The anti-emetic action of the neurokinin(1) receptor antagonist CP-99,994 does not require the presence of the area postrema in the dog

Microinjection and ligand binding studies have implicated NK(1) receptors in the area postrema (AP) in the emetic response to intragastric copper sulphate that is mediated by abdominal vagal afferents. Because these afferents terminate in the brainstem in the nucleus tractus solitarius in close proximity to the AP or in the AP itself, the results of such studies may be difficult to interpret. The present study has demonstrated in the dog that the emetic response to intragastric copper sulphate is unaffected by AP ablation, demonstrated functionally by absence of an emetic response to apomorphine (100 microg kg(-1) i.v.). In AP ablated animals the selective NK(1) receptor antagonist CP-99, 994 (1 mg kg(-1) i.v.) blocked the emetic response to copper sulphate as it did in intact animals. The results demonstrate that the AP is not involved in the blockade of the emetic response to intragastric copper sulphate by an NK(1) receptor antagonist and hence provides further support for other sites proposed such as the nucleus tractus solitarius and central pattern generator.

Effects of CP-99, 994, a tachykinin NK(1) receptor antagonist, on abdominal afferent vagal activity in ferrets: evidence for involvement of NK(1) and 5-HT(3) receptors

The effect of CP-99, 994, a tachykinin NK(1) receptor antagonist, on abdominal vagal afferent nerve activity in the ferret was investigated. Substance P (1 microg/kg, i.v.) increased vagal afferent activity by 449.0+/-51.9% and this was reduced to 145.9+/-5.7% (p<0.01) by pre-treatment with CP-99, 994 (1 mg/kg, i.v.), and to 149.5+/-1.5% (p<0.001) by granisetron (1 mg/kg, i.v.), a 5-HT(3) receptor antagonist. In addition, the increase in vagal nerve activity induced by 5-HT (25 microg/kg, i.v., 552.0+/-57.0% increase from pre-injection level) was significantly reduced (401.3+/-10.6% increase from pre-injection level, p<0.05) by CP-99, 994 (100 microg/kg, i.v.). These results provide evidence for an involvement of peripheral NK(1) and 5-HT(3) receptors in substance P-induced vagal afferent activation. While the functional consequences (if any) of such peripheral effects were not investigated, they could contribute either directly (e.g. by blockade of receptors on vagal afferents) or indirectly (e.g. modulation of 5-HT release or reduction of local inflammatory response) to the antiemetic effects of CP-99, 994 against cisplatin and other emetic agents acting primarily via the vagus.

Retching and vomiting in neurologically impaired children after fundoplication: predictive preoperative factors

BACKGROUND/PURPOSE

In neurologically impaired children, retching and recurrent vomiting are common after Nissen fundoplication. The aim of this study was to identify whether there are preoperative factors that predict their occurrence.

METHODS

Twenty neurologically impaired children (8 boys, 12 girls; age range, 3 months to 8 years) were studied prospectively by taking a detailed history of behaviors and symptoms associated with feeding before and after Nissen fundoplication for gastroesophageal reflux.

RESULTS

Preoperatively, children could be classified into 2 groups. Children in group A had symptoms suggestive of only gastroesophageal reflux (effortless "vomiting" or regurgitation), whereas children in group B exhibited one or more features associated with activation of the emetic reflex (pallor, sweating, retching, forceful vomiting). Postoperatively 0 of 8 in group A retched compared with 8 of 12 in group B (P <.005, Fishers Exact test).

CONCLUSIONS

Children at high risk of retching, and ultimately vomiting, after antireflux surgery may be identified clinically preoperatively. They have symptoms that are specifically caused by activation of the emetic reflex rather than to gastroesophageal reflux. In these cases, antireflux surgery could be considered inappropriate and hence be avoided.

Conditioned food aversion in Suncus murinus (house musk shrew) - a new model for the study of nausea in a species with an emetic reflex

The lack of a small animal model with an emetic reflex in which the relationship between conditioned food aversion and emesis could be investigated prompted a study of the insectivore, Suncus murinus (the house musk shrew). A novel food (either tuna or chicken cat food) was paired (C+) with a single exposure to either nicotine (4 mg/kg sc), motion (1 Hz, 4 cm, 10 min) or lithium chloride (100 mg/kg ip) or was paired (C-) with either saline or sham exposure to motion. Nicotine and motion both induced emesis (retching/vomiting) but lithium chloride did not. All three treatments produced a conditioned food aversion after a single pairing with consumption of C+ food. When given a choice between the two foods, S. murinus given lithium chloride, motion exposure and nicotine consumed, respectively, only 25%, 23% and 1% of their total intake from the C+ food. This study shows that a conditioned food aversion can be readily induced in S. murinus and that the induction of emesis can be uncoupled from food aversion. S. murinus provides a promising new model in which the relationship between emesis, nausea and conditioned food aversion can be investigated.

Cardiorespiratory reflexes in a working heart-brainstem preparation of the house musk shrew, Suncus murinus

In this study, we adapted the working heart-brainstem preparation (WHBP) from rodents to the Insectivore, Suncus murinus. Suncus WHBPs had a baseline heart rate of 333 +/- 8 beats min(-1), a perfusion pressure of 69 +/- 2 mm Hg and a respiratory cycle length of 6.5 +/- 0.7 s. Administration of atropine produced an increase in heart rate of 26 +/- 9 beats min(-1) indicative of the presence of cardiac vagal tone. Activation of baroreceptors produced pressure-dependent reflex falls in heart rate and reduced respiratory cycle length. The baroreceptor reflex sensitivity in Suncus WHBP was a decrease in heart rate of 8.1 +/- 1.4 beats min(-1) mm Hg(-1). Activation of peripheral chemoreceptors with aortic injections of sodium cyanide (0.1-12.5 microg) produced a dose-dependent reflex fall in heart rate and reduced respiratory cycle length. The reflex falls in heart rate evoked by baroreceptor and peripheral chemoreceptor stimulation were both atropine-sensitive. We conclude that viable WHBP can be prepared from Suncus and that Suncus WHBP is a novel non-rodent model in which to study brainstem-mediated reflexes.

The emetic and anti-emetic effects of the capsaicin analogue resiniferatoxin in Suncus murinus, the house musk shrew

1. In SUNCUS: murinus the ultrapotent capsaicin analogue resiniferatoxin (RTX) induced an emetic response in the dose range 1 - 1000 microg kg(-1), s.c. The latency was inversely related to dose and ranged from 41.2+/-4.4 min. (1 microg kg(-1), s.c.) to 2.7+/-0.6 min. (1000 microg kg(-1), s.c.). 2. The emetic response to RTX (10 or 100 microg kg(-1), s.c.) was blocked or markedly reduced by pre-treatment with RTX (100 microg kg(-1), s.c.), 8-OH-DPAT (100 microg kg(-1), s.c.), morphine (2 mg kg(-1), s.c.), neonatal capsaicin (100 mg kg(-1), s.c.) and the NK(1) receptor antagonist CP-99,994 (10 - 20 mg kg(-1), s.c.) but not by the 5-HT(3) receptor antagonist tropisetron (200 microg kg(-1), s.c.). 3. RTX (100 microg kg(-1), s.c.) induced c-fos-like immunoreactivity in the area postrema and parts of the nucleus tractus solitarius. This pattern is consistent with the proposal that the emetic effect is mediated via one or both of these structures and an involvement of substance P is discussed. 4. RTX (10 and 100 microg kg(-1), s.c.) had broad-spectrum antiemetic effects in Suncus as indicated by its ability to block or markedly reduce the emetic response to motion (1 Hz, 4 cm lateral, 10 min.), cisplatin (20 mg kg(-1), i.p.), intragastric copper sulphate (40 mg kg(-1), p.o.), nicotine (10 mg kg(-1), s.c.) and RTX (100 microg kg(-1), s.c.) itself. 5. It is proposed that the site of the anti-emetic effect is in the nucleus tractus solitarius and mechanisms involving the modulation of substance P release are discussed. 6. The general utility of SUNCUS: for investigations of vanilloid receptors is reviewed in the light of the exquisite sensitivity of the emetic reflex in this species to resiniferatoxin.

The emetic reflex in a reptile (Crocodylus porosus)

The emetic (vomiting) reflex in a crocodilian, Crocodylus porosus, was characterised for the first time using the plant alkaloid veratrine (5 mg kg(−)(1) i.v. or i.p.) as an emetic stimulus. The latency to the onset of vomiting was 8.0+/−0.9 min (mean +/− s.e.m., N=5 animals). Vomiting was preceded by a clearly defined set of prodromal behaviours including, in temporal sequence, rhythmic contraction of the pharynx, sneezing and jaw snapping. Expulsion of vomitus was not particularly forceful and was accompanied by lateral shaking of the head. Physiological studies revealed that vomiting was accompanied by oscillatory (9.1+/−0.7 oscillations over 29.7+/−3. 6 s, N=9 episodes in three animals) increases in intraperitoneal pressure (7.0+/−0.9 kPa, cf. 0.7+/−0.1 kPa during respiration). The significance of these results is discussed in the context of the role(s) of vomiting as a protective reflex and as a mechanism for removal of indigestible food residues (e.g. fur, claws) from the gut.

The effects of cyclophosphamide on neurotransmission in the urinary bladder of Suncus murinus, the house musk shrew

This study has shown that cyclophosphamide treatment of the insectivore Suncus murinus, causes a down regulation in both muscarinic and P2X receptors, together with a reduced responsiveness to exogenous histamine (0.3 mM) in the urinary bladder. Electrical field stimulation (70 V, 0.3 ms, 0.5-16 Hz, 10 s every 5 min) of bladders from both control and cyclophosphamide-treated animals showed identical responses. Since post-junctional alterations have been revealed by the reduced responsiveness to exogenous carbachol (0.1 microM-3 mM) and beta,gamma-methylene ATP (0.3-300 microM), it would appear that in the bladders of cyclophosphamide-treated animals there is also a pre-junctional effect, increased transmitter release compensating for the down regulation of the receptors. As the pattern of neurotransmission of the bladder of suncus more closely resembles that of human detrusor than other commonly studied laboratory animals, this insectivore appears to be a useful animal model for the study of bladder neurotransmission in pathophysiological conditions.

Vagal changes following cancer chemotherapy: implications for the development of nausea

Many physiological changes that occur contemporaneously with nausea are mediated by the autonomic nervous system, but the specific autonomic changes associated with nausea have not been characterized. Cardiac parasympathetic (vagal) activity as indicated by heart rate variability, measured as the standard deviation of successive differences (SDSD) in beat-to-beat intervals, was assessed in 24 women with ovarian cancer immediately prior to and accompanying nausea that occurred following anticancer chemotherapy. A progressive increase in SDSD followed infusion of the chemotherapy agent, indicating a rise in cardiac parasympathetic (vagal) activity, with onset of nausea consistently occurring after the peak activity had been reached, at a time when SDSD was decreasing. An increase in parasympathetic activity seems to set the stage for the expression of nausea but an additional stimulus is apparently needed to finally trigger the event.

Induction of emetic, pyrexic, and behavioral effects of Staphylococcus aureus enterotoxin B in the ferret

Ferrets which had been orally dosed with 5 mg of Staphylococcal enterotoxin B (SEB) responded with an increase in subcutaneous temperature. At 75 min, the subcutaneous temperature was significantly higher (+ 0.9 degrees C +/- 0.38 degrees C, P < 0.007) than in control animals. Animals dosed with 1 or 2 mg of SEB responded with a small, but not significant, increase in subcutaneous temperature. All of the animals dosed with 5 mg of SEB retched and vomited. The mean latency for the onset of retching was 105 +/- 36 min, and the mean latency for the onset of vomiting was 106 +/- 34 min. The mean number of retches was 17.8 +/- 19.6, and the mean number of vomits was 2.0 +/- 1.5. These findings indicate that ferrets can be used as alternatives to primates for the study of the biological activities of SEB.

Nissen-type fundoplication and its effects on the emetic reflex and gastric motility in the ferret

Recurrent vomiting with failure to thrive is a common problem in neurologically impaired children. Many undergo fundoplication to control the underlying gastro-oesophageal reflux. The results of surgery are not always satisfactory and post-operative retching may be a major problem - a symptom indicative of activation of the emetic reflex. An animal model of antireflux surgery has been developed and used to investigate the effects of such surgery upon the emetic reflex and vagal influences on gastric motility. Following surgery, animals responded to a previously subemetic dose of a centrally acting opiate receptor agonist (loperamide), suggesting that fundoplication may sensitize the emetic reflex. A gastric vago-vagal reflex (tonic inhibition of corpus tone) and responses to direct stimulation of vagal motor efferents (both cholinergic and nonadrenergic noncholinergic responses) were not significantly affected by antireflux surgery. Mechanisms by which neural damage may sensitize the emetic reflex are discussed, together with the possible clinical implications for the management of post-operative symptoms in neurologically impaired children.

The effect of the NK1 receptor antagonist CP-99,994 on emesis and c-fos protein induction by loperamide in the ferret

The site of the anti-emetic action of the neurokinin1 receptor antagonist CP-99,994 was studied in the ferret using the centrally acting opiate receptor agonist loperamide at a dose (0.5 mg/kg s.c.) which induced emesis in all animals tested. CP-99,994 (1 mg/kg, s.c.x2) abolished the emetic response (retching and vomiting) and the behaviours (licking, wet dog shakes, mouth scratching and gagging) induced by loperamide over a 2-h observation period. The enantiomer of this compound CP-100,263 (1 mg/kg, s.c.x2) did not have any significant effect on emesis or related behaviours. Loperamide (0.5 mg/kg s.c.) administration (but not its vehicle) resulted in dense fos-like immunoreactivity (FLI) mainly throughout the rostro-caudal extent of the nucleus tractus solitarius but not the area postrema. Although CP-99,994 (1 mg/kgx2) abolished the loperamide-induced emesis, it did not have any statistically significant effect on FLI in the brainstem. In loperamide and CP-100,263 (1 mg/kg, s.c.x2) treated animals FLI was comparable to that in animals treated with loperamide and CP-99,994. The results from this study taken together with those from previous studies indicate that loperamide exerts its emetic effect via nucleus tractus solitarius dendrites projecting into the area postrema. The lack of significant effect of CP-99,994 on the FLI induced by loperamide in this nucleus suggests that it is acting at a site "deep" in the nucleus tractus solitarius or elsewhere. The marked reduction in behaviours associated with loperamide administration by CP-99,994 provides a preliminary indication that NK1 receptor antagonist (as represented by CP-99,994) may in the clinic have effects on behaviours induced by emetic agents in addition to their previously described effects on retching and vomiting.

Fundamentals of neurogastroenterology

Current concepts and basic principles of neurogastroenterology in relation to functional gastrointestinal disorders are reviewed. Neurogastroenterology is emphasized as a new and advancing subspecialty of clinical gastroenterology and digestive science. As such, it embraces the investigative sciences dealing with functions, malfunctions, and malformations in the brain and spinal cord, and the sympathetic, parasympathetic and enteric divisions of the autonomic innervation of the digestive tract. Somatomotor systems are included insofar as pharyngeal phases of swallowing and pelvic floor involvement in defecation, continence, and pelvic pain are concerned. Inclusion of basic physiology of smooth muscle, mucosal epithelium, and the enteric immune system in the neurogastroenterologic domain relates to requirements for compatibility with neural control mechanisms. Psychologic and psychiatric relations to functional gastrointestinal disorders are included because they are significant components of neurogastroenterology, especially in relation to projections of discomfort and pain to the digestive tract.

Cyclic vomiting syndrome: timing, targets, and treatment--a basic science perspective

Nausea and vomiting are both elements of the system that evolved to defend the body against toxins accidentally ingested with the food. When they are induced by an ingested toxin, they are considered to be an appropriate response, but in many clinical settings (eg, anticancer chemotherapy, anesthesia and surgery, raised intracranial pressure) both responses are inappropriate in that the vomiting does not remove the cause and the nausea may lead to aversion to further treatment. Cyclic vomiting syndrome (CVS) is a particularly intense and prolonged example of inappropriate activation of this protective reflex. This review argues that insights into the pattern of emesis in CVS can be gained by examining the basic unit (quantum) of emesis, the emetic episode usually comprising retches followed by a vomit. Two (of several) possible mechanisms for the induction of the intense vomiting in CVS are discussed: (1) defects in intrinsic pathways (eg, opioid neurons) that may modulate the brain-stem emetic mechanisms, and (2) defects in the regulation of cellular mechanisms (eg, cAMP, ion channels) in cells at critical locations in the emetic pathway (eg, nucleus tractus solitarius, area postrema). If it is not possible to identify the causal mechanism of CVS, then will it be possible to treat CVS? This question is discussed in the context of the identification of universal or broad-spectrum antiemetic agents with recent preclinical studies with neurokinin-1 receptor antagonists reviewed to illustrate that such an approach is feasible.

Nissen fundoplication may induce gastric myoelectrical disturbance in children

BACKGROUND

Recurrent vomiting with failure to thrive is a common problem in neurologically impaired children. Many undergo fundoplication to control the underlying gastroesophageal reflux, but the results of surgery are not always satisfactory, and postoperative retching may be a major problem. Retching is part of the emetic reflex and is associated with nausea, which is itself associated with disturbed gastric electrical control activity, resulting in a gastric dysrhythmia.

METHODS

By recording gastric electrical control activity before and after Nissen fundoplication using the noninvasive technique of surface electrogastrography, the authors have shown that (1) Neurologically impaired children with gastroesophageal reflux more commonly have a preexisting gastric dysrhythmia (65% neurologically impaired v 20% neurologically normal children with gastroesophageal reflux, P<.05), (2) Children who retch preoperatively are three times more likely to retch postoperatively, and (3) 25% of neurologically impaired children may start to retch postoperatively for the first time.

CONCLUSION

The authors propose that in neurologically impaired children, loss of central inhibitory mechanisms may result in inappropriate activation of the emetic reflex, which may be heightened by antireflux surgery.

Neuropharmacology of emesis and its relevance to anti-emetic therapy. Consensus and controversies

Recent great advances in the neuropharmacology of the emetic pathways have led to better therapy and improved insight into pathophysiological processes in patients undergoing chemo- and radiotherapy. This article gives an overview of the area, outlines current controversies and makes recommendations for future clinical studies.

Neuromuscular transmission and innervation in the urinary bladder of the insectivore Suncus murinus

In isolated preparations of the urinary bladder detrusor of the house musk shrew Suncus murinus (order: insectivora; family: Soricidae), electrical field stimulation (0.5-32 pulses/s) evoked neurogenic contractile responses that were markedly attenuated by atropine (1 microM). The non-cholinergic component was reduced but not abolished by the P2-purinoceptor antagonist, suramin (300 microM). Thus, neuromuscular transmission in the suncus urinary bladder is effected by cholinergic and purinergic nerves together with an as-yet unidentified component. Using immunohistochemical methods, the suncus urinary bladder was seen to be supplied by nerves containing neuropeptide Y, tyrosine hydroxylase, vasoactive intestinal polypeptide, galanin, substance P, calcitonin gene-related peptide and type I nitric oxide synthase. The pattern of responses to electrical field stimulation was more similar to that of humans and Old World primates, than to that of rodents or lagomorphs. The pattern of innervation of the bladder wall, in terms of the distribution of populations containing a given neuropeptide, was very similar to that in humans. Hence, Suncus murinus may provide a novel species for modelling the neuropharmacology of the human bladder, and also for studying the evolution of autonomic innervation.

Cyclophosphamide increases 5-hydroxytryptamine release from the isolated ileum of the rat

We recently reported that chronic administration of cyclophosphamide significantly increased urinary 5-hydroxyindole acetic acid (5-HIAA) excretion in rats indicative of a release of 5-hydroxytryptamine (5-HT) from intestinal enterochromaffin (EC) cells. Cyclophosphamide is considered to be an inactive prodrug and require conversion to active emetic metabolities (e.g. phosphoramide mustard) by hepatic metabolism. However the presence of cytochrome P450 in the intestine raises the possibility of cyclophosphamide metabolism in the wall of the intestine, a site which would have considerable significance for 5-HT release and the emetic effects of cyclophosphamide. The aim of this study was to investigate whether cyclophosphamide could induce the release of 5-HT from the isolated ileum and to examine its mechanism of action. Cyclophosphamide (10(-6)M and 10(-7)M) induced a concentration dependent increase of 5-HT from rat isolated ileum. This cyclophosphamide-induced 5-HT release was significantly reduced by granisetron (10(-6)M and 10(-7)M) or atropine (10(-7)M and 10(-6)M). Tetrodotoxin (10(-6)M completely inhibited the increased 5-HT release induced by cyclophosphamide. These results suggest that cyclophosphamide has the capacity to induce 5-HT release via activation of enteric cholinergic neurons. In addition the in vitro study demonstrate for the first time that cyclophosphamide may be activated to emetic metabolites at extra-hepatic sites (e.g. intestine) and that conversion at these sites could contribute to the mechanism of cyclophosphamide induced emesis.

An electrophysiological investigation of the effects of cisplatin and the protective actions of dexamethasone on cultured dorsal root ganglion neurones from neonatal rats

In this study we have investigated the acute and chronic effects of cisplatin on whole cell currents in cultured dorsal root ganglion neurones. Consistent with effects on action potentials measured under current clamp, acute (5 min) application of cisplatin (5 microM) attenuated voltage-activated potassium, and mixed cation currents by approximately 50% in both cases. Chronic treatment (5-7 days) of cultured neurones with 5 microM cisplatin also resulted in greatly reduced voltage-activated potassium currents (by 50%) and calcium currents (by 60%) compared to events recorded from neurones not treated with cisplatin. In contrast, the amplitude of inward cation current activated by hyperpolarization was doubled by 5-12 days treatment with cisplatin. Studies on action potential after-depolarizations and calcium-activated chloride currents suggest that cisplatin disturbs calcium homeostatic mechanisms. These observations may account for anode break spike excitation and the low efficiency with which cells buffer intracellular calcium following cisplatin treatment. Dexamethasone has been found to enhance the anti-emetic effects of 5-HT3 receptor antagonists in patients treated with cisplatin. For this reason the actions of dexamethasone were studied in combination with cisplatin treatment. Although acute application of dexamethasone (1-10 microM) produced transient depolarizations and bursts of action potentials, after 5 minutes application it had no effect on membrane potential, input resistance, or the properties of action potentials evoked by depolarizing current commands.(ABSTRACT TRUNCATED AT 250 WORDS)

Cisplatin acutely reduces 5-hydroxytryptamine-induced vagal depolarization in the rat: protective action of dexamethasone

The effect of the anti-cancer cytotoxic drug cisplatin on KCl and 5-hydroxytryptamine (5-HT)-induced depolarization in the rat isolated cervical vagus nerve was investigated using the 'grease gap' extracellular recording technique. KCl (10 mM) perfused onto the isolated nerve previously incubated for 2 h in 10 microM cisplatin initiated a d.c. potential of 1.06 +/- 0.09 mV compared to a potential of 1.29 +/- 0.13 mV in control nerves. Perfusion with 5 microM 5-HT produced a markedly reduced depolarization (0.23 +/- 0.02 mV) in cisplatin-treated nerves compared with control nerves (0.42 +/- 0.04 mV, P = 0.005). This effect was enhanced when 5-HT was reapplied 30 min later (0.19 +/- 0.02 mV in cisplatin-treated compared with 0.42 +/- 0.03 mV in controls, P < 0.0001). The inhibitory effect of cisplatin on 5-HT-induced depolarization was found to be significantly (P = 0.004) reduced by the addition of dexamethasone (10 microM) to the incubation buffer (0.34 +/- 0.04 mV). These results are discussed in the light of the emetic and neurotoxic effects of cisplatin and the protective effects of dexamethasone.

The anti-emetic effects of CP-99,994 in the ferret and the dog: role of the NK1 receptor

1. The selective NK1 receptor antagonist, CP-99,994, produced dose-related (0.1-1.0 mg kg-1, s.c.) inhibition of vomiting and retching in ferrets challenged with central (loperamide and apomorphine), peripheral (CuSO4) and mixed central and peripheral (ipecac, cisplatin) emetic stimuli. 2. Parallel studies with the enantiomer, CP-100,263 (1 mg kg-1, s.c.), which is > 1,000 fold less potent as a NK1 antagonist, indicated that it was without significant effect against CuSO4, loperamide, cisplatin and apomorphine-induced emesis. Against ipecac, it inhibited both retching and vomiting, expressing approximately 1/10th the potency of CP-99,994. 3. The 5-HT3 receptor antagonist, tropisetron (1 mg kg-1, s.c.) inhibited retching and vomiting to cisplatin and ipecac, but not CuSO4 or loperamide. 4. CP-99,994 (1 mg kg-1, i.v.) blocked retching induced by electrical stimulation of the ventral abdominal vagus without affecting the cardiovascular response, the apnoeic response to central vagal stimulation or the guarding and hypertensive response to stimulation of the greater splanchnic nerves. CP-99,994 (1 mg kg-1, i.v.) did not alter baseline cardiovascular and respiratory parameters and it failed to block the characteristic heart rate, blood pressure and respiratory rate/depth changes in response to i.v. 2-methyl-5-HT challenge (von Bezold-Jarisch reflex). 5. Using in vitro autoradiography, [3H]-substance P was shown to bind to several regions of the ferret brainstem with the density of binding in the nucleus tractus solitarius being much greater than in the area postrema. This binding was displaced by CP-99,994 in a concentration-related manner. 6. In dogs, CP-99,994 (40 micrograms kg-1 bolus and 300 micrograms kg-1 h-1, i.v.) produced statistically significant reductions in vomiting to CuSO4 and apomorphine as well as retching to CuSO4. 7. Together, these studies support the hypothesis that the NK1 receptor antagonist properties of CP-99,994 are responsible for its broad spectrum anti-emetic effects. They also suggest that CP-99,994 acts within the brainstem, most probably within the nucleus tractus solitarius although the involvement of the area postrema could not be excluded.

Thermoregulatory effects of resiniferatoxin in the rat

When administered acutely, the vanilloid (capsaicin) receptor agonist resiniferatoxin induces marked hypothermia in the ferret, rat and mouse. The aim of this study was to further characterise the thermoregulatory effects of resiniferatoxin in the rat in an attempt to understand the mechanism by which resiniferatoxin induces this hypothermic effect. Three doses of resiniferatoxin were administered (50, 100, 200 micrograms/kg s.c.) in separate animals at an ambient temperature (Ta) of 20 degrees C but there was no apparent dose-related effect on the decrease in colonic temperature over this range. Resiniferatoxin (50 micrograms/kg s.c.) decreased whole body oxygen consumption when measured below thermoneutrality (Ta = 20 degrees C) but not at thermoneutrality (Ta = 29 degrees C); likewise there was no hypothermic response to resiniferatoxin when measured at a Ta of 29 degrees C. Operant responding for radiant heat in a cold environment (-8 degrees C) was also measured in resiniferatoxin-treated (50 micrograms/kg s.c.) rats. These experiments showed that resiniferatoxin-treated rats attempted to defend body temperature by lever pressing for more radiant heat. However, this was not sufficient to reverse the hypothermia. Two repeat doses, 1 week apart, had little or no effect on colonic temperature, oxygen consumption or operant responding in the cold. Resiniferatoxin (50 micrograms/kg s.c.) also produced hypothermia (Ta = 20 degrees C) in neonatally capsaicinized adult rats. The exact site and mode of action is still under investigation, but it is postulated that resiniferatoxin activates, and then destroys or desensitizes warm thermoreceptors.

Actions of cisplatin on the electrophysiological properties of cultured dorsal root ganglion neurones from neonatal rats

In this study we have employed the whole cell patch clamp technique to investigate the effects of an anti-cancer drug cisplatin on basic electrophysiological properties of cultured dorsal root ganglion neurones from neonatal rats. The results show that within the clinical concentration range, cisplatin (0.1 to 10 microM) caused a decrease in input conductance, and complex changes in resting membrane potential in these cultured sensory neurones. The dominant effects of cisplatin on input conductance may be due to inhibition of leak conductances. Transplatin (5 microM) was significantly less effective than cisplatin at reducing input conductance which suggests a degree of stereoselectivity. Cisplatin (1 to 5 microM) transiently increased excitability of the cultured neurones as reflected by a reduction in the threshold for activation of action potentials by 8 mV. The rise time, peak amplitude and duration of action potentials were not changed by acute application of 5 microM cisplatin. Long term treatment of neurones with cisplatin (5 microM), for up to 1 week reduced the viability of the cultures, and attenuated neurone excitability, although input conductance of the cells was significantly increased to 322 +/- 49 M omega (n = 9) compared with controls of 210 +/- 20 M omega (n = 30; P < 0.05). Acute and chronic treatment of cultured neurones with cisplatin therefore produced contrasting actions.

Resinferatoxin, an ultrapotent capsaicin analogue, has anti-emetic properties in the ferret

Resinferatoxin (100 micrograms/kg, s.c.), the ultrapotent analogue of capsaicin, when given acutely blocked radiation-(200 rads) and copper sulphate (40 mg% 30 ml, p.o.)-induced emesis in ferrets and substantially decreased loperamide (0.5 mg/kg, s.c.)-induced vomiting, without significantly affecting the von Bezold-Jarisch reflex or gag reflex. It also produced a decrease in core temperature as has been reported for capsaicin. The observation that resinferatoxin reduced or blocked emesis induced by both centrally (loperamide) and peripherally (CuSO4, radiation) acting stimuli suggests a novel anti-emetic action that may provide an insight into clinically useful innovative anti-emetics. The mechanism by which resinferatoxin has its anti-emetic effect is at present unknown, although the combination of results from the present study suggest a central site of action involving modulation of release of neurotransmitter, possibly in the nucleus tractus solitarius.

Stimulation of gastrointestinal motility by cisplatin in the ferret: activation of an intrinsic cholinergic mechanism dissociated from emesis

Motility was recorded from the corpus, antrum and small intestine of the urethane anaesthetised ferret. The gastrointestinal effects of the highly emetic cytotoxic anticancer agent, cisplatin were investigated following intravenous administration (10 mg/kg i.v.). Following injection, cisplatin induced a prompt onset (< 2 min) increase in motility (tone and contraction amplitude) in all regions with a duration of < 15 min. Acute vagotomy did not abolish the effect but reduced the peak amplitude in the antrum only. Chronic subdiaphragmatic vagotomy significantly enhanced the cisplatin-induced rise in tone in the corpus, the contraction amplitude in the antrum and the duration of the response in the duodenum. The stimulatory effect of cisplatin was blocked in all regions by atropine but not naloxone or the 5-HT3 receptor antagonist ondansetron. This study reports a previously undescribed gastrointestinal motility effect of cisplatin in vivo that is temporally dissociated from emesis. It is proposed that the results provide evidence for a neuroactive effect of cisplatin on enteric cholinergic neurones.

The neuropharmacology of loperamide-induced emesis in the ferret: the role of the area postrema, vagus, opiate and 5-HT3 receptors

Loperamide, an opiate receptor agonist, commonly used in the treatment of diarrhoea, reliably induced emesis in the ferret, when given subcutaneously. The response latency was short (less than 10 min) and the emesis lasted for approx 70 min. The dose-response curve for the emetic response was "bell-shaped" and all animals responded at 0.5 mg/kg but none at 5 mg/kg (s.c.). The response was unaffected by dopamine D2 receptor antagonism (domperidone 1.0 mg/kg, s.c.) or 5-HT3 receptor antagonism (granisetron or ondansetron 1.0 mg/kg, s.c.). The onset of the response was delayed for about 60 min by naloxone or naloxone methiodide (1.0 mg/kg, s.c.) and abolished by naloxanazine (1.0 mg/kg, s.c.), reported to be relatively selective for mu receptors. The results implicate mu receptors (possibly mu 1) in the induction of emesis by loperamide and provide some support for activation of opiate receptors also having anti-emetic effects, as suggested in previous studies. The emetic response to loperamide was unaffected by abdominal vagotomy but was abolished by ablation of the area postrema, indicating that loperamide-induced emesis may be used as a test for ablation of the area postrema in studies of the emetic mechanism in the ferret.

Morphine 6-glucuronide: a metabolite of morphine with greater emetic potency than morphine in the ferret

1. The emetic potencies of morphine and its metabolite morphine 6-glucuronide have been determined in the ferret by constructing dose-response curves for mean total retches and vomits for subcutaneous doses of 0.05 mg kg-1 to 5 mg kg-1. Morphine 6-glucuronide induced retching and vomiting at lower doses than morphine and at a maximal dose induced more retching and vomiting than morphine. 2. The emesis induced by both morphine and morphine 6-glucuronide was abolished by the preadministration of naloxone (0.5 mg kg-1 s.c.). 3. The 5-HT3 receptor antagonists granisetron and ondansetron (1 mg kg-1, s.c.) failed to abolish or reduce emesis induced by either compound. 4. At a high-dose (5 mg kg-1), morphine but not morphine 6-glucuronide failed to induce emesis and abolished the emesis induced by the cytotoxic drug, cyclophosphamide (200 mg kg-1, i.p.). 5. Preliminary pharmacokinetic studies of intravenous and subcutaneous morphine and morphine 6-glucuronide revealed that morphine 6-glucuronide accounts for less than 1% of the metabolic product of morphine in the ferret. Peak plasma levels of the two compounds after their subcutaneous administration were obtained within 10 min. The metabolic profile of morphine was not dose-dependent. There was no relationship between plasma level and emetic response for either compound.

Are all 5-HT3 receptor antagonists the same?

A number of 5-HT3 receptor antagonists are currently in clinical development as antiemetics. In this paper we focus on two of these antagonists, granisetron and ondansetron, and compare their antimetic activity against cisplatin (10 mg/kg i.v.)- or whole body X-irradiation (200 rads)-induced emesis in the conscious ferret. The results presented here have been discussed in the light of the recently published literature. Our data suggest that in comparison to ondansetron, granisetron is a more potent, longer acting and pharmacologically "cleaner" compound with a more conventional dose-response profile. The possible impact of these features upon the performance of these compounds in the clinic is discussed particularly with respect to dosing regimens and clinical efficacy. Differences appear to be emerging between granisetron and ondansetron in both these respects, although a direct head-to-head clinical comparison has yet to be carried out. This would involve studies monitoring a sufficiently high number of patients receiving severely emetogenic regimes to allow real clinical differences to be detected with the appropriate statistical power.

Preliminary evidence for the involvement of the putative 5-HT4 receptor in zacopride- and copper sulphate-induced vomiting in the ferret

Previous studies of the mechanism of zacopride-induced emesis in ferrets have concluded that it is mediated predominantly by an antagonist effect on 5-HT3 receptors although the possibility of a contribution from an agonist effect at 5-HT4 receptors was not excluded. This study shows that zacopride (200 micrograms/kg p.o.)-induced emesis can be blocked by a 'high dose' (1000 micrograms/kg) of ICS205930 but not by a low dose (100 micrograms/kg) or by 'high doses' (1000 micrograms/kg) of another more selective 5-HT3 receptor antagonist granisetron. As ICS205930, at high doses, is reported to be a 5-HT4 receptor antagonist it appears likely that activation of 5HT4-receptors contributes to emesis induced by zacopride. 'High' doses of ICS205930, but not granisetron or ondansetron, can also block the vagally mediated emesis induced by oral CuSO4 suggesting that 5-HT4 receptors involved in emesis are closely associated with abdominal vagal afferents.

Adaptation of the mechanisms controlling gastric motility following chronic vagotomy in the ferret

Changes in gastric motility were studied in the urethane-anaesthetized ferret following acute or chronic (3 weeks) vagotomy. The stomach was divided into the corpus and antrum and the effects of vagotomy on tone, frequency and contraction amplitude were investigated separately in the two gastric regions. In the corpus tone is kept at low levels by vagal activation of nonadrenergic, non-cholinergic (NANC) inhibitory neurones and also tonic sympathetic inhibition of intramural cholinergic activity. Frequency of contractions is also low due to tonic inhibition of cholinergic neurones by the vagus but not the sympathetic nervous system. There appears to be little vagal involvement in contraction amplitude but there is sympathetic inhibition of this parameter again via inhibition of cholinergic neurones. In the antrum there is no vagally driven inhibition of tone but a sympathetic inhibition of cholinergic neurones tends to reduce tone in the intact animal. Frequency of contractions does not appear to be extrinsically modulated. The vagus is tonically excitatory with regard to contraction amplitude in the antrum whereas the sympathetic nervous system is inhibitory, again via inhibition of cholinergic neurones. After chronic vagotomy some adaptation appears to take place within the surviving control systems in both the corpus and the antrum. Changes in cholinergic function have been suggested previously and are corroborated in this study. In addition novel alterations in intrinsic NANC systems and the remaining sympathetic innervation have been demonstrated in both regions of the stomach which tended to reduce the effects of vagotomy and return values for the parameters measured toward those observed in intact animals. The contribution of the cholinergic, adrenergic and NANC neurotransmitter systems to the post-vagotomy motility patterns differed in the corpus and antrum.

The abdominal visceral innervation and the emetic reflex: pathways, pharmacology, and plasticity

In recent years the role of the area postrema in the emetic reflex has been predominant and the involvement of the abdominal visceral innervation has tended to be overlooked. This paper attempts to redress the balance reflex by reviewing aspects of the existing literature and complementing this with original studies from the ferret. In view of the widespread use of the ferret in studies of emesis and particularly in the characterization of the antiemetic actions of 5-HT3 receptor antagonist, the opportunity is taken to assess the suitability of this species for studies of emesis. It is concluded that the ferret is sensitive to a wide range of emetic stimuli including intragastric irritants, opiate and dopamine receptor agonists, many cytotoxic drugs, and radiation. For several stimuli it is more sensitive than other species and for radiation on the basis of its ED100 it appears to be the most sensitive of the laboratory animals studied. Using electrical stimulation of the central end of the dorsal vagal trunk in the abdomen in conscious and anaesthetized animals, the vagal afferents were shown to be capable of eliciting emesis. Using lesioning studies an involvement of the vagus in the emetic response to a number of cytotoxic drugs (e.g., cisplatinum, cyclophosphamide, mustine) and radiation was demonstrated, although the magnitude of the effect varied with the different stimuli. An attempt is made to reconcile these observations with previous studies of area postrema ablation. The problems of interpreting the effects of nerve lesions are critically discussed in light of preliminary evidence presented here that there may be a degree of plasticity in the emetic pathway following such lesions. The range of antiemetic effects of 5-HT3 receptor antagonists is reviewed and an attempt is made to identify the site(s) at which these agents act. Results are presented that suggest a link between the vagus and 5-HT3 receptor antagonism. These studies are discussed together with others and lead us to propose that (in the ferret) 5-HT3 receptor antagonists have their main antiemetic effect by acting on vagal afferent terminals in the wall of the upper gut with an additional minor site either in the nucleus tractus solitarius or presynaptically on the vagal afferent terminals in the medulla where binding sites for 5-HT3 receptor ligands have recently been demonstrated in this species.

Evidence for presynaptic 5-hydroxytryptamine3 recognition sites on vagal afferent terminals in the brainstem of the ferret

Antagonists acting at the 5-hydroxytryptamine3 receptor are potent anti-emetic agents in cases of cytotoxic- and radiation-induced vomiting, and binding sites for these compounds have been described in brainstem areas known to be involved in mediation of nausea and vomiting. We have used autoradiography to examine the distribution of one of these antagonists, [3H]granisetron in the caudal brainstem of the ferret, a commonly used animal model for physiological investigations of emesis. The highest density of binding sites was found to be in the dorsomedial region of the nucleus of the solitary tract, the principal terminus for gastric vagal afferent fibres. Lower levels of binding were observed in the area postrema and the dorsal motor nucleus of the vagus. Following unilateral nodose ganglion excision, displaceable binding of [3H]granisetron in the nucleus of the solitary tract was attenuated on the ipsilateral side by 65%. Bilateral subdiaphragmatic vagotomy abolished binding of [3H]granisetron in the entire dorsal vagal complex. These results provide strong circumstantial evidence that 5-hydroxytryptamine3 receptors are located on vagal afferent terminals in the ferret brainstem.

Differential release of vasopressin and oxytocin in response to abdominal vagal afferent stimulation or apomorphine in the ferret

The aim of this study was to investigate whether direct afferent stimulation of the abdominal vagus could promote release of the neurohypophyseal hormones. The nucleus of the solitary tract is the major recipient of vagal afferent information, and this region of the brainstem may also be activated by stimulation of the area postrema. For this reason apomorphine, a D2 dopaminergic agonist which acts on the area postrema, and can evoke vasopressin secretion in man, was also investigated for its effect on vasopressin and oxytocin release. Our results show that vasopressin, but not oxytocin is released in vast amounts in response to electrical afferent stimulation of the abdominal vagus. Administration of apomorphine also evoked a massive vasopressin release with less marked effects on oxytocin. The possible functional implications of these results are discussed especially in the context of nausea and vomiting.

Vagally mediated gastric motor and emetic reflexes evoked by stimulation of the antral mucosa in anaesthetized ferrets

1. In the urethane-anaesthetized ferret chemical (NaCl, NaOH or HCl) or mechanical (stroking) stimulation of the gastric antral mucosa evoked a decrease in corpus pressure and inhibition of contractions in the presence of guanethidine, adrenalectomy and sectioned greater splanchnic nerves. 2. The fall in corpus pressure was present following administration of atropine but was abolished by vagotomy. 3. Preliminary evidence, using 100 mM-NaOH as the stimulus, is presented that the effects on corpus motility are due to simultaneous activation of the vagal efferents supplying the intramural non-adrenergic non-cholinergic inhibitory neurones and inhibition of those supplying the intramural cholinergic neurones. 4. The possible roles of this antro-corpus vago-vagal reflex in the regulation of gastric emptying and in the prodromal phase of vomiting are discussed.

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.

The role of the abdominal visceral innervation and 5-hydroxytryptamine M-receptors in vomiting induced by the cytotoxic drugs cyclophosphamide and cis-platin in the ferret

We have used the ferret as an animal model to investigate the emetic action of the cytotoxic drugs cyclophosphamide and cis-platin. Using selective nerve lesions, a crucial role for the abdominal innervation in the genesis of retching and vomiting in response to these agents has been demonstrated. A combination of bilateral abdominal vagotomy and greater splanchnic nerve section can totally abolish retching and vomiting in response to intraperitoneal cis-platin or intravenous cyclophosphamide. Intraperitoneal cyclophosphamide still produced retching but vomiting was markedly reduced, demonstrating complex and probably separate control mechanisms for retching and vomiting. The effect of a widely used anti-emetic, metoclopramide, was compared to that of nerve lesions. While effective this compound did not totally control retching or vomiting to either drug. Recent studies have attributed metoclopramide's action to its ability to antagonize 5-HT M-receptors (5-HT-3 receptors). Therefore we investigated BRL 24924, a gastro-kinetic agent with more specific 5-HT M-receptor antagonist properties. This agent was extremely potent in almost totally abolishing retching and vomiting in response to cyclophosphamide, given by either an intravenous or intraperitoneal route, and totally abolished cis-platin-induced vomiting for at least 4 h. Clearly the abdominal visceral innervation plays a complex and major role in the emesis produced by these two cytotoxic drugs; circumstantial evidence suggests that 5-HT M-receptors on visceral afferent nerves mediate this action, but other possibly central sites of action of the 5-HT M-receptor antagonists cannot be excluded.

The effect of peptides on the motility of the stomach, intestine and rectum in the skate (Raja)

1. Pentagastrin (10(-8)-2 X 10(-6) M) was found to increase motor activity in the cardiac stomach and spiral intestine but only occasionally in the pyloric stomach and not at all in the rectum. 2. Substance P increased motor activity in both parts of the stomach and the rectum (10(-8)-5 X 10(-7) M) but had only a slight effect on the spiral intestine. 3. No effect on the activity of any part of the gut was seen with VIP (10(-7) M), neurotensin (2 X 10(-6) M) or bradykinin (2 X 10(-5) M). 4. The responses to pentagastrin or substance P were not abolished by TTX (10(-6) M). 5. The implications of these results for the understanding of the control of gut motility in elasmobranchs is discussed.

Antiemetic properties of the 5HT3-receptor antagonist, GR38032F

GR38032F is a highly selective 5HT3-receptor antagonist which inhibits vomiting induced by cisplatin, cyclophosphamide or X-radiation in the ferret. Since cisplatin selectively increased the levels of 5HT and 5HIAA in the intestinal mucosa, a possible site of the antiemetic action of GR38032F may be on 5HT3-receptors on vagal afferents in the small intestine. The potent antiemetic action of GR38032F should be of clinical value in reducing the nausea and vomiting associated with radiotherapy or chemotherapy of cancer.

Variation of the ferret skull (Mustela putorius furo L.) in relation to stereotaxic landmarks

The ferret skull was investigated to identify reliable extracranial landmarks for stereotaxy. The skulls of 56 ferrets of both sexes were measured in a stereotaxic apparatus. Neither body weight nor an index of skull length proved to be reliable predictors of intracranial location. Sutures fused too early in life for lambda and bregma to be useful as landmarks in adult ferrets. The position of extracranial features was used to predict the position of intracranial features. For rostral intracranial features, the supraorbital processes were found to be the best predictors. Although the occipital crest was not the best predictor for posterior structures, it was the most practical. Using these landmarks, the prediction of intracranial location could be improved by more than 30%. Sexual dimorphism was found for all features examined except those nearest the interaural line. Female skulls were significantly smaller than male skulls and had less prominent sagittal and occipital crests. Males showed a substantial variation in the structures surrounding the pituitary gland. Fitches were also found to differ from albinos in having a more marked development of the sagittal crest.

Evidence for an extra-abdominal site of action for the 5-HT3 receptor antagonist BRL24924 in the inhibition of radiation-evoked emesis in the ferret

Recent studies have implicated 5-HT3(5-HT-M) receptors in the genesis of retching and vomiting evoked by antineoplastic agents. Such receptors have so far only been located peripherally, notably on the vagus. Therefore, the effects of bilateral abdominal vagotomy and antagonism of 5-HT3 receptors have been investigated on retching and vomiting induced by radiation. The gastrokinetic substituted benzamide BRL24924, (Beecham Pharmaceuticals) which has 5-HT3 receptor antagonist properties, was used. Using the ferret, it was shown that whole body x-radiation produced retching and vomiting, which was most severe during the 30 min following irradiation, and continued for at least 90 min. Abdominal vagotomy almost totally abolished the retching and vomiting, occurring during the 30 min immediately after irradiation. The following 60 min period was similar to that of control animals. This would suggest that the emetic events can be divided into a vagally-dependent and independent phase. In a small dose, BRL 24924 mimicked abdominal vagtotomy, in a larger dose, it almost totally abolished the retching and vomiting throughout the entire 90 min period. These results suggest that 5-HT3 receptor antagonists are capable of ameliorating radiation-induced retching and vomiting and that, while an important site of their action could be the abdominal vagi, other areas are probably also involved.

Injection of baclofen into the ventromedial hypothalamus stimulates gastric motility in the rat

Injection of 2 micrograms (+/-)-baclofen into the ventromedial hypothalamus (VMH) of urethane-anaesthetized rats resulted in an increase in gastric tone and amplitude of contractions. This effect was curtailed by administration of atropine methyl nitrate (20 mg/kg i.p.) or bilateral cervical vagotomy. These results provide evidence for a hypothalamic modulation of gastric motility by the vagus. Baclofen, possibly acting on receptors insensitive to gamma-aminobutyric acid (GABA), may be mimicking a vagal activation system, located within the ventro-medial hypothalamus.