In vivo 123I IBZM SPECT imaging of striatal dopamine-2 receptor occupancy in schizophrenic patients treated with olanzapine in comparison to clozapine and haloperidol

Informing individualized multi-scale neural signatures of clozapine response in patients with treatment-refractory schizophrenia

Clozapine is currently the only antipsychotic with demonstrated efficacy in treatment-refractory schizophrenia (TRS). However, response to clozapine differs widely between TRS patients, and there are no available clinical or neural predictive indicators that could be used to increase or accelerate the use of clozapine in patients who stand to benefit. Furthermore, it remains unclear how the neuropharmacology of clozapine contributes to its therapeutic effects. Identifying the mechanisms underlying clozapine's therapeutic effects across domains of symptomatology could be crucial for development of new optimized therapies for TRS. Here, we present results from a prospective neuroimaging study that quantitatively related heterogeneous patterns of clinical clozapine response to neural functional connectivity at baseline. We show that we can reliably capture specific dimensions of clozapine clinical response by quantifying the full variation across item-level clinical scales, and that these dimensions can be mapped to neural features that are sensitive to clozapine-induced symptom change. Thus, these features may act as "failure modes" that can provide an early indication of treatment (non-)responsiveness. Lastly, we related the response-relevant neural maps to spatial expression profiles of genes coding for receptors implicated in clozapine's pharmacology, demonstrating that distinct dimensions of clozapine symptom-informed neural features may be associated with specific receptor targets. Collectively, this study informs prognostic neuro-behavioral measures for clozapine as a more optimal treatment for selected patients with TRS. We provide support for the identification of neuro-behavioral targets linked to pharmacological efficacy that can be further developed to inform optimal early treatment decisions in schizophrenia.

Clozapine's multiple cellular mechanisms: What do we know after more than fifty years? A systematic review and critical assessment of translational mechanisms relevant for innovative strategies in treatment-resistant schizophrenia

Almost fifty years after its first introduction into clinical care, clozapine remains the only evidence-based pharmacological option for treatment-resistant schizophrenia (TRS), which affects approximately 30% of patients with schizophrenia. Despite the long-time experience with clozapine, the specific mechanism of action (MOA) responsible for its superior efficacy among antipsychotics is still elusive, both at the receptor and intracellular signaling level. This systematic review is aimed at critically assessing the role and specific relevance of clozapine's multimodal actions, dissecting those mechanisms that under a translational perspective could shed light on molecular targets worth to be considered for further innovative antipsychotic development. In vivo and in vitro preclinical findings, supported by innovative techniques and methods, together with pharmacogenomic and in vivo functional studies, point to multiple and possibly overlapping MOAs. To better explore this crucial issue, the specific affinity for 5-HT₂R, D1R, α_2c, and muscarinic receptors, the relatively low occupancy at dopamine D2R, the interaction with receptor dimers, as well as the potential confounder effects resulting in biased ligand action, and lastly, the role of the moiety responsible for lipophilic and alkaline features of clozapine are highlighted. Finally, the role of transcription and protein changes at the synaptic level, and the possibility that clozapine can directly impact synaptic architecture are addressed. Although clozapine's exact MOAs that contribute to its unique efficacy and some of its severe adverse effects have not been fully understood, relevant information can be gleaned from recent mechanistic understandings that may help design much needed additional therapeutic strategies for TRS.

Dopamine transporter (DAT) imaging in Parkinson's disease and related disorders

This review gives an insight into the beginnings of dopamine transporter (DAT) imaging in the early 1990s, focussing on single photon emission tomography (SPECT). The development of the method and its consolidation as a now widely used clinical tool is described. The role of DAT-SPECT in the diagnosis and differential diagnosis of PD, atypical parkinsonian syndromes and several other different neurological disorders is reviewed. Finally the clinical research using DAT-SPECT as a biomarker for the progression of PD, for the detection of a preclinical dopaminergic lesion and its correlation with neuropathological findings is outlined.

Impact cérébral structurel et fonctionnel de la Clozapine chez les patients souffrant de schizophrénie : revue systématique des études longitudinales en neuroimagerie

OBJECTIF

L'objectif de cette revue est d'identifier les corrélats anatomo-fonctionnels cérébraux lors d'un traitement par clozapine (CLZ) ainsi que les marqueurs anatomo-fonctionnels prédictifs de la réponse à la CLZ.

MÉTHODES

Nous avons réalisé une revue systématique de la littérature avec les bases de données MEDLINE et Web of Science afin d'identifier et d'examiner toutes les études longitudinales en neuroimagerie investiguant l'impact cérébral de la CLZ.

RÉSULTATS

30 études ont été incluses et analysées. La CLZ induit une diminution du volume et de la perfusion dans les noyaux gris centraux chez les patients répondeurs. Un plus grand volume de substance grise et perfusion dans ces structures avant l'instauration de la CLZ étaient associés à une meilleure réponse au traitement. La diminution de volume et de perfusion au niveau du cortex préfrontal (CPF) est observée malgré l'instauration de CLZ mais de façon moins importante chez les patients sous CLZ que chez les patients sous antipsychotiques typiques. Un plus grand volume au niveau du CPF avant l'instauration de la CLZ est associé à une meilleure réponse clinique dans la majorité des études. Enfin, la CLZ semble induire une réduction des altérations au niveau de la substance blanche.

CONCLUSION

Les corrélats anatomo-fonctionnels de la CLZ différent de ceux des autres antipsychotiques avec une action spécifique de la CLZ au niveau des ganglions de la base et du CPF pouvant participer à sa supériorité en termes de réponse clinique. Plusieurs données cliniques et d'imagerie conduisent à l'hypothèse d'un meilleur pronostic associé à une instauration plus rapide de la CLZ.

Resting-state functional connectivity in treatment response and resistance in schizophrenia: A systematic review

BACKGROUND

Treatment-resistant schizophrenia (TRS) and treatment-responsive schizophrenia may exhibit distinct pathophysiology. Several functional magnetic resonance imaging (fMRI) studies have used resting-state functional connectivity analyses (rs-FC) in TRS patients to identify markers of treatment resistance. However, to date, existing findings have not been systematically evaluated.

METHODS

A systematic literature search using Embase, MEDLINE, PsycINFO, ProQuest, PUBMED, and Scopus was performed. The query sought fMRI articles investigating rs-FC in treatment response or resistance in patients with schizophrenia. Only studies that examined treatment response, operationalized as the explicit categorization of patients by their response to antipsychotic medication, were considered eligible. Pairwise comparisons between patient groups and controls were extracted from each study.

RESULTS

The search query identified 159 records. Ten studies met inclusion criteria. Five studies examined not TRS (NTRS), and 8 studies examined TRS. Differences in rs-FC analysis methodology precluded direct comparisons between studies. However, disruptions in areas involved in visual and auditory information processing were implicated in both patients with TRS and NTRS. Changes in connectivity with sensorimotor network areas tended to appear in the context of TRS but not NTRS. Moreover, there was some indication that this connectivity could be affected by clozapine.

CONCLUSIONS

Functional connectivity may provide clinically meaningful biomarkers of treatment response and resistance in schizophrenia. Studies generally identified similar areas of disruption, though methodological differences largely precluded direct comparison between disruption effects. Implementing data sharing as standard practice will allow future reviews and meta-analyses to identify rs-FC correlates of TRS.

Acute anxiety disorder, major depressive disorder, bipolar disorder and schizophrenia are related to different patterns of nigrostriatal and mesolimbic dopamine dysfunction

Dopamine (DA) receptor and transporter dysfunctions play a major role in the pathophysiology of neuropsychiatric diseases including anxiety disorder (AD), major depressive disorder (MDD), bipolar disorder (BD) in the manic (BDman) or depressive (BDdep) state and schizophrenia (SZ). We performed a PUBMED search, which provided a total of 239 in vivo imaging studies with either positron emission tomography (PET) or single-proton emission computed tomography (SPECT). In these studies, DA transporter binding, D1 receptor (R) binding, D2R binding, DA synthesis and/or DA release in patients with the primary diagnosis of acute AD (n=310), MDD (n=754), BDman (n=15), BDdep (n=49) or SZ (n=1532) were compared to healthy individuals. A retrospective analysis revealed that AD, MDD, BDman, BDdep and SZ differed as to affected brain region(s), affected synaptic constituent(s) and extent as well as direction of dysfunction in terms of either sensitization or desensitization of transporter and/or receptor binding sites. In contrast to AD and SZ, in MDD, BDman and BDdep, neostriatal DA function was normal, whereas MDD, BDman, and BDdep were characterized by the increased availability of prefrontal and frontal DA. In contrast to AD, MDD, BDman and BDdep, DA function in SZ was impaired throughout the nigrostriatal and mesolimbocortical system with an increased availability of DA in the striatothalamocortical and a decreased availability in the mesolimbocortical pathway.

Psychomotor symptoms of schizophrenia map on the cerebral motor circuit

Schizophrenia is a devastating disorder thought to result mainly from cerebral pathology. Neuroimaging studies have provided a wealth of findings of brain dysfunction in schizophrenia. However, we are still far from understanding how particular symptoms can result from aberrant brain function. In this context, the high prevalence of motor symptoms in schizophrenia such as catatonia, neurological soft signs, parkinsonism, and abnormal involuntary movements is of particular interest. Here, the neuroimaging correlates of these motor symptoms are reviewed. For all investigated motor symptoms, neural correlates were found within the cerebral motor system. However, only a limited set of results exists for hypokinesia and neurological soft signs, while catatonia, abnormal involuntary movements and parkinsonian signs still remain understudied with neuroimaging methods. Soft signs have been associated with altered brain structure and function in cortical premotor and motor areas as well as cerebellum and thalamus. Hypokinesia is suggested to result from insufficient interaction of thalamocortical loops within the motor system. Future studies are needed to address the neural correlates of motor abnormalities in prodromal states, changes during the course of the illness, and the specific pathophysiology of catatonia, dyskinesia and parkinsonism in schizophrenia.

Neuroimaging findings in treatment-resistant schizophrenia: A systematic review: Lack of neuroimaging correlates of treatment-resistant schizophrenia

BACKGROUND

Recent developments in neuroimaging have advanced the understanding of biological mechanisms underlying schizophrenia. However, neuroimaging correlates of treatment-resistant schizophrenia (TRS) and superior effects of clozapine on TRS remain unclear.

METHODS

Systematic search was performed to identify neuroimaging characteristics unique to TRS and ultra-resistant schizophrenia (i.e. clozapine-resistant [URS]), and clozapine's efficacy in TRS using Embase, Medline, and PsychInfo. Search terms included (schizophreni*) and (resistan* OR refractory OR clozapine) and (ASL OR CT OR DTI OR FMRI OR MRI OR MRS OR NIRS OR PET OR SPECT).

RESULTS

25 neuroimaging studies have investigated TRS and effects of clozapine. Only 5 studies have compared TRS and non-TRS, collectively providing no replicated neuroimaging finding specific to TRS. Studies comparing TRS and healthy controls suggest that hypometabolism in the prefrontal cortex, hypermetabolism in the basal ganglia, and structural anomalies in the corpus callosum contribute to TRS. Clozapine may increase prefrontal hypoactivation in TRS although this was not related to clinical improvement; in contrast, evidence has suggested a link between clozapine efficacy and decreased metabolism in the basal ganglia and thalamus.

CONCLUSION

Existing literature does not elucidate neuroimaging correlates specific to TRS or URS, which, if present, might also shed light on clozapine's efficacy in TRS. This said, leads from other lines of investigation, including the glutamatergic system can prove useful in guiding future neuroimaging studies focused on, in particular, the frontocortical-basal ganglia-thalamic circuits. Critical to the success of this work will be precise subtyping of study subjects based on treatment response/nonresponse and the use of multimodal neuroimaging.

Receptor targets for antidepressant therapy in bipolar disorder: an overview

The treatment of bipolar depression is one of the most challenging issues in contemporary psychiatry. Currently only quetiapine and the olanzapine-fluoxetine combination are officially approved by the FDA against this condition. The neurobiology of bipolar depression and the possible targets of bipolar antidepressant therapy remain relatively elusive. We performed a complete and systematic review to identify agents with definite positive or negative results concerning efficacy followed by a second systematic review to identify the pharmacodynamic properties of these agents. The comparison of properties suggests that the stronger predictors for antidepressant efficacy in bipolar depression were norepinephrine alpha-1, dopamine D1 and histamine antagonism, followed by 5-HT2A, muscarinic and dopamine D2 and D3 antagonism and eventually by norepinephrine reuptake inhibition and 5HT-1A agonism. Serotonin reuptake which constitutes the cornerstone in unipolar depression treatment does not seem to play a significant role for bipolar depression. Our exhaustive review is compatible with a complex model with multiple levels of interaction between the major neurotransmitter systems without a single target being either necessary or sufficient to elicit the antidepressant effect in bipolar depression.

The role of striatal dopamine D2 receptors in the occurrence of extrapyramidal side effects: iodine-123-iodobenzamide single photon emission computed tomography study

Levels above 75% of striatal dopamine 2 receptor occupancy (D2RO) have been associated with extrapyramidal symptoms (EPS). The aim of the present study is to investigate the relationship between D2RO and EPS in a sample of psychotic patients in current treatment with both typical and atypical antipsychotics. Brain iodine-123-iodobenzamide single photon emission computed tomography ((123)I-IBZM SPECT) was performed in 81 patients taking stable doses of haloperidol, risperidone, olanzapine, quetiapine, clozapine or ziprasidone. First, the degree of D2RO and Positive and Negative Syndrome Scale (PANSS) scores was compared between the group of patients who presented EPS and the group free of EPS. Afterwards, these variables were compared among the different antipsychotic medications. The group with EPS presented means of D2RO significantly higher than the group free of EPS. Significant differences in D2RO were found in clozapine, quetiapine and ziprasidone groups compared with the haloperidol group. No differences were observed between either olanzapine or risperidone and haloperidol. No quetiapine- or clozapine-treated patients developed EPS. Haloperidol and risperidone demonstrated a relationship between striatal D2RO and EPS. The findings suggest that higher D2RO is related to appearance of EPS. Occupancy in the group with EPS was in agreement with previous studies that suggested a high degree of D2RO is necessary for the occurrence of EPS.

Reboxetine enhances the olanzapine-induced antipsychotic-like effect, cortical dopamine outflow and NMDA receptor-mediated transmission

Preclinical data have shown that addition of the selective norepinephrine transporter (NET) inhibitor reboxetine increases the antipsychotic-like effect of the D(2/3) antagonist raclopride and, in parallel, enhances cortical dopamine output. Subsequent clinical results suggested that adding reboxetine to stable treatments with various antipsychotic drugs (APDs) may improve positive, negative and depressive symptoms in schizophrenia. In this study, we investigated in rats the effects of adding reboxetine to the second-generation APD olanzapine on: (i) antipsychotic efficacy, using the conditioned avoidance response (CAR) test, (ii) extrapyramidal side effect (EPS) liability, using a catalepsy test, (iii) dopamine efflux in the medial prefrontal cortex and the nucleus accumbens, using in vivo microdialysis in freely moving animals and (iv) cortical N-methyl-D-aspartate (NMDA) receptor-mediated transmission, using intracellular electrophysiological recording in vitro. Reboxetine (6 mg/kg) enhanced the suppression of CAR induced by a suboptimal dose (1.25 mg/kg), but not an optimal (2.5 mg/kg) dose of olanzapine without any concomitant catalepsy. Addition of reboxetine to the low dose of olanzapine also markedly increased cortical dopamine outflow and facilitated prefrontal NMDA receptor-mediated transmission. Our data suggest that adjunctive treatment with a NET inhibitor may enhance the therapeutic effect of low-dose olanzapine in schizophrenia without increasing EPS liability and add an antidepressant action, thus in principle allowing for a dose reduction of olanzapine with a concomitant reduction of dose-related side effects, such as EPS and weight gain.

Basolateral amygdala involvement in memory reconsolidation processes that facilitate drug context-induced cocaine seeking

Understanding the neurobiological underpinnings of putative memory stabilization processes that maintain context-response-cocaine associations in long-term memory and underlie contextual control over addictive behavior is of great interest from an addiction treatment perspective. Using an instrumental animal model of contextual drug relapse we show that the protein synthesis inhibitor anisomycin, administered into the basolateral amygdala (BLA) immediately after limited (15- or 60-min) re-exposure to a previously cocaine-paired context, subsequently disrupted the ability of the previously cocaine-paired context to reinstate extinguished cocaine-seeking behavior relative to vehicle. Consistent with a BLA-mediated memory reconsolidation deficit, a similar impairment in cocaine-seeking behavior was not observed in (i) 'no-reactivation' control groups that received anisomycin into the BLA after (re)exposure to either a novel unpaired or an extinction-paired context or in (ii) a neuroanatomical control group that received anisomycin into the posterior caudate-putamen, dorsally adjacent to the BLA, after re-exposure to the cocaine-paired context. Furthermore, anisomycin administered into the BLA after brief (5-min) or extensive (120-min) re-exposure to the cocaine-paired context (which was sufficient to extinguish cocaine-seeking behavior in a vehicle control group) also failed to alter responding. Together, these findings suggest that re-exposure to a cocaine-paired context in the absence of cocaine reinforcement is sufficient to trigger memory reconsolidation processes that support future drug-seeking behavior. The presence and duration of drug-related memory reactivation critically influences, and anisomycin-sensitive mechanisms in the BLA selectively control, this phenomenon. These findings support the feasibility of novel pharmacotherapeutic approaches that selectively inhibit the reconsolidation of cocaine-related memories in order to prevent drug relapse.

Within-subject comparison of striatal D2 receptor occupancy measurements using [123I]IBZM SPECT and [11C]Raclopride PET

Antipsychotic-induced D2 receptor occupancy values tend to be lower when measured with [(123)I]IBZM SPECT than with [(11)C]Raclopride PET. To clarify this issue, D2 receptor occupancy was measured in the same subjects using both techniques. Twenty patients with schizophrenia on monotherapy with risperidone (n=7; 3-9 mg/d), olanzapine (n=5; 5-20 mg/d) or clozapine (n=8; 150-450 mg/d) at stable doses, and ten healthy volunteers (HV) underwent both a [(123)I]IBZM SPECT and a [(11)C]Raclopride PET examinations in random order on different days within a week. Patients with schizophrenia were scanned at a fixed interval after last dose administration. Quantification of receptor availability was performed using the most conventional methods from the literature: the tissue ratio derived specific uptake ratios (SUR) were used for SPECT, and simplified reference tissue model (SRTM) derived binding potentials (BP(ND)) for PET. Analysis was performed using both occipital cortex and cerebellum as reference regions for both modalities. Striatal D2 receptor occupancy was measured as the percentage reduction of [(123)I]IBZM SUR or [(11)C]Raclopride BP(ND) compared to the population average measured in HV using the same modality. Occupancy values measured by SPECT were lower than those measured with PET, by 12.4% and 13.8% when occipital cortex and cerebellum were used as reference regions. This difference should be taken in consideration when interpreting reported antipsychotic striatal D2 receptor occupancy values from the literature.

Clozapine versus typical neuroleptic medication for schizophrenia

BACKGROUND

Long-term drug treatment of schizophrenia with typical antipsychotics has limitations: 25 to 33% of patients have illnesses that are treatment-resistant. Clozapine is an antipsychotic drug, which is claimed to have superior efficacy and to cause fewer motor adverse effects than typical drugs for people with treatment-resistant illnesses. Clozapine carries a significant risk of serious blood disorders, which necessitates mandatory weekly blood monitoring at least during the first months of treatment.

OBJECTIVES

To evaluate the effects of clozapine compared with typical antipsychotic drugs in people with schizophrenia.

SEARCH STRATEGY

For the current update of this review (March 2006) we searched the Cochrane Schizophrenia Group Trials Register.

SELECTION CRITERIA

All relevant randomised clinical trials (RCTs).

DATA COLLECTION AND ANALYSIS

We extracted data independently. For dichotomous data we calculated relative risks (RR) and their 95% confidence intervals (CI) on an intention-to-treat basis, based on a fixed-effect model. We calculated numbers needed to treat/harm (NNT/NNH) where appropriate. For continuous data, we calculated weighted mean differences (WMD) again based on a fixed-effect model.

MAIN RESULTS

We have included 42 trials (3950 participants) in this review. Twenty-eight of the included studies are less than 13 weeks in duration, and, overall, trials were at significant risk of bias. We found no significant difference in the effects of clozapine and typical neuroleptic drugs for broad outcomes such as mortality, ability to work or suitability for discharge at the end of the study. Clinical improvements were seen more frequently in those taking clozapine (n=1119, 14 RCTs, RR 0.72 CI 0.7 to 0.8, NNT 6 CI 5 to 8). Also, participants given clozapine had fewer relapses than those on typical antipsychotic drugs (n=1303, RR 0.62 CI 0.5 to 0.8, NNT 21 CI 15 to 49). BPRS scores showed a greater reduction of symptoms in clozapine-treated patients, (n=1145, 16 RCTs, WMD -4.22 CI -5.4 to -3.1), although the data were heterogeneous (Chi(2) 0.0001, I(2) 66%). Short-term data from the SANS negative symptom scores favoured clozapine (n=196, 5 RCTs, WMD -5.92 CI -7.8 to -4.1). We found clozapine to be more acceptable in long-term treatment than conventional antipsychotic drugs (n=982, 16 RCTs, RR 0.60 CI 0.5 to 0.7, NNT 15 CI 12 to 20). Blood problems occurred more frequently in participants receiving clozapine (3.2%) compared with those given typical antipsychotics (0%) (n=1031, 13 RCTs, RR 7.09 CI 2.0 to 25.6). Clozapine participants experienced more drowsiness, hypersalivation, or temperature increase, than those given conventional neuroleptics. However, clozapine patients experienced fewer motor adverse effects (n=1433, 18 RCTs, RR 0.58 CI 0.5 to 0.7, NNT 5 CI 4 to 6).The clinical effects of clozapine were more pronounced in participants resistant to typical neuroleptics in terms of clinical improvement (n=370, 4 RCTs, RR 0.71 CI 0.6 to 0.8, NNT 4 CI 3 to 6) and symptom reduction. Thirty-four per cent of treatment-resistant participants had a clinical improvement with clozapine treatment.

AUTHORS' CONCLUSIONS

Clozapine may be more effective in reducing symptoms of schizophrenia, producing clinically meaningful improvements and postponing relapse, than typical antipsychotic drugs - but data are weak and prone to bias. Participants were more satisfied with clozapine treatment than with typical neuroleptic treatment. The clinical effect of clozapine, however, is, at least in the short term, not reflected in measures of global functioning such as ability to leave the hospital and maintain an occupation. The short-term benefits of clozapine have to be weighed against the risk of adverse effects. Within the context of trials, the potentially dangerous white blood cell decline seems to be more frequent in children and adolescents and in the elderly than in young adults or people of middle-age.The existing trials have largely neglected to assess the views of participants and their families on clozapine. More community-based long-term randomised trials are needed to evaluate the efficacy of clozapine on global and social functioning as trials in special groups such as people with learning disabilities.

Pharmacokinetics and time-course of D(2) receptor occupancy induced by atypical antipsychotics in stabilized schizophrenic patients

The (123)I-IBZM SPECT measured D(2) receptor occupancy (D(2)RO) in chronically dosed, stabilized schizophrenic patients and its relationship with antipsychotic (AP) pharmacokinetics (PK) over time is still unclear. The aims of this study were: 1) To define the relationship between striatal D(2) receptor occupancy (D( 2)RO) and plasma concentration (C(P)) in stabilized schizophrenic patients on clinically relevant doses using (123)I-IBZM SPECT; 2) To investigate the time course of AP-induced D(2)RO and corresponding C(P). Forty-six schizophrenic patients on their clinically required doses of risperidone, olanzapine, clozapine or quetiapine were included. D( 2)RO and C(P) were measured over time following a sparse-sampling experimental design, and individual PK and D(2)RO-time profiles were estimated using a population approach. Observed striatal D(2)RO and C(P) ranges were 28-75% and 9.4-60.5 ng/mL for risperidone, 22-84% and 8.6-89.5 ng/mL for olanzapine, 5-53% and 41.6-818.2 ng/mL for clozapine and 0-64% and 37.9-719.6 ng/mL for quetiapine. A PK-D(2)RO relationship was found for the four APs. D(2)RO pattern over time was stable for risperidone, olanzapine and clozapine but fluctuating for quetiapine. Stabilized schizophrenic patients show a wide range of both D(2)RO and C(P) at clinically effective doses of the four AP, suggesting that clinical response to these AP may be maintained with D(2)RO below 65%. D(2)RO patterns over time differ between AP. These results should be considered for accurate interpretation of D(2)RO measurements, proper design of studies and optimization of drug regimens for patients on AP treatment.

Challenge by the murine brain: multi-pinhole SPECT of 123I-labelled pharmaceuticals

This protocol presents an improved method for SPECT imaging based on multi-pinhole techniques, applied to the visualisation of neurotracers in small animal models. Three types of collimators with 6-pinhole apertures adapted to special requirements for the imaging of the brain of mice and rats and to full body imaging in mice are employed in the experiments. A conventional triple-headed TRIAD/Trionix SPECT system was upgraded with pyramidal supports and shieldings onto the multi-pinhole collimators were installed. The system was employed for the assessment of the uptake of [123I]FP-CIT and [123I]IBZM, well known tracers of dopamine transport and dopamine D2/D3 receptors, respectively. Requirements regarding the applied radioactivity are reported, as well as further conditions determining the effectiveness of the detection of the uptake of [123I]FP-CIT and [123I]IBZM. The measurements in mice required only 20-25% of the activity described in previous studies. Dynamic measurements are presented, with a time resolution as high as 10 min in the brain of rats. Due to the lower signal intensity obtained for mice, the time resolution was 42min for [123I]FP-CIT, with a ratio ROI/background of 5.4, and 17 min for [123I]IBZM, with the ratio ROI/background of 4.5 (1.6-7.4).

Striatal D(2) receptor occupancy in bipolar patients treated with olanzapine

We explored the relationship between striatal dopamine-2 (D(2)) receptor occupancy and extra-pyramidal symptoms (EPS) in bipolar patients receiving olanzapine. Seventeen patients with a DSM-IV diagnosis of bipolar disorder were treated with 5-45 mg/day olanzapine for at least 14 days. After that period, D(2) receptor occupancy was determined using Iodobenzamide (IBZM) and SPECT. EPS were assessed by the Simpson-Angus Scale (SAS) and Barnes-Akathisia Scale (BAS). We found a dose-dependent increase in occupancy: 5 mg led to 28-50%, 10 mg to 40-68%, 15 mg to 69%, 20 mg to 57-66%, 30 mg to 66% and 45 mg to 80% D(2) receptor occupancy; and a significant correlation between plasma levels and occupancy (R(2)=.55, P=.001). Similar to schizophrenic patients, bipolar patients did not exhibit EPS at D(2) occupancy levels of 28 to 80%. Although we did not find an increased vulnerability for acute EPS in bipolar patients receiving olanzapine at clinical relevant doses, this needs to be replicated with larger sample sizes.

EPS profiles: the atypical antipsychotics are not all the same

Within the first few years after chlorpromazine began to be used to treat psychosis, it was observed that it could cause many kinds of neurologic reactions that resembled those seen in idiopathic Parkinson's disease. These reactions were termed "extrapyramidal side effects" (EPS) because of their resemblance to the signs of Parkinson's disease, which were associated with degeneration of the dopamine nerve tracks located in the extrapyramidal region of the central nervous system. Eventually this association of dopamine loss, antipsychotics, and parkinsonism became a central part of the dopamine hypothesis of schizophrenia. Unfortunately, this association was also used to support the hypothesis that EPS were absolutely necessary for antipsychotic efficacy--hence the term "neuroleptic" rather than "antipsychotic." This theory, now discredited, was used to justify the practice of inducing EPS as a means to gauge whether an antipsychotic would be effective. The demonstration that clozapine, an antipsychotic virtually devoid of EPS, has better efficacy for psychosis than any other "neuroleptic" disproved the theory that EPS were fundamentally linked to efficacy. Because the idea of a relationship between EPS and efficacy was so ingrained in clinical practice, clozapine was called "atypical." Our understanding of the relationship between EPS and antipsychotic response has come full circle. With the introduction of clozapine and other newer antipsychotics, it has become clear that EPS are harmful and serve no beneficial purpose. The availability of newer antipsychotics with a lower EPS burden means that, at least in theory, it is now possible to treat psychosis without EPS in the vast majority of patients. In practice, however, EPS remain a significant problem even in the era of atypical or second generation antipsychotics (SGAs). One limitation is that the concept of "atypicality," when used to denote antipsychotic efficacy without EPS, is a relative not an absolute concept. Because all of the post-clozapine SGAs still affect the dopamine D2 receptor, it may be more accurate to say these medications have lower EPS liabilities that the earlier "neuroleptic" antipsychotics; i.e., relatively fewer patients will get EPS at therapeutic doses of one of the newer medications and, when EPS do occur, they tend to be less severe. Nonetheless, reduced EPS are not the same as no EPS, and most of the newer antipsychotics can still cause EPS in some patients. The incidence of EPS differs among the SGAs, with risperidone associated with the most and clozapine and quetiapine with the fewest EPS. The likelihood of developing EPS with a first-line SGA depends not only on the specific agent, but also on the rapidity of dose escalation, the target dose, and the patient's intrinsic vulnerability to EPS. Even with the SGAs, clinicians should not be lulled into believing EPS cannot happen, but need to be able to recognize and manage both overt and subtle manifestations of EPS. This review discusses differences among the SGAs in EPS liability, relationships between dosing and type of EPS, and situations in which differences in EPS liability among the SGAs are clinically relevant.

Serotonin transporter occupancy induced by paroxetine in patients with major depression disorder: a 123I-ADAM SPECT study

RATIONALE

To assess the paroxetine-induced serotonin transporter (SERT) occupancy (SERTocc) using in vivo (123)I-ADAM SPECT.

OBJECTIVES

(123)I-ADAM SPECT was used to investigate the SERTocc induced by paroxetine in major depression disorder (MDD) patients, to compare the SERT availability in drug-free MDD patients and healthy volunteers, and to study the relationship between paroxetine plasma concentrations (Cp) and SERTocc.

MATERIALS AND METHODS

Measures of SERT availability by means of (123)I-ADAM SPECT were obtained in ten MDD patients before and after 4- to 6-week treatment with paroxetine 20 mg/day. (123)I-ADAM SPECT measures of SERT availability from a group of ten previously studied age-matched healthy volunteers were used for comparison. The relationship between percentages of SERTocc and paroxetine Cp was studied using an E (max) model.

RESULTS

Mean SERTocc values were 66.4 +/- 9.5% in midbrain, 63.0 +/- 9.6% in thalamus, and 61.3 +/- 10.9% in striatum. No significant differences in SERTocc were found among these three regions. No significant differences in mean SERT availability were found in any region between drug-free MDD patients (midbrain = 1.14 +/- 0.15; thalamus = 0.85 +/- 0.13; striatum = 0.70 +/- 0.07) and healthy volunteers (midbrain = 1.19 +/- 0.22; thalamus = 0.96 +/- 0.14; striatum = 0.67 +/- 0.15). The E (max) model returned a SERTocc(max) = 70.5% and a Cp(50) = 2.7 ng/ml.

CONCLUSIONS

Using (123)I-ADAM SPECT, treatment with paroxetine 20 mg/day leads to more than 60% SERTocc on average in cerebral regions with known high SERT density. Data from this study do not support the existence of SERT availability differences between drug-free MDD patients and healthy volunteers. Finally, the E (max) model is suitable for the study of paroxetine Cp relationship to (123)I-ADAM SPECT-measured SERTocc. This approach may be useful for pharmacokinetic-pharmacodynamic relationships in drug development.

Dopamine D2 receptor occupancy by risperidone: implications for the timing and magnitude of clinical response

The objective of the study is to investigate whether dopamine D2 receptor occupancy by risperidone and plasma levels over time can account for therapeutic efficacy and the latency period to response. Thirty-eight examinations with (123)I-IBZM single photon emission computed tomography were performed on 22 patients with schizophrenia, at diagnosis, 48 h after starting risperidone treatment and at a stable dose. Risperidone plasma levels were determined and psychopathologic evaluations (Brief Psychiatric Rating Scale, Positive and Negative Syndrome Scale) were carried out. No differences in the striatal/occipital (S/O) ratio or plasma levels were found between examinations at the 48-h time point and when a stable dose level had been established, so these parameters could not account for the latency period required for clinical response. D2 receptor occupancy at 48 h correlated positively with clinical improvement after 2 weeks of treatment. Therefore, if these results are confirmed, D2 receptor occupancy at the beginning of treatment with risperidone may be a predictor of subsequent clinical response.

Occupancy of striatal and extrastriatal dopamine D2/D3 receptors by olanzapine and haloperidol

There have been conflicting reports as to whether olanzapine produces lower occupancy of striatal dopamine D(2)/D(3) receptor than typical antipsychotic drugs and preferential occupancy of extrastriatal dopamine D(2)/D(3) receptors. We performed [(18)F] fallypride PET studies in six schizophrenic subjects treated with olanzapine and six schizophrenic subjects treated with haloperidol to examine the occupancy of striatal and extrastriatal dopamine receptors by these antipsychotic drugs. [(18)F] setoperone PET studies were performed in seven olanzapine-treated subjects to determine 5-HT(2A) receptor occupancy. Occupancy of dopamine D(2)/D(3) receptors by olanzapine was not significantly different from that seen with haloperidol in the putamen, ventral striatum, medial thalamus, amygdala, or temporal cortex, that is, 67.5-78.2% occupancy; olanzapine produced no preferential occupancy of dopamine D(2)/D(3) receptors in the ventral striatum, medial thalamus, amygdala, or temporal cortex. There was, however, significantly lower occupancy of substantia nigra/VTA dopamine D(2)/D(3) receptors in olanzapine-treated compared to haloperidol-treated subjects, that is, 40.2 vs 59.3% (p=0.0014, corrected for multiple comparisons); in olanzapine-treated subjects, the substantia nigra/VTA was the only region with significantly lower dopamine D(2)/D(3) receptor occupancy than the putamen, that is, 40.2 vs 69.2% (p<0.001, corrected for multiple comparison). Occupancy of 5-HT(2A) receptors was 85-93% in the olanzapine- treated subjects. The results of this study demonstrated that olanzapine does not produce preferential occupancy of extrastriatal dopamine D(2)/D(3) receptors but does spare substantia nigra/VTA receptors. Sparing of substantia nigra/VTA dopamine D(2)/D(3) receptor occupancy may contribute to the low incidence of extrapyramidal side effects in olanzapine-treated patients.

Predictors and markers of clozapine response

RATIONALE

With other atypical antipsychotics now available, having predictors of clozapine response would be of considerable value, offering clinicians guidance in their decision as to when, and if, a trial of clozapine is warranted.

OBJECTIVES

The aim was to review existing evidence regarding identified predictors and markers of clozapine response.

METHODS

Relevant studies were identified through PUBMED searches (1975-June 2004) and cross-referencing of reviews and included studies. The data were summarized under two main categories: clinical (general, neurological, cognitive/neuropsychological, clozapine levels) and biological (biochemical, endocrine, genetic, metabolic, morphological, dopamine D2 receptor occupancy). 'Reliable' predictors/markers were defined a priori as those with support of at least two independent reports that addressed overall response, with no contradictory findings to date. 'Potential' predictors/markers had the support of a single report that addressed overall response and at least one other evaluating treatment outcome but not directly addressing response status.

RESULTS AND CONCLUSIONS

Higher baseline clinical symptoms and functioning in the previous years and low cerebrospinal homovanillic acid/5-hydroxyindoleacetic acid levels were identified as reliable. Three potential measures were identified: reduction of frontal cortex metabolic activity, reduction of caudate volume, and improvement in P50 sensory gating.

Cerebral metabolic changes induced by clozapine in schizophrenia and related to clinical improvement

RATIONALE

The study of the different effects on brain metabolism between typical and atypical antipsychotics would aid in understanding their mechanisms of action. Clozapine is of special interest, since it is one of the most effective antipsychotic drugs and demonstrates a distinctive mechanism of action in pre-clinical studies with respect to typical neuroleptics.

OBJECTIVE

To study the differences in cerebral activity induced by clozapine as compared to those produced by haloperidol.

METHODS

[18F]Fluoro-deoxy-glucose (FDG)-positron emission tomography (PET) scans were obtained in the resting condition before and after 6 months of treatment with clozapine in 22 treatment-resistant patients with schizophrenia. Before inclusion, patients had been chronically treated with classical drugs, and all of them received haloperidol during the last month. Data were analyzed with statistical parametric mapping (SPM'99) methods, comparing pre-treatment and post-treatment conditions. The association between the changes in symptom scores and metabolism was also assessed to corroborate the functional relevance of possible metabolic changes.

RESULTS

Clozapine decreased prefrontal and basal ganglia activity, and increased occipital metabolism, including primary and association visual areas. The change in negative symptoms was related with the decrease of basal ganglia activity; the improvement in disorganization related to the metabolic decrease in the motor area, and the change in positive symptoms was associated to the increase of activity in the visual area.

CONCLUSIONS

These results show that haloperidol and clozapine produce different patterns of metabolic changes in schizophrenia. Compared to the haloperidol baseline, clozapine inhibited the metabolic activity of the prefrontal and motor cortical regions and basal ganglia and induced a higher activation of the visual cortex. The improvement in disorganization, negative and positive syndromes with clozapine may be respectively associated with metabolic changes in the motor area, basal ganglia, and visual cortex.

Occupancy of dopamine D2 receptors by the atypical antipsychotic drugs risperidone and olanzapine: theoretical implications

RATIONALE

To examine the D2 occupancy of two commonly used antipsychotic medications and relate this to the D2 occupancy by endogenous dopamine in schizophrenia.

OBJECTIVES

The aim of this study is to compare the occupancy of striatal D2 receptors by the atypical antipsychotic medications risperidone and olanzapine at fixed dosages and to estimate the effect on D2 occupancy by dopamine as a result of these treatments.

METHODS

Seven patients with schizophrenia taking risperidone 6 mg/day and nine patients with schizophrenia taking olanzapine 10 mg/day underwent an [123I]IBZM SPECT scan after 3 weeks of treatment. The specific to non-specific equilibrium partition coefficient (V3") after bolus plus constant infusion of the tracer was calculated as [(striatal activity)/(cerebellar activity)]-1. D2 receptor occupancy was calculated by comparing V3" measured in treated patients to an age-corrected V3" value derived from a group of untreated patients with schizophrenia, previously published, according to the following formula: OCC=1-(V3" treated/V3" drug free).

RESULTS

V3" was significantly lower in risperidone treated patients compared with olanzapine treated patients (0.23+/-0.06 versus 0.34+/-0.08, P=-0.01), which translated to a significantly larger occupancy in schizophrenic patients treated with risperidone compared to olanzapine (69+/-8% versus 55 +/-11%, P=0.01). Data from our previous study were used to calculate the occupancy of striatal D2 receptors by antipsychotic medications required to reduce the occupancy of these receptors by endogenous dopamine to control values. In medication-free patients with schizophrenia, the occupancy of striatal D2 receptors by endogenous dopamine is estimated at 15.8%. In healthy controls, the occupancy of striatal D2 receptors by dopamine is estimated at 8.8%. In order to reduce the dopamine occupancy of striatal D2 receptors in patients with schizophrenia to control values, 48% receptor occupancy by antipsychotic medications is required.

CONCLUSIONS

These data indicate that the dosage of these medications, found to be effective in the treatment of schizophrenia, reduces DA stimulation of D2 receptors to levels slightly lower than those found in unmedicated healthy subjects.

Role of neuroactive steroid allopregnanolone in antipsychotic-like action of olanzapine in rodents

Olanzapine increases brain allopregnanolone (ALLO) levels sufficiently to modulate neuronal activity by allosterically regulating GABAA receptors. Recently, we reported the antipsychotic-like profile of ALLO in rodents. The present study examined the hypothesis that olanzapine-induced elevation of endogenous neurosteroid ALLO is vital for its neuroleptic-like action. The conditioned avoidance response (CAR) and apomorphine-induced climbing behavioral paradigms were used in rodents. Administration of ALLO (1 microg, intracerebroventricular (i.c.v.)) or neurosteroidogenic agents such as the mitochondrial diazepam binding inhibitor receptor agonist, FGIN 1-27 (0.5 microg, i.c.v.) or the ALLO precursor, progesterone (10 mg/kg, i.p.) significantly potentiated olanzapine-induced blockade of CAR and apomorphine-induced climbing. In contrast, these agents failed to alter the antipsychotic-like effect of risperidone and haloperidol. On the other hand, inhibition of the endogenous biosynthesis of neurosteroids by the 3beta-hydroxysteroid dehydrogenase inhibitor, trilostane (30 mg/kg, i.p.), the 3alpha-hydroxysteroid oxidoreductase inhibitor, indomethacin (5 mg/kg, i.p.), or the GABAA receptor antagonist bicuculline (1 mg/kg, i.p.) and dehydroepiandrosterone sulfate (DHEAS) (1 mg/kg, i.p.) blocked the effect of olanzapine, but not of risperidone and haloperidol. Socially isolated animals, known to exhibit decreased brain ALLO and GABAA receptor functions, displayed a shortening in the muscimol-induced loss of righting reflex and an increased susceptibility to apomorphine-induced climbing. Administration of olanzapine, but not of haloperidol and risperidone, normalized the duration of muscimol-elicited loss of righting reflex. Although all three antipsychotics proved capable of antagonizing the apomorphine-induced climbing, a dose almost five times higher of olanzapine was required in socially isolated animals. The data obtained suggest that enhancement of the GABAergic tone plays a key role in the antipsychotic-like effect exerted by olanzapine in rodents, likely as a consequence of augmented levels of neuroactive steroids, in particular ALLO, in the brain. The present findings provide the first specific behavioral evidence in support of the hypothesis that neuroactive steroid ALLO- mediated GABAergic modulation is essential for the antipsychotic-like action of olanzapine.

Cerebral D2 and 5-HT2 receptor occupancy in Schizophrenic patients treated with olanzapine or clozapine

We report the results of a double-blind, randomized prospective trial on D2 and 5-HT2 receptor occupancy and the clinical effects of olanzapine versus clozapine in a sample of neuroleptic-refractory schizophrenic patients. Receptor occupancy was evaluated in different cortical areas and in basal ganglia using [18F] fluoro-ethyl-spiperone ([18F] FESP) and positron emission tomography (PET). A total of 15 neuroleptic-free patients completed the study undergoing a baseline and a post-treatment PET scan (olanzapine, nine patients, one female; clozapine, six patients, three female) 8 weeks after starting treatment. PET data were analysed both by regions of interest and on a voxel-by-voxel basis using Statistical Parametric Mapping (SPM96). Olanzapine and clozapine induced a similar and significant inhibition of [18F] FESP binding index in the cortex. In the basal ganglia, receptor occupancy was significantly higher with olanzapine than with clozapine (p=0.0018). By contrast, no differences in receptor occupancy were detected at the level of the pituitary gland. Clinical outcomes, in particular a full extra pyramidal tolerability, were similar. In this sample of neuroleptic-refractory schizophrenic patients, olanzapine and clozapine showed a different pattern of occupancy of D2-like receptor despite a common lack of extrapyramidal side-effects.

Positron emission tomography and single photon emission CT molecular imaging in schizophrenia

We reviewed findings from PET and SPECT studies that have contributed to our understanding of the pathophysiology and treatment of schizophrenia. The most robust set of findings pertains to imaging of presynaptic dopaminergic function in the striatum. The results of these studies have been consistent in showing that schizophrenia, at least during episodes of illness exacerbation, is associated with increased activity of DA neurons; this increased presynaptic activity is associated with positive symptoms and good therapeutic response. Studies of cortical DA function are less numerous and less consistent. In the future, technical advances in PET instrumentation and radioligand development should contribute to a clarification of the role of prefrontal DA in the cognitive impairment that is presented by these patients. An important drawback of the literature in this field is the generally low number of subjects that are included in studies (typically less than 20 per group). Small samples are necessitated by the cost of these investigations, but also, in some instances, to the difficulty in recruiting appropriate clinical subjects (such as drug-free patients who have schizophrenia). In conditions that are characterized by marked heterogeneity, such as major depressive disorders, this factor is bound to yield divergent results across studies. Another source of discrepancy is the variety of technical approaches to data acquisition and analysis. For example, analytical methods range from "empirical" or "semiquantitative" (typically a region of interest to a region of reference ratio measured at one time point) to model-based methods that use an arterial input function. The limitations that are associated with empirical analytical methods might account for artifactual results, especially when the effect size of the between-group difference and the number of subjects are small [149]. In addressing these limitations it will be important to increase the availability of these techniques beyond a few academic centers, to promote multi-center studies in well-characterized populations, and to standardize analytical methods. Until recently, SPECT was the only widely available technique, and SPECT studies have provided a substantial contribution to this field. With the current increase in PET camera availability, the development of [18F]-based molecular imaging probes will provide unique opportunities for further dissemination of these techniques. The article reviewed seminal findings obtained with PET and SPECT molecular imaging of schizophrenia. These techniques do not play a major role in the diagnosis and treatment of this disorder, remain essentially research tools. The results that have been produced by this field to date suggest that PET will significantly contribute to unraveling the biologic bases of psychiatric disorders and may contribute to their clinical management. Moreover, it is foreseeable that PET will become increasingly involved in the development of new psychiatric medications. Expanding the availability of PET and the current radiopharmaceutical portfolio will be critical for these predictions to become reality.

Cerebral metabolism and risperidone treatment in schizophrenia

This paper compares the metabolic changes associated with risperidone treatment in schizophrenia to those induced by haloperidol, as a representative typical neuroleptic. A group of 11 schizophrenic patients of recent onset underwent two [18F] fluoro-desoxi-glucose (FDG)-positron emission tomography (PET) scans at rest: the first one at the moment of the diagnosis, after a minimal treatment with haloperidol followed by wash-out, and the second one after 6 months on risperidone. The study also included 34 patients on chronic haloperidol for comparison. PET images were analyzed using Statistical Parametric Mapping (SPM'99) methods. The only change after treatment with risperidone with respect to the baseline was a slight increase in activity in the primary visual area and the right insula. Patients on chronic haloperidol showed increased activity in the motor cortex and cerebellum, as compared to both minimally treated and risperidone-treated patients. The pattern of metabolic changes induced by risperidone appears to be different from that produced by typical antipsychotics.

Radiopharmaceuticals for single-photon emission computed tomography brain imaging

In the past 10 years, significant progress on the development of new brain-imaging agents for single-photon emission computed tomography has been made. Most of the new radiopharmaceuticals are designed to bind specific neurotransmitter receptor or transporter sites in the central nervous system. Most of the site-specific brain radiopharmaceuticals are labeled with (123)I. Results from imaging of benzodiazepine (gamma-aminobutyric acid) receptors by [(123)I]iomazenil are useful in identifying epileptic seizure foci and changes of this receptor in psychiatric disorders. Imaging of dopamine D2/D3 receptors ([(123)I]iodobenzamide and [(123)I]epidepride) and transporters [(123)I]CIT (2-beta-carboxymethoxy-3-beta(4-iodophenyl)tropane) and [(123)I]FP-beta-CIT (N-propyl-2-beta-carboxymethoxy-3-beta(4-iodophenyl)-nortropane has proven to be a simple but powerful tool for differential diagnosis of Parkinson's and other neurodegenerative diseases. A (99m)Tc-labeled agent, [(99m)Tc]TRODAT (technetium, 2-[[2-[[[3-(4-chlorophenyl)-8-methyl-8-azabicyclo [3,2,1]oct-2-yl]methyl](2-mercaptoethyl)amino]ethyl]amino] ethanethiolato(3-)]oxo-[1R-(exo-exo)]-), for imaging dopamine transporters in the brain has been successfully applied in the diagnosis of Parkinson's disease. Despite the fact that (123)I radiopharmaceuticals have been widely used in Japan and in Europe, clinical application of (123)I-labeled brain radiopharmaceuticals in the United States is limited because of the difficulties in supplying such agents. Development of (99m)Tc agents will likely extend the application of site-specific brain radiopharmaceuticals for routine applications in aiding the diagnosis and monitoring treatments of various neurologic and psychiatric disorders.

Can antipsychotic drugs be classified by their effects on a particular group of dopamine neurons in the brain?

During the four decades that research has been carried out on antipsychotic drugs, a variety of methods have been used to study the effects of these compounds on dopamine neurotransmission. An important issue in this research was to find an explanation for the difference between "typical" and "atypical" antipsychotic drugs. The hypothesis that the beneficial properties and the motor side effects of antipsychotic drugs result from their effects on different groups of dopamine neurons has received considerable attention. Numerous researchers have tried to discover regiospecific actions of antipsychotic drugs in mesolimbic and in mesocortical dopamine neurons. An overview of these research attempts is presented here. Electrophysiological studies showed a selective action of atypical antipsychotic drugs on A10 dopamine neurons. It was found that chronic treatment with these compounds induced a preferential depolarisation block of the A10 neurons that project to the mesolimbic areas. The model represents certain clinical features of antipsychotic drug use and offers a possible explanation for the lack of extrapyramidal side effects of atypical antipsychotic drugs. Dopamine neurons projecting from A10 to the frontal cortex are also considered as a possible site of action of atypical antipsychotic drugs. Microdialysis studies have shown that certain atypical antipsychotic drugs selectively enhance the release of dopamine in the prefrontal cortex when compared with typical antipsychotic drugs. The finding that repeated treatment with antipsychotic drugs increased dopamine D(2) receptor binding in the frontal cortex confirms the significance of this brain area. These properties might indeed explain certain beneficial effects of atypical antipsychotic drugs such as improvement of cognitive dysfunction. However the effects of typical and atypical antipsychotic drugs in the frontal cortex could not be fully differentiated, which illustrates the difficulty of localising clinical effects of antipsychotic drugs in terms of regional dopamine neurons. Recently new insights into the mechanism of action of typical and atypical antipsychotic drugs have been published. Clinical positron emission tomography (PET) studies have indicated that a moderate dopamine D(2) receptor occupancy, probably combined with a high dissociation rate, might provide the optimal clinical conditions for an antipsychotic drug, without inducing extrapyramidal side effects. Moreover the efficacy of benzamides as atypical antipsychotic drugs suggests that low to moderate dopamine D(2) blockade is probably the most important-if not the only-criterion that determines "atypicality". Interestingly these new insights are based on PET studies of the human basal ganglia and not on the comparison of different brain areas. Apparently, according to this concept an ideal antipsychotic drug need not to act on a particular type of dopamine neurons, as it is the moderate dopamine D(2) receptor occupancy that determines the desirable clinical effects. It is concluded that both beneficial actions and side effects, of antipsychotic drugs might be dose dependently localised in A9 as well as A10 dopamine neurons.

Neuroreceptor imaging in psychiatric disorders

Molecular imaging, the study of receptors, transporters and enzymes, as well as other cellular processes, has grown in recent years to be one of the most active neuroimaging areas. The application of single photon emission tomography (SPECT) and positron emission tomography (PET) techniques to the study of psychiatric illness has lead to increased understanding of disease processes as well as validated, in vivo, theories of illness etiology. Within the field of psychiatry these techniques have been applied most widely to the study of schizophrenia. Studies within schizophrenia are largely limited to either the dopamine or serotonin system. This is due in large part to the availability of suitable radiotracers as well as the current theories on the etiology of the illness. Two basic study designs are used when studying schizophrenia using molecular imaging and make up the majority of studies reviewed in this manuscript. The first type, termed "clinical studies," compares the findings from PET and SPECT studies in those with schizophrenia to normal controls in an attempt to understand the pathophysiology of the illness. The second study design, termed "occupancy studies," uses these techniques to enhance the understanding of the mechanism of action of the medications used in treating this illness. This review will focus on the findings of molecular imaging studies in schizophrenia, focusing, for the most part, on the serotonin and dopamine systems. Emphasis will be placed on how these findings and techniques are currently being used to inform the development of novel treatments for schizophrenia.

Striatal dopamine D2 receptor binding of risperidone in schizophrenic patients as assessed by 123I-iodobenzamide SPECT: a comparative study with olanzapine

The aim of this investigation was to compare the degree of striatal dopamine-(D2) receptor blockade by two atypical antipsychotic drugs, risperidone and olanzapine. The percentage of D2 receptor occupancy during treatment was calculated by comparing the results of 123I-iodobenzamide SPECT with those from healthy control subjects. Twenty inpatients suffering from schizophrenia or schizoaffective psychosis according to DSM IV/ICD-10 criteria were treated with clinically recommended doses of risperidone and compared with 13 inpatients treated with up to 20 mg olanzapine. Neuroleptic dose and D2 receptor blockade correlated strongly for both risperidone (Pearson r = -0.86, p = 0.0001) and olanzapine (Pearson r = -0.77, p = 0.002). There was no significant difference between the D2 receptor occupancy of the two substances when given in the clinically recommended dose range (unpaired t-test, t = -0.112, p = 0.911).

Receptor and transporter imaging studies in schizophrenia, depression, bulimia and Tourette's disorder--implications for psychopharmacology

Considerable progress has been achieved over the past 15 years in uncovering the biological basis of major psychiatric disorders. To determine patterns of brain dysfunction and to uncover the mechanism of action of centrally active compounds we used single photon emission computerized tomography (SPECT) as well as positron emission tomography (PET) in patients diagnosed with schizophrenia, depression, bulimia and Tourette's disorder. Striatal D2 and 5-HT1A receptors were studied in schizophrenia and 5-HT transporters (5-HTT) in depression and bulimia. Patients were either drug-naïve or drug free, or we studied the influence of specifically acting compounds on receptor/transporter occupancy. We could demonstrate that atypical antipsychotics have a dose-dependent (with the exception of clozapine and quetiapine) lower striatal D2 receptor occupancy rate compared with typical neuroleptics, paralleling the more favourable extrapyramidal side effects of atypical antipsychotics. However, no association between striatal D2 receptor occupancy rates and antipsychotic efficacy has been found. The measurement of 5-HT1A receptors in drug-naïve schizophrenic patients using the in vivo PET methodology revealed an increase of cortical 5-HT1A receptor binding potential in schizophrenia. beta-CIT as a ligand for measurement of 5-HT transporter densities (5-HTT) revealed lower rates in depression compared to age- and sex-matching healthy controls, a measurement that has also been obtained for bulimia. We also documented seasonal variations in brain serotonergic function by our finding of reduced brain 5-HTT availability in winter (compared to summer) in healthy controls. Furthermore, displaceable [123I] beta-CIT binding in the area corresponding to the left striatum (representing predominantly the density of dopamine transporters) was significantly reduced in SAD patients compared to healthy controls. In depression as well as in bulimia, selective serotonin reuptake inhibitors significantly decreased the beta-CIT binding potential, however, no significant dose relationship has been obtained in depression. Genotyping depressed patients for the serotonin transporter promoter gene region (5-HTTLPR) did not provide evidence for in vivo functional regulation of 5-HTT availability by 5-HTTLPR in the thalamus-hypothalamus and mesencephalon-pons of healthy subjects. In patients suffering from Tourette's disorder (TD) we were unable to detect differences of dopamine transporter densities between psychotropic drug-naïve TD patients and controls. Furthermore, no difference could be found between currently treated (with antipsychotics) and psychotropic drug-naïve TD patients. Our data provide insight into the pathophysiology of neuropsychiatric disorders and may guide future psychopharmacological drug developments.

Prolactin responses to acute clomipramine and haloperidol of male schizophrenic patients in a drug-free state and after treatment with clozapine or with olanzapine

Atypical neuroleptics share a common feature, showing higher affinity for 5-HT2 receptors than for D2 dopamine receptors, but show considerable differences in their clinical and pharmacological properties. In clinical doses, they occupy serotonergic receptors near saturation, but show considerable differences regarding the D2 receptor occupancies, with clozapine showing the lowest degree of occupation. We assessed serotonergic and dopaminergic receptor responsiveness in two groups of male schizophrenic patients, one treated with the atypical neuroleptic clozapine (14 patients, doses 200-600 mg/d) and the other treated with olanzapine (11 patients, doses 10-30 mg/d). We measured the prolactin responses to the acute administration of a serotonergic drug, clomipramine, and a dopaminergic one, haloperidol. Tests were first performed in the drug-free state, and were repeated after the patients had been treated with stable doses of either drug for six weeks. Clomipramine administration induced significant increases of prolactin in the drug-free state. These responses were eliminated after treatment of the patients with either drug, thereby indicating a high 5-HT receptor occupancy by both clozapine and olanzapine. The prolactin responses to haloperidol were not altered after treatment with clozapine, but were significantly reduced after the olanzapine treatment. The baseline prolactin levels were not influenced by clozapine treatment, and were moderately but significantly increased after treatment with olanzapine. The results indicate that there is a difference between the two drugs in their capacity to block dopamine receptors at the hypothalamus-pituitary level, and match the results obtained by SPECT receptor binding studies for striatal dopamine receptors.

Choosing the right dose of antipsychotics in schizophrenia: lessons from neuroimaging studies

Despite vast clinical experience with antipsychotics, there is no broad consensus on the doses of these substances that should be administered. Currently, most antipsychotics are administered empirically according to clinical dose-finding studies, in which arbitrarily selected doses were tested to find the "most efficient" dose range in a patient population, with no regard for the molecular effects of the tested drug. Brain imaging studies using nuclear medical techniques, such as positron emission tomography (PET) or single photon emission computed tomography (SPECT), can now provide a rationale for doses, directly derived from the central effects of the drugs on neurotransmitter receptors measured in vivo. PET results indicate that occupancy of at least 65% of dopamine D(2) receptors is needed for clinical response to antipsychotics, and that occupancy rates exceeding 72 and 78% are associated with a high risk for elevation of prolactin levels and motor adverse effects, respectively. For example, clinical studies with haloperidol do not point to an advantage of dosages exceeding 5 mg/day. The relevance of D(2) receptor occupancy for drug administration is also borne out by studies relating the effects of antipsychotics to their D(2) receptor occupancy in relevant animal models. Taken together, neuroimaging and clinical studies, as well as animal models, provide a rationale for the use of relatively low doses of typical antipsychotics and equivalent doses of novel antipsychotics. The lower risk of adverse effects with appropriate doses of antipsychotics may further enhance compliance and outcome. This seems to be particularly important in individuals experiencing a first episode of schizophrenia, as they appear to be especially responsive to pharmacotherapy and quite sensitive to adverse effects.

Broad therapeutic uses of atypical antipsychotic medications

The atypical antipsychotics have a low incidence of extrapyramidal side effects (EPS), have improved tardive dyskinesia profiles, and have a broad range of therapeutic efficacy. These agents offer important therapeutic advantages that extend beyond their initial regulatory approval in several conditions and patient groups. The use of atypical antipsychotics is most relevant in the treatment of mood disorders, where these medications are being used increasingly for acute mood stabilization and in patients who are resistant to other treatments. Similar circumstances and clinical advantages pertain to the use of atypical antipsychotics in the treatment of behavioral disturbances in patients with dementia and in the management of personality disorders-both circumstances where conventional antipsychotics were initially poorly tolerated because of EPS. The low incidence of EPS associated with atypical antipsychotics is highly beneficial in several neuropsychiatric conditions. The extent to which endocrine and metabolic dysregulations associated with atypical antipsychotics will influence antipsychotics' role remains to be determined. As therapeutic opportunities evolve and diversify, atypical antipsychotics, because of favorable adverse-effect profiles, will have enhanced patient tolerability and use in nonpsychiatric conditions.

Double-blind olanzapine vs. haloperidol D2 dopamine receptor blockade in schizophrenic patients: a baseline-endpoint

The aim of this study was to compare in vivo striatal D2 dopamine receptor occupancy induced by olanzapine and haloperidol in schizophrenic patients using a baseline-endpoint [(123)I]IBZM single photon computed emission tomography (SPECT) design. The relationships of striatal D2 receptor occupancy with clinical efficacy and extrapyramidal symptoms (EPS) were also assessed. Twenty-seven inpatients with schizophrenia or schizophreniform disorder were included in a 4-week prospective, randomized, double-blind, parallel and comparative clinical trial. Thirteen patients were treated with haloperidol (10 mg/day) and 14 with olanzapine (10 mg/day). Ratings of clinical status and EPS were obtained weekly. The percentage of D2 receptor occupancy was estimated by using basal ganglia (striatum)/frontal cortex IBZM uptake ratios obtained from each patient before and after 4 weeks of maintained antipsychotic treatment. Olanzapine led to a mean striatal D2 receptor occupancy of 49% (range 28-69%), which was significantly lower than that induced by haloperidol (mean 64%, range 46-90%). The baseline-endpoint SPECT design used in this study revealed lower antipsychotic D2 occupancy percentage values than those reported in the literature, using other approaches. The degree of striatal D2 receptor occupancy correlated to the EPS, which predominantly appeared in patients on haloperidol. No relationship was found between the striatal D2 receptor occupancy and clinical improvement. Olanzapine induced a lower striatal D2 occupancy than haloperidol. This low striatal D2 occupancy, together with the lower incidence of EPS in olanzapine-treated patients, contributed to confirm the atypical behavior of this new antipsychotic drug. Nevertheless, conclusions based on SPECT-estimated percentages of antipsychotic D2 occupancy should be cautious, since the SPECT design could influence the results. In this regard, SPECT studies including baseline and endpoint examinations should be encouraged.

D2 receptor occupancy under recommended and high doses of olanzapine: an iodine-123-iodobenzamide SPECT study

The aim of this study was to compare the degree of striatal dopamine D2 receptor availability in patients treated with recommended (5-20 mg, mean dose 11.9 +/- 6.3 mg daily) and higher doses (25-40 mg, mean 32.1 +/- 5.6 mg daily) of the novel antipsychotic drug olanzapine by means of [123I] IBZM Single photon emission computed tomography (SPECT). The results were compared to those of a group of 10 untreated, healthy, age- and sex-matched controls. The degree of dopamine D2 receptor occupancy in the patient group was correlated with the presence of extrapyramidal symptoms (EPS). A total of 20 patients who met the DSM III R criteria for schizophrenia or schizoaffective disorder received a clinically effective antipsychotic monotherapy with olanzapine. The mean daily dose of olanzapine ranged from 0.05-0.6 mg/kg body weight. The dopamine D2 receptor binding was reduced in all patients treated with olanzapine. Specific IBZM binding expressed as the [STR-BKG]/BKG ratio ranged from 0.13-0.61 (healthy controls 0.95). The D2 receptor availability revealed an exponential dose-response relationship (r = - 0.85, p < 0.001). The frequency of EPS induced by olanzapine was considerably lower. Only one patient, treated with 40 mg olanzapine, suffered from severe EPS symptoms and had to be given biperiden. There were no significant differences in the presence of EPS symptoms between patients with recommended doses and those with higher doses of olanzapine.

Neuropsychological and conditioned blocking performance in patients with schizophrenia: assessment of the contribution of neuroleptic dose, serum levels and dopamine D2-receptor occupancy

Patients with schizophrenia show impairments of attention and neuropsychological performance, but the extent to which this is attributable to antipsychotic medication remains largely unexplored. We describe here the putative influence of the dose of antipsychotic medication (chlorpromazine equivalents, CPZ), the antipsychotic serum concentration of dopamine (DA) D2-blocking activity and the approximated central dopamine D2-receptor occupancy (DA D2-occupancy), on conditioned blocking (CB) measures of attention and performance on a neuropsychological battery, in 108 patients with schizophrenia (compared with 62 healthy controls). Antipsychotic serum concentration and D2-occupancy were higher in patients with a paranoid versus non-paranoid diagnosis, and in female versus male patients (independent of symptom severity). Controlling for D2-occupancy removed the difference between high CB in paranoid and impaired low CB in non-paranoid patients. Similar partial correlations for antipsychotic drug dose and serum levels of DA D2-blocking activity with performance of the trail-making and picture completion tests (negative) and the block-design task (positive) showed the functional importance of DA-related activity. High estimates of central DA D2-occupancy were related to impaired verbal fluency but were associated with improved recall of stories, especially in paranoid patients. This, the first study of its kind, tentatively imputes a role for DA D2-related activity in left frontal (e.g. CB, verbal fluency) and temporal lobe functions (verbal recall) as well as in some non-verbal abilities mediated more in the right hemisphere in patients with schizophrenia.

Clozapine versus typical neuroleptic medication for schizophrenia

BACKGROUND

Long-term drug treatment of schizophrenia with conventional antipsychotics has limitations: 25-33% of patients have illnesses that are treatment-resistant. Clozapine is an atypical antipsychotic drug, which is claimed to have superior efficacy and to cause fewer motor adverse effects than typical drugs for people with treatment-resistant illnesses. Clozapine carries a significant risk of serious blood disorders, which necessitates mandatory weekly blood monitoring at least during the first months of treatment.

OBJECTIVES

To evaluate the effects of clozapine for schizophrenia in comparison to typical antipsychotic drugs.

SEARCH STRATEGY

Publications in all languages were searched from the following databases: Biological Abstracts (1982-1999), The Cochrane Library CENTRAL (Issue 2, 1999), Cochrane Schizophrenia Group's Specialised Register (1999), EMbase (1980-1999), ISI Citation Index, LILACS (1982-1999), MEDLINE (1966-1999), and PsycLIT (1974-1999). Reference list screening of included papers was performed. Authors of recent trials and the manufacturer of clozapine contacted.

SELECTION CRITERIA

All randomised controlled trials comparing clozapine with typical antipsychotic drugs were included by independent assessment by at least two reviewers.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by at least two reviewers. Authors of trials published since 1980 were contacted for additional and missing data. Odds ratios (OR) and 95% confidence intervals (CI) of homogeneous dichotomous data were calculated with the Peto method. A random effects model was used for heterogeneous dichotomous data. Where possible the numbers needed to treat (NNT) or needed to harm (NNH) were also calculated. Weighted or standardised means were calculated for continuous data.

MAIN RESULTS

Currently the review includes 31 studies, 26 of which are less than 13 weeks in duration. These studies include 2589 participants, most of whom were men (74%). The average age was 38 years. There was no difference in the effects of clozapine and typical neuroleptic drugs for broad outcomes such as mortality, ability to work or suitability for discharge at end of the study. Clinical improvement was seen more frequently in those taking clozapine (random effects OR 0.4 CI 0.2-0.6, NNT 6) both in the short and the long term. Also, in the short term, participants on clozapine had fewer relapses than those on typical antipsychotic drugs (OR 0.6 CI 0.4-0.8, NNT 20 CI 17-38), and this may be true for long-term treatment as well. Symptom assessment scales showed a greater reduction of symptoms in clozapine-treated patients. Clozapine treatment was more acceptable than low-potency antipsychotics such as chlorpromazine (OR 0.6 CI 0.4-0.9) but did not differ from acceptability of high-potency neuroleptics such as haloperidol (random effects OR 0.8 CI 0.4-1.5). Clozapine was more acceptable in long-term treatment than conventional antipsychotic drugs (random effects OR 0.4 CI 0.2-0.7, NNT 6 CI 3-111). Patients were more satisfied with clozapine treatment (OR 0.5 CI 0.3-0.8, NNT 12 CI 7-37), but they experienced more hypersalivation, temperature increase, and drowsiness than those given conventional neuroleptics. However, clozapine patients experience fewer motor side effects and less dry mouth. The clinical efficacy of clozapine was more pronounced in participants resistant to typical neuroleptics in terms of clinical improvement (random effects OR 0.2 CI 0.1-0.5, NNT 5 CI 4-7) and symptom reduction. Thirty-two percent of treatment resistant people had a clinical improvement with clozapine treatment.

REVIEWER'S CONCLUSIONS

This systematic review confirms that clozapine is convincingly more effective than typical antipsychotic drugs in reducing symptoms of schizophrenia, producing clinically meaningful improvements and postponing relapse. Patients were more satisfied with clozapine treatment than with typical neuroleptic treatment. (ABSTRACT TRUNCATED

Newer atypical antipsychotic medication versus clozapine for schizophrenia

BACKGROUND

Clozapine is an atypical antipsychotic drug, which is claimed to have superior efficacy and to cause fewer movement disorders. However, clozapine carries a significant risk of serious blood disorders. Newer atypical antipsychotics are safer alternatives that might share the benefits of clozapine. It is thus of interest to compare the effectiveness of newer atypical antipsychotics with the effectiveness of clozapine.

OBJECTIVES

To evaluate the clinical effects of newer atypical antipsychotic drugs in comparison to clozapine for schizophrenia.

SEARCH STRATEGY

Publications in all languages were searched from the following databases: Biological Abstracts/BIOSIS (1980-1999), The Cochrane Schizophrenia Group's Register of Trials (1998), The Cochrane Library CENTRAL Register (Issue 4, 1999), EMBASE (1980-1998), MEDLINE (1966-1999), LILACS/CD-ROM (1998), and PsycLIT/PsycINFO (1974-1999). Trials were also sought from recent conference proceedings and reference lists of included papers. Authors of recent trials and the manufacturers of clozapine, iloperidone, olanzapine, quetiapine, remoxipride, risperidone, sertindole, ziprasidone and zotepine were contacted.

SELECTION CRITERIA

All randomised controlled trials comparing clozapine with newer atypical antipsychotic drugs were included by independent assessment by two reviewers.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two reviewers. Relative risks (RR) and 95% confidence intervals (CI) of homogenous dichotomous data were calculated. A random effects model was used for heterogeneous dichotomous data. Where possible the number needed to treat (NNT) statistic with 95%CI were also calculated. Weighted or standardised means were calculated for continuous data. Due to the small number of included studies, sensitivity analyses or funnel plot statistics were not undertaken for this version of the review.

MAIN RESULTS

The current review includes eight studies (22 papers), of which three studies are 4-6 weeks in duration and only one study is of more than 12 weeks' duration. Newer atypical drugs seemed to be broadly similar to clozapine using a clinical global index or trialists' definitions of improvement, but this result was obtained from a relatively small number of studies. Due to the small number of studies and patients, wide confidence intervals were seen when their effectiveness as measured by symptom rating scales was compared. Social functioning was better in patients on newer atypical medication (risperidone) than in those on clozapine, but this finding is based on a single underpowered trial and has to be interpreted with caution. Clozapine and newer atypical drugs showed their adverse effect profile to be dissimilar: while clozapine produced more fatigue, hypersalivation, nausea, and orthostatic dizziness, new atypical drugs, with the exception of olanzapine, produced more extrapyramidal symptoms. The impact of these drugs and their effects on patients' day-to-day quality of life, service use, hospital admission, and pharmacoeconomics was not measured.

REVIEWER'S CONCLUSIONS

The equal effectiveness and tolerability of new atypical drugs in comparison with clozapine is not yet demonstrated. Lack of statistical power to determine the comparative efficacy and effectiveness of newer atypical drugs makes it difficult to judge whether newer drugs are more effective, less effective or equivalent. Trials of sufficient power, with longer duration, measuring clinically important outcomes, are needed to assess the true comparative clinical effectiveness, tolerability and cost effectiveness of newer drugs in relation to clozapine.