Dopamine transporter availability in medication free and in bupropion treated depression: a 99mTc-TRODAT-1 SPECT study

A randomized placebo controlled trial demonstrates the effect of dl-methylephedrine on brain functions is weaker than that of pseudoephedrine

Intellectual drug doping in athletics by using stimulants that affect central nervous system functions has been diversified. Stimulants are regulated by the World Anti-Doping Agency according to their levels of urinary concentration. Positron emission tomography could evaluate how stimulants affect central nervous system functions. We aimed to evaluate the effect of stimulants on brain function by examining the difference in brain dopamine transporter occupancy by PET after administration of dl-methylephedrine or pseudoephedrine at the clinical maximum daily dose. Four PET scans without and with drug administration (placebo, dl-methylephedrine 150 mg and pseudoephedrine 240 mg) were performed. The concentrations of dl-methylephedrine and pseudoephedrine in plasma and urine were measured. DAT occupancies in the striatum with placebo, dl-methylephedrine and pseudoephedrine were calculated by PET images. The urinary concentration of dl-methylephedrine (12.7 µg/mL) exceeded the prohibited concentration (10 µg/mL), but the DAT occupancy with dl-methylephedrine (6.1%) did not differ (p = 0.92) from that with placebo (6.2%). By contrast, although the urinary concentration of pseudoephedrine (144.8 µg/mL) was below the prohibited concentration (150 μg/mL), DAT occupancy with pseudoephedrine was 18.4%, which was higher than that with placebo (p = 0.009). At the maximum clinical dose, dl-methylephedrine was shown to have weaker effects on brain function than pseudoephedrine.

Dynamic quantitative monitoring of cerebrospinal fluid monoamine neurotransmitter markers during the modeling process of chronic stress-induced depression in monkeys (Macaca mulatta)

BACKGROUND

Depression is known as the "mental cold" and is also considered a major cause of disability worldwide. It is estimated that over 300 million people worldwide suffer from severe depression, equivalent to 4.4% of the world's population. The monoamine hypothesis of depression predicts the underlying pathophysiological mechanisms of depression, but in-depth research has failed to find convincing evidence.

METHOD

In this study, we will dynamically and strictly quantitatively monitor the concentration changes of monoamine transmitters in the cerebrospinal fluid (CSF) of macaques, based on our previous work. In the experiment, timed and quantitative collection of CSF samples from macaques was performed and the concentration of monoamine transmitters was determined.

RESULT

The results showed that after 2 months of chronic stress, the concentrations of high vanillin acid (HVA) and 3,4-dihydroxy-phenylacetic acid were significantly higher in the maternal separation (MS) group, whereas there was no significant difference in dopamine and 5-hydroxyindoleacetic acid.

CONCLUSION

This study is the first to observe the long-term dynamic relationship between early adversity, chronic stress, adolescent depression, and CSF monoamine concentrations. The research suggests that MS and chronic stress play an undeniable role in the pathogenesis of depression and that concentrations of HVA and dihydroxyphenylacetic acid are likely to serve as early markers of depressive-like symptoms in macaques.

Update Lessons from PET Imaging Part II: A Systematic Critical Review on Therapeutic Plasma Concentrations of Antidepressants

BACKGROUND

Compared with antipsychotics, the relationship between antidepressant blood (plasma or serum) concentrations and target engagement is less well-established.

METHODS

We have discussed the literature on the relationship between plasma concentrations of antidepressant drugs and their target occupancy. Antidepressants reviewed in this work are citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline, venlafaxine, duloxetine, milnacipran, tricyclic antidepressants (amitriptyline, nortriptyline, and clomipramine), bupropion, tranylcypromine, moclobemide, and vortioxetine. Four electronic databases were systematically searched.

RESULTS

We included 32 articles published 1996-2022. A strong relationship between serotonin transporter (SERT) occupancy and drug concentration is well established for selective serotonin reuptake inhibitors. Lower limits of recommended therapeutic reference ranges largely corroborate with the findings from positron emission tomography studies (80% SERT occupancy). Only a few novel studies have investigated alternative targets, that is, norepinephrine transporters (NETs), dopamine transporters (DATs), or monoamine oxidase A (MAO-A). For certain classes of drugs, positron emission tomography study data are inconclusive. Low DAT occupancy after bupropion treatment speculates its discussed mechanism of action. For MAO inhibitors, a correlation between drug concentration and MAO-A occupancy could not be established.

CONCLUSIONS

Neuroimaging studies are critical in TDM-guided therapy for certain antidepressants, whereas for bupropion and MAO inhibitors, the available evidence offers no further insight. Evidence for selective serotonin reuptake inhibitors is strong and justifies a titration toward suggested ranges. For SNRIs, duloxetine, and venlafaxine, NETs are sufficiently occupied, well above the SERT efficacy threshold. For these drugs, a titration toward higher concentrations (within the recommended range) should be considered in case of no response at lower concentrations.

Effects of medication on dopamine transporter imaging using [123I]I-FP-CIT SPECT in routine practice

PURPOSE

Dopamine transporter (DAT) imaging is used to support the diagnosis of neurodegenerative parkinsonian disorders. Specific medications have been reported to confound the interpretation of [123I]I-FP-CIT SPECT scans, but there is limited data. The aim of the current study is to identify potential medication effects on the interpretation of [123I]I-FP-CIT SPECT scans in routine practice.

MATERIALS AND METHODS

Consecutive patients undergoing a [123I]I-FP-CIT SPECT/CT scan on a 360° CZT camera between September 2019 and December 2022 were included. An exhaustive review of patient medications (antidepressants, antipsychotics, anti-epileptics, anti-parkinsonians, benzodiazepines, lithium, opioids, and stimulants) was performed. Two experienced nuclear physicians, blinded to the medication reports, interpreted the [123I]I-FP-CIT SPECT scans visually and a semi-quantitative analysis was performed using a local normal database.

RESULTS

The study included 305 patients (71.0 ± 10.4, 135 women) and 145 (47.5%) visually interpreted normal scans. In normal scans, the striatum/occiput radioligand uptake ratio was decreased by noradrenergic and specific serotonergic antidepressants (NASSAs) (n = 15, z-score of - 0.93) and opioid medication (tramadol, n = 6, z-score of - 0.85) and was associated with a younger age in the multivariate analysis. In the overall population, the striatum/occiput ratio was influenced by NASSAs and associated with consensual visual analysis, age, sex, and anti-parkinsonian medications related to the status of the disease.

CONCLUSION

Our study confirms the potential impact of antidepressant (NASSA) and opioid (tramadol) medications on the semi-quantitative analysis of [123I]I-FP-CIT SPECT scans. However, when performing a visual analysis, only NASSAs significantly impacted the interpretation of [123I]I-FP-CIT SPECT scans.

Neuroimaging Techniques in Differentiating Parkinson's Disease from Drug-Induced Parkinsonism: A Comprehensive Review

Neuroimaging can provide significant benefits in evaluating patients with movement disorders associated with drugs. This literature review describes neuroimaging techniques performed to distinguish Parkinson's disease from drug-induced parkinsonism. The dopaminergic radiotracers already reported to assess patients with drug-induced parkinsonism are [123I]-FP-CIT, [123I]-β-CIT, [99mTc]-TRODAT-1, [18F]-DOPA, [18F]-AV-133, and [18F]-FP-CIT. The most studied one and the one with the highest number of publications is [123I]-FP-CIT. Fludeoxyglucose (18F) revealed a specific pattern that could predict individuals susceptible to developing drug-induced parkinsonism. Another scintigraphy method is [123I]-MIBG cardiac imaging, in which a relationship between abnormal cardiac imaging and normal dopamine transporter imaging was associated with a progression to degenerative disease in individuals with drug-induced parkinsonism. Structural brain magnetic resonance imaging can be used to assess the striatal region. A transcranial ultrasound is a non-invasive method with significant benefits regarding costs and availability. Optic coherence tomography only showed abnormalities in the late phase of Parkinson's disease, so no benefit in distinguishing early-phase Parkinson's disease and drug-induced parkinsonism was found. Most methods demonstrated a high specificity in differentiating degenerative from non-degenerative conditions, but the sensitivity widely varied in the studies. An algorithm was designed based on clinical manifestations, neuroimaging, and drug dose adjustment to assist in the management of patients with drug-induced parkinsonism.

Dopamine in major depressive disorder: A systematic review and meta-analysis of in vivo imaging studies

BACKGROUND

Major depressive disorder (MDD) is a leading cause of global disability. Several lines of evidence implicate the dopamine system in its pathophysiology. However, the magnitude and consistency of the findings are unknown. We address this by systematically reviewing in vivo imaging evidence for dopamine measures in MDD and meta-analysing these where there are sufficient studies.

METHODS

Studies investigating the dopaminergic system using positron emission tomography or single photon emission computed tomography in MDD and a control group were included. Demographic, clinical and imaging measures were extracted from each study, and meta-analyses and sensitivity analyses were conducted.

RESULTS

We identified 43 studies including 662 patients and 801 controls. Meta-analysis of 38 studies showed no difference in mean or mean variability of striatal D2/3 receptor availability (g = 0.06, p = 0.620), or combined dopamine synthesis and release capacity (g = 0.19, p = 0.309). Dopamine transporter (DAT) availability was lower in the MDD group in studies using DAT selective tracers (g = -0.56, p = 0.006), but not when tracers with an affinity for serotonin transporters were included (g = -0.21, p = 0.420). Subgroup analysis showed greater dopamine release (g = 0.49, p = 0.030), but no difference in dopamine synthesis capacity (g = -0.21, p = 0.434) in the MDD group. Striatal D1 receptor availability was lower in patients with MDD in two studies.

CONCLUSIONS

The meta-analysis indicates striatal DAT availability is lower, but D2/3 receptor availability is not altered in people with MDD compared to healthy controls. There may be greater dopamine release and lower striatal D1 receptors in MDD, although further studies are warranted. We discuss factors associated with these findings, discrepancies with preclinical literature and implications for future research.

A systematic review of the potential effects of medications and drugs of abuse on dopamine transporter imaging using [123I]I-FP-CIT SPECT in routine practice

PURPOSE

In routine practice, dopamine transporter (DAT) imaging is frequently used as a diagnostic tool to support the diagnosis of Parkinson's disease or dementia with Lewy bodies. In 2008, we published a review on which medications and drugs of abuse may influence striatal [123I]I-FP-CIT binding and consequently may influence the visual read of an [123I]I-FP-CIT SPECT scan. We made recommendations on which drugs should be withdrawn before performing DAT imaging in routine practice. Here, we provide an update of the original work based on published research since 2008.

METHODS

We performed a systematic review of literature without language restriction from January 2008 until November 2022 to evaluate the possible effects of medications and drugs of abuse, including the use of tobacco and alcohol, on striatal DAT binding in humans.

RESULTS

The systematic literature search identified 838 unique publications, of which 44 clinical studies were selected. Using this approach, we found additional evidence to support our original recommendations as well as some new findings on potential effect of other medications on striatal DAT binding. Consequently, we updated the list of medications and drugs of abuse that may influence the visual read of [123I]I-FP-CIT SPECT scans in routine clinical practice.

CONCLUSION

We expect that a timely withdrawal of these medications and drugs of abuse before DAT imaging may reduce the incidence of false-positive reporting. Nevertheless, the decision to withdraw any medication must be made by the specialist in charge of the patient's care and considering the pros and cons of doing so.

Altered levels of dopamine transporter in the frontal pole and the striatum in mood disorders: A postmortem study

Dopamine dysregulation is known to play a major role in the pathophysiology of major depressive disorders (MDD) and bipolar disorders (BD). The dopamine transporter (DAT) plays a critical role in regulating dopamine concentration at the synaptic cleft and therefore could have an important role in the molecular pathology of MDD and BD. To test this hypothesis, we measured levels of [³H]mazindol binding to DAT in Brodmann's area (BA) 10, BA 17 as well as in the dorsal and ventral striatum from 15 controls, 15 patients with MDD and 15 patients with BD, obtained postmortem, using in situ radioligand binding with autoradiography. Compared to controls, levels of [³H]mazindol binding to DAT was significantly higher in BA10 from patients with MDD but not BD. There was no significant difference in [³H]mazindol binding to DAT in BA 17 or the dorsal and ventral striatum from patients with MDD or BD. In addition, levels of [³H]mazindol binding show no correlation with donor age, postmortem interval, tissue pH, sex or duration of illness. In conclusion, our data suggest that changes in levels of DAT may be selectively affecting dopamine homeostasis in BA 10 in patients with MDD.

Gender differences in cocaine-induced hyperactivity and dopamine transporter trafficking to the plasma membrane

As well known, cocaine induces stimulant effects and dopamine transporter (DAT) trafficking to the plasma membrane of dopaminergic neurons. In the present study, we examined cocaine-induced hyperactivity along with cocaine-induced DAT trafficking and the recovery rate of the dopaminergic system in female rats in comparison with male rats, demonstrating interesting gender differences. Female rats are initially more sensitive to cocaine than male rats in terms of both the DAT trafficking and hyperactivity induced by cocaine. Particularly, intraperitoneal (i.p.) administration of 5 mg/kg cocaine induced significant hyperactivity and DAT trafficking in female rats but not in male rats. After repeated cocaine exposures (i.e., i.p. administration of 20 mg/kg cocaine every other day from Day 0 to Day 32), cocaine-induced hyperactivity in female rats gradually became a clear pattern of two phases, with the first phase of the hyperactivity lasting for only a few minutes and the second phase lasting for over an hour beginning at ~30 min, which is clearly different from that of male rats. It has also been demonstrated that the striatal DAT distribution of female rats may recover faster than that of male rats after multiple cocaine exposures. Nevertheless, despite the remarkable gender differences, our recently developed long-acting cocaine hydrolase, known as CocH5-Fc(M6), can similarly and effectively block cocaine-induced DAT trafficking and hyperactivity in both male and female rats.

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.

Case Report: Bupropion Reduces the [123I]FP-CIT Binding to Striatal Dopamine Transporter

The diagnosis of parkinsonian syndromes in patients with severe depression may be challenging due to overlapping clinical phenomena, especially regarding psychomotor and affective symptoms. [¹²³I]FP-CIT-SPECT is a useful method to detect degenerative parkinsonian disorders. However, some drugs may influence the tracer binding and thus alter the result. We present a case of 56-year-old female inpatient with difficult-to-treat late-onset depression. Since the current major depressive episode (MDE) was accompanied by psychotic features including delusions and hallucinations as well as hypokinesia, stooped posture and hypomimia, underlying degenerative parkinsonism was suspected. The pathologic [¹²³I]FP-CIT-SPECT scan under ongoing antidepressant therapy with bupropion 300 mg/die (serum level of bupropion 43 ng/ml and hydroxybupropion 2,332 ng/ml) showed reduced [¹²³I]FP-CIT binding throughout the striatum. The scan normalized upon a wash-out phase of four half-time periods (serum level of bupropion was 0.4 ng/ml and for hydroxybupropion 80.5 ng/ml). Our report should serve as a cautionary note for use of [¹²³I]FP-CIT in depressed patients, particularly in those treated with drugs interfering with the dopamine transporter. Furthermore, our case argues for a need of consultation of a movement disorder specialist prior to dopamine transporter imaging.

The Novelty of Bupropion As a Dopaminergic Antidepressant for the Treatment of Adult Attention Deficit Hyperactive Disorder

Attention deficit hyperactive disorder (ADHD), a hyperactivity disorder prevalent among children may continue as an adulthood attention deficit. To date, treating an individual with an adult ADHD may be an arduous task as it involves numerous challenges, which include a need for high index of suspicion to diagnose this medical condition. Many psychiatric disorders masquerade as ADHD and delay the necessary assessment and proper treatment for this debilitating medical disorder. Adult ADHD is often misdiagnosed (or under diagnosed) due to the fact that this medical condition is being masked by the patients' high level of intellectual achievement. As the ADHD in adult persists, it may end-up with impairment in the personal-social-occupational function in which the management becomes a great challenge. The treatment of ADHD can be optimized by using various drugs targets agents like norepinephrine-dopamine reuptake inhibitor (NDRI), with or without psycho stimulants like methylphenidate, which is marketed as Ritalin. Bupropion, an NDRI has a novel effect on ADHD as the molecule exerts its effects by modulating the reward-pleasure mesolimbic dopaminergic system and at the same time regulates the elevating mood dimension of the noradrenergic neurotransmission. The role of Bupropion in the neural and psychopharmacological perspective treatment of ADHD was deliberated. The present review highlights the novel effects of Bupropion in ADHD treatment, together with the help of other successful bio-psycho-social measures. This may be of immense benefit to the psychiatrists for treating their patients.

Bupropion Causes Misdiagnosis in Brain Dopamine Transporter Imaging for Parkinsonism

The objective of this study was to report long-lasting effects of bupropion on brain dopamine transporter (DAT) in a patient with depression and parkinsonism.

The Relationship Between the Striatal Dopaminergic Neuronal and Cognitive Function With Aging

Both cognitive function and striatal dopamine function decline by normal aging. However, the relationship among these three factors remains unclear. The aim of this study was to elucidate the association among age-related changes in the striatal dopamine transporter (DAT) and cognitive function in healthy subjects. The 30 healthy volunteers were enrolled in this research, the age ranged from 41 to 82 (64.5 ± 11.5, mean ± SD). All subjects were scanned with both T1-weighted magnetic resonance imaging (MRI) and ¹²³I-FP-CIT single-photon emission computed tomography (SPECT) images. The Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) was used to evaluate cognitive function. Six spherical regions of interest (ROI) using 10 mm in diameter on the caudate nucleus, anterior putamen and posterior putamen were manually drawn on MRI image which was applied onto SPECT image. The relationship between striatal occipital ratio (SOR) values and WAIS-III subscore were analyzed by multiple regression analysis. Subscores which was significant were further analyzed by path analyses. Full intelligence quotient (IQ), verbal IQ, verbal comprehension were all positively correlated with age-adjusted striatal DAT binding (P < 0.01). Multiple regression analyses revealed that the coding digit symbol correlated with all striatal regions except for the left caudate (P < 0.04). Picture completion and right caudate, similarities and left caudate also showed a positive correlation (P < 0.04). Path analysis found that the right caudate and picture completion; the left caudate and similarities were correlated independently from age, whereas the models of coding digit symbol were not significant. These results suggest that age-based individual diversity of striatal DAT binding was associated with verbal function, and the caudate nucleus plays an important role in this association.

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

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

Circuit Mechanisms of Reward, Anhedonia, and Depression

Pleasure and motivation are important factors for goal-directed behavior and well-being in both animals and humans. Intact hedonic capacity requires an undisturbed interplay between a number of different brain regions and transmitter systems. Concordantly, dysfunction of networks encoding for reward have been shown in depression and other psychiatric disorders. The development of technological possibilities to investigate connectivity on a functional level in humans and to directly influence networks in animals using optogenetics among other techniques has provided new important insights in this field of research.In this review, we aim to provide an overview on the neurobiological substrates of anhedonia on a network level. For this purpose, definition of anhedonia and the involved reward components are described first, then current data on reward networks in healthy individuals and in depressed patients are summarized, and the roles of different neurotransmitter systems involved in reward processing are specified. Based on this information, the impact of different therapeutic approaches on reward processing is described with a particular focus on deep brain stimulation (DBS) as a possibility for a direct modulation of human brain structures in vivo.Overall, results of current studies emphasize the importance of anhedonia in psychiatric disorders and the relevance of targeting this phenotype for a successful psychiatric treatment. However, more data incorporating these results for the refinement of methodological approaches are needed to be able to develop individually tailored therapeutic concepts based on both clinical and neurobiological profiles of patients.

Molecular basis of atypicality of bupropion inferred from its receptor engagement in nervous system tissues

Despite decades of clinical use and research, the mechanism of action (MOA) of antidepressant medications remains poorly understood. Selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) are the most commonly prescribed antidepressants-atypical antidepressants such as bupropion have also proven effective, while exhibiting a divergent clinical phenotype. The difference in phenotypic profiles presumably lies in the differences among the MOAs of SSRIs/SNRIs and bupropion. We integrated the ensemble of bupropion's affinities for all its receptors with the expression levels of those targets in nervous system tissues. This "combined target tissue" profile of bupropion was compared to those of duloxetine, fluoxetine, and venlafaxine to isolate the unique target tissue effects of bupropion. Our results suggest that the three monoamines-serotonin, norepinephrine, and dopamine-all contribute to the common antidepressant effects of SSRIs, SNRIs, and bupropion. At the same time, bupropion is unique in its action on 5-HT3AR in the dorsal root ganglion and nicotinic acetylcholine receptors in the pineal gland. These unique tissue-specific activities may explain unique therapeutic effects of bupropion, such as pain management and smoking cessation, and, given melatonin's association with nicotinic acetylcholine receptors and depression, highlight the underappreciated role of the melatonergic system in bupropion's MOA.

Bupropion for attention deficit hyperactivity disorder (ADHD) in adults

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is a prevalent neurobiological condition, characterised by behavioral and cognitive symptoms such as inattention, impulsivity and/or excessive activity. The syndrome is commonly accompanied by psychiatric comorbidities and is associated with educational and occupational underachievement.Although psychostimulant medications are the mainstay of treatment for ADHD, not all adults respond optimally to, or can tolerate, these medicines. Thus, alternative non-stimulant treatment approaches for ADHD have been explored. One of these alternatives is bupropion, an aminoketone antidepressant and non-competitive antagonism of nicotinic acetylcholine receptors. Bupropion is registered for the treatment of depression and smoking cessation, but is also used off-label to treat ADHD.

OBJECTIVES

To assess the effects and safety of bupropion for the treatment of adults with ADHD.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, and seven other databases in February 2017. We also searched three trials registers and three online theses portals. In addition, we checked references of included studies and contacted study authors to identify potentially relevant studies that were missed by our search.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) that evaluated the effects (including adverse effects) of bupropion compared to placebo in adults with ADHD.

DATA COLLECTION AND ANALYSIS

Two review authors (WV, GB) independently screened records and extracted data using a data extraction sheet that we tested in a pilot study. We extracted all relevant data on study characteristics and results. We assessed risks of bias using the Cochrane 'Risk of bias' tool, and assessed the overall quality of evidence using the GRADE approach. We used a fixed-effect model to pool the results across studies.

MAIN RESULTS

We included six studies with a total of 438 participants. Five studies were conducted in the USA, and one in Iran. All studies evaluated a long-acting version of bupropion, with the dosage ranging from 150 mg up to 450 mg daily. Study intervention length varied from six to 10 weeks. Four studies explicitly excluded participants with psychiatric comorbidity and one study included only participants with opioid dependency. Four studies were funded by industry, but the impact of this on study results is unknown. Two studies were publicly funded and in one of these studies, the lead author was a consultant for several pharmaceutical companies and also received investigator-driven funding from two companies, however none of these companies manufacture bupropion. We judged none of the studies to be free of bias because for most risk of bias domains the study reports failed to provide sufficient details. Using the GRADE approach, we rated the overall quality of evidence as low. We downgraded the quality of the evidence because of serious risk of bias and serious imprecision due to small sample sizes.We found low-quality evidence that bupropion decreased the severity of ADHD symptoms (standardised mean difference -0.50, 95% confidence interval (CI) -0.86 to -0.15, 3 studies, 129 participants), and increased the proportion of participants achieving clinical improvement (risk ratio (RR) 1.50, 95% CI 1.13 to 1.99, 4 studies, 315 participants), and reporting an improvement on the Clinical Global Impression - Improvement scale (RR 1.78, 95% CI 1.27 to 2.50, 5 studies, 337 participants). There was low-quality evidence that the proportion of participants who withdrew due to any adverse effect was similar in the bupropion and placebo groups (RR 1.20, 95% CI 0.35 to 4.10, 3 studies, 253 participants). The results were very similar when using a random-effects model and when we analysed only studies that excluded participants with a psychiatric comorbidity.

AUTHORS' CONCLUSIONS

The findings of this review, which compared bupropion to placebo for adult ADHD, indicate a possible benefit of bupropion. We found low-quality evidence that bupropion decreased the severity of ADHD symptoms and moderately increased the proportion of participants achieving a significant clinical improvement in ADHD symptoms. Furthermore, we found low-quality evidence that the tolerability of bupropion is similar to that of placebo. In the pharmacological treatment of adults with ADHD, extended- or sustained-release bupropion may be an alternative to stimulants. The low-quality evidence indicates uncertainty with respect to the pooled effect estimates. Further research is very likely to change these estimates. More research is needed to reach more definite conclusions as well as clarifying the optimal target population for this medicine. Treatment response remains to be reported in a DSM5-diagnosed population. There is also a lack of knowledge on long-term outcomes.

Imaging TMS: antidepressant mechanisms and treatment optimization

With the antidepressant efficacy of Transcranial Magnetic Stimulation well-established by several meta-analyses, there is growing interest in its mechanism of action. TMS has been shown to engage, and in some cases, normalize functional connectivity and neurotransmitter levels within networks dysfunctional in the depressed state. In this review, I will suggest candidate biomarkers, based on neuroimaging, that may be predictive of response to TMS. I will then review the effects of TMS on networks and neurotransmitter systems involved in depression. Throughout, I will also discuss how our current understanding of response predication and network engagement may be used to personalize treatment and optimize its efficacy.

Network-Guided Transcranial Magnetic Stimulation for Depression

PURPOSE OF REVIEW

First, we will identify candidate predictive biomarkers of antidepressant response of TMS based on the neuroimaging literature. Next, we will review the effects of TMS on networks involved in depression. Finally, we will discuss ways in which our current understanding of network engagement by TMS may be used to optimize its antidepressant effect.

RECENT FINDINGS

The past few years has seen significant interest in the antidepressant mechanisms of TMS. Studies using functional neuroimaging and neurochemical imaging have demonstrated engagement of networks known to be important in depression. Current evidence supports a model whereby TMS normalizes network function gradually over the course of several treatments. This may, in turn, mediate its antidepressant effect.

SUMMARY

One strategy to optimize the antidepressant effect of TMS is to more precisely target networks relevant in depression. We propose methods to achieve this using functional and neurochemical imaging.

Bupropion interferes with the image diagnosis of Parkinson's disease

Major depressive disorder (MDD) and Parkinson's disease (PD) share symptoms such as tremor. Bupropion, a norepinephrine-dopamine reuptake inhibitor, shows weak dopamine transporter (DAT) occupancy. We report here on a patient with MDD whose hand tremors might have been misdiagnosed as PD by single-photon emission computed tomography (SPECT) under bupropion use. A 66-year-old male patient with MDD had been receiving bupropion 150 mg per day for 6 months. His mood symptoms improved partially with bupropion treatment, however, hand tremors persisted. The neurological examination revealed bilateral hand tremors without other typical signs for PD. The SPECT using Tc-99m TRODAT-1 revealed decreased DAT binding capacity in bilateral striata. Under the impression of atypical PD, the patient was advised to take anti-Parkinson's drug. Bupropion was discontinued for 14 days to confirm the test. The follow-up SPECT after 14 days found improvement for the uptake ratio of striata. From then onward, the anti-Parkinson's drug was not used due to the lack of typical sign(s) for PD. The patient's mental and physical status remained stable without worsening of hand tremors during follow-up. Tc-99m TRODAT-1 SPECT is helpful for the evaluation of DAT and the diagnosis of PD. However, the interpretation of the SPECT image might be biased by the use of certain drugs such as bupropion for its binding to DAT. Bupropion may decrease the Tc-99m TRODAT-1 binding to DAT. The effect of drugs on DAT should be carefully assessed while interpreting the Tc-99m TRODAT-1 image. Our findings suggest that all drugs that may alter DAT occupancy should be listed as the reference for Tc-99m TRODAT-1 image reading.

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.

Incongruent reduction of dopamine transporter availability in different subgroups of alcohol dependence

The dopamine transporter (DAT) plays a crucial role in the pathogenesis of alcohol dependence (AD) and major depression (MD), and males have more risk factors for the development of AD. However, imaging studies on brain DAT availability in males with AD comorbid with MD (AD/MD) are limited, and the association of DAT availability with cognitive function and depressive scores in patients with AD/MD has not been analyzed. Hence, this study examined the relationship between brain DAT availability, cognitive function, and depressive symptoms in different subgroups of males with AD.Single-photon emission computed tomography imaging with Tc-TRODAT-1 as a ligand was used to measure striatal DAT availability in 49 patients with AD (28 pure AD and 21 AD/MD) and 24 age- and sex-matched healthy volunteers. The Wisconsin Card Sorting Test (WCST) and 17-item Hamilton Depression Rating Scale were used to assess neurocognitive function and depressive scores, respectively. Patients with AD showed a significant reduction of DAT availability in 3 brain regions (P < 0.001), and this reduction was more pronounced in the patients with pure AD compared to healthy controls. The patients with AD showed significantly poorer performance on the WCST, but only in the control group was DAT availability significantly negatively correlated with total errors and perseverative errors (P < 0.001).These preliminary findings suggest that DAT availability is associated with neurocognitive function, and incongruent reduction of DAT may play a pathophysiological role in different subgroups of AD. In addition, decreased DAT availability may be associated with the severity of depressive symptoms in patients with AD/MD.

Development of a Rat Plasma and Brain Extracellular Fluid Pharmacokinetic Model for Bupropion and Hydroxybupropion Based on Microdialysis Sampling, and Application to Predict Human Brain Concentrations

Administration of bupropion [(±)-2-(tert-butylamino)-1-(3-chlorophenyl)propan-1-one] and its preformed active metabolite, hydroxybupropion [(±)-1-(3-chlorophenyl)-2-[(1-hydroxy-2-methyl-2-propanyl)amino]-1-propanone], to rats with measurement of unbound concentrations by quantitative microdialysis sampling of plasma and brain extracellular fluid was used to develop a compartmental pharmacokinetics model to describe the blood-brain barrier transport of both substances. The population model revealed rapid equilibration of both entities across the blood-brain barrier, with resultant steady-state brain extracellular fluid/plasma unbound concentration ratio estimates of 1.9 and 1.7 for bupropion and hydroxybupropion, respectively, which is thus indicative of a net uptake asymmetry. An overshoot of the brain extracellular fluid/plasma unbound concentration ratio at early time points was observed with bupropion; this was modeled as a time-dependent uptake clearance of the drug across the blood-brain barrier. Translation of the model was used to predict bupropion and hydroxybupropion exposure in human brain extracellular fluid after twice-daily administration of 150 mg bupropion. Predicted concentrations indicate that preferential inhibition of the dopamine and norepinephrine transporters by the metabolite, with little to no contribution by bupropion, would be expected at this therapeutic dose. Therefore, these results extend nuclear imaging studies on dopamine transporter occupancy and suggest that inhibition of both transporters contributes significantly to bupropion's therapeutic efficacy.

Antidepressant drug development: Focus on triple monoamine reuptake inhibition

Many patients with major depressive disorder (MDD) only partially respond, and some have no clinically meaningful response, to current widely used antidepressant drugs. Due to the purported role of dopamine in the pathophysiology of depression, triple-reuptake inhibitors (TRIs) that simultaneously inhibit serotonin (5-HT), norepinephrine (NE) and dopamine reuptake could be a useful addition to the armamentarium of treatments for MDD. A TRI should more effectively activate mesolimbic dopamine-related reward-networks, restore positive mood and reduce potent 5-HT reuptake blockade associated "hypodopaminergic" adverse effects of decreased libido, weight gain and "blunting" of emotions. On the other hand, dopaminergic effects raise concern over abuse liability and TRIs may have many of the cardiovascular effects associated with NET inhibition. Several clinical development programs for potential TRI antidepressants have failed to demonstrate significantly greater efficacy than placebo or standard of care. Successful late-stage clinical development of a TRI is more likely if experimental research studies in the target population of depressed patients have demonstrated target engagement that differentially and dose-dependently improves assessments of reward-network dysfunction relative to existing antidepressants. TRI treatment could be individualized on the basis of predictive markers such as the burden of decreased positive mood symptoms and/or neuroimaging evidence of reward network dysfunction. This review focuses on how the next generation of monoamine-based treatments could be efficiently developed to address unmet medical need in MDD.

Molecular imaging of striatal dopamine transporters in major depression--a meta-analysis

BACKGROUND

Increasing studies have revealed the dopamine transporter (DAT) availability altered in striatum associated with major depression. However, the results remain inconsistent.

METHODS

To assess the alteration of striatal DAT availability in major depression, we performed a meta-analysis based on 12 case-control molecular imaging studies, including a total of 209 depressed patients and 314 healthy controls. Hedges׳ g and corresponding 95% confidence intervals (CIs) for striatal DAT availability in major depression compared with controls were estimated.

RESULTS

Our meta-analysis revealed no evidence for the alteration of striatal DAT availability in major depression (Hedges׳ g=0.09, CI 95% from -0.43 to 0.61, P=0.73). Meta-regression analyses suggested that there were no moderating effects for age, gender, year of publication, sample size, medication exposures and severity of depression on the hedges׳g values for striatal DAT availability.

LIMITATIONS

The results should be treated with caution because of the significant heterogeneity and the potential interference of confounding factors in this meta-analysis.

CONCLUSIONS

Our results showed no altered striatal DAT availability in major depression and indicated that striatal DAT may not implicated in the pathophysiology of major depression.

Safety, pharmacokinetic, and positron emission tomography evaluation of serotonin and dopamine transporter occupancy following multiple-dose administration of the triple monoamine reuptake inhibitor BMS-820836

RATIONALE

BMS-820836 is a novel antidepressant that selectively inhibits the reuptake of serotonin, norepinephrine, and dopamine.

OBJECTIVE

This Phase I study assessed safety, tolerability, and pharmacokinetics of multiple daily doses of BMS-820836 in healthy subjects. Central serotonin transporter (SERT) and dopamine transporter (DAT) occupancy were assessed using positron emission tomography and [(11)C]MADAM or [(11)C]PE2I, respectively.

METHODS

Fifty-seven healthy volunteers were enrolled in this double-blind, placebo-controlled, ascending multiple-dose study (ClincalTrials.gov identifier: NCT00892840). Eight participants in seven dose cohorts received oral doses of BMS-820836 (0.1-4 mg) or placebo for 14 days to assess safety, tolerability, and pharmacokinetics. Additionally, SERT and DAT occupancies were evaluated in 4-8 subjects per cohort at 8 h post-dose on Day 10 and 24 h post-dose on Day 15 at anticipated steady-state conditions.

RESULTS

Most adverse events were mild to moderate; there were no serious safety concerns. Median maximum concentrations of BMS-820836 were observed at 4.0-5.5 h post-dose; estimated elimination half-life was 44-74 h. About 80 % striatal SERT occupancy was achieved after multiple doses of 0.5 mg BMS-820836 at both 8 and 24 h post-dose. Striatal DAT occupancy ranged between 14 % and 35 % at 8 h post-dose with a slight decline at 24 h post-dose.

CONCLUSIONS

Multiple daily doses of up to 4 mg BMS-820836 appeared to be generally safe and well tolerated in a healthy population. SERT and DAT occupancies were in a range associated with therapeutic efficacy of antidepressants. Together with the pharmacokinetic profile of BMS-820836, the occupancy data support once-daily administration.

Randomized, placebo-controlled trial of bupropion in methamphetamine-dependent participants with less than daily methamphetamine use

AIMS

Two previous randomized trials found an effect for bupropion in reducing methamphetamine use in the subgroup with lower frequency of methamphetamine use at baseline. This study aimed to replicate these results by comparing bupropion versus placebo in methamphetamine-dependent participants with less than daily methamphetamine use at baseline.

METHODS

Methamphetamine-dependent volunteers reporting methamphetamine use on ≤29 of past 30 days were randomized to bupropion 150 mg twice daily (n = 41) or placebo (n = 43) and out-patient counseling for 12 weeks. The primary outcome was the proportion achieving end-of-treatment (EOT) methamphetamine abstinence (weeks 11 and 12) for bupropion versus placebo. A post-hoc analysis compared EOT abstinence by medication adherence assessed via plasma bupropion/hydroxybupropion level.

RESULTS

There was no significant difference in EOT abstinence between bupropion (29%, 12 of 41) and placebo (14%, six of 43; P = 0.087). Among participants receiving bupropion, EOT abstinence was significantly higher in participants assessed as medication adherent by plasma bupropion/hydroxybupropion levels (54%, seven of 13) compared to non-adherent participants (18%, five of 28; P = 0.018). Medication adherence by plasma levels was low (32%).

CONCLUSIONS

Bupropion may be efficacious for reducing methamphetamine in people with less than daily baseline methamphetamine use, but the evidence remains inconclusive.

Rational site-directed pharmacotherapy for major depressive disorder

It is now accepted that major depressive disorder (MDD) is not a single pathophysiological entity. It is therefore not surprising that remission rates to a first antidepressant trial are low. In addition, antidepressants may target various neuronal elements for which there are gene polymorphisms, such as the serotonin (5-HT) reuptake transporter, which may modulate response. Acting on a single monoaminergic target, such as inhibiting the 5-HT transporter, may confer efficacy in MDD, but other targets may be used and/or combined in treatment-resistant patients. These include the blockade of norepinephrine transporters, monoamine oxidase, 5-HT(2A), 5-HT(1B) and 5-HT7 receptors, and the activation of 5-HT(1A) and dopamine 2 receptors. While antidepressants may have more than one of these properties, so do atypical antipsychotics. When using the latter medications, however, their regimens should be below those effective in treating psychosis to avoid dopamine 2 antagonism, which could be counter-productive in MDD. In some patients, combining medications from treatment initiation may also provide additional therapeutic benefits.

Differences of various region-of-interest methods for measuring dopamine transporter availability using 99mTc-TRODAT-1 SPECT

This study was to investigate whether various region-of-interest (ROI) methods for measuring dopamine transporter (DAT) availabilities by single photon emission computed tomography (SPECT) are statistically different, whether results of medical research are thereby influenced, and causes of these differences. Eighty-four healthy adults with ^99mTc-TRODAT-1 SPECT and magnetic resonance imaging (MRI) scans were included. Six major analysis approaches were compared: (1) ROI drawn on the coregistered MRI; (2) ROIs drawn on the SPECT images; (3) standard ROI templates; (4) threshold-ROIs; (5) atlas-based mappings with coregistered MRI; and (6) atlas-based mappings with SPECT images. Using the atlas-based approaches we assessed the influence of striatum ROIs by slice-wise and voxel-wise comparisons. In (5) and (6), three partial-volume correction (PVC) methods were also explored. The results showed that DAT availabilities obtained from different methods were closely related but quite different and leaded to significant differences in determining the declines of DAT availability per decade (range: 5.95–11.99%). Use of 3D whole-striatum or more transverse slices could avoid biases in measuring the striatal DAT declines per decade. Atlas-based methods with PVC may be the preferable methods for medical research.

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.

Longitudinal evaluation using FP-CIT in patients with parkinsonism

OBJECTIVE

To assess a group of patients with parkinsonism using serial studies with FP-CIT, basically the initial false negative results.

METHODS

Restrospective study of 92 patients (55 men and 37 women) who had undergone 2 different FP-CIT studies because of discrepancies between study results and clinical progression. The mean elapsed time between the studies was 26 months (SD: 6). We performed a semi-quantitative study using the patient's clinical history and the available literature to analyse discrepant cases with a normal initial study and subsequent pathological findings.

RESULTS

A total of 184 studies were completed for 92 patients; 11 of those 92 showed discrepancies between initial and subsequent studies. Among the 11 discrepant cases, 7 showed a normal initial study and pathological findings at a later date. Analysis of the predominant clinical features that might explain this behaviour revealed that 4 of these 7 subjects presented tremor-dominant parkinsonism. Regarding the rest, 1 presented early stage parkinsonism and was treated with antidopaminergic agents; 1 was classified as probable multisystem atrophy type C, and the third showed clinical signs of atypical parkinsonism without any causes of those signs being identified.

CONCLUSIONS

Serial FP-CIT studies are unnecessary in the large majority of cases, but they may be justifiable in certain clinical situations.

The interaction between dopamine transporter function, gender differences, and possible laterality in depression

The Dopamine Transporter (DAT) can reflect the general state of striatal dopamine activity. This current study examined the role of DAT in depressed patients before and after bupropion treatment. Twenty-three patients with major depression were treated with bupropion for 8 weeks. Before and after the treatment, they and 20 normal subjects received the radioligand (99m)Tc-TRODAT-1 single photon emission tomography scan (SPECT). Subjects were assessed with the Hamilton Depression Rating Scale. All DAT images were spatially normalized to an averaged brain template, and the specific binding ratios of the striatum, caudate, and putamen were calculated according the formulae of: [region counts] / [occipital counts] - 1. Depressed patients had greater DAT availability on both sides of the striatum. DAT binding was significantly decreased in the striatum after bupropion treatment. Women had higher initial and final DAT binding in the right and left caudate when compared to depressed men. DAT binding decreased in all areas of the brain in women after successful antidepressant treatment, but only in the right caudate of men. Depressed patients had a greater availability of DAT; it was decreased after bupropion treatment.Women seemed to have more DAT availability.

Higher striatal dopamine transporter density in PTSD: an in vivo SPECT study with [(99m)Tc]TRODAT-1

RATIONALE

Some evidence suggests a hyperdopaminergic state in posttraumatic stress disorder (PTSD). The 9-repetition allele (9R) located in the 3' untranslated region of the dopamine transporter (DAT) gene (SLC6A3) is more frequent among PTSD patients. In vivo molecular imaging studies have shown that healthy 9R carriers have increased striatal DAT binding. However, no prior study evaluated in vivo striatal DAT density in PTSD.

OBJECTIVES

The objective of this study was to evaluate in vivo striatal DAT density in PTSD.

METHODS

Twenty-one PTSD subjects and 21 control subjects, who were traumatized but asymptomatic, closely matched comparison subjects evaluated with the Clinician-Administered PTSD Scale underwent a single-photon emission computed tomography scan with [(99m)TC]-TRODAT-1. DAT binding potential (DAT-BP) was calculated using the striatum as the region of the interest and the occipital cortex as a reference region.

RESULTS

PTSD patients had greater bilateral striatal DAT-BP (mean ± SD; left, 1.80 ± 0.42; right, 1.78 ± 0.40) than traumatized control subjects (left, 1.62 ± 0.32; right, 1.61 ± 0.31; p = 0.039 for the left striatum and p = 0.032 for the right striatum).

CONCLUSIONS

These results provide the first in vivo evidence for increased DAT density in PTSD. Increases in DAT density may reflect higher dopamine turnover in PTSD, which could contribute to the perpetuation and potentiation of exaggerated fear responses to a given event associated with the traumatic experience. Situations that resemble the traumatic event turn to be interpreted as highly salient (driving attention, arousal, and motivation) in detriment of other daily situations.

Dopaminergic dysfunction and psychiatric symptoms in movement disorders: a 123I-FP-CIT SPECT study

PURPOSE

Psychiatric symptoms frequently occur in patients with movement disorders. They are not a mere reaction to chronic disability, but most likely due to a combination of psychosocial factors and biochemical dysfunction underlying the movement disorder. We assessed dopamine transporter (DAT) availability by means of (123)I-FP-CIT SPECT, and motor and psychiatric features in patients with Parkinson's disease, primary dystonia and essential tremor, exploring the association between SPECT findings and symptom severity.

METHODS

Enrolled in the study were 21 patients with Parkinson's disease, 14 patients with primary dystonia and 15 patients with essential tremor. The severity of depression symptoms was assessed using the Hamilton depression rating scale, anxiety levels using the Hamilton anxiety rating scale and hedonic tone impairment using the Snaith-Hamilton pleasure scale. Specific (123)I-FP-CIT binding in the caudate and putamen was calculated based on ROI analysis. The control group included 17 healthy subjects.

RESULTS

As expected, DAT availability was significantly decreased in patients with Parkinson's disease, whereas in essential tremor and dystonia patients it did not differ from that observed in the control group. In Parkinson's disease patients, an inverse correlation between severity of depression symptoms and DAT availability in the left caudate was found (r = -0.63, p = 0.002). In essential tremor patients, levels of anxiety symptoms were inversely correlated with DAT availability in the left caudate (r = -0.69, p = 0.004). In dystonia patients, the severities of both anxiety and depression symptoms were inversely associated with DAT availability in the left putamen (r = -0.71, p = 0.004, and r = -0.75, p = 0.002, respectively). There were no correlations between psychometric scores and (123)I-FP-CIT uptake ratios in healthy subjects.

CONCLUSION

We found association between presynaptic dopaminergic function and affective symptoms in different movement disorders. Interestingly, the inverse correlation was present in each group of patients, supporting the fascinating perspective that common subcortical substrates may be involved in both anxiety and depression dimensions and movement disorders.

Key players in major and bipolar depression--a retrospective analysis of in vivo imaging studies

In the present study, we evaluated the contribution of the individual synaptic constituents of all assessed neurotransmitter systems by subjecting all available in vivo imaging studies on patients with unipolar major depressive disorder (MDD) and bipolar depression (BD) to a retrospective analysis. In acute MDD, findings revealed significant increases of prefrontal and frontal DA synthesis, decreases of thalamic and midbrain SERT, increases of insular SERT, decreases of midbrain 5-HT(1A) receptors and decreases of prefrontal, frontal, occipital and cingulate 5-HT(2A) receptors, whereas, in remission, decreases of striatal D₂ receptors, midbrain SERT, frontal, parietal, temporal, occipital and cingulate 5-HT(1A) receptors and parietal 5-HT(2A) receptors were observed. In BD, findings indicated a trend towards increased striatal D₂ receptors in depression and mania, decreased striatal DA synthesis in remission and decreased frontal D₁ receptors in all three conditions. Additionally, there is some evidence that ventrostriatal and hippocampal SERT may be decreased in depression, whereas in remission and mania elevations of thalamic and midbrain SERT, respectively, were observed. Moreover, in depression, limbic 5-HT(1A) receptors were elevated, whereas in mania a decrease of both cortical and limbic 5-HT(2A) receptor binding was observed. Furthermore, in depression, prefrontal, frontal, occipital and cingulate M2 receptor binding was found to be reduced. From this, a complex pattern of dysregulations within and between neurotransmitter systems may be derived, which is likely to be causally linked not only with the subtype and duration of disease but also with the predominance of individual symptoms and with the kind and duration of pharmacological treatment(s).

Monoamine oxidase A inhibitor occupancy during treatment of major depressive episodes with moclobemide or St. John's wort: an [11C]-harmine PET study

BACKGROUND

Monoamine oxidase A (MAO-A) inhibitor antidepressants raise levels of multiple monoamines, whereas the selective serotonin reuptake inhibitors (SSRIs) only raise extracellular serotonin. Despite this advantage of MAO-A inhibitors, there is much less frequent development of MAO inhibitors compared with SSRIs. We sought to measure brain MAO-A occupancy after 6 weeks of treatment in depressed patients with a clinically effective dose of a selective MAO-A inhibitor and measure MAO-A occupancy after repeated administration of St. John's wort, an herb purported to have MAO-A inhibitor properties.

METHODS

Participants underwent 2 [(11)C]-harmine positron emission tomography scans. Healthy controls completed a test-retest condition, and depressed patients were scanned before and after repeated administration of moclobemide or St. John's wort for 6 weeks at the assigned dose. We measured MAO-A VT, an index of MAO-A density, in the prefrontal, anterior cingulate and anterior temporal cortices, putamen, thalamus, midbrain and hippocampus.

RESULTS

We included 23 participants (10 controls and 13 patients with major depressive disorder [MDD]) in our study. Monoamine oxidase A VT decreased significantly throughout all regions after moclobemide treatment in patients with MDD compared with controls (repeated-measures analysis of variance, F1,15 = 71.08-130.06, p < 0.001 for all regions, mean occupancy 74% [standard deviation 6%]). Treatment with St. John's wort did not significantly alter MAO-A VT.

LIMITATIONS

The occupancy estimates are limited by the sample size of each treatment group; hence, our estimate for the overall moclobemide occupancy of 74% has a 95% confidence interval of 70%-78%, and we can estimate with 95% certainty that the occupancy of St. John's wort is less than 5%.

CONCLUSION

For new MAO-A inhibitors, about 74% occupancy at steady-state dosing is desirable. Consistent with this, St. John's wort should not be classified as an MAO-A inhibitor. The magnitude of MAO-A blockade during moclobemide treatment exceeds the elevation of MAO-A binding during illness by at least 30%, suggesting that the treatment effect should exceed the disease effect when designing selective antidepressants for this target.

Enhancement of serotonergic and noradrenergic neurotransmission in the rat hippocampus by sustained administration of bupropion

RATIONALE

Previous studies reported that bupropion, an effective antidepressant, exerts modulatory actions on serotonin (5-HT) and norepinephrine (NE) neurons.

OBJECTIVES

This study examined effects of bupropion administration on 5-HT and NE neurotransmission in hippocampus.

METHODS

Electrophysiological recordings were obtained from anesthetized Sprague-Dawley rats. Subcutaneously implanted minipumps delivered saline or bupropion (30 mg/kg/day) for 2 and 14 days.

RESULTS

Although sustained bupropion administration did not alter the sensitivity of 5-HT(1A) and α₂-adrenergic receptors, the tonic activation of postsynaptic 5-HT(1A) receptors by endogenous 5-HT was enhanced in 14-day bupropion-treated rats to a greater extent than in the 2-day and control rats, as revealed by the greater disinhibitory action of the 5-HT(1A) antagonist WAY-100635 on hippocampus pyramidal neurons. The function of terminal 5-HT(1B) autoreceptors was not changed as determined by the unaltered effectiveness of different frequencies of stimulation of the ascending 5-HT fibers. The function of α₂-adrenergic receptors on 5-HT terminals was, however, diminished, as indicated by the lesser effect of the α₂-adrenoceptor agonist clonidine. Tonic activation of postsynaptic α₂- and α₁-adrenoceptors by endogenous NE was also increased in 14-day bupropion-treated rats, as indicated by the greater effect of the α₂- and α₁-adrenoceptor antagonists idazoxan and prazosin, respectively, on pyramidal firing. The function of terminal α₂-adrenergic autoreceptors was attenuated since increasing frequency of stimulation of the ascending NE pathway produced a lesser degree of suppression of pyramidal neurons in rats administered bupropion than the control.

CONCLUSION

Enhancement of 5-HT and NE transmissions in hippocampus by prolonged bupropion may account for its effectiveness in major depression.

Striatal dopamine transporter availability in unmedicated bipolar disorder

OBJECTIVES

Dopamine transmission abnormalities have been implicated in the etiology of bipolar disorder (BPD). However, there is a paucity of receptor imaging studies in BPD, and little information is available about the dopamine system in BPD. Reuptake of synaptic dopamine by the dopamine transporter (DAT) is the principal mechanism regulating dopamine neurotransmission, and is often used as a marker for presynaptic dopamine function. This positron emission tomography (PET) study investigated whether DAT availability differed between BPD and healthy control subjects.

METHODS

A total of 11 unmedicated BPD patients in either the euthymic or depressed phase and 13 closely matched healthy subjects underwent PET imaging with the DAT-selective radiotracer [(11) C]CFT and a structural magnetic resonance imaging (MRI) scan. Striatal binding potential (BP(ND) ) was estimated using the multilinear reference tissue model. Region of interest and analyses were conducted to test for differences in [(11) C]CFT BP(ND) between groups.

RESULTS

Unmedicated BPD subjects had significantly lower DAT availability relative to healthy controls in bilateral dorsal caudate.

CONCLUSIONS

The results of this study support the hypothesis that there are abnormalities in the dopaminergic system in BPD, and suggest that DAT availability may be related to the neuropathology of BPD. Future studies are needed to determine if DAT availability cycles with disease phase.

The role of molecular imaging in the diagnosis and management of neuropsychiatric disorders

Neuropsychiatric disorders are becoming a major socioeconomic burden to modern society. In recent years, a dramatic expansion of tools has facilitated the study of the molecular basis of neuropsychiatric disorders. Molecular imaging has enabled the noninvasive characterization and quantification of biological processes at the cellular, tissue, and organism levels in intact living subjects. This technology has revolutionized the practice of medicine and has become critical to quality health care. New advances in research on molecular imaging hold promise for personalized medicine in neuropsychiatric disorders, with adjusted therapeutic doses, predictable responses, reduced adverse drug reactions, early diagnosis, and personal health planning. In this paper, we discuss the development of radiotracers for imaging dopaminergic, serotonergic, and noradrenergic systems and β-amyloid plaques. We will underline the role of molecular imaging technologies in various neuropsychiatric disorders, describe their unique strengths and limitations, and suggest future directions in the diagnosis and management of neuropsychiatric disorders.

Smoking-induced change in intrasynaptic dopamine concentration: effect of treatment for Tobacco Dependence

The aim of this study was to determine whether standard treatments for Tobacco Dependence affect smoking-induced changes in intrasynaptic dopamine (DA) concentration. Forty-three otherwise healthy adult cigarette smokers (10 to 40 cigarettes per day) were treated with either practical group counseling (PGC) psychotherapy (n=14), bupropion HCl (n=14), or matching pill placebo (n=15) (random assignment) for 8 weeks. Before and after treatment, each subject underwent a bolus-plus-continuous-infusion (11)C-raclopride positron emission tomography (PET) scanning session, during which he or she smoked a regular cigarette. The PET scanning outcome measure of interest was percent change in smoking-induced (11)C-raclopride binding potential (BP(ND)) in the ventral caudate/nucleus accumbens (VCD/NAc), as an indirect measure of DA release. Although the entire study sample had a smaller mean smoking-induced reduction in VCD/NAc BP(ND) after treatment (compared to before treatment), this change was highly correlated with smaller total cigarette puff volumes (and not other treatment variables). These data indicate that smoking-induced DA release is dose-dependent, and is not significantly affected by reductions in daily smoking levels or treatment type.

Higher dopamine transporter density in Parkinson's disease patients with depression

RATIONALE

Depression is a frequent non-motor symptom in Parkinson's disease (PD) with increasing rates with the progression of the disease. Molecular imaging studies have shown a reduction of dopamine transporter (DAT) density in depressed PD patients (dPD); however, DAT role in the pathophysiology of PD depression is not clear since clinical matching was inappropriate and DAT reduction could be attributed to PD severity.

OBJECTIVES

To further examine the role of DAT in PD depression, this study compared thoroughly matched depressed vs. non-depressed PD patients (ndPD).

MATERIALS AND METHODS

Twenty PD patients (n = 10 ndPD; n = 10 dPD) matched for age and disease severity were submitted to brain SPECT imaging with [(99m)Tc]-TRODAT-1, a DAT radioligand. DAT-binding potential was calculated using regions of interest bilaterally drawn in the striatum, caudate, and putamen. Depression was defined according to Beck Depression Inventory (BDI; cut-off >18).

RESULTS

Mean BDI scores were higher in dPD (25.0 +/- 5.6) than in ndPD patients (8.0 +/- 1.9, p < 0.0001). DAT density was greater on dPD especially in the left caudate (dPD 0.87 +/- 0.19 vs. ndDP 0.69 +/- 0.18, p = 0.02) and right putamen (dPD 0.37 +/- 0.07 vs. ndPD 0.28 +/- 0.13, p = 0.03) than in ndPD patients.

CONCLUSION

Our results suggest that in vivo DAT density is increased in dPD patients as compared to ndPD, suggesting that DAT is implicated in the pathophysiology of PD depression.

Relevance of norepinephrine-dopamine interactions in the treatment of major depressive disorder

Central dopaminergic and noradrenergic systems play essential roles in controlling several forebrain functions. Consequently, perturbations of these neurotransmissions may contribute to the pathophysiology of neuropsychiatric disorders. For many years, there was a focus on the serotonin (5‐HT) system because of the efficacy of selective serotonin reuptake inhibitors (SSRIs), the most prescribed antidepressants in the treatment of major depressive disorder (MDD). Given the interconnectivity within the monoaminergic network, any action on one system may reverberate in the other systems. Analysis of this network and its dysfunctions suggests that drugs with selective or multiple modes of action on dopamine (DA) and norepinephrine (NE) may have robust therapeutic effects. This review focuses on NE‐DA interactions as demonstrated in electrophysiological and neurochemical studies, as well as on the mechanisms of action of agents with either selective or dual actions on DA and NE. Understanding the mode of action of drugs targeting these catecholaminergic neurotransmitters can improve their utilization in monotherapy and in combination with other compounds particularly the SSRIs. The elucidation of such relationships can help design new treatment strategies for MDD, especially treatment‐resistant depression.

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.

Effects of treatment for tobacco dependence on resting cerebral glucose metabolism

While bupropion HCl and practical group counseling (PGC) are commonly used treatments for tobacco dependence, the effects of these treatments on brain function are not well established. For this study, 54 tobacco-dependent cigarette smokers underwent resting (18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET) scanning before and after 8 weeks of treatment with bupropion HCl, PGC, or pill placebo. Using Statistical Parametric Mapping (SPM 2), changes in cerebral glucose metabolism from before to after treatment were compared between treatment groups and correlations were determined between amount of daily cigarette usage and cerebral glucose metabolism. Compared with placebo, the two active treatments (bupropion HCl and PGC) had reductions in glucose metabolism in the posterior cingulate gyrus. Further analysis suggested that PGC had a greater effect than bupropion HCl on glucose metabolism in this region. We also found positive correlations between daily cigarette use and glucose metabolism in the left occipital gyrus and parietal-temporal junction. There were no significant negative correlations between daily cigarette use and glucose metabolism. Our findings suggest that bupropion HCl and PGC reduce neural activity much as the performance of a goal-oriented task does in the default mode network of the brain, including the posterior cingulate gyrus. Thus, this study supports the theory that active treatments for tobacco dependence move the brain into a more goal-oriented state.