Current developments and controversies: does the serotonin transporter gene-linked polymorphic region (5-HTTLPR) modulate the association between stress and depression?

Depression in adolescence and young adulthood: the difficulty to integrate motivational/emotional systems

Depression is presented as a multi-factorial bio-psycho-social expression that has evolved primarily as an effect of stressors related to the motivational/emotional systems that regulate the BrainMind in our relationship with conspecifics. These stressors may be caused by two sources of threat, firstly, the loss of bonding with the caregiver and later with a partner and/or group which relates to the SEPARATION (PANIC/GRIEF) system, secondly, social defeat as an expression of the social competition and social dominance. The sexual maturity drives the individual to social competition and social dominance, even if the latter often occurs before sexual maturity, e.g., chickens, dogs, non-human primates, and humans. Depression is an evolutionarily conserved mechanism in mammals to terminate both separation anxiety, so as to protect the vulnerable social brain from the consequences of prolonged separation anxiety, and the stress of social competition when social defeat is predictable. Adolescence and Young adulthood are particularly susceptible to these two types of threat because of human developmental characteristics that are summarized by the term neoteny. This refers to the slowing down of growth and development, resulting in both a prolonged period of dependence on a caring/protective adult and the persistence of juvenile characteristics throughout life. Therefore, neoteny makes the transition from childhood to sexual maturity more dramatic, making the integration of the SEPARATION (PANIC/GRIEF) system with the dynamics of social competition and dominance more stressful and a source of depression. Stress is an expression of the HPA-Hypothalamic-Pituitary-Adrenal axis that articulates with other systems, mainly the autonomic nervous system and the immune-inflammatory system. The latter is believed to be one of the most significant components in the dynamics of depressive processes, connected to the prodromes of its activation in childhood, under the pressure of environmental and relational stressors which can lead to learned helplessness. The recurrence of stressors makes it easier for the immune-inflammatory system to be activated in later life, which could make a significant contribution to the establishment of a depressive disease. The possible contribution of children's identification processes with their parents' depressive personalities through observational learning is considered.

The S/S Genotype of the 5-HTTLPR (Serotonin-Transporter-Linked Promoter Region) Variant of the SLC6A4 Gene Decreases the Risk of Pre-Eclampsia

Pre-eclampsia (PE) is a disorder characterized by hypertension in the second trimester of pregnancy that results from abnormal placentation affecting fetal development and maternal health. Previous studies have shown the role of serotonin (5-HT) that leads to poor placental perfusion, where S/S and S/L polymorphisms promote the solute carrier family 6 member 4 (SLC6A4) gene associated with the risk of developing changes in the microvasculature of the placenta. This study looked at the association between the gene variant 5-HTTLPR (serotonin-transporter-linked promoter region) of the SLC6A4 gene and the occurrence of PE. A total of 200 women were included: 100 cases (pregnant with PE) and 100 controls (pregnant without complications). Genotyping of the 5-HTTLPR variant was performed using polymerase chain reaction (PCR). Associations between the presence of the genetic variant of interest and PE and other clinical features were evaluated statistically. The frequencies of S/S, S/L, and L/L genotypes were 32%, 53%, and 15% for the cases and 55%, 25%, and 20% in the control group. Compared to the controls, the genotype frequencies S/S vs. S/L + L/L (recessive model) in the cases group were different (p = 0.002). The S/S genotype decreased the probability of PE (OR = 0.39, 95% IC: 0.22-0.69, p = 0.002) and PE with severity criteria (OR = 0.39, 95% IC: 0.17-0.91, p = 0.045). The 5-HTTLPR gene variant of the SLC6A4 gene modifies the risk of PE development among the studied population.

Neurobiological mechanisms of mood disorders: Stress vulnerability and resilience

Stress is an important factor in the development of several human pathologies. The response of rodents and humans to stress depends on many factors; some people and rodents develop stress-related mood disorders, such as depression and anxiety in humans, depression-like and anxiety-like behavior in mice and rats, while others report no new psychological symptoms in response to chronic or acute stress, and are considered susceptible and resilient to stress, respectively. Resilience is defined as the ability to thrive in the face of adversity and is a learned process that can help protect against occupational stressors and mental illnesses. There is growing interest in the underlying mechanisms involved in resilience and vulnerability to depression caused by stress, and some studies have demonstrated that individual variability in the way animals and humans respond to stress depends on several mechanisms, such as oxidative stress, neuronal plasticity, immunology and genetic factors, among others not discussed in this review, this review provides a general overview about this mechanism.

Preliminary Evidence That the Short Allele of 5-HTTLPR Moderates the Association of Psychiatric Symptom Severity on Suicide Attempt: The Example in Obsessive-Compulsive Disorder

BACKGROUND

The severity of symptoms represents an important source of distress in patients with a psychiatric disease. However, the extent to which this endogenous stress factor interacts with genetic vulnerability factors for predicting suicide risks remains unclear.

METHODS

We evaluated whether the severity of symptoms interacts with a genetic vulnerability factor (the serotonin transporter gene-linked promoter region variation) in predicting the frequency of lifetime suicide attempts in patients with a psychiatric disease. Symptom severity and 5-HTTLPR polymorphism were collected from a sample of 95 patients with obsessive-compulsive disorder (OCD). Lifetime suicide attempt was the primary outcome, and antecedent of multiple suicide attempts was the secondary outcome.

RESULTS

The gene-by-symptoms interaction was associated with an excess risk of suicide attempts (OR = 4.39, 95CI[1.44, 13.38], p < 0.009) and of multiple suicide attempts (OR = 4.18, 95CI[1.04, 16.77], p = 0.043). Symptom severity (moderate, severe, or extreme) was associated with an approximately five-fold increase in the odds of a lifetime suicide attempt in patients carrying one or two copies of the short allele of 5-HTTLPR. No such relationship was found for patients carrying the long allele.

CONCLUSION

This study provides preliminary evidence for the gene-by-stress interaction on suicide attempt when stress is operationalized as symptom severity. Progress in suicide research may come from efforts to investigate the gene-by-symptoms interaction hypothesis in a variety of diseases.

Flotillin-1 interacts with the serotonin transporter and modulates chronic corticosterone response

Aberrant serotonergic neurotransmission in the brain is considered at the core of the pathophysiological mechanisms involved in neuropsychiatric disorders. Gene by environment interactions contribute to the development of depression and involve modulation of the availability and functional activity of the serotonin transporter (SERT). Using behavioral and in vivo electrophysiological approaches together with biochemical, molecular-biological and molecular imaging tools we establish Flotillin-1 (Flot1) as a novel protein interacting with SERT and demonstrate its involvement in the response to chronic corticosterone (CORT) treatment. We show that genetic Flot1 depletion augments chronic CORT-induced behavioral despair and describe concomitant alterations in the expression of SERT, activity of serotonergic neurons and alterations of the glucocorticoid receptor transport machinery. Hence, we propose a role for Flot1 as modulatory factor for the depressogenic consequences of chronic CORT exposure and suggest Flotillin-1-dependent regulation of SERT expression and activity of serotonergic neurotransmission at the core of the molecular mechanisms involved.

Advance in Stress for Depressive Disorder

Stress is an adaptive response to environment aversive stimuli and a common life experience of one's daily life. Chronic or excessive stress especially that happened in early life is found to be deleterious to individual's physical and mental health, which is highly related to depressive disorders onset. Stressful life events are consistently considered to be the high-risk factors of environment for predisposing depressive disorders. In linking stressful life events with depressive disorder onset, dysregulated HPA axis activity is supposed to play an important role in mediating aversive impacts of life stress on brain structure and function. Increasing evidence have indicated the strong association of stress, especially the chronic stress and early life stress, with depressive disorders development, while the association of stress with depression is moderated by genetic risk factors, including polymorphism of SERT, BDNF, GR, FKBP5, MR, and CRHR1. Meanwhile, stressful life experience particularly early life stress will exert epigenetic modification in these risk genes via DNA methylation and miRNA regulation to generate long-lasting effects on these genes expression, which in turn cause brain structural and functional alteration, and finally increase the vulnerability to depressive disorders. Therefore, the interaction of environment with gene, in which stressful life exposure interplay with genetic risk factors and epigenetic modification, is essential in predicting depressive disorders development. As the mediator of environmental risk factors, stress will function together with genetic and epigenetic mechanism to influence brain structure and function, physiology and psychology, and finally the vulnerability to depressive disorders.

Association of Migraine Headaches With Suicidal Ideation Among Pregnant Women in Lima, Peru

BACKGROUND

Suicide is a leading cause of maternal death globally, and suicide prevalence rates have been shown to be increased in those with migraine. No previous study has examined the association between migraine and suicidal ideation during pregnancy.

OBJECTIVE

To examine the association between migraine and suicidal ideation among a cohort of pregnant women.

METHODS

A cross-sectional study was conducted among 3372 pregnant women attending prenatal care clinics in Lima, Peru. Suicidal ideation and depression were assessed using the Patient Health Questionnaire-9 (PHQ-9) scale during early pregnancy. Migraine classification (including migraine and probable migraine) was based on International Classification of Headache Disorders-III beta criteria. Multivariable logistic regression analyses were performed to estimate odds ratios (OR) and 95% confidence intervals (95% CI).

RESULTS

Suicidal ideation was more common among those with migraine (25.6%) as compared to those with probable migraine (22.1%, P < .001) or non-migraineurs (12.3%, P < .001). After adjusting for confounders, including depression, those with migraine or probable migraine had a 78% increased odds of suicidal ideation (OR = 1.78; 95% CI: 1.46-2.17), as compared with non-migraineurs. Women with both migraine and depression had a 4.14-fold increased odds of suicidal ideation (OR = 4.14; 95% CI: 3.17-5.42) compared to those with neither condition.

CONCLUSION

Migraine is associated with increased odds of suicidal ideation in pregnant women even when controlling for depression. These findings support the consideration of screening women with comorbid migraine and depression for suicidal behavior during pregnancy.

Serotonin transporter polymorphism (5HTTLPR), severe childhood abuse and depressive symptom trajectories in adulthood

BACKGROUND

Cross-sectional studies suggest that the serotonin transporter promoter region polymorphism (5-HTT gene-linked polymorphic region, 5HTTLPR) moderates the relationship between childhood abuse and major depressive disorder.

AIMS

To examine whether the 5HTTLPR polymorphism moderates the effect childhood abuse has on 5-year depressive symptom severity trajectories in adulthood.

METHOD

At 5-year follow-up, DNA from 333 adult primary care attendees was obtained and genotyped for the 5HTTLPR polymorphism. Linear mixed models were used to test for a genotype × childhood abuse interaction effect on 5-year depressive symptom severity trajectories.

RESULTS

After covariate adjustment, homozygous s allele carriers with a history of severe childhood abuse had significantly greater depressive symptom severity at baseline compared with those without a history of severe childhood abuse and this effect persisted throughout the 5-year period of observation.

CONCLUSIONS

The 5HTTLPR s/s genotype robustly moderates the effects of severe childhood abuse on depressive symptom severity trajectories in adulthood.

DECLARATION OF INTEREST

None.

COPYRIGHT AND USAGE

© The Royal College of Psychiatrists 2015. This is an open access article distributed under the terms of the Creative Commons Non-Commercial, No Derivatives (CC BY-NC-ND) licence.

Genetic determinants of depression: recent findings and future directions

LEARNING OBJECTIVES

After participating in this activity, learners should be better able to: 1. Evaluate current evidence regarding the genetic determinants of depression 2. Assess findings from studies of gene-environment interaction 3. Identify challenges to gene discovery in depression Depression is one of the most prevalent, disabling, and costly mental health conditions in the United States and also worldwide. One promising avenue for preventing depression and informing its clinical treatment lies in uncovering the genetic and environmental determinants of the disorder as well as their interaction (G × E). The overarching goal of this review article is to translate recent findings from studies of genetic association and G × E related to depression, particularly for readers without in-depth knowledge of genetics or genetic methods. The review is organized into three major sections. In the first, we summarize what is currently known about the genetic determinants of depression, focusing on findings from genome-wide association studies (GWAS). In the second section, we review findings from studies of G × E, which seek to simultaneously examine the role of genes and exposure to specific environments or experiences in the etiology of depression. In the third section, we describe the challenges to genetic discovery in depression and promising strategies for future progress.

Gene-environment interaction in major depression: focus on experience-dependent biological systems

Major depressive disorder (MDD) is a multifactorial and polygenic disorder, where multiple and partially overlapping sets of susceptibility genes interact each other and with the environment, predisposing individuals to the development of the illness. Thus, MDD results from a complex interplay of vulnerability genes and environmental factors that act cumulatively throughout individual's lifetime. Among these environmental factors, stressful life experiences, especially those occurring early in life, have been suggested to exert a crucial impact on brain development, leading to permanent functional changes that may contribute to lifelong risk for mental health outcomes. In this review, we will discuss how genetic variants (polymorphisms, SNPs) within genes operating in neurobiological systems that mediate stress response and synaptic plasticity, can impact, by themselves, the vulnerability risk for MDD; we will also consider how this MDD risk can be further modulated when gene × environment interaction is taken into account. Finally, we will discuss the role of epigenetic mechanisms, and in particular of DNA methylation and miRNAs expression changes, in mediating the effect of the stress on the vulnerability risk to develop MDD. Taken together, we aim to underlie the role of genetic and epigenetic processes involved in stress- and neuroplasticity-related biological systems on the development of MDD after exposure to early life stress, thereby building the basis for future research and clinical interventions.

Effects of genetic and early environmental risk factors for depression on serotonin transporter expression and methylation profiles

The serotonin transporter (SERT) gene-linked polymorphic region (5-HTTLPR) has been implicated in moderating the link between life stress and depression. However, respective molecular pathways of gene-environment (GxE) interaction are largely unknown. Sustained alterations in SERT gene expression profiles, possibly mediated by epigenetic modifications, are a frequent correlate of depression and may thus constitute a putative mediator of GxE interaction. Here, we aimed to investigate joint effects of 5-HTTLPR and self-reported environmental adversity throughout the lifespan (prenatal, early and recent stress/trauma) on in vivo SERT mRNA expression in peripheral blood cells. To further evaluate whether environmentally induced changes in SERT expression are mediated by epigenetic modifications, we analyzed 83 CpG sites within a 799-bp promoter-associated CpG island of the SERT gene using the highly sensitive method of bisulfite pyrosequencing. Participants were 133 healthy young adults. Our findings show that both the 5-HTTLPR S allele and maternal prenatal stress/child maltreatment are associated with reduced in vivo SERT mRNA expression in an additive manner. Remarkably, individuals carrying both the genetic and the environmental risk factors exhibited 32.8% (prenatal stress) and 56.3% (child maltreatment) lower SERT mRNA levels compared with those without any risk factor. Our data further indicated that changes in SERT mRNA levels were unlikely to be mediated by DNA methylation profiles within the SERT CpG island. It is thus conceivable that the persistent changes in SERT expression may in turn relate to altered serotonergic functioning and possibly convey differential disease vulnerability associated with 5-HTTLPR and early adversity.

The 5-HTTLPR genotype modulates heart rate variability and its adjustment by pharmacological panic challenge in healthy men

Abnormal serotonin transporter (5-HTT) function and autonomic nervous system (ANS) dysregulation has been proposed in panic disorder. However, in contrast to hypothalamo-pituitary-adrenocortical (HPA) functioning, ANS reactivity during panic response has yet not been investigated in humans with respect to the 5-HTT genotype. The present study assessed the influence of challenging by cholecystokinin tetrapeptide (CCK-4) on heart rate variability (HRV) measures, to monitor autonomic reactivity and its relationship to 5-HTT-linked polymorphic region (5-HTTLPR) genotypes. We hypothesized substantial effects of the 5-HTTLPR genotype on autonomic reactivity. We studied 30 healthy young men, 15 of each with the long/long (l/l) or short/short (s/s) genotype for the 5-HTTLPR. All participants received an intravenous application of 50 μg CCK-4. HRV measures were assessed in both groups at baseline and immediately after CCK-4 application. Our results indicated lower parasympathetic activity in s/s carriers during baseline, time and frequency domain measures. CCK-4 application significantly enhanced the sympathetic tone in both groups, leading to diminished group differences. A significant treatment by genotype effect indicated reduced autonomic reactivity to CCK-4 challenge in the s/s compared to l/l carriers. Our findings show enhanced sympathetic and/or diminished cardiac vagal activity under basal conditions and blunted autonomic reactivity in s/s vs. l/l carriers. Our study provides novel data supporting claims that the s/s genotype represents a genetic vulnerability factor associated with inadequate hyporeactivity to stress and extends current knowledge on the impact of the central serotonergic activity on the sympathoadrenal pathway.

Gene-environment interactions and intermediate phenotypes: early trauma and depression

This review focuses on current research developments in the study of gene by early life stress (ELS) interactions and depression. ELS refers to aversive experiences during childhood and adolescence such as sexual, physical or emotional abuse, emotional or physical neglect as well as parental loss. Previous research has focused on investigating and characterizing the specific role of ELS within the pathogenesis of depression and linking these findings to neurobiological changes of the brain, especially the stress response system. The latest findings highlight the role of genetic factors that increase vulnerability or, likewise, promote resilience to depression after childhood trauma. Considering intermediate phenotypes has further increased our understanding of the complex relationship between early trauma and depression. Recent findings with regard to epigenetic changes resulting from adverse environmental events during childhood promote current endeavors to identify specific target areas for prevention and treatment schemes regarding the long-term impact of ELS. Taken together, the latest research findings have underscored the essential role of genotypes and epigenetic processes within the development of depression after childhood trauma, thereby building the basis for future research and clinical interventions.

GLAST/EAAT1 regulation in cultured Bergmann glia cells: role of the NO/cGMP signaling pathway

Glutamate, the major excitatory amino acid, activates a wide variety of signal transduction cascades. Ionotropic and metabotropic glutamate receptors are critically involved in long-term synaptic changes, although recent findings suggest that the electrogenic Na(+)-dependent glutamate transporters, responsible for its removal from the synaptic cleft participate in the signaling transactions triggered by this amino acid. Glutamate transporters are profusely expressed in glia therefore most of its uptake occurs in this cellular compartment. In the cerebellar cortex, Bergmann glial cells enwrap glutamatergic synapses and participate in the recycling of its neurotransmitter through the glutamate/glutamine shuttle. It has long been acknowledged that glutamatergic transmission in the cerebellar molecular layer results in cGMP accumulation within Bergmann glia cells. In this context, we decided to investigate a plausible role of the nitric oxide/cGMP-signaling pathway in the regulation of Bergmann glia glutamate transporters. To this end, the well-established model of primary cultures of chick cerebellar Bergmann glial cells was used. Confluent monolayers were exposed to the nitric oxide donor, sodium nitroprusside, or to the non-hydrolysable cGMP analog dbcGMP and the [(3)H] D-aspartate uptake activity measured. An increase in uptake activity, related to an augmentation in VMax, was detected with both treatments. The signaling cascade includes NO/cGMP/PKG and Ca(2+) influx through the Na(+)/Ca(2+) exchanger and might be related to the plasma membrane glutamate transporters turnover. Interestingly enough, an inhibitor of the cGMP dependent protein kinase was capable to abolish the sodium nitroprusside induced Ca(2+) influx. These results provide an insight into the physiological role of cGMP in the cerebellum.

Personalized medicine in major depressive disorder -- opportunities and pitfalls

The sequencing of the human genome in the early days of this millennium was greeted with great fanfare as this accomplishment was expected to revolutionize medicine and result in individualized treatments based on the genetic make-up of the patient. The ultimate promise of personalized medicine would be fulfilled with the identification of disease biomarkers that would be widely available for use in diagnosis and treatment. Progress, however, has been slow in providing disease biomarkers or approved diagnostic tests. This is true for major depressive disorder (MDD), despite its prevalence in the general population and the widespread acceptance of its biological basis. Studies using strategies like genome-wide association and candidate gene analyses have identified a number of possible biomarkers of MDD, including serum levels of neurotrophic factors, inflammatory cytokines and HPA axis hormones, but none have proven sufficiently powerful for clinical use. The lack of biologically based tests available for use in identifying patients with MDD is a significant impediment to personalized and more effective treatment, because it means diagnosis continues to be driven by subjective symptoms. While genetic studies of MDD have not yet led to diagnostic and treatment biomarkers, progress in determining the role of the genome in drug metabolism heralds the first effort in personalized prescribing for the antidepressants. The FDA suggested and approved genotyping tests for common variants of drug metabolism genes, such as the cytochrome p450s. By using these tests a physician can select an appropriate antidepressant for a given patient, as differences in clearance, half-life, and peak blood concentrations are controlled by genetic variability in drug metabolism. Personalization in drug choice can be achieved because these tests: (1) identify responders and non-responders; (2) provide alerts to possible adverse drug events; and (3) help optimize dose. Improved ways of diagnosing and prescribing effective treatments for MDD are needed, as the available methods are inadequate and symptom based. In the foreseeable future, further interrogation of the genome may serve as the basis for development of new personalized medicine strategies for diagnosis and treatment of MDD.

Stress-related depression: neuroendocrine, genetic, and therapeutical aspects

OBJECTIVE

To summarize current concepts on neuroendocrine and genetic principles underlying stress-related depression and to discuss the challenges of personalized treatment in depression.

METHODS

Review of the literature pertaining to genetic and neuroendocrine basis of stress-related depression including aspects of treatment response with a focus on the hypothalamus-pituitary-adrenal (HPA) axis.

RESULTS

There is increasing evidence that genetic polymorphisms and dysregulation of the HPA axis are associated with the pathophysiology of stress-related depression. Individual stress hormone reactivity seems to be determined by a combination of genetic and environmental factors, contributing to both, resilience or vulnerability.

CONCLUSIONS

Although substantial progress has been made, current knowledge is still limited. Further basic and clinical research is needed to identify specific subgroups and to minimize heterogeneity of the depression phenotype. A better characterization is essential to detect genetic and functional predictors of antidepressant treatment response to follow the vision of personalized therapy in psychiatry.

The COMT Val158Met polymorphism modulates working memory performance under acute stress

BACKGROUND

One of the most widely studied genetic polymorphisms regarding cognitive and emotional phenotypes is the COMT Val158Met polymorphism that influences dopamine availability in the prefrontal cortex (PFC). The PFC is the key brain structure for higher cognitive functions such as working memory, as well as an important regulatory site and target of the psychoendocrine stress response. Dopamine is thought to influence PFC functions in an inverted u-shaped manner. Thus, a stress-related increase in prefrontal dopamine is hypothesized to exert differential effects on working memory performance depending on the genetically determined baseline dopamine level in the PFC.

METHOD

Thirty-three healthy young subjects homozygous for the COMT Val158Met polymorphism were selected from a larger pre-genotyped sample. They performed an n-back working memory task after exposure to a laboratory psychosocial stress induction paradigm (The Trier Social Stress Test for Groups; TSST-G).

RESULTS

Under stress, working memory performance of Met homozygotes was significantly worse than working memory performance of Val homozygotes. Importantly, this genotype effect was restricted to the medium difficulty level of the n-back task.

CONCLUSION

Our results demonstrate that working memory performance under stress is influenced by genetic variation in prefrontal dopamine levels. More generally, our results point to the importance of considering the complex interaction of genes, environment, and task variables.

Association between the serotonin transporter triallelic genotype and eating problems is moderated by the experience of childhood trauma in women

OBJECTIVE

This study investigated a potential interaction between the triallelic polymorphism of the serotonin transporter gene (SLC6A4) promoter and the experience of childhood trauma on the number of problem eating behaviors.

METHOD

The study sample was comprised of 439 (64.7% female) Caucasian college students (mean age = 22.49, SD = 6.12). Participants completed questionnaires that assessed eating problems and experience of trauma in childhood (ages 0-12) and donated cheek cells for 5-HTTLPR and rs25531 genotyping.

RESULTS

Women carrying a lower expressing allele (i.e., L(G) or S) who were exposed to higher levels of childhood trauma reported significantly higher mean numbers of eating problems (gender × genotype × trauma interaction, p = .006).

DISCUSSION

These results are consistent with findings that the lower expressing alleles of the SLC6A4 promoter are associated with increased sensitivity to the negative impact of childhood stressors on adult behavioral outcomes.

Neural mechanisms underlying 5-HTTLPR-related sensitivity to acute stress

OBJECTIVE

Many studies have shown that 5-HTTLPR genotype interacts with exposure to stress in conferring risk for psychopathology. However, the specific neural mechanisms through which this gene-by-environment interaction confers risk remain largely unknown, and no study to date has directly examined the modulatory effects of 5-HTTLPR on corticolimbic circuit responses during exposure to acute stress.

METHOD

An acute laboratory stressor was administered to 51 healthy women during blood-oxygen-level-dependent functional magnetic resonance imaging. In this task, participants were threatened with electric shocks of uncertain intensity, which were unpredictably delivered to the wrist after a long anticipatory cue period of unpredictable duration.

RESULTS

Relative to women carrying the L allele, those with the SS genotype showed enhanced activation during threat anticipation in a network of regions, including the amygdala, hippocampus, anterior insula, thalamus, pulvinar, caudate, precuneus, anterior cingulate cortex, and medial prefrontal cortex. Individuals with the SS genotype also displayed enhanced positive coupling between medial prefrontal cortex activation and anxiety experience, whereas enhanced negative coupling between insula activation and perceived success at regulating anxiety was observed in individuals carrying the L allele.

CONCLUSIONS

These findings suggest that during stress exposure, neural systems that enhance fear and arousal, modulate attention toward threat, and perseverate on emotional salience of the threat may be engaged preferentially in individuals with the SS genotype. This may be one mechanism underlying the risk for psychopathology conferred by the S allele upon exposure to life stressors.

A protective genetic variant for adverse environments? The role of childhood traumas and serotonin transporter gene on resilience and depressive severity in a high-risk population

Genetic aspects may influence the effect of early adverse events on psychological well being in adulthood. In particular, a common polymorphism within the serotonin transporter gene (5-HTTLPR short/long) has been associated to the risk for stress-induced psychopathology. In the present study we investigated the role of childhood traumas and 5-HTTLPR on measures of psychological resilience and depression in a sample of individuals at a high risk for psychological distress (763 male prisoners). The 5-HTTLPR genotype did not influence resilience and depressive severity. However, a significant interaction was observed between 5-HTTLPR and childhood traumas on both resilience and depressive severity. In particular, among subjects exposed to severe childhood trauma only, the long-allele was associated to lower resilience scores and increased current depressive severity as compared to short/short homozygous. Sex specific effects, difference in type and duration of stressors and the specific composition of the sample may explain discrepancy with many studies reporting the short-allele as a vulnerability factor for reactivity to stress. We here speculated that in males the long-allele may confer lower resilience and therefore higher vulnerability for depressive symptoms in subjects exposed to early stress and currently living in stressful environments.

Bonsai trees in your head: how the pavlovian system sculpts goal-directed choices by pruning decision trees

When planning a series of actions, it is usually infeasible to consider all potential future sequences; instead, one must prune the decision tree. Provably optimal pruning is, however, still computationally ruinous and the specific approximations humans employ remain unknown. We designed a new sequential reinforcement-based task and showed that human subjects adopted a simple pruning strategy: during mental evaluation of a sequence of choices, they curtailed any further evaluation of a sequence as soon as they encountered a large loss. This pruning strategy was Pavlovian: it was reflexively evoked by large losses and persisted even when overwhelmingly counterproductive. It was also evident above and beyond loss aversion. We found that the tendency towards Pavlovian pruning was selectively predicted by the degree to which subjects exhibited sub-clinical mood disturbance, in accordance with theories that ascribe Pavlovian behavioural inhibition, via serotonin, a role in mood disorders. We conclude that Pavlovian behavioural inhibition shapes highly flexible, goal-directed choices in a manner that may be important for theories of decision-making in mood disorders.

Planning is tricky because choices we make now affect future choices, and future choices and outcomes should guide current choices. Because there are exponentially many combinations of future choices and actions, brute-force approaches that consider all possible combinations work only for trivially small problems. Here, we describe how humans use a simple Pavlovian strategy to cut an expanding decision tree down to a computationally manageable size. We find that humans use this strategy even when it is disadvantageous, and that the tendency to use it is related to mild depressive symptoms. The findings, we suggest, can be interpreted within a theoretical framework which relates Pavlovian behavioural inhibition to serotonin and mood disorders.

Differential serotonin transport is linked to the rh5-HTTLPR in peripheral blood cells

The human serotonin transporter (SERT) gene possesses a 43-base pair (bp) insertion-deletion promoter polymorphism, the h5-HTTLPR. Genotype at this locus correlates with variation in anxiety-related personality traits and risk for major depressive disorder in many studies. Yet, the complex effects of the h5-HTTLPR, in combination with closely associated single-nucleotide polymorphisms (SNPs), continue to be debated. Moreover, although SERT is of high clinical significance, transporter function in vivo remains difficult to assess. Rhesus express a promoter polymorphism related to the h5-HTTLPR. The rh5-HTTLPR has been linked to differences in stress-related behavior and cognitive flexibility, although allelic variations in serotonin uptake have not been investigated. We studied the serotonin system as it relates to the 5-HTTLPR in rhesus peripheral blood cells. Sequencing of the rh5-HTTLPR revealed a 23-bp insertion, which is somewhat longer than originally reported. Consistent with previous reports, no SNPs in the rh5-HTTLPR and surrounding genomic regions were detected in the individuals studied. Reductions in serotonin uptake rates, cell surface SERT binding, and 5-hydroxyindoleacetic acid/serotonin ratios, but not SERT mRNA levels, were associated with the rh5-HTTLPR short allele. Thus, serotonin uptake rates are differentiable with respect to the 5-HTTLPR in an easily accessible native peripheral tissue. In light of these findings, we foresee that primary blood cells, in combination with high sensitivity functional measurements enabled by chronoamperometry, will be important for investigating alterations in serotonin uptake associated with genetic variability and antidepressant responsiveness in humans.

A new public health genomics model for common complex diseases, with an application to common behavioral disorders

AIM

In the light of common forms of gene-environment interplay, particularly epigenomics and ecogenetics, the incorporation of envirome data into public health genomics models becomes necessary. Developing and restructuring public health genomics models is essential within the context of common complex diseases.

MATERIALS & METHODS

We developed a novel theoretical model integrating a gene-environment interaction paradigm into public health genomics, which integrates four main sources of data: personal genome data, personal envirome data, molecular genetic/genomic evidence and environmental factors implicated in gene-environment interactions underlying common complex disease phenotypes. Collectively, this knowledge is fed into public health policy development.

RESULTS

This model is the first public health genomics model that incorporates gene-environment interactions within the context of common complex disorders, and is applied to behavioral conditions.

CONCLUSION

Our model proposes, for the first time, an understanding of behavioral disorders from the genomic perspective, combining it with known environmental factors within the framework of public health. Application of this model will enable evidence-based behavioral interventions at the public health level and facilitate genome-based public health policy development for behavioral conditions.

Genetic variation in serotonin transporter function affects human fear expression indexed by fear-potentiated startle

The serotonin transporter (SERT) plays a crucial role in anxiety. Accordingly, variance in SERT functioning appears to constitute an important pathway to individual differences in anxiety. The current study tested the hypothesis that genetic variation in SERT function is associated with variability in the basic reflex physiology of defense. Healthy subjects (N=82) were presented with clearly instructed cues of shock threat and safety to induce robust anxiety reactions. Subjects carrying at least one short allele for the 5-HTTLPR polymorphism showed stronger fear-potentiated startle compared to long allele homozygotes. However, short allele carriers showed no deficit in the downregulation of fear after the offset of threat. These results suggest that natural variation in SERT function affects the magnitude of defensive reactions while not affecting the capacity for fear regulation.

SLC6 neurotransmitter transporters: structure, function, and regulation

The neurotransmitter transporters (NTTs) belonging to the solute carrier 6 (SLC6) gene family (also referred to as the neurotransmitter-sodium-symporter family or Na(+)/Cl(-)-dependent transporters) comprise a group of nine sodium- and chloride-dependent plasma membrane transporters for the monoamine neurotransmitters serotonin (5-hydroxytryptamine), dopamine, and norepinephrine, and the amino acid neurotransmitters GABA and glycine. The SLC6 NTTs are widely expressed in the mammalian brain and play an essential role in regulating neurotransmitter signaling and homeostasis by mediating uptake of released neurotransmitters from the extracellular space into neurons and glial cells. The transporters are targets for a wide range of therapeutic drugs used in treatment of psychiatric diseases, including major depression, anxiety disorders, attention deficit hyperactivity disorder and epilepsy. Furthermore, psychostimulants such as cocaine and amphetamines have the SLC6 NTTs as primary targets. Beginning with the determination of a high-resolution structure of a prokaryotic homolog of the mammalian SLC6 transporters in 2005, the understanding of the molecular structure, function, and pharmacology of these proteins has advanced rapidly. Furthermore, intensive efforts have been directed toward understanding the molecular and cellular mechanisms involved in regulation of the activity of this important class of transporters, leading to new methodological developments and important insights. This review provides an update of these advances and their implications for the current understanding of the SLC6 NTTs.

Natural and engineered coding variation in antidepressant-sensitive serotonin transporters

The presynaptic serotonin (5-HT) transporter (SERT) is a key regulator of 5-HT signaling and is a major target for antidepressant medications and psychostimulants. In recent years, studies of natural and engineered genetic variation in SERT have provided new opportunities to understand structural dimensions of drug interactions and regulation of the transporter, to explore 5-HT contributions to antidepressant action, and to assess the impact of SERT-mediated 5-HT contributions to neuropsychiatric disorders. Here we review three examples from our recent studies where genetic changes in SERT, identified or engineered, have led to new models, findings, and theories that cast light on new dimensions of 5-HT action in the CNS and periphery. First, we review our work to identify specific residues through which SERT recognizes antagonists, and the conversion of this knowledge to the creation of mice lacking high-affinity antidepressant and cocaine sensitivity. Second, we discuss our studies of functional coding variation in SERT that exists in commonly used strains of inbred mice, and how this variation is beginning to reveal novel 5-HT-associated phenotypes. Third, we review our identification and functional characterization of multiple, hyperactive SERT coding variants in subjects with autism. Each of these activities has driven the development of new model systems that can be further exploited to understand the contribution of 5-HT signaling to risk for neuropsychiatric disorders and their treatment.

The influence of psychiatric screening in healthy populations selection: a new study and meta-analysis of functional 5-HTTLPR and rs25531 polymorphisms and anxiety-related personality traits

BACKGROUND

A genetic liability for anxiety-related personality traits in healthy subjects has been associated with the functional serotonin transporter promoter polymorphism (5-HTTLPR), although the data are somewhat conflicting. Moreover, only one study has investigated the functional significance of the 5-HTTLPR/rs25531 haplotypes in relation to anxiety traits in healthy subjects. We tested whether the 5-HTTLPR polymorphism and the 5-HTTLPR/rs25531 haplotypes are linked to Harm Avoidance (HA) using an association study (STUDY I) and a meta-analytic approach (STUDY II).

METHODS

STUDY I: A total of 287 unrelated Italian volunteers were screened for DSM-IV Axis I disorders and genotyped for the 5-HTTLPR and rs25531 (A/G) polymorphisms. Different functional haplotype combinations were also analyzed. STUDY II: A total of 44 studies were chosen for a meta-analysis of the putative association between 5-HTTLPR and anxiety-related personality traits.

RESULTS

STUDY I: In the whole sample of 287 volunteers, we found that the SS genotype and S'S' haplotypes were associated with higher scores on HA. However, because the screening assessed by Mini-International Neuropsychiatric Interview (M.I.N.I.) showed the presence of 55 volunteers affected by depression or anxiety disorders, we analyzed the two groups ("disordered" and "healthy") separately. The data obtained did indeed confirm that in the "healthy" group, the significant effects of the SS genotype and S'S' haplotypes were lost, but they remained in the "disordered" group. STUDY II: The results of the 5-HTTLPR meta-analysis with anxiety-related traits in the whole sample confirmed the association of the SS genotype with higher anxiety-related traits scores in Caucasoids; however, when we analyzed only those studies that used structured psychiatric screening, no association was found.

CONCLUSIONS

This study demonstrates the relevance to perform analyses on personality traits only in DSM-IV axis I disorder-free subjects. Furthermore, we did not find an association between functional serotonin transporter gene polymorphisms and anxiety traits in healthy subjects screened through a structured psychiatric interview.