Comparison of the effects of antidepressants and their metabolites on reuptake of biogenic amines and on receptor binding.

1. The present survey compares the effects of antidepressants and their principal metabolites on reuptake of biogenic amines and on receptor binding. The following antide-pressants were included in the study: the tricyclic antidepressants amitriptyline, dothiepin, and lofepramine and the atypical antidepressant bupropion, which all have considerable market shares in the UK and/or US markets; the selective serotonin reuptake inhibitors (SSRIs) citalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline; and the recently approved antidepressants venlafaxine and nefazodone. 2. Amitriptyline has similar in vitro reuptake inhibitory potencies for 5-HT and NA, whereas the metabolite nortriptyline is preferentially a NA reuptake inhibitor. Both amitriptyline and nortriptyline are also 5-HT2 receptor antagonists. 3. Dothiepin has equipotent 5-HT and NA reuptake inhibitory activity, whereas northiaden shows a slight selectivity for NA reuptake inhibition. Dothiepin and northiaden are also 5-HT2 receptor antagonists. The slow elimination rate of northiaden (36-46 hr) compared to dothiepin (14-24 hr) suggests that northiaden contributes significantly to the therapeutic effect of dothiepin. 4. Lofepramine is extensively metabolized to desipramine. Desipramine plays an important role in the antidepressant activity of lofepramine, as the plasma elimination half-life of lofepramine (4-6 hr) is much shorter than that of desipramine (24 hr). Both compounds are potent and selective inhibitors of NA reuptake. 5. The five approved SSRIs, citalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline, are potent 5-HT reuptake inhibitors, and the demethyl metabolites, norfluoxetine, demethylsertraline, and demethylcitalopram, also show selectivity. Paroxetine and sertraline are the most potent inhibitors of 5-HT reuptake, whereas citalopram is the most selective. Fluoxetine is the least selective and the metabolite of fluoxetine, norfluoxetine, is a more selective and more potent 5-HT reuptake inhibitor than the parent compound and has an extremely long half-life (7-15 compared to 1-3 days). Thus the metabolite plays an important role for the therapeutic effect of fluoxetine. Fluoxetine is also a 5-HT2C receptor antagonist. Demethylsertraline is a weaker and less selective 5-HT reuptake inhibitor in vitro than sertraline, but demethylsertraline has a very long half-life (62-104 hr) compared to the parent compound (24 hr) and it might play a role in the therapeutic effects of sertraline. Demethylcitalopram has about a 10 times lower 5-HT reuptake inhibitory potency in vitro than citalopram, and the elimination half-lives are approximately 1.5 and 2 days, respectively. 6. Bupropion and hydroxybupropion are weak inhibitors of biogenic amine reuptake. The mechanisms of action responsible for the clinical effects of bupropion are not fully understood, but it has been suggested that both dopaminergic and noradrenergic components play a role and that the hydroxybupropion metabolite contributes significantly to the antidepressant activity. 7. Venlafaxine and O-demethylvenlafaxine are weak inhibitors of 5-HT and NA reuptake, and the selectivity ratios are close to one. O-Demethylvenlafaxine is eliminated more slowly than venlafaxine (plasma half-lives of 5 and 11 hr, respectively), and it is likely that it contributes to the overall therapeutic effect of venlafaxin. 8. Nefazodone and alpha-hydroxynefazodone are equipotent 5-HT and NA reuptake inhibitors. Both compounds are also 5-HT2 receptor antagonists. Both parent compound and metabolite have short elimination half-lives.

Differentiation of classical and novel antipsychotics using animal models.

The criteria that have been used to differentiate classical and atypical antipsychotics include measures of neurological and cognitive side effects and therapeutic effects. Novel antipsychotic compounds with few or no extrapyramidal syndromes (EPS) can be differentiated from classical neuroleptics by a number of animal models for limbic selectivity and dose-response separation between behavioral and pharmacological parameters analogous to EPS and antipsychotic effects. The results obtained using these models seem to be concordant with clinical findings. Moreover, animal models expand our understanding of the pharmacological mechanisms responsible for EPS and for the therapeutic effects of antipsychotics, and they allow an examination of the possible effects of new compounds on cognition. Here we review a number of key reports on the differentiation of classical and novel antipsychotics using animal models.

Serotonin 5-HT2 receptor, dopamine D2 receptor, and alpha 1 adrenoceptor antagonists. Conformationally flexible analogues of the atypical antipsychotic sertindole.

Conformationally flexible analogues of the atypical antipsychotic sertindole (1-[2-[4-[5-chloro -1-(4-fluorophenyl)-1H-indol-3-yl]-4-piperidinyl]ethyl]-2-imidazolidi non e) were synthesized. Replacement of the 4-piperidinyl ring in sertindole by a 2-(methylamino)ethoxy group or a 2-(methylamino)ethyl group (e.g. 1-[2-[2-[5-chloro-1-(4-fluorophenyl)-1H -indol-3-yloxy]ethyl-methylamino]ethyl]-2-imidazolidinone and 1-[3-[[2-[5-chloro-1-(4-fluorophenyl)-1H-indol-3-yl] -ethyl]methylamino]propyl]-2-imidazolidinone results in binding affinities for serotonin 5-HT2A and dopamine D2 receptors, as well as alpha 1 adrenoceptors, which are very similar to those of sertindole. (Methylamino)alkyl groups of other chain lengths, 3-(methylamino)propyloxy groups, and 2-(methylamino)ethylsulfanyl groups do not have such properties. The capability of the 2-(methylamino)ethoxy group and the 2-(methylamino)ethyl group to replace the 4-piperidinyl ring in sertindole is reflected in molecular modeling studies using recently published receptor-interaction models for 5-HT2 and D2 receptors. Structure-affinity investigations concerning the substituents in the indole nucleus and the 2-imidazolidinone ring system in the 2-(methylamino)ethoxy and the 2-(methylamino)ethyl analogues of sertindole have led to high affinity serotonin 5-HT2A receptor antagonists with selectivity versus dopamine D2 receptors and alpha 1 adrenoceptors (e.g. 1-[2-[[2-[6-chloro-1-(4-fluorophenyl) -1H-indol-3-yloxy]ethyl]methylamino]-ethyl]-2-imidazolidinone and 1-[3-[[2-[6-chloro-1-(4-fluorophenyl) -1H-indol-3-yl]ethyl]methylamino]propyl]-2-imidazolidinone). The latter derivative has also high selectivity for 5-HT2A receptors versus serotonin 5-HT2C receptors. Replacement of the basic amino group by nitrogen-containing six-membered rings has led to 5-chloro-1-(4-fluorophenyl)-3-[(4-methylpiperazinyl)-ethoxy]-1H-in dole, which has high affinity for dopamine D2, versus low affinity for serotonin 5-HT2A receptors and alpha 1 adrenoceptors.

Enhanced D1 affinity in a series of piperazine ring substituted 1-piperazino-3-arylindans with potential atypical antipsychotic activity.

A study of the effect of aromatic substitution on D1 and D2 affinity in a series of previously reported trans-1-piperazino-3-phenylindans shows similar structure-activity relationships for the two receptor sites. 6-Substituted derivatives have affinity for both receptors, and 6-chloro-or 6-fluoro-substituted derivatives show preference for D1 receptors. D1 affinity and selectivity are significantly increased in a series of new piperazine ring substituted derivatives. Potent D1 and D2 antagonism in vivo are confined to derivatives with relatively small substituents in the 2-position of the piperazine ring (e.g. 2-methyl,2,2-dimethyl, 2-spirocyclobutyl or 2-spirocyclopentyl). Consequently, the effect of aromatic substitution is examined in a series of 1-(2,2-dimethylpiperazino)-3-arylindans. All these compounds except the 4-, 5-, 7- and 4'-chloro-substituted derivatives have potent D1 affinity (IC50's below 10 nM) and the majority of the compounds antagonize SK&F 38393-induced circling in 6-OHDA-lesioned rats with ED50 values about 1 mumol/kg. In vitro all compounds show preference for D1 receptors, but in vivo they are equally effective as D1 and D2 antagonists. The compounds have high affinity for 5-HT2 receptors and selected compounds show high affinity for alpha 1 adrenoceptors. Furthermore, a subgroup consisting of (-)-38, (-)-39, (-)-41, and (-)-54 does not induce catalepsy in rats. These compounds have the potential of being "atypical" antipsychotics and have consequently been selected for further studies. The non-receptor-blocking enantiomers are shown to be inhibitors of DA and NE uptake in accordance with previous observations in compounds unsubstituted in the piperazine ring. Two compounds, (+)-38 and (+)-40, block DA uptake with IC50 values below 10 nM. Finally, the observed structure-activity relationships are discussed in relation to previously published pharmacophore models for D2 and 5-HT2 receptors. It is concluded that the piperazine substituents might induce a different binding mode at the dopamine receptor sites, perhaps only at the D1 receptor site.

Isolation-induced aggression in mice: effects of 5-hydroxytryptamine uptake inhibitors and involvement of postsynaptic 5-HT1A receptors.

The inhibitory potencies of selective serotonin (5-hydroxytryptamine, 5-HT) uptake inhibitors on isolation-induced aggressive behaviour in male mice were studied. Furthermore, the role of postsynaptic 5-HT1A receptors in the mediation of aggressive behaviour was studied. The selective 5-HT uptake inhibitors, sertraline, floxetine, femoxetine and fluvoxamine, showed weak antiaggressive effects, and citalopram and paroxetine were ineffective. This rank of potencies corresponded with neither uptake inhibitory potencies in vitro nor potentiation of 1-5-hydroxytryptophan (1,5-HTP)-induced motor effects in vivo, as citalopram and paroxetine were among the most potent compounds in these tests. A subeffective dose of 1,5-HTP (110 mumol/kg = 25 mg/kg, s.c.) potentiated the antiaggressive effect of citalopram and paroxetine more than 110 and 1600 times, respectively. The effects of sertraline, fluvoxamine, fluoxetine and femoxetine were only potentiated 3, 36, 4 and 16 times, respectively. The 5-HT releasing compound fenfluramine inhibited the aggressive behaviour dose dependently, and depletion of 5-HT by treatment with p-chloro-phenylalanine methyl ester attenuated this effect significantly. p-Chloro-phenylalanine methyl ester was ineffective itself, but potentiated the antiaggressive effect of the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamin)tetralin (8-OH-DPAT). The beta-adrenoceptor/5-HT1A receptor antagonist, (-)-penbutolol, reversed the antiaggressive effects of 8-OHDPAT. In conclusion, selective 5-HT uptake inhibitors act in different ways on isolation-induced aggressive behaviour, and postsynaptic 5-HT1A receptors are involved in mediating the aggressive behaviour.

Pharmacological characterization of selective serotonin reuptake inhibitors (SSRIs).

Established antidepressants including tricyclic antidepressants (TCAs), tetracyclic antidepressants and monoamine oxidase inhibitors (MAOIs) affect a series of neurotransmitter functions. In the debate of clinical efficacy much attention has focused on the uptake of noradrenaline (NA) and serotonin (5-HT) as a means to increase neuronal activity. Most antidepressants, whether classic or new, inhibit the uptake of either one or the other or both transmitters. Besides that, all of the classical antidepressants potently inhibit a series of neurotransmitter receptors. A series of newer antidepressants preferentially increase 5-HT transmission by inhibiting 5-HT uptake. Selective serotonin reuptake inhibitors (SSRIs) are those which preferably inhibit 5-HT uptake compared with NA, and which at the same time have no or only slight effect on other uptake mechanisms, neurotransmitter receptors, enzymes, etc. Five SSRIs are currently marked, i.e. citalopram, fluoxetine, fluvoxamine, paroxetine and sertraline. They all fulfil the above-mentioned criteria. Citalopram is the most selective 5-HT-uptake inhibitor, whereas paroxetine is the most potent. By and large the rank order of selectivity is equal in in vitro studies, in biochemical in vivo studies and in behavioural studies. Selectivity and potency for 5-HT uptake do not coincide. The selectivity of SSRIs is also founded on the lack of inhibition of receptors for different neurotransmitters, e.g. acetylcholine, histamine, NA, 5-HT or dopamine (DA), as well as monoamine oxidase (MAO). Citalopram, fluoxetine and sertraline are metabolized to compounds possessing similar properties as the parent drugs, whereas this is not the case with the metabolites of fluvoxamine and paroxetine. Upon repeated administration SSRIs maintain the selective and potent inhibition of 5-HT uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereospecific and selective 5-HT2 antagonism in a series of 5-substituted trans-1-piperazino-3-phenylindans.

A study of the effect of aromatic substitution on 5-HT2, D2, and alpha 1 receptor affinity in a subseries of new and previously synthesized 1-piperazino-3-phenylindans indicated that high 5-HT2 selectivity could be obtained in 5-substituted derivatives. Accordingly, a series of 5-substituted derivatives was synthesized with the goal of obtaining stereospecific and selective, centrally acting 5-HT2 antagonists. This goal was fulfilled in 5-chloro- or 5-fluoro-substituted compounds with 2-(3-alkyl-2-oxoimidazolidin-1-yl)ethyl- or 2-(tetrahydro-2-oxo-1H-pyrimidin-1-yl)ethylpiperazine substituents, as well as in their imidazolidine-2-thione or pyrimidine-2-thione analogues. The most interesting derivatives were resolved either directly via diastereomeric salts or by syntheses from resolved starting materials. Optical purity was determined by a 1H NMR method, using the chiral shift reagent (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol. The compound (-)-trans-1-[2-[4-[5-chloro-3-(4-fluorophenyl)-2,3-dihydro-1H-inden++ +-1- yl]piperazin-1-yl]ethyl]-3-isopropyl-2-imidazolidinone ((-)-20) had the overall best profile with a high stereoselectivity (eudismic ratio: 68) and a high selectivity versus D2 and alpha 1 receptors (affinity ratios 182 and 191, respectively). It had a potent central effect but was shorter-acting than the tetrahydropyrimidinone or thione derivatives ((-)-39, (+)-40, (-)-41, and (+)-42). The observed activities of the compounds are settled in perspective in relation to a recently proposed D2 receptor interaction model. While there are no indications so far that trans-1-piperazino-3-phenylindans interact with D2 and 5-HT2 receptors in different conformations, the present study shows important differences in aromatic substitution effects. Only 5-HT2 receptors are able to accommodate a 5-substituent in the indan benzene ring, thus allowing syntheses of highly selective compounds.

Interaction of the antiemetic metopimazine and anticancer agents with brain dopamine D2, 5-hydroxytryptamine3, histamine H1, muscarine cholinergic and alpha 1-adrenergic receptors.

The interactions of the antiemetic metopimazine (MPZ) and of the chemotherapeutic agents, cisplatin, carboplatin, doxorubicin, etoposide and vincristine were investigated at five neurotransmitter receptor binding sites. MPZ had nanomolar affinity for alpha 1, dopamine D2 and histamine H1 receptors, weak affinity for muscarinic cholinergic receptors, but no affinity for 5-hydroxytryptamine3 (5-HT3) receptors. Except for vincristine, which showed nanomolar affinity of muscarinic cholinergic receptors, none of the chemotherapeutic agents showed affinity for any of the receptors investigated at concentrations ranging between 10(-5) and 10(-7) M. Accordingly, chemotherapy-induced nausea and vomiting seems to be mediated by mechanisms other than the direct interaction of cytostatics with the neurotransmitter receptors investigated. Our finding that MPZ is without affinity for 5-HT3 receptors and therefore seems to mediate its antiemetic effect predominantly by dopamine D2 receptor blockade makes it an interesting drug for use in combinations with the new class of antiemetics, the 5-HT3 receptor antagonists. Data obtained in a recent clinical trial support this observation.

The role of serotonergic mechanisms in inhibition of isolation-induced aggression in male mice.

The role of serotonergic (5-HT) receptor subtypes in mediation of aggressive behaviour in isolated male mice has been studied. Increase of attack latency was used as a simple measure of antiaggressive behaviour. 5-HT1A agonists (BAY R 1531, 8-OHDPAT, flesinoxan, gepirone, 5MeO DMT, buspirone, ipsapirone, BMY 14802) completely inhibit the aggressive behaviour irrespective of their intrinsic activities. Also the putative antagonists spiroxatrine and NAN 190 as well as the non-selective 5-HT1 agonists RU 24969, TFMPP, mCPP and eltoprazine have an antiaggressive effect. The mixed 5-HT1A and beta-adrenoceptor antagonists (-)-alprenolol and pindolol are ineffective and do not inhibit the effect of 8-OHDPAT. Neither does the non-selective 5-HT antagonist metergoline. The antiaggressive effect correlates with 5-HT1A receptor affinity in vitro and with generalization to the 8-OHDPAT-induced discriminative stimulus. The selective 5-HT uptake inhibitor citalopram does not inhibit aggressive behaviour. The 5-HT2 agonist DOI has an antiaggressive effect only at high doses, whereas the 5-HT2 antagonist ritanserin and the 5-HT3 antagonist ondansetron are ineffective. Prazosin (alpha 1-adrenoceptor antagonist), clonidine (alpha 2-adrenoceptor agonist), clenbuterol (beta-adrenoceptor agonist), ketanserin (5-HT2 receptor and alpha 1-adrenoceptor antagonist), clozapine and (-)-octoclothepin (dopamine (DA), 5-HT2 receptor and alpha 1-adrenoceptor antagonist) all show an antiaggressive effect. SCH 23390 (DA D1 receptor antagonist) and emonapride (DA D2 receptor antagonist) are ineffective. In conclusion, 5-HT1A receptors are involved in mediation of isolation-induced aggressive behaviour in mice. The involvement of other 5-HT receptor subtypes needs further clarification. The adrenergic system may also be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective, centrally acting serotonin 5-HT2 antagonists. 1. 2- and 6-substituted 1-phenyl-3-(4-piperidinyl)-1H-indoles.

A series of 1-[2-[4-(1H-indol-3-yl)-1-piperidinyl]ethyl]-2-imidazolidinones has been synthesized. The 1-position of the indole is substituted with phenyl groups and in the 2- or 6-positions are additional substituents. An analogous series with the imidazolidinone ring opened to corresponding urea derivatives was also prepared. High potency and selectivity for 5-HT2 receptors (as compared with D2 and alpha 1 receptor affinities) were obtained with medium-large substituents such as 6-chloro, 6-methyl, and 6-trifluoromethyl or a 2-methyl substituent. Larger 6-substituents such as isopropyl considerably reduced activity, while the smaller 6-fluoro substituent afforded unselective compounds. Selective 5-HT2 antagonists were found by combining 6-substitution with both unsubstituted 1-phenyl and substituted 1-phenyl groups (2-F, 4-F, 4-Cl). However, 3-substitution of the phenyl group markedly reduced 5-HT2 receptor affinity, especially with a 3-trifluoromethyl substituent. Introduction of a 3-(2-propyl) substituent in the imidazolidinone ring reduced binding to alpha 1 adrenoceptors with a factor of 3-8. Practically no influence on 5-HT2 and D2 receptor affinities were found by the presence of this substituent compared to the 3-unsubstituted derivatives. Compounds with potent receptor binding also potently inhibited the quipazine-induced head twitch syndrome in rats. The compounds were equally active after oral and subcutaneous administration and they had a long duration of action (> 24 h). Especially urea derivatives were found to be considerably more potent at 24 h than at 2 h after subcutaneous administration. Some of the compounds potently inhibited isolation-induced aggression in mice, an effect which, however, did not correlate to 5-HT2 receptor-mediated activities. On the basis of these structure-activity studies 1-[2-[4-[6-chloro-1-(4-fluorophenyl)-1H-indol-3-yl]-1- piperidinyl]ethyl]-3-(2-propyl)-2-imidazolidinone (Lu 26-042, compound 4c) was selected for further pharmacological and toxicological investigations.

Partial and full dopamine D1 receptor agonists in mice and rats: relation between behavioural effects and stimulation of adenylate cyclase activity in vitro.

The dopamine (DA) D1 agonists, SK&F 83959, SK&F 75670, SK&F 38993, SK&F 81297 and SK&F 80723, had variable abilities to stimulate adenylate cyclase activity in rat striatal homogenates. Their efficacies, in relation to the effect of 100 microM DA were 0, 33, 69, 68 and 81%, respectively. In rats, all compounds induced (1) contralateral circling behaviour after unilateral 6-hydroxy-DA lesions, (2) ipsilateral circling behaviour after midbrain hemitransection after cotreatment with the D2 agonist quinpirole and (3) oral stereotypies after their combination with quinpirole. Maximum effects and rank order of potencies were similar in the three test models. In mice SK&F 83959, SK&F 75670 and SK&F 38393 inhibited methylphenidate-induced gnawing behaviour and induced no or only weak hypermotility. SK&F 81297 induced marked hypermotility which was partially inhibited by SK&F 83959 and SK&F 75670 and was completely blocked by the D1 antagonist, SCH 23390. It is concluded that no relation could be demonstrated between the efficacy to stimulate adenylate cyclase and to induce circling behaviours and stereotypies in rats. In contrast, a relation between biochemical and behavioural efficacies was found in the mouse models. The results suggest that different subtypes of D1 receptors mediate the behavioural effects reported in this study.

Noncataleptogenic, centrally acting dopamine D-2 and serotonin 5-HT2 antagonists within a series of 3-substituted 1-(4-fluorophenyl)-1H-indoles.

A series of 1-(4-fluorophenyl)-1H-indoles substituted at the 3-position with 1-piperazinyl, 1,2,3,6-tetrahydro-4-pyridinyl, and 4-piperidinyl was synthesized. Within all three subseries potent dopamine D-2 and serotonin 5-HT2 receptor affinity was found in ligand binding studies. Quipazine-induced head twitches in rats were inhibited by most derivatives as a measure of central 5-HT2 receptor antagonism. Piperazinyl and tetrahydropyridyl indoles were cataleptogenic, while piperidyl substituted indoles surprisingly were found to be noncataleptogenic or only weakly cataleptogenic. Noncataleptogenic piperidyl derivatives also failed to block dopaminergic-mediated stereotypies, that is methyl phenidate-induced gnawing behavior in mice. These profiles resemble that of the atypical neuroleptic clozapine. 1-Ethyl-2-imidazolidinone was found to be the optimal substituent of the basic nitrogen atom in order to avoid catalepsy. The atypical neuroleptic 1-[2-[4-[5-chloro-1-(4-fluorophenyl)-1H-indol-3-yl]-1-piperidinyl] ethyl]-2-imidazolidinone (sertindole, compound 14c) was selected for further development as a result of these structure/activity studies.

The acute effect of sertindole on brain 5-HT2, D2 and alpha 1 receptors (ex vivo radioreceptor binding studies).

The ability of sertindole to influence the ex vivo binding of 3H-ketanserin, 3H-prazosin and 3H-spiperone to 5-HT2 receptors, alpha 1-adrenoceptors and DA D2 receptors, respectively, in rat brain has been studied after acute treatment. Sertindole is a potent, long acting compound which readily passes the blood-brain barrier. It dose-dependently binds to all three receptors types. In line with in vivo behavioural experiments sertindole has the most pronounced effect on 5-HT2 receptors, lower effect on alpha 1-adrenoceptors and the lowest effect on striatal D2 receptors.

The pharmacological effect of citalopram residues in the (S)-(+)-enantiomer.

The enantiomers of citalopram and N-demethylcitalopram have been investigated. Based on the inhibition of 5-HT uptake in vitro and the potentiation of 1-5-HTP in vivo the pharmacological activity resides in the (+)-enantiomers (the eutomers*) with the 1-(S) absolute configuration. In the 5-HT uptake test eudismic ratios of 167 and 6.6 are obtained for the enantiomers of citalopram and N-demethylcitalopram, respectively. The pharmacological profile of the eutomers of citalopram and N-demethylcitalopram very much resembles the profile of the respective racemates.

Octoclothepin enantiomers. A reinvestigation of their biochemical and pharmacological activity in relation to a new receptor-interaction model for dopamine D-2 receptor antagonists.

Octoclothepin (1) was resolved into its R and S enantiomers via the diastereomeric tartaric acid salts. The enantiomers were shown to be of high optical purity by 1H NMR with use of the chiral shift reagent (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol. Pharmacological and biochemical testing confirmed that (S)-1 is the more potent dopamine (DA) D-2 antagonist both in vitro and in vivo, although the R enantiomer still has significant D-2 antagonistic activity. In contrast, both enantiomers were equally active in test models detecting activity at D-1 receptors, serotonin-2 (5-HT2) receptors and alpha 1 adrenoceptors. Contrary to a previous prediction, it was found that norepinephrine (NE) uptake inhibition was confined solely to the S enantiomer. Overall, (S)-1 has a "classical" neuroleptic profile, while the R enantiomer has a more "atypical" profile. These pharmacological profiles seem to be in agreement with the reported clinical profiles of the two enantiomers. A previous conformational study was revised in light of the biochemical test results with enantiomers of known optical purity. Their relative D-2 receptor affinity corresponded well with the calculated conformational energy difference between their "active conformations" deduced from a previously reported new D-2 receptor model. Also the high enantioselectivity of (S)-1 at the NE uptake site could be explained after a detailed conformational analysis showing strict requirements for the orientation of the piperazine lone-pair direction at the NE uptake site.

Pre- and postsynaptic dopaminergic activities of indolizidine and quinolizidine derivatives of 3-(3-hydroxyphenyl)-N-(n-propyl)piperidine (3-PPP). Further developments of a dopamine receptor model.

Pre- and postsynaptic dopaminergic activities of a series of indolizidine and quinolizidine analogues of 3-(3-hydroxyphenyl)-N-(n-propyl)piperidine (3-PPP) have been studied. The pharmacological data have been interpreted in terms of a previously reported model for interactions with dopamine pre- and postsynaptic D2-receptors and molecular mechanics (MM2(85] calculated geometries and conformational energies. The model has been further developed with respect to the receptor topography in the vicinity of the nitrogen binding site. In particular, a novel spatial orientation of the important "propyl cleft" has been proposed. This cleft is suggested to be located mainly above a plane through the receptor-bound substrate. The biologically active agonist and antagonist conformations of the enantiomers of 3-PPP have been reinvestigated.

L-5-HTP facilitates the electrically stimulated flexor reflex in pithed rats: evidence for 5-HT2-receptor mediation.

Different serotonin (5-HT) receptor agonists were tested on the electrically stimulated flexor reflex in pithed rats. The 5-HT2 receptor agonist, (1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) [+/-)DOI), the mixed 5-HT1/5-HT2 receptor agonist, quipazine, and the 5-HT precursor, l-5-HTP, showed agonistic activity upon intravenous injection while 5-HT was without effect. A combination of the peripheral decarboxylase inhibitor, Ro 4-4602 (benzerazide), the specific 5-HT-uptake inhibitor, citalopram, and l-5-HTP induced a prolonged (greater than 3 h) increase of the flexor reflex in pithed rats. Different compounds were tested for an inhibitory effect against this l-5-HTP-induced flexor reflex. The 5-HT2 antagonists (ketanserin, methergoline and methiothepin) were potent antagonists. (-)Alprenolol (5-HT1A and 5-HT1B receptor antagonist) and the 5-HT3-receptor antagonist, ICS 205-930, were without an antagonistic effect. The inhibitory potencies in the reflex model (l-5-HTP, citalopram and Ro 4-4602) were significantly correlated (r = 0.83, P less than 0.01, r2 = 0.69) with the potencies to inhibit l-5-HTP-induced head twitches and quipazine-induced head twitches (r = 0.81, P less than 0.01, r2 = 0.66). There was less correlation (r = 0.75, P less than 0.01, r2 = 0.56) with the affinities for 5-HT2 receptors in vitro. There was no significant correlation between inhibitory potencies in the reflex model and affinities for dopamine (DA) D-2 receptors or alpha 1-adrenoceptors (r2 = 0.13 and 0.14, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine D-2 agonists with high and low efficacies: differentiation by behavioural techniques.

The effects of the dopamine (DA) D-2 antagonist YM 09151-2 and the DA D-2 agonists terguride, preclamol, EMD 23448, B-HT 920, quinpirole and (-)-NPA were studied in a battery of behavioural tests in order to evaluate their relative efficacies. Furthermore, their affinities for DA D-2 receptors labelled by 3H-N-0437 were measured in vitro. All agonists reduced spontaneous locomotor activity and induced marked contralateral circling behaviour in 6-hydroxy-DA-lesioned rats. Quinpirole and (-)-NPA increased motor activity after high doses. YM 09151-2 did not induce circling. In hemitransected rats quinpirole and (-)-NPA had weak effects when given alone, whereas the other agonists were ineffective. After combination with DA D-1 agonist SK&F 38393, B-HT 920 became effective, and the effects of quinpirole and (-)-NPA were facilitated. EMD 23448, preclamol and terguride were not active. In contrast, the two latter compounds fully inhibited the response to apomorphine. In stereotypy experiments a similar activity pattern was observed. Finally, drug discrimination studies showed that quinpirole, (-)-NPA and B-HT 920 substituted for the stimulus effects induced by d-amphetamine or (-)-NPA in different groups of rats. EMD 23448 induced intermediate effects, whereas preclamol and terguride had weak effects. None of the partial agonists inhibited the response of d-amphetamine. YM 09151-2 potently inhibited the effect of d-amphetamine. The results suggest that DA D-2 agonists can be ranked according to gradually increasing agonist efficacies rather than classified into autoreceptor-selective versus nonselective D-2 agonists. Implications of this hypothesis are discussed.

Effect of a dopamine D-1 agonist in rats treated chronically with zuclopenthixol.

We have previously demonstrated long-lasting increases in vacuous chewing movements (VCM) and tongue protrusions in rats treated discontinuously (DISC), but not continuously (CONT), with neuroleptics. To test whether this increase in mouth movements could be a result of exaggerated activity at the D-1 site, 34 rats were divided into three groups receiving the neuroleptic zuclopenthixol (ZU) DISC or CONT for 15 weeks, or no treatment. After withdrawal DISC treated animals showed an increase in oral activity compared to CONT treated. Two weeks after termination of medication the animals were tested with the D-1 agonist SK&F 38393. The increases in VCM after SK&F 38393 did not differ among the groups, but in contrast to control (CTRL) rats, treated rats showed a significant increase in tongue protrusions. There were no significant differences in the densities of D-1 and D-2 receptors in the striatum between the groups. The increase in tongue protrusions after SK&F 38393 in neuroleptic treated animals implies behavioural D-1 receptor supersensitivity. No significant differences in the rise in tongue protrusions and VCM after SK&F 38393 were seen between DISC and CONT treated animals. Our results thus do not indicate that increased D-1 receptor responsiveness is significant for the rise in spontaneous oral activity found after neuroleptic withdrawal.