Decreased striatal dopamine transporter binding assessed with [<Superscript>123</Superscript>I] FP-CIT in first-episode schizophrenic patients with and without short-term antipsychotic-induced parkinsonism

Rationale Drug-induced parkinsonism (DIP) is one of the main causes of treatment drop-out in schizophrenic patients causing a high incidence of relapse that leads patients to a bad clinical prognosis. The dopaminergic nigrostriatal pathway is involved in the movement control, so the study of the dopamine transporter (DAT) could be of great value to determine its implication in the appearance of DIP. Objective The goal of the study is to determine the striatal DAT binding assessed with [¹²³I] FP-CIT SPECT in first-episode neuroleptic-naive schizophrenic in-patients with DIP after short-term antipsychotic treatment. Method The [¹²³I] FP-CIT binding ratios of ten schizophrenic in-patients who developed DIP during the first 4-week period of risperidone treatment (6±2 mg/day) were compared with ten schizophrenic in-patients treated with the same doses of risperidone and who do not developed DIP and with ten age-matched healthy subjects. Quantitative analyses of SPECTs were performed using regions of interest located in caudate, putamen and occipital cortex. Parkinsonism was assessed by the Simpson–Angus Scale and the psychopathological status by the Clinical General Impression and Positive and Negative Syndrome Scales. Results Whole striatal [¹²³I] FP-CIT binding ratios were significantly lower in patients with and without DIP than in healthy subjects (p<0.001). This was also observed in whole putamen (p<0.001) and caudate nucleus (p<0.001). Females showed higher whole striatal [¹²³I] FP-CIT binding ratios than males (p<0.05). No differences in psychopathological scales were observed between patients with and without DIP. Conclusion Our first-episode schizophrenic patients with and without DIP after short-term risperidone treatment have a decreased striatal DAT binding assessed with [¹²³I] FP-CIT. This alteration could be related to the schizophrenic disease or may be secondary to the antipsychotic treatment.     

In vivo measurement of the vesicular monoamine transporter in schizophrenia.

Given evidence for excessive striatal dopamine activity in schizophrenia, we sought to test the hypothesis that dopaminergic innervation in the striatum is abnormally elevated, and a secondary hypothesis that age-related loss is accelerated. Twelve schizophrenic subjects on stable doses of medications, along with 12 age and sex-matched healthy control subjects, underwent positron emission tomography (PET) studies with [11C]dihydrotetrabenazine (DTBZ), which binds to the vesicular monoamine transporter, type 2 (VMAT2). DTBZ binding reflects principally dopaminergic projections in the striatum and appears in animal models, over treatment periods as long as two weeks, not to be regulated by antipsychotic drugs. Using an equilibrium analysis, we obtained measurements of the binding potential (BP) of [11C]DTBZ, as well as a transport (K(1)) measure, corresponding to regional cerebral blood flow. BP in the striatum showed no difference between the patient and control groups, and no differential effect of age. We did not find evidence supporting the hypothesis that excessive dopamine activity in schizophrenia could be explained by increased density of striatal dopamine terminals.     

Use of amphetamine by recreational users of ecstasy (MDMA) is associated with reduced striatal dopamine transporter densities: a [123I]β-CIT SPECT study – preliminary report

RATIONALE: Tablets sold as ecstasy often contain not only 3,4-methylenedioxymethamphetamine (MDMA) but other compounds well known to cause dopaminergic neurotoxicity, such as (meth)amphetamine. Furthermore, the use of ecstasy in the Netherlands is often combined with the use of amphetamine. However, little is known about the effects of ecstasy use or the combination of ecstasy and amphetamine use on dopamine (DA) neurones in the human brain. OBJECTIVES: This study was designed to investigate the effects of ecstasy as well as the combined use of ecstasy and amphetamine on the density of nigrostriatal DA neurones. METHODS: [123I]beta-CIT SPECT was used to quantify striatal DA transporters. Striatal [123I]beta-CIT binding ratios of control subjects ( n=15) were compared with binding ratios of ecstasy users ( n=29) and individuals with a history of combined ecstasy and amphetamine use ( n=9) after adjustment for age. RESULTS: Striatal [123I]beta-CIT binding ratios were significantly lower in combined ecstasy and amphetamine users compared to sole ecstasy users (6.75 versus 8.46, respectively: -20.2%, P=0.007). Binding ratios were significantly higher in ecstasy users when compared to controls (8.46 versus 7.47, respectively: +13.2%, P=0.045). CONCLUSIONS: These initial observations suggest that the sole use of ecstasy is not related to dopaminergic neurotoxicity in humans. In contrast, the reported use of amphetamine by regular users of ecstasy seems to be associated with a reduction in nigrostriatal DA neurones.     

The striatal dopamine transporter in first-episode, drug-naive schizophrenic patients: evaluation by the new SPECT-ligand[99mTc]TRODAT-1

Following the current hypothesis that acute schizophrenic psychotic illness is associated with a striatal 'hyperdopaminergic state', presynaptic integrity and dopamine transporter (DAT) density in first-episode, neuroleptic-naive schizophrenic patients was measured by single-photon-emission-tomography (SPECT) and compared with that in healthy control subjects. A new SPECT-ligand for assessment of the striatal DAT, the Technetium-99m-labelled tropane TRODAT-1 ([99mTc]TRODAT-1), was used. Ten inpatients suffering from a first acute schizophrenic episode and 10 age- and sex-matched healthy control subjects underwent SPECT with [99mTc]TRODAT-1. On the day of SPECT, psychopathological ratings were performed with the Brief Psychiatric Rating Scale (BPRS), the Positive and Negative Syndrome Scale (PANSS) and Schedule for Assessment of Negative Symptoms (SANS). Patients had not previously received any neuroleptic or antidepressant medication. Mean specific TRODAT-1 binding in the striatum did not differ significantly between the patient and the age- and sex-matched control group (1.25 vs. 1.28). Variance was significantly higher in the patient group. The data obtained with the new ligand in first-episode, drug-naive schizophrenic patients are in line with the PET results from the group of Laakso et al. in a comparable patient sample. [99mTc]TRODAT-1 seems to be a valuable new SPECT-ligand in the evaluation of the presynaptic site of the striatal dopaminergic synapse in schizophrenia.     

Dopamine receptor changes after long-term haloperidol treatment in rats

Tardive dyskinesia is a neurological syndrome associated with prolonged neuroleptic treatment of schizophrenic patients (Crane 1968; Faurbye 1970; Faurbye et al 1964). It has been suggested that tardive dyskinesia results from chemical denervation of central dopamine neurons and subsequent development of supersensitivity of the postsynaptic receptor (Rubovits & Klawans 1972). Experiments based on animal models of tardive dyskinesia support this hypothesis. Chronic neuroleptic treatment increases postsynaptic dopamine receptor sensitivity when measured either behaviourally or biochemically (Christensen et al 1976; Klawans & Rubovits 1972; Moore & Thornburg 1975; Sayers et al 1975; Tarsy & Baldessarini 1974; Von Voigtlander et al 1975). The molecular basis for this behavioural change has been reported to be an increase in the number of receptor sites with no change in their affinity as measured by ³H-neuroleptic binding to striatal membrane homogenates (Burt et al 1977; Klawans et al 1977; Muller & Seeman 1977). Previous biochemical reports of the development of model tardive dyskinesia after neuroleptic treatment of animals have generally used treatment periods of 3 weeks or less (Burt et al 1977; Klawans et al 1977; Muller & Seeman 1977). Only one report treated animals for longer periods (Clow et al 1978). In the present experiments we studied the kinetics of [³H]spiroperidol binding to rat caudate nucleus homogenates after 3 and 10 weeks of haloperidol treatment.     

No change in striatal dopamine re-uptake site density in psychotropic drug naive and in currently treated Tourette's disorder patients: a [(123)I]-beta-CIT SPECt-study.

BACKGROUND: There is evidence that Tourette's disorder (TD) is associated with abnormalities in the dopaminergic system involving the dopamine transporter (DAT). Data from [(123)I]-beta-CIT single photon emission computed tomography (SPECT) studies and postmortem findings concerning DAT densities in TD patients are not conclusive. The objective of our study was to measure DAT densities with [(123)I]-beta-CIT binding in TD patients who were either psychotropic drug naive or currently treated with antipsychotics (AP) and healthy controls. METHOD: Altogether 20 TD patients were investigated. A total of 15 patients were psychotropic drug naive and five were currently treated with AP. Ten psychotropic drug naive patients were compared with ten age and sex matched healthy subjects. Five currently treated patients were compared with five age and sex matched psychotropic drug naive TD patients. The investigation was carried out using [(123)I]-beta-CIT (2-beta-carbomethoxy-3-beta(4-iodophenyl)-tropane and SPECT. Regions of interest (ROI) were drawn over the striatum and the cerebellum. RESULTS: The DAT densities measured by the striatal/cerebellar (S/C) binding ratio did not differ between drug naive TD patients and the controls. The difference between currently AP treated and psychotropic drug naive TD patients did not reach the level of significance. There was no correlation between the ratio and severity of tics and illness. CONCLUSION: Our study with psychotropic drug naive TD patients contributed to clarify the inconsistent results concerning the DAT.     

Signs of striatal dopamine transporter density increase in association with improvement of tardive dyskinesia in a patient with schizophrenia,as demonstrated by a DAT scan

The imaging of the dopamine transporter could demonstrate the implication of dopaminergic pathway in the appearance of tardive dyskinesia. We report a case with psychotic and tardive dyskinesia symptoms. A DAT scan showed decreased dopamine transporter uptake in the area of brain's basal gaglia. A trial with quetiapine improved both psychotic and TD symptoms while a second DAT scan showed improvement status. We conclude that increased dopamine transporter uptake seemed to associate with the improvement of TD.     

Differential declines in striatal nicotinic receptor subtype function after nigrostriatal damage in mice

Nigrostriatal damage leads to a reduction in striatal nicotinic acetylcholine receptors (nAChRs) in rodents, monkeys, and patients with Parkinson's disease. The present studies were undertaken to investigate whether these nAChR declines are associated with alterations in striatal nAChR function and, if so, to identify the receptor subtypes involved. To induce nigrostriatal damage, mice were injected with the selective dopaminergic toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We measured [(125)I]3 beta-(4-iodophenyl)tropane-2 beta-carboxylic acid isopropyl ester (RTI-121, dopamine transporter), (125)I-alpha-conotoxin MII (putative alpha 6-containing sites in the central nervous system), (125)I-epibatidine (multiple sites), 5-[(125)I]iodo-3-[2(S)-azetidinylmethoxy]pyridine-2HCl ([(125)I]A85380; beta2-containing sites), and (125)I-alpha-bungarotoxin (alpha 7-containing sites) binding in brains from control and MPTP-treated mice, as well as nAChR function by [(3)H]dopamine release, [(3)H]GABA release, and [(86)Rb(+)] efflux. After MPTP treatment, declines were observed in striatal dopamine transporter levels, both binding and functional measures of striatal alpha-conotoxin MII-sensitive nAChRs, and selected measures of striatal alpha-conotoxin MII-resistant nAChRs. In contrast, (125)I-alpha-bungarotoxin binding sites were not altered after nigrostriatal damage. The changes in striatal nAChRs were selective, with no declines in cortex, thalamus, or septum. Those striatal binding and functional measures of nAChRs that decreased with MPTP treatment correlated with dopamine transporter declines, an observation suggesting that the binding and functional changes in nAChRs are limited to dopaminergic terminals. The present results are the first to demonstrate differential alterations in nAChR subtype function after nigrostriatal damage, with a close correspondence between changes in receptor binding sites and function. These data suggest that the declines in nAChR sites observed in Parkinson's disease brains may be of functional significance.     

Striatal dopamine transporter density in major depression

Rationale: There are no previous data available regarding [¹²³I]β-CIT binding to the dopamine transporter sites in the basal ganglia in depressed patients. Objective: The present study tested the hypothesis that the brain DAT density in depressed patients is lower than that in matched healthy controls. Methods: Fifteen drug-naive outpatients with major depression and 18 healthy controls were investigated using single photon emission computerized tomography (SPECT) with a high-affinity dopamine transporter specific radioligand, ¹²³I-labeled β-CIT (2β-carbomethoxy-3β-(4-iodophenyl)-tropane). Results: We found a significantly higher [¹²³I]β-CIT uptake in both sides of the basal ganglia in patients with major depression than in the controls (Mann-Whitney U-test, P = 0.002 on the right and P = 0.003 on the left). Conclusions: The radioligand uptake reflecting the DAT density was significantly higher among the patients than in the controls. This finding is unexpected, since it is generally believed that monoaminergic neurotransmission is lower in depression, and therefore it could be assumed that a reduction in dopamine transmission would lead to secondary down-regulation of DAT density. However, it is possible that up-regulation of the DAT may be the primary alteration, which leads to lower intrasynaptic dopamine concentration and to lower dopamine neural transmission. Received: 20 October 1998/Final version: 25 January 1999     

In vivo (123)I IBZM SPECT imaging of striatal dopamine 2 receptor occupancy in schizophrenic patients

RATIONALE: Single photon emission computed tomography (SPECT) using (123)I iodobenzamide (IBZM) as tracer substance has been shown to be a useful tool to visualize dopamine 2 (D2) receptor occupancy. OBJECTIVES: We investigated the striatal D2 receptor occupancy of zotepine which is referred to the class of atypical antipsychotic drugs. METHODS: (123)I IBZM and SPECT were used to visualize striatal dopamine 2 (D2) receptor occupancy in zotepine-treated schizophrenic patients. Two groups of schizophrenic patients receiving either 150 mg/day zotepine (n=6) or 300 mg/day (n=6) underwent examination. For the quantification of striatal D2 receptor occupancy, striatal IBZM binding in patients treated with antipsychotics was compared to untreated healthy controls (n=8) reported earlier. RESULTS: Zotepine led to a mean overall striatal D2 receptor occupancy of 73%. Patients with 150 mg daily showed a significantly lower occupancy (65.8%, SD=6.2) than patients with 300 mg/day (77.8%, SD=10.7; P<0.05). No clinically relevant extrapyramidal side effects occurred during treatment with zotepine. CONCLUSIONS: There was no correlation between the degree of striatal D2 receptor occupancy and clinical improvement.     

Striatal dopamine D2/3 receptor binding following dopamine depletion in subjects at Ultra High Risk for psychosis

Altered striatal dopaminergic neurotransmission is thought to be fundamental to schizophrenia. Increased presynaptic dopaminergic activity ([¹⁸F]–DOPA PET) may predate the onset of psychotic symptoms and correlates to clinical symptoms in subjects at Ultra High Risk (UHR) for developing psychosis. Postsynaptic dopaminergic neurotransmission has not been investigated yet in UHR patients. We hypothesized that synaptic dopamine concentration would be increased in UHR patients, and that synaptic dopamine concentration would be related to symptom severity. 14 UHR patients and 15 age and IQ matched controls completed an [¹²³I]–IBZM SPECT scan at baseline and again after dopamine depletion with alpha-methyl-para-tyrosine (AMPT). We measured changes in radiotracer binding potential, compared these between UHR patients and controls, and correlated these to symptom severity. The UHR group as a whole did not differ significantly from controls. AMPT significantly reduced symptom severity in the UHR group (p=0.014). Higher synaptic dopamine concentration predicted larger reduction of positive symptoms following depletion in the UHR group (p=0.01). In UHR patients, positive symptoms responded to dopamine depletion, comparable to observations in schizophrenia, suggesting a similar mechanism. Higher synaptic dopamine concentration was associated with more severe positive symptoms and a greater reduction of these symptoms following depletion.     

Dopamine transporter density and novelty seeking among alcoholics.

OBJECTIVE: The aim of this study was to investigate a putative association between the personality trait of novelty seeking (NS) and dopaminergic neuronal activity in the human brain. METHOD: We studied the striatal dopamine transporter (DAT) density of 30 (18 early and 12 late-onset) alcoholics and 26 healthy controls with beta-CIT ([123I]-2-beta-carbomethoxy-3-beta-(4-iodophenyl)-tropane) and SPET (Single Photon Emission Tomography); personality traits were assessed with the Tridimensional Personality Questionnaire (TPQ). RESULTS: DAT density correlated significantly with both NS (r = 0.46, p = 0.011) and age (r = -0.50, p = 0.005) in the alcoholics, generally. NS scores were higher in alcoholics with antisocial personality disorder (p = 0.004) than among other alcoholics. CONCLUSION: Among alcoholics, NS correlated positively with DAT density, which is in line with Cloninger's theory concerning personality and character.     

Effects of tiapride in tardive dyskinesia

Tiapride, a selective D2 dopaminergic receptor blocking agent from the substituted benzamide class, was evaluated in a blind video-controlled trial in 10 psychiatric patients with tardive dyskinesia. There was a significant decrease in dyskinesia with a parallel increase in parkinsonism. This relationship between two opposite effects on movement suggests a common pathophysiological basis lying on a reciprocal hyper- and hypoactivity of the dopaminergic striatal system. Nevertheless, other mechanisms may be involved, for the evolution of individual parkinsonian and dyskinesia scores is not necessarily opposite: the tiapride-induced parkinsonism was generally acceptable and in two cases, the dyskinesia scores were reduced without an increase in parkinsonism. Therefore, more dyskinetic patients have to be evaluated in long-term studies with tiapride, before this drug could be recommended in tardive dyskinesia, when dyskinetic movements become intolerable.     

Molindone compared to haloperidol in a guinea-pig model of tardive dyskinesia

Molindone was compared with haloperidol in animal models of tardive dyskinesia. Treatment with molindone for 14 days at 3, 6, 20 and 40 mg/kg, enhanced the stereotyped behavioral response induced by apomorphine and increased the number of D-2 dopamine receptors in the striatum (B_max) labelled by high affinity (K_d = 40 pmol) binding or [³H]spiroperidol in the guinea-pig. Molindone at 1 mg/kg, caused no behavioral supersensitivity or change in the binding of dopamine receptors. Chronic administration of haloperidol (0.1, 0.5 and 5.0 mg/kg) also increased both the behavioral response to apomorphine and the number of dopamine receptors. Haloperidol, at 0.02 and 0.004 mg/kg, had no effect. Molindone potentiated dopaminergic activity in animal models in a similar way to other neuroleptics, suggesting that its use may also result in tardive dyskinesia.     

Dopamine transporter and D2-receptor density in late-onset alcoholism

Rationale: Late onset type 1 alcoholism has been suggested to be associated with an underlying dopaminergic defect. Therefore, it is relevant to study both postsynaptic D₂-receptor and presynaptic dopamine transporter (DAT) densities among alcoholics. Objective: We investigated DAT densities, along with striatal and extrastriatal dopamine D₂-receptor densities, in nine non-violent late-onset male alcoholics, who had no major mental disorder nor antisocial personality disorder (ASPD), and nine healthy controls. Methods: [¹²³I]PE2I and [¹²³I]epidepride were used in SPECT imaging. Results: DAT occupancy ratios (striatum/cerebellum) were significantly lower among alcoholics than in controls. Extrastriatal D₂-receptor occupancy ratios (temporal pole/cerebellum) were not significantly different between the groups. Conclusions: Striatal presynaptic DAT densities are decreased among type 1 alcoholics, and this finding is not associated with recent alcohol abuse. Received: 22 March 1999 / Final version: 25 June 1999     

Decrease in alpha3*/alpha6* nicotinic receptors but not nicotine-evoked dopamine release in monkey brain after nigrostriatal damage

Nicotinic acetylcholine receptors (nAChRs) are decreased in the striata of patients with Parkinson's disease (PD) or in experimental models after nigrostriatal damage. Because presynaptic nAChRs on striatal dopamine terminals mediate dopamine release, receptor loss may contribute to behavioral deficits in PD. The present experiments were done to determine whether nAChR function is affected by nigrostriatal damage in nonhuman primates, because this model shares many features with PD. Initial characterization of nicotine-evoked [3H]dopamine release from monkey striatal synaptosomes revealed that release was calcium-dependent and inhibited by selective nAChR antagonists. It is noteworthy that a greater proportion (approximately 70%) of release was inhibited by the alpha3*/alpha6* antagonist alpha-conotoxinMII (alpha-CtxMII) compared with rodents. Monkeys were lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and [3H]dopamine release, dopamine transporter, and nAChRs were measured. As anticipated, lesioning decreased the transporter and alpha3*/alpha6* nAChRs in caudate and putamen. In contrast, alpha3*/alpha6* nAChR-evoked [3H]dopamine release was reduced in caudate but not putamen, demonstrating a dissociation between nAChR sites and function. A different pattern was observed in the mesolimbic dopamine system. Dopamine transporter levels in nucleus accumbens were not reduced after MPTP, as expected; however, there was a 50% decline in alpha3*/alpha6* nAChR sites with no decrease in alpha3*/alpha6* receptor-evoked dopamine release. No declines in alpha-CtxMII-resistant nAChR (alpha4*) binding or nicotine-evoked release were observed in any region. These results show a selective preservation of alpha3*/alpha6* nAChR-mediated function in the nigrostriatal and mesolimbic dopamine systems after nigrostriatal damage. Maintenance of function in putamen, a region with a selective loss of dopaminergic terminals, may be important in PD.     

Tamoxifen protects male mice nigrostriatal dopamine against methamphetamine-induced toxicity

The selective estrogen receptor modulator tamoxifen and estradiol were shown to protect nigrostriatal dopamine concentration loss by methamphetamine in female mice whereas male mice were protected only by tamoxifen. The present study examined the protective properties of tamoxifen in male mice on several nigrostriatal dopaminergic markers and body temperature. Intact male mice were administered 12.5 or 50 microg tamoxifen 24 h before methamphetamine treatment. Basal body temperatures of male mice remained unchanged by the tamoxifen treatment. Methamphetamine reduced striatal dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid concentrations, striatal and substantia nigra dopamine and vesicular monoamine transporter specific binding as well substantia nigra dopamine and vesicular monoamine transporter mRNA levels and increased striatal preproenkephalin mRNA levels. These methamphetamine effects were not altered by 12.5 microg tamoxifen except for increased striatal dopamine metabolites and turnover. Tamoxifen at 50 microg reduced the methamphetamine effect on striatal dopamine concentration, dopamine transporter specific binding and prevented the increase in preproenkephalin mRNA levels; in the substantia nigra tamoxifen prevented the decrease of dopamine transporter mRNA levels. The present results show a tamoxifen dose-dependent prevention of loss of various dopaminergic markers against methamphetamine-induced toxicity in male mice. Since this is the only known hormonal protection of male mice against methamphetamine toxicity, these findings provide important new information on specific parameters of nigrostriatal dopaminergic function preserved by tamoxifen.     

Stimulating effects of the antihistamine fexofenadine: testing the dopamine transporter hypothesis

Rationale First- and second-generation antihistamines are known to produce different degrees of sedation. However, a few studies have shown that the H1-antagonist fexofenadine produces mild stimulating effects. One hypothesis suggests that this is due to fexofenadine producing an increase in dopamine levels by blocking the dopamine transporter.Objective In this study, it was investigated whether a high dose of fexofenadine blocks the dopamine transporter in the striatum. In addition, the effect of fexofenadine on cognitive performance and motor impulsivity was investigated.Methods Sixteen healthy subjects were given either placebo or fexofenadine 360 mg. The binding potential of N-w-fluoropropyl-2β-carbomethoxy-3β-[4-iodophenyl] nortropane ([¹²³I]FP-CIT) was measured using single-photon emission computed tomography (SPECT). Cognitive performance was measured in 40 subjects (20 placebo, 20 fexofenadine) using a digit symbol substitution test (DSST) and a stop signal task. In addition, subjective and physiological effects of fexofenadine were observed.Results The SPECT data demonstrated that there was no difference in the binding potential of FP-CIT at the dopamine transporter in the striatum between the placebo- and fexofenadine-treated subjects. The behavioral results showed that fexofenadine improved performance on the DSST at T _max of the drug. Fexofenadine did not affect motor impulsivity, subjective experience, or physiological measures.Conclusion No evidence was provided to support the hypothesis that fexofenadine stimulates performance by blocking the dopamine transporter. The behavioral data suggest that a high dose of fexofenadine can stimulate performance in cognitive tasks.     

Extrapyramidal reactions and amine metabolites in cerebrospinal fluid during haloperidol and clozapine treatment of schizophrenic patients

8 male schizophrenic patients participated in a double-blind, cross over study of the extrapyramidal side-effects of haloperidol and clozapine (acute dystonia, Parkinsonism and tardive dyskinesia), together with their effect on homo-vanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF). Haloperidol (9 mg/day) caused Parkinsonism, reduced tardive dyskinesias and increased the HVA concentration in the CSF. Clozapine (225 mg/day) had no effect on the neurological phenomena but reduced HVA and 5-HIAA concentrations in the CSF. During the discontinuation phase following the administration of haloperidol, tardive dyskinesia occurred or was aggravated; this did not occur after administration of clozapine. Accordingly, it is suggested that clozapine does not induce dopaminergic hypersensibility and, therefore, will not induce tardive dyskinesias.Part of this work was presented at the 9th C.I.N.P. Congress, Paris, July 7–12, 1974.     

Striatal and temporal cortical D2/D3 receptor occupancy by olanzapine and sertindole in vivo: a [123I]epidepride single photon emission tomography (SPET) study

RATIONALE: Previous work suggests clozapine preferentially targets limbic cortical dopamine systems, which could help account for its lack of extrapyramidal side effects (EPS) and superior therapeutic efficacy. OBJECTIVES: To test the hypothesis that olanzapine, a novel atypical antipsychotic drug, occupies temporal cortical D2/D3 receptors to a greater extent than striatal D2/D3 receptors in vivo. METHODS: Nine schizophrenic patients taking either olanzapine [(n=5; mean (SD) age: 32.5 (6.5) years; daily dose: 18.3 (2.6) mg] or sertindole [(n=4; mean (SD) age: 30.3 (7.4) years; daily dose: 16 (5.6) mg] were studied with [123I]epidepride ((S)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5-iodo-2,3-dimethoxybenz amide) and single photon emission tomography (SPET). An estimate of [123I]epidepride 'specific binding' to D2/D3 receptors was obtained in patients and age-matched healthy volunteers. A summary measure was generated representing striatal and temporal cortical relative %D2/D3 receptor occupancy by antipsychotic drugs. Occupancy data were compared with previously studied groups of patients receiving typical antipsychotic drugs (n=12) and clozapine (n=10). RESULTS: Mean striatal and temporal cortical %D2/D3 receptor occupancy in olanzapine-treated patients was 41.3% (SD 17.9) and 82.8% (SD 4.2), respectively. Unexpectedly low levels of striatal relative %D2/D3 receptor occupancy were seen in two patients with typical antipsychotic-drug-induced movement disorder prior to switching to olanzapine. In the temporal cortex, mean D2/D3 dopamine receptor occupancy levels above 80% were seen for all antipsychotic drugs studied. CONCLUSIONS: The atypical antipsychotic drugs olanzapine and sertindole, in common with clozapine, demonstrate higher occupancy of temporal cortical than striatal D2/D3 dopamine receptors in vivo at clinically useful doses. This could help mediate their atypical clinical profile of therapeutic efficacy with few extrapyramidal side effects. Limbic selective blockade of D2/D3 dopamine receptors could be a common action of atypical antipsychotic drugs.