Altered serotonin and dopamine transporter availabilities in brain of depressed patients upon treatment with escitalopram: A [123 I]β-CIT SPECT study

Subanesthetic S-ketamine does not acutely alter striatal dopamine transporter binding in healthy Sprague Dawley female rats

Major depressive disorder is one of the most prevalent mental health disorders, posing a global socioeconomic burden. Conventional antidepressant treatments have a slow onset of action, and 30% of patients show no clinically significant treatment response. The recently approved fast-acting antidepressant S-ketamine, an N-methyl-D-aspartate receptor antagonist, provides a new approach for treatment-resistant patients. However, knowledge of S-ketamine's mechanism of action is still being established. Depressed human subjects have lower striatal dopamine transporter (DAT) availability compared to healthy controls. Rodent studies report increased striatal dopamine concentration in response to acute ketamine administration. In vivo [18F]FE-PE2I ([18F]-(E)-N-(3-iodoprop-2-enyl)-2β-carbofluoroethoxy-3β-(4'-methyl-phenyl) nortropane) positron emission tomography (PET) imaging of the DAT has not previously been applied to assess the effect of acute subanesthetic S-ketamine administration on DAT availability. We applied translational in vivo [18F]FE-PE2I PET imaging of the DAT in healthy female rats to evaluate whether an acute subanesthetic intraperitoneal dose of 15 mg/kg S-ketamine alters DAT availability. We also performed [3H]GBR-12935 autoradiography on postmortem brain sections. We found no effect of acute S-ketamine administration on striatal DAT binding using [18F]FE-PE2I PET or [3H]GBR-12935 autoradiography. This negative result does not support the hypothesis that DAT changes are associated with S-ketamine's rapid antidepressant effects, but additional studies are warranted.

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.

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.

Serotonin and dopamine transporter availability in social anxiety disorder after combined treatment with escitalopram and cognitive-behavioral therapy

Selective serotonin reuptake inhibitors (SSRIs) and internet-based cognitive behavioral therapy (ICBT) are recommended treatments of social anxiety disorder (SAD), and often combined, but their effects on monoaminergic signaling are not well understood. In this multi-tracer positron emission tomography (PET) study, 24 patients with SAD were randomized to treatment with escitalopram+ICBT or placebo+ICBT under double-blind conditions. Before and after 9 weeks of treatment, patients were examined with positron emission tomography and the radioligands [¹¹C]DASB and [¹¹C]PE2I, probing the serotonin (SERT) and dopamine (DAT) transporter proteins respectively. Both treatment combinations resulted in significant improvement as measured by the Liebowitz Social Anxiety Scale (LSAS). At baseline, SERT-DAT co-expression was high and, in the putamen and thalamus, co-expression showed positive associations with symptom severity. SERT-DAT co-expression was also predictive of treatment success, but predictor-outcome associations differed in direction between the treatments. After treatment, average SERT occupancy in the SSRI + ICBT group was >80%, with positive associations between symptom improvement and occupancy in the nucleus accumbens, putamen and anterior cingulate cortex. Following placebo+ICBT, SERT binding increased in the raphe nuclei. DAT binding increased in both groups in limbic and striatal areas, but relations with symptom improvement differed, being negative for SSRI + ICBT and positive for placebo + ICBT. Thus, serotonin-dopamine transporter co-expression exerts influence on symptom severity and remission rate in the treatment of social anxiety disorder. However, the monoamine transporters are modulated in dissimilar ways when cognitive-behavioral treatment is given concomitantly with either SSRI-medication or pill placebo.

Neferine alleviates chronic stress-induced depression by regulating monoamine neurotransmitter secretion and gut microbiota structure

Neferine (Nef) might possess anti-depressive properties; however, its therapeutic effects are yet to be elucidated. Therefore, in this study, we aimed to explore the anti-depressant property of Nef using a mouse model of chronic stress-induced depression. Fifteen depression-prone mice were randomly selected and divided into three groups, namely, the model, Nef, and fluoxetine (Flu) groups. We observed that in tail suspension and forced swimming tests, the Nef and Flu treatments significantly decreased the immobility time of the depressed mice, and increased their sucrose preference indices. Moreover, both Nef and Flu treatments induced significant increases in the levels of anti-depressant neurotransmitters, including dopamine (DA), serotonin (5-HT), and norepinephrine (NE), and also reduced pathological damage to the hippocampus of the depressed mice. Incidentally, Illumina MiSeq sequencing analysis demonstrated that the relative abundance of Lactobacillus in the intestinal microbiota of depressed mice was restored after Nef/Flu treatment. Moreover, colonic Lactobacillus abundance was positively correlated with the levels of DA, 5-HT, and NE in the hippocampus of the mice. In conclusion, Nef improved monoamine neurotransmitter secretion and modulated the intestinal flora structure, particularly the abundance of Lactobacillus. Hence, it showed considerable anti-depressant potential, and might be a prospective anti-depressant therapeutic agent.

Dopamine dysfunction in depression: application of texture analysis to dopamine transporter single-photon emission computed tomography imaging

Dopamine dysfunction has been associated with depression. However, results of recent neuroimaging studies on dopamine transporter (DAT), which reflect the function of the dopaminergic system, are inconclusive. The aim of this study was to apply texture analysis, a novel method to extract information about the textural properties of images (e.g., coarseness), to single-photon emission computed tomography (SPECT) imaging in depression. We performed SPECT using ¹²³I-ioflupane to measure DAT binding in 150 patients with major depressive disorder (N = 112) and bipolar disorder (N = 38). The texture features of DAT binding in subregions of the striatum were calculated. We evaluated the relationship between the texture feature values (coarseness, contrast, and busyness) and severity of depression, and then examined the effects of medication and diagnosis on such relationship. Furthermore, using the data from 40 healthy subjects, we examined the effects of age and sex on the texture feature values. The degree of busyness of the limbic region in the left striatum linked to the severity of depression (p = 0.0025). The post-hoc analysis revealed that this texture feature value was significantly higher in both the severe and non-severe depression groups than in the remission group (p = 0.001 and p = 0.028, respectively). This finding remained consistent after considering the effect of medication. The effects of age and sex in healthy individuals were not evident in this texture feature value. Our findings imply that the application of texture analysis to DAT-SPECT may provide a state-marker of depression.

Factors related to the length of stay for major depressive disorder patients in China: A real-world retrospective study

Background

As numerous patients with depression have to be hospitalized because of various reasons, the demand far exceeds the limited bed count in the psychiatry department. Controlling the length of stay (LOS) of the patient is gradually being considered an effective method to alleviate this problem. Given the lack of statistical evidence of the LOS of patients with major depressive disorder (MDD) in China and the strain on the limited psychiatric resources, the purpose of our study was to investigate the LOS of patients with MDD among in-patient samples and to analyze related factors of the LOS in China by building a regression model.

Method

The data were exported from the electronic medical record system. A total of three categories of independent variables were enrolled in our study, namely, demographic, clinical, and biochemical. Univariate analysis and binominal regression analysis were applied comprehensively to find the factors related to the LOS among MDD samples. The discrimination accuracy of the model was evaluated by the receiver operating characteristic (ROC) analysis. ROC analysis indicated that the discrimination accuracy of our model was acceptable (AUC = 0.790, 95% CI = 0.714–0.865, P < 0.001).

Result

A total of 254 patients were finally brought into analysis after filtering. Regression analysis indicated that abnormal LDL was the only risk factor of long LOS (OR = 3.352, 95% CI = 1.087–10.337, P = 0.035) among all the kinds of variables. Notably, in the statistically irrelevant factors of the LOS, the category of anti-depressant drugs [serotonin–norepinephrine reuptake inhibitor (SNRI) or selective serotonin reuptake inhibitor (SSRI)] prescribed to patients with MDD was not associated statistically with the LOS, which was against our initial hypothesis that the LOS of patients with MDD treated with SNRI would vary from that of the patients treated with SSRI.

Conclusion

Up to our knowledge, our research is the first study to show the potential factors related to the LOS from various domains, especially biochemical indexes, and the effect of drugs, among clinical patients with MDD in China. Our results could provide a theoretical reference for efficient psychiatry hospitalization management and prioritization of allocating medical resources. Future studies are required for updating independent variables which are potentially related to the LOS and verifying existing results in a larger sample.

Systematic review and meta-analysis on the therapeutic reference range for escitalopram: Blood concentrations, clinical effects and serotonin transporter occupancy

INTRODUCTION

A titration within a certain therapeutic reference range presupposes a relationship between the blood concentration and the therapeutic effect of a drug. However, this has not been systematically investigated for escitalopram. Furthermore, the recommended reference range disagrees with mean steady state concentrations (11-21 ng/ml) that are expected under the approved dose range (10-20 mg/day). This work systematically investigated the relationships between escitalopram dose, blood levels, clinical effects, and serotonin transporter occupancy.

METHODS

Following our previously published methodology, relevant articles were systematically searched and reviewed for escitalopram.

RESULTS

Of 1,032 articles screened, a total of 30 studies met the eligibility criteria. The included studies investigated escitalopram blood levels in relationship to clinical effects (9 studies) or moderating factors on escitalopram metabolism (12 studies) or serotonin transporter occupancy (9 studies). Overall, the evidence for an escitalopram concentration/effect relationship is low (level C).

CONCLUSION

Based on our findings, we propose a target range of 20-40 ng/ml for antidepressant efficacy of escitalopram. In maintenance treatment, therapeutic response is expected, when titrating patients above the lower limit. The lower concentration threshold is strongly supported by findings from neuroimaging studies. The upper limit for escitalopram's reference range rather reflects a therapeutic maximum than a tolerability threshold, since the incidence of side effects in general is low. Concentrations above 40 ng/ml should not necessarily result in dose reductions in case of good clinical efficacy and tolerability. Dose-related escitalopram concentrations in different trials were more than twice the expected concentrations from guideline reports.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=215873], identifier [CRD42020215873].

Expectancy effects on serotonin and dopamine transporters during SSRI treatment of social anxiety disorder: a randomized clinical trial

It has been extensively debated whether selective serotonin reuptake inhibitors (SSRIs) are more efficacious than placebo in affective disorders, and it is not fully understood how SSRIs exert their beneficial effects. Along with serotonin transporter blockade, altered dopamine signaling and psychological factors may contribute. In this randomized clinical trial of participants with social anxiety disorder (SAD) we investigated how manipulation of verbally-induced expectancies, vital for placebo response, affect brain monoamine transporters and symptom improvement during SSRI treatment. Twenty-seven participants with SAD (17 men, 10 women), were randomized, to 9 weeks of overt or covert treatment with escitalopram 20 mg. The overt group received correct treatment information whereas the covert group was treated deceptively with escitalopram, described as an active placebo in a cover story. Before and after treatment, patients underwent positron emission tomography (PET) assessments with the [11C]DASB and [11C]PE2I radiotracers, probing brain serotonin (SERT) and dopamine (DAT) transporters. SAD symptoms were measured by the Liebowitz Social Anxiety Scale. Overt was superior to covert SSRI treatment, resulting in almost a fourfold higher rate of responders. PET results showed that SERT occupancy after treatment was unrelated to anxiety reduction and equally high in both groups. In contrast, DAT binding decreased in the right putamen, pallidum, and the left thalamus with overt SSRI treatment, and increased with covert treatment, resulting in significant group differences. DAT binding potential changes in these regions correlated negatively with symptom improvement. Findings support that the anxiolytic effects of SSRIs involve psychological factors contingent on dopaminergic neurotransmission while serotonin transporter blockade alone is insufficient for clinical response.

The Effect of Escitalopram on Central Serotonergic and Dopaminergic Systems in Patients with Cervical Dystonia, and Its Relationship with Clinical Treatment Effects: A Double-Blind Placebo-Controlled Trial

Purpose: The pathophysiology of cervical dystonia (CD) is thought to be related to changes in dopamine and serotonin levels in the brain. We performed a double-blind trial with escitalopram (selective serotonin reuptake inhibitor; SSRI) in patients with CD. Here, we report on changes in dopamine D_2/3 receptor (D2/3R), dopamine transporter (DAT) and serotonin transporter (SERT) binding potential (BP_ND) after a six-week treatment course with escitalopram or placebo. Methods: CD patients had [123I]FP-CIT SPECT (I-123 fluoropropyl carbomethoxy-3 beta-(4-iodophenyltropane) single-photon emission computed tomography) scans, to quantify extrastriatal SERT and striatal DAT, and [123I]IBZM SPECT (I-123 iodobenzamide SPECT) scans to quantify striatal D2/3R BPND before and after six weeks of treatment with either escitalopram or placebo. Treatment effect was evaluated with the Clinical Global Impression scale for dystonia, jerks and psychiatric symptoms, both by physicians and patients. Results: In both patients treated with escitalopram and placebo there were no significant differences after treatment in SERT, DAT or D2/3R BP_ND. Comparing scans after treatment with escitalopram (n = 8) to placebo (n = 8) showed a trend (p = 0.13) towards lower extrastriatal SERT BPND in the SSRI group (median SERT occupancy of 64.6%). After treatment with escitalopram, patients who reported a positive effect on dystonia or psychiatric symptoms had significantly higher SERT occupancy compared to patients who did not experience an effect. Conclusion: Higher extrastriatal SERT occupancy after treatment with escitalopram is associated with a trend towards a positive subjective effect on dystonia and psychiatric symptoms in CD patients.

Extrastriatal 123I-FP-CIT SPECT impairment in Parkinson's disease - the PPMI cohort

Background

Neuropathological data and nuclear medicine imaging show extensive serotonergic impairment in Parkinson’s disease (PD). We undertook a case-controlled analysis of ¹²³I-FP-CIT SPECT images to measure extrastriatal serotonergic transporters (SERT) in PD using the Parkinson’s Progression Markers Initiative (PPMI) cohort.

Methods

We included all PD (n = 154) and Control subjects (n = 62) with available ¹²³I-FP-CIT SPECT imaging and high-resolution T1-weighted MRI for coregistration (PD: mean age 61.6 years, 62% male, disease duration 26 months, MDS-UPDRS III score 22). ¹²³I-FP-CIT SPECT images were processed with PETPVE12 using an exploratory voxel-wise analysis including partial-volume effect correction. Linear regressions were performed in the PD group to assess correlations between region of interest ¹²³I-FP-CIT uptake and clinical motor and non-motor impairment.

Results

Compared to Controls, PD exhibited an uptake reduction in bilateral caudate nucleus, putamen, insula, amygdala and right pallidum (family-wise error (FWE)-corrected p <  0.05). While lower putaminal uptake on the contralateral side to clinically more affected side was associated with higher MDS-UPDRS III score (p = 0.022), we found a trend association between higher geriatric depression scale and lower pallidum uptake (p = 0.09). Higher SCOPA-AUT gastrointestinal subscore was associated with lower uptake in mean putamen and caudate nucleus (p = 0.01 to 0.03), whereas urological subscore was inversely correlated with mean caudate nucleus, putamen, and pallidum uptake (p = 0.002 to 0.03). REM sleep behaviour disorder screening questionnaire was associated with lower ¹²³I-FP-CIT binding in caudate nucleus, putamen and pallidum (all p <  0.05). No significant association was found for Montreal Cognitive Assessment (all p > 0.45) or excessive daytime sleepiness (all p > 0.29).

Conclusions

In addition to the well-established striatal deficit, this study provides evidence of a major extrastriatal ¹²³I-FP-CIT impairment, and therefore of an altered serotonergic transmission in early PD.

Lower midbrain dopamine transporter availability in depressed patients: Report from high-resolution PET imaging

BACKGROUND

A reduced presynaptic dopamine neurotransmission has long been implicated in major depressive disorder (MDD). However, molecular imaging studies that assessed the dopamine transporter (DAT) availability have led to inconsistent results, partly due to methodological considerations, and to exclusive focus on the striatum, precluding findings in extra-striatal regions.

METHODS

Herein, we leveraged our database of high-resolution Positron Emission Tomography (PET) images acquired with a highly selective radiotracer, [¹¹C]PE2I, to assess striatal and extra-striatal DAT availability in eight patients treated for depression compared to twenty-four healthy controls.

RESULTS

Statistical parametric mapping and voxel-based analyses of PET images detected a significant lower DAT availability in depressed patients within the superior part of the midbrain (right, p_FWE = 0.002; left, p_FWE = 0.006), a region including the ventral tegmental area and the substantia nigra from where the mesocorticolimbic and nigrostriatal dopamine pathways originate. A similar difference was found in the right dorsal putamen (p_FWE = 0.012).

LIMITATIONS

The statistical power was limited to detect only large effects, due to the size of the patients' sample.

CONCLUSIONS

The findings support the hypothesis that a reduced presynaptic dopamine function plays a role in the pathophysiology of depression, and that extra-striatal dopamine function should be further investigated.

Gut Microbiota Regulates Depression-Like Behavior in Rats Through the Neuroendocrine-Immune-Mitochondrial Pathway

PURPOSE

Gut microbiota affects various physiological functions in the host and has crucial effects on the nervous system. There is increasing evidence of a correlation between gut microbiota and depression; however, the mechanisms underlying the regulation of depression-like behavior by gut microbiota remain unclear. In this study, we assessed the regulatory mechanism of gut microbiota on depression-like behavior in rats.

METHODS

We transplanted fecal microbiota obtained from patients with depression and healthy individuals into germ-free (GF) rats (n=18) through fecal microbiota transplantation technology. Next, we assessed the affective behavior in the rats using the forced swimming test and a sucrose preference test. We used enzyme-linked immunosorbent assay (ELISA) to determine the hippocampal levels of 5-hydroxytryptamine (5-HT), dopamine (DA), and noradrenaline (NE) and the serum levels of corticosterone (CORT), adrenocorticotropic hormone (ACTH), corticotropin-releasing hormone (CRH), tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin-6 (IL-6), interleukin-1 (IL-1), interleukin-1 (IL-4), and interleukin-1 (IL-10). The mitochondrial morphology of small intestinal epithelial cells was observed through transmission electron microscopy.

RESULTS

Rats that received fecal microbiota from patients with depression (depression microbiota) exhibited depression-like behavior. They presented decreased levels of hippocampal neurotransmitters, serum CORT levels, and anti-inflammatory cytokine levels, as well as increased ACTH, CRH, and serum levels of multiple pro-inflammatory cytokines. Observation of the mitochondria ultrastructure showed damaged mitochondria in the intestinal epithelial cells, significant endoplasmic reticulum expansion, and border aggregation of nuclear chromatin.

CONCLUSION

Our findings suggested that the depression-like behaviors induced by the depression microbiota through the neuroendocrine-immune-mitochondrial pathway, which were associated with neuroendocrine disorders, inflammatory responses, and mitochondrial damage.

Assessment of Striatal Dopamine Transporter Binding in Individuals With Major Depressive Disorder: In Vivo Positron Emission Tomography and Postmortem Evidence

IMPORTANCE

Major depressive disorder (MDD) might involve dopamine (DA) reductions. The DA transporter (DAT) regulates DA clearance and neurotransmission and is sensitive to DA levels, with preclinical studies (including those involving inescapable stressors) showing that DAT density decreases when DA signaling is reduced. Despite preclinical data, evidence of reduced DAT in MDD is inconclusive.

OBJECTIVE

Using a highly selective DAT positron emission tomography (PET) tracer ([11C] altropane), DAT availability was probed in individuals with MDD who were not taking medication. Levels of DAT expression were also evaluated in postmortem tissues from donors with MDD who died by suicide.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional PET study was conducted at McLean Hospital (Belmont, Massachusetts) and Massachusetts General Hospital (Boston) and enrolled consecutive individuals with MDD who were not taking medication and demographically matched healthy controls between January 2012 and March 2014. Brain tissues were obtained from the Douglas-Bell Canada Brain Bank. For the PET component, 25 individuals with current MDD who were not taking medication and 23 healthy controls recruited from McLean Hospital were included (all provided usable data). For the postmortem component, 15 individuals with depression and 14 healthy controls were considered.

INTERVENTION

PET scan.

MAIN OUTCOMES AND MEASURES

Striatal and midbrain DAT binding potential was assessed. For the postmortem component, tyrosine hydroxylase and DAT levels were evaluated using Western blots.

RESULTS

Compared with 23 healthy controls (13 women [56.5%]; mean [SD] age, 26.49 [7.26] years), 25 individuals with MDD (19 women [76.0%]; mean [SD] age, 26.52 [5.92] years) showed significantly lower in vivo DAT availability in the bilateral putamen and ventral tegmental area (Cohen d range, -0.62 to -0.71), and both reductions were exacerbated with increasing numbers of depressive episodes. Unlike healthy controls, the MDD group failed to show an age-associated reduction in striatal DAT availability, with young individuals with MDD being indistinguishable from older healthy controls. Moreover, DAT availability in the ventral tegmental area was lowest in individuals with MDD who reported feeling trapped in stressful circumstances. Lower DAT levels (and tyrosine hydroxylase) in the putamen of MDD compared with healthy controls were replicated in postmortem analyses (Cohen d range, -0.92 to -1.15).

CONCLUSIONS AND RELEVANCE

Major depressive disorder, particularly with recurring episodes, is characterized by decreased striatal DAT expression, which might reflect a compensatory downregulation due to low DA signaling within mesolimbic pathways.

Dopamine Transporter and Reward Anticipation in a Dimensional Perspective: A Multimodal Brain Imaging Study

Dopamine function and reward processing are highly interrelated and involve common brain regions afferent to the nucleus accumbens, within the mesolimbic pathway. Although dopamine function and reward system neural activity are impaired in most psychiatric disorders, it is unknown whether alterations in the dopamine system underlie variations in reward processing across a continuum encompassing health and these disorders. We explored the relationship between dopamine function and neural activity during reward anticipation in 27 participants including healthy volunteers and psychiatric patients with schizophrenia, depression, or cocaine addiction, using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) multimodal imaging with a voxel-based statistical approach. Dopamine transporter (DAT) availability was assessed with PET and [11C]PE2I as a marker of presynaptic dopamine function, and reward-related neural response was assessed using fMRI with a modified Monetary Incentive Delay task. Across all the participants, DAT availability in the midbrain correlated positively with the neural response to anticipation of reward in the nucleus accumbens. Moreover, this relationship was conserved in each clinical subgroup, despite the heterogeneity of mental illnesses examined. For the first time, a direct link between DAT availability and reward anticipation was detected within the mesolimbic pathway in healthy and psychiatric participants, and suggests that dopaminergic dysfunction is a common mechanism underlying the alterations of reward processing observed in patients across diagnostic categories. The findings support the use of a dimensional approach in psychiatry, as promoted by the Research Domain Criteria project to identify neurobiological signatures of core dysfunctions underling mental illnesses.

New Trends and Current Status of Positron-Emission Tomography and Single-Photon-Emission Computerized Tomography Radioligands for Neuronal Serotonin Receptors and Serotonin Transporter

The critical role of serotonin (5-hydroxytryptamine; 5-HT) and its receptors (5-HTRs) in the pathophysiology of diverse neuropsychiatric and neurodegenerative disorders render them attractive diagnostic and therapeutic targets for brain disorders. Therefore, the in vivo assessment of binding of 5-HT receptor ligands under a multitude of physiologic and pathologic scenarios may support more-accurate identification of disease and its progression and the patient's response to therapy as well as the screening of novel therapeutic strategies. The present Review aims to focus on the current status of radioligands used for positron-emission tomography (PET) and single-photon-emission computerized tomography (SPECT) imaging of human brain serotonin receptors. We further elaborate upon and emphasize the attributes that qualify a radioligand for theranostics on the basis of its frequency of use in clinics, its benefit to risk assessment in humans, and its continuous evolution, along with the major limitations.

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.

A prospective, longitudinal study of platelet serotonin and plasma brain-derived neurotrophic factor concentrations in major depression: effects of vortioxetine treatment

BACKGROUND

Various antidepressants occupy brain serotonin transporter (SERT), decrease platelet serotonin (5-HT) concentration, and normalize reduced plasma brain-derived neurotrophic factor (BDNF) concentrations in depressed patients. Vortioxetine is a recently introduced antidepressant with a multimodal mechanism of action. In addition to SERT inhibition, vortioxetine acts via different 5-HT receptors. To further elucidate its mechanism of action, we have investigated the effects of vortioxetine on platelet 5-HT and plasma BDNF concentrations in patients with major depression.

METHODS

Platelet 5-HT and plasma BDNF concentrations were determined in 44 healthy subjects at baseline and in 44 depressed patients before and after 4 weeks of treatment with vortioxetine (5-15 mg daily). Platelet 5-HT concentration was determined using the ortho-phthalaldehyde-enhanced fluorometric method, and plasma BDNF concentration using a commercial enzyme-linked immunosorbent assay (Quantikine ELISA, R&D Systems).

RESULTS

At baseline, platelet 5-HT concentrations did not differ between depressed and control subjects, but plasma BDNF values were lower (p = 0.011; ω = 0.80) in depressed patients than in healthy subjects. Vortioxetine treatment significantly (p < 0.0001; ω = 0.80) decreased platelet 5-HT concentration and significantly (p = 0.004; ω = 0.80) increased plasma BDNF concentration in depressed patients compared to their baseline values. Age, gender, and smoking were not significantly associated with platelet 5-HT and plasma BDNF concentrations.

CONCLUSION

Despite a novel mechanism of action, vortioxetine shares some common effects with other antidepressants. This study is the first to show that, in addition to clinical improvement, 4 weeks of treatment with vortioxetine (5-15 mg daily), decreased platelet 5-HT and increased plasma BDNF concentrations in depressed patients.

[Research progress of depression and the application of esketamine]

The pathogenesis and etiology of still remain unknown. Current evidence suggests that the occurrence of depression may be related to a reduced secretion of neurotransmitters, neuronal apoptosis, inflammation, intestinal flora and other factors. Although the commonly used antidepressants such as SSRIs, SNRIs, NaSSA, and SARIs produce some therapeutic effects, they fail to relieve the full spectrum of the symptoms of depression. In recent years, esketamine was found to produce a potent and a long-lasting antidepressant effect by acting on the NMDA receptors. Herein the authors review the progress in the study of the pathogenesis and drug therapies of depression, the efficacy of esketamine treatment and the underlying mechanism, and the prospect of esketamine treatment. Currently the mechanism of the antidepressant effect of esketamine remains indeterminate and its clinical application is limited, but its effect in rapidly alleviating the symptoms of depression suggests its bright prospect for clinical applications.