Interactions between BDNF Val66Met polymorphism and early life stress predict brain and arousal pathways to syndromal depression and anxiety

Brain derived Neurotropic Factor (BDNF) is associated with childhood abuse but not cognitive domains in first episode psychosis

BACKGROUND

The Brain-derived Neurotrophic Factor (BDNF) modulates cognitive processes and is associated with increased risk of schizophrenia. Childhood trauma (CT) is frequent in patients with psychosis and severely affects course and outcome.

AIMS

We investigated the hypothesis that BDNF is associated with both CT and cognitive deficits in a sample of first-episode psychosis (FEP) cases and unaffected controls.

METHOD

Participants with FEP and healthy controls were recruited between August 2008 and July 2011 from South London, UK. Childhood traumatic events were detected using the Childhood Experience of Care and Abuse Questionnaire (CECA-Q). Neuropsychological data were also collected. BDNF plasma levels were measured from fasting blood samples.

RESULTS

Data were available on 87 FEP patients and 152 controls. Our results showed a significant effect of separation (F=5.5; df=1,115; p=.02), physical (F=4.7; df=1, 118; p=.03) and sexual abuse (F=5.4; df=1,117; p=.02) on BDNF levels with lower levels among those who experienced the traumatic event compared to those who did not. Physical abuse predicted lower plasma levels of BDNF (β=-.30; p=.03) whereas sexual and/or physical abuse showed a trend (β=-.26; p=.06) in FEP patients but not in unaffected controls. No association between BDNF plasma levels and cognitive functions was found among patients with FEP and controls.

CONCLUSION

Our findings suggest the possible involvement of BDNF in the onset of first-episode psychosis in individuals exposed to early trauma and propose BDNF as a potential clinical biomarker to detect the detrimental effects of CT on human brain plasticity.

Additive gene-environment effects on hippocampal structure in healthy humans

Hippocampal volume loss has been related to chronic stress as well as genetic factors. Although genetic and environmental variables affecting hippocampal volume have extensively been studied and related to mental illness, limited evidence is available with respect to G × E interactions on hippocampal volume. The present MRI study investigated interaction effects on hippocampal volume between three well-studied functional genetic variants (COMT Val158Met, BDNF Val66Met, 5-HTTLPR) associated with hippocampal volume and a measure of environmental adversity (life events questionnaire) in a large sample of healthy humans (n = 153). All three variants showed significant interactions with environmental adversity with respect to hippocampal volume. Observed effects were additive by nature and driven by both recent as well as early life events. A consecutive analysis of hippocampal subfields revealed a spatially distinct profile for each genetic variant suggesting a specific role of 5-HTTLPR for the subiculum, BDNF Val66Met for CA4/dentate gyrus, and COMT Val158Met for CA2/3 volume changes. The present study underscores the importance of G × E interactions as determinants of hippocampal volume, which is crucial for the neurobiological understanding of stress-related conditions, such as mood disorders or post-traumatic stress disorder (PTSD).

Differential susceptibility to effects of maternal sensitivity? A study of candidate plasticity genes

Here we tested whether there was genetic moderation of effects of early maternal sensitivity on social–emotional and cognitive–linguistic development from early childhood onward and whether any detected Gene × Environment interaction effects proved consistent with differential-susceptibility or diathesis–stress models of Person × Environment interaction (N= 695). Two new approaches for evaluating models were employed with 12 candidate genes. Whereas maternal sensitivity proved to be a consistent predictor of child functioning across the primary-school years, candidate genes did not show many main effects, nor did they tend to interact with maternal sensitivity/insensitivity. These findings suggest that the developmental benefits of early sensitive mothering and the costs of insensitive mothering look more similar than different across genetically different children in the current sample. Although acknowledgement of this result is important, it is equally important that the generally null Gene × Environment results reported here not be overgeneralized to other samples, other predictors, other outcomes, and other candidate genes.

Brain-derived neurotrophic factor Val66Met polymorphism association with antidepressant efficacy: a systematic review and meta-analysis

INTRODUCTION

Previous studies of the association of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism with antidepressant efficacy are inconsistent. Thus, we conducted a systematic review and meta-analysis.

METHODS

We searched MEDLINE, PubMed, EMBASE, and Chinese Databases (Biomedical Literature Database, National Knowledge Infrastructure, Weipu, and WanFang) up to March 2013 for relevant studies (584 retrieved, 16 met inclusion criteria). We conducted six comparisons for both response and remission rates for three genotypes in Caucasians and Asians (4 weeks or ≥6 weeks; selective serotonin reuptake inhibitors [SSRIs], serotonin-noradrenaline reuptake inhibitors, or mixed antidepressants).

RESULTS

Met carriers had a better response rate than Val/Val. In Asians, the Met carrier was positively associated with response rate (odds ratio; 95% confidence interval: 1.48; 1.02-2.14) in the SSRI group (1.81; 1.10-2.97) and with treatments ≥6 weeks. Met/Val showed a positive association with the response rate versus homozygotes (1.60; 1.20-2.13) and for ≥6 weeks (mixed antidepressant, 1.36; 1.04-1.77; SSRI, 1.55; 1.11-2.17). There was a weak effect of Met/Val versus Val/Val in response to SSRIs (mixed time, 2.07; 1.48-2.89; ≥6 weeks, 2.25; 1.53-3.32). For remission, Met/Val was better than the homozygotes (1.71; 1.09-2.68, Asians, SSRIs only).

DISCUSSION

Our meta-analysis confirms the effects of the BDNF polymorphism on SSRI response in Asians. This effect may be dependent on ethnic origin because BDNF had a lesser influence on response in mixed race studies. Antidepressants were more effective in groups with a treatment duration ≥6 weeks. Thus, future investigators should carefully consider their outcome observation end point.

BDNF Val66Met genotype interacts with childhood adversity and influences the formation of hippocampal subfields

Childhood stress and genetic factors like the Val66MET polymorphism of the brain derived neurotrophic factor (BDNF) gene are associated with a higher risk for developing major depressive disorder (MDD) and might also influence hippocampal changes. The aim of this study was to determine which hippocampal dentate gyrus and cornu ammonis subfields are altered in MDD compared to healthy controls and which subfields are affected by the BDNF Val66Met polymorphism and child adversity. Adult patients with MDD and healthy matched controls underwent high-resolution magnetic resonance imaging. Automatic segmentation using the programme FreeSurfer was used to segment the hippocampal subfields dentate gyrus (DG/CA4), CA1 and CA2/3. The history of possible childhood adversity was assessed using the Childhood Trauma Questionnaire and the Val66Met BDNF SNP (rs6265) genotypes were obtained. Patients with MDD had significantly smaller CA4/DG and CA2/3 volumes compared to healthy controls. Furthermore, there was a significant interactive effect of BDNF allele and childhood adversity on CA2/3 and CA4/DG volumes. Met allele carriers without childhood adversity had larger and with childhood adversity smaller CA4/DG and CA2/3 volumes than Val-allele homozygotes. Our results highlight stress by gene interactions as relevant for hippocampal volume reductions, in particular for the subfield CA2/3 and dentate gyrus.

Translational findings on brain-derived neurotrophic factor and anxiety: contributions from basic research to clinical practice

BACKGROUND/AIMS

Anxious responses are evolutionarily adaptive, but excessive fear can become disabling and lead to anxiety disorders. Translational models of anxiety might be useful sources for understanding the neurobiology of fear and anxiety and can contribute to future proposals of therapeutic intervention for the disorders studied. Brain-derived neurotrophic factor (BDNF), which is known for its importance on neuroplasticity and contextual memory, has emerged as a relevant element for emotional memory. Recent studies show that the Val(66)Met BDNF polymorphism correlates with various psychiatric disorders, including anxiety, but there are several differences between experimental and clinical studies.

METHODS

In this work, we review the literature focused on the BDNF Val(66)Met polymorphism and anxiety, and discuss biological findings from animal models to clinical studies.

RESULTS

As occurs with other psychiatric disorders, anxiety correlates with anatomical, behavioral and physiological changes related to the BDNF polymorphism. In animal studies, it has been shown that a significant decrease in regulated secretion from both BDNFVal/Met and BDNFMet/Met neurons represented a significant decrease in available BDNF.

CONCLUSION

These studies suggest that developing pharmacological strategies facilitating the release of BDNF from synapses or prolongation of the half-life of secreted BDNF may improve the therapeutic responses of humans expressing the BDNF polymorphism.

What keeps a body moving? The brain-derived neurotrophic factor val66met polymorphism and intrinsic motivation to exercise in humans

Individuals who are intrinsically motivated to exercise are more likely to do so consistently. In previous research, those with at least one copy of the methionine (met) allele in the brain-derived neurotrophic factor gene (BDNF; rs6265) had greater increases in positive mood and lower perceived exertion during exercise. This study examined whether genotype for BDNF is also related to intrinsic motivation, measured by self-report during a treadmill exercise session and a free-choice behavioral measure (continuing to exercise given the option to stop) among 89 regular exercisers (age M = 23.58, SD = 3.95). Those with at least one copy of the met allele reported greater increases in intrinsic motivation during exercise and were more likely to continue exercising when given the option to stop (55 vs. 33%). Results suggest that underlying genetic factors may partially influence perceptions of inherent rewards associated with exercise and might inform the development of individually targeted interventions.

The BDNF-Val66Met polymorphism modulates parental rearing effects on adult psychiatric symptoms: a community twin-based study

PURPOSE

To test whether firstly, different parental rearing components were associated with different dimensions of psychiatric symptoms in adulthood, secondly BDNF-Val66Met polymorphism moderated this association and thirdly, this association was due to genetic confounding.

METHOD

Perceived parental rearing according to Parental Bonding Instrument (PBI), psychiatric symptoms evaluated with the Brief Symptom Inventory (BSI) and the BDNF-Val66Met polymorphism were analyzed in a sample of 232 adult twins from the general population.

RESULTS

In the whole sample, paternal care was negatively associated with depression. Maternal overprotection was positively associated with paranoid ideation, obsession-compulsion and somatization. Gene-environment interaction effects were detected between the BDNF-Val66Met polymorphism and maternal care on phobic anxiety, paternal care on hostility, maternal overprotection on somatization and paternal overprotection also in somatization. In the subsample of MZ twins, intrapair differences in maternal care were associated with anxiety, paranoid ideation and somatization.

CONCLUSIONS

Met carriers were, in general, more sensitive to the effects of parental rearing compared to Val/Val carriers in relation to anxiety and somatization. Contra-intuitively, our findings suggest that high rates of maternal care might be of risk for Met carriers regarding anxiety. Results from analyses controlling for genetic confounding were in line with this finding.

The serotonin-BDNF duo: developmental implications for the vulnerability to psychopathology

Serotonin (5-HT) and brain-derived neurotrophin factor (BDNF) are known to modulate behavioral responses to stress and to mediate the therapeutic efficacy of antidepressant agents through neuroplastic and epigenetic mechanisms. While the two systems interact at several levels, this scenario is complicated by a number of variants including brain region specificity, 5-HT receptor selectivity and timing. Based on recent insights obtained using 5-HT transporter (5-HTT) knockout rats we here set-out and discuss the crucial role of neurodevelopmental mechanisms and the contribution of transcription factors and epigenetic modifications to this interaction and its variants. 5-HTT knockout in rats, as well as the low activity short allelic variant of the serotonin transporter human polymorphism, consistently show reduced BDNF mRNA and protein levels in the hippocampus and in the prefrontal cortex. This starts during the second postnatal week, is preceded by DNA hypermethylation during the first postnatal week, and it is developmentally paralleled by reduced expression of key transcription factors. The reduced BDNF levels, in turn, affect 5-HT1A receptor-mediated intracellular signaling and thereby the serotonergic phenotype of the neurons. We propose that such a negative spiral of modifications may affect brain development and reduce its resiliency to environmental challenges during critical time windows, which may lead to phenotypic alterations that persist for the entire life. The characterization of 5-HT-BDNF interactions will eventually increase the understanding of mental illness etiology and, possibly, lead to the identification of novel molecular targets for drug development.

Neurobiology of stress, depression, and rapid acting antidepressants: remodeling synaptic connections

Stress and depression are associated with atrophy and loss of neurons in limbic and cortical brain regions that could contribute to the symptoms of depression. Typical monoamine reuptake inhibitor antidepressants have only modest efficacy and require long-term treatment, and are only weakly effective in blocking or reversing these structural changes caused by stress. Recent findings demonstrate that ketamine, an NMDA receptor antagonist, produces rapid antidepressant actions in difficult to treat depressed patients. In addition, preclinical studies demonstrate that ketamine rapidly increases synaptic connections in the prefrontal cortex by increasing glutamate signaling and activation of pathways that control the synthesis of synaptic proteins. Moreover, ketamine rapidly reverses the synaptic deficits caused by exposure to chronic stress in rodent models. Studies of the signaling mechanisms underlying the actions of ketamine have provided novel approaches and targets for new rapid acting antidepressants with decreased side effects, as well as a better understanding of the neurobiology of stress, depression, and treatment response.

Genetic Role of BDNF Val66Met and 5-HTTLPR Polymorphisms on Depressive Disorder

OBJECTIVE

We investigated possible association between depressive disorders and BDNF Val66Met and 5-HTTLPR. Brain derived neurotrophic factor (BDNF) gene and serotonin transporter (SLC6A4) gene are promising candidate genes for depressive disorders. It has been suggested that BDNF promotes the survival and differentiation of serotonergic neurons and that serotonergic transmission exerts powerful control over BDNF gene expression.

METHODS

Final analyses were performed on 186 patients with depressive disorders and 1032 controls. Val66Met polymorphism of BDNF gene and 5-HTTLPR polymorphism of serotonin transporter gene were genotyped and allele and genotypic associations on the diagnosis of depression and age at onset of depression were analyzed.

RESULTS

The 5-HTTLPR was positively associated with depressive affected status in the total sample and in females (p=0.038 for allelewise, p=0.015 for genotype-wise associations), but, not in males. The BDNF Val66Met showed no association with depression. BDNF Val66Met and 5-HTTLPR alone were not associated with age at onset of depression. Additional analysis on the interaction between BDNF Val66Met and 5-HTTLPR found a significant association with age at onset of depression in the entire patient group. This association was also found in the female but not in the male patient group. None of the positive results survived Bonferroni correction for multiple testing.

CONCLUSION

This result suggested that BDNF Val66Met and 5-HTTLPR may contribute to depressive disorders in a complex way and that the genetic effect could differ by gender. Further studies with large number of patients will be necessary.

The Brain Derived Neurotrophic Factor and Personality

The study of the biological basis of personality is a timely research endeavor, with the aim of deepening our understanding of human nature. In recent years, a growing body of research has investigated the role of the brain derived neurotrophic factor (BDNF) in the context of individual differences across human beings, with a focus on personality traits. A large number of different approaches have been chosen to illuminate the role of BDNF for personality, ranging from the measurement of BDNF in the serum/plasma to molecular genetics to (genetic) brain imaging. The present review provides the reader with an overview of the current state of affairs in the context of BDNF and personality.

The association of the BDNF Val66Met polymorphism and the hippocampal volumes in healthy humans: a joint meta-analysis of published and new data

BACKGROUND

The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism (refSNP Cluster Report: rs6265) is a common and functionally relevant single nucleotide polymorphism (SNP). The gene itself, as well as the SNP rs6265, have been implicated in hippocampal learning and memory. However, imaging genetic studies have produced controversial results about the impact of this SNP on hippocampal volumes in healthy subjects.

METHODS

We examined the association between the rs6265 polymorphism and hippocampal volume in 643 healthy young subjects using automatic segmentation and subsequently included these data in a meta-analysis based on published studies with 5298 healthy subjects in total.

RESULTS

We found no significant association between SNP rs6265 and hippocampal volumes in our sample (g=0.05, p=0.58). The meta-analysis revealed a small, albeit significant difference in hippocampal volumes between genotype groups, such that Met-carriers had slightly smaller hippocampal volumes than Val/Val homozygotes (g=0.09, p=0.04), an association that was only evident when manual (g=0.22, p=0.01) but not automatic tracing approaches (g=0.04, p=0.38) were used. Studies using manual tracing showed evidence for publication bias and a significant decrease in effect size over the years with increasing sample sizes.

CONCLUSIONS

This study does not support the association between SNP rs6265 and hippocampal volume in healthy individuals. The weakly significant effect observed in the meta-analysis is mainly driven by studies with small sample sizes. In contrast, our original data and the meta-analysis of automatically segmented hippocampal volumes, which was based on studies with large samples sizes, revealed no significant genotype effect. Thus, meta-analyses of the association between rs6265 and hippocampal volumes should consider possible biases related to measuring technique and sample size.

The Association Between Peer and own Aggression is Moderated by the BDNF Val-met Polymorphism

Peer antisocial behavior robustly predicts adolescents' own behavior but not all adolescents are equally vulnerable to their peers' influence and genetic factors may confer vulnerability. This study used data of n = 3081 adolescents from the Avon Longitudinal Study of Parents and Children (ALSPAC) to examine whether BDNF, a polymorphism that affects psychological functioning, moderates the association between affiliation with aggressive peers at age 10 and own aggression at age 15. A significant gene-environment interaction was found, where those who affiliated with aggressive peers in childhood showed increased risk for being aggressive in adolescence if they carried the BDNF met-met variant compared to val-val carriers. Our findings underline the importance of both biological and social factors for adolescent development.

Genetic approaches to understanding post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is increasingly recognized as both a disorder of enormous mental health and societal burden, but also as an anxiety disorder that may be particularly understandable from a scientific perspective. Specifically, PTSD can be conceptualized as a disorder of fear and stress dysregulation, and the neural circuitry underlying these pathways in both animals and humans are becoming increasingly well understood. Furthermore, PTSD is the only disorder in psychiatry in which the initiating factor, the trauma exposure, can be identified. Thus, the pathophysiology of the fear and stress response underlying PTSD can be examined and potentially interrupted. Twin studies have shown that the development of PTSD following a trauma is heritable, and that genetic risk factors may account for up to 30-40% of this heritability. A current goal is to understand the gene pathways that are associated with PTSD, and how those genes act on the fear/stress circuitry to mediate risk vs. resilience for PTSD. This review will examine gene pathways that have recently been analysed, primarily through candidate gene studies (including neuroimaging studies of candidate genes), in addition to genome-wide associations and the epigenetic regulation of PTSD. Future and on-going studies are utilizing larger and collaborative cohorts to identify novel gene candidates through genome-wide association and other powerful genomic approaches. Identification of PTSD biological pathways strengthens the hope of progress in the mechanistic understanding of a model psychiatric disorder and allows for the development of targeted treatments and interventions.

Interaction between stress and the BDNF Val66Met polymorphism in depression: a systematic review and meta-analysis

BACKGROUND

Major depression is a disabling psychiatric illness with complex origins. Life stress (childhood adversity and recent stressful events) is a robust risk factor for depression. The relationship between life stress and Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene has received much attention. The aim of the present work was to review and conduct a meta-analysis on the results from published studies examining this interaction.

METHODS

A literature search was conducted using PsychINFO and PubMed databases until 22 November 2013. A total of 22 studies with a pooled total of 14,233 participants met the inclusion criteria, the results of which were combined and a meta-analysis performed using the Liptak-Stouffer z-score method.

RESULTS

The results suggest that the Met allele of BDNF Val66Met significantly moderates the relationship between life stress and depression (P = 0.03). When the studies were stratified by type of environmental stressor, the evidence was stronger for an interaction with stressful life events (P = 0.01) and weaker for interaction of BDNF Val66Met with childhood adversity (P = 0.051).

CONCLUSIONS

The interaction between BDNF and life stress in depression is stronger for stressful life events rather than childhood adversity. Methodological limitations of existing studies include poor measurement of life stress.

Association of BDNF Val66Met polymorphism with HPA and SAM axis reactivity to psychological and physical stress

BACKGROUND

Decreased expression of brain-derived neurotrophic factor (BDNF) is implicated in enhanced stress responses. The BDNF Val66Met polymorphism is associated with psychological changes; for example, carriers of the Met allele exhibit increased harm avoidance as well as a higher prevalence of depression and anxiety disorder.

METHODS

To analyze the effects of BDNF Val66Met on stress responses, we tested 226 university students (88 women and 138 men) using a social stress procedure (Trier Social Stress Test [TSST]) and an electrical stimulation stress test. Stress indices were derived from repeated measurements of salivary α-amylase, salivary cortisol, heart rate, and psychological testing during the stress tests. All subjects were genotyped for the Val66Met polymorphism (G196A).

RESULTS

A significant three-way interaction (time [3 levels] × BDNF [Val/Val, Val/Met, Met/Met]; P<0.05) was demonstrated that revealed different salivary cortisol responses in the TSST but not in electrical stimulation. Met/Met women had stronger cortisol responses than Val/Met and Val/Val individuals in the TSST. Met/Met men exhibited stronger salivary cortisol responses than Val/Met and Val/Val individuals in the TSST.

CONCLUSION

These results indicate that a common, functionally significant polymorphism in BDNF had different effects on hypothalamic-pituitary-adrenocortical axis reactivity but not on sympathetic adrenomedullary reactivity in TSST and electrical stimulation tests.

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.

Beyond risk, resilience, and dysregulation: Phenotypic plasticity and human development

We provide a theoretical and empirical basis for the claim that individual differences exist in developmental plasticity and that phenotypic plasticity should be a subject of study in its own right. To advance this argument, we begin by highlighting challenges that evolutionary thinking poses for a science of development and psychopathology, including for the diathesis–stress framework that has (fruitfully) guided so much empirical inquiry on developmental risk, resilience, and dysregulation. With this foundation laid, we raise a series of issues that the differential-susceptibility hypothesis calls attention to, while highlighting findings that have emerged over just the past several years and are pertinent to some of the questions posed. Even though it is clear that this new perspective on Person × Environment interaction is stimulating research and influencing how hypotheses are framed and data interpreted, a great many topics remain that need empirical attention. Our intention is to encourage students of development and psychopathology to treat phenotypic plasticity as an individual-difference construct while exploring unknowns in the differential-susceptibility equation.

Pregnant mothers with resolved anxiety disorders and their offspring have reduced heart rate variability: implications for the health of children

Objective

Active anxiety disorders have lasting detrimental effects on pregnant mothers and their offspring but it is unknown if historical, non-active, maternal anxiety disorders have similar effects. Anxiety-related conditions, such as reduced autonomic cardiac control, indicated by reduced heart rate variability (HRV) could persist despite disorder resolution, with long-term health implications for mothers and children. The objective in this study is to test the hypotheses that pregnant mothers with a history of, but not current anxiety and their children have low HRV, predicting anxiety-like offspring temperaments.

Methods

The participants in this case-control study consist of 56 women during their first trimester and their offspring (15 male, 29 female). Women had a history of an anxiety disorder (n=22) or no psychopathology (n=34) determined using the Mini-International Neuropsychiatric Interview. The main outcome measures were indices of autonomic cardiac control including root mean square of successive differences (RMSSD) and high frequency (HF) variability. Children’s fearfulness was also assessed using the Laboratory Temperament Assessment Battery (Lab-TAB)-Locomotor Version.

Results

HRV was lower in women and children in the past anxiety group compared to controls. HRV measures for mothers and children were positively correlated in the anxiety group only. In all children, low HRV measures at 2-4 months were associated with a higher chance of fearful behavior at 9-10 months.

Conclusions

Pregnant women with previous but not current anxiety and their children have low HRV. Children with low HRV tend to show more fearfulness. These findings have implications for identifying children at risk of anxiety disorders and point to possible underlying mechanisms of child psychopathology.

BDNF Val66Met modifies the risk of childhood trauma on obsessive-compulsive disorder

Childhood trauma has been linked to the development of later psychopathology, including obsessive-compulsive disorder (OCD). Although evidence exists to suggest that genetic and environmental factors are involved in the aetiology of OCD, little attention has been paid to the interactions that exist between genes and environment. The aim of this study was to investigate gene-by-environment interactions between childhood trauma and the BDNF Val66Met variant in patients with OCD. Childhood trauma was assessed in 134 OCD patients and 188 controls using the Childhood Trauma Questionnaire (CTQ). Linear regression models were used for statistical analyses. Gene-environment interactions were estimated by including a combined genotype and CTQ score in the models as interaction terms. All analyses were adjusted for age, gender, CTQ minimisation-denial score and home language by including them in the logistic regression models as covariates. Childhood trauma, specifically emotional abuse and neglect, increased the odds of having OCD significantly (p < 0.001). Although no significant association was observed between BDNF Val66Met and the development of OCD, interaction analysis indicated that the BDNF Met-allele interacted with childhood emotional abuse to increase the risk of OCD significantly in a dose-dependent manner (p = 0.024). To our knowledge, this is one of the first studies to investigate gene-environment interactions in OCD, and the findings indicate the importance of collating genetic and environmental variables in future studies.

Chronic administration of baicalein decreases depression-like behavior induced by repeated restraint stress in rats

Baicalein (BA), a plant-derived active flavonoid present in the root of Scutellaria baicalensis, has been widely used for the treatment of stress-related neuropsychiatric disorders including depression. Previous studies have demonstrated that repeated restraint stress disrupts the activity of the hypothalamic-pituitary-adrenal (HPA) axis, resulting in depression. The behavioral and neurochemical basis of the BA effect on depression remain unclear. The present study used the forced swimming test (FST) and changes in brain neurotransmitter levels to confirm the impact of BA on repeated restraint stress-induced behavioral and neurochemical changes in rats. Male rats received 10, 20, or 40 mg/kg BA (i.p.) 30 min prior to daily exposure to repeated restraint stress (2 h/day) for 14 days. Activation of the HPA axis in response to repeated restraint stress was confirmed by measuring serum corticosterone levels and the expression of corticotrophin-releasing factor in the hypothalamus. Daily BA administration significantly decreased the duration of immobility in the FST, increased sucrose consumption, and restored the stress-related decreases in dopamine concentrations in the hippocampus to near normal levels. BA significantly inhibited the stress-induced decrease in neuronal tyrosine hydroxylase immunoreactivity in the ventral tegmental area and the expression of brain-derived neurotrophic factor (BDNF) mRNA in the hippocampus. Taken together, these findings indicate that administration of BA prior to the repeated restraint stress significantly improves helpless behaviors and depressive symptoms, possibly by preventing the decrease in dopamine and BDNF expression. Thus, BA may be a useful agent for the treatment or alleviation of the complex symptoms associated with depression.

Disorders and borders: psychiatric genetics and nosology

Over the past century, the definition and classification of psychiatric disorders has evolved through a combination of historical trends, clinical observations, and empirical research. The current nosology, instantiated in the DSM-5 and ICD-10, rests on descriptive criteria agreed upon by a consensus of experts. While the development of explicit criteria has enhanced the reliability of diagnosis, the validity of the current diagnostic categories has been the subject of debate and controversy. Genetic studies have long been regarded as a key resource for validating the boundaries among diagnostic categories. Genetic epidemiologic studies have documented the familiality and heritability of clinically defined psychiatric disorders and molecular genetic studies have begun to identify specific susceptibility variants. At the same time, there is growing evidence from family, twin and genomic studies that genetic influences on psychiatric disorders transcend clinical boundaries. Here I review this evidence for cross-disorder genetic effects and discuss the implications of these findings for psychiatric nosology. Psychiatric genetic research can inform a bottom-up reappraisal of psychopathology that may help the field move beyond a purely descriptive classification and toward an etiology-based nosology.

The interacting effect of the BDNF Val66Met polymorphism and stressful life events on adolescent depression is not an artifact of gene-environment correlation: evidence from a longitudinal twin study

BACKGROUND

Confounding introduced by gene-environment correlation (rGE) may prevent one from observing a true gene-environment interaction (G × E) effect on psychopathology. The present study investigated the interacting effect of the BDNF Val66Met polymorphism and stressful life events (SLEs) on adolescent depression while controlling for the rGE by two means: separating pure environmental factors (independent SLEs) from the environmental factors under partial genetic control (dependent SLEs) and adopting a prospective longitudinal design.

METHODS

A total of 780 pairs of Chinese twins, aged 11-17 years (mean = 13.6, SD = 1.8) at intake, were followed up twice. Self-reported depression symptoms at Time 1 and Time 2 were assessed by the Children's Depression Inventory (CDI). SLEs occurring between Time 1 and Time 2 were assessed by a self-reported checklist. SLEs were differentiated into independent and dependent ones and were validated by heritability analyses using twin design. The interacting effects between the BDNF Val66Met polymorphism and numbers of SLEs (total SLEs and independent SLEs) on intraindividual change of depression symptoms were examined.

RESULTS

After controlling for sex, age, age square, and Time 1 depression, both total SLEs × BDNF Val66Met genotype and independent SLEs × BDNF Val66Met genotype significantly predicted Time 2 depression. Val allele carriers (Val/Val and Val/Met) were more susceptible to the detrimental effects of stress.

CONCLUSIONS

There is a true G × E effect underlying the observed interaction between BDNF Val66Met polymorphism and environmental stress on depression.

Early exposure to traumatic stressors impairs emotional brain circuitry

Exposure to early life trauma (ELT) is known to have a profound impact on mental development, leading to a higher risk for depression and anxiety. Our aim was to use multiple structural imaging methods to systematically investigate how traumatic stressors early in life impact the emotional brain circuits, typically found impaired with clinical diagnosis of depression and anxiety, across the lifespan in an otherwise healthy cohort. MRI data and self-reported histories of ELT from 352 healthy individuals screened for no psychiatric disorders were analyzed in this study. The volume and cortical thickness of the limbic and cingulate regions were assessed for all participants. A large subset of the cohort also had diffusion tensor imaging data, which was used to quantify white matter structural integrity of these regions. We found a significantly smaller amygdala volume and cortical thickness in the rostral anterior cingulate cortex associated with higher ELT exposure only for the adolescence group. White matter integrity of these regions was not affected. These findings demonstrate that exposure to early life trauma is associated with alterations in the gray matter of cingulate-limbic regions during adolescence in an otherwise healthy sample. These findings are interesting in the context that the affected regions are central neuroanatomical components in the psychopathology of depression, and adolescence is a peak period for risk and onset of the disorder.

Animal models in translational studies of PTSD

Understanding the neurobiological mechanisms of post-traumatic stress disorder (PTSD) is of vital importance for developing biomarkers and more effective pharmacotherapy for this disorder. The design of bidirectional translational studies addressing all facets of PTSD is needed. Animal models of PTSD are needed not only to capture the complexity of PTSD behavioral characteristics, but also to address experimentally the influence of variety of factors which might determine an individual's vulnerability or resilience to trauma, e.g., genetic predisposition, early-life experience and social support. The current review covers recent translational approaches to bridge the gap between human and animal PTSD research and to create a framework for discovery of biomarkers and novel therapeutics.

Environmental and pharmacological modulations of cellular plasticity: role in the pathophysiology and treatment of depression

Atrophy of neurons and gross structural alterations of limbic brain regions, including the prefrontal cortex (PFC) and hippocampus, have been reported in brain imaging and postmortem studies of depressed patients. Preclinical findings have suggested that prolonged negative stress can induce changes comparable to those seen in major depressive disorder (MDD), through dendritic retraction and decreased spine density in PFC and hippocampal CA3 pyramidal neurons. Interestingly, recent studies have suggested that environmental and pharmacological manipulations, including antidepressant medication, exercise, and diet, can block or even reverse many of the molecular changes induced by stress, providing a clear link between these factors and susceptibility to MDD. In this review, we will discuss the environmental and pharmacological factors, as well as the contribution of genetic polymorphisms, involved in the regulation of neuronal morphology and plasticity in MDD and preclinical stress models. In particular, we will highlight the pro-depressive changes incurred by stress and the reversal of these changes by antidepressants, exercise, and diet.

Divergent functional effects of sazetidine-a and varenicline during nicotine withdrawal

Smoking is the largest preventable cause of death in the United States. Furthermore, a recent study found that <10% of quit attempts resulted in continuous abstinence for 1 year. With the introduction of pharmacotherapies like Chantix (varenicline), a selective α4β2 nicotinic partial agonist, successful quit attempts have significantly increased. Therefore, novel subtype-specific nicotinic drugs, such as sazetidine-A, present a rich area for investigation of therapeutic potential in smoking cessation. The present studies examine the anxiety-related behavioral and functional effects of the nicotinic partial agonists varenicline and sazetidine-A during withdrawal from chronic nicotine in mice. Our studies indicate that ventral hippocampal-specific infusions of sazetidine-A, but not varenicline, are efficacious in reducing nicotine withdrawal-related anxiety-like phenotypes in the novelty-induced hypophagia (NIH) paradigm. To further investigate functional differences between these partial agonists, we utilized voltage-sensitive dye imaging (VSDi) in ventral hippocampal slices to determine the effects of sazetidine-A and varenicline in animals chronically treated with saline, nicotine, or undergoing 24 h withdrawal. These studies demonstrate a functional dissociation of varenicline and sazetidine-A on hippocampal network activity, which is directly related to previous drug exposure. Furthermore, the effects of the nicotinic partial agonists in VSDi assays are significantly correlated with their behavioral effects in the NIH test. These findings highlight the importance of drug history in understanding the mechanisms through which nicotinic compounds may be aiding smoking cessation in individuals experiencing withdrawal-associated anxiety.

Neurobiology of secure infant attachment and attachment despite adversity: a mouse model

Attachment to an abusive caregiver has wide phylogenetic representation, suggesting that animal models are useful in understanding the neural basis underlying this phenomenon and subsequent behavioral outcomes. We previously developed a rat model, in which we use classical conditioning to parallel learning processes evoked during secure attachment (odor-stroke, with stroke mimicking tactile stimulation from the caregiver) or attachment despite adversity (odor-shock, with shock mimicking maltreatment). Here we extend this model to mice. We conditioned infant mice (postnatal day (PN) 7-9 or 13-14) with presentations of peppermint odor and either stroking or shock. We used (14) C 2-deoxyglucose (2-DG) to assess olfactory bulb and amygdala metabolic changes following learning. PN7-9 mice learned to prefer an odor following either odor-stroke or shock conditioning, whereas odor-shock conditioning at PN13-14 resulted in aversion/fear learning. 2-DG data indicated enhanced bulbar activity in PN7-9 preference learning, whereas significant amygdala activity was present following aversion learning at PN13-14. Overall, the mouse results parallel behavioral and neural results in the rat model of attachment, and provide the foundation for the use of transgenic and knockout models to assess the impact of both genetic (biological vulnerabilities) and environmental factors (abusive) on attachment-related behaviors and behavioral development.

No influence of brain-derived neurotrophic factor (BDNF) polymorphisms on treatment response in a naturalistic sample of patients with major depression

The role of the brain-derived neurotrophic factor (BDNF) in the pathophysiology of major depressive disorder (MDD) remains to be elucidated. Recent post hoc analyses indicated a potential association of three polymorphisms in the BDNF gene with worse treatment outcome in patients with the subtype of melancholic depression. We aimed at replicating these findings in a German naturalistic multicenter follow-up. Three polymorphisms in the BDNF gene (rs7103411, rs6265 (Val66Met) and rs7124442) were genotyped in 324 patients with MDD and 470 healthy controls. We applied univariate tests and logistic regression models stratifying for depression subtype and gender. The three polymorphisms were not associated with MDD as diagnosis. Further, no associations were found in univariate tests. With logistic regression, we only found a tendency towards an association of the rs6265 (Val66Met) polymorphism with overall response to treatment (response rates: GG (val/val) < GA (val/met) < AA (met/met); p = 0.0129) and some gender differences for the rs6265 (Val66Met) and rs7103411 polymorphisms. Treatment outcome stratified for subtypes of depression did not differ significantly between the investigated polymorphisms or using haplotype analyses. However, results showed a tendency towards significance. At this stage, we cannot support an influence of these three polymorphisms. Further studies in larger patient samples to increase sample sizes of subgroups are warranted.

A longitudinal study of BDNF promoter methylation and genotype with poststroke depression

INTRODUCTION

Brain derived neurotrophic factor (BDNF) has been shown to play an important role in the pathophysiology of mood disorders including poststroke depression (PSD). BDNF secretion is influenced by epigenetic and genetic profiles. This study aimed to investigate whether BDNF gene promoter methylation status and val66met polymorphism were associated with depression ascertained at two weeks and one year after stroke.

METHODS

A total of 286 patients were evaluated two weeks after stroke, and 222 (78%) were followed one year later. Depression (major or minor depressive disorder) was diagnosed according to DSM-IV criteria, and classified into prevalent, persistent, and incident PSD according to presence at the two examinations. Depression severity was assessed by the Hospital Anxiety and Depression Scale-depression subscale and the Hamilton Depression Rating Scale. The effects of BDNF methylation status and genotype on PSD status were investigated using multivariate logistic regression models. The associations of BDNF methylation status and genotype with score on depression assessment scales were estimated using partial correlation tests and general linear models, respectively.

RESULTS

Higher BDNF methylation status was independently associated with prevalent, persistent and particularly with incident PSD, and with worsening depressive symptoms over follow-up but not with baseline severity. The BDNF val66met polymorphism was independently associated with prevalent PSD, but not with persistent and incident PSD nor with depressive symptoms severity. No significant methylation-genotype interactions were found.

LIMITATIONS

Methylation status was investigated with limited area of the BDNF gene and sample size was relatively small.

CONCLUSIONS

A role for BDNF in PSD was supported, and associations with BDNF gene methylation status may represent a target for drug development.

The Role of the Val66Met Polymorphism of the Brain Derived Neurotrophic Factor Gene in Coping Strategies Relevant to Depressive Symptoms

Disturbances of brain derived neurotrophic factor (BDNF) signalling have been implicated in the evolution of depression, which likely arises, in part, as a result of diminished synaptic plasticity. Predictably, given stressor involvement in depression, BDNF is affected by recent stressors as well as stressors such as neglect experienced in early life. The effects of early life maltreatment in altering BDNF signalling may be particularly apparent among those individuals with specific BDNF polymorphisms. We examined whether polymorphisms of the Val66Met genotype might be influential in moderating how early-life events play out with respect to later coping styles, cognitive flexibility and depressive features. Among male and female undergraduate students (N = 124), childhood neglect was highly related to subsequent depressive symptoms. This outcome was moderated by the BDNF polymorphism in the sense that depressive symptoms appeared higher in Met carriers who reported low levels of neglect than in those with the Val/Val allele. However, under conditions of high neglect depressive symptoms only increased in the Val/Val individuals. In effect, the Met polymorphism was associated with depressive features, but did not interact with early life neglect in predicting later depressive features. It was further observed that among the Val/Val individuals, the relationship between neglect and depression was mediated by emotion-focused styles and diminished perceived control, whereas this mediation was not apparent in Met carriers. In contrast to the more typical view regarding this polymorphism, the data are consistent with the perspective that in the presence of synaptic plasticity presumably associated with the Val/Val genotype, neglect allows for the emergence of specific appraisal and coping styles, which are tied to depression. In the case of the reduced degree of neuroplasticity expected in the Met carriers, early life adverse experiences are not tied to coping styles, and hence less likely to be translated into depressive states.

Gender-specific effects of brain-derived neurotrophic factor Val66Met polymorphism and childhood maltreatment on anxiety

BACKGROUND

Although the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is thought to play an important role in the pathophysiology of anxiety, studies on the association between the BDNF polymorphism and anxiety have reported inconsistent results. As possible confounders in determining anxiety, childhood maltreatment and gender as well as their interactions with BDNF polymorphism have been suggested. This study examined the effect of BDNF genotype, childhood maltreatment, and their interaction on anxiety levels by gender.

METHODS

A total of 206 unrelated Korean healthy young adults (108 were male and the mean age was 23.1 ± 3.2 years) were genotyped for the BDNFVal66Met polymorphism. Measures for anxiety and childhood maltreatment were completed. The main and interaction effects of BDNF polymorphism and childhood maltreatment on anxiety were analyzed by general linear models in all subjects and then in gender-stratified groups.

RESULTS

Gender-specific analyses revealed that the interaction effect was significant only in males (p = 0.014). Interestingly, male subjects with the Val/Met genotype tended to be resilient against the increased anxiety after childhood maltreatment. In females, the main effects of both BDNF genotype and childhood maltreatment were significant (p = 0.024 and p = 0.009, respectively) and post-hoc analysis revealed that the Val/Val genotype was associated with a higher anxiety than the Met/Met genotype (p = 0.004).

CONCLUSIONS

Our results support the interaction effect between the BDNFVal66Met polymorphism and childhood maltreatment in determining anxiety and further emphasize the possible moderating role of gender in this gene-environment interaction.

Synaptic regulation of affective behaviors; role of BDNF

Brain derived neurotrophic factor (BDNF), a neurotrophin essential for nervous system development and synaptic plasticity, has been found to have a significant influence on affective behaviors. The notion that an impairment in BDNF signaling might be involved in affective disorders is originated primarily from the opposing effects of antidepressants and stress on BDNF signaling. Antidepressants enhance BDNF signaling and synaptic plasticity. On the other hand, negative environmental factors such as severe stress suppress BDNF signaling, impair synaptic activity and increase susceptibility to affective disorders. Postmortem studies provided strong support for decreased BDNF signaling in depressive disorders. Remarkably, studies in humans with a single nucleotide polymorphism in the BDNF gene, the BDNF Val66Met which affects regulated release of BDNF, showed profound deficits in hippocampal and prefrontal cortical (PFC) plasticity and cognitive behaviors. BDNF regulates synaptic mechanisms responsible for various cognitive processes including attenuation of aversive memories, a key process in the regulation of affective behaviors. The unique role of BDNF in cognitive and affective behaviors suggests that cognitive deficits due to altered BDNF signaling might underlie affective disorders. Understanding how BDNF modulates synapses in neural circuits relevant to affective behaviors, particularly the medial prefrontal cortical (mPFC)-hippocampus-amygdala pathway, and its interaction with development, sex, and environmental risk factors might shed light on potential therapeutic targets for affective disorders. This article is part of the Special Issue entitled 'BDNF Regulation of Synaptic Structure, Function, and Plasticity'.

Impact of early vs. late childhood early life stress on brain morphometrics

Previous studies of early life trauma suggest that in addition to its emotional impact, exposure to early life stress (ELS) is associated with alterations in brain structure. However, little attention has been devoted to the relationship between emotional processing and brain integrity as a function of age of ELS onset. In the present study we examined whether ELS onset in older ages of youth rather than younger ages is associated with smaller limbic and basal ganglia volumes as measured by magnetic resonance imaging (MRI). We hypothesized that later age of manifestation during youth is associated with smaller volumetric morphology in limbic and basal ganglia volumes in adulthood. A total of 173 individuals were divided into three groups based on the age of self-reported ELS. The three groups included individuals only experiencing early childhood ELS (1 month-7 years, n = 38), those only experiencing later childhood ELS (8 years -17 years, n = 59), and those who have not experienced ELS (n = 76). Anterior cingulate cortex (ACC), hippocampus, amygdala, insula and caudate volumes were measured using a T1-weighted MRI. Analyses confirmed that later childhood ELS was associated with volumetric reductions in the ACC and insula volumes, while ELS experienced between the ages of 1 month and 7 years was not associated with lower brain volumes in these regions. The results may reflect the influence of more fully developed emotional processing of ELS on the developing brain and reinforce a body of research implicating both the ACC and insula in neuropsychiatric disorders and emotional regulation.

The brain-derived neurotrophic factor Val66Met polymorphism moderates early deprivation effects on attention problems

Adverse early care is associated with attention regulatory problems, but not all so exposed develop attention problems. In a sample of 612 youth (girls = 432, M = 11.82 years, SD = 1.5) adopted from institutions (e.g., orphanages) in 25 countries, we examined whether the Val66Met polymorphism of the brain-derived neurotrophic factor gene moderates attention problems associated with the duration of institutional care. Parent-reported attention problem symptoms were collected using the MacArthur Health and Behavior Questionnaire. DNA was genotyped for the brain-derived neurotrophic factor Val66Met (rs6265) single nucleotide polymorphism. Among youth from Southeast (SE) Asia, the predominant genotype was valine/methionine (Val/Met), whereas among youth from Russia/Europe and Caribbean/South America, the predominant genotype was Val/Val. For analysis, youth were grouped as carrying Val/Val or Met/Met alleles. Being female, being from SE Asia, and being younger when adopted were associated with fewer attention regulatory problem symptoms. Youth carrying at least one copy of the Met allele were more sensitive to the duration of deprivation, yielding an interaction that followed a differential susceptibility pattern. Thus, youth with Val/Met or Met/Met genotypes exhibited fewer symptoms than Val/Val genotypes when adoption was very early and more symptoms when adoption occurred later in development. Similar patterns were observed when SE Asian youth and youth from other parts of the world were analyzed separately.

Current status on behavioral and biological markers of PTSD: a search for clarity in a conflicting literature

Extensive research has identified stereotypic behavioral and biological abnormalities in post-traumatic stress disorder (PTSD), such as heightened autonomic activity, an exaggerated startle response, reduced basal cortisol levels and cognitive impairments. We have reviewed primary research in this area, noting that factors involved in the susceptibility and expression of PTSD symptoms are more complex and heterogeneous than is commonly stated, with extensive findings which are inconsistent with the stereotypic behavioral and biological profile of the PTSD patient. A thorough assessment of the literature indicates that interactions among myriad susceptibility factors, including social support, early life stress, sex, age, peri- and post-traumatic dissociation, cognitive appraisal of trauma, neuroendocrine abnormalities and gene polymorphisms, in conjunction with the inconsistent expression of the disorder across studies, confounds attempts to characterize PTSD as a monolithic disorder. Overall, our assessment of the literature addresses the great challenge in developing a behavioral and biomarker-based diagnosis of PTSD.

Gene × environment interactions in the prediction of response to antidepressant treatment

Major depressive disorder (MDD) is responsible for an increasing individual and global health burden. Extensive research on the genetic disposition to develop MDD and to predict the response to antidepressant treatment has yet failed to identify strong genetic effects. The concept of gene × environment interaction takes into account that environmental factors have been identified as important components in the development of MDD and combines both, genetic predisposition and environmental exposure, to elucidate complex traits such as MDD. Here, we review the current research on gene × environment interactions with regard to the development of MDD as well as response to antidepressant treatment. We hypothesize that gene × environment interactions delineate specific biological subtypes of depression and that individuals with such pathophysiological distinct types of depression will likely respond to different treatments. The elucidation of gene × environment interactions may thus not only help to understand the pathophysiology of MDD but could also provide markers for a personalized antidepressant therapy.

Brain-derived neurotrophic factor Val66Met polymorphism and early life adversity affect hippocampal volume

The interaction between adverse life events during childhood and genetic factors is associated with a higher risk to develop major depressive disorder (MDD). One of the polymorphisms found to be associated with MDD is the Val66MET polymorphism of brain-derived neurotrophic factor (BDNF). The aim of our two-center study was to determine how the BDNF Val66Met polymorphism and childhood adversity affect the volumetric measures of the hippocampus in healthy individuals and people with MDD. In this two-center study, 62 adult patients with MDD and 71 healthy matched controls underwent high-resolution magnetic resonance imaging. We used manual tracing of the bilateral hippocampal structure with help of the software BRAINS2, assessed childhood adversity using the Childhood Trauma Questionnaire and genotyped Val66Met BDNF SNP (rs6265). MDD patients had smaller hippocampal volumes, both in the left and right hemispheres (F = 5.4, P = 0.022). We also found a significant interaction between BDNF allele and history of childhood adversity (F = 6.1, P = 0.015): Met allele carriers in our samples showed significantly smaller hippocampal volumes when they did have a history of childhood adversity, both in patients and controls. Our results highlight how relevant stress-gene interactions are for hippocampal volume reductions. Subjects exposed to early life adversity developed smaller hippocampal volumes when they carry the Met-allele of the BDNF polymorphism.

Cortisol and depression: three questions for psychiatry

BACKGROUND

Cortisol plays a multifaceted role in major depression disorder (MDD). Diurnal rhythms are disturbed, there is increased resistance to the feedback action of glucocorticoids, excess cortisol may induce MDD, basal levels may be higher and the post-awakening cortisol surge accentuated in those at risk for MDD. Does this suggest new avenues for studying MDD or its clinical management?

METHOD

The relevant literature was reviewed.

RESULTS

Cortisol contributes to genetic variants for the risk for MDD and the way that environmental events amplify risk. The corticoids' influence begins prenatally, but continues into adulthood. The impact of cortisol at each phase depends not only on its interaction with other factors, such as psychological traits and genetic variants, but also on events that have, or have not, occurred previously.

CONCLUSIONS

This review suggests that the time is now right for serious consideration of the role of cortisol in a clinical context. Estimates of cortisol levels and the shape of the diurnal rhythm might well guide the understanding of subtypes of MDD and yield additional indicators for optimal treatment. Patients with disturbed cortisol rhythms might benefit from restitution of those rhythms; they may be distinct from those with more generally elevated levels, who might benefit from cortisol blockade. Higher levels of cortisol are a risk for subsequent depression. Should manipulation of cortisol or its receptors be considered as a preventive measure for some of those at very high risk of future MDD, or to reduce other cortisol-related consequences such as long-term cognitive decline?

Understanding resilience

Resilience is the ability to adapt successfully in the face of stress and adversity. Stressful life events, trauma, and chronic adversity can have a substantial impact on brain function and structure, and can result in the development of posttraumatic stress disorder (PTSD), depression and other psychiatric disorders. However, most individuals do not develop such illnesses after experiencing stressful life events, and are thus thought to be resilient. Resilience as successful adaptation relies on effective responses to environmental challenges and ultimate resistance to the deleterious effects of stress, therefore a greater understanding of the factors that promote such effects is of great relevance. This review focuses on recent findings regarding genetic, epigenetic, developmental, psychosocial, and neurochemical factors that are considered essential contributors to the development of resilience. Neural circuits and pathways involved in mediating resilience are also discussed. The growing understanding of resilience factors will hopefully lead to the development of new pharmacological and psychological interventions for enhancing resilience and mitigating the untoward consequences.

The val66met polymorphism of brain-derived neurotrophic factor is associated with human esophageal hypersensitivity

BACKGROUND

Recent evidence implicates brain-derived neurotrophic factor (BDNF) in visceral hypersensitivity and pain in functional gastrointestinal disorders. We hypothesized that presence of the val66met polymorphism in the BDNF gene would be linked to increased esophageal sensitivity to electrical stimulation.

METHODS

A total of 39 healthy volunteers (20 males, mean age 30) compliant with inclusion criteria after screening procedures were genotyped for BDNF polymorphisms and completed an Hospital Anxiety and Depression Scale (HADS) questionnaire. Sensory (ST) and pain (PT) thresholds in the proximal (PE) and distal (DE) esophagus were determined using electrical stimuli to a swallowed intraluminal catheter with bipolar electrodes by an investigator blinded to the subjects' genotype. For comparison, somatic ST and PT (hand and foot) were also tested. HADS scores together with esophageal and somatic thresholds were then correlated with BDNF polymorphism status.

KEY RESULTS

Eleven of 39 (28%) volunteers had at least one Met allele (Met carriers). When compared with Val/Val, Met carriers had lower esophageal PT (Median PT [mA]: Val/Val vs Met carriers, PE; 49.4 vs 44.3, P = 0.033, DE: 63.8 vs 55.4, P = 0.045) with higher proportion of Val/Val subjects in the upper quartile for PT in both PE (P = 0.021) and DE (P = 0.033), yet similar somatic PT (Median PT [mA] Hand; 33.6 vs 38.0, P = 0.22, Foot; 44.7 vs 44.0, P = 0.48). Sensitivity results were independent of anxiety (P = 0.66) and depression (P = 0.33) scores.

CONCLUSIONS & INFERENCES

val66met BDNF polymorphisms are associated with increased esophageal sensitivity to experimental electrical stimulation. Thus, BDNF genotype may be a useful biomarker for electrical sensitivity in the healthy human esophagus.

Brain-derived neurotrophic factor (BDNF) Val66Met and adulthood chronic stress interact to affect depressive symptoms

BACKGROUND

BDNF Val66Met by chronic stress interaction has been studied using childhood stress as a moderator, but has not been widely studied using chronic stress in adulthood.

METHODS

Two independent samples were used: Duke-CG (238 Caucasians) and MESA (5524 Caucasians, African Americans and Hispanics). Chronic stress in Duke-CG was operationalized as having primary caregiving responsibility for a spouse or relative with diagnosed Alzheimer's disease or other major dementia; chronic stress in MESA was defined using chronic burden score constructed from self-reported problems of health (self and someone close), job, finance and relationships. CES-D scale was the measure of depression in both samples. The BDNF Val66Met by adulthood chronic stress interaction predicting CES-D was examined using linear regression, adjusted for covariates.

RESULTS

The main effect of BDNF Val66Met genotype on CES-D scores was non-significant (ps > 0.607) but the adulthood chronic stress indicator was significant (ps < 0.001) in both samples. The BDNF Val66Met genotype by adulthood chronic stress interaction was also significant (ps < 0.039) in both samples. The impact of chronic stress in adulthood on CES-D scores was significantly larger in Val/Val genotype individuals than Met carriers.

CONCLUSION

We found in two independent samples that depression levels increased significantly more as a function of adulthood chronic stress Val/Val genotype carriers than Met carriers. Individuals with the Val/Val genotype and chronic stress exposure could be targeted for interventions designed to reduce risk of depression if this finding is confirmed in future studies.

Effects of the BDNF Val66Met polymorphism on white matter microstructure in healthy adults

The BDNF Val(66)Met polymorphism, a possible risk variant for mental disorders, is a potent modulator of neural plasticity in humans and has been linked to deficits in gray matter structure, function, and cognition. The impact of the variant on brain white matter structure, however, is controversial and remains poorly understood. Here, we used diffusion tensor imaging to examine the effects of BDNF Val(66)Met genotype on white matter microstructure in a sample of 85 healthy Caucasian adults. We demonstrate decreases of fractional anisotropy and widespread increases in radial diffusivity in Val/Val homozygotes compared with Met-allele carriers, particularly in prefrontal and occipital pathways. These data provide an independent confirmation of prior imaging genetics work, are consistent with complex effects of the BDNF Val(66)Met polymorphism on human brain structure, and may serve to generate hypotheses about variation in white matter microstructure in mental disorders associated with this variant.

BDNF-TrkB signaling and neuroprotection in schizophrenia

Neurotrophins such as brain-derived neurotropic factor (BDNF), play critical role in neuronal survival, synaptic plasticity and cognitive functions. BDNF is known to mediate its action through various intracellular signaling pathways triggered by activation of tyrosine kinase receptor B (TrkB). Evidence from clinical as well pre-clinical studies indicate alterations in BDNF signaling in schizophrenia. Moreover, several antipsychotic drugs have time-dependent effects on BDNF levels in both schizophrenia subjects and animal models of schizophrenia. Given the emerging interest in neuroplasticity in schizophrenia understanding the neuroprotective and cell survival roles of BDNF signaling will enhance our knowledge of its diverse effects, which may lead to more effective treatments for schizophrenia. This article will present an overview of recent findings on the role of BDNF signaling in the pathophysiology and treatment of schizophrenia, with a special focus on its neuroprotective effects.