beta-CIT SPECT demonstrates blockade of 5HT-uptake sites by citalopram in the human brain in vivo

Altered intrinsic neural timescales and neurotransmitter activity in males with tobacco use disorder

Previous researches of tobacco use disorder (TUD) has overlooked the hierarchy of cortical functions and single modality design separated the relationship between macroscopic neuroimaging aberrance and microscopic molecular basis. At present, intrinsic timescale gradient of TUD and its molecular features are not fully understood. Our study recruited 146 male subjects, including 44 heavy smokers, 50 light smokers and 52 non-smokers, then obtained their rs-fMRI data and clinical scales related to smoking. Intrinsic neural timescale (INT) method was performed to describe how long neural information was stored in a brain region by calculating the autocorrelation function (ACF) of each voxel to examine the difference in the ability of information integration among the three groups. Then, correlation analyses were conducted to explore the relationship between INT abnormalities and clinical scales of smokers. Finally, cross-modal JuSpace toolbox was used to investigate the association between INT aberrance and the expression of specific receptor/transporters. Compared to healthy controls, TUD subjects displayed decreased INT in control network (CN), default mode network (DMN), sensorimotor areas and visual cortex, and such trend of decreasing INT was more pronounced in heavy smokers. Moreover, various neurotransmitters (including dopaminergic, acetylcholine and μ-opioid receptors) were involved in the molecular mechanism of timescale decreasing and differed in heavy and light smokers. These findings supplied novel insights into the brain functional aberrance in TUD from an intrinsic neural dynamic perspective and confirm INT was a potential neurobiological marker. And also established the connection between macroscopic imaging aberrance and microscopic molecular changes in TUD.

Modulation of functional networks related to the serotonin neurotransmitter system by citalopram: Evidence from a multimodal neuroimaging study

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) potentiate serotonergic neurotransmission by blocking the serotonin transporter (5-HTT), but the functional brain response to SSRIs involves neural circuits beyond regions with high 5-HTT expression. Currently, it is unclear whether and how changes in 5-HTT availability after SSRI administration modulate brain function of key serotoninergic circuits, including those characterized by high availability of the serotonin 1A receptor (5-HT1AR).

AIM

We investigated the association between 5-HTT availability and 5-HTT- and 5-HT1AR-enriched functional connectivity (FC) after an acute citalopram challenge.

METHODS

We analyzed multimodal data from a dose-response, placebo-controlled, double-blind study, in which 45 healthy women were randomized into three groups receiving placebo, a low (4 mg), or high (16 mg) oral dose of citalopram. Receptor-Enhanced Analysis of functional Connectivity by Targets was used to estimate 5-HTT- and 5-HT1AR-enriched FC from resting-state and task-based fMRI. 5-HTT availability was determined using [123I]FP-CIT single-photon emission computerized tomography.

RESULTS

5-HTT availability was negatively correlated with resting-state 5-HTT-enriched FC, and with task-dependent 5-HT1AR-enriched FC. Our exploratory analyses revealed lower 5-HT1AR-enriched FC in the low-dose group compared to the high-dose group at rest and the placebo group during the emotional face-matching task.

CONCLUSIONS

Taken together, our findings provide evidence for differential links between 5-HTT availability and brain function within 5-HTT and 5-HT1AR pathways and in context- and dose-dependent manner. As such, they support a potential pivotal role of the 5-HT1AR in the effects of citalopram on the brain and add to its potential as a therapeutic avenue for mood and anxiety disturbances.

Convergent molecular and structural neuroimaging signatures of first-episode depression

BACKGROUND

Convergent studies have demonstrated morphological abnormalities in various brain regions in depression patients. However, the molecular underpinnings of the structural impairments remain largely unknown, despite a pressing need for treatment targets and mechanisms. Here, we investigated the gray matter volume (GMV) alteration in patients with depression and its underlying molecular architecture.

METHODS

We recruited 195 first-episode, treatment-naïve depression patients and 78 gender-, age-, and education level-matched healthy controls (HCs) who underwent high-resolution T1-weighted magnetic resonance scans. Voxel-based morphometry (VBM) was adopted to calculate the GMV differences between two groups. Then we analyzed the spatial correlation between depression-induced alteration in GMV and density maps of 10 receptors/transporters deriving from prior molecular imaging in healthy people.

RESULTS

Compared to HCs, the depression group had significantly increased GMV in the left ventral portions of the ventral medial prefrontal cortex, parahippocampal gyrus, amygdala, the right superior parietal lobule and precuneus while decreased GMV in the bilateral hippocampus extending to the thalamus and cerebellum. The GMV alteration introduced by depression was spatially correlated with serotonin receptors (5-HT1a, 5-HT1b, and 5-HT2a), dopamine receptors (D1 and D2) and GABAergic receptor (GABAa) densities.

LIMITATIONS

The conclusions drawn in this study were obtained from a single dataset.

CONCLUSIONS

This study reveals abnormal GMV alteration and provides a series of neurotransmitters receptors possibly related to GMV alteration in depression, which facilitates an integrative understanding of the molecular mechanism underlying the structural abnormalities in depression and may provide clues to new treatment strategies.

Integrative Functional, Molecular, and Transcriptomic Analyses of Altered Intrinsic Timescale Gradient in Depression

The pathophysiology and pharmacology of depression are hypothesized to be related to the imbalance of excitation–inhibition that gives rise to hierarchical dynamics (or intrinsic timescale gradient), further supporting a hierarchy of cortical functions. On this assumption, intrinsic timescale gradient is theoretically altered in depression. However, it remains unknown. We investigated altered intrinsic timescale gradient recently developed to measure hierarchical brain dynamics gradient and its underlying molecular architecture and brain-wide gene expression in depression. We first presented replicable intrinsic timescale gradient in two independent Chinese Han datasets and then investigated altered intrinsic timescale gradient and its possible underlying molecular and transcriptional bases in patients with depression. As a result, patients with depression showed stage-specifically shorter timescales compared with healthy controls according to illness duration. The shorter timescales were spatially correlated with monoamine receptor/transporter densities, suggesting the underlying molecular basis of timescale aberrance and providing clues to treatment. In addition, we identified that timescale aberrance-related genes ontologically enriched for synapse-related and neurotransmitter (receptor) terms, elaborating the underlying transcriptional basis of timescale aberrance. These findings revealed atypical timescale gradient in depression and built a link between neuroimaging, transcriptome, and neurotransmitter information, facilitating an integrative understanding of depression.

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

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

Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants

Objectives: More than 40 drugs are available to treat affective disorders. Individual selection of the optimal drug and dose is required to attain the highest possible efficacy and acceptable tolerability for every patient.Methods: This review, which includes more than 500 articles selected by 30 experts, combines relevant knowledge on studies investigating the pharmacokinetics, pharmacodynamics and pharmacogenetics of 33 antidepressant drugs and of 4 drugs approved for augmentation in cases of insufficient response to antidepressant monotherapy. Such studies typically measure drug concentrations in blood (i.e. therapeutic drug monitoring) and genotype relevant genetic polymorphisms of enzymes, transporters or receptors involved in drug metabolism or mechanism of action. Imaging studies, primarily positron emission tomography that relates drug concentrations in blood and radioligand binding, are considered to quantify target structure occupancy by the antidepressant drugs in vivo. Results: Evidence is given that in vivo imaging, therapeutic drug monitoring and genotyping and/or phenotyping of drug metabolising enzymes should be an integral part in the development of any new antidepressant drug.Conclusions: To guide antidepressant drug therapy in everyday practice, there are multiple indications such as uncertain adherence, polypharmacy, nonresponse and/or adverse reactions under therapeutically recommended doses, where therapeutic drug monitoring and cytochrome P450 genotyping and/or phenotyping should be applied as valid tools of precision medicine.

Low dopamine transporter binding in the nucleus accumbens in geriatric patients with severe depression

AIM

Dysfunction of dopaminergic neurons in the central nervous system is considered to be related to major depressive disorder (MDD). Especially, MDD in geriatric patients is characterized by anhedonia, which is assumed to be associated with reduced dopamine neurotransmission in the reward system. Dopamine transporter (DAT) is considered to reflect the function of the dopamine nerve system. However, previous DAT imaging studies using single photon emission computed tomography or positron emission tomography (PET) have shown inconsistent results. The radioligand [¹⁸ F]FE-PE2I for PET enables more precise evaluation of DAT availability. Hence, we aimed to evaluate the DAT availability in geriatric patients with MDD using [¹⁸ F]FE-PE2I.

METHODS

Eleven geriatric patients with severe MDD and 27 healthy controls underwent PET with [¹⁸ F]FE-PE2I, which has high affinity and selectivity for DAT. Binding potentials (BP_ND ) in the striatum (caudate and putamen), nucleus accumbens (NAc), and substantia nigra were calculated. BP_ND values were compared between MDD patients and healthy controls.

RESULTS

MDD patients showed significantly lower DAT BP_ND in the NAc (P = 0.009), and there was a trend of lower BP_ND in the putamen (P = 0.032) compared to controls.

CONCLUSION

We found low DAT in the NAc and putamen in geriatric patients with severe MDD, which could be related to dysregulation of the reward system.

Neurobiology of Chronic Stress-Related Psychiatric Disorders: Evidence from Molecular Imaging Studies

Chronic stress accounts for billions of dollars of economic loss annually in the United States alone, and is recognized as a major source of disability and mortality worldwide. Robust evidence suggests that chronic stress plays a significant role in the onset of severe and impairing psychiatric conditions, including major depressive disorder, bipolar disorder, and posttraumatic stress disorder. Application of molecular imaging techniques such as positron emission tomography and single photon emission computed tomography in recent years has begun to provide insight into the molecular mechanisms by which chronic stress confers risk for these disorders. The present paper provides a comprehensive review and synthesis of all positron emission tomography and single photon emission computed tomography imaging publications focused on the examination of molecular targets in individuals with major depressive disorder, posttraumatic stress disorder, or bipolar disorder to date. Critical discussion of discrepant findings and broad strengths and weaknesses of the current body of literature is provided. Recommended future directions for the field of molecular imaging to further elucidate the neurobiological substrates of chronic stress-related disorders are also discussed. This article is part of the inaugural issue for the journal focused on various aspects of chronic stress.

Topography of Dopamine Transporter Availability in the Cerebellar Variant of Multiple System Atrophy

Background

Voxel-wise comparison of [¹²³I]-2β-carbomethoxy-3beta-(4-iodophenyl)tropane ([¹²³I]β-CIT) radioligand distribution measured by single-photon emission computed tomography (SPECT) revealed distinct patterns of reduced dopamine transporter (DAT) availability in the Parkinson's variant of MSA (MSA-P). The aim of this study was to identify the monoamine transporter distribution pattern in patients with the cerebellar variant of MSA (MSA-C). Additionally, monoamine transporter availability was investigated in a small cohort of patients with sporadic adult-onset ataxia (SAOA).

Methods

[¹²³I]β-CIT SPECT was performed in patients with MSA-C (n = 12), MSA-P (n = 14), SAOA (n = 5), and controls (n = 15) matched for age. Parametric images of [¹²³I]β-CIT binding potential (BP_ND) were generated and analyzed by statistical parametric mapping (SPM) and region of interest (ROI) analysis.

Results

SPM localized significant reductions of [¹²³I]β-CIT BP_ND in the striatum, midbrain, and pons in MSA-C compared to controls. When compared with MSA-P, the striatal DAT decline was significantly less affected in MSA-C. ROI analysis revealed reductions of striatal and midbrain [¹²³I]β-CIT binding in MSA-C compared to SAOA, whereas no significant difference was apparent between the SAOA and control groups.

Conclusions

Midbrain and pontine monoaminergic transporter binding was severely impaired in MSA-C, matching the underlying pathological features. Striatal DAT availability was relatively less affected in MSA-C compared to MSA-P, reflecting measureable, but less-profound, degeneration of the nigrostriatal dopaminergic projections. Preliminary results of reduced striatal and midbrain [¹²³I]β-CIT binding in MSA-C, compared to SAOA, suggest that the potential of DAT-SPECT as a surrogate marker in the diagnostic workup of patients with adult-onset cerebellar ataxia should be further investigated.

The serotonin transporter in depression: Meta-analysis of in vivo and post mortem findings and implications for understanding and treating depression

BACKGROUND

Altered serotonin transporter levels have been reported in blood and brain of patients with major depressive disorders. However, the strength and consistency of the evidence for altered serotonin transporter availability in major depressive disorder is not clear.

METHODS

To address this, a comprehensive meta-analysis was conducted of all available in vivo neuroimaging and post mortem studies reporting serotonin transporter availability in patients with depression compared with healthy controls.

RESULTS

The final sample consisted of fifty (n=27 in vivo and n=25 post mortem) studies including 877 patients with depression (mean age: 42.9 years) and 968 healthy controls (mean age: 42.7 years). In vivo neuroimaging studies indicated reduced serotonin transporter binding in the striatum (g=-0.39, p=0.01), the amygdala (g=-0.37, p=0.01) and the brainstem (g=-0.31, p=0.01), including the midbrain (g=-0.27, p=0.02), but no significant alteration in the thalamus or the hippocampus. The post mortem findings indicated no significant change in serotonin transporter binding in depression in the brainstem (p=0.64), the frontal cortex (p=0.75) and the hippocampus (p=0.32, corrected for publication bias). Although there were too few studies for a meta-analysis, the post mortem studies in the amygdala and striatum showed reduced SERT binding in MDD in absolute terms, consistent with the imaging findings.

LIMITATIONS

A number of potential factors might have biased the results of the present meta-analysis such as the imaging modality (post mortem or in vivo neuroimaging), partial volume effects, susceptibility of some radiotracers to synaptic serotonin levels or binding to other monoamine transporters.

CONCLUSIONS

The results indicate that serotonin transporter availability in depressed patients is reduced in key regions of the limbic system. This provides direct support for the serotonin hypothesis of depression, and underlines the importance of the serotonin transporter as a target of pharmacological treatments.

The serotonin transporter in psychiatric disorders: insights from PET imaging

Over the past 20 years, psychotropics affecting the serotonergic system have been used extensively in the treatment of psychiatric disorders. Molecular imaging, in particular PET, has allowed for elucidation of the essential contribution of the serotonin transporter to the pathophysiology of various psychiatric disorders and their treatment. We review studies that use PET to measure cerebral serotonin transporter activity in psychiatric disorders, focusing on major depressive disorder and antidepressant treatment. We also discuss opportunities and limitations in the application of this neuroimaging method in clinical practice. Although results from individual studies diverge, meta-analysis indicates a trend towards reduced serotonin transporter availability in patients with major depressive disorder. Inconsistencies in results might suggest symptom heterogeneity in major depressive disorder and might therefore be relevant for stratification of patients into clinical subsets. PET has enabled the elucidation of mechanisms of response to selective serotonin reuptake inhibitors (SSRIs) and hence provides a basis for rational pharmacological treatment of major depressive disorder. Such imaging studies have also suggested that the pattern of serotonin transporter binding before treatment might predict response to antidepressant treatment, which could potentially be clinically useful in the future. Additionally, this Review discusses PET studies investigating the serotonin transporter in anxiety, obsessive-compulsive disorder, and eating disorders. Few studies have shown changes in serotonin transporter activity in schizophrenia and attention deficit hyperactivity disorder. By showing the scarcity of data in these psychiatric disorders, we highlight the potential for further investigation in this field.

Imaging studies on dopamine transporter and depression: a review of literature and suggestions for future research

We review the conflicting results from imaging studies of dopamine transporter availability in depressed patients and also discuss the heterogeneity of the variables involved. Major depression includes diverse clinical manifestations and in recent years there has been an increasing interest in the identification of homogeneous phenotypes and different clinical subtypes of depression, e.g. anhedonic depression, retarded depression, etc. In addition, the use of different radioligands and imaging techniques, diverse rating scales, together with the lack of control of clinical variables (clinical course, recent or past use of substances of abuse, etc.) make it difficult to clearly identify neuronal regions or networks with consistently abnormal structures or functions in major depressive disorder. It is probably necessary to build a shared approach between clinicians and researchers in order to identify standardized procedures to better understand the role of the dopamine transporter in depression. We outline a list of major issues and also suggest some standardized procedures in collecting clinical and imaging data on major depressed patients. Our aim is to delineate a possible "modus operandi" that would be a proposal for neuroreceptor studies on major depression.

Greater striatal dopamine transporter density may be associated with major depressive episode

BACKGROUND

We examined striatal dopamine transporter (DAT) distribution volume ratio (DVR) values in subjects with unipolar or bipolar major depressive episode (versus non-depressed healthy volunteers) using the selective DAT radioligand [(99m)Tc]TRODAT-1 and single photon emission computed tomography (SPECT). We hypothesized that striatal DVR values would be greater in depressed versus non-depressed subjects, and that greater DVR values may represent a possible clinical biomarker of depression.

METHODS

[(99m)Tc]TRODAT-1 spect images were acquired from 39 depressed and 103 non-depressed drug-free subjects. The primary outcome measure was the DVR value of [(99m)Tc]TRODAT-1 binding for the putamen region and the combined putamen plus caudate region.

RESULTS

DVR values were significantly correlated across all striatal regions within both subject groups (p<0.005). Depressed subjects had significantly greater DVR values (versus non-depressed subjects) in the putamen (p<0.0005) and the combined putamen plus caudate (p<0.0005) regions. There was no difference in DVR values between unipolar (n=24) and bipolar (n=15) depressed subjects, and no difference in DVR values for depressed subjects with or without prior antidepressant exposure. The predictive probability of the putamen or combined putamen plus caudate DVR value to distinguish depressed from non-depressed subjects was significant (p<0.0005).

LIMITATIONS

DAT values could potentially be influenced by age, gender, diagnosis, prior psychotropic dug exposure, illness length, or symptom severity.

CONCLUSION

Results confirm prior observations of greater striatal DAT density in depressed versus non-depressed subjects, and suggest that greater DVR values may possibly represent a potential diagnostic biomarker for distinguish depressed from non-depressed individuals.

Association between the dexamethasone suppression test and serotonin transporter availability in healthy volunteer: a SPECT with [(123)I] ADAM study

Most common psychiatric diseases have been found to be associated with disturbance of both the hypothalamic-pituitary-adrenal (HPA) axis and the brain serotonergic system. The aim of this study was to explore the neuroendocrine relationships between the dexamethasone suppression test (DST) and serotonin transporter (SERT) availability in healthy volunteers. Sixty-six participants (30 males and 36 females) were recruited from the community. The DST suppression rate (D%) is the reduction in cortisol level from Day 1 (D1) to Day 2 (D2) in proportion to the Day 1 cortisol level (D%=(D1-D2)/D1×100%). SPECT with [(123)I] ADAM was used to measure SERT availability. A significant correlation between D% and SERT availability was noted in all subjects (Spearman's ρ=0.26, p=0.03) and in the male subjects (Spearman's ρ=0.41, p=0.02). SERT availability may be sensitive to changes in DST, especially in males.

Dopamine transporter binding in social anxiety disorder: the effect of treatment with escitalopram

Social anxiety disorder (SAD) is characterised by fear of social or performance situations where the individual is exposed to unfamiliar people or to possible scrutiny by others. The literature on dopamine ligands and dopamine genotypes in SAD is however inconsistent. In this study we measured the effects of SSRI pharmacotherapy on dopamine transporter (DAT) binding in patients with SAD, also addressing variability in DAT genotype. Adult subjects meeting DSM-IV criteria for generalised SAD were studied before and after 12 weeks of pharmacotherapy with the selective serotonin reuptake inhibitor (SSRI) escitalopram. DAT single photon emission computed tomography (SPECT) using (123)I-FP-CIT was performed at baseline, and repeated at 12 weeks. Striatal DAT binding was analysed for changes following therapy, and for correlations with clinical efficacy, in the whole group as well as for a subgroup with the A10/A10 DAT genotype. The study included 14 subjects (9 male, 5 female) with a mean (SD) age of 41 (±13) years. The subjects' Liebowitz Social Anxiety Scale (LSAS) score was significantly decreased following pharmacotherapy. In the combined group the left caudate and left putamen showed clusters of increased DAT binding after therapy. The left caudate changes were also observed in the subgroup of 9 A10/A10 homozygotes. However no correlation was found between improved symptoms and DAT binding. The changes found in DAT binding in the caudate and putamen may be due to serotonergic activation of dopamine function by SSRI therapy. This is consistent with previous work indicating decreased DAT binding in SAD, and increased DAT binding after SSRI administration.

Body image, sexual function and depression in Korean patients with breast cancer: modification by 5-HTT polymorphism

BACKGROUND

Nearly 50% of women with breast cancer show depressive symptoms after diagnosis and treatment. The purpose of this study was to clarify how psychosocial factors (body image, sexuality, and social relationships) and genetic factors (functional polymorphism of the serotonin transporter-linked promoter region) influence depression.

METHODS

The participants were categorized by DSM-IV diagnoses; scored according to their depressive symptoms, body image and social and sexual function (BIRS), self-esteem, and quality of life; and genotyped by functional polymorphism of the serotonin transporter promoter.

RESULTS

Patients with depressive symptoms showed low self-esteem, poor body image, relationship problems, and low quality of life. Genotype frequencies did not differ between two groups categorized by the presence or absence of depressive symptoms. However, the patients with the short allele of the 5-HTTLPR had significantly higher HAM-D scores (F = 7.59, p = 0.047).

CONCLUSION

The results suggest that psychosocial factors related to breast cancer treatment such as body image, self-esteem, and interpersonal relationship influence the development of depressive symptoms. The 5-HTTLPR may be associated with the severity of depressive symptoms rather than susceptibility to the development of depressive symptoms.

Imaging the effects of genetic polymorphisms on radioligand binding in the living human brain: A review on genetic neuroreceptor imaging of monoaminergic systems in psychiatry

Imaging genetics is a research field that describes the impact of genetic risk variants on brain structure and function. While magnetic resonance based imaging techniques are able to provide complex information on a system level, positron emission tomography (PET) and single photon emission computer tomography (SPECT) allow for determination of distribution and density of single receptor molecules in the human brain. Major psychiatric disorders are highly heritable, and have been associated with a dysregulation in brain dopamine and serotonin systems. Understanding the role of genetic polymorphisms within these neurotransmitter systems on brain phenotype is essential. This review tries to cover the literature on the impact of gene variants implicated in psychiatric disorders on serotonin, dopamine, and MAO-A radioligand binding in living humans. The majority of PET and SPECT studies investigated the role of polymorphisms within genes coding for the serotonin and dopamine transporters, the serotonin 1A receptor, and the dopamine D2 receptor on G protein coupled receptors or transporter proteins critically involved in serotonin or dopamine neurotransmission. Other studies investigated the impact of variants in genes for monoamine oxidase-A (MAO-A) or brain derived neurotrophic factor on monoamine transporters, receptors, or MAO-A activity. Two main findings in healthy subjects emerge from the current literature: one is an increased binding of the selective ligand [(11)C]DASB to serotonin transporters in subjects homozygous for the triallelic 5-HTTLPR LA allele. The other one is decreased binding of the radioligand [(11)C]raclopride to dopamine D2 receptors in D2 Taq1 A1 allele carriers. Other findings reported are highly interesting but require independent replication.

Diencephalic serotonin transporter availability predicts both transporter occupancy and treatment response to sertraline in obsessive-compulsive checkers

BACKGROUND

To our knowledge, no studies have investigated the predictive value of central serotonin transporter (SERT) availability for treatment response to serotonin reuptake inhibitors (SSRIs) in patients with obsessive-compulsive disorder (OCD). This study used brain imaging to examine the relationship between pretreatment SERT availability and transporter occupancy as well as treatment response by sertraline in patients displaying prominent behavioral checking compulsions (OC checkers).

METHODS

Single photon emission computed tomography (SPECT) was used to measure thalamic-hypothalamic SERT availability with [(123)I]-2beta-carbomethoxy-3beta-(4-iodophenyl)-tropane in 28 nondepressed OC checkers at baseline and after 14 weeks of treatment with sertraline (175 mg daily). SERT availability was correlated with OC severity and treatment response as assessed with the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). Associations between individual transporter occupancies and clinical parameters were investigated.

RESULTS

1) Correlation analyses between thalamic-hypothalamic SERT availability and OC severity showed significant negative associations at baseline and after treatment with sertraline. 2) Pretreatment SERT availability correlated significantly with both transporter occupancy and treatment response; in addition, a positive association was found between transporter occupancy and treatment response directly. 3) Using multivariate statistical models, the data demonstrated that higher pretreatment SERT availability significantly predicted higher occupancy rates as well as better treatment response 14 weeks later.

CONCLUSIONS

Higher pretreatment thalamic-hypothalamic SERT availability may predict both higher occupancy rates and better treatment response to sertraline. The data suggest a strong connection between transporter occupancy and treatment response.

Changes in thalamus-hypothalamus serotonin transporter availability during clomipramine administration in patients with obsessive-compulsive disorder

To the authors' knowledge there is as of yet no study demonstrating in vivo alterations in human serotonin transporters (SERT) during clomipramine treatment in patients with obsessive-compulsive disorder. The only study in which SERT binding has been investigated in obsessive-compulsive disorder (OCD) patients before and after treatment is a small pilot study by Stengler-Wenzke et al (2006), who treated five OCD patients with citalopram. In the study at hand, we measured transporter availability in the thalamus-hypothalamus with [(123)I] beta-CIT single photon emission computed tomography (SPECT) in 24 patients with DSM-IV OCD. All patients displayed prominent behavioral checking compulsions (OC-checkers). At baseline and upon medication after 12 weeks of treatment with clomipramine (150 mg daily) 24 non-depressed OC-checkers underwent a SPECT measurement of brain SERT availability using [(123)I]-2beta-carbomethoxy-3beta-(4-iodophenyl)tropane. For quantification of brain serotonin transporter availability, a ratio of specific to non-displaceable [(123)I] beta-CIT brain binding was used (BP(ND)=(thalamus and hypothalamus-cerebellum)/cerebellum). The SERT availability was compared between baseline and after treatment and correlated with severity of OC symptomatology and treatment response as assessed with the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). After treatment with clomipramine patients showed a 48% reduced brain serotonin transporter availability in the thalamus-hypothalamus, as compared with values at baseline (0.72+/-0.12 vs 1.39+/-0.18, p<0.001). Correlations between brain SERT availability and OC symptomatology (Y-BOCS scores) revealed significantly negative associations both at baseline and after treatment (r=-0.46; p<0.05 and r=-0.53; p<0.01 respectively). These data suggest that the SERT availability values could be considered a biological indicator of disease severity. Moreover, in search of predictors we found that higher pretreatment SERT availability significantly predicted better treatment response 12 weeks later (B=14.145+/-4.514; t=3.133; p=0.005). These results provide further support for an important role of alterations in serotonergic neurons in the pathophysiology of OCD.

Applying neuroimaging ligands to study major depressive disorder

The recent increase in radioligands available for neuroimaging major depressive disorder has led to advancements in our understanding of the pathophysiology of this illness and improved antidepressant development. Major depressive disorder can be defined as an illness of recurrent major depressive episodes of persistently low mood, dysregulated sleep, appetite and weight, anhedonia, cognitive impairment, and suicidality. The main target sites investigated with radioligand neuroimaging include receptor sites that regulate in response to lowered monoamine levels, targets related to removal of monoamines, uptake of ligands related to regional brain function, and target sites of antidepressants.

Anxiety is associated with reduced central serotonin transporter availability in unmedicated patients with unipolar major depression: a [11C]DASB PET study

Serotonergic dysfunction may contribute to negative mood states in affective disorders. Some in vivo imaging studies showed reduced availability of serotonin transporters (5-HTT) in the brainstem and thalamus of patients with major depression. We tested the hypothesis that 5-HTT availability is reduced in unmedicated unipolar patients with major depression compared to healthy control subjects matched for gender, age, genotype and smoking status. Availability of 5-HTT was measured in vivo with positron emission tomography and [(11)C]-3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile (DASB) in the midbrain, thalamus and amygdala. DASB binding was correlated with the severity of depression (Beck's Depression Inventory), anxiety (Spielberger's State-Trait Anxiety Inventory) and personality traits (Temperament and Character Inventory). Patients with major depression displayed reduced 5-HTT availability in the thalamus (P=0.005). In patients, low serotonin transporter availability correlated with high anxiety (thalamus: r=-0.78, P=0.004; midbrain: r=-0.78, P=0.004; amygdala: r=-0.80, P=0.003). Correlations with severity of depression were weaker and did not survive correction for multiple testing. These results support the hypothesis that central serotonergic dysfunction is associated with negative mood states in affective disorders. In the thalamus, a low serotonin reuptake capacity may interfere with thalamic control of cortical excitability and contribute to anxiety rather than depression per se in major depression.

Role of DAT-SPECT in the diagnostic work up of parkinsonism

The diagnosis of idiopathic Parkinson's disease (PD) can be achieved with high degrees of accuracy in cases with full expression of classical clinical features. However, diagnostic uncertainty remains in early disease with subtle or ambiguous signs. Functional imaging has been suggested to increase the diagnostic yield in parkinsonian syndromes with uncertain clinical classification. Loss of striatal dopamine nerve terminal function, a hallmark of neurodegenerative parkinsonism, is strongly related to decreases of dopamine transporter (DAT) density, which can be measured by single photon emission computed tomography (SPECT). The use of DAT-SPECT facilitates the differential diagnosis in patients with isolated tremor symptoms not fulfilling PD or essential tremor criteria, drug-induced, psychogenic and vascular parkinsonism as well as dementia when associated with parkinsonism. This review addresses the value of DAT-SPECT in early differential diagnosis, and its potential as a screening tool for subjects at risk of developing PD as well as issues around the assessment of disease progression.

Increased serotonin and dopamine transporter binding in psychotropic medication-naive patients with generalized social anxiety disorder shown by 123I-beta-(4-iodophenyl)-tropane SPECT

There is circumstantial evidence for the involvement of serotonergic and dopaminergic systems in the pathophysiology of social anxiety disorder. In the present study, using SPECT imaging we examined the (123)I-beta-(4-iodophenyl)-tropane binding potential for the serotonin and dopamine transporters in patients with a generalized social anxiety disorder and in age- and sex-matched healthy controls.

METHODS

Twelve psychotropic medication-naïve patients with social anxiety disorder, generalized type (5 women and 7 men) and 12 sex- and age-matched healthy controls were studied. Volumes of interest were constructed on MRI-coregistered SPECT scans. Binding ratios were compared using the Mann-Whitney U test. Possible correlations between binding patterns and symptomatology were assessed using the Spearman rank correlation coefficient.

RESULTS

Significantly higher binding potentials were found for the serotonin in the left and right thalamus of patients. Patients had also a significantly higher binding potential for the dopamine transporter in the striatum.

CONCLUSION

The present study provided direct evidence for abnormalities in both the dopaminergic and the serotonergic systems in patients with generalized social anxiety disorder.

Loss of thalamic serotonin transporters in early drug-naïve Parkinson's disease patients is associated with tremor: an [(123)I]beta-CIT SPECT study

In vitro studies revealed serotonin transporter (5-HTT) decline in Parkinson’s disease (PD). Yet, few studies investigated thalamic 5-HTT in vivo and its effect on PD heterogeneity. We analyzed thalamic [¹²³I]β-CIT binding (mainly reflecting 5-HTT binding) in 32 drug-naïve PD patients and 13 controls with SPECT. Twenty-six patients were examined twice (17 months apart). Based on UPDRS scores, we identified subgroups of patients with moderate/severe tremor (PD_T) and without tremor (PD_WT) at the time of clinical diagnosis. Additionally, depressive symptoms were evaluated using the Beck Depression Inventory (BDI) at baseline. Mean thalamic specific to non-specific [¹²³I]β-CIT binding ratio was lower in patients when compared to controls, and further decreased during follow-up. At baseline, average thalamic ratio was significantly lower in the PD_T than in the PD_WT subgroup. No correlation was found between BDI scores and thalamic binding ratios. Our findings show decline of [¹²³I]β-CIT binding to thalamic 5-HTT in PD and its possible contribution to tremor onset.

[123I]-beta-CIT SPECT imaging shows reduced thalamus-hypothalamus serotonin transporter availability in 24 drug-free obsessive-compulsive checkers

Numerous findings indicate alterations in brain serotonin systems in obsessive-compulsive disorder (OCD). We investigated the in vivo availability of thalamus-hypothalamus serotonin transporters (SERT) in patients with DSM-IV OCD who displayed prominent behavioral checking compulsions (OC-checkers). Four hours after injection of [(123)I]-2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ([(123)I]-beta-CIT), single photon emission computed tomography (SPECT) scans were performed in 24 medication-free non-depressed OC-checkers and 24 age- and gender-matched healthy controls. For quantification of brain serotonin transporter availability, a ratio of specific to non-displaceable [(123)I]-beta-CIT brain binding was used (V''(3)=(thalamus and hypothalamus-cerebellum)/cerebellum). Drug-free non-depressed OC-checkers showed an 18% reduced brain serotonin transporter availability in the thalamus and hypothalamus, as compared with healthy control subjects (1.38+/-0.19 vs 1.69+/-0.21; p<0.001). There was a strong negative correlation between severity of OC symptomatology (Y-BOCS scores) and SERT availability (r=-0.80; p<0.001). Moreover, we found a significant positive correlation between illness duration and serotonin transporter availability (r=0.43; p<0.05). This first report of significantly reduced [(123)I]-beta-CIT binding in the thalamus-hypothalamus region in OC-checkers suggests reduced brain serotonin transporter availability, which is more pronounced with increased severity of OC symptomatology and short duration of illness. The results provide direct evidence for an involvement of the serotonergic system in the pathophysiology of OCD.

Displacement of serotonin and dopamine transporters by venlafaxine extended release capsule at steady state: a [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)-tropane single photon emission computed tomography imaging study

Both positron emission tomography and single photon emission computed tomography (SPECT) studies suggest that saturation of serotonin transporters (SERT) is present during treatment with therapeutic doses of selective serotonin reuptake inhibitors (SSRIs). Selective serotonin reuptake inhibitors also appear to increase the availability of dopamine transporters (DAT). The current study measured SERT occupancy and modulation of DAT by the serotonin/norepinephrine reuptake inhibitor (SNRI) venlafaxine using [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)-tropane SPECT. Eight healthy subjects were administered open-label venlafaxine extended release capsules (75 mg/d for 4 days followed by 150 mg/d for 5 days). Venlafaxine significantly inhibited [123I]beta-CIT binding to SERT in the brainstem (55.4%) and the diencephalon (54.1%). In contrast, venlafaxine increased [123I]beta-CIT binding to DAT in the striatum (10.1%) after 5 days of administration of 150 mg/d. The displacement of [123I]beta-CIT from brain SERT and the increase in striatal [123I]beta-CIT binding to DAT appear similar to previous work with the SSRI citalopram (40 mg/d). A literature review of SERT occupancy by marketed SSRIs and the SNRI venlafaxine using SPECT ([123I]beta-CIT) or positron emission tomography ([11C](N, N-Dimethyl-2-(2-amino-4-cyanophenylthio)-benzylamine) imaging suggests that therapeutic doses of SNRI are associated with virtual saturation of the serotonin transporter.

Serotonin transporter and dopamine transporter imaging in the canine brain

The serotonergic and dopaminergic systems are involved in a wide range of emotional and behavioral aspects of animals and humans and are involved in many neuropsychiatric disorders. Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are designed to block the 5-HT transporter (SERT), thereby increasing the available 5-HT in the brain. Functional imaging with specific SERT and dopamine transporter (DAT) ligands contributes to the study of the SSRI-transporter interaction. First, we evaluated the feasibility of a canine model in the study of the SERT and DAT with the radioligands [123I]-beta-CIT and [123I]-FP-CIT as well as single-photon emission computed tomography imaging. Second, we studied the effect of SSRIs (sertraline, citalopram and escitalopram) on the SERT and DAT in two dogs. The position of the canine model in the study of the SERT and DAT is discussed and compared with other animal models.

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

RATIONALE

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

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

In vivo imaging of serotonin transporter occupancy by means of SPECT and [123I]ADAM in healthy subjects administered different doses of escitalopram or citalopram

BACKGROUND

Escitalopram is a dual serotonin reuptake inhibitor (SSRI) approved for the treatment of depression and anxiety disorders. It is the S-enantiomer of citalopram, and is responsible for the serotonin reuptake activity, and thus for its pharmacological effects. Previous studies pointed out that clinically efficacious doses of other SSRIs produce an occupancy of the serotonin reuptake transporter (SERT) of about 80% or more. The novel radioligand [123I]ADAM and single photon emission computer tomography (SPECT) were used to measure midbrain SERT occupancies for different doses of escitalopram and citalopram.

METHODS

Twenty-five healthy subjects received a single dose of escitalopram [5 mg (n=5), 10 mg (n=5), and 20 mg (n=5)] or citalopram [(10 mg (n=5) and 20 mg (n=5)]. Midbrain SERT binding was measured with [(123)I]ADAM and SPECT on two study days, once without study drug and once 6 h after single dose administration of the study drug. The ratio of midbrain-cerebellum/cerebellum was the outcome measure (V3") for specific binding to SERT in midbrain. Subsequently, SERT occupancy levels were calculated using the untreated baseline level for each subject. An Emax model was used to describe the relationship between S-citalopram concentrations and SERT occupancy values. Additionally, four subjects received placebo to determine test-retest variability.

RESULTS

Single doses of 5, 10, or 20 mg escitalopram led to a mean SERT occupancy of 60+/-6, 64+/-6, and 75+/-5%, respectively. SERT occupancies for subjects treated with single doses of 10 and 20 mg citalopram were 65+/-10 and 70+/-6%, respectively. A statistically significant difference was found between SERT occupancies after application of 10 and 20 mg escitalopram, but not for 10 and 20 mg citalopram. There was no statistically significant difference between the SERT occupancies of either 10 mg citalopram or 10 mg escitalopram, or between 20 mg citalopram and 20 mg escitalopram. Emax was slightly higher after administration of citalopram (84%) than escitalopram (79%). In the test-retest study, a mean SERT "occupancy" of 4% was found after administration of placebo, the intraclass correlation coefficient was 0.92, and the repeatability coefficient was 0.25.

CONCLUSION

SPECT and [123I]ADAM were used to investigate SERT occupancies after single doses of escitalopram or citalopram. The test-retest study revealed good reproducibility of SERT quantification. Similar SERT occupancies were found after administration of equal doses (in respect to mg) of escitalopram and citalopram, giving indirect evidence for a fractional blockade of SERT by the inactive R-citalopram.

How psychotherapy changes the brain--the contribution of functional neuroimaging

A thorough investigation of the neural effects of psychotherapy is needed in order to provide a neurobiological foundation for widely used treatment protocols. This paper reviews functional neuroimaging studies on psychotherapy effects and their methodological background, including the development of symptom provocation techniques. Studies of cognitive behavioural therapy (CBT) effects in obsessive-compulsive disorder (OCD) were consistent in showing decreased metabolism in the right caudate nucleus. Cognitive behavioural therapy in phobia resulted in decreased activity in limbic and paralimbic areas. Interestingly, similar effects were observed after successful intervention with selective serotonin reuptake inhibitors (SSRI) in both diseases, indicating commonalities in the biological mechanisms of psycho- and pharmacotherapy. These findings are discussed in the context of current neurobiological models of anxiety disorders. Findings in depression, where both decreases and increases in prefrontal metabolism after treatment and considerable differences between pharmacological and psychological interventions were reported, seem still too heterogeneous to allow for an integrative account, but point to important differences between the mechanisms through which these interventions attain their clinical effects. Further studies with larger patient numbers, use of standardised imaging protocols across studies, and ideally integration with molecular imaging are needed to clarify the remaining contradictions. This effort is worthwhile because functional imaging can then be potentially used to monitor treatment effects and aid in the choice of the optimal therapy. Finally, recent advances in the functional imaging of hypnosis and the application of neurofeedback are evaluated for their potential use in the development of psychotherapy protocols that use the direct modulation of brain activity as a way of improving symptoms.

Topography of cerebral monoamine transporter availability in families with SCA2 mutations: a voxel-wise [123I]beta-CIT SPECT analysis

PURPOSE

The purpose of this study was to investigate the monoamine transporter status of dopamine, serotonin and norepinephrine throughout the brain in spinocerebellar ataxia type 2 (SCA2). To this end, nine patients were studied with [(123)I]beta-CIT SPECT.

METHODS

Data were compared with ten age-matched healthy control subjects and ten patients with young-onset Parkinson's disease (YOPD), matched for age. Parametric SPECT images of the specific-to-non-displaceable equilibrium partition coefficient (V (3)''), which is proportional to the receptor density (B (max)), were generated. In order to objectively localise focal changes in beta-CIT uptake throughout the brain volume without having to make an a priori hypothesis as to their location, statistical parametric mapping (SPM) was applied to SPECT images. Data clusters revealed by SPM, showing significant differences in V (3)'' values between groups, were transformed onto the individual V (3)'' image to obtain mean regional uptake values.

RESULTS

Both SCA2 and YOPD patients showed significant decreases in striatal [(123)I]beta-CIT SPECT uptake when compared with controls. However, in SCA2 patients, additional reductions in caudate/anterior putamen, midbrain and pons [(123)I]beta-CIT uptake were localised with SPM.

CONCLUSION

Voxel-wise analysis of [(123)I]beta-CIT SPECT revealed more widespread decline of monoamine transporter availability in SCA2 than in YOPD, reflecting differences in the underlying pathology. We suggest that the quantification of midbrain and pons [(123)I]beta-CIT signal is likely to improve the diagnostic accuracy in patients presenting with clinical features of both SCA2 and YOPD at initial investigation.

Serotonin transporter imaging with [123I]beta-CIT SPECT before and after one year of citalopram treatment of obsessive-compulsive disorder

BACKGROUND

Two thirds of patients with obsessive-compulsive disorder (OCD) respond to treatment with selective serotonin reuptake inhibitors (SSRIs). The neurobiological mechanisms of SSRI action and failure to respond to SSRI treatment remain to be elucidated.

OBJECTIVES

The aim of this pilot study was to quantify changes in the availability of serotonin transporter (SERT) in the course of SSRI treatment and to relate these changes to improvements of clinical symptoms.

METHODS

Ten patients with OCD were investigated at baseline and 5 of them after 1 year of SSRI treatment with citalopram 60 mg per day using brain single photon emission computed tomography and [123I]beta-CIT. Specific-to-nondisplaceable [123I]beta-CIT binding ratios (V3'') were calculated in SERT-rich brainstem, midbrain and thalamus using a magnetic resonance imaging-based region of interest (ROI) analysis. Symptom severity was evaluated with the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS).

RESULTS

V3'' differed significantly between pretreatment and follow-up scans in all three brain regions, thalamus, midbrain as well as in brainstem. In thalamic ROI, differ ences in SERT availability and Y-BOCS ratings correlated. In midbrain, a trend toward a significant association was found. In brainstem, no relationship was revealed.

CONCLUSIONS

Higher occupancy of SERT by citalopram seems to be associated with better clinical response after 1 year of SSRI treatment of patients with OCD.

Serotonin transporter residual availability during long-term antidepressant therapy does not differentiate responder and nonresponder unipolar patients

BACKGROUND

Serotonin transporters (SERT) are a major target for antidepressant medication, although there have been limited in vivo studies of SERT availability in patients being treated with antidepressants. It is not known whether SERT availability differs in treatment-responsive and -nonresponsive patients receiving long-term treatment. In this study, we used single photon emission computed tomography (SPECT) to compare SERT residual availability in unipolar responders and nonresponders during long-term antidepressant treatment. Dopamine transporter (DAT) availability was also assessed in the same patients to examine the relationship between the two transporter systems.

METHODS

Twenty-four medicated unipolar patients were recruited, of whom 11 were responders and 13 were nonresponders. All patients underwent SPECT with [123I] beta-carbomethoxy-3-beta-(4 iodophenyl)tropane. Brain SERT was measured in the brain stem and diencephalon, and DAT was measured in the striatum. Residual availability was calculated as a ratio of specific to nonspecific uptake, with the occipital region used as the nonspecific reference region.

RESULTS

There was no difference between responders and nonresponders in SERT availability. Dopamine transporter availability was similar in responders and nonresponders, and there was no association between SERT and DAT availability.

CONCLUSIONS

Serotonin transporter availability does not discriminate responders and nonresponders during long-term treatment with antidepressants.

Imaging of serotonin transporters and its blockade by citalopram in patients with major depression using a novel SPECT ligand [123I]-ADAM

We studied the midbrain SERT availability in patients with major depression and assessed the relation of SERT occupancy by citalopram to the treatment response. 21 non-medicated patients with major depression and 13 healthy controls were examined by [(123)I]-ADAM SPECT. The midbrain SERT availability (SERT V(3)'') was calculated using individual MRI scans. In 13/21 patients SPECT was repeated 7 days after oral medication with citalopram (10 mg/day). We found no significant difference in the mean midbrain SERT availability between the studied patients with major depression and healthy controls (0.86 +/- 0.27 vs. 0.71 +/- 0.44, p = 0.069). The mean SERT occupancy accounted to 61%. The degree of SERT blockade by citalopram did not correlate with the reduction in HAMD total score. Treatment with low-dosed citalopram caused individually variable occupancy of the midbrain-SERT and a rapid clinical improvement in 54% of the investigated patients.

Sex differences in diencephalon serotonin transporter availability in major depression

BACKGROUND

Major depression is more prevalent in women than men. The present study evaluated if previous findings that demonstrated decreased 5-hydroxytryptamine (5-HT) transporter availability in depressed patients would be confirmed in a larger sample and also evaluated sex differences.

METHODS

Depressed (n = 32) and healthy subjects (n = 32), including 16 pairs of women and men, participated in an iodine-123-2 beta-carbomethoxy-3beta-(4-iodophenyltropane) ([(123)I]beta-CIT) single photon emission computed tomography (SPECT) and a magnetic resonance imaging (MRI) scan. Participants were administered [(123)I]beta-CIT (225.7 +/- 3.7 MBq) and imaged 23.0 +/- 1.6 hours later. Statistical analyses included analysis of variance and a regression analysis of the main and interactive effects of age, sex, and depression.

RESULTS

Overall, depressed patients demonstrated 12% lower diencephalon and no change in striatal or brainstem [(123)I]beta-CIT uptake. Significant age by sex, sex by depression, and age by sex by depression interactions were noted due to 22% lower diencephalon [(123)I]beta-CIT uptake in depressed women compared with less than a 1% decrease in depressed men.

CONCLUSIONS

As observed previously, diencephalon 5-HT transporter availability is decreased in depressed patients. However, the decrease appears to be sex-specific and age-dependent. These findings suggest that serotonergic mechanisms mediating depressed mood differ between men and women in an age-dependent manner and may explain why young women respond better to treatment with selective serotonin reuptake inhibitor (SSRI) antidepressants.

SERT and DAT availabilities under citalopram treatment in obsessive-compulsive disorder (OCD)

Serotonin and dopamine transporter (SERT, DAT) availabilities have prospectively been investigated using [123I]beta-CIT and single photon emission computed tomography in subjects with obsessive-compulsive disorder under treatment with the selective serotonin reuptake inhibitor citalopram. SERT availability decreased by a mean 36.5%, whereas DAT availability increased by about 40%. The data point at a citalopram induced modulation of both serotonergic and dopaminergic activity and support the notion of functional interactions of monoaminergic systems in the human brain.

Serotonin transporter binding in Tourette Syndrome

Recent studies provided evidence for an involvement of the dopaminergic system in the pathophysiology of Tourette Syndrome (TS). However, little is known about possible impairment of other neurotransmitter systems. In obsessive-compulsive disorder (OCD), a common comorbidity in TS, it is suggested that the serotonergic system plays a major role in the pathogenesis. We, therefore, used [I-123]2[beta]-carbomethoxy-3[beta]-(4-iodophenyl)tropane ([123I]beta-CIT) and single photon emission computed tomography (SPECT) to investigate serotonin transporter (SERT) binding capacity in 12 patients with TS with various degrees of associated obsessive compulsive behaviour (OCB) and 16 age-matched healthy controls. Binding ratios in TS patients not receiving serotonin reuptake inhibitors (SSRI) (n=8) were significantly reduced compared to age-adjusted ratios from normal controls (2.8 versus 3.2, p=0.003). Treatment with SSRI resulted in a significant reduction of SERT availability. Performing linear regression analysis for this small group, SSRI-free patients indicated trends for a negative correlation between [123I]beta-CIT binding on SERT and OCB (r=-0.78, p=0.023) as well as complex motor tics (r=-0.68, p=0.064). In healthy controls, but not in the TS group, we found an age-related decline in SERT binding capacity (0.28% decrease per year, p=0.038). Our data are in agreement with previous results suggesting an impairment of the serotonergic system in TS. It can be speculated that the reduction in SERT binding capacity is associated with the degree of comorbid OCB.

Validation of [(123)I]beta-CIT SPECT to assess serotonin transporters in vivo in humans: a double-blind, placebo-controlled, crossover study with the selective serotonin reuptake inhibitor citalopram

Disturbances in the serotonin (5-HT) system are associated with various neuropsychiatric disorders. The 5-HT system can be studied in vivo by measuring 5-HT transporter (SERT) densities using (123)iodine-labeled 2beta-carbomethoxy-3beta(4-iodophenyl)tropane ([(123)I]beta-CIT) and single photon emission computed tomography (SPECT). Validation of this technique is important because [(123)I]beta-CIT does not bind selectively to SERTs. Some studies have validated this technique in vivo in the human brain in SERT-rich areas, but the technique has not been validated yet in SERT-low cortical areas. The aim of this study was to further validate [(123)I]beta-CIT SPECT in assessing SERTs in vivo in humans in both SERT-rich and SERT-low areas. A double-blind, placebo-controlled, crossover design was used with the selective 5-HT reuptake inhibitor (SSRI) citalopram. Six male subjects underwent two [(123)I]beta-CIT SPECT sessions: one after pretreatment with citalopram and one after placebo. Scans were acquired 4 h and 22-27 h p.i., and both region-of-interest and voxel-by-voxel analyses were performed. Citalopram reduced [(123)I]beta-CIT binding ratios in SERT-rich midbrain and (hypo)thalamus. Binding ratios were also lower after citalopram in SERT-low cortical areas, but statistical significance was only reached in several cortical areas using voxel-by-voxel analysis. In addition, citalopram increased binding ratios in the DAT-rich striatum and increased absolute uptake in the cerebellum. The results show that [(123)I]beta-CIT SPECT is a valid technique to study SERT binding in vivo in human brain in SERT-rich areas. Although we provide some evidence that [(123)I]beta-CIT SPECT may be used to measure SERTs in SERT-low cortical areas, these measurements must be interpreted with caution.

Voxel-wise analysis of [123I]beta-CIT SPECT differentiates the Parkinson variant of multiple system atrophy from idiopathic Parkinson's disease

To investigate the cerebral dopamine transporter status in the early stages of the parkinson-variant of multiple system atrophy (MSA-P), 15 patients with MSA-P and a disease duration up to 3 years were studied with [123I]beta-CIT single photon emission computed tomography (SPECT). Data were compared with 13 age-matched healthy control subjects and 15 patients with idiopathic Parkinson's disease (IPD), matched for age and disease duration. Parametric SPECT images of the specific-to-nondisplaceable equilibrium partition coefficient (V3''), which is proportional to the receptor density (Bmax) have been generated. To objectively localize focal changes in dopaminergic function throughout the entire brain volume without having to make an a priori hypothesis as to their location, statistical parametric mapping (SPM) was applied to our [123I]beta-CIT SPECT study. Both MSA-P and IPD patients showed significant decreases in striatal [123I]beta-CIT SPECT uptake. However, in MSA-P patients an additional reduction in midbrain [123I]beta-CIT signal was localized with SPM compared with control subjects (MSA-P, V3'': 0.89 +/- 0.37 versus controls V3'': 1.81 +/- 0.38; P < 0.001) and patients with IPD (V3'': 1.84 +/- 0.26; P < 0.001). Stepwise linear discriminant analysis of mean [123I]beta-CIT uptake in the putamen, caudate and midbrain identified the caudate and midbrain as indices to classify correctly 95.2% of subjects as either normal, patients with MSA-P or IPD. Voxel-wise analysis of [123I]beta-CIT SPECT revealed more widespread decline of monoaminergic transporter availability in MSA-P compared with IPD, matching the underlying pathological features. We suggest that the quantification of midbrain DAT signal should be included in the routine clinical analysis of [123I]beta-CIT SPECT in patients with uncertain parkinsonism.

In vivo quantification by SPECT of [123I] ADAM bound to serotonin transporters in the brains of rabbits

BACKGROUND

A novel radioiodine ligand [(123)I] ADAM (2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine) has been suggested as a promising serotonin transporter (SERT) imaging agent for the central nervous system. In this study, the biodistribution of SERTs in the rabbit brain was investigated using [(123)I] ADAM and mapping images of the same animal produced by both single-photon emission computed tomography (SPECT) and microautoradiography. A semiquantification method was adopted to deduce the optimum time for SPECT imaging, whereas the input for a simple fully quantitative tracer kinetic model was provided from arterial blood sampling data.

METHODS

SPECT imaging was performed on female rabbits postinjection of 185 MBq [(123)I] ADAM. The time-activity curve obtained from the SPECT images was used to quantify the SERTs, for which the binding potential was calculated from the kinetic modeling of [(123)I] ADAM. The kinetic data were analyzed by the nonlinear least squares method. The effects of the selective serotonin reuptake inhibitors fluoxetine and p-chloroamphetamine (PCA) on rabbits were also evaluated. After scanning, the same animal was sacrificed and the brain was removed for microautoradiography. Regions-of-interest were analyzed using both SPECT and microautoradiography images. The SPECT images were coregistered manually with the corresponding microautoradiography images for comparative study.

RESULTS

During the time interval 90-100 min postinjection, the peak specific binding levels in different brain regions were compared and the brain stem was shown to have the highest activity. The target-to-background ratio was 1.89+/-0.02. Similar studies with fluoxetine and PCA showed a background level for SERT occupation. Microautoradiography demonstrated a higher level of anatomical details of the [(123)I] ADAM distribution than that obtained by SPECT imaging of the rabbit brain.

CONCLUSION

SPECT imaging of the rabbit brain with [(123)I] ADAM showed high affinity, high specificity, and favorable kinetics. The time-activity curve showed that the accumulation of the [(123)I] ADAM in the brain stem reached a maximum between 90 and 100 min postinjection. The microautoradiography provides high-resolution images of the rabbit brain. Our results for the [(123)I] ADAM biodistribution in the rabbit brains demonstrate that this new radioligand is suitable as a selective SPECT imaging agent for SERTs.

PET brain imaging with [11C](+)McN5652 shows increased serotonin transporter availability in major depression

BACKGROUND

Alterations in the brain serotonin (5-HT) system have been found in patients with depression. We used the selective 5-HT transporter site ligand [11C](+)McN5652 and positron emission tomography (PET) to examine the hypothesis that alterations in 5-HT transporter levels may be present in selected regions of the brain in depressed patients.

METHODS

Four drug free depressed patients and four healthy control subjects were studied using [11C](+)McN5652 and PET. The distribution volume (DV) ratio of the PET ligand in selected regions of interest (ROIs) compared to cerebellum were calculated for the ROIs.

RESULTS

Patients showed significantly larger DV ratios in the left frontal cortex (P=0.013) and right cingulate cortex (P=0.043) compared to control subjects.

LIMITATION

The sample size was modest with gender differences between the subject groups. The PET agent, [11C](+)McN5652, may have a lower binding affinity for the 5-HT transporter in the cortical regions compared to other brain regions.

CONCLUSION

These findings suggest that 5-HT transporter sites may be increased in the frontal and cingulate cortices of depressed patients. These alterations in 5-HT transporter sites may be of pathophysiologic significance in the etiology of depression and its treatment.

Serotonin and dopamine transporter availabilities correlate with the loudness dependence of auditory evoked potentials in patients with obsessive-compulsive disorder

Brain monoaminergic function is involved in the pathophysiology of psychiatric disorders. The loudness dependence (LD) of the N1/P2 component of auditory evoked potentials has been proposed as a noninvasive indicator of central serotonergic function, whereas single photon emission computed tomography (SPECT) and [123I]beta-CIT can be used to visualize both serotonin (SERT) and dopamine transporters (DAT). The aim of the study was to correlate LD and SPECT measures in patients with obsessive-compulsive disorder, a condition with evidence for a serotonergic dysfunction. A total of 10 subjects received both neurophysiological and imaging investigations. Evoked potentials were recorded following the application of acoustic stimuli with increasing intensities. The LD of the relevant subcomponents (tangential dipoles) was investigated using dipole source analysis. SPECT was performed 20-24 h after injection of a mean 140 MBq [123I]beta-CIT. As a measure of brain SERT and DAT availabilities, a ratio of specific to nonspecific [123I]beta-CIT binding for the midbrain . pons region (SERT) and the striatum (DAT) was used. The LD of the right tangential dipole correlated significantly with both SERT and DAT availabilities (Pearson's correlations: rho = 0.69, p < 0.05, and rho = 0.80, p < 0.01, respectively). The correlations remained significant after controlling for the effects of age, gender, and severity of clinical symptoms. Associations between LD and both SERT and DAT availabilities further validate the use of neurophysiological approaches as noninvasive indirect measures of neurochemical brain function and point at a hypothesized interconnection of central monoaminergic systems.

Brain serotonin transporter availability predicts treatment response to selective serotonin reuptake inhibitors

BACKGROUND

Few studies have investigated the predictive value of central serotonin transporter (SERT) availability for treatment response to serotonin reuptake inhibitors (SSRIs). This study used brain imaging to examine the relationship between pretreatment brain SERT availability and transporter occupancy by SSRIs with treatment response in two independent depressed populations.

METHODS

Study 1: Twenty-three patients with major depression underwent a single photon emission computed tomography (SPECT) measurement of brain SERT availability using [123I]beta-CIT ([123I]methyl 3beta-(4-iodophenyl) tropane-2beta-carboxylate. The SERT availability was correlated with treatment response to fluoxetine (20 mg/day) assessed with weekly Hamilton Depression Rating Scale (HDRS) for 6 weeks. Study 2: The second group included 10 depressed patients who received 6 weeks of paroxetine treatment (20 mg/day) and serial SPECT scans (baseline, during, and after the treatment).

RESULTS

In Study 1, higher pretreatment diencephalic SERT availability significantly predicted better treatment response 4 weeks later. Similar results were found in Study 2 and supported Study 1 findings. The data showed that greater occupancy of diencephalic transporters by paroxetine correlated with better treatment response.

CONCLUSIONS

Higher pretreatment availability and greater occupancy of SERT in diencephalon may predict better treatment course in response to SSRIs.

In search of a depressed mouse: utility of models for studying depression-related behavior in genetically modified mice

The ability to modify mice genetically has been one of the major breakthroughs in modern medical science affecting every discipline including psychiatry. It is hoped that the application of such technologies will result in the identification of novel targets for the treatment of diseases such as depression and to gain a better understanding of the molecular pathophysiological mechanisms that are regulated by current clinically effective antidepressant medications. The advent of these tools has resulted in the need to adopt, refine and develop mouse-specific models for analyses of depression-like behavior or behavioral patterns modulated by antidepressants. In this review, we will focus on the utility of current models (eg forced swim test, tail suspension test, olfactory bulbectomy, learned helplessness, chronic mild stress, drug-withdrawal-induced anhedonia) and research strategies aimed at investigating novel targets relevant to depression in the mouse. We will focus on key questions that are considered relevant for examining the utility of such models. Further, we describe other avenues of research that may give clues as to whether indeed a genetically modified animal has alterations relevant to clinical depression. We suggest that it is prudent and most appropriate to use convergent tests that draw on different antidepressant-related endophenotypes, and complimentary physiological analyses in order to provide a program of information concerning whether a given phenotype is functionally relevant to depression-related pathology.