reduces emesis and gastric emptying but the latter is associated with nausea. How is the paradox explained? Q2: Do non-CB receptor actions of endocannabinoids (for example TRPV1) also modulate emesis? Q3: Is pathology necessary (gastritis, gastro-oesophageal reflux) to observe CB2 receptor function? Intestinal Transit and Secretion. Reduced by endocannabinoids at CB1 receptors, but not by CB2 receptor agonists. Q1: Do the effects of endocannabinoids rapidly diminish with repeat-dosing? Q2: Do CB2 receptors need to be pathologically upregulated before they are active? Inflammation. CB1, CB2 and TRPV1 receptors may mediate an ability of endocannabinoids to reduce GI inflammation or its consequences. Q1: Are CB2 receptors upregulated by inflammatory or other pathology? Pain. Colonic bacterial flora may upregulate CB2 receptor expression and thereby increase intestinal sensitivity to noxious stimuli. Q1: Are CB2 receptors the interface between colonic bacteria and enteric- or extrinsic nerve sensitivity? Relevance of endocannabinoids to humans. Perhaps apart from appetite, this is largely unknown.

Why is the neurobiology of nausea and vomiting so important?

Nausea and vomiting are important as biological systems for drug side effects, disease co-morbidities, and defenses against food poisoning. Vomiting can serve the function of emptying a noxious chemical from the gut, and nausea appears to play a role in a conditioned response to avoid ingestion of offending substances. The sensory pathways for nausea and vomiting, such as gut and vestibular inputs, are generally defined but the problem of determining the brain's final common pathway and central pattern generator for nausea and vomiting is largely unsolved. A neurophysiological analysis of brain pathways provides an opportunity to more closely determine the neurobiology of nausea and vomiting and its prodromal signs (e.g., cold sweating, salivation).

Is there a need to identify new anti-emetic drugs?

Nausea and vomiting occur in a large number of disease conditions and as side effects of many drug treatments, including use of analgesics and anesthesia in surgery and chemotherapy in cancer treatment. Current anti-emetics provide relief from only some sources of vomiting, with more limited benefits for the control of nausea. Elucidation of forebrain pathways that generate nausea and brainstem circuitry controlling emesis are significant obstacles for the development of effective universal anti-nausea and anti-emetic treatments.

Purinergic P2X receptor activation induces emetic responses in ferrets and Suncus murinus (house musk shrews)

BACKGROUND AND PURPOSE

Despite the rapid progress made in understanding the significant role played by signalling via extracellular ATP in physiology and pathology, there has been no clear information generated on its involvement in the emetic response.

EXPERIMENTAL APPROACH

In the present study, the emetogenic potential of extracellular ATP signalling in mammalian species was examined using ferrets and Suncus murinus (house musk shrews). A slowly degradable ATP analogue, alpha,beta-methyleneATP (alpha,beta-meATP), was used to activate the P2X receptors, and either the non-selective P2 receptor antagonist, pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), or the specific P2X(3) homomer and P2X(2/3) heteromer antagonist, A-317491, were tested against the agonist-induced response.

KEY RESULTS

Intraperitoneal injection of alpha,beta-meATP produced significant emetic responses in ferrets (1 - 30 mg kg(-1)) and in Suncus murinus (5 - 50 mg kg(-1)). The responses occurred frequently within the first 10 min after administration, much less frequently from 11 to 60 min and no responses occurred later than 60 min. The emetic responses were completely inhibited by intraperitoneal pre-treatment with PPADS (100 mg kg(-1)) or A-317491 (100 mg kg(-1)). Abdominal surgical vagotomy did not reduce the emetic response in Suncus murinus significantly.

CONCLUSIONS AND IMPLICATIONS

These results for the first time indicate that the activation of P2X receptors evokes emetic responses in mammalian species. The P2X(3) homomer and.or P2X(2/3) heteromer in the area postrema could be responsible for the emetic response. This finding contributes to the elucidation of the roles played by extracellular ATP signalling in various emetic symptoms.

Chemosensitivity of unmyelinated axons in isolated human gastric vagus nerve

Vagal afferent neurons from the stomach may be activated not only by chemical stimuli in the mucosa but also by circulating factors. In the present study, we have used electrophysiological techniques to characterize functional activity of several receptors for chemical mediators on unmyelinated axons in isolated fascicles of human gastric vagus nerve. Application of agonists at the nicotinic acetylcholine receptor (nAChR), 5-HT(3) subtype of serotonin receptor, and the transient receptor potential vanilloid receptor-1 (TRPV1) resulted in a change in the height and/or threshold of the C-fiber compound action potential. These effects were blocked by specific antagonists of nAChR (mecamylamine), 5-HT(3) (Y-25130), and TRPV1 (capsazepine). We conclude that the chemosensitivity of unmyelinated vagal axons can be studied using isolated segments of human gastric vagus nerve. The presence of receptors indicates that circulating factors may modify vagal afferent neurons also by effects on the axonal membrane.