Neurochemical Characteristics of Amisulpride

Neurochemical Characteristics of Amisulpride, an AtypicalDopamine D2/D3 Receptor Antagonist with Both Presynapticand Limbic Selectivity

H. SCHOEMAKER, Y. CLAUSTRE, D. FAGE, L. ROUQUIER, K. CHERGUI, O. CURET, A. OBLIN, F. GONON,C. CARTER, J. BENAVIDES and B. SCATTON

Synthelabo Recherche, CNS Research Department (H.S., Y.C., D.F., L.R., O.C., A.O., C.C., J.B., B.S.), Bagneux, France and Centre HospitalierLyon-Sud (K.C., F.G.), Pierre-Benite, France

Accepted for publication October 1, 1996

ABSTRACTThe benzamide derivative amisulpride shows a unique thera-peutic profile being antipsychotic, at high doses, and disinhibi-tory, at low doses, while giving rise to only a low incidence ofextrapyramidal side effects. In vitro, amisulpride has high affin-ity and selectivity for the human dopamine D2 (Ki 5 2.8 nM) andD3 (Ki 5 3.2 nM) receptors. Amisulpride shows antagonistproperties toward D3 and both pre- and postsynaptic D2-likedopamine receptors of the rat striatum or nucleus accumbensin vitro. At low doses (#10 mg/kg) amisulpride preferentiallyblocks presynaptic dopamine autoreceptors that control dopa-mine synthesis and release in the rat, whereas at higher doses(40–80 mg/kg) postsynaptic dopamine D2 receptor occupancyand antagonism is apparent. In contrast, haloperidol is active inall of these paradigms within the same dose range. Amisulpridepreferentially inhibits in vivo binding of the D2/D3 antagonist[3H]raclopride to the limbic system (ID50 5 17 mg/kg) in com-

parison to the striatum (ID50 5 44 mg/kg) of the rat, increasesstriatal and limbic tissue 3,4-dihydroxyphenylacetic acid levelswith similar potency and efficacy, and preferentially increasesextracellular 3,4-dihydroxyphenylacetic acid levels in the nu-cleus accumbens when compared to the striatum. Haloperidolshows similar potency for the displacement of in vivo [3H]ra-clopride binding in striatal and limbic regions and preferentiallyincreases striatal tissue 3,4-dihydroxyphenylacetic acid levels.The present data characterize amisulpride as a specific dopa-mine receptor antagonist with high and similar affinity for thedopamine D2 and D3 receptor. In vivo, it displays a degree oflimbic selectivity and a preferential effect, at low doses, ondopamine D2/D3 autoreceptors. This atypical profile may ex-plain the therapeutic efficacy of amisulpride in the treatment ofboth positive and negative symptoms of schizophrenia.

Clinically, atypical neuroleptics are defined as drugs activein the treatment of schizophrenia but with a lesser propen-sity than conventional neuroleptics to induce extrapyramidalside effects. Furthermore, some neuroleptics, such as cloza-pine, are considered atypical because of their therapeuticefficacy in the treatment of schizophenic patients resistant toconventional neuroleptics.Most neuroleptics display high affinity for the dopamine

D2 receptor subtype in direct relation to their therapeuticpotency or plasma concentration at therapeutically activedoses (Seeman, 1992). It has thus been suggested that theatypical characteristics of certain neuroleptics necessarilyderive from additional pharmacological properties, such asantagonism toward 5-HT2A or 5-HT2C, muscarinic cholin-

ergic or alpha-1 adrenergic receptors (Meltzer, 1991; Schmidtet al., 1995), or an interaction with s recognition sites (Ferriset al., 1991).Molecular biological techniques have recently provided ev-

idence that the dopamine D1 receptor comprises a class ofreceptors, positively coupled to adenylate cyclase, that in-cludes, besides the classical D1 receptor (also termed D1A),the D5 or D1B receptor (Sunahara et al., 1991) and possiblythe mammalian equivalents of the D1C (Sugamori et al.,1994) and D1D (Demchyshyn et al., 1995) receptors. Simi-larly, the dopamine D2 receptor family is now thought toinclude the D2, D3 (Sokoloff et al., 1990) and D4 (Van Tol etal., 1991) subtypes. In particular, the D3 and D4 receptorsubtypes have generated recent interest as potential thera-peutic targets in the treatment of schizophrenia because oftheir preferential limbic localization (Sokoloff et al., 1990;Received for publication April 16, 1996.

ABBREVIATIONS: L-dopa, L-3,4-dihydroxyphenylalanine; DOPAC, 3,4-dihydroxyphenylacetic acid; HVA, homovanillic acid; DOPEG, 3,4-dihy-droxyphenylethyleneglycol; 5-HTP, 5-hydroxytryptophane; 5-HT, serotonin; 5-HIAA, 5-hydroxyindoleacetic acid; NSD-1015, m-hydroxybenzyl-hydrazine dihydrochloride; 7-OH-DPAT, (6)7-hydroxy-N,N-di-n-propyl-2-aminotetralin; ANOVA, analysis of variance; HPLC, high-performanceliquid chromatography; QNB, quinuclidinyl benzylate; TBOB, t-butylbicycloorthobenzoate; PEA, phenylisopropyladenosine; NECA, N-ethylcar-boxamidoadenosine; CHO cells, Chinese hamster ovary cells.

0022-3565/97/2801-0083$03.00/0THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 280, No. 1Copyright © 1997 by The American Society for Pharmacology and Experimental Therapeutics Printed in U.S.A.JPET 280:83–97, 1997

83

by guest on May 5, 2012

jpet.aspetjournals.orgD

ownloaded from

http://jpet.aspetjournals.org/

Van Tol et al., 1991). The D3 subtype is selectively recognizedby several agonists and antagonists known for their selectiv-ity for the dopamine autoreceptor (Sokoloff et al., 1992a, c),although it is present mainly on dopaminoceptive cells, inparticular in the limbic system (Sokoloff et al., 1990, 1992c).Thus it has been suggested that stimulation of a postsynapticdopamine D3 receptor might be inhibitory to rat locomotoractivity (Svensson et al., 1994; Waters et al., 1993b). The D4

receptor represents the subtype of D2 receptors for whichclozapine shows the highest affinity (Van Tol et al., 1991).Amisulpride (fig. 1) is a substituted benzamide derivative

with dopamine receptor antagonist properties in vitro and invivo (Chivers et al., 1988; Perrault et al., 1997; Scatton et al.,1994; Sokoloff et al., 1990). Although in clinical studies itsefficacy in the treatment of schizophrenia has been clearlydemonstrated, its most notable characteristic is its atypicalprofile. Thus, although amisulpride is efficacious in treatingthe positive symptoms of schizophrenia, it does so at doses(400–1200 mg/day) that, according to present experience,have only a low propensity to induce extrapyramidal sideeffects. In addition, amisulpride possesses disinhibitory ef-fects at lower doses (50–300 mg/day) and is successfullyused, at these doses, in treatment of the negative symptomsof schizophrenia and of dysthymia, a form of chronic depres-sion (Boyer et al., 1990; Boyer et al., 1995; Delcker et al.,1990; Paillere Martinot et al., 1995; Saletu et al., 1994).These atypical therapeutic characteristics of amisulpridemay be a reflection of its atypical neuropharmacological pro-file. Thus, amisulpride, similarly to classical neuroleptics,antagonizes the hyperactivity or stereotypies that resultfrom the direct or indirect activation of postsynaptic dopami-nergic receptors by (high doses of) dopaminomimetics such asapomorphine or amphetamine in the rat (Perrault et al.,1997). Nevertheless, amisulpride does not provoke catalepsyin the rat, which is characteristic of postsynaptic D2 block-ade, even at doses maximally effective in these experimentalparadigms (Perrault et al., 1997). At lower doses, amisulpridepotentiates apomorphine- and amphetamine-induced stereo-typed behavior in mice, particularly favoring a transitionfrom sniffing to gnawing behavior (Vasse et al., 1985). Fur-thermore, low doses of amisulpride inhibit hypokinesia in-duced by the administration of low doses of apomorphine,7-OH-DPAT or quinpirole in rats (Perrault et al., 1997). Clas-sical neuroleptics such as haloperidol are devoid of suchprostereotypic effects and inhibit the diverse behavioral ef-fects of dopamine agonists within the same dose range.Various hypotheses have been put forward to explain the

spectrum of animal behaviors provoked by dopaminomimet-ics and the dichotomy in their antagonism by atypical neu-roleptics. These include the presence of behaviorally suppres-

sant dopamine receptors in the nucleus accumbens (Waterset al., 1993b) or frontal cortex (Carter and Pycock, 1980) andthe presence of inhibitory dopamine autoreceptors (Di Chiaraet al., 1986). Thus, in addition to postsynaptic dopaminereceptors, D2-like autoreceptors have been amply demon-strated and are thought to be involved in the regulation ofneuronal firing (Lejeune andMillan, 1995), dopamine release(Suaud-Chagny et al., 1991) and tyrosine hydroxylase acti-vation (Claustre et al., 1985; Walters and Roth, 1976). Theirmolecular identity, however, remains subject to debate. Al-ternatively, drug activity at nondopaminergic receptors, suchas alpha-1 adrenoceptors (Wiszniowska-Szafraniec et al.,1983), 5-HT receptor subtypes (Carter and Pycock, 1981;Mogilnicka et al., 1977), beta adrenergic receptors (Costall etal., 1978), muscarinic cholinergic receptors (Christensen etal., 1976) and histamine H1 receptors (Dadkar et al., 1976),may modulate the expression of dopamine receptor activa-tion or blockade.In view of the established atypical profile of amisulpride in

the treatment of schizophrenia and dysthymia, and in view ofcurrent hypotheses with respect to dopamine receptor sub-types and the possible contribution of nondopaminergic ef-fects to neuroleptic atypicity, we have sought to define itsneurochemical characteristics and mechanism of action,largely in comparison with that of the typical neuroleptichaloperidol. To this end, we studied the interaction of amisul-pride with a variety of drug receptor and recognition sites invitro, which demonstrated that amisulpride is highly specificand selective for both the dopamine D2 and D3 receptorsubtypes. Its antagonist character was demonstrated in vitroby its inhibition of dopamine D3 receptor-mediated mitogen-esis and by its pre- and postsynaptic effects on neurotrans-mitter release and was demonstrated in vivo by its effects onindices of dopamine synthesis, release and metabolism andon ACh levels. These studies show that amisulpride displaysa degree of limbic selectivity and a preferential effect, at lowdoses, on D2/D3 autoreceptors as compared with the classicalneuroleptic, haloperidol.The behavioral characteristics of amisulpride are de-

scribed in a companion paper (Perrault et al., 1997).Some of the data presented here have previously been

reported in abstract form (Scatton et al., 1994; Schoemaker etal., 1995).

Materials and MethodsAnimals. Unless otherwise indicated, adult male Sprague-Daw-

ley rats (OFA or COBS, Iffa Credo, St. Germain sur l’arbresle,France, or Charles River, St. Aubin-les-Elbeus, France), DunkinHartley guinea pigs (Iffa Credo) and Fauves de Bourgogne rabbits(ESD, Romans, France) were used.Throughout these studies, the phrase the limbic system refers to

the nucleus accumbens and the olfactory tubercle.Materials and drugs. Pig choroid plexi and bovine caudate nu-

clei were obtained from CollectOrgane (Paris, France). Cell linesexpressing the human dopamine receptor subtypes or membranepreparations thereof were obtained from: D1 and D5 (New EnglandNuclear, Boston, MA), D2S and D3 (Dr. J.-C. Schwartz, INSERM,Paris, France), D4.4 (Receptor Biology, Baltimore, MD).Radioligands were obtained from the following sources: [3H]spip-

erone, [3H]SCH 23390, [3H]GBR12935, [3H]prazosin, [3H]clonidine,[3H]dihydroalprenolol, [3H]desipramine, [3H]serotonin, [3H]quip-azine, [3H]quinuclidinyl benzylate, [3H]pyrilamine, [3H]flumazenil,

Fig. 1. Amisulpride, (6)-4-amino-N-1((1-ethyl-2-pyrrolidinyl)methyl)-5-(ethylsulphonyl)-2-methoxybenzamide.

84 Schoemaker et al. Vol. 280



ownloaded from


[3H]TBOB, [3H]nipecotic acid, [3H]strychnine, [3H]CGP 39653,[3H]glycine, [3H]MK801, [3H]AMPA, [3H]kainate, [3H]angiotensinII, [5-methyl-3H]-nitrendipine, [benzoyl-2,5-3H]-batrachotoxinin A20-a-benzoate, [3H]Ro5-4864, [3H]raclopride, [3H]dopamine,[14C]choline, [125I]angiotensin II (New England Nulear/DuPont deNemours, Boston, MA); [125I]iodosulpride, [3H]7-OH-DPAT, [3H]me-sulergine, [3H]GR 113808, ((2)N6-R[G-3H]-phenylisopropylad-enosine, 59-N-ethylcarboxamido [8(n)-3H]-adenosine, [3H]idazoxan,[3H]thymidine (Amersham, Little Chalfont, UK); [3H]8-OH-DPAT(CEA, Saclay, France); [3H]GABA (Dositek, Orsay, France). [3H]ifen-prodil was custom-synthesized by Amersham. Amisulpride, sulpride,haloperidol, remoxipride, clozapine and 7-OH-DPAT were synthe-sized at Synthelabo Recherche (Bagneux, France). All other chemi-cals were obtained commercially at the highest purity available.Drugs were administered through the i.p. route, except when

indicated otherwise; control groups received an equal volume of thecorresponding vehicle. Amisulpride was administered as a hydro-chloride salt. Doses refer to the free base equivalent.Radioligand binding studies in vitro. Studies of radioligand

binding to various receptor and/or drug recognition sites were per-formed essentially as described by the authors indicated: the humandopamine D2 receptor expressed in CHO cells (1.0 nM [125I]iodosul-pride; Sokoloff et al., 1992a), the human dopamine D3 receptor ex-pressed in CHO cells (0.2 nM [125I]iodosulpride; Sokoloff et al.,1992a), the human dopamine D4.4 receptor expressed in CHO cells(0.5 nM [3H]spiperone; Van Tol et al., 1991), the human dopamine D1

receptor in Sf9 cells (1.6 nM [3H]SCH23390; Sunahara et al., 1991),the human dopamine D5 receptor expressed in Sf9 cells (1.8 nM[3H]SCH23390; Sunahara et al., 1991), the dopamine D1 receptor inrat striatum (0.3 nM [3H]SCH23390; Billard et al., 1984), the dopa-mine D2 receptor in rat striatum (0.3 nM [3H]spiperone; Briley andLanger, 1978), the dopamine D3 receptor in bovine caudate nucleus(0.8 nM [3H]7-OH-DPAT in the presence of 0.2 mM eliprodil; Schoe-maker, 1993), the plasma membrane dopamine transporter from therat striatum (1 nM [3H]GBR12935; Janowsky et al., 1986), thealpha-1A adrenoceptor in the rat salivary gland (0.2 nM [3H]prazo-sin; Faure et al., 1994), the alpha-1B adrenoceptor in the rat liver(0.1 nM [3H]prazosin; Faure et al., 1994), the alpha-2 adrenoceptor inthe rat cerebral cortex (5 nM [3H]clonidine; Pimoule and Langer,1982), the beta adrenoceptor in the rat cerebral cortex (2 nM [3H]di-hydroalprenolol; Mogilnicka et al., 1980), the plasma membranenoradrenaline transporter from the rat vas deferens (2 nM [3H]de-sipramine; Raisman et al., 1982), the 5-HT1A receptor in rat hip-pocampus (1 nM [3H]8-OH-DPAT in the presence of 3 mMparoxetine;Sanger and Schoemaker, 1992; Schoemaker and Langer, 1986), the5-HT1B receptor in rat striatum (5 nM [3H]5-HT in the presence of100 nM 8-OH-DPAT and 100 nM mesulergine; Herrick-Davis et al.,1988; Heuring and Peroutka, 1987; Peroutka, 1986), the 5-HT1Dreceptor in bovine caudate nucleus (2 nM [3H]5-HT in the presence of100 nM 8-OH-DPAT and 100 nM mesulergine; Herrick-Davis et al.,1988; Heuring and Peroutka, 1987), the 5-HT2A receptor in ratcerebral cortex (0.4 nM [3H]spiperone; Hicks et al., 1984), the 5-HT2Creceptor in the pig choroid plexus (1 nM [3H]mesulergine; Pazos etal., 1984; Yagaloff and Hartig, 1986), the 5-HT3 receptor in the ratcerebral cortex (0.8–0.9 nM [3H]quipazine in the presence of 10 nMketanserin and 100 nM paroxetine; Angel et al., 1993), the 5-HT4receptor in the guinea pig striatum (0.1 nM [3H]GR 113808; Gross-man et al., 1993), the muscarinic cholinergic receptor in the ratcortex (0.3 nM [3H]quinuclidinyl benzylate; Yamamura and Snyder,1974), the histamine H1 receptor in the guinea pig cerebellum (1 nM[3H]pyrilamine; Tran et al., 1978), the GABAA receptor in rat brain(4 nM [3H]GABA; Langer et al., 1985), the v1/benzodiazepine recep-tor in the rat cerebellum (1 nM [3H]flumazenil; Arbilla et al., 1985),the v2/benzodiazepine receptor in the rat spinal cord (1 nM[3H]flumazenil; Arbilla et al., 1985), the v5/benzodiazepine receptorin the rat hippocampus (1 nM [3H]flumazenil in the presence of 5 mMzolpidem; Tan and Schoemaker, 1993), the picrotoxin site of theGABAA receptor channel in the rat cerebral cortex (2 nM [3H]TBOB;

Van Rijn et al., 1990), the GABAB receptor in rat brain (10 nM[3H]GABA; Hill and Bowery, 1981), the presynaptic GABA trans-porter in the rat cerebral cortex (5 mM [3H]nipecotic acid; Vargas etal., 1993), the strychnine-sensitive glycine receptor in the rat spinalcord (2 nM [3H]strychnine; Young and Snyder, 1974; Young andSnyder, 1973), the glutamate recognition site of the NMDA receptorin whole rat brain (1.5 nM [3H]CGP 39653; Sills et al., 1991), thestrychnine-insensitive glycine recognition site of the NMDA receptorin the whole rat brain (14–17 nM [3H]glycine; Kishimoto et al., 1981;Zukin et al., 1974), the polyamine-sensitive modulatory site of theNMDA receptor complex in the rat cerebral cortex (1 nM [3H]ifen-prodil in the presence of 3 mM GBR 12909; Schoemaker et al., 1991),the NMDA receptor-ion channel site in well-washed membranesfrom the whole rat brain (2 nM [3H]MK801; Reynolds et al., 1987;Wong et al., 1988), the quisqualate/AMPA subtype of glutamatereceptors in the rat brain (4 nM [3H]AMPA; Honore et al., 1982;Honore and Drejer, 1988), the kainate subtype of glutamate recep-tors in the rat brain (2 nM [3H]kainate; Simon et al., 1976), theadenosine A1 receptor in rat hippocampal membranes (3 nM (2)N6-R[G-3H]-phenylisopropyladenosine; Schwabe and Trost, 1980), theadenosine A2 receptor in rat striatal membranes (4 nM 59-N-ethylcarboxamido[8(n)-3H]-adenosine in the presence of 50 nM N6-cyclopentyladenosine; Bruns et al., 1986), the angiotensin II AT1receptor in rabbit adrenocortical membranes (2 nM [3H]angiotensinII; Glossmann et al., 1974), the angiotensin II AT2 receptor in mem-branes from the rat adrenal medulla (0.1 nM [125I]angiotensin II;Glossmann et al., 1974), the L-type Ca11 channel in rat cerebralcortex (0.1 nM [5-methyl-3H]-nitrendipine; Schoemaker and Langer,1989), the Na1 channel in rat cerebral cortex (2 nM [benzoyl-2,5-3H]-batrachotoxinin A 20-a-benzoate in the presence of 1 mM tetrodo-toxin and scorpion toxin; Pauwels et al., 1986), s recognition sites inrat cortex (0.5 nM [3H]ifenprodil; Schoemaker et al., 1991), the p-site(peripheral benzodiazepine receptor) in the rat kidney (0.5 nM[3H]Ro 5-4864; Schoemaker et al., 1983), the imidazoline I2 recogni-tion site in the whole rat brain (1 nM [3H]idazoxan in the presence of10 mM (2)adrenaline; Le Rouzic et al., 1995).Radioactivity was quantified using liquid scintillation spectom-

etry. Data from radioligand inhibition experiments were evaluatedby graphical methods or by linear or nonlinear regression analysiswhen appropriate and, unless indicated otherwise, are presented asthe drug concentration required to inhibit 50% of specific radioligandbinding (IC50) or are converted to Ki values as described by Chengand Prusoff (1973).Dopamine D3 receptor-stimulated mitogenic activity in

vitro. The functional effects of amisulpride at the dopamine D3

receptor subtype were assessed as described by Pilon et al. (1994)and Sautel et al. (1995). Briefly, the mitogenic response elicited inNG108-15 neuroblastoma-glioma cells stably transfected with hu-man dopamine D3 receptor cDNA by the addition of 10 nM quinpirolein the presence of 1 mM forskolin was quantified by the incorporationof [3H]thymidine. Antagonism of quinpirole-induced mitogenesis wasmeasured in the presence of increasing (0.1–100 nM) concentrationsof amisulpride.Radioligand binding studies in vivo. In vivo [3H]raclopride

binding to rat brain structures was measured according to a previ-ously described procedure (Kohler et al., 1985). The radioligand (9mCi/200 ml) was injected into the tail vein of male Sprague-Dawleyrats 45 min before sacrifice. Test drug or vehicle was administered ina final volume of 1 ml 75 min before [3H]raclopride. Brain structures(striatum, limbic system and cerebellum) were dissected by hand,and the incorporated radioactivity was measured after overnightdigestion in 0.5 ml of Soluene. The radioactivity incorporated intothe cerebellum was taken as nonspecific binding.[3H]Spiperone binding in vivo was studied according to a similar

protocol. The radioligand (5 mCi/200 ml) was administered into thetail vein 60 min before sacrifice. Drug or vehicle was given 60 minbefore the radioligand.

1997 Amisulpride; Neurochemical Profile 85



ownloaded from


Neurotransmitter release in vitro. The modulation of electri-cally evoked [3H]dopamine and [14C]ACh release from slices (1 3 1 30.3 mm) of the rat striatum and nucleus accumbens was studiedessentially as described by Arbilla and Langer (1984). Briefly, sliceswere incubated with 0.1 mM [3H]dopamine and 19 mM [14C]cholinefor 30 min at 37°C in Krebs buffer (mM: NaCl, 118; KCl, 4.7; CaCl2,1.3; MgCl2, 1.2; NaH2PO4, 1.0; NaHCO3, 25.0; glucose, 11.0; EDTA,0.04, equilibrated with 5% CO2/95% O2). Slices were then washed,transferred to superfusion chambers (1 slice/chamber) and super-fused with Krebs buffer supplemented with 10 mM hemicholinium-3for 60 min at a flow rate of 0.7 or 1 ml/min. After this period,fractions (7 and 6 min, respectively) were collected until the end ofthe experiment. Slices were initially stimulated electrically (2 min, 3Hz, 2 ms, 16 mA) in the absence of amisulpride or 7-OH-DPAT, 74min after the beginning of the superfusion, and were stimulated 40min thereafter in their presence. Amisulpride or 7-OH-DPAT wasadded to the superfusion buffer 20 min before the second stimulationperiod. When the interaction between amisulpride and 7-OH-DPATwas studied, amisulpride was present in the superfusion buffer as of20 min before the first stimulation period. In each case, the stimu-lation-evoked [3H] and [14C] overflow (S1 and S2, respectively) wascalculated with respect to the spontaneous outflow (sp1 and sp2,respectively) in the fractions immediately before stimulation. Al-though both the neurotransmitter and derived metabolites probablycontribute to stimulation-evoked [3H] and [14C] overflow (see, forinstance, Parker and Cubeddu, 1985), the terms [3H]dopamine and[14C]ACh are used for convenience.Microdialysis studies. Adult male Sprague-Dawley rats were

anesthetized with chloral hydrate (400 mg/kg), and guide cannulaewere stereotaxically implanted onto the dura mater above the stri-atum and the nucleus accumbens (10.7 mm anterior, 13 mm lateraland 11.7 mm anterior, 11.0 mm lateral from bregma, respectively)(Paxinos and Watson, 1982). At least 5 days after surgery, microdi-alysis probes (Carnegy Medicine) 250 mm in diameter with an ex-posed membrane length of 4 (striatum) and 2 (nucleus accumbens)mm were positioned within the guide cannulae (vertical coordinates:27 mm and 28 mm, respectively, from the dura surface) and per-fused with artificial CSF (mM: NaCl, 147; KCl, 4; CaCl2, 1.2; MgCl2,1.0) using a CMA/100 pump (BAS) at a flow rate of 2 ml/min. Twenty-minute dialysate fractions were collected in a valve loop and ana-lyzed online using HPLC with electrochemical detection. The aver-age concentration of five stable fractions immediately preceding drugadministration was defined as the 100% control value.Electrically evoked dopamine release in vivo. Presynaptic

autoregulation of electrically evoked dopamine release in the ratolfactory tubercle was studied in vivo as described by Suaud-Chagnyet al. (1991). Briefly, dopamine release was monitored every 1 s withelectrochemically treated 12-mm-diameter carbon-fiber electrodes(1.6 mm lateral, 1.7 mm anterior to bregma and 9.0 mm below thecortical surface) combined with differential pulse amperometry withthe final potential adjusted to 185 mV. Bipolar stimulating elec-trodes were implanted in the ascending dopaminergic pathway at 1.2mm lateral and 4.0 mm posterior to bregma, at a depth adjusted foreach experiment so that the stimulation-evoked dopamine responsewas maximal. Electrical stimulation was by twenty 1-s trains of sixsquare wave form current pulses (pulse interval 70 ms, 250 mA, 0.5ms) and was repeated every 10 min.Monoamines and metabolites in vivo. Two hours after drug

administration, animals were sacrificed by decapitation, and thebrain structures (frontal cortex, striatum and limbic system) weredissected on ice. Samples were then weighed, homogenized in 20volumes of 0.1 M HClO4 and centrifuged at 10,000 3 g for 10 min.Dopamine and DOPAC levels were measured in the supernatant byHPLC with electrochemical detection as described previously (Serm-erdjian-Rouquier et al., 1981). ACh and choline levels were measuredin aliquots of a buffered supernatant (0.5 M Tris-citrate, pH 4) byHPLC with electrochemical detection using platinum electrodes(Asano et al., 1986).

Measurement of dopamine and 5-HT synthesis rates. Therate of dopamine and 5-HT synthesis was estimated by measuringthe accumulation of dopa and 5-HTP, respectively, 30 min after theadministration of NSD-1015 (100 mg/kg) (Claustre et al., 1985). Thepresynaptic modulation of dopamine synthesis (Walters and Roth,1976) was studied by co-administration of g-hydroxy-butyric acid(750 mg/kg) 45 min before sacrifice. Amisulpride and 7-OH-DPATwere given 75 and 15 min, respectively, before g-hydroxy-butyricacid. Dopa and 5-HTP levels were measured by HPLC with electro-chemical detection according to Sermerdjian-Rouquier et al. (1981).Statistical analyses. Statistical differences between groups were

assessed using the ANOVA test, followed by Dunnett’s or Duncan’stest where appropriate. Simple statistical comparisons were doneusing a two-tailed Student’s t test. ED50 values for drug inhibition ofin vivo radioligand binding in the striatum and limbic system weretested for statistical identity using the partial F test.

ResultsIn vitro radioligand binding studies. Amisulpride

shows high affinity toward the cloned and stably transfectedhuman dopamine D2 (Ki 5 2.8 6 0.4 nM; n 5 7) and D3 (Ki 53.2 6 0.3 nM; n 5 7) receptor subtypes labeled with [125I]io-dosulpiride and fails to recognize the D1, D4 and D5 receptorsubtypes. Both haloperidol and clozapine recognize all hu-man dopamine receptor subtypes (table 1).In agreement with its high affinity for the human D2 and

D3 receptor subtypes, amisulpride potently inhibits radioli-gand binding to the native dopamine D2 receptor in mem-branes from the rat striatum (IC50 5 21 nM, table 2). Simi-larly, amisulpride recognizes the native bovine dopamine D3

receptor labeled with [3H]7-OH-DPAT, at low concentrations(IC50 5 2.9 nM). The selectivity of amisulpride for dopaminereceptors of the D2 family was studied using [

3H]SCH23390to label the D1 receptor in the rat striatum; amisulpride failsto affect the binding of this radioligand at concentrations upto 10 mM. In contrast, haloperidol inhibits radioligand bind-ing to the native dopamine D2 receptor at lower concentra-tions than in the case of the D3 receptor and, in addition,recognizes the native D1 receptor subtype (table 2). Clozapinerecognizes these three dopamine receptor subtypes with sim-ilar affinity. The dopamine D4 and D5 receptors are currentlynot accessible to radioligand binding studies in their nativestate.Amisulpride was devoid of significant affinity (IC50 . 1

mM) for radioligand binding to a variety of other neurotrans-mitter receptors and/or drug recognition sites (table 2), whichattested to its selectivity. Both haloperidol and clozapine

TABLE 1Affinity of amisulpride for molecularly identified human dopaminereceptor subtypes in vitroStudies of radioligand binding to human dopamine receptor subtypes transfectedinto CHO (D2 receptor family) or Sf9 (D1 receptor family) cells were performed asdescribed in “Materials and Methods”. Data represent the mean of at least twoindependent experiments performed in duplicate.

Drug

K (nM)

D2 Receptor Family D1 Receptor Family

D2 D3 D4 D1 D5

Amisulpride 2.8 3.2 .1000 .1000 .1000Haloperidol 0.60 2.3 3.8 27a 48a

Clozapine 80 230 89 141a 250a

a, Data taken from Sunahara et al. (1991).




ownloaded from


recognize with high affinity the 5-HT2A serotonergic and thealpha-1 adrenergic receptor subtypes. In addition, haloperi-dol inhibits radioligand binding to s-sites, whereas clozapineaffects binding to 5-HT2C, 5-HT3 and H1 histamine receptors.In vivo radioligand binding studies. [3H]Raclopride se-

lectively recognizes D2 and D3 receptors in vitro and may beused as a label for D2-like receptors in vivo (Kohler et al., 1985).Amisulpride displaces [3H]raclopride binding in vivo (fig. 2)with an ED50 value of 17.3 6 1.86 mg/kg in the rat limbicsystem but is significantly (P , .05) less active in displacingbinding in the striatum (ED50 5 43.66 6.2mg/kg; table 3). Likeamisulpride, sulpiride is more potent in displacing [3H]raclo-pride binding in the limbic system, whereas remoxipride andhaloperidol show similar activity in both brain regions.Spiperone similarly recognizes dopamine D2 and D3 recep-

tors (Sokoloff et al., 1990) and, in addition, labels the 5-HT2receptor in vivo (Laduron et al., 1978). [3H]Spiperone bindingto D2-like receptors in vivo is significantly (P , .05) moresensitive to inhibition by amisulpride in the limbic systemthan in the striatum (ED50 5 29 6 5 and 87 6 9 mg/kg,

respectively; n 5 5–14/group). [3H]Spiperone binding in thefrontal cortex, which mainly represents 5-HT2 receptors (La-duron et al., 1978), is not affected by amisulpride at doses upto 100 mg/kg.Dopamine D3 receptor-mediated mitogenesis in

vitro. Quinpirole (10 nM) stimulated [3H]thymidine incorpo-ration, a measure of mitogenesis, in NG108-15 cells stablytransfected with the human D3 dopamine receptor, to171.9 6 5.0% of controls (100.0 6 4.6%; n 5 3; P , .01).Although amisulpride (100 nM) failed to stimulate [3H]thy-midine incorporation (95.8 6 7.1%; n 5 3; P . .05 vs. control),it inhibited quinpirole-elicited [3H]thymidine incorporationwith an IC50 value of 22 6 3 nM (n 5 3).Neurotransmitter release studies in vitro. Dopamine

D2/D3 receptor antagonism can be demonstrated in vitro bystudying the modulation of neurotransmitter release. Thusthe electrically stimulated [3H]dopamine release from slicesof the striatum or the nucleus accumbens is subject to inhib-itory modulation through a D2-like (D2/D3) terminal autore-ceptor and is inhibited by the D2/D3 agonist 7-OH-DPAT with

TABLE 2Inhibitory effects of amisulpride against radioligand binding to native receptor and drug recognition sites in vitroDrug inhibition of radioligand binding to native receptor and drug recognition sites in vitro was studied as described in “Materials and Methods”.

Receptor/Site Radioligand

IC50 (mM)

Amisul-pride Haloperidol Clozapine

Dopamine D1 [3H]SCH23390 .10 0.25 0.59D2 [3H]spiperone 0.021 0.0020 0.43D3 [3H]7-OH-DPAT 0.0029 0.0065 0.88Transporter [3H]GBR12935 .100 — 41

Noradrenaline a1A [3H]prazosin 7.1 0.029 0.0078a1B [3H]prazosin 14.1 0.0072 0.0031a2 [3H]clonidine 1.6 50 0.81b [3H]dihydroalprenolol .10 .10 .10Transporter [3H]desipramine .10 .10 .1

5-HT 5-HT1A [3H]8-OH-DPAT .10 2.5 1.75-HT1B [3H]5-HT .10 .10 1.35-HT1D [3H]5-HT .10 .10 1.65-HT2A [3H]spiperone 2.0 0.072 0.0035-HT2C [3H]mesulergine .10 10 0.0115-HT3 [3H]quipazine .10 .10 0.225-HT4 [3H]GR113808 .10 .10 .10

ACh M [3H]QNB .100 .10 0.50Histamine H1 [3H]pyrilamine .10 1.8 0.023GABA A GABA [3H]GABA .100 .100 .100

v1 [3H]flumazenil .100 .10 .10v2 [3H]flumazenil .100 .10 .10v5 [3H]flumazenil .10 .10 .10channel [3H]TBOB .100 .10 .10

B [3H]GABA .100 .100 .100Transporter [3H]nipocotic acid .100 .100 .100

Glycine (strychnine-sensitive) [3H]strychnine .10 .10 .10Glutamate NMDA Glutamate [3H]CGP39653 .100 .10 .10

Glycine [3H]glycine .100 .10 .10Polyamine [3H]ifenprodil .10 0.70 5.0Channel [3H]MK801 .10 .10 .10

AMPA [3H]AMPA .100 .10 .10Kainate [3H]kainate .100 .10 .10

Adenosine A1 [3H]PEA .10 .10 .10A2 [3H]NECA .10 .10 .10

Angiotensin II AT1 [3H]angiotensin II .10 .10 .10AT2 [3H]angiotensin II .10 .10 .10

Ca11 channel L [3H]nitrendipine .10 1.7 .10Na1 channel [3H]batrachotoxinin A .10 7 .10P-site (BZp) [3H]RO5-4864 .10 .10 .10Imidazoline I2 [3H]idazoxan .10 .10 .10Sigma [3H]ifenprodil .10 0.024 6.4




ownloaded from


EC50 values of 13.9 6 0.7 and 4.7 6 0.6 nM, respectively. Atmaximally effective concentrations, 7-OH-DPAT reduces theevoked release to 3.7% and 13.8% of controls in the striatumand nucleus accumbens, respectively.

The effects of amisulpride were studied alone and againsta concentration of 7-OH-DPAT that produces approximately70% of its maximal inhibitory effect on evoked [3H]dopamineoverflow (30 nM in the striatum, 10 nM in the nucleus ac-cumbens). Amisulpride slightly but significantly increased[3H]dopamine release from slices of the rat striatum (S2/S1 50.88 6 0.04 under control conditions, n 5 6; 1.04 6 0.08 in thepresence of 100 nM amisulpride, n 5 4; P , .05) and opposedthe inhibitory effects of 7-OH-DPAT in both brain areas (fig.3).Electrically stimulated [14C]ACh (formed after preincuba-

tion with [14C]choline) release from slices of the rat striatumis inhibited through the stimulation of a postsynaptic D2

receptor (Arbilla and Langer, 1984). The dopamine D2/D3

agonist 7-OH-DPAT inhibited electrical stimulation-evoked[14C]ACh release from rat striatal slices with an IC50 value of19.5 6 4.7 nM to a maximum of 23% of control values.Amisulpride opposed the effects of 7-OH-DPAT, thus attest-ing to postsynaptic dopamine receptor blockade. Amisulprideconcentration-response curves against the effects of 30 nM7-OH-DPAT on [3H]dopamine release (EC50 5 2.2 6 0.3 nM)and [14C]ACh (EC50 5 1.2 6 0.3 nM) release are compared infigure 4. Amisulpride did not affect basal [3H]dopamine or[14C]ACh efflux at any concentration tested (data not shown).Effects on dopaminergic neurotransmission in vivo.

Tissue dopamine and DOPAC levels. The effects of amisul-pride, haloperidol, sulpiride and clozapine on regional dopa-mine and DOPAC tissue levels are shown in table 4. Thedoses of the latter three reference compounds were chosen asthose previously shown to have maximal effects on dopamineturnover in the striatum (Scatton et al., 1977).Only the highest dose of amisulpride (100 mg/kg) signifi-

cantly reduced dopamine levels in the striatum or limbicsystem. No other neuroleptic significantly decreased dopa-mine levels in the striatum at the doses used. Sulpiridesignificantly decreased limbic dopamine levels by approxi-mately 10%.Amisulpride increased tissue DOPAC levels in a dose-de-

pendent manner in all brain regions. This effect was signif-icant (P , .05) from 2.5 to 100 mg/kg in the limbic system andfrom 10 to 100 mg/kg in the striatum. Apart from this differ-ence in threshold sensitivity, no differences in the potency ofamisulpride were observed between the two regions studied.The maximal effects of amisulpride (100 mg/kg) were similarin the limbic system and striatum (319% and 285% of con-trols, respectively).Haloperidol significantly increased tissue DOPAC levels in

both regions (P , .001). At the dose tested, its effects weremore marked in the striatum (344%) than in the limbic(265%) system. The effects of sulpiride, like those of amisul-pride, were of a similar order of magnitude in each region(striatum 5 290%, limbic 5 272%). Clozapine had a rela-tively minor effect on striatal (159%) and limbic (174%) tis-sue DOPAC levels.Dopamine synthesis. The effects of amisulpride on tyrosine

hydroxylase activity, the rate-limiting step in dopamine syn-thesis that is subject to negative-feedback modulationthrough dopamine autoreceptors (Claustre et al., 1985;Walters and Roth, 1976), were specifically addressed afterinhibition of L-dopa decarboxylase by pretreatment withNSD-1015 (100 mg/kg).Amisulpride significantly increased the synthesis of dopa-

Fig. 2. Displacement by amisulpride of [3H]raclopride binding to the ratstriatum and limbic system in vivo. Data represent specific [3H]raclo-pride binding, the cerebellum being used as a measure of nonspecificbinding, and are the mean with S.E.M. of results obtained from six ratsper group. Test drugs were administered 75 min before the radioligand.

TABLE 3Comparative potencies of several neuroleptics at inhibiting invivo[3H]raclopride-specific binding in the rat striatum and limbicstructuresIn vivo [3H]raclopride binding to the striatum, the limbic system and the cerebel-lum, taken to represent nonspecific binding, amounted to 270, 80 and 27 dpm/mgtissue, respectively. Specific binding to the striatum and to the limbic systemaccounted for 90% and 70% of the total binding, respectively. ED50 values,shown as mean 6 S.E.M. (n 5 6/group), represent the estimated doses requiredto produce a half-maximal inhibition of radioligand binding. Drugs were admin-istered 75 min before sacrifice.

DrugED50 (mg/kg i.p.)

Striatum Limbic System

Amisulpride 43.6 6 6.2* 17.3 6 1.86Sulpiride 45.5 6 6.5* 14.6 6 1.5Remoxipride 1.07 6 0.12 1.04 6 0.23Haloperidol 0.07 6 0.01 0.11 6 0.02

* P , .05 vs. corresponding drug ED50 value in the limbic system.




ownloaded from


mine, as measured by the accumulation of dopa, in the ratstriatum and limbic system at doses of 20 and 100 mg/kg(table 5). It shows a relative selectivity for the limbic system(ED50 5 18.6 6 4.7 mg/kg) as compared with the striatum(ED50 5 43.7 6 6.5 mg/kg). At the dose of 100 mg/kg, itsmaximal effects appear similar to those of haloperidol (0.3mg/kg, table 5).In order to isolate presynaptic regulatory mechanisms,

pharmacologically, animals were additionally pretreatedwith g-hydroxy-butyrate to block neuronal impulse flow(Claustre et al., 1985). Under these conditions, dopa accumu-lation is increased to approximately 210% and 115% of con-trols in the striatum and limbic system, respectively. Amisul-pride (0.5–75 mg/kg, table 6) fails to provoke an additionalincrease in dopa accumulation in the striatum but slightlyaccelerates, at 75 mg/kg, dopamine synthesis in the limbicsystem. In both brain regions, haloperidol modestly but sig-nificantly stimulates the accumulation of dopa.Activation of terminal dopamine autoreceptors by the ad-

ministration of 7-OH-DPAT (0.082 mg/kg s.c.) to g-hydroxy-butyrate-pretreated animals results in a decrease in dopaaccumulation in both regions (table 7). Amisulpride opposesthe effects of 7-OH-DPAT with ED50 values of 10.6 6 5.2 and10.4 6 6.4 mg/kg in the striatum and limbic system, respec-tively.Effects on extracellular dopamine and DOPAC as mea-

sured by microdialysis. In comparison with vehicle-treatedcontrols, amisulpride (10 mg/kg) increases extracellular do-pamine levels, measured by the technique of microdialysiscoupled to online HPLC with electrochemical detection, inboth the striatum and nucleus accumbens (fig. 5). Maximallevels, approximately 150% of controls, are reached within 60min of drug administration. Amisulpride, administered atthe dose of 30 mg/kg, produced similar effects (data notshown). A concomitant but slightly delayed increase in ex-tracellular DOPAC levels in the striatum and the nucleus

accumbens reached, 140 min after drug administration,137 6 7% and 200 6 22%, respectively. The effect of amisul-pride on dialysate DOPAC levels appeared greater in thenucleus accumbens than in the striatum.In comparison, the effects of haloperidol were studied at a

dose (0.03 mg/kg) that yields an occupancy (21%–30%) of[3H]raclopride-labeled D2-like receptors in vivo similar tothat produced by 10 mg/kg of amisulpride (19%–37%). Com-pared with vehicle-treated controls, haloperidol increasedextracellular dopamine concentrations to 140% to 150% ofbasal values in both brain regions (fig. 6). Like amisulpride,haloperidol appeared to increase dialysate DOPAC levels to agreater extent in the nucleus accumbens than in the stria-tum.Effects on stimulation-evoked dopamine release in the ol-

factory tubercle. The administration of amisulpride (0.5–15mg/kg s.c.) provokes a time- and dose-dependent increase inthe stimulation-evoked dopamine release, measured by dif-ferential pulse amperometry in the rat olfactory tubercle (fig.7). Its maximal effect, obtained at a dose of 10 mg/kg, issimilar to that previously seen after haloperidol (0.5 mg/kgs.c.; Suaud-Chagny et al., 1991).Evoked dopamine release at different doses of amisulpride,

measured 90 min after drug administration and expressed asa percentage of vehicle-treated controls, is shown in figure 8.The ED50 value of amisulpride for its enhancement of stim-ulation-evoked dopamine release may be estimated as 3.7mg/kg s.c.Effects on striatal choline and ACh levels. Amisul-

pride, sulpiride, haloperidol and clozapine did not affect stri-atal choline levels at the doses tested. Amisulpride decreasedstriatal ACh levels significantly at 30 and 100 mg/kg (87.5%and 56.3% of control levels, respectively). Haloperidol (2 mg/kg) and sulpiride (100 mg/kg) decreased striatal ACh levelsto a similar extent (68% and 62% of controls, respectively),

Fig. 3. Effect of amisulpride on electrically evoked [3H]dopamine release from the rat striatum and nucleus accumbens in vitro. The effect ofamisulpride on electrically evoked [3H]dopamine release was studied using slices prepared from the rat striatum and nucleus accumbens. Sliceswere initially stimulated electrically (2 min, 3 Hz, 16 mA) in the absence of amisulpride or 7-OH-DPAT and, 40 min thereafter, in their presence.Amisulpride or 7-OH-DPAT (30 nM for the striatum, 10 nM for the nucleus accumbens) was added to the superfusion buffer 20 min before thesecond stimulation period. When the interaction between amisulpride and 7-OH-DPAT was studied, amisulpride was present in the superfusionbuffer as of 20 min before the first stimulation period. In each case, the stimulation-evoked [3H]-overflow (S1 and S2, respectively) was calculatedwith respect to the spontaneous outflow in the fractions immediately before stimulation (sp1 and sp2, respectively). Data are shown as the meanand S.E.M. of 3 to 11 observations. * and †: P , .05 compared with control and 7-OH-DPAT, respectively.




ownloaded from


whereas clozapine (10 mg/kg) was without significant effect(table 8).

DiscussionThe present studies indicate that amisulpride, in compar-

ison with other neuroleptics both typical and atypical, pos-sesses complex neurochemical characteristics and can largelybe defined as a specific dopamine receptor antagonist with ahigh degree of selectivity for the D2 and D3 receptor subtypesthat it recognizes in vitro with similar affinity. In vivo, theseproperties translate into a degree of selectivity for the pre-synaptic dopamine autoreceptors that control the dopaminer-gic system and for its limbic projections.Selectivity for the dopaminergic system. The present

data confirm and extend previous reports (Chivers et al.,1988) in showing that amisulpride is highly selective for theD2 receptor family. Within this class of receptors, it recog-nizes the cloned human and native D2 (rat) and D3 (bovine)subtypes with similar and low-nanomolar (Ki 5 3 nM) affin-ity in vitro. In this respect, amisulpride is similar to drugs

such as sulpiride, AJ76 and UH232 that show a D2/D3 affin-ity ratio close to unity and is different from the classicalneuroleptics, such as haloperidol, which generally showhigher affinity for the D2 than for the D3 receptor in vitro(Sokoloff et al., 1990, 1992a). Previous studies have shownthat amisulpride recognizes the two isoforms of the humanD2 receptor (D2S and D2L) with equal affinity (Malmberg etal., 1993).The mitogenic response to dopamine agonists of NG108-15

cells stably transfected with human dopamine D3 receptorcDNA is one of the few functional effects unequivocally asso-ciated with this receptor subtype (Pilon et al., 1994; Sautel etal., 1995). In this test, amisulpride inhibited the stimulationof mitogenesis induced by quinpirole with a potency (IC50 522 nM) compatible with its affinity for the dopamine D3

receptor but failed to stimulate mitogenesis when addedalone. Thus amisulpride behaves as a full antagonist at thehuman dopamine D3 receptor.Like other neuroleptics of the benzamide structure,

amisulpride does not recognize the dopamine D4 receptorsubtype (Van Tol et al., 1991), subtypes of the D1 receptorfamily (Sunahara et al., 1991) or the plasma membrane do-pamine transporter.Among the different 5-HT receptors studied, amisulpride

recognizes only the 5-HT2A subtype, albeit with low affinity(IC50 5 2.0 mM). This observation agrees well with the IC50(5.6 mM) reported by Chivers et al. (1988) against the 5-HT2Areceptor labeled using [3H]ketanserin and with the observa-tion that amisulpride fails to inhibit the binding of [3H]spip-erone to the 5-HT2A receptor of the rat frontal cortex in vivo(ID50 . 100 mg/kg). In this respect, amisulpride thus differsfrom the majority of dopamine receptor antagonists, i.e., neu-roleptics, that often do possess high affinity for this receptor(Meltzer et al., 1989; Stockmeier et al., 1993). On the basis ofan analysis of the affinity of neuroleptics for the 5-HT2 re-ceptor and their degree of atypicity, Meltzer et al. (1989)suggested that both properties are closely associated.Clearly, this conclusion does not apply to amisulpride.Drug affinity for muscarinic cholinergic and alpha-1 ad-

renergic receptors or s recognition sites has been suggestedto contribute to antipsychotic therapeutic activity or atypic-ity (Ferris et al., 1991; Meltzer, 1991). Amisulpride fails todisplay significant affinity (IC50 . 1 mM) for any of thesereceptors, so they are not expected to contribute to its atyp-ical profile as a neuroleptic.Amisulpride does not display significant activity against

radioligand binding to the alpha-2 adrenoceptor or the nor-epinephrine transporter, or to receptors involved in GABAer-gic or glutamatergic neurotransmission, the histamine H1

receptor, the strychnine-sensitive glycine receptor, adenosinereceptor subtypes, the angiotensin AT1 and AT2 receptors,the Na1 or L-type Ca11 channel, p-sites (i.e., peripheral-typebenzodiazepine) or I2 imidazoline recognition sites.Thus, much like other neuroleptics derived from the ben-

zamide structure, such as sulpiride, remoxipride and raclo-pride (Chivers et al., 1988; Leysen et al., 1993), amisulprideis highly selective for the dopamine D2 receptor family.Within the D2 receptor family, amisulpride specifically rec-ognizes its D2 and D3 subtypes with high and equal affinityin vitro. It seems reasonable to suggest that its neurophar-macological and clinical profile would derive from these char-acteristics.

Fig. 4. Effect of amisulpride on electrically evoked [3H]dopamine and[14C]ACh release from the rat striatum in vitro. The effects of amisul-pride (■) on the 7-OH-DPAT (30 nM)-induced (E) inhibition of electri-cally evoked [3H]dopamine and [14C]ACh release were studied usingslices prepared from the rat striatum. Data are shown as a percentageof the corresponding S2/S1 control (F) ratio ([

3H]dopamine: 0.92 6 0.02,n 5 32; [14C]ACh: 0.90 6 0.01, n 5 37).




ownloaded from


Presynaptic dopamine autoreceptor selectivity. Asstated in the Introduction, amisulpride, like most neurolep-tics, antagonizes the hyperactivity and stereotypies that re-sult from the activation of postsynaptic dopaminergic recep-tors by (high doses of) direct- or indirect-actingdopaminomimetics such as apomorphine or amphetamine(Perrault et al., 1997). However, a characteristic feature ofamisulpride is that at lower doses, it potentiates apomor-phine- and amphetamine-induced stereotyped behavior

(Vasse et al., 1985) and inhibits hypokinesia induced by theadministration of low (presynaptic) doses of apomorphine,7-OH-DPAT or quinpirole (Perrault et al., 1997). The aim ofthe present study was to examine whether the effects of lowand high doses of amisulpride could be neurochemically dis-criminated at the level of dopaminergic neurotransmission.The IC50 values of 7-OH-DPAT for inhibiting electrically

TABLE 4Effects of amisulpride on dopamine and DOPAC levels in the rat brainAnimals were sacrificed 120 min after injection of drugs, and tissue levels of dopamine and DOPAC were determined by HPLC with electrochemical detection. Dataare the mean and S.E.M. of 12 animals for each experimental group and are presented as absolute levels and (in parentheses) as a percentage of the correspondingcontrol value.

Drug Dose(mg/kg i.p.)

Nanograms per Gram of Wet Tissue Weight


Dopamine DOPAC Dopamine DOPAC

Control — 8560 6 427 821 6 50 3635 6 86 403 6 13(100.0 6 5.0) (100.0 6 6.1) (100.0 6 2.4) (100.0 6 3.2)

Amisulpride 0.1 8244 6 281 815 6 40 3574 6 164 403 6 18(96.3 6 3.3) (99.3 6 4.9) (98.3 6 4.5) (100.0 6 4.5)

0.5 8133 6 292 822 6 44 3759 6 151 429 6 15(95.0 6 3.4) (100.1 6 5.4) (103.4 6 4.2) (106.5 6 3.7)

2.5 7952 6 323 910 6 52 3853 6 221 507 6 33**(92.9 6 3.8) (110.8 6 6.3) (106.0 6 6.1) (125.8 6 8.2)

10 8194 6 381 1189 6 87** 3781 6 142 678 6 47***(95.7 6 4.5) (144.8 6 10.6) (104.0 6 3.9) (168.2 6 11.7)

30 7811 6 370 1549 6 114*** 3234 6 207 828 6 69**(91.3 6 4.3) (188.7 6 13.9) (89.0 6 5.7) (205.5 6 17.1)

100 7169 6 350* 2339 6 136*** 3007 6 146** 1287 6 53***(83.8 6 4.1) (284.9 6 16.6) (82.7 6 4.0) (319.4 6 13.2)

Haloperidol 0.2 7903 6 405 2824 6 179*** 3528 6 98 1062 6 41***(92.3 6 4.7) (344.0 6 21.8) (97.1 6 2.7) (263.5 6 13.2)

Sulpiride 100 7828 6 372 2378 6 172*** 3281 6 117* 1096 6 72***(91.4 6 4.3) (289.6 6 21.0) (90.3 6 3.2) (272.0 6 17.9)

Clozapine 10 8749 6 283 1302 6 38*** 3917 6 170 700 6 25***(102.2 6 3.3) (158.6 6 4.6) (107.8 6 4.7) (173.7 6 6.2)

* P , .05, ** P , .01, *** P , .001 compared with the corresponding control group.

TABLE 5Effects of amisulpride on dopamine synthesis in the rat brainRats received NSD-1015 (100 mg/kg) 90 min after the administration of amisul-pride or its vehicle control and were sacrificed 30 min thereafter. Data areexpressed as the mean and S.E.M. (n 5 3–7/group). Dopa levels calculated as apercentage of the corresponding control groups are shown in parentheses.


Dopa Level (ng/g wet tissue weight)


Control — 932 6 20 537 6 31(100 6 2) (100 6 6)

Amisulpride 0.2 1035 6 73 604 6 30(111 6 8) (112 6 6)

2 1135 6 48 678 6 60(122 6 5) (126 6 11)

20 2027 6 100** 1047 6 120*(217 6 11) (195 6 22)

100 3384 6 629** 1406 6 58**(363 6 67) (262 6 11)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Control — 1451 6 86 710 6 33

(100 6 6) (100 6 5)Haloperidol 0.03 1440 6 101 690 6 43

(99 6 7) (97 6 6)0.1 3377 6 362* 1070 6 135*

(233 6 25) (151 6 19)0.3 5306 6 252* 1395 6 81*

(366 6 17) (196 6 11)

* P , .05, ** P , .01 against respective controls.

TABLE 6Effects of amisulpride on dopamine synthesis in the rat brainafter blockade of impulse flowRats received NSD-1015 (100 mg/kg) 90 min after the administration of amisul-pride or its vehicle control and were sacrificed 30 min thereafter. g-Hydroxy-butyric acid was administered 45 min before sacrifice. Because the data foramisulpride derive from multiple experiments, they are expressed as a percent-age of the control value for each experiment. Mean control dopa levels variedfrom 1038 6 80 to 1451 6 86 and from 592 6 19 to 710 6 33 ng/g wet tissueweight for the striatum and limbic system, respectively, in the case of amisulpride.In the case of haloperidol, control dopa levels were 1038 6 80 and 619 6 30 ng/gwet tissue weight for the striatum and limbic system, respectively. Shown are themean and S.E.M. (n 5 3–7/group).


Dopa Level (% control)


Control — 100 6 2 100 6 41 g-Hydroxy-bu-tyrate

750 225 6 6 115 6 5

1 Amisulpride 0.5 209 6 20 101 6 51 224 6 22 123 6 42 193 6 11 114 6 65 184 6 27 114 6 620 198 6 17 127 6 575 208 6 26 139 6 13*

Control — 100 6 8 100 6 51 g-Hydroxy-bu-tyrate

750 199 6 24 110 6 6

1 Haloperidol 0.03 225 6 16 118 6 70.1 288 6 25* 137 6 80.3 281 6 28* 143 6 8*

* P , .05 vs. the g-hydroxy-butyrate group.




ownloaded from


evoked [3H]dopamine and [14C]ACh release from slices of therat striatum in vitro are similar within experimental limits.Similarly, the EC50 values of amisulpride in opposing theeffects of 7-OH-DPAT (30 nM) in this model were indistin-guishable (2.2 and 1.2 nM, respectively). Together, theseobservations suggest a close pharmacological similarity be-tween these populations of pre- and postsynaptic dopaminereceptors. Gifford and Johnson (1993), using quinpirole asthe agonist in an otherwise similar experimental approach,came to an identical conclusion using AJ-76 and UH-232,dopamine antagonists for which a selectivity for the dopa-mine autoreceptor has been amply demonstrated in vivo (Jo-hansson et al., 1985; Svensson et al., 1986; Waters et al.,1993a, 1994). Thus, for reasons that remain to be explored,this in vitro model may not be fully representative of in vivodrug effects.As a second approach to characterizing the interaction of

amisulpride with presynaptic dopaminergic systems, westudied its effects on extracellular dopamine levels, using themicrodialysis technique coupled to online HPLC analysis andelectrochemical detection. Amisulpride at low doses (10 mg/kg) increased dialysate dopamine levels in both striatum andnucleus accumbens. Its effects at this dose were similar tothose of haloperidol at 0.03 mg/kg, a dose expected to yield anoccupancy of D2-like receptors in vivo similar to that pro-duced by amisulpride at 10 mg/kg.The effects of amisulpride on terminal dopamine autore-

ceptors that modulate impulse flow-dependent release in therat olfactory tubercle were studied by differential pulse am-perometry in vivo. Because of the experimental design, wherethe impulse flow is imposed by electrical stimulation of theascending pathways, the modulation of dopamine release asmeasured does not depend on postsynaptic or somatoden-dritic autoreceptors but takes place at the terminal level(Suaud-Chagny et al., 1991). The design is thus differentfrom that in the microdialysis technique as employed, whereextracellular dopamine levels depend on the modulation ofspontaneous neuronal firing and dopamine release throughsomatodendritic as well as terminal autoreceptors. Dopa-

mine release evoked by electrical stimulation of the ascend-ing pathways was inhibited by the mixed dopamine agonistapomorphine with an ED50 value of 70 mg/kg, as well as bythe D2/D3 receptor agonist quinpirole, whereas maximallyeffective doses of haloperidol (0.5 mg/kg) and sulpiride (50mg/kg) increased stimulation-evoked dopamine release 4- to5-fold (Suaud-Chagny et al., 1991). Amisulpride similarlyincreased the amplitude of dopamine release, its maximaleffect (a 5-fold increase) being observed at 10 mg/kg. Amisul-pride was approximately 3 times as active as sulpiride in thisrespect and showed an ED50 value of 3.7 mg/kg. It should benoted that the absolute potencies of both agonists (apomor-phine) and antagonists (amisulpride, haloperidol) are fullywithin the range for behavioral effects thought to be medi-

TABLE 7Effects of 7-OH-DPAT and amisulpride on dopamine synthesis inthe rat brain after blockade of impulse flowRats received NSD-1015 (100 mg/kg) 90 min after the administration of amisul-pride or its vehicle control and were sacrificed 30 min thereafter. g-Hydroxy-butyric acid was administered 45 min before sacrifice. Data are expressed as themean and S.E.M. (n 5 3–7/group). Dopa levels calculated as a percentage of thecorresponding control groups are shown in parentheses.


Dopa Level (ng/g tissue weight)


Control — 1320 6 126 541 6 23(100 6 10) (100 6 4)

1 g-Hydroxy-bu 750 2866 6 188 622 6 34tyrate (217 6 14) (115 6 6)1 7-OH-DPAT 0.082a 1333 6 94 357 6 21

(101 6 7) (66 6 4)1 Amisulpride 5 1452 6 56 370 6 36

(110 6 4) (68 6 6)20 2172 6 305* 541 6 63*

(165 6 23) (100 6 12)75 2388 6 239* 570 6 57*

(181 6 6) (105 6 11)a 7-OH-DPAT: 0.082 mg/kg s.c.* p , .05 vs. the g-hydroxy-butyrate 1 7-OH-DPAT group.

Fig. 5. Effects of amisulpride on extracellular dopamine and DOPAClevels, as measured by microdialysis, in the rat striatum and nucleusaccumbens. Extracellular dopamine and DOPAC levels in the rat stri-atum (n 5 4) and nucleus accumbens (n 5 6) were measured after theadministration of amisulpride (10 mg/kg i.p.), using the microdialysistechnique. Dialysates were collected as 20-min fractions and analyzedby online HPLC coupled to electrochemical detection. Data are shownas a percentage of basal outflow, taken over five stable fractionsimmediately before drug administration, and represent the mean andS.E.M.




ownloaded from


ated by presynaptic dopamine autoreceptors (Perrault et al.,1997), which further attests to the validity of the model.Thus it is clear that amisulpride behaves as an antagonist

toward presynaptic dopamine receptors that modulate[3H]dopamine release in vitro as well as in vivo. At higherdoses, amisulpride possesses characteristics found in classi-cal neuroleptics. Thus amisulpride occupies postsynaptic D2-like receptors in the rat striatum, labeled using [3H]raclo-pride or [3H]spiperone (ED50 5 44 and 87 mg/kg,respectively), and stimulates dopamine turnover, increasingtissue DOPAC levels with similar potency and effectivenessin the striatum and limbic system. Its maximal effects weresimilar to those of haloperidol and sulpiride and greater thanthose of clozapine. Although striatal ACh levels were signif-icantly decreased only from 30 mg/kg amisulpride, inspection

of the relative overall dose-response curves for the effects ofamisulpride on tissue DOPAC and ACh levels does not sug-gest any critical differences in potency. Both phenomena thusare likely to be related.In a result consistent with its stimulation of dopamine

turnover, amisulpride increased the rate of dopamine syn-thesis (ED50 5 20–40 mg/kg), as reflected by the increase indopa accumulation after the administration of NSD-1015. Itis also likely that in this model, its effects were not mediatedthrough presynaptic receptor occupancy at the level of thedopamine nerve terminal because they were largely elimi-nated by pretreatment with g-hydroxy-butyrate (table 6),although we cannot rule out the possibility that low synaptic

Fig. 6. Effects of haloperidol on extracellular dopamine and DOPAClevels, as measured by microdialysis, in the rat striatum and nucleusaccumbens. Extracellular dopamine and DOPAC levels in the rat stri-atum (n 5 6) and nucleus accumbens (n 5 6) were measured after theadministration of haloperidol (0.03 mg/kg i.p.), using the microdialysistechnique. Dialysates were collected as 20-min fractions and analyzedby on-line HPLC coupled to electrochemical detection. Data are shownas a percentage of basal outflow, taken over five stable fractionsimmediately before drug administration, and represent the mean andS.E.M.

Fig. 7. Effects of amisulpride on the amplitude of evoked dopaminerelease in the rat olfactory tubercle in vivo. The effect of amisulpridewas studied on dopamine release evoked by electrical stimulations ofthe ascending dopaminergic pathway, which were repeated every 10min. Dopamine release was measured using an electrochemicallytreated carbon-fiber electrode implanted in the olfactory tubercle andwas recorded every 1 s. Data are expressed as a percentage of themean evoked dopamine release during the three stimulations immedi-ately before s.c. drug administration, and represent the mean andS.E.M. of four (amisulpride) or six (vehicle) rats per group.

Fig. 8. Dose-response curve of the effect of amisulpride on stimulation-evoked dopamine release in the rat olfactory tubercle in vivo. The effectof amisulpride, administered at the dose of 0.5, 1, 3, 5, 10 and 15 mg/kgs.c., on dopamine release was studied as described in fig. 7. Shown isthe effect, expressed as a percentage of the mean evoked dopaminerelease in vehicle-treated controls, of amisulpride 90 min after drugtreatment (mean 6 S.E.M.; n 5 4/group).




ownloaded from


concentrations of dopamine after impulse-flow blockade pre-vented expression of a presynaptic component that mightcontribute under control conditions. In contrast, haloperidolincreased dopa accumulation in the absence as well as in thepresence of g-hydroxy-butyrate, which suggests that its ef-fects on dopamine synthesis are mediated by postsynaptic (asevidenced in the absence of g-hydroxy-butyrate) as well aspresynaptic (as evidenced in the presence of g-hydroxy-bu-tyrate) mechanisms.7-OH-DPAT decreased the rate of dopa accumulation after

pretreatment with NSD-1015 and g-hydroxy-butyrate. Un-der those conditions where impulse flow was interrupted,amisulpride opposed the effects of 7-OH-DPAT with an ED50

value of approximately 10 mg/kg. The fact that, particularlyin the striatum, amisulpride failed to increase dopa accumu-lation after NSD-1015 and g-hydroxy-butyrate pretreatmentyet opposed the effects of 7-OH-DPAT needs to be exploredfurther. It may be that synaptic concentrations of dopamineare too low after blockade of neuronal activity to allow dopa-mine autoreceptor antagonism to be expressed. A low endog-enous DA tonus may similarly explain why g-hydroxy-bu-tyrate administration caused only a small, nonsignificantincrease in dopa accumulation in the limbic system, eventhough the effects of 7-OH-DPAT clearly demonstrated thepresence of synthesis-modulating DA autoreceptors in thisarea. Alternatively, the modulation of dopamine synthesis byendogenous dopamine and the exogenous agonist 7-OH-DPAT may be mediated at least in part through different(extrajunctional?) dopamine receptor subtypes, differentiallyrecognized by amisulpride in vivo. Recent evidence suggeststhat the molecularly defined D3 receptor might be a candi-date for this dopamine autoreceptor subtype (Meller et al.,1993; Nissbrandt et al., 1995). Pharmacological studies invitro (Aretha and Galloway, 1996) and in vivo (Aretha et al.,1995) support this hypothesis. In particular, the selectivedopamine D3 receptor antagonist (1)-S 14297 fails to affectdopamine synthesis in vivo, as assessed by its effects ontissue DOPAC/dopamine ratios, when studied alone, but op-poses the inhibitory effects of 7-OH-DPAT on this parameter(Gobert et al., 1995).Thus all available data suggest that, in vivo, amisulpride

affects presynaptic parameters of dopaminergic neurotrans-

mission at doses lower than those that block postsynapticdopamine receptors. These data are in full agreement withthe observations that amisulpride preferentially blocks be-havioral effects thought to be associated with the stimulationof presynaptic dopamine receptors (Perrault et al., 1997).Selectivity for limbic D2/D3 receptors. It has been sug-

gested that the atypical character of certain neurolepticsarises from a greater effect on the limbic system, which isthought to be involved in emotional and cognitive processes,than on the extrapyramidal system, which is intimately re-lated to the control of motor behavior (Bischoff, 1992; Melt-zer, 1993; Scatton and Zivkovic, 1985).By using [3H]raclopride, a high-affinity radioligand for do-

pamine D2 and D3 receptors, we have shown that amisul-pride as well as its analog sulpiride, but not haloperidol orremoxipride, displayed a preferential affinity for limbic do-pamine D2 (1 D3) receptors. Using the nonbenzamide dopa-mine antagonist [3H]spiperone as the radioligand, we con-firmed the limbic selectivity of amisulpride. Theseobservations are consistent with previous in vivo bindingstudies using [3H]spiperone (Bischoff, 1992). At first, theregional differences in displacing potencies of amisulpridewould not seem to be related to a selective inhibition of[3H]raclopride binding of a particular dopamine receptor sub-type, because in vitro, amisulpride displays a similar affinityfor D2 and D3 dopamine receptors. Moreover, the low densityand restricted distribution of the mRNA coding for the D3

subtype (Sokoloff et al., 1990, 1992b) suggests that the pres-ence of dopamine D3 receptors cannot account for the in vivopharmacological differences between limbic and striatal[3H]raclopride binding sites. Nevertheless, the dose-ratio ofamisulpride for the occupation of D2 and D3 receptors in vivoremains to be established. In addition, and even though D3

mRNA is expressed at low levels, the D3 receptor density maybe equal to that of the D2 receptor in the nucleus accumbens(Booze and Wallace, 1995).Microdialysis studies point to a second regionally specific

effect of amisulpride. Thus, although amisulpride at lowdoses (10 mg/kg) produced an essentially similar increase instriatal and limbic dialysate dopamine levels, dialysateDOPAC levels were increased to a greater extent in thelimbic system. Although the origin of such differential effectsremains unknown, it has been reported that the dopaminereceptors that control extracellular dopamine and DOPAClevels may be localized at the terminal and somatodendriticlevels, respectively. Thus the local infusion of dopamine ago-nists or antagonists, including haloperidol, raclopride, AJ76or UH232, into the striatum or nucleus accumbens only min-imally affects extracellular DOPAC levels (Imperato and DiChiara, 1988; Timmerman et al., 1990; Waters et al., 1994).However, significant increases and decreases, respectively,are observed after their systemic administraiton, which sug-gests that extracellular DOPAC levels in the projection fieldsare a function of impulse flow and thus are modulatedthrough postsynaptic receptors or somatodendritic autore-ceptors (Waters et al., 1994). On the basis of this hypothesis,it would follow that amisulpride increases dopaminergic neu-ronal activity to a greater extent in the limbic than in thestriatal projections. Electrophysiological studies are inprogress to test this hypothesis.A further index of a potential limbic selectivity in the

interaction of amisulpride with dopaminergic neurotrans-

TABLE 8The effects of amisulpride, haloperidol, sulpiride and clozapineon rat striatal ACh and choline levelsAnimals were sacrificed 120 min after injection of drugs, and tissue levels of AChand choline were determined by HPLC with electrochemical detection. Data arethe mean and S.E.M. of six animals for each experimental group.


Nanomoles per Gram of Wet Tissue Weight

ACh Choline

Control — 16 6 1 184 6 6Amisulpride 0.1 16 6 2 175 6 7

0.5 16 6 1 176 6 102.5 14 6 1 173 6 710 16 6 1 190 6 1230 14 6 1* 194 6 9100 9 6 1*** 182 6 11

Haloperidol 0.2 11 6 1** 175 6 7Sulpiride 100 10 6 0*** 181 6 10Clozapine 10 13 6 1 189 6 12

* P , .05, ** P , .01, *** P , .001 compared with the control group (n 56/group).




ownloaded from


mission is its stimulation of tyrosine hydroxylase activity.Thus amisulpride increased dopa accumulation in the limbicsystem with higher potency (ED50 5 18.6 mg/kg) than in thestriatum (ED50 5 43.7 mg/kg). Also in this case, it appearsthat the origin of limbic selectivity is not at the level of theterminal autoreceptor, because amisulpride opposed the ef-fects of 7-OH-DPAT, after the administration of g-hydroxy-butyrate, with similar potency in both regions.Within the higher dose ranges, amisulpride increased limbic

and striatal DOPAC tissue levels to a similar degree in eachregion. In this respect, amisulpride differs markedly from clas-sical neuroleptics such as haloperidol, whose effects on tissueDOPAC levels are considerably more pronounced in striatalregions (Scatton et al., 1977), and can be grouped together withthe atypical neuroleptics clozapine and sulpiride.Taken together, the present results demonstrate that after

systemic administration, amisulpride preferentially inter-acts with limbic dopamine D2-like receptors. Regional differ-ences in pharmacological effects may be related to the re-gional brain distribution of systemically administeredamisulpride (Kohler et al., 1992). Alternatively, a regionalselectively may arise from the differential involvement ofdopamine D2 and D3 receptor subtypes in the striatal andlimbic systems.Conclusions. With reference to other neuroleptics, amisul-

pride displays several characteristic features. Thus its specific-ity and selectivity for D2-like (D2 and D3) receptors are uncom-mon and are largely confined to neuroleptics from thesubstituted benzamide series. Although average clinical dosesand plasma concentrations of neuroleptics appear to correlatewith D2 receptor affinity (Seeman, 1992), which suggests thatD2 receptor occupancy constitutes a major molecular target fortherapeutic efficacy, additional pharmacological mechanismsare thought to participate in, or to contribute to, an atypicaltherapeutic spectrum. Among these are an antagonism toward5-HT2A or 5-HT2C receptors, muscarinic cholinergic receptors oralpha adrenoceptors or an affinity toward s recognition sites(Ferris et al., 1991; Meltzer, 1991; Schmidt et al., 1995). Thepresent data suggest that selective dopamine D2 antagonismcan also lead to therapeutically efficacious atypical neurolep-tics. Within the dopamine D2 receptor family, amisulpride se-lectivity recognizes the D2 and D3 subtypes. The observationthat amisulpride shows only low affinity for the D4 subtypewould support the suggestion (Seeman, 1992) that drug affinityfor the dopamine D4 receptor is not an absolute requirement fortherapeutic efficacy in the treatment of schizophrenia. Amisul-pride selectively recognizes the D2 and D3 subtypes with equalaffinity, unlike most conventional neuroleptics, which displayhigher affinity for the D2 than for the D3 subtype. Although thefunctional significance of the D3 dopamine receptor subtyperemains to be firmly established, it is tempting to speculate thata causal relationship exists with the selectivity of amisulpridefor dopamine autoreceptors. Thus, in vivo, amisulpride selec-tively affects presynaptic dopamine receptors that control do-pamine synthesis and release, at doses below those that pro-duce significant postsynaptic D2 receptor occupancy, decreasestriatal ACh levels, provoke an increase in dopamine turnoveror block apomorphine-induced gnawing. The involvement ofboth D2 and D3 receptor subtypes in [

3H]raclopride/[3H]spiper-one binding in vivo, as well as dopamine synthesis and releasemodulation, taken together with a greater relative abundanceof D3 vs. D2 receptors in the limbic than in the striatal regions,

may be the basis of the selectivity of amisulpride for the limbicdopaminergic system.In summary, amisulpride has complex neurochemical ef-

fects on central dopaminergic neurotransmission but appearsto show a selectivity, at low doses, for dopamine autorecep-tors involved in the presynaptic regulation of dopaminergicneurotransmission, as well as a selectivity for its limbic pro-jections. These characteristics probably contribute to its ther-apeutic activity in the treatment of dysthymia and negativesymptoms of schizophrenia at low doses, and in the treat-ment of the positive symptoms of schizophrenia at highdoses, because low doses selectively increase dopaminergicactivity whereas high doses block postsynaptic D2 receptors.

Acknowledgments

The authors gratefully acknowledge Drs. S. Tan, A.-M. Galzin andD. Graham for their contribution to in vitro receptor binding studiesas well as the excellent technical assistance of N. Allouard, M. Bas,N. Brunel, D. Chautrel, G. Danielou, G. Darles, C. Delatte, F. De-mange, P. Gaubert, C. Lemaire, B. Peny, C. Sellier, A. Thiola, F.Thuret, M. Vasseur, and M. Vinay.

References

ANGEL, I., SCHOEMAKER, H., PROUTEAU, M., GARREAU, M. AND LANGER, S. Z.:Litoxetine: A selective 5-HT uptake inhibitor with concomitant 5-HT3 recep-tor antagonist and antiemetic properties. Eur. J. Pharmacol. 232: 139–145,1993.

ARBILLA, S., DEPOORTERE, H., GEORGE, P. AND LANGER, S. Z.: Pharmacologicalprofile of the imidazopyridine zolpidem at benzodiazepine receptors andelectrocorticogram in rats. Naunyn Schmiedebergs Arch. Pharmacol. 330:248–251, 1985.

ARBILLA, S. AND LANGER, S. Z.: Differential effects of the stereoisomers of 3PPPon dopaminergic and cholinergic neurotransmission in superfused slices ofthe corpus striatum. Naunyn Schmiedebergs Arch. Pharmacol. 327: 6–13,1984.

ARETHA, C. W. AND GALLOWAY, M. P.: Dopamine autoreceptor reserve in vitro:Possible role of dopamine D3 receptors. Eur. J. Pharmacol. 305: 119–122,1996.

ARETHA, C. W., SINHA, A. AND GALLOWAY, M. P.: Dopamine D3-preferring ligandsact at synthesis modulating autoreceptors. J. Pharmacol. Exp. Ther. 274:609–613, 1995.

ASANO, M., MIYAUCHI, T., KATO, T., FUJIMORI, K. AND YAMAMOTO, K.: Determina-tion of acetylcholine and choline in rat brain tissue by liquid chromatogra-phy/electrochemistry using an immobilized enzyme post column reactor. J.Liquid Chromatogr. 9: 199–215, 1986.

BILLARD, W., RUPERTO, V., CROSBY, G., IORIO, L. C. AND BARNETT, A.: Character-ization of the binding of 3H-SCH 23390, a selective D-1 receptor antagonistligand, in rat striatum. Life Sci. 35: 1885–1893, 1984.

BISCHOFF, S.: Limbic selective neuroleptics. Clin. Neuropharmacol. 15S: 265–266, 1992.

BOOZE, R. M. AND WALLACE, D. R.: Dopamine D2 and D3 receptors in the ratstriatum and nucleus accumbens: Use of 7-OH-DPAT and [125I]-iodosul-pride. Synapse 19: 1–13, 1995.

BOYER, P., LECRUBIER, Y. AND PUECH, A. J.: Treatment of positive and negativesymptoms: Pharmacologic approaches. Mod. Probl. Pharmacopsychiat. 24:152–174, 1990.

BOYER, P., LECRUBIER, Y., PUECH, A. J., DEWAILLY, J. AND AUBIN, F.: Treatment ofnegative symptoms in schizophrenia with amisulpride. Br. J. Psychiat. 166:68–72, 1995.

BRILEY, M. AND LANGER, S. Z.: Two binding sites for 3H-spiroperidol on ratstriatal membranes. Eur. J. Pharmacol. 50: 283–284, 1978.

BRUNS, R. F., LU, G. H. AND PUGSLEY, T. A.: Characterization of the A2 adenosinereceptor labeled by [3H]NECA in rat striatal membranes. Mol. Pharmacol.29: 331–346, 1986.

CARTER, C. J. AND PYCOCK, C. J.: Behavioral and biochemical effects of dopamineand noradrenaline depletion within the medial prefrontal cortex of the rat.Brain Res. 192: 163–176, 1980.

CARTER, C. J. AND PYCOCK, C. J.: The role of 5-hydroxytryptamine in dopamine-dependent stereotyped behaviour. Neuropharmacology 20: 261–265, 1981.

CHENG, Y.-C. AND PRUSOFF, W. H.: Relationship between the inhibition constant(Ki) and the concentration of inhibitor which causes a 50% inhibition (I50) ofan enzymatic reaction. Biochem. Pharmacol. 22: 3099–3108, 1973.

CHIVERS, J. K., GOMMEREN, W., LEYSEN, J. E., JENNER, P. AND MARSDEN, C. D.:Comparison of the in vitro receptor selectivity of substituted benzamidedrugs for brain neurotransmitter receptors. J. Pharm. Pharmacol. 40: 415–421, 1988.

CHRISTENSEN, A., FJALLAND, B. AND MOLLER-NIELSEN, I.: On the supersensitivity




ownloaded from


of dopamine receptors induced by neuroleptics. Psychopharmacology 48:1–6, 1976.

CLAUSTRE, Y., FAGE, D., ZIVKOVIC, B. AND SCATTON, B.: Relative selectivity of6,7-dihydroxy-2-dimethylaminotetralin, N-n-propyl-3-(3-hydroxyphenyl)pi-peridine, N-n-propylnorapomorphine and pergolide as agonists at striataldopamine autoreceptors and postsynaptic dopamine receptors. J. Pharma-col. Exp. Ther. 232: 519–525, 1985.

COSTALL, B., NAYLOR, R. J. AND NOHRIA, V.: Climbing behaviour induced byapomorphine in mice: A potential model for the detection of neurolepticactivity. Eur. J. Pharmacol. 50: 39–50, 1978.

DADKAR, N. K., DOHADWALLA, A. N. AND BHATTACHARYA, B. K.: Influence ofpheniramine and chlorpheniramine on apomorphine-induced compulsivegnawing in mice. Psychopharmacology 48: 7–10, 1976.

DELCKER, A., SCHOON, M. L., OCZKOWSKI, B. AND GAERTNER, H. J.: Amisulprideversus haloperidol in the treatment of schizophrenic patients—Results of adouble-blind study. Pharmacopsychiatry 23: 125–130, 1990.

DEMCHYSHYN, L. L., SUGAMORI, K. S., LEE, F. J. S., HAMADANIZADEH, S. A. ANDNIZNIK, H. B.: The dopamine D1D receptor—Cloning and characterization ofthree pharmacologically distinct D1-like receptors from Gallus domesticus.J. Biol. Chem. 270: 4005–4012, 1995.

DI CHIARA, G., CORSINI, G. U., MEREU, G. P., TISSARI, A. AND GESSA, G. L.:Self-inhibitory dopamine receptors: Their role in the biochemical and behav-ioural effects of low doses of apomorphine. Dopamine, ed. by P. J. Roberts, G.N. Woodruff and L. L. Iversen, pp. 275, Raven Press, New York, 1986.

FAURE, C., PIMOULE, C., ARBILLA, S., LANGER, S. Z. AND GRAHAM, D.: Expressionof a1-adrenoceptor subtypes in rat tissues: Implications for a1-adrenoceptorclassification. Eur. J. Pharmacol. 268: 141–149, 1994.

FERRIS, C. D., HIRSCH, D. J., BROOKS, B. P. AND SNYDER, S. H.: s Receptors: Frommolecule to man. J. Neurochem. 57: 729–737, 1991.

GIFFORD, A. N. AND JOHNSON, K. M.: A pharmacological analysis of the effects of(1)-AJ 76 and (1)-UH 232 at release regulating pre- and postsynapticdopamine receptors. Eur. J. Pharmacol. 237: 169–175, 1993.

GLOSSMANN, H., BAUKAL, A. J. AND CATT, K. J.: Properties of angiotensin IIreceptors in the bovine and rat adrenal cortex. J. Biol. Chem. 249: 825–834,1974.

GOBERT, A., RIVET, J. M., AUDINOT, V., CISTARELLI, L., SPEDDING, M., VIAN, J.,PEGLION, J. L. AND MILLAN, M. J.: Functional correlates of dopamine D3,receptor activation in the rat in vivo and their modulation by the selectiveantagonist, (1)-S 14297: II. Both D2 and “Silent” D3 autoreceptors controlsynthesis and release in mesolimbic, mesocortical and nigrostriatal path-ways. J. Pharmacol. Exp. Ther. 275: 899–913, 1995.

GROSSMAN, C. J., KILPATRICK, G. J. AND BUNCE, K. T.: Development of a radioli-gand binding assay for 5-HT4 receptors in guinea-pig and rat brain. Br. J.Pharmacol. 109: 618–624, 1993.

HERRICK-DAVIS, K., TITELER, M., LEONHARDT, S., STRUBLE, R. AND PRICE, D.:Serotonin 5-HT1D receptors in human prefrontal cortex and caudate: Inter-action with a GTP binding protein. J. Neurochem. 51: 1906–1912, 1988.

HEURING, R. E. AND PEROUTKA, S. J.: Characterization of a novel 3H-5-hydroxytryptamine binding site subtype in bovine brain membranes. J. Neu-rosci. 7: 894–903, 1987.

HICKS, P. E., SCHOEMAKER, H. AND LANGER, S. Z.: 5HT-receptor antagonistproperties of SCH 23390 in vascular smooth muscle and brain. Eur. J. Phar-macol. 105: 339–342, 1984.

HILL, D. R. AND BOWERY, N. G.: 3H-Baclofen and 3H-GABA bind to bicuculline-insensitive GABAB sites in rat brain. Nature (Lond.) 290: 149–152, 1981.

HONORE, T., LAURIDSEN, J. AND KROGSGAARD LARSEN, P.: The binding of[3H]AMPA, a structural analogue of glutamic acid, to rat brain membranes.J. Neurochem. 38: 173–178, 1982.

HONORE, T. AND DREJER, J.: Chaotropic ions affect the conformation of quisqual-ate receptors in rat cortical membranes. J. Neurochem. 51: 457–461, 1988.

IMPERATO, A. AND DI CHIARA, G.: Effects of locally applied D-1 and D-2 receptoragonists and antagonists studied with brain dialysis. Eur. J. Pharmacol.156: 385–393, 1988.

JANOWSKY, A., BERGER, P., VOCCI, F., LABARCA, R., SKOLNICK, P. AND PAUL, S. M.:Characterization of sodium-dependent 3H-GBR-12935 binding in brain: Aradioligand for selective labelling of the dopamine transport complex.J. Neurochem. 46: 1272–1276, 1986.

JOHANSSON, A. M., ARVIDSSON, L. E., HACKSELL, U., NILSSON, J. L. G., SVENSSON,K., HJORTH, S., CLARK, D., CARLSSON, A., SANCHEZ, D., ANDERSSON, B. AND

WIKSTROM, H.: Novel dopamine receptor agonists and antagonists with pref-erential action on autoreceptors. J. Med. Chem. 28: 1049–1053, 1985.

KISHIMOTO, H., SIMON, J. R. AND APRISON, M. H.: Determination of the equilib-rium dissociation constants and number of glycine binding sites in severalareas of the rat central nervous system, using a sodium-independent system.J. Neurochem. 37: 1015–1024, 1981.

KOHLER, C., HALL, H., OGREN, S. O. AND GAWELL, L.: Specific in vitro and in vivobinding of 3H-raclopride, a potent substituted benzamide drug with highaffinity for dopamine D-2 receptors in the rat brain. Biochem. Pharmacol.34: 2251–2259, 1985.

KOHLER, C., RADESATER, A. C., KARLSSON-BOETHIUS, G., BRYSKE, B. AND WILDMAN,M.: Regional distribution and in vivo binding of the atypical antipsychoticdrug remoxipride. A biochemical and autoradiographic analysis in the ratbrain. J. Neural Transm. 87: 49–62, 1992.

LADURON, P. M., JANSSEN, P. F. M. AND LEYSEN, J. E.: Spiperone: A ligand of

choice for neuroleptic receptors. 2. Regional distribution and in vivo dis-placement of neuroleptic drugs. Biochem. Pharmacol. 27: 317–321, 1978.

LANGER, S. Z., ARBILLA, S., SCATTON, B., ZIVKOVIC, B., GALZIN, A. M., LLOYD, K. G.AND BARTHOLINI, G.: Progabide and SL 75.102: Interaction with GABA recep-tors and effects on neurotransmitter and receptor systems. In Epilepsy andGABA Receptor Agonists, ed. by G. Bartholini, L. Bossi, K. G. Lloyd and P.L. Morselli, pp. 81–90, Raven Press, New York, 1985.

LE ROUZIC, M., ANGEL, I., SCHOEMAKER, H., ALLEN, J., ARBILLA, S. AND LANGER, S.Z.: Binding of [3H]cirazoline to an imidazoline site in rat brain and kidneymembranes. Eur. J. Pharmacol. 278: 261–264, 1995.

LEJEUNE, F. AND MILLAN, M. J.: Activation of dopamine D3 autoreceptors inhib-its firing of ventral tegmental dopaminergic neurones in vivo. Eur. J. Phar-macol. 275: R7–R9, 1995.

LEYSEN, J. E., JANSSEN, P. M. F., SCHOTTE, A., LUYTEN, W. H. M. L. AND MEGENS,A. A. H. P.: Interaction of antipsychotic drugs with neurotransmitter recep-tor sites in vitro and in vivo in relation to pharmacological and clinicaleffects: Role of 5HT2 receptors. Psychopharmacology (Berl) 112: S40–S54,1993.

MALMBERG, Å., JACKSON, D. M., ERIKSSON, A. AND MOHELL, N.: Unique bindingcharacteristics of antipsychotic agents interacting with human dopamineD2A, D2B and D3 receptors. Mol. Pharmacol. 43: 749–754, 1993.

MELLER, E., BOHMAKER, K., GOLDSTEIN, M. AND BASHAM, D. A.: Evidence thatstriatal synthesis-inhibiting autoreceptors are dopamine D3 receptors. Eur.J. Pharmacol. 249: R5–R6, 1993.

MELTZER, H. Y.: The mechanism of action of novel antipsychotic drugs. Schizo-phr. Bull. 17: 263–287, 1991.

MELTZER, H. Y.: New drugs for the treatment of schizophrenia. Psychiatr. Clin.North Am. 16: 365–385, 1993.

MELTZER, H. Y., MATSUBARA, S. AND LEE, J.-C.: Classification of typical andatypical antipsychotic drugs on the basis of dopamine D-1, D-2 and seroto-nin2 pKi values. J. Pharmacol. Exp. Ther. 251: 238–246, 1989.

MOGILNICKA, E., SCHEEL-KRUGER, J., KLIMEK, V. AND GOLEMBIOWSKA-NIKITIN, K.:The influence of antiserotonergic agents on the action of dopaminergicdrugs. Pol. J. Pharmacol. Pharm. 20: 31–38, 1977.

MOGILNICKA, E., ARBILLA, S., DEPOORTERE, H. AND LANGER, S. Z.: Rapid eyemovement sleep deprivation decreases the density of 3H-dihydroalprenololand 3H-imipramine binding sites in the rat cerebral cortex. Eur. J. Pharma-col. 65: 289–292, 1980.

NISSBRANDT, H., EKMAN, A., ERIKSSON, E. AND HEILIG, M.: Dopamine D3 receptorantisense influences dopamine synthesis in rat brain. NeuroReport 6: 573–576, 1995.

PAILLERE MARTINOT, M. L., LECRUBIER, Y., MARTINOT, J. L. AND AUBIN, F.: Im-provement of some schizophrenic deficit symptoms with low doses of amisul-pride. Am. J. Psychiatry 152: 130–134, 1995.

PARKER, E. M. AND CUBEDDU, L. X.: Evidence for autoreceptor modulation ofendogenous dopamine release from rabbit caudate nucleus in vitro. J. Phar-macol. Exp. Ther. 232: 492–500, 1985.

PAUWELS, P. J., LEYSEN, J. E. AND LADURON, P. M.: [3H]Batrachotoxinin A20-a-benzoate binding to sodium channels in rat brain: Characterization andpharmacological significance. Eur. J. Pharmacol. 124: 291–298, 1986.

PAXINOS, G. AND WATSON, C.: The Rat Brain in Stereotaxic Coordinates. Aca-demic Press, Sydney, Australia, 1982.

PAZOS, A., HOYER, D. AND PALACIOS, J. M.: The binding of serotonergic ligands tothe porcine choroid plexus: Characterization of a new type of serotoninrecognition site. Eur. J. Pharmacol. 106: 539–546, 1984.

PEROUTKA, S. J.: Pharmacological differentiation and characterization of5-HT1A, 5-HT1B, and 5-HT1C binding sites in rat frontal cortex. J. Neuro-chem. 47: 529–540, 1986.

PERRAULT, G., DEPOORTERE, R., MOREL, E., SANGER, D. J. AND SCATTON, B.:Psychopharmacological profile of amisulpride, an antipsychotic drug withpresynaptic D2/D3 dopamine receptor antagonist activity and limbic selec-tivity. J. Pharmacol. Exp. Ther. 1997.

PILON, C., LEVESQUE, D., DIMITRIADOU, V., GRIFFON, N., MARTRES, M.-P.,SCHWARTZ, J.-C. AND SOKOLOFF, P.: Functional coupling of the human dopa-mine D3 receptor in a transfected NG 108-15 neuroblastoma-glioma hybridcell line. Eur. J. Pharmacol.-Molec. Pharm. 268: 129–139, 1994.

PIMOULE, C. AND LANGER, S. Z.: Duct ligation decreases [3H]clonidine binding inrat submaxillary glands. Eur. J. Pharmacol. 82: 85–88, 1982.

RAISMAN, R., SETTE, M., PIMOULE, C., BRILEY, M. AND LANGER, S. Z.: High-affinity[3H]desipramine binding in the peripheral and central nervous system: Aspecific site associated with the neuronal uptake of noradrenaline. Eur.J. Pharmacol. 78: 345–351, 1982.

REYNOLDS, I. J., MURPHY, S. N. AND MILLER, R. J.: 3H-labeled MK-801 binding tothe excitatory amino acid receptor complex from rat brain is enhanced byglycine. Proc. Natl. Acad. Sci. U.S.A. 84: 7744–7748, 1987.

SALETU, B., KUFFERLE, B., GRUNBERGER, J., FOLDES, P., TOPITZ, A. AND ANDERER,P.: Clinical, EEG mapping and psychometric studies in negative schizophre-nia: Comparative trials with amisulpride and fluphenazine. Neuropsycho-biology 29: 125–135, 1994.

SANGER, D. J. AND SCHOEMAKER, H.: Discriminative stimulus properties of 8-OH-DPAT: Relationship to affinity for 5HT1A receptors. Psychopharmacology108: 85–92, 1992.

SAUTEL, F., GRIFFON, N., LEVESQUE, D., PILON, C., SCHWARTZ, J.-C. AND SOKOLOFF,P.: A functional test identifies dopamine agonists selective for D3 versus D2receptors. NeuroReport 6: 329–332, 1995.




ownloaded from


SCATTON, B., BISCHOFF, S., DEDEK, J. AND KORF, J.: Regional effects of neurolep-tics on dopamine metabolism and dopamine-sensitive adenylate cyclaseactivity. Eur. J. Pharmacol. 44: 287–292, 1977.

SCATTON, B., PERRAULT, G., SANGER, D. J., SCHOEMAKER, H., CARTER, C., FAGE, D.,GONON, F., CHERGUI, K., CUDENNEC, A. AND BENAVIDES, J.: Pharmacologicalprofile of amisulpride, an atypical neuroleptic which preferentially blockspresynaptic D2/D3 receptors. Neuropsychopharmacology 10: 242S, 1994.

SCATTON, B. AND ZIVKOVIC, B.: Neuroleptics and the limbic system. In Psycho-pharmacology of the Limbic System, ed. by M. R. Trimble and E. Zarifian,pp. 174–197, Oxford University Press, Oxford, 1985.

SCHMIDT, C. J., SORENSEN, S. M., KEHNE, J. H., CARR, A. A. AND PALFREYMAN, M.G.: The role of 5-HT2A receptors in antipsychotic activity. Life Sci. 56:2209–2222, 1995.

SCHOEMAKER, H.: [3H]7-OH-DPAT labels both dopamine D3 receptors and ssites in the bovine caudate nucleus. Eur. J. Pharmacol. 242: R1–R2, 1993.

SCHOEMAKER, H., BOLES, R. G., HORST, W. D. AND YAMAMURA, H. I.: Specifichigh-affinity binding sites for [3H]Ro 5-4864 in rat brain and kidney.J. Pharmacol. Exp. Ther. 225: 61–69, 1983.

SCHOEMAKER, H., CLAUSTRE, Y., OBLIN, A., ROUQUIER, L., DEPOORTERE, R., FAGE,D., PERRAULT, G., CARTER, C., BENAVIDES, J. AND SCATTON, B.: Amisulpride, anatypical antipsychotic, preferentially blocks dopamine D2/D3 autoreceptors.(Abstract) Soc. Neurosci. 21: 1995.

SCHOEMAKER, H. AND LANGER, S. Z.: [3H]8-OH-DPAT labels the serotonin trans-porter in the rat striatum. Eur. J. Pharmacol. 124: 371–373, 1986.

SCHOEMAKER, H. AND LANGER, S. Z.: Effects of Ca11 on [3H]diltiazem bindingand its allosteric interaction with dihydropyridine calcium channel bindingsites in the rat cortex. J. Pharmacol. Exp. Ther. 248: 710–715, 1989.

SCHOEMAKER, H., OBLIN, A. AND LANGER, S. Z.: Binding of [3H]ifenprodil, andNMDA antagonist, to polyamine and sigma sites in the cerebral cortex.FASEB J. 5: A703, 1991.

SCHWABE, U. AND TROST, T.: Characterization of adenosine receptors in rat brainby (2)[3H]N6-phenylisopropyladenosine. Naunyn Schmiedebergs Arch.Pharmacol. 313: 179–187, 1980.

SEEMAN, P.: Dopamine receptor sequences. Therapeutic levels of neurolepticsoccupy D2 receptors, clozapine occupies D4. Neuropsychopharmacology 7:261–284, 1992.

SERMERDJIAN-ROUQUIER, L., BOSSI, L. AND SCATTON, B.: Determination of 5-hy-droxytryptophan, serotonin and 5-hydroxyindoleacetic acid in rat and hu-man brain and biological fluids by reversed-phase high-performance liquidchromatography with electrochemical detection. J. Chromatog. 218: 663–670, 1981.

SILLS, M. A., FAGG, G., POZZA, M., ANGST, C., BRUNDISH, D. E., HURT, S. D.,WILUSZ, E. J. AND WILLIAMS, M.: [3H]CGP 39653: A new N-methyl-D-aspartate antagonist radioligand with low nanomolar affinity in rat brain.Eur. J. Pharmacol. 192: 19–24, 1991.

SIMON, S. R., YOUNG, A. R. AND SNYDER, S. H.: Binding of [3H]kainic acid, ananalogue of L-glutamate, to brain membranes. J. Neurochem. 26: 141–147,1976.

SOKOLOFF, P., ANDRIEUX, M., BESANCCON, R., PILON, C., MARTRES, M. P., GIROS, B.AND SCHWARTZ, J.-C.: Pharmacology of human dopamine D3 receptor ex-pressed in a mammalian cell line: Comparison with D2 receptor. Eur.J. Pharmacol. 225: 331–337, 1992a.

SOKOLOFF, P., GIROS, B., MARTRES, M. P., ANDRIEUX, M., BESANCON, R., PILON, C.,BOUTHENET, M. L., SOUIL, E. AND SCHWARTZ, J.-C.: Localization and function ofthe D3 dopamine receptor. Arzneimittelforschung 42: 224–230, 1992b.

SOKOLOFF, P., GIROS, B., MARTRES, M. P., BOUTHENET, M. L. AND SCHWARTZ, J.-C.:Molecular cloning and characterization of a novel dopamine receptor (D3) asa target for neuroleptics. Nature (Lond.) 347: 146–151, 1990.

SOKOLOFF, P., MARTRES, M. P., GIROS, B., BOUTHENET, M. L. AND SCHWARTZ, J.-C.:The third dopamine receptor (D3) as a novel target for antipsychotics. Bio-chem. Pharmacol. 43: 659–666, 1992c.

STOCKMEIER, C. A., DICARLO, J. J., ZHANG, Y., THOMPSON, P. AND MELTZER, H. Y.:Characterization of typical and atypical antipsychotic drugs based on in vivooccupancy of serotonin2 and dopamine2 receptors. J. Pharmacol. Exp. Ther.266: 1374–1384, 1993.

SUAUD-CHAGNY, M. F., PONEC, J. AND GONON, F.: Presynaptic autoinhibition ofthe electrically evoked dopamine release studied in the rat olfactory tubercleby in vivo electrochemistry. Neuroscience 45: 641–652, 1991.

SUGAMORI, K. S., DEMCHYSHYN, L. L., CHUNG, M. AND NIZNIK, H. B.: D-1A, D-1B,and D-1C dopamine receptors from Xenopus laevis. Proc. Natl. Acad. Sci.U.S.A. 91: 10536–10540, 1994.

SUNAHARA, R. K., GUAN, H.-C., O’DOWD, B. F., SEEMAN, P., LAURIER, L. G., NG, G.,GEORGE, S. R., TORCHIA, J., VAN TOL, H. H. M. AND NIZNIK, H. B.: Cloning of thegene for a human dopamine D5 receptor with higher affinity for dopaminethan D1. Nature (Lond.) 350: 614–619, 1991.

SVENSSON, K., JOHANSSON, A. M., MAGNUSSON, T. AND CARLSSON, A.: (1)-AJ76 and(1)-UH232: Central stimulants acting as preferential dopamine autorecep-tor antagonists. Naunyn-Schmiedeberg’s Arch. Pharmacol. 334: 234–245,1986.

SVENSSON, K., CARLSSON, A., HUFF, R. M., KLING-PETERSEN, T. AND WATERS, N.:Behavioral and neurochemical data suggest functional differences betweendopamine D2 and D3 receptors. Eur. J. Pharmacol. 263: 235–243, 1994.

TAN, S. AND SCHOEMAKER, H.: [3H]Flumazenil may label the native a5-containing omega (BZ) receptor subtype in the neonatal rat cerebral cortex.Br. J. Pharmacol. 108: 295P, 1993.

TIMMERMAN, W., DE VRIES, J. B. AND WESTERINK, B. H. C.: Effects of D-2 agonistson the release of dopamine: Localization of the mechanism of action. NaunynSchmiedebergs Arch. Pharmacol. 342: 650–654, 1990.

TRAN, V. T., CHANG, R. S. AND SNYDER, S. H.: Histamine H1 receptors identifiedin mammalian brain membranes with [3H]mepyramine. Proc. Natl. Acad.Sci. U.S.A. 75: 6290–6294, 1978.

VAN RIJN, C. M., WILLEMS-VAN BREE, E., VAN DER VELDEN, T. J. A. M. AND DE

MIRANDA, J. F. R.: Binding of the cage convulsant, [3H]TBOB, to sites linkedto the GABAA receptor complex. Eur. J. Pharmacol. 179: 419–425, 1990.

VAN TOL, H. H. M., BUNZOW, J. R., GUAN, H.-C., SUNAHARA, R. K., SEEMAN, P.,NIZNIK, H. B. AND CIVELLI, O.: Cloning of the gene for a human dopamine D4receptor with high affinity for the antipsychotic clozapine. Nature (Lond.)350: 610–614, 1991.

VARGAS, F., THURET, F. AND LLOYD, K. G.: Characterization of the nipecoticbinding to rat brain membranes. Gen. Pharmacol. 24: 321–327, 1993.

VASSE, M., PROTAIS, P., COSTENTIN, J. AND SCHWARTZ, J.-C.: Unexpected potenti-ation by discriminant benzamide derivatives of stereotyped behaviours elic-ited by dopamine agonists in mice. Naunyn Schmiedebergs Arch. Pharma-col. 329: 108–116, 1985.

WALTERS, J. R. AND ROTH, R. H.: Dopaminergic neurons: An in vivo system formeasuring drug interactions with presynaptic receptors. Naunyn Schmiede-bergs Arch. Pharmacol. 296: 5–14, 1976.

WATERS, N., LAGERKVIST, S., LOFBERG, L., PIERCEY, M. AND CARLSSON, A.: Thedopamine D3 receptor and autoreceptor preferring antagonists (1)-AJ76 and(1)-UH232; A microdialysis study. Eur. J. Pharmacol. 242: 151–163, 1993a.

WATERS, N., HANSSON, L., LOFBERG, L. AND CARLSSON, A.: Intracerebral infusionof (1)-AJ76 and (1)-UH232: Effects on dopamine release and metabolism invivo. Eur. J. Pharmacol. 251: 181–190, 1994.

WATERS, N., SVENSSON, K., HAADSMA-SVENSSON, S. R., SMITH, M. W. AND CARLS-SON, A.: The dopamine D3-receptor: A postsynaptic receptor inhibitory on ratlocomotor activity. J. Neural. Transm. 94: 11–19, 1993b.

WISZNIOWSKA-SZAFRANIEC, G. L., BANEK, K., REICHENBERG, K. AND VETULANI, J.:Facilitation by alpha-adrenolytics of apomorphine gnawing behaviour: De-pression of threshold apomorphine concentration in the striatum of the rat.Pharmacol. Biochem. Behav. 19: 19–22, 1983.

WONG, E. H. F., KNIGHT, A. R. AND WOODRUFF, G. N.: [3H]MK-801 labels a siteon the N-methyl-D-aspartate receptor channel complex in rat brain mem-branes. J. Neurochem. 50: 274–281, 1988.

YAGALOFF, K. A. AND HARTIG, P. R.: Solubilization and characterization of theserotonin 5-HT1c site from pig choroid plexus. Mol. Pharmacol. 29: 120–125,1986.

YAMAMURA, H. I. AND SNYDER, S. H.: Muscarinic cholinergic binding in rat brain.Proc. Natl. Acad. Sci. U.S.A. 71: 1725–1729, 1974.

YOUNG, A. B. AND SNYDER, S. H.: Strychnine binding associated with glycinereceptors of the central nervous system. Proc. Natl. Acad. Sci. U.S.A. 70:2832–2836, 1973.

YOUNG, A. B. AND SNYDER, S. H.: The glycine synaptic receptor: Evidence thatstrychnine binding is associated with the ionic conductance mechanism.Proc. Natl. Acad. Sci. U.S.A. 71: 4002–4005, 1974.

ZUKIN, S. R., YOUNG, A. B. AND SNYDER, S. H.: Gamma-aminobutyric acidbinding to receptor sites in the rat central nervous system. Proc. Natl. Acad.Sci. U.S.A. 71: 4802–4807, 1974.

Send reprint requests to: Dr. Hans Schoemaker, Synthelabo Recherche,CNS Research Department, 31 ave Paul Vaillant-Couturier, BP 110, 92225Bagneux, France.




ownloaded from


Neurochemical Characteristics of Amisulpride

Documents

cns research

pig choroid

differential

performance

tyrosine hydroxylase

histamine

naunyn schmiedebergs

adult male