Positron emission tomography studies of the D₁ dopamine receptor in schizophrenia

This thesis is based on investigations of central D1-dopamine receptor (D1R) binding in vivo using positron emission tomography (PET). The aims were i) to examine the antipsychotic effect of a D1R antagonist in schizophrenia and ii) to test the dopamine hypothesis of schizophrenia by comparing D1R binding between patients and healthy subjects. SCH39166, is the first selective D1R antagonist that was developed both as a PET radioligand for D1R and as an antipsychotic drug. The D1-receptor occupancy of SCH39166 was determined with PET and [11C]SCH39166 in a dose-response fashion after single oral doses in healthy volunteers. The D1R occupancy in the putamen was about 70 % after 100 mg. The conclusion was that this dose would be adequate to investigate potential antipsychotic effect of a D1R antagonist in schizophrenia. SCH39166 was then given orally in escalating doses to 17 acutely ill drug free schizophrenic patients (DSM-IIIR) in an open 4-week study. The drug had to be withdrawn prematurely in ten patients due to deterioration or refusal to take SCH39166. In the nine patients participating for more than 2 weeks, the drug did not have an apparent antipsychotic effect. After withdrawal of SCH39166, the patients improved when treated with classical neuroleptics or clozapine. The result of the study does not support the prediction that selective D1R antagonism have antipsychotic effect in schizophrenia. To better inform statistical evaluation of any cross sectional evaluation of D1R binding a testretest PET study of the D1R selective radioligand [11C]SCH23390 was performed in fifteen healthy subjects to compare different methodologies of image analysis. The binding potential (BPND ) values were compared following manual and automated delineation of regions of interest (ROI’s) as well as with and without frame-by-frame realignment. No significant differences were observed for repeatability using automated and manual delineation methods whereas frame-by-frame realignment generated higher BPND values and improved repeatability. The results suggest that the choice of ROI delineation method is not an important condition for reliability, whereas thorough movement correction is of importance. A cohort of 18 first-episode neuroleptic-naïve patients with schizophrenia or schizophreniform psychosis and 17 healthy control subjects were examined with PET and [11C]SCH23390. The patients had a statistically significant lower D1R BPND in frontal cortex with a moderate effect size. This suggests a reduction of prefrontal D1R density in the pathophysiology of schizophrenia. Study II and IV provides indirect support for the hypothesis of frontal hypodopaminergia. The observation of a low D1R-binding in schizophrenia may explain why a D1R-antagonist (which further reduces the availability of D1R) has no obvious antipsychotic effect. The findings provide support for current developments of D1R-agonists for the treatment of schizophrenia

Test-retest reproducibility of [11C]-l-deprenyl-D2 binding to MAO-B in the human brain

Abstract Background [11C]-l-deprenyl-D2 is a positron emission tomography (PET) radioligand for measurement of the monoamine oxidase B (MAO-B) activity in vivo brain. The estimation of the test-retest reproducibility is important for accurate interpretation of PET studies. Results We performed two [11C]-l-deprenyl-D2 scans for six healthy subjects and evaluated the test-retest variability of this radioligand. MAO-B binding was quantified by two tissue compartment model (2TCM) with three rate constants (K 1, k 2, k 3) using metabolite-corrected plasma radioactivity. The λk 3 defined as (K 1/k 2) × k 3 was also calculated. The correlation between MAO-B binding and age, and the effect of partial volume effect correction (PVEc) for the reproducibility were also estimated. %difference of k 3 was 2.6% (medial frontal cortex) to 10.3% (hippocampus), and that of λk 3 was 5.0% (thalamus) to 9.2% (cerebellum). Mean %difference of all regions were 5.3 and 7.0% in k 3 and λk 3, respectively. All regions showed below 10% variabilities except the hippocampus in k 3 (10.3%). Intraclass correlation coefficient (ICC) of k 3 was 0.78 (hippocampus) to 0.98 (medial frontal cortex), and that of λk 3 was 0.78 (hippocampus) to 0.95 (thalamus). Mean ICC were 0.94 and 0.89 in k 3 and λk 3, respectively. The highest positive correlation with age was observed in the hippocampus, as r = 0.75 in k 3 and 0.76 in λk 3. After PVEc, mean %difference were 5.6 and 7.2% in k 3 and λk 3, respectively. Mean ICC were 0.92 and 0.90 for k 3 and λk 3, respectively. These values were almost the same as those before PVEc. Conclusions The present results indicate that k 3 and λk 3 of [11C]-l-deprenyl-D2 are reliable parameters for test-retest reproducibility with healthy subjects both before and after PVEc. The studies with patients of larger sample size are required for further clinical applications

[11C]SCH23390 binding to the D-1-dopamine receptor in the human brain : a comparison of manual and automated methods for image analysis

Background: The D-1-dopamine receptor radioligand [C-11] SCH23390 has been frequently used in PET studies. In drug-naive patients with schizophrenia, the findings have been inconsistent, with decreases, increases, and no change in the frontal cortex D-1-dopamine receptors. While these discrepancies are likely primarily due to a lack of statistical power in these studies, we speculated that an additional explanation may be the differences due to methods of image analysis between studies, affecting reliability as well as bias between groups. Methods: Fifteen healthy subjects underwent two PET measurements with [C-11] SCH23390 on the same day. The binding potential (BPND) was compared using a 95% confidence interval following manual and automated delineation of a region of interest (ROI) as well as with and without frame-by-frame realignment. Results: Automated target region delineation produced lower BPND values, while automated delineation of the reference region yielded higher BPND values. However, no significant differences were observed for repeatability using automated and manual delineation methods. Frame-by-frame realignment generated higher BPND values and improved repeatability. Conclusions: The results suggest that the choice of ROI delineation method is not an important factor for reliability, whereas the improved results following movement correction confirm its importance in PET image analysis. Realignment is therefore especially important for measurements in patient populations such as schizophrenia or Parkinson's disease, where motion artifacts may be more prevalent

Reliability of volumetric and surface-based normalisation and smoothing techniques for PET analysis of the cortex : A test-retest analysis using [11C]SCH-23390

Parametric voxelwise analysis is a commonly used tool in neuroimaging, as it allows for identification of regions of effects in the absence of a strong a-priori regional hypothesis by comparing each voxel of the brain independently. Due to the inherent imprecision of single voxel measurements, spatial smoothing is performed to increase the signal-to-noise ratio of single-voxel estimates. In addition, smoothing compensates for imprecisions in anatomical registration, and allows for the use of cluster-based statistical thresholding. Smoothing has traditionally been applied in three dimensions, without taking the tissue types of surrounding voxels into account. This procedure may be suitable for subcortical structures, but is problematic for cortical regions for which grey matter often constitutes only a small proportion of the smoothed signal. New methods have been developed for cortical analysis in which voxels are sampled to a surface, and smoothing is restricted to neighbouring regions along the cortical grey matter in two dimensions. This procedure has recently been shown to decrease intersubject variability and bias of PET data. The aim of this study was to compare the variability, bias and test-retest reliability of volumetric and surface-based methods as they are applied in practice. Fifteen healthy young males were each measured twice using the dopamine D1 receptor radioligand [11C]SCH-23390, and analyses were performed at the level of individual voxels and vertices within the cortex. We found that surface-based methods yielded higher BPND values, lower coefficient of variation, less bias, better reliability and more precise estimates of parametric binding. All in all, these results suggest that surface-based methods exhibit superior performance to volumetric approaches for voxelwise analysis of PET data, and we advocate for their use when a ROI-based analysis is not appropriate

Is dopamine D1 receptor availability related to social behavior? : A positron emission tomography replication study

Background Associations between dopamine receptor levels and pro- and antisocial behavior have previously been demonstrated in human subjects using positron emission tomography (PET) and self-rated measures of personality traits. So far, only one study has focused on the dopamine D1-receptor (D-1-R), finding a positive correlation with the trait social desirability, which is characterized by low dominant and high affiliative behavior, while physical aggression showed a negative correlation. The aim of the present study was to replicate these previous findings using a new independent sample of subjects. Materials and methods Twenty-six healthy males were examined with the radioligand [C-11]SCH-23390, and completed the Swedish universities Scales of Personality (SSP) which includes measures of social desirability and physical trait aggression. The simplified reference tissue model with cerebellum as reference region was used to calculate BPND values in the whole striatum and limbic striatum. The two regions were selected since they showed strong association between D-I-R availability and personality scores in the previous study. Pearson's correlation coefficients and replication Bayes factors were then employed to assess the replicability and robustness of previous results. Results There were no significant correlations (all p values >0.3) between regional BPND values and personality scale scores. Replication Bayes factors showed strong to moderate evidence in favor no relationship between Dl-receptor availability and social desirability (striatum BF01 = 12.4; limbic striatum BF01 = 7.2) or physical aggression scale scores (limbic striatum BF01 = 3.3), compared to the original correlations. Discussion We could not replicate the previous findings of associations between D1-R availability and either pro- or antisocial behavior as measured using the SSP. Rather, there was evidence in favor of failed replications of associations between BPND and scale scores. Potential reasons for these results are restrictive variance in both PET and personality outcomes due to high sample homogeneity, or that the previous findings were false positives

Additional file 1: of [11C]SCH23390 binding to the D1-dopamine receptor in the human brain—a comparison of manual and automated methods for image analysis

Table S1. Mean BPND values of [11C]SCH23390 in the morning and afternoon, the absolute variability, and ICC in 15 healthy men in four brain regions. There are eight BPND values for each region derived from the different combinations of methods in the analysis process. (DOCX 18 kb

Prior and posterior distributions underlying the replication Bayes factors.

<p>In each graph the dotted line denotes the prior which is determined by the correlation from the original study. The posterior (solid line) is obtained by updating the prior using the correlation from the present study. The Savage-Dickey Ratio (the ratio between the heights of the two dots) is then used to calculate the Bayes factor in favor of the original correlation over the null-hypothesis of no correlation. See Verhagen & Wagenmakers [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193770#pone.0193770.ref014" target="_blank">14</a>] for a full explanation of this procedure. In this study, data support the null hypothesis over the original correlations and the Bayes factors hence signifies failed replications.</p

Correlations between SocDes and PhTA scores and ROI BPND from the previous [9] and present study.

<p>The table also displays the replication BFs which denotes how much support there is for a successful replication, by quantifying how much evidence there is in favor of the original correlation compared to no correlation. Note that the correlation between PhTA and STR was not significant in the original study but have still been included here for completeness.</p

Relationships between D1-R BP_ND in striatum and social desirability and physical trait aggression.

<p>The dotted lines indicate the 95% confidence intervals. Raw scale scores have been transformed to T-scores for illustrative purposes in this figure.</p

D1-R BP_ND map and regions of interest.

<p>The top row displays an average D1-R BP_ND brain map of all subjects. The middle row shows the whole-striatum ROI (red). The bottom row shows the limbic striatum ROI (yellow) used in this replication study.</p