Jean-Louis Peglion

5-HT2C receptors mediate penile erections in rats: actions of novel and selective agonists and antagonists.

The mixed 5-HT2A/5-HT2B/5-HT2C receptor agonist, m-(chlorophenyl)piperazine (mCPP), elicited penile erections in rats, an action mimicked by the selective 5-HT2C receptor agonist, RO 60-0175 (S)-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine), whereas the preferential 5-HT2B receptor agonist, BW 723C86 (1-[5-(thienylmethoxy)-1H-3-indoyl] propan-2-amine) was ineffective. The actions of mCPP and RO 60-0175 were dose-dependently abolished by the novel 5-HT2B/5-HT2C receptor antagonists, SB 200,646 (1-(1-methylindol-5-yl)-3-(3-pyridyl) urea) and SB 206,553 (5 methyl-1-(3-pyridil-carbamoyl)-1,2,3,5-tetrahydropyrrolo[2,3 -f]indole). In contrast, penile erections were not significantly affected by the selective 5-HT2B receptor antagonist, SB 204,741 (1-(1-methylindol-5-yl)-3-(3-methylisothiazol-5-yl)-urea) nor by the selective 5-HT2A receptor antagonist, MDL 100,907 ([R(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-p iperidine-methanol]). These data provide rigorous pharmacological evidence that activation of 5-HT2C receptor elicits penile erections in the rat. This model should, thus, be of use for characterising novel ligands at this site.

Stereospecific in vitro and in vivo effects of the new sinus node inhibitor (+)-S 16257

The effects of the two isomers, (+)-S 16257 and (-)-S 16260, of a new bradycardic agent, (+/-)-S 15544 (7,8-dimethoxy 3-[3-[[(4.5-dimethoxybenzocyclobutan-1-yl)methyl] methylamino]propyl]1,3,4,5-tetrahydro-2H-3-benzazepin-2-one), were compared in vitro and in vivo on cardiac spontaneous rate and repolarization time. In the isolated rabbit sino-atrial node, the three compounds (3 microM) were equi-effective to reduce the action potential firing rate. In anesthetized pigs, both isomers (0.03, 0.1, 0.3 and 1 mg kg(-1) i.v.) were equipotent to reduce heart rate. For all compounds, the negative chronotropic effect resulted from a reduction in the slope of diastolic depolarization of pacemaker cells. In sino-atrial node cells, (-)-S 16260 (3 microM) increased action potential duration while (+)-S 16257 had a smaller effect. In driven guinea-pig papillary muscles exposed to increasing concentrations of compounds (0.1 to 10 microM) a small prolongation of action potential duration was observed. This prolongation was more marked in rabbit Purkinje fibers stimulated at a low rate. In all cardiac preparations the highest prolongation was observed with (-)-S 16260. In vivo, (-)-S 16260 prolonged QTc at the two highest doses tested while (+)-S 16257 had no effect. In conclusion, resolution of (+/-)-S 15544 into its two enantiomers yielded compounds with the same bradycardic effects. Of the isomers, (+)-S 16257 has an increased specificity with minimal direct effect on action potential repolarization.

Anti-ischemic effects of ivabradine, a selective heart rate-reducing agent, in exercise-induced myocardial ischemia in pigs.

The effects of ivabradine, a novel heart rate-reducing agent that inhibits the cardiac pacemaker current If, were compared with those of the &bgr;-adrenergic blocker propranolol, in a model of exercise-induced regional myocardial ischemia in pigs. Five Yucatan micropigs were chronically instrumented to measure hemodynamics, regional myocardial contractility, and local electrograms, and a fixed stenosis of the left anterior descending coronary artery was induced using a clip. Each animal underwent three experiments on different days, each consisting of two treadmill exercise sessions, 4 hours apart. Ivabradine 5 mg/kg, propranolol 5 mg/kg, or vehicle was administered orally 3 hours before the second exercise session. Exercises before treatment and after vehicle produced reproducible hemodynamic changes and regional myocardial ischemia in the area perfused by the stenosed coronary artery, indicated by ST segment shift and regional contractile dysfunction. Ivabradine and propranolol were equipotent in reducing heart rate at rest and limiting tachycardia during exercise. Ivabradine, unlike propranolol, did not reduce left ventricular contractility at rest or during exercise, and did not increase atrio-ventricular conduction time. Both compounds reduced the exercise-induced ST segment shift in the ischemic region by approximately 80%, but ivabradine preserved systolic shortening to a significantly greater degree than propranolol (P < 0.05).

Modulation of mesolimbic dopamine release by the selective dopamine D3 receptor antagonist, (+)-S 14297

In Chinese hamster ovary cells stably transfected with recombinant rat dopamine D2 or D3 receptors, the naphthofurane antagonist, (+)-S 14297 [(+)-[7-(N,N-dipropylamino)-5,6,7,8-tetrahydro- naphtho(2,3b)dihydro,2,3-furane]], displayed a pronounced preference for dopamine D3 versus D2 receptors: Ki values = 13 and 365 nM, respectively. In contrast, its distomer, (-)-S 17777, showed low affinity (296 versus 3403 nM). The aminotetralin agonist, (+)-7-OH-DPAT (7-hydroxy-2-(di-n-propylamino)tetralin), also showed high affinity at dopamine D3 (1.8 nM) versus D2 (96 nM) receptors while its (-)-isomer showed low affinity (71 and 1461 nM). In freely moving rats, (+)-7-OH-DPAT (0.16 mg/kg s.c.)-but not (-)-7-OH-DPAT-decreased dialysate levels of dopamine in the nucleus accumbens. (+)-S 14297 (1.25 mg/kg s.c.) markedly inhibited the action of (+)-7-OH-DPAT without influencing dopamine levels alone. Further, this action was stereospecific in that (-)-S 17777 (20.0 mg/kg s.c.) was inactive. In conclusion, data obtained with the novel, selective dopamine D3 receptor antagonist, (+)-S 14297 suggest that dopamine D3 autoreceptors modulate the release of dopamine from mesolimbic dopaminergic neurones.

S 15535: a highly selective benzodioxopiperazine 5-HT1A receptor ligand which acts as an agonist and an antagonist at presynaptic and postsynaptic sites respectively

The novel benzodioxopiperazine, S 15535 (4-(benzodioxan-5-yl)1-(indan-2- yl)piperazine), displayed high affinity for 5-HT1A binding sites (1.8 nM) whereas its affinity was 100-fold lower at other 5-HT receptor types, at alpha 1, alpha 2- and beta-adrenoceptors and at dopamine D1 and D2 receptors. In vivo, S 15535 (0.16-10 mg/kg s.c.) acted as an antagonist at postsynaptic 5-HT1A receptors in completely blocking the flat-body posture and hypothermia elicited by the 5-HT1A receptor agonist, 8-OH-DPAT. It had no effect when applied alone. At presynaptic 5-HT1A receptors, S 15535 acted as an agonist in inhibiting striatal accumulation of 5-hydroxytryptophan (0.04-0.63 mg/kg s.c.) and in spiperone reversibly reducing electrical activity of the dorsal raphe nucleus (0.004-0.031 mg/kg i.v.). At doses up to 40.0 mg/kg s.c., S 15535 neither inhibited methylphenidate-induced gnawing nor elicited ptosis suggesting a lack of antagonist properties at, respectively, dopamine D2 receptors and alpha 1-adrenoceptors. In conclusion, S 15535 is a potent 5-HT1A ligand which acts, in vivo, as a highly selective agonist and antagonist at presynaptic and postsynaptic 5-HT1A receptors, respectively.

S 14297, a novel selective ligand at cloned human dopamine D3 receptors, blocks 7-OH-DPAT-induced hypothermia in rats

The selective dopamine D3 receptor agonist, 7-OH-DPAT ((+)-7-hydroxy-2-(di-n-propylamino)tetralin) and the novel naphthofurane, S 14297 ((+)-[7-(N,N-dipropylamino)-5,6,7,8-tetrahydro- naphtho(2,3b)dihydro,2,3-furane]), bound with high affinity and selectivity to recombinant, human dopamine D3 versus D2 receptors stably transfected into Chinese hamster ovary cells: Ki values = 2 versus 103 nM for 7-OH-DPAT and 13 versus 297 nM for S 14297. In contrast, the putative dopamine D3 receptor antagonist, AJ 76 (cis-(+)-5-methoxy-1-methyl-2-(n- propylamino)tetralin), displayed low affinity and selectivity for dopamine D3 versus D2 sites (70 versus 154 nM). 7-OH-DPAT (0.01-0.16 mg/kg s.c.) provoked hypothermia in rats, an action abolished by S 14297 (0.04-0.63 mg/kg s.c.) and, less potently, by AJ 76 (0.16-2.5 mg/kg s.c.). S 14297 (20.0 mg/kg s.c.) did not modify prolactin secretion. These data suggest that dopamine D3 receptors mediate hypothermia in the rat and that S 14297 acts as a selective antagonist at these sites.

Tetracyclic analogues of [+]-S 14297: Synthesis and determination of affinity and selectivity at cloned human dopamine D3 vs D2 receptors

Abstract Starting from the structure of the preferential D 3 antagonist S 14297 ( 1 ), we have prepared a series of cis and trans tetracyclic derivatives of general formula I in order to improve potency and selectivity for D 3 receptors. The trans oxazino derivative 2c , showed slightly increased affinity at D 3 receptors and double the selectivity for D 3 over D 2 receptors, in comparison to S 14297. Cis derivatives and compounds where R 1 is aralkyl were totally devoid of activity.

Improvement in the selectivity and metabolic stability of the serotonin 5-HT(1A) ligand, S 15535: a series of cis- and trans-2-(arylcycloalkylamine) 1-indanols.

S 15535 (1) displays a distinctive profile of agonist and antagonist (weak partial agonist) activity at pre- and postsynaptic 5-HT(1A) receptors, respectively. It has proven to be active in several models predictive of anxiolytic, antidepressant, and procognitive properties. In an attempt to increase its selectivity and metabolic stability, and guided by the results of human metabolic studies, we prepared a series of cis- and trans-2-(arylcycloalkylamine) 1-indanols. Irrespective of the nature of the arylcycloalkylamine moiety or the presence of substituents on the indanol ring, trans isomers invariably showed the highest affinity for human, recombinant h5-HT(1A) receptors. Among them, compounds 39, 42, 45, 49, 52, 53, 54, 57, 61, 64, 67, and 70 displayed similar or higher affinity than the parent compound 1 (pK(i) > or = 9.1). Lack of selectivity toward alpha1-adrenoceptors has been frequently encountered with 5-HT(1A) ligands. While S 15535 itself presents reasonable selectivity (158-fold) in this respect, trans piperazine derivatives 4-trans,35, 39, 41, 47, 64, 68, 69, 70, 71 displayed even more pronounced selectivity vs alpha1-adrenoceptors, with the nitro derivative 70 being highly selective (1259-fold). However, among the set of trans piperidines prepared, only 64, which also bears a nitro on the indanol ring, displayed selectivity greater than the parent compound 1. All trans derivatives behaved as partial agonists at h5-HT(1A) receptors, as determined by their submaximal stimulation of [35S]GTPgammaS binding to a level comparable to that observed with S 15535. In metabolic stability studies in vitro using human microsomes and hepatocytes, only trans piperazines and, in particular, 35, 39, 41, 68, 69, and 70, showed an improvement relative to 1, whereas trans piperidines did not. Compounds 35, 39, 41, and 70, which combined both improved selectivity and metabolic stability, and which retained the distinctive pharmacological characteristics of S 15535, were evaluated in animal models of anxiety. Of these, 35, which showed the highest oral bioavailability in vivo in rats, was resolved into its two isomers 36 and 37. The eutomer 37 displayed 47% oral bioavailability in the rat and was potently active (0.1-0.5 mg/kg, s.c.) in the rat ultrasonic vocalization and social interaction models, predictive of anxiolytic activity. In conclusion, 2-(arylcycloalkylamine) 1-indanols represent a novel class of potent 5-HT(1A) ligands in which the presence of the hydroxyl group in the benzylic position enhances selectivity, while substituents on the phenyl ring of the indanol moiety improve both selectivity and metabolic stability.

Discriminative stimulus properties of S32504, a novel D3/D2 receptor agonist and antiparkinson agent, in rats: attenuation by the antipsychotics, aripiprazole, bifeprunox, N-desmethylclozapine, and by selective antagonists at dopamine D2 but not D3 receptors

RationaleDrug-discrimination studies have proven instructive in the characterization of psychotropic agents, a procedure applied herein to the novel antiparkinson agent, S32504. This highly selective agonist at dopamine D3 and (less potently) D2 receptors displays potent antiparkinson, neuroprotective and antidepressant properties (Millan et al., J Pharmacol Exp Ther 309:936–950, 2004a; Millan et al., J Pharmacol Exp Ther 309:903–920, 2004b; Millan et al., J Pharmacol Exp Ther 309:921–935, 2004c).ObjectivesTo generate a discriminative stimulus (DS) with S32504 and undertake substitution/antagonism studies with diverse antiparkinson and antipsychotic agents.Materials and methodsUsing a two-lever, fixed-ratio 10 schedule, rats were trained to recognize S32504 (0.04xa0mg/kg, s.c.) from saline.ResultsS32504 displayed dose-dependent and stereospecific substitution in comparison to its less active racemic form, (±) S31411, and to its inactive (−) distomer, S32601. Apomorphine, and the selective D3/D2 receptor agonists, ropinirole, PD128,907, 7-OH-DPAT and CGS15855A, fully (=80%) substituted for S32504, whereas D4 and D1/D5 receptor agonists were ineffective. The selective D3 vs D2 receptor partial agonist, BP897, did not substitute for S32504 and the selective D3 receptor antagonists, S33084, SB277,011, GR218,231, PNU99194A and S14297, did not block its DS properties. By contrast, S32504 lever selection was blocked by the preferential D2 vs D3 receptor antagonists, L741,626 and S23199, and by the D2/D3 antagonists, raclopride and haloperidol. The D2/D3 receptor partial agonists and antipsychotics, aripiprazole, bifeprunox, N-desmethylclozapine and preclamol did not substitute for S32504: indeed, they dose-dependently attenuated its DS properties.ConclusionThe antiparkinson agent, S32504, displays DS properties principally mediated by high-efficacy activation of D2 receptors Antipsychotics known to act as partial agonists at D2/D3 receptors attenuate DS properties of S32504, actions reflecting their low efficacy at these sites.

Differential influence of selective 5-HT5A vs 5-HT1A, 5-HT1B, or 5-HT2C receptor blockade upon light-induced phase shifts in circadian activity rhythms: Interaction studies with citalopram

Though serotonergic mechanisms modulate circadian rhythms, roles of individual serotonin (5-HT) receptors remain uncertain since data are lacking for antagonists. Herein, both the 5-HT(5A) receptor antagonist, A843277 (10 mg/kg), and the 5-HT(1B) antagonist, SB224289 (1 mg/kg), inhibited light-induced phase advances in hamster circadian wheel-running rhythms. Conversely, though 5-HT(1A) and 5-HT(7) receptors are likewise implicated in circadian scheduling, their blockade by WAY100635 (0.5 mg/kg) and SB269970 (1 mg/kg), respectively, was ineffective. Since actions of 5-HT reuptake inhibitors are modified by antagonists, we evaluated their influence on suppression of phase advances by citalopram (10 mg/kg). Its action was potentiated by WAY100635 and the 5-HT(2C) antagonist, SB242084 (1 mg/kg), but not by A842377, SB224289, SB269970, and antagonists at 5-HT(2A) (MDL100907) and 5-HT(6) (SB399885) receptors. In conclusion, this is the first in vivo evidence for an influence of 5-HT(5A) receptors upon circadian rhythms, but no single class of 5-HT receptor mediates their control by citalopram.