The neurophysiology of vomiting

Metoclopramide and Propofol to Prevent Nausea and Vomiting during Cesarean Section under Spinal Anesthesia: A Randomized, Placebo-Controlled, Double-Blind Trial

BACKGROUND

Intra-operative nausea, vomiting and retching (NVR) are frequently associated with subarachnoid anesthesia (SA) in women undergoing cesarean section (CS). In this study performed in women undergoing CS under SA with a risk factor control strategy, we compared saline (placebo), propofol, metoclopramide and both drugs to prevent NVR.

METHODS

We recorded NVR events in 110 women undergoing CS who were randomized after umbilical cord clamping to receive saline (S; n = 27), metoclopramide 10 mg (M; n = 28), propofol 1 mg/kg/h (P; n = 27) or both drugs (PM; n = 28).

RESULTS

The proportion of women with intra-operative nausea was: S: 17/27 (63%); P: 15/27 (56%); M: 13/28 (46%); PM: 6/28 (21%) (p = 0.012, Cramér's V = 0.31 (large effect). The proportion of women with intra-operative vomiting/retching was: S: 9/27 (33%); M: 7/27 (25%); P: 3/28 (11%); PM 2/28 (7%) (p = 0.049, Cramér's V = 0.26 (medium effect). Post-hoc multiple comparisons revealed a significant reduction in NVR episodes and NRS scores between the PM group and control. Sedation scores did not differ among groups.

CONCLUSION

In women undergoing CS under SA with a risk factor control strategy, combined propofol and metoclopramide reduce nausea and vomiting.

Deoxynivalenol: Mechanisms of action and its effects on various terrestrial and aquatic species

Deoxynivalenol, a type B trichothecene mycotoxin produced by Fusarium species of fungi, is a ubiquitious contaminant of cereal grains worldwide. Chronic, low dose consumption of feeds contaminated with DON is associated with a wide range of symptoms in terrestrial and aquatic species including decreased feed intake and feed refusal, reduced weight gain, and altered nutritional efficiency. Acute, high dose exposure to DON may be associated with more severe symptoms such as vomiting, diarrhea, intestinal inflammation and gastrointestinal hemorrhage. The toxicity of DON is partly related to its ability to disrupt eukaryotic protein synthesis via binding to the peptidyl transferase site of the ribosome. Moreover, DON exerts its effects at the cellular level by activating mitogen activated protein kinases (MAPK) through a process known as the ribotoxic stress response (RSR). The outcome of DON-associated MAPK activation is dose and duration dependent; acute low dose exposure results in immunostimulation characterized by the upregulation of cytokines, chemokines and other proinflammatory-related proteins, whereas longer term exposure to higher doses generally results in apoptosis, cell cycle arrest, and immunosuppression. The order of decreasing sensitivity to DON is considered to be: swine > rats > mice > poultry ≈ ruminants. However, studies conducted within the past 10 years have demonstrated that some species of fish, such as rainbow trout, are highly sensitive to DON. The aims of this review are to explore the effects of DON on terrestrial and aquatic species as well as its mechanisms of action, metabolism, and interaction with other Fusarium mycotoxins. Notably, a considerable emphasis is placed on reviewing the effects of DON on different species of fish.

The 5-HT3 Receptor Affects Rotavirus-Induced Motility

Rotavirus infection is highly prevalent in children, and the most severe effects are diarrhea and vomiting. It is well accepted that the enteric nervous system (ENS) is activated and plays an important role, but knowledge of how rotavirus activates nerves within ENS and to the vomiting center is lacking. Serotonin is released during rotavirus infection, and antagonists to the serotonin receptor subtype 3 (5-HT₃ receptor) can attenuate rotavirus-induced diarrhea. In this study, we used a 5-HT₃ receptor knockout (KO) mouse model to investigate the role of this receptor in rotavirus-induced diarrhea, motility, electrolyte secretion, inflammatory response, and vomiting reflex. The number of diarrhea days (P = 0.03) and the number of mice with diarrhea were lower in infected 5-HT₃ receptor KO than wild-type pups. In vivo investigation of fluorescein isothiocyanate (FITC)-dextran transit time showed that intestinal motility was lower in the infected 5-HT₃ receptor KO compared to wild-type mice (P = 0.0023). Ex vivo Ussing chamber measurements of potential difference across the intestinal epithelia showed no significant difference in electrolyte secretion between the two groups. Immediate early gene cFos expression level showed no difference in activation of the vomiting center in the brain. Cytokine analysis of the intestine indicated a low effect of inflammatory response in rotavirus-infected mice lacking the 5-HT₃ receptor. Our findings indicate that the 5-HT₃ receptor is involved in rotavirus-induced diarrhea via its effect on intestinal motility and that the vagus nerve signaling to the vomiting center occurs also in the absence of the 5-HT₃ receptor. IMPORTANCE The mechanisms underlying rotavirus-induced diarrhea and vomiting are not yet fully understood. To better understand rotavirus pathophysiology, characterization of nerve signaling within the ENS and through vagal efferent nerves to the brain, which have been shown to be of great importance to the disease, is necessary. Serotonin (5-HT), a mediator of both diarrhea and vomiting, has been shown to be released from enterochromaffin cells in response to rotavirus infection and the rotavirus enterotoxin NSP4. Here, we investigated the role of the serotonin receptor 5-HT₃, which is known to be involved in the nerve signals that regulate gut motility, intestinal secretion, and signal transduction through the vagus nerve to the brain. We show that the 5-HT₃ receptor is involved in rotavirus-induced diarrhea by promoting intestinal motility. The findings shed light on new treatment possibilities for rotavirus diarrhea.

Which Antiemetic?

The choice of antiemetic should not be arbitrary, but should be based on knowledge of the different pathways of the various stimuli that lead to nausea and vomiting and the neuroreceptors involved. The steps to be taken in choosing an appropriate antiemetic are described. They are (a) to establish the probable cause of the nausea and vomiting, (b) to consider the afferent pathways involved, (c) to define the neuroreceptors activated at each of these sites, (d) to select the group of antiemetics that antagonizes these neuroreceptors, and (e) to choose the most potent antiemetic with the fewest side effects in that group. Causes for failure to respond to a chosen antiemetic are considered and the action to be taken is described.

Chronic nausea and vomiting: evaluation and treatment

Nausea is an uneasy feeling in the stomach while vomiting refers to the forceful expulsion of gastric contents. Chronic nausea and vomiting represent a diverse array of disorders defined by 4 weeks or more of symptoms. Chronic nausea and vomiting result from a variety of pathophysiological processes, involving gastrointestinal and non-gastrointestinal causes. The prevalence of chronic nausea and vomiting is unclear, although the epidemiology of specific conditions, such as gastroparesis and cyclic vomiting syndrome, is better understood. The economic impact of chronic nausea and vomiting and effects on quality of life are substantial. The initial diagnostic evaluation involves distinguishing gastrointestinal causes of chronic nausea and vomiting (e.g., gastroparesis, cyclic vomiting syndrome) from non-gastrointestinal causes (e.g., medications, vestibular, and neurologic disorders). After excluding anatomic, mechanical and biochemical causes of chronic nausea and vomiting, gastrointestinal causes can be grouped into two broad categories based on the finding of delayed, or normal, gastric emptying. Non-gastrointestinal disorders can also cause chronic nausea and vomiting. As a validated treatment algorithm for chronic nausea and vomiting does not exist, treatment should be based on a thoughtful discussion of benefits, side effects, and costs. The objective of this monograph is to review the evaluation and treatment of patients with chronic nausea and vomiting, emphasizing common gastrointestinal causes.

Calcium-Sensing Receptor and Transient Receptor Ankyrin-1 Mediate Emesis Induction by Deoxynivalenol (Vomitoxin)

The common foodborne mycotoxin deoxynivalenol (DON, vomitoxin) can negatively impact animal and human health by causing food refusal and vomiting. Gut enteroendocrine cells (EECs) secrete hormones that mediate DON's anorectic and emetic effects. In prior work utilizing a cloned EEC model, our laboratory discovered that DON-induced activation of calcium-sensing receptor (CaSR), a G-coupled protein receptor (GPCR), and transient receptor ankyrin-1 (TRPA1), a transient receptor potential (TRP) channel, drives Ca2+-mediated hormone secretion. Consistent with these in vitro findings, CaSR and TRPA1 mediate DON-induced satiety hormone release and food refusal in the mouse, an animal model incapable of vomiting. However, the roles of this GPCR and TRP in DON's emetic effects remain to be determined. To address this, we tested the hypothesis that DON triggers emesis in mink by activating CaSR and TRPA1. Oral gavage with selective agonists for CaSR (R-568) or TRPA1 (allyl isothiocyanate; AITC) rapidly elicited emesis in the mink in dose-dependent fashion. Oral pretreatment of the animals with the CaSR antagonist NPS-2143 or the TRP antagonist ruthenium red (RR), respectively, inhibited these responses. Importantly, DON-induced emesis in mink was similarly inhibited by oral pretreatment with NPS-2143 or RR. In addition, these antagonists suppressed concurrent DON-induced elevations in plasma peptide YY3-36 and 5-hydroxytryptamine-hormones previously demonstrated to mediate the toxin's emetic effects in mink. Furthermore, antagonist co-treatment additively suppressed DON-induced emesis and peptide YY 3-36 release. To summarize, the observations here strongly suggest that activation of CaSR and TRPA1 might have critical roles in DON-induced emesis.

Synthesis and Pharmacological Evaluation of [11C]Granisetron and [18F]Fluoropalonosetron as PET Probes for 5-HT3 Receptor Imaging

Serotonin-gated ionotropic 5-HT₃ receptors are the major pharmacological targets for antiemetic compounds. Furthermore, they have become a focus for the treatment of irritable bowel syndrome (IBS) and there is some evidence that pharmacological modulation of 5-HT₃ receptors might alleviate symptoms of other neurological disorders. Highly selective, high-affinity antagonists, such as granisetron (Kytril) and palonosetron (Aloxi), belong to a family of drugs (the "setrons") that are well established for clinical use. To enable us to better understand the actions of these drugs in vivo, we report the synthesis of 8-fluoropalonosetron (15) that has a binding affinity (K_i = 0.26 ± 0.05 nM) similar to the parent drug (K_i = 0.21 ± 0.03 nM). We radiolabeled 15 by nucleophilic ¹⁸F-fluorination of an unsymmetrical diaryliodonium palonosetron precursor and achieved the radiosynthesis of 1-(methyl-¹¹C)-N-granisetron ([¹¹C]2) through N-alkylation with [¹¹C]CH₃I, respectively. Both compounds [¹⁸F]15 (chemical and radiochemical purity >95%, specific activity 41 GBq/μmol) and [¹¹C]2 (chemical and radiochemical purity ≥99%, specific activity 170 GBq/μmol) were evaluated for their utility as positron emission tomography (PET) probes. Using mouse and rat brain slices, in vitro autoradiography with both [¹⁸F]15 and [¹¹C]2 revealed a heterogeneous and displaceable binding in cortical and hippocampal regions that are known to express 5-HT₃ receptors at significant levels. Subsequent PET experiments suggested that [¹⁸F]15 and [¹¹C]2 are of limited utility for the PET imaging of brain 5-HT₃ receptors in vivo.

What is nausea? A historical analysis of changing views

The connotation of "nausea" has changed across several millennia. The medical term 'nausea' is derived from the classical Greek terms ναυτια and ναυσια, which designated the signs and symptoms of seasickness. In classical texts, nausea referred to a wide range of perceptions and actions, including lethargy and disengagement, headache (migraine), and anorexia, with an awareness that vomiting was imminent only when the condition was severe. However, some recent articles have limited the definition to the sensations that immediately precede emesis. Defining nausea is complicated by the fact that it has many triggers, and can build-up slowly or rapidly, such that the prodromal signs and symptoms can vary. In particular, disengagement responses referred to as the "sopite syndrome" are typically present only when emetic stimuli are moderately provocative, and do not quickly culminate in vomiting or withdrawing from the triggering event. This review considers how the definition of "nausea" has evolved over time, and summarizes the physiological changes that occur prior to vomiting that may be indicative of nausea. Also described are differences in the perception of nausea, as well as the accompanying physiological responses, that occur with varying stimuli. This information is synthesized to provide an operational definition of nausea.

Ictal vomiting as a sign of temporal lobe epilepsy confirmed by stereo-EEG and surgical outcome

Vomiting is uncommon in patients with epilepsy and has been reported in both idiopathic and symptomatic epilepsies. It is presumed to originate in the anterior part of the temporal lobe or insula. To date, 44 cases of nonidiopathic focal epilepsy and seizures associated with ictal vomiting have been reported. Of the 44 cases, eight were studied using invasive exploration (3 stereo-EEG/5 subdural grids). Here, we report a 4-year-and-7-month-old patient with a history of febrile convulsion in the second year of life and who developed episodes of vomiting and complex partial seizures at 3 years of age. Scalp EEG showed no electrical modification during vomiting while the complex partial seizure displayed a clear right temporal origin. Brain MR showed hippocampal volume reduction with mild diffuse blurring of the temporal lobe. Stereoelectroencephalography study confirmed the mesiotemporal origin of the seizures and showed that the episodes of vomiting were strictly related to an ictal discharge originating in the mesial temporal structures without insular diffusion. The patient is now seizure-free (18 months) after removal of the right anterior and mesial temporal structures. In all the reported patients, seizures seemed to start in mesial temporal structures. The grid subgroup is more homogeneous, and the most prominent characteristic (4/5) is the involvement of both mesial and lateral temporal structures at the time of vomiting. In the S-EEG group, there is evidence of involvement of either the anterior temporal structures alone (2/3) or both insular cortices (1/3). Our case confirms that vomiting could occur when the ictal discharge is limited to the anterior temporal structure without insular involvement. Regarding the pathophysiology of vomiting, the role of subcortical structures such as the dorsal vagal complex and the central pattern generators (CPG) located in the reticular area is well established. Vomiting as an epileptic phenomenon seems to be related to the involvement of temporal structures, mainly mesial structures (amygdala) and with an uncertain role of the insula. An intriguing hypothesis is that the ictal discharge in mesial structures determines seizure manifestation that could be explained not only by tonic activation of the cortex, but also by 'release' (reduction of inhibition?) of the CPG responsible for involuntary motor behaviors.

Neurenteric cyst of the area postrema

Neurenteric cysts are CNS lesions most frequently occurring in the spinal cord. Intracranial neurenteric cysts are rarer, typically presenting with headache, mass effect, or location-specific symptoms. The area postrema is known as the emetic center of the brain; lesions can cause nausea and vomiting. Our case, featuring a neurenteric cyst of the area postrema, illustrates the importance of considering a neurological etiology for nonspecific symptoms that otherwise elude explanation. Our patient presented with acute decompensated hydrocephalus upon exploratory abdominal laparoscopy for unresolving abdominal pain. The patient had an eight-month history of unexplained intermittent nausea, vomiting, and abdominal pain. These bouts increased in frequency during the weeks before acute presentation, prompting exploratory abdominal laparoscopy. The acute decompensation was managed by ventriculostomy, and cranial MRI revealed a cystic mass by the floor of the fourth ventricle. After the patient stabilized and returned to neurological baseline, suboccipital craniectomy and resection were performed. The mass was histologically identified as a neurenteric cyst. The patient was free from neurological complaints at one-year follow-up, indicating that the successful resection of the area postrema-associated neurenteric cyst resolved her previous symptoms. Thus, some intracranial lesions can masquerade as nonspecific symptoms, presenting a challenge to accurate diagnosis.

Peptide YY3-36 and 5-hydroxytryptamine mediate emesis induction by trichothecene deoxynivalenol (vomitoxin)

Deoxynivalenol (DON, vomitoxin), a trichothecene mycotoxin produced by Fusarium sp. that frequently occurs in cereal grains, has been associated with human and animal food poisoning. Although a common hallmark of DON-induced toxicity is the rapid onset of emesis, the mechanisms for this adverse effect are not fully understood. Recently, our laboratory has demonstrated that the mink (Neovison vison) is a suitable small animal model for investigating trichothecene-induced emesis. The goal of this study was to use this model to determine the roles of two gut satiety hormones, peptide YY3-36 (PYY3-36) and cholecystokinin (CCK), and the neurotransmitter 5-hydroxytryptamine (5-HT) in DON-induced emesis. Following ip exposure to DON at 0.1 and 0.25mg/kg bw, emesis induction ensued within 15-30min and then persisted up to 120min. Plasma DON measurement revealed that this emesis period correlated with the rapid distribution and clearance of the toxin. Significant elevations in both plasma PYY3-36 (30-60min) and 5-HT (60min) but not CCK were observed during emesis. Pretreatment with the neuropeptide Y2 receptor antagonist JNJ-31020028 attenuated DON- and PYY-induced emesis, whereas the CCK1 receptor antagonist devezapide did not alter DON's emetic effects. The 5-HT3 receptor antagonist granisetron completely suppressed induction of vomiting by DON and the 5-HT inducer cisplatin. Granisetron pretreatment also partially blocked PYY3-36-induced emesis, suggesting a potential upstream role for this gut satiety hormone in 5-HT release. Taken together, the results suggest that both PYY3-36 and 5-HT play contributory roles in DON-induced emesis.

Comparison of emetic potencies of the 8-ketotrichothecenes deoxynivalenol, 15-acetyldeoxynivalenol, 3-acetyldeoxynivalenol, fusarenon X, and nivalenol

Although the acute toxic effects of trichothecene mycotoxin deoxynivalenol (DON or vomitoxin), a known cause of human food poisoning, have been well characterized in several animal species, much less is known about closely related 8-ketotrichothecenes that similarly occur in cereal grains colonized by toxigenic fusaria. To address this, we compared potencies of DON, 15-acetyldeoxynivalenol (15-ADON), 3-acetyldeoxynivalenol (3-ADON), fusarenon X (FX), and nivalenol (NIV) in the mink emesis model following intraperitoneal (ip) and oral administration. All five congeners dose-dependently induced emesis by both administration methods. With increasing doses, there were marked decreases in latency to emesis with corresponding increases in emesis duration and number of emetic events. The effective doses resulting in emetic events in 50% of the animals for ip exposure to DON, 15-ADON, 3-ADON, FX, and NIV were 80, 170, 180, 70, and 60 µg/kg bw, respectively, and for oral exposure, they were 30, 40, 290, 30, and 250 µg/kg bw, respectively. The emetic potency of DON determined here was comparable to that reported in analogous studies conducted in pigs and dogs, suggesting that the mink is a suitable small animal model for investigating acute trichothecene toxicity. The use of a mouse pica model, based on the consumption of kaolin, was also evaluated as a possible surrogate for studying emesis but was found unsuitable. From a public health perspective, comparative emetic potency data derived from small animal models such as the mink should be useful for establishing toxic equivalency factors for DON and other trichothecenes.

Current concepts in the management of postoperative nausea and vomiting

Postoperative nausea and vomiting (PONV) are still common following surgery. This is not only distressing to the patient, but increases costs. The thorough understanding of the mechanism of nausea and vomiting and a careful assessment of risk factors provide a rationale for appropriate management of PONV. Strategy to reduce baseline risk and the adoption of a multimodal approach will most likely ensure success in the management of PONV.

An overview of the clinical use of ondansetron in preschool age children

The introduction of 5-HT₃ receptor antagonist has revolutionized the prevention and treatment of nausea and vomiting in preschool aged children. These distressing symptoms, arising from multiple etiologies such as anesthesia, chemotherapy, and viral infection, are a major concern of patients and their families. Clinical research has demonstrated the antiemetic effectiveness of ondansetron in children. Although most of these studies focus primarily on preventing vomiting across the pediatric age group, they provide strong evidence for the use of ondansetron in preschool age children. For children at high risk, pediatric practice guidelines recommend ondansetron in conjunction with other antiemetics to achieve complete control of symptoms.

Cannabinoid-induced reduction in antral pacemaker frequency: a telemetric study in the ferret

BACKGROUND

The gastric myoelectric activity (GMA) is the electrical pacesetter potential, which drives gastric motility. Cannabinoids have broad-spectrum antiemetic and antinauseant activity. Paradoxically, they inhibit intestinal peristalsis and reduce gastric motility but their effect on GMA remains unknown.

METHODS

Ferrets were surgically implanted with radiotelemetry transmitters to record GMA, body temperature and heart rate. The effect of WIN 55,212-2 (1 mg kg(-1), i.p.), an agonist at the cannabinoid type 1 and 2 receptors was examined in conscious, unrestrained ferrets. WIN 55,212-2 was also compared to the anandamide upregulator URB 597 (5 mg kg(-1), i.p.) for a potential to modulate the emetic response and behavioral changes induced by apomorphine (0.25 mg kg(-1), s.c.).

KEY RESULTS

WIN 55,212-2 decreased GMA frequency (8.1 ± 0.4 cpm, compared to 9.6 ± 0.1 cpm in vehicle-treated animals, n = 6, P < 0.01). Apomorphine induced 9.0 ± 1.6 emetic episodes, WIN 55,212-2 inhibited the emetic response (3.3 ± 1.0 episodes, n = 6, P < 0.05) but URB 597 had no effect (9.0 ± 1.5 episodes). Apomorphine-induced hyperactivity in vehicle-treated animals (6.5 ± 3.6-16.6 ± 4.9 active behavior counts, n = 6, P < 0.01), which was reduced by WIN 55,212-2 (5.0 ± 1.5 counts, n = 6, P < 0.05).

CONCLUSIONS & INFERENCES

WIN 55,212-2 demonstrated clear antiemetic efficacy, which extends the broad-spectrum antiemetic efficacy of cannabinoids to dopamine receptor agonists in the ferret. Our results, however, suggest a more limited spectrum of action for URB 597. WIN 55,212-2 decreased the frequency of the antral electrical pacemaker, which reveals new insights into the mechanism regulating the decrease in motility induced by cannabinoids.

New tools in the treatment of motility disorders in children

Gastrointestinal motility disorders can develop in neurologically impaired children and those with congenital malformations of the gut. It is characterized by moderate to severe abdominal pain, vomiting, and failure to thrive. Antral dysmotility after fundoplication and increased sympathetic over activity are 2 factors associated with this condition that make it difficult to treat. This paper proposes a management strategy using metoclopramide, celiac plexus blockade, and thoracic splanchnectomy. It reviews our experience with 11 patients.

[Management of chemotherapy-induced emesis: what is the standard after 20 years of clinical research]

BACKGROUND

The knowledge of the importance, the physiopathological mechanisms, and the management of the chemotherapy-induced emesis has increased exponentially during the last 20 years. High-dosage metoclopramide (MCP) therapy has been introduced in the eighties and serotonine type-3 receptor antagonists (5-HT(3) antagonists) have been used since the late eighties and early nineties. Due to both classes of substances the results of the antiemetic therapies have improved drastically. After 20 years of intensive clinical research it seems to be appropriate to come to an intermediate conclusion.

METHOD

With the aid of an overview and a new analysis of the literature published on this topic so far, the current state of research is shown (including the fields in which further improvement will be necessary), and suggestions are made, wherever it seemed possible, to attain the "gold standard" in antiemetic therapy.

RESULTS AND CONCLUSIONS

In connection with all highly or very highly emetogenic chemotherapies, an antiemetic prophylaxis should be initiated on the day of therapy, especially when using platinum or most of the cyclophosphamide-based regimes for cancer treatment. The recommended prophylaxis consists of a combination of 5-HT(3) antagonists with a corticosteroid. To combat the so-called delayed emesis on the days following therapy, all patients should undergo an oral corticoid therapy, possibly in combination with MCP (especially platinum-therapy patients), less frequently with 5-HT(3) antagonists. With these means of prophylaxis emesis can be prevented/avoided completely in most patients, and nausea can at least be reduced. It is sufficient to administer a single dose of 5-HT(3) antagonists prior to chemotherapy. For ondansetron and granisetron, the best documented substances within this class of drugs, 8 mg (ondansteron) and 3 mg (granisetron) are considered standard dosages. Among the corticoids, most data have been accumulated for dexamethasone. A standard dose of 10 to 20 mg can be administered prior to chemotherapy. Right after and especially on the days following chemotherapy higher dosages seem to be indicated.

PROSPECT

Further therapy improvements, especially concerning emesis and nausea on the days following chemotherapy, are necessary and are currently object of clinical research.

Electrophysiologic, morphologic, and serologic features of chronic unexplained nausea and vomiting: lessons learned from 121 consecutive patients

BACKGROUND

Despite substantive morbidity, unexplained nausea and vomiting has not been evaluated in a systematic manner via surgically obtained biopsies and direct electrophysiology of the gut, and this information has not been correlated with serologic information. We investigated consecutive patients with unexplained and refractory chronic nausea and vomiting to define the presence of morphologic, physiologic, and/or serologic abnormalities.

METHODS

In all, 101 of 121 consecutive patients who experienced chronic nausea and vomiting of unknown etiology evaluated in 1 tertiary referral center over a 10-year period were profiled qualitatively by full-thickness small bowel biopsies with hematoxylin and eosin (H&E) and Smith's Silver stains, quantitatively by intraoperative gastric electrophysiology, and semiquantitatively, when it became available, by serum autoimmune Western blot analysis.

RESULTS

Overall, 79 of 101 patients had abnormal full-thickness biopsy (70 neuropathies and 9 myopathies) and frequent serum autoimmune abnormalities (mean score = 13.2, normal < 3.0). In addition, 96 of 101 patients had abnormal frequency and/or uncoupling on gastric electrophysiology. Patients with small-intestinal myopathy showed a diversity of diagnoses; some patients with neuropathy had abdominal pain that correlated with autoimmune scores on Western blot.

CONCLUSION

Patients with refractory and unexplained nausea and vomiting have a high incidence of both small bowel morphologic abnormalities (primarily neuropathies) and gastric electrophysiologic abnormalities, which are associated commonly with serologic autoimmune activation. Similar histomorphologic, physiologic, and serologic measures should be considered in the diagnostic evaluation of any patient with refractory or unexplained nausea and vomiting.

Predicting adaptive behavior in the environment from central nervous system dynamics

To generate adaptive behavior, the nervous system is coupled to the environment. The coupling constrains the dynamical properties that the nervous system and the environment must have relative to each other if adaptive behavior is to be produced. In previous computational studies, such constraints have been used to evolve controllers or artificial agents to perform a behavioral task in a given environment. Often, however, we already know the controller, the real nervous system, and its dynamics. Here we propose that the constraints can also be used to solve the inverse problem--to predict from the dynamics of the nervous system the environment to which they are adapted, and so reconstruct the production of the adaptive behavior by the entire coupled system. We illustrate how this can be done in the feeding system of the sea slug Aplysia. At the core of this system is a central pattern generator (CPG) that, with dynamics on both fast and slow time scales, integrates incoming sensory stimuli to produce ingestive and egestive motor programs. We run models embodying these CPG dynamics--in effect, autonomous Aplysia agents--in various feeding environments and analyze the performance of the entire system in a realistic feeding task. We find that the dynamics of the system are tuned for optimal performance in a narrow range of environments that correspond well to those that Aplysia encounter in the wild. In these environments, the slow CPG dynamics implement efficient ingestion of edible seaweed strips with minimal sensory information about them. The fast dynamics then implement a switch to a different behavioral mode in which the system ignores the sensory information completely and follows an internal "goal," emergent from the dynamics, to egest again a strip that proves to be inedible. Key predictions of this reconstruction are confirmed in real feeding animals.

The use of acupuncture in controlling the gag reflex in patients requiring an upper alginate impression: an audit

BACKGROUND

A pronounced gag reflex (GR) can be a problem to both the acceptance and delivery of dental treatment. Despite a range of management strategies, some patients cannot accept even simple dental treatment. The aim of this study was to evaluate the use of acupuncture point CV-24 in controlling a profound gag reflex during dental treatment requiring an upper alginate impression.

METHOD

Members of the British Dental Acupuncture Society were invited to take part in an audit of the role of acupuncture point CV-24 in controlling the gag reflex. They were issued with patient inclusion criteria, a standardised procedure instruction sheet and a recording form. All patients fulfilling the inclusion criteria had an upper dental alginate impression taken (or an attempt made at it) before acupuncture, and a second upper alginate impression taken immediately after acupuncture of point CV-24. The GR assessment was undertaken prior to insertion of the acupuncture needle using the Gagging Severity Index (GSI); and after the acupuncture and impression taking using the Gagging Prevention Index (GPI). Both the GSI and GPI were recorded at three stages of the dental impression taking procedure, ie, when the empty impression tray was tried in the mouth, when the loaded tray was inserted into the mouth, and on completion of the impression taking.

RESULTS

Twenty-one dentists submitted 64 case reports of which 37 fulfilled the inclusion criteria. Prior to acupuncture all 37 patients (20 females and 17 males with a mean age of 46.8 years) were unable to accept the impression taking. After acupuncture of point CV-24, an improvement of between 51-55% (mean 53%) for the three stages of impression taking was noticed. Thirty patients (81%) were able to accept the impression taking, whereas seven (19%) remained unable to tolerate the procedure. Assessed by the GSI and GPI, there was a significant decrease in GR scores at all three stages of the impression taking procedure (median 3 vs 1; 4 vs 2; 4 vs 2; p < 0.0001). Thus before acupuncture, the patients had moderate to severe GR and after acupuncture the GR had reduced to a level which only complicated dental treatment slightly.

CONCLUSION

Our results indicate that acupuncture of point CV-24 is an effective method of controlling severe GR during dental treatment including impression taking. However, the results of the current audit need to be tested in a randomised controlled study in order to substantiate the effectiveness of this method.

Sensory transmission in the gastrointestinal tract

The gastrointestinal (GI) tract must balance ostensibly opposite functions. On the one hand, it must undertake the process of digestion and absorption of nutrients. At the same time, the GI tract must protect itself from potential harmful antigenic and pathogenic material. Central to these processes is the ability to 'sense' the mechanical and chemical environment in the gut wall and lumen in order to orchestrate the appropriate response that facilitates nutrient assimilation or the rapid expulsion through diarrhoea and/or vomiting. In this respect, the GI tract is richly endowed with sensory elements that monitor the gut environment. Enteric neurones provide one source of such sensory innervation and are responsible for the ability of the decentralized gut to perform complex reflex functions. Extrinsic afferents not only contribute to this reflex control, but also contribute to homeostatic mechanisms and can give rise to sensations, under certain circumstances. The enteric and extrinsic sensory mechanisms share a number of common features but also some remarkably different properties. The purpose of this review is to summarize current views on sensory processing within both the enteric and extrinsic innervation and to specifically address the pharmacology of nociceptive extrinsic sensory pathways.

Therapeutic Modalities for the Prophylactic Management of Postoperative Nausea and Vomiting

The occurrence of postoperative nausea and vomiting (PONV) remains one of the most common complications after general anesthesia. The causes of PONV are multimodal, involving several physiologic pathways that stimulate the vomiting center, including the chemoreceptor trigger zone, the gastrointestinal tract, the vestibular system, the cerebral cortex, and the midbrain. Significant research has been published focusing on the use of different pharmacologic agents and varying anesthetic techniques to prevent and manage PONV. The addition of therapeutic modalities to the arsenal of prophylactic management techniques may decrease patient incidence of PONV by directing treatment to various pathways that stimulate the vomiting center. The purpose of this article is to review briefly the literature and discuss three therapeutic modalities for preventing PONV: perioperative oxygen administration, perioperative intravenous fluid administration, and differing fasting protocols.

Cyanobacterial lipopolysaccharides and human health - a review

Cyanobacterial lipopolysaccharide/s (LPS) are frequently cited in the cyanobacteria literature as toxins responsible for a variety of heath effects in humans, from skin rashes to gastrointestinal, respiratory and allergic reactions. The attribution of toxic properties to cyanobacterial LPS dates from the 1970s, when it was thought that lipid A, the toxic moiety of LPS, was structurally and functionally conserved across all Gram-negative bacteria. However, more recent research has shown that this is not the case, and lipid A structures are now known to be very different, expressing properties ranging from LPS agonists, through weak endotoxicity to LPS antagonists. Although cyanobacterial LPS is widely cited as a putative toxin, most of the small number of formal research reports describe cyanobacterial LPS as weakly toxic compared to LPS from the Enterobacteriaceae. We systematically reviewed the literature on cyanobacterial LPS, and also examined the much lager body of literature relating to heterotrophic bacterial LPS and the atypical lipid A structures of some photosynthetic bacteria. While the literature on the biological activity of heterotrophic bacterial LPS is overwhelmingly large and therefore difficult to review for the purposes of exclusion, we were unable to find a convincing body of evidence to suggest that heterotrophic bacterial LPS, in the absence of other virulence factors, is responsible for acute gastrointestinal, dermatological or allergic reactions via natural exposure routes in humans. There is a danger that initial speculation about cyanobacterial LPS may evolve into orthodoxy without basis in research findings. No cyanobacterial lipid A structures have been described and published to date, so a recommendation is made that cyanobacteriologists should not continue to attribute such a diverse range of clinical symptoms to cyanobacterial LPS without research confirmation.

Studies for the emetic mechanisms of ipecac syrup (TJN-119) and its active components in ferrets: involvement of 5-hydroxytryptamine receptors

Ipecac syrup, prepared from a galentical ipecac, contains the nauseant alkaloids cephaeline and emetine. The involvement of receptors and serotonin- and dopamine-metabolizing enzymes in the emesis induced by ipecac syrup and these components was investigated. 1) In ferrets, the selective 5-HT3-receptor antagonist ondansetron (0.5 mg/kg, p.o.) prevented each emesis induced by TJN-119 (0.5 mL/kg, p.o.), cephaeline (0.5 mg/kg, p.o.) and emetine (5.0 mg/kg, p.o.), but the intraperitoneal administration of the selective dopamine D2-receptor antagonist sulpiride failed to significantly suppress the TJN-119, cephaeline and emetine-induced emesis at a dose of 0.1 mg/kg that blocked apomorphine-induced emesis. 2) In the receptor binding assays, cephaeline and emetine had a distinct affinity to 5-HT4 receptor, but no or weak affinity to 5-HT1A, 5-HT3, nicotine, M3, beta1, NK1, and D2 receptors. 3) Cephaeline and emetine did not affect activities of metabolic enzymes of 5-HT and dopamine (MAO-A, MAO-B, tryptophan 5-hydroxylase and tyrosine hydroxylase) in vitro. These results suggest that 5-HT3 receptor plays an important role in the emetic action of TJN-119, cephaeline and emetine, and the 5-HT4 receptor may be involved in their mechanisms.

Effects of acetylcholine and GABA on neurons in the area postrema of Suncus murinus brainstem slices

Slices (400 microm) containing the area postrema were prepared from three Japanese house musk shrews. Data reported are from 16 representative units. Units fell into one of three separate groups with spontaneous firing rates of 36-41/s, 16-18/sec. and 6-8/sec., possibly reflecting different set points of an endogenous pacemaker. Most neurons did not respond to ionophoresis of GABA or ACh. In those that did, ACh briefly increased spike frequency in a dose-dependent manner. The firing pattern suggests that the membrane potential was depolarized strongly, coupled with an extremely large conductance increase. Bath perfusion of curare, but not atropine, inhibited the response. Ionophoresis of GABA caused strong inhibition. The data show Suncus AP contains neurons that are sensitive to nicotine and GABA and may be emetogenic.

Rhodes Index of Nausea and Vomiting--Form 2 in pregnant women. A confirmatory factor analysis

BACKGROUND

Despite widespread application of Rhodes Index of Nausea and Vomiting-Form 2 (INV2) in practice and research, empirical analyses have not been consistently performed to verify the a priori factors that guided the subclass construction of the symptoms.

OBJECTIVES

To examine the dimensional structure of Rhodes INV in a sample of pregnant women.

METHOD

Data were collected from 152 pregnant women who were experiencing some degree of nausea and vomiting during early pregnancy and analyzed using structural equation modeling techniques. Five competing measurement structures were tested and compared. The structure (model) that provided the closest fit to the data was selected and relationships (factor loadings) between the constructs and indicators were established.

RESULTS

The model fitting the data the closest was a three-factor structure measuring nausea, vomiting, and retching as three separate, but correlated dimensions. The factor loadings were high (0.73-0.96) and significant (p < .001). The model treating nausea and vomiting as a one-factor concept as well as the model including two factors named symptom occurrence and symptom distress did not fit the data.

CONCLUSION

Rhodes INV2 is a valid measurement tool if subscales are formed to reflect the multidimensional structure of nausea and vomiting in pregnancy.

Imiquimod-elicited emesis is mediated by the area postrema, but not by direct neuronal activation

The immunomodulator, imiquimod, has been shown to have antiviral and antitumor properties in animal models. It also has been reported to alter cytokine levels in both animals and humans. However, because imiquimod appeared to be emetic, studies were conducted to determine the degree of sensitivity, and the pathways involved. Subcutaneous administration of > or = 10 mg/kg imiquimod to ferrets elicited emesis with latencies as short as 2'; 12 and 15 mg/kg were optimal doses. Emetic responsiveness was eliminated by complete ablation of the area postrema, but was unaffected by bilateral supradiaphragmatic section of the vagus nerve. This indicates that the emesis is produced by an activation of the chemoreceptor trigger zone B the area postrema. Ferret brain stem slices (450 microm) were preincubated in oxygenated Krebs-Ringer and then mounted in a submerged slice recording chamber. Extracellular recordings of spontaneous and ionophoretically evoked activity of area postrema neurons were obtained for up to 8 h, while the effect of bath-applied imiquimod was determined. Under control conditions, neurons showed a low frequency spontaneous discharge. Introduction of imiquimod (concentration range, 1 x 10(-7) to 5 x 10(-8)M) had no effect on neuronal firing. With ionophoresis of glutamate from an independent micropipette, a brief excitatory response was obtained. We conclude that imiquimod does not directly excite area postrema neurons. It is likely that imiquimod causes synthesis and release of some unknown emetic substance(s), very possibly cytokines.

Modulation of gastric motor activity by a centrally acting stimulus, circular vection, in humans

The aims of this study were to investigate gastric motor correlates of vection, a centrally acting stimulus, and relate these responses to the induction of motion sickness symptoms. Antral contractile activity and gastric volume retained after a liquid nutrient meal (600 ml) were assessed by magnetic resonance imaging in healthy subjects during two different protocols. Vection was induced by an optokinetic drum, and subjects repeatedly rated the intensity of vection and nausea on 0-10 analog scales. Vection delayed gastric emptying [99% (89-102%) [median (interquartile ranges)] of volume retained at 28 min; control situation: 79% (69-81%), P < 0.05]. Antral contractile activity followed a distinct time course of rapid decrease [-64% (-72 to -59%) change from baseline activity] immediately after onset of drum rotation followed by gradual recovery upon withdrawal of the stimulus. No relationship was found between the severity of nausea and inhibition of gastric emptying or antral contractile activity. The inhibition of antral contractile activity appears to be a good measure of the peripheral response to vection but is probably independent of subjective symptom induction.

Vomiting and gastric motility in infants with cow's milk allergy

BACKGROUND

Regurgitation and vomiting are common manifestations of cow's milk protein allergy (CMPA) in infants and are usually ascribed to gastroesophageal reflux (GER). Gastric anaphylaxis can induce antral dysmotility in the rat, and therefore the hypothesis for the current study was that cow's milk in sensitized infants may impair antral motility, thereby promoting GER and reflex vomiting.

METHODS

Seven vomiting infants with CMPA and nine with primary GER underwent a challenge with cow's milk formula. Electrogastrography (EGG) was used to measure the spectral frequency (bradygastria = 1.5-2.4 cycles per minute [cpm], normogastria = 2.5-3.9 cpm, tachygastria = 4.0-9.0 cpm) and the postprandial-to-fasting power ratio of gastric electrical activity, whereas gastric half-emptying time (T1/2) was measured by electrical impedance tomography (EIT).

RESULTS

In CMPA and GER, respectively, during fasting, the frequency distribution (mean +/- SD) of the EGG was as follows: normogastria 47.9%+/-12.5% versus 52.2%+/-9.8%, bradygastria 24.1%+/-5.7% versus 22.8%+/-8.3%, and tachygastria 28.0% 8.5% versus 25.0% 8.3%. In contrast, after the cow's milk challenge, the difference between the two groups was statistically significant: normogastria 33.1%+/-8.8% versus 70.6%+/-8.6% (P < 0.0001). bradygastria 38.0%+/-15.5% versus 15.7%+/-5.2% (P = 0.002), and tachygastria 28.9%+/-10.6% versus 13.4%+/-4.6% (P = 0.001. The postprandial/ fasting power ratio (mean +/- SD) was 3.2+/-1.9 in CMPA and 8.1+/-2.1 in GER (P < 0.0001). Gastric T1/2 (mean +/- SD) of the cow's milk meal was 89.0+/-26.3 minutes versus 54.0+/-12.6 minutes (P = 0.003). In infants with GER all EGG parameters and gastric T1/2 were similar to that in 10 healthy control infants.

CONCLUSIONS

In sensitized infants, cow's milk induces severe gastric dysrhythmia and delayed gastric emptying, which in turn may exacerbate GER and induce reflex vomiting. Electrogastrography and EIT can be useful in the assessment of vomiting, GER, and CMPA in infants.

Insufficient effectiveness of 5-hydroxytryptamine-3 receptor antagonists due to oral morphine administration in patients with cisplatin-induced emesis

PURPOSE

To compare the effect of 5-hydroxytryptamine-3 (5HT(3)) receptor antagonists in cancer patients receiving chemotherapy including cisplatin (CDDP), with or without sustained-release oral morphine (MS Contin; Shionogi Co, Osaka, Japan).

PATIENTS AND METHODS

We retrospectively studied 58 lung cancer patients given chemotherapy including at least 50 mg/m(2) CDDP with 5-HT(3) receptor antagonists between January 1996 and December 1997. Number of vomiting episodes, average proportions of hospital-supplied meals consumed (0 to 100%, as an index of appetite), and nausea severity scores (0 to 2 points, subjective patient judgment) were compared between oral morphine-administered (+) and morphine-free (-) groups.

RESULTS

Sixteen morphine(+) and 42 morphine(-) cases were used. In cases of acute emesis (within 24 hours after CDDP injection), morphine(+) and morphine(-) groups were significantly different in number of vomiting episodes (1.25 and 0.14, respectively; P <.0001), appetite (58.13% and 90.24%; P <.0001), and nausea severity scores (1.63 and 0.62; P <.0001). In delayed-emesis cases (24 to 120 hours after CDDP), these groups differed significantly in number of vomiting episodes (1.94 and 0.43, respectively; P =.0001), appetite (23.13% and 52.08%; P <.0001), and nausea severity (1.38 and 0.91; P =.009). There were no significant differences in sex, age, anticancer drugs concurrent with CDDP, CDDP dose, corticosteroid administration, clinical stage, or type of 5-HT(3) antagonist.

CONCLUSIONS

These data suggest that morphine can markedly reduce the effectiveness of 5-HT(3) receptor antagonists in patients receiving chemotherapy that includes CDDP. These results require confirmation by reinvestigation of clinical data on the efficacy of 5-HT(3) receptor antagonists and by extensive prospective analyses.

A preliminary report on pain thresholds in bulimia nervosa during a bulimic episode

Subjects with bulimia nervosa (BN) have been shown to exhibit abnormal satiety responses. Short-term satiety is largely mediated by afferent vagal activity. Activation of afferent vagal fibers has also been found to stimulate a descending pain inhibitory pathway that leads to elevation in somatosensory pain thresholds. Therefore, the study of pain thresholds in BN subjects may lead to a better understanding of afferent vagal function in this disorder. In this preliminary study, pressure pain thresholds were assessed in nine subjects with BN on 3 consecutive days during a binge-eating and vomiting (B/V) episode, during a normal meal, and after an overnight fast. A significant time versus condition effect was found with a significant change in the pain threshold in BN subjects under the B/V condition only. These data are consistent with the hypothesis that vagal afferent activation by a B/V episode also activates the descending pain inhibitory pathway.

-The effect of ondansetron on intracranial pressure and cerebral perfusion pressure in neurosurgical patients-

OBJECTIVE

To determine the effect of ondansetron on intracranial pressure (ICP), mean arterial pressure (MAP) and cerebral perfusion pressure (CPP).

STUDY DESIGN

Prospective, comparative, randomized double-blind study.

PATIENTS

Twenty-six patients undergoing intracranial surgery.

METHOD

Induction was obtained with propofol (1-2.5 mg.kg-1), fentanyl (1.5 micrograms.kg-1) and pancuronium (0.1 mg.kg-1), and maintenance was achieved with propofol and fentanyl. Intermittent positive pressure ventilation was used to ensure mild hypocapnia at 35 +/- 2 mmHg. Positioning of the patient was followed by 15 minutes steady-state. Patient received thereafter either 8 mg ondansetron or a placebo intravenously. The ICP was measured using a lumbar malleable spinal needle. CPP was calculated using the formula CCP = MAP-ICP. All variables were measured every minute for 15 minutes.

RESULTS

The ICP, MAP and CPP did not differ between the two groups. There were no differences in the highest ICP values in patients receiving either ondansetron or placebo (11 +/- 5 versus 9 +/- 5, mean +/- SD), respectively.

CONCLUSION

Intravenous administration of 8 mg ondansetron affects neither cerebral hemodynamics nor ICP.

Vomiting and gastroesophageal motor activity in children with disorders of the central nervous system

BACKGROUND

Vomiting is common in children with disorders of the central nervous system (CNS) and is usually ascribed to gastroesophageal reflux (GER). However, recent acquisitions on the pathophysiology of vomiting suggest that the dysmotility of the foregut may be more widespread.

METHODS

Fifty-five children with CNS disorders, 50 of whom suffered from retching and/or vomiting (18 following fundoplication) were studied. We assessed GER by 24 hour pH monitoring and endoscopy, gastric electrical activity by electrogastrography, and gastric half-emptying time (T1/2) of a milk meal be electrical impedance tomography.

RESULTS

Of the 50 vomiting patients, 29 had GER (reflux index of 5.7%-87.4%; controls: < 5%), and 31 had gastric dysrhythmias (12 tachyarrhythmia at 5.5-11.2 cpm, 4 bradyarrhythmia at 1.7-1.9 cpm, 15 unstable electrical activity; controls; 2.2-4.0 cpm). Sixteen patients had GER and gastric dysrhythmias. Eleven of 18 patients with fundoplication had gastric dysrhythmias. Gastric T1/2 was delayed in 12 of 13 patients with gastric dysrhythmia (6 with GER), versus 2 of 5 with GER alone. No abnormalities were detected in the 5 patients who did not suffer from vomiting.

CONCLUSIONS

Children with CNS disorders who vomit have abnormal gastric motility as often as GER. Following fundoplication, many patients continue to have symptoms possibly related to gastric dysrhythmias, the effects of which may be unmasked by fundoplication. Foregut dysmotility may be related to abnormal modulation of the enteric nervous system by the CNS or to involvement of the enteric nervous system by the same process affecting the brain.

Ondansetron dose response curve in high-risk pediatric patients

STUDY OBJECTIVE

To establish a dose-response relationship for ondansetron, and to evaluate any effects of oral premedication with metoclopramide in pediatric patients undergoing tonsillectomy and adenoidectomy and strabismus surgery.

DESIGN

Prospective, randomized, double blind study.

SETTING

University affiliated, 280-bed pediatric hospital.

PATIENTS

320 ASA physical status l and II patients between the ages of 2 and 12 years undergoing tonsillectomy and adenoidectomy or strabismus surgery.

INTERVENTIONS

Patients were randomized to eight investigational groups. Patients in all eight groups underwent a standard anesthetic. Groups 1, 2, 3, and 4 received intravenous (i.v.) saline or i.v. ondansetron at doses of 0.05 mg/kg, 0.1 mg/kg and 0.15 mg/kg, respectively. Groups 5, 6, 7, and 8 received oral metoclopramide 0.15 mg/kg as well as i.v. saline, and ondansetron 0.05 mg/kg, 0.1 mg/kg, or 0.15 mg/kg. Patients were evaluated for emetic episodes prior to and following discharge.

MEASUREMENTS AND MAIN RESULTS

All doses of ondansetron 0.05 mg/kg, 0.1 mg/kg, and 0.15 mg/kg were significantly more effective than placebo in reducing the incidence of emesis prior to, following discharge, and during the first 24 postoperative hours (p < 0.001). There were no significant differences in the occurrence of emesis between the groups receiving ondansetron 0.05 mg/kg, 0.1 mg/kg, and 0.15 mg/kg. The addition of oral metoclopramide 0.15 mg/kg had no effect on the incidence of emesis in the ondansetron or placebo study groups.

CONCLUSIONS

Ondansetron is an effective medication for the treatment and prevention of postoperative nausea and vomiting, and a dose of ondansetron 0.05 mg/kg is as effective as 0.1 mg/kg and 0.15 mg/kg. Metoclopramide 0.15 mg/kg has no effect on the incidence of postoperative nausea and vomiting.

Gastric motility patterns for digestion and vomiting evoked by sympathetic nerve stimulation and 5-hydroxytryptamine in the dogfish Scyliorhinus canicula

The sympathetic control of motor activity in the stomach of the dogfish Scyliorhinus canicula and its pharmacology was studied in freshly killed animals with the abdominal viscera superfused in situ with elasmobranch Ringer by recording gastric pressure and by quantitative analysis of video-tape recordings of the activity. Little spontaneous activity was seen in the stomach, although in two animals retrograde contractions occurred in the spiral intestine. The effects of electrical stimulation of the splanchnic (sympathetic) nerves varied markedly with frequency. At 4 Hz after a latency of about 1 min there was a slight increase in the overall level of contractile activity in both cardiac and pyloric regions of the stomach, which persisted throughout the stimulation period (5-7 min). At 16 Hz a contraction was visible in the pyloric region within 10 s of the start of stimulation. Over the next 30 s this contraction proceeded cranially becoming more powerful as it swept into the cardiac region. This contraction returned the contents of the pyloric stomach to the cardiac stomach past the valve-like junction between them. This contraction continued into the cardiac stomach and in some animals propelled the contents into the oesophagus. About 2 min after the start of stimulation there followed a series of contractions in both gastric regions, predominantly in the circular muscle. In the cardiac region these contractions occurred alternately in the proximal and distal regions. Occasionally a large contraction passed a bolus of material from the cardiac to the pyloric region. No movements or pressure changes were observed in the stomach after stimulation of the vagus, although contractions were readily induced in the oesophagus. It is proposed that the initial large retrograde contraction provides a mechanism by which the animal can vomit indigestible or accidentally ingested material. In contrast the later motor patterns suggest that this type of activity is involved in more normal digestive functions of mixing food with gastric secretions, trituration and gastric emptying. Evidence is presented which implicates 5-hydroxytryptamine as a principal neurotransmitter involved in the genesis of the retrograde contraction by the splanchnic nerve.

Single-blind study of the effects of intravenous dolasetron mesylate versus ondansetron on electrocardiographic parameters in normal volunteers

A single-blind, randomized, five-way cross-over, safety and tolerability trial was conducted to determine whether intravenous (i.v.) dolasetron mesylate at varying single doses induces changes in ECG intervals in healthy volunteers and to compare these changes with a single intravenous dose of ondansetron or placebo. Thirty healthy male volunteers received 1.2, 1.8, and 2.4 mg/kg i.v. dolasetron mesylate, 32 mg i.v. ondansetron, and placebo on 5 separate days. ECGs were recorded at intervals during the 24 h after study drug administration. The changes in ECG intervals observed after dolasetron mesylate or ondansetron were acute, transient, and asymptomatic. Dolasetron mesylate resulted in slight but statistically significant dose-related increases in heart rate (HR) and PR and QRS intervals (between h 0 and 4). A statistically significant increase in QTc interval was detected with both dolasetron mesylate (2.4 mg/kg) and ondansetron. Ondansetron also produced a slight but statistically significant increase in JT interval and a decrease in HR. These changes in ECG intervals were usually observed between h 0 and 4; all parameters returned to baseline within 8 h of treatment. The results demonstrate that both dolasetron mesylate and ondansetron prolong the QTc interval. However, dolasetron mesylate predominantly altered ECG parameters indicative of ventricular depolarization (QRS duration), whereas ondansetron predominantly affected ventricular repolarization as measured by a prolongation in the JT interval. Both dolasetron and ondansetron were well tolerated. The adverse event (AE) rate was 13.3% (4 of 30); all AE were of mild or moderate severity and were distributed across all dose arms.

Ondansetron decreases postoperative vomiting in pediatric patients undergoing tonsillectomy and adenoidectomy

One of the most frequently performed pediatric surgical procedures is tonsillectomy and adenoidectomy. Nausea and vomiting and the inability to tolerate oral fluids lead to unplanned hospitalizations. Despite treatment with metoclopramide and droperidol, nausea and vomiting continue to be high after this procedure. We designed this investigation to compare currently utilized antiemetics to ondansetron, a new serotonin antagonist, in hopes of decreasing the occurrence of nausea and vomiting in patients undergoing tonsillectomy and adenoidectomy. This prospective, randomized, double-blinded clinical trial compared ondansetron, droperidol, and placebo administered at the induction of general anesthesia and the incidence of vomiting postoperatively. One-hundred sixty-five children between the ages of 2 and 12 years undergoing ambulatory adenotonsillectomy were enrolled and completed this investigation. The primary outcome measure was the elimination of vomiting during the 24-h investigative period following surgery. Both ondansetron and droperidol significantly lowered the incidence of postoperative emesis after tonsillectomy and adenoidectomy (P < 0.012) compared to placebo. Ondansetron was significantly more effective than droperidol in reducing emesis after discharge (P < 0.025). Both ondansetron and droperidol are effective in decreasing emesis when given before surgical incision in pediatric patients undergoing tonsillectomy and adenoidectomy. Ondansetron's antiemetic effect persists for up to 24 h following surgery with significant reductions in emesis. Ondansetron's effectiveness in eliminating vomiting without sedation or other side effects suggests that it should be considered as part of the standard management in pediatric patients undergoing tonsillectomy and adenoidectomy.

Nausea and vomiting in patients with cancer

Nausea and vomiting in advanced cancer, occurring as a manifestation of the disease process or as a complication of drugs used for symptom control, can be controlled rapidly in most instances using the protocol described. This involves an informed appraisal of the cause or causes of nausea and vomiting, combined with application of knowledge of the mechanisms of emesis and the action of antiemetics. Different mechanisms appear to responsible for emesis after chemotherapy and irradiation and for anticipatory vomiting. Ondansetron combined with dexamethasone appears to be the most effective regimen for post-cisplatin emesis. For less emetogenic agents, dexamethasone alone, or in combination with ondansetron for refractory cases, gives good control. For the control of vomiting induced by single-fraction radiotherapy to the upper abdomen, ondansetron is very effective. Management of anticipatory vomiting should concentrate on prevention, but once vomiting is established, behavioral therapy and the amnesic properties of lorazepam may be used.

Activation of peripheral and/or central chemoreceptors changes retching activities of Bötzinger complex neurons and induces expulsion in decerebrate dogs

Fictive expulsion can be induced by electrical stimulation of the carotid sinus nerve during fictive retching or by discontinuing artificial ventilation in decerebrate paralyzed dogs. Both the phrenic and abdominal muscle nerves discharge during the early phase of fictive expulsion, but only the abdominal muscle nerve continues to discharge during the late phase. To determine whether Bötzinger complex (BOT) neurons participate in expulsion, responses to sinus nerve stimulation were examined in 47 non-respiratory (N-RES), 15 inspiratory (INS) and 12 expiratory (EXP) BOT neurons during eupnea. About 80% of the neurons produced excitatory or inhibitory responses. FIring patterns were observed in 61 N-RES, 39 INS and 56 EXP BOT neurons during expulsion induced by sinus nerve stimulation or by discontinuation of artificial ventilation. An activity pattern similar to that of the phrenic nerve was exhibited during fictive retching and expulsions by 13 N-RES< 3 INS and 8 EXP neurons, and a firing pattern like that of the abdominal muscle nerve was produced by 11 N-RES, 6 INS and 5 EXP neurons. Bursts were limited to the late phase of expulsion and to the period just after expulsion in 5 N-RES, 3 INS and 3 EXP neurons, and in 8 N-RES and 21 EXP neurons, respectively. Firings of the two latter groups of neurons decreased concomitantly with each retch or during retching. These results suggest that neurons of the two latter groups play crucial roles in the central patterning of neuronal expulsion activities.

The role of serotonin as a mediator of emesis induced by different stimuli

The aim of this work was to evaluate the impact of changes in serotonin metabolism on the pathophysiology of different types of emesis: pregnancy-induced emesis, emesis associated with inner-ear dysfunction, and cisplatin-induced emesis. The urinary excretion of 5-hydroxyindoleacetic acid (5-HIAA), the main metabolite of serotonin, was measured in 13 women with pregnancy-induced emesis, 12 patients who had nausea and vomiting following inner-ear dysfunctions, 27 patients with cisplatin-induced emesis and a control group of 21 women. 5-HIAA was measured with a fluorescence polarization immunoassay (Abbott) and corrected for varying urine concentrations. Both patients with emesis associated with inner-ear dysfunction and patients with pregnancy-associated emesis showed a similar 5-HIAA excretion pattern compared with the control group. No correlation between intensity of nausea or vomiting and changes in 5-HIAA excretion could be detected. In patients receiving cisplatin, the 5-HIAA excretion increased rapidly within the 12 h following cisplatin administration and returned to baseline levels after 24 h. There was a parallel increase of 5-HIAA excretion and numbers of emetic episodes in the first 12 h, but delayed emesis was not associated with elevated 5-HIAA excretion. Our results provide evidence that serotonin is involved in the pathophysiology of cisplatin-induced acute emesis. Cisplatin-induced delayed emesis, pregnancy-associated emesis, and emesis due to inner-ear dysfunction are not associated with elevated levels of 5-HIAA excretion. The serotonin pathway probably represents only one of many different afferent mechanisms capable of initiating the emesis cascade.

Variables related to nausea and vomiting during pregnancy

Seventy to 90 percent of all pregnant women experience nausea, and 50 percent have at least one episode of vomiting or retching. A continuous measure was used to quantify symptoms of nausea with or without vomiting or retching during pregnancy in 126 women. Relationships between symptoms and selected variables were evaluated. Nausea with or without vomiting or retching was associated with maternal age, occupation, parity, cigarette smoking, infant gender, and the personality trait of independence. Significant associations were entered into multiple regression equations. Fourteen percent of the variation in symptoms overall, 25.1 percent of the variation in nausea symptoms, and 16.6 percent of the variation in vomiting or retching symptoms were explained by a combination of these selected independent variables. Although this study found associations, independent variables contributed little to predicting or explaining the presence and severity of nausea and vomiting during pregnancy. More sensitive measures and evaluation are required to understand and treat this perplexing phenomenon.

The role of alpha-adrenergic mechanisms within the area postrema in dopamine-induced emesis

Intracerebroventricular injection of dopamine (0.5-4.0 mg) produced dose-dependent and short-lasting emesis (1-8 min) in cats, which was abolished after ablation of the area postrema. Relatively selective alpha 2-adrenoceptor antagonists (yohimbine and idazoxan) and a mixed alpha 1- and alpha 2-adrenoceptor antagonist (tolazoline), but not a non-selective alpha 1-adrenoceptor antagonist (prazosin), injected intracerebroventricularly inhibited the emesis induced by intracerebroventricular dopamine. However, dopamine receptor antagonists (chlorpromazine, droperidol, spiperone, domperidone, triflupromazine, sulpiride and metoclopramide), an antimuscarinic drug (atropine), a ganglionic blocking agent (mecamylamine), an opioid receptor antagonist (naloxone) and a 5-HT receptor antagonist (methysergide), all injected intracerebroventricularly, had no significant effect on emesis evoked by intracerebroventricular dopamine. The emetic response to intracerebroventricular dopamine was attenuated in cats pretreated with intracerebroventricular reserpine, 6-hydroxydopamine, alpha-methyl-p-tyrosine and hemicholinium-3. It is postulated that dopamine-induced emesis is mediated through the release of noradrenaline acting at alpha 2-adrenoceptors and that it depends on the integrity of monoaminergic and possibly cholinergic structures within the area postrema. It appears, therefore, that the emetic effect of intracerebroventricular dopamine is mediated by adrenergic rather than dopaminergic mechanisms in the area postrema, at least in the cat.

A randomized cross-over study of high-dose metoclopramide plus dexamethasone versus granisetron plus dexamethasone in patients receiving chemotherapy with high-dose cisplatin

We carried out a randomized, single-blind, cross-over trial to compare the antiemetic effect, for both acute and delayed emesis, of granisetron plus dexamethasone (GRN+Dx) with that of high-dose metoclopramide plus dexamethasone (HDMP+Dx). Fifty-four patients with primary or metastatic lung cancer, given single-dose cisplatin (> 80 mg/m2) chemotherapy more than twice, were enrolled in this study. They were treated with both HDMP+Dx and GRN+Dx in two consecutive chemotherapy courses. On day 1, patients experienced a mean of 2.5 (SD = 4.3) and 0.1 (SD = 0.4) episodes of vomiting in the HDMP+Dx and the GRN+Dx groups, respectively (P = 0.0008). Complete response rate on day 1 was 45 and 90% in the HDMP+Dx and the GRN+Dx groups, respectively (P = 0.0001). Patients treated with GRN+Dx had a tendency to suffer more episodes of vomiting than the HDMP+Dx group on days 2-5, but it was not statistically significant. Twenty-four patients (57%) preferred the GRN+Dx treatment and 14 patients (33%), HDMP+Dx. In the HDMP+Dx group, nine patients (21%) had an extrapyramidal reaction, and 5 patients (12%) had constipation that lasted for at least two days. In contrast, no patients had extrapyramidal reactions, and 18 patients (43%) had constipation in the GRN+Dx group (P < 0.01). GRN+Dx was more effective than HDMP+Dx only in preventing the acute emesis induced by cisplatin. An effective treatment for delayed emesis is still needed.

A dose-finding study of granisetron, a novel antiemetic, in patients receiving high-dose cisplatin. Granisetron Study Group

In this double-blind study, the efficacy and safety of a single intravenous dose of a novel antiemetic, granisetron, was assessed at two dose levels (40 micrograms/kg and 160 micrograms/kg). A group of 355 patients were given prophylactic granisetron prior to receiving high-dose cisplatin chemotherapy. In the first 24 h, 57% and 59% of patients, respectively, experienced no vomiting and no more than mild nausea. Two further doses of granisetron (40 micrograms/kg) were permitted in the first 24 h to treat any emergent symptoms of nausea and vomiting; 66 patients (39%) in the 40-micrograms/kg treatment group and 56 patients (34%) in the 160-micrograms/kg group received at least one additional dose. Additional treatment with granisetron resulted in resolution or improvement of symptoms in at least 73% of these patients. Over the 7-day study period, 52% of patients in the lower-dose group and 48% in the higher required no further conventional antiemetic therapy. The two different dose levels were equal both in terms in efficacy and safety. Granisetron was well tolerated throughout the dose range of the study [40-240 micrograms kg-1 (24 h)-1]. The commonest adverse event was headache, seen in 14%-16% of patients. In all but one case this resolved spontaneously or responded to simple treatment.

The physiology and pharmacology of postoperative nausea and vomiting

The main function of emesis is to remove toxins from the body. The emetic response will also be triggered by cancer chemotherapy and radiotherapy or surgery under general anaesthesia. The mechanism of activation of the vomiting system is dependent on stimulation of gastrointestinal (mechanoreceptors and chemoreceptors) and/or central pathways which activate the chemoreceptor trigger zone in the area postrema. Postoperative emesis is activated by a range of factors before, during and after anaesthesia. The precise mechanism of action of any one of the influencing factors can only be speculated as there has been very little basic research into this area, due largely to the lack of an appropriate model for postoperative nausea and vomiting. The range of agents used in the prevention and treatment of emesis are effective to varying degrees, but some are associated with poor side effect profiles making them particularly unsuitable for prophylactic use. Newer antiemetics, which selectively antagonise 5-HT3 receptors, have proved effective and well tolerated in the treatment of chemotherapy-induced emesis and postoperative nausea and vomiting.