Genetics of emotional regulation: the role of the serotonin transporter in neural function

The serotonin transporter linked polymorphic region and brain-derived neurotrophic factor valine to methionine at position 66 polymorphisms and maternal history of depression: associations with cognitive vulnerability to depression in childhood

Preliminary work indicates that cognitive vulnerability to depression may be associated with variants of the serotonin transporter promoter polymorphism (5-HTTLPR) and the valine to methionine at position 66 (val66met) polymorphism of the brain-derived neurotrophic factor (BDNF) gene; however, existing reports come from small samples. The present study sought to replicate and extend this research in a sample of 375 community-dwelling children and their parents. Following a negative mood induction, children completed a self-referent encoding task tapping memory for positive and negative self-descriptive traits. Consistent with previous work, we found that children with at least one short variant of the 5-HTTLPR had enhanced memory for negative self-descriptive traits. The BDNF val66met polymorphism had no main effect but was moderated by maternal depression, such that children with a BDNF methionine allele had a heightened memory for negative self-descriptive traits when mothers had experienced depression during children's lifetimes; in contrast, children with a methionine allele had low recall of negative traits when mothers had no depression history. The findings provide further support for the notion that the 5-HTTLPR is associated with cognitive markers of depression vulnerability and that the BDNF methionine allele moderates children's sensitivity to contextual factors.

Occupancy of serotonin transporters in the amygdala by paroxetine in association with attenuation of left amygdala activation by negative faces in major depressive disorder

Amygdala hyperactivation in major depressive disorder (MDD) might be attenuated by selective serotonin reuptake inhibitors (SSRIs), but the working mechanism remains unclear. We hypothesized that higher amygdala serotonin transporter (SERT) occupancy by paroxetine results in greater attenuation of amygdala activation by negative facial expressions in MDD patients. We treated fifteen MDD patients (22-55 years) with paroxetine 20-50mg/day. After 6 and 12 weeks, we quantified (1) clinical response (≥50% decrease in Hamilton Depression Rating Scale (HDRS), (2) SERT occupancy in both amygdala measured by repeated [123I]β-CIT single photon emission computed tomography (SPECT), and (3) amygdala activation when viewing fearful and angry (negative) faces with repeated functional MRI scans. Response rates were 4/15 and 9/15 at 6 and 12 weeks, respectively. Attenuation of left amygdala activation was associated with amygdala SERT occupancy (P=0.006) and response (P=0.015). This association may provide a rationale for decreased limbic activity seen during treatment of MDD. It might also explain the rapid decrease in negative attentional bias and amygdala activation caused by SSRIs.

Daily stress reactivity and serotonin transporter gene (5-HTTLPR) variation: internalizing responses to everyday stress as a possible transdiagnostic phenotype

Background

Recent studies examining the interaction between the 5-HTTLPR locus in the serotonin transporter gene and life stress in predicting depression have yielded equivocal results, leading some researchers to question whether 5-HTTLPR variation indeed regulates depressive responses to stress. Two possible sources of inconsistent data in this literature are imprecise stress assessment methodologies and a restricted focus on depression phenotypes as the outcome of interest, as opposed to transdiagnostic emotional symptoms such as internalizing and externalizing dimensions. The present study aimed to address these critical limitations in prior research by examining how 5-HTTLPR acts in concert with idiographically assessed daily life stress to predict transdiagnostic emotional outcomes.

Results

One hundred and four healthy young adults genotyped for 5-HTTLPR reported on their life stress exposure and internalizing and externalizing experiences for 14 consecutive days. As hypothesized, daily stress levels were associated with severity of internalizing symptoms, but only for 5-HTTLPR S allele carriers. Additional analyses revealed that these interactive effects of 5-HTTLPR and daily life stress on internalizing symptoms extended to both the distress and fear subdomains of internalizing symptoms.

Conclusions

Considered together, these results support the validity of the 5-HTTLPR stress sensitivity hypothesis and suggest for the first time that variation at 5-HTTLPR moderates the effects of daily life stress on broadband symptom profiles.

Is serotonin transporter genotype associated with epigenetic susceptibility or vulnerability? Examination of the impact of socioeconomic status risk on African American youth

We hypothesized that presence of the short allele in the promoter region of the serotonin transporter would moderate the effect of early cumulative socioeconomic status (SES) risk on epigenetic change among African American youth. Contrasting hypotheses regarding the shape of the interaction effect were generated using vulnerability and susceptibility frameworks and applied to data from a sample of 388 African American youth. Early cumulative SES risk assessed at 11-13 years based on parent report interacted with presence of the short allele to predict differential methylation assessed at age 19. Across multiple tests, a differential susceptibility perspective rather than a diathesis-stress framework best fit the data for genes associated with depression, consistently demonstrating greater epigenetic response to early cumulative SES risk among short allele carriers. A pattern consistent with greater impact among short allele carriers also was observed using all cytosine nucleotide-phosphate-guanine nucleotide sites across the genome that were differentially affected by early cumulative SES risk. We conclude that the short allele is associated with increased responsiveness to early cumulative SES risk among African American youth, leading to epigenetic divergence for depression-related genes in response to exposure to heightened SES risk among short allele carriers in a "for better" or "for worse" pattern.

The evolutionary history of SLC6A4 and the role of plasticity in Macaca

Serotonin has been repeatedly indicated as a biological marker of behavior. In particular, the serotonin transporter gene, SLC6A4, has been the focus of a large body of research. Interestingly, both rhesus macaques (Macaca mulatta) and humans have independently evolved a number of shared polymorphisms for this gene, which is indicative of parallel evolution between the two species. However, little is known about the evolution of this gene, particularly within macaques. Although there are several hypotheses as to the adaptive values of various polymorphisms, few authors have gone beyond theoretical discussion. Here, we examined the genetic variation in SLC6A4 within and between several species of macaques and investigate whether selection has played a significant role in its evolutionary history. In addition, we assayed the promoter region polymorphism, 5-HTTLPR, which is known to play a significant role in regulating both serotonin turnover and behavior. In examining the distribution of the 5-HTTLPR polymorphism, we identified significant differences between Indian and Chinese populations of Macaca mulatta; furthermore, we discovered its presence in Macaca cyclopis, which has not been described before. In regard to the evolutionary history of SLC6A4, we found little evidence for selection and conclude that SLC6A4 largely evolved through neutral processes, possibly due to its potential role in regulating behavioral plasticity. However, we also found very low levels of linkage between the coding regions and 5-HTTLPR. Because we limited evolutionary analyses to the coding regions, it is possible that the promoter region shows a distinct evolutionary history from SLC6A4.

Depression-like effect of prenatal buprenorphine exposure in rats

Studies indicate that perinatal opioid exposure produces a variety of short- and long-term neurobehavioral consequences. However, the precise modes of action are incompletely understood. Buprenorphine, a mixed agonist/antagonist at the opioid receptors, is currently being used in clinical trials for managing pregnant opioid addicts. This study provides evidence of depression-like consequence following prenatal exposure to supra-therapeutic dose of buprenorphine and sheds light on potential mechanisms of action in a rat model involving administration of intraperitoneal injection to pregnant Sprague-Dawley rats starting from gestation day 7 and lasting for 14 days. Results showed that pups at postnatal day 21 but not the dams had worse parameters of depression-like neurobehaviors using a forced swimming test and tail suspension test, independent of gender. Neurobehavioral changes were accompanied by elevation of oxidative stress, reduction of plasma levels of brain-derived neurotrophic factor (BDNF) and serotonin, and attenuation of tropomyosin-related kinase receptor type B (TrkB) phosphorylation, extracellular signal-regulated kinase (ERK) phosphorylation, protein kinase A activity, cAMP response element-binding protein (CREB) phosphorylation, and CREB DNA-binding activity. Since BDNF/serotonin and CREB signaling could orchestrate a positive feedback loop, our findings suggest that the induction of oxidative stress, reduction of BDNF and serotonin expression, and attenuation of CREB signaling induced by prenatal exposure to supra-therapeutic dose of buprenorphine provide evidence of potential mechanism for the development of depression-like neurobehavior.

Association between Neurocognitive Impairment and the Short Allele of the 5-HTT Promoter Polymorphism in Depression: A Pilot Study

Depression has been shown to be associated with cognitive deficits in various cognitive domains. However, it is still unclear which factors contribute to cognitive impairment. The objective of this study was to find out whether a functional polymorphism in the promoter region of the serotonin transporter (5-HTTLPR) gene is associated with the impairment of cognitive functioning among depressed patients. In a pilot study, a sample of 19 patients with major depressive disorder (MDD) and 19 healthy controls was investigated with an extensive psychiatric and neuropsychological examination. All participants were genotyped for 5-HTTLPR. Depressed patients with the short allele of the 5-HTT promoter region exhibited inferior cognitive performance compared to patients with the long allele polymorphism. In healthy controls, no association between genotype and cognitive performance was found. The result suggests that in MDD patients with the short allele of the 5-HTTLPR polymorphism the vulnerability to cognitive impairment is increased compared to MDD patients without the short allele inheritance. These preliminary findings need to be confirmed in a larger cohort of MDD patients.

Genetic polymorphisms in monoamine systems and outcome of cognitive behavior therapy for social anxiety disorder

Objective

The role of genetics for predicting the response to cognitive behavior therapy (CBT) for social anxiety disorder (SAD) has only been studied in one previous investigation. The serotonin transporter (5-HTTLPR), the catechol-o-methyltransferase (COMT) val158met, and the tryptophan hydroxylase-2 (TPH2) G-703Tpolymorphisms are implicated in the regulation of amygdala reactivity and fear extinction and therefore might be of relevance for CBT outcome. The aim of the present study was to investigate if these three gene variants predicted response to CBT in a large sample of SAD patients.

Method

Participants were recruited from two separate randomized controlled CBT trials (trial 1: n = 112, trial 2: n = 202). Genotyping were performed on DNA extracted from blood or saliva samples. Effects were analyzed at follow-up (6 or 12 months after treatment) for both groups and for each group separately at post-treatment. The main outcome measure was the Liebowitz Social Anxiety Scale Self-Report.

Results

At long-term follow-up, there was no effect of any genotype, or gene × gene interactions, on treatment response. In the subsamples, there was time by genotype interaction effects indicating an influence of the TPH2 G-703T-polymorphism on CBT short-term response, however the direction of the effect was not consistent across trials.

Conclusions

None of the three gene variants, 5-HTTLPR, COMTval158met and TPH2 G-703T, was associated with long-term response to CBT for SAD.

Trial Registration

ClinicalTrials.gov (ID-NCT0056496)

50 years of hurdles and hope in anxiolytic drug discovery

Anxiety disorders are the most prevalent group of psychiatric diseases, and have high personal and societal costs. The search for novel pharmacological treatments for these conditions is driven by the growing medical need to improve on the effectiveness and the side effect profile of existing drugs. A huge volume of data has been generated by anxiolytic drug discovery studies, which has led to the progression of numerous new molecules into clinical trials. However, the clinical outcome of these efforts has been disappointing, as promising results with novel agents in rodent studies have very rarely translated into effectiveness in humans. Here, we analyse the major trends from preclinical studies over the past 50 years conducted in the search for new drugs beyond those that target the prototypical anxiety-associated GABA (γ-aminobutyric acid)-benzodiazepine system, which have focused most intensively on the serotonin, neuropeptide, glutamate and endocannabinoid systems. We highlight various key issues that may have hampered progress in the field, and offer recommendations for how anxiolytic drug discovery can be more effective in the future.

Polymorphism in serotonin receptor 3B is associated with pain catastrophizing

Pain catastrophizing, a coping style characterized by excessively negative thoughts and emotions in relation to pain, is one of the psychological factors that most markedly predicts variability in the perception of pain; however, only little is known about the underlying neurobiology. The aim of this study was to test for associations between psychological variables, such as pain catastrophizing, anxiety and depression, and selected polymorphisms in genes related to monoaminergic neurotransmission, in particular serotonin pathway genes. Three hundred seventy-nine healthy participants completed a set of psychological questionnaires: the Pain Catastrophizing Scale (PCS), the State-Trait Anxiety Inventory and Beck’s Depression Inventory, and were genotyped for 15 single nucleotide polymorphisms (SNPs) in nine genes. The SNP rs1176744 located in the serotonin receptor 3_B gene (5-HTR3B) was found to be associated with pain catastrophizing scores: both the global score and the subscales of magnification and helplessness. This is the first study to show an association between 5-HTR3B and PCS scores, thus suggesting a role of the serotonin pathway in pain catastrophizing. Since 5-HTR3B has previously been associated with descending pain modulation pathways, future studies will be of great interest to elucidate the molecular pathways involved in the relation between serotonin, its receptors and pain catastrophizing.

Impact of 5-HTTLPR and BDNF polymorphisms on response to sertraline versus transcranial direct current stimulation: implications for the serotonergic system

Transcranial direct current stimulation (tDCS) has been intensively investigated as a non-pharmacological treatment for major depressive disorder (MDD). While many studies have examined the genetic predictors of antidepressant medications, this issue remains to be investigated for tDCS. In the current study, we evaluated whether the BDNF Val66Met and the 5-HTT (5-HTTLPR) polymorphisms were associated with tDCS antidepressant response. We used data from a factorial trial that evaluated the efficacy of tDCS and sertraline and enrolled 120 moderate-to-severe, antidepressant-free participants. In the present study, we used analyses of variance to evaluate whether the BDNF (Val/Val vs. Met-carries) and 5-HTTLPR alleles (long/long vs short-carriers) were predictors of tDCS (active/sham) and sertraline (sertraline/placebo) response. Analyses were conducted on the polymorphisms separately and also on their interaction. Genotype frequencies were in Hardy-Weinberg equilibrium. BDNF polymorphism was not associated with treatment response. We found that 5-HTTLPR predicted tDCS effects as long/long homozygotes displayed a larger improvement comparing active vs. sham tDCS, while short-allele carriers did not. A dose-response relationship between active-sham differences with the long allele was also suggested. These results strengthen the role of the serotonergic system in the tDCS antidepressant effects and expand previous findings that reported that tDCS mechanisms of action partially involve serotonergic receptors. Therefore, we hypothesize that tDCS is a neuromodulation technique that acts over depression through the modulation of serotonergic system and that tDCS "top-down" antidepressant effects might not be optimal in brain networks with a hyperactive amygdala inducing bottom-up effects, such as occurs in short-carriers.

Serotonin transporter genotype modulates functional connectivity between amygdala and PCC/PCu during mood recovery

The short (S) allele of the serotonin transporter-linked polymorphic region (5-HTTLPR) has been associated with increased susceptibility to depression. Previous neuroimaging studies have consistently showed increased amygdala activity during the presentation of negative stimuli or regulation of negative emotion in the homozygous short allele carriers, suggesting the key role of amygdala response in mediating increased risk for depression. The brain default mode network (DMN) has also been shown to modulate amygdala activity. However, it remains unclear whether 5-HTTLPR genetic variation modulates functional connectivity (FC) between the amygdala and regions of DMN. In this study, we re-analyzed our previous imaging dataset and examined the effects of 5-HTTLPR genetic variation on amygdala connectivity. A total of 15 homozygous short (S/S) and 15 homozygous long individuals (L/L) were scanned in functional magnetic resonance imaging (fMRI) during four blocks: baseline, sad mood, mood recovery, and return to baseline. The S/S and L/L groups showed a similar pattern of FC and no differences were found between the two groups during baseline and sad mood scans. However, during mood recovery, the S/S group showed significantly reduced anti-correlation between amygdala and posterior cingulate cortex/precuneus (PCC/PCu) compared to the L/L group. Moreover, PCC/PCu-amygdala connectivity correlated with amygdala activity in the S/S group but not the L/L group. These results suggest that 5-HTTLPR genetic variation modulates amygdala connectivity which subsequently affects its activity during mood regulation, providing an additional mechanism by which the S allele confers depression risk.

Interaction between the 5-HTTLPR genotype, impact of stressful life events, and trait neuroticism on depressive symptoms in healthy volunteers

INTRODUCTION

Recent biopsychological research on stress-related psychopathology shows promising evidence for the 5-hydroxytryptamine (5-HT) transporter linked polymorphic region (5-HTTLPR) genotype by life event interaction on depression. Yet, there appears to be variability in replicating such findings. From leading cognitive models of depression, it can be deduced that mainly high-impact events, particularly in stress-vulnerable, high trait neuroticism individuals who possess low coping abilities, can cause depression.

OBJECTIVE

The current study therefore examines the interaction between the 5-HTTLPR genotype, impact of life events, and trait neuroticism on depression symptoms.

PARTICIPANTS AND METHODS

A group of 771 healthy individuals, 595 women and 176 men aged 21.0±2.1 years, were genotyped for the 5-HTTLPR polymorphism and were rated for depressive symptoms, impact of life events, and neuroticism.

RESULTS

Only the low-allele expressing (S) 5-HTTLPR carriers showed vulnerability to depression exclusively when they also reported exposure to high-impact events and showed high neuroticism.

CONCLUSION

This suggests that cognitive vulnerabilities may mediate the 5-HTTLPR genotype by life event interaction on depression.

The expression of platelet serotonin transporter (SERT) in human obesity

Background

Serotonin (5-HT) is a well-known modulator of eating behavior. However, the molecular mechanisms linking its action to body weight balance have been only partially elucidated. Since platelets are a suitable peripheral model to study 5-HT transport, metabolism and release, we herein evaluated the expression of the platelet 5-HT re-uptake system (SERT) by [³H]-paroxetine binding assay. A cohort of 114 unrelated individuals (34 males, 80 females; age, mean ± SD: 38.57 ± 12.47 years) without major psychiatric disorders, was recruited following a naturalistic design regarding age or gender and classified accordingly to their body mass index (BMI). Subjects were divided into 5 groups: normal-weight (NW), overweight (OW) and grade I-III obese (OB) individuals. For gender analyses, data were transformed into [³H]-paroxetine density (B_max)/BMI ratios to overcome both the disparity of women vs. men number and anthropometric differences between sexes.

Results

[³H]-paroxetine B_max (SERT density, fmol/mg proteins) was reduced in platelet membranes of grade II (p < 0.01) and III (p < 0.001) obese subjects vs. controls and in overweight subjects (p < 0.05) vs. grade III obese individuals. Considering all patients together, a strong negative correlation between B_max and BMI (r = −0.449; P < 0.0001) was demonstrated. Conversely, [³H]-paroxetine K_D (dissociation constant, nM) did not differ among groups. No gender-related variation concerning B_max/BMI ratios was observed in this cohort of subjects.

Conclusions

The down-regulation of SERT in platelet membranes of severe human obesity (BMI > 35 Kg/m²) confirms the involvement of 5-HT system in body weight gain. Moreover, this findings may help to elucidate those monoamine-endocrine networks acting on fat storage, adipocyte signaling and energy balance. Targeting 5-HT/5-HT-related markers will possibly uncover the existence of human obesity subtypes.

Convergent effects of mouse Pet-1 deletion and human PET-1 variation on amygdala fear and threat processing

Serotonin is critical for shaping the development of neural circuits regulating emotion. Pet-1 (FEV-1) is an ETS-domain transcription factor essential for differentiation and forebrain targeting of serotonin neurons. Constitutive Pet-1 knockout (KO) causes major loss of serotonin neurons and forebrain serotonin availability, and behavioral abnormalities. We phenotyped Pet-1 KO mice for fear conditioning and extinction, and on a battery of assays for anxiety- and depression-related behaviors. Morphology of Golgi-stained neurons in basolateral amygdala (BLA) and prelimbic cortex was examined. Using human imaging genetics, a common variant (rs860573) in the PET-1 (FEV) gene was tested for effects on threat-related amygdala reactivity and psychopathology in 88 Asian-ancestry subjects. Pet-1 KO mice exhibited increased acquisition and expression of fear, and elevated fear recovery following extinction, relative to wild-type (WT). BLA dendrites of Pet-1 KO mice were significantly longer than in WT. Human PET-1 variation associated with differences in amygdala threat processing and psychopathology. This novel evidence for the role of Pet-1 in fear processing and dendritic organization of amygdala neurons and in human amygdala threat processing extends a growing literature demonstrating the influence of genetic variation in the serotonin system on emotional regulation via effects on structure and function of underlying corticolimbic circuitry.

The Influence of Major Life Events on Economic Attitudes in a World of Gene-Environment Interplay

The role of "genes" on political attitudes has gained attention across disciplines. However, person-specific experiences have yet to be incorporated into models that consider genetic influences. Relying on a gene-environment interplay approach, this study explicates how life-events, such as losing one's job or suffering a financial loss, influence economic policy attitudes. The results indicate genetic and environmental variance on support for unions, immigration, capitalism, socialism and property tax is moderated by financial risks. Changes in the magnitude of genetic influences, however, are temporary. After two years, the phenotypic effects of the life events remain on most attitudes, but changes in the sources of individual differences do not. Univariate twin models that estimate the independent contributions of genes and environment on the variation of attitudes appear to provide robust baseline indicators of sources of individual differences. These estimates, however, are not event or day specific. In this way, genetic influences add stability, while environment cues change, and this process is continually updated.

The role of the dorsal raphé nucleus in reward-seeking behavior

Pharmacological experiments have shown that the modulation of brain serotonin levels has a strong impact on value-based decision making. Anatomical and physiological evidence also revealed that the dorsal raphé nucleus (DRN), a major source of serotonin, and the dopamine system receive common inputs from brain regions associated with appetitive and aversive information processing. The serotonin and dopamine systems also have reciprocal functional influences on each other. However, the specific mechanism by which serotonin affects value-based decision making is not clear. To understand the information carried by the DRN for reward-seeking behavior, we measured single neuron activity in the primate DRN during the performance of saccade tasks to obtain different amounts of a reward. We found that DRN neuronal activity was characterized by tonic modulation that was altered by the expected and received reward value. Consistent reward-dependent modulation across different task periods suggested that DRN activity kept track of the reward value throughout a trial. The DRN was also characterized by modulation of its activity in the opposite direction by different neuronal subgroups, one firing strongly for the prediction and receipt of large rewards, with the other firing strongly for small rewards. Conversely, putative dopamine neurons showed positive phasic responses to reward-indicating cues and the receipt of an unexpected reward amount, which supports the reward prediction error signal hypothesis of dopamine. I suggest that the tonic reward monitoring signal of the DRN, possibly together with its interaction with the dopamine system, reports a continuous level of motivation throughout the performance of a task. Such a signal may provide "reward context" information to the targets of DRN projections, where it may be integrated further with incoming motivationally salient information.

Independent effects of 5' and 3' functional variants in the serotonin transporter gene on suicidal behavior in the context of childhood trauma

The serotonin transporter, encoded by the SLC6A4 gene, influences the synaptic actions of serotonin and is responsive to stress hormones. We hypothesized that 5-HTTLPR, a functional SLC6A4 promoter polymorphism, and two tightly-linked, putatively functional 3' UTR SNPs (rs3813034, rs1042173) might have independent effects on suicidal behavior in the context of childhood trauma (CT). DNA and Childhood Trauma Questionnaire scores were available for a total of 474 African Americans, including 112 suicide attempters and 362 non-suicide attempters. Genotyping was performed for the triallelic 5-HTTLPR polymorphism, 14 SLC6A4 haplotype-tagging SNPs, and 186 ancestry informative markers. There were independent G × E interactive effects of 5-HTTLPR (p = 0.017) and the rs3813034-rs1042173 diplotype (p = 0.011) on suicidal behavior. In individuals exposed to high CT the risk of suicide attempt was 0.52 in carriers of the low activity 5-HTTLPR variant and 0.32 in medium/high activity variant carriers. Likewise, CT exposed carriers of the major rs3813034-rs1042173 ATAT diplotype had an increased risk of suicidal behavior relative to the ATCG/CGCG diplotype carriers (0.40 vs 0.31). Neither the 5' nor the 3' functional variants had an effect in individuals without CT: suicide attempt risk = 0.12-0.22. In individuals exposed to high CT the prevalence of suicide attempt was 0.56 in carriers of both 5' and 3' risk variants, 0.39 in carriers of one risk variant and 0.25 in individuals without either risk variant. Our findings suggest that the 5' and 3'SLC6A4 functional variants have independent effects on the risk for suicidal behavior in CT exposed individuals.

Afraid to help: social anxiety partially mediates the association between 5-HTTLPR triallelic genotype and prosocial behavior

There is growing evidence that the serotonin system influences prosocial behavior. We examined whether anxiety mediated the association between variation in the serotonin transporter gene regulatory region (5-HTTLPR) and prosocial behavior. We collected self-reported tendencies to avoid certain situations and history of helping others using standard instruments and buccal cells for standard 5-HTTLPR genotyping from 398 undergraduate students. Triallelic 5-HTTLPR genotype was significantly associated with prosocial behavior and the effect was partially mediated by social anxiety, such that those carrying the S' allele reported higher levels of social avoidance and lower rates of helping others. These results are consistent with accounts of the role of serotonin on anxiety and prosocial behavior and suggest that targeted efforts to reduce social anxiety in S' allele carriers may enhance prosocial behavior.

Sex differences in emotion-related cognitive processes in irritable bowel syndrome and healthy control subjects

Greater responsiveness of emotional arousal circuits in relation to delivered visceral pain has been implicated as underlying central pain amplification in irritable bowel syndrome (IBS), with female subjects showing greater responses than male subjects. Functional magnetic resonance imaging was used to measure neural responses to an emotion recognition paradigm, using faces expressing negative emotions (fear and anger). Sex and disease differences in the connectivity of affective and modulatory cortical circuits were studied in 47 IBS (27 premenopausal female subjects) and 67 healthy control subjects (HCs; 38 premenopausal female subjects). Male subjects (IBS+HC) showed greater overall brain responses to stimuli than female subjects in prefrontal cortex, insula, and amygdala. Effective connectivity analyses identified major sex- and disease-related differences in the functioning of brain networks related to prefrontal regions, cingulate, insula, and amygdala. Male subjects had stronger connectivity between anterior cingulate subregions, amygdala, and insula, whereas female subjects had stronger connectivity to and from the prefrontal modulatory regions (medial/dorsolateral cortex). Male IBS subjects demonstrate greater engagement of cortical and affect-related brain circuitry compared to male control subjects and female subjects, when viewing faces depicting emotions previously shown to elicit greater behavioral and brain responses in male subjects.

Neuroethology of primate social behavior

A neuroethological approach to human and nonhuman primate behavior and cognition predicts biological specializations for social life. Evidence reviewed here indicates that ancestral mechanisms are often duplicated, repurposed, and differentially regulated to support social behavior. Focusing on recent research from nonhuman primates, we describe how the primate brain might implement social functions by coopting and extending preexisting mechanisms that previously supported nonsocial functions. This approach reveals that highly specialized mechanisms have evolved to decipher the immediate social context, and parallel circuits have evolved to translate social perceptual signals and nonsocial perceptual signals into partially integrated social and nonsocial motivational signals, which together inform general-purpose mechanisms that command behavior. Differences in social behavior between species, as well as between individuals within a species, result in part from neuromodulatory regulation of these neural circuits, which itself appears to be under partial genetic control. Ultimately, intraspecific variation in social behavior has differential fitness consequences, providing fundamental building blocks of natural selection. Our review suggests that the neuroethological approach to primate behavior may provide unique insights into human psychopathology.

Genetic and pharmacological manipulations of the serotonergic system in early life: neurodevelopmental underpinnings of autism-related behavior

Serotonin, in its function as neurotransmitter, is well-known for its role in depression, autism and other neuropsychiatric disorders, however, less known as a neurodevelopmental factor. The serotonergic system is one of the earliest to develop during embryogenesis and early changes in serotonin levels can have large consequences for the correct development of specific brain areas. The regulation and functioning of serotonin is influenced by genetic risk factors, such as the serotonin transporter polymorphism in humans. This polymorphism is associated with anxiety-related symptoms, changes in social behavior, and cortical gray and white matter changes also seen in patients suffering from autism spectrum disorders (ASD). The human polymorphism can be mimicked by the knockout of the serotonin transporter in rodents, which are as a model system therefore vital to explore the precise neurobiological mechanisms. Moreover, there are pharmacological challenges influencing serotonin in early life, like prenatal/neonatal exposure to selective serotonin reuptake inhibitors (SSRI) in depressed pregnant women. There is accumulating evidence that this dysregulation of serotonin during critical phases of brain development can lead to ASD-related symptoms in children, and reduced social behavior and increased anxiety in rodents. Furthermore, prenatal valproic acid (VPA) exposure, a mood stabilizing drug which is also thought to interfere with serotonin levels, has the potency to induce ASD-like symptoms and to affect the development of the serotonergic system. Here, we review and compare the neurodevelopmental and behavioral consequences of serotonin transporter gene variation, and prenatal SSRI and VPA exposure in the context of ASD.

The role of the serotonergic and GABA system in translational approaches in drug discovery for anxiety disorders

There is ample evidence that genetic factors play an important role in anxiety disorders. In support, human genome-wide association studies have implicated several novel candidate genes. However, illumination of such genetic factors involved in anxiety disorders has not resulted in novel drugs over the past decades. A complicating factor is the heterogeneous classification of anxiety disorders in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) and diverging operationalization of anxiety used in preclinical and clinical studies. Currently, there is an increasing focus on the gene × environment (G × E) interaction in anxiety as genes do not operate in isolation and environmental factors have been found to significantly contribute to the development of anxiety disorders in at-risk individuals. Nevertheless, extensive research on G × E mechanisms in anxiety has not resulted in major breakthroughs in drug discovery. Modification of individual genes in rodent models has enabled the specific study of anxiety in preclinical studies. In this context, two extensively studied neurotransmitters involved in anxiety are the gamma-aminobutyric acid (GABA) and 5-HT (5-hydroxytryptamine) system. In this review, we illustrate the complex interplay between genes and environment in anxiety processes by reviewing preclinical and clinical studies on the serotonin transporter (5-HTT), 5-HT1A receptor, 5-HT2 receptor, and GABAA receptor. Even though targets from the serotonin and GABA system have yielded drugs with known anxiolytic efficacy, the relation between the genetic background of these targets and anxiety symptoms and development of anxiety disorders is largely unknown. The aim of this review is to show the vast complexity of genetic and environmental factors in anxiety disorders. In light of the difficulty with which common genetic variants are identified in anxiety disorders, animal models with translational validity may aid in elucidating the neurobiological background of these genes and their possible role in anxiety. We argue that, in addition to human genetic studies, translational models are essential to map anxiety-related genes and to enhance our understanding of anxiety disorders in order to develop potentially novel treatment strategies.

Neuroimaging methods for adolescent substance use disorder prevention science

Magnetic resonance imaging (MRI) methods safely provide in vivo indicators of cerebral macrostructure, microstructure, and activation that can be examined in relation to substance use disorder (SUD) risks and effects. This article will provide an overview of MRI approaches, including volumetric measures, diffusion tensor imaging, and functional MRI, that have been applied to studies of adolescent neuromaturation in relationship to risk phenotypes and adolescent SUD. To illustrate these applications, examples of research findings will be presented. MRI indicators have demonstrated that neurobiological maturation continues throughout adolescence. MRI research has suggested that variations in neurobiological maturation may contribute to SUD risk, and that substance use adversely influences adolescent brain development. Directly measured neurobiological variables may be viable preventive intervention targets and outcome indicators. Further research is needed to provide definitive findings on neurodevelopmental immaturity as an SUD risk and to determine the directions such observations suggest for advancing prevention science.

Improved cognitive flexibility in serotonin transporter knockout rats is unchanged following chronic cocaine self-administration

Cocaine dependence is associated with orbitofrontal cortex (OFC)-dependent cognitive inflexibility in both humans and laboratory animals. A critical question is whether cocaine self-administration affects pre-existing individual differences in cognitive flexibility. Serotonin transporter knockout (5-HTT(-/-) ) mice show improved cognitive flexibility in a visual reversal learning task, whereas 5-HTT(-/-) rats self-administer increased amounts of cocaine. Here we assessed: (1) whether 5-HTT(-/-) rats also show improved cognitive flexibility (next to mice); and (2) whether this is affected by cocaine self-administration, which is increased in these animals. Results confirmed that naïve 5-HTT(-/-) rats (n = 8) exhibit improved cognitive flexibility, as measured in a sucrose reinforced reversal learning task. A separate group of rats was subsequently trained to intravenously self-administer cocaine (0.5 mg/kg/infusion), and we observed that the 5-HTT(-/-) rats (n = 10) self-administered twice as much cocaine [632.7 mg/kg (±26.3)] compared with 5-HTT(+/+) rats (n = 6) [352.3 mg/kg (±62.0)] over 50 1-hour sessions. Five weeks into withdrawal the cocaine-exposed animals were tested in the sucrose-reinforced reversal learning paradigm. Interestingly, like the naïve 5-HTT(-/-) rats, the cocaine exposed 5-HTT(-/-) rats displayed improved cognitive flexibility. In conclusion, we show that improved reversal learning in 5-HTT(-/-) rats reflects a pre-existing trait that is preserved during cocaine-withdrawal. As 5-HTT(-/-) rodents model the low activity s-allele of the human serotonin transporter-linked polymorphic region, these findings may have heuristic value in the treatment of s-allele cocaine addicts.

Genetic and neurocognitive foundations of emotion abnormalities in bipolar disorder

INTRODUCTION

Bipolar Disorder (BD) is a serious mood disorder, the aetiology of which is still unclear. The disorder is characterised by extreme mood variability in which patients fluctuate between markedly euphoric, irritable, and elevated states to periods of severe depression. The current research literature shows that BD patients demonstrate compromised neurocognitive ability in addition to these mood symptoms. Viable candidate genes implicated in neurocognitive and socioemotional processes may explain the development of these core emotion abnormalities. Additionally, links between faulty neurocognition and impaired socioemotional ability complement genetic explanations of BD pathogenesis. This review examines associations between cognition indexing prefrontal neural regions and socioemotional impairments including emotion processing and regulation. A review of the effect of COMT and TPH2 on these functions is also explored.

METHODS

Major computer databases including PsycINFO, Google Scholar, and Medline were consulted in order to conduct a comprehensive review of the genetic and cognitive literature in BD.

RESULTS

This review determines that COMT and TPH2 genetic variants contribute susceptibility to abnormal prefrontal neurocognitive function which oversees the processing and regulation of emotion. This provides for greater understanding of some of the emotional and cognitive symptoms in BD.

CONCLUSIONS

Current findings in this direction show promise, although the literature is still in its infancy and further empirical research is required to investigate these links explicitly.

Contextual fear conditioning in virtual reality is affected by 5HTTLPR and NPSR1 polymorphisms: effects on fear-potentiated startle

The serotonin (5-HT) and neuropeptide S (NPS) systems are discussed as important genetic modulators of fear and sustained anxiety contributing to the etiology of anxiety disorders. Sustained anxiety is a crucial characteristic of most anxiety disorders which likely develops through contextual fear conditioning. This study investigated if and how genetic alterations of the 5-HT and the NPS systems as well as their interaction modulate contextual fear conditioning; specifically, function polymorphic variants in the genes coding for the 5-HT transporter (5HTT) and the NPS receptor (NPSR1) were studied. A large group of healthy volunteers was therefore stratified for 5HTTLPR (S+ vs. LL carriers) and NPSR1 rs324981 (T+ vs. AA carriers) polymorphisms resulting in four genotype groups (S+/T+, S+/AA, LL/T+, LL/AA) of 20 participants each. All participants underwent contextual fear conditioning and extinction using a virtual reality (VR) paradigm. During acquisition, one virtual office room (anxiety context, CXT+) was paired with an unpredictable electric stimulus (unconditioned stimulus, US), whereas another virtual office room was not paired with any US (safety context, CXT−). During extinction no US was administered. Anxiety responses were quantified by fear-potentiated startle and ratings. Most importantly, we found a gene × gene interaction on fear-potentiated startle. Only carriers of both risk alleles (S+/T+) exhibited higher startle responses in CXT+ compared to CXT−. In contrast, anxiety ratings were only influenced by the NPSR1 polymorphism with AA carriers showing higher anxiety ratings in CXT+ as compared to CXT−. Our results speak in favor of a two level account of fear conditioning with diverging effects on implicit vs. explicit fear responses. Enhanced contextual fear conditioning as reflected in potentiated startle responses may be an endophenotype for anxiety disorders.

A neurogenetics approach to understanding individual differences in brain, behavior, and risk for psychopathology

Neurogenetics research has begun to advance our understanding of how genetic variation gives rise to individual differences in brain function, which, in turn, shapes behavior and risk for psychopathology. Despite these advancements, neurogenetics research is currently confronted by three major challenges: (1) conducting research on individual variables with small effects, (2) absence of detailed mechanisms, and (3) a need to translate findings toward greater clinical relevance. In this review, we showcase techniques and developments that address these challenges and highlight the benefits of a neurogenetics approach to understanding brain, behavior and psychopathology. To address the challenge of small effects, we explore approaches including incorporating the environment, modeling epistatic relationships and using multilocus profiles. To address the challenge of mechanism, we explore how non-human animal research, epigenetics research and genome-wide association studies can inform our mechanistic understanding of behaviorally relevant brain function. Finally, to address the challenge of clinical relevance, we examine how neurogenetics research can identify novel therapeutic targets and for whom treatments work best. By addressing these challenges, neurogenetics research is poised to exponentially increase our understanding of how genetic variation interacts with the environment to shape the brain, behavior and risk for psychopathology.

Inflammatory vulnerability associated with the rh5-HTTLPR genotype in juvenile rhesus monkeys

Individual variation in serotonergic function is associated with reactivity, risk for affective disorders, as well as an altered response to disease. Our study used a nonhuman primate model to further investigate whether a functional polymorphism in the promoter region for the serotonin transporter gene helps to explain differences in proinflammatory responses. Homology between the human and rhesus monkey polymorphisms provided the opportunity to determine how this genetic variation influences the relationship between a psychosocial stressor and immune responsiveness. Leukocyte numbers in blood and interleukin-6 (IL-6) responses are sensitive to stressful challenges and are indicative of immune status. The neutrophil-to-lymphocyte ratio and cellular IL-6 responses to in vitro lipopolysaccharide stimulation were assessed in 27 juvenile male rhesus monkeys while housed in stable social groups (NLL  = 16, NS  = 11) and also in 18 animals after relocation to novel housing (NLL  = 13, NS  = 5). Short allele monkeys had significantly higher neutrophil-to-lymphocyte ratios than homozygous Long allele carriers at baseline [t(25) = 2.18, P = 0.02], indicative of an aroused state even in the absence of disturbance. In addition, following the housing manipulation, IL-6 responses were more inhibited in short allele carriers (F1,16  = 8.59, P = 0.01). The findings confirm that the serotonin transporter gene-linked polymorphism is a distinctive marker of reactivity and inflammatory bias, perhaps in a more consistent manner in monkeys than found in many human studies.

Functional and structural neural network characterization of serotonin transporter knockout rats

Brain serotonin homeostasis is crucially maintained by the serotonin transporter (5-HTT), and its down-regulation has been linked to increased vulnerability for anxiety- and depression-related behavior. Studies in 5-HTT knockout (5-HTT^-/-) rodents have associated inherited reduced functional expression of 5-HTT with increased sensitivity to adverse as well as rewarding environmental stimuli, and in particular cocaine hyperresponsivity. 5-HTT down-regulation may affect normal neuronal wiring of implicated corticolimbic cerebral structures. To further our understanding of its contribution to potential alterations in basal functional and structural properties of neural network configurations, we applied resting-state functional MRI (fMRI), pharmacological MRI of cocaine-induced activation, and diffusion tensor imaging (DTI) in 5-HTT^-/- rats and wild-type controls (5-HTT^+/+). We found that baseline functional connectivity values and cocaine-induced neural activity within the corticolimbic network was not significantly altered in 5-HTT^-/- versus 5-HTT^+/+ rats. Similarly, DTI revealed mostly intact white matter structural integrity, except for a reduced fractional anisotropy in the genu of the corpus callosum of 5-HTT^-/- rats. At the macroscopic level, analyses of complex graphs constructed from either functional connectivity values or structural DTI-based tractography results revealed that key properties of brain network organization were essentially similar between 5-HTT^+/+ and 5-HTT^-/- rats. The individual tests for differences between 5-HTT^+/+ and 5-HTT^-/- rats were capable of detecting significant effects ranging from 5.8% (fractional anisotropy) to 26.1% (pharmacological MRI) and 29.3% (functional connectivity). Tentatively, lower fractional anisotropy in the genu of the corpus callosum could indicate a reduced capacity for information integration across hemispheres in 5-HTT^-/- rats. Overall, the comparison of 5-HTT^-/- and wild-type rats suggests mostly limited effects of 5-HTT genotype on MRI-based measures of brain morphology and function.

Identifying serotonergic mechanisms underlying the corticolimbic response to threat in humans

A corticolimbic circuit including the amygdala and medial prefrontal cortex (mPFC) plays an important role in regulating sensitivity to threat, which is heightened in mood and anxiety disorders. Serotonin is a potent neuromodulator of this circuit; however, specific serotonergic mechanisms mediating these effects are not fully understood. Recent studies have evaluated molecular mechanisms mediating the effects of serotonin signalling on corticolimbic circuit function using a multi-modal neuroimaging strategy incorporating positron emission tomography and blood oxygen level-dependent functional magnetic resonance imaging. This multi-modal neuroimaging strategy can be integrated with additional techniques including imaging genetics and pharmacological challenge paradigms to more clearly understand how serotonin signalling modulates neural pathways underlying sensitivity to threat. Integrating these methodological approaches offers novel opportunities to identify mechanisms through which serotonin signalling contributes to differences in brain function and behaviour, which in turn can illuminate factors that confer risk for illness and inform the development of more effective treatment strategies.

Development × environment interactions control tph2 mRNA expression

Adverse early life experience is thought to increase an individual's susceptibility to mental health disorders, including anxiety and affective disorders, later in life. Our previous studies have shown that post-weaning social isolation of female rats during a critical period of development sensitizes an anxiety-related serotonergic dorsal raphe nucleus (DR) system in adulthood. Therefore, we investigated how post-weaning social isolation, in combination with a challenge with the anxiogenic drug, N-methyl-beta-carboline-3-carboxamide (FG-7142; a partial inverse agonist at the benzodiazepine allosteric site on the GABAA receptor), affects home cage behavior and serotonergic gene expression in the DR of female rats using in situ hybridization histochemistry. Juvenile female rats were reared in isolation or groups of three for a 3-week period from weaning (postnatal day (PD) 21 to mid-adolescence (PD42)), after which all rats were group-reared for an additional 16 days until adulthood. Among vehicle-treated rats, isolation-reared rats had decreased rodent tryptophan hydroxylase 2 (tph2) mRNA expression in ventral and ventrolateral subdivisions of the DR, a pattern observed previously in a rat model of panic disorder. Isolation-reared rats, but not group-reared rats, responded to FG-7142 with increased duration of vigilance and arousal behaviors. In addition, FG-7142 decreased tph2 expression, measured 4h following treatment, in multiple subregions of the DR of group-reared rats but had no effect in isolation-reared rats. No treatment effects were observed on 5-HT1A receptor or serotonin transporter gene expression. These data suggest that adolescent social isolation alters tph2 expression in specific subregions of the DR and alters the effects of stress-related stimuli on behavior and serotonergic systems.

Effects of AKAP5 Pro100Leu genotype on working memory for emotional stimuli

Recent investigations addressing the role of the synaptic multiadaptor molecule AKAP5 in human emotion and behavior suggest that the AKAP5 Pro100Leu polymorphism (rs2230491) contributes to individual differences in affective control. Carriers of the less common Leu allele show a higher control of anger as indicated by behavioral measures and dACC brain response on emotional distracters when compared to Pro homozygotes. In the current fMRI study we used an emotional working memory task according to the n-back scheme with neutral and negative emotional faces as target stimuli. Pro homozygotes showed a performance advantage at the behavioral level and exhibited enhanced activation of the amygdala and fusiform face area during working memory for emotional faces. On the other hand, Leu carriers exhibited increased activation of the dACC during performance of the 2-back condition. Our results suggest that AKAP5 Pro100Leu effects on emotion processing might be task-dependent with Pro homozygotes showing lower control of emotional interference, but more efficient processing of task-relevant emotional stimuli.

Influence of serotonin transporter promoter variation on the effects of separation from parent/partner on depression

BACKGROUND

Loss of parent during childhood or loss of partner has been associated with adulthood depression. The serotonin transporter polymorphism (5-HTTLPR) has been reported to moderate stress sensitivity reflected for example in the relationship between childhood maltreatment and depression. Therefore, the effect of 5-HTT promoter variation on the relationship between the loss of parent or partner and depression was examined.

METHOD

411 depressive cases and 1347 control subjects from a large well-characterized longitudinal population-based sample of adult Swedes with data on life history and life situation, including psychiatric diagnostic instruments, were studied. Their DNA was genotyped for the mini-haplotype 5-HTTLPR-rs25531.

RESULTS

Individuals with low 5-HTT activity variants had an increased risk of depression given loss of partner last year compared to those with high activity variants. Conversely, 5-HTT activity variation appeared not to strongly influence the risk of depression given loss of parent during childhood.

LIMITATION

Small sample size for those with losses of both parent and partner. Limited power to detect small interaction effects.

CONCLUSION

The increased risk of depression given last year loss of partner appeared to be influenced by genetic variation regulating 5-HTT activity. This adds to previous findings of 5-HTT x stressful life events interactions on depression and is in agreement with stronger GxE effects when using objective environmental measures.

Genetic origins of social networks in rhesus macaques

Sociality is believed to have evolved as a strategy for animals to cope with their environments. Yet the genetic basis of sociality remains unclear. Here we provide evidence that social network tendencies are heritable in a gregarious primate. The tendency for rhesus macaques, Macaca mulatta, to be tied affiliatively to others via connections mediated by their social partners - analogous to friends of friends in people - demonstrated additive genetic variance. Affiliative tendencies were predicted by genetic variation at two loci involved in serotonergic signalling, although this result did not withstand correction for multiple tests. Aggressive tendencies were also heritable and were related to reproductive output, a fitness proxy. Our findings suggest that, like humans, the skills and temperaments that shape the formation of multi-agent relationships have a genetic basis in nonhuman primates, and, as such, begin to fill the gaps in our understanding of the genetic basis of sociality.

Individual differences in recovery from traumatic fear

Although exposure to major psychological trauma is unfortunately common, risk for related neuropsychiatric conditions, such as post-traumatic stress disorder (PTSD), varies greatly among individuals. Fear extinction offers a tractable and translatable behavioral readout of individual differences in learned recovery from trauma. Studies in rodent substrains and subpopulations are providing new insights into neural system dysfunctions associated with impaired fear extinction. Rapid progress is also being made in identifying key molecular circuits, epigenetic mechanisms, and gene variants associated with differences in fear extinction. Here, we discuss how this research is informing understanding of the etiology and pathophysiology of individual differences in risk for trauma-related anxiety disorders, and how future work can help identify novel diagnostic biomarkers and pharmacotherapeutics for these disorders.

Psilocybin biases facial recognition, goal-directed behavior, and mood state toward positive relative to negative emotions through different serotonergic subreceptors

BACKGROUND

Serotonin (5-HT) 1A and 2A receptors have been associated with dysfunctional emotional processing biases in mood disorders. These receptors further predominantly mediate the subjective and behavioral effects of psilocybin and might be important for its recently suggested antidepressive effects. However, the effect of psilocybin on emotional processing biases and the specific contribution of 5-HT2A receptors across different emotional domains is unknown.

METHODS

In a randomized, double-blind study, 17 healthy human subjects received on 4 separate days placebo, psilocybin (215 μg/kg), the preferential 5-HT2A antagonist ketanserin (50 mg), or psilocybin plus ketanserin. Mood states were assessed by self-report ratings, and behavioral and event-related potential measurements were used to quantify facial emotional recognition and goal-directed behavior toward emotional cues.

RESULTS

Psilocybin enhanced positive mood and attenuated recognition of negative facial expression. Furthermore, psilocybin increased goal-directed behavior toward positive compared with negative cues, facilitated positive but inhibited negative sequential emotional effects, and valence-dependently attenuated the P300 component. Ketanserin alone had no effects but blocked the psilocybin-induced mood enhancement and decreased recognition of negative facial expression.

CONCLUSIONS

This study shows that psilocybin shifts the emotional bias across various psychological domains and that activation of 5-HT2A receptors is central in mood regulation and emotional face recognition in healthy subjects. These findings may not only have implications for the pathophysiology of dysfunctional emotional biases but may also provide a framework to delineate the mechanisms underlying psylocybin's putative antidepressant effects.

Age-related effect of serotonin transporter genotype on amygdala and prefrontal cortex function in adolescence

The S and LG alleles of the serotonin transporter-linked polymorphic region (5-HTTLPR) lower serotonin transporter expression. These low-expressing alleles are linked to increased risk for depression and brain activation patterns found in depression (increased amygdala activation and decreased amygdala-prefrontal cortex connectivity). Paradoxically, serotonin transporter blockade relieves depression symptoms. Rodent models suggest that decreased serotonin transporter in early life produces depression that emerges in adolescence, whereas decreased serotonin transporter that occurs later in development ameliorates depression. However, no brain imaging research has yet investigated the moderating influence of human development on the link between 5-HTTLPR and effect-related brain function. We investigated the age-related effect of 5-HTTLPR on amygdala activation and amygdala-prefrontal cortex connectivity using a well-replicated probe, an emotional face task, in children and adolescents aged 9-19 years. A significant genotype-by-age interaction predicted amygdala activation, such that the low-expressing genotype (S/S and S/LG ) group showed a greater increase in amygdala activation with age compared to the higher expressing (LA /LA and S/LA ) group. Additionally, compared to the higher expressing group, the low-expressing genotype group exhibited decreased connectivity between the right amygdala and ventromedial prefrontal cortex with age. Findings indicate that low-expressing genotypes may not result in the corticolimbic profile associated with depression risk until later adolescence.

The functional epistasis of 5-HTTLPR and BDNF Val66Met on emotion processing: a preliminary study

An epistatic interaction of 5-HTTLPR and BDNF Val66Met polymorphisms has been implicated in the structure of rostral anterior cingulate cortex (rACC) and amygdala (AMY): key regions associated with emotion processing. However, a functional epistasis of 5-HTTLPR and BDNF Val66Met on overt emotion processing has yet to be determined. Twenty-eight healthy, Caucasian female participants provided saliva samples for genotyping and underwent functional magnetic resonance imaging (fMRI) during which an emotion processing protocol were presented. Confirming the validity of this protocol, we observed blood oxygen level-dependent (BOLD) activity consistent with fMRI meta-analyses on emotion processing. Region-of-interest analysis of the rACC and AMY revealed main effects of 5-HTTLPR and BDNF Val66Met, and an interaction of 5-HTTLPR and BDNF Val66Met. The effect of the BDNF Met66 allele was dependent on 5-HTTLPR alleles, such that participants with S and Met alleles had the greatest rACC and AMY activation during the presentation of emotional images relative to other genetic groupings. Increased activity in these regions was interpreted as increased reactivity to emotional stimuli, suggesting that those with S and Met alleles are more reactive to emotional stimuli relative to other groups. Although limited by a small sample, this study contributes novel and preliminary findings relating to a functional epistasis of the 5-HTTLPR and BDNF Val66Met genes in emotion processing and provides guidance on appropriate methods to determine genetic epistasis in fMRI.

Genes, Economics, and Happiness

We explore the influence of genetic variation on subjective well-being by employing a twin design and genetic association study. In a nationally-representative twin sample, we first show that about 33% of the variation in life satisfaction is explained by genetic variation. Although previous studies have shown that baseline happiness is significantly heritable, little research has considered molecular genetic associations with subjective well-being. We study the relationship between a functional polymorphism on the serotonin transporter gene (5-HTTLPR) and life satisfaction. We initially find that individuals with the longer, transcriptionally more efficient variant of this genotype report greater life satisfaction (n=2,545, p=0.012). However, our replication attempts on independent samples produce mixed results indicating that more work needs to be done to better understand the relationship between this genotype and subjective well-being. This work has implications for how economists think about the determinants of utility, and the extent to which exogenous shocks might affect individual well-being.

The relation of developmental changes in brain serotonin transporter (5HTT) and 5HT1A receptor binding to emotional behavior in female rhesus monkeys: effects of social status and 5HTT genotype

The goal of the present study was to examine how social subordination stress and 5HTT polymorphisms affect the development of brain serotonin (5HT) systems during the pubertal transition in female rhesus monkeys. We also examined associations with developmental changes in emotional reactivity in response to a standardized behavioral test, the Human Intruder (HI). Our findings provide the first longitudinal evidence of developmental increases in 5HT1A receptor and 5HTT binding in the brain of female primates from pre- to peripuberty. The increase in 5HT1A BP(ND) in these socially housed female rhesus monkeys is a robust finding, occurring across all groups, regardless of social status or 5HTT genotype, and occurring in the left and right hemispheres of all prefrontal regions studied, as well as the amygdala, hippocampus, hypothalamus, and raphe nuclei. 5HTT BP(ND) also showed an increase with age in raphe, anterior cingulate cortex, and dorsolateral prefrontal cortex. These changes in brain 5HT systems take place as females establish more adult-like patterns of social behavior, as well as during the HI paradigm. Indeed, the main developmental changes in behavior during the HI (increase in freezing and decrease in submission/appeasement) were related to neurodevelopmental increases in 5HT1A receptors and 5HTT, because the associations between these behaviors and 5HT endpoints emerge at peripuberty. We detected an effect of social status on 5HT1A BP(ND) in the hypothalamus and on 5HTT BP(ND) in the orbitofrontal cortex, with subordinates showing higher BP(ND) than dominants in both cases during the pubertal transition. No main effects of 5HTT genotype were observed for 5HT1A or 5HTT BP(ND). Our findings indicate that adolescence in female rhesus monkeys is a period of central 5HT reorganization, partly influenced by exposure to the social stress of subordination, that likely functions to integrate adrenal and gonadal systems and shape the behavioral response to emotionally challenging social situations.

The Southern Illinois Twins and Siblings Study (SITSS): description and update

This update on the Southern Illinois Twins and Siblings Study (SITSS) documents some of the follow-up studies that have been conducted and results that have been obtained from this sample. At the current time, 283 twin pairs, 8 triplet families, 98 non-twin sibling pairs, and 287 singletons have been enrolled in SITSS. Twins and triplets are tested as young as 1 year of age and then every year on their birthday through age 5 years. A variety of follow-up studies have been conducted for SITSS children through age 20. Results thus far have demonstrated significant genetic influences on social behaviors such as aggression, victimization, and attention toward facial expressions. Interesting interactions have been documented between the dopamine receptor D4 gene (DRD4) and the social environment (parental sensitivity or peer aggression) as they predict children's aggressive behaviors. In addition, increased difficulty with social interactions has been noted for twins versus singletons. Thus, this multi-trait, multi-method behavior genetic data set contributes to our understanding of the etiology of social behaviors in preschoolers and to predictors of similar behaviors through adolescence.