A. Gobert

S32006, a novel 5-HT2C receptor antagonist displaying broad-based antidepressant and anxiolytic properties in rodent models.

RationaleSerotonin (5-HT)2C receptors are implicated in the control of mood, and their blockade is of potential interest for the management of anxiodepressive states.ObjectivesHerein, we characterized the in vitro and in vivo pharmacological profile of the novel benzourea derivative, S32006.Materials and methodsStandard cellular, electrophysiological, neurochemical, and behavioral procedures were used.ResultsS32006 displayed high affinity for human (h)5-HT2C and h5-HT2B receptors (pKis, 8.4 and 8.0, respectively). By contrast, it had negligible (100-fold lower) affinity for h5-HT2A receptors and all other sites examined. In measures of Gq-protein coupling/phospholipase C activation, S32006 displayed potent antagonist properties at h5-HT2C receptors (pKB values, 8.8/8.2) and h5-HT2B receptors (7.8/7.7). In vivo, S32006 dose-dependently (2.5–40.0xa0mg/kg, i.p. and p.o.) abolished the induction of penile erections and a discriminative stimulus by the 5-HT2C receptor agonist, Ro60,0175, in rats. It elevated dialysis levels of noradrenaline and dopamine in the frontal cortex of freely moving rats, and accelerated the firing rate of ventrotegmental dopaminergic and locus ceruleus adrenergic neurons. At similar doses, S32006 decreased immobility in a forced-swim test in rats, reduced the motor depression elicited by 5-HT2C and α2-adrenoceptor agonists, and inhibited both aggressive and marble-burying behavior in mice. Supporting antidepressant properties, chronic (2–5xa0weeks) administration of S32006 suppressed “anhedonia” in a chronic mild stress procedure and increased both expression of BDNF and cell proliferation in rat dentate gyrus. Finally, S32006 (0.63–40xa0mg/kg, i.p. and p.o) displayed anxiolytic properties in Vogel conflict and social interaction tests in rats.ConclusionS32006 is a potent 5-HT2C receptor antagonist, and possesses antidepressant and anxiolytic properties in diverse rodent models.

Clozapine inhibits serotoninergic transmission by an action at α1-adrenoceptors not at 5-HT1A receptors

This study examined the mechanism underlying the influence of clozapine upon serotoninergic transmission in the rat. In vitro, clozapine manifested weak affinity at 5-HT1A receptors (pKi = 6.5) as compared to the agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (9.0), but high affinity at alpha 1-adrenoceptors (8.2) as compared to the alpha 1-adrenoceptor antagonist, prazosin (9.7). Ex vivo, clozapine (inhibitory dose (ID)50 = 0.7 mg/kg s.c.) mimicked prazosin (0.5) in potently occupying central alpha 1-adrenoceptors whereas, as compared to 8-OH-DPAT (0.2), it failed to occupy 5-HT1A receptors (> 10.0). The firing of serotoninergic neurones in the dorsal raphe nucleus was abolished by 8-OH-DPAT, clozapine and prazosin with ID50 values of 0.006, 0.09 and 0.07 mg/kg i.v., respectively. At comparable doses, they reduced striatal turnover of 5-HT. While the 5-HT1A receptors antagonists, (-)-tertatolol (2.0 mg/kg i.v.) and spiperone (0.63 mg/kg i.v.), blocked the action of 8-OH-DPAT upon dorsal raphe nucleus firing, they failed to modify the effect of clozapine and prazosin. In contrast, the alpha 1-adrenoceptor agonist, cirazoline (0.005 mg/kg i.v.) prevented the actions of clozapine and prazosin, but not that of 8-OH-DPAT. It is concluded that clozapine only weakly interacts with 5-HT1A receptors and that its potent alpha 1-adrenoceptor antagonist properties underlie inhibition of serotoninergic transmission.

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.

The selective serotonin (5-HT)1A receptor ligand, S15535, displays anxiolytic-like effects in the social interaction and Vogel models and suppresses dialysate levels of 5-HT in the dorsal hippocampus of freely-moving rats

Abstract. Rationale: The benzodioxane, S15535, possesses low intrinsic activity and marked selectivity at 5-HT1A receptors, hippocampal populations of which are implicated in anxious states. Objective: Herein, we examined its potential anxiolytic actions in relation to its influence upon extracellular levels of 5-HT in the dorsal hippocampus of freely-moving rats. Its effects were compared with those of other anxiolytic agents: the 5-HT1A agonists, buspirone and 8-hydroxy-2-(di-n-propylamino)-tetralin HBr (8-OH-DPAT), the 5-HT2C antagonist, SB206,553 and the benzodiazepine, diazepam. Methods: Potential anxiolytic actions were evaluated in the Vogel conflict paradigm (increase in punished responses) and the social interaction (SI) test (increase in active SI) in rats. Extracellular levels of 5-HT were determined by microdialysis. Results: In analogy to diazepam, S15535 increased punished responses in the Vogel test. This action was dose dependently expressed over a broad (16-fold) dose range. Buspirone and 8-OH-DPAT were likewise active, but yielded highly biphasic dose–response curves. SB206,553 was dose dependently active in this model. In the SI test, S15535 similarly mimicked the anxiolytic-like effect of diazepam and was active over a broad dose range. Buspirone and 8-OH-DPAT again showed biphasic dose–response curves, as did SB206,553. In both the Vogel and SI tests, the anxiolytic-like effects of S15535 were abolished by the selective 5-HT1A receptor antagonist, WAY100,635, which was inactive alone. S15535 exerted its anxiolytic-like effects with a more pronounced separation to motor-disruptive doses than the other drugs. Finally, S15535 suppressed dialysate levels of 5-HT in the dorsal hippocampus, an action abolished by WAY100,635. Buspirone, 8-OH-DPAT and diazepam, but not SB206,553, also reduced 5-HT levels. Conclusion: Likely reflecting its distinctive ability to selectively and preferentially activate pre- versus postsynaptic 5-HT1A receptors, S15535 suppresses hippocampal 5-HT release and displays marked anxiolytic-like effects over a broad dose range in the relative absence of motor perturbation.

Genetic Deletion of Trace Amine 1 Receptors Reveals Their Role in Auto-Inhibiting the Actions of Ecstasy (MDMA)

“Ecstasy” [3,4-methylenedioxymetamphetamine (MDMA)] is of considerable interest in light of its prosocial properties and risks associated with widespread recreational use. Recently, it was found to bind trace amine-1 receptors (TA1Rs), which modulate dopaminergic transmission. Accordingly, using mice genetically deprived of TA1R (TA1-KO), we explored their significance to the actions of MDMA, which robustly activated human adenylyl cyclase-coupled TA1R transfected into HeLa cells. In wild-type (WT) mice, MDMA elicited a time-, dose-, and ambient temperature-dependent hypothermia and hyperthermia, whereas TA1-KO mice displayed hyperthermia only. MDMA-induced increases in dialysate levels of dopamine (DA) in dorsal striatum were amplified in TA1-KO mice, despite identical levels of MDMA itself. A similar facilitation of the influence of MDMA upon dopaminergic transmission was acquired in frontal cortex and nucleus accumbens, and induction of locomotion by MDMA was haloperidol-reversibly potentiated in TA1-KO versus WT mice. Conversely, genetic deletion of TA1R did not affect increases in DA levels evoked by para-chloroamphetamine (PCA), which was inactive at hTA1 sites. The TA1R agonist o-phenyl-3-iodotyramine (o-PIT) blunted the DA-releasing actions of PCA both in vivo (dialysis) and in vitro (synaptosomes) in WT but not TA1-KO animals. MDMA-elicited increases in dialysis levels of serotonin (5-HT) were likewise greater in TA1-KO versus WT mice, and 5-HT-releasing actions of PCA were blunted in vivo and in vitro by o-PIT in WT mice only. In conclusion, TA1Rs exert an inhibitory influence on both dopaminergic and serotonergic transmission, and MDMA auto-inhibits its neurochemical and functional actions by recruitment of TA1R. These observations have important implications for the effects of MDMA in humans.

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.

WAY 100,135 and (−)-tertatolol act as antagonists at both 5-HT1A autoreceptors and postsynaptic 5-HT1A receptors in vivo

In binding studies, WAY 100,135 (N-tertiobutyl-3-[4-(2-methoxyphenyl)-piperazinyl]-2-phenylpropana mide) and (-)-tertatolol showed affinities (Ki) of 29 nM and 10 nM, respectively, at 5-HT1A receptors. In vivo, they both dose dependently blocked the flat-body posture and corticosterone secretion provoked by an action of the 5-HT1A receptor agonist, S 14671 (1-[2-(2-thenoyl-amino)ethyl]-4-[1-(7- methoxynaphtyl)]piperazine), at postsynaptic 5-HT1A receptors. Alone, they exerted little effect. The firing rate of dorsal raphe neurones, which bear inhibitory 5-HT1A autoreceptors, was reduced by S 14671 whereas it was not affected by WAY 100,135 and was increased by (-)-tertatolol. Both WAY 100,135 and (-)-tertatolol blocked the ability of S 14671 to inhibit raphe firing. In conclusion, these data demonstrate that WAY 100,135 and (-)-tertatolol behave as antagonists at both 5-HT1A autoreceptors and postsynaptic 5-HT1A receptors in vivo.

S33138 [N-[4-[2-[(3aS,9bR)-8-Cyano-1,3a,4,9b-tetrahydro[1]-benzopyrano[3,4-c]pyrrol-2(3H)-yl)-ethyl]phenylacetamide], a Preferential Dopamine D3 versus D2 Receptor Antagonist and Potential Antipsychotic Agent. II. A Neurochemical, Electrophysiological and Behavioral Characterization in Vivo

The novel benzopyranopyrrolidine, S33138 [N-[4-[2-[(3aS,9bR)-8-cyano-1,3a,4,9b-tetrahydro[1]benzopyrano[3,4-c]pyrrol-2(3H)-yl)-ethyl]phenylacetamide], is a preferential antagonist of cloned human D3 versus D2L and D2S receptors. In mice, S33138 (0.04–2.5 mg/kg i.p.) increased levels of mRNA encoding c-fos in D3 receptor-rich Isles of Calleja and nucleus accumbens more potently than in D2 receptor-rich striatum. Furthermore, chronic (3 weeks) administration of S33138 to rats reduced the number of spontaneously active dopaminergic neurones in the ventral tegmental area (0.16–10.0 p.o.) more potently than in the substantia nigra (10.0). In primates treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, antiparkinson actions of the D3/D2 agonist, ropinirole, were potentiated by low doses of S33138 (0.01–0.16 p.o.) but diminished by a high dose (2.5). Consistent with antagonism of postsynaptic D3/D2 sites, S33138 attenuated hypothermia and yawns elicited by the D3/D2 agonist 7-OH-DPAT [(+)-7-dihydroxy-2-(di-n-propylamino)-tetralin] in rats, and it blocked (0.01–0.63, s.c.) discriminative properties of PD128,907 [(+)-(4aR,10bR)-3,4, 4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol; trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolininecarboxamide]. Suggesting antagonist properties at D3/D2 autoreceptors, S33138 prevented (0.16–2.5 s.c.) the inhibitory influence of PD128,907 upon dopamine release in frontal cortex, nucleus accumbens, and striatum and abolished (0.004–0.25 i.v.) its inhibition of ventral tegmental dopaminergic neuron firing. At higher doses, antagonist actions of S33138 (0.5–4.0 i.v.) at α2C-adrenoceptors were revealed by an increased firing rate of adrenergic perikarya. Finally, antagonism of 5-hydroxytryptamine (5-HT2A and 5-HT7) receptors was shown by blockade of 1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane-induced head twitches (0.63–10.0 s.c.) and 5-carboxytryptamine-induced hypothermia (2.5–20.0 i.p.), respectively. In conclusion, S33138 displays modest antagonist properties at central α2C-adrenoceptors, 5-HT2A and 5-HT7 receptors. Furthermore, in line with its in vitro actions, it more potently blocks cerebral populations of D3 versus D2 receptors.

The potent activity of the 5-HT1A receptor agonists, S 14506 and S 14671, in the rat forced swim test is blocked by novel 5-HT1A receptor antagonists.

The high efficacy methoxynaphtylpiperazine 5-HT1A receptor agonists, S 14506 (1-[2-(4-fluorobenzoylamino)ethyl]-4-(7-methoxynaphtyl)piper azine) and S 14671 (1-[2-(2-thenoylamino)ethyl]-4[1-(7-methoxynaphtyl]piperazin e), potently reduced the duration of immobility in the forced swimming test in rats [minimal effective dose (MED): 0.01 mg/kg, s.c., in each case]; in contrast, the prototypic 5-HT1A receptor agonist, 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide], was much less potent (MED: 0.63 mg/kg). The action of S 14671 (0.16 mg/kg) was completely blocked by the potent 5-HT1A receptor antagonist, SDZ 216-525 (4-(4-[4-(1,1,3-trioxo-2H-1,2-benzoisothiazol-2- yl)butyl]-1-piperazinyl)1H-indole-2-carboxylate) (0.63 mg/kg) and by the novel, selective 5-HT1A receptor antagonist, (+)-WAY 100,135 (N-tertiobutyl-3-[4-(2-methoxyphenyl)piperazinylphenyl propanamide): the effect of the latter was expressed dose dependently (Inhibitory Dose50: 35 mg/kg). Similarly, in the presence of (+)-WAY 100,135, S 14506 (0.63 mg/kg) failed to reduce immobility. Pretreatment with parachlorophenylalanine (3 x 300 mg/kg per day, i.p.), which profoundly depleted cerebral pools of 5-HT, modified neither baseline immobility nor the actions of S 14506 and S 14671. It is concluded that S 14506 and S 14671 possess exceptionally potent activity in the forced swimming test and that their actions reflect the activation of postsynaptic 5-HT1A receptors.