In vivo activity of bupropion at the human dopamine transporter as measured by positron emission tomography

Using Drift Diffusion and RL Models to Disentangle Effects of Depression On Decision-Making vs. Learning in the Probabilistic Reward Task

The Probabilistic Reward Task (PRT) is widely used to investigate the impact of Major Depressive Disorder (MDD) on reinforcement learning (RL), and recent studies have used it to provide insight into decision-making mechanisms affected by MDD. The current project used PRT data from unmedicated, treatment-seeking adults with MDD to extend these efforts by: (1) providing a more detailed analysis of standard PRT metrics-response bias and discriminability-to better understand how the task is performed; (2) analyzing the data with two computational models and providing psychometric analyses of both; and (3) determining whether response bias, discriminability, or model parameters predicted responses to treatment with placebo or the atypical antidepressant bupropion. Analysis of standard metrics replicated recent work by demonstrating a dependency between response bias and response time (RT), and by showing that reward totals in the PRT are governed by discriminability. Behavior was well-captured by the Hierarchical Drift Diffusion Model (HDDM), which models decision-making processes; the HDDM showed excellent internal consistency and acceptable retest reliability. A separate "belief" model reproduced the evolution of response bias over time better than the HDDM, but its psychometric properties were weaker. Finally, the predictive utility of the PRT was limited by small samples; nevertheless, depressed adults who responded to bupropion showed larger pre-treatment starting point biases in the HDDM than non-responders, indicating greater sensitivity to the PRT's asymmetric reinforcement contingencies. Together, these findings enhance our understanding of reward and decision-making mechanisms that are implicated in MDD and probed by the PRT.

Integrative Pharmacology in the Treatment of Substance Use Disorders

The detrimental physical, mental, and socioeconomic effects of substance use disorders (SUDs) have been apparent to the medical community for decades. However, it has become increasingly urgent in recent years to develop novel pharmacotherapies to treat SUDs. Currently, practitioners typically rely on monotherapy. Monotherapy has been shown to be superior to no treatment at all for most substance classes. However, many randomized controlled trials (RCTs) have revealed that monotherapy leads to poorer outcomes when compared with combination treatment in all specialties of medicine. The results of RCTs suggest that monotherapy frequently fails since multiple dysregulated pathways, enzymes, neurotransmitters, and receptors are involved in the pathophysiology of SUDs. As such, research is urgently needed to determine how various neurobiological mechanisms can be targeted by novel combination treatments to create increasingly specific yet exceedingly comprehensive approaches to SUD treatment. This article aims to review the neurobiology that integrates many pathophysiologic mechanisms and discuss integrative pharmacology developments that may ultimately improve clinical outcomes for patients with SUDs. Many neurobiological mechanisms are known to be involved in SUDs including dopaminergic, nicotinic, N-methyl-D-aspartate (NMDA), and kynurenic acid (KYNA) mechanisms. Emerging evidence indicates that KYNA, a tryptophan metabolite, modulates all these major pathophysiologic mechanisms. Therefore, achieving KYNA homeostasis by harmonizing integrative pathophysiology and pharmacology could prove to be a better therapeutic approach for SUDs. We propose KYNA-NMDA-α7nAChRcentric pathophysiology, the "conductor of the orchestra," as a novel approach to treat many SUDs concurrently. KYNA-NMDA-α7nAChR pathophysiology may be the "command center" of neuropsychiatry. To date, extant RCTs have shown equivocal findings across comparison conditions, possibly because investigators targeted single pathophysiologic mechanisms, hit wrong targets in underlying pathophysiologic mechanisms, and tested inadequate monotherapy treatment. We provide examples of potential combination treatments that simultaneously target multiple pathophysiologic mechanisms in addition to KYNA. Kynurenine pathway metabolism demonstrates the greatest potential as a target for neuropsychiatric diseases. The investigational medications with the most evidence include memantine, galantamine, and N-acetylcysteine. Future RCTs are warranted with novel combination treatments for SUDs. Multicenter RCTs with integrative pharmacology offer a promising, potentially fruitful avenue to develop novel therapeutics for the treatment of SUDs.

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.

Bupropion Mediated Effects on Depression, Attention Deficit Hyperactivity Disorder, and Smoking Cessation

Bupropion had been in use since the late 1980s as an unconventional treatment for depression. Unlike other antidepressants, bupropion has no serotonergic activity and inhibits the reuptake of norepinephrine and dopamine. The drug has been used to treat depression, Attention Deficit Hyperactivity Disorder (ADHD), and smoking cessation. This investigation reviews the pharmacokinetic and pharmacodynamic effects of bupropion and its mechanisms of action and interactions with other drugs. We evaluated the efficacy of major on and off-label uses of bupropion, focusing on the indications, benefits, and adverse effects. Our review demonstrates that bupropion is superior to placebo and non-inferior to SSRIs such as escitalopram in treating major depressive disorder. More research is needed to determine positive patient-centered outcomes such as increases in quality of life. In the case of ADHD, the evidence for efficacy is mixed with poorly conducted randomized clinical trials, small sample sizes, and a lack of long-term assessments. The same is true in the case of bipolar disorder in which there is still limited and controversial data available on bupropion's safety and efficacy. In the case of smoking cessation, bupropion is found to be an effective anti-smoking drug with synergistic benefits when used as a combination therapy. We conclude that bupropion has the potential to provide benefit for a subset of patients who do not tolerate other typical antidepressants or anti-smoking therapies or for those whose treatment goals align with bupropion's unique side effect profile, such as smokers who wish to quit and lose weight. Additional research is needed to determine the drug's full clinical potential, particularly in the areas of adolescent depression and combination therapy with varenicline or dextromethorphan. Clinicians should use this review to understand the varied uses of the drug and identify the situations and patient populations in which bupropion can lend its greatest benefit.

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.

Different depression: motivational anhedonia governs antidepressant efficacy in Huntington's disease

Depression is more common in neurodegenerative diseases such as Huntington's disease than the general population. Antidepressant efficacy is well-established for depression within the general population: a recent meta-analysis showed serotonin norepinephrine reuptake inhibitors, tricyclic antidepressants and mirtazapine outperformed other antidepressants. Despite the severe morbidity, antidepressant choice in Huntington's disease is based on Class IV evidence. We used complementary approaches to determine treatment choice for depression in Huntington's disease: propensity score analyses of antidepressant treatment outcome using the ENROLL-HD data set, and a dissection of the cognitive mechanisms underlying depression in Huntington's disease using a cognitive battery based on the Research Domain Criteria for Depression. Study 1 included ENROLL-HD 5486 gene-positive adult patients started on an antidepressant medication for depression. Our outcome measures were depression (Hospital Anxiety and Depression Scale or Problem Behaviours Assessment 'Depressed Mood' item) at first follow-up (primary outcome) and all follow-ups (secondary outcome). The intervention was antidepressant class. We used Svyglm&Twang in R to perform propensity scoring, using known variables (disease progression, medical comorbidity, psychiatric morbidity, sedatives, number of antidepressants, demographics and antidepressant contraindications) to determine the probability of receiving different antidepressants (propensity score) and then included the propensity score in a model of treatment efficacy. Study 2 recruited 51 gene-positive adult patients and 26 controls from the South Wales Huntington's Disease Management Service. Participants completed a motor assessment, in addition to measures of depression and apathy, followed by tasks measuring consummatory anhedonia, motivational anhedonia, learning from reward and punishment and reaction to negative outcome. We used generalised linear models to determine the association between task performance and depression scores. Study 1 showed selective serotonin reuptake inhibitors outperformed serotonin norepinephrine reuptake inhibitors on the primary outcome (P = 0.048), whilst both selective serotonin reuptake inhibitors (P = 0.00069) and bupropion (P = 0.0045) were superior to serotonin norepinephrine reuptake inhibitors on the secondary outcome. Study 2 demonstrated an association between depression score and effort for reward that was not explained by apathy. No other mechanisms were associated with depression score. We found that selective serotonin reuptake inhibitors and bupropion outperform serotonin norepinephrine reuptake inhibitors at alleviating depression in Huntington's disease. Moreover, motivational anhedonia appears the most significant mechanism underlying depression in Huntington's disease. Bupropion is improves motivational anhedonia and has a synergistic effect with selective serotonin reuptake inhibitors. This work provides the first large-scale, objective evidence to determine treatment choice for depression in Huntington's disease, and provides a model for determining antidepressant efficacy in other neurodegenerative diseases.

Dopamine, Serotonin, and Structure/Function Brain Defects as Biological Bases for Treatment Response in Delusional Disorder: A Systematic Review of Cases and Cohort Studies

Although blockade of dopamine receptors D2 and D3 appears to be the main mechanism of antipsychotic action, treatment response variability calls for an examination of other biological systems. Our aim is to systematically review reports of treatment response in delusional disorder (DD) in order to help determine its biological bases. Computerized searches of ClinicalTrials.gov, PubMed, and Scopus databases (from 1999 to September 2021) were systematically reviewed, in keeping with PRISMA directives. We used the search terms: (treat * OR therap * AND (delusional disorder)). We included all studies that explored the biological mechanisms of treatment response in DD, as diagnosed by ICD or DSM criteria. A total of 4344 records were initially retrieved, from which 14 papers were included: case reports, case series, and cohort studies. Findings point to (1) dopaminergic dysfunction (based on biochemical and genetic studies), (2) serotonergic dysfunction (based on partial agonism/antagonism of drugs), and (3) brain structure/function impairment, especially in the temporal and parietal lobes, as crucial factors in treatment response. Further studies with higher levels of evidence are needed to help clinicians determine treatment.

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.

Energizing effects of bupropion on effortful behaviors in mice under positive and negative test conditions: modulation of DARPP-32 phosphorylation patterns

Motivational symptoms such as anergia, fatigue, and reduced exertion of effort are seen in depressed people. To model this, nucleus accumbens (Nacb) dopamine (DA) depletions are used to induce a low-effort bias in rodents tested on effort-based decision-making. We evaluated the effect of the catecholamine uptake blocker bupropion on its own, and after administration of tetrabenazine (TBZ), which blocks vesicular storage, depletes DA, and induces depressive symptoms in humans. Male CD1 mice were tested on a 3-choice-T-maze task that assessed preference between a reinforcer involving voluntary physical activity (running wheel, RW) vs. sedentary activities (sweet food pellet intake or a neutral non-social odor). Mice also were tested on the forced swim test (FST), two anxiety-related measures (dark-light box (DL), and elevated plus maze (EPM)). Expression of phosphorylated DARPP-32 (Thr34 and Thr75) was evaluated by immunohistochemistry as a marker of DA-related signal transduction. Bupropion increased selection of RW activity on the T-maze. TBZ reduced time running, but increased time-consuming sucrose, indicating an induction of a low-effort bias, but not an effect on primary sucrose motivation. In the FST, bupropion reduced immobility, increasing swimming and climbing, and TBZ produced the opposite effects. Bupropion reversed the effects of TBZ on the T-maze and the FST, and also on pDARPP32-Thr34 expression in Nacb core. None of these manipulations affected anxiety-related parameters. Thus, bupropion improved active behaviors, which were negatively motivated in the FST, and active behaviors that were positively motivated in the T-maze task, which has implications for using catecholamine uptake inhibitors for treating anergia and fatigue-like symptoms.

Acute and chronic bupropion treatment does not prevent morphine-induced conditioned place preference in mice

A substantial barrier to the treatment of Opioid Use Disorder (OUD) is the elevated relapse rates in affected patients, and a significant contributor to these events of relapse is exposure to cues and contexts that are intensely associated with prior drug abuse. The neurotransmitter dopamine plays a key role in reward-related behaviors, and previous studies have illustrated that dopamine hypofunction in periods of abstinence serves to prompt drug craving and seeking. We hypothesized that restoration of dopaminergic signaling could attenuate drug-seeking behaviors. Therefore, we investigated whether use of an FDA-approved drug, bupropion, an inhibitor of the dopamine transporter (DAT), or a dopamine uptake inhibitor with high affinity for DAT, JHW 007, was able to decrease preference for a drug-paired context. In these experiments, mice underwent 5 days of non-contingent morphine (10 mg/kg) exposure in a conditioned place preference (CPP) paradigm. We found that systemic injection of bupropion (20 mg/kg, i. p.) or intracranial injection of JHW 007 into the nucleus accumbens shell did not prevent the expression of morphine CPP. We then investigated whether chronic bupropion treatment (via implanted osmotic pumps) would influence morphine CPP. We observed that chronic bupropion treatment for 21 days following morphine conditioning did not attenuate the prolonged preference for morphine-paired contexts. Overall, with our dose and paradigm, neither acute nor chronic bupropion diminishes morphine CPP. Continued studies should address FDA-approved medications and their potential for recovery in OUD patients.

Prescription psychostimulants for the treatment of stimulant use disorder: a systematic review and meta-analysis

RATIONALE

Agonist-based pharmacologic intervention is an accepted approach in treatment of opioid and tobacco use disorders.

OBJECTIVES

We conducted a systematic review and meta-analysis to evaluate usefulness of an agonist approach as treatment of (psycho)stimulant use disorder (PSUD).

METHODS

We reviewed PubMed/Medline, LILACS, and ClinicalTrials.gov databases searching for randomized, double-blind, placebo-controlled, parallel-design studies evaluating outcomes of individuals treated for cocaine- or amphetamine-type substance use disorder. We combined results of all trials that included the following prescription psychostimulants (PPs): modafinil, methylphenidate, or amphetamines (mixed amphetamine salts, lisdexamphetamine, and dextroamphetamine). The combined sample consisted of 2889 patients. Outcomes of interest included the following: drug abstinence (defined as 2-3 weeks of sustained abstinence and the average maximum days of consecutive abstinence), percentage of drug-negative urine tests across trial, and retention in treatment. We conducted random-effects meta-analyses and assessed quality of evidence using the GRADE system.

RESULTS

Thirty-eight trials were included. Treatment with PPs increases rates of sustained abstinence [risk ratio (RR) = 1.45, 95% confidence interval (CI) = (1.10, 1.92)] and duration of abstinence [mean difference (MD) = 3.34, 95% CI = (1.06, 5.62)] in patients with PSUD, particularly those with cocaine use disorder (very low-quality evidence). Prescription amphetamines were particularly efficacious in promoting sustained abstinence in patients with cocaine use disorder [RR = 2.44, 95% CI = (1.66, 3.58)], and higher doses of PPs were particularly efficacious for treatment of cocaine use disorder [RR = 1.95, 95% CI = (1.38, 2.77)] (moderate-quality evidence). Treatment with prescription amphetamines also yielded more cocaine-negative urines [MD = 8.37%, 95% CI = (3.75, 12.98)]. There was no effect of PPs on the retention in treatment.

CONCLUSION

Prescription psychostimulants, particularly prescription amphetamines given in robust doses, have a clinically significant beneficial effect to promote abstinence in the treatment of individuals with PSUD, specifically the population with cocaine use disorder.

The association of COMT genotype with buproprion treatment response in the treatment of major depressive disorder

BACKGROUND

Pharmacodynamics and pharmacogenetics are being explored in pharmacological treatment response for major depressive disorder (MDD). Interactions between genotype and treatment response may be dose dependent. In this study, we examined whether MDD patients with Met/Met, Met/Val, and Val/Val COMT genotypes differed in their response to bupropion in terms of depression scores.

METHODS

This study utilized a convenience sample of 241 adult outpatients (≥18 years) who met DSM-5 criteria for MDD and had visits at a Midwest psychopharmacology clinic between February 2016 and January 2017. Exclusion criteria included various comorbid medical, neurological, and psychiatric conditions and current use of benzodiazepines or narcotics. Participants completed genetic testing and the 9 question patient-rated Patient Health Questionnaire (PHQ-9) at each clinic visit (M = 3.8 visits, SD = 1.5) and were prescribed bupropion or another antidepressant drug. All participants were adherent to pharmacotherapy treatment recommendations for >2 months following genetic testing.

RESULTS

Participants were mostly Caucasian (85.9%) outpatients (154 female and 87 male) who were 44.5 years old, on average (SD = 17.9). For Val carriers, high bupropion doses resulted in significantly lower PHQ-9 scores than no bupropion (t(868) = 5.04, p < .001) or low dose bupropion (t(868) = 3.29, p = .001). Val carriers differed significantly from Met/Met patients in response to high dose bupropion (t(868) = -2.03, p = .04), but not to low dose bupropion.

CONCLUSION

High-dose bupropion is beneficial for MDD patients with Met/Val or Val/Val COMT genotypes, but not for patients with Met/Met genotype. Prospective studies are necessary to replicate this pharmacodynamic relationship between bupropion and COMT genotypes and explore economic and clinical outcomes.

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 increases activation in nucleus accumbens during anticipation of monetary reward

RATIONALE

Bupropion is used for major depressive disorder, smoking cessation aid, and obesity. It blocks reuptake of dopamine and noradrenaline and antagonizes nicotinic acetylcholine receptor. Animal studies showed that bupropion enhanced rewarding effects. In addition, bupropion has the potential to treat patients with reward processing dysfunction. However, neural substrates underlying the bupropion effects on reward function in human subjects are not fully understood.

OBJECTIVES

We investigated single-dose administration of bupropion on neural response of reward anticipation in healthy subjects using a monetary incentive delay (MID) task by functional magnetic resonance imaging (fMRI), especially focusing on nucleus accumbens (NAc) activity to non-drug reward stimuli under bupropion treatment.

METHODS

We used a randomized placebo-controlled within-subject crossover design. Fifteen healthy adults participated in two series of an fMRI study, taking either placebo or bupropion. The participants performed the MID task during the fMRI scanning. The effects of bupropion on behavioral performance and blood oxygenation level-dependent (BOLD) signal in NAc during anticipation of monetary gain were analyzed.

RESULTS

We found that bupropion significantly increased BOLD responses in NAc during monetary reward anticipation. The increased BOLD responses in NAc were observed with both low and high reward incentive cues. There was no significant difference between placebo and bupropion in behavioral performance.

CONCLUSIONS

Our findings provide support for the notion that bupropion enhances non-drug rewarding effects, suggesting a possible mechanism underlying therapeutic effects for patients with motivational deficit.

Prediction of Drug Permeability Using In Vitro Blood-Brain Barrier Models with Human Induced Pluripotent Stem Cell-Derived Brain Microvascular Endothelial Cells

The strong barrier function of the blood–brain barrier (BBB) protects the central nervous system (CNS) from xenobiotic substances, while the expression of selective transporters controls the transportation of nutrients between the blood and brain. As a result, the delivery of drugs to the CNS and prediction of the ability of specific drugs to penetrate the BBB can be difficult. Although in vivo pharmacokinetic analysis using rodents is a commonly used method for predicting human BBB permeability, novel in vitro BBB models, such as Transwell models, have been developed recently. Induced pluripotent stem cells (iPSCs) have the potential to differentiate into various types of cells, and protocols for the differentiation of iPSCs to generate brain microvascular endothelial cells (BMECs) have been reported. The use of iPSCs makes it easy to scale-up iPSC-derived BMECs (iBMECs) and enables production of BBB disease models by using iPSCs from multiple donors with disease, which are advantageous properties compared with models that utilize primary BMECs (pBMECs). There has been little research on the value of iBMECs for predicting BBB permeability. This study focused on the similarity of iBMECs to pBMECs and investigated the ability of iPSC-BBB models (monoculture and coculture) to predict in vivo human BBB permeability using iBMECs. iBMECs express BMEC markers (e.g., VE-cadherin and claudin-5) and influx/efflux transporters (e.g., Glut-1, SLC7A5, CD220, P-gp, ABCG2, and MRP-1) and exhibit high barrier function (transendothelial electrical resistance, >1000 Ω × cm²) as well as similar transporter expression profiles to pBMECs. We determined that the efflux activity using P-glycoprotein (P-gp) transporter is not sufficient in iBMECs, while in drug permeability tests, iPSC-derived BBB models showed a higher correlation with in vivo human BBB permeability compared with a rat BBB model and the Caco-2 model. In a comparison between monoculture and coculture models, the coculture BBB model showed higher efflux activity for compounds with low CNS permeability (e.g., verapamil and thioridazine). In conclusion, iPSC-BBB models make it possible to predict BBB permeability, and employing coculturing can improve iPSC-BBB function.

[Hypothermic Action of Oseltamivir Not Dependent on Its Anti-influenza Virus Action]

Although the anti-influenza virus drug oseltamivir ameliorates the fever of influenza, adverse events related to its hypothermic effect have been reported. We found that oseltamivir causes dose-dependent hypothermia in normal mice, and have been studying the pharmacological mechanisms responsible for 12 years. Oseltamivir blocks nicotinic cholinergic transmission at sympathetic ganglia and reduces sympathetic modulation of brown adipose tissue (BAT), a heat generator. Oseltamivir was found to target the ion channels of nicotinic acetylcholine receptors, as demonstrated by patch clamp experiments with cells expressing the human α3β4 nicotinic receptor. Metabolized oseltamivir carboxylate, which inhibits the influenza virus neuraminidase, did not elicit hypothermia and ion channel suppression. Body temperature was decreased by intracerebroventricular administration of oseltamivir. Because this hypothermic effect was inhibited by dopamine D₂ receptor blockade, it was suggested that oseltamivir centrally stimulates the D₂ receptor. In Japan, the package inserts for oseltamivir and amantadine indicate very similar adverse neuropsychiatric reactions for the two drugs (abnormal behavior, consciousness disturbance, convulsion, delirium, delusion, hallucination). A literature search revealed that in some previous studies, oseltamivir and amantadine were shown to block the ion channel systems and activate the dopaminergic nervous system via several mechanisms. Therefore the similarity of the adverse reactions elicited by oseltamivir and amantadine was considered attributable to their similar pharmacological effects.

Comprehensive molecular pharmacology screening reveals potential new receptor interactions for clinically relevant opioids

Most clinically used opioids are thought to induce analgesia through activation of the mu opioid receptor (MOR). However, disparities have been observed between the efficacy of opioids in activating the MOR in vitro and in inducing analgesia in vivo. In addition, some clinically used opioids do not produce cross-tolerance with each other, and desensitization produced in vitro does not match tolerance produced in vivo. These disparities suggest that some opioids could be acting through other targets in vivo, but this has not been comprehensively tested. We thus screened 9 clinically relevant opioids (buprenorphine, hydrocodone, hydromorphone, morphine, O-desmethyl-tramadol, oxycodone, oxymorphone, tapentadol, tramadol) against 9 pain-related receptor targets (MOR, delta opioid receptor [DOR], kappa opioid receptor [KOR], nociceptin receptor [NOP], cannabinoid receptor type 1 [CB1], sigma-1 receptor [σ1R], and the monoamine transporters [NET/SERT/DAT]) expressed in cells using radioligand binding and functional activity assays. We found several novel interactions, including monoamine transporter activation by buprenorphine and σ1R binding by hydrocodone and tapentadol. Tail flick anti-nociception experiments with CD-1 mice demonstrated that the monoamine transporter inhibitor duloxetine selectively promoted buprenorphine anti-nociception while producing no effects by itself or in combination with the most MOR-selective drug oxymorphone, providing evidence that these novel interactions could be relevant in vivo. Our findings provide a comprehensive picture of the receptor interaction profiles of clinically relevant opioids, which has not previously been performed. Our findings also suggest novel receptor interactions for future investigation that could explain some of the disparities observed between opioid performance in vitro and in vivo.

Treatment strategies for ADHD: an evidence-based guide to select optimal treatment

Attention-deficit/hyperactivity disorder (ADHD) is a common and impairing disorder affecting children, adolescents, and adults. Several treatment strategies are available that can successfully ameliorate symptoms, ranging from pharmacological to dietary interventions. Due to the increasing range of available options, an informed selection or prioritization of treatments is becoming harder for clinicians. This review aims to provide an evidence-based appraisal of the literature on ADHD treatment, supplemented by expert opinion on plausibility. We outline proposed mechanisms of action of established pharmacologic and non-pharmacologic treatments, and we review targets of novel treatments. The most relevant evidence supporting efficacy and safety of each treatment strategy is discussed. We review the individualized features of the patient that should guide the selection of treatments in a shared decision-making continuum. We provide guidance for optimizing initiation of treatment and follow-up of patients in clinical settings.

Dopamine compartmentalization, selective dopaminergic vulnerabilities in Parkinson's disease and therapeutic opportunities

Progressive depletion of selected dopamine neurons is central to much Parkinson's disease (PD) disability. Although symptomatic treatments can ameliorate the disabilities that this neuronal depletion causes, no current strategy is documented to slow these losses. There is substantial evidence that dopamine in intracytoplasmic/extravesicular neuronal compartments can be toxic. Here, I review evidence that supports roles for dopamine compartmentalization, mediated largely by serial actions of plasma membrane SLC6A3/DAT and vesicular SLC18A2/VMAT2 transporters, in the selective patterns of dopamine neuronal loss found in PD brains. This compartmentalization hypothesis for the dopamine cell type specificity of PD lesions nominates available drugs for amelioration of damage arising from miscompartmentalized dopamine and raises cautions in using other drugs.

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.

Why are Antidepressant Drugs Effective Smoking Cessation Aids?

BACKGROUND

Before the advent of varenicline, antidepressant drugs were reported to exhibit better clinical efficacy than nicotine replacement therapy as smoking cessation aids. The most studied is bupropion, a clinically-effective antidepressant, the first to be marketed throughout Europe for smoking cessation. Since depression and tobacco smoking have a high incidence of cooccurrence, this would implicate an underlying link between these two conditions. If this correlation can be confirmed, then by treating one condition the related state would also be treated.

OBJECTIVES

This review article will evaluate the various theories relating to the use of antidepressant drugs as smoking cessation aids and the underlying mechanisms link tobacco smoking and depression to explain the action of antidepressants in smoking cessation. One plausible theory of self-medication which proposes that people take nicotine to treat their own depressive symptoms and the affective withdrawal symptoms seen with abstinence from the drug. If the depression can instead be treated with antidepressants, then they may stop smoking altogether. Another theory is that the neurobiological pathways underlying smoking and depression may be similar. By targeting the pathways of depression in the brain, antidepressants would also treat the pathways affected by smoking and ease nicotine cravings and withdrawal. The role of genetic variation predisposing an individual to depression and initiation of tobacco smoking has also been discussed as a potential link between the two conditions. Such variation could either occur within the neurobiological pathways involved in both disorders or it could lead to an individual being depressed and selfmedicating with nicotine.

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.

Cocaine Abuse, Traumatic Brain Injury, and Preexisting Brain Lesions as Risk Factors for Bupropion-Associated Psychosis

BACKGROUND AND OBJECTIVE

Bupropion is generally considered safe and is widely used both as a monotherapy and as an augmentation agent for the treatment of major depression. Concerns have been raised about bupropion's propensity to precipitate new psychosis and worsen existing psychotic symptoms, although the mechanism is poorly understood. Three cases are reported in which bupropion use was associated with psychosis. The aim of the study was to explore the risk factors and possible mechanisms of psychosis in each case.

CASE REPORTS

Case 1 describes the interaction of cocaine abuse sensitization in a patient who developed psychosis with a lower dosage of bupropion. Cases 2 and 3 discuss the role of traumatic brain injury and structural brain lesions in increasing the risk of psychosis when using bupropion.

CONCLUSIONS

Cocaine abuse, traumatic brain injury, and preexisting brain lesions appear to be risk factors for developing psychosis in persons taking bupropion. In such cases, clinicians should carefully assess the risks and benefits and closely monitor patients for symptoms of psychosis.

Membrane transporters as mediators of synaptic dopamine dynamics: implications for disease

Dopamine was first identified as a neurotransmitter localized to the midbrain over 50 years ago. The dopamine transporter (DAT; SLC6A3) and the vesicular monoamine transporter 2 (VMAT2; SLC18A2) are regulators of dopamine homeostasis in the presynaptic neuron. DAT transports dopamine from the extracellular space into the cytosol of the presynaptic terminal. VMAT2 then packages this cytosolic dopamine into vesicular compartments for subsequent release upon neurotransmission. Thus, DAT and VMAT2 act in concert to move the transmitter efficiently throughout the neuron. Accumulation of dopamine in the neuronal cytosol can trigger oxidative stress and neurotoxicity, suggesting that the proper compartmentalization of dopamine is critical for neuron function and risk of disease. For decades, studies have examined the effects of reduced transporter function in mice (e.g. DAT-KO, VMAT2-KO, VMAT2-deficient). However, we have only recently been able to assess the effects of elevated transporter expression using BAC transgenic methods (DAT-tg, VMAT2-HI mice). Complemented with in vitro work and neurochemical techniques to assess dopamine compartmentalization, a new focus on the importance of transporter proteins as both models of human disease and potential drug targets has emerged. Here, we review the importance of DAT and VMAT2 function in the delicate balance of neuronal dopamine.

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.

Pharmacogenetic Optimization of Smoking Cessation Treatment

Worldwide, approximately one billion people smoke cigarettes. Cigarette smoking persists in part because long-term smoking cessation rates are modest on existing treatments. Smoking cessation outcomes are influenced by genetic factors, including genetic variation in enzymes that metabolize nicotine and smoking cessation medications, as well as in receptor targets for nicotine and treatment medications. For example, smokers with genetically slow nicotine metabolism have higher cessation success on behavioural counseling and nicotine patches compared with smokers with genetically fast nicotine metabolism. In this review, we highlight new progress in our understanding of how genetic variation in the pharmacological targets of nicotine and smoking cessation medications could be used to tailor smoking cessation therapy, increase quit rates, and reduce tobacco-related harm.

Psychostimulant drugs for cocaine dependence

BACKGROUND

Cocaine dependence is a severe disorder for which no medication has been approved. Like opioids for heroin dependence, replacement therapy with psychostimulants could be an effective therapy for treatment.

OBJECTIVES

To assess the effects of psychostimulants for cocaine abuse and dependence. Specific outcomes include sustained cocaine abstinence and retention in treatment. We also studied the influence of type of drug and comorbid disorders on psychostimulant efficacy.

SEARCH METHODS

This is an update of the review previously published in 2010. For this updated review, we searched the Cochrane Drugs and Alcohol Group Trials Register, CENTRAL, MEDLINE, Embase and PsycINFO up to 15 February 2016. We handsearched references of obtained articles and consulted experts in the field.

SELECTION CRITERIA

We included randomised parallel group controlled clinical trials comparing the efficacy of a psychostimulant drug versus placebo.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included 26 studies involving 2366 participants. The included studies assessed nine drugs: bupropion, dexamphetamine, lisdexamfetamine, methylphenidate, modafinil, mazindol, methamphetamine, mixed amphetamine salts and selegiline. We did not consider any study to be at low risk of bias for all domains included in the Cochrane 'Risk of bias' tool. Attrition bias was the most frequently suspected potential source of bias of the included studies. We found very low quality evidence that psychostimulants improved sustained cocaine abstinence (risk ratio (RR) 1.36, 95% confidence interval (CI) 1.05 to 1.77, P = 0.02), but they did not reduce cocaine use (standardised mean difference (SMD) 0.16, 95% CI -0.02 to 0.33) among participants who continued to use it. Furthermore, we found moderate quality evidence that psychostimulants did not improve retention in treatment (RR 1.00, 95% CI 0.93 to 1.06). The proportion of adverse event-induced dropouts and cardiovascular adverse event-induced dropouts was similar for psychostimulants and placebo (RD 0.00, 95% CI -0.01 to 0.01; RD 0.00, 95% CI -0.02 to 0.01, respectively). When we included the type of drug as a moderating variable, the proportion of patients achieving sustained cocaine abstinence was higher with bupropion and dexamphetamine than with placebo. Psychostimulants also appeared to increase the proportion of patients achieving sustained cocaine and heroin abstinence amongst methadone-maintained, dual heroin-cocaine addicts. Retention to treatment was low, though, so our results may be compromised by attrition bias. We found no evidence of publication bias.

AUTHORS' CONCLUSIONS

This review found mixed results. Psychostimulants improved cocaine abstinence compared to placebo in some analyses but did not improve treatment retention. Since treatment dropout was high, we cannot rule out the possibility that these results were influenced by attrition bias. Existing evidence does not clearly demonstrate the efficacy of any pharmacological treatment for cocaine dependence, but substitution treatment with psychostimulants appears promising and deserves further investigation.

Negative association of pretreatment cigarette use with smoking-induced striatal dopamine release in smokers receiving bupropion treatment

BACKGROUND AND OBJECTIVES

In an effort to help identify factors that maintain heavy smoking, this study tested the association of pretreatment cigarette use (cigarettes per day) with striatal dopamine release during smoking-cessation treatment.

METHODS

Thirteen regular smokers (≥10 cigarettes per day) were evaluated on parameters of smoking behavior, and they entered a smoking cessation treatment protocol, including bupropion administration and individual counseling for 2 months. On week 7 of treatment, 10 of the participants underwent brain scans using [(11) C]raclopride with positron emission tomography to assess smoking-induced dopamine release in the caudate nucleus and putamen, inferred from changes in dopamine D2 -type receptor availability.

RESULTS

Receptor availability, measured as binding potential referred to non-displaceable uptake (BPND ) in both striatal regions re-demonstrated a significant decrease after smoking a cigarette; and pre-treatment cigarette use significantly negatively correlated with smoking-induced dopamine release in the caudate.

CONCLUSIONS AND SIGNIFICANCE

The negative association of cigarette use with dopamine release suggests tolerance or down-regulation of the dopamine system by chronic smoking, or a pre-existing condition that promotes more frequent smoking. This association should be regarded as preliminary evidence that warrants verification. (Am J Addict 2016;25:486-492).

Extending the Role of Associative Learning Processes in Nicotine Addiction

Compulsive smoking is a worldwide public health problem. Although research has confirmed the importance of associative learning processes in nicotine addiction, therapies targeting nicotine-associated cues still have a high relapse rate. Most theories conceptualize nicotine as an ‘outcome’ that reinforces behaviors and/or changes the affective value of stimuli. Albeit important, this view does not capture the complexity of associative processes involved in nicotine addiction. For example, nicotine serves as a conditional stimulus acquiring new appetitive/affective properties when paired with a non-drug reward. Also, nicotine functions as an occasion setter that participates in higher-order associative processes that likely permit a more pervasive influence of conditioned cues that are resistant to typically cue-exposure therapy techniques. Finally, nicotine appears to amplify the salience of other stimuli that have some incentive value resulting in enhanced nicotine selfadministration and conditioned reinforcement processes. Future smoking intervention strategies should take into consideration these additional associative learning processes.

Activational and effort-related aspects of motivation: neural mechanisms and implications for psychopathology

Motivation has been defined as the process that allows organisms to regulate their internal and external environment, and control the probability, proximity and availability of stimuli. As such, motivation is a complex process that is critical for survival, which involves multiple behavioural functions mediated by a number of interacting neural circuits. Classical theories of motivation suggest that there are both directional and activational aspects of motivation, and activational aspects (i.e. speed and vigour of both the instigation and persistence of behaviour) are critical for enabling organisms to overcome work-related obstacles or constraints that separate them from significant stimuli. The present review discusses the role of brain dopamine and related circuits in behavioural activation, exertion of effort in instrumental behaviour, and effort-related decision-making, based upon both animal and human studies. Impairments in behavioural activation and effort-related aspects of motivation are associated with psychiatric symptoms such as anergia, fatigue, lassitude and psychomotor retardation, which cross multiple pathologies, including depression, schizophrenia, and Parkinson's disease. Therefore, this review also attempts to provide an interdisciplinary approach that integrates findings from basic behavioural neuroscience, behavioural economics, clinical neuropsychology, psychiatry, and neurology, to provide a coherent framework for future research and theory in this critical field. Although dopamine systems are a critical part of the brain circuitry regulating behavioural activation, exertion of effort, and effort-related decision-making, mesolimbic dopamine is only one part of a distributed circuitry that includes multiple neurotransmitters and brain areas. Overall, there is a striking similarity between the brain areas involved in behavioural activation and effort-related processes in rodents and in humans. Animal models of effort-related decision-making are highly translatable to humans, and an emerging body of evidence indicates that alterations in effort-based decision-making are evident in several psychiatric and neurological disorders. People with major depression, schizophrenia, and Parkinson's disease show evidence of decision-making biases towards a lower exertion of effort. Translational studies linking research with animal models, human volunteers, and clinical populations are greatly expanding our knowledge about the neural basis of effort-related motivational dysfunction, and it is hoped that this research will ultimately lead to improved treatment for motivational and psychomotor symptoms in psychiatry and neurology.

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.

The pharmacology of effort-related choice behavior: Dopamine, depression, and individual differences

This review paper is focused upon the involvement of mesolimbic dopamine (DA) and related brain systems in effort-based processes. Interference with DA transmission affects instrumental behavior in a manner that interacts with the response requirements of the task, such that rats with impaired DA transmission show a heightened sensitivity to ratio requirements. Impaired DA transmission also affects effort-related choice behavior, which is assessed by tasks that offer a choice between a preferred reinforcer that has a high work requirement vs. less preferred reinforcer that can be obtained with minimal effort. Rats and mice with impaired DA transmission reallocate instrumental behavior away from food-reinforced tasks with high response costs, and show increased selection of low reinforcement/low cost options. Tests of effort-related choice have been developed into models of pathological symptoms of motivation that are seen in disorders such as depression and schizophrenia. These models are being employed to explore the effects of conditions associated with various psychopathologies, and to assess drugs for their potential utility as treatments for effort-related symptoms. Studies of the pharmacology of effort-based choice may contribute to the development of treatments for symptoms such as psychomotor slowing, fatigue or anergia, which are seen in depression and other disorders.

Triple reuptake inhibitors as potential next-generation antidepressants: a new hope?

The current therapy for depression is less than ideal with remission rates of only 25-35% and a slow onset of action with other associated side effects. The persistence of anhedonia originating from depressed dopaminergic activity is one of the most treatment-resistant symptoms of depression. Therefore, it has been hypothesized that triple reuptake inhibitors (TRIs) with potency to block dopamine reuptake in addition to serotonin and norepinephrine transporters should produce higher efficacy. The current review comprehensively describes the development of TRIs and discusses the importance of evaluation of in vivo transporter occupancy of TRIs, which should correlate with efficacy in humans.

A comparison of presynaptic and postsynaptic dopaminergic agonists on inhibitory control performance in rats perinatally exposed to PCBs

Polychlorinated Biphenyls (PCBs) are very stable environmental contaminants whose exposure induces a number of health and cognitive concerns. Currently, it is well known that PCB exposure leads to poor performance on inhibitory control tasks. It is also well known that dopamine (DA) depletion within medial prefrontal cortex (mPFC) leads to poor performance on inhibitory control tasks. However, what is not well established is whether or not the inhibitory control problems found following PCB exposure are mediated by DA depletion in mPFC. This study was an investigation into the link between perinatal exposure to PCBs, the effect of this exposure on DA neurotransmission in the mPFC, and inhibitory-control problems during adulthood using a rodent model. The current study served to determine if microinjections of different DA agonists (the presynaptic DA transporter inhibitor and vesicular monoamine transporter agonist bupropion, the postsynaptic DA receptor 2 (DAD2) agonist quinpirole, and the postsynaptic DA receptor 1 (DAD1) agonist SKF81297) directly into the mPFC would differentially improve performance on an inhibitory control task in rats perinatally exposed to an environmentally relevant PCB mixture. Findings suggest several significant sex-based differences on differential reinforcement of low rates (DRL) 15 performance as well as some evidence of differential effectiveness of the DA agonists based on PCB exposure group.

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.

The VMAT-2 inhibitor tetrabenazine alters effort-related decision making as measured by the T-maze barrier choice task: reversal with the adenosine A2A antagonist MSX-3 and the catecholamine uptake blocker bupropion

RATIONALE

Depressed people show effort-related motivational symptoms, such as anergia, retardation, lassitude, and fatigue. Animal tests can model these motivational symptoms, and the present studies characterized the effort-related effects of the vesicular monoamine transport (VMAT-2) inhibitor tetrabenazine. Tetrabenazine produces depressive symptoms in humans and, at low doses, preferentially depletes dopamine.

OBJECTIVES

The current studies investigated the effects of tetrabenazine on effort-based decision making using the T-maze barrier task.

METHODS

Rats were tested in a T-maze in which the choice arms of the maze contain different reinforcement densities, and under some conditions, a vertical barrier was placed in the high-density arm to provide an effort-related challenge. The first experiment assessed the effects of tetrabenazine under different maze conditions: a barrier in the arm with 4 food pellets and 2 pellets in the no barrier arm (4-2 barrier), 4 pellets in one arm and 2 pellets in the other with no barrier in either arm (no barrier), and 4 pellets in the barrier arm with no pellets in the other (4-0 barrier).

RESULTS

Tetrabenazine (0.25-0.75 mg/kg IP) decreased selection of the high cost/high reward arm when the barrier was present, but had no effect on choice under the no barrier and 4-0 barrier conditions. The effects of tetrabenazine on barrier climbing in the 4-2 condition were reversed by the adenosine A2A antagonist MSX-3 and the catecholamine uptake inhibitor and antidepressant bupropion.

CONCLUSIONS

These studies have implications for the development of animal models of the motivational symptoms of depression and other disorders.

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.

Bupropion increases selection of high effort activity in rats tested on a progressive ratio/chow feeding choice procedure: implications for treatment of effort-related motivational symptoms

BACKGROUND

Depression and related disorders are characterized by deficits in behavioral activation, exertion of effort, and other psychomotor/motivational dysfunctions. Depressed patients show alterations in effort-related decision making and a bias towards selection of low effort activities. It has been suggested that animal tests of effort-related decision making could be useful as models of motivational dysfunctions seen in psychopathology.

METHODS

Because clinical studies have suggested that inhibition of catecholamine uptake may be a useful strategy for treatment of effort-related motivational symptoms, the present research assessed the ability of bupropion to increase work output in rats responding on a test of effort-related decision-making (ie, a progressive ratio/chow feeding choice task). With this task, rats can choose between working for a preferred food (high-carbohydrate pellets) by lever pressing on a progressive ratio schedule vs obtaining a less preferred laboratory chow that is freely available in the chamber.

RESULTS

Bupropion (10.0-40.0 mg/kg intraperitoneal) significantly increased all measures of progressive ratio lever pressing, but decreased chow intake. These effects were greatest in animals with low baseline levels of work output on the progressive ratio schedule. Because accumbens dopamine is implicated in effort-related processes, the effects of bupropion on markers of accumbens dopamine transmission were examined. Bupropion elevated extracellular dopamine levels in accumbens core as measured by microdialysis and increased phosphorylated dopamine and cyclic-AMP related phosphoprotein 32 kDaltons (pDARPP-32) immunoreactivity in a manner consistent with D1 and D2 receptor stimulation.

CONCLUSION

The ability of bupropion to increase exertion of effort in instrumental behavior may have implications for the pathophysiology and treatment of effort-related motivational symptoms in humans.

Pharmacogenetics of nicotine and associated smoking behaviors

This chapter summarizes genetic factors that contribute to variation in nicotine pharmacokinetics and nicotine's pharmacological action in the central nervous system (CNS), and how this in turn influences smoking behaviors. Nicotine, the major psychoactive compound in cigarette smoke, is metabolized by a number of enzymes, including CYP2A6, CYP2B6, FMOs, and UGTs, among others. Variation in the genes encoding these enzymes, in particular CYP2A6, can alter the rate of nicotine metabolism and smoking behaviors. Faster nicotine metabolism is associated with higher cigarette consumption and nicotine dependence, as well as lower quit rates. Variation in nicotine's CNS targets and downstream signaling pathways can also contribute to interindividual differences in smoking patterns. Binding of nicotine to neuronal nicotinic acetylcholine receptors (nAChRs) mediates the release of several neurotransmitters including dopamine and serotonin. Genetic variation in nAChRs, and in transporter and enzyme systems that leads to altered CNS levels of dopamine and serotonin, is associated with a number of smoking behaviors. To date, the precise mechanism underpinning many of these findings remains unknown. Considering the complex etiology of nicotine addiction, a more comprehensive approach that assesses the contribution of multiple gene variants, and their interaction with environmental factors, will likely improve personalized therapeutic approaches and increase smoking cessation rates.

Mesolimbic Dopamine and the Regulation of Motivated Behavior

It has been known for some time that nucleus accumbens dopamine (DA) is involved in aspects of motivation , but theoretical approaches to understanding the functions of DA have continued to evolve based upon emerging data and novel concepts. Although it has become traditional to label DA neurons as "reward" neurons, the actual findings are more complicated than that, because they indicate that DA neurons can respond to a variety of motivationally significant stimuli. Moreover, it is important to distinguish between aspects of motivation that are differentially affected by dopaminergic manipulations. Studies that involve nucleus accumbens DA antagonism or depletion indicate that accumbens DA does not mediate primary food motivation or appetite. Nevertheless, DA is involved in appetitive and aversive motivational processes including behavioral activation , exertion of effort, sustained task engagement, and Pavlovian-to-instrumental transfer. Interference with accumbens DA transmission affects instrumental behavior in a manner that interacts with the response requirements of the task and also shifts effort-related choice behavior, biasing animals toward low-effort alternatives. Dysfunctions of mesolimbic DA may contribute to motivational symptoms seen in various psychopathologies, including depression , schizophrenia, parkinsonism, and other disorders.

In vivo activity of modafinil on dopamine transporter measured with positron emission tomography and [¹⁸F]FE-PE2I

Modafinil, a wake-promoting drug used to treat narcolepsy, is a dopamine transporter inhibitor and is said to have very low abuse liability; this, however, is still up for debate. We conducted a dopamine transporter (DAT) occupancy study with modafinil (200 or 300 mg) in ten healthy volunteers using positron emission tomography (PET) with [¹⁸F]FE-PE2I, a new PET radioligand with high affinity and selectivity for the dopamine transporter, to characterize its relation to abuse liability. Mean striatal DAT occupancies were 51.4% at 200 mg and 56.9% at 300 mg. There was a significant correlation between occupancy and plasma concentration, indicating dose dependency of DAT inhibition by modafinil in the striatum, and especially in the nucleus accumbens. This study showed that DAT occupancy by modafinil was close to that of methylphenidate, indicating that modafinil may be near the same level as methylphenidate in relation to abuse liability in terms of dopaminergic transmission.

Tesofensine, a novel triple monoamine re-uptake inhibitor with anti-obesity effects: dopamine transporter occupancy as measured by PET

Tesofensine (TE) is a novel triple monoamine re-uptake inhibitor inducing a potent inhibition of the re-uptake process in the synaptic cleft of the neurotransmitters dopamine, norepinephrine, and serotonin. In recent preclinical and clinical evaluations TE showed a robust anti-obesity effect, but the specific mechanism of this triple monoamine re-uptake inhibitor still needs to be further elucidated. This positron emission tomography (PET) study, using [¹¹C]βCIT-FE, aimed to assess the degree of the dopamine transporter (DAT) occupancy, at constant TE plasma levels, following different oral, multiple doses of TE during totally 8-12 days. In addition, the relationships between DAT occupancy and TE plasma concentrations, or doses, were investigated to enable assessment of DAT occupancies in subsequent clinical trials. The results demonstrated that TE induced a dose-dependent blockade of DAT following multiple doses of 0.125-1 mg TE at anticipated steady-state conditions. The mean striatal DAT occupancy varied dose-dependently between 18% and 77%. A sigmoid E(max) model well described the relationship between striatal DAT occupancy and TE plasma concentrations or doses. It was estimated that the maximum achievable DAT occupancy was about 80% and that half of this effect was accomplished by approximately 0.25 mg TE and a plasma drug concentration of 4 ng/ml. The results indicated an important mechanism of action of TE on DAT. Further, these results suggest that the previously reported dose-dependent weight loss, in TE treated subjects, was in part mediated by an up-regulation of dopaminergic pathways due to enhanced amounts of synaptic dopamine after blockade of DAT.

Antidepressant combinations: cutting edge psychopharmacology or passing fad?

This article reviews the rationale for and history of combining antidepressants, as well as the current state of the evidence, in the treatment of major depression. Although it has long been suggested that some individuals may benefit from regimens that combine two dissimilar antidepressants, enthusiasm for this practice has waxed and waned and there was never a strong empirical foundation to support this practice. The tangibly better safety profiles of the newer generation antidepressants, both singly and in combination, have permitted greater use of such combinations in contemporary practice than ever before. Combinations that pair a selective serotonin reuptake inhibitor (SSRI) or serotonin norepinephrine reuptake inhibitor (SNRI) with a dissimilar antidepressant, such as bupropion or mirtazapine, are now widely used for patients who have not responded to trials of first- or second-line antidepressant monotherapies and have been tested as a potential way of speeding the benefits of treatment. However, there still is no strong evidence that even the most widely used combinations have particular merit and clinicians should be mindful that alternatives exist with more established efficacy. Moreover, aside from selected cases of drug-drug interactions, it may take full therapeutic doses of both drugs across a typically adequate duration of exposure to achieve the desired effects of combined treatment.

Bupropion for the treatment of seasonal affective disorder

INTRODUCTION

Seasonal affective disorder (SAD) is a psychiatric illness with recurring depressive episodes during particular seasons, mostly winter. Bupropion is effective in the preventive treatment of SAD and is probably also effective in the acute treatment of SAD.

AREAS COVERED

This review covers the pharmacokinetics and pharmacodynamics of bupropion. The authors also evaluate bupropion's clinical efficacy as well as its safety and tolerability.

EXPERT OPINION

Bupropion is available in an immediate release formulation, as well as a sustained release formulation and an extended release (XR) formulation. The XR formulation is recommended for SAD due to its ease of use and is the only formulation currently used as a therapy. Due to the predictable nature of SAD, the use of bupropion XR is considered a relevant treatment option. Bupropion's efficacy is shown in three trials that started in autumn at a time when SAD symptoms were not yet present although treatment effects were relatively small compared with a placebo. Bupropion was also shown to have efficacy in an open-label study. That being said, in order to reach definitive conclusions about its efficacy with acute treatment of SAD, more placebo-controlled trials are needed.

Monoamine transporter occupancy of a novel triple reuptake inhibitor in baboons and humans using positron emission tomography

The selection of a therapeutically meaningful dose of a novel pharmaceutical is a crucial step in drug development. Positron emission tomography (PET) allows the in vivo estimation of the relationship between the plasma concentration of a drug and its target occupancy, optimizing dose selection and reducing the time and cost of early development. Triple reuptake inhibitors (TRIs), also referred to as serotonin-norepinephrine-dopamine reuptake inhibitors, enhance monoaminergic neurotransmission by blocking the action of the monoamine transporters, raising extracellular concentrations of those neurotransmitters. GSK1360707 [(1R,6S)-1-(3,4-dichlorophenyl)-6-(methoxymethyl)-4-azabicyclo[4.1.0]heptane] is a novel TRI that until recently was under development for the treatment of major depressive disorder; its development was put on hold for strategic reasons. We present the results of an in vivo assessment of the relationship between plasma exposure and transporter blockade (occupancy). Studies were performed in baboons (Papio anubis) to determine the relationship between plasma concentration and occupancy of brain serotonin reuptake transporter (SERT), dopamine reuptake transporter (DAT), and norepinephrine uptake transporter (NET) using the radioligands [(11)C]DASB [(N,N-dimethyl-2-(2-amino-4-cyanophenylthio) benzylamine], [(11)C]PE2I [N-(3-iodoprop-2E-enyl)-2β-carbomethoxy-3β-(4-methylphenyl)nortropane], and [(11)C]2-[(2-methoxyphenoxy)phenylmethyl]morpholine (also known as [(11)C]MRB) and in humans using [(11)C]DASB and [(11)C]PE2I. In P. anubis, plasma concentrations resulting in half-maximal occupancy at SERT, DAT, and NET were 15.16, 15.56, and 0.97 ng/ml, respectively. In humans, the corresponding values for SERT and DAT were 6.80 and 18.00 ng/ml. GSK1360707 dose-dependently blocked the signal of SERT-, DAT-, and NET-selective PET ligands, confirming its penetration across the blood-brain barrier and blockade of all three monoamine transporters in vivo.