Effects of WAY 100635 on antipsychotic-induced catalepsy in 5-HT depleted animals: a role for tonic activation of 5-HT(1A) receptors

The selective 5-HT 1A receptor agonist, NLX-112, overcomes tetrabenazine-induced catalepsy and depression-like behavior in the rat

Tetrabenazine, a preferential inhibitor of the vesicular monoamine transporter type 2, depletes the brain monoamines dopamine, serotonin and norepinephrine. Tetrabenazine and deutetrabenazine (Austedo ®) are used to treat chorea associated with Huntington's disease. However, both compounds are known to aggravate Parkinsonism and depression observed in Huntington's disease patients. NLX-112 (a.k.a. befiradol/F13640) is a highly selective, potent and efficacious serotonin 5-HT 1A agonist. In animal models, it has robust efficacy in combating other iatrogenic motor disorders such as L-DOPA-induced dyskinesia and has marked antidepressant-like activity in rodent tests. In the present study, we investigated, in rats, the efficacy of NLX-112 to counteract tetrabenazine-induced catalepsy (a model of Parkinsonism) and tetrabenazine-induced potentiation of immobility in the forced swim test (FST, a model to detect antidepressant-like activity). The prototypical 5-HT 1A agonist, (±)8-OH-DPAT, and the 5-HT 1A partial agonist/dopamine D2 receptor blocker, buspirone, were used as comparators. Both NLX-112 and (±)8-OH-DPAT (0.16-2.5 mg/kg p.o. or s.c., respectively) abolished catalepsy induced by tetrabenazine (2 mg/kg i.p.). In comparison, buspirone (0.63-5.0 mg/kg p.o.) was ineffective and even tended to potentiate tetrabenazine-induced catalepsy at 0.63 mg/kg. In the FST, NLX-112 and (±)8-OH-DPAT (0.63 mg/kg) strongly reduced immobility when administered alone but also significantly opposed potentiation of immobility induced by tetrabenazine (1.5 mg/kg i.p.). Buspirone (0.63 and 2.5 mg/kg p.o.) had no effect by itself or against tetrabenazine. These results strongly suggest that selective and highly efficacious 5-HT 1A agonists, such as NLX-112, may be useful in combating tetrabenazine-induced Parkinsonism and/or depression in Huntington's disease patients.

F15063, a potential antipsychotic with dopamine D(2)/D(3) receptor antagonist and 5-HT(1A) receptor agonist properties: influence on immediate-early gene expression in rat prefrontal cortex and striatum

Brain region-specific modulation of immediate-early gene (IEG) may constitute a marker of antipsychotic drug-like activity. We investigated the effects of the putative antipsychotic drug N-[(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)ethyl]-3-(cyclopent-1-enyl)-benzylamine (F15063), a compound that targets both dopamine D(2) and serotonin 5-HT(1A) receptors, in comparison with haloperidol and clozapine on rat mRNA expression of IEG i.e. the zinc-fingered transcription factors c-fos, fosB, zif268, c-jun and junB, two transcription factors of the nuclear receptor family nur77 and nor1, and the effector IEG arc. F15063 (10 mg/kg) and clozapine (10 mg/kg), but not haloperidol (0.63 mg/kg), induced c-fos and fosB mRNA expression in prefrontal cortex, a region associated with control of cognition and negative symptoms of schizophrenia. In striatum, only c-fos, fosB, junB and nur77 were induced by clozapine whereas all IEG mRNAs were increased by haloperidol and F15063 (from 2.5 mg/kg) with similar high efficacy despite a total absence of F15063-induced catalepsy. However, at 0.63 mg/kg, F15063 induced a lower degree of striatal IEG mRNA expression than haloperidol and pretreatment with the serotonin 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl-N-(2-pyridinyl)cyclohexane carboxamide trihydrochloride (WAY100635) (0.63 mg/kg) increased the level of IEG mRNA induction by F15063. Furthermore, (+)-8-hydroxy-2-(di-n-propylamino)tetralin [(+)-8-OH-DPAT] at 0.16 mg/kg decreased haloperidol-induced striatal IEG mRNA expression although it exerted no effects on its own. These results are consistent with an activation of serotonin 5-HT(1A) receptors by F15063, thus reducing D(2) blockade-induced striatal IEG mRNA. Furthermore, the substantial F15063-induced expression of IEGs such as c-fos in striatum is not related to cataleptogenic activity and may act more as a marker of efficacious dopamine D(2) receptor blockade.

Pharmacological profiles in rats of novel antipsychotics with combined dopamine D2/serotonin 5-HT1A activity: comparison with typical and atypical conventional antipsychotics

Combining antagonist/partial agonist activity at dopamine D2 and agonist activity at serotonin 5-HT1A receptors is one of the approaches that has recently been chosen to develop new generation antipsychotics, including bifeprunox, SSR181507 and SLV313. There have been, however, few comparative data on their pharmacological profiles. Here, we have directly compared a wide array of these novel dopamine D2/5-HT1A and conventional antipsychotics in rat models predictive of antipsychotic activity. Potency of antipsychotics to antagonize conditioned avoidance, methylphenidate-induced behaviour and D-amphetamine-induced hyperlocomotion correlated with their affinity at dopamine D2 receptors. Potency against ketamine-induced hyperlocomotion was independent of affinity at dopamine D2 or 5-HT1A receptors. Propensity to induce catalepsy, predictive of occurrence of extrapyramidal side effects, was inversely related to affinity at 5-HT1A receptors. As a result, preferential D2/5-HT1A antipsychotics displayed a large separation between doses producing 'antipsychotic-like' vs. cataleptogenic actions. These data support the contention that 5-HT1A receptor activation greatly reduces or prevents the cataleptogenic potential of novel antipsychotics. They also emphasize that interactions at 5-HT1A and D2 receptors, and the nature of effects (antagonism or partial agonism) at the latter has a profound influence on pharmacological activities, and is likely to affect therapeutic profiles.

Antipsychotic-like vs cataleptogenic actions in mice of novel antipsychotics having D2 antagonist and 5-HT1A agonist properties

A new generation of proven or potential antipsychotics, including aripiprazole, bifeprunox, SSR181507 and SLV313, exhibit agonist actions at serotonin 5-HT1A receptors, but little comparative data are available on their pharmacological profiles. Here, we compared in mice the in vivo antipsychotic-like vs cataleptogenic activities of these compounds with those of drugs that exhibit little interaction at 5-HT1A receptors, such as haloperidol, olanzapine and risperidone. All the drugs dose-dependently reduced apomorphine-induced climbing or sniffing and, with the exception of ziprasidone, produced complete suppression of these responses. In the bar catalepsy test, when administered alone, haloperidol, olanzapine and risperidone produced marked catalepsy, whereas, at doses up to 40 mg/kg, aripiprazole, SLV313, SSR181507, and sarizotan produced little or no catalepsy. The latter compounds, therefore, displayed a large separation between doses with 'antipsychotic-like' and those with cataleptogenic actions. When 5-HT1A receptors were blocked by pretreatment with WAY100635 (2.5 mg/kg, s.c.), cataleptogenic properties of SSR181507 and sarizotan were unmasked, and the catalepsy induced by bifeprunox was enhanced. In the case of aripiprazole and SLV313, although WAY100635 produced upward shifts in their dose-response, the magnitude of catalepsy appeared to reach an asymptotic plateau, suggesting that other mechanisms may be involved in their low cataleptogenic liability. The present data confirm that 5-HT1A receptor activation reduces or even completely prevents the cataleptogenic potential of novel antipsychotic agents. Further, they indicate that the balance of affinity and/or efficacy between D2 and 5-HT1A receptors profoundly influences their pharmacological activities, and will likely impact their therapeutic profiles.

Anticataleptic properties of alpha2 adrenergic antagonists in the crossed leg position and bar tests: differential mediation by 5-HT1A receptor activation

RATIONALE

Recent studies suggest that alpha(2) adrenoceptor blockade may improve the antipsychotic-like effects of neuroleptics and attenuate dopamine D(2) receptor antagonist-induced catalepsy. However, several alpha(2) adrenergic antagonists also display serotonin 5-HT(1A) receptor agonist activity, which may contribute to anticataleptic actions.

OBJECTIVES

In this study, we examined a series of alpha(2) adrenergic antagonists to determine the role of activity at serotonin 5-HT(1A) receptors in their anticataleptic effects.

METHODS

Catalepsy in rats induced by the antipsychotic haloperidol (2.5 mg/kg, SC) was measured using the cross-legged position (CLP) and bar tests. The compounds examined in this study, in decreasing rank order of alpha(2) adrenergic versus 5-HT(1A) receptor selectivity, were atipamezole, methoxy-idazoxan (RX821002), efaroxan, idazoxan, and yohimbine. Antagonism studies were conducted using the selective 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide dihydrochloride (WAY100635).

RESULTS

Idazoxan, efaroxan, and yohimbine significantly attenuated the cataleptic effects of haloperidol (2.5 mg/kg, SC) in the CLP test and the actions of their highest doses were significantly blocked by pre-treatment with WAY100635 (0.63 mg/kg, SC). In contrast to the other compounds, methoxy-idazoxan was ineffective in the CLP test. Atipamezole exhibited anticataleptic effects in the bar and CLP tests which were not blocked by WAY100635. Similarly, the anticataleptic effects of methoxy-idazoxan and idazoxan in the bar test were not blocked by WAY100635.

CONCLUSIONS

Serotonin 5-HT(1A) receptors play a prominent role in anticataleptic effects of certain alpha(2) adrenergic antagonists in the CLP test, whereas alpha(2)-adrenergic mechanisms are likely to be primarily responsible for the anticataleptic effects of these ligands in the bar test.

The effect of a 5-HT1A receptor agonist on striatal dopamine release

5-HT1A receptor agonists consistently reduce neuroleptic induced catalepsy in rats. A serotonin-dopamine interaction has been proposed to underlie this effect. Specifically, 5-HT1A receptor agonists may reduce the activity of serotonergic projections that inhibit dopaminergic nigrostriatal neurones, therefore increasing dorsal striatal dopamine levels and partially overcoming the neuroleptic blockade of D2 receptors. We tested the hypothesis that 5-HT1A receptor agonists increase striatal dopamine release in man using PET scanning with the selective D2 receptor radioligand [11C]raclopride, which is sensitive to endogenous dopamine levels. Six healthy volunteers received two PET scans, one after placebo, the other after 1 mg flesinoxan, a selective 5-HT1A receptor agonist. Binding potential values for striatal subdivisions were determined using a simplified reference tissue model. We did not find any difference in striatal [11C]raclopride binding between conditions, even though flesinoxan lead to typical 5-HT1A receptor agonist side effects and produced elevation of growth hormone in five of the six subjects. Our results suggest that the anticataleptic effect of 5-HT1A receptor agonists is not mediated by striatal dopamine release, and indicates a need for further research with other suitable 5-HT1A receptor agonists.

Cocaine-induced ???active immobility??? and its modulation by the serotonin1A receptor

'Active immobility' (AI) is an independent behaviour that can be characterized by behavioural immobility, an increased muscular rigidity and the sustaining of an unusual posture. In previous studies with cocaine we observed, concomitant with hyperlocomotion and increased rearing activity, an increase in AI in well-habituated animals, which may constitute another 'positive' acute effect of cocaine on behaviour. The contribution of the serotonergic (5-HT) system to AI is well established. However, little information exists about the contribution of particular 5-HT-receptor subtypes. In order to examine a possible role of the 5-HT1A receptor on this effect of cocaine, we systematically re-analysed four previous experiments in well-habituated animals and one in little-habituated animals, focusing on the acute behavioural effects of cocaine on AI. We found that, in well-habituated animals, cocaine at a medium dose (10 mg/kg, i.p.) induces AI behaviour, which, however, does not correlate with cocaine effects on locomotion, rearing or grooming behaviour. However, there was no effect of cocaine (1, 5 or 15 mg/kg, i.p.) on AI in little-habituated animals. The 5-HT1A-receptor antagonist, WAY 100635 [N-[2-(4-2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide trihydrochloride] (0.4 mg/kg, i.p.), potentiated cocaine-induced AI in well-habituated animals, while the 5-HT1A-receptor agonist, 8-OH-DPAT (0.2 mg/kg, i.p.), attenuated it. The local application of 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin] into the nucleus accumbens (0, 1, 10 micromol/l) or hippocampus (0, 0.1, 1, 10 micromol/l) modulated cocaine-induced AI in a complex way. These results showed that cocaine induces AI at a medium dose in well-habituated but not in little-habituated animals. The cocaine-induced AI in well-habituated animals can be potentiated by systemic 5-HT1A-receptor antagonism and attenuated by 5-HT1A-receptor agonism. Two experiments with local activation of postsynaptic 5-HT1A receptors revealed that both nucleus accumbens and hippocampal 5-HT1A-receptor populations are involved in the expression of cocaine-induced AI.

Effects of Lesopitron on the Central Nervous System Arising from Its Interaction with 5-HT1A Receptors

Lesopitron acts as a ligand for central serotonin 5-HT1A receptors. Ki obtained from [3H]8-OH-DPAT competition studies was 104.8 +/- 10.6 nmol/l. As lesopitron did not affect the binding of [3H]paroxetine, involvement of the serotonin reuptake system in the effects of lesopitron is rejected. Lesopitron inhibits haloperidol-induced catalepsy that is the consequence of its action on 5-HT1A autoreceptors. The ability of lesopitron to induce 5-HT syndrome reflects post-synaptic 5-HT1A receptor activation and the reversion of 8-OHDPAT-induced 5-HT syndrome by lesopitron suggests a partial agonist effect on this receptor-type. Lesopitron induced a hypothermic effect due to the enhanced activation of post-synaptic 5-HT1A receptors. The agonist effect of lesopitron on 5-HT1A receptors and its marked hypothermic effect is an added value for this drug and a stimulus to the study of its possible neuroprotective action.

5-HT1A receptor activation and anti-cataleptic effects: high-efficacy agonists maximally inhibit haloperidol-induced catalepsy

Studies have shown that 5-HT1A receptor ligands modulate antipsychotic-induced catalepsy. Here, we further examined the role of intrinsic activity at 5-HT1A receptors in these effects. The anti-cataleptic effects of 5-HT(1A) receptor ligands with positive intrinsic activity [from high to low: 3-chloro-4-fluorophenyl-(4-fluoro-4-[[(5-methyl-6-methylamino-pyridin-2-ylmethyl)-amino]-methyl]-piperidin-1-yl-methanone fumaric acid salt (F 13714), eptapirone, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), 2-[4-[4-(7-methoxy-1-naphtyl) piperazino]butyl]-4-methyl-2H,4H-1,2,4-triazin-3,5-dione maleic acid salt (F 11461), buspirone, 2-[4-[4-(7-benzofuranyl)piperazino]butyl]-4-methyl-2H,4H-1,2,4-triazin-3,5-dione (F 12826), ipsapirone, and (s)-N-tert-butyl-3-(4-(2-methoxyphenyl)piperazine-1-yl)-2-phenylpropanamide hydrochloride (WAY 100135)] and negative intrinsic activity [N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide dihydrochloride (WAY 100635)] were examined. Catalepsy was induced by the classical antipsychotic haloperidol (0.63 mg/kg) and measured in the cross-legged position test and in the bar test. All 5-HT1A receptor agonists, except WAY 100135, significantly attenuated the effects of haloperidol in the cross-legged position test. All agonists had similar effects in the bar test, except ipsapirone, which failed to attenuate haloperidol-induced catalepsy. In contrast to the effects observed with the agonists, the inverse agonist WAY 100635 appeared to enhance haloperidol-induced catalepsy in both tests, in agreement with earlier findings. The maximal effects of the 5-HT1A receptor ligands to attenuate catalepsy correlated positively with the rank order of their intrinsic activity at 5-HT1A receptors (either catalepsy test: r(S)=0.92, P<0.001). F 13714, which had the highest intrinsic activity, maximally inhibited haloperidol-induced catalepsy in the cross-legged position and bar tests (100% and 99% inhibition, respectively). Because the magnitude of the anti-cataleptic effects of 5-HT1A receptor ligands correlates positively with their intrinsic activity, it is likely that F 13714 has marked anti-cataleptic effects because of its high intrinsic activity at 5-HT1A receptors.

Cataleptic effect of neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one in mice: modulation by serotonergic agents

The neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) induced catalepsy in mice is modified by dopaminergic, adenosinergic and GABAergic agents. In light of serotonergic agents being implicated in antipsychotic-induced catalepsy and their ability to increase brain neurosteroid content, the present study was undertaken to investigate the effect of various 5-HT agents on catalepsy induced by 3alpha,5alpha-THP in mice. Pretreatment with selective serotonin reuptake inhibitor, fluoxetine (5 mg/kg, i.p.), 5-HT releaser, fenfluramine (10 mg/kg, i.p.), 5-HT(1A) receptor agonist, 8-OH-DPAT (0.3 mg/kg, s.c.), 5-HT1B/1C receptor agonist, TFMPP (3 mg/kg, i.p.), 5-HT2A/1C receptor agonist, DOI (1.5 mg/kg, s.c.) and 5-HT3 agonist, 2-methylserotonin (5 mg/kg, i.p.) potentiated the catalepsy induced by exogenous administration of 3alpha,5alpha-THP. Furthermore, FGIN 1-27, an MDR agonist that increases endogenous content of 3alpha,5alpha-THP although per se failed to exhibit any cataleptic effect but enhanced the cataleptic response in combination with these serotonergic agents. The potentiating action of 5-HT1A, 5-HT2A/1C or 5-HT3 receptor agonist on 3alpha,5alpha-THP induced catalepsy was not blocked by prior administration of sub-effective dose (1 mg/kg, s.c.) of their respective receptor antagonists pindolol, ritanserin or ondansetron or by pretreatment with serotonergic neurotoxin 5,7-DHT (100 microg/mouse, i.c.v.). However this effect of different serotonergic agents was antagonized by the GABA(A) receptor antagonist, bicuculline (1 mg/kg, i.p.) or the 3alpha-hydroxysteroid oxidoreductase enzyme inhibitor, indomethacin (5 mg/kg, i.p.). The 5-HT agents enhance neurosteroid-induced catalepsy by increasing GABAergic tone, likely as a consequence of increased brain content of 3alpha,5alpha-THP.

Catalepsy induced by the 5-HT(1A) receptor antagonist WAY 100635 in rats pretreated with the selective serotonin reuptake inhibitor citalopram

Neither a high dose of the selective serotonin reuptake inhibitor citalopram (100 micromol kg(-1) s.c.), nor the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide 3HCl (WAY 100635) (0.1--0.4 micromol kg(-1) s.c.) produced any evidence of catalepsy in adult male rats. When combined with citalopram, however, WAY 100635 produced a dose-dependent, and statistically significant, catalepsy in the inclined grid test.