Brain areas essential or non-essential for emesis

Physiology of the Digestive Tract Correlates of Vomiting

Emesis is composed of 3 independent digestive tract correlates that are individually organized by a brainstem neural network and all 3 hierarchically organized by a central pattern generator. The central pattern generator may be in the Bötzinger nucleus of the brain stem. The digestive tract sensory mechanisms that activate vomiting are the digestive tract mucosa or chemoreceptive trigger zone of the area postrema. Regardless of the initial stimulus, the area postrema may be activated in order to inhibit orthograde digestive tract motility and reflux blocking reflexes that would interfere with anterograde movement, which is the basic purpose of vomiting. The digestive tract correlates are (1) relaxation of the upper stomach and contraction of the lower pharynx, (2) retrograde giant contraction, and (3) the pharyngo-esophageal responses during retching and vomitus expulsion. The proximal gastric response allows gastroesophageal reflux, the lower pharyngeal response prevents supra-esophageal reflux, and both last the duration of the vomit process. The retrograde giant contraction empties the proximal digestive tract of noxious agents and supplies the stomach with fluids to neutralize the gastric acid which protect the esophagus from damage during expulsion. The retch mixes the gastric contents with acid neutralizer and gives momentum to the expelled bolus. During vomitus expulsion the esophagus is maximally stretched longitudinally which stiffens its wall to allow rapid transport as the suprahyoid muscles and diaphragmatic dome contract, and the hiatal fibers relax.

Pathophysiology and Therapy of Associated Features of Migraine

Migraine is a complex and debilitating disorder that is broadly recognised by its characteristic headache. However, given the wide array of clinical presentations in migraineurs, the headache might not represent the main troublesome symptom and it can even go unnoticed. Understanding migraines exclusively as a pain process is simplistic and certainly hinders management. We describe the mechanisms behind some of the most disabling associated symptoms of migraine, including the relationship between the central and peripheral processes that take part in nausea, osmophobia, phonophobia, vertigo and allodynia. The rationale for the efficacy of the current therapeutic arsenal is also depicted in this article. The associated symptoms to migraine, apart from the painful component, are frequent, under-recognised and can be more deleterious than the headache itself. The clinical anamnesis of a headache patient should enquire about the associated symptoms, and treatment should be considered and individualised. Acknowledging the associated symptoms as a fundamental part of migraine has permitted a deeper and more coherent comprehension of the pathophysiology of migraine.

Crucial involvement of catecholamine neurotransmission in postoperative nausea and vomiting: Whole-transcriptome profiling in the rat nucleus of the solitary tract

The genetic mechanisms of postoperative nausea and vomiting (PONV) and the involvement of the catecholamine system in the brain have not been elucidated. Eating kaolin clay as a type of pica has been examined as an alternative behavior to emesis. Here, we evaluated changes in whole-transcriptome analysis in the nucleus of the solitary tract (NTS) in a rat pica model as a surrogate behavior of PONV to elucidate the molecular genetic mechanisms of the development of PONV and the involvement of the catecholamine system in the NTS. First, kaolin pica behaviors were investigated in 71 female Wistar rats following isoflurane anesthesia, surgical insult or morphine administration. Multiple linear regression analysis showed that 3 mg/kg morphine increased kaolin intake by 2.8 g (P = 0.0002). Next, total RNA and protein were extracted from the dissected NTS, and whole-transcriptome sequencing (RNA-seq) was performed to identify PONV-associated genes and to verify the involvement of the catecholamine system. The gene expression levels of tyrosine hydroxylase and dopamine beta-hydroxylase in the catecholamine biosynthesis pathway decreased significantly in the PONV model. Release of noradrenaline, a catecholamine pathway end product, may have increased at the synaptic terminal of the NTS neuron after pica behavior. Systematic administration of α2 adrenergic receptor agonists after surgery reduced kaolin intake from 3.2 g (control) to 1.0 g (P = 0.0014). These results indicated that catecholamine neurotransmission was involved in the development of PONV in the NTS.

Neuroimmunogastroenterology: At the Interface of Neuroimmunology and Gastroenterology

The central nervous system (CNS) is an important regulator of the gastrointestinal tract, and CNS dysfunction can result in significant and disabling gastrointestinal symptom manifestation. For patients with neuroimmunologic and neuroinflammatory conditions, the recognition of gastrointestinal symptoms is under-appreciated, yet the gastrointestinal manifestations have a dramatic impact on quality of life. The current treatment strategies, often employed independently by the neurologist and gastroenterologist, raise the question of whether such patients are being treated optimally when siloed in one specialty. Neuroimmunogastroenterology lies at the borderlands of medical specialties, and there are few resources to guide neurologists in this area. Here, we provide an overview highlighting the potential mechanisms of crosstalk between immune-mediated neurological disorders and gastrointestinal dysfunction.

New insights into the pathophysiology and risk factors for PONV

Postoperative nausea and vomiting (PONV) affects patient outcomes and satisfaction. New research has centered on evaluation of post-discharge and opioid-related nausea and vomiting. Mechanical and drug effects stimulate the release of central nervous system neurotransmitters acting at receptors in the vomiting center, area postrema, and nucleus of the solitary tract. Brain surgery has allowed insight into specific central emetogenic areas. Stimuli from peripheral organs act through afferent vagus neurons and a parasympathetic response causing nausea and vomiting. Opioids stimulate mu receptors in the chemoreceptor trigger zone and cholinergic receptors in the vestibular system. Opioids also affect gastrointestinal (GI) tract mechanics by decreasing gastric emptying, intestinal motility, GI peristalsis, and secretions. Regional blocks and non-opioid multimodal analgesia help to decrease nausea and vomiting. Patient, surgery, and anesthesia factors contribute to risk and degree of PONV experienced. Pharmacogenetics plays a role in gene typing as antiemetic medication metabolism results in varying drug effectiveness. Risk scoring systems are available. Individualized multimodal plans can be designed as part of an enhanced recovery after surgery protocol.

Evolution and Functional Differentiation of the Diaphragm Muscle of Mammals

Symmorphosis is a concept of economy of biological design, whereby structural properties are matched to functional demands. According to symmorphosis, biological structures are never over designed to exceed functional demands. Based on this concept, the evolution of the diaphragm muscle (DIAm) in mammals is a tale of two structures, a membrane that separates and partitions the primitive coelomic cavity into separate abdominal and thoracic cavities and a muscle that serves as a pump to generate intra-abdominal (Pab ) and intrathoracic (Pth ) pressures. The DIAm partition evolved in reptiles from folds of the pleural and peritoneal membranes that was driven by the biological advantage of separating organs in the larger coelomic cavity into separate thoracic and abdominal cavities, especially with the evolution of aspiration breathing. The DIAm pump evolved from the advantage afforded by more effective generation of both a negative Pth for ventilation of the lungs and a positive Pab for venous return of blood to the heart and expulsive behaviors such as airway clearance, defecation, micturition, and child birth. © 2019 American Physiological Society. Compr Physiol 9:715-766, 2019.

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.

Role of the abdominal vagus and hindbrain in inhalational anesthesia-induced vomiting

The incidence of postoperative nausea and vomiting (PONV) can be as high as 80% in patients with risk factors (e.g., females, history of motion sickness). PONV delays postoperative recovery and costs several hundred million dollars annually. Cell-based assays show that halogenated ethers (e.g., isoflurane) activate 5-HT₃ receptors, which are found on gastrointestinal vagal afferents and in the hindbrain - key pathways for producing nausea and vomiting. This project evaluated the role of the vagus and activation of the hindbrain in isoflurane-induced emesis in musk shrews, a small animal model with a vomiting reflex, which is lacking in rats and mice. Sham-operated and abdominal vagotomized shrews were exposed to 1 to 3% isoflurane to determine effects on emesis; vagotomy was confirmed by lack of vagal transport of the neuronal tracer Fluoro-Gold. In an additional study, shrews were exposed to isoflurane and hindbrain c-Fos was measured at 90min after exposure using immunohistochemistry. There were no statistically significant effects of vagotomy on isoflurane-induced emesis compared to sham-operated controls. Isoflurane exposure produced a significant increase in c-Fos-positive cells in the nucleus of the solitary tract and vestibular nuclei but not in the area postrema or dorsal motor nucleus. These results indicate that the abdominal vagus plays no role in isoflurane-induced emesis and suggest that isoflurane activates emesis by action on the hindbrain, as shown by c-Fos labeling. Ultimately, knowledge of the mechanisms of inhalational anesthesia-induced PONV could lead to more targeted therapies to control PONV.

Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions

Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.

Pharmacogenetics of chemotherapy-induced nausea and vomiting

Chemotherapy-induced nausea and vomiting (CINV) is associated with distressing adverse effects observed in patients during cytotoxic chemotherapy. One of the potential factors explaining suboptimal response to currently used antiemetics is variability in genes encoding enzymes and proteins that play a role in the action of antiemetic drugs. Pharmacogenomics studies of CINV are sparse and focus mainly on polymorphisms associated with serotonin receptor, drug metabolism and drug transport. Currently, the role of pharmacogenetics in mechanisms of CINV has not been fully unraveled, and it is premature to implement results of pharmacogenetic association studies of antiemetic drugs in clinical practice. More uniform studies, with genetic profiles and biomarkers relevant for the proposed target and transporter mechanisms, are needed.

The origin of nausea in migraine-a PET study

Background

Nausea is a common and disabling symptom of migraine. The origin of nausea is not well understood although functional connections between trigeminal neurons and the nucleus tractus solitarius may explain occurrence of nausea with pain. However, nausea occurs as a premonitory symptom in about a quarter of patients, suggesting that a primary brain alteration unrelated to the experience of pain may be the reason for nausea.

Methods

We performed positron emission tomography scans with H₂¹⁵O PET in premonitory phase of nitroglycerin-induced migraine and compared patients with and without nausea.

Results

The results showed activation in rostral dorsal medulla and periaqueductal grey (PAG) in the nausea group, which was absent in the no nausea group. The rostral dorsal medullary area included the nucleus tractus solitarius, dorsal motor nucleus of the vagus nerve and the nucleus ambiguus, all of which are thought to be involved in brain circuits mediating nausea.

Conclusions

The results demonstrate that nausea can occur as a premonitory symptom in migraine, independent of pain and trigeminal activation. This is associated with activation of brain structures known to be involved in nausea. We conclude that nausea is a centrally driven symptom in migraine.

Motion sickness: more than nausea and vomiting

Motion sickness is a complex syndrome that includes many features besides nausea and vomiting. This review describes some of these factors and points out that under normal circumstances, many cases of motion sickness go unrecognized. Motion sickness can occur during exposure to physical motion, visual motion, and virtual motion, and only those without a functioning vestibular system are fully immune. The range of vulnerability in the normal population varies about 10,000 to 1. Sleep deprivation can also enhance susceptibility. Systematic studies conducted in parabolic flight have identified velocity storage of semicircular canal signals-velocity integration-as being a key factor in both space motion sickness and terrestrial motion sickness. Adaptation procedures that have been developed to increase resistance to motion sickness reduce this time constant. A fully adequate theory of motion sickness is not presently available. Limitations of two popular theories, the evolutionary and the ecological, are described. A sensory conflict theory can explain many but not all aspects of motion sickness elicitation. However, extending the theory to include conflicts related to visceral afferent feedback elicited by voluntary and passive body motion greatly expands its explanatory range. Future goals should include determining why some conflicts are provocative and others are not but instead lead to perceptual reinterpretations of ongoing body motion. The contribution of visceral afferents in relation to vestibular and cerebellar signals in evoking sickness also deserves further exploration. Substantial progress is being made in identifying the physiological mechanisms underlying the evocation of nausea, vomiting, and anxiety, and a comprehensive understanding of motion sickness may soon be attainable. Adequate anti-motion sickness drugs without adverse side effects are not yet available.

Integration of vestibular and emetic gastrointestinal signals that produce nausea and vomiting: potential contributions to motion sickness

Vomiting and nausea can be elicited by a variety of stimuli, although there is considerable evidence that the same brainstem areas mediate these responses despite the triggering mechanism. A variety of experimental approaches showed that nucleus tractus solitarius, the dorsolateral reticular formation of the caudal medulla (lateral tegmental field), and the parabrachial nucleus play key roles in integrating signals that trigger nausea and vomiting. These brainstem areas presumably coordinate the contractions of the diaphragm and abdominal muscles that result in vomiting. However, it is unclear whether these regions also mediate the autonomic responses that precede and accompany vomiting, including alterations in gastrointestinal activity, sweating, and changes in blood flow to the skin. Recent studies showed that delivery of an emetic compound to the gastrointestinal system affects the processing of vestibular inputs in the lateral tegmental field and parabrachial nucleus, potentially altering susceptibility for vestibular-elicited vomiting. Findings from these studies suggested that multiple emetic inputs converge on the same brainstem neurons, such that delivery of one emetic stimulus affects the processing of another emetic signal. Despite the advances in understanding the neurobiology of nausea and vomiting, much is left to be learned. Additional neurophysiologic studies, particularly those conducted in conscious animals, will be crucial to discern the integrative processes in the brain stem that result in emesis.

Why does vomiting stop a migraine attack?

Migraine is commonly associated with nausea and vomiting, though, interestingly, vomiting has also been reported by some patients to be therapeutic, and may actually stop a migraine attack. In this review, we will first discuss the epidemiology of nausea and vomiting in migraine. Further, we will briefly review the connections between the enteric nervous system, the autonomic nervous system, and the central nervous system as they pertain to understanding the question of "Why does vomiting stop a migraine attack?"

[Treatment of nausea and vomiting with prokinetics and neuroleptics in palliative care patients : a review]

BACKGROUND

Many recommendations concerning the treatment of nausea and vomiting in palliative care patients exist but what is the evidence for this? Most studies dealing with this topic have focused on cancer patients under chemotherapy and/or radiation therapy or on patients with postoperative nausea. Cancer patients without chemotherapy or radiation therapy, patients without postoperative nausea, and patients having other diseases with palliative care aspects, such as acquired immunodeficiency syndrome (AIDS), chronic obstructive pulmonary disease (COPD), progressive heart failure, amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) have been underrepresented in studies on nausea and vomiting so far.

OBJECTIVES

The aim of this review was to determine the level of evidence for the treatment of nausea and vomiting with prokinetics and neuroleptics in palliative care patients suffering from far advanced cancer and no longer being treated with chemotherapy or radiation therapy, AIDS, COPD, progressive heart failure, ALS or MS.

METHODS

Two different electronic databases (PubMed und Embase) were used to identify studies. Furthermore, a hand search for related articles was performed. No restriction was made concerning study types. Studies with patients undergoing chemotherapy radiation therapy or suffering from postoperative nausea, pediatric studies and studies published neither in English nor in German were excluded.

RESULTS

A total of 30 studies fulfilling the inclusion criteria were found. All studies focused on cancer patients. Despite intensive research studies in patients with AIDS, COPD, heart failure, ALS or MS were not detected. Metoclopramide is seen as an effective drug in many studies whereas the evidence for it is moderate at best. Within the group of neuroleptics, levosupiride and levomepromazine seem to have good antiemetic potential but the evidence level is low.

CONCLUSION

In patients with advanced cancer not being treated with chemotherapy or radiation therapy, metoclopramide can be used to reduce nausea and vomiting. Neuroleptics, such as levosulpiride or levomepromazine are alternatives but their adverse effects have to be considered carefully. The evidence level for prokinetics and neuroleptics is moderate to low. Concerning palliative care of patients with diseases other than cancer no studies exist. More well designed studies in palliative care patients are needed in order to facilitate evidence based antiemetic therapy. The English full text version of this article will be available in SpringerLink as of November 2012 (under "Supplemental").

The role of vagal neurocircuits in the regulation of nausea and vomiting

Nausea and vomiting are among the most frequently occurring symptoms observed by clinicians. While advances have been made in understanding both the physiological as well as the neurophysiological pathways involved in nausea and vomiting, the final common pathway(s) for emesis have yet to be defined. Regardless of the difficulties in elucidating the precise neurocircuitry involved in nausea and vomiting, it has been accepted for over a century that the locus for these neurocircuits encompasses several structures within the medullary reticular formation of the hindbrain and that the role of vagal neurocircuits in particular are of critical importance. The afferent vagus nerve is responsible for relaying a vast amount of sensory information from thoracic and abdominal organs to the central nervous system. Neurons within the nucleus of the tractus solitarius not only receive these peripheral sensory inputs but have direct or indirect connections with several other hindbrain, midbrain and forebrain structures responsible for the co-ordination of the multiple organ systems. The efferent vagus nerve relays the integrated and co-ordinated output response to several peripheral organs responsible for emesis. The important role of both sensory and motor vagus nerves, and the available nature of peripheral vagal afferent and efferent nerve terminals, provides extensive and readily accessible targets for the development of drugs to combat nausea and vomiting.

Pathophysiological and neurochemical mechanisms of postoperative nausea and vomiting

Clinical research shows that postoperative nausea and vomiting (PONV) is caused primarily by the use of inhalational anesthesia and opioid analgesics. PONV is also increased by several risk predictors, including a young age, female sex, lack of smoking, and a history of motion sickness. Genetic studies are beginning to shed light on the variability in patient experiences of PONV by assessing polymorphisms of gene targets known to play roles in emesis (serotonin type 3, 5-HT3; opioid; muscarinic; and dopamine type 2, D2, receptors) and the metabolism of antiemetic drugs (e.g., ondansetron). Significant numbers of clinical trials have produced valuable information on pharmacological targets important for controlling PONV (e.g., 5-HT3 and D2), leading to the current multi-modal approach to inhibit multiple sites in this complex neural system. Despite these significant advances, there is still a lack of fundamental knowledge of the mechanisms that drive the hindbrain central pattern generator (emesis) and forebrain pathways (nausea) that produce PONV, particularly the responses to inhalational anesthesia. This gap in knowledge has limited the development of novel effective therapies of PONV. The current review presents the state of knowledge on the biological mechanisms responsible for PONV, summarizing both preclinical and clinical evidence. Finally, potential ways to advance the research of PONV and more recent developments on the study of postdischarge nausea and vomiting (PDNV) are discussed.

Novel dynamic measures of emetic behavior in musk shrews

The emetic reflex occurs as a pattern of motor responses produced by a network of neurons in the hindbrain. Despite an understanding of the sequence of motor outputs that form an emetic episode (EE), the variability in the dynamics of multiple EEs across time remains a mystery. Many clinical investigations rely on once a day patient recall of total amount of vomiting, and preclinical studies frequently report only the total number of EE per unit time. The aim of the current study was to develop novel temporal measures of emetic activation in a preclinical model. Male and female musk shrews were tested with prototypical emetic stimuli: motion exposure (1 Hz), nicotine (5 mg/kg, sc), and copper sulfate (120 mg/kg, ig). New emetic measures included duration (time from first to last episode), rate, standard deviation of the inter-episode interval (SD-I), and a survival analysis of emetic latency (analyzed with Cox regression). Behavioral patterns associated with emesis were also assessed using statistical temporal pattern (T-pattern) analysis to measure nausea-like behaviors (e.g., immobility). The emetic stimuli produced different levels of total EE number, duration, rate, and SD-I. A typical antiemetic, the neurokinin 1 receptor antagonist CP-99,994, suppressed the number of EEs but was less effective for reducing the duration or prolonging the emetic latency. Overall, the current study shows the use of novel dynamic behavioral measures to more comprehensively assess emesis and the impact of therapies.

A physiological perspective for utility or futility of alcohol-based hand rub gel against nausea-vomiting: is it P-6 acupoint or transnasal aroma?

Nausea-vomiting is a common and unpleasant phenomenon with numerous underlying mechanisms and pathways that are not always well elucidated. In clinical practice, refractory nausea-vomiting is encountered in several settings. Antiemetic medications may reduce these symptoms but are not always effective in all patients. In the absence of a well-defined optimal strategy for management of nausea-vomiting, the search for better approaches to treat this distressing symptom continues. One of the alternative treatment approaches is a compounded formulation called ABHR gel that is comprised of multiple antiemetic medications and has been shown to be useful for symptomatic relief in some patients with refractory nausea-vomiting. It has been suggested that alternative mechanisms should be explored to explain the perceived efficacy of ABHR gel, because transdermal absorption leading to nil-to-minimal or subtherapeutic blood concentrations of active ingredients does not explain the role of ABHR gel in the treatment of nausea-vomiting. In the current paper, we discuss possible mechanisms that may explain ABHR transdermal gel's efficacy. Compounded ABHR transdermal gel formulation's efficacy in antagonizing nausea-vomiting that has been recently questioned may be explained by alternative mechanisms mediated through the P-6 acupoint stimulation and facial-nasal, cooling-related counterstimulation.

Cisplatin : an old drug with a newfound efficacy -- from mechanisms of action to cytotoxicity

INTRODUCTION

Cisplatin is a highly effective antineoplastic drug with an extremely current mechanism of action. Cisplatin-induced side effects are dose-dependent and limit the administration of increased dosages, thus compromising its therapeutic efficacy.

AREAS COVERED

This review aims to describe the emerging knowledge about the biochemical mechanisms that mediate cisplatin cytotoxicity and side effects. A specific section is devoted to discuss the pathogenesis of cisplatin-related toxicities and the potential measures to counteract them.

EXPERT OPINION

Although cisplatin has been used for a long time, only recently its exact mechanism of action has been better defined. The cytotoxic activity of cisplatin is largely dependent on the glycolytic metabolism of tumor cells: cisplatin redirects cancer cells to oxidative phosphorylation from the 'Warburg effect', which is considered one of the most important mechanisms of tumor cell survival. The interference of cisplatin with glucose metabolism is also a cause of its relevant toxicities. The emerging knowledge on the complex mechanisms, which mediate cisplatin cytotoxicity and side effect, may lead to a more appropriate and safe use of this drug. Further studies are warranted to define and implement its effectiveness in combination with targeted drugs able to interfere with cellular energy metabolism, such as mTOR inhibitors.

Mechanisms, causes, investigation and management of vomiting disorders in cats: a literature review

Vomiting is a common presenting complaint in feline practice. This article differs from previous reviews in that it is an evidence-based review of the mechanisms, causes, investigation and management of vomiting in the domestic cat. Published evidence was reviewed, and then used to make recommendations for clinical assessment, diagnosis, antiemetic drug treatment, dietary management and monitoring of cats presenting with vomiting. The strength of the evidence on which recommendations are made (and areas where evidence is lacking for cats) has been highlighted throughout.

Processing of vestibular inputs by the medullary lateral tegmental field of conscious cats: implications for generation of motion sickness

The dorsolateral reticular formation of the caudal medulla, the lateral tegmental field (LTF), participates in generating vomiting. LTF neurons exhibited complex responses to vestibular stimulation in decerebrate cats, indicating that they received converging inputs from a variety of labyrinthine receptors. Such a convergence pattern of vestibular inputs is appropriate for a brain region that participates in generating motion sickness. Since responses of brainstem neurons to vestibular stimulation can differ between decerebrate and conscious animals, the current study examined the effects of whole-body rotations in vertical planes on the activity of LTF neurons in conscious felines. Wobble stimuli, fixed-amplitude tilts, the direction of which moves around the animal at a constant speed, were used to determine the response vector orientation, and also to ascertain whether neurons had spatial-temporal convergence (STC) behavior (which is due to the convergence of vestibular inputs with different spatial and temporal properties). The proportion of LTF neurons with STC behavior in conscious animals (25 %) was similar to that in decerebrate cats. Far fewer neurons in other regions of the feline brainstem had STC behavior, confirming findings that many LTF neurons receive converging inputs from a variety of labyrinthine receptors. However, responses to vertical plane vestibular stimulation were considerably different in decerebrate and conscious felines for LTF neurons lacking STC behavior. In decerebrate cats, most LTF neurons had graviceptive responses to rotations, similar to those of otolith organ afferents. However, in conscious animals, the response properties were similar to those of semicircular canal afferents. These differences show that higher centers of the brain that are removed during decerebration regulate the labyrinthine inputs relayed to the LTF, either by gating connections in the brainstem or by conveying vestibular inputs directly to the region.

Responses of neurons in the caudal medullary lateral tegmental field to visceral inputs and vestibular stimulation in vertical planes

The dorsolateral reticular formation of the caudal medulla, or the lateral tegmental field (LTF), has been classified as the brain's "vomiting center", as well as an important region in regulating sympathetic outflow. We examined the responses of LTF neurons in cats to rotations of the body that activate vestibular receptors, as well as to stimulation of baroreceptors (through mechanical stretch of the carotid sinus) and gastrointestinal receptors (through the intragastric administration of the emetic compound copper sulfate). Approximately half of the LTF neurons exhibited graviceptive responses to vestibular stimulation, similar to primary afferents innervating otolith organs. The other half of the neurons had complex responses, including spatiotemporal convergence behavior, suggesting that they received convergent inputs from a variety of vestibular receptors. Neurons that received gastrointestinal and baroreceptor inputs had similar complex responses to vestibular stimulation; such responses are expected for neurons that contribute to the generation of motion sickness. LTF units with convergent baroreceptor and vestibular inputs may participate in producing the cardiovascular system components of motion sickness, such as the changes in skin blood flow that result in pallor. The administration of copper sulfate often modulated the gain of responses of LTF neurons to vestibular stimulation, particularly for units whose spontaneous firing rate was altered by infusion of drug (median of 459%). The present results raise the prospect that emetic signals from the gastrointestinal tract modify the processing of vestibular inputs by LTF neurons, thereby affecting the probability that vomiting will occur as a consequence of motion sickness.

The role of area postrema neurons expressing H-channels in the induction mechanism of nausea and vomiting

The area postrema is one of the circumventricular organs, lacks a blood-brain barrier, and is well known as the chemoreceptor trigger zone for emesis. Area postrema neurons are sensitive to emetic chemical substances carried in the blood plasma. Our previous study demonstrated the presence of 3 types of neurons characterized by different ion channels expressed in each cell type, but the type or types of area postrema neurons involved in the induction of nausea and/or emesis have remained unclear. To clarify the role of the most populous cells, which express the hyperpolarization-activated cation channel (H-channel), in induction of nausea and/or emesis, we investigated the effects of ZD7288 (an H-channel inhibitor) on apomorphine-induced conditioned taste aversion (CTA) to saccharin and c-Fos expression in the area postrema. We found that ZD7288 inhibited the acquisition of CTA and reduced apomorphine-induced c-Fos expression in the area postrema, indicating the involvement of the cells expressing H-channels in the induction of nausea and/or emesis. Finally, we discuss the role of cells expressing H-channels in the mechanism of nausea and/or vomiting.

Integrative responses of neurons in parabrachial nuclei to a nauseogenic gastrointestinal stimulus and vestibular stimulation in vertical planes

The parabrachial and adjacent Kölliker-Fuse (PBN/KF) nuclei play a key role in relaying visceral afferent inputs to the hypothalamus and limbic system and are, thus, believed to participate in generating nausea and affective responses elicited by gastrointestinal (GI) signals. In addition, the PBN/KF region receives inputs from the vestibular system and likely mediates the malaise associated with motion sickness. However, previous studies have not considered whether GI and vestibular inputs converge on the same PBN/KF neurons, and if so, whether the GI signals alter the responses of the cells to body motion. The present study, conducted in decerebrate cats, tested the hypothesis that intragastric injection of copper sulfate, which elicits emesis by irritating the stomach lining, modifies the sensitivity of PBN/KF neurons to vertical plane rotations that activate vestibular receptors. Intragastric copper sulfate produced a 70% median change in the gain of responses to vertical plane rotations of PBN/KF units, whose firing rate was modified by the administration of the compound; the response gains for 16 units increased and those for 17 units decreased. The effects were often dramatic: out of 51 neurons tested, 13 responded to the rotations only after copper sulfate was injected, whereas 10 others responded only before drug delivery. These data show that a subset of PBN/KF neurons, whose activity is altered by a nauseogenic stimulus also respond to body motion and that irritation of the stomach lining can either cause an amplification or reduction in the sensitivity of the units to vestibular inputs. The findings imply that nausea and affective responses to vestibular stimuli may be modified by the presence of emetic signals from the GI system.

Integrative responses of neurons in nucleus tractus solitarius to visceral afferent stimulation and vestibular stimulation in vertical planes

Anatomical studies have demonstrated that the vestibular nuclei project to nucleus tractus solitarius (NTS), but little is known about the effects of vestibular inputs on NTS neuronal activity. Furthermore, lesions of NTS abolish vomiting elicited by a variety of different triggering mechanisms, including vestibular stimulation, suggesting that emetic inputs may converge on the same NTS neurons. As such, an emetic stimulus that activates gastrointestinal (GI) receptors could alter the responses of NTS neurons to vestibular inputs. In the present study, we examined in decerebrate cats the responses of NTS neurons to rotations of the body in vertical planes before and after the intragastric administration of the emetic compound copper sulfate. The activity of more than one-third of NTS neurons was modulated by vertical vestibular stimulation, with most of the responsive cells having their firing rate altered by rotations in the head-up or head-down directions. These responses were aligned with head position in space, as opposed to the velocity of head movements. The activity of NTS neurons with baroreceptor, pulmonary, and GI inputs could be modulated by vertical plane rotations. However, injection of copper sulfate into the stomach did not alter the responses to vestibular stimulation of NTS neurons that received GI inputs, suggesting that the stimuli did not have additive effects. These findings show that the detection and processing of visceral inputs by NTS neurons can be altered in accordance with the direction of ongoing movements.

Mechanisms of Broad-Spectrum Antiemetic Efficacy of Cannabinoids against Chemotherapy-Induced Acute and Delayed Vomiting

Chemotherapy-induced nausea and vomiting (CINV) is a complex pathophysiological condition and consists of two phases. The conventional CINV neurotransmitter hypothesis suggests that the immediate phase is mainly due to release of serotonin (5-HT) from the enterochromaffin cells in the gastrointestinal tract (GIT), while the delayed phase is a consequence of release of substance P (SP) in the brainstem. However, more recent findings argue against this simplistic neurotransmitter and anatomical view of CINV. Revision of the hypothesis advocates a more complex, differential and overlapping involvement of several emetic neurotransmitters/modulators (e.g. dopamine, serotonin, substance P, prostaglandins and related arachidonic acid derived metabolites) in both phases of emesis occurring concomitantly in the brainstem and in the GIT enteric nervous system (ENS) [1]. No single antiemetic is currently available to completely prevent both phases of CINV. The standard antiemetic regimens include a 5-HT₃ antagonist plus dexamethasone for the prevention of acute emetic phase, combined with an NK₁ receptor antagonist (e.g. aprepitant) for the delayed phase. Although NK₁ antagonists behave in animals as broad-spectrum antiemetics against different emetogens including cisplatin-induced acute and delayed vomiting, by themselves they are not very effective against CINV in cancer patients. Cannabinoids such as D⁸-THC also behave as broad-spectrum antiemetics against diverse emetic stimuli as well as being effective against both phases of CINV in animals and patients. Potential side effects may limit the clinical utility of direct-acting cannabinoid agonists which could be avoided by the use of corresponding indirect-acting agonists. Cannabinoids (both phyto-derived and synthetic) behave as agonist antiemetics via the activation of cannabinoid CB₁ receptors in both the brainstem and the ENS emetic loci. An endocannabinoid antiemetic tone may exist since inverse CB₁ agonists (but not the corresponding silent antagonists) cause nausea and vomiting.

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.

Receptor-selective agonists induce emesis and Fos expression in the brain and enteric nervous system of the least shrew (Cryptotis parva)

Research on the mechanisms of emesis has implicated multiple neurotransmitters via both central (dorsal vagal complex) and peripheral (enteric neurons and enterochromaffin cells) anatomical substrates. Taking advantage of advances in receptor-specific agonists, and utilizing Fos expression as a functional activity marker, this study demonstrates a strong, but incomplete, overlap in anatomical substrates for a variety of emetogens. We used cisplatin and specific agonists to 5-HT(3) serotonergic, D(2)/D(3) dopaminergic, and NK(1) tachykininergic receptors to induce vomiting in the least shrew (Cryptotis parva), and quantified the resulting Fos expression. The least shrew is a small mammal whose responses to emetic challenges are very similar to its human counterparts. In all cases, the enteric nervous system, nucleus of the solitary tract, and dorsal motor nucleus of the vagus demonstrated significantly increased Fos immunoreactivity (Fos-IR). However, Fos-IR induction was notably absent from the area postrema following the dopaminergic and NK(1) receptor-specific agents. Two brain nuclei not usually discussed regarding emesis, the dorsal raphe nucleus and paraventricular thalamic nucleus, also demonstrated increased emesis-related Fos-IR. Taken together, these data suggest the dorsal vagal complex is part of a common pathway for a variety of distinct emetogens, but there are central emetic substrates, both medullary and diencephalic, that can be accessed without directly stimulating the area postrema.

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.

Antiemetics: an update and the MASCC guidelines applied in clinical practice

Nausea and vomiting are two of the most severe problems for patients treated with chemotherapy. Until the late 1970s, nausea and vomiting induced by chemotherapy was an almost neglected research area. With the introduction of cisplatin, the cytotoxin with the highest emetic potential, research was stimulated and has now resulted in the development of two new classes of antiemetics, the serotonin and neurokinin antagonists. A large number of trials have fine-tuned antiemetic therapy and made evidence-based recommendations possible for the majority of patients receiving chemotherapy. This Review discusses the pathophysiology of nausea and vomiting, the development of antiemetics, highlights some of the newest antiemetics, and finally summarizes recommendations from the evidence-based guidelines developed by the Multinational Association of Supportive Care in Cancer.

Mechanisms underlying postoperative nausea and vomiting and neurotransmitter receptor antagonist-based pharmacotherapy

Postoperative nausea and vomiting (PONV) is one of the most common and distressing complications following surgery, and understanding the mechanism(s) underlying PONV is essential to providing optimal prophylaxis and/or treatment of PONV. The knowledge base of PONV physiology has significantly expanded over the past decade. This article reviews the risk factors for the development of PONV and the mechanisms of action of pharmacological agents (including antagonists of serotonin 5-HT(3), dopaminergic D(2), histamine H(1), muscarinic cholinergic, opioid and neurokinin NK(1) receptors) for the management (i.e. prophylaxis and treatment) of PONV. NK(1) receptor antagonists, with their unique mechanism of action, are a particularly promising area of research as they appear to be efficacious in preventing PONV during both the early and the late postoperative periods. A successful PONV management strategy includes: (i) identifying patients at risk; (ii) keeping the baseline risk low; and (iii) using a combination of antiemetics acting on different receptors in moderate- to high-risk patients.

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).

Signals for nausea and emesis: Implications for models of upper gastrointestinal diseases

Nausea and vomiting are amongst the most common symptoms encountered in medicine as either symptoms of diseases or side effects of treatments. In a more biological setting they are also important components of an organism's defences against ingested toxins. Identification of treatments for nausea and vomiting and reduction of emetic liability of new therapies has largely relied on the use of animal models, and although such models have proven invaluable in identification of the anti-emetic effects of both 5-hydroxytryptamine(3) and neurokinin(1) receptor antagonists selection of appropriate models is still a matter of debate. The present paper focuses on a number of controversial issues and gaps in our knowledge in the study of the physiology of nausea and vomiting including: The choice of species for the study of emesis and the underlying behavioural (e.g. neophobia), anatomical (e.g. elongated, narrow abdominal oesophagus with reduced ability to shorten) and physiological (e.g. brainstem circuitry) mechanisms that explain the lack of a vomiting reflex in certain species (e.g. rats); The choice of response to measure (emesis[retching and vomiting], conditioned flavour avoidance or aversion, ingestion of clay[pica], plasma hormone levels[e.g. vasopressin], gastric dysrhythmias) and the relationship of these responses to those observed in humans and especially to the sensation of nausea; The stimulus coding of nausea and emesis by abdominal visceral afferents and especially the vagus-how do the afferents encode information for normal postprandial sensations, nausea and finally vomiting?; Understanding the central processing of signals for nausea and vomiting is particularly problematic in the light of observations that vomiting is more readily amenable to pharmacological treatment than is nausea, despite the assumption that nausea represents "low" intensity activation of pathways that can evoke vomiting when stimulated more intensely.

Dexamethasone has a central antiemetic mechanism in decerebrated cats

Dexamethasone is an effective antiemetic drug, but its mechanism of action is unclear. We designed this study to investigate the direct antiemetic action of dexamethasone in the medulla of cats. By using an oscillographic vomiting model, decerebrated cats received microinjections of dexamethasone 100 nL (1 microg, n = 7; 0.1 microg, n = 7) into the bilateral nuclei tractus solitarii, which led to a significant prolongation of the latency (1 microg, 6.4 +/- 1.1 min versus 28.2 +/- 4.9 min, P < 0.05; 0.1 microg, 6.7 +/- 1.1 min versus 27.1 +/- 5.0 min, P < 0.05) of the first emetic episode and significantly decreased the frequency of emetic episodes (1 microg, 2.7 +/- 0.8 versus 0.1 +/- 0.4, P < 0.05; 0.1 microg, 2.9 +/- 0.9 versus 0.3 +/- 0.5, P < 0.05) induced by xylazine. Pretreatment with mifepristone, a glucocorticoid receptor antagonist, blocked the antiemetic effect of dexamethasone in the bilateral nuclei tractus solitarii. However, microinjection of dexamethasone into the unilateral nucleus tractus solitarius alone did not alter the latency of the first emetic episode or the frequency of emetic episodes induced by xylazine. Local application of dexamethasone into the area postrema had no effect on the latency of the first emetic episode or the frequency of emetic episodes induced by xylazine. These results suggest that dexamethasone exerts its central antiemetic action through an activation of the glucocorticoid receptors in the bilateral nuclei tractus solitarii in the medulla.

Aromatherapy with peppermint, isopropyl alcohol, or placebo is equally effective in relieving postoperative nausea

To determine whether aromatherapy can reduce postoperative nausea, the investigators studied 33 ambulatory surgery patients who complained of nausea in the PACU. After indicating the severity of nausea on a 100-mm visual analogue scale (VAS), subjects received randomized aromatherapy with isopropyl alcohol, oil of peppermint, or saline (placebo). The vapors were inhaled deeply through the nose from scented gauze pads held directly beneath the patients' nostrils and exhaled slowly through the mouth. Two and 5 minutes later, the subjects rated their nausea on the VAS. Overall nausea scores decreased from 60.6 +/- 4.3 mm (mean +/- SE) before aromatherapy to 43.1 +/- 4.9 mm 2 minutes after aromatherapy (P <.005), and to 28.0 +/- 4.6 mm 5 minutes after aromatherapy (P < 10(-6)). Nausea scores did not differ between the treatments at any time. Only 52% of the patients required conventional intravenous (IV) antiemetic therapy during their PACU stay. Overall satisfaction with postoperative nausea management was 86.9 +/- 4.1 mm and was independent of the treatment group. Aromatherapy effectively reduced the perceived severity of postoperative nausea. The fact that a saline "placebo" was as effective as alcohol or peppermint suggests that the beneficial effect may be related more to controlled breathing patterns than to the actual aroma inhaled.

Induction of Fos protein in neurons in the medulla oblongata after motion- and X-irradiation-induced emesis in musk shrews (Suncus murinus)

To clarify the anatomical location of medullary neurons associated with vomiting, the musk shrew (Suncus murinus), a small animal used as a model for emesis, was exposed to various emetic stimuli and patterns of neuronal excitation were investigated by Fos immunohistochemistry. In motion experiments, musk shrews were shaken for 30 min on a tabletop shaker (displacement=25 mm and frequency=1.2 Hz). Ten of fifteen animals vomited frequently (Mo-FV group); the other five animals did not vomit (Mo-NV group). In radiation experiments, X-ray irradiation (10 Gy) of the whole body caused frequent vomiting in all of seven experimental animals (Ra-FV group). In the Mo-FV group, many Fos-immunoreactive (Fos-ir) neurons were detected in the nucleus of the solitary tract (NTS) and the reticular formation. The distribution pattern of Fos-ir neurons in the Mo-NV group was similar to that in the Mo-FV group, but the Mo-NV group had significantly fewer positive neurons in the NTS and the reticular formation around the nucleus ambiguus. In the Ra-FV group, numerous Fos-ir neurons were observed in the area postrema, an area containing no positive neurons in the motion-stimulated animals. The number of Fos-ir neurons in the NTS of the Ra-FV group was not statistically different from that of the Mo-NV group. In the Mo-FV and Ra-FV groups, Fos-ir neurons were clustered in the reticular formation at the dorsal-dorsomedial edge of the nucleus ambiguus at the level of the rostral medulla, while few such clusters were observed in the Mo-NV group. These neurons may play a role in the regulation of the vomiting response.

Area postrema mediates gastric motor response induced by apomorphine in rats

The effects of apomorphine administration on the autonomic responses were investigated in rats. Distinctive gastric motor responses were observed after the intravenous administration of apomorphine (0.1 mg/kg body weight). Gastric motor responses in the distal stomach induced by apomorphine administration were classified into two types. One type involved inhibition of phasic contractions which appeared just after the administration of apomorphine. The other involved an increase in the frequency of small phasic contractions accompanied by increased gastric tone appearing with a relatively longer delay. No relaxation was observed in either the proximal or distal stomach. These gastric motor responses showed a dose-response effect to the amount of apomorphine administered (0.002-0.1 mg/kg body weight). In addition, submandibular salivary secretion was observed in response to the intravenous administration of apomorphine at a dose of 3 or 10 mg/kg body weight. Pretreatment with domperidone (1 or 2 mg/kg body weight) or the ablation of the area postrema (AP) abolished the gastric motor response and salivary secretion induced by the administration of apomorphine. In conclusion, rats showed definitive autonomic phenomena in response to the administration of apomorphine. Dopamine 2-like receptors situated in the AP mediate apomorphine-induced autonomic phenomena in rats.

Central nervous mechanisms of cough

Cough is an airway defensive reflex substantially consisting in a modified respiratory act. Transection experiments have shown that the fundamental structures responsible for this reflex are located within the medulla oblongata. Electrical stimulation applied to the medulla failed to provide convincing evidence of a cough centre distinct from the brainstem respiratory network. In fact, electrical stimuli affect not only neuronal somata, but also intramedullary cough-related pathways. Studies on the behaviour of medullary respiratory neurones have led to the conclusion that the same respiratory neurones involved in the generation of the eupnoeic pattern of breathing also participate in the production of the cough motor pattern. These findings support the existence of multifunctional neural networks in the mammal brainstem. Bötzinger complex expiratory neurones with augmenting discharge patterns have been suggested to convey an excitatory drive to the expiratory bulbospinal neurones of the caudal ventral respiratory group and, hence, to expiratory motoneurones. The excitatory drive to caudal medullary expiratory neurones is mediated by ionotropic glutamate receptors. Recent lines of evidence indicate that the Bötzinger complex and the caudal ventral respiratory group have a crucial role in determining both the inspiratory and the expiratory components of the cough motor pattern.

Cajal's prophetic functional considerations on respiratory reflexes: new questions about old answers

In the "Histology of the Nervous System" (Histologie, Spanish edition, 1899, 1904; French translation, 1909, 1911; all citations are from the American translation, 1995) Cajal did not only describe the origins and central pathways of cranial nerves but his detailed observations led him to numerous conclusions about the functional organization of brainstem reflexes. From studies of vagal and glossopharyngeal afferents he proposed a structural organization of the nucleus tractus solitarii (NTS). His view has been considerably changed by several authors on the basis of modern tracing studies. However, detailed histological examinations of functionally identified sensory fibers provided new understanding of a functional organization of the solitary nucleus that is very well in line with Cajal's original descriptions. The prophetic character of Cajal's concepts of structural-functional relations becomes even more evident by a reconsideration of his explanations of the reflexes underlying respiration, coughing and vomiting. Recent electrophysiological studies of spontaneously rhythmically active in vitro preparations have provided us with new insights in respiratory control. However, it appears that quite a number of Cajal's key questions concerning respiratory reflexes are still not solved. Therefore, a reconsideration of old and partly forgotten concepts might indeed provide a novel understanding of the structural and functional organization of brainstem reflexes.

Immunohistochemical demonstration of c-fos protein in neurons of the medulla oblongata of the musk shrew (Suncus murinus) after veratrine administration

We subcutaneously injected 0.5 mg/kg veratrine into the musk shrew (Suncus murinus), observed the presence or absence, latency, and the incidence of vomiting in each animal for 90 min, and selected animals that frequently vomited (FV group) and those that did not vomit (NV group). Subsequently, animal brains were removed, and the induction of c-fos protein (Fos) was immunohistochemically examined to evaluate neuronal activity in the medulla oblongata. The distribution of Fos-positive neurons in the medulla oblongata was similar between FV and NV groups, with numerous neurons along the entire length of the nucleus of the solitary tract and in the ventrolateral reticular formation. Both veratrine-injected groups showed higher numbers of positive neurons than the saline administered group. However, while the FV group showed a high concentration of positive neurons in the dorsal-dorsomedial reticular formation of the nucleus ambiguus in the rostral medulla, the NV group showed few positive neurons in this area. Fos activity in neurons in this area appeared to be higher in animals with a higher incidence of vomiting.

Role of autonomic nervous system for development and suppression of motion sickness in Suncus murinus

To clarify the role of autonomic nervous function in motion sickness, the effect of agents that act on the autonomic nervous system on the motion stimuli-induced emesis was studied in two strains of Suncus murinus (Jic:SUN-Her and Jic:SUN-Ler) with congenitally different sensitivity to veratrine sulfate. We demonstrated significant differences between the two strains in sensitivity to motion stimuli. Isoproterenol (2.5 mg kg(-1), s.c.) significantly prolonged the latency to the first emetic episode induced by motion stimuli and significantly decreased the number of emetic episodes in Jic:SUN-Her suncus. Hexamethoium (2.0 mg kg(-1), s.c.) tended to shorten the latency in Jic:SUN-Ler. Acetylcholine (1.2 mg kg(-1), s.c.) enhanced the emetic response in Jic:SUN-Ler, but atropine (4.0 mg kg(-1), s.c.) suppressed motion stimuli-induced emetic response in Jic:SUN-Her. These results suggest that the predominance of parasympathetic nervous activity is relevant to the enhancement of motion stimuli-induced emetic response, whereas the predominance of sympathetic nervous activity suppresses motion stimuli-induced emetic response. Norepinephrine (0.8 mg kg(-1), s.c.) enhanced motion stimuli-induced emesis contrary to isoproterenol in Jic:SUN-Ler although both drugs are adrenergic agents. However, atropine pretreatment (4.0 mg kg(-1), s.c.) inhibits norepinephrine-induced emetic response. It was considered that norepinephrine-induced emetic response might be dependent on a secondary increase of parasympathetic nervous activity due to bororeflex. Moreover, the different emetic response in Jic:SUN-Her and Jic:SUN-Ler suncus to motion stimuli and drug administration mentioned above indicated that different participation of autonomic nervous activity and/or afferent information from the baroreceptor in the emetic response may exist between these animal groups.

Central neurocircuitry associated with emesis

Ingestion of toxin, traumatic events, adverse drug reactions, and motion can all result in nausea and emesis. In addition, cyclic vomiting syndrome is quite prevalent in the pediatric population. Coordination of the various autonomic changes associated with emesis occurs at the level of the medulla oblongata of the hindbrain. Chemosensitive receptors detect emetic agents in the blood and relay this information by means of neurons in the area postrema to the adjacent nucleus tractus solitarius (NTS). Abdominal vagal afferents that detect intestinal luminal contents and gastric tone also terminate in the NTS (gelatinosus, commissural, and medial subnuclei). The NTS is viscerotopically organized into subnuclei that subserve diverse functions related to swallowing (subnucleus centralis), gastric sensation (subnucleus gelatinosus), laryngeal and pharyngeal sensation (intermediate and interstitial NTS), baroreceptor function (medial NTS), and respiration (ventrolateral NTS). Neurons from the NTS project to a central pattern generator (CPG), which coordinates the sequence of behaviors during emesis, as well as directly to diverse populations of neurons in the ventral medulla and hypothalamus. Thus, it is critical to realize that there is not an isolated "vomiting center," but rather groups of loosely organized neurons throughout the medulla that may be activated in sequence by a CPG. The newer antiemetic agents appear to block receptors in the peripheral endings of vagal afferents to reduce "perception" of emetic stimuli and/or act in the dorsal vagal complex. A primary site of action of 5-HT(3)-receptor antagonists is by means of the vagal afferents. Neurokinin-1 receptor (NK(1)R) antagonists are antiemetics, because they act at a site in the dorsal vagal complex. Part of their effectiveness may be the result of inhibition of the NK(1)R on vagal motor neurons to prevent fundic relaxation, which is a prodromal event essential for emesis. Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the major psychoactive component of marijuana, can be therapeutically useful as an antiemetic. The site of action of Delta(9)-THC is on cannabinoid CB1 receptors in the dorsal vagal complex. However, it decreases fundic tone and antral motility. It is not easy to predict the potential antiemetic effects of drugs that alter motility. Although antiemetic drugs are available for management of acute chemotherapeutic-induced emesis, few treatments are effective for delayed emesis or cyclic vomiting syndrome.

Vestibular modulation of plasma vasopressin levels in rats

Recent studies, which have shown an increase of plasma vasopressin (VP) in experimental motion sickness and the efficacy of VP antagonists for motion sickness, suggest an important role of VP in the development of vestibulo-autonomic responses. We have recently found evidence of the co-existence of vasopressinergic neurons with the stress-sensitive chemokinergic neuronal system in the hypothalamo-pituitary pathway in rats, which uses cytokine-induced neutrophil chemoattractant (CINC) as an effector molecule. In this study, to elucidate possible roles of VP and CINC in the vestibulo-autonomic responses, we simultaneously measured plasma VP and CINC concentrations after electrical or caloric vestibular stimulation in urethane-anesthetized rats. Electrical vestibular stimulation with more than 200 microA increased the plasma levels of VP in a current intensity-dependent manner, and stimulation with 500 microA increased the plasma VP levels to 350% of the normal control group, which received no stimulation. Caloric vestibular stimulation with cold water increased the plasma VP levels to 262% of the control group, which received caloric stimulation with water at 37 degrees C, and stimulation with warm water tended to increase the plasma VP levels. Plasma CINC levels were neither affected by electrical nor caloric vestibular stimulation. These findings indicate that vestibular stimulation increased plasma levels of VP but not CINC, and this vestibular-induced activation of VP neurons may be involved in a mechanism of vestibulo-autonomic responses.