The physiology and pharmacology of emesis

Association between DRD2 and DRD3 gene polymorphisms and gastrointestinal symptoms induced by levodopa therapy in Parkinson's disease

Levodopa is the most used drug to treat motor symptoms in Parkinson's disease (PD). However, dopaminergic side effects such as nausea and vomiting may occur. Several evidences indicate a major role for dopamine receptors D2 (DRD2) and D3 (DRD3) in emetic activity. The aim of this study was to investigate the relationship of DRD2 rs1799732 and DRD3 rs6280 gene polymorphisms with gastrointestinal (GI) symptoms induced by levodopa in PD patients. Two hundred and seventeen PD patients on levodopa therapy were investigated. DRD2 rs1799732 and DRD3 rs6280 polymorphisms were genotyped by PCR-based methods. Multiple Poisson regression method with robust variance estimators was performed to assess the association between polymorphisms and gastrointestinal symptoms. The analyses showed that DRD2 Ins/Ins (prevalence ratio (PR)=2.374, 95% confidence interval (CI): 1.105-5.100; P=0.027) and DRD3 Ser/Ser genotypes (PR=1.677, 95% CI 1.077-2.611; P=0.022) were independent and predictors of gastrointestinal symptoms associated with levodopa therapy. Despite all the efforts to alleviate GI symptoms, this adverse effect still occurs in PD patients. Pharmacogenetic studies of GI symptoms induced by levodopa therapy have the potential to display new ways to better understand the molecular mechanisms involved in these side effects.

Neuronal inclusions of α-synuclein contribute to the pathogenesis of Krabbe disease

Demyelination is a major contributor to the general decay of neural functions in children with Krabbe disease. However, recent reports have indicated a significant involvement of neurons and axons in the neuropathology of the disease. In this study, we have investigated the nature of cellular inclusions in the Krabbe brain. Brain samples from the twitcher mouse model for Krabbe disease and from patients affected with the infantile and late-onset forms of the disease were examined for the presence of neuronal inclusions. Our experiments demonstrated the presence of cytoplasmic aggregates of thioflavin-S-reactive material in both human and murine mutant brains. Most of these inclusions were associated with neurons. A few inclusions were detected to be associated with microglia and none were associated with astrocytes or oligodendrocytes. Thioflavin-S-reactive inclusions increased in abundance, paralleling the development of neurological symptoms, and distributed throughout the twitcher brain in areas of major involvement in cognition and motor functions. Electron microscopy confirmed the presence of aggregates of stereotypic β-sheet folded proteinaceous material. Immunochemical analyses identified the presence of aggregated forms of α-synuclein and ubiquitin, proteins involved in the formation of Lewy bodies in Parkinson's disease and other neurodegenerative conditions. In vitro assays demonstrated that psychosine, the neurotoxic sphingolipid accumulated in Krabbe disease, accelerated the fibrillization of α-synuclein. This study demonstrates the occurrence of neuronal deposits of fibrillized proteins including α-synuclein, identifying Krabbe disease as a new α-synucleinopathy.

Vomiting as a reliable sign of concussion

Concussion is the most common type of traumatic brain injury, with headache being the most frequent symptom of mild traumatic brain injury (MTBI) (including dizziness, vomiting, nausea, lack of motor coordination or difficulty balancing). Concussion may be caused by a blow to the head, or by acceleration forces without a direct impact. Often, MTBI occurs as the result of a sports injury. Loss of consciousness is always present, unlike vomiting. Therefore, we hypothesize vomiting to be considered as a cardinal sign of concussion. Stimulation of vomiting centres finally triggers vomiting. Professional boxers and mixed martial arts competitions reluctantly agree with stringent rules and protective clothing. We discuss the issue of further protection for those engaged in these and other sports.

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.

Zingiber officinale Rosc. modulates gamma radiation-induced conditioned taste aversion

The aim of the present study was to investigate the neurobehavioral protective efficacy of a hydroalcoholic extract of ginger (Zingiber officinale Rosc.) in mitigating gamma radiation-induced conditioned taste aversion in Sprague-Dawley rats. Administration of Zingiber extract 1 h before 2-Gy gamma irradiation was effective in blocking the saccharin avoidance response for 5 post-treatment observational days, both in a dose- and time-dependent manner, with 200 mg/kg b.w. i.p. being the most effective dose. Highest saccharin intake in all the groups was observed on the fifth post-treatment day. The potential of ginger extract to inhibit lipid peroxidation induced by radiation (2 Gy) and ascorbate-ion stress in brain homogenate and its ability to scavenge highly reactive superoxide anions were evaluated. The 1000-microg/ml and 2000-microg/ml concentration of ginger extract showed the highest efficiency in scavenging free radicals and in inhibiting lipid peroxidation. The lipid peroxidation and superoxide-anion scavenging ability of the extract further supports its radioprotective properties. The results clearly establish the neurobehavioral efficacy of ginger extract and the antioxidant properties appear to be a contributing factor in its overall ability to modulate radiation-induced conditioned taste aversion. Ginger extract has tremendous potential for clinical applications in mitigation of radiation-induced emesis in humans.

Roles of substance P and NK(1) receptor in the brainstem in the development of emesis

The emetic response is primarily a protective reflex occurring in a wide variety of vertebrates in response to the ingestion of toxic compounds. The role of the nuclei in the brainstem, including the area postrema, nucleus tractus solitarius, the dorsal motor nucleus of the vagus, and the central pattern generator for vomiting, as well as the involvement of the abdominal visceral innervation relevant to the emetic reflex, have all been discussed by many researchers. The introduction of serotonin 5-HT(3)-receptor antagonists into clinical practice allowed for a dramatic improvement in the management of vomiting. However, vomiting still remains a significant problem. The mechanism of the emetic response is even more complicated than was first thought. This review attempts to bring together some of the evidence suggesting the roles of substance P and its receptor, neurokinin NK(1) receptor, in the brainstem nuclei in the development of emesis. Accordingly, NK(1)-receptor antagonists might represent novel drugs for the management of major types of emesis.

Oral and pharyngeal reflexes in the mammalian nervous system: their diverse range in complexity and the pivotal role of the tongue

The oral cavity and pharynx are anatomically separate but functionally integrated regions of the head. The two regions are involved in complex motor responses that include feeding, chewing, swallowing, speech, and respiration. The multiple sensory receptors that innervate these two regions provide the first link in reflexes that control muscles of the entire head, upper gastrointestinal tract, and airway. Most of the reflexes affect the diversity of muscles that compose the tongue, which is vital to all stages of feeding and which continually affects the patency of the airway. Oral-pharyngeal reflexes are evident in the mammalian fetus and continually emerge as the animal or human matures. Some of the first reflexes in the oral region are geared toward nourishment. As the central nervous system matures and the oral and pharyngeal regions develop morphologically, new reflexes develop. Many of these reflexes are protective both of the tissue in the oral cavity, such as the tongue, and of the upper airway in preventing aspiration. While simple reflexes can be evoked in isolation, most reflexes combine with more complex oral and pharyngeal responses such as chewing and vocalization. Oral-pharyngeal reflexes demonstrate a range in complexity. Some sensory stimuli will evoke a series of responses, as is often evident in the infant, and other stimuli will evoke a complex multiple-level recruitment of muscles in a sequence, as in pharyngeal swallowing. Certain sensory inputs evoke an entire motor behavior pattern, such as taste avoidance or facial expression. The oral-pharyngeal reflexes are critical to maintaining life and ultimately serve functions that the oral and pharyngeal regions have in common, such as communication, feeding, and breathing.

The diaphragm: two physiological muscles in one

To the respiratory physiologist or anatomist the diaphragm muscle is of course the prime mover of tidal air. However, gastrointestinal physiologists are becoming increasingly aware of the value of this muscle in helping to stop gastric contents from refluxing into the oesophagus. The diaphragm should be viewed as two distinct muscles, crural and costal, which act in synchrony throughout respiration. However, the activities of these two muscular regions can diverge during certain events such as swallowing and emesis. In addition, transient crural muscle relaxations herald the onset of spontaneous acid reflux episodes. Studying the motor control of this muscular barrier may help elucidate the mechanism of these episodes. In the rat, the phrenic nerve divides into three branches before entering the diaphragm, and it is possible to sample single neuronal activity from the crural and costal branches. This review will discuss our recent findings with regard to the type of motor axons running in the phrenic nerve of the rat. In addition, we will outline our ongoing search for homologous structures in basal vertebrate groups. In particular, the pipid frogs (e.g. the African clawed frog, Xenopus laevis) possess a muscular band around the oesophagus that appears to be homologous to the mammalian crural diaphragm. This structure does not appear to interact directly with the respiratory apparatus, and could suggest a role for this region of the diaphragm, which was not originally respiratory.

Establishment of an animal model for radiation-induced vomiting in rats using pica

We investigated whether radiation-induced pica, a behavior characterized by the eating of a non-food substance, such as kaolin, can be used as an index of radiation-induced vomiting in rats. Since there was an individual difference in the susceptibility to pica, we selected rats that actually ate kaolin following X-ray irradiation, and used them for the experiment. The total-body irradiation (TBI) increased kaolin consumption in a dose-dependent manner (sham, 0.05 +/- 0.03 (SEM) g; 2 Gy, 0.38 +/- 0.11 g; 4 Gy, 1.54 +/- 0.28 g; 8 Gy, 3.55 +/- 0.67 g), and the increased kaolin consumption after 4 Gy of TBI was inhibited by a pretreatment with the serotonin 5-HT3 receptor antagonist ondansetron (2 mg/kg, i.p.) (saline, 1.49 +/- 0.33 g; ondansetron, 0.75 +/- 0.11 g). Furthermore, 4 Gy of abdominal irradiation was more effective to induce pica than that of head irradiation (abdomen: 0.37 +/- 0.05 g, head: 0.06 +/- 0.01 g). These findings suggested that peripheral serotonergic pathway is predominantly involved in the development of radiation-induced pica in rats and that the radiation-induced pica could be useful as a behavioral index for the severity of radiation-induced vomiting in rats.

Migraine-associated vomiting and asystole in a child

A variety of symptoms that accompany migraine in the child and adult are mediated by the autonomic nervous system. Significant effects on cardiac rhythm are uncommon, but can be life threatening. We describe a 3-year-old girl in whom migraine-associated vomiting precipitated cardiac asystole which was effectively treated with a cardiac pacemaker.

Clonidine-induced emesis: a multitransmitter pathway concept

The emetic effect of clonidine injected into the cerebral ventricles through chronically implanted cannulae was investigated in unanaesthetized cats. Clonidine (0.1-300 micrograms) induced dose-dependent and shortlasting emesis. The emesis induced by the supramaximal dose of clonidine (100 micrograms) was not abolished after the ablation of area postrema. Both the alpha 2 adrenoceptor blocking agent idazoxan and the mixed alpha 1 and alpha 2 adrenoceptor antagonist phenoxybenzamine, injected intracerebroventricularly, attenuated or abolished the emesis induced by clonidine (100 micrograms). On the other hand, the alpha 2 adrenoceptor blocking agent yohimbine, the alpha 1 adrenoceptor blocking drug prazosin and the non-selective beta-adrenoceptor antagonist propranolol, injected into the cerebral ventricles, had no significant effect on clonidine-induced emesis. The antimuscarinic drug atropine injected into the cerebral ventricles prevented the clonidine-induced emesis in a dose-dependent manner. The dopamine antagonist chlorpromazine, the 5-hydroxytryptamine blocking agent methysergide and the histamine H1 and H2 receptor antagonists, antazoline and cimetidine, injected intracerebroventricularly reduced or abolished the emesis produced by clonidine. The ganglionic blocking substance mecamylamine and the opioid antagonist naloxone, all injected into the cerebral ventricles, had no significant effect on clonidine-induced emesis. In cats pretreated with the intracerebroventricular competitive inhibitor of the synthesis of catecholamines, alpha-methyl-p-tyrosine, as well as with the inhibitor of acetylcholine synthesis hemicholinium-3, the emesis caused by clonidine was depressed or abolished. The clonidine-induced emesis was also abolished when catecholamine stores were depleted by intracerebroventricular reserpine. However, the clonidine-induced emesis was not significantly changed when 5-hydroxylryptaminergic nerve terminals were damaged by 5,6-dihydroxytryptamine. It follows, therefore, that cholinergic and noradrenergic mechanisms are of basic importance for the emetic action of clonidine. With regard to receptors, the emesis induced by clonidine injected into the cerebral ventricles, is mediated at least in part through alpha-adrenoceptors, muscarinic cholinoceptors, 5-hydroxytryptamine receptors and H1 and H2 histamine receptors. These receptors appear to be located mostly presynaptically and they transmit emetic impulses to neurones integrating them into emesis. However, the direct effect of clonidine on postsynaptic receptors cannot be excluded, particularly when muscarinic and 5-hydroxytryptamine receptors are implicated. Taken together, these results point to the existence of a multitransmitter pathway/s outside the area postrema, subserving the central regulation of emesis.

Physiology of chemotherapy-induced emesis and antiemetic therapy. Predictive models for evaluation of new compounds

The physiology of emesis has been studied for several hundred years, focusing on the different centres involved and the mechanics of expulsion. The vomiting centre receives inputs from various emetic detectors such as the gut, the vestibular labyrinths and the chemoreceptor trigger zone. Emesis is a common disabling effect in motion sickness, postoperative conditions and in radio- and chemotherapy. Our current understanding of the mechanisms has been provided mainly by the recent introduction of serotonin 5-HT3 receptor antagonists into therapeutic use. Nevertheless, despite the considerable advances made in the understanding of the different pathways involved in emesis, there are number of areas that still require experimental investigation. Different animal and human models are available to study the physiology of emesis and to evaluate the antiemetic activity of new compounds, but they need to be predictors of clinical situations.

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 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.

Enantioselective inhibition of apomorphine-induced emesis in the ferret by the neurokinin1 receptor antagonist CP-99,994

These studies have examined the effects of the selective neurokinin1 (NK1) receptor antagonist CP-99,994 on the retching and vomiting response to apomorphine. CP-99,994 (1-3 mg/kg i.p.) attenuated retching and vomiting induced by apomorphine (0.25 mg/kg s.c.) with complete inhibition of retching and vomiting at the 3 mg/kg dose. In contrast CP-100,263 (3 mg/kg i.p.), the enantiomer of CP-99,994 with 1000-fold lower affinity for the NK1 receptor, was without effect.

Hypercapnia and hypoxia which develop during retching participate in the transition from retching to expulsion in dogs

The roles of arterial and central chemoreceptors in the transition from retching to expulsion during vomiting were studied. In spontaneously breathing decerebrate dogs, actual vomiting induced by activation of abdominal vagal afferents always consisted of retching and subsequent expulsion phases. Pulmonary ventilation almost stopped during the retching phase. Arterial blood CO2 tension gradually increased and reached a maximum near the time of the transition from the retching phase to the expulsion phase. Similarly, when end-tidal CO2 was maintained higher than 4.6 +/- 0.7% in paralyzed, artificially ventilated decerebrate dogs, stimulation of abdominal vagal afferents induced fictive retching and fictive expulsion, which were identified from the characteristic discharge patterns of the motor nerves to the costal and hiatal parts of the diaphragm, the abdominal muscles and the digastric muscle. However, only fictive retching occurred at an end-tidal CO2 of less than 3.7 +/- 0.7%. Although end-tidal CO2 was at a low level, fictive retching was followed by fictive expulsion when artificial ventilation was interrupted during the fictive retching phase and when sinus nerve afferents were stimulated. Even after sino-aortic denervation, fictive retching and subsequent fictive expulsion could be induced by stimulation of either vagal afferents or the solitary tract and nucleus, but the threshold level of end-tidal CO2 which enabled the induction of fictive expulsion increased after denervation. These results indicate that the activity of arterial and/or central chemoreceptor afferents must exceed some critical level to induce the transition from the retching phase to the expulsion phase.

Differential function of the costal and crural diaphragm during emesis in canines

In six mongrel dogs under thiopental anesthesia, piezoelectric transducers and bipolar electromyographic (EMG) wires were installed onto left costal, medial crural and lateral crural segments of the diaphragm. During CO2 rebreathing, shortening and EMG activity increased significantly in all three regions of the diaphragm compared to resting breathing. During emesis, (1) both shortening and EMG activity significantly increased compared to resting in costal segment; however, (2) lateral crural shortening was not increased in spite of significant increase in EMG activity; furthermore, (3) the medial crural segment lengthened without any increased EMG activity. These results demonstrate a differential recruitment of costal and crural diaphragm segments, and an additional differential activity within the crural segment between medial and lateral crural regions, during emesis. This activity of the canine diaphragm is consistent with a central influence of emesis upon individual regions of the diaphragm.

Behavioral studies of emetic sensitivity in the ferret

The ferrets' responsiveness to several known and putative emetic agents was evaluated using a variety of agents that were injected subcutaneously and/or intravenously. Apomorphine was consistently emetic at relatively high doses (100 micrograms/kg) when injected subcutaneously in large male ferrets (> or = 1.4 kg). The responsiveness to apomorphine was anomalous in that subcutaneous injections produced a more consistent response than intravenous ones. In addition, ferrets rapidly become tolerant or tachyphylactic to subcutaneously administered apomorphine. Area postrema ablation, but not abdominal vagotomy, rendered ferrets refractory to the emetic effects of apomorphine. This species, relative to dog and humans, proved to be insensitive to a variety of pharmacologic agents including angiotensin II, gastrin, histamine, Leu-enkephalin, neurotensin, serotonin, and vasopressin. Cisplatin elicited forceful retching and emesis. Emetic responses were obtained with substance P and Met-enkephalin in individual animals but were inconsistent. Sensitivity to DAGO [D-Ala2,MePhe4,Gly-ol5 enkephalin] was variable. Results of this study indicate that the ferret is not an optimal model for all forms of emesis.

Pancopride, a potent and long-acting 5-HT3 receptor antagonist, is orally effective against anticancer drug-evoked emesis

Pancopride ((+-)N-(1-azabicyclo-[2,2,2]-oct-3-yl)-2-cyclopropylmethoxy-4-ami no-5-chlorobenzamide) is a new potent and selective 5-HT3 receptor antagonist, orally and parenterally effective against cytotoxic drug-induced emesis. In vitro, pancopride displayed high affinity (Ki = 0.40 nM) for [3H]GR65630-labelled 5-HT3 recognition sites in membranes from the cortex of rat brains. In vivo, pancopride antagonized 5-HT-induced bradycardia in anaesthetized rats when administered i.v. 5 min (ID50 = 0.56 microgram/kg) or p.o. 60 min (ID50 = 8.7 micrograms/kg) before 5-HT challenge. A single oral dose (10 micrograms/kg) of pancopride produced a significant inhibition of the bradycardic reflex over an 8-h period. Pancopride dose dependently inhibited the number of vomiting episodes and delayed the onset of vomiting induced by cisplatin in dogs (ID50 = 3.6 micrograms/kg i.v. and 7.1 micrograms/kg p.o.). Pancopride was also effective in blocking mechlorethamine- and dacarbazine-induced emesis. Unlike metoclopramide, pancopride was shown to lack any measurable antidopaminergic activity both in vitro and in vivo. These results support clinical data, indicating that pancopride will be a useful drug for treating cytostatic-induced emesis in humans.

New pharmacologic approaches to the prevention of space/motion sickness

Fundamental approaches in selection of new agents for evaluation in prevention of space/motion sickness (SMS) are reviewed. The discussion centers on drugs under investigation at the Johnson Space Center. Methodology that employs the rotating chair for measuring SMS symptomatology and susceptibility is described. The most obvious approach to the development of new agents relies on selection of agents from drug classes that possess pharmacologic properties of established anti-motion sickness agents. A second approach selects drugs that are used to prevent emesis caused by means other than exposure to motion. The third approach relies on basic research that characterizes individual differences in susceptibility. The hypothesis is: detection of individual differences leads to identification of specific drugs, which target physiologic systems that show individual differences. These physiologic systems are targets for therapy and may play a role in the etiology of SMS. Two drugs that reduce susceptibility to SMS include dexamethasone and d(CH2)5Tyr(Me)AVP, a vasopressin (AVP)V1 antagonist. The latter peptide has demonstrated complete blockade of emesis and other significant symptoms in squirrel monkeys. These studies were predicated on observations that subjects who were more resistant to SMS had higher plasma AVP after severe nausea than subjects with lower resistances. Investigations are underway to test a 0.5-mg intravenous dose in humans. Kappa opioid agonists inhibit AVP release and offer new therapeutic possibilities and advantages over AVP peptides. This review details the experimental data collected on AVP and adrenocorticotropin. The literature supports interrelated roles for AVP and opioid peptides in SMS. Experimental testing of kappa agonists is warranted because specific opioid agonists act at neuroanatomical sites causing nausea and vomiting. It is argued opioid receptors in the chemoreceptor trigger zone and vomiting center stimulate and inhibit the emetic response, respectively. The evidence suggests kappa and/or mu receptors at VC are involved in inhibition of emesis, whereas delta opioid receptors at CTZ are involved in stimulation of emesis.

Antiemetic prophylaxis with promethazine or droperidol in paediatric outpatient strabismus surgery

This randomized, double-blind study evaluated the antiemetic efficacy and the side-effects of promethazine pretreatment (0.5 mg.kg-1 IV + 0.5 mg.kg-1 IM) versus droperidol + placebo pretreatment (droperidol, 0.075 mg.kg-1 IV + physiological saline, 0.02 ml.kg-1 IM). One hundred unpremedicated ASA physical status I children ranging from two to ten years, and undergoing outpatient strabismus surgery were studied. All children received inhalational anaesthesia with halothane, nitrous oxide and oxygen. Neither opioids nor muscle relaxants were used. The incidence of vomiting and/or retching and the incidence of side-effects were determined in the post-anaesthesia recovery room (PARR), in the short-stay surgical unit (SSSU), and after discharge from the hospital (including the journey and the stay at home during the first postoperative day). Promethazine and droperidol were equally effective in reducing the incidence of vomiting before discharge to two and eight per cent respectively. On the contrary, the incidence of vomiting after discharge and overall were significantly less with promethazine (ten and ten per cent) than with droperidol pretreatment (54 and 56 per cent) (P less than 0.0001). Promethazine permitted the time to discharge from the hospital to be reduced to an average of three hours, without increasing the incidence of vomiting postdischarge. Promethazine pretreatment is much less expensive than droperidol pretreatment. The incidence of restlessness was significantly less with droperidol (eight per cent) than with promethazine (36 per cent) (P less than 0.001). Promethazine pretreatment demands the use of an analgesic like acetaminophen in order to reduce the incidence of postoperative pain and restlessness.(ABSTRACT TRUNCATED AT 250 WORDS)

The responses of arginine vasopressin and adrenocorticotrophin to nausea induced by ipecacuanha

Ipecacuanha syrup induces emesis by an early peripheral (gastric irritant) action and a later central effect at the chemoreceptor trigger zone (CTZ). We have studied the responses of plasma AVP, ACTH and ACTH-precursors to early and late ipecacuanha-induced nausea in nine healthy male subjects. Symptom severity was assessed using a linear analogue scale. All subjects reported 'early' nausea (N1) with a latency of 16 +/- 2 min (mean +/- SEM) and eight subjects vomited. Six subjects experienced recurrent nausea (N2) (latency 106 +/- 10.4 min) of whom five also vomited. The interval between the cessation of N1 and the onset of N2 was 55 +/- 10.8 min (range 25-80 min). The severity of nausea at the onset of N1 or N2 was similar but the AVP and ACTH responses were highly variable. Thus, while mean plasma AVP concentrations increased during both symptom periods, in three subjects during N1 and in three subjects during N2 plasma AVP concentrations did not rise above the normal range, despite marked symptoms. No clear pattern of AVP response to distinguish early peripheral from late central ipecacuanha-induced emesis was demonstrated. Whilst mean plasma ACTH concentrations increased during both N1 and N2 there were no changes in mean plasma ACTH-precursor concentrations. Analysis of pooled data for N1 and N2 demonstrated direct correlations between the nausea score and the peak incremental plasma responses of either AVP or ACTH and, despite the variability, peak incremental concentrations of AVP and of ACTH were also correlated. The data indicate that there is no difference in the AVP responses to peripherally or centrally stimulated ipecacuanha-induced nausea.(ABSTRACT TRUNCATED AT 250 WORDS)

Emetic activity of zacopride in ferrets and its antagonism by pharmacological agents

Zacopride administered orally was more emetic in fed than in fasted ferrets. The emetic activity of zacopride (0.1 mg/kg p.o.) was inhibited (100%) by 0.1 mg/kg i.p. of zacopride and 1 mg/kg i.p. of ICS 205-930. Haloperidol (3.16 mg/kg i.p.) and prochlorperazine (3.16 mg/kg i.p.) were weakly effective. N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide, a 5-HT1P antagonist, was inactive. Thus, the emetic activity of zacopride, like that of cisplatin, is blocked by 5-HT3 receptor antagonists.

The antiemetic profile of zacopride

The antiemetic activity of zacopride against a variety of emetogenic agents has been determined in dogs. Zacopride was highly effective in inhibiting emesis due to a wide range of cancer chemotherapeutic agents, particularly cisplatin. It was well absorbed orally since the dose of zacopride required to inhibit cisplatin-induced emesis in dogs by 90% was 28 micrograms kg-1 both by i.v. and p.o. routes. Further, zacopride (1 mg kg-1 p.o.), administered after the onset of cisplatin-induced emesis, reduced the number of subsequent emetic episodes by 91%. Zacopride at 0.1, 1, or 3.16 mg kg-1 p.o. or i.v., reduced the number of emetic episodes due to dacarbazine, mechlorethamine, adriamycin, actinomycin D, or peptide YY by 100, 100, 86, 96 and 79%, respectively. However, zacopride was not effective in inhibiting emesis due to either apomorphine, copper sulphate, protoveratrine A, histamine, or pilocarpine. No adverse effects attributed to zacopride were observed. Zacopride is thus a unique and potent antiemetic agent as it selectively inhibits the emetic response to cancer chemotherapy agents and peptide YY.

Neuroinhibition of xylazine induced emesis

Xylazine produces retching and vomiting presumably by activation of the chemoreceptor trigger zone (CTZ). The purpose of this project was to investigate whether neuroinhibition can prevent xylazine vomiting. Inhibitory neurons in the cervical vagus nerve of cats were stimulated with implanted cuff electrodes. Female cats, weighing from 3 to 4 kg, were anaesthetized with pentobarbital for surgical implantation of electrodes. After full recovery from surgery, animals were tested in weekly sessions. Stimulation was via a pulse generator connected to photon coupled linear isolator supplying constant current. Videotape was used to record observations. The range of effective stimulation was 1-10 ma, 4-100 Hz and 0.3-0.6 msec. Stimulation was initiated thirty sec. after subcutaneous injection of xylazine, 0.66 mg/kg. Stimulation of the inhibitory nerve group of the cervical vagus was effective in preventing vomiting in over 85% of the experimental trials. In addition to preventing emesis during stimulation, the latency of xylazine emesis was increased over control values. Repeated experimental trials of stimulation coupled with xylazine injection could result in the complete absence of emesis.

Responses of plasma oxytocin and arginine vasopressin to nausea induced by apomorphine and ipecacuanha

Apomorphine, a centrally-acting emetic, was administered subcutaneously (50 micrograms/kg) to nine normal subjects (four male, five female; aged 22-36 years) and four patients with idiopathic diabetes insipidus (DI) (one male, three female; aged 24-49 years). In the normal subjects this stimulus caused nausea (and vomiting in seven of nine) with a latency of 9.5 +/- 0.9 min which was followed by a large increase in plasma arginine vasopressin (AVP) concentration (from 0.9 +/- 0.2 pmol/l to 249 +/- 104 pmol/l at 15 min after the onset of symptoms; mean +/- SEM, P less than 0.01). There was a small but significant increase in plasma oxytocin (OXT) concentration (from 1.6 +/- 0.4 pmol/l to 6.2 +/- 3.4 pmol/l; P less than 0.05). Mean arterial pressure (MAP) fell slightly (from 87 +/- 1.9 mm Hg to 71 +/- 4.4 mm Hg; P less than 0.05) 15 min after the onset of nausea; there was no change in blood haematocrit or plasma osmolality and sodium concentration. In the DI patients apomorphine produced nausea (with vomiting in three of four) with a latency of 10.0 +/- 1.4 min but failed to cause an increase in either plasma AVP or OXT. In the DI patients the fall in MAP did not reach statistical significance (83 +/- 4 mm Hg to 71 +/- 11 mm Hg); there was also no change in haematocrit, osmolality or sodium concentration. Ipecacuanha, an emetic with both peripheral and central actions, was administered orally to seven normal subjects (three male, four female; aged 22-36 years) six of whom also underwent apomorphine tests.(ABSTRACT TRUNCATED AT 250 WORDS)

The neurophysiology of vomiting

Nausea and vomiting can be induced by a wide variety of stimuli such as pregnancy, space travel, raised intracranial pressure, radiation and cytotoxic drugs. The mechanisms by which all these diverse stimuli culminate in a final common act is unknown. From studies in the 1950s a model of the emetic reflex emerged consisting of a chemoreceptor trigger zone in the area postrema and a vomiting centre in the brain stem. This concept has been reviewed and revised in the light of recent studies. Many discussions of emesis involve detailed descriptions of the gastrointestinal events associated with the act of vomiting only-nausea and retching receiving little attention. Here we have tried to give a broader view by considering the neurophysiology of such events and have included nausea and retching, phenomena that are usually inseparable from vomiting. The possible biological function of these events is also discussed. The involvement of visceral systems (such as the heart, airways and gut) is included, and particular attention is paid to vagal mechanisms underlying the changes in gut motor activity. Emesis has long been thought to be organized by a 'vomiting centre'; the possibility that this vomiting centre could be the parvocellular reticular formation is reviewed, as is the concept that the 'centre' is larger than an anatomically defined single group of cells. The mechanism of action of two clinically relevant emetic stimuli--radiation and cytotoxic drugs-is considered in detail. Recent studies of the antiemetic properties of novel 5-HT-3 receptor antagonists against radiation and cytotoxic drug-induced vomiting are discussed; these studies suggest that important advances will be made in the treatment of emesis induced by these and other related agents.

Suncus murinus as a new experimental model for motion sickness

Characteristics of motion sickness and effects of possible prophylactic drugs were studied using Suncus murinus (house musk shrew) for its potential use as an experimental model in motion sickness. Mild reciprocal shaking (amplitude: 10-40 mm; frequency: 0.5-3.0 Hz) induced vomiting in most of Suncus murinus within 2 min. Adaptation was observed when the motion stimulus was repeated with an interval of 2 to 3 days. During the repetitive motion training, both the ratio of sensitive animals and the number of vomiting episodes decreased, and the time from the start of shaking to the first vomiting was extended. Subcutaneous injection of scopolamine (100 mg/kg), chlorpromazine (8 mg/kg), promethazine (50 mg/kg), diphenhydramine (20 mg/kg), chlorphenylamine (20 mg/kg) and methamphetamine (2 mg/kg) decreased the emetic effect of motion sickness, but pyrilamine (20 mg/kg), meclizine (20 mg/kg) and dimenhydrinate (32 mg/kg) were not effective or very weak. These results indicate that the Suncus murinus is sensitive to the motion stimulus and antiemetic drugs are effective as prophylaxis. The Suncus murinus is useful as a new experimental animal model for motion sickness.

Suncus murinus: a new experimental model in emesis research

Effects of various emetic and antiemetic drugs were studied using Suncus murinus for its potential use as an experimental model in emetic research. Subcutaneous injection of nicotine bitartrate (10-15 mg/kg), veratrine sulfate (0.5-1.0 mg/kg), emetine dihydrochloride (40-80 mg/kg) and oral administration of copper sulfate (20-100 mg/kg) caused dose-dependent emesis in suncus. The ED50 of nicotine, veratrine, emetine and copper sulfate were 7.9, 0.4, 47.6 and 21.4 mg/kg, respectively. However, subcutaneously injected apomorphine hydrochloride (0.1-100 mg/kg), digitoxin (0.5-1.0 mg/kg) and orally administered emetine dihydrochloride (10-80 mg/kg) did not induce the vomiting. Chlorpromazine and promethazine decreased the emetic effect of nicotine, veratrine and copper sulfate, but scopolamine hydrobromide was not effective. These results indicate that the Suncus murinus is sensitive to various emetic and antiemetic drugs and can be used as a new experimental animal model for the emesis. Emetic behavior of suncus was discussed in comparison with other animals.