BDNF Val66Met allele is associated with reduced hippocampal volume in healthy subjects

The BDNF Val66Met polymorphism and anxiety: support for animal knock-in studies from a genetic association study in humans

Mounting evidence shows that the brain derived neurotrophic factor (BDNF) plays a crucial role in depression and anxiety. The discovery of a functional variant of the BDNF gene--the BDNF Val66Met polymorphism--led to new insights into the molecular genetic mechanisms underlying these emotional disorders. Although there is evidence from animal research that the homozygous BDNF 66Met variant is associated with anxiety-like behaviour, findings from personality research using self-report-measures as indicators of trait anxiety are heterogenous. Recent seminal findings from a study using a knock-in mouse design suggest that this Met66Met group is of particular interest for the investigation of the molecular genetic mechanisms of anxiety and anxiety-related personality traits in humans. In a sample of 610 Caucasian participants, subjects homozygous for the 66Met allele scored significantly higher than Val66 allele carriers on anxiety-related facets of the construct 'harm avoidance' (i.e., 'anticipatory worry' and 'fear of uncertainty') of the Temperament and Character Inventory. This finding adds to a small plurality of studies that associates the 66Met allele, rather than the Val66 allele, with higher anxiety scores. Importantly, the present results furthermore suggest that it is the occurrence of not one but two 66Met alleles that is associated with high trait anxiety.

Imaging genetics and development: challenges and promises

Excitement with the publication of the human genome has served as catalyst for scientists to uncover the functions of specific genes. The main avenues for understanding gene function have been in behavioral genetics on one end and on the other end, molecular mouse models. Attempts to bridge these approaches have used brain imaging to conveniently link anatomical abnormalities seen in knockout/transgenic mouse models and abnormal patterns of brain activity seen in humans. Although a convenient approach, this article provides examples of challenges for imaging genetics, its application to developmental questions, and promises for future directions. Attempts to link genes, brain, and behavior using behavioral genetics, imaging genetics, and mouse models of behavior are described. Each of these approaches alone, provide limited information on gene function in complex human behavior, but together, they are forming bridges between animal models and human psychiatric disorders.

Prenatal exposure to maternal depressed mood and the MTHFR C677T variant affect SLC6A4 methylation in infants at birth

Background

Prenatal and early postnatal exposure to maternal depression may “program” childhood behavior via epigenetic processes such as DNA methylation. Methylenetetrahydro-folate reductase (MTHFR) is an important enzyme in the generation of methyl groups for DNA methylation. The common MTHFR C677T variant is associated with depression in men and non-pregnant women, and with global changes in DNA methylation. This study investigated the effect of maternal MTHFR C677T genotype on antenatal maternal mood, and their impact on the gene-specific methylation in pregnant women and their newborn infants. The methylation status of SLC6A4, which encodes the transmembrane serotonin transporter, and BDNF, which encodes brain derived neurotrophic factor, were assessed because of their potential role in behaviour.

Methods/Principal Findings

Depressed mood was assessed by the Edinburgh Postnatal Depression Scale (EPDS) and the Hamilton Rating Scale for Depression (HAM-D) in women (n = 82, all taking folate) during the 2^nd and 3^rd trimesters of pregnancy. The methylation status of SLC6A4 and BDNF were assessed in 3rd trimester maternal peripheral leukocytes and in umbilical cord leukocytes collected from their infants at birth. Women with the MTHFR 677TT genotype had greater 2^nd trimester depressed mood (p<0.05). Increased 2^nd trimester maternal depressed mood (EPDS scores) was associated with decreased maternal and infant SLC6A4 promoter methylation (p<0.05), but had no effect on BDNF promoter methylation.

Conclusions

These findings show that the MTHFR C677T variant is associated with greater depressed mood during pregnancy. We further showed that prenatal exposure to maternal depressed mood affects gene-specific DNA methylation patterns. These findings support the concept that alterations in epigenetic processes may contribute to developmental programming of behaviour by maternal depression.

The study of BDNF Val66Met polymorphism in Chinese schizophrenic patients

Accumulating evidence showed that brain-derived neurotrophic factor (BDNF) may be involved in the pathophysiology of schizophrenia. Recent studies have reported that the Val66Met polymorphism of the BDNF gene may be associated with susceptibility for schizophrenia and age of onset of this disease, with mix results. In the present study, the BDNF Val66Met gene polymorphism was examined in 387 inpatients (259 men and 128 women) meeting the DSM-IV criteria for schizophrenia and unrelated 365 healthy controls (255 men and 110 women). The schizophrenia symptomatology was assessed by the Positive and Negative Syndrome Scale (PANSS). Age of onset was defined as the age at which the psychotic symptoms first appeared. Our results showed that genotype frequency distributions and allelic frequencies did not differ between patients and controls. No interaction was found between sex and genotypes. Analysis of covariance (ANCOVA) showed a significance of the BDNF Val66Met genotypes on the age of onset (F=3.76, p<0.02), after adjusting sex, age and duration of illness. Furthermore, ANCOVA showed that the significance of the BDNFVal66Met genotypes on age of onset was increased comparing the Val66Met heterozygotes with the combination of Val66Val and Met66Met homozygotes (F=5.85, p<0.01). Our results suggest that the BDNF Val66Met polymorphism may not contribute directly to the susceptibility to schizophrenia, but to the onset of the disease. Furthermore, our results show the heterozygous effect of the BDNF Val66Met gene on the clinical variability of schizophrenia phenotype.

Involvement of BDNF in age-dependent alterations in the hippocampus

It is known since a long time that the hippocampus is sensitive to aging. Thus, there is a reduction in the hippocampal volume during aging. This age-related volume reduction is paralleled by behavioral and functional deficits in hippocampus-dependent learning and memory tasks. This age-related volume reduction of the hippocampus is not a consequence of an age-related loss of hippocampal neurons. The morphological changes associated with aging include reductions in the branching pattern of dendrites, as well as reductions in spine densities, reductions in the densities of fibers projecting into the hippocampus as well as declines in the rate of neurogenesis. It is very unlikely that a single factor or a single class of molecules is responsible for all these age-related morphological changes in the hippocampus. Nevertheless, it would be of advantage to identify possible neuromodulators or neuropeptides that may contribute to these age-related changes. In this context, growth factors may play an important role in the maintenance of the postnatal hippocampal architecture. In this review it is hypothesized that brain-derived neurotrophic factor (BDNF) is a factor critically involved in the regulation of age-related processes in the hippocampus. Moreover, evidences suggest that disturbances in the BDNF-system also affect hippocampal dysfunctions, as e.g. seen in major depression or in Alzheimer disease.

Impact of the HTR3A gene with early life trauma on emotional brain networks and depressed mood

BACKGROUND

The risk for mental illnesses such as depression is increasingly conceptualized as the product of gene-environment interactions and their impact on brain structure and function. The role of serotonin 3A receptor gene (HTR3A -42C>T polymorphism) and its interaction with early life stress (ELS) was investigated in view of the receptor's localization to brain regions central to emotion processing.

METHODS

Fronto-limbic grey matter (GM) loss was measured using magnetic resonance imaging and assessed using voxel-based morphometry analysis in 397 nonclinical individuals from the Brain Resource International Database. Negative mood symptoms were also assessed.

RESULTS

The HTR3A CC genotype group, compared to the T carriers, demonstrated comparative loss to GM in hippocampal structures, which extended to the frontal cortices for those CC genotype individuals also exposed to ELS. Elevations in depressed mood were also evident.

CONCLUSIONS

These findings suggest that the HTR3A CC genotype may be associated with alterations in brain structures central to emotion processing, particularly when exposed to stress, and further highlight the potential role of the serotonin system in the pathophysiology of affective disorders. In contrast, those individuals with the T allele, in particular the TT genotype, may be more protected from such alterations combined with minimal exposure to ELS events.

BDNF polymorphism rs6265 and hippocampal structure and memory performance in healthy control subjects

Brain-derived neurotrophic factor (BDNF) is highly expressed in the hippocampus of many species, including humans. The single-nucleotide polymorphism rs6265 on the BDNF gene is thought to alter activity-dependent secretion of the protein, and previous research suggests that the Met allele is associated with smaller hippocampal volumes and poorer memory performance in human populations. For this study, we genotyped 154 healthy human subjects for the Val66Met polymorphism. The effects of genotype upon hippocampal volume, as assessed using high resolution magnetic resonance imaging and high-dimensional brain mapping, and upon memory performance, as assessed using a battery of neuropsychological tests, were determined. We found that genotype had no significant effect on hippocampal structure, nor did it have a significant effect on memory performance, covarying for age. Age, however, was significantly related to changes in whole brain volume and performance on memory tasks. We concluded that in a large cohort of healthy human subjects, the Met allele of rs6265 is not associated with hippocampal structure or memory performance.

Early life stressors and genetic influences on the development of bipolar disorder: the roles of childhood abuse and brain-derived neurotrophic factor

OBJECTIVES

Although there is increasing research exploring the psychosocial influences and biological underpinnings of bipolar disorder, relatively few studies have specifically examined the interplay between these factors in the development of this illness. Social-biological models within a developmental psychopathology perspective are necessary to advance our understanding of the processes involved in the onset and course of bipolar disorder. This article presents a review of the empirical literature linking childhood abuse to bipolar disorder, the research to date on the possible role of brain-derived neurotrophic factor (BDNF) in the development of this disorder, followed by a discussion of how childhood abuse may interact with BDNF.

METHODS

A literature search was conducted using Psycinfo to identify relevant articles on childhood abuse, BDNF, and bipolar disorder.

RESULTS

The extant research implicates both childhood abuse and BDNF in the etiology of bipolar disorder. Specifically, there is growing evidence associating early abuse to the development of bipolar disorder. Similarly, the BDNF Val66 allele has been linked with increased susceptibility to bipolar disorder. Based on existing research, a genetic diathesis-transactional stress model is proposed incorporating childhood abuse and the BDNF gene in the pathogenesis of bipolar disorder.

CONCLUSIONS

Although there is some support for this model, the relatively modest amount of relevant literature highlights the need for further research. An integrative theoretical framework including both social and biological processes in bipolar disorder is important for the development of effective prevention and treatment strategies for this disorder.

Brain-derived neurotrophic factor G196A polymorphism and clinical features in Parkinson's disease

OBJECTIVES

Parkinson's disease (PD) is characterized by the dopaminergic neuronal death in substantia nigra, and genetic factors appear to be involved in the pathophysiology of this disease. Brain-derived neurotrophic factor (BDNF) is widely expressed in the central nervous system and is necessary for the survival of dopaminergic neurons in substantia nigra. G196A, a common polymorphism of the BDNF gene, not only affects cognitive and motor processes, but also is associated with various psychiatric disorders. We evaluated whether G196A polymorphism is associated with PD and/or modifies clinical manifestations in PD patients.

METHODS

We included 193 PD patients and 300 control subjects. G196A polymorphism was screened by restriction fragment length polymorphism analysis. Clinical features of each patient were examined in detail. The possible association between genotype and clinical characteristics were determined by bivariate and multivariate analyses.

RESULTS

The distribution of G196A allele and genotype frequency was similar between PD and control subjects. Clinical characteristics, including Hoehn-Yahr stage, motor symptoms, non-motor symptoms (depression, cognitive dysfunction, psychiatric dysfunctions, and sleep behavior disorder), and dyskinesias, were not associated with this polymorphism.

CONCLUSIONS

G196A polymorphism is not a risk factor for PD and does not seem to modify clinical features in PD patients studied here.

Age-Related Olfactory Decline is Associated with the BDNF Val66met Polymorphism: Evidence from a Population-Based Study

The present study investigates the effect of the brain-derived neurotrophic factor (BDNF) val66met polymorphism on change in olfactory function in a large scale, longitudinal population-based sample (n = 836). The subjects were tested on a 13 item force-choice odor identification test on two test occasions over a 5-year-interval. Sex, education, health-related factors, and semantic ability were controlled for in the statistical analyses. Results showed an interaction effect of age and BDNF val66met on olfactory change, such that the magnitude of olfactory decline in the older age cohort (70–90 years old at baseline) was larger for the val homozygote carriers than for the met carriers. The older met carriers did not display larger age-related decline in olfactory function compared to the younger group. The BDNF val66met polymorphism did not affect the rate of decline in the younger age cohort (45–65 years). The findings are discussed in the light of the proposed roles of BDNF in neural development and maintenance.

Decreased BDNF in patients with antipsychotic naïve first episode schizophrenia

OBJECTIVE

Brain-derived neurotrophic factor (BDNF) is a key factor known to mediate neuronal proliferation, differentiation, survival and response to stress. Decreases in BDNF levels have been reported in schizophrenia, but studies in treatment naïve patients are few. Herein we report on serum BDNF levels in a series of patients with first-episode treatment naïve psychoses in comparison to age matched healthy controls.

METHOD

Fasting serum BDNF levels were measured in 41 patients with treatment naive first episode psychosis (24 with schizophrenia, schizoaffective disorder or schizophreniform disorder, and 17 with non-schizophrenia psychotic disorders) and 41 age-matched healthy controls.

RESULTS

A three group analyses of covariance (ANCOVA) showed a diagnosis effect (p=.038) in which patients with schizophrenia had lesser serum BDNF levels than patient with non-schizophrenia psychosis, who in turn had lesser BDNF levels than matched healthy controls. Planned two-group ANCOVAs suggested that patients with schizophrenia had lower serum BDNF level than matched controls (p=.016), whereas patients with non-schizophrenia psychosis did not differ from controls. There were no age effects on BDNF, but there was a trend (p=.08) for a gender by group interaction with greater reductions in female patients with schizophrenia. The BDNF levels did not correlate with magnitude of smoking, body mass index, severity of positive and negative symptoms or overall functioning.

CONCLUSIONS

Serum BDNF may be reduced at the onset of psychosis but its role in the pathogenesis of schizophrenia remains unclear. Elucidating the role of BDNF in schizophrenia and related psychotic disorders may provide an important therapeutic target. Further studies are also needed to examine if patients with schizophrenia have more pronounced reductions in BDNF than those with affective psychosis.

Brain-derived neurotrophic factor val66met polymorphism and hippocampal activation during episodic encoding and retrieval tasks

Brain-derived neurotrophic factor (BDNF) is a neurotrophin which has been shown to regulate cell survival and proliferation, as well as synaptic growth and hippocampal long-term potentiation. A naturally occurring single nucleotide polymorphism in the human BDNF gene (val66met) has been associated with altered intercellular trafficking and regulated secretion of BDNF in met compared to val carriers. Additionally, previous studies have found a relationship between the BDNF val66met genotype and functional activity in the hippocampus during episodic and working memory tasks in healthy young adults. Specifically, studies have found that met carriers exhibit both poorer performance and reduced neural activity within the medial temporal lobe (MTL) when performing episodic memory tasks. However, these studies have not been well replicated and have not considered the role of behavioral differences in the interpretation of neural differences. The current study sought to control for cognitive performance in investigating the role of the BDNF val66met genotype on neural activity associated with episodic memory. Across item and relational memory tests, met carriers exhibited increased MTL activation during both encoding and retrieval stages, compared to noncarriers. The results suggest that met carriers are able to recruit MTL activity to support successful memory processes, and reductions in cognitive performance observed in prior studies are not a ubiquitous effect associated with variants of the BDNF val66met genotype.

Central role of the brain in stress and adaptation: links to socioeconomic status, health, and disease

The brain is the key organ of stress reactivity, coping, and recovery processes. Within the brain, a distributed neural circuitry determines what is threatening and thus stressful to the individual. Instrumental brain systems of this circuitry include the hippocampus, amygdala, and areas of the prefrontal cortex. Together, these systems regulate physiological and behavioral stress processes, which can be adaptive in the short-term and maladaptive in the long-term. Importantly, such stress processes arise from bidirectional patterns of communication between the brain and the autonomic, cardiovascular, and immune systems via neural and endocrine mechanisms underpinning cognition, experience, and behavior. In one respect, these bidirectional stress mechanisms are protective in that they promote short-term adaptation (allostasis). In another respect, however, these stress mechanisms can lead to a long-term dysregulation of allostasis in that they promote maladaptive wear-and-tear on the body and brain under chronically stressful conditions (allostatic load), compromising stress resiliency and health. This review focuses specifically on the links between stress-related processes embedded within the social environment and embodied within the brain, which is viewed as the central mediator and target of allostasis and allostatic load.

Effect of Met66 allele of the BDNF rs6265 SNP on regional gray matter volumes in patients with multiple sclerosis: A voxel-based morphometry study

The rs6265 single nucleotide polymorphism (SNP) is a genetic variation in the brain-derived neurotrophic factor (BDNF) gene wherein the presence of the A-allele at rs6265 causes replacement of a valine (Val) at position 66 by methionine (Met). We reported recently that the Met66 allele was associated with lower brain damage as evidenced by measurement of gray matter (GM) volume in multiple sclerosis (MS) patients. The objective of this study was to determine the voxel-wise regional GM differences between the Val66Val and Met66 allele groups in MS patients by using voxel-based morphometry (VBM)-optimized analysis corrected for lesion misclassification in Statistical Parametric Mapping (SPM5). High-resolution 3D-T1-weighted SPGR images from a total of 188 MS patients were acquired on a 1.5T MRI. The Val66Val group included 129 MS patients and the Met66 allele group (comprised of Val66Met or Met66Met genotypes) included 59 MS patients. The SPM analysis of covariance tool was used to assess group differences after controlling for variation in head size, MS disease course and gender. VBM analysis did not yield significant family wise error (FWE) corrected results. This was also confirmed with the non-parametric analysis using threshold-free cluster enhancement (TFCE) method. However, the results from VBM as well as the TFCE analyses (p<0.001, uncorrected) showed higher GM volume in the cingulate of MS patients with Met66 allele than those with Val66Val. Future studies are warranted to investigate longitudinally possible protective role of the Met66 allele of the BDNF rs6265 SNP in relation to specific GM regions.

Brain-derived neurotrophic factor is associated with age-related decline in hippocampal volume

Hippocampal volume shrinks in late adulthood, but the neuromolecular factors that trigger hippocampal decay in aging humans remains a matter of speculation. In rodents, brain-derived neurotrophic factor (BDNF) promotes the growth and proliferation of cells in the hippocampus and is important in long-term potentiation and memory formation. In humans, circulating levels of BDNF decline with advancing age, and a genetic polymorphism for BDNF has been related to gray matter volume loss in old age. In this study, we tested whether age-related reductions in serum levels of BDNF would be related to shrinkage of the hippocampus and memory deficits in older adults. Hippocampal volume was acquired by automated segmentation of magnetic resonance images in 142 older adults without dementia. The caudate nucleus was also segmented and examined in relation to levels of serum BDNF. Spatial memory was tested using a paradigm in which memory load was parametrically increased. We found that increasing age was associated with smaller hippocampal volumes, reduced levels of serum BDNF, and poorer memory performance. Lower levels of BDNF were associated with smaller hippocampi and poorer memory, even when controlling for the variation related to age. In an exploratory mediation analysis, hippocampal volume mediated the age-related decline in spatial memory and BDNF mediated the age-related decline in hippocampal volume. Caudate nucleus volume was unrelated to BDNF levels or spatial memory performance. Our results identify serum BDNF as a significant factor related to hippocampal shrinkage and memory decline in late adulthood.

The brain-derived neurotrophic factor Val66Met polymorphism, hippocampal volume, and cognitive function in geriatric depression

OBJECTIVE

The Val66Met polymorphism of the brain-derived neurotrophic factor (BDNF) gene is associated with geriatric depression. In studies of younger adults without depression, met allele carriers exhibit smaller hippocampal volumes and have poorer performance on neuropsychological tests. The authors examined the relationship between the BDNF gene and hippocampal volumes in depressed and nondepressed older individuals and its relationship with memory functions mediated by the hippocampus.

DESIGN

One hundred seventy-six elderly depressed white participants and 88 nondepressed participants completed clinical assessments, neuropsychological testing, and provided blood samples for genotyping. One hundred seventy-three participants also underwent brain magnetic resonance imaging. Statistical modeling tested the relationship between genotype and hippocampal volume and function while controlling for diagnosis and other covariates.

RESULTS

BDNF genotype was not associated with a difference in performance on tests mediated by the hippocampus, including word list learning, prose recall, nonverbal memory, or digit span. After controlling for covariates, BDNF genotype was not significantly associated with hippocampal volume (F[1, 171] = 1.10, p = 0.30).

CONCLUSION

Despite different findings in younger populations, the BDNF Val66Met polymorphism is not significantly associated with hippocampal volume or function in a geriatric population. The authors hypothesize that other factors may have a stronger effect on hippocampal structure in older individuals and that the association between the Val66Met polymorphism and geriatric depression is mediated through other mechanisms.

BDNF Val66Met is associated with introversion and interacts with 5-HTTLPR to influence neuroticism

Brain-derived neurotrophic factor (BDNF) regulates synaptic plasticity and neurotransmission, and has been linked to neuroticism, a major risk factor for psychiatric disorders. A recent genome-wide association (GWA) scan, however, found the BDNF Val66Met polymorphism (rs6265) associated with extraversion but not with neuroticism. In this study, we examine the links between BDNF and personality traits, assessed using the Revised NEO Personality Inventory (NEO-PI-R), in a sample from SardiNIA (n=1560) and the Baltimore Longitudinal Study of Aging (BLSA; n=1131). Consistent with GWA results, we found that BDNF Met carriers were more introverted. By contrast, in both samples and in a meta-analysis inclusive of published data (n=15251), we found no evidence for a main effect of BDNF Val66Met on neuroticism. Finally, on the basis of recent reports of an epistatic effect between BDNF and the serotonin transporter, we explored a Val66Met x 5-HTTLPR interaction in a larger SardiNIA sample (n=2333). We found that 5-HTTLPR LL carriers scored lower on neuroticism in the presence of the BDNF Val variant, but scored higher on neuroticism in the presence of the BDNF Met variant. Our findings support the association between the BDNF Met variant and introversion and suggest that BDNF interacts with the serotonin transporter gene to influence neuroticism.

The brain-derived neurotrophic factor Val66Met polymorphism affects memory formation and retrieval of biologically salient stimuli

Brain-derived neurotrophic factor (BDNF) is involved in memory and the pathophysiology of various neuropsychiatric disorders. A single nucleotide polymorphism in the human BDNF gene (Val66Met) affects memory, and influences Alzheimer's disease and depression vulnerability in a sex-specific manner. Recent animal studies suggest that BDNF mediates memory for emotional experiences in the amygdala, but it is currently unknown whether BDNF Val66Met influences memory processing in the amygdala. Here, we investigated its effect on the successful encoding and recognition of biologically salient stimuli. Forty-seven healthy volunteers memorized and recognized faces while their brain activity was measured with event-related functional MRI. No significant differences in memory performance were observed between Val homozygotes and Met allele carriers. The imaging results demonstrated BDNF genotype x sex interactions in the amygdala during memory formation, and in the prefrontal cortex and posterior cingulate cortex during memory retrieval. Subsequent tests showed a larger contribution of these brain regions to successful encoding and retrieval in male Met allele carriers than male Val homozygotes, whereas no significant differences were observed in females. These results provide preliminary evidence that the BDNF Val66Met polymorphism influences specific mnemonic operations underlying encoding and retrieval of salient stimuli, and suggest less efficient memory processing in male Met allele carriers. Furthermore, the sex-specific genotype effects may contribute to sex-specific effects of BDNF Val66Met on depression vulnerability.

Sexually dimorphic effect of the Val66Met polymorphism of BDNF on susceptibility to Alzheimer's disease: New data and meta-analysis

Conflicting results have been reported as to whether genetic variations (Val66Met and C270T) of the brain-derived neurotrophic factor gene (BDNF) confer susceptibility to Alzheimer's disease (AD). We genotyped these polymorphisms in a Japanese sample of 657 patients with AD and 525 controls, and obtained weak evidence of association for Val66Met (P = 0.063), but not for C270T. After stratification by sex, we found a significant allelic association between Val66Met and AD in women (P = 0.017), but not in men. To confirm these observations, we collected genotyping data for each sex from 16 research centers worldwide (4,711 patients and 4,537 controls in total). The meta-analysis revealed that there was a clear sex difference in the allelic association; the Met66 allele confers susceptibility to AD in women (odds ratio = 1.14, 95% CI 1.05-1.24, P = 0.002), but not in men. Our results provide evidence that the Met66 allele of BDNF has a sexually dimorphic effect on susceptibility to AD.

Neural plasticity, human genetics, and risk for alcohol dependence

Opportunities for advances in the neurobiology of alcohol dependence have been facilitated by the development of sophisticated neurophysiological and neuroimaging techniques that allow us to have a window on developmental changes in brain structure and function. The search for genes that may increase susceptibility to alcohol dependence has been greatly facilitated by the recognition that intermediate phenotypes, sometimes referred to as endophenotypes, may be closer to the genetic variation than is the more complex alcohol dependence phenotype. This chapter will review the evidence that the brain is highly plastic, exhibiting major postnatal changes, especially during adolescence, in neural circuits that appear to influence addiction susceptibility. This chapter will suggest that heritable aspects of brain structure and function that are seen developmentally may be an important endophenotypic characteristic associated with familial risk for developing alcohol dependence. Finally, a review of studies showing associations between brain structural and functional characteristics and specific genes will be offered.

Brain plasticity and genetic factors

Brain plasticity refers to changes in brain function and structure that arise in a number of contexts. One area in which brain plasticity is of considerable interest is recovery from stroke, both spontaneous and treatment-induced. A number of factors influence these poststroke brain events. The current review considers the impact of genetic factors. Polymorphisms in the human genes coding for brain-derived neurotrophic factor (BDNF) and apolipoprotein E (ApoE) have been studied in the context of plasticity and/or stroke recovery and are discussed here in detail. Several other genetic polymorphisms are indirectly involved in stroke recovery through their modulating influences on processes such as depression and pharmacotherapy effects. Finally, new genetic polymorphisms that have not been studied in the context of stroke are proposed as new directions for study. A better understanding of genetic influences on recovery and response to therapy might allow improved treatment after stroke.

Imaging phenotypes of major depressive disorder: genetic correlates

Imaging techniques are a potentially powerful method of identifying phenotypes that are associated with, or are indicative of, a vulnerability to developing major depressive disorder (MDD). Here we identify seven promising MDD-associated traits identified by magnetic resonance imaging (MRI) or positron emission tomography (PET). We evaluate whether these traits are state-independent, heritable endophenotypes, or state-dependent phenotypes that may be useful markers of treatment efficacy. In MDD, increased activity of the amygdala in response to negative stimuli appears to be a mood-congruent phenomenon, and is likely moderated by the 5-HT transporter gene (SLC6A4) promoter polymorphism (5-HTTLPR). Hippocampal volume loss is characteristic of elderly or chronically-ill samples and may be impacted by the val66met brain-derived neurotrophic factor (BDNF) gene variant and the 5-HTTLPR SLC6A4 polymorphism. White matter pathology is salient in elderly MDD cohorts but is associated with cerebrovascular disease, and is unlikely to be a useful marker of a latent MDD diathesis. Increased blood flow or metabolism of the subgenual anterior cingulate cortex (sgACC), together with gray matter volume loss in this region, is a well-replicated finding in MDD. An attenuation of the usual pattern of fronto-limbic connectivity, particularly a decreased temporal correlation in amygdala-anterior cingulate cortex (ACC) activity, is another MDD-associated trait. Concerning neuroreceptor PET imaging, decreased 5-HT(1A) binding potential in the raphe, medial temporal lobe, and medial prefrontal cortex (mPFC) has been strongly associated with MDD, and may be impacted by a functional single nucleotide polymorphism in the promoter region of the 5-HT(1A) gene (HTR1A: -1019 C/G; rs6295). Potentially indicative of inter-study variation in MDD etiology or mood state, both increased and decreased binding potential of the 5-HT transporter has been reported. Challenges facing the field include the problem of phenotypic and etiological heterogeneity, technological limitations, the confounding effects of medication, and non-disease related inter-individual variation in brain morphology and function. Further advances are likely as epigenetic, copy-number variant, gene-gene interaction, and genome-wide association (GWA) approaches are brought to bear on imaging data.

BDNF genotype modulates resting functional connectivity in children

A specific polymorphism of the brain-derived neurotrophic factor (BDNF) gene is associated with alterations in brain anatomy and memory; its relevance to the functional connectivity of brain networks, however, is unclear. Given that altered hippocampal function and structure has been found in adults who carry the methionine (met) allele of the BDNF gene and the molecular studies elucidating the role of BDNF in neurogenesis and synapse formation, we examined the association between BDNF gene variants and neural resting connectivity in children and adolescents. We observed a reduction in hippocampal and parahippocampal to cortical connectivity in met-allele carriers within both default-mode and executive networks. In contrast, we observed increased connectivity to amygdala, insula and striatal regions in met-carriers, within the paralimbic network. Because of the known association between the BDNF gene and neuropsychiatric disorder, this latter finding of greater connectivity in circuits important for emotion processing may indicate a new neural mechanism through which these gene-related psychiatric differences are manifest. Here we show that the BDNF gene, known to regulate synaptic plasticity and connectivity in the brain, affects functional connectivity at the neural systems level. In addition, we demonstrate that the spatial topography of multiple high-level resting state networks in healthy children and adolescents is similar to that observed in adults.

Brain-derived neurotrophic factor as a model system for examining gene by environment interactions across development

There has been a dramatic rise in gene x environment studies of human behavior over the past decade that have moved the field beyond simple nature versus nurture debates. These studies offer promise in accounting for more variability in behavioral and biological phenotypes than studies that focus on genetic or experiential factors alone. They also provide clues into mechanisms of modifying genetic risk or resilience in neurodevelopmental disorders. Yet, it is rare that these studies consider how these interactions change over the course of development. In this paper, we describe research that focuses on the impact of a polymorphism in a brain-derived neurotrophic factor (BDNF) gene, known to be involved in learning and development. Specifically we present findings that assess the effects of genotypic and environmental loadings on neuroanatomic and behavioral phenotypes across development. The findings illustrate the use of a genetic mouse model that mimics the human polymorphism, to constrain the interpretation of gene-environment interactions across development in humans.

The neurotrophic and neuroprotective effects of psychotropic agents

Accumulating evidence suggests that psychotropic agents such as mood stabilizers, antidepressants, and antipsychotics realize their neurotrophic/neuroprotective effects by activating the mitogen activated protein kinaselextracellular signal-related kinase, PI3-kinase, and winglesslglycogen synthase kinase (GSK) 3 signaling pathways. These agents also upregulate the expression of trophic/protective molecules such as brain-derived neurotrophic factor, nerve growth factor, B-cell lymphoma 2, serine-threonine kinase, and Bcl-2 associated athanogene 1, and inactivate proapoptotic molecules such as GSK-3, They also promote neurogenesis and are protective in models of neurodegenerative diseases and ischemia. Most if not all, of this evidence was collected from animal studies that used clinically relevant treatment regimens. Furthermore, human imaging studies have found that these agents increase the volume and density of brain tissue, as well as levels of N-acetyl aspartate and glutamate in selected brain regions. Taken together, these data suggest that the neurotrophic/neuroprotective effects of these agents have broad therapeutic potential in the treatment, not only of mood disorders and schizophrenia, but also neurodegenerative diseases and ischemia.

No association of the Val66Met polymorphism of the brain-derived neurotrophic factor with hippocampal volume in major depression

Recently, an association of the Val66Met polymorphism of the brain-derived neurotrophic factor with hippocampal volume in patients with major depression has been reported. Here, we aimed at replicating this finding in an independent German sample. We included 79 patients with unipolar major depressive episodes and 84 healthy comparison participants. The brain-derived neurotrophic factor Val66Met polymorphism was determined in all participants. The volume of the hippocampus was manually traced on high-resolution magnetic resonance images. The hippocampal volumes of patients were significantly smaller than those of the comparison participants, confirming previous reports. There was, however, no Val66Met effect on hippocampal volume in either group. To conclude, we did not replicate the Val66Met effect on hippocampal volume in neither patients with major depression nor in healthy participants.

The BDNF Val66Met polymorphism impacts parahippocampal and amygdala volume in healthy humans: incremental support for a genetic risk factor for depression

BACKGROUND

The role of the brain-derived neurotrophic factor (BDNF) in the pathogenesis of affective disorders such as depression has been controversial. Mounting evidence comes from structural imaging, that the functional BDNF Val66Met polymorphism influences the hippocampal volume with carriers of the 66Met allele (Val/Met and Met/Met group) having smaller hippocampi. Given that stress-induced atrophy of the hippocampus is associated with the pathogenesis of affective disorders, the functional BDNF Val66Met polymorphism could be an incremental risk factor.

METHOD

Eighty-seven healthy Caucasian participants underwent structural imaging and were genotyped for the BDNF Val66Met polymorphism. Data were analysed by means of voxel-based morphometry (VBM).

RESULTS

Region of interest (ROI) analyses revealed an association between the 66Met allele and smaller parahippocampal volumes and a smaller right amygdala. In addition, the whole-brain analysis showed that the thalamus, fusiformus gyrus and several parts of the frontal gyrus were smaller in 66Met allele carriers.

CONCLUSIONS

This study demonstrates that the impact of the BDNF Val66Met polymorphism is not confined to the hippocampus but also extends to the parahippocampal gyrus and the amygdala.

The genetics of episodic memory

INTRODUCTION

Studies suggest that there is a considerable genetic contribution to individual episodic memory performance. Identifying genes which impact recollection may further elucidate an emerging biology and pave the way towards novel cognitive interventions. To date, several candidate genes have been explored and a few seem to have modest but measurable effects.

METHODS

Here we review the biology of memory with particular focus on episodic memory, critically appraise the published evidence supporting the role of several candidate genes, and make suggestions for future pathways of research.

RESULTS

We found moderate evidence for several candidate genes implicated in episodic memory formation, with converging lines of neurobiologic evidence especially strong for only a select few. Perhaps unexpectedly, little work has been done on other aspects of memory, including the semantic and autobiographical systems.

CONCLUSIONS

Larger studies utilizing more elaborate methodologies to measure the spectrum of episodic memory are required to move the field forward.

BDNF val66met polymorphism influences motor system function in the human brain

Brain-derived neurotrophic factor (BDNF) is important to brain functions such as plasticity and repair. A single nucleotide polymorphism for this growth factor, val(66)met, is common and associated with decreased activity-dependent BDNF release. The current study evaluated the effects of this polymorphism in relation to human brain motor system function, short-term plasticity, and learning. Functional magnetic resonance imaging (fMRI) scanning during right index finger movement (n = 24) identified activation in a broad sensorimotor network. However, subjects with the polymorphism showed smaller activation volume within several brain regions as compared with subjects without the polymorphism. Repeat fMRI after 25 min of right index finger training found that the 2 genotype groups modulated brain activation differently. In several brain regions, subjects with the polymorphism showed greater activation volume reduction, whereas subjects without the polymorphism showed greater activation volume expansion. On a driving-based motor learning task (independent cohort, n = 29), subjects with the polymorphism showed greater error during short-term learning and poorer retention over 4 days, relative to subjects without the polymorphism. The presence of this BDNF polymorphism is associated with differences in brain motor system function, altered short-term plasticity, and greater error in short-term motor learning. The broader implications of these findings are considered.

Depression and antidepressants: molecular and cellular aspects

Clinical depression is viewed as a physical and psychic disease process having a neuropathological basis, although a clear understanding of its ethiopathology is still missing. The observation that depressive symptoms are influenced by pharmacological manipulation of monoamines led to the hypothesis that depression results from reduced availability or functional deficiency of monoaminergic transmitters in some cerebral regions. However, there are limitations to current monoamine theories related to mood disorders. Recently, a growing body of experimental data has showed that other classes of endogenous compounds, such as neuropeptides and amino acids, may play a significant role in the pathophysiology of affective disorders. With the development of neuroscience, neuronal networks and intracellular pathways have been identified and characterized, describing the existence of the interaction between monoamines and receptors in turn able to modulate the expression of intracellular proteins and neurotrophic factors, suggesting that depression/antidepressants may be intermingled with neurogenesis/neurodegenerative processes.

Brain-derived neurotrophic factor: role in depression and suicide

Depression and suicidal behavior have recently been shown to be associated with disturbances in structural and synaptic plasticity. Brain-derived neurotrophic factor (BDNF), one of the major neurotrophic factors, plays an important role in the maintenance and survival of neurons and in synaptic plasticity. Several lines of evidence suggest that BDNF is involved in depression, such that the expression of BDNF is decreased in depressed patients. In addition, antidepressants up-regulate the expression of BDNF. This has led to the proposal of the "neurotrophin hypothesis of depression". Increasing evidence demonstrates that suicidal behavior is also associated with lower expression of BDNF, which may be independent from depression. Recent genetic studies also support a link of BDNF to depression/suicidal behavior. Not only BDNF, but abnormalities in its cognate receptor tropomycin receptor kinase B (TrkB) and its splice variant (TrkB.T1) have also been reported in depressed/suicidal patients. It has been suggested that epigenetic modulation of the Bdnf and Trkb genes may contribute to their altered expression and functioning. More recently, impairment in the functioning of pan75 neurotrophin receptor has been reported in suicide brain specimens. pan75 neurotrophin receptor is a low-affinity neurotrophin receptor that, when expressed in conjunction with low availability of neurotropins/Trks, induces apoptosis. Overall, these studies suggest the possibility that BDNF and its mediated signaling may participate in the pathophysiology of depression and suicidal behavior. This review focuses on the critical evidence demonstrating the involvement of BDNF in depression and suicide.

BDNF Val66Met polymorphism influences age differences in microstructure of the Corpus Callosum

Brain-derived neurotrophic factor (BDNF) plays an important role in neuroplasticity and promotes axonal growth, but its secretion, regulated by a BDNF gene, declines with age. The low-activity (met) allele of common polymorphism BDNF val66met is associated with reduced production of BDNF. We examined whether age-related reduction in the integrity of cerebral white matter (WM) depends on the BDNF val66met genotype. Forty-one middle-aged and older adults participated in the study. Regional WM integrity was assessed by fractional anisotropy (FA) computed from manually drawn regions of interest in the genu and splenium of the corpus callosum on diffusion tensor imaging scans. After controlling for effects of sex and hypertension, we found that only the BDNF 66met carriers displayed age-related declines in the splenium FA, whereas no age-related declines were shown by BDNF val homozygotes. No genotype-related differences were observed in the genu of the corpus callosum. This finding is consistent with a view that genetic risk for reduced BDNF affects posterior regions that otherwise are considered relatively insensitive to normal aging. Those individuals with a genetic predisposition for decreased BDNF expression may not be able to fully benefit from BDNF-based plasticity and repair mechanisms.

Arginine vasopressin and oxytocin modulate human social behavior

Increasing evidence suggests that two nonapeptides, arginine vasopressin and oxytocin, shape human social behavior in both nonclinical and clinical subjects. Evidence is discussed that in autism spectrum disorders genetic polymorphisms in the vasopressin-oxytocin pathway, notably the arginine vasopressin receptor 1a (AVPR1a), the oxytocin receptor (OXTR), neurophysin I and II, and CD38 (recently shown to be critical for social behavior by mediating oxytocin secretion) contribute to deficits in socialization skills in this group of patients. We also present first evidence that CD38 expression in lymphoblastoid cells derived from subjects diagnosed with autism is correlated with social skill phenotype inventoried by the Vineland Adaptive Behavioral Scales. Additionally, we discuss molecular genetic evidence that in nonclinical subjects both AVPR1a and OXTR genes contribute to prosocial or altruistic behavior inventoried by two experimental paradigms, the dictator game and social values orientation. The role of the AVPR1a is also analyzed in prepulse inhibition. Prepulse inhibition of the startle response to auditory stimuli is a largely autonomic response that resonates with social cognition in both animal models and humans. First results are presented showing that intranasal administration of arginine vasopressin increases salivary cortisol levels in the Trier Social Stress test. To summarize, accumulating studies employing a broad array of cutting-edge tools in psychology, neuroeconomics, molecular genetics, pharmacology, electrophysiology, and brain imaging are beginning to elaborate the intriguing role of oxytocin and arginine vasopressin in human social behavior. We expect that future studies will continue this advance and deepen our understanding of these complex events.

Heritability of regional and global brain structure at the onset of puberty: a magnetic resonance imaging study in 9-year-old twin pairs

Puberty represents the phase of sexual maturity, signaling the change from childhood into adulthood. During childhood and adolescence, prominent changes take place in the brain. Recently, variation in frontal, temporal, and parietal areas was found to be under varying genetic control between 5 and 19 years of age. However, at the onset of puberty, the extent to which variation in brain structures is influenced by genetic factors (heritability) is not known. Moreover, whether a direct link between human pubertal development and brain structure exists has not been studied. Here, we studied the heritability of brain structures at 9 years of age in 107 monozygotic and dizygotic twin pairs (N = 210 individuals) using volumetric MRI and voxel-based morphometry. Children showing the first signs of secondary sexual characteristics (N = 47 individuals) were compared with children without these signs, based on Tanner-stages. High heritabilities of intracranial, total brain, cerebellum, and gray and white matter volumes (up to 91%) were found. Regionally, the posterior fronto-occipital, corpus callosum, and superior longitudinal fascicles (up to 93%), and the amygdala, superior frontal and middle temporal cortices (up to 83%) were significantly heritable. The onset of secondary sexual characteristics of puberty was associated with decreased frontal and parietal gray matter densities. Thus, in 9-year-old children, global brain volumes, white matter density in fronto-occipital and superior longitudinal fascicles, and gray matter density of (pre-)frontal and temporal areas are highly heritable. Pubertal development may be directly involved in the decreases in gray matter areas that accompany the transition of our brains from childhood into adulthood.

Neuronal correlates of brain-derived neurotrophic factor Val66Met polymorphism and morphometric abnormalities in bipolar disorder

The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism has been proposed as a possible candidate for involvement in the pathophysiology of bipolar disorder (BD). To determine whether an association exists between the BDNF Val66Met genotype and morphometric abnormalities of the brain regions involved in memory and learning in BD and healthy subjects. Forty-two BD patients and 42 healthy subjects were studied. Interactions between BDNF Val66Met genotype and diagnosis in gray (GM) volumes were analyzed using an optimized voxel-based morphometry technique. Declarative memory function was assessed with the California Verbal Learning Test II. Left and right anterior cingulate GM volumes showed a significant interaction between genotype and diagnosis such that anterior cingulate GM volumes were significantly smaller in the Val/Met BD patients compared with the Val/Val BD patients (left P=0.01, right P=0.01). Within-group comparisons revealed that the Val/Met carriers showed smaller GM volumes of the dorsolateral prefrontal cortex compared with the Val/Val subjects within the BD patient (P=0.01) and healthy groups (left P=0.03, right P=0.03). The Val/Met healthy subjects had smaller GM volumes of the left hippocampus compared with the Val/Val healthy subjects (P<0.01). There was a significant main effect of diagnosis on memory function (P=0.04), but no interaction between diagnosis and genotype was found (P=0.48). The findings support an association between the BDNF Val66Met genotype and differential gray matter content in brain structures, and suggest that the variation in this gene may play a more prominent role in brain structure differences in subjects affected with BD.

Ethnic differences in brain-derived neurotrophic factor Val66Met polymorphism in Croatian and Korean healthy participants

AIM

To compare the frequency of alleles and genotypes in brain-derived neurotrophic factor (BDNF) val66met polymorphism in ethnically homogenous Caucasian (from Croatia) and ethnically homogenous Asian (from South Korea) healthy participants, as inter-population differences in BDNF val66met may be responsible for the divergent findings in genetic and association studies.

METHODS

BDNF val66met was genotyped in 800 (556 Croatian and 244 Korean) healthy participants. Frequencies of alleles and genotypes were evaluated using a chi(2) test.

RESULTS

The frequencies for genotypes (chi(2)2=114.69; P<0.001) and alleles (chi(2)1=120.07; P<0.001) between Korean and Croatian individuals differed significantly, due to significantly lower (46.3% and 19.5%, P<0.001) frequency of "Met" allele and significantly higher (53.7% and 80.5%, P<0.001) frequency of "Val" allele in Croatian than in Korean participants.

CONCLUSION

The study found significant ethnic differences in BDNF val66met polymorphism. The most frequent genotype among Korean participants was "Met/Val" and they had similar distribution of "Met" and "Val" alleles. In contrast, the most frequent genotype among Caucasian participants was "Val/Val" and they had different distribution of "Met" and "Val" alleles. These ethnic differences require matching participants for ethnicity in pharmacogenetic studies and in the studies investigating genetic variations in neuropsychiatric disorders.

Development of a new genotyping assay for detection of the BDNF Val66Met polymorphism using melting-curve analysis

Brain-derived neurotrophic factor (BDNF) plays a critical role in the growth, differentiation and survival of neurons in the CNS. Recent research has suggested that BDNF may be implicated in the etiology of mood disorders and schizophrenia, as well as in the therapeutic action of some drugs, such as antidepressants and antipsychotics. This study aimed to develop a simple, fast and accurate new method for detecting the Val66Met polymorphism of the BDNF gene in schizophrenia patients using melting-curve analysis and a DNA-specific dye, SYBR Green I. A group of 30 schizophrenia patients were analyzed to detect the BDNF Val66Met polymorphism (rs6265) using the new genotyping method based on the analysis of fluorescence melting curves of PCR products that were labeled with SYBR Green I. The genotype results were confirmed for all 30 samples using the specific BDNF TaqMan allele discrimination assay. This new method allows the analysis of both alleles in the same reaction tube using SYBR Green I, with no need for additional steps. The addition of a GC clamp makes this method universally applicable, since the melting temperature of one allele can be adjusted as necessary to give the distinctive separation of melting curves. Therefore, this new method is simple, fast and accurate for determining the presence of the BDNF Val66Met polymorphism. It may also be useful for the analysis of other SNPs in pharmacogenetic studies.

BDNF Val66Met polymorphism is associated with cognitive impairment in Italian patients with Parkinson's disease

BACKGROUND AND PURPOSE

A possible association between Parkinson's disease (PD) and the polymorphism of Brain Derived Neurotrophic Factor (BDNF) G196A (Val66Met) has been suggested by different studies that nevertheless yielded-contrasting result. The purpose of this study was to analyze such possible association in a cohort of Italian PD patients.

METHODS

The BDNF polymorphisms were analyzed in 294 Italian patients with PD; results were compared to those obtained in 233 age- and sex-matched healthy controls (HC) enrolled from two tertiary centres in Italy. Polymorphisms were determined by Restriction Fragment Length Polymorphism (RFLP) analysis; correlations between BDNF G196A polymorphism, and cognitive function were established by sub analyzing the results upon dividing PD patients based on their Mini Mental State Examination (MMSE) score.

RESULTS

Univariate analysis showed a highly significant correlation between the BDNF(AA) genotype and a MMSE score < or =24. Hence, the distribution of this genotype in PD individuals with a MMSE score < or =24 was significantly increased compared to PD patients with an MMSE score >24 and HC (P < 0.001 in both cases). Multivariate analyses showed that BDNF (AA) genotype was associated to a sixfold risk of cognitive impairment.

CONCLUSIONS

The BDNF(AA) homozygote genotype is over-represented in PD patients compared with normal individuals; this genotype was significantly correlated to cognitive impairment, age and disease severity. These results, although preliminary, could be important in establishing novel diagnostic and therapeutic approaches to PD.

Cerebrospinal fluid concentration of brain-derived neurotrophic factor and cognitive function in non-demented subjects

Background

Brain-derived neurotrophic factor (BDNF) is an activity-dependent secreted protein that is critical to organization of neuronal networks and synaptic plasticity, especially in the hippocampus. We tested hypothesis that reduced CSF BDNF is associated with age-related cognitive decline.

Methodology/Principal Findings, and Conclusions/Significance

CSF concentration of BDNF, Aβ₄₂ and total tau were measured in 128 cognitively normal adults (Normals), 21 patients with Alzheimer's disease (AD), and nine patients with Mild Cognitive Impairment. Apolipoprotein E and BDNF SNP rs6265 genotype were determined. Neuropsychological tests were performed at baseline for all subjects and at follow-up visits in 50 Normals. CSF BDNF level was lower in AD patients compared to age-matched Normals (p = 0.02). CSF BDNF concentration decreased with age among Normals and was higher in women than men (both p<0.001). After adjusting for age, gender, education, CSF Aβ₄₂ and total tau, and APOE and BDNF genotypes, lower CSF BDNF concentration was associated poorer immediate and delayed recall at baseline (both p<0.05) and in follow up of approximately 3 years duration (both p<0.01).

Conclusions/Significance

Reduced CSF BDNF was associated with age-related cognitive decline, suggesting a potential mechanism that may contribute in part to cognitive decline in older individuals.

Variant BDNF Val66Met polymorphism affects extinction of conditioned aversive memory

Brain-derived neurotrophic factor (BDNF) plays important roles in activity-dependent plasticity processes, such as long-term potentiation, learning, and memory. The recently reported human BDNF Val66Met (BDNF(Met)) polymorphism has been shown to lead to altered hippocampal volume and impaired hippocampal-dependent memory and is associated with a variety of neuropsychiatric disorders. There are few studies, however, that investigate the effect of the BDNF(Met) polymorphism on hippocampal-independent memory processes. A conditioned taste aversion (CTA) task was used for studying the mechanisms of long-term, hippocampal-independent, nondeclarative memory in the mammalian brain. Using the CTA paradigm, we found a novel impairment in extinction learning, but not acquisition or retention, of aversive memories resulting from the variant BDNF(Met). BDNF(Met) mice were slower to extinguish an aversive CTA memory compared with wild-type counterparts. Moreover, the BDNF(Met) was associated with smaller volume and decreased neuronal dendritic complexity in the ventromedial prefrontal cortex (vmPFC), which plays a significant role in extinction of CTA. Finally, this delay in extinction learning could be rescued pharmacologically with a cognitive enhancer, d-cycloserine (DCS). To our knowledge, this is the first evidence that the BDNF(Met) polymorphism contributes to abnormalities in memory extinction. This abnormality in extinction learning may be explained by alterations in neuronal morphology, as well as decreased neural activity in the vmPFC. Importantly, DCS was effective in rescuing this delay in extinction, suggesting that when coupled with behavior therapy, DCS may be an effective treatment option for anxiety disorders in humans with this genetic variant BDNF.

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

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

Brain derived neurotrophic factor Val66Met polymorphism, the five factor model of personality and hippocampal volume: Implications for depressive illness

Altered hippocampal volume, the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism, and neuroticism have each been implicated in the etiology of psychiatric disorders, especially depression. However, the relationship between these variables is not well understood. Here, we determined the effects of the BDNF Val66met polymorphism on the five-factor personality dimensions (assessed using the NEO-FFI), trait depression (assessed with the DASS-21) in a cross-sectional cohort of 467 healthy volunteers. A large matched subset of this cohort was also assessed for grey matter volume of the hippocampus and contiguous temporal cortical regions using magnetic resonance imaging. In Met carriers, elevations in neuroticism and trait depression and stress were associated with lower mean hippocampal volume, but there were no such associations in Val homozygotes. Trait depression, in particular, was found to moderate the effects of BDNF genotypes on hippocampal volume. Met carriers with high trait depression showed a reduction in grey matter volume of the mean hippocampus compared with Val homozygotes. These findings suggest that even in otherwise healthy subjects, trait depression may contribute to the susceptibility of Met carriers to hippocampal grey matter loss.

Biological changes associated with healthy versus pathological aging: a symposium review

The Douglas Mental Health University Institute, in collaboration with the McGill Centre for Studies in Aging, organized a 2-day symposium entitled "Biological Changes Associated with Healthy Versus Pathological Aging" that was held in 13 and 14 December 2007 on the Douglas campus. The symposium involved presentations on current trends in aging and dementia research across several sub-disciplines: genetics, neurochemistry, structural and functional neuroimaging and clinical treatment and rehabilitation. The goal of this symposium was to provide a forum for knowledge-transfer between scientists and clinicians with different specializations in order to promote cross-fertilization of research ideas that would lead to future collaborative neuroscience research in aging and dementia. In this review article, we summarize the presentations made by the 13 international scientists at the symposium and highlight: (i) past research, and future research trends in neuroscience of aging and dementia and (ii) links across levels of analysis that can lead to fruitful transdisciplinary research programs that will advance knowledge about the neurobiological changes associated with healthy aging and dementia.

BDNF Val66Met polymorphism is associated with HPA axis reactivity to psychological stress characterized by genotype and gender interactions

BACKGROUND

A key protein in maintaining neuronal integrity throughout the life span is brain-derived neurotrophic factor (BDNF). The BDNF gene is characterized by a functional polymorphism, which has been associated with stress-related disorders such as anxiety-related syndromes and depression, prompting us to examine individual responses by Genotype and Sex to a standardized social stress paradigm. Gender differences in BDNFxstress responses were posited because estrogen induces synthesis of BDNF in several brain regions.

METHODS

97 university students (51 females and 46 males) participated in a social stress procedure (Trier Social Stress Test, TSST). Indices of stress were derived from repeated measurement of cortisol, blood pressure, and heart rate during the TSST. All subjects were genotyped for the Val66Met polymorphism.

RESULTS

Tests of within-subject effects showed a significant three-way interaction (SPSS GLM repeated measures: Time (eight levels)xBDNF (val/val, val/met)xSex: p=0.0002), which reflects gender differences in the pattern of cortisol rise and decline during the social challenge. In male subjects, val/val homozygotes showed a greater rise in salivary cortisol than val/met heterozygotes. In female subjects, there was a trend for the opposite response, which is significant when area under the curve increase (AUCi) was calculated for the val/val homozygotes to show the lowest rise. Overall, the same pattern of results was observed for blood pressure and heart rate.

CONCLUSIONS

These results indicate that a common, functionally significant polymorphism in the BDNF gene modulates HPA axis reactivity and regulation during the TSST differently in men and women. Findings may be related to gender differences in reactivity and vulnerability to social stress.

Effects of the brain-derived neurotrophic growth factor val66met variation on hippocampus morphology in bipolar disorder

Histological and behavioral research in bipolar disorder (BD) implicates structural abnormalities in the hippocampus. Brain-derived neurotrophic growth factor (BDNF) protein is associated with hippocampal development and plasticity, and in mood disorder pathophysiology. We tested the hypotheses that both the BDNF val66met polymorphism and BD diagnosis are associated with decreased hippocampus volume, and that individuals with BD who carry the met allele have the smallest hippocampus volumes compared to individuals without BD and val/val homozygotes. We further explored localization of morphological differences within hippocampus in BD associated with the met allele. Twenty individuals with BD and 18 healthy comparison (HC) subjects participated in high-resolution magnetic resonance imaging scans from which hippocampus volumes were defined and measured. We used linear mixed model analysis to study effects of diagnosis and BDNF genotype on hippocampus volumes. We then employed three-dimensional mapping to localize areas of change within the hippocampus associated with the BDNF met allele in BD. We found that hippocampus volumes were significantly smaller in BD compared to HC subjects, and presence of the BDNF met allele was associated with smaller hippocampus volume in both diagnostic groups. The BD subgroup who carried the BDNF met allele had the smallest hippocampus volumes, and three-dimensional mapping identified these decreases as most prominent in left anterior hippocampus. These results support effects of BD diagnosis and BDNF genotype on hippocampus structure and suggest a genetic subgroup within BD who may be most vulnerable to deficits in hippocampus and may most benefit from interventions that influence BDNF-mediated signaling.