The significance of chloride in the inhibitory action of disodium cromoglycate on immunologically-stimulated rat peritoneal mast cells.

BACKGROUND: The microelectrode array (MEA) was used to investigate the pharmacological relevance of chloride (Cl-) ions in antigen-dependent mast cell activation and the inhibitory effect of disodium cromoglycate (DSCG) on mast cell activation. METHODS: The movements of ions across the cellular membrane and the potential relationship between Cl- channels and DSCG during immunological activation were investigated using the MEA. The results were then subsequently compared with the amount of histamine released from anti-IgE activated peritoneal mast cells. RESULTS: The inclusion of charybdotoxin (ChTX) in Cl--free buffer showed that the measured field potentials during antigen-stimulated peritoneal mast cell were a combination of Cl- influx and K+ efflux. The delayed onset time of Cl- influx indicated the presence of a delayed outwardly-rectifying Cl- current in the antigen-stimulated peritoneal mast cells. The use of 5-nitro-2-(3-phenylpropylamino) benzoic acid demonstrated that the activated mast cell membrane potential can be stabilised, thereby reducing the amount of histamine released from the anti-IgE activated mast cells. The correlation between the results of the histamine release assay and the electrophysiological measurements demonstrated the importance of Cl- to anti-IgE dependent mast cell activation. The inhibitory effect of DSCG on anti-IgE activated cells, however, did not correlate with the presumed influx of Cl-. CONCLUSIONS: The MEA data suggest that Cl- influx is crucial to IgE-dependent mast cell degranulation. GENERAL SIGNIFICANCE: While the MEA cannot yield information about single channel properties, it is convenient to use and can provide information on the global changes in electrophysiological responses of non-excitable cells.

The use of microelectrode array (MEA) to study the protective effects of potassium channel openers on metabolically compromised HL-1 cardiomyocytes.

The microelectrode array (MEA) was used to evaluate the cardioprotective effects of adenosine triphosphate sensitive potassium (K(ATP)) channel activation using potassium channel openers (KCOs) on HL-1 cardiomyocytes subjected to acute chemically induced metabolic inhibition. Beat frequency and extracellular action potential (exAP) amplitude were measured in the presence of metabolic inhibitors (sodium azide (NaN(3)) or 2-deoxyglucose (2-DG)) or KCOs (pinacidil (PIN, a cyanoguanidine derivative, activates sarcolemmal K(ATP) channels) or SDZ PCO400 (SDZ, a benzopyran derivative, activates mitochondrial K(ATP) channels)). The protective effects of these KCOs on metabolically inhibited HL-1 cells were subsequently investigated. Signal shapes indicated that NaN(3) and 2-DG reduced the rate of the sodium (Na(+)) influx signal as reflected by a reduction in beat frequency. PIN and SDZ appeared to reduce both rate of depolarization and extent of the Na(+) influx signals. Pre-treating cardiomyocytes with PIN (0.1 mM), but not SDZ, prevented the reduction of beat frequency associated with NaN(3)- or 2-DG-induced metabolic inhibition. The exAP amplitude was not affected by either KCO. The cardioprotective effect of PIN relative to SDZ may be due to the opening of different K(ATP) channels. This metabolic inhibition model on the MEA may provide a stable platform for the study of cardiac pathophysiology in the future.

Effects of 5-HT3 receptor antagonists on models of acute and delayed emesis induced by cisplatin in the ferret.

The emetic profile of action of cisplatin 5 and 10 mg/kg i.p. was investigated in the ferret over a 72 and 24 hr period respectively. The 5-HT3 receptor antagonists ondansetron and alosetron markedly antagonized or abolished the emesis during the "acute phase" and, whilst antagonizing the emesis during the delayed phase, also revealed a 5-HT3 receptor antagonist resistant component. These cisplatin paradigms may provide models relevant to the study of acute and delayed emesis induced by cisplatin in man.

The interaction of dexamethasone with ondansetron on drug-induced emesis in the ferret.

The potential of dexamethasone (0.5-20 mg/kg i.p.) to antagonize the emesis induced by cisplatin (10 mg/kg i.v.), apomorphine (0.25 mg/kg s.c.), morphine (0.5 mg/kg s.c.) and copper sulphate (100 mg/kg intragastric) was investigated alone and in combination with ondansetron in the ferret. There was a trend for dexamethasone 0.1-5 mg/kg to reduce cisplatin-induced emesis and for 0.05-2.5 mg/kg to delay the onset of apomorphine-induced emesis but doses of dexamethasone up to 20 mg/kg were without effect to modify morphine- or copper sulphate-induced emesis. The combination of dexamethasone 2.5 mg/kg with ondansetron 0.1 mg/kg did not have additive effects to reduce cisplatin-induced emesis but did reduce significantly the total numbers of episodes recorded. Ondansetron 1 mg/kg was without effect to modify apomorphine-, morphine- or copper sulphate-induced emesis but the combination pretreatment of ondansetron 1 mg/kg with dexamethasone 2.5 and 5 mg/kg reduced significantly apomorphine-induced retching. Data are discussed in terms of the antiemetic effectiveness of dexamethasone to antagonize chemotherapy-induced emesis in man.

The actions of fentanyl to inhibit drug-induced emesis.

The ability of fentanyl to inhibit drug-induced emesis was investigated in the ferret. Initial studies established that morphine, in small doses (0.025-0.5 mg/kg s.c.), induced emesis in the ferret that decreased at the larger doses of 1 and 2 mg/kg (s.c.). Fentanyl (10-80 micrograms/kg s.c.) failed to induce emesis but in this dose range prevented the emesis induced by morphine (0.5 mg/kg s.c.), apomorphine (0.25 mg/kg s.c.), copper sulphate (100 mg/kg intragastric) and cisplatin (10 mg/kg i.v.). The antiemetic effects could be obtained in the absence of sedation or motor impairment. The antagonism by fentanyl of apomorphine-, copper sulphate- and cisplatin-induced emesis was inhibited by naloxone (0.1 or 0.5 mg/kg s.c.). It is concluded that fentanyl exerts a broad spectrum of actions to inhibit drug-induced emesis. An autoradiographic study of the binding of [3H]DAGO to the brainstem of the ferret indicated high densities of mu recognition sites in the area postrema, nucleus tractus solitarius, dorsal motor nucleus of the vagus, reticular medulla and other sites. The results are discussed in terms of balanced facilitatory and inhibitory opioid systems, regulating emesis and that the antiemetic actions of fentanyl reflect an important, although not necessarily an exclusive, action at mu opioid receptors.

Fluphenazine, ICS 205-930 and dl-fenfluramine differentially antagonise drug-induced emesis in the ferret.

The intravenous injection of cisplatin (10 mg/kg), the subcutaneous injection of apomorphine (0.125-1 mg/kg) and lisuride (0.001-0.1 mg/kg), the oral administration of ipecacuanha (0.3-2.4 mg/kg) and the intragastric administration of copper sulphate (25-100 mg/kg), induced a vomiting and retching response in the ferret. Pretreatment with dl-fenfluramine (5 mg/kg i.p.) prevented or reduced the emesis induced by cisplatin, apomorphine, ipecacuanha and lisuride but failed to significantly antagonise copper sulphate-induced emesis. The 5-HT3 receptor antagonist ICS 205-930 (0.1 mg/kg i.p.) prevented emesis induced by cisplatin and ipecacuanha but failed to prevent or significantly reduce the emesis induced by apomorphine, lisuride or copper sulphate. Dopamine receptor antagonists, including fluphenazine (0.1-1.0 mg/kg i.p.) prevented apomorphine- and lisuride-induced emesis but were less potent or had inconsistent actions to antagonise cisplatin- or ipecacuanha-induced emesis and failed to inhibit the emesis induced by copper sulphate. The data indicate that dopamine and/or 5-HT3 receptor systems are involved in drug-induced emesis but that emesis caused by gastric irritation induced by copper sulphate is mediated by different receptor mechanisms.

An interaction of ondansetron and dexamethasone antagonizing cisplatin-induced acute and delayed emesis in the ferret.

1. Cisplatin, 5 mg kg-1, i.p., administered as a single treatment, induced an acute (day 1) and delayed (days 2 and 3) emetic response in the ferret that was used to investigate the potential anti-emetic activity of ondansetron and dexamethasone and their interaction over a three day period. 2. Ondansetron, 1 mg kg-1, i.p., administered three times per day in two experiments, antagonized significantly the retching and vomiting that occurred on days 1 and 2 by 60-76 and 73-84%. On the third day of treatment there was a trend for a 38% reduction in one experiment and a 74% reduction in the other. 3. There was a trend for dexamethasone, 1 mg kg-1, i.p., administered as a single daily injection for three days, to reduce by 37% the retching and vomiting response that occurred on day 1, the reduction of 77% on day 2 achieved significance and dexamethasone non-significantly increased the retching and vomiting response by 46% on day 3. However, dexamethasone 1 mg kg-1 i.p. administered three times per day for three days significantly reduced the retching + vomiting response by 85, 97 and 86% on days 1, 2 and 3 respectively. 4. The combination of dexamethasone, 1 mg kg-1, i.p., as single daily injections with ondansetron, 1 mg kg-1, i.p., administered three times per day improved the control of the retching and vomiting response, significantly reducing the total numbers of retches and vomits by more than 70% over a three day period. The combination of dexamethasone (1.0 mg kg-1) and ondansetron (1.0 mg kg-1), both administered three times daily, abolished cisplatin-induced emesis over the three day period. 5. The three times per day administration of ondansetron, 1 mg kg-1, i.p., plus dexamethasone, 1 mg kg-1, i.p., administered only on day 1 prevented day 1 emesis but did not modify the retching and vomiting that occurred on days 2 and 3. 6. The present results indicate that ondansetron and dexamethasone significantly reduce cisplatin-induced emesis in the ferret during both the acute and delayed phase; drug/co-treatment can exert an additive action to abolish cisplatin-induced emesis. The ferret model may be useful to detect anti-emetic drug action for treatment of chemotherapy-induced acute and delayed emesis in man.

The action of the NK1 tachykinin receptor antagonist, CP 99,994, in antagonizing the acute and delayed emesis induced by cisplatin in the ferret.

1. The anti-emetic effects of the NK1 tachykinin receptor antagonist, CP 99,994 (10 mg kg-1) were investigated in the ferret using a cisplatin-induced acute (day 1) and delayed (day 2 and 3) retching and vomiting model. 2. With a single cisplatin (10 mg kg-1) emetogenic challenge, the i.p. administration of CP 99,994 given as a single injection immediately following the first emetic episode, promptly abolished the retching and vomiting for a 4 h period. CP 99,994 was as efficacious as ondansetron (1.0 mg kg-1). The general toxicity of cisplatin 10 mg kg-1 precluded its use in studies of delayed emesis. 3. With a single cisplatin (5 mg kg-1) emetogenic challenge, the single administration of either CP 99,994 (10 mg kg-1) or ondansetron (1.0 mg kg-1) immediately following the first emetic episode markedly reduced or abolished the retching and vomiting for 4 h. Such single treatments failed to modify significantly the intensity of delayed emesis appearing on the second and third day. 4. With a cisplatin (5 mg kg-1) emetogenic challenge, administration of CP 99,994 (10 mg kg-1) at 8 hourly intervals, the first injection being administered 30 s post cisplatin, was associated with 4 or more abolitions of emesis during both the acute and delayed phase. A 4 hourly administration of CP 99,994 for 20 h during delayed emesis completely abolished the retching and vomiting. 5. It is concluded that cisplatin 5 mg kg-1 provides an emetogenic challenge causing an acute and delayed phase of retching and vomiting and that CP 99,994 can abolish both phases. The results may be relevant to the understanding and treatment of chemotherapy-induced emesis in man.

Non-prostanoid prostacyclin mimetics as neuronal stimulants in the rat: comparison of vagus nerve and NANC innervation of the colon.

The spontaneous activity of the rat isolated colon is suppressed by prostacyclin analogues such as cicaprost (IC(50)=4.0 nM). Activation of prostanoid IP(1)-receptors located on NANC inhibitory neurones is involved. However, several non-prostanoids, which show medium to high IP(1) agonist potency on platelet and vascular preparations, exhibit very weak inhibitory activity on the colon. The aim of the study was to investigate this discrepancy. Firstly, we have demonstrated the very high depolarizing potency of cicaprost on the rat isolated vagus nerve (EC(50)=0.23 nM). Iloprost, taprostene and carbacyclin were 7.9, 66, and 81 fold less potent than cicaprost, indicating the presence of IP(1) as opposed to IP(2)-receptors. Three non-prostanoid prostacyclin mimetics, BMY 45778, BMY 42393 and ONO-1301, although much less potent than cicaprost (195, 990 and 1660 fold respectively), behaved as full agonists on the vagus nerve. On re-investigating the rat colon, we found that BMY 45778 (0.1 - 3 microM), BMY 42393 (3 microM) and ONO-1301 (3 microM) behaved as specific IP(1) partial agonists, but their actions required 30 - 60 min to reach steady-state and only slowly reversed on washing. This profile contrasted sharply with the rapid and readily reversible contractions elicited by a related non-prostanoid ONO-AP-324, which is an EP(3)-receptor agonist. The full versus partial agonism of the non-prostanoid prostacyclin mimetics may be explained by the markedly different IP(1) agonist sensitivities of the two rat neuronal preparations. However, the slow kinetics of the non-prostanoids on the NANC system of the colon remain unexplained, and must be taken into account when characterizing neuronal IP-receptors.

Genital grooming and emesis induced by vanilloids in Suncus murinus, the house musk shrew.

The potential of resiniferatoxin and capsaicin to modulate emesis and genital grooming was investigated in Suncus murinus. Resinifertoxin (3-30 nmol, i.c.v.), E-capsaicin (10-100 nmol, i.c.v.) and Z-capsaicin (100 nmol, i.c.v.) induced emesis (P<0.05) and subsequently antagonised the emetic response induced by intragastric copper sulphate (480.6 micromol/kg; P<0.05). However, resiniferatoxin failed to affect nicotine-induced (30.7 mol/kg, s.c.) emesis (P>0.05). Only resiniferatoxin induced genital grooming that was antagonised (P<0.05) by capsazepine (300-600 nmol, i.c.v.) and ruthenium red (3 nmol, i.c.v.). E-capsaicin-induced emesis was antagonised by capsazepine (300-600 nmol, i.c.v.; P<0.05) and ruthenium red (3 nmol, i.c.v.; P<0.05) but resiniferatoxin-induced emesis was resistant to capsazepine (30-600 nmol, i.c.v.; P>0.05). The emetic action of resiniferatoxin but not E-capsaicin was subject to tachyphylaxis. In cross-tachyphylaxis experiments, E-capsaicin reduced the genital grooming induced by resiniferatoxin (P<0.05). The data are discussed in relation to the classification of vanilloid receptors and mechanisms involved in emesis and genital grooming.

The actions of ondansetron and dexamethasone to antagonise cisplatin-induced emesis in the ferret.

The ability of ondansetron and dexamethasone to antagonise cisplatin 10 mg/kg i.p. induced emesis was investigated in the ferret during a 24 h period. Ondansetron 0.5-5 mg/kg, as a single injection, effectively antagonised the response for approximately 4 h and revealed a subsequent response that was sensitive to further ondansetron treatment. The three times per day administration of dexamethasone 1 mg/kg i.p. alone or combined with ondansetron 1 mg/kg i.p. significantly reduced the vomiting response by 49 and 79%, respectively. The results are discussed in terms of their relevance to acute and delayed emesis in man.

Profiles of emetic action of cisplatin in the ferret: a potential model of acute and delayed emesis.

The emetic profile of action of cisplatin 5 and 10 mg/kg i.p. was investigated in the ferret over a 72 and 40 h period respectively. Cisplatin 10 mg/kg induced retching and vomiting which rapidly declined after the first 8 h. Cisplatin 5 mg/kg induced a less intense emetic response which declined after 16 h but reappeared at approximately 32 h to reveal a 'delayed' retching and vomiting response. The use of cisplatin 5 mg/kg may offer a regimen to model cytotoxic acute and delayed emesis.

Inhibition of emesis by tachykinin NK1 receptor antagonists in Suncus murinus (house musk shrew).

The anti-emetic potential of CP-122,721 ((+)-2S,3S)-3-(2-methoxy-5-trifluoromethoxybenzyl)amino-2-phenylpi peridine), CP-99,994 ((+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine), CP-100,263 ((-)-(2R,3R)-3-(2-methoxybenzylamino)-2-phenylpiperidine), RP 67580 ((3R, 7aR)-7,7-diphenyl-2-[1-imino-2-(2-methoxyphenyl)ethyl] po-hydroisoindol-4-one), FK 888 (N2-[(4R)-4-hydroxy-1-(1-methyl-1H-in-dole-3-yl)carbonyl-L-propyl] -N-methyl-N-phenylmethyl-1-3-(2-naphthyl)-alaninamide) and GR 82334 ([D-Pro9[spiro-g-lactam]Leu10]-physalaemin-(1-11)) was investigated to inhibit nicotine (5 mg/kg, s.c.)-, copper sulphate pentahydrate (120 mg/kg, intragastric)- and motion (4 cm horizontal displacement at 1 Hz for 5 min)-induced emesis in Suncus murinus. A 30 min intraperitoneal pre-treatment with CP-122,721, CP-99,994, RP 67580 and FK 888 significantly (P < 0.05) antagonized nicotine-induced emesis with ID50 values of 2.1, 2.3, 13.5 and 19.2 mg/kg, respectively CP-100,263, the less active enantiomer of CP-99,994, was inactive at doses up to 10 mg/kg. Infusion of GR 82334, CP-122,721, CP-99,994 and FK 888 into the dorsal vagal complex of the hindbrain also antagonized nicotine-induced emesis yielding ID50 values of 1.1, 3.0, 3.3 and 58.0 microg/dorsal vagal complex, respectively RP 67580 and CP-100,263 were inactive. RP 67580 and FK 888 failed to antagonize copper sulphate-induced emesis but CP-122,721 and CP-99,994 were active yielding ID50 values of 2.2 and 3.0 mg/kg, i.p., respectively. CP-99,994 also completely prevented motion-induced emesis at 10 mg/kg, i.p. (P < 0.05) and RP 67580 produced a significant reduction of motion-induced emesis at 10 mg/kg, i.p. (P < 0.05). These studies provide evidence of a central site of action of tachykinin NK1 receptor antagonists to inhibit nicotine-induced emesis in S. murinus and confirm the broad profile of inhibitory action. The rank order of potency of the antagonists following the intra-dorsal vagal complex administration suggests that the S. murinus tachykinin NK1 receptor has a unique pharmacological profile.

5-HT3 receptors are not involved in conditioned taste aversions induced by 5-hydroxytryptamine, ipecacuanha or cisplatin.

We have used the rat to examine the involvement of the 5-HT3 receptor in the mechanism(s) of conditioned taste aversion induced by 5-hydroxytryptamine (5-HT) and selected emetic drugs. 5-HT, ipecacuanha and cisplatin all induced conditioned taste aversion at doses known to induce emesis in other species but the responses were resistant to treatment with the 5-HT3 receptor antagonists ondansetron and granisetron. Further, m-chlorophenylbiguanide, a selective and potent 5-HT3 receptor agonist, failed to induce a conditioned taste aversion. The data provide strong evidence that the 5-HT3 receptor is not involved in conditioned taste aversion mechanisms in the rat. Results are discussed in terms of the usefulness of the rat conditioned taste aversion paradigm to anti-emetic research.

The effect of 5-HT receptor ligands on the uptake of [3H]5-hydroxytryptamine into rat cortical synaptosomes.

The effect of 5-HT receptor agonists and antagonists to inhibit [3H]5-HT uptake was investigated in rat cortical synaptosomes. The 5-HT (5-hydroxytryptamine) uptake inhibitors paroxetine and fluoxetine yielded pKi values of 8.41 +/- 0.12 and 7.43 +/- 0.06 respectively. The 5-HT3/5-HT4 receptor antagonist tropisetron and the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) had similar inhibitory potencies to cocaine (pKi values of 6.58 +/- 0.04, 6.47 +/- 0.14 and 6.45 +/- 0.12 respectively). The dopamine and noradrenaline uptake inhibitors GBR12909 and desipramine had comparable values of 6.5 +/- 0.05 and 6.13 +/- 0.07. Other 5-HT receptor ligands had pKi values less than 6.0 (R(+)-zacopride, MDL72222, R(+)/S(-)-zacopride) or 5.0 (5-methoxytryptamine, m-chlorophenylbiguanide, S(-)-zacopride, SDZ205-557, ondansetron and renzapride). It is concluded, with the possible exception of tropisetron and 8-OH-DPAT, that it is unlikely that the effects of the 5-HT receptor ligands to inhibit 5-HT uptake contribute to their effects in vivo.

Cisplatin-induced emesis in the cat: effect of granisetron and dexamethasone.

The emetic action of cisplatin was investigated in the cat using a closed circuit video recording system. In initial investigations, cisplatin 3 and 5 mg/kg, i.v. induced emesis over a 2-day period following a latency of 17.6+/-9.6 and 15.6+/-7.8 h, respectively. The anti-emetic efficacy of granisetron and dexamethasone was investigated in the cisplatin 5 mg/kg, i.v.-induced emesis model. In these experiments, cisplatin induced 47.0+/-14.0 and 20.0+/-9.0 retches+vomits on days 1 and 2, respectively, following a latency of 2.4+/-0.4 h. Granisetron (1 mg/kg, i.m.) administered three times per day reduced significantly the retching+vomiting response induced by cisplatin on days 1 and 2 by 100.0% (P<0.05) and 75.0% (P<0.05), respectively; dexamethasone (0.01-1 mg/kg, i.m.) administered three times per day reduced significantly the retching+vomiting response by 68.8-100.0% (P<0.05) and 33.3-100.0% (P<0.05) on days 1 and 2, respectively. The emetic action of cisplatin 7.5 mg/kg, i.v. was also investigated. This dose of cisplatin-induced emesis following a latency of 1.2+/-0.2 h and comprised 119.0+/-20.8 retches+vomits over a 24-h period. Granisetron and dexamethasone antagonized the emesis occurring in the first 3-h period (P<0.05) but were less effective to antagonize the subsequent emetic response (P0.05). The pharmacological sensitivity of low dose cisplatin-induced emesis in the cat is variable but unique and not representative of the clinical situation.

Action of glucocorticoids to antagonise cisplatin-induced acute and delayed emesis in the ferret.

Cisplatin 5 mg/kg, i.p. induced an acute (day 1) and delayed (days 2 and 3) emetic response in the ferret that was used to investigate the potential anti-emetic activity of several glucocorticoids. Betamethasone (0.3-3 mg/kg, i.p.) reduced the emesis occurring during the initial 0-24-h period by 71.1-99.5% (P<0.05). The action of methylprednisolone (1.0-10.0 mg/kg, i.p.) and hydrocortisone (1.0-30.0 mg/kg, i.p.) could not be assessed because the controls exhibited weak emetic responses and dexamethasone produced a non-significant 64.0% reduction at 0.3 mg/kg (P>0.05). However, all glucocorticoids dose-dependently reduced retching+vomiting during the subsequent 24-56-h period. The rank order of anti-emetic potency was betamethasone (ID(80)<0.3 mg/kg)>/=dexamethasone (ID(80)=0.32 mg/kg)>methylprednisolone (ID(80)=0.66 mg/kg)&z.Gt;hydrocortisone (ID(80)>30 mg/kg). Dexamethasone was ineffective to antagonise the retching+vomiting response during the 24-56-h period when the administration was delayed until 24 h post-cisplatin injection. None of the glucocorticoids reduced the retching+vomiting response occurring during the 56-72-h period. In conclusion, the rank order of anti-emetic potency suggests that inflammation, or mediators of inflammation, contribute to the retching+vomiting response induced by cisplatin.

Modulation of emesis by fentanyl and opioid receptor antagonists in Suncus murinus (house musk shrew).

The anti-emetic mechanism of action of fentanyl to inhibit nicotine (5 mg/kg, s.c.)-induced emesis was investigated in Suncus murinus. The anti-emetic action of fentanyl (40 microg/kg, s.c.) was antagonised by the opioid receptor antagonists naltrexone (1 mg/kg, s.c.), naloxone (1 mg/kg, s.c.), M8008 (16S-methylcyprenorphine; 1 mg/kg, s.c.) and MR 2266 (5,9-diethyl-2-(3-furylmethyl)2'-hydroxy-7,7-benzomorphan; 1 mg/kg) but not by naloxone methylbromide (1 mg/kg, s.c.), naloxone methyliodide (1 mg/kg, s.c.), naltrindole (1 mg/kg, s.c.), DIPPA (2-(3,4-dichlorophenyl)-N-methyl-N-[1S)-1-(3-isothiocyanatophenyl)-2-(1- pyrrolidinyl)-ethyl]acetamide; 3 mg/kg, i.p.) or naloxonazine (35 mg/kg, i.p.). This indicates an involvement of mu2-opioid receptors within the brain to mediate the anti-emetic effect of fentanyl. In other studies, naloxone 10-60 mg/kg, s.c. induced dose-related emesis but naltrexone was only emetic at 60 mg/kg, s.c. and naloxone methylbromide failed to induce emesis at doses up to 60 mg/kg, s.c. The emesis induced by a high dose of naloxone 60 mg/kg, s.c. was antagonized by CP-99,994 ((+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine; 3-30 mg/kg, i.p.), 8-OH-DPAT, ((+/-)-8-hydroxy-dipropylaminotetralin; 0.003-0.3 mg/kg, s.c.), buspirone (3 mg/kg, s.c.) and fluphenazine (1-3 mg/kg, i.p.) but not by naltrexone (1-30 mg/kg, s.c.), metoclopramide (0.3-3 mg/kg, i.p.), sulpiride (0.3-3 mg/kg, i.p.), domperidone (0.1-3 mg/kg, i.p.), ondansetron (0.3-3 mg/kg, i.p.), granisetron (0.3-3 mg/kg, i.p.), scopolamine (0.3-3 mg/kg, i.p.) or promethazine (0.3-3 mg/kg, i.p.). The data is discussed in relation to opioid receptor mechanisms moderating emesis and the identification of potential sites of drug action available to inhibit the emetic reflex.

Identification and distribution of 5-HT3 recognition sites within the human brainstem.

The present studies demonstrate the presence of specific [3H]GR65630 binding sites within the human brainstem using the techniques of in vitro receptor autoradiography and ligand binding to homogenates. Autoradiography revealed the greatest accumulation of specific binding in the area postrema and subpostrema (AP/ASP). A lower level of specific binding was identified in the nucleus tractus solitarius (excluding area subpostrema). No specific binding was evident in the remainder of the hindbrain at this level. Discrete dissection followed by ligand binding to homogenates revealed that the specific binding of [3H]GR65630 (defined by the presence of 30 microM metoclopramide) was differentially distributed with highest levels in the AP/ASP (112.1 fmol/mg protein) and lower levels in the dorsal vagal complex (nucleus tractus solitarius--excluding the area subpostrema--dorsal motor nucleus of the vagus and hypoglossal nucleus) (DVC) and olivary nucleus (ON) (22.9 and 3.9 fmol/mg, respectively). No specific binding was detectable in the reticular formation (RF) located ventral to the dorsal vagal complex. The specific [3H]GR65630 binding site was pharmacologically similar to the 5-HT3 receptor since the potent and selective 5-HT3 receptor antagonists ICS 205-930 and zacopride (100 nM) and the agonist 5-HT (10 microM) inhibited binding to the same extent as metoclopramide in each of the individual areas (90, 60 and 20% in the AP/ASP, DVC and ON, respectively). The 5-HT1-like and 5-HT2 receptor antagonist methysergide (10 microM) failed to compete for the binding site. 5-HT3 receptor recognition sites within the AP/ASP and the DVC may be functionally involved in the ability of 5-HT3 receptor antagonists to control emesis.

Topographical distribution of 5-HT3 receptor recognition sites in the ferret brain stem.

The distribution of [3H]zacopride (1.0 nM) to putative 5-HT3 receptor recognition sites in the ferret hindbrain was assessed using autoradiography. Specific binding (defined by the inclusion of granisetron, 1.0 microM) was heterogeneously distributed with highest density within the dorsal vagal complex (area postrema, nucleus tractus solitarius and dorsal motor nucleus of the vagus nerve). Lower densities were detected in the spinal trigeminal nerve complex whilst no other significant specific binding was detected ventral to the dorsal vagal complex. The location of 5-HT3 receptor recognition sites within the dorsal vagal complex may provide sites of action for zacopride and other 5-HT3 receptor antagonists to inhibit the emesis induced by cancer chemotherapeutic agents and x-radiation.