Assessment of spatial normalization of PET ligand images using ligand-specific templates

GABAergic dysfunction in essential tremor: an 11C-flumazenil PET study

Essential tremor is the most common movement disorder, but the underlying pathophysiology is not well understood. A primary overactivity of cerebellothalamic output pathways is the most conspicuous finding, as indicated by animal and human studies. It has been argued that this overactivity may be due to impaired central inhibition, and converging evidence points toward a potential role of gamma-aminobutyric acid (GABA) dysfunction in tremor generation.

METHODS

Using (11)C-flumazenil and PET, we calculated the distribution volume, an index of availability of benzodiazepine receptor sites of the GABA(A) complex, in a group of 8 patients with bilateral essential tremor, as compared with 11 healthy controls.

RESULTS

Significant increases in binding of (11)C-flumazenil at the benzodiazepine receptor site of the GABA(A) receptor in the cerebellum, the ventrolateral thalamus, and the lateral premotor cortex were identified in the essential tremor group.

CONCLUSION

Essential tremor is associated with reduced GABAergic function and increased availability of benzodiazepine receptor sites in brain regions implicated specifically in tremor genesis. This finding is thought to reflect overactivity of cerebellothalamic circuits and, hence, lends support to the "GABA hypothesis" of essential tremor.

Significant decreases in frontal and temporal [11C]-raclopride binding after THC challenge

Delta9-tetrahydrocannabinol (THC) increases prefrontal cortical dopamine release in animals, but this is yet to be examined in humans. In man, striatal dopamine release can be indexed using [11C]-raclopride positron emission tomography (PET), and recent reports suggest that cortical [11C]-raclopride binding may also be sensitive to dopaminergic challenges. Using an existing dataset we examined whether THC alters [11C]-raclopride binding potential (BP(ND)) in cortical regions. Thirteen healthy volunteers underwent two [11C]-raclopride PET scans following either oral 10 mg THC or placebo. Significant areas of decreased cortical [11C]-raclopride BP(ND) were identified using whole brain voxel-wise analysis and quantified using a region of interest (ROI) ratio analysis. Effect of blood flow on binding was estimated using a simplified reference tissue model analysis. Results were compared to [11C]-raclopride test-retest reliability in the ROIs identified using a separate cohort of volunteers. Voxel-wise analysis identified three significant clusters of decreased [11C]-raclopride BP(ND) after THC in the right middle frontal gyrus, left superior frontal gyrus and left superior temporal gyrus. Decreases in [11C]-raclopride BPND following THC were greater than test-retest variability in these ROIs. R1, an estimate of blood flow, significantly decreased in the left superior frontal gyrus in the THC condition but was unchanged in the other ROIs. Decreased frontal binding significantly correlated to catechol-o-methyl transferase (COMT) val108 status. We have demonstrated for the first time significant decreases in bilateral frontopolar cortical and left superior temporal gyrus [11C]-raclopride binding after THC. The interpretation of these findings in relation to prefrontal dopamine release is discussed.

Competition between 11C-raclopride and endogenous dopamine in Parkinson's disease

OBJECTIVE

The aim of this study was to understand whether the increase in 11C-raclopride binding in the striatum of patients with Parkinson's disease (PD) is associated with the depletion of endogenous dopamine.

METHODS

Positron emission tomography (PET) scans of the two dopamine D2 receptor ligands, 11C-raclopride and 11C-N-methylspiperone (11C-NMSP), and the dopamine transporter ligand, 11C-2beta-carbomethoxy-3beta-(4-fluorophenyl)-tropane, were performed on five patients with PD and seven controls. The binding of each tracer was calculated by using a (region-cerebellum)/cerebellum ratio in the caudate, anterior putamen, and posterior putamen.

RESULTS

In patients with PD, the 11C-raclopride to 11C-NMSP ratios in the posterior putamen, which was the subregion of the striatum with the lowest binding of 11C-2beta-carbomethoxy-3beta-(4-fluorophenyl)-tropane, were the largest among all three subregions of the striatum. In controls, the 11C-raclopride to 11C-NMSP ratios in all three subregions of the striatum were within a constant range.

CONCLUSION

In patients with PD, the kinetic difference between 11C-raclopride and 11C-NMSP was found prominently in the posterior putamen, in which presynaptic degeneration occurred most profoundly. Therefore, we concluded that the increase in 11C-raclopride binding in the striatum of patients with PD was strongly associated with the depletion of endogenous dopamine. 11C-NMSP can be chosen in the place of 11C-raclopride in cases in which it may be essential to eliminate the influence of endogenous dopamine.

Acute effect of the anti-addiction drug bupropion on extracellular dopamine concentrations in the human striatum: an [11C]raclopride PET study

Bupropion is an effective medication in treating addiction and is widely used as an aid to smoking cessation. Bupropion inhibits striatal dopamine reuptake via dopamine transporter blockade, but it is unknown whether this leads to increased extracellular dopamine levels at clinical doses in man. The effects of bupropion on extracellular dopamine levels in the striatum were investigated using [(11)C]raclopride positron emission tomography (PET) imaging in rats administered saline, 11 or 25 mg/kg bupropion i.p. and in healthy human volunteers administered either placebo or 150 mg bupropion (Zyban Sustained-Release). A cognitive task was used to stimulate dopamine release in the human study. In rats, bupropion significantly decreased [(11)C]raclopride specific binding in the striatum, consistent with increases in extracellular dopamine concentrations. In man, no significant decreases in striatal [(11)C]raclopride specific binding were observed. Levels of dopamine transporter occupancy in the rat at 11 and 25 mg/kg bupropion i.p. were higher than predicted to occur in man at the dose used. Thus, these data indicate that, at the low levels of dopamine transporter occupancy achieved in man at clinical doses, bupropion does not increase extracellular dopamine levels. These findings have important implications for understanding the mechanism of action underlying bupropions' therapeutic efficacy and for the development of novel treatments for addiction and depression.

Mapping brain morphological and functional conversion patterns in amnestic MCI: a voxel-based MRI and FDG-PET study

PURPOSE

To reveal the morphological and functional substrates of memory impairment and conversion to Alzheimer disease (AD) from the stage of amnestic mild cognitive impairment (aMCI).

METHODS

Brain MRI and FDG-PET were performed in 20 patients with aMCI and 12 controls at baseline. During a mean follow-up of about 2 years, 9 patients developed AD (converters), and 11 did not (nonconverters). All images were processed with SPM2. FDG-PET and segmented grey matter (GM) images were compared in: (1) converters versus controls, (2) nonconverters versus controls, and (3) converters versus nonconverters.

RESULTS

As compared to controls, converters showed lower GM density in the left parahippocampal gyrus and both thalami, and hypometabolism in the precuneus, posterior cingulate and superior parietal lobule in the left hemisphere. Hypometabolism was found in nonconverters as compared to controls in the left precuneus and posterior cingulated gyrus. As compared to nonconverters, converters showed significant hypometabolism in the left middle and superior temporal gyri.

CONCLUSION

The discordant topography between atrophy and hypometabolism reported in AD is already present at the aMCI stage. Posterior cingulate-precuneus hypometabolism seemed to be an early sign of memory deficit, whereas hypometabolism in the left temporal cortex marked the conversion to AD.

Cortical dopamine D2/D3 receptors and verbal memory in man

INTRODUCTION

It has been previously reported that hippocampal dopamine D2/D3 receptors are involved in the regulation of verbal memory and learning in healthy volunteers. We tested this hypothesis further and studied whether cortical dopamine D2/D3 receptor availability in vivo is associated with verbal memory as assessed with the revised Wechsler Memory Scale (WMS-R).

METHODS

Forty healthy Finnish subjects were evaluated according to the WMS-R and scanned with positron emission tomography (PET) and dopamine D2/D3 receptor radioligand [(11)C]FLB457 for the measurement of cortical D2/D3 receptor binding.

RESULTS

WMS-R verbal memory and learning parameters did not significantly correlate with D2/D3 receptor binding potential (BP(ND)) in the studied cortical regions.

CONCLUSIONS

Our findings do not support a major role for cortical D2/D3 receptors in the regulation of verbal memory in healthy individuals.

The implication of nigrostriatal dopaminergic degeneration in the pathogenesis of REM sleep behavior disorder

BACKGROUND AND PURPOSE

The pathogenesis of rapid eye movement (REM) sleep behavior disorder (RBD) is not clear despite its frequent association with Parkinson's disease (PD). We investigated whether the nigrostriatal dopaminergic system is involved in the development of idiopathic RBD.

METHODS

Fourteen patients with RBD, 14 patients with PD and 12 normal controls were included in the study. The diagnosis of RBD was confirmed on polysomnography. All the participants performed single-photon emission computed tomography imaging 3 h after injection of [(123)I]FP-CIT. During REM sleep of the RBD patients, each 30-s epoch was rated as 'tonic' when there was at least 50% of tonically maintained chin electromyography (EMG) activity in the epoch. Phasic EMG activities were calculated as the percentage of 3-s mini-epoch containing phasic EMG events (leg and chin, separately).

RESULTS

The RBD patients showed a trend of lower binding in the striatum than the normal controls (P = 0.07), and the significance was revealed in the putamen (P = 0.02). However, in 11 individual cases of the 14 RBD patients, the dopamine transporter (DAT) densities in the putamen still remained within the normal range. In the RBD patients, there was no correlation between EMG activities and DAT densities.

CONCLUSIONS

Nigrostriatal dopaminergic degeneration could be a part of the pathogenesis of RBD, but not essential for the development of RBD. The lack of correlation between RBD severity and DAT densities suggests that another pathogenic process not related to nigrostriatal dopaminergic transmission may be implicated in RBD.

Influence of escitalopram treatment on 5-HT 1A receptor binding in limbic regions in patients with anxiety disorders

There is an increasing interest in the underlying mechanisms of the antidepressant and anxiolytic treatment effect associated with changes in serotonergic neurotransmission after treatment with selective serotonin (5-HT) reuptake inhibitors (SSRIs) in humans. The 5-HT(1A) receptor is known to play a crucial role in the pathophysiology of affective disorders, and altered 5-HT(1A) receptor binding has been found in anxiety patients. SSRI treatment raises the 5-HT level in the synaptic cleft and might change postsynaptic receptor densities. Therefore, our study in patients suffering from anxiety disorders investigated the effects of long-term treatment with escitalopram on the 5-HT(1A) receptor. A longitudinal positrone emission tomography (PET) study in 12 patients suffering from anxiety disorders was conducted. Two dynamic PET scans were performed applying the selective 5-HT(1A) receptor antagonist [carbonyl-(11)C]WAY-100635. Eight regions of interest were defined a priori (orbitofrontal cortex, amygdala, hippocampus, subgenual cortex, anterior and posterior cingulate cortex, dorsal raphe nucleus and cerebellum as reference). After the baseline PET scan, patients were administered escitalopram (average dose of 11.2+/-6.0 mg day(-1)) for a minimum of 12 weeks. A second PET scan was conducted after 109+/-27 days. 5-HT(1A) receptor binding potentials in 12 patients were assessed by PET applying the Simplified Reference Tissue Model.There was a significant reduction in the 5-HT(1A) receptor binding potential after a minimum of 12 weeks of escitalopram treatment in the hippocampus (P=0.006), subgenual cortex (P=0.017) and posterior cingulate cortex (P=0.034). The significance of the hippocampus region survived the Bonferroni-adjusted threshold for multiple comparisons. These PET data in humans in vivo demonstrate a reduction of the 5-HT(1A) binding potential after SSRI treatment.

C957T polymorphism of the human dopamine D2 receptor gene predicts extrastriatal dopamine receptor availability in vivo

The C957T (rs6277) single nucleotide polymorphism (SNP) of the human dopamine D2 receptor (DRD2) gene (DRD2) affects DRD2 mRNA stability and has been shown to predict striatal DRD2 availability (B(max)/K(D)) in vivo in man. Specifically, the C/C genotype is associated with low striatal DRD2 availability (C/C<C/T<T/T). It is not known, however, whether this pattern of genetic regulation of DRD2 expression also applies to low density DRD2 populations in extrastriatal regions. We analyzed extrastriatal DRD2 availability (indexed by binding potential, BP(ND)) measured in 38 healthy male volunteers with 3D-PET and the high-affinity DRD2 radioligand [(11)C]FLB457. The subjects were genotyped for the C957T as well as for two other widely studied DRD2 SNPs, the TaqIA (rs1800497) and the -141C Ins/Del (rs1799732). Statistical analyses showed that the C957T C/C genotype was associated with high extrastriatal DRD2 BP(ND) throughout the cortex and the thalamus (C/C>C/T>T/T). Also the TaqIA A1 allele carriers (p=0.101) tended to have higher extrastriatal DRD2 BP(ND) compared to non-carriers whereas the -141C Ins/Del genotype did not influence extrastriatal DRD2 BP(ND). Our findings indicate that the DRD2 SNPs regulate DRD2 availability in the human cortex and in the thalamus in vivo. However, the regulation pattern is different from that observed previously for striatal DRD2 availability in vivo, which may reflect distinct functional roles of dopamine and DRD2 in the cortex versus the striatum. The results provide useful information for the interpretation of genetic studies exploring the role of the DRD2 in normal physiology as well as in psychiatric and neurological diseases.

Reproducibility of automated simplified voxel-based analysis of PET amyloid ligand [11C]PIB uptake using 30-min scanning data

PURPOSE

Positron emission tomography (PET) with 11C-labelled Pittsburgh compound B ([11C]PIB) enables the quantitation of beta-amyloid accumulation in the brain of patients with Alzheimer's disease (AD). Voxel-based image analysis techniques conducted in a standard brain space provide an objective, rapid and fully automated method to analyze [11C]PIB PET data. The purpose of this study was to evaluate both region- and voxel-level reproducibility of automated and simplified [11C]PIB quantitation when using only 30 min of imaging data.

METHODS

Six AD patients and four healthy controls were scanned twice with an average interval of 6 weeks. To evaluate the feasibility of short scanning (convenient for AD patients), [11C]PIB uptake was quantitated using 30 min of imaging data (60 to 90 min after tracer injection) for region-to-cerebellum ratio calculations. To evaluate the reproducibility, a test-retest design was used to derive absolute variability (VAR) estimates and intraclass correlation coefficients at both region-of-interest (ROI) and voxel level.

RESULTS

The reproducibility both at the region level (VAR 0.9-5.5%) and at the voxel level (VAR 4.2-6.4%) was good to excellent. Based on the variability estimates obtained, power calculations indicated that 90% power to obtain statistically significant difference can be achieved using a sample size of five subjects per group when a 15% change from baseline (increase or decrease) in [11C]PIB accumulation in the frontal cortex is anticipated in one group compared to no change in another group.

CONCLUSION

Our results showed that an automated analysis method based on an efficient scanning protocol provides reproducible results for [11C]PIB uptake and appears suitable for PET studies aiming at the quantitation of amyloid accumulation in the brain of AD patients for the evaluation of progression and treatment effects.

The dopaminergic basis of human behaviors: A review of molecular imaging studies

This systematic review describes human molecular imaging studies which have investigated alterations in extracellular DA levels during performance of behavioral tasks. Whilst heterogeneity in experimental methods limits meta-analysis, we describe the advantages and limitations of different methodological approaches. Interpretation of experimental results may be limited by regional cerebral blood flow (rCBF) changes, head movement and choice of control conditions. We revisit our original study of striatal DA release during video-game playing [Koepp, M.J., Gunn, R.N., Lawrence, A.D., Cunningham, V.J., Dagher, A., Jones, T., Brooks, D.J., Bench, C.J., Grasby, P.M., 1998. Evidence for striatal dopamine release during a video game. Nature 393, 266-268] to illustrate the potentially confounding influences of head movement and alterations in rCBF. Changes in [(11)C]raclopride binding may be detected in extrastriatal as well as striatal brain regions-however we review evidence which suggests that extrastriatal changes may not be clearly interpreted in terms of DA release. Whilst several investigations have detected increases in striatal extracellular DA concentrations during task components such as motor learning and execution, reward-related processes, stress and cognitive performance, the presence of potentially biasing factors should be carefully considered (and, where possible, accounted for) when designing and interpreting future studies.

Regional analysis of age-related decline in dopamine transporters and dopamine D2-like receptors in human striatum

The purpose of this study was to evaluate the mechanisms of age-related decline of dopamine transporter (DAT) and dopamine D(2)-like receptor (D2R) densities in the human striatum by focusing on regional difference.

METHODS

Positron emission tomography (PET) with [(11)C]CFT and [(11)C]raclopride for measuring DATs and D2Rs, respectively, was performed on 16 healthy volunteers ranging from 21 to 74 years in age. To evaluate in detail the regional difference within the striatum, in addition to the conventional region-of-interest-based analysis, we created a parametric image that enabled us to visualize the regional decline rate on a voxel-by-voxel basis, mapping the slope of the regression line between the age and uptake index of each tracer.

RESULTS

The decreasing rates corresponded to 6.1, 5.5, and 5.6% per decade for DATs and 5.8, 4.9, and 4.8% per decade for D(2)Rs in the caudate nucleus, anterior putamen, and posterior putamen, respectively. The caudate nucleus for both DATs and D(2)Rs were the fastest among the striatum, and the regional difference of the decreasing rate for DATs was consistently associated with that for D2Rs. Meanwhile, previous histological studies have shown that age-related cell loss in the substantia nigra is likely to preferentially affect its dorsomedial part, which projects to the caudate nucleus.

CONCLUSIONS

These results suggested that neuronal cell loss in the substantia nigra may be associated with the age-related DAT decline, and DAT decline may be associated functionally with age-related D2R decline.

Hypothalamic involvement in Huntington's disease: an in vivo PET study

Recent studies have shown alterations in metabolism, sleep and circadian rhythms as well as in several neuropeptides derived from the hypothalamic-pituitary axis in Huntington's disease patients; however, the pathology underlying these abnormalities is not known. Our aim was to assess in vivo D(2) receptor's loss/dysfunction and increases in microglial activation in the hypothalamus of symptomatic Huntington's disease patients and premanifest Huntington's disease gene carriers using PET with (11)C-raclopride (RAC), a specific D(2) receptor ligand and (11)C-(R)-PK11195 (PK), a marker of microglial activation. We have studied 9 symptomatic Huntington's disease patients (age = 46.8 +/- 4.7 years; mean +/- SD) and 10 premanifest Huntington's disease gene carriers (age = 41.9 +/- 8.2 years; mean +/- SD). RAC and PK findings for these subjects were compared with those of a group of normal controls (RAC, n = 9; PK, n = 10). In the symptomatic Huntington's disease group, we found a significant decrease (P = 0.0012) in mean hypothalamic RAC binding potential (BP) and a significant increase in mean hypothalamic PK BP (P = 0.0008). Similarly, a significant decrease (P = 0.0143) in mean hypothalamic RAC BP and a significant increase in mean hypothalamic PK BP (P = 0.0057) were observed in the premanifest Huntington's disease group. Hypothalamic RAC and PK BP values correlated with each other in combined Huntington's disease groups (r = -0.6180, P = 0.0048) but not with striatal RAC and PK BP values. Our data demonstrate, for the first time, significant D(2) receptor loss and microglia activation in the hypothalamus of Huntington's disease. These pathological changes occur very early in the course of the disease and may partly explain the development of commonly reported symptoms in Huntington's disease including progressive weight loss, alterations in sexual behaviour and disturbances in the wake-sleep cycle.

Measurement of central mu-opioid receptor binding in vivo with PET and [11C]carfentanil: a test-retest study in healthy subjects

PURPOSE

[(11)C]Carfentanil has been widely used in positron emission tomography (PET) studies for measuring micro-opioid receptor binding in humans, but the reproducibility of the binding parameter estimates is unknown.

MATERIALS AND METHODS

Eight healthy volunteers were scanned twice during the same day with [(11)C]carfentanil PET, and binding to receptors was assessed with both reference tissue and arterial plasma input-based models using region of interest (ROI) and voxel-based quantification.

RESULTS

The two-tissue compartmental model distribution volume (V(T)) was highly reproducible as indicated by low variability (VAR < 6%) and high intraclass correlation coefficients (ICC > 0.93). BP(ND) (BP relative to the nondisplaceable tissue compartment) was also highly reproducible (VAR < 10%, ICC > 0.90) both at ROI- and voxel-level, and reference tissue-based models provided stable estimates after 40 min.

CONCLUSIONS

The reproducibility of [(11)C]carfentanil binding parameter estimates is excellent with outcome measures based on both arterial plasma and reference tissue input, and a scanning time of 40 min appears sufficient.

Loss of asymmetry in D2 receptors of putamen in unaffected family members at increased genetic risk for schizophrenia

OBJECTIVE

Dopamine dysregulation has been implicated in the pathophysiology of schizophrenia. The present study was performed to examine whether unaffected relatives at high genetic risk of schizophrenia have dopamine dysregulation in comparison with healthy controls.

METHOD

Eleven unaffected relatives from families with two or more first- or second-degree relatives with schizophrenia (n = 9) or with a monozygotic schizophrenic twin (n = 2) and 11 age- and sex-matched controls were examined using positron emission tomography (PET) with [(11)C] raclopride. Subjects also underwent extensive neuropsychological testing.

RESULTS

Subjects with high genetic risk showed a loss of asymmetry of D(2) receptors in the putamen in comparison with healthy controls. In addition, they showed significantly poorer performance on neuropsychological tests than controls.

CONCLUSION

Our results suggest that dopamine dysregulation and neuropsychological dysfunction may be present in subjects at high genetic risk of schizophrenia. However, further studies are required to confirm these findings.

Evidence of dopamine dysfunction in the hypothalamus of patients with Parkinson's disease: an in vivo 11C-raclopride PET study

A mild to moderate reduction in dopamine, noradrenaline and serotonin levels alongside a progressive loss of hypocretin cells and melanin hormone concentrating cells has been reported in the hypothalamus of PD at postmortem. Hypothalamic uptake of (18)F-dopa PET, an in vivo marker of dysfunction of monoaminergic neurons, is also significantly reduced in these patients. These data indicate a general impairment of hypothalamic function in PD. Dopamine receptors play an important role in the regulation of hypothalamic pathways. To date, possible changes in hypothalamic D(2) receptor availability have not been investigated in PD. The objective in this study was to assess dopamine D(2) receptor availability in hypothalamus of patients with idiopathic Parkinson's disease (PD) using positron emission tomography (PET) with (11)C-raclopride (RAC). We evaluated D(2) binding in RAC PET images of 14 PD patients using both region of interest (ROI) analysis and a voxel based approach. ROIs for the hypothalamus were traced on the subject's MRI co-registered to the PET image. (11)C-raclopride binding potentials (BP) for hypothalamus were obtained by applying ROIs onto parametric images. Findings were compared with those of 9 normal controls. We found a significant reduction in the mean hypothalamic RAC BP of the PD patients compared with the normal controls (0.2714+/-0.06 vs. 0.3861+/-0.04; mean+/-SD; p=0.0005). ROI results were confirmed with statistical parametric mapping (SPM). Individual hypothalamic BP values of PD patients did not correlate with age, disease duration, disease severity and levodopa equivalent dose. It remains to be ascertained whether the reductions in hypothalamic D(2) receptor availability seen in PD are disease related, the results of chronic exposure to levodopa or both. Our results provide further evidence of dopaminergic dysfunction in the hypothalamus in PD, and this may contribute to the development of sleep, endocrine and autonomic disorders.

The serotonin-1A receptor distribution in healthy men and women measured by PET and [carbonyl-11C]WAY-100635

PURPOSE

The higher prevalence rates of depression and anxiety disorders in women compared to men have been associated with sexual dimorphisms in the serotonergic system. The present positron emission tomography (PET) study investigated the influence of sex on the major inhibitory serotonergic receptor subtype, the serotonin-1A (5-HT(1A)) receptor.

METHODS

Sixteen healthy women and 16 healthy men were measured using PET and the highly specific radioligand [carbonyl-(11)C]WAY-100635. Effects of age or gonadal hormones were excluded by restricting the inclusion criteria to young adults and by controlling for menstrual cycle phase. The 5-HT(1A) receptor BP(ND) was quantified using (1) the 'gold standard' manual delineation approach with ten regions of interest (ROIs) and (2) a newly developed delineation method using a PET template normalized to the Montreal Neurologic Institute space with 45 ROIs based on automated anatomical labeling.

RESULTS

The 5-HT(1A) receptor BP(ND) was found equally distributed in men and women applying both the manual delineation method and the automated delineation approach. Women had lower mean BP(ND) values in every region investigated, with a borderline significant sex difference in the hypothalamus (p = 0.012, uncorrected). There was a high intersubject variability of the 5-HT(1A) receptor BP(ND) within both sexes compared to the small mean differences between men and women.

CONCLUSIONS

To conclude, when measured in the follicular phase, women do not differ from men in the 5-HT(1A) receptor binding. To explain the higher prevalence of affective disorders in women, further studies are needed to evaluate the relationship between hormonal status and the 5-HT(1A) receptor expression.

Decreased brain serotonin 5-HT1A receptor availability in medication-naive patients with major depressive disorder: an in-vivo imaging study using PET and [carbonyl-11C]WAY-100635

Serotonin (5-HT) is involved in the pathophysiology of major depressive disorder (MDD). Among the numerous serotonergic receptors, the 5-HT1A receptor subtype is of interest because of its involvement in cognition, hippocampal neurogenesis, and mechanism of action of antidepressant drugs. Previous imaging studies have suggested altered availability of 5-HT1A receptors in MDD but prior antidepressant medication and chronicity of the illness may confound the interpretation. We examined 21 drug-naive primary-care patients with MDD using positron emission tomography (PET) imaging with [carbonyl-11C]WAY-100635, a radioligand for 5-HT1A receptors, along with 15 healthy control subjects. Binding to receptors was assessed both regionally and at voxel level with the binding potential (BP) that was estimated using arterial blood input. Compared with healthy controls, the BP of [carbonyl-11C]WAY-100635 was reduced in patients with MDD in most brain regions, ranging from -9% to -25%. Voxel-level analysis confirmed this finding by showing a widespread reduction of [carbonyl-11C]WAY-100635 BP. No statistically significant associations were observed between BP and total HAMD scores in the patients, but lower BP was associated with higher likelihood of insomnia. This study demonstrated a widespread reduction in the availability of serotonin 5-HT1A receptors in a relatively large sample of drug-naive primary-care patients with MDD, suggesting the involvement of this receptor subtype in the pathophysiology of the illness. Lack of correlation with overall severity of the illness may relate to a largely trait-like nature of this abnormality in depressive disorders.

Striatal dopamine D2 receptors in medication-naive patients with major depressive disorder as assessed with [11C]raclopride PET

RATIONALE

Among other monoamine neurotransmitters, dopamine is implicated in the pathophysiology of major depression. Experimental studies suggest the involvement of the mesolimbic dopamine system in the mechanism of action of antidepressant drugs. Previous in vivo imaging studies have studied striatal dopamine D2 receptor availability in depression but the results are equivocal thus far.

OBJECTIVE

To study the striatal and thalamic dopamine D2 receptor availability in drug-naive patients with major depression was the aim of this study.

MATERIALS AND METHODS

Caudate, putamen, and thalamic dopamine D2 receptor availability was estimated using positron emission tomography and [11C]raclopride in 25 treatment-seeking drug-free patients (of whom 24 were drug-naive) with major depression (primary care patients) as well as in 19 demographically similar healthy control subjects. Receptor availability was expressed as the binding potential (BP ND), and analyses were carried out based on both regional and voxel-level BP ND estimates.

RESULTS

No statistically significant differences in [11C]raclopride BP ND were observed between the groups either in the caudate nucleus (+1.7%, CI -4.8% to +8.3%), putamen (-1.0%, CI -7.2% to 5.1%), thalamus (-2.4%, CI -8.7% to 4.0%), or ventral striatum (-3.8%, CI -9.3% to +1.6%). In the patients, depressive symptoms were not associated with [11C]raclopride BP ND in any region.

CONCLUSIONS

The findings in this sample of treatment-seeking, drug-naive and predominantly first-episode patients with major depression do not support the involvement of striatal dopamine D2 receptors in the pathophysiology of the illness, but do not exclude the potential importance of dopaminergic mechanisms in antidepressant drug action.

Mechanisms of dopaminergic and serotonergic neurotransmission in Tourette syndrome: clues from an in vivo neurochemistry study with PET

Tourette syndrome (TS) is a neuropsychiatric disorder with childhood onset characterized by motor and phonic tics. Obsessive-compulsive disorder (OCD) is often concomitant with TS. Dysfunctional tonic and phasic dopamine (DA) and serotonin (5-HT) metabolism may play a role in the pathophysiology of TS. We simultaneously measured the density, affinity, and brain distribution of dopamine D2 receptors (D2-R's), dopamine transporter binding potential (BP), and amphetamine-induced dopamine release (DA(rel)) in 14 adults with TS and 10 normal adult controls. We also measured the brain distribution and BP of serotonin 5-HT2A receptors (5-HT2AR), and serotonin transporter (SERT) BP, in 11 subjects with TS and 10 normal control subjects. As compared with controls, DA rel was significantly increased in the ventral striatum among subjects with TS. Adults with TS+OCD exhibited a significant D(2)-R increase in left ventral striatum. SERT BP in midbrain and caudate/putamen was significantly increased in adults with TS (TS+OCD and TS-OCD). In three subjects with TS+OCD, in whom D2-R, 5-HT2AR, and SERT were measured within a 12-month period, there was a weakly significant elevation of DA rel and 5-HT2A BP, when compared with TS-OCD subjects and normal controls. The current study confirms, with a larger sample size and higher resolution PET scanning, our earlier report that elevated DA rel is a primary defect in TS. The finding of decreased SERT BP, and the possible elevation in 5-HT2AR in individuals with TS who had increased DA rel, suggest a condition of increased phasic DA rel modulated by low 5-HT in concomitant OCD.

Measurement of striatal and extrastriatal dopamine transporter binding with high-resolution PET and [11C]PE2I: quantitative modeling and test-retest reproducibility

[(11)C]PE2I is a novel positron emission tomography (PET) radiotracer for the dopamine transporter (DAT). The reproducibility and reliability of [(11)C]PE2I measurements, especially in the small DAT-rich brain regions, is unknown and of critical importance to the interpretation of the data. Five healthy volunteers were scanned twice during the same day using [(11)C]PE2I and the HRRT PET scanner. Methods based on metabolite-corrected arterial plasma curve and reference region were used to estimate distribution volumes (V(T)) and binding potential (BP). Within-subject and between-subject variabilities were compared. [(11)C]PE2I accumulated in the DAT-rich striatum and the midbrain. Equilibrium of specific binding appeared late in the striatum, whereas it was reached earlier in the midbrain. Plasma metabolite analysis showed that the potentially brain-penetrant 4-hydroxymethyl metabolite represented 15% to 20% of total plasma radioactivity. V(T) and BP measurements were associated with low within-subject variability. Measurement of DAT binding in small brain regions, including the substantia nigra, is reproducible and reliable using [(11)C]PE2I and high-resolution research tomograph. A scanning time of more than 70 mins is required for the striatum, while less is sufficient for DAT quantification in the midbrain. The previously suggested involvement of the potentially brain-penetrant radioactive metabolite in the quantification should be further studied.

Cognitive deficits and striato-frontal dopamine release in Parkinson's disease

Idiopathic Parkinson's disease (PD) is often accompanied by a pattern of executive deficits similar to those found in patients with frontal lobe lesions. We investigated whether such cognitive deficits are attributable to frontal lobe dysfunction as a direct consequence of impaired mesocortical dopaminergic transmission or an indirect consequence of impaired nigrostriatal dopaminergic function. For this purpose, changes in synaptic dopamine levels during task performance were monitored using a marker of dopamine D2-receptor availability (11)C-raclopride (RAC) PET. During RAC PET, seven patients with early symptomatic PD and seven age-matched healthy controls performed two types of behavioural task, a spatial working memory task (SWT) and a visuomotor control task (VMT). The SWT involves an executive process which is known to be impaired by both frontal lobe lesions and PD while the VMT is a control test for the visuomotor component of the SWT. Parametric images of RAC binding potential during performance of each task were generated, and compared between the tasks using voxel-based statistical parametric mapping as well as region of interest analysis. In controls, RAC binding was reduced in the dorsal caudate during performance of the SWT compared with the VMT, compatible with increased levels of endogenous dopamine release due to the executive process. In PD patients, this RAC binding reduction was not observed. In contrast, RAC binding in the anterior cingulate cortex within the medial prefrontal cortex was reduced by a comparable level during the SWT both in controls and PD patients. Statistical comparisons between controls and PD patients confirmed significantly attenuated dopamine release in the dorsal caudate in PD, but preserved levels of medial prefrontal dopamine release. Our data suggest that executive deficits in early patients with PD are associated with impaired nigrostriatal dopaminergic function resulting in abnormal processing in the cortico-basal ganglia circuit. In contrast, mesocortical dopaminergic transmission appears well preserved in early PD patients.

Assessment of parameter settings for SPM5 spatial normalization of structural MRI data: application to type 2 diabetes

Spatial normalization is the process of standardizing images of different subjects into the same anatomical space. The goal of this work was to assess standard and unified methods in SPM5 for the normalization of structural magnetic resonance imaging (MRI) data acquired in mid-life/elderly subjects with diabetes. In this work, we examined the impact of different parameters (i.e. nonlinear frequency cutoff, nonlinear regularization and nonlinear iterations) on the normalization, in terms of the residual variability. Total entropy was used to assess the residual anatomical variability after spatial normalization in a sample of 14 healthy mid-life/elderly control subjects and 24 mid-life/elderly subjects with type 2 diabetes. Spatial normalization was performed using default settings and by varying a single parameter or a combination of parameters. Descriptive statistics and nonparametric tests were used to examine differences in total entropy. Statistical parametric mapping analyses were performed to evaluate the influence of parameter settings on the spatial normalization. Total entropy results and SPM analyses suggest that the best parameters for the spatial normalization of mid-life/elderly image data to the MNI template, when applying the standard approach, correspond to the default cutoff (25 mm), heavy regularization, and the default number of nonlinear iterations (16). On the other hand, when applying the unified approach, the default parameters were the best for spatial normalization of mid-life/elderly image data to the MNI priors. These findings are relevant for studies of structural brain alterations that may occur in normal aging, chronic medical conditions, neuropsychiatric disorders, and neurodegenerative disorders.

Task-related interaction between basal ganglia and cortical dopamine release

Dopamine (DA) is a powerful neuromodulator for a wide variety of behaviors. Considerable evidence accumulated from rodent and monkey experiments over the last two decades suggests that DA activity in the frontal cortex is reciprocally linked to that in functionally related basal ganglia (BG) structures. However, the functional importance of this in humans is still unknown. To address this issue, we measured endogenous DA release using positron emission tomography in 15 healthy subjects as they practiced the first training session of a finger sequence learning task. Significant results were observed not only in striatal areas but also in extrastriatal "motor" regions, bilaterally. Faster learning was specifically coupled to lower DA release in the sensorimotor part of the globus pallidus pars interna (GPi) contralateral to the moving hand, which was paralleled by a higher increase in DA levels in the pre-supplementary motor area (pre-SMA). This finding provides original evidence supporting a motor-learning-related interaction between DA release in left GPi and pre-SMA, a mechanism that may also apply to other anatomically and functionally interconnected BG and frontal cortical areas as a function of behavior.

Striatal dopamine synthesis in first-degree relatives of patients with schizophrenia

BACKGROUND

First degree relatives (FDR) of patients with schizophrenia have higher risk of developing schizophrenia than the general population. Previous positron emission tomography (PET) studies have shown that striatal presynaptic dopamine synthesis capacity is increased in schizophrenia. We investigated whether this same phenomenon is shared by individuals with increased genetic risk for schizophrenia.

METHODS

We used 6-[18F]-fluorodopa (FDOPA) PET imaging to measure striatal dopamine synthesis capacity. We studied 17 nonpsychotic subjects with an FDR with schizophrenia. This group was compared to 17 healthy subjects with no FDRs with schizophrenia.

RESULTS

A conventional region of interest (ROI)-analysis indicated that FDOPA uptake (K(i)) in the caudate-putamen was statistically significantly higher in the FDR group than in the control group. A voxel-level analysis confirmed these results.

CONCLUSIONS

These results suggest that the changes of striatal presynaptic dopamine synthesis seen previously in neuroleptic-naive schizophrenic patients is also present in FDRs of patients with schizophrenia. These findings have implications for the early detection of psychosis as well as for pharmacological interventions in individuals at risk for psychosis.

Dopamine D2 receptor occupancy levels of acute sulpiride challenges that produce working memory and learning impairments in healthy volunteers

RATIONALE

In humans, the effects of dopaminergic agents administered systemically are less clear-cut than studies in experimental animals where agents can be applied locally in the brain. DA receptor occupancy could clearly contribute to the variance in findings, although this is typically not known.

OBJECTIVES

The objective of the study was to measure the DA D2 receptor occupancy of sulpiride 200 and 400 mg and relate this to changes in task performance.

MATERIALS AND METHODS

Positron emission tomography scans were acquired in ten healthy volunteers with [11C]-raclopride. Striatal drug occupancy was calculated as the percentage change in binding potential between placebo and drug scans. All volunteers received placebo and sulpiride 400 mg, with four receiving 200 mg on a third session. Immediate post-scan neuropsychological assessment included working memory and learning tasks.

RESULTS

Striatal sulpiride occupancy was approximately 17% (200 mg) and approximately 28% (400 mg), with similar occupancy within the midbrain. Neuropsychological data analysis was restricted to the higher dose (n = 10). Accuracy on the spatial working memory and spatial learning tasks was impaired after the drug, and the former was inversely related to occupancy.

CONCLUSION

Doses of sulpiride typically used in human cognitive studies produced low levels of DA D2 receptor occupancy compared to that considered efficacious in the treatment of schizophrenia. The levels of occupancy were sufficient to replicate impairments on a spatial working memory task and impair spatial learning. The relationship between occupancy and working memory was suggestive of presynaptic effects, although the precise mechanism underlying the impairment will require studies of wider ranges of occupancy within and outside of the striatum.

Correlation of human cold pressor pain responses with 5-HT(1A) receptor binding in the brain

We determined whether serotonin 5-HT(1A) receptor availability in the brain is associated with cold pressor pain (CPP) or sympathetic reflex responses. Psychophysical testing was performed in eleven healthy males who had participated in a positron emission tomography study with [carbonyl-(11)C]WAY-100635 ligand for the assessment of 5-HT(1A) receptor binding potential (BP). Psychophysical testing consisted of determining CPP threshold, tolerance, intensity, unpleasantness and CPP threshold modulation by conditioning CPP. Autonomic control was assessed by determining the cutaneous vasoconstriction responses in the finger induced by CPP and Valsalva maneuver. CPP intensity was inversely correlated with 5-HT(1A) BP in multiple cortical and subcortical areas, including the prefrontal and cingulate cortices, insula, amygdala and the dorsal raphe. CPP unpleasantness was not significantly correlated with 5-HT(1A) BP in any of the regions of interest. Increase of CPP threshold by conditioning CPP was directly correlated with 5-HT(1A) BP in the amygdala and medial prefrontal cortex. Vasoconstriction induced by Valsalva but not CPP was directly correlated with 5-HT(1A) BP in the ventral part of the anterior cingulate cortex and the anterior insula. The results suggest that 5-HT(1A) receptors in the brain influence pain and Valsalva-induced sympathetic vasoconstriction reflex. In general, subjects with high availability of 5-HT(1A) receptors have low CPP intensity accompanied by a high capacity for central suppression of pain or a sympathetic vasoconstriction response by a Valsalva maneuver.

Extrastriatal D2 and striatal D2 receptors in depressive illness: pilot PET studies using [11C]FLB 457 and [11C]raclopride

BACKGROUND

Reduced dopaminergic function may occur in depressive disorders. In this paper the results of two pilot studies examining different aspects of the dopamine system in depression are presented. First, the binding of [(11)C]FLB 457 to extrastriatal D(2) receptors was measured in a group of depressed patients. Second, the hypothesis that selective serotonin reuptake inhibiting (SSRI) antidepressants affect the striatal binding of [(11)C]raclopride was tested.

METHODS

In the first study the binding of [(11)C]FLB 457 was compared between 7 people with depression and 7 healthy controls. In the second study the binding of [(11)C]raclopride to striatal D(2/3) receptors was compared between 8 people taking SSRI antidepressant medication and 8 healthy controls.

RESULTS

There was no difference in the binding of [(11)C]FLB 457 between the two groups. [(11)C]raclopride binding was reduced in the dorsal striatum of people taking antidepressants suggesting either that D(2/3) expression was reduced, or that dopamine release was increased, compared to untreated controls.

LIMITATIONS

The depressed patients were not severely depressed and were not matched for gender with controls. In the raclopride group the patients and controls were not matched by gender and were taking different SSRI antidepressants.

CONCLUSION

We found no support for the hypothesis that dopamine D(2) receptor expression is altered in extrastriatal brain regions in depression. SSRI antidepressants were associated with reduced [(11)C]raclopride binding in the dorsal striatum supporting the hypothesis that therapeutic effects of such drugs may, in part, be due to changes in the dopamine system.

Role of ventral striatal dopamine D1 receptor in cigarette craving

BACKGROUND

Several theories of cigarette craving suggest that dopaminergic function in the ventral striatum plays an important role. The objective of this study was to determine correlations between craving-related brain activation and dopamine D1 receptor (D1R) binding in smokers.

METHODS

Twelve smokers and 12 nonsmoking controls underwent [(15)O]H(2)O-positron emission tomography activation study and D1R-binding study using [(11)C]SCH 23390, and the correlations between receptor binding and cue-induced regional cerebral blood flow (rCBF) changes were assessed. Consecutive D1R-binding changes were examined during a period of 6 months of postsmoking abstinence in five smokers.

RESULTS

Cue-induced activation was observed in the left ventral striatum including the nucleus accumbens in smokers. D1R binding in the ventral striatum showed a negative relationship with cue-induced craving and rCBF changes. D1R binding was significantly low in smokers, and there was a trend of increase after smoking abstinence.

CONCLUSIONS

D1R binding and cue-induced rCBF changes in the ventral striatum suggest the important role of D1R in this region in cigarette craving.

Reduced serotonin-1A receptor binding in social anxiety disorder

BACKGROUND

Results from studies in serotonin-1A (5-HT1A) knockout mice and previous positron emission tomography (PET) studies in humans imply a role for 5-HT1A receptors in normal state anxiety as well as in certain anxiety disorders. The objective of this study was to investigate 5-HT1A receptor binding potential (BP) in social anxiety disorder (SAD).

METHODS

Using PET and [carbonyl-11C]WAY-100635, we compared a homogeneous group of 12 unmedicated, male SAD patients with 18 healthy control subjects (HC). A multivariate ANOVA with all regional BP values as dependent variables, age and four radiochemical variables as covariates was performed.

RESULTS

We found a significantly lower 5-HT1A BP in several limbic and paralimbic areas but not in the hippocampus (p = .234) of SAD patients. The difference in 5-HT1A binding was most significant in the amygdala (-21.4%; p = .003). There was also a more than 20% lower 5-HT(1A) BP of SAD patients in the anterior cingulate cortex (p = .004), insula (p = .003), and dorsal raphe nuclei (p = .030).

CONCLUSIONS

The lower 5-HT1A binding in the amygdala and mesiofrontal areas of SAD patients is consistent with 1) preclinical findings of elevated anxiety in 5-HT1A knockout mice, 2) a previous PET study in healthy volunteers showing an inverse correlation between 5-HT1A BP and state anxiety, and 3) another human PET study in patients with panic disorder showing reduced 5-HT1A binding, thus corroborating the potential validity of 5-HT1A receptors as targets in the treatment of human anxiety disorders.

PET imaging of neurokinin-1 receptors with [(18)F]SPA-RQ in human subjects: assessment of reference tissue models and their test-retest reproducibility

[(18)F]SPA-RQ (substance P antagonist receptor quantifier) labels the substance P-preferring (NK(1)) receptor in human brain. A prior study showed that [(18)F]SPA-RQ brain uptake can be quantified with a reference tissue method and thereby avoid invasive blood sampling. The purposes of this study were to compare three different reference tissue methods and to assess test-retest reproducibility. Eight healthy subjects underwent two [(18)F]SPA-RQ scans. We calculated the binding potential (BP), which is proportional to receptor density, from both regional volume of interest and voxel-wise data. We compared three reference tissue methods: simplified reference tissue model, multilinear reference tissue model (MRTM), and its two-parameter version (MRTM2). The three methods generated equivalent values of regional BP, but MRTM2 was the most resistant to noise. Temporally stable values of BP were obtained with 240 min of imaging data. MRTM2 had excellent test-retest reproducibility, with high reliability (intraclass correlation > 0.9) and low variability (< 10%). In addition to regional volume of interest analysis, we also created parametric images of BP, variability, and reliability based on voxel-wise time-activity data. The reproducibility of parametric BP was also good, with variability < 20% and reliability > 0.7 in gray matter regions. In conclusion, a two-parameter reference tissue method (MRTM2) provided reproducible and reliable measurements of [(18)F]SPA-RQ brain uptake using 240 min of both regional and voxel-wise data.

Fluvoxamine treatment and D2 receptors: a pet study on OCD drug-naïve patients

Changes in D(2) receptors during antidepressant therapy have been reported in patients with major depressive disorder using PET/SPET. The aim of this study was to evaluate modifications in D(2) receptors that might occur in patients affected by obsessive-compulsive disorder (OCD) during serotonin reuptake sites inhibitors (SSRIs). To this purpose, we measured the in vivo binding of [(11)C]raclopride ([(11)C]Rac)in the brain of a group of OCD naïve patients before and after the repeated administration of the inhibitor SSRI fluvoxamine. Eight patients with a Diagnostic and Statistical Manual of Mental Disorders IVth edition diagnosis of OCD completed the study undergoing a PET scan and a complete clinical evaluation before and during treatment with fluvoxamine. Patients have been compared also with a group of nine age-matched normal volunteers. Fluvoxamine treatment significantly improved clinical symptoms and increased [(11)C]Rac binding potential (BP) in the basal ganglia of OCD patients (7.5+/-5.2, 6.9+/-6.9, and 9.9+/-9.3% in dorsal caudate, dorsal putamen, and ventral basal ganglia, respectively; p<0.01) to values closer to those observed in the group of normal subjects. Chronic treatment with fluvoxamine induces a slight but significant increase in striatal [(11)C]Rac BP of previously drug-naïve OCD patients. The modifications in D(2) receptor availability might be secondary to fluvoxamine effects on serotoninergic activity.

Statistical neuroanatomy of the human inferior frontal gyrus and probabilistic atlas in a standard stereotaxic space

We manually defined the inferior frontal gyrus (IFG) on high-resolution MRIs in native space in 30 healthy subjects (15 female, median age 31 years; 15 male, median age 30 years), resulting in 30 individual atlases. Using standard software (SPM99), these were spatially transformed to a widely used stereotaxic space (MNI/ICBM 152) to create probabilistic maps. In native space, the total IFG volume was on average 5%, and the gray matter (GM) portion 12% larger in women (not significant). Expressed as a percentage of ipsilateral frontal lobe volume (i.e., correcting for brain size), the IFG was an average of 20%, and the GM portion of the IFG 27%, larger in women (P < 0.005). Correcting for total lobar volume yielded the same result. No asymmetry was found in IFG volumes. There were significant positional differences between the right and left IFGs, with the right IFG being further lateral in both native and stereotaxic space. Variability was similar on the left and right, but more pronounced anteriorly and superiorly. We show differences in IFG volume, composition, and position between sexes and between hemispheres. Applications include probabilistic determination of location in group studies, automatic labeling of new scans, and detection of anatomical abnormalities in patients.

The effect of nicotine on striatal dopamine release in man: A [11C]raclopride PET study

In common with many addictive substances and behaviors nicotine activates the mesolimbic dopaminergic system. Brain microdialysis studies in rodents have consistently shown increases in extrasynaptic DA levels in the striatum after administration of nicotine but PET experiments in primates have given contradicting results. A recent PET study assessing the effect of smoking in humans showed no change in [(11)C]raclopride binding in the brain, but did find that "hedonia" correlated with a reduction in [(11)C]raclopride binding suggesting that DA may mediate the positive reinforcing effects of nicotine. In this experiment we measured the effect of nicotine, administered via a nasal spray, on DA release using [(11)C]raclopride PET, in 10 regular smokers. There was no overall change in [(11)C]raclopride binding after nicotine administration in any of the striatal regions examined. However, the individual change in [(11)C]raclopride binding correlated with change in subjective measures of "amused" and "happiness" in the associative striatum (AST) and sensorimotor striatum (SMST). Nicotine concentration correlated negatively with change in BP in the limbic striatum. Nicotine had significant effects on cardiovascular measures including pulse rate, systolic blood pressure (BPr), and diastolic BPr. Baseline [(11)C]raclopride binding potential (BP) in the AST correlated negatively with the Fagerström score, an index of nicotine dependence. These results support a role for the DA system in nicotine addiction, but reveal a more complex relationship than suggested by studies in animals.

Striatal dopamine (D2) receptor availability predicts socially desirable responding

Research in non-human primates has implicated striatal dopamine (D2) receptor function in the expression of social dominance--a fundamental component of social extraversion. We predicted that trait extraversion - indexed by the revised Eysenck Personality Questionnaire (EPQ-R) - would correlate with striatal DA (D2) receptor measures - indexed by [(11)C]-Raclopride binding potential (BP) - in 28 healthy post-menopausal females (mean age=75 years; range=58-91 years). Region of interest (ROI) and voxel-based statistical parametric mapping (SPM) analyses were performed, using a reference tissue model for [(11)C]-Raclopride. ROI analysis showed moderately significant negative correlations between extraversion and BP measures in the left caudate and between psychoticism scores and BP in the right putamen. Unexpectedly, scores on the Lie scale, a measure of socially desirable responding, were significantly and negatively correlated with BP measures in the putamen and survived Bonferroni correction on the right side. After controlling for the potential confounding of self-report bias in high Lie scorers, only the correlation between Lie scores and BP measures in the right putamen remained significant. Voxel-based analysis showed only Lie scores to be significantly and negatively correlated with BP measures in the right putamen. We explored this association further by applying an ROI-based approach to data on a previously scanned sample of young adults (n=13) and found a similar pattern of association, which achieved trend level significance in the right putamen. Although unanticipated, the relationship observed between BP measures in the right putamen and Lie scores is consistent with dopaminergic involvement in socially rewarding behaviour. How this relates to dopaminergic tone will need to be further explored.

Memory and frontal lobe functions; possible relations with dopamine D2 receptors in the hippocampus

Cerebral cortical regions are thought to be important for cognitive functions such as memory and executive function. Although the functional associations between dopamine D2 receptors and motor and cognitive functions have been extensively examined in the striatum using positron emission tomography (PET), the role of dopamine D2 receptors in extrastriatal regions has been unexplored. We aimed to investigate the relationship between dopamine D2 receptors in extrastriatal regions and the performance of a broad spectrum of cognitive functions including memory, language, attention, and executive function in healthy subjects. Extrastriatal dopamine D2 receptors were measured in 25 male subjects using PET with [(11)C]FLB457. After the PET scans, a battery of neuropsychological tests was administered to all subjects. We found that the binding potential (BP) of [(11)C]FLB457 in the hippocampus was positively correlated with memory function. Furthermore, BP of [(11)C]FLB457 in the hippocampus, but not in the prefrontal cortex, was associated with frontal lobe functions such as executive function and verbal fluency. Our findings suggest that dopamine D2 receptors in the hippocampus might affect the local hippocampal function, but also brain functions outside the hippocampus such as the prefrontal cortex.

Increased occupancy of dopamine receptors in human striatum during cue-elicited cocaine craving

In all, 19 research subjects, with current histories of frequent cocaine use, were exposed to cocaine-related cues to elicit drug craving. We measured the change of occupancy of dopamine at D2-like receptors with positron emission tomography (PET) and inferred a change of intrasynaptic dopamine (endogenous dopamine release), based on the displacement of radiotracer [(11)C]raclopride. Receptor occupancy by dopamine increased significantly in putamen of participants who reported cue-elicited craving compared to those who did not. Further, the intensity of craving was positively correlated with the increase in dopamine receptor occupancy in the putamen. These results provide direct evidence that occupancy of dopamine receptors in human dorsal striatum increased in proportion to subjective craving, presumably because of increased release of intrasynaptic dopamine.

Changes in central 5-HT(1A) receptor binding in mesial temporal epilepsy measured by positron emission tomography with [(11)C]WAY100635

OBJECTIVE

The possible involvement of the brain 5-HT(1A) receptor in epilepsy has been indicated in animal seizure models. Recent in vivo neuroimaging studies demonstrated decreased 5-HT(1A) receptor binding in epilepsy. Using positron emission tomography (PET) with [(11)C]WAY100635, we investigated 5-HT(1A) receptor binding in patients with mesial temporal lobe epilepsy and aimed to clarify the involvement of the brain 5-HT(1A) receptor system in epilepsy.

METHOD

PET measurements with [(11)C]WAY100635 were performed on 23 healthy volunteers and 13 patients who were diagnosed with mesial temporal lobe epilepsy based on clinical symptoms and electroencephalogram (EEG) findings. They had non-lesional mesial temporal lobe epilepsy with unilateral EEG foci and no hippocampal atrophy on magnetic resonance imaging. The binding potential (BP) of [(11)C]WAY100635 was calculated by the reference tissue model method. Data were analyzed for each region of interest (ROI) and on a voxel-by-voxel basis by statistical parametric mapping (SPM) system.

RESULTS

ROI and voxel-based analyses consistently demonstrated that 5-HT(1A) receptor BP was significantly decreased in the temporal lobe, hippocampus and amygdala on the ipsilateral side of the EEG focus compared to controls. In addition, decreased 5-HT(1A) receptor BP was also observed on the contralateral side of the amygdala.

CONCLUSION

5-HT(1A) receptor binding in patients with mesial temporal lobe epilepsy decreased predominantly in the ipsilateral mesial temporal lobe structures but also in the contralateral side. The imaging of 5-HT(1A) receptor binding by PET detects functional changes of the limbic system in mesial temporal lobe epilepsy, proving to be a sensitive and useful method.

IBZM tool: a fully automated expert system for the evaluation of IBZM SPECT studies

PURPOSE

Visual reading of [(123)I]IBZM SPECT scans depends on the experience of the interpreter. Therefore, semi-quantification of striatal IBZM uptake is commonly considered mandatory. However, semi-quantification is time consuming and prone to error, particularly if the volumes of interest (VOIs) are positioned manually. Therefore, the present paper proposes a new software tool ("IBZM tool") for fully automated and standardised processing, evaluation and documentation of [(123)I]IBZM SPECT scans.

METHODS

The IBZM tool is an easy-to-use SPM toolbox. It includes automated procedures for realignment and summation of multiple frames (motion correction), stereotactic normalisation, scaling, VOI analysis of striatum-to-reference ratio R, classification of R and standardised display. In order to evaluate the tool, which was developed at the University of Hamburg, the tool was transferred to the University of Hannover. There it was applied to 27 well-documented subjects: eight patients with multi-system atrophy (MSA), 12 patients with Parkinson's disease (PD) and seven controls. The IBZM tool was compared with manual VOI analysis.

RESULTS

The sensitivity and specificity of the IBZM tool for the differentiation of the MSA subjects from the controls were 100% and 86%, respectively. The IBZM tool provided improved statistical power compared with manual VOI analysis.

CONCLUSION

The IBZM tool is an expert system for the detection of reduced striatal D(2) availability on [(123)I]IBZM SPECT scans. The standardised documentation supports visual and semi-quantitative evaluation, and it is useful for presenting the findings to the referring physician. The IBZM tool has the potential for widespread use, since it appears to be fairly independent of the performance characteristics of the particular SPECT system used. The tool is available free of charge.

Opioidergic activation in the medial pain system after heat pain

Opioids modulate the affective component of pain and in vivo data indicate that opioids induce activation changes in the rostral ACC, insula and other brain areas. Hence, opioidergic release is to be expected in these brain regions following experimental pain stimulation. We examined healthy volunteers during heat pain and control subjects during rest using [18F]fluorodiprenorphine-PET. Pain stimulation led to significant reduction of diprenorphine binding in limbic and paralimbic brain areas including the rostral ACC and insula. The finding of altered opioidergic receptor availability in the rostral ACC after experimental nociceptive pain is novel and provides direct evidence for the involvement of this region in endogenous opioidergic inhibition of pain.

Quantification analysis of 123I-IPT single photon emission computed tomography uptake in the striatum of parkinsonism with the standard magnetic resonance template

This study evaluated the striatal specific binding ratio (SBR), the anterior to posterior ratio of the striatum (APR) and its reproducibility by employing a template-based registration (TBR) method using the coregistered to the standard T1 magnetic resonance (MR) template (SMRT) as a replacement for the MR image of each patient. The 123I-IPT single photon emission computed tomography (SPECT) images of 30 patients with Idiopathic Parkinson's disease (IPD) and 11 normal controls were analyzed. The region of interest (ROI) was positioned manually in the same slice showing the highest striatal activity using the manual ROI method, while the ROI were positioned automatically in the mid striatal slice of the SPECT image coregistered to the SMRT. The SBR obtained using the TBR method showed a strong correlation with those using the manual method in all groups: normal controls (r = 0.851, P = 0.001), early IPD (r = 0.841, P < 0.001), and severe IPD (r = 0.702, P = 0.007). The APR obtained by the TBR correlated with those using the manual method in only the early IPD (r = 0.72, P = 0.001), while those obtained using the manual method showed no correlation in the three groups (P > 0.05). The reproducibility (rmsCV) of the TBR method was 7.2% (normal controls, 5.2%; mild IPD, 4.2%; severe IPD, 10.8%), while the reproducibility of the manual method was 31% (normal controls, 19.7%; mild IPD, 21.7%; severe IPD, 46.2%). This shows that the use of 123I-IPT SPECT for assessing IPD is affected by the method used to position the striatal ROI. This study showed that the TBR method using the SMRT is useful in diagnosing the IPD and assessing the disease severity with a high reproducibility, indicating a possibility of using the TBR method as a good replacement for the manual method.

Striatal dopamine D1 and D2 receptor balance in twins at increased genetic risk for schizophrenia

The dopamine hypothesis of schizophrenia postulates that a dysfunctional dopaminergic system is a major pathophysiological mechanism in the disease. Most studies have focused on striatal dopamine D2 receptors, but a disturbed link between dopamine D1 and D2 receptors has also been proposed. Schizophrenia is highly heritable, and recent evidence suggests that alterations in the dopaminergic system confer susceptibility for schizophrenia instead of being solely related to the to overt expression of the disease. To explore the impact of genetic vulnerability for schizophrenia on the balance of striatal dopamine D1 and D2 receptors, we studied monozygotic (MZ) and dizygotic (DZ) unaffected co-twins from twin pairs discordant for schizophrenia as well as healthy control twins using positron emission tomography (PET). Both [(11)C]SCH 23390 and [(11)C]raclopride were used to quantitate D1 and D2 receptor binding, respectively, in the same individuals during the same day. The association between D1 and D2 receptor binding was analyzed using conventional region of interests as well as voxel-wise D1/D2 ratio maps. All levels of analyses failed to show any differences in D1/D2 ratio between the unaffected MZ or DZ co-twins and control twins. We noted rostrocaudally declining and dorsoventrally increasing gradients in D1/D2 ratio in the striatum, with no differences between groups in these gradients. In this sample, we did not find evidence for an association between increased genetic risk for schizophrenia and altered D1/D2 receptor balance in the striatum.

Is psychological stress in man associated with increased striatal dopamine levels?: A [11C]raclopride PET study

In rodents, stress causes rapid increases in extracellular dopamine (DA) concentration in cortical and subcortical brain regions, and positron emission tomography (PET) studies in healthy humans have suggested psychological and pharmacological stressors are associated with increased DA concentration in the striatum. In this experiment, we measured the effect of stress, induced by difficult mental arithmetic, on [11C]raclopride binding in order to index striatal DA release. To refine measurements and facilitate interpretation of results a combination of head movement correction, a carefully designed control condition and bolus infusion administration of [11C]raclopride were employed. Fourteen healthy volunteers were scanned using [11C]raclopride PET. Physiological and psychological responses to the task were consistent with a stress response with changes in cardiovascular, hormonal, and subjective state indices. No change of ventral or dorsal striatal [11C]raclopride binding was found in the stress condition compared to nonstress. This negative result suggests that significant DA release does not occur in the striatum in healthy humans after mild, psychological stress.

Cortical 6-[18F]fluoro-l-dopa uptake and frontal cognitive functions in early Parkinson's disease

Patients with Parkinson's disease (PD) have already at the early stages of the disease impaired performance especially in tests measuring frontal lobe functions such as attention. The pathophysiological basis of these deficits is unclear. In the present study, 21 non-demented, non-medicated patients at the early stage of PD and 24 healthy controls underwent a positron emission tomography (PET) scan with 6-[18F]fluoro-L-dopa (Fdopa) as the tracer. In addition, the PD patients performed a neuropsychological test battery, including a test measuring sustained attention (VIG) and a test requiring suppressed attention (Stroop). Both voxel-based Statistical Parametric Mapping (SPM) and automated region of interest (ROI) analysis were employed. Compared to controls, the PD patients had decreased Fdopa uptake in the striatum and a large cortical area of increased Fdopa uptake. The reaction time in the VIG test correlated positively with the Fdopa uptake of the dorsolateral prefrontal cortex and the performance in the Stroop test correlated negatively with the Fdopa uptake in an area including the medial frontal cortex and the anterior cingulate. The results show that cortical Fdopa uptake is increased in early non-medicated PD and suggest that the changes in frontal Fdopa uptake are related to cognitive impairments found in early PD.

Atlas-guided non-uniform attenuation correction in cerebral 3D PET imaging

Photon attenuation in tissues is the primary physical degrading factor limiting both visual qualitative interpretation and quantitative analysis capabilities of reconstructed Positron Emission Tomography (PET) images. This study investigates the implementation and applicability of transmission atlas-guided attenuation correction in cerebral 3D PET imaging, thus eliminating the need for acquisition of a measured transmission scan. Patient-specific attenuation map is derived by anatomic standardization through nonlinear warping of a stereotactic transmission template obtained by averaging 11 scans of normal subjects. This template is coregistered to a specially designed tracer-specific 18F-[FDG] template constructed by scanning 17 normal subjects in resting condition during tracer uptake in a dark room. This emission template is first coregistered and spatially normalized to preliminary PET images of subjects corrected for scatter and attenuation using an approximate calculated method. The resulting transformation matrices are recorded and re-applied to the transmission template. The derived attenuation map is then forward projected to generate attenuation correction factors to be used for correcting the subjects' PET data. Twelve cerebral clinical studies are used for evaluation of the developed attenuation correction technique as compared to the standard pre-injection measured transmission-based method used in clinical routine. Statistical Parametric Mapping (SPM2) analysis is used to assess significant differences between images obtained using both techniques. The subjective qualitative assessment shows no significant visual differences between atlas-guided and transmission-based attenuation correction methods. However, the quantitative voxel-based analysis comparing atlas-guided to transmission-based attenuation corrections suggest that regional brain metabolic activity increases significantly bilaterally in the superior frontal and precentral gyri, in addition to the left middle temporal gyrus and the left frontal lobe. Conversely, activity decreases in the corpus callosum in the left parasagittal region. A new non-uniform attenuation correction method is thus proposed, which is suitable for both research and clinical routine applications in 3D brain PET imaging on a transmissionless PET scanner or when a patient-specific transmission scan is not available.

Brain 5-HT1A receptor binding in chronic fatigue syndrome measured using positron emission tomography and [11C]WAY-100635

BACKGROUND

Research from neuroendocrine challenge and other indirect studies has suggested increased central 5-HT function in chronic fatigue syndrome (CFS) and increased 5-HT1A receptor sensitivity. We assessed brain 5-HT1A receptor binding potential directly using the specific radioligand [11C]WAY-100635 and positron emission tomography (PET).

METHODS

We selected 10 patients from a tertiary referral clinic who fulfilled the CDC consensus criteria for CFS. To assemble a homogenous group and avoid confounding effects, we enrolled only subjects who were completely medication-free and did not have current comorbid psychiatric illness. We also scanned 10 healthy control subjects.

RESULTS

There was a widespread reduction in 5-HT1A receptor binding potential in CFS relative to control subjects. This was particularly marked in the hippocampus bilaterally, where a 23% reduction was observed.

CONCLUSIONS

There is evidence of decreased 5-HT1A receptor number or affinity in CFS. This may be a primary feature of CFS, related to the underlying pathophysiology, or a finding secondary to other processes, such as previous depression, other biological changes or the behavioral consequences of CFS.

MR-based automatic delineation of volumes of interest in human brain PET images using probability maps

The purpose of this study was to develop and validate an observer-independent approach for automatic generation of volume-of-interest (VOI) brain templates to be used in emission tomography studies of the brain. The method utilizes a VOI probability map created on the basis of a database of several subjects' MR-images, where VOI sets have been defined manually. High-resolution structural MR-images and 5-HT(2A) receptor binding PET-images (in terms of (18)F-altanserin binding) from 10 healthy volunteers and 10 patients with mild cognitive impairment were included for the analysis. A template including 35 VOIs was manually delineated on the subjects' MR images. Through a warping algorithm template VOI sets defined from each individual were transferred to the other subjects MR-images and the voxel overlap was compared to the VOI set specifically drawn for that particular individual. Comparisons were also made for the VOI templates 5-HT(2A) receptor binding values. It was shown that when the generated VOI set is based on more than one template VOI set, delineation of VOIs is better reproduced and shows less variation as compared both to transfer of a single set of template VOIs as well as manual delineation of the VOI set. The approach was also shown to work equally well in individuals with pronounced cerebral atrophy. Probability-map-based automatic delineation of VOIs is a fast, objective, reproducible, and safe way to assess regional brain values from PET or SPECT scans. In addition, the method applies well in elderly subjects, even in the presence of pronounced cerebral atrophy.