Effects of HTR1A C(-1019)G on amygdala reactivity and trait anxiety

5-HTP inhibits eosinophilia via intracellular endothelial 5-HTRs; SNPs in 5-HTRs associate with asthmatic lung function

Background

Previous research showed that 5-hydroxytryptophan (5HTP), a metabolic precursor of serotonin, reduces allergic lung inflammation by inhibiting eosinophil migration across endothelial monolayers.

Objective

It is unknown if serotonin receptors are involved in mediating this 5HTP function or if serotonin receptor (HTR) single nucleotide polymorphisms (SNPs) associate with lung function in humans.

Methods

Serotonin receptor subtypes were assessed by qPCR, western blot, confocal microscopy, pharmacological inhibitors and siRNA knockdown. HTR SNPs were assessed in two cohorts.

Results

Pharmacological inhibition or siRNA knockdown of the serotonin receptors HTR1A or HTR1B in endothelial cells abrogated the inhibitory effects of 5HTP on eosinophil transendothelial migration. In contrast, eosinophil transendothelial migration was not inhibited by siRNA knockdown of HTR1A or HTR1B in eosinophils. Surprisingly, these HTRs were intracellular in endothelial cells and an extracellular supplementation with serotonin did not inhibit eosinophil transendothelial migration. This is consistent with the inability of serotonin to cross membranes, the lack of selective serotonin reuptake receptors on endothelial cells, and the studies showing minimal impact of selective serotonin reuptake inhibitors on asthma. To extend our HTR studies to humans with asthma, we examined the CHIRAH and GALA cohorts for HTR SNPs that affect HTR function or are associated with behavior disorders. A polygenic index of SNPs in HTRs was associated with lower lung function in asthmatics.

Conclusions

Serotonin receptors mediate 5HTP inhibition of transendothelial migration and HTR SNPs associate with lower lung function. These results may serve to aid in design of novel interventions for allergic inflammation.

5-HT1A Receptors on Dentate Gyrus Granule Cells Confer Stress Resilience

BACKGROUND

Hyperactivity of granule cells in the ventral dentate gyrus (vDG) promotes vulnerability to chronic stress. However, which receptors in the vDG could be targeted to inhibit this hyperactivity and confer stress resilience is not known. The serotonin 1A receptor (5-HT1AR) is a Gi protein-coupled inhibitory receptor that has been implicated in stress adaptation, anxiety, depression, and antidepressant responses. 5-HT1ARs are highly expressed in the DG, but their potential to promote stress resilience by regulating granule cell activity has never been examined.

METHODS

We exposed male and female mice expressing 5-HT1ARs only in DG granule cells to 10 days of chronic social defeat stress (CSDS) and treated them with the 5-HT1AR agonist 8-OH-DPAT every day 30 minutes before each defeat throughout the CSDS paradigm. We then used whole-cell current clamp recordings, immunohistochemistry for the immediate early gene cFos, corticosterone immunoassays, and behavioral testing to determine how activating 5-HT1ARs on granule cells affects DG activity, neuroendocrine stress responses, and avoidance behavior.

RESULTS

We found that activating 5-HT1ARs hyperpolarized DG granule cells and reduced cFos+ granule cells in the vDG following CSDS, indicating that 5-HT1AR activation rescued stress-induced vDG hyperactivity. Moreover, 5-HT1AR activation dampened corticosterone responses to CSDS and prevented the development of stress-induced avoidance in the social interaction test and in the open field test.

CONCLUSIONS

Our findings show that activating 5-HT1ARs on DG granule cells can prevent stress-induced neuronal hyperactivity of the vDG and confer resilience to chronic stress.

Genetic variation of the 5-HT1A rs6295, 5-HT2A rs6311, and CNR1 rs1049353 and an altered endocannabinoid system in depressed patients

BACKGROUND

The reasons for developing depression are not fully understood. However, it is known that the serotonergic system plays a role in the etiology, but the endocannabinoid system receives attention.

METHOD

In this study, 161 patients with a depressive disorder and 161 healthy participants were examined for the distribution of the CNR1 rs4940353, 5-HT2A rs6311, and 5-HT1A rs6295 by high-resolution melting genotyping. The concentration of arachidonoyl ethanolamide (AEA) and 2-arachidonoylglycerol (2-AG) in the blood was measured by liquid chromatography-tandem mass spectrometry. Additionally, depression and anxiety symptoms were evaluated based on self-questionnaires. Fifty-nine patients participated in a second appointment to measure the concentration of AEA, 2-AG, and symptoms of depression and anxiety.

RESULTS

We observed higher AEA and decreased 2-AG concentrations in patients with depression compared to healthy participants. During the treatment, the concentrations of AEA and 2-AG did not change significantly. In patients higher symptoms of anxiety correlated with lower concentrations of 2-AG. Gender differences were found concerning increased 2-AG concentration in male patients and increased anxiety symptoms in female patients. Genotypic variations of 5-HT1A rs6295 and 5-HT2A rs6311 are associated with altered serotonergic activity and serotonin content in patients.

CONCLUSION

In conclusion, it seems that the endocannabinoid system, especially the endocannabinoids 2-AG and AEA, and genetic variations of the 5-HT1A and 5-HT2A could play a role in patients with depression and may be involved in a depressive disorder.

Accumbofrontal tract integrity is related to early life adversity and feedback learning

Abuse, neglect, exposure to violence, and other forms of early life adversity (ELA) are incredibly common and significantly impact physical and mental development. While important progress has been made in understanding the impacts of ELA on behavior and the brain, the preponderance of past work has primarily centered on threat processing and vigilance while ignoring other potentially critical neurobehavioral processes, such as reward-responsiveness and learning. To advance our understanding of potential mechanisms linking ELA and poor mental health, we center in on structural connectivity of the corticostriatal circuit, specifically accumbofrontal white matter tracts. Here, in a sample of 77 youth (Mean age = 181 months), we leveraged rigorous measures of ELA, strong diffusion neuroimaging methodology, and computational modeling of reward learning. Linking these different forms of data, we hypothesized that higher ELA would be related to lower quantitative anisotropy in accumbofrontal white matter. Furthermore, we predicted that lower accumbofrontal quantitative anisotropy would be related to differences in reward learning. Our primary predictions were confirmed, but similar patterns were not seen in control white matter tracts outside of the corticostriatal circuit. Examined collectively, our work is one of the first projects to connect ELA to neural and behavioral alterations in reward-learning, a critical potential mechanism linking adversity to later developmental challenges. This could potentially provide windows of opportunity to address the effects of ELA through interventions and preventative programming.

Stress-Related Dysfunction of Adult Hippocampal Neurogenesis-An Attempt for Understanding Resilience?

Newborn neurons in the adult hippocampus are regulated by many intrinsic and extrinsic cues. It is well accepted that elevated glucocorticoid levels lead to downregulation of adult neurogenesis, which this review discusses as one reason why psychiatric diseases, such as major depression, develop after long-term stress exposure. In reverse, adult neurogenesis has been suggested to protect against stress-induced major depression, and hence, could serve as a resilience mechanism. In this review, we will summarize current knowledge about the functional relation of adult neurogenesis and stress in health and disease. A special focus will lie on the mechanisms underlying the cascades of events from prolonged high glucocorticoid concentrations to reduced numbers of newborn neurons. In addition to neurotransmitter and neurotrophic factor dysregulation, these mechanisms include immunomodulatory pathways, as well as microbiota changes influencing the gut-brain axis. Finally, we discuss recent findings delineating the role of adult neurogenesis in stress resilience.

Oligonucleotides as therapeutic tools for brain disorders: Focus on major depressive disorder and Parkinson's disease

Remarkable advances in understanding the role of RNA in health and disease have expanded considerably in the last decade. RNA is becoming an increasingly important target for therapeutic intervention; therefore, it is critical to develop strategies for therapeutic modulation of RNA function. Oligonucleotides, including antisense oligonucleotide (ASO), small interfering RNA (siRNA), microRNA mimic (miRNA), and anti-microRNA (antagomir) are perhaps the most direct therapeutic strategies for addressing RNA. Among other mechanisms, most oligonucleotide designs involve the formation of a hybrid with RNA that promotes its degradation by activation of endogenous enzymes such as RNase-H (e.g., ASO) or the RISC complex (e.g. RNA interference - RNAi for siRNA and miRNA). However, the use of oligonucleotides for the treatment of brain disorders is seriously compromised by two main limitations: i) how to deliver oligonucleotides to the brain compartment, avoiding the action of peripheral RNAses? and once there, ii) how to target specific neuronal populations? We review the main molecular pathways in major depressive disorder (MDD) and Parkinson's disease (PD), and discuss the challenges associated with the development of novel oligonucleotide therapeutics. We pay special attention to the use of conjugated ligand-oligonucleotide approach in which the oligonucleotide sequence is covalently bound to monoamine transporter inhibitors (e.g. sertraline, reboxetine, indatraline). This strategy allows their selective accumulation in the monoamine neurons of mice and monkeys after their intranasal or intracerebroventricular administration, evoking preclinical changes predictive of a clinical therapeutic action after knocking-down disease-related genes. In addition, recent advances in oligonucleotide therapeutic clinical trials are also reviewed.

Serotonin Receptor 1A Variation Is Associated with Anxiety and Agonistic Behavior in Chimpanzees

Serotonin is a neurotransmitter that plays an important role in regulating behavior and personality in humans and other mammals. Polymorphisms in genes coding for the serotonin receptor subtype 1A (HTR1A), the serotonin transporter (SLC6A4), and the serotonin degrading enzyme monoamine oxidase A (MAOA) are associated with anxiety, impulsivity, and neurotic personality in humans. In primates, previous research has largely focused on SLC6A4 and MAOA, with few studies investigating the role of HTR1A polymorphic variation on behavior. Here, we examined variation in the coding region of HTR1A across apes, and genotyped polymorphic coding variation in a sample of 214 chimpanzees with matched measures of personality and behavior. We found evidence for positive selection at three amino acid substitution sites, one in chimpanzees-bonobos (Thr26Ser), one in humans (Phe33Val), and one in orangutans (Ala274Gly). Investigation of the HTR1A coding region in chimpanzees revealed a polymorphic site, where a C/A single nucleotide polymorphism changes a proline to a glutamine in the amino acid sequence (Pro248Gln). The substitution is located in the third intracellular loop of the receptor, a region important for serotonin signal transduction. The derived variant is the major allele in this population (frequency 0.67), and is associated with a reduction in anxiety, decreased rates of male agonistic behavior, and an increase in socio-positive behavior. These results are the first evidence that the HTR1A gene may be involved in regulating social behavior in chimpanzees and encourage further systematic investigation of polymorphic variation in other primate populations with corresponding data on behavior.

Translational Studies in the Complex Role of Neurotransmitter Systems in Anxiety and Anxiety Disorders

Discovery of innovative anxiolytics is severely hampering. Existing anxiolytics are developed decades ago and are still the therapeutics of choice. Moreover, lack of new drug targets forecasts a severe jeopardy in the future treatment of the huge population of CNS-diseased patients. We simply lack the knowledge on what is wrong in brains of anxious people (normal and diseased). Translational research, based on interacting clinical and preclinical research, is extremely urgent. In this endeavor, genetic and genomic approaches are part of the spectrum of contributing factors. We focus on three druggable targets: serotonin transporter, 5-HT_1A, and GABA_A receptors. It is still uncertain whether and how these targets are involved in normal and diseased anxiety processes. For serotonergic anxiolytics, the slow onset of action points to indirect effects leading to plasticity changes in brain systems leading to reduced anxiety. For GABA_A benzodiazepine drugs, acute anxiolytic effects are found indicating primary mechanisms directly influencing anxiety processes. Close translational collaboration between fundamental academic and discovery research will lead to badly needed breakthroughs in the search for new anxiolytics.

Exploring common changes after acute mental stress and acute tryptophan depletion: Resting-state fMRI studies

Stress and low serotonin levels are important biological factors in depression and anxiety etiologies. Although studies indicate that low serotonin levels, stress, and other factors may interact in depression/anxiety psychopathology, few studies have investigated the potentially shared neural substrates. We conducted resting-state fMRI scans pre- and post-stress task, and under control and tryptophan depletion condition, to explore the common changes induced by acute mental stress (AMS) and acute tryptophan depletion (ATD). The present study targeted regions within core brain networks - default mode network, salience network, executive control network, and emotion network - reported altered in AMS and ATD, and used regional homogeneity (ReHo) and functional connectivity (FC) analyses to explore their overlapped effects. We additionally examined the relationships among core neural networks - operationalized as an index of resource allocation bias that quantifies the shift from internal to external modes of processing. We found both manipulations induced increased ReHo of the amygdala and decreased ReHo of the posterior cingulate cortex (PCC). The PCC-amygdala FC was negatively correlated with the change of negative affect, whereas the right dorsolateral prefrontal cortex and right anterior insula FC was positively associated with anxiety level. In addition, we found that a greater shift to an external mode was correlated with higher anxiety level under both conditions. Common changes induced by acute mental stress and acute tryptophan depletion confirmed our hypothesis that AMS and ATD induce changes in common neural pathways, which in turn might mark vulnerability to depression and anxiety.

Maternal and infant characteristics connected to shared pleasure in dyadic interaction

The aim of the study was to analyze which maternal factors (depressive symptoms, effect of life events, maternal sensitivity and structuring) and infant characteristics (temperament, social withdrawal symptoms, interactive behavior, genotype, gender) contribute to shared pleasure (SP) in parent-infant interaction. Participants were 113 mother-infant dyads. The mothers filled in the Edinburgh Postnatal Depression Scale, the Infant Behavior Questionnaire, and the Life Events Questionnaire. The dyads were videotaped in a free-play situation, and the videos were analyzed using the Alarm Distress Baby Scale and the Emotional Availability Scales. The infants were genotyped for four genes involved in emotion regulation. The occurrence and duration of SP (SP-MD) in mother-infant interactions were analyzed from the videotapes. Higher maternal sensitivity and depressive symptoms, better infant responsiveness, and the infant having the GG variant of the gene tryptophan hydroxylase isoform 2 (TPH2) -307 were associated with the occurrence of SP. Lower level depressive symptoms, better maternal structuring, and greater infant involvement were associated with the longer duration of SP. Those dyads where the mother and infant were best able to read each other's positive cues and to respond to them were more likely to experience mutual positive affect, as seen in SP.

Genetic, epigenetic and posttranscriptional mechanisms for treatment of major depression: the 5-HT1A receptor gene as a paradigm

Major depression and anxiety are highly prevalent and involve chronic dysregulation of serotonin, but they remain poorly understood. Here, we review novel transcriptional (genetic, epigenetic) and posttranscriptional (microRNA, alternative splicing) mechanisms implicated in mental illness, focusing on a key serotonin-related regulator, the serotonin 1A (5-HT1A) receptor. Functional single-nucleotide polymorphisms and stress-induced DNA methylation of the 5-HT1A promoter converge to differentially alter pre- and postsynaptic 5-HT1A receptor expression associated with major depression and reduced therapeutic response to serotonergic antidepressants. Major depression is also associated with altered levels of splice factors and microRNA, posttranscriptional mechanisms that regulate RNA stability. The human 5-HT1A 3′-untranslated region is alternatively spliced, removing microRNA sites and increasing 5-HT1A expression, which is reduced in major depression and may be genotype-dependent. Thus, the 5-HT1A receptor gene illustrates the convergence of genetic, epigenetic and posttranscriptional mechanisms in gene expression, neurodevelopment and neuroplasticity, and major depression. Understanding gene regulatory mechanisms could enhance the detection, categorization and personalized treatment of major depression.

Replication in Imaging Genetics: The Case of Threat-Related Amygdala Reactivity

BACKGROUND

Low replication rates are a concern in most, if not all, scientific disciplines. In psychiatric genetics specifically, targeting intermediate brain phenotypes, which are more closely associated with putative genetic effects, was touted as a strategy leading to increased power and replicability. In the current study, we attempted to replicate previously published associations between single nucleotide polymorphisms and threat-related amygdala reactivity, which represents a robust brain phenotype not only implicated in the pathophysiology of multiple disorders, but also used as a biomarker of future risk.

METHODS

We conducted a literature search for published associations between single nucleotide polymorphisms and threat-related amygdala reactivity and found 37 unique findings. Our replication sample consisted of 1117 young adult volunteers (629 women, mean age 19.72 ± 1.25 years) for whom both genetic and functional magnetic resonance imaging data were available.

RESULTS

Of the 37 unique associations identified, only three replicated as previously reported. When exploratory analyses were conducted with different model parameters compared to the original findings, significant associations were identified for 28 additional studies: eight of these were for a different contrast/laterality; five for a different gender and/or race/ethnicity; and 15 in the opposite direction and for a different contrast, laterality, gender, and/or race/ethnicity. No significant associations, regardless of model parameters, were detected for six studies. Notably, none of the significant associations survived correction for multiple comparisons.

CONCLUSIONS

We discuss these patterns of poor replication with regard to the general strategy of targeting intermediate brain phenotypes in genetic association studies and the growing importance of advancing the replicability of imaging genetics findings.

Effects on gene expression and behavior of untagged short tandem repeats: the case of arginine vasopressin receptor 1a (AVPR1a) and externalizing behaviors

Genome-wide association studies (GWAS) of complex, heritable, behavioral phenotypes have yielded an incomplete accounting of the genetic influences. The identified loci explain only a portion of the observed heritability, and few of the loci have been shown to be functional. It is clear that current GWAS techniques overlook key components of phenotypically relevant genetic variation, either because of sample size, as is frequently asserted, or because of methodology. Here we use arginine vasopressin receptor 1a (AVPR1a) as an in-depth model of a methodologic limitation of GWAS: the functional genetic variation (in the form of short tandem repeats) of this key gene involved in affiliative behavior cannot be captured by current GWAS methodologies. Importantly, we find evidence of differential allele expression, twofold or more, in at least a third of human brain samples heterozygous for a reporter SNP in the AVPR1a transcript. We also show that this functional effect and a downstream phenotype, externalizing behavior, are predicted by AVPR1a STRs but not SNPs.

Serotonin receptor 1A promoter polymorphism, rs6295, modulates human anxiety levels via altering parasympathetic nervous activity

OBJECTIVE

The G-allele of the -1019C/G (rs6295) promoter polymorphism of the serotonin receptor 1A (HTR1A) gene has been implicated in anxiety; however, the underlying neurophysiological processes are still not fully understood. Recent evidence indicates that low parasympathetic (vagal) tone is predictive of anxiety. We thus conducted a structural equation model (SEM) to examine whether the HTR1A rs6295 variant can affect anxiety by altering parasympathetic nervous activity.

METHOD

A sample of 1141 drug-free healthy Han Chinese was recruited for HTR1A genotyping. Autonomic nervous function was assessed by short-term spectral analysis of heart rate variability (HRV). Anxiety and stress levels were evaluated by the Beck Anxiety Inventory (BAI) and the Perceived Stress Scale (PSS) respectively.

RESULTS

The number of the HTR1A G allele was inversely correlated with high-frequency power (HF), a parasympathetic index of HRV. The HF index was negatively associated with BAI scores. Furthermore, the good-fitting SEM, adjusting for confounding variables (e.g., age and PSS levels), revealed a significant pathway linking rs6295 variant to BAI scores via HF index modulation.

CONCLUSION

These results are the first to show that HTR1A -1019C/G polymorphism influences anxiety levels by modulating parasympathetic tone, providing a neurophysiological insight into the role of HTR1A in human anxiety.

The effects of stimulus novelty and negativity on BOLD activity in the amygdala, hippocampus, and bed nucleus of the stria terminalis

The amygdala responds to stimulus novelty, which may correspond to an evaluation of novel stimuli for potential threat, and trait anxiety may modulate this response. The bed nucleus of the stria terminalis (BNST) may also be sensitive to novelty as it responds to both uncertainty and threat. If so, a BNST novelty response may also be affected by trait anxiety and interact with stimulus negativity. We presented participants with novel and repeated negative and neutral images while measuring brain activity via fMRI, and assessed participants’ self-reported trait anxiety. We expected to replicate past findings of novelty responses in the hippocampus and amygdala that are independent of stimulus negativity. We also expected BNST novelty-sensitivity and that trait anxiety would predict greater sensitivity to both novelty and negativity in the amygdala and BNST, but not the hippocampus. Our a priori analyses replicated past findings of a novelty response that was independent of valence in the hippocampus and amygdala. The BNST exhibited a novelty response for negative, but not neutral, images. Trait anxiety did not modulate the response to novelty or negativity in any of the ROIs investigated. Our findings suggest that the BNST plays a role in the detection of novelty.

Key words: novelty; bed nucleus of the stria terminalis; BNST; amygdale; fMRI; BST

Effect of Citalopram on Emotion Processing in Humans: A Combined 5-HT1A [11C]CUMI-101 PET and Functional MRI Study

A subset of patients started on a selective serotonin reuptake inhibitor (SSRI) initially experience increased anxiety, which can lead to early discontinuation before therapeutic effects are manifest. The neural basis of this early SSRI effect is not known. Presynaptic dorsal raphe neuron (DRN) 5-HT_1A receptors are known to have a critical role in affect processing. Thus we investigated the effect of acute citalopram on emotional processing and the relationship between DRN 5-HT_1A receptor availability and amygdala reactivity. Thirteen (mean age 48±9 years) healthy male subjects received either a saline or citalopram infusion intravenously (10 mg over 30 min) on separate occasions in a single-blind, random order, crossover design. On each occasion, participants underwent a block design face-emotion processing task during fMRI known to activate the amygdala. Ten subjects also completed a positron emission tomography (PET) scan to quantify DRN 5-HT_1A availability using [¹¹C]CUMI-101. Citalopram infusion when compared with saline resulted in a significantly increased bilateral amygdala responses to fearful vs neutral faces (left p=0.025; right p=0.038 FWE-corrected). DRN [¹¹C]CUMI-101 availability significantly positively correlated with the effect of citalopram on the left amygdala response to fearful faces (Z=2.51, p=0.027) and right amygdala response to happy faces (Z=2.33, p=0.032). Our findings indicate that the initial effect of SSRI treatment is to alter processing of aversive stimuli and that this is linked to DRN 5-HT1A receptors in line with evidence that 5-HT1A receptors have a role in mediating emotional processing.

Serotonin-1A receptor C-1019G polymorphism affects brain functional networks

The serotonin-1A (5-HT1A) receptor is strongly implicated in major depression and other affective disorders due to its negative regulation of serotonin neurone firing rates. Behavioural and clinical studies have repeatedly reported that the −1019G allele carries a high susceptibility for affective disorders. However, the underlying pathophysiology remains unknown. Here, we employed a genetic neuroimaging strategy in 99 healthy human subjects to explore the effect of serotonin-1A receptor polymorphism on brain resting-state functional connectivity (FC). We used functional magnetic resonance imaging, along with a seed-based approach, to identify three main brain networks: the default mode network (DMN), the salience network (SN) and the central executive network. We observed a significant decrease in the FC of the DMN within the dorsolateral and ventromedial prefrontal cortices in G-carriers. Furthermore, compared with the C-homozygote group, we observed decreased FC of the SN within the ventromedial prefrontal cortex and subgenual anterior cingulate cortex in the G-carrier group. Our results indicate that 5-HT1A receptor genetic polymorphism modulates the activity of resting-state FC within brain networks including the DMN and SN. These genotype-related alterations in brain networks and FC may provide novel insights into the neural mechanism underlying the predisposition for affective disorders in G allele carriers.

Genetic association analysis of serotonin and signal transduction pathways in suicide attempters from an Italian sample of psychiatric patients

Genetic factors have been reported to contribute to the liability of suicide. We aimed to investigate functional polymorphisms in eight genes (serotonin transporter, SLC6A4; receptors, 5HTR1A, 1B, 5HTR2A; Tryptophan Hydroxylase, TPH1, TPH2; Monoamine Oxidase, MAOA and G Protein Subunit Beta 3, GNB3) to investigate their predictive value for suicide. The possible confounding effects of gender and phenotypic patients dissection were also valued. A sample of 111 consecutive psychiatric inpatients was recruited and assessed using specific psychometric instruments. Genomic DNA was isolated from peripheral white blood cell samples and polymorphisms were genotyped by pyrosequencing technology. Although no differences were observed between allele and genotype frequencies for all polymorphisms and suicide attempt (SA), a polygenic risk score was detected for three genes HTR2A (A-1438G), TPH1 and TPH2 increasing the prediction of SA risk (Thresh=0.43, p=0.038, R²=0.053). Moreover some nominal associations were obtained after gender and phenotypic dissection stratification (TEMPS-A, TEMPs-H, GSMD, SHSS, GAF, CGI) for SLC6A4 (5-HTTLPR), HTR1A (C-1019G), HTR2A (A-1438G), TPH1 (A799C) and GNB3 (C825T) genes, that were lost after Bonferroni correction. This is a first evidence that specific additive combinations of genes could increase the prediction of SA risk and that gender and phenotypic dissection could influence the association of the genes with SA. This could represent a further study also for future meta-analyses on larger samples.

The influence of the rs6295 gene polymorphism on serotonin-1A receptor distribution investigated with PET in patients with major depression applying machine learning

Major depressive disorder (MDD) is the most common neuropsychiatric disease and despite extensive research, its genetic substrate is still not sufficiently understood. The common polymorphism rs6295 of the serotonin-1A receptor gene (HTR1A) is affecting the transcriptional regulation of the 5-HT_1A receptor and has been closely linked to MDD. Here, we used positron emission tomography (PET) exploiting advances in data mining and statistics by using machine learning in 62 healthy subjects and 19 patients with MDD, which were scanned with PET using the radioligand [carbonyl-¹¹C]WAY-100635. All the subjects were genotyped for rs6295 and genotype was grouped in GG vs C allele carriers. Mixed model was applied in a ROI-based (region of interest) approach. ROI binding potential (BP_ND) was divided by dorsal raphe BP_ND as a specific measure to highlight rs6295 effects (BP_Div). Mixed model produced an interaction effect of ROI and genotype in the patients' group but no effects in healthy controls. Differences of BP_Div was demonstrated in seven ROIs; parahippocampus, hippocampus, fusiform gyrus, gyrus rectus, supplementary motor area, inferior frontal occipital gyrus and lingual gyrus. For classification of genotype, 'RandomForest' and Support Vector Machines were used, however, no model with sufficient predictive capability could be computed. Our results are in line with preclinical data, mouse model knockout studies as well as previous clinical analyses, demonstrating the two-pronged effect of the G allele on 5-HT_1A BP_ND for, we believe, the first time. Future endeavors should address epigenetic effects and allosteric heteroreceptor complexes. Replication in larger samples of MDD patients is necessary to substantiate our findings.

Disentangling the effects of novelty, valence and trait anxiety in the bed nucleus of the stria terminalis, amygdala and hippocampus with high resolution 7T fMRI

The hippocampus and amygdala exhibit sensitivity to stimulus novelty that is reduced in participants with inhibited temperament, which is related to trait anxiety. Although the bed nucleus of the stria terminalis (BNST) is highly connected to the amygdala and is implicated in anxiety, whether the BNST responds to novelty remains unstudied, as well as how trait anxiety may modulate this response. Additionally how novelty, stimulus negativity and trait anxiety interact to affect activity in these areas is also unclear. To address these questions, we presented participants with novel and repeated, fearful and neutral faces, while measuring brain activity via fMRI, and also assessed participants' self-reported trait anxiety. As the small size of the BNST makes assessing its activity at typical fMRI resolution difficult, we employed high resolution 7 Tesla scanning. Our results replicate findings of novelty sensitivity that is independent of valence in the hippocampus. Our results also provide novel evidence for a BNST novelty response toward neutral, but not fearful faces. We also found that the novelty response in the hippocampus and BNST was blunted in participants with high trait anxiety. Additionally, we found left amygdala sensitivity to stimulus negativity that was blunted for high trait anxiety participants. These findings extend past research on the response to novel stimuli in the hippocampus and amygdala at high resolution, and are the first to demonstrate trait anxiety modulated novelty sensitivity in the BNST that is dependent on stimulus valence.

Awareness of Emotional Stimuli Determines the Behavioral Consequences of Amygdala Activation and Amygdala-Prefrontal Connectivity

Conscious awareness of negative cues is thought to enhance emotion-regulatory capacity, but the neural mechanisms underlying this effect are unknown. Using continuous flash suppression (CFS) in the MRI scanner, we manipulated visual awareness of fearful faces during an affect misattribution paradigm, in which preferences for neutral objects can be biased by the valence of a previously presented stimulus. The amygdala responded to fearful faces independently of awareness. However, when awareness of fearful faces was prevented, individuals with greater amygdala responses displayed a negative bias toward unrelated novel neutral faces. In contrast, during the aware condition, inverse coupling between the amygdala and prefrontal cortex reduced this bias, particularly among individuals with higher structural connectivity in the major white matter pathway connecting the prefrontal cortex and amygdala. Collectively, these results indicate that awareness promotes the function of a critical emotion-regulatory network targeting the amygdala, providing a mechanistic account for the role of awareness in emotion regulation.

Developmental psychopathology in an era of molecular genetics and neuroimaging: A developmental neurogenetics approach

The emerging field of neurogenetics seeks to model the complex pathways from gene to brain to behavior. This field has focused on imaging genetics techniques that examine how variability in common genetic polymorphisms predict differences in brain structure and function. These studies are informed by other complimentary techniques (e.g., animal models and multimodal imaging) and have recently begun to incorporate the environment through examination of Imaging Gene × Environment interactions. Though neurogenetics has the potential to inform our understanding of the development of psychopathology, there has been little integration between principles of neurogenetics and developmental psychopathology. The paper describes a neurogenetics and Imaging Gene × Environment approach and how these approaches have been usefully applied to the study of psychopathology. Six tenets of developmental psychopathology (the structure of phenotypes, the importance of exploring mechanisms, the conditional nature of risk, the complexity of multilevel pathways, the role of development, and the importance of who is studied) are identified, and how these principles can further neurogenetics applications to understanding the development of psychopathology is discussed. A major issue of this piece is how neurogenetics and current imaging and molecular genetics approaches can be incorporated into developmental psychopathology perspectives with a goal of providing models for better understanding pathways from among genes, environments, the brain, and behavior.

An oxytocin receptor polymorphism predicts amygdala reactivity and antisocial behavior in men

Variability in oxytocin (OXT) signaling is associated with individual differences in sex-specific social behavior across species. The effects of OXT signaling on social behavior are, in part, mediated through its modulation of amygdala function. Here, we use imaging genetics to examine sex-specific effects of three single-nucleotide polymorphisms in the human oxytocin receptor gene (OXTR; rs1042778, rs53576 and rs2254298) on threat-related amygdala reactivity and social behavior in 406 Caucasians. Analyses revealed that among men but not women, OXTR rs1042778 TT genotype was associated with increased right amygdala reactivity to angry facial expressions, which was uniquely related to higher levels of antisocial behavior among men. Moderated meditation analysis suggested a trending indirect effect of OXTR rs1042778 TT genotype on higher antisocial behavior via increased right amygdala reactivity to angry facial expressions in men. Our results provide evidence linking genetic variation in OXT signaling to individual differences in amygdala function. The results further suggest that these pathways may be uniquely important in shaping antisocial behavior in men.

Nonexocytotic serotonin release tonically suppresses serotonergic neuron activity

The firing activity of serotonergic neurons in raphe nuclei is regulated by negative feedback exerted by extracellular serotonin (5-HT)o acting through somatodendritic 5-HT1A autoreceptors. The steady-state [5-HT]o, sensed by 5-HT1A autoreceptors, is determined by the balance between the rates of 5-HT release and reuptake. Although it is well established that reuptake of 5-HTo is mediated by 5-HT transporters (SERT), the release mechanism has remained unclear. It is also unclear how selective 5-HT reuptake inhibitor (SSRI) antidepressants increase the [5-HT]o in raphe nuclei and suppress serotonergic neuron activity, thereby potentially diminishing their own therapeutic effect. Using an electrophysiological approach in a slice preparation, we show that, in the dorsal raphe nucleus (DRN), continuous nonexocytotic 5-HT release is responsible for suppression of phenylephrine-facilitated serotonergic neuron firing under basal conditions as well as for autoinhibition induced by SSRI application. By using 5-HT1A autoreceptor-activated G protein-gated inwardly rectifying potassium channels of patched serotonergic neurons as 5-HTo sensors, we show substantial nonexocytotic 5-HT release under conditions of abolished firing activity, Ca(2+) influx, vesicular monoamine transporter 2-mediated vesicular accumulation of 5-HT, and SERT-mediated 5-HT transport. Our results reveal a cytosolic origin of 5-HTo in the DRN and suggest that 5-HTo may be supplied by simple diffusion across the plasma membrane, primarily from the dense network of neurites of serotonergic neurons surrounding the cell bodies. These findings indicate that the serotonergic system does not function as a sum of independently acting neurons but as a highly interdependent neuronal network, characterized by a shared neurotransmitter pool and the regulation of firing activity by an interneuronal, yet activity-independent, nonexocytotic mechanism.

The functional serotonin 1a receptor promoter polymorphism, rs6295, is associated with psychiatric illness and differences in transcription

The G/C single-nucleotide polymorphism in the serotonin 1a receptor promoter, rs6295, has previously been linked with depression, suicide and antidepressant responsiveness. In vitro studies suggest that rs6295 may have functional effects on the expression of the serotonin 1a receptor gene (HTR1A) through altered binding of a number of transcription factors. To further explore the relationship between rs6295, mental illness and gene expression, we performed dual epidemiological and biological studies. First, we genotyped a cohort of 1412 individuals, randomly split into discovery and replication cohorts, to examine the relationship between rs6295 and five psychiatric outcomes: history of psychiatric hospitalization, history of suicide attempts, history of substance or alcohol abuse, current posttraumatic stress disorder (PTSD), current depression. We found that the rs6295G allele is associated with increased risk for substance abuse, psychiatric hospitalization and suicide attempts. Overall, exposure to either childhood or non-childhood trauma resulted in increased risk for all psychiatric outcomes, but we did not observe a significant interaction between rs6295 and trauma in modulating psychiatric outcomes. In conjunction, we also investigated the potential impact of rs6295 on HTR1A expression in postmortem human brain tissue using relative allelic expression assays. We found more mRNA produced from the C versus the G-allele of rs6295 in the prefrontal cortex (PFC), but not in the midbrain of nonpsychiatric control subjects. Further, in the fetal cortex, rs6295C allele exhibited increased relative expression as early as gestational week 18 in humans. Finally, we found that the C:G allelic expression ratio was significantly neutralized in the PFC of subjects with major depressive disorder (MDD) who committed suicide as compared with controls, indicating that normal patterns of transcription may be disrupted in MDD/suicide. These data provide a putative biological mechanism underlying the association between rs6295, trauma and mental illness. Moreover, our results suggest that rs6295 may affect transcription during both gestational development and adulthood in a region-specific manner, acting as a risk factor for psychiatric illness. These findings provide a critical framework for conceptualizing the effects of a common functional genetic variant, trauma exposure and their impact on mental health.

Imaging genetics studies on monoaminergic genes in major depressive disorder

Although depression is the leading cause of disability worldwide, current understanding of the neurobiology of depression has failed to be translated into clinical practice. Major depressive disorder (MDD) pathogenesis is considered to be significantly influenced by multiple risk genes, however genetic effects are not simply expressed at a behavioral level. Therefore the concept of endophenotype has been applied in psychiatric genetics. Imaging genetics applies anatomical or functional imaging technologies as phenotypic assays to evaluate genetic variation and their impact on behavior. This paper attempts to provide a comprehensive review of available imaging genetics studies, including reports on genetic variants that have most frequently been linked to MDD, such as the monoaminergic genes (serotonin transporter gene, monoamine oxidase A gene, tryptophan hydroxylase-2 gene, serotonin receptor 1A gene and catechol-O-methyl transferase gene), with regard to key structures involved in emotion processing, such as the hippocampus, amygdala, anterior cingulate cortex and orbitofrontal cortex.

Genetic influences on the neural and physiological bases of acute threat: A research domain criteria (RDoC) perspective

The NIMH Research Domain Criteria (RDoC) initiative aims to describe key dimensional constructs underlying mental function across multiple units of analysis-from genes to observable behaviors-in order to better understand psychopathology. The acute threat ("fear") construct of the RDoC Negative Valence System has been studied extensively from a translational perspective, and is highly pertinent to numerous psychiatric conditions, including anxiety and trauma-related disorders. We examined genetic contributions to the construct of acute threat at two units of analysis within the RDoC framework: (1) neural circuits and (2) physiology. Specifically, we focused on genetic influences on activation patterns of frontolimbic neural circuitry and on startle, skin conductance, and heart rate responses. Research on the heritability of activation in threat-related frontolimbic neural circuitry is lacking, but physiological indicators of acute threat have been found to be moderately heritable (35-50%). Genetic studies of the neural circuitry and physiology of acute threat have almost exclusively relied on the candidate gene method and, as in the broader psychiatric genetics literature, most findings have failed to replicate. The most robust support has been demonstrated for associations between variation in the serotonin transporter (SLC6A4) and catechol-O-methyltransferase (COMT) genes with threat-related neural activation and physiological responses. However, unbiased genome-wide approaches using very large samples are needed for gene discovery, and these can be accomplished with collaborative consortium-based research efforts, such as those of the Psychiatric Genomics Consortium (PGC) and Enhancing Neuro Imaging Genetics through Meta-Analysis (ENIGMA) Consortium.

5-HT1A receptors on mature dentate gyrus granule cells are critical for the antidepressant response

Selective serotonin reuptake inhibitors (SSRIs) are widely used antidepressants, but the mechanisms by which they influence behavior are only partially resolved. Adult hippocampal neurogenesis is necessary for some of the responses to SSRIs, but it is unknown whether the mature dentate gyrus granule cells (mature DG GCs) also contribute. We deleted Serotonin 1A receptor (5HT1AR; a receptor required for the SSRI response) specifically from DG GCs and found that the effects of the SSRI fluoxetine on behavior and the Hypothalamic-Pituitary-Adrenal (HPA) axis were abolished. By contrast, mice lacking 5HT1ARs only in young adult born granule cells (abGCs) showed normal fluoxetine responses. Importantly, 5HT1AR deficient mice engineered to express functional 5HT1ARs only in DG GCs responded to fluoxetine, indicating that 5HT1ARs in DG GCs are sufficient to mediate an antidepressant response. Taken together, these data indicate that both mature DG GCs and young abGCs must be engaged for an antidepressant response.

Regional Homogeneity of Resting-State Brain Activity Suppresses the Effect of Dopamine-Related Genes on Sensory Processing Sensitivity

Sensory processing sensitivity (SPS) is an intrinsic personality trait whose genetic and neural bases have recently been studied. The current study used a neural mediation model to explore whether resting-state brain functions mediated the effects of dopamine-related genes on SPS. 298 healthy Chinese college students (96 males, mean age = 20.42 years, SD = 0.89) were scanned with magnetic resonance imaging during resting state, genotyped for 98 loci within the dopamine system, and administered the Highly Sensitive Person Scale. We extracted a “gene score” that summarized the genetic variations representing the 10 loci that were significantly linked to SPS, and then used path analysis to search for brain regions whose resting-state data would help explain the gene-behavior association. Mediation analysis revealed that temporal homogeneity of regional spontaneous activity (ReHo) in the precuneus actually suppressed the effect of dopamine-related genes on SPS. The path model explained 16% of the variance of SPS. This study represents the first attempt at using a multi-gene voxel-based neural mediation model to explore the complex relations among genes, brain, and personality.

Can we observe epigenetic effects on human brain function?

Imaging genetics has identified many contributions of DNA sequence variation to individual differences in brain function, behavior, and risk for psychopathology. Recent studies have extended this work beyond the genome by mapping epigenetic differences, specifically gene methylation in peripherally assessed DNA, onto variability in behaviorally and clinically relevant brain function. These data have generated understandable enthusiasm for the potential of such research to illuminate biological mechanisms of risk. We use our research on the effects of genetic and epigenetic variation in the human serotonin transporter on brain function to generate a guardedly optimistic opinion that the available data encourage continued research in this direction, and suggest strategies to promote faster progress.

Amygdala reactivity and negative emotionality: divergent correlates of antisocial personality and psychopathy traits in a community sample

Previous studies have emphasized that antisocial personality disorder (APD) and psychopathy overlap highly but differ critically in several features, notably negative emotionality (NEM) and possibly amygdala reactivity to social signals of threat and distress. Here we examined whether dimensions of psychopathy and APD correlate differentially with NEM and amygdala reactivity to emotional faces. Testing these relationships among healthy individuals, dimensions of psychopathy and APD were generated by the profile matching technique of Lynam and Widiger (2001), using facet scales of the NEO Personality Inventory-Revised, and amygdala reactivity was measured using a well-established emotional faces task, in a community sample of 103 men and women. Higher psychopathy scores were associated with lower NEM and lower amygdala reactivity, whereas higher APD scores were related to greater NEM and greater amygdala reactivity, but only after overlapping variance in APD and psychopathy was adjusted for in the statistical model. Amygdala reactivity did not mediate the relationship of APD and psychopathy scores to NEM. Supplemental analyses also compared other measures of factors within psychopathy in predicting NEM and amygdala reactivity and found that Factor 2 psychopathy was positively related to NEM and amygdala reactivity across measures of psychopathy. The overall findings replicate seminal observations on NEM in psychopathy by Hicks and Patrick (2006) and extend this work to neuroimaging in a normative population. They also suggest that one critical way in which APD and psychopathy dimensions may differ in their etiology is through their opposing levels of NEM and amygdala reactivity to threat.

Transcriptional dys-regulation in anxiety and major depression: 5-HT1A gene promoter architecture as a therapeutic opportunity

The etiology of major depression remains unclear, but reduced activity of the serotonin (5-HT) system remains implicated and treatments that increase 5-HT neurotransmission can ameliorate depressive symptoms. 5-HT1A receptors are critical regulators of the 5- HT system. They are expressed as both presynaptic autoreceptors that negatively regulate 5-HT neurons, and as post-synaptic heteroreceptors on non-serotonergic neurons in the hippocampus, cortex, and limbic system that are critical to mediate the antidepressant actions of 5-HT. Thus, 5-HT1A auto- and heteroreceptors have opposite actions on serotonergic neurotransmission. Because most 5-HT1A ligands target both auto- and heteroreceptors their efficacy has been limited, resulting in weak or unclear responses. We propose that by understanding the transcriptional regulation of the 5-HT1A receptor it may be possible to regulate its expression differentially in raphe and projection regions. Here we review the transcriptional architecture of the 5-HT1A gene (HTR1A) with a focus on specific DNA elements and transcription factors that have been shown to regulate 5-HT1A receptor expression in the brain. Association studies with the functional HTR1A promoter polymorphism rs6295 suggest a new model for the role of the 5-HT1A receptor in susceptibility to depression involving early deficits in cognitive, fear and stress reactivity as stressors that may ultimately lead to depression. We present evidence that by targeting specific transcription factors it may be possible to oppositely regulate 5-HT1A auto- and heteroreceptor expression, synergistically increasing serotonergic neurotransmission for the treatment of depression.

Strain-dependent variations in stress coping behavior are mediated by a 5-HT/GABA interaction within the prefrontal corticolimbic system

BACKGROUND

Serotonin and γ-aminobutyric acid (GABA) transmission is crucial in coping strategies.

METHODS

Here, using mice from 2 inbred strains widely exploited in behavioral neurochemistry, we investigated whether serotonin transmission in medial prefrontal cortex and GABA in basolateral amygdala determine strain-dependent liability to stress response and differences in coping.

RESULTS

C57BL/6J mice displayed greater immobility in the forced swimming test, higher serotonin outflow in medial prefrontal cortex, higher GABA outflow in basolateral amygdala induced by stress, and higher serotonin 1A receptor levels in medial prefrontal cortex accompanied by lower GABAb receptor levels in basolateral amygdala than DBA/2J mice. In assessing whether serotonin in medial prefrontal cortex determines GABA functioning in response to stress and passive coping behavior in C57BL/6J and DBA/2J mice, we observed that selective prefrontal serotonin depletion in C57BL/6J and DBA/2J reduced stress-induced GABA outflow in basolateral amygdala and immobility in the forced swimming test.

CONCLUSIONS

These results show that strain-dependent prefrontal corticolimbic serotonin/GABA regulation determines the strain differences in stress-coping behavior in the forced swimming test and point to a role of a specific neuronal system in genetic susceptibility to stress that opens up new prospects for innovative therapies for stress disorders.

Specific and common genes implicated across major mental disorders: a review of meta-analysis studies

Major efforts have been directed at family-based association and case-control studies to identify the involvement of candidate genes in the major disorders of mental health. What remains unknown is whether candidate genes are associated with multiple disorders via pleiotropic mechanisms, and/or if other genes are specific to susceptibility for individual disorders. Here we undertook a review of genes that have been identified in prior meta-analyses examining specific genes and specific mental disorders that have core disruptions to emotional and cognitive function and contribute most to burden of illness- major depressive disorder (MDD), anxiety disorders (AD, including panic disorder and obsessive compulsive disorder), schizophrenia (SZ) and bipolar disorder (BD) and attention deficit hyperactivity disorder (ADHD). A literature review was conducted up to end-March 2013 which included a total of 1519 meta-analyses across 157 studies reporting multiple genes implicated in one or more of the five disorders studied. A total of 134 genes (206 variants) were identified as significantly associated risk variants for MDD, AD, ADHD, SZ or BD. Null genetic effects were also reported for 195 genes (426 variants). 13 genetic variants were shared in common between two or more disorders (APOE e4, ACE Ins/Del, BDNF Val66Met, COMT Val158Met, DAOA G72/G30 rs3918342, DAT1 40-bp, DRD4 48-bp, SLC6A4 5-HTTLPR, HTR1A C1019G, MTHR C677T, MTHR A1298C, SLC6A4 VNTR and TPH1 218A/C) demonstrating evidence for pleiotrophy. Another 12 meta-analyses of GWAS studies of the same disorders were identified, with no overlap in genetic variants reported. This review highlights the progress that is being made in identifying shared and unique genetic mechanisms that contribute to the risk of developing several major psychiatric disorders, and identifies further steps for progress.

Genetic and early environmental influences on the serotonin system: consequences for brain development and risk for psychopathology

BACKGROUND

Despite more than 60 years of research in the role of serotonin (5-HT) in psychopathology, many questions still remain. From a developmental perspective, studies have provided more insight into how 5-HT dysfunctions acquired in utero or early in life may modulate brain development. This paper discusses the relevance of the developmental role of 5-HT for the understanding of psychopathology. We review developmental milestones of the 5-HT system, how genetic and environmental 5-HT disturbances could affect brain development and the potential role of DNA methylation in 5-HT genes for brain development.

METHODS

Studies were identified using common databases (e.g., PubMed, Google Scholar) and reference lists.

RESULTS

Despite the widely supported view that the 5-HT system matures in early life, different 5-HT receptors, proteins and enzymes have different developmental patterns, and development is brain region-specific. A disruption in 5-HT homeostasis during development may lead to structural and functional changes in brain circuits that modulate emotional stress responses, including subcortical limbic and (pre)frontal areas. This may result in a predisposition to psychopathology. DNA methylation might be one of the underlying physiologic mechanisms.

LIMITATIONS

There is a need for prospective studies. The impact of stressors during adolescence on the 5-HT system is understudied. Questions regarding efficacy of drugs acting on 5-HT still remain.

CONCLUSION

A multidisciplinary and longitudinal approach in designing studies on the role of 5-HT in psychopathology might help to bring us closer to the understanding of the role of 5-HT in psychopathology.

Serotonin 1A and Serotonin 4 Receptors: Essential Mediators of the Neurogenic and Behavioral Actions of Antidepressants

Selective serotonin reuptake inhibitors are the mostly widely used treatment for major depressive disorders and also are prescribed for several anxiety disorders. However, similar to most antidepressants, selective serotonin reuptake inhibitors suffer from two major problems: They only show beneficial effects after 2 to 4 weeks and only about 33% of patients show remission to first-line treatment. Thus, there is a considerable need for development of more effective antidepressants. There is a growing body of evidence supporting critical roles of 5-HT1A and 5-HT4 receptor subtypes in mediating successful depression treatments. In addition, appropriate activation of these receptors may be associated with a faster onset of the therapeutic response. This review will examine the known roles of 5-HT1A and 5-HT4 receptors in mediating both the pathophysiology of depression and anxiety and the treatment of these mood disorders. At the end of the review, the role of these receptors in the regulation of adult hippocampal neurogenesis will also be discussed. Ultimately, we propose that novel antidepressant drugs that selectively target these serotonin receptors could be developed to yield improvements over current treatments for major depressive disorders.

5-HTTLPR, HTR1A, and HTR2A cumulative genetic score interacts with mood reactivity to predict mood-congruent gaze bias

Genetic variation within the serotonin system has been associated with biased attention for affective stimuli and, less consistently, with vulnerability for major depressive disorder. In particular, 5-HTTLPR, HTR1A (rs6295), and HTR2A (rs6311) polymorphisms have been linked with biased cognition. The present study developed a serotonergic cumulative genetic score (CGS) that quantified the number of risk alleles associated with these candidate polymorphisms to yield a single CGS. The CGS was then used to model genetic influence on the relationship between reactivity to a negative mood induction and negatively biased cognition. A passive-viewing eye-tracking task was administered to 170 healthy volunteers to assess sustained attention for positive, dysphoric, neutral, and threatening scenes. Participants were then induced into a sad mood and readministered the passive-viewing task. Change in gaze bias, as a function of reactivity to mood induction, was the primary measure of cognitive vulnerability. Results suggest that, although none of the individual genes interacted with mood reactivity to predict change in gaze bias, individuals with higher serotonin CGS were significantly more likely to look toward dysphoric images and away from positive images as mood reactivity increased. These findings suggest that a CGS approach may better capture genetic influences on cognitive vulnerability and reaffirm the need to examine multilocus approaches in genomic research.

The functional -1019C/G HTR1A polymorphism and mechanisms of fear

Serotonin receptor 1A gene (HTR1A) knockout mice show pronounced defensive behaviour and increased fear conditioning to ambiguous conditioned stimuli. Such behaviour is a hallmark of pathological human anxiety, as observed in panic disorder with agoraphobia (PD/AG). Thus, variations in HTR1A might contribute to neurophysiological differences within subgroups of PD/AG patients. Here, we tested this hypothesis by combining genetic with behavioural techniques and neuroimaging. In a clinical multicentre trial, patients with PD/AG received 12 sessions of manualized cognitive-behavioural therapy (CBT) and were genotyped for HTR1A rs6295. In four subsamples of this multicentre trial, exposure behaviour (n=185), defensive reactivity measured using a behavioural avoidance test (BAT; before CBT: n=245; after CBT: n=171) and functional magnetic resonance imaging (fMRI) data during fear conditioning were acquired before and after CBT (n=39). HTR1A risk genotype (GG) carriers more often escaped during the BAT before treatment. Exploratory fMRI results suggest increased activation of the amygdala in response to threat as well as safety cues before and after treatment in GG carriers. Furthermore, GG carriers demonstrated reduced effects of CBT on differential conditioning in regions including the bilateral insulae and the anterior cingulate cortex. Finally, risk genotype carriers demonstrated reduced self-initiated exposure behaviour to aversive situations. This study demonstrates the effect of HTR1A variation on defensive behaviour, amygdala activity, CBT-induced neural plasticity and normalization of defence behaviour in PD/AG. Our results, therefore, translate evidence from animal studies to humans and suggest a central role for HTR1A in differentiating subgroups of patients with anxiety disorders.

Menstrual cycle influence on cognitive function and emotion processing-from a reproductive perspective

The menstrual cycle has attracted research interest ever since the 1930s. For many researchers the menstrual cycle is an excellent model of ovarian steroid influence on emotion, behavior, and cognition. Over the past years methodological improvements in menstrual cycle studies have been noted, and this review summarizes the findings of methodologically sound menstrual cycle studies in healthy women. Whereas the predominant hypotheses of the cognitive field state that sexually dimorphic cognitive skills that favor men are improved during menstrual cycle phases with low estrogen and that cognitive skills that favor women are improved during cycle phases with increased estrogen and/or progesterone, this review has not found sufficient evidence to support any of these hypotheses. Mental rotation has gained specific interest in this aspect, but a meta-analysis yielded a standardized mean difference in error rate of 1.61 (95% CI -0.35 to 3.57), suggesting, at present, no favor of an early follicular phase improvement in mental rotation performance. Besides the sexually dimorphic cognitive skills, studies exploring menstrual cycle effects on tasks that probe prefrontal cortex function, for instance verbal or spatial working memory, have also been reviewed. While studies thus far are few, results at hand suggest improved performance at times of high estradiol levels. Menstrual cycle studies on emotional processing, on the other hand, tap into the emotional disorders of the luteal phase, and may be of relevance for women with premenstrual disorders. Although evidence at present is limited, it is suggested that emotion recognition, consolidation of emotional memories, and fear extinction is modulated by the menstrual cycle in women. With the use of functional magnetic resonance imaging, several studies report changes in brain reactivity across the menstrual cycle, most notably increased amygdala reactivity in the luteal phase. Thus, to the extent that behavioral changes have been demonstrated over the course of the menstrual cycle, the best evidence suggests that differences in sexually dimorphic tasks are small and difficult to replicate. However, emotion-related changes are more consistently found, and are better associated with progesterone than with estradiol such that high progesterone levels are associated with increased amygdala reactivity and increased emotional memory.

The impact of cue learning, trait anxiety and genetic variation in the serotonin 1A receptor on contextual fear

In everyday life, aversive events are usually associated with certain predictive cues. Normally, the acquisition of these contingencies enables organisms to appropriately respond to threat. Presence of a threat cue clearly signals 'danger', whereas absence of such cues signals a period of 'safety'. Failure to identify threat cues may lead to chronic states of anxious apprehension in the context in which the threat has been imminent, which may be instrumental in the pathogenesis of anxiety disorders. In this study, existing data from 150 healthy volunteers in a cue and context virtual reality fear conditioning paradigm were reanalyzed. The aim was to further characterize the impact of cue acquisition and trait anxiety, and of a single nucleotide polymorphism in the serotonin 1A receptor gene (5-HTR1A, rs6295), on cued fear and contextual anxiety before and after fear contingencies were explicitly introduced. Fear conditioned responding was quantified with fear potentiation of the eyeblink startle reflex and subjective fear ratings. First, we replicated previous findings that the inability to identify danger cues during acquisition leads to heightened anxious apprehension in the threat context. Second, in subjects who did not identify the danger cue initially, contextual fear was associated with trait anxiety after the contingencies were explicitly instructed. Third, genetic variability within 5-HTR1A (rs6295) was associated with contextual fear independent of awareness or trait anxiety. These findings confirm that failure to acquire cue contingencies impacts contextual fear responding, in association with trait anxiety. The observed 5-HTR1A effect is in line with models of anxiety, but needs further replication.

Attachment-security priming attenuates amygdala activation to social and linguistic threat

A predominant expectation that social relationships with others are safe (a secure attachment style), has been linked with reduced threat-related amygdala activation. Experimental priming of mental representations of attachment security can modulate neural responding, but the effects of attachment-security priming on threat-related amygdala activation remains untested. Using functional magnetic resonance imaging, the present study examined the effects of trait and primed attachment security on amygdala reactivity to threatening stimuli in an emotional faces and a linguistic dot-probe task in 42 healthy participants. Trait attachment anxiety and attachment avoidance were positively correlated with amygdala activation to threatening faces in the control group, but not in the attachment primed group. Furthermore, participants who received attachment-security priming showed attenuated amygdala activation in both the emotional faces and dot-probe tasks. The current findings demonstrate that variation in state and trait attachment security modulates amygdala reactivity to threat. These findings support the potential use of attachment security-boosting methods as interventions and suggest a neural mechanism for the protective effect of social bonds in anxiety disorders.

There is no association between the serotonin receptor gene and bipolar I disorder in the Korean population

OBJECTIVE

Despite the close relationship between the functional polymorphism C(-1019)G (rs6295) of the serotonergic 1A receptor (5-HT1A) and mood, few studies have investigated the relationship between rs6295 and bipolar disorder.

AIMS

In this study, we aimed to investigate whether rs6295 is associated with clinical prognosis and treatment response in patients with bipolar I disorder acute manic episodes.

METHODS

One hundred twenty-eight patients with bipolar I disorder and one hundred sixty-eight healthy controls were recruited. Associations between patients with bipolar I disorder and healthy controls were compared. In addition, age at onset, number of admissions, and treatment response, including response rate, mean changes in manic symptoms, number of anti-manic agents and the total dosage of mood stabilizers for acute manic symptoms were compared between the rs6295 GG and CG+ CC groups in patients with bipolar I disorder. We conducted a separate subgroup analysis according to gender.

RESULTS

There were no differences in frequency between patients and controls. In patients with bipolar disorder, clinical prognosis and treatment response were no different between GG and CG+ CC groups. However, in a subgroup analysis according to gender, male, but not female, patients in the GG group had a longer duration of illness and a greater number of both previous episodes and psychiatric ward admissions than did the GC+ CC group.

CONCLUSIONS

Further studies should investigate the relationship between 5-HT1A polymorphisms and bipolar disorder in terms of mood episode and gender.

Feature-based representations of emotional facial expressions in the human amygdala

The amygdala plays a central role in processing facial affect, responding to diverse expressions and features shared between expressions. Although speculation exists regarding the nature of relationships between expression- and feature-specific amygdala reactivity, this matter has not been fully explored. We used functional magnetic resonance imaging and principal component analysis (PCA) in a sample of 300 young adults, to investigate patterns related to expression- and feature-specific amygdala reactivity to faces displaying neutral, fearful, angry or surprised expressions. The PCA revealed a two-dimensional correlation structure that distinguished emotional categories. The first principal component separated neutral and surprised from fearful and angry expressions, whereas the second principal component separated neutral and angry from fearful and surprised expressions. This two-dimensional correlation structure of amygdala reactivity may represent specific feature-based cues conserved across discrete expressions. To delineate which feature-based cues characterized this pattern, face stimuli were averaged and then subtracted according to their principal component loadings. The first principal component corresponded to displacement of the eyebrows, whereas the second principal component corresponded to increased exposure of eye whites together with movement of the brow. Our results suggest a convergent representation of facial affect in the amygdala reflecting feature-based processing of discrete expressions.

Beyond genotype: serotonin transporter epigenetic modification predicts human brain function

We examined epigenetic regulation in regards to behaviorally and clinically relevant human brain function. Specifically, we found that increased promoter methylation of the serotonin transporter gene predicted increased threat-related amygdala reactivity and decreased mRNA expression in postmortem amygdala tissue. These patterns were independent of functional genetic variation in the same region. Furthermore, the association with amygdala reactivity was replicated in a second cohort and was robust to both sampling methods and age.

Regulatory variant of the TPH2 gene and early life stress are associated with heightened attention to social signals of fear in infants

BACKGROUND

Cross-species evidence suggests that genetic and experiential factors act early in development to establish individual emotional traits, but little is known about the mechanisms that emerge during this period to mediate long-term outcomes. Here, we tested the hypothesis that known genetic and environmental risk conditions may heighten infants' natural tendency to attend to threat-alerting stimuli, resulting in a cognitive bias that may contribute to emotional vulnerability.

METHODS

Data from two samples of 5-7-month-old infants (N = 139) were used to examine whether established candidate variations in the serotonin-system genes, i.e., TPH2 SNP rs4570625 (-703 G/T) and HTR1A SNP rs6295 (-1019 G/C), and early rearing condition (maternal stress and depressive symptoms) are associated with alterations in infants' attention to facial expressions. Infants were tested with a paradigm that assesses the ability to disengage attention from a centrally presented stimulus (a nonface control stimulus or a neutral, happy, or fearful facial expression) toward the location of a new stimulus in the visual periphery (a geometric shape).

RESULTS

TPH2 -703 T-carrier genotype (i.e., TT homozygotes and heterozygotes), presence of maternal stress and depressive symptoms, and a combination of the T-carrier genotype and maternal depressive symptoms were associated with a relatively greater difficulty disengaging attention from fearful facial expressions. No associations were found with infants' temperamental traits.

CONCLUSIONS

Alterations in infants' natural attentional bias toward fearful facial expressions may emerge prior to the manifestation of emotional and social behaviors and provide a sensitive marker of early emotional development.

Alterations in the serotonin system in schizophrenia: a systematic review and meta-analysis of postmortem and molecular imaging studies

Serotonergic dysfunction is thought to contribute to the pathophysiology of schizophrenia but the evidence has not been systematically synthesised before. We therefore systematically reviewed postmortem and in vivo molecular imaging studies of serotonin function in schizophrenia. We identified fifty relevant studies investigating eight different serotonin receptor systems in a total of 684 patients and 675 controls. Meta-analysis of postmortem studies found an elevation in prefrontal 5-HT1A receptors with a moderate to large effect size (N=8, 85 patients and 94 controls, SMD=0.60; CI: 0.17-1.03; p=0.007) and a reduction with a large effect size in prefrontal 5-HT2A receptors (N=8, 168 patients and 163 controls, SMD=-0.73; CI: -1.33, -0.12; p=0.019) in schizophrenia vs healthy controls. The evidence for alterations in serotonin transporter availability or other serotonin receptors (5-HT1B; 5-HT1D; 5-HT3; 5-HT4; 5-HT7) is limited. There are fewer studies investigating 5-HT receptors in schizophrenia with neuroimaging. Findings indicated possible 5-HT alterations at psychosis onset, although due to the limited number it was not possible to combine studies in a meta-analysis. Further in vivo studies, particularly in drug naive patients using radiotracers that can index high affinity states, will help determine if the postmortem findings are primary or secondary to other factors.

MicroRNA 135 is essential for chronic stress resiliency, antidepressant efficacy, and intact serotonergic activity

The link between dysregulated serotonergic activity and depression and anxiety disorders is well established, yet the molecular mechanisms underlying these psychopathologies are not fully understood. Here, we explore the role of microRNAs in regulating serotonergic (5HT) neuron activity. To this end, we determined the specific microRNA "fingerprint" of 5HT neurons and identified a strong microRNA-target interaction between microRNA 135 (miR135), and both serotonin transporter and serotonin receptor-1a transcripts. Intriguingly, miR135a levels were upregulated after administration of antidepressants. Genetically modified mouse models, expressing higher or lower levels of miR135, demonstrated major alterations in anxiety- and depression-like behaviors, 5HT levels, and behavioral response to antidepressant treatment. Finally, miR135a levels in blood and brain of depressed human patients were significantly lower. The current results suggest a potential role for miR135 as an endogenous antidepressant and provide a venue for potential treatment and insights into the onset, susceptibility, and heterogeneity of stress-related psychopathologies.