PET STUDIES OF DOPAMINE RECEPTORS IN RELATION TO ANTIPSYCHOTIC DRUG TREATMENT

Error analysis for PET measurement of dopamine D2 receptor occupancy by antipsychotics with [11C]raclopride and [11C]FLB 457

Dopamine D(2) receptor occupancy by antipsychotic drugs has been measured with positron emission tomography (PET) by comparing the binding potential (BP) values before and after drug administration. This occupancy has been found to be related to clinical effects and side effects. In this study, we evaluated the uncertainty of the quantitative analysis for estimating the dopamine D(2) receptor occupancy by antipsychotics in simulation and human studies of [(11)C]raclopride and for the high affinity ligand [(11)C]FLB 457. Time-activity curves of [(11)C]raclopride and [(11)C]FLB 457 were simulated, and the reliability of BP estimated by a simplified reference tissue model and the calculated occupancy were investigated for various noise levels, BP values, and scan durations. Then, in the human PET study with and without antipsychotics, the uncertainty of BP and occupancy estimates and the scan duration required for a reliable estimation were investigated by a bootstrap approach. Reliable and unbiased estimates of [(11)C]raclopride BP(ND) could be obtained with recording as short as 32 min, with the relative standard deviation (SD) of the striatal occupancy remaining less than 10%. Conversely, in [(11)C]FLB 457 studies, the mean value increased and SD of the temporal cortex and thalamus exceeded 10% when the scan duration was shorter than 60 min. These results demonstrated that dopamine D(2) receptor occupancy by antipsychotics can be estimated precisely with an optimal scan duration with [(11)C]raclopride and [(11)C]FLB 457.

In vitro binding of [(11)C]raclopride with ultrahigh specific activity in rat brain determined by homogenate assay and autoradiography

OBJECTIVE

The aim of this study was to characterize the in vitro binding of [(11)C]raclopride with ultrahigh specific activity (SA) in the striatum and cerebral cortex of rat brain.

METHODS

[(11)C]Raclopride, a dopamine D(2) receptor ligand, with an ultrahigh SA of 4880+/-2360 GBq/micromol (132+/-64 Ci/micromol, n=25) was synthesized. In vitro binding experiment was performed using brain homogenate assay and autoradiography (ARG).

RESULTS

In vitro homogenate assay demonstrated that high SA [(11)C]raclopride (2520-6340 GBq/micromol; 68-171 Ci/micromol) had two-affinity (high and low) binding sites in the striatum and cerebral cortex of rat brain. In the striatum, K(d,high) and B(max,high) values were 0.005+/-0.002 nM and 0.19+/-0.04 fmol/mg tissue, respectively, while K(d,low) and B(max,low) values were 2.2+/-1.0 nM and 35.8+/-16.4 fmol/mg tissue, respectively. In the cerebral cortex, K(d,high) and B(max,high) values were 0.061+/-0.087 nM and 0.2+/-0.2 fmol/mg tissue, respectively, while K(d,low) and B(max,low) values were 2.5+/-3.2 nM and 5.5+/-4.8 fmol/mg tissue, respectively. On the other hand, only one binding site was found in the striatum and no binding site was identified in the cerebral cortex using low SA [(11)C]raclopride (44 GBq/micromol; 1.2 Ci/micromol). In vitro ARG for the rat brain using high SA [(11)C]raclopride (6212 GBq/micromol; 168 Ci/micromol) gave a coronal image of the striatum and cerebral cortex with a higher signal/noise ratio than using low SA [(11)C]raclopride (40 GBq/micromol; 1.1 Ci/micromol).

CONCLUSION

Using ultrahigh SA [(11)C]raclopride for the in vitro homogenate assay, we succeeded in detecting two-affinity binding sites of [(11)C]raclopride, not only in the striatum but also in the cerebral cortex of rat brain.

Time course of the antipsychotic effect and the underlying behavioral mechanisms

Antipsychotic drugs work for patients only when given repeatedly. The overall temporal pattern of symptom improvement is not clear. Some recent data question the traditional 'delayed-onset' hypothesis and suggest that the onset of antipsychotic response may be relatively early, and the improvement may grow with repeated treatment. The present study systematically examined the time course of the antipsychotic effect and the underlying behavioral mechanisms using a conditioned avoidance response (CAR) model. Rats repeatedly treated with either typical (haloperidol) or atypical (olanzapine, risperidone) antipsychotics, but not anxiolytics (chlordiazepoxide), show an early-onset, progressive across-session decline in avoidance responding, which re-emerges when the treatment is stopped. This effect is dose-dependent, transferable between antipsychotics, and cannot be attributed to simple sedation or motor side effects. Furthermore, we found that the pattern of this drug-induced decline depends on the number of exposures to the conditioned stimulus in the presence of the drug, and is best understood as the result of drug-induced attenuation of the reinforcing effectiveness of the conditioned stimulus. We also found that repeated drug exposure can create a drug interoceptive state that allows the attenuated reinforcing property of the stimulus to be maintained over time. Together, these data provide preclinical support for the newly postulated 'early-onset' hypothesis, and suggest that the repeated antipsychotic CAR model may be useful for understanding the neurochemical and behavioral mechanisms underlying the clinical effects of antipsychotics in patients with schizophrenia.

Anticholinergics for neuroleptic-induced acute akathisia

BACKGROUND

Neuroleptic-induced akathisia is one of the most common and distressing early-onset adverse effects of first generation 'typical' antipsychotic drugs. It is associated with poor compliance with treatment, and thus, ultimately, with an increased risk of relapse. We assessed the role of anticholinergic drugs as an adjunct therapy to standard antipsychotic medication in the pharmacological treatment of this adverse effect.

OBJECTIVES

To review anticholinergic drugs for neuroleptic-induced acute akathisia.

SEARCH STRATEGY

We searched the Cochrane Schizophrenia Group's Register (October 1999), Biological Abstracts (1982-1999), CINAHL (1982-1999), Cochrane Library (Issue 4 1999), EMBASE (1980-1999), LILACS (1982-1999), MEDLINE (1966-1999) and PsycLIT (1974-1999). References of all identified studies were inspected for more trials and we contacted first authors. Each included study was sought as a citation on the Science Citation Index database. For this 2005-6 update, we searched the Cochrane Schizophrenia Group's Register (July 2005).

SELECTION CRITERIA

We included all randomised clinical trials of adjunctive anticholinergic drugs in addition to antipsychotic medication compared with placebo, for people with neuroleptic-induced acute akathisia.

DATA COLLECTION AND ANALYSIS

We quality assessed and extracted data independently. We calculated the fixed effects relative risk (RR), the 95% confidence intervals (CI) and, where appropriate, the number needed to treat (NNT) for homogeneous dichotomous data on an intention-to-treat basis. For continuous data, we calculated weighted mean differences (WMD).

MAIN RESULTS

We identified no relevant randomised controlled trials.

AUTHORS' CONCLUSIONS

At present, there is no reliable evidence to support or refute the use of anticholinergics for people suffering from neuroleptic-induced acute akathisia. Akathisia is a distressing movement disorder that remains highly prevalent in people with schizophrenia, both in the developed and developing world. This review highlights the need for well designed, conducted and reported clinical trials to address the claims of open studies as regards the effects of the anticholinergic group of drugs for akathisia.

Central action beta-blockers versus placebo for neuroleptic-induced acute akathisia

BACKGROUND

Neuroleptic-induced akathisia is a common, distressing early-onset adverse effect of neuroleptic drugs. It has been associated with poor treatment compliance and an increased risk of relapse.

OBJECTIVES

To determine the effects of central action beta-blockers compared with placebo for people with neuroleptic-induced acute akathisia.

SEARCH STRATEGY

We updated previous searches of the Cochrane Schizophrenia Group Register (May 1999), Biological Abstracts (January 1982-March 1999), The Cochrane Library (issue 3 1999), EMBASE (January 1980-March 1999), LILACS (January 1982-March 1999), MEDLINE (January 1964-March 1999), PsycLIT (January 1974-March 1999), and SCISEARCH by searching the Cochrane Schizophrenia Group Register (November 2003). We sought further references from published trials and their authors.

SELECTION CRITERIA

We included all randomised controlled clinical trials of central action beta-blockers versus placebo for people with neuroleptic-induced acute akathisia.

DATA COLLECTION AND ANALYSIS

Working independently, we selected and critically appraised studies, extracted data and analysed on an intention-to-treat basis. Where possible and appropriate we calculated risk ratios (RR) and their 95% confidence intervals (CI) with the number needed to treat (NNT). For continuous data we calculated Weighted Mean Differences (WMD).

MAIN RESULTS

We identified three randomised controlled trials (total n=51, maximum duration 72 hours). We were not able to draw any firm conclusions from such a small data set. In the two 48 hour studies no-one experienced full remission of akathisia, and only one person in each group experienced a 50% remission (n=11, 1 RCT, RR 1.04 CI 0.59 -1.83). One trial stated that no adverse effects occurred in the two groups (n=20, 1 RCT, RR not estimable). The 72 hour study did not show any statistical difference between the central acting beta-blocker (ICI 118,551) and placebo for the outcome 'no change/worse' (n=10, RR 0.22 CI 0.0 to 1.5).

REVIEWERS' CONCLUSIONS

There are insufficient data to recommend beta-blocking drugs for akathisia. These drugs are experimental for this problem, and this review highlights the need for more evaluative studies.

Effects of typical and atypical antipsychotic drugs on maternal behavior in postpartum female rats

Understanding the effects of antipsychotic drugs (APDs) on social behaviors such as maternal behavior is valuable for understanding the complete spectrum of therapeutic and side-effects of antipsychotics. Although previous studies have suggested that typical antipsychotics impair maternal behavior, the effects of the atypical antipsychotics have not been systematically explored. The purpose of the present report was to examine the effects of typical (haloperidol, HAL) and several atypical (clozapine, CLZ; risperidone, RIS; quetiapine, QUE) antipsychotics on maternal behavior in female rats. Maternal behaviors were examined repeatedly over a period of 24 h after a single injection of a range of doses of HAL, CLZ, RIS or QUE on Day 6 postpartum. All antipsychotic drugs, typical or atypical, elicited a qualitatively similar disruptive effect on the active components of maternal behavior such as pup approach, pup retrieval and nest building at clinically relevant doses. However, HAL caused a prolonged disruption, whereas CLZ, RIS and QUE induced an early onset but shorter duration disruption. In addition, only the atypical antipsychotics showed some inhibitory effects on nursing behavior, possibly due to sedative side-effects shared by all atypical antipsychotics. The current generation of atypical antipsychotics shows a disruptive influence on maternal behavior similar to that of the typical antipsychotics. This effect may be intrinsic to antipsychotic activity or may be reflective of a side-effect. Since the latter is more likely, this may be an effect to avoid in the design of future antipsychotics.

Neuroreceptor imaging of stress and mood disorders

Techniques such as positron emission tomography and single photon emission computed tomography allow for the imaging of neurotransmitter receptors and transporters in the brain. These tools have been used to investigate serotonergic, dopaminergic, and opioidergic function in healthy subjects as well as in patients with major depressive disorder, bipolar disorder, and other mood disorders. Pharmacologic challenges, such as amphetamine challenge, and physiologic stressors, such as pain challenge, have been used to further examine the function of these neurotransmitter systems. Neuroimaging of patient populations before and after medication treatment may be useful to understand changes in neurotransmission that accompany disease remission. As new radiotracers with higher selectivity for the various receptors and transporters are developed, imaging techniques may provide new insights into the pathophysiology of mood disorders, leading to improved diagnosis and treatment.

Anticholinergics for neuroleptic-induced acute akathisia

BACKGROUND

Neuroleptic-induced akathisia is one of the most common and distressing early-onset adverse effects of conventional antipsychotic drugs, being associated with poor compliance with treatment, and thus, ultimately, with an increased risk of relapse. This review assesses the role of anticholinergic drugs as an adjunct to standard antipsychotic medication in the pharmacological treatment of this problem.

OBJECTIVES

To determine the clinical effects of anticholinergic drugs for neuroleptic-induced acute akathisia.

SEARCH STRATEGY

The reviewers undertook electronic searches of Biological Abstracts (1982-1999), CINAHL (1982-1999), Cochrane Library (Issue 4 1999), Cochrane Schizophrenia Group's Register (October 1999), EMBASE (1980-1999), LILACS (1982-1999), MEDLINE (1966-1999) and PsycLIT (1974-1999). References of all identified studies were inspected for more trials and first authors contacted. Each included study was sought as a citation on the Science Citation Index database.

SELECTION CRITERIA

All randomised clinical trials of anticholinergic drugs versus placebo for people with neuroleptic-induced acute akathisia.

DATA COLLECTION AND ANALYSIS

Two reviewers, working independently, selected, quality assessed and extracted data. These data were then analysed on an intention-to-treat basis. For homogeneous dichotomous data the fixed effects relative risk (RR), the 95% confidence intervals (CI) and, where appropriate, the number needed to treat (NNT) were calculated on an intention-to-treat basis. For continuous data, reviewers calculated weighted mean differences.

MAIN RESULTS

No randomised controlled trials could be included.

REVIEWER'S CONCLUSIONS

At present, there is no reliable evidence to support or refute the use of anticholinergics for people suffering from neuroleptic-induced acute akathisia. Akathisia is a most distressing movement disorder that remains highly prevalent, both in the developed and developing world. This review highlights the need for well designed, conducted and reported clinical trials to address the claims of open studies as regards the effects of the anticholinergic group of drugs for akathisia.

Benzodiazepines for neuroleptic-induced acute akathisia

BACKGROUND

Neuroleptic-induced akathisia is one of the most common and distressing early-onset adverse effects of antipsychotic drugs, being associated with poor compliance with treatment, and thus, ultimately, to an increase risk of relapse. This review assesses the role of benzodiazepines in the pharmacological treatment of this problem.

OBJECTIVES

To determine the effects of benzodiazepines versus placebo for people with neuroleptic-induced acute akathisia.

SEARCH STRATEGY

Biological Abstracts (January 1982-March 1999), The Cochrane Library (Issue 3 1999), The Cochrane Schizophrenia Group's Register (May 2001), EMBASE (January 1980-March 1999), LILACS (January 1982-March 1999), MEDLINE (January 1964-March 1999), PsycLIT (January 1974-March 1999), and SCISEARCH were searched. Further references were sought from published trials and their authors.

SELECTION CRITERIA

All randomised clinical trials comparing benzodiazepines with placebo for people with antipsychotic-induced acute akathisia.

DATA COLLECTION AND ANALYSIS

Two reviewers, working independently, selected, quality assessed and extracted data. These data were then analysed on an intention-to-treat basis. For homogeneous dichotomous data the fixed effects relative risk (RR), the 95% confidence intervals (CI) and, where appropriate, the number needed to treat (NNT) were calculated on an intention-to-treat basis. For continuous data, reviewers calculated weighted mean differences.

MAIN RESULTS

Two small (total N=27) randomised controlled trials were included. By seven to 14 days, there was a reduction in symptoms for those patients receiving clonazepam compared with placebo (2 RCTs, N=26, RR 0.09 CI 0.01 to 0.6, NNT 1.2 CI 0.9 to 1.5). No significant difference was found for adverse events (2 RCTs, N=26, RR 3.00 CI 0.2 to 62) or the need for anticholinergic medication (2 RCTs, N=26, RR 1.56 CI 0.9 to 2.7). No one left the two studies early. Data on mental, social and family outcomes could not be pooled and there was little or no data on user satisfaction, deaths, violence, criminal behaviour and costs.

REVIEWER'S CONCLUSIONS

Over a short follow-up period, the use of benzodiazepines may reduce the symptoms of antipsychotic-induced acute akathisia. This review highlights the need for well designed, conducted and reported clinical trials to address the claims of open studies.

Potentials and pitfalls using high affinity radioligands in PET and SPET determinations on regional drug induced D2 receptor occupancy--a simulation study based on experimental data

The D2 dopamine receptor density ranges from 0.2 to 40 nM among human brain regions. For high density regions radioligands like [(11)C]raclopride provide accurate and reliable estimates of the receptor density. In research on neuropsychiatric disorders there is, however, a growing need for quantitative approaches that accurately measure D2 dopamine receptor occupancy induced by drugs or endogenous dopamine in regions with low receptor density. The new high affinity radioligands [(11)C]FLB 457 and [(123)I]epidepride have been shown to provide a signal for extrasriatal D2 dopamine receptor populations in the human brain in vivo. Initial observations indicate, however, that the time required to reach equilibrium is dependent on receptor density. Ratio analyses may thus not be readily used for comparisons among different brain regions. The aim of the present simulation study was to examine commonly used approaches for calculation of drug induced D2 dopamine receptor occupancy among regions with widely different receptor density. The input functions and the rate constants of [(11)C]FLB 457 and the reference ligand [(11)C]raclopride were first used in a simulation estimating the effect of receptor density on equilibrium time. In a second step we examined how errors produced by inaccurate determination of the binding potential parameter propagate to calculations of drug induced receptor occupancy. The simulations showed a marked effect of receptor density on equilibrium time for [(11)C]FLB 457, but not for [(11)C]raclopride. For [(11)C]FLB 457, a receptor density above about 7 nM caused the time of equilibrium to fall beyond time of data acquisition (1 h). The use of preequilibrium data caused the peak equilibrium and the end time ratio approaches but not the simplified reference tissue model (SRTM) approach to underestimate the binding potential and thus also the drug occupancy calculated for high-density regions. The study supports the use of ratio and SRTM analyses in extrastriatal low-density receptor regions for which the high affinity ligand [(11)C]FLB 457 was developed. However, in high-density regions such as the human striatum simple ratio approaches cannot be validly applied, whereas the SRTM approach has higher potential to provide valid estimates. Interestingly, the results suggest that published data on a proposed extrastriatal selectivity for the antipsychotic drugs clozapine and olanzapine may be due to erroneous estimations of the binding potential when using ratio approaches.

Should the treatment of schizophrenia include old antipsychotic drugs?

Clozapine, although not suitable as a first-line drug, is superior to all other antipsychotics in terms of minimizing positive symptoms, reducing side effects, and treating treatment-resistant patients. There is little evidence that other newer drugs share these benefits. For certain patients it is not difficult to justify, on clinical grounds, the additional cost of prescribing clozapine. The case for prescribing one of the other newer drugs in preference to a traditional antipsychotic is often less clear-cut. Traditional antipsychotics clearly still have a role in the treatment of schizophrenia and they remain the authors' preferred choice of first-line therapy.