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

Social influences on health: is serotonin a critical mediator?

The influence of social relationships on health has been well documented for many years, yet identifying the physiological mechanisms responsible for these effects has proved more challenging. This review assesses the potential role of the serotonin system in affecting sensitivity to the health-related effects of the social environment. Building on recent studies of genetic variation in the serotonin system, particularly focusing on a polymorphism (5-HTTLPR) in the serotonin transporter gene, we provide evidence that activity within the serotonin system is critically involved in setting sensitivity to social experiences. Furthermore, we highlight the effects of the 5-HTTLPR on sensitivity to both positive and negative social experiences. In a positive environment, individuals with the short allele, and particularly the short/short genotype, function better psychologically than those with the long/long genotype. Conversely, when exposed to adverse environments or in the absence of social support, individuals with the short allele are at high risk for a variety of negative health outcomes. This serotoninergic involvement in social sensitivity seems to occur in concert with other neurochemical systems, such as the opioid system, which will also be discussed. Although this differential sensitivity to social experiences is initially determined in the brain, it has physiological effects on downstream pathways that more directly affect disease mechanisms, such as the hypothalamic-pituitary-adrenal axis, which is a particular focus of this review. The serotonin system, as indexed by the 5-HTTLPR, is an important link between the social environment and health.

Platelet monoamine oxidase activity predicts alcohol sensitivity and voluntary alcohol intake in rhesus monkeys

Platelet monoamine oxidase B (MAO-B) has been proposed to be a biological marker for the properties of monoamine systems, with low activity being associated with vulnerability for high scores on personality traits such as sensation seeking, monotony avoidance, and impulsiveness, as well as for vulnerability for alcoholism. In the present study, platelet MAO-B activity was analysed in 78 rhesus macaques, and its relation to voluntary alcohol intake and behaviours after intravenous alcohol administration was observed. Monkeys with low platelet MAO-B activity had low levels of 5-hydroxyindole acetic acid in cerebrospinal fluid and showed excessive aggression after alcohol administration. A novel finding was that animals with low platelet MAO-B activity showed less intoxication following alcohol administration. As we have shown previously, they also voluntarily consumed more alcohol. We here replicate results from studies on both humans and non-human primates, showing the utility of platelet MAO as a marker for risk behaviours and alcohol abuse. Furthermore, we link platelet MAO activity to alcohol sensitivity.

Altered sleep homeostasis after restraint stress in 5-HTT knock-out male mice: a role for hypocretins

Restraint stress produces changes in the sleep pattern that are mainly characterized by a delayed increase in rapid eye movement sleep (REMS) amounts. Because the serotonin (5-HT) and the hypocretin (hcrt) systems that regulate REMS are interconnected, we used mutant mice deficient in the 5-HT transporter (5-HTT(-/-)) to examine the role of 5-HT and hcrt neurotransmissions in the sleep response to stress. In contrast to wild-type mice, restraint stress did not induce a delayed increase in REMS amounts in 5-HTT(-/-) mice, indicating impaired sleep homeostasis in mutants. However, pharmacological blockade of the hcrt type 1 receptor (hcrt-R1) before restraint stress restored the REMS increase in 5-HTT(-/-) mice. In line with this finding, 5-HTT(-/-) mutants displayed after restraint stress higher long-lasting activation of hypothalamic preprohcrt neurons than wild-type mice and elevated levels of the hcrt-1 peptide and the hcrt-R1 mRNA in the anterior raphe area. Thus, hypocretinergic neurotransmission was enhanced by stress in 5-HTT(-/-) mice. Furthermore, in 5-HTT(-/-) but not wild-type mice, hypothalamic levels of the 5-HT metabolite 5-hydroxyindole acetic acid significantly increased after restraint stress, indicating a marked enhancement of serotonergic neurotransmission in mutants. Altogether, our data show that increased serotonergic -and in turn hypocretinergic- neurotransmissions exert an inhibitory influence on stress-induced delayed REMS. We propose that the direct interactions between hcrt neurons in the hypothalamus and 5-HT neurons in the anterior raphe nuclei account, at least in part, for the adaptive sleep-wakefulness regulations triggered by acute stress.

[Neurobiological aspects of reactive and proactive violence in antisocial personality disorder and "psychopathy"]

Impulsive-reactive violent offenders show increased autonomic activity in response to negative emotional and threatening stimuli. A volume reduction and/or activity decrease of frontal brain structures associated with impulse control and the regulation of fear and anger are likewise found in combination with a fear-related hyperactivity of the amygdala. In addition, impulsive aggression is facilitated by variants of gene polymorphisms influencing the serotonergic system. Conversely, proactive-instrumental violent offender with psychopathy, who are characterized by a lack of empathy and remorse, demonstrate an autonomic hypo-responsivity as well as dysfunctions of the amygdala and of cortical regions related to empathic and social behavior. Developmentally, aggressive children exhibit temperamental differences from early childhood on that are characteristic of a developmental pathway towards either reactive or proactive violence later in life. Exposure to negative environmental factors like ineffective parenting or childhood maltreatment has been related to a heightened risk for developing reactive violence. A developmental trajectory of proactive violence, however, has been related to a mostly genetically determined callous unemotional temperament of the child that disrupts the parental socialization efforts during childhood.

Stathmin, a gene regulating neural plasticity, affects fear and anxiety processing in humans

The identification of biological mechanisms underlying emotional behavior is crucial for our understanding of the pathogenesis of mental disorders. Besides genes modulating neural transmission and influencing amygdala reactivity and anxiety-related temperamental traits a different plasticity regulating genes affect interindividual differences in emotional regulation. Recently it has been demonstrated that stathmin, a regulator of microtubule formation which affects long-term potentiation (LTP), controls learned and innate fear responses in rodents, but its role in human emotion regulation is unknown. We hypothesized that in humans the gene coding for stathmin (STMN1), which is highly expressed in the lateral nucleus of the amygdala and associated thalamic and cortical structures, influences behavioral responses to fear and anxiety stimuli by way of two common single nucleotide polymorphisms (rs182455, SNP1; rs213641, SNP2). These polymorphisms are located within or close to the putative transcriptional control region. We used the acoustic startle paradigm and a standardized laboratory protocol for the induction of fear and psychosocial stress in 106 healthy volunteers to investigate the impact of stathmin gene variation on two fear- and anxiety-controlling effector-systems of the amygdala. We found that STMN1 genotype interacting with individuals' gender significantly impacts fear and anxiety responses as measured with the startle and cortisol stress response. We therefore conclude that STMN1 genotype has functional relevance for the acquisition and expression of basic fear and anxiety responses also in humans.

Gestational exposure to the organophosphate chlorpyrifos alters social-emotional behaviour and impairs responsiveness to the serotonin transporter inhibitor fluvoxamine in mice

BACKGROUND

The organophosphate chlorpyrifos (CPF) is a pesticide largely used worldwide. Studies from animal models indicate that CPF exposure during development at low doses can target different neurotransmitter systems in the absence of overt cholinergic effects.

METHODS

Late gestational exposure (gestational days 14-17) to CPF at the dose of 6 mg/kg was evaluated in CD-1 mice at adulthood. Neurobehavioural effects likely involving serotonin (5-hydroxytryptamine, 5HT) transmission were assessed both in males and females, through the light-dark exploration test to assess CPF effects on anxiety profiles and the forced swimming test to evaluate the response to the 5HT transporter (5HTT) inhibitor fluvoxamine (30 mg/kg). In females only, we evaluated the effects of gestational exposure to CPF on maternal aggression, under basal condition or after injection of fluvoxamine.

RESULTS

Gestational CPF exposure increased anxiety levels only in female mice, as shown by the augmented thigmotaxis behaviour and the lower latency to enter in the dark compartment. In the forced swimming test, no differences between CPF and control mice were found when assessed under basal condition (saline administration), but both male and female CPF mice missed to show the typical behavioural effects of the 5HTT inhibitor fluvoxamine. During maternal aggression, CPF females showed lower propensity to and intensity of aggressive behaviour, together with mild decreased responsiveness to fluvoxamine administration.

CONCLUSIONS

Overall, the present results confirm a specific and sex-dependent vulnerability of affective/emotional domains to developmental CPF exposure. Furthermore, data provide clear indication on the disrupting effects of prenatal CPF on serotoninergic transmission.

Pharmacological facilitation of fear extinction and the search for adjunct treatments for anxiety disorders--the case of yohimbine

There is current interest in identifying drugs that facilitate fear extinction, as this form of learning is the basis of certain cognitive therapies for anxiety disorders. Following an initial report several years ago that the alpha2-adrenoreceptor antagonist yohimbine facilitated extinction in mice, more recent studies have shown mixed effects or even impairment. It has become clear that the effect of yohimbine on extinction depends on a number of factors, including genetic background, contextual variables and the presence of competing behaviors. To what extent theses effects of yohimbine are mediated through the alpha2-adrenoreceptor, as opposed to other sites of action, is also uncertain. More work is needed before this drug can be approved as a pharmacological adjunct for extinction-based therapies. More generally, the case of yohimbine may serve as a model for the development of other extinction facilitators.

Pharmacological or genetic inactivation of the serotonin transporter improves reversal learning in mice

Growing evidence supports a major contribution of cortical serotonin (5-hydroxytryptamine, 5-HT) to the modulation of cognitive flexibility and the cognitive inflexibility evident in neuropsychiatric disorders. The precise role of 5-HT and the influence of 5-HT gene variation in mediating this process is not fully understood. Using a touch screen-based operant system, we assessed reversal of a pairwise visual discrimination as an assay for cognitive flexibility. Effects of constitutive genetic or pharmacological inactivation of the 5-HT transporter (5-HTT) on reversal were examined by testing 5-HTT null mice and chronic fluoxetine-treated C57BL/6J mice, respectively. Effects of constitutive genetic loss or acute pharmacological depletion of 5-HT were assessed by testing Pet-1 null mice and para-chlorophenylalanine (PCPA)-treated C57BL/6J mice, respectively. Fluoxetine-treated C57BL/6J mice made fewer errors than controls during the early phase of reversal when perseverative behavior is relatively high. 5-HTT null mice made fewer errors than controls in completing the reversal task. However, reversal in Pet-1 null and PCPA-treated C57BL/6J mice was not different from controls. These data further support an important role for 5-HT in modulating reversal learning and provide novel evidence that inactivating the 5-HTT improves this process. These findings could have important implications for understanding and treating cognitive inflexibility in neuropsychiatric disease.

Adverse early life experience and social stress during adulthood interact to increase serotonin transporter mRNA expression

Anxiety disorders, depression and animal models of vulnerability to a depression-like syndrome have been associated with dysregulation of serotonergic systems in the brain. To evaluate the effects of early life experience, adverse experiences during adulthood, and potential interactions between these factors on serotonin transporter (slc6a4) mRNA expression, we investigated in rats the effects of maternal separation (180 min/day from days 2 to 14 of life; MS180), neonatal handing (15 min/day from days 2 to 14 of life; MS15), or normal animal facility rearing (AFR) control conditions with or without subsequent exposure to adult social defeat on slc6a4 mRNA expression in the dorsal raphe nucleus (DR) and caudal linear nucleus. At the level of specific subdivisions of the DR, there were no differences in slc6a4 mRNA expression between MS15 and AFR rats. Among rats exposed to a novel cage control condition, increased slc6a4 mRNA expression was observed in the dorsal part of the DR in MS180 rats, relative to AFR control rats. In contrast, MS180 rats exposed to social defeat as adults had increased slc6a4 mRNA expression throughout the DR compared to both MS15 and AFR controls. Social defeat increased slc6a4 mRNA expression, but only in MS180 rats and only in the "lateral wings" of the DR. Overall these data demonstrate that early life experience and stressful experience during adulthood interact to determine slc6a4 mRNA expression. These data support the hypothesis that early life experience and major stressful life events contribute to dysregulation of serotonergic systems in stress-related neuropsychiatric disorders.

Volition diminishes genetically mediated amygdala hyperreactivity

Individuals carrying the short allele of a common polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR) exhibit heightened amygdala responses to passive stimulation with aversive emotional material. In turn, the level of amygdala activation in response to emotion can be decreased by will, for example by using cognitive emotion regulation strategies. In the present study, 37 female subjects (s-carriers: n=21; l/l-homozygotes: n=16) performed an emotion regulation task during functional magnetic resonance imaging to determine whether cognitive emotion regulation can modulate the genetically determined amygdala hyperreactivity in 5-HTTLPR short allele carriers. Our results demonstrate that cognitive emotion regulation diminishes the difference in amygdala reactivity to threat-related stimuli between 5-HTTLPR genotype groups. Furthermore, we also provide evidence that the effect of cognitive regulation is mediated through altered coupling between the amygdala and prefrontal regulatory regions. Our findings demonstrate that while the presence of the 5-HTTLPR short allele leads to heightened responses in the amygdala, cognitive regulation can modify genetically mediated effects upon brain function by volitionally altering prefrontal-amygdala connectivity.

Altered expression and modulation of activity-regulated cytoskeletal associated protein (Arc) in serotonin transporter knockout rats

A gene variant in the human serotonin transporter (SERT) can increase the vulnerability to mood disorders. SERT knockout animals show similarities to the human condition and represent an important tool to investigate the mechanisms underlying the pathologic condition in humans. Along this line of thinking, we used SERT KO rats (SERT(+/-) and SERT(-/-)) to investigate abnormalities in the expression and function of the activity-regulated gene Arc (Activity-regulated cytoskeletal associated protein) and the early inducible gene Zif-268, (zinc finger binding protein clone 268), which are important players in neuronal plasticity. We found lower basal Arc mRNA levels in hippocampus and prefrontal cortex of mutant rats in comparison with wild-type animals. Moreover SERT mutant rats show altered stress responsiveness. Indeed an acute swim stress significantly up-regulated the levels of Arc mRNA in hippocampus and prefrontal cortex, as well as of Zif-268 in frontal cortex, only in SERT(+/-) and SERT(-/-) rats. These alterations may be associated to behavioral traits linked to SERT and may contribute to the neuroplastic and morphological changes observed in depression.

Association of the serotonin transporter gene promoter region (5-HTTLPR) polymorphism with biased attention for emotional stimuli

A deletion polymorphism in the serotonin transporter-linked polymorphic region (5-HTTLPR) has been associated with vulnerability to affective disorders, yet the mechanism by which this gene confers vulnerability remains unclear. Two studies examined associations between the 5-HTTLPR polymorphism and attentional bias for emotional stimuli among nondepressed adults. Biased attention, attention engagement, and difficulty with attention disengagement were assessed with a spatial cuing task using emotional stimuli. Results from Study 1 (N = 38) indicated that short 5-HTTLPR allele carriers experienced greater difficulty disengaging their attention from sad and happy stimuli compared with long allele homozygotes. Study 2 participants (N = 144) were genotyped for the 5-HTTLPR polymorphism, including single nucleotide polymorphism rs25531 in the long allele of the 5-HTTLPR. Consistent with Study 1, individuals homozygous for the low-expressing 5-HTTLPR alleles (i.e., S and LG) experienced greater difficulty disengaging attention from sad, happy, and fear stimuli than high-expressing 5-HTTLPR homozygotes. Because this association exists in healthy adults, it may represent a susceptibility factor for affective disorders that becomes problematic during stressful life experiences.

Genetic and attachment influences on adolescents' regulation of autonomy and aggressiveness

BACKGROUND

Adolescence is a time when intense emotions are elicited within the parent-adolescent relationship, often when autonomy subjectively is endangered. As emotion dysregulation is one of the risk processes for the development of psychopathology, adolescence may be perceived as a highly sensitive period for maladjustment. Inter-individual differences in emotionality and emotion regulation have been shown to be influenced or moderated by molecular genetic differences in the serotonin transporter gene (5-HTT) and by attachment patterns. We investigated whether both the 5-HTT and attachment are associated with emotionality and emotion regulation in an observed adolescent-mother interaction and the personality traits aggressiveness and anxiety in adolescence.

METHODS

Ninety-one adolescents at age 12 were observed in interaction with their mothers during a standardized emotion-eliciting social task to assess emotionality and emotion regulation in relation to autonomy. Adolescents' aggressiveness and anxiety were assessed by mother report. Concurrent attachment quality was determined by an attachment interview. DNA samples were collected in order to assess the 5-HTTLPR, a repeat polymorphism in the promoter region of the serotonin transporter gene.

RESULTS

While the short allele of the serotonin transporter gene was associated with a higher overall rate of autonomy behaviors, attachment security was related to more agreeable and less hostile autonomy. A significant interaction revealed a moderating effect of attachment security. Carriers of the short version of the 5-HTTLPR showed more agreeable autonomy when they had a secure attachment behavior strategy but showed more hostile autonomy when they were insecurely attached. Carriers of the short version of the 5-HTTLPR and insecurely attached adolescents were rated as more aggressive.

CONCLUSIONS

The study suggests a gene-attachment interaction in adolescents where the adolescent's attachment status moderates a genetically based higher negative reactivity in response to threats to autonomy in social interactions.

Polymorphism of the serotonin transporter gene modulates brain and physiological responses to acute stress in Japanese men

A short (S) variant, compared to a long (L) variant, of the promoter region of the serotonin transporter gene-linked polymorphic region (5HTTLPR) has been related to emotional hyper-reactivity. We tested whether the 5HTTLPR could modulate acute stress responses in the brain and, the cardiovascular and neuroendocrine systems. Ten Japanese male participants carrying double copies of the S alleles and 10 Japanese males carrying S and L alleles conducted a mental arithmetic task, and their regional cerebral blood flow by (15)O positron emission tomography and cardiovascular and neuroendocrine parameters were measured. During the acute stress task, the participants with the SS alleles showed stronger reactivity in blood pressure and secretion of epinephrine, compared to the participants with the SL and LL alleles. Furthermore, the SS carriers showed greater activation in stress-related brain regions such as the hypothalamus, cerebellum, midbrain, and pulvinar compared to the SL and LL carriers during the acute stress task. The present findings indicated that the S allele of the 5HTTLPR is associated with greater brain and physiological reactivity to acute stress in Japanese men.

Serotonin transporter genotype modulates amygdala activity during mood regulation

Recent studies have implicated the short allele of the serotonin transporter-linked polymorphic region (5-HTTLPR) in depression vulnerability, particularly in the context of stress. Several neuroimaging studies have shown that 5-HTTLPR genotype predicts amygdala reactivity to negatively valenced stimuli, suggesting a mechanism whereby the short allele confers depression risk. The current study investigated whether 5-HTTLPR genotype similarly affects neural activity during an induced sad mood and during recovery from sad mood. Participants were 15 homozygous short (S) and 15 homozygous long (L) individuals. Regional cerebral blood flow was measured with perfusion functional magnetic resonance imaging during four scanning blocks: baseline, sad mood, mood recovery and following return to baseline. Comparing mood recovery to baseline, both whole brain analyses and template-based region-of-interest analyses revealed greater amygdala activity for the S vs the L-group. There were no significant amygdala differences found during the induced sad mood. These results demonstrate the effect of the S allele on amygdala activity during intentional mood regulation and suggest that amygdala hyperactivity during recovery from a sad mood may be one mechanism by which the S allele confers depression risk.

The neurobiology of individual differences in complex behavioral traits

Neuroimaging, especially BOLD fMRI, has begun to identify how variability in brain function contributes to individual differences in complex behavioral traits. In parallel, pharmacological fMRI and multimodal PET/fMRI are identifying how variability in molecular signaling pathways influences individual differences in brain function. Against this background, functional genetic polymorphisms are being utilized to understand the origins of variability in signaling pathways as well as to model efficiently how such emergent variability impacts behaviorally relevant brain function. This article provides an overview of a research strategy seeking to integrate these complementary technologies and utilizes existing empirical data to illustrate its effectiveness in illuminating the neurobiology of individual differences in complex behavioral traits. The article also discusses how such efforts can contribute to the identification of predictive markers that interact with environmental factors to precipitate disease and to develop more effective and individually tailored treatment regimes.

Serotonin transporter gene, depressive symptoms, and interleukin-6

BACKGROUND

We explored the relationship of genetic variants of the serotonin transporter gene SLC6A4, a key regulator of the serotonergic neurotransmission, with both depressive symptoms and plasma interleukin-6 (IL-6) levels.

METHODS AND RESULTS

We genotyped 20 polymorphisms in 360 male twins (mean age, 54 years) from the Vietnam Era Twin Registry. Current depressive symptoms were measured with the Beck Depression Inventory II. IL-6 was assessed using a commercially available ELISA kit. Genotype associations were analyzed using generalized estimating equations. To study how SLC6A4 genetic vulnerability influences the relationship between depressive symptoms and IL-6, bivariate models were constructed using structural equation modeling. Of the 20 polymorphisms examined, the effective number of independent tests was 6, and the threshold of significance after Bonferroni correction was 0.008. There were 6 single-nucleotide polymorphisms significantly associated with Beck Depression Inventory (P< or =0.008), including rs8071667, rs2020936, rs25528, rs6354, rs11080122, and rs8076005, and 1 single-nucleotide polymorphism was borderline associated (rs12150214, P=0.017). Of these 7 single-nucleotide polymorphisms, 3 were also significantly associated with IL-6 (P<0.008), including rs25528, rs6354, and rs8076005, and the other 4 were borderline associated (P=0.009 to 0.025). The subjects with 1 copy of the minor allele of these 7 single-nucleotide polymorphisms had higher Beck Depression Inventory scores and IL-6 levels. Further bivariate modeling revealed that approximately 10% of the correlation between Beck Depression Inventory and IL-6 could be explained by the SLC6A4 gene.

CONCLUSIONS

Genetic vulnerability involving the SLC6A4 gene is significantly associated with both increased depressive symptoms and elevated IL-6 plasma levels. Common pathophysiological processes may link depression and inflammation, and implicate the serotonin pathway in neural-immune interactions.

Genetic variation in 5HTTLPR is associated with emotional resilience

Emotional resilience can be defined as the ability to maintain healthy and stable levels of psychological functioning in the wake of stress and trauma. Although genes that contribute to psychopathology (often in interaction with environmental stressors) are being detected with increasing consistency, genes that influence resilience to stress have been less studied. In this study, 423 undergraduate college students completed a psychometrically sound 10-item self-report measure of resilience (CDRISC-10) and provided blood for DNA. Linear and logistic regression analyses were used to model relationships between the serotonin transporter promoter polymorphism (5HTTLPR) and CDRISC-10 scores and categories, respectively. CDRISC-10 scores were normally distributed (mean 26.17, SD 5.88 [range 5-40]). In models adjusting for ancestry proportion scores (to mitigate confounding by population stratification) and other covariates, each copy of the "s" allele of 5HTTLPR was associated with approximately 1-point lower CDRISC-10 score. Each copy of the "s" allele was associated with increased (adjusted OR = 1.53, 95% CI 1.06-2.21, P = 0.024) odds of being in the low resilient category (>1 SD below the mean), compared to being homozygous for the "l" allele. These findings suggest that variation in 5HTTLPR is associated with individual differences in emotional resilience, defined as an individual's ability to withstand and bounce back from stress. This relationship may explain the frequently observed interaction between 5HTTLPR and life stressors in predicting adverse mental health outcomes (e.g., depressive symptoms). Replication is needed, in concert with identification of other genes that influence emotional resilience and related phenotypes.

Serotonin transporter availability in the amygdala and bed nucleus of the stria terminalis predicts anxious temperament and brain glucose metabolic activity

The serotonin transporter (5-HTT) plays a critical role in regulating serotonergic neurotransmission and is implicated in the pathophysiology of anxiety and affective disorders. Positron emission tomography scans using [(11)C]DASB [(11)C]-3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile] to measure 5-HTT availability (an index of receptor density and binding) were performed in 34 rhesus monkeys in which the relationship between regional brain glucose metabolism and anxious temperament was previously established. 5-HTT availability in the amygdalohippocampal area and bed nucleus of the stria terminalis correlated positively with individual differences in a behavioral and neuroendocrine composite of anxious temperament. 5-HTT availability also correlated positively with stress-induced metabolic activity within these regions. Collectively, these findings suggest that serotonergic modulation of neuronal excitability in the neural circuitry associated with anxiety mediates the developmental risk for affect-related psychopathology.

Accurate, Large-Scale Genotyping of 5HTTLPR and Flanking Single Nucleotide Polymorphisms in an Association Study of Depression, Anxiety, and Personality Measures

BACKGROUND

The length polymorphism repeat in the promoter region of the serotonin transporter gene (5HTTLPR) is one of the most studied polymorphisms for association with a range of psychiatric and personality phenotypes. However, the original 5HTTLPR assay is prone to bias toward short allele calling.

METHODS

We designed new assays for the 5HTTLPR suitable for large-scale genotyping projects and we genotyped 13 single nucleotide polymorphisms (SNPs) in a 38-kilobase region around the 5HTTLPR, including SNP rs25531, a polymorphism of the 5HTTLPR long allele. Association analysis was conducted for major depression and/or anxiety disorder in unrelated cases (n = 1161) and control subjects (n = 1051) identified through psychiatric interviews administered to a large population sample of Australian twin families. Participants had been scored for personality traits several years earlier (n > or = 2643 unrelated individuals).

RESULTS

We identified a two-SNP haplotype proxy for 5HTTLPR; the CA haplotype of SNPs rs4251417 and rs2020934 is coupled with the short allele of 5HTTLPR (r(2) = .72). We found evidence for association (p = .0062, after accounting for multiple testing) for SLC6A4 SNPs rs6354 and rs2020936 (positioned in a different linkage disequilibrium [LD] block about 15.5 kb from 5HTTLPR) with anxiety and/or depression and neuroticism, with the strongest association for recurrent depression with onset in young adulthood (odds ratio = 1.55, 95% confidence interval = 1.16-2.06).

CONCLUSIONS

The associated SNPs are in the same LD block as the variable number of tandem repeats serotonin transporter intron 2 marker, for which association has previously been reported.

Serotonin transporter gene promoter region polymorphism and selective processing of emotional images

Several studies have now documented that the serotonin transporter promoter region (5-HTTLPR) polymorphism predicts neural response to affective images in brain regions involved in the experience of emotion. However, the behavioral consequences of this genetic effect are less well known. The current study used eye-tracking methodology to examine how individuals genotyped for the 5-HTTLPR allocated their attention when simultaneously presented an array of positive and negative emotional scenes. Short 5-HTTLPR allele homozygotes displayed a bias to focus on positive images, particularly in the first half of the 30s trial. In contrast, long 5-HTTLPR allele homozygotes viewed the stimuli in a more evenhanded fashion. Thus, short 5-HTTLPR allele homozygotes may be attempting to regulate greater reactivity to negative stimuli by purposefully turning their attention towards positive stimuli. Although this sensitivity may have benefits under benign conditions, it may also increase vulnerability to affective disorders when cognitive resources needed to turn attention away from negative stimuli are compromised.

The temporal dynamics of voluntary emotion regulation

BACKGROUND

Neuroimaging has demonstrated that voluntary emotion regulation is effective in reducing amygdala activation to aversive stimuli during regulation. However, to date little is known about the sustainability of these neural effects once active emotion regulation has been terminated.

METHODOLOGY/PRINCIPAL FINDINGS

We addressed this issue by means of functional magnetic resonance imaging (fMRI) in healthy female subjects. We performed an active emotion regulation task using aversive visual scenes (task 1) and a subsequent passive viewing task using the same stimuli (task 2). Here we demonstrate not only a significantly reduced amygdala activation during active regulation but also a sustained regulation effect on the amygdala in the subsequent passive viewing task. This effect was related to an immediate increase of amygdala signal in task 1 once active emotion regulation has been terminated: The larger this peak postregulation signal in the amygdala in task 1, the smaller the sustained regulation effect in task 2.

CONCLUSIONS/SIGNIFICANCE

In summary, we found clear evidence that effects of voluntary emotion regulation extend beyond the period of active regulation. These findings are of importance for the understanding of emotion regulation in general, for disorders of emotion regulation and for psychotherapeutic interventions.

Conserved role for the serotonin transporter gene in rat and mouse neurobehavioral endophenotypes

The serotonin transporter knockout (SERT(-/-)) mouse, generated in 1998, was followed by the SERT(-/-) rat, developed in 2006. The availability of SERT(-/-) rodents creates the unique possibility to study the conservation of gene function across species. Here we summarize SERT(-/-) mouse and rat data, and discuss species (dis)similarities in neurobehavioral endophenotypes. Both SERT(-/-) rodent models show a disturbed serotonergic system, altered nociception, higher anxiety, decreased social behavior, as well as increased negative emotionality, behavioral inhibition and decision making. Used to model a wide range of psychiatric disorders, SERT(-/-) rodents may be particularly valuable in research on neurodevelopmental disorders such as depression, anxiety, and possibly autism. We conclude that SERT function is conserved across mice and rats and that their behavioral profile arises from common neurodevelopmental alterations. Because mice and rats have species-specific characteristics that confer differential research advantages, a comparison of the two models has heuristic value in understanding the mechanisms and behavioral outcome of SERT genetic variation in humans.

Neurotransmission-related genetic polymorphisms, negative affectivity traits, and gender predict tobacco abstinence symptoms across 44 days with and without nicotine patch

Genetic and personality trait moderators of tobacco abstinence-symptom trajectories were assessed in a highly controlled study. Based on evidence suggesting their importance in stress reactivity and smoking, moderators studied were serotonin transporter gene (5-HTTLPR) and dopamine D2 receptor gene (DRD2) polymorphisms and personality traits related to negative affect (NA). Smokers were randomly assigned to quit smoking with nicotine or placebo patches. Financial incentives resulted in 80% verified abstinence across the 44-day study. Individuals with 1 or 2 short alleles of 5-HTTLPR (S carriers) experienced larger increases in NA symptoms than did those without a short allele. Nicotine replacement therapy (NRT) alleviated anxiety only in S carriers. NRT reduced NA to a greater extent in DRD2 A1 carriers than in A2A2 individuals during the 1st 2 weeks of treatment (when on the 21-mg patch); however, A1 carriers experienced a renewal of NA symptoms when switched to the 7-mg patch and when off the patch, while A2A2 individuals continued to benefit from NRT. The results suggest that the effects of genotype and treatment may vary across different durations of abstinence, treatment doses, and genotypes.

Genetic and environmental influence on attachment disorganization

BACKGROUND

Empirical studies demonstrate that maternal sensitivity is associated with attachment security in infancy, while maternal frightening/frightened behavior is related to attachment disorganization. However, attachment disorganization is also predicted by individual dispositions in infancy. Indeed, recent studies indicate a link between attachment disorganization and DRD4 gene polymorphisms, thus suggesting a genetic vulnerability for attachment disorganization. The aims of our study were twofold, to test a) a possible direct link between molecular genetic variations and attachment disorganization, and b) a possible gene-environment interaction with a moderating effect of early maternal caregiving.

METHODS

Attachment security and disorganization, as well as quality of maternal behavior were assessed in the infants of the Regensburg Longitudinal Study IV (N = 106) at the age of 12 months. DNA samples were collected in order to assess the exon III repeat polymorphism in the coding region and the -521 C/T single nucleotide polymorphism (SNP) in the regulatory region of the DRD4 gene and a repeat polymorphism (5-HTTLPR) in the promoter region of the serotonin transporter gene.

RESULTS

Significant associations were found between attachment disorganization and the short polymorphism of the serotonin transporter gene. Also, a gene-environment interaction indicated that this genetic association was only valid for infants of mothers exhibiting low responsiveness. No other significant genetic associations with attachment disorganization were apparent.

CONCLUSIONS

The study suggests a gene-environment interaction whereby biological determinants of attachment disorganization are moderated by social experiences. Different pathways of the development of attachment disorganization are discussed based on a bio-behavioral model of development.

Influence of sex and corticotropin-releasing factor pathways as determinants in serotonin sensitivity

Stress sensitivity and sex are predictive factors in affective disorder susceptibility. Serotonin (5-HT) pathway recruitment by corticotropin-releasing factor (CRF) during stress is necessary in adaptive coping behaviors, but sex differences in such responses have not been investigated. Using selective 5-HT reuptake inhibitor (SSRI) administration to acutely elevate 5-HT in a genetic model of stress sensitivity, we examined behavioral and physiological responses in male and female stress-sensitive CRF receptor-2-deficient (R2KO) mice. Chronic SSRI treatment was used to confirm outcomes were specific to acute 5-HT elevation and not antidepressant efficacy. We hypothesized that R2KO mice would show a greater sensitivity to acute changes in 5-HT and that, because females typically are more stress sensitive, R2KO females would be the most responsive. Our results supported this hypothesis because females of both genotypes and R2KO males showed a greater sensitivity to an acute 10 mg/kg dose of citalopram in a tail suspension test, displaying decreased immobile time and increased latency to immobility. Furthermore, acute citalopram promoted significant anxiogenic-like effects that were specific to R2KO females in the elevated plus maze and light-dark box tests. Chronic citalopram did not produce these behavioral changes, supporting specificity to acute 5-HT modulation. Mechanistically, females had decreased hippocampal 5-HT transporter (SERT) levels, whereas R2KO mice showed reduced SERT in the prefrontal cortex, supporting a possible intersection of sex and genotype where R2KO females would have the lowest SERT to be blocked by the SSRI. This sensitivity to 5-HT-mediated anxiety in females may underlie a heightened vulnerability to stress-related affective disorders.

Valence focus and self-esteem lability: reacting to hedonic cues in the social environment

Individuals differ in the extent to which they emphasize feelings of pleasure or displeasure in their verbal reports of emotional experience, termed valence focus (VF). Two event-contingent, experience-sampling studies examined the relationship between VF and sensitivity to pleasant and unpleasant social cues. It was predicted, and found, that individuals with greater VF (i.e., who emphasized feelings of pleasure/displeasure in reports of emotional experience) demonstrated greater self-esteem lability (i.e., larger changes in self-esteem) to pleasant and unpleasant information contained in social interactions than did those lower in VF. These effects held even after statistically controlling for possible confounding variables (neuroticism, affect intensity). Implications for understanding the psychological impact of valenced interpersonal events are discussed.

Upregulation of serotonin transporter by alcohol in human dendritic cells: possible implication in neuroimmune deregulation

BACKGROUND

Alcohol is the most widely abused substance and its chronic consumption causes neurobehavioral disorders. It has been shown that alcohol affects the function of immune cells. Dendritic cells (DC) serve as the first line of defense against infections and are known to accumulate neurotransmitters such as 5-hydroxytryptamine (5-HT). The enzyme monoamine oxidase-A (MAO-A) degrades 5-HT that is associated with clinical depression and other neurological disorders. 5-HT is selectively transported into neurons through the serotonin transporter (SERT), which is a member of the sodium- and chloride-dependent neurotransmitter transporter (SLC6) family. SERT also serves as a receptor for psychostimulant recreational drugs. It has been demonstrated that several drugs of abuse such as amphetamine and cocaine inhibit the SERT expression; however, the role of alcohol is yet to be elucidated. We hypothesize that alcohol can modulate SERT and MAO-A expression in DC, leading to reciprocal downregulation of 5-HT in extracellular medium.

METHODS

Dendritic cells were treated with different concentrations (0.05% to 0.2%v/v) of alcohol for 24-72 hours and processed for SERT and MAO-A expression using Q-PCR and Western blots analysis. In addition, SERT function in DC treated with alcohol both in the presence and absence of imipramine, a SERT inhibitor was measured using 4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide uptake assay. 5-HT levels in culture supernatant and intracellular 5-hydroxy indole acetic acid (5-HIAA) and cyclic AMP were also quantitated using ELISA.

RESULTS

Dendritic cells treated with 0.1% alcohol for 24 hours showed significant upregulation of SERT and MAO-A expression compared with untreated DC. We also observed that 0.1% alcohol enhanced the function of SERT and decreased extracellular 5-HT levels compared with untreated DC cultures, and this was associated with the elevation of intracellular 5-HIAA and cyclic AMP levels.

CONCLUSIONS

Our study suggests that alcohol upregulates SERT and MAO-A by elevating cyclic AMP, which may lead to decreased concentration of 5-HT in the extracellular medium. As 5-HT is a major neurotransmitter and an inflammatory mediator, its alcohol-mediated depletion may cause both neurological and immunological deregulation.

Genetic relationship between anxiety-related and fear-related behaviors in BXD recombinant inbred mice

Mood and anxiety disorders, and rodent phenotypic measures modeling these disorders, have a strong genetic component. Various assays are used to study the neurobiological basis of fear-related and anxiety-related behaviors, phenotype genetically modified mice, and elucidate pharmacological modulation of these behaviors for medication development. Earlier work, however, suggests that different trait measures are mediated by partly overlapping but ultimately distinct genetic factors. In this study, we assessed a novel panel of 23 C57BL/6JxDBA/2J (BXD) recombinant inbred strains on various trait measures of Pavlovian fear conditioning and anxiety-like behavior (novel open field, elevated plus-maze), as well as sensory (acoustic startle, prepulse inhibition of startle) and motor (baseline coordination and learning on accelerating rotarod) function. Results showed that traits were continuously distributed across strains and had modest to strong R values. Principal components analysis resolved the data into five factors: factor 1 loaded fear-related traits, factor 2 loaded elevated plus-maze measures as well as context fear, factor 3 loaded novel open field measures and plus-maze closed arm entries, factor 4 loaded rotarod motor function, and factor 5 loaded acoustic startle and prepulse inhibition. These data add to evidence that murine measures of fear-like and anxiety-like traits reflect distinct constructs mediated by dissociable gene variants.

Serotonin transporter binding and genotype in the nonhuman primate brain using [C-11]DASB PET

The length polymorphism of the serotonin (5-HT) transporter gene promoter region has been implicated in altered 5-HT function and, in turn, neuropsychiatric illnesses, such as anxiety and depression. The nonhuman primate has been used as a model to study anxiety-related mechanisms in humans based upon similarities in behavior and the presence of a similar 5-HT transporter gene polymorphism. Stressful and threatening contexts in the nonhuman primate model have revealed 5-HT transporter genotype dependent differences in regional glucose metabolism. Using the rhesus monkey, we examined the extent to which serotonin transporter genotype is associated with 5-HT transporter binding in brain regions implicated in emotion-related pathology.

METHODS

Genotype data and high resolution PET scans were acquired in 29 rhesus (Macaca mulatta) monkeys. [C-11]DASB dynamic PET scans were acquired for 90 min in the anesthetized animals and images of distribution volume ratio (DVR) were created to serve as a metric of 5-HT transporter binding for group comparison based on a reference region method of analysis. Regional and voxelwise statistical analysis were performed with corrections for anatomical differences in gray matter probability, sex, age and radioligand mass.

RESULTS

There were no significant differences when comparing l/l homozygotes with s-carriers in the regions of the brain implicated in anxiety and mood related illnesses (amygdala, striatum, thalamus, raphe nuclei, temporal and prefrontal cortex). There was a significant sex difference in 5-HT transporter binding in all regions with females having 18%-28% higher DVR than males.

CONCLUSIONS

Because these findings are consistent with similar genotype findings in humans, this further strengthens the use of the rhesus model for studying anxiety-related neuropathologies.

Impact of the tryptophan hydroxylase 1 gene A218C polymorphism on amygdala activity in response to affective facial stimuli in patients with major depressive disorder

Tryptophan hydroxylase-1 (TPH1) is the rate-limiting enzyme in serotonin biosynthesis, and allelic variations at the TPH1 locus have been implicated in the pathophysiology of depression. Using 1.5-Tesla functional magnetic resonance imaging, we investigated the possible relationship between TPH1 A218C polymorphism and amygdala response to negative facial stimuli in 26 right-handed female subjects with major depressive disorder (MDD). Genotyping was performed with the polymerase chain reaction. We found a significant association between A allele of the TPH1 A218C polymorphism and neural activations in response to negative facial stimuli. Subjects with the A allele of the TPH1 A218C polymorphism showed greater brain activity in the bilateral amygdala under the sad vs. the neutral condition compared with subjects homozygous for the C allele. Our results suggest that the A218C polymorphism of the TPH1 gene serves as a modulator of amygdala activity in patients with MDD.

5-HTTLPR genotype influences amygdala volume

BACKGROUND

Functional imaging studies in healthy individuals revealed an association between 5-HTTLPR genotype and neuronal activity in the amygdala. The aim of this study was firstly to investigate a possible overall impact of the 5-HTTLPR on amygdala volume in patients with bipolar disorder and healthy individuals and secondly to test a diagnosis specific influence of the 5-HTTLPR on amygdala volume.

METHODS

We performed a region of interest analysis of amygdala volume in 37 patients with bipolar I disorder and 37 healthy control subjects. The 5-HTTLPR genotype of each proband was determined and the subjects were separated according to 5-HTTLPR genotype and for statistical analyses the groups SS and SL were combined and compared with the group LL.

RESULTS

This study shows that carriers of the short allele (SL or SS) of the 5-HTTLPR polymorphism exhibit a relatively increased volume of the right amygdala compared to homozygous L-allele carriers irrespective of diagnosis status. However, further analyses with the factors genotype and diagnosis were not able to reproduce this result.

CONCLUSIONS

The present findings are consistent with the view that the 5-HTTLPR polymorphism might modulate neuronal size or number in the amygdala. It would be worthwhile investigating the relationship between serotonin transporter function and amygdala function and volume in further studies.

Local perfusion of corticosterone in the rat medial hypothalamus potentiates D-fenfluramine-induced elevations of extracellular 5-HT concentrations

The dorsomedial hypothalamus (DMH) plays an important role in coordinating physiological and behavioral responses to stress-related stimuli. In vertebrates, DMH serotonin (5-HT) concentrations increase rapidly in response to acute stressors or corticosterone (CORT). Recent studies suggest that CORT inhibits postsynaptic clearance of 5-HT from the extracellular fluid in the DMH by blocking organic cation transporter 3 (OCT3), a polyspecific CORT-sensitive transport protein. Because OCTs are low-affinity, high-capacity transporters, we hypothesized that CORT effects on extracellular 5-HT are most pronounced in the presence of elevated 5-HT release. We predicted that local application of CORT into the DMH would potentiate the effects of d-fenfluramine, a 5-HT-releasing agent, on extracellular 5-HT. These experiments were conducted using in vivo microdialysis in freely-moving male Sprague-Dawley rats implanted with a microdialysis probe into the medial hypothalamus (MH), which includes the DMH. In Experiment 1, rats simultaneously received intraperitoneal (i.p.) injections of 1 mg/kg D-fenfluramine or saline and either 200 ng/mL CORT or dilute ethanol (EtOH) vehicle delivered to the MH by reverse-dialysis for 40 min. In Experiment 2, 5 microM D-fenfluramine and either 200 ng/mL CORT or EtOH vehicle were concurrently delivered to the MH for 40 min using reverse-dialysis. CORT potentiated the increases in extracellular 5-HT concentrations induced by either i.p. or intra-MH administration of D-fenfluramine. Furthermore, CORT and D-fenfluramine interacted to alter home cage behaviors. Our results support the hypothesis that CORT inhibition of OCT3-mediated 5-HT clearance from the extracellular fluid contributes to stress-induced increases in extracellular 5-HT and 5-HT signaling.

Frontal-limbic white matter pathway associations with the serotonin transporter gene promoter region (5-HTTLPR) polymorphism

Variation in the serotonin transporter gene-linked polymorphic region (5-HTTLPR) has been associated with heightened neural activity in limbic and prefrontal regions in response to emotional stimuli. The current study examined whether the 5-HTTLPR polymorphism is also associated with alterations in microstructure of frontal-limbic white matter (WM) tracts. Thirty-seven (mean age, 20.51 years; range, 13-28) female participants were genotyped for the 5-HTTLPR polymorphism. Diffusion MRI was collected and a probabilistically defined tract of the uncinate fasciculus (UF), a WM pathway connecting the amygdala to medial and orbital prefrontal cortex, was used to generate fractional anisotropy (FA) values for participants. Regression analyses indicated a significant inverse association between number of low-expressing 5-HTTLPR alleles and FA values for the left frontal UF region, beta = - 0.42, p = 0.005. Furthermore, there was a positive association between age and FA values for bilateral frontal regions of the UF; these effects explained 39 and 20% of the variance in FA values for left and right frontal regions, respectively. 5-HTTLPR genotype and age appear to independently influence the WM microstructure of the UF. The observed reduction in FA values among low-expressing 5-HTTLPR allele carriers may contribute to biased regulation of emotional stimuli.

Using genetic data in cognitive neuroscience: from growing pains to genuine insights

Research that combines genetic and cognitive neuroscience data aims to elucidate the mechanisms that underlie human behaviour and experience by way of 'intermediate phenotypes': variations in brain function. Using neuroimaging and other methods, this approach is poised to make the transition from health-focused investigations to inquiries into cognitive, affective and social functions, including ones that do not readily lend themselves to animal models. The growing pains of this emerging field are evident, yet there are also reasons for a measured optimism.

Medial prefrontal cortex 5-HT(2A) density is correlated with amygdala reactivity, response habituation, and functional coupling

Feedback inhibition of the amygdala via medial prefrontal cortex (mPFC) is an important component in the regulation of complex emotional behaviors. The functional dynamics of this corticolimbic circuitry are, in part, modulated by serotonin (5-HT). Serotonin 2A (5-HT(2A)) receptors within the mPFC represent a potential molecular mechanism through which 5-HT can modulate this corticolimbic circuitry. We employed a multimodal neuroimaging strategy to explore the relationship between threat-related amygdala reactivity, assessed using blood oxygen level-dependent functional magnetic resonance imaging, and mPFC 5-HT(2A) density, assessed using [(18)F]altanserin positron emission tomography in 35 healthy adult volunteers. We observed a significant inverse relationship wherein greater mPFC 5-HT(2A) density was associated with reduced threat-related right amygdala reactivity. Remarkably, 25-37% of the variability in amygdala reactivity was explained by mPFC 5-HT(2A) density. We also observed a positive correlation between mPFC 5-HT(2A) density and the magnitude of right amygdala habituation. Furthermore, functional coupling between the amygdala and mPFC was positively correlated with 5-HT(2A) density suggesting that effective integration of emotionally salient information within this corticolimbic circuitry may be modulated, at least in part, by mPFC 5-HT(2A). Collectively, our results indicate that mPFC 5-HT(2A) is strongly associated with threat-related amygdala reactivity as well as its temporal habituation and functional coupling with prefrontal regulatory regions.

Reward circuitry is perturbed in the absence of the serotonin transporter

The serotonin transporter (SERT) modulates the entire serotonergic system in the brain and influences both the dopaminergic and norepinephrinergic systems. These three systems are intimately involved in normal physiological functioning of the brain and implicated in numerous pathological conditions. Here we use high-resolution magnetic resonance imaging (MRI) and spectroscopy to elucidate the effects of disruption of the serotonin transporter in an animal model system: the SERT knock-out mouse. Employing manganese-enhanced MRI, we injected Mn(2+) into the prefrontal cortex and obtained 3D MR images at specific time points in cohorts of SERT and normal mice. Statistical analysis of co-registered datasets demonstrated that active circuitry originating in the prefrontal cortex in the SERT knock-out is dramatically altered, with a bias towards more posterior areas (substantia nigra, ventral tegmental area, and Raphé nuclei) directly involved in the reward circuit. Injection site and tracing were confirmed with traditional track tracers by optical microscopy. In contrast, metabolite levels were essentially normal in the SERT knock-out by in vivo magnetic resonance spectroscopy and little or no anatomical differences between SERT knock-out and normal mice were detected by MRI. These findings point to modulation of the limbic cortical-ventral striatopallidal by disruption of SERT function. Thus, molecular disruptions of SERT that produce behavioral changes also alter the functional anatomy of the reward circuitry in which all the monoamine systems are involved.

Association of serotonin transporter gene polymorphism and emotion regulation

Metacognitive strategies of emotion regulation such as an objective perspective of one's self are known as primary factors in mindfulness intervention. Earlier studies, however, suggest that the effect of mindfulness differs because of the individual variability. In this study, we investigated the influence of the serotonin transporter gene polymorphism during the application of a metacognitive strategy of emotion regulation. Short (S) homozygotes showed more negative emotional states than SL individuals in both metacognition and control conditions. The high frequency of heart rate variability, however, increased in the metacognition condition only in S homozygotes. This result indicated that the metacognitive strategy of emotion regulation is more effective for increasing parasympathetic dominance in S homozygotes than in SL individuals.

Excess of serotonin affects embryonic interneuron migration through activation of the serotonin receptor 6

The discovery that a common polymorphism (5-HTTLPR, short variant) in the human serotonin transporter gene (SLC6A4) can influence personality traits and increase the risk for depression in adulthood has led to the hypothesis that a relative increase in the extracellular levels of serotonin (5-HT) during development could be critical for the establishment of brain circuits. Consistent with this idea, a large body of data demonstrate that 5-HT is a strong neurodevelopmental signal that can modulate a wide variety of cellular processes. In humans, serotonergic fibers appear in the developing cortex as early as the 10th gestational week, a period of intense neuronal migration. In this study we hypothesized that an excess of 5-HT could affect embryonic cortical interneuron migration. Using time-lapse videometry to monitor the migration of interneurons in embryonic mouse cortical slices, we discovered that the application of 5-HT decreased interneuron migration in a reversible and dose-dependent manner. We next found that 5-HT6 receptors were expressed in cortical interneurons and that 5-HT6 receptor activation decreased interneuron migration, whereas 5-HT6 receptor blockade prevented the migratory effects induced by 5-HT. Finally, we observed that interneurons were abnormally distributed in the cerebral cortex of serotonin transporter gene (Slc6a4) knockout mice that have high levels of extracellular 5-HT. These results shed new light on the neurodevelopmental alterations caused by an excess of 5-HT during the embryonic period and contribute to a better understanding of the cellular processes that could be modulated by genetically controlled differences in human 5-HT homeostasis.

Reduced stress-sensitivity or increased reward experience: the psychological mechanism of response to antidepressant medication

Depression has often been associated with increased negative affect reactivity to stress (Stress-Sensitivity) and reduced capacity to experience pleasure or positive affect (Reward Experience). To date, no studies have prospectively examined changes in Stress-Sensitivity and Reward Experience following antidepressant treatment. The sample included 83 depressed patients and 22 healthy controls. A randomized controlled trial was carried out with patients receiving either imipramine or placebo for 6 weeks. At baseline and 6 weeks, patients and controls participated in an Experience Sampling procedure, prospectively measuring ecologically valid daily life appraisals of activities and mood states. The course of depression was assessed with the Hamilton Depression Rating Scale (HDRS). Multilevel linear regression analyses showed that patients had higher negative and lower positive appraisals of activities than controls. In addition, patients showed increased Stress-Sensitivity (negative affect reactivity to negatively appraised activities). Treatment with imipramine decreased Stress-Sensitivity and increased Reward Experience (positive affect reactivity to positively appraised activities). Changes in Stress-Sensitivity and Reward Experience were in part reducible to changes in the process of activity appraisal itself. However, increase in Reward Experience, but not decrease in Stress-Sensitivity, discriminated between patients who responded and those who did not, independent of changes in the process of activity appraisal itself. Response to treatment in depression may be conditional on restoration of hedonic capacity, the cerebral substrate of which requires further study in relation to antidepressant response. A search for (synergistic) antidepressant therapies specifically targeting ability to experience reward may be warranted.

Looking on the bright side: biased attention and the human serotonin transporter gene

Humans differ in terms of biased attention for emotional stimuli and these biases can confer differential resilience and vulnerability to emotional disorders. Selective processing of positive emotional information, for example, is associated with enhanced sociability and well-being while a bias for negative material is associated with neuroticism and anxiety. A tendency to selectively avoid negative material might also be associated with mental health and well-being. The neurobiological mechanisms underlying these cognitive phenotypes are currently unknown. Here we show for the first time that allelic variation in the promotor region of the serotonin transporter gene (5-HTTLPR) is associated with differential biases for positive and negative affective pictures. Individuals homozygous for the long allele (LL) showed a marked bias to selectively process positive affective material alongside selective avoidance of negative affective material. This potentially protective pattern was absent among individuals carrying the short allele (S or SL). Thus, allelic variation on a common genetic polymorphism was associated with the tendency to selectively process positive or negative information. The current study is important in demonstrating a genotype-related alteration in a well-established processing bias, which is a known risk factor in determining both resilience and vulnerability to emotional disorders.

Amygdala function and 5-HTT gene variants in adolescent anxiety and major depressive disorder

BACKGROUND

Associations between a functional polymorphism in the serotonin transporter gene and amygdala activation have been found in healthy, depressed, and anxious adults. This study explored these gene-brain associations in adolescents by examining predictive effects of serotonin transporter gene variants (S and L(G) allele carriers vs. L(A) allele homozygotes) and their interaction with diagnosis (healthy vs. patients) on amygdala responses to emotional faces.

METHODS

Functional magnetic resonance data were collected from 33 healthy adolescents (mean age: 13.71, 55% female) and 31 medication-free adolescents with current anxiety or depressive disorders (or both; mean age: 13.58, 56% female) while viewing fearful, angry, happy, and neutral facial expressions under varying attention states.

RESULTS

A significant three-way genotype-by-diagnosis-by-face-emotion interaction characterized right amygdala activity while subjects monitored internal fear levels. This interaction was decomposed to map differential gene-brain associations in healthy and affected adolescents. First, consistent with healthy adult data, healthy adolescents with at least one copy of the S or L(G) allele showed stronger amygdala responses to fearful faces than healthy adolescents without these alleles. Second, patients with two copies of the L(A) allele exhibited greater amygdala responses to fearful faces relative to patients with S or L(G) alleles. Third, although weaker, genotype differences on amygdala responses in patients extended to happy faces. All effects were restricted to the fear-monitoring attention state.

CONCLUSIONS

S/L(G) alleles in healthy adolescents, as in healthy adults, predict enhanced amygdala activation to fearful faces. Contrary findings of increased activation in patients with L(A)L(A) relative to the S or L(G) alleles require further exploration.

The psychobiology of resilience

Although adverse environments are well known to be a risk factor for psychopathology, many individuals respond adaptively to such environments. There is growing interest in the underlying mechanisms involved in such resilience. Several cognitive-affective processes may be involved, and these may be mediated by particular neuronal circuits and neurochemical systems. This article summarizes some of the relevant work on the role of fear conditioning, reward processing, and social behavior in resilience. There is a growing body of data on how particular gene-environment interactions affect these processes, and thus underpin resilience. Ultimately, a better understanding of the mechanisms underpinning resilience may lead to novel interventions.

Serotonergic systems, anxiety, and affective disorder: focus on the dorsomedial part of the dorsal raphe nucleus

Depressed suicide patients have elevated expression of neuronal tryptophan hydroxylase 2 (TPH2) mRNA and protein in midbrain serotonergic neurons, as well as increases in brain serotonin turnover. The mechanisms underlying these changes are uncertain, but increased TPH2 expression and serotonin turnover could result from genetic influences, adverse early life experiences, or acute stressful life events, all of which can alter serotonergic neurotransmission and have been implicated in determining vulnerability to major depression. Emerging evidence suggests that there are several different stress-related subsets of serotonergic neurons, each with a unique role in the integrated stress response. Here we review our current understanding of how genetic and environmental factors may influence TPH2 mRNA expression and serotonergic neurotransmission, focusing in particular on the dorsomedial part of the dorsal raphe nucleus. This subdivision of the dorsal raphe nucleus is selectively innervated by key forebrain structures implicated in regulation of anxiety states, it gives rise to projections to a distributed neural system mediating anxiety states, and serotonergic neurons within this subdivision are selectively activated by a number of stress- and anxiety-related stimuli. A better understanding of the anatomical and functional properties of specific stress- or anxiety-related serotonergic systems should aid our understanding of the neural mechanisms underlying the etiology of anxiety and affective disorders.

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

CONTEXT

Serotonin 1A (5-hydroxytryptamine 1A [5-HT(1A)]) autoreceptors mediate negative feedback inhibition of serotonergic neurons and play a critical role in regulating serotonin signaling involved in shaping the functional response of major forebrain targets, such as the amygdala, supporting complex behavioral processes. A common functional variation (C[-1019]G) in the human 5-HT(1A) gene (HTR1A) represents 1 potential source of such interindividual variability. Both in vitro and in vivo, -1019G blocks transcriptional repression, leading to increased autoreceptor expression. Thus, -1019G may contribute to relatively decreased serotonin signaling at postsynaptic forebrain target sites via increased negative feedback.

OBJECTIVES

To evaluate the effects of HTR1A C(-1019)G on amygdala reactivity and to use path analyses to explore the impact of HTR1A-mediated variability in amygdala reactivity on individual differences in trait anxiety. We hypothesized that -1019G, which potentially results in decreased serotonin signaling, would be associated with relatively decreased amygdala reactivity and related trait anxiety.

DESIGN

Imaging genetics in participants from an archival database.

PARTICIPANTS

Eighty-nine healthy adults.

RESULTS

Consistent with prior findings, -1019G was associated with significantly decreased threat-related amygdala reactivity. Importantly, this effect was independent of that associated with another common functional polymorphism that affects serotonin signaling, 5-HTTLPR. While there were no direct genotype effects on trait anxiety, HTR1A C(-1019)G indirectly predicted 9.2% of interindividual variability in trait anxiety through its effects on amygdala reactivity.

CONCLUSIONS

Our findings further implicate relatively increased serotonin signaling, associated with a genetic variation that mediates increased 5-HT(1A) autoreceptors, in driving amygdala reactivity and trait anxiety. Moreover, they provide empirical documentation of the basic premise that genetic variation indirectly affects emergent behavioral processes related to psychiatric disease risk by biasing the response of underlying neural circuitries.