Analgesic effect of GT-0198, a structurally novel glycine transporter 2 inhibitor, in a mouse model of neuropathic pain.

This study was conducted to identify the characteristic pharmacological features of GT-0198 that is phenoxymethylbenzamide derivatives. GT-0198 inhibited the function of glycine transporter 2 (GlyT2) in human GlyT2-expressing HEK293 cells and did not bind various major transporters or receptors of neurotransmitters in a competitive manner. Thus, GT-0198 is considered to be a comparatively selective GlyT2 inhibitor. Intravenous, oral, and intrathecal injections of GT-0198 decreased the pain-related response in a model of neuropathic pain with partial sciatic nerve ligation. This result suggests that GT-0198 has an analgesic effect. The analgesic effect of GT-0198 was abolished by the intrathecal injection of strychnine, a glycine receptor antagonist. Therefore, GT-0198 is considered to exhibit its analgesic effect via the activation of a glycine receptor by glycine following presynaptic GlyT2 inhibition in the spinal cord. In summary, GT-0198 is a structurally novel GlyT2 inhibitor bearing a phenoxymethylbenzamide moiety with in vivo efficacy in behavioral models of neuropathic pain.

Cannabinoid type-1 receptor reduces pain and neurotoxicity produced by chemotherapy.

Painful peripheral neuropathy is a dose-limiting complication of chemotherapy. Cisplatin produces a cumulative toxic effect on peripheral nerves, and 30-40% of cancer patients receiving this agent experience pain. By modeling cisplatin-induced hyperalgesia in mice with daily injections of cisplatin (1 mg/kg, i.p.) for 7 d, we investigated the anti-hyperalgesic effects of anandamide (AEA) and cyclohexylcarbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB597), an inhibitor of AEA hydrolysis. Cisplatin-induced mechanical and heat hyperalgesia were accompanied by a decrease in the level of AEA in plantar paw skin. No changes in motor activity were observed after seven injections of cisplatin. Intraplantar injection of AEA (10 µg/10 µl) or URB597 (9 µg/10 µl) transiently attenuated hyperalgesia through activation of peripheral CB1 receptors. Co-injections of URB597 (0.3 mg/kg daily, i.p.) with cisplatin decreased and delayed the development of mechanical and heat hyperalgesia. The effect of URB597 was mediated by CB1 receptors since AM281 (0.33 mg/kg daily, i.p.) blocked the effect of URB597. Co-injection of URB597 also normalized the cisplatin-induced decrease in conduction velocity of Aα/Aß-fibers and reduced the increase of ATF-3 and TRPV1 immunoreactivity in dorsal root ganglion (DRG) neurons. Since DRGs are a primary site of toxicity by cisplatin, effects of cisplatin were studied on cultured DRG neurons. Incubation of DRG neurons with cisplatin (4 µg/ml) for 24 h decreased the total length of neurites. URB597 (100 nM) attenuated these changes through activation of CB1 receptors. Collectively, these results suggest that pharmacological facilitation of AEA signaling is a promising strategy for attenuating cisplatin-associated sensory neuropathy.

Dual role of mosapride citrate hydrate on the gastric emptying evaluated by the breath test in conscious rats.

Mosapride citrate hydrate (mosapride) has been known to act as a 5-HT4 agonist and to enhance gastric emptying. However, its mode of action, such as time course and dosage effect, on gastric emptying has not been clarified. This study aimed to clarify these points by the breath test using [1-(13)C]acetic acid in conscious rats. Mosapride significantly and dose-dependently enhanced the gastric emptying increased Cmax and AUC120 min at doses between 0.1 and 3 mg/kg. Pre-treatment with GR113808 (5-HT4 antagonist) significantly attenuated the enhancement of gastric emptying by mosapride. On the contrary, at a dose of 30 mg/kg, mosapride significantly inhibited the gastric emptying. The major metabolite (M1: 5-HT3 receptor antagonist) significantly inhibited gastric emptying at doses of 19.2 and 64.1 mg/kg (equimolar to 30 and 100 mg/kg of mosapride, respectively), suggesting that the inhibitory effect by mosapride may be caused at least in part by the 5-HT3 receptor antagonistic effect of M1. These findings show that mosapride has dual role on the gastric emptying and may support the usefulness of mosapride for the therapy of postprandial distress syndrome such as early satiation and postprandial fullness.

Effects of mosapride citrate, a 5-HT4-receptor agonist, on gastric distension-induced visceromotor response in conscious rats.

Mosapride citrate (mosapride), a prokinetic agent with 5-HT(4)-receptor agonistic activity, is known to enhance gastric emptying and alleviate symptoms in patients with functional dyspepsia (FD). As hyperalgesia and delayed gastric emptying play an important role in the pathogenesis of FD, we used in this study balloon gastric distension to enable abdominal muscle contractions and characterized the visceromotor response (VMR) to such distension in conscious rats. We also investigated the effects of mosapride on gastric distension-induced VMR in the same model. Mosapride (3-10 mg/kg, p.o.) dose-dependently inhibited gastric distension-induced VMR in rats. However, itopride even at 100 mg/kg failed to inhibit gastric distension-induced VMR in rats. Additionally, a major metabolite M1 of mosapride, which possesses 5-HT(3)-receptor antagonistic activity, inhibited gastric distension-induced VMR. The inhibitory effect of mosapride on gastric distension-induced visceral pain was partially, but significantly inhibited by SB-207266, a selective 5-HT(4)-receptor antagonist. This study shows that mosapride inhibits gastric distension-induced VMR in conscious rats. The inhibitory effect of mosapride is mediated via activation of 5-HT(4) receptors and blockage of 5-HT(3) receptors by a mosapride metabolite. This finding indicates that mosapride may be useful in alleviating FD-associated gastrointestinal symptoms via increase in pain threshold.

Modeling medulloblastoma in vivo and with human cerebellar organoids.

Medulloblastoma (MB) is the most common malignant brain tumor in children and among the subtypes, Group 3 MB has the worst outcome. Here, we perform an in vivo, patient-specific screen leading to the identification of Otx2 and c-MYC as strong Group 3 MB inducers. We validated our findings in human cerebellar organoids where Otx2/c-MYC give rise to MB-like organoids harboring a DNA methylation signature that clusters with human Group 3 tumors. Furthermore, we show that SMARCA4 is able to reduce Otx2/c-MYC tumorigenic activity in vivo and in human cerebellar organoids while SMARCA4 T910M, a mutant form found in human MB patients, inhibits the wild-type protein function. Finally, treatment with Tazemetostat, a EZH2-specific inhibitor, reduces Otx2/c-MYC tumorigenesis in ex vivo culture and human cerebellar organoids. In conclusion, human cerebellar organoids can be efficiently used to understand the role of genes found altered in cancer patients and represent a reliable tool for developing personalized therapies.

Inhibition of matrix metalloproteinase expression and cellular invasion by NF-κB inhibitors of microbial origin.

Matrix metalloproteinases (MMPs) are zinc-dependent extracellular matrix remodeling endopeptidases. MMPs cleave various matrix proteins such as collagen, elastin, gelatin and casein. MMPs are often implicated in pathological processes, such as cancer progression including metastasis. Meanwhile, microorganisms produce various secondary metabolites having unique structures. We designed and synthesized dehydroxymethylepoxyquinomicin (DHMEQ) based on the structure of epoxyquinomicin C derived from Amycolatopsis as an inhibitor of NF-κB. This compound inhibited cancer cell migration and invasion. Since DHMEQ is comparatively unstable in the body, we designed and synthesized a stable DHMEQ analog, SEMBL. SEMBL also inhibited cancer cell migration and invasion. We also looked for inhibitors of cancer cell migration and invasion from microbial culture filtrates. As a result, we isolated a known compound, ketomycin, from Actinomycetes. DHMEQ, SEMBL, and ketomycin are all NF-κB inhibitors, and inhibited the expression of MMPs in the inhibition of cellular migration and invasion. These are all compounds with comparatively low toxicity, and may be useful for the development of anti-metastasis agents.

Sarcolemmal K(ATP) channel triggers opioid-induced delayed cardioprotection in the rat.

Recently, the involvement of sarcolemmal K(ATP) (sarcK(ATP)) channels in ischemic and pharmacological preconditioning (IPC and PPC) has been minimized by numerous studies suggesting a primary role for mitochondrial K(ATP) (mitoK(ATP)) channels in early and delayed cardioprotection. Although the mitoK(ATP) channel has clearly been shown to be a distal effector of delayed IPC and PPC, studies implicating it as a trigger of protection in delayed IPC are lacking. Accordingly, we characterized the role of cardiac K(ATP) channels as triggers or distal effectors of delayed cardioprotection induced by opioids in rats, and the data suggest that the sarcK(ATP) channel triggers and that the mitoK(ATP) channel is a distal effector of opioid-induced delayed cardioprotection.

The effect of amixin and agmatine on cytochrome C release from isolated mitochondria

Mitochondrial nicotinic acetylcholine receptors (nAChRs) control permeability transition pore formation and cytochrome c release in the presence of apoptogenic factors. This study demonstrates that pharmacological agents amixin and agmatine affect mitochondrial nAChR functioning: they slightly suppress cytochrome c release from mouse brain and liver mitochondria stimulated with apoptogenic dose of Са2+ and prevent the effect of α7 nAChR agonist PNU282987. We conclude that mitochondria may be one of therapeutic targets of amixin and agmatine.

A 3-aminobenzamide-resistant labeled protein in [32P]NAD+-labeled cells.

A series of proteins are covalently labeled when human lymphocytes are incubated with [32P]NAD+. The majority of this labeling is effectively inhibited when the lymphocytes are coincubated with 3-aminobenzamide, a potent inhibitor of poly(ADP-ribose) polymerase. However, labeling of a 72 000 molecular weight protein was resistant to the inhibitory effect of 3-aminobenzamide. Labeling of this protein from [32P]NAD+ was shown to be Mg2+-dependent. The 72 000 molecular weight protein could also be labeled on incubation with [alpha-32P]ATP, [gamma-32P]ATP and [32P]orthophosphate, but not from [3H]NAD+ or [14C]NAD+. In the present study, we show that the 72 000 molecular weight protein is not ADP-ribosylated but rather, phosphorylated on incubation with [32P]NAD+. This phosphorylation appears to occur via an Mg2+-dependent conversion of NAD+ to AMP with the eventual utilization of the alpha-phosphate for phosphorylation of the 72 000 molecular weight protein.

Delta-opioid receptor agonist SNC80 induces peripheral antinociception via activation of ATP-sensitive K+ channels.

We investigated the effect of several K+ channel blockers on the antinociception induced by delta-opioid receptor agonist SNC80 using the paw pressure test, in which pain sensitivity is increased by an intraplantar injection (2 microg) of prostaglandin E2 (PGE2). Administration of SNC80 (20, 40 and 80 microg/paw) caused a decrease in the hyperalgesia induced by PGE2, in a dose-dependent manner. The possibility of higher dose of SNC80 (80 microg) causing a central or systemic effect was excluded since administration of the drug into the contralateral paw did not elicit antinociception in the right paw. Specific blockers of ATP-sensitive K+ channels, glibenclamide (20, 40 and 80 microg/paw) and tolbutamide (40, 80 and 160 microg/paw), antagonized the peripheral antinociception induced by SNC80 (80 microg). On the other hand, charybdotoxin (2 microg/paw), a large-conductance blocker of Ca(2+)-activated K+ channels, and dequalinium (50 microg/paw), a small conductance selective blocker of Ca(2+)-activated K+ channels, did not modify the effect of SNC80. This effect also remained unaffected by intraplantar administration of the voltage-dependent K+ channel blockers tetraethylammonium (30 microg/paw) and 4-aminopyridine (10 microg/paw), and of a non-specific K+ channel blocker, cesium (500 microg/paw). This study provides evidence that the peripheral antinociceptive effect of SNC80 result from the activation of ATP-sensitive K+ channels, and the other K+ channels are not involved.

The anxiolytic-like effect of 5-HT1B receptor ligands in rats: a possible mechanism of action.

We have examined the effect of lesions of 5-hydroxytryptamine (5-HT) neurons, produced by p-chloroamphetamine (p-CA; 2 x 10 mg kg(-1)), and the influence of flumazenil (Ro 15-1788, 10 mg kg(-1)), a benzodiazepine receptor antagonist, on the anxiolytic-like activity of CP 94253 (5-propoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-pyrrolo[3,2-b]pyridine), a 5-HT1B receptor agonist, SB 216641 (N-[3-[3-(dimethylamino)ethoxy]-4-methoxyphenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-[1,1'-biphenyl]-4-carboxamide), a 5-HT1B receptor antagonist, and GR 127935 (N-[4-methoxy-3-(4-methyl-l-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-l, l'-biphenyl-4-carboxamide), a 5-HT1B/1D receptor antagonist, in the Vogel conflict drinking test in rats. Diazepam was used as a reference compound. CP 94253 (2.5 mg kg(-1)), SB 216641 (2.5 mg kg(-1)), GR 127935 (10 mg kg(-1)) and diazepam (5 mg kg(-1)) significantly increased the number of shocks accepted during experimental sessions in the conflict drinking test in vehicle- and p-CA-pretreated rats. Flumazenil did not change the anxiolytic-like effect of CP 94253 (2.5 mg kg(-1)), but wholly blocked the anxiolytic-like effects of SB 216641 (2.5 mg kg(-1)), GR 127935 (10 mg kg(-1)) and diazepam (5 mg kg(-1)). p-CA and flumazenil alone were inactive in the conflict drinking test. The results suggested that the anxiolytic-like effect of the 5-HT1B receptor ligands CP 94253, SB 216641 and GR 127935 was possibly linked to the postsynaptic 5-HT1B receptors or/and 5-HT1B heteroreceptors. The results suggested also that benzodiazepine receptors were indirectly involved in the effects of SB 216641 and GR 127935 (but not of CP 94253), which might have been due to a possible interaction between the 5-HT and the GABA/benzodiazepine systems.

The X-ray structure of Plasmodium falciparum dihydroorotate dehydrogenase bound to a potent and selective N-phenylbenzamide inhibitor reveals novel binding-site interactions.

Plasmodium species are protozoan parasites that are the causative agent of malaria. Malaria is a devastating disease, and its treatment and control have been hampered by the propensity of the parasite to become drug-resistant. Dihydroorotate dehydrogenase (DHODH) has been identified as a promising new target for the development of antimalarial agents. Here, the X-ray structure of P. falciparum DHODH bound to a potent and selective N-phenylbenzamide-based inhibitor (DSM59) is described at 2.3 Å resolution. The structure elucidates novel binding-site interactions and shows how conformational flexibility of the enzyme leads to the ability to bind diverse chemical structures with high affinity. This information provides new insight into the design of high-affinity DHODH inhibitors for the treatment of malaria.

Effects of URB597 as an inhibitor of fatty acid amide hydrolase on WIN55, 212-2-induced learning and memory deficits in rats.

Cannabinoid and endocannabinoid systems have been implicated in several physiological functions including modulation of cognition. In this study we evaluated the effects and interaction between fatty-acid amide hydrolase (FAAH) inhibitor URB597 and CB1 receptor agonist WIN55, 212-2 on memory using object recognition and passive avoidance learning (PAL) tests. Learning and memory impairment was induced by WIN 55, 212-2 administration (1mg/kg, i.p.) 30min before the acquisition trial. URB597 (0.1, 0.3 and 1mg/kg, i.p.) or SR141716A (1mg/kg, i.p.) was injected to rats 10min before WIN 55, 212-2 or URB597 respectively. URB597 (0.3 and 1mg/kg) but not 0.1mg/kg induced higher discrimination index (DI) in object recognition test and enhanced memory acquisition in PAL test. The cognitive enhancing effect of URB597 was blocked by a CB1 receptor antagonist, SR141716A which at this dose alone had no effect on cognition. WIN55, 212-2 caused cognition deficits in both tests. URB597 (0.3 and 1mg/kg) treatment could alleviate the negative influence of WIN 55, 212-2 on cognition and memory. These results indicate URB597 potential to protect against memory deficits induced by cannabinoid. Therefore, in combination with URB597 beneficial effects, this study suggests that URB597 has recognition and acquisition memory enhancing effects. It may also constitute a novel approach for the treatment of cannabinoid induced memory deficits and lead to a better understanding of the brain mechanisms underlying cognition.

Involvement of the strychnine-sensitive glycine receptor in the anxiolytic effects of GlyT1 inhibitors on maternal separation-induced ultrasonic vocalization in rat pups.

Several studies have shown that glycine transporter 1 (GlyT1) inhibitors have anxiolytic actions. There are two types of glycine receptor: the strychnine-sensitive glycine receptor (GlyA) and the strychnine-insensitive glycine receptor (GlyB); however, which receptor is the main contributor to the anxiolytic actions of GlyT1 inhibitors is yet to be determined. Here, we clarified which glycine receptor is the main contributor to the anxiolytic effects of GlyT1 inhibitors by using maternal separation-induced ultrasonic vocalization (USV) by rat pups as an index of anxiety. We confirmed that administration of the benzodiazepine diazepam or the selective serotonin reuptake inhibitor escitaloplam, which are both clinically proven anxiolytics, or the GlyT1 inhibitor SSR504734 (2-chloro-N-[(S)-phenyl[(2S)-piperidin-2-yl] methyl]-3-trifluoromethyl benzamide), decreases USV in rat pups. In addition, we showed that another GlyT1 inhibitor, ALX5407 ((R)-N-[3-(4'-fluorophenyl)-3(4'-phenylphenoxy)propyl]sarcosine) also decreases USV in rat pups. SSR504734- or ALX5407-induced decreases in USV were dose-dependently reversed by administration of the GlyA antagonist strychnine, whereas the diazepam- or escitalopram-induced decreases in USV were not. Furthermore, GlyT1-induced decreases in USV were not reversed by administration of the GlyB antagonist L-687,414. Together, these results suggest that GlyA activation is the main contributor to the anxiolytic actions of GlyT1 inhibitors and that the anxiolytic actions of diazepam and escitalopram cannot be attributed to GlyA activation. Our findings provide new insights into the importance of the activation of GlyA in the anxiolytic effects of GlyT1 inhibitors.

Zacopride and BRL 24924 induce an increase in EEG-energy in rats.

1. The substituted benzamides, zacopride and BRL 24924 induced dose-dependent increases of the total EEG-energy of rats when applied intracerebroventricularly (i.c.v.) with ED50 values of 8.0 +/- 0.6 and 3.6 +/- 0.9 micrograms, respectively. Not only the energy of the low frequency hippocampal theta rhythm but also that of the other frequency bands was increased. 2. In contrast to i.c.v. application intraperitoneal administration of zacopride or BRL 24924 (1 and 10 mg kg-1) did not lead to an increase in EEG-energy. 3. The increase in EEG-energy induced by zacopride (10 micrograms, i.c.v.) was blocked by ICS 205-930 (1 microgram, i.c.v.). Neither the 5-HT3 receptor agonist 2-methyl-5-hydroxytryptamine (30 micrograms, i.c.v.) nor the selective 5-HT3 receptor antagonist MDL 72222 (30 micrograms, i.c.v.) had any effect upon rat EEG. 4. Scopolamine (0.01 micrograms and 0.1 micrograms, i.c.v.) dose-dependently antagonized the effect of zacopride (10 micrograms, i.c.v.). 5. An agonist action of zacopride and BRL 24924 and inhibition of these effects by ICS 205-930 but not by MDL 72222 was recently described in isolated colliculi neurones from neonatal mice. The receptor involved was described as '5-HT4'. The present results indicate that the central effects of zacopride and BRL 24924 may be due to activation of such a 5-HT receptor.

Possible pharmacokinetic and pharmacodynamic factors affecting parkinsonism inducement by cinnarizine and flunarizine.

Potentialities of cinnarizine [1-(diphenylmethyl)-4-(3-phenyl-2-propenyl)piperazine, CZ] and its fluorine derivative flunarizine [1-[bis(4-fluorophenyl)-methyl]-4-(3-phenyl-2-propenyl)piperazine, FZ] to induce parkinsonism as an adverse effect were evaluated pharmacokinetically and pharmacodynamically in rats. In multiple-dose experiments, CZ or FZ was given to rats at a daily dose of 20 mumol/kg for 1, 5, 10, 15, and 30 days, and CZ, FZ, and the ring-hydroxylated metabolites of their cinnamyl moiety [1-(diphenylmethyl)-4-[3-(4'-hydroxyphenyl)-2-propenyl]piperazine, C-2 and 1-[bis(4-fluorophenyl)methyl]-4-[3-(4'- hydroxyphenyl)propenyl]piperazine, F-2] in the plasma and striatum were determined 24 hr after the final dose. Plasma and striatum concentrations of the above compounds except for FZ reached steady state after 10 doses, but their concentrations of FZ continued to increase throughout the experiments. The concentrations obtained after the 30 doses were in the order of FZ > F-2 > CZ > C-2 for the plasma and of F-2 > FZ > CZ > C-2 for the striatum. The ratios of striatum to plasma concentrations of C-2 and F-2 were 2.4 and 3 times higher than those of the parent drugs. Binding affinities of CZ, FZ, and their 10 metabolites for rat striatal dopamine D-2 receptors (D2-R) were assessed by competitive radioligand-binding studies using [3H]-N-[(2RS,3RS)-1-benzyl-2-methyl-3-pyrrolidinyl]-5-chloro-2-met hoxy- 4-methylamino-benzamide ([3H]-YM-09151-2). The IC50s calculated from their Ki values were in the order of F-2 < C-2 < FZ < CZ < C-4 << F-1, indicating that C-2 and F-2 exhibit higher affinities for D2-R than the parent drugs, whereas affinities of other metabolites were 1 to 2 orders of magnitude less than those of C-2 and F-2. These results suggest some important roles of C-2 and F-2 in the development of parkinsonism as active metabolites during chronic medication with CZ and FZ, respectively.

Involvement of tryptophan residue(s) in the specific binding of agonists/antagonists to 5-HT3 receptors in NG108-15 clonal cells.

Chemical modification of the 5-HT3 receptors in membranes from NG108-15 hybridoma cells was achieved using protein modifying reagents specific for various amino acid residues: N-bromosuccinimide for tryptophan, dithiothreitol for cystine, sodium tetrathionate for cysteine, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline for aspartic and glutamic acids, diethylpyrocarbonate for histidine, tetranitromethane for tyrosine and 2,3-butanedione for arginine. Among all the reagents tested, N-bromosuccinimide produced the largest alteration in the specific binding of [3H]zacopride onto 5-HT3 receptors. A significant reduction in Bmax (approximately 50%) with no change in Kd were noted on [3H]zacopride specific binding to membranes which were incubated with 40 microM N-bromosuccinimide for 60 min at 25 degrees. The occupancy of 5-HT3 receptor binding sites by various 5-HT3 agonists and antagonists (phenylbiguanide, ondansetron, granisetron, MDL 72222) prevented, at least partially, any subsequent reduction in [3H]zacopride specific binding by N-bromosuccinimide treatment. However, neither m-chloro-phenylbiguanide, among the agonists, nor zacopride, among the antagonists, were able to prevent the effect of N-bromosuccinimide, suggesting that variations might exist in the molecular mechanisms implicated in the binding of 5-HT3 ligands to the recognition site on 5-HT3 receptors. Nevertheless, these data support the suggestion that tryptophan residue(s) are probably involved in the binding of agonists and antagonists onto 5-HT3 receptors in NG108-15 cell membranes.

NMDA receptor antagonists inhibit catalepsy induced by either dopamine D1 or D2 receptor antagonists.

In the present study, we investigated the ability of NMDA receptor antagonists to inhibit catalepsy induced by haloperidol, or SCH23390 and clebopride, selective dopamine D1 and D2 receptor antagonists respectively. Catalepsy was measured by recording the time the animal remained with its forepaws placed over a rod 6 cm above the bench. Pretreatment with either the non-competitive NMDA receptor antagonist, MK-801 (0.25-0.5 mg/kg i.p.) or the competitive antagonist, LY274614 (10-20 mg/kg i.p.) reduced the cataleptic response produced by haloperidol (10 mg/kg), SCH23390 (2.5-10 mg/kp i.p.) or clebopride (5-20 mg/kg i.p.). This demonstrates that NMDA receptor antagonists will reduce both dopamine D1 and D2 receptor antagonist-induced catalepsy. Muscle relaxant doses of chlordiazepoxide (10 mg/kg i.p.) failed to reduce the catalepsy induced by haloperidol, suggesting that the anticataleptic effect of the NMDA receptor antagonists was not due to a non-specific action. These results support the hypothesis that NMDA receptor antagonists may have beneficial effects in disorders involving reduced dopaminergic function, such as Parkinson's disease.

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.

Antagonism of [3H]zacopride binding to 5-HT3 recognition sites by its (R) and (S) enantiomers.

[3H]Zacopride exhibits high affinity (Kd less than or equal to 1 nM) for 5-HT3 binding sites (inhibited by ICS 205-930) in rabbit intestinal muscularis and vagus nerve, human jejunum, rat intestinal muscularis and rat brain cortex. Its binding was inhibited by several 5-HT3 antagonists that displayed similar rank orders of potency in the tissues examined. Zacopride's (S) enantiomer was significantly more potent than its (R) enantiomer (21- to 42-fold in rabbit and human; 8- to 12-fold in rat) as an inhibitor of [3H]zacopride binding. These studies indicate that the utility of [3H]zacopride as a high affinity 5-HT3 ligand resides with the (S) enantiomer.