Effects of amperozide in schizophrenia. An open study of a potent 5-HT2 receptor antagonist

Human accelerated genome regions with value in medical genetics and drug discovery

Accumulated evolutionary knowledge not only benefits our understanding of the pathogenesis of diseases, but also help in the search for new drug targets. This is further supported by the recent finding that human accelerated regions (HARs) identified by comparative genomic studies are linked to human neural system evolution and are also associated with neurological disorders. Here, we analyze the associations between HARs and diseases and drugs. We found that 32.42% of approved drugs target at least one HAR gene, which is higher than the ratio of in-research drugs. More interestingly, HAR gene-targeted drugs are most significantly enriched with agents treating neurological disorders. Thus, HAR genes have important implications in medical genetics and drug discovery.

A systematic microdialysis study of dopamine transmission in the accumbens shell/core and prefrontal cortex after acute antipsychotics

RATIONALE

The only systematic in vivo studies comparing antipsychotic (AP) effects on nucleus accumbens (NAc) shell and core dopamine (DA) transmission are voltammetric studies performed in pargyline-pretreated, halothane-anaesthetized rats. Studies in freely moving rats not pretreated with pargyline are not available. This study was intended to fill this gap by the use of in vivo microdialysis in freely moving rats.

METHODS

Male Sprague-Dawley rats were implanted with microdialysis probes in the NAc shell and core and medial prefrontal cortex (PFCX). The next day, rats were administered intravenously with two or three doses of APs, and dialysate DA was monitored in 10-min samples. Some rats were pretreated with pargyline (75 mg/kg i.p.) and after 1 h were given clozapine or risperidone.

RESULTS

Clozapine, risperidone, quetiapine, raclopride, sulpiride and amisulpride increased DA preferentially in the NAc shell. Such preferential effect on shell DA was not observed after haloperidol, chlorpromazine and olanzapine. In contrast to voltammetric studies, a preferential effect on NAc core DA was not observed after any dose of AP. Pargyline pretreatment did not reduce but actually amplified the preferential effect of clozapine and risperidone on NAc shell DA.

CONCLUSIONS

Apart from raclopride and olanzapine, the APs with lower extrapyramidal effects could be distinguished from typical APs on the basis of their ability to preferentially stimulate DA transmission in the NAc shell. There was no relationship between stimulation of PFCX DA and atypical APs profile. The differences between this study and voltammetry studies were not attributable to pargyline pretreatment.

Novel cell-based hepatitis C virus infection assay for quantitative high-throughput screening of anti-hepatitis C virus compounds

Therapy for hepatitis C virus (HCV) infection has advanced with the recent approval of direct-acting antivirals in combination with peginterferon and ribavirin. New antivirals with novel targets are still needed to further improve the treatment of hepatitis C. Previously reported screening methods for HCV inhibitors either are limited to a virus-specific function or apply a screening method at a single dose, which usually leads to high false-positive or -negative rates. We developed a quantitative high-throughput screening (qHTS) assay platform with a cell-based HCV infection system. This highly sensitive assay can be miniaturized to a 1,536-well format for screening of large chemical libraries. All candidates are screened over a 7-concentration dose range to give EC50s (compound concentrations at 50% efficacy) and dose-response curves. Using this assay format, we screened a library of pharmacologically active compounds (LOPAC). Based on the profile of dose-dependent curves of HCV inhibition and cytotoxicity, 22 compounds with adequate curves and EC50s of <10 μM were selected for validation. In two additional independent assays, 17 of them demonstrated specific inhibition of HCV infection. Ten potential candidates with efficacies of >70% and CC50s (compound concentrations at 50% cytotoxicity) of <30 μM from these validated hits were characterized for their target stages in the HCV replication cycle. In this screen, we identified both known and novel hits with diverse structural and functional features targeting various stages of the HCV replication cycle. The pilot screen demonstrates that this assay system is highly robust and effective in identifying novel HCV inhibitors and that it can be readily applied to large-scale screening of small-molecule libraries.

Benzodiazepine tapering: a prospective study

BACKGROUND

Benzodiazepines (BZD) are the most widely used sedative-hypnotics, and evidence is rapidly accumulating suggesting potential BZD dependence, association of chronic use with adverse effects and a definite abstinence syndrome produced by withdrawal.

AIMS

The present investigation followed prospectively long-term BZD users over 1 year following graded BZD withdrawal in terms of clinical and withdrawal symptoms.

METHODS

Clinical symptoms were measured by the Comprehensive Psychopathological Rating Scale (CPRS) and by the Newcastle Anxiety and Depression Diagnostic Index (NADDI) in a sample of BZD users over a 50-week period following graded BZD withdrawal.

RESULTS

The results showed that the frequency and severity of clinical symptomatology measured by both scales significantly decreased over time. A detailed analysis of possible patterns of symptoms on both scales revealed four patterns: 1) a gradual decrease over the 50-week time period; 2) an increase in the severity of symptoms at the onset of tapering and a decrease in severity post-tapering; 3) an increase in the severity of symptoms 4 weeks after the cessation of BZD tapering; and 4) no change over the 50-week time period. Rate of BZD withdrawal was associated with CPRS ratings of global illness at admission and at end of treatment, but was not associated with duration or dosage of BZDs, type of BZD, prescriptive and/or non-prescriptive drug use prior to admission, marital status, sex or age.

CONCLUSIONS

The results of the present study provide a detailed picture of the pattern of symptoms, their time course and multidimensional determinants of the BZD withdrawal symptoms.

NMDA receptor antagonist effects, cortical glutamatergic function, and schizophrenia: toward a paradigm shift in medication development

There is an urgent need to improve the pharmacotherapy of schizophrenia despite the introduction of important new medications. New treatment insights may come from appreciating the therapeutic implications of model psychoses. In particular, basic and clinical studies have employed the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, ketamine, as a probe of NMDA receptor contributions to cognition and behavior. These studies illustrate a translational neuroscience approach for probing mechanistic hypotheses related to the neurobiology and treatment of schizophrenia and other disorders. Two particular pathophysiologic themes associated with schizophrenia, the disturbance of cortical connectivity and the disinhibition of glutamatergic activity may be modeled by the administration of NMDA receptor antagonists. The purpose of this review is to consider the possibility that agents that attenuate these two components of NMDA receptor antagonist response may play complementary roles in the treatment of schizophrenia.

Insights into the structure and function of 5-HT(2) family serotonin receptors reveal novel strategies for therapeutic target development

5-HT(2) family serotonin receptors, principal sites of action of serotonin in the brain, represent major molecular targets for drugs used in treating a variety of diseases including schizophrenia, depression, anxiety, eating disorders, obsessive-compulsive disorder, chronic pain conditions and obesity. The 5-HT(2) family of receptors has three members: 5-HT(2A), 5-HT(2B) and 5-HT(2C). Therefore, it is likely that subtype-selective compounds will be needed to avoid serious side effects and to enhance therapeutic indices. Unfortunately, recent insights into the structure and function of 5-HT(2A) receptors have revealed that structurally-diverse agonists and antagonists have distinct modes of interacting with 5-HT(2A) receptors, complicating efforts at structure-based drug-design. These distinct binding modes would not have been predicted based on conventional structure-activity relationships or static docking models. Fortunately, these complicated binding modes can be predicted and simulated using molecular dynamics, allowing for the possibility of structure-based drug design. Thus, provided appropriately sophisticated drug design strategies are employed, it is likely that uniquely valuable medications will result which could have great potential for treating a variety of mental and physical illnesses.

The effects of amperozide on cocaine-induced social withdrawal in rats

Cocaine decreases social interactions in both humans and animals, but it is not known whether the drugged animal withdraws from an undrugged conspecific, the undrugged conspecific avoids the drugged animal, or a combination of these two factors occurs. In the first experiment, the source of cocaine-induced social withdrawal was determined using a tether paradigm, in which the movement of one of the rats was restricted to one half of the observation chamber, such that the freely moving rat had the option of escaping social interactions. There were decreases in social interactions in the condition in which both rats were freely moving, and in the condition in which the undrugged rat was tethered, but not when the drugged rat was tethered and could not escape social contact. A second experiment was conducted to test the efficacy of the potent serotonin receptor antagonist, amperozide, in attenuating cocaine-induced social withdrawal using the condition in which the drugged rat was freely moving. Either amperozide (1.0, 3.0, and 5.0 mg/kg) or saline vehicle was injected into rats 1 h before receiving a 30.0 mg/kg cocaine dose. Cocaine decreased social interactions. Amperozide restored social interactions to near control levels and elevated social interactions in the animals treated with saline vehicle.

The cardiovascular effects of amperozide: interactions with cocaine

Amperozide is a 5-HT2A receptor antagonist that significantly reduces the acquisition and expression, by rats, of a cocaine conditioned place preference. In order to rule out the possibility that amperozide affects a cocaine conditioned place preference due to effects on blood pressure or heart rate, the cardiovascular effects of amperozide were investigated. Alternating cumulative doses of amperozide (0.5, 1.0, 1.5 and 2.5 mg kg(-1)) or saline and phenylephrine (8 microg kg(-1)) were administered through the femoral vein of awake freely-moving Sprague-Dawley rats and blood pressure and heart rate were recorded from the femoral artery. A single dose of cocaine (5.0 mg kg(-1)) was administered after all the amperozide or saline doses were given. Amperozide (0.5, 1.0, 1.5 and 2.5 mg kg(-1)) did not have any significant effect on blood pressure compared to the saline control treatment to the same animals. However, 0.5 mg kg(-1) amperozide significantly decreased heart rate at 5 and 10 min. after administration. but higher doses did not further depress heart rate. Amperozide did not affect the increased blood pressure and decreased heart rate caused by phenylephrine. an alpha1-adrenoceptor agonist. In addition, amperozide did not affect the cardiovascular response to an intravenous dose of 5.0 mg kg(-1) cocaine. These results suggest that amperozide does not cause direct cardiovascular effects. The mechanism by which the lowest dose of amperozide caused a decrease in heart rate is unknown. Amperozide affects neither alpha-adrenoceptor mediated vasoconstriction nor the increased sympathetic activity caused by the peripheral and central effects of cocaine. The significance of these results, in terms of locomotor activity and the cocaine conditioned place preference paradigm, is discussed.

Serotonin 5-HT2C agonists selectively inhibit morphine-induced dopamine efflux in the nucleus accumbens

In vivo microdialysis was used to compare the effects of serotonergic drugs on morphine- and cocaine-induced increases in extracellular dopamine (DA) concentrations in the rat nucleus accumbens (NAc). Systemic administration of the 5-HT2A/2C agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (2.5 mg/kg, s.c. ) prevented the increase in extracellular DA in the NAc produced by morphine (5 mg/kg, i.p.). In contrast, this dose of DOI had no effect on the ability of cocaine (10 mg/kg, i.p.) to increase extracellular DA concentrations in the NAc. A 5-HT2C selective agonist, 6-chloro-2-[1-piperazinyl]-pyrazine (MK-212, 5 mg/kg, s.c.) also inhibited morphine-induced increases in extracellular DA concentrations in the NAc. Pretreatment of rats with the selective 5-HT2A antagonist, amperozide, had no effect on morphine-induced elevation of NAc DA concentrations. In order to determine if inhibition of the firing of 5-HT neurons contributes to the serotonin agonist-mediated inhibition of morphine-induced accumbens DA release, rats were pretreated with the 5-HT1A agonist, 8-OHDPAT. At a dose of 100 microg/kg (sc), 8-OHDPAT did not interfere with morphine's ability to increase DA concentrations in the NAc. These results suggest that the activation of 5-HT2C receptors selectively inhibits morphine-induced DA release in the NAc in a manner which is independent of the inhibition of 5-HT neurons.

Risperidone inhibits 5-hydroxytryptaminergic neuronal activity in the dorsal raphe nucleus by local release of 5-hydroxytryptamine

1. The effects of risperidone on brain 5-hydroxytryptamine (5-HT) neuronal functions were investigated and compared with other antipsychotic drugs and selective receptor antagonists by use of single cell recording and microdialysis in the dorsal raphe nucleus (DRN). 2. Administration of risperidone (25-400 micrograms kg-1, i.v.) dose-dependently decreased 5-HT cell firing in the DRN, similar to the antipsychotic drug clozapine (0.25-4.0 mg kg-1, i.v.), the putative antipsychotic drug amperozide (0.5-8.0 mg kg-1, i.v.) and the selective alpha 1-adrenoceptor antagonist prazosin (50-400 micrograms kg-1, i.v.). 3. The selective alpha 2-adrenoceptor antagonist idazoxan (10-80 micrograms kg-1, i.v.), in contrast, increased the firing rate of 5-HT neurones in the DRN, whereas the D2 and 5-HT2A receptor antagonists raclopride (25-200 micrograms kg-1, i.v.) and MDL 100,907 (50-400 micrograms kg-1, i.v.), respectively, were without effect. Thus, the alpha 1-adrenoceptor antagonistic action of the antipsychotic drugs might, at least partly, cause the decrease in DRN 5-HT cell firing. 4. Pretreatment with the selective 5-HT1A receptor antagonist WAY 100,635 (5.0 micrograms kg-1, i.v.), a drug previously shown to antagonize effectively the inhibition of 5-HT cells induced by risperidone, failed to prevent the prazosin-induced decrease in 5-HT cell firing. This finding argues against the notion that alpha 1-adrenoceptor antagonism is the sole mechanism underlying the inhibitory effect of risperidone on the DRN cells. 5. The inhibitory effect of risperidone on 5-HT cell firing in the DRN was significantly attenuated in rats pretreated with the 5-HT depletor PCPA (p-chlorophenylalanine; 300 mg kg-1, i.p., day-1 for 3 consecutive days) in comparison with drug naive animals. 6. Administration of risperidone (2.0 mg kg-1, s.c.) significantly enhanced 5-HT output in the DRN. 7. Consequently, the reduction in 5-HT cell firing by risperidone appears to be related to increased availability of 5-HT in the somatodendritic region of the neurones leading to an enhanced 5-HT1A autoreceptor activation and, in turn, to inhibition of firing, and is probably only to a minor extent caused by its alpha 1-adrenoceptor antagonistic action.

Further investigations of the interactions of antipsychotics with the (-)2,5-dimethoxy-4-methylamphetamine (DOM) discriminative stimulus

Stimulus control induced by (-)-2,5-dimethoxy-4-methylamphetamine (DOM) is believed to be mediated by agonism at 5-HT2A receptors. We hypothesized that blockade of (-) DOM-induced stimulus control may thus prove useful in the pre-clinical characterization of novel antipsychotic agents by providing an in vivo index of antagonism at that receptor. A previous study (Fiorella et al., 1995a) observed no antagonism by typical agents such as haloperidol and thioridazine, partial antagonism by the atypical agent, clozapine, and full antagonism by risperidone, a second atypical antipsychotic. The present investigation extends these observations to include seven additional drugs: SCH 23390, sulpiride, amperozide, melperone, octoclothepin, tiospirone and ritanserin. Of the drugs tested in rats in which (-) DOM-induced stimulus control had reliably been established, only tiospirone and ritanserin produced complete antagonism of the (-) DOM stimulus. Intermediate levels of antagonism were observed following treatment with amperozide, melperone, and octoclothepin. Finally, SCH 23390 and sulpiride yielded no evidence of antagonistic activity in (-) DOM-trained animals. Because clozapine and risperidone are both classified as atypical antipsychotics yet yield different degrees of antagonism of (-) DOM-induced stimulus control, we tested the substitution of risperidone for clozapine in rats trained with clozapine as a discriminative stimulus. No significant substitution was observed. In conclusion it appears that complete or partial antagonism of the (-) DOM stimulus serves as an effective pre-clinical means of identifying antipsychotics with significant 5-HT2A antagonist properties. However, the failure of risperidone to substitute for clozapine in pigeons (Hoenicke et al., 1992) and in rats (present study) suggests that despite their shared 5-HT2A antagonist properties, clozapine and risperidone differ with respect to their stimulus effects.

Interaction of the novel antipsychotic drug amperozide and its metabolite FG5620 with central nervous system receptors and monoamine uptake sites: relation to behavioral and clinical effects

Behavioral, biochemical, and electrophysiological studies suggest that amperozide affects mesolimbic and mesocortical dopamine neurotransmission. The receptor binding profile of amperozide is discussed and related to behavioral and clinical, i.e., antipsychotic, effects of the drug. As previously reported, amperozide displayed high affinity for serotonin 5-HT2A receptors (Ki = 16 nmol/L), and moderate affinity for striatal dopamine D2 (Ki = 540 nmol/L) and cortical alpha 1-adrenergic receptors (Ki = 172 nmol/L). In the present study amperozide displayed low affinity for several serotonin receptor subtypes as well as for the dopamine D4 receptor transfected in COS7 cells (Ki D4.2 = 769 nmol/L and Ki D4.4 = 384 nmol/L). Amperozide was very weak or did not interact with several other receptor species including adrenergic, histaminergic, muscarinic, benzodiazepine, gamma-aminobutyric acid, amino acid, opiate, and Ca channels; however, amperozide was found to compete for [3H]paroxetine binding for the serotonin transporter in the nanomolar range (Ki = 49 nmol/L). In vitro and in vivo binding potency of amperozide correlates best with behavioral effects, indicating 5-HT2A antagonism, although serotonin uptake inhibition may contribute to the effects of amperozide on dopamine neurotransmission. The metabolite of amperozide, FG5620, displayed 5-10 times lower pharmacologic activity than amperozide. These properties of amperozide may suggest that the antipsychotic effects of amperozide are mediated by 5-HT2A receptors, although 5-HT uptake inhibition and alpha 1-adrenergic receptor-mediated effects may be considered, particularly at higher doses.

Effect of chronic antipsychotic drug treatment on preprosomatostatin and preprotachykinin A mRNA levels in the medial prefrontal cortex, the nucleus accumbens and the caudate putamen of the rat

In situ hybridization histochemistry was used to study the expression of preprosomatostatin (PPSOM) and preprotachykinin A (PPT-A) mRNA in the medial prefrontal cortex (mPFC), the nucleus accumbens (NAC) and the caudate putamen (CP) of the rat after chronic (21 days) treatment with the classical antipsychotic drug haloperidol (1 mg/kg i.p.), the atypical antipsychotic drugs clozapine (15 mg/kg i.p.) and amperozide (5 mg/kg i.p.), and the selective dopamine (DA)-D2/D3 receptor antagonist raclopride (2 mg/kg i.p.). Whereas amperozide markedly elevated the numerical density of PPSOM mRNA expressing neurons in the mPFC (52%), the other drugs did not significantly affect PPSOM mRNA levels in any of the brain regions studied. Amperozide also altered PPT-A mRNA expression in the mPFC, i.e. a decrease (22%) was found. Of the other drugs tested only haloperidol significantly decreased PPT-A mRNA levels in the NAC shell (14%), in the dorso-lateral CP (19%) and in the medial CP (15%). In view of the differences between amperozide and the other drugs studied, as regards both pre-clinical and clinical characteristics, we suggest that the specific effects of amperozide on PPSOM and PPT-A mRNA in the mPFC may be related to its 5-HT releasing action in the frontal cortex, an effect possibly caused by its alpha2-adrenoceptor blocking activity. This effect, in turn, may be related to an antidepressant-like action that this compound exhibits in animal studies. The decrease in PPT-A mRNA levels seen after the haloperidol treatment is probably due to its potent DA-D2 receptor antagonism and may be related to side-effects, rather than therapeutic effects of this drug.

Comparison of neurotensin responses to MDL 100,907, a selective 5HT2A antagonist, with clozapine and haloperidol

The unique pharmacological profile of atypical antipsychotics, such as clozapine, suggests that action on non-dopaminergic transmitter systems might contribute to the unique therapeutic benefits of these drugs. In order to test this possibility, the response of neurotensin systems to drugs with antipsychotic potential was examined because of this peptide's putative association with psychiatric disorders. The effects of treatments by haloperidol, clozapine, and MDL 100,907 (a selective 5HT2A antagonist thought to have antipsychotic activity) on NT pathways were determined in various extrapyramidal and limbic regions and compared. The response of neurotensin systems was determined by measuring neurotensin-like immunoreactivity after 1, 2, 4, and 5 drug administrations. It was observed that tissue content of this peptide in caudate and nucleus accumbens regions tended to be elevated after 1 or 2 drug administrations, but had either returned or was returning to control levels after 4 or 5 drug administrations. In general, the extrapyramidal and limbic neurotensin levels responded in a similar manner to clozapine and the 5HT2A antagonist, but differently for haloperidol in most regions examined. An important exception was in the nucleus accumbens, where all three drugs had similar effects on neurotensin tissue levels. These results suggest that 5HT2A receptors exert basal control over some extrapyramidal and limbic neurotensin systems and this interaction might contribute to the antipsychotic effects of these drugs.

Effects of long-term abstinence on psychological functioning: a prospective longitudinal analysis comparing alcohol-dependent patients and healthy volunteers

Using a prospective longitudinal design, differences between abstinent alcohol-dependent patients (n = 15) and abstinent healthy volunteers (n = 11) were determined with respect to their psychological functioning and alcohol consumption patterns following abstinence. Results showed no differences in alcohol consumption. In 20% of the patients and 9% of the controls more than 10% of protocols indicated alcohol intake, and in 27% of the patients and 27% of the controls less than 10% of protocols indicated alcohol intake. Total abstinence was reported by 53% of the patients and by 64% of the controls. For patients, validation of self-reported alcohol consumption was carried out via biological markers. Patients and controls differed in terms of increased sleep, euphoria, concentration, initiative, anxiety, negative and positive craving, pessimistic thoughts, autonomic disturbances, and humour. A gradual normalization back to baseline levels was observed for some symptoms. These results suggest that affective/mood states may be unstable for alcoholics, and further, that these symptoms may be related to the protracted withdrawal syndrome or may represent residual symptomatology.

The effects of raclopride on vacuous jaw movements in rats following acute administration

Classic neuroleptics produce a syndrome of vacuous jaw movements in rats, whereas atypical neuroleptics like clozapine do not. The present study compared the effects of repeated administration of raclopride, clozapine, haloperidol, or vehicle on vacuous jaw movements in rats over a 4-week period. Rats received an IP injection of drug once a day. On days 1, 8, 15, and 29 the rats were observed for a 5-min period by two trained observers who recorded their vacuous jaw movements. The dose-response curves at which each drug produced vacuous jaw movements are presented and discussed in terms of their predictive capabilities of early onset extrapyramidal side effects.

Differential actions of typical and atypical antipsychotic drugs on dopamine release in the core and shell of the nucleus accumbens

The effects of acute administration of typical and atypical antipsychotic drugs on extracellular dopamine (DA) concentrations in brain were examined in two subdivisions of the nucleus accumbens (NAC), the core and the shell, which are largely associated with motor control and limbic functions, respectively, by using in vivo differential normal pulse voltammetry in anesthetized, pargyline pretreated rats. The following drugs were studied: haloperidol (0.1 and 1.0 mg/kg), clozapine (1.0 and 5.0 mg/kg), amperozide (1.0 and 2.0 mg/kg), risperidone (0.1 and 1.0 mg/kg), the selective 5-HT2A/5-HT2C receptor antagonist ritanserin (1 mg/kg) and the selective DA-D2/D3 receptor antagonist raclopride (10 and 320 micrograms/kg). Drugs with predominantly high 5-HT2 receptor antagonistic action, such as amperozide and ritanserin, as well as low doses of either risperidone or clozapine increased DA concentrations to a greater extent in the shell than in the core subdivision of the NAC. In contrast, drugs with a more potent D2 receptor antagonistic action, such as haloperidol and raclopride, as well as high doses of either risperidone or clozapine, elicited a larger DA increase in the core than in the shell. Consequently, atypical antipsychotics characterized by potent 5-HT2 receptor antagonism can be differentiated from typical antipsychotic drugs on the basis of their preferential effect on DA transmission in the shell region of the NAC.

Risperidone: regional effects in vivo on release and metabolism of dopamine and serotonin in the rat brain

The antipsychotic drug risperidone shows high affinity for both central serotonin (5-HT)2A and dopamine (DA)-D2 receptors in vivo. By employing microdialysis in freely moving rats, the effects of acute risperidone administration on regional brain DA and 5-HT release and metabolism were compared with the corresponding effects of the atypical antipsychotic drug clozapine as well as amperozide, the selective DA-D2 receptor antagonist raclopride and the selective 5-HT2A/5-HT2C receptor antagonist ritanserin. Risperidone (0.2 or 2.0 mg/kg, SC) was found to increase DA release and metabolism to about the same extent in three major projection areas of the mesotelencephalic dopaminergic system, i.e. the nucleus accumbens (NAC), the medial prefrontal cortex (MPC) and the lateral striatum (STR). In contrast, clozapine and amperozide (both 10.0 mg/kg, SC), as well as raclopride (2.0 mg/kg, SC), were all found differentially to affect DA release and metabolism in the three projections areas. Specifically, clozapine and amperozide enhanced DA release in the MPC to a greater extent than in the NAC or the STR, whereas raclopride instead preferentially increased DA release in the NAC and the STR but not in the MPC. Ritanserin (3.0 mg/kg, SC) did not exert any major effects on DA metabolism in the three areas studied. In contrast to the regionally rather homogenous activation of brain DA systems caused by risperidone, the drug was found to enhance brain 5-HT metabolism preferentially in the MPC, as indicated by the elevated extracellular concentration of 5-hydroxyindoleacetic acid (5-HIAA) in this region. A similar elevation of the 5-HIAA level in the MPC was observed after amperozide and, to some extent, after clozapine and ritanserin administration. The risperidone-induced (2.0 mg/kg, SC) elevation of 5-HIAA concentrations in the frontal cortex was found to be paralleled by an increased 5-HT release in this brain area. Consequently, our findings demonstrate a pharmacological profile of risperidone, as reflected in brain DA metabolism, in between that of clozapine and the DA-D2 antagonists. The preferential activation of 5-HT release and metabolism in frontal cortical areas might be of particular relevance for the ameliorating effect of risperidone on negative symptoms in schizophrenia, especially when associated with depression.

Synthesis of dopamine and 5-HT in anatomical regions of the rat's brain is unaffected by sustained infusion of amperozide

The 5-HT2A antagonist, amperozide, is considered to be a potentially useful drug for the treatment of substance abuse. The effects of this drug on the Sprague-Dawley rat were examined on the synthesis of dopamine and serotonin (5-HT) as well as on the intakes of food and water and the level of body weight. Amperozide was delivered subcutaneously by osmotic minipump in doses of 2.5 mg/kg or 5.0 mg/kg per day for 7 days. After injection of 100 mg/kg NSD-1015, each brain was dissected post mortem into midbrain, pons, hypothalamus, septum, nucleus accumbens, striatum, frontal cortex and the hippocampus. Neither concentration of amperozide altered the synthesis of dopamine or 5-HT, as measured in terms of the formation of 1-3,4-dihydroxyphenylalanine (L-DOPA) and 5-hydroxytryptophan (5-HTP), respectively, in any of the 8 brain regions analyzed. Both doses of amperozide reduced food intake by 20% within 24 hr after implantation of the pumps, but feeding resumed postoperatively at the control level within 48 hr. Amperozide affected neither the intake of water nor the level of body weight. The lack of effect on the synthesis of dopamine and 5-HT and the absence of side effects on the intakes of food and water suggest that amperozide may be a specific agent for suppressing alcohol drinking.

Studies of four novel diphenylbutylpiperazinepyridyl derivatives on release and inhibition of reuptake of dopamine, serotonin and noradrenaline by rat brain in vitro

Four novel diphenylbutylpiperazinepyridyl derivatives (FG5865 (2-[4-[4,4-bis(4-fluorophenyl)butyl]-1-piperazinyl]-3-pyridine- carboxamide), FG5891 (2-[4-[4,4-bis(4-fluorophenyl)butyl]-1-piperazinyl]-N-methyl-3- pyridinecarboxamide), FG5893 (2-[4-[4,4-bis(4-fluorophenyl)butyl]-1-piperazinyl]-3- pyridinecarboxylic acid methyl ester) and FG5909 (2-[4-[4,4-bis(4-fluorophenyl)butyl]-1-piperazinyl]-3-hydroxypyridine) were tested concerning their effects on in vitro release and reuptake of neurotransmitters. Serotonin, noradrenaline and dopamine were those considered, with rat synaptosomes prepared respectively from frontal cortex, cortex and striatum. FG5865, FG5891, FG5893 and FG5909 were found to potently inhibit the uptake of all three neurotransmitters. In addition, FG5865, FG5891 and FG5893 increased the release of serotonin and dopamine from perfused frontal cortical and striatal tissue; FG5865 was most potent in this regard. The release induced by the FG compounds was, however, much less than that induced by e.g. fenfluramine or amphetamine. All four FG compounds were also found to inhibit glutamate-stimulated release of dopamine from striatal tissue; for FG5893 this inhibition occurred at nanomolar concentrations.

Differential effects of repeated administration of novel antipsychotic drugs on the activity of midbrain dopamine neurons in the rat

Five potential antipsychotics (i.e. risperidone, olanzapine, seroquel, ziprasidone and amperozide) were given daily for 21 days to rats and the effect on the number of spontaneously active dopamine neurons in ventral tegmental area and substantia nigra pars compacta was determined. Standard electrophysiological measurements (i.e. single unit recording technique) were used. Risperidone, olanzapine and amperozide showed some selectivity (at one particular dose) for decreasing the number of active dopamine neurons in the ventral tegmental area. However, risperidone induced a U-shaped dose-response curve. The highest dose of amperozide inhibited the activity in substantia nigra pars compacta, showing a liability to induce extrapyramidal side-effects. Seroquel and ziprasidone inhibited the activity in both areas indicating a classical antipsychotic profile (i.e. high liability to cause extrapyramidal side-effects).

Seroquel (ICI 204 636), a putative "atypical" antipsychotic, in schizophrenia with positive symptomatology: results of an open clinical trial and changes of neuroendocrinological and EEG parameters

Preclinical data indicated that seroquel (ICI 204 636), a dibenzothiazepine with 5-HT2 and D2-like receptor antagonistic properties, might be an effective antipsychotic agent, causing fewer extrapyramidal side effects than typical neuroleptics. In the present study, 12 patients suffering from schizophrenia or schizophreniform disorder with predominantly positive symptomatology were treated in an open clinical trial for 4 weeks with seroquel at a maximum dosage of 750 mg/day. The drug was generally well tolerated, and virtually no adverse extrapyramidal side effects such as acute dystonia, parkinsonism or akathisia were observed. Total scores for BPRS (item score 0-6; baseline: 42.0 +/- 2.3; mean +/- SEM), SAPS (64.5 +/- 4.8) and SANS (55.0 +/- 4.3) showed a moderate decrease at the end of treatment (BPRS: 30.0 +/- 3.5; SAPS: 36.1 +/- 6.7; SANS: 42.5 +/- 5.9), when intention-to-treat analysis was applied. There were considerable interindividual differences in treatment response, with some subjects showing almost full remission of positive symptoms, in contrast to about half of the patients who showed no satisfactory clinical improvement. Interestingly, patients showing good antipsychotic response reported slight initial side effects like mild sedation. Prolactin and TSH levels were not altered during seroquel administration. As to pharmaco-EEG investigations, seroquel caused a moderate increase of the absolute power in the alpha, theta, and beta frequency bands, paralleled by a decrease of delta activity. There were no signs of paroxysmal EEG activity under seroquel.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that 5-HT(2) Antagonism Elicits a 5-HT(3)-Mediated Increase in Dopamine Transmission

Amperozide, a novel atypical antipsychotic drug with few extrapyramidal side effects, is a strong serotonin(2) (5-HT(2)) antagonist but has low affinity for dopamine receptors in vitro. The effect of amperozide on the dopaminergic synapse was studied with an in vivo microdialysis technique using anesthetized male Sprague-Dawley rats. Following implantation of dialysis probes into the striatum and nucleus accumbens (NuAc), amperozide was intravenously infused as six consecutive incremental doses (0.5, 0.5, 1.0, 2.0, 4.0 and 8.0 mg/kg) at intervals of 15 min. From the beginning of drug infusion, perfusates were collected in fractions every 30 min throughout a total period of 120 min. The samples were then immediately analyzed by high-performance liquid chromatography with electrochemical detection. Amperozide induced a dose-related elevation of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5-HIAA) levels in both areas. p-Chlorophenylalanine (pCPA) pretreatment abolished the production of 5-HIAA in both areas and attenuated the amperozide-induced rise of DOPAC but not of dopamine. After pretreatment with an intravenous 5-HT(3) antagonist, MDL 72222, the amperozide-induced changes in dopamine, DOPAC and 5-HIAA in both areas were lower than in the saline control group. Preliminary data showed that after pCPA pretreatment, incremental concentrations of the 5-HT(3) agonist 1-(m-chlorophenyl)-biguanide perfused via the probe also produced significant elevation of dopamine and DOPAC levels in these two areas. Taken together, these results suggest that amperozide may directly block 5-HT(2) receptors in the striatum and NuAc, thereby enhancing 5-HT transmission. The enhanced 5-HT transmission may activate postsynaptic 5-HT(3) receptors located on the dopaminergic terminals, leading to changes in dopamine transmission in these two areas. Copyright 1995 S. Karger AG, Basel

The selective 5-HT2A receptor antagonist, MDL 100,907, increases dopamine efflux in the prefrontal cortex of the rat

Diminished function within the mesocortical dopamine system has been to hypothesized to contribute directly to the negative and indirectly to the positive symptoms of schizophrenia. Based on the proposed role of 5-HT2 receptor blockade in the antipsychotic profile of clozapine and its preferential augmentation of prefrontal dopamine release, we have examined the effects of the selective 5-HT2A receptor antagonist, R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl]-4-piperidi ne- methanol (MDL 100,907), on dopamine release in the rat medial prefrontal cortex using in vivo microdialysis. The results indicate that local 5-HT2A receptors exert a tonic inhibitory influence on dopamine efflux in the medial prefrontal cortex. These observations are consistent with the hypothesis that 5-HT2A receptor blockade contributes to the unique antipsychotic profile of clozapine and that MDL 100,907 may have antipsychotic activity.

Systemic administration of amperozide, a new atypical antipsychotic drug, preferentially increases dopamine release in the rat medial prefrontal cortex

The putative atypical antipsychotic drug amperozide (APZ) shows high affinity for serotonin 5-HT2 receptors but only low affinity for dopamine (DA) D2 receptors. By employing microdialysis, we examined the effects of APZ on extracellular concentrations of DA in the nucleus accumbens (NAC), the dorsolateral striatum (STR) and the medial prefrontal cortex (MPC) of awake rats. A 5.0 mg/kg (SC) dose of APZ failed to affect DA concentrations in the NAC, while it increased DA outflow in the STR (by 46%) and the MPC (by 207%). A higher dose of APZ (10 mg/kg, SC) enhanced dialysate DA from the NAC and the STR by 30%, and from the MPC by 326%. Similarly, clozapine (2.5 and 10 mg/kg, SC) produced a greater release of DA in the MPC (+ 127 and + 279%) than in the NAC (+ 52 and + 98%). The selective 5-HT2 receptor antagonist ritanserin (1.5 and 3.0 mg/kg, SC) also produced a slightly higher increase of DA output in the MPC (+ 25 and + 47%) compared with the NAC (+ 19 and + 21%). In contrast, the selective D2 receptor antagonist raclopride (0.5 and 2.0 mg/kg, SC) increased DA release in the NAC (+ 65 and + 119%) to a greater extent than in the MPC (+ 45 and + 67%). These data suggest that the 5-HT2 receptor antagonistic properties of APZ and clozapine may contribute to their preferential effects on DA transmission in the MPC. Infusion of low doses (1, 10 microM, 40 min) of APZ through the probe in the DA terminal areas did not affect significantly DA outflow, while infusion of high doses (100, 1000 microM, 40 min) resulted in a more pronounced elevation of DA levels in the NAC (up to 961%) and the STR (up to 950%) than in the MPC (up to 316%). These findings indicate that the selective action of systemically administered APZ on DA in the MPC is most likely mediated at a level other than the terminal region. Taken together, the present results provide support for the notion that 5-HT2 receptor antagonism may be of considerable significance for the action of atypical antipsychotic drugs on mesolimbocortical dopaminergic neurotransmission.

Comparison of the action of the 5-HT2 antagonists amperozide and trazodone on preference for alcohol in rats

Previous studies in the rat demonstrated that the 5-hydroxytryptamine2 (5-HT2) antagonist amperozide attenuates the volitional intake of both alcohol and cocaine solutions in a free-choice situation. However, another 5-HT2 antagonist, ritanserin, has not been found to reduce alcohol drinking consistently in the rat. In this study, trazodone was compared to amperozide for its effect on the volitional consumption of alcohol because, like amperozide, trazodone is a potent 5-HT2 receptor antagonist but a weak inhibitor of 5-HT reuptake. Male Sprague-Dawley rats were induced to drink alcohol by 10 mg/kg cyanamide injected for 3 days b.i.d. One week later the rats were offered a choice of water and increasing concentrations of alcohol solutions ranging from 3% to 30% v/v in a three-bottle two-choice paradigm. After the concentration of alcohol that produced maximal daily intake was determined for each rat, trazodone or amperozide was injected b.i.d. SC in doses of 1.0 mg/kg or 2.5 mg/kg for three days. Whereas the higher dose of amperozide produced a significant, 55.6% decrease from pretreatment baseline of alcohol intake, trazodone did not alter alcohol preference at either the 1.0- or 2.5-mg/kg dose. These results are discussed in terms of whether the antagonism of 5-HT2 receptors by amperozide is critical to its attenuating effect on preference for alcohol solutions.

Effects of amperozide on schedule-induced polydipsia in rats

Schedule-induced polydipsia occurs when food-deprived rats are exposed to a fixed-interval feeding schedule (FI = 60 s) for 1 h every day. Amperozide, a novel antipsychotic drug with a strong affinity for the 5-HT2 receptor, was injected i.p. after completion of the requisite training sessions. The experimental rationale is that although the intensity of licking behavior in schedule-induced polydipsia can be taken as an index for anxiety, the drug-induced motor dysfunction should be assessed. In experiment 1, we tested the effect of amperozide on schedule-induced polydipsia at doses of 2, 4, and 8 mg/kg. The data showed that each dose significantly diminished the amount of licking and water intake. The number of presses decreased only at the dose of 8 mg/kg. During five post-treatment daily sessions for 5 days, these three measures returned to normal levels except that the number of pellets earned during the sessions did not significantly change. In addition, the number of presses showed a rebound after the termination of amperozide administration. In experiment 2, in addition to the total water intake, number of licks, pellets earned and presses, we also analyzed the postpellet temporal variation in the number of licks and presses in each schedule-induced polydipsia session. The drug was stopped for one day after each dose of 0.2, 0.4, 0.8 and 1.6 mg/kg of amperozide. The data showed that doses from 0.2 to 0.8 mg/kg did not alter any measure in drug-treated sessions and that the dose of 1.6 mg/kg decreased the number of licks and water intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of striatal 5-hydroxytryptamine2 receptors reduces the increase in extracellular concentrations of dopamine produced by the amphetamine analogue 3,4-methylenedioxymethamphetamine

5-Hydroxytryptamine2 (5-HT2) receptor antagonists have been shown to interfere with the stimulation of striatal dopamine synthesis and release produced by the amphetamine analogue 3,4-methylenedioxymethamphetamine (MDMA). To localize the receptors responsible for the attenuation of MDMA-induced release, 5-HT2 receptor antagonists were infused via the microdialysis probe directly into the brains of awake, freely moving rats before the systemic administration of MDMA. Intrastriatal infusions of the selective 5-HT2 antagonist MDL 100,907 produced a concentration-dependent inhibition of MDMA-induced dopamine release. Similar results were observed with intrastriatal infusions of the 5-HT2 antagonist amperozide. In contrast, infusion of MDL 100,907 into the mid-brain region near the dopaminergic cell bodies was without effect on the MDMA-induced elevation of extracellular dopamine in the ipsilateral striatum. Neither antagonist attenuated basal transmitter efflux nor the MDMA-stimulated release of [3H]dopamine from striatal slices in vitro indicating that the in vivo effect of the antagonists was not due to inhibition of the dopamine uptake carrier. Intrastriatal infusion of tetrodotoxin reduced both basal and MDMA-stimulated dopamine efflux and eliminated the effect of intrastriatal MDL 100,907. The results indicate that 5-HT2 receptors located in the striatum augment the release of dopamine produced by high doses of MDMA. Furthermore, these 5-HT2 receptors appear to be located on nondopaminergic elements of the striatum.

The limbic functional selectivity of amperozide is not mediated by dopamine D2 receptors as assessed by in vitro and in vivo binding

Behavioural, biochemical and electrophysiological studies suggest that amperozide affects mesolimbic dopamine neurotransmission. Amperozide is a potent 5-HT2, receptor antagonist with only a moderate affinity for rat brain dopamine D2 receptors. The brain regional dopamine D2 receptor binding properties of amperozide were investigated by using in vitro and in vivo radioligand binding techniques. Amperozide displaced [3H]spiroperidol binding from rat striatal and limbic dopamine D2 receptors with moderate affinity (Ki = 540 +/- 118 nM and Ki = 403 +/- 84 nM, respectively). The dopamine D2 receptor antagonist l-sulpiride and the agonist dopamine did not show different affinity in the two brain regions. Amperozide potently displaced in vivo [3H]spiroperidol binding in rat frontal cortex (ID50 = 1.4 mg/kg s.c.) but was devoid of effect in striatum, olfactory tubercle and nucleus accumbens (ID50 > 100 mg/kg s.c.). Chronic administration of amperozide (5 mg/kg p.o.) for three weeks did not result in any change of maximal dopamine D2 receptor number in either striatal or limbic tissue. The effects of amperozide on dopamine neurotransmission are thus not likely to occur by a direct interaction with dopamine D2 receptors in either striatal or limbic tissue. The functional limbic selectivity might rather be mediated by serotoninergic pathways.

Amperozide, a 5-HT2 antagonist, attenuates craving for cocaine by rats

Amperozide, a novel 5-HT2 receptor antagonist with little affinity for the dopamine receptor, suppresses the intake of alcohol in rats without affecting food intake or inducing other side effects. Because of these actions, amperozide was examined for its efficacy on the oral preference by the rat for a solution of cocaine. In this study, rats were selected for their voluntary consumption of at least 10 mg/kg of cocaine per day in a two-choice paradigm. A solution of 0.02% to 0.06% cocaine plus 0.03% saccharin in water was offered to each animal simultaneously with a solution of only 0.03% saccharin in water. The consumption of food and both fluids, as well as body weight, was recorded daily for three successive periods: 4 days of pretreatment baseline; 3 days during injections of either amperozide or the saline vehicle solution; and 4 days postinjections. Amperozide was administered SC twice daily in a dose of 0.5, 1.0, or 2.5 mg/kg. The volitional intake of cocaine was significantly reduced not only during the 3-day period of injections of amperozide but also during the 4-day posttreatment period. Amperozide exerted little or no effect on the intake of food or on body weight. Radioligand binding experiments confirmed that amperozide has at least a twentyfold greater affinity for 5-HT2 receptors in the frontal cortex of the rat, as compared to striatal DA1 and DA2 receptors, with the proportion value similar to that of the 5-HT2 receptor antagonist, ritanserin.(ABSTRACT TRUNCATED AT 250 WORDS)

The atypical antipsychotic drug amperozide enhances rat cortical and striatal dopamine efflux

Previous behavioral, biochemical, and electrophysiological studies have indicated that amperozide, a putative atypical antipsychotic drug with potent 5-HT2 receptor antagonist potency, preferentially affects mesocorticolimbic, as compared to mesostriatal dopamine neurons. The present experiment utilized in vivo microdialysis to compare the effects of amperozide on dopamine efflux in medial prefrontal cortex versus caudate-putamen in the freely moving rat. The results demonstrated that amperozide produced a greater elevation of cortical dopamine. These results were similar to those observed with clozapine but not haloperidol.

5-HT1A autoreceptor-mediated effects of the amperozide congeners, FG5865 and FG5893, on rat brain 5-hydroxytryptamine neurochemistry in vivo

The two diphenylbutylpiperazinepyridinyl derivatives, FG5865 and FG5893, have a unique receptor binding profile in that they show very high and essentially equipotent affinities for both 5-HT1A and 5-HT2 receptors. The present report describes the acute effects of FG5865 and FG5893 on presynaptic 5-hydroxytryptamine (5-HT) neuronal function in the rat CNS, using established ex vivo and in vivo neurochemical techniques. Post-mortem measurements of tissue levels of 5-HT, its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and of the formation of 5-hydroxytryptophan (5-HTP; after inhibition of aromatic amino acid decarboxylase by NSD 1015) showed that FG5865 (0.1-20 mg/kg, s.c.) and FG5893 (0.1-20 mg/kg, s.c.) dose dependently decreased the synthesis and the metabolism/turnover of 5-HT--this to an extent comparable to the reference 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin. Reserpine (5 mg/kg, s.c.) pretreatment did not prevent the FG5893-induced decrease of 5-HT synthesis rate. In contrast, about 25-50 times higher doses of FG5865 were required to produce a comparable decrease in brain 5-HT synthesis in reserpinized vs. non-pretreated rats. In in vivo microdialysis experiments, both FG5865 (0.1-3.0 mg/kg, s.c.) and FG5893 (0.03-1.0 mg/kg, s.c.) caused a marked and dose-dependent decrease of 5-HT release in the ventral hippocampus. Pretreatment with the 5-HT1A receptor antagonist, (+/-)-pindolol (8 mg/kg, s.c.), abolished the FG5865 (0.3 mg/kg, s.c.)-induced reduction of 5-HT release, and (-)-pindolol (8 mg/kg, s.c.) similarly reversed the FG5893 (0.3 mg/kg, s.c.)-induced decrease. Local infusion of FG5865 into the ventral hippocampus (10 microM, 20-min pulse) resulted in a rapid and transient elevation of the 5-HT output, an effect that was independent of extracellular Ca2+. FG5893, on the other hand, did not affect the 5-HT release upon local administration. The results demonstrate that FG5865 and FG5893 potently affect a range of neurochemical indices of rat brain 5-HT neuronal activity in vivo, in a way consistent with indirect (FG5865) and direct (FG5865 and FG5893) stimulation of the 5-HT1A autoreceptors in the raphe nuclei.

Interaction of antipsychotic drugs with neurotransmitter receptor sites in vitro and in vivo in relation to pharmacological and clinical effects: role of 5HT2 receptors

In the introductory section an overview is given of the strategies which have been proposed in the search for side-effect free antipsychotics. Special attention is paid to the role of predominant 5HT2 receptor blockade over D2 blockade. Whereas D2 receptor blockade seems to be essential for the treatment of positive symptoms of schizophrenia, it also underlies the induction of extrapyramidal side effects (EPS). Predominant 5HT2 receptor blockade may reduce the EPS liability and can ameliorate negative symptoms of schizophrenia. We further report a nearly complete list of neuroleptics that are on the European market and eight new antipsychotics that recently entered clinical trial, 5HT2 and D2 receptor binding affinity (Ki values) and the rank order in affinity for various neurotransmitter receptor subtypes are also discussed. For the eight new antipsychotics and for six reference compounds the complete receptor binding profile (including 33 radioligand receptor binding and neurotransmitter uptake models) is reported. Furthermore, for a series of 120 compounds the relative affinity for D2 receptors and D3 receptors (a recently cloned new dopamine receptor subtype) is compared. Finally, original findings are reported for the new antipsychotic risperidone and for haloperidol and clozapine on the in vivo occupation of neurotransmitter receptors in various brain areas after systemic treatment of rats or guinea pigs. The receptor occupation by the drugs was measured ex vivo by quantitative receptor autoradiography. The receptor occupancy was related to the motor activity effects of the test compounds (measurements were done in the same animals) and to the ability of the drugs to antagonize various 5HT2 and D2 receptor mediated effects. With risperidone a high degree of central 5HT2 receptor occupation was achieved before other neurotransmitter receptors became occupied. This probably co-underlies the beneficial clinical properties of the drug. Antagonism of the various D2 receptor-mediated effects was achieved at widely varying degrees of D2 receptor occupancy, from just about 10% to more than 70%. For therapeutic application it may be of prime importance to carefully titrate drug dosages. Antipsychotic effects may be achieved at a relatively low degree of D2 receptor occupancy at which motor disturbances are still minimal. With drugs such as risperidone that produce shallow log dose-effect curves, differentiation between the various D2 receptor mediated effects may be made more easily, allowing EPS-free maintenance therapy of schizophrenic patients.

Amperozide, a Novel Antipsychotic Drug, Inhibits the Ability of d-Amphetamine to Increase Dopamine Release In Vivo in Rat Striatum and Nucleus Accumbens

The in vivo effects of amperozide, a novel atypical antipsychotic drug, on the release of dopamine (DA) and the output of its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were investigated in the striatum and the nucleus accumbens of awake, freely moving rats using microdialysis. Amperozide (2-10 mg/kg, s.c.) significantly increased extracellular levels of DA in both the striatum and nucleus accumbens in a dose-dependent manner. It had a similar but lesser effect on extracellular DOPAC levels in both regions. d-Amphetamine (2 mg/kg, s.c.) alone produced a very large (43-fold) increase in DA release, together with a 70% decrease in DOPAC levels in both the striatum and the nucleus accumbens. Amperozide (1-5 mg/kg, s.c.) 30 min before d-amphetamine (2 mg/kg) dose-dependently attenuated d-amphetamine-induced DA release but had no effect on the d-amphetamine-induced decrease in extracellular DOPAC levels in both regions. The effect of amperozide on d-amphetamine-induced DA release in the nucleus accumbens may explain the inhibitory effect of amperozide on amphetamine-induced locomotor activity. However, the failure of amperozide to block amphetamine-induced stereotypy, despite marked inhibition of striatal DA release, suggests the need to reexamine the importance of striatal DA for amphetamine-induced stereotypy.

Effect of amperozide on rat cortical 5-HT2 and striatal and limbic dopamine D2 receptor occupancy: implications for antipsychotic action

Amperozide (FG 5606, N-ethyl-4-[4',4'-bis(p-fluorophenyl)butyl]-1-piperazine-carboxamide) is an atypical antipsychotic drug which has relatively weak in vitro affinity for striatal dopamine2 (D2) receptors and strong affinity for cortical 5-HT2 receptors. The in vivo affinity for 5-HT2 binding sites in rat cortex was 1.1 mg/kg. In striatum or olfactory tubercle, doses of amperozide up to 40 mg/kg did not displace radioligand binding to D2 receptors. Amperozide, haloperidol and ritanserin had similar in vivo potency in blocking the 5-HT2 binding site, but only haloperidol displaced D2 receptor binding. Based on the clinically effective dose of amperozide (0.14-0.28 mg/kg per day), it is suggested that the antipsychotic effect of amperozide is related, in part, to its in vivo interaction with the 5-HT2 receptor and that amperozide cannot be expected to exert its antipsychotic action by blockade of D2 receptors in the striatum or limbic regions.