Effects of Selective Serotonin Reuptake Inhibitors on Interregional Relation of Serotonin Transporter Availability in Major Depression

Shared and unique transcriptomic signatures of antidepressant and probiotics action in the mammalian brain

Understanding the shared and divergent mechanisms across antidepressant (AD) classes and probiotics is critical for improving treatment for mood disorders. Here we examine the transcriptomic effects of bupropion (NDRI), desipramine (SNRI), fluoxetine (SSRI) and a probiotic formulation (Lacidofil®) on 10 regions across the mammalian brain. These treatments massively alter gene expression (on average, 2211 differentially expressed genes (DEGs) per region-treatment combination), highlighting the biological complexity of AD and probiotic action. Intersection of DEG sets against neuropsychiatric GWAS loci, sex-specific transcriptomic portraits of major depressive disorder (MDD), and mouse models of stress and depression reveals significant similarities and differences across treatments. Interestingly, molecular responses in the infralimbic cortex, basolateral amygdala and locus coeruleus are region-specific and highly similar across treatments, whilst responses in the Raphe, medial preoptic area, cingulate cortex, prelimbic cortex and ventral dentate gyrus are predominantly treatment-specific. Mechanistically, ADs concordantly downregulate immune pathways in the amygdala and ventral dentate gyrus. In contrast, protein synthesis, metabolism and synaptic signaling pathways are axes of variability among treatments. We use spatial transcriptomics to further delineate layer-specific molecular pathways and DEGs within the prefrontal cortex. Our study reveals complex AD and probiotics action on the mammalian brain and identifies treatment-specific cellular processes and gene targets associated with mood disorders.

Effects of gender-affirming hormone therapy on gray matter density, microstructure and monoamine oxidase A levels in transgender subjects

MAO-A catalyzes the oxidative degradation of monoamines and is thus implicated in sex-specific neuroplastic processes that influence gray matter (GM) density (GMD) and microstructure (GMM). Given the exact monitoring of plasma hormone levels and sex steroid intake, transgender individuals undergoing gender-affirming hormone therapy (GHT) represent a valuable cohort to potentially investigate sex steroid-induced changes of GM and concomitant MAO-A density. Here, we investigated the effects of GHT over a median time period of 4.5 months on GMD and GMM as well as MAO-A distribution volume. To this end, 20 cisgender women, 11 cisgender men, 20 transgender women and 10 transgender men underwent two MRI scans in a longitudinal design. PET scans using [11C]harmine were performed before each MRI session in a subset of 35 individuals. GM changes determined by diffusion weighted imaging (DWI) metrics for GMM and voxel based morphometry (VBM) for GMD were estimated using repeated measures ANOVA. Regions showing significant changes of both GMM and GMD were used for the subsequent analysis of MAO-A density. These involved the fusiform gyrus, rolandic operculum, inferior occipital cortex, middle and anterior cingulum, bilateral insula, cerebellum and the lingual gyrus (post-hoc tests: pFWE+Bonferroni < 0.025). In terms of MAO-A distribution volume, no significant effects were found. Additionally, the sexual desire inventory (SDI) was applied to assess GHT-induced changes in sexual desire, showing an increase of SDI scores among transgender men. Changes in the GMD of the bilateral insula showed a moderate correlation to SDI scores (rho = - 0.62, pBonferroni = 0.047). The present results are indicative of a reliable influence of gender-affirming hormone therapy on 1) GMD and GMM following an interregional pattern and 2) sexual desire specifically among transgender men.

PET-based brain molecular connectivity in neurodegenerative disease

PURPOSE OF REVIEW

Molecular imaging has traditionally been used and interpreted primarily in the context of localized and relatively static neurochemical processes. New understanding of brain function and development of novel molecular imaging protocols and analysis methods highlights the relevance of molecular networks that co-exist and interact with functional and structural networks. Although the concept and evidence of disease-specific metabolic brain patterns has existed for some time, only recently has such an approach been applied in the neurotransmitter domain and in the context of multitracer and multimodal studies. This review briefly summarizes initial findings and highlights emerging applications enabled by this new approach.

RECENT FINDINGS

Connectivity based approaches applied to molecular and multimodal imaging have uncovered molecular networks with neurodegeneration-related alterations to metabolism and neurotransmission that uniquely relate to clinical findings; better disease stratification paradigms; an improved understanding of the relationships between neurochemical and functional networks and their related alterations, although the directionality of these relationships are still unresolved; and a new understanding of the molecular underpinning of disease-related alteration in resting-state brain activity.

SUMMARY

Connectivity approaches are poised to greatly enhance the information that can be extracted from molecular imaging. While currently mostly contributing to enhancing understanding of brain function, they are highly likely to contribute to the identification of specific biomarkers that will improve disease management and clinical care.

Structure-function coupling and hierarchy-specific antidepressant response in major depressive disorder

BACKGROUND

Extensive research has explored altered structural and functional networks in major depressive disorder (MDD). However, studies examining the relationships between structure and function yielded heterogeneous and inconclusive results. Recent work has suggested that the structure-function relationship is not uniform throughout the brain but varies across different levels of functional hierarchy. This study aims to investigate changes in structure-function couplings (SFC) and their relevance to antidepressant response in MDD from a functional hierarchical perspective.

METHODS

We compared regional SFC between individuals with MDD (n = 258) and healthy controls (HC, n = 99) using resting-state functional magnetic resonance imaging and diffusion tensor imaging. We also compared antidepressant non-responders (n = 55) and responders (n = 68, defined by a reduction in depressive severity of >50%). To evaluate variations in altered and response-associated SFC across the functional hierarchy, we ranked significantly different regions by their principal gradient values and assessed patterns of increase or decrease along the gradient axis. The principal gradient value, calculated from 219 healthy individuals in the Human Connectome Project, represents a region's position along the principal gradient axis.

RESULTS

Compared to HC, MDD patients exhibited increased SFC in unimodal regions (lower principal gradient) and decreased SFC in transmodal regions (higher principal gradient) (p < 0.001). Responders primarily had higher SFC in unimodal regions and lower SFC in attentional networks (median principal gradient) (p < 0.001).

CONCLUSIONS

Our findings reveal opposing SFC alterations in low-level unimodal and high-level transmodal networks, underscoring spatial variability in MDD pathology. Moreover, hierarchy-specific antidepressant effects provide valuable insights into predicting treatment outcomes.

Serotonin transporter availability in physically aggressive personality disordered patients: associations with trait and state aggression, and response to fluoxetine

RATIONALE

Characterizing the neuroanatomical basis of serotonergic abnormalities in severe, chronic, impulsive aggression will allow for rational treatment selection, development of novel therapeutics, and biomarkers to identify at-risk individuals.

OBJECTIVES

The aim of this study is to identify associations between regional serotonin transporter (5-HTT) availability and trait and state aggression, as well as response to the anti-aggressive effects of fluoxetine.

METHODS

We examined 5-HTT availability using positron emission tomography (PET) imaging with [¹¹C]DASB in personality disordered patients with current physical intermittent explosive disorder (IED; n = 18), and healthy comparison participants (HC; n = 11), in the anterior cingulate cortex (ACC), amygdala (AMY), ventral striatum (VST), and midbrain (MID). After PET imaging, IED patients were treated with fluoxetine 20 mg daily (n = 9) or placebo (n = 6) for 12 weeks. Trait and state aggression, trait callousness, and childhood trauma were assessed.

RESULTS

In IED patients, trait aggression was positively associated with [¹¹C]DASB binding in the ACC and VST; covarying for trait callousness and childhood trauma enhanced these correlations. Baseline state aggression was positively correlated with ACC [¹¹C]DASB in IED patients. Greater baseline VST [¹¹C]DASB binding predicted greater decreases in state aggression with fluoxetine treatment.

CONCLUSIONS

Consistent with prior reports, ACC 5-HTT is related to trait aggression, and adjusting for factors related to proactive (callousness) and reactive (childhood trauma) aggression subtypes further resolves this relationship. Novel findings of the study include a better understanding of the association between regional 5-HTT availability and state aggression, and the involvement of VST 5-HTT with trait aggression, and with the anti-aggressive effects of fluoxetine.

Enhanced availability of serotonin limits muscle activation during high-intensity, but not low-intensity, fatiguing contractions

Serotonin (5-HT) modulates motoneuron excitability during muscle contractions, where the release of 5-HT in the central nervous system (CNS) is linked to the intensity of physical activity. Although there is evidence that enhanced availability of 5-HT can exacerbate fatigue, these effects on the development of fatigue during different contraction intensities are largely unknown. The purpose of this study was to investigate how enhanced 5-HT availability affects voluntary muscle activation and corticospinal excitability during fatigue-inducing contractions. Two experiments were performed. In the first experiment (n = 11), twelve isometric elbow flexions at 20% maximal voluntary contractions (MVC) were performed for 2-min each with 40-s rest periods. In the second experiment (n = 14), twelve maximal isometric elbow flexions were held for 10-s each with 40-s rest periods. In both experiments, the selective serotonin reuptake inhibitor (20 mg paroxetine), or a placebo, was administered in a two-way crossover-design. Muscle responses to transcranial magnetic stimulation (TMS) of the motor cortex (both experiments 1 and 2), as well as motor point stimulation of the elbow flexors (experiment 2) were assessed. Paroxetine reduced both motor cortical (p = 0.018) and motor point voluntary activation (p = 0.036) during the maximal contraction protocol. Paroxetine also reduced exercise-induced lengthening of the TMS silent period during the submaximal (p = 0.037) and maximal (p = 0.002) contraction protocols. Activation of inhibitory 5-HT_1A receptors on motoneurons likely exacerbated exercise-induced reductions in voluntarily drive to the elbow flexors. However, 5-HT modulation of motor activity also appeared at the supraspinal level.

Anxiolytic and antidepressants' effect of Crataegus pinnatifida (Shan Zha): biochemical mechanisms

Depression and anxiety disorders are highly prevalent. Selective serotonin reuptake inhibitors (SSRIs) are the current first-line treatment for depression, but they have pronounced limitations. Traditional Chinese medicine can serve as a safe and effective alternative to conventional drugs, particularly since many herbal remedies have already been approved for human use as food additives, making the transition from bench to bedside more efficient. We previously demonstrated that a novel herbal treatment (NHT) induces anxiolytic- and antidepressant-like effects. NHT consists of four herbs: Crataegus pinnatifida (Shan Zha), Triticum aestivum (Fu Xiao Mai), Lilium brownii (Baihe), and the fruit of Ziziphus jujuba (Da Zao). In the current study, we examined the antidepressant-like and anxiolytic-like activities of each individual herb on stressed mice and compared those to the effects of NHT and escitalopram. We show here that Shan Zha is sufficient to produce an anxiolytic and antidepressant-like effect similar to NHT or the escitalopram through activation of 5-HT1A receptor and an elevation in BDNF levels in the hippocampus and Pre-frontal cortex (PFC). Chronic treatment with Shan Zha did not alter serotonin transporter levels in the PFC, as opposed to escitalopram treatment. These results were confirmed in vitro, as none of the herbs blocked SERT activity in Xenopus oocytes. Notably, Shan Zha is sold as a nutritional supplement; thus, its transition to clinical trials can be easier. Once its efficacy and safety are substantiated, Shan Zha may serve as an alternative to conventional antidepressants.

Neurotransmitter Dysfunction in Irritable Bowel Syndrome: Emerging Approaches for Management

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder whose aetiology is still unknown. Most hypotheses point out the gut-brain axis as a key factor for IBS. The axis is composed of different anatomic and functional structures intercommunicated through neurotransmitters. However, the implications of key neurotransmitters such as norepinephrine, serotonin, glutamate, GABA or acetylcholine in IBS are poorly studied. The aim of this review is to evaluate the current evidence about neurotransmitter dysfunction in IBS and explore the potential therapeutic approaches. IBS patients with altered colorectal motility show augmented norepinephrine and acetylcholine levels in plasma and an increased sensitivity of central serotonin receptors. A decrease of colonic mucosal serotonin transporter and a downregulation of α2 adrenoceptors are also correlated with visceral hypersensitivity and an increase of 5-hydroxyindole acetic acid levels, enhanced expression of high affinity choline transporter and lower levels of GABA. Given these neurotransmitter dysfunctions, novel pharmacological approaches such as 5-HT₃ receptor antagonists and 5-HT₄ receptor agonists are being explored for IBS management, for their antiemetic and prokinetic effects. GABA-analogous medications are being considered to reduce visceral pain. Moreover, agonists and antagonists of muscarinic receptors are under clinical trials. Targeting neurotransmitter dysfunction could provide promising new approaches for IBS management.

Functional connectivity within an anxiety network and associations with anxiety symptom severity in middle-aged adults with and without autism

Anxiety is highly prevalent in autism spectrum disorders (ASDs). However, few functional magnetic resonance imaging (fMRI) studies of ASDs have focused on anxiety (and fewer still on anxiety in middle-aged adults). Thus, relationships between atypical connectivity and anxiety in this population are poorly understood. The current study contrasted functional connectivity within anxiety network regions across adults (40-64 years) with and without autism, and tested for group by functional connectivity interactions on anxiety. Twenty-two adults with ASDs (16 males) and 26 typical control (TC) adults (22 males) completed the Beck Anxiety Inventory and a resting-state fMRI scan. An anxiety network consisting of 12 regions of interest was defined, based on a meta-analysis in TC individuals and two studies on anxiety in ASDs. We tested for main effects of group and group by anxiety interactions on connectivity within this anxiety network, controlling for head motion using ANCOVA. Results are reported at an FDR adjusted threshold of q < 0.1 (corrected) and p < 0.05 (uncorrected). Adults with ASDs showed higher anxiety and underconnectivity within the anxiety network, mostly involving bilateral insula. Connectivity within the anxiety network in the ASD group showed distinct relationships with anxiety symptoms that did not relate to ASD symptom severity. Functional connectivity involving the bilateral posterior insula was positively correlated with anxiety in the ASD (but not the TC) group. Increased anxiety in middle-aged adults with ASD is associated with atypical functional connectivity, predominantly involving bilateral insula. Results were not related to ASD symptom severity suggesting independence of anxiety-related effects. LAY SUMMARY: Anxiety is very common in adults with autism but the brain basis of this difference is not well understood. We compared functional connectivity between anxiety-related brain regions in middle-aged adults with and without autism. Adults with autism were more anxious and showed weaker functional connections between these regions. Some relationships between functional connectivity and higher anxiety were specific to the autism group. Results suggest that anxiety functions differently in autism.

Beneficial and harmful effects of antidepressants versus placebo, 'active placebo', or no intervention for adults with major depressive disorder: a protocol for a systematic review of published and unpublished data with meta-analyses and trial sequential analyses

BACKGROUND

Major depressive disorder is one of the most common, burdensome, and costly psychiatric disorders worldwide. Antidepressants are frequently used to treat major depressive disorder. It has been shown repeatedly that antidepressants seem to reduce depressive symptoms with a statistically significant effect, but the clinical importance of the effect sizes seems questionable. Both beneficial and harmful effects of antidepressants have not previously been sufficiently assessed. The main objective of this review will be to evaluate the beneficial and harmful effects of antidepressants versus placebo, 'active placebo', or no intervention for adults with major depressive disorder.

METHODS/DESIGN

A systematic review with meta-analysis will be reported as recommended by Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA), bias will be assessed with the Cochrane Risk of Bias tool-version 2 (ROB2), our eight-step procedure will be used to assess if the thresholds for clinical significance are crossed, Trial Sequential Analysis will be conducted to control for random errors, and the certainty of the evidence will be assessed with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. To identify relevant trials, we will search both for published and unpublished trials in major medical databases from their inception to the present. Clinical study reports will be obtained from regulatory authorities and pharmaceutical companies. Two review authors will independently screen the results of the literature searches, extract data, and perform risk of bias assessment. We will include any published or unpublished randomised clinical trial comparing one or more antidepressants with placebo, 'active placebo', or no intervention for adults with major depressive disorder. The following active agents will be included: agomelatine, amineptine, amitriptyline, bupropion, butriptyline, cianopramine, citalopram, clomipramine, dapoxetine, demexiptiline, desipramine, desvenlafaxine, dibenzepin, dosulepin, dothiepin, doxepin, duloxetine, escitalopram, fluoxetine, fluvoxamine, imipramine, iprindole, levomilnacipran, lofepramine, maprotiline, melitracen, metapramine, milnacipran, mirtazapine, nefazodone, nortriptyline, noxiptiline, opipramol, paroxetine, protriptyline, quinupramine, reboxetine, sertraline, trazodone, tianeptine, trimipramine, venlafaxine, vilazodone, and vortioxetine. Primary outcomes will be depressive symptoms, serious adverse events, and quality of life. Secondary outcomes will be suicide or suicide attempt, suicidal ideation, and non-serious adverse events.

DISCUSSION

As antidepressants are commonly used to treat major depressive disorder in adults, a systematic review evaluating their beneficial and harmful effects is urgently needed. This review will inform best practice in treatment and clinical research of this highly prevalent and burdensome disorder.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42020220279.

Effects of SSRI treatment on GABA and glutamate levels in an associative relearning paradigm

Impaired cognitive flexibility represents a widespread symptom in psychiatric disorders, including major depressive disorder (MDD), a disease, characterized by an imbalance of neuro-transmitter concentrations. While memory formation is mostly associated with glutamate, also gamma-Aminobutyric acid (GABA) and serotonin show attributions in a complex interplay between neurotransmitter systems. Treatment with selective serotonin reuptake inhibitors (SSRIs) does not solely affect the serotonergic system but shows downstream effects on GABA- and glutamatergic neurotransmission, potentially helping to restore cognitive function via neuroplastic effects. Hence, this study aims to elaborate the effects of associative relearning and SSRI treatment on GABAergic and glutamatergic function within and between five brain regions using magnetic resonance spectroscopy imaging (MRSI).

In this study, healthy subjects were randomized into four groups which underwent three weeks of an associative relearning paradigm, with or without emotional connotation, under SSRI (10mg escitalopram) or placebo administration. MRSI measurements, using a spiral-encoded, 3D-GABA-edited MEGA-LASER sequence at 3T, were performed on the first and last day of relearning. Mean GABA+/tCr (GABA+ = GABA + macromolecules; tCr = total creatine) and Glx/tCr (Glx = glutamate + glutamine) ratios were quantified in a ROI-based approach for the hippocampus, insula, putamen, pallidum and thalamus, using LCModel. A total of 66 subjects ((37 female, mean age ± SD = 25.4±4.7) for Glx/tCr and 58 subjects (32 female, mean age ± SD = 25.1±4.7) for GABA+/tCr were included in the final analysis.

A significant measurement by region and treatment (SSRI vs placebo) interaction on Glx/tCr ratios was found (p_cor=0.017), with post hoc tests confirming differential effects on hippocampus and thalamus (p_cor=0.046). Moreover, treatment by time comparison, for each ROI independently, showed a reduction of hippocampal Glx/tCr ratios after SSRI treatment (p_uncor=0.033). No significant treatment effects on GABA+/tCr ratios or effects of relearning condition on any neurotransmitter ratio could be found.

Here, we showed a significant SSRI- and relearning-driven interaction effect of hippocampal and thalamic Glx/tCr levels, suggesting differential behavior based on different serotonin transporter and receptor densities. Moreover, an indication for Glx/tCr adaptions in the hippocampus after three weeks of SSRI treatment could be revealed. Our findings are in line with animal studies reporting glutamate adaptions in the hippocampus following chronic SSRI intake. Due to the complex interplay of serotonin and hippocampal function, involving multiple serotonin receptor subtypes on glutamatergic cells and GABAergic interneurons, the interpretation of underlying neurobiological actions remains challenging.

Depressive-like state sensitizes 5-HT1A and 5-HT1B auto-receptors in the dorsal raphe nucleus sub-system

Dorsal raphe (DR) and median raphe (MR) 5-HT neurons are two distinct sub-systems known to be regulated by 5-HT_1A and 5-HT_1B auto-receptors. Whether the auto-receptors in each sub-system are functionally altered in depressive-like state remains unknown. The present study is aimed to study a specific circuit (DR-ventral hippocampus and MR-dorsal hippocampus) within each sub-system to investigate changes in receptor sensitivity in the pathogenesis of depression. A mouse model of depression was developed through the social defeat paradigm, and was then treated with fluoxetine (FLX). 5-HT_1A auto-receptor in the neuronal cell body (DR or MR) and 5-HT_1B auto-receptor in the axonal terminal (ventral or dorsal hippocampus) were directly targeted by local perfusion of antagonists (5-HT_1A: WAY100635; 5-HT_1B: GR127935) through reverse microdialysis. Time courses of dialysate 5-HT measured at the axonal terminal were subsequently determined for each circuit. At baseline, 5-HT_1A and 5-HT_1B antagonists dose-dependently increased dialysate 5-HT, with sub-circuit specificity. In the depressive-like state, greater increases in dialysate 5-HT were observed only in the DR-ventral hippocampus circuit following local delivery of both antagonists, which were then fully restored following the FLX treatment. In contrast, no changes were observed in the MR-dorsal hippocampus circuit. Our results demonstrate differential changes in sensitivities of 5-HT_1A and 5-HT_1B auto-receptors in the DR-ventral hippocampus and MR-dorsal hippocampus circuits. 5-HT_1A and 5-HT_1B auto-receptors in the DR-ventral hippocampus circuit are sensitized in the depressive-like state. Taken together, these results suggest that the DR sub-system maybe the neural substrate mediating depressive phenotypes.

Optimization of preprocessing strategies in Positron Emission Tomography (PET) neuroimaging: A [11C]DASB PET study

Positron Emission Tomography (PET) is an important neuroimaging tool to quantify the distribution of specific molecules in the brain. The quantification is based on a series of individually designed data preprocessing steps (pipeline) and an optimal preprocessing strategy is per definition associated with less noise and improved statistical power, potentially allowing for more valid neurobiological interpretations. In spite of this, it is currently unclear how to design the best preprocessing pipeline and to what extent the choice of each preprocessing step in the pipeline minimizes subject-specific errors. To evaluate the impact of various preprocessing strategies, we systematically examined 384 different pipeline strategies in data from 30 healthy participants scanned twice with the serotonin transporter (5-HTT) radioligand [¹¹C]DASB. Five commonly used preprocessing steps with two to four options were investigated: (1) motion correction (MC) (2) co-registration (3) delineation of volumes of interest (VOI's) (4) partial volume correction (PVC), and (5) kinetic modeling. To quantitatively compare and evaluate the impact of various preprocessing strategies, we used the performance metrics: test-retest bias, within- and between-subject variability, the intraclass-correlation coefficient, and global signal-to-noise ratio. We also performed a power analysis to estimate the required sample size to detect either a 5% or 10% difference in 5-HTT binding as a function of preprocessing pipeline. The results showed a complex downstream dependency between the various preprocessing steps on the performance metrics. The choice of MC had the most profound effect on 5-HTT binding, prior to the effects caused by PVC and kinetic modeling, and the effects differed across VOI's. Notably, we observed a negative bias in 5-HTT binding across test and retest in 98% of pipelines, ranging from 0 to 6% depending on the pipeline. Optimization of the performance metrics revealed a trade-off in within- and between-subject variability at the group-level with opposite effects (i.e. minimization of within-subject variability increased between-subject variability and vice versa). The sample size required to detect a given effect size was also compromised by the preprocessing strategy, resulting in up to 80% increases in sample size needed to detect a 5% difference in 5-HTT binding. This is the first study to systematically investigate and demonstrate the effect of choosing different preprocessing strategies on the outcome of dynamic PET studies. We provide a framework to show how optimal and maximally powered neuroimaging results can be obtained by choosing appropriate preprocessing strategies and we provide recommendations depending on the study design. In addition, the results contribute to a better understanding of methodological uncertainty and variability in preprocessing decisions for future group- and/or longitudinal PET studies.

Making Sense of Connectivity

In addition to the assessment of local alterations of specific brain regions, the investigation of entire networks with in vivo neuroimaging techniques has gained increasing attention. In general, connectivity analysis refers to the investigation of links between brain regions, with the aim to characterize their interactions and information transfer. These may represent or relate to different physiological characteristics (structural, functional, or metabolic information) and can be calculated across different levels of granularity (2 regions vs whole brain). In this article, we provide an overview of different connectivity analysis approaches with interpretations and limitations as well as examples in pharmacological imaging and clinical applications. Structural connectivity obtained from diffusion MRI enables the reconstruction of neuronal fiber tracts. These physical links represent major constraints of functional connections, which are in turn defined as correlations between signal time courses. In addition, molecular connectivity approaches based on PET imaging enable the assessment of interregional associations of metabolic demands and neurotransmitter systems. Application of these approaches in clinical investigations has demonstrated novel alterations in various neurological and psychiatric disorders on a network level. Future work should aim for the combined assessment of multiple imaging modalities and to establish robust biomarkers for clinical use. These advancements will further improve the biological interpretation of connectivity metrics and networks of the human brain.

Antidepressant Effect of Tetragonia tetragonoides (Pall.) Kuntze Extract on Serotonin Turnover

Tetragonia tetragonoides (Pall.) Kuntze (TTK) is a groundcover found along coastal areas of the Korean peninsula. TTK is traditionally used to improve women's health and treat gastrointestinal diseases. Use of herbal medicines in the treatment of mood disorders has recently been suggested as an alternative therapeutic strategy. In the present study, we determined that consumption of TTK extract ameliorated progression of depressive-like symptoms in ovariectomized (OVX) rats and further examined the mechanisms involved, i.e., synthesis, release, and reuptake(s) of serotonin (also known as 5-HT). We assessed the mRNA expression levels of tryptophan hydroxylases (TPH-1 and TPH-2) and serotonin transporter (SERT) as well as the reuptake activity of serotonin in RBL-2H3 cells. We also determined whether or not TTK extract regulates the serum level of serotonin and improves depressive-like symptoms in 0.5, 1, and 2% TTK-fed OVX female rats in a forced swimming test. Our results show that the mRNA levels of TPH-1 and SERT were significantly reduced, whereas the mRNA level of TPH-2 was dose-dependently elevated by TTK (50 and 100 μg/mL) in RBL-2H3 cells. TTK significantly inhibited LPS- (lipopolysaccharide-) induced serotonin uptake in RBL-2H3 cells in a dose-dependent manner. The serum level(s) of serotonin was elevated by 1% and 2% TTK treatment in OVX female rats. Moreover, immobility time in the forced swimming test was reduced by 1% and 2% TTK treatment but not altered by 0.5% TTK treatment in OVX female rats. Taken together, these results indicate that TTK may significantly inhibit depressive-like symptoms due to upregulation of serotonin level(s) and regulation of serotonin reuptake activity. Thus, TTK may exert beneficial effects on depression during pre- or/and postmenopausal periods via modulation of serotonin synthesis and metabolism.

Cerebral serotonin transporter measurements with [11C]DASB: A review on acquisition and preprocessing across 21 PET centres

Positron Emission Tomography (PET) imaging has become a prominent tool to capture the spatiotemporal distribution of neurotransmitters and receptors in the brain. The outcome of a PET study can, however, potentially be obscured by suboptimal and/or inconsistent choices made in complex processing pipelines required to reach a quantitative estimate of radioligand binding. Variations in subject selection, experimental design, data acquisition, preprocessing, and statistical analysis may lead to different outcomes and neurobiological interpretations. We here review the approaches used in 105 original research articles published by 21 different PET centres, using the tracer [¹¹C]DASB for quantification of cerebral serotonin transporter binding, as an exemplary case. We highlight and quantify the impact of the remarkable variety of ways in which researchers are currently conducting their studies, while implicitly expecting generalizable results across research groups. Our review provides evidence that the foundation for a given choice of a preprocessing pipeline seems to be an overlooked aspect in modern PET neuroscience. Furthermore, we believe that a thorough testing of pipeline performance is necessary to produce reproducible research outcomes, avoiding biased results and allowing for better understanding of human brain function.

Brain and behavioral correlates of insulin resistance in youth with depression and obesity

Depression, together with insulin resistance, is increasingly prevalent among youth. These conditions have traditionally been compartmentalized, but recent evidence suggests that a shared brain motivational network underlies their co-occurrence. We posit that, in the context of depressive symptoms, insulin resistance is associated with aberrant structure and functional connectivity in the Anterior Cingulate Cortex (ACC) and hippocampus. This motivational neural circuit underlies dysfunctional behavioral responses and increased sensitivity to rewarding aspects of ingesting high calorie food that lead to disinhibition of eating even when satiated. To investigate this shared mechanism, we evaluated a sample of forty-two depressed and overweight (BMI > 85th%) youth aged 9 to 17. Using ACC and hippocampus structural and seed-based regions of interest, we investigated associations between insulin resistance, depression, structure (ACC thickness, and ACC and hippocampal area), and resting-state functional connectivity (RSFC). We predicted that aberrant associations among these neural and behavioral characteristics would be stronger in insulin resistant compared to insulin sensitive youth. We found that youth with greater insulin resistance had higher levels of anhedonia and more food seeking behaviors, reduced hippocampal and ACC volumes, and greater levels of ACC and hippocampal dysconnectivity to fronto-limbic reward networks at rest. For youth with high levels of insulin resistance, thinner ACC and smaller hippocampal volumes were associated with more severe depressive symptoms, whereas the opposite was true for youth with low levels of insulin resistance. The ACC-hippocampal motivational network that subserves depression and insulin resistance separately, may represent a critical neural interaction that link these syndromes together.

Parcellation of the Human Cerebral Cortex Based on Molecular Targets in the Serotonin System Quantified by Positron Emission Tomography In vivo

Parcellation of distinct areas in the cerebral cortex has a long history in neuroscience and is of great value for the study of brain function, specialization, and alterations in neuropsychiatric disorders. Analysis of cytoarchitectonical features has revealed their close association with molecular profiles based on protein density. This provides a rationale for the use of in vivo molecular imaging data for parcellation of the cortex with the advantage of whole-brain coverage. In the current work, parcellation was based on expression of key players of the serotonin neurotransmitter system. Positron emission tomography was carried out for the quantification of serotonin 1A (5-HT1A, n = 30) and 5-HT2A receptors (n = 22), the serotonin-degrading enzyme monoamine oxidase A (MAO-A, n = 32) and the serotonin transporter (5-HTT, n = 24) in healthy participants. Cortical protein distribution maps were obtained using surface-based quantification. Based on k-means clustering, silhouette criterion and bootstrapping, five distinct clusters were identified as the optimal solution. The defined clusters proved of high explanatory value for the effects of psychotropic drugs acting on the serotonin system, such as antidepressants and psychedelics. Therefore, the proposed method constitutes a sensible approach towards integration of multimodal imaging data for research and development in neuropharmacology and psychiatry.

Alteration of the affective modulation of the startle reflex during antidepressant treatment

Whereas the amplitude of the startle reflex varies with stimulus valence in the normal population, a lack of this affective modulation has been reported in patients with major depressive disorder. The present study sought to clarify blunted startle modulation as a feature of depression by comparing 16 patients diagnosed with major depression prior to and after 2 weeks of SSRI treatment, and 16 healthy controls. The affect-modulated startle reflex paradigm and the Self-Assessment Manikin were used to probe affective reactivity. In addition, a preliminary analysis of change in affective reactivity pattern was performed with depressed patients who could be assessed in the eighth week of treatment (n = 13). The control group showed a linear trend in response across valence categories, which was stable over sessions. Blunted affective reactivity was observed only in the patients and persisted after 2 weeks of treatment. Nevertheless, a linear trend could be detected in the eighth week of treatment. These findings confirm that the affective reactivity is blunted in depression and provide initial evidence for the lack of change in the early phase of SSRI antidepressant treatment. Nevertheless, in a small group, the emergence of a linear trend in response was evident later with treatment. Large-scale studies are required to assess the relation between the treatment response and the change in affective modulation of the startle reflex, as a potential biomarker.

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.

The anti-inflammatory mechanism of antidepressants - SSRIs, SNRIs

The cytokine theory of depression no longer brings about any doubts. Experiments and research studies conducted in the last ten years have confirmed that both physical and psychological (emotional) stress increases the likelihood of occurrence of mental disorders (including depressive disorders) owing to the action of a series of hormonal and biochemical mechanisms. Selective serotonin reuptake inhibitors (SSRI) as well as serotonin and norepinephrine reuptake inhibitors (SNRIs) are some of the most commonly applied drugs in the world during pharmacotherapy of recurrent depressive disorder. The underestimated anti-inflammatory and anti-oxidative effect may be one of the potential mechanisms of action of the preparations mentioned above. The detailed specificity of action of this mechanism still remains unknown. The aim of our work will be to perform a review of contemporary literature in order to present the latest scientific reports regarding the anti-inflammatory effects of SSRIs and SNRIs. The mechanism of anti-inflammatory action may serve as a possible explanation for the efficacy of antidepressants from the groups of SSRIs and SNRIs.

Understanding the pathophysiology of depression: From monoamines to the neurogenesis hypothesis model - are we there yet?

A number of factors (biogenic amine deficiency, genetic, environmental, immunologic, endocrine factors and neurogenesis) have been identified as mechanisms which provide unitary explanations for the pathophysiology of depression. Rather than a unitary construct, the combination and linkage of these factors have been implicated in the pathogenesis of depression. That is, environmental stressors and heritable genetic factors acting through immunologic and endocrine responses initiate structural and functional changes in many brain regions, resulting in dysfunctional neurogenesis and neurotransmission which then manifest as a constellation of symptoms which present as depression.

Cyclodextrins improving the physicochemical and pharmacological properties of antidepressant drugs: a patent review

INTRODUCTION

Depression is a serious mood disorder and is one of the most common mental illnesses. Despite the availability of several classes of antidepressants, a substantial percentage of patients are unresponsive to these drugs, which have a slow onset of action in addition to producing undesirable side effects. Some scientific evidence suggests that cyclodextrins (CDs) can improve the physicochemical and pharmacological profile of antidepressant drugs (ADDs). The purpose of this paper is to disclose current data technology prospects involving antidepressant drugs and cyclodextrins.

AREAS COVERED

We conducted a patent review to evaluate the antidepressive activity of the compounds complexed in CDs, and we analyzed whether these complexes improved their physicochemical properties and pharmacological action. The present review used 8 specialized patent databases for patent research, using the term 'cyclodextrin' combined with 'antidepressive agents' and its related terms. We found 608 patents. In the end, considering the inclusion criteria, 27 patents reporting the benefits of complexation of ADDs with CDs were included.

EXPERT OPINION

The use of CDs can be considered an important tool for the optimization of physicochemical and pharmacological properties of ADDs, such as stability, solubility and bioavailability.