RESUMEN
OBJECTIVE: To evaluate the efficacy and safety of pregabalin in the treatment of postherpetic neuralgia (PHN). METHODS: The authors conducted a multicenter, parallel-group, double-blind, placebo-controlled, 8-week, randomized clinical trial in PHN, defined as pain for 3 or more months following herpes zoster rash healing. Patients (n = 173) were randomized to treatment with pregabalin or placebo. Patients randomized to pregabalin received either 600 mg/day (creatinine clearance > 60 mL/min) or 300 mg/day (creatinine clearance 30 to 60 mL/min). The primary efficacy measure was the mean of the last seven daily pain ratings. Secondary endpoints included additional pain ratings, sleep interference, quality of life, mood, and patient and clinician ratings of global improvement. RESULTS: Pregabalin-treated patients had greater decreases in pain than patients treated with placebo (endpoint mean scores 3.60 vs 5.29, p = 0.0001). Pain was significantly reduced in the pregabalin-treated patients after the first full day of treatment and throughout the study, and significant improvement on the McGill Pain Questionnaire total, sensory, and affective pain scores was also found. The proportions of patients with >or=30% and >or=50% decreases in mean pain scores were greater in the pregabalin than in the placebo group (63% vs 25% and 50% vs 20%, p = 0.001). Sleep also improved in patients treated with pregabalin compared to placebo (p = 0.0001). Both patients and clinicians were more likely to report global improvement with pregabalin than placebo (p = 0.001). Given the maximal dosage studied, pregabalin had acceptable tolerability compared to placebo despite a greater incidence of side effects, which were generally mild to moderate in intensity. CONCLUSIONS: Treatment of PHN with pregabalin is safe, efficacious in relieving pain and sleep interference, and associated with greater global improvement than treatment with placebo.
Asunto(s)
Analgésicos no Narcóticos/uso terapéutico , Herpes Zóster/complicaciones , Neuralgia/tratamiento farmacológico , Ácido gamma-Aminobutírico/análogos & derivados , Ácido gamma-Aminobutírico/uso terapéutico , Adulto , Afecto , Anciano , Analgésicos no Narcóticos/efectos adversos , Mareo/inducido químicamente , Método Doble Ciego , Edema/inducido químicamente , Femenino , Humanos , Masculino , Persona de Mediana Edad , Neuralgia/etiología , Neuralgia/psicología , Neuralgia/virología , Dimensión del Dolor , Pregabalina , Calidad de Vida , Seguridad , Trastornos del Inicio y del Mantenimiento del Sueño/tratamiento farmacológico , Trastornos del Inicio y del Mantenimiento del Sueño/etiología , Fases del Sueño , Resultado del Tratamiento , Ácido gamma-Aminobutírico/efectos adversosRESUMEN
PD 158771 has been described in receptor binding and biochemical tests as a partial agonist at dopamine (DA) D2 and D3 receptors as well as an agonist at serotonin (5-HT)(1A) receptors. The present studies describe the profile of PD 158771 in rodent and primate behavioral tests. PD 158771 reduced spontaneous locomotor activity in mice (ED(50)=0.38 mg/kg, i.p.) and rats (ED(50) = 1.2 mg/kg, i.p. and 0.16 mg/kg, s.c.), and reduced amphetamine-stimulated locomotion in mice (ED(50) = 0.13 mg/kg, i.p.). At relatively higher doses up to 3 mg/kg, s.c. in rats, PD 158771 did not produce locomotor stimulation or induce stereotypy, indicating a lack of postsynaptic DA agonist activity. PD 158771 reduced apomorphine stimulated locomotion in rats at a dose 4.6-fold greater than those that reduced spontaneous locomotor activity, indicating weak postsynaptic DA antagonist actions; results consistent with a partial agonist profile. PD 158771 produced anxiolytic-like effects in the water-lick (Vogel) conflict test, effects possibly due to the 5-HT(1A) activity. However, PD 158771 was inactive in the water wheel behavioral despair model in rats, indicating lack of antidepressant properties. Similar to known antipsychotics, PD 158771 produced a potent and long-lasting inhibition of conditioned avoidance responding in squirrel monkeys. In contrast to standard antipsychotics, and similar to clozapine, PD 158771 did not cause catalepsy in rats at a dose 20-fold higher than the ED(50) dose for locomotor inhibition. PD 158771 also had a somewhat lower liability than haloperidol to produce extrapyramidal dysfunction in squirrel and cebus monkeys sensitized to the dystonic effects of haloperidol. The data indicate that PD 158771 is a DA partial agonist with weak intrinsic activity that selectively activates brain DA autoreceptors. PD 158771 produced behavioral effects consistent with potential antipsychotic and anxiolytic efficacy, and has an improved profile in the extrapyramidal side effect model when compared to certain currently available antipsychotic agents.
Asunto(s)
Antipsicóticos/farmacología , Conducta Animal/efectos de los fármacos , Agonistas de Dopamina/farmacología , Piperazinas/farmacología , Pirimidinas/farmacología , Receptores de Dopamina D2/agonistas , Receptores de Serotonina/efectos de los fármacos , Agonistas de Receptores de Serotonina/farmacología , Animales , Ansiolíticos/farmacología , Antidepresivos/farmacología , Reacción de Prevención/efectos de los fármacos , Enfermedades de los Ganglios Basales/inducido químicamente , Enfermedades de los Ganglios Basales/psicología , Catalepsia/inducido químicamente , Cebus , Conflicto Psicológico , Masculino , Ratones , Actividad Motora/efectos de los fármacos , Ratas , Ratas Endogámicas WKY , Ratas Sprague-Dawley , Ratas Wistar , Receptores de Dopamina D3 , Receptores de Serotonina 5-HT1 , Saimiri , Agonistas de Receptores de Serotonina/metabolismoRESUMEN
As part of a program to develop dopamine D4 antagonists for the treatment of schizophrenia, we discovered a series of 6- and 7-(phenylpiperazinyl)- and -(phenylpiperidinyl)methylbenzoxazinones through mass screening of our compound library. A structure-activity relationship SAR study was carried out involving substituents on the phenyl ring, and several selective D4 antagonists were identified. The 7-substituted benzoxazinones showed more activity in neurochemical and behavioral tests than the 6-substituted series. One of the most potent and selective compounds (26) was found to have potent activity in animal tests predictive of antipsychotic activity in humans after oral administration. This paper describes the SAR of the benzoxazinone series and the preclinical characterization of 26.
Asunto(s)
Antipsicóticos/farmacología , Antagonistas de Dopamina/farmacología , Antagonistas de los Receptores de Dopamina D2 , Oxazinas/farmacología , Ácido 3,4-Dihidroxifenilacético/metabolismo , Animales , Antipsicóticos/química , Células CHO , Cuerpo Estriado/efectos de los fármacos , Cuerpo Estriado/metabolismo , Cricetinae , Dopamina/biosíntesis , Dopamina/metabolismo , Antagonistas de Dopamina/química , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Espectroscopía de Resonancia Magnética , Oxazinas/química , Ratas , Receptores de Dopamina D4RESUMEN
152255 (E-1,1'-(2-butene-1,4-diyl)bis[2-[4-[3-(1-piperidinyl)propoxy]-phe nyl]-1H-benzimidazole]) exhibited high affinity (Ki = 12.7 nM) for human dopamine (DA) D3 receptors expressed in CHO K1 cells but not for DA D2L receptors (Ki = 565 nM), DA D42 or DA D1 receptors (Ki > 3 microM) and a number of other neurotransmitter receptors. Affinity for human muscarinic receptors was seen in vitro but no functional muscarinic agonist and/or antagonist action was observed in vivo. Antagonist activity at DA D3 receptors was demonstrated by blockade of quinpirole-stimulated [3H]-thymidine uptake in D3 transfected cells, an effect that was 28-fold more potent than in D2-transfected cells. Unlike classical DA D2 antagonists, PD 152255 did not increase rat brain DA synthesis and it increased locomotion in habituated rats. However, like antipsychotics, PD 152255 reduced locomotor activity in mice and reduced spontaneous and amphetamine-stimulated locomotion in nonhabituated rats. These results demonstrate that PD 152255 is a DA D3 antagonist that may have antipsychotic activity.
Asunto(s)
Antipsicóticos/farmacología , Bencimidazoles/farmacología , Antagonistas de Dopamina/farmacología , Antagonistas de los Receptores de Dopamina D2 , Piperidinas/farmacología , Animales , Monoaminas Biogénicas/biosíntesis , Química Encefálica/efectos de los fármacos , Células CHO , Antagonistas Colinérgicos/farmacología , Cricetinae , Relación Dosis-Respuesta a Droga , Masculino , Ratones , Actividad Motora/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Receptores de Dopamina D3 , Transducción de Señal/efectos de los fármacos , Timidina/metabolismoRESUMEN
PD 108635 (1) was identified as a potent dopamine D4 ligand and we wanted to replace the benzylic alcohol with a metabolically more stable moiety. Investigations led to the discovery of a series of isoindolinones having D4 affinity.
Asunto(s)
Indoles/química , Indoles/farmacología , Receptores de Dopamina D2/efectos de los fármacos , Animales , Actividad Motora/efectos de los fármacos , Ratas , Receptores de Dopamina D4 , Receptores de Serotonina/metabolismo , Estereoisomerismo , Relación Estructura-Actividad , Difracción de Rayos XRESUMEN
PURPOSE: To study the pharmacokinetics (PK) and pharmacodynamics (PD) of an investigational antipsychotic agent, CI-1007, in rats and monkeys. METHODS: CI-1007 and a pharmacologically active metabolite, PD 147693 (M1), were evaluated in animal antipsychotic tests (inhibition of dopamine neuron firing and spontaneous locomotor activity in rats, and inhibition of continuous avoidance in monkeys). Plasma concentrations of CI-1007 and M1 were determined using validated HPLC assays. Log-linear and link models were used for PK/PD analysis. RESULTS: CI-1007 and M1 have shown similar effects on dopamine neuron firing (2.5 mg/kg i.p.), and produced dose-related effects on spontaneous locomotor activity in rats (0.3-30 mg/kg p.o.) and on continuous avoidance in monkeys (0.6-1.2 mg/kg p.o.). After pharmacologically active CI-1007 doses, mean plasma CI-1007 Cmax increased from 19 to 200 ng/ml in Sprague-Dawley rats at doses of 3-30 mg/ kg, and from 8.1 to 34 ng/ml in squirrel monkeys at doses of 0.6-1.2 mg/kg, but corresponding plasma M1 Cmax values were near or below the limit of quantitation (5 ng/ml). CI-1007 EC50 was 31.1 ng/ml in rats, calculated from a long-linear regression. In monkeys, CI-1007 ECe50, gamma, and Keo at 0.6 and 1.2 mg/kg were 4.8 and 4.5 ng/ml, 1.9 and 2.0, and 0.47 and 0.48 hr-1, respectively, calculated by the link model. CONCLUSIONS: CI-1007 has shown dose-related pharmacokinetics and pharmacodynamics in rats and monkeys. Although M1 produces antipsychotic-like effects similar to CI-1007, the contribution of M1 to the activity of the parent drug may not be significant in rats and monkeys as based on plasma levels. CI-1007 plasma concentration correlates log-linearly with inhibition effect from the rat locomotor study. The counter-clockwise hysteresis relationship of CI-1007 plasma concentration and inhibition effect from the monkey avoidance test was described by a link model, and the resulting Ce (concentration in effect compartment) versus effect profile exhibits a sigmoidal curve.
Asunto(s)
1-Metil-4-fenil-1,2,3,6-Tetrahidropiridina/análogos & derivados , Antipsicóticos/farmacocinética , 1-Metil-4-fenil-1,2,3,6-Tetrahidropiridina/sangre , 1-Metil-4-fenil-1,2,3,6-Tetrahidropiridina/farmacocinética , 1-Metil-4-fenil-1,2,3,6-Tetrahidropiridina/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Antipsicóticos/sangre , Antipsicóticos/farmacología , Reacción de Prevención/efectos de los fármacos , Dopamina/fisiología , Masculino , Actividad Motora/efectos de los fármacos , Inhibición Neural/efectos de los fármacos , Neuronas/fisiología , Ratas , Ratas Sprague-Dawley , Ratas Wistar , SaimiriRESUMEN
The pharmacology of PD 144418 (1-propyl-5-(3-p-tolyl-isoxazol-5-yl)-1,2,3,6-tetrahydropyridine) was characterized using neurochemical, biochemical and behavioral techniques. For sigma (sigma 1 and sigma 2 respectively) sites, PD 144418 affinities were determined using whole guinea pig brain membranes with [3H](+)-pentazocine and neuroblastoma x glioma cell membranes using [3H]1,3,di-O-tolylguanidine (DTG) in the presence of 200 nM (+)-pentazocine. PD 144418 exhibited an affinity for sigma 1 of 0.08 nM (Ki) versus a K1 of 1377 nM for sigma 2 site. Additional receptor binding studies indicated that PD 144418 lacked affinity for dopaminergic, adrenergic, muscarinic and a variety of other receptors. In vitro studies indicated that PD 144418 reversed the N-methyl-D-aspartate (NMDA)-induced increase in cyclic GMP (cGMP) in rat cerebellar slices without affecting the basal levels, suggesting that sigma 1 sites may be important in the regulation of glutamine-induced actions. PD 144418 potentiated the decrease in 5-hydroxytryptophan caused by haloperidol in the mesolimbic region, but by itself had no effect in 5-hydroxytrypamine (5-HT) and dopamine (DA) synthesis. Behaviorally, similar to other sigma ligands, PD 144418 antagonized mescaline-induced scratching at doses that did not alter spontaneous motor activity. This action is suggestive of potential antipsychotic property. It exhibited no anxiolytic and antidepressant properties in the models used. These results show that PD 144418 is a very selective sigma 1 agent, devoid of any significant affinity for other receptors and that sigma 1 site may modulate actions in the CNS.
Asunto(s)
Conducta Animal/efectos de los fármacos , Isoxazoles/farmacología , Piridinas/farmacología , Receptores sigma/efectos de los fármacos , Animales , Encéfalo/metabolismo , Calcio/metabolismo , Células Cultivadas , GMP Cíclico/metabolismo , Cobayas , Haloperidol/farmacología , Isoxazoles/metabolismo , Masculino , Ratones , Actividad Motora/efectos de los fármacos , N-Metilaspartato/farmacología , Piridinas/metabolismo , Ratas , Ratas Sprague-Dawley , Ratas Wistar , Receptores sigma/metabolismoRESUMEN
A series of arylpiperazines and tetrahydropyridines joined to indoles by semirigid cycloalkyl spacers were prepared. Target compounds were studied for their ability to bind to the DA D2 receptor in vitro and to inhibit dopamine synthesis and spontaneous locomotor activity in rats. Effects of tether length and relative stereochemistry were assessed for a series of 2-pyridylpiperazines. The cyclohexylethyl spacer was found to be the most active in the series. Further studies explored effects of changes in the arylpiperazine and indole portions of the molecule. From these studies trans-2-[[4-(1H-3-indolyl)cyclohexyl]ethyl]-4- (2-pyridinyl)piperazine (30a) was selected for further evaluation. It was characterized as a partial agonist of DA D2 receptors in vitro and caused decreases in dopamine synthesis and release as well as dopamine neuronal firing. Compound 30a was shown to be devoid of behavioral effects associated with postsynaptic DA D2 receptor activation. Furthermore, compound 30a was shown both to decrease DA synthesis and to inhibit Sidman avoidance responding in squirrel monkeys. These findings suggest that DA D2 partial agonists with the appropriate level of intrinsic activity can act to decrease dopamine synthesis and release and may have potential utility as antipsychotic agents.
Asunto(s)
Autorreceptores/agonistas , Agonistas de Dopamina/síntesis química , Agonistas de Dopamina/farmacología , Indoles/síntesis química , Indoles/farmacología , Receptores de Dopamina D2/agonistas , Animales , Autorreceptores/metabolismo , Conducta Animal/efectos de los fármacos , Células CHO , Cricetinae , Ciclohexanos/síntesis química , Ciclohexanos/metabolismo , Ciclohexanos/farmacología , Agonistas de Dopamina/metabolismo , Humanos , Indoles/metabolismo , Cinética , Masculino , Ratones , Piperazinas/síntesis química , Piperazinas/metabolismo , Piperazinas/farmacología , Piridinas/síntesis química , Piridinas/metabolismo , Piridinas/farmacología , Ratas , Ratas Sprague-Dawley , Receptores de Dopamina D2/metabolismo , SaimiriRESUMEN
CI-1007 has been described in receptor binding and biochemical tests as a dopamine (DA) partial agonist that exhibits DA autoreceptor agonist effects. The present studies describe the profile of CI-1007 in electrophysiological and behavioral tests. CI-1007 inhibited the firing of substantia nigra DA neurons with intrinsic DA agonist activity that was less than that of the full agonists apomorphine and talipexole but greater than that of the weak partial agonist SDZ 208-912. CI-1007 was more potent after intracerebroventricular versus intraperitoneal injection in inhibiting spontaneous locomotor activity in mice, indicating a central site of action. In rats, CI-1007 inhibited locomotor activity after i.v. and p.o. injection, but did not produce locomotor stimulation or induce stereotypy, indicating a lack of postsynaptic DA agonist activity. The relative potencies of CI-1007 for inhibiting apomorphine-stimulated behaviors versus spontaneous locomotor activity in rodents indicated weak postsynaptic DA antagonist actions, consistent with a partial agonist profile. Similar to known antipsychotics, CI-1007 potently inhibited Sidman avoidance responding in squirrel monkeys, but, in contrast to most available antipsychotics, CI-1007 caused only mild extrapyramidal dysfunction in squirrel and cebus monkeys sensitized to the dystonic effects of haloperidol. These data indicate that CI-1007 is a DA partial agonist of moderate intrinsic activity that activates brain DA autoreceptors, produces behavioral effects predictive of antipsychotic efficacy and has a low liability for induction of extrapyramidal side effects.
Asunto(s)
1-Metil-4-fenil-1,2,3,6-Tetrahidropiridina/análogos & derivados , Antipsicóticos/farmacología , Agonistas de Dopamina/farmacología , 1-Metil-4-fenil-1,2,3,6-Tetrahidropiridina/farmacología , Animales , Apomorfina/farmacología , Autorreceptores/efectos de los fármacos , Reacción de Prevención/efectos de los fármacos , Enfermedades de los Ganglios Basales/inducido químicamente , Masculino , Ratones , Actividad Motora/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , SaimiriRESUMEN
The pyridine analogs of 5-hydroxy-2-(di-n-propylamino)tetralin (5-OH-DPAT), 4-6, were synthesized, and their biological activity was compared to that of 5-OH-DPAT. Compounds 4 and 6 exhibited activity similar to 5-OH-DPAT in dopamine (DA) D2 and D3 receptor binding and in autoreceptor activation as measured by their ability to reverse the gamma-butyrolactone-induced increase in rat DA synthesis. Behaviorally, 4 and 6 decreased locomotor activity (LMA) in rats (sc) at low doses but did not increase LMA to the same extent as 5-OH-DPAT at higher doses, indicating that 4 and 6 may be more selective for the DA autoreceptor. While 4 was less active orally in rats, 6 appeared to retain most of its behavioral potency. Analog 5 showed little activity in vivo or in vitro.
Asunto(s)
8-Hidroxi-2-(di-n-propilamino)tetralin/análogos & derivados , Dopaminérgicos/farmacología , Piridinas/farmacología , 8-Hidroxi-2-(di-n-propilamino)tetralin/química , 8-Hidroxi-2-(di-n-propilamino)tetralin/farmacología , Animales , Células CHO , Cricetinae , Dopaminérgicos/química , Masculino , Ratones , Actividad Motora/efectos de los fármacos , Unión Proteica , Piridinas/química , Ratas , Receptores Dopaminérgicos/metabolismo , Receptores de Dopamina D2/metabolismo , Relación Estructura-ActividadRESUMEN
In in vitro studies, SR 48692, a nonpeptide neurotensin receptor antagonist, inhibited the binding of [3H] or [125I]neurotensin to membrane preparations from 10-day-old mouse brains and from HT-29 cells with Ki values of 3.9 and 8.6 nM, respectively. SR 48692 also antagonized the neurotensin-induced mobilization of intracellular calcium in HT-29 cells, in agreement with previous findings. In rat cerebellar slices SR 48692 blocked the increase in cyclic GMP levels evoked by neurotensin in a dose-dependent manner. In vivo, SR 48692 antagonized the increase in rat brain mesolimbic dopamine turnover induced by the systemically active neurotensin peptide, EI [(N-Me)Arg-Lys-Pro-Trp-tert-Leu-Leu]. No effects on dopamine turnover of either EI or SR 48692 were observed in the striatum. SR 48692 did not antagonize the EI-induced decreases in mouse body temperature and spontaneous locomotor activity (LMA) or the decreases in LMA induced by ICV-administered neurotensin. Although other explanations are possible, these findings support the hypothesis that a subtype of the NT receptor may mediate the locomotor and hypothermic actions of this peptide and that it is different from the NT receptor that is involved in dopamine turnover.
Asunto(s)
Neurotensina/agonistas , Pirazoles/farmacología , Quinolinas/farmacología , Animales , Química Encefálica , Calcio/metabolismo , Carcinoma/tratamiento farmacológico , Carcinoma/patología , Células Cultivadas , Neoplasias del Colon/tratamiento farmacológico , Neoplasias del Colon/patología , GMP Cíclico/farmacología , Dopamina/metabolismo , Humanos , Hipotermia/tratamiento farmacológico , Locomoción/efectos de los fármacos , Masculino , Membranas/metabolismo , Ratones , Neurotensina/antagonistas & inhibidores , Neurotensina/metabolismo , Oligopéptidos/farmacología , Psicotrópicos/farmacología , Ensayo de Unión Radioligante , RatasRESUMEN
Neurotensin (NT), is a linear tetradecapeptide (pGlu1-Leu2-Tyr3-Glu4-Asn5- Lys6-Pro7-Arg8-Arg9-Pro10-Tyr11-Ile12-Leu13) that has been found in the central nervous system and peripheral tissues and appears to have a variety of physiological properties. A C-terminal hexapeptide analogue [N alpha Me-Arg-Lys-Pro-Trp-Tle-Leu, (1) Tle = tert-leucine] has recently been reported to have high affinity for the NT receptor and appears to possess central activity after systemic administration. In an effort to probe the structure-activity and conformational properties of the dipeptide, Pro-Trp for binding and functional activity, these residues have been substituted with several natural and unnatural amino acids. Some of these analogues have binding affinities similar to compound 1, while in other cases, such as D-amino acid substitutions, the peptides had negligible binding affinity. In general, the Pro10 position seems more tolerant of substitution by amino acids that favor a reverse turn, rather than those that favor an extended conformation. The Trp11 position accepted extra steric bulk more readily than conformational constraints.
Asunto(s)
Neurotensina/análogos & derivados , Neurotensina/química , Oligopéptidos/síntesis química , Conformación Proteica , Animales , Animales Recién Nacidos , Encéfalo/metabolismo , Membrana Celular/metabolismo , Indicadores y Reactivos , Ratones , Neurotensina/metabolismo , Oligopéptidos/química , Receptores de Neurotensina/metabolismo , Relación Estructura-ActividadRESUMEN
(+/-)-PD 128483, ((+/-)-4,5,5a,6,7,8-hexahydro-6-methylthiazolo[4,5-f]-quinolin+ ++-2-amine, maleate (1:1)), is a racemic compound that is a p.o. active dopamine (DA) partial agonist that has DA autoreceptor agonist effects and displays antipsychoticlike activity in preclinical tests. In in vitro receptor binding assays, (+/-)-PD 128483 and its enantiomers bound selectively to DA D-2 receptors vs. DA D-1 receptors and showed no affinity for adrenergic alpha-1 or serotonin1A receptors, but had affinity for adrenergic alpha-2 receptors. In tests of DA agonist effects, including reversal of the tau-butyrolactone-stimulated increase in brain dopa synthesis in striatum and inhibition of DA neuronal firing, the rank order of efficacy was (+)-PD 128483 > (+/-)-PD 128483 > (-)-PD 128483. (+/-)-PD 128483 and (+)-PD 128483 inhibited, whereas (-)-PD 128483 increased, brain DA synthesis in normal rats. (+/-)-PD 128483 and (-)-PD 128483 inhibited spontaneous locomotion in rats and did not produce locomotor stimulation or stereotypies. In contrast, (+)-PD 128483 inhibited locomotor activity at low doses, but at relatively high doses increased locomotion and induced stereotypy in rats. (-)-PD 128483 consistently inhibited Sidman avoidance responding in squirrel monkeys. (+/-)-PD 128483 inhibited Sidman avoidance responding in one group of monkeys, but had minimal effects in another group. (+)-PD 128483 did not inhibit avoidance responding. In squirrel or cebus monkeys sensitized to the acute dystonic effects of haloperidol, only (-)-PD 128483 induced extrapyramidal dysfunction. These results indicate that (+/-)-PD 128483 is a DA partial agonist which produces DA autoreceptor agonist effects and has a preclinical behavioral profile suggestive of antipsychotic activity.