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

Brain-Derived Neurotrophic Factor (BDNF) as a Predictor of Treatment Response in Schizophrenia and Bipolar Disorder: A Systematic Review

Brain-derived neurotrophic factor (BDNF) is a potential biomarker of response to treatment in psychiatric disorders. As it plays a role in the pathophysiological development of schizophrenia and bipolar disorder, it is of interest to study its role in predicting therapeutic responses in both conditions. We carried out a systematic review of the literature, looking for differences in baseline BDNF levels and the Val66Met BDNF polymorphism in these disorders between responders and non-responders, and found information showing that the Val/Val genotype and higher baseline BDNF levels may be present in patients that respond successfully to pharmacological and non-pharmacological treatments. However, there is still limited evidence to support the role of the Val66Met polymorphism and baseline BDNF levels as predictors of treatment response.

Brain-derived neurotrophic factor Val66Met and neuropsychological functioning after early childhood traumatic brain injury

OBJECTIVE

The present study examined the differential effect of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism on neuropsychological functioning in children with traumatic brain injury (TBI) relative to orthopedic injury (OI).

METHODS

Participants were drawn from a prospective, longitudinal study of children who sustained a TBI (n = 69) or OI (n = 72) between 3 and 7 years of age. Children completed a battery of neuropsychological measures targeting attention, memory, and executive functions at four timepoints spanning the immediate post-acute period to 18 months post-injury. Children also completed a comparable age-appropriate battery of measures approximately 7 years post-injury. Parents rated children's dysexecutive behaviors at all timepoints.

RESULTS

Longitudinal mixed models revealed a significant allele status × injury group interaction with a medium effect size for verbal fluency. Cross-sectional models at 7 years post-injury revealed non-significant but medium effect sizes for the allele status x injury group interaction for fluid reasoning and immediate and delayed verbal memory. Post hoc stratified analyses revealed a consistent pattern of poorer neuropsychological functioning in Met carriers relative to Val/Val homozygotes in the TBI group, with small effect sizes; the opposite trend or no appreciable effect was observed in the OI group.

CONCLUSIONS

The results suggest a differential effect of the BDNF Val66Met polymorphism on verbal fluency, and possibly fluid reasoning and immediate and delayed verbal memory, in children with early TBI relative to OI. The Met allele-associated with reduced activity-dependent secretion of BDNF-may confer risk for poorer neuropsychological functioning in children with TBI.

BDNF-related mutations in major depressive disorder: a systematic review

OBJECTIVE

A better understanding of the genetic, molecular and cellular mechanisms of brain-derived neurotrophic factor (BDNF) and its association with neuroplasticity could play a pivotal role in finding future therapeutic targets for novel drugs in major depressive disorder (MDD). Because there are conflicting results regarding the exact role of BDNF polymorphisms in MDD still, we set out to systematically review the current evidence regarding BDNF-related mutations in MDD.

METHODS

We conducted a keyword-guided search of the PubMed and Embase databases, using 'BDNF' or 'brain-derived neurotrophic factor' and 'major depressive disorder' and 'single-nucleotide polymorphism'. We included all publications in line with our exclusion and inclusion criteria that focused on BDNF-related mutations in the context of MDD.

RESULTS

Our search yielded 427 records in total. After screening and application of our eligibility criteria, 71 studies were included in final analysis. According to present overall scientific data, there is a possibly major pathophysiological role for BDNF neurotrophic systems to play in MDD. However, on the one hand, the synthesis of evidence makes clear that likely no overall association of BDNF-related mutations with MDD exists. On the other hand, it can be appreciated that solidifying evidence emerged on specific significant sub-conditions and stratifications based on various demographic, clinico-phenotypical and neuromorphological variables.

CONCLUSIONS

Further research should elucidate specific BDNF-MDD associations based on demographic, clinico-phenotypical and neuromorphological variables. Furthermore, biomarker approaches, specifically combinatory ones, involving BDNF should be further investigated.

BDNF rs6265 differentially influences neurometabolites in the anterior cingulate of healthy and bipolar disorder subjects

Brain-derived neurotrophic factor (BDNF) is the most abundant brain neurotrophin and plays a critical role in neuronal growth, survival and plasticity, implicated in the pathophysiology of Bipolar Disorders (BD). The single-nucleotide polymorphism in the BDNF gene (BDNF rs6265) has been associated with decreased hippocampal BDNF secretion and volume in met carriers in different populations, although the val allele has been reported to be more frequent in BD patients. The anterior cingulate cortex (ACC) is a key center integrating cognitive and affective neuronal connections, where consistent alterations in brain metabolites such as Glx (Glutamate + Glutamine) and N-acetylaspartate (NAA) have been consistently reported in BD. However, little is known about the influence of BDNF rs6265 on neurochemical profile in the ACC of Healthy Controls (HC) and BD subjects. The aim of this study was to assess the influence of BDNF rs6265 on ACC neurometabolites (Glx, NAA and total creatine- Cr) in 124 euthymic BD type I patients and 76 HC, who were genotyped for BDNF rs6265 and underwent a 3-Tesla proton magnetic resonance imaging and spectroscopy scan (¹ H-MRS) using a PRESS ACC single-voxel (8cm³) sequence. BDNF rs6265 polymorphism showed a significant two-way interaction (diagnosis × genotype) in relation to NAA/Cr and total Cr. While met carriers presented increased NAA/Cr in HC, BD-I subjects with the val allele revealed higher total Cr, denoting an enhanced ACC metabolism likely associated with increased glutamatergic metabolites observed in BD-I val carriers. However, these results were replicated only in men. Therefore, our results support evidences that the BDNF rs6265 polymorphism exerts a complex pleiotropic effect on ACC metabolites influenced by the diagnosis and sex.

Deciphering the Effect of Different Genetic Variants on Hippocampal Subfield Volumes in the General Population

The aim of this study was to disentangle the effects of various genetic factors on hippocampal subfield volumes using three different approaches: a biologically driven candidate gene approach, a hypothesis-free GWAS approach, and a polygenic approach, where AD risk alleles are combined with a polygenic risk score (PRS). The impact of these genetic factors was investigated in a large dementia-free general population cohort from the Study of Health in Pomerania (SHIP, n = 1806). Analyses were performed using linear regression models adjusted for biological and environmental risk factors. Hippocampus subfield volume alterations were found for APOE ε4, BDNF Val, and 5-HTTLPR L allele carriers. In addition, we were able to replicate GWAS findings, especially for rs17178139 (MSRB3), rs1861979 (DPP4), rs7873551 (ASTN2), and rs572246240 (MAST4). Interaction analyses between the significant SNPs as well as the PRS for AD revealed no significant results. Our results confirm that hippocampal volume reductions are influenced by genetic variation, and that different variants reveal different association patterns that can be linked to biological processes in neurodegeneration. Thus, this study underlines the importance of specific genetic analyses in the quest for acquiring deeper insights into the biology of hippocampal volume loss, memory impairment, depression, and neurodegenerative diseases.

BDNF and its Role in the Alcohol Abuse Initiated During Early Adolescence: Evidence from Preclinical and Clinical Studies

Brain-derived neurotrophic factor (BDNF) is a crucial brain signaling protein that is integral to many signaling pathways. This neurotrophin has shown to be highly involved in brain plastic processes such as neurogenesis, synaptic plasticity, axonal growth, and neurotransmission, among others. In the first part of this review, we revise the role of BDNF in different neuroplastic processes within the central nervous system. On the other hand, its deficiency in key neural circuits is associated with the development of psychiatric disorders, including alcohol abuse disorder. Many people begin to drink alcohol during adolescence, and it seems that changes in BDNF are evident after the adolescent regularly consumes alcohol. Therefore, the second part of this manuscript addresses the involvement of BDNF during adolescent brain maturation and how this process can be negatively affected by alcohol abuse. Finally, we propose different BNDF enhancers, both behavioral and pharmacological, which should be considered in the treatment of problematic alcohol consumption initiated during the adolescence.

A Meta-Analysis of Brain-Derived Neurotrophic Factor Effects on Brain Volume in Schizophrenia: Genotype and Serum Levels

AIM

The Val66Met single-nucleotide polymorphism (SNP) on the BDNF gene has established pleiotropic effects on schizophrenia incidence and morphologic alterations in the illness. The effects of brain-derived neurotrophic factor (BDNF) on brain volume measurements are however mixed seeming to be less established for most brain regions. The current meta-analytic review examined (1) the association of the Val66Met SNP and brain volume alterations in schizophrenia by comparing Met allele carriers to Val/Val homozygotes and (2) the association of serum BDNF with brain volume measurements.

METHOD

Studies included in the meta-analyses were identified through an electronic search of PubMed and PsycInfo (via EBSCO) for English language publications from January 2000 through December 2017. Included studies had conducted a genotyping procedure of Val66Met or obtained assays of serum BDNF and obtained brain volume data in patients with psychotic disorders. Nonhuman studies were excluded.

RESULTS

Study 1 which included 52 comparisons of Met carriers and Val/Val homozygotes found evidence of lower right and left hippocampal volumes among Met allele carriers with schizophrenia. Frontal measurements, while also lower among Met carriers, did not achieve statistical significance. Study 2 which included 7 examinations of the correlation between serum BDNF and brain volume found significant associations between serum BDNF levels and right and left hippocampal volume with lower BDNF corresponding to lower volumes.

DISCUSSION

The meta-analyses provided evidence of associations between brain volume alterations in schizophrenia and variations on the Val66Met SNP and serum BDNF. Given the limited number of studies, it remains unclear if BDNF effects are global or regionally specific.

Effect of the interaction between BDNF Val66Met polymorphism and daily physical activity on mean diffusivity

Numerous studies have reported that the Met allele of the brain-derived neurotrophic factor (BDNF) gene polymorphism reduces neural plasticity. A reduction in mean diffusivity (MD) in diffusion tensor imaging (DTI) characteristically reflects the neural plasticity that involves increased tissue components. In this study, we revealed that the number of Met-BDNF alleles was negatively associated with MD throughout the whole-brain gray and white matter areas of 743 subjects using DTI and whole-brain multiple regression analyses. Within the same sample, the region of interest analysis revealed that the number of Met-BDNF alleles significantly and positively correlated with the mean FA value in the body of the corpus callosum. In addition, we observed interaction effects between BDNF Val66Met polymorphism and daily physical activity levels on MD, but not FA, in significant clusters of the bilateral hemisphere (n = 577 subjects). Post-hoc multiple regression analyses revealed that after correcting for confounding variables, there was a significant negative correlation between the physical activity level and mean MD of the whole brain in the Val/Val group [standardized partial regression coefficient (β) = -0.196, P = 0.005, t = -2.825], but not in the Val/Met (β = 0.050, P = 0.412, t = 0.822) and Met/Met groups (β = 0.092, P = 0.382, t = 0.878). These results underscore the importance of the interaction between physical activity and the BDNF Val66Met polymorphism, which affects the plasticity of neural mechanisms.

Translating the immediate effects of S-Ketamine using hippocampal subfield analysis in healthy subjects-results of a randomized controlled trial

Antidepressant doses of ketamine rapidly facilitate synaptic plasticity and modify neuronal function within prefrontal and hippocampal circuits. However, most studies have demonstrated these effects in animal models and translational studies in humans are scarce. A recent animal study showed that ketamine restored dendritic spines in the hippocampal CA1 region within 1 h of administration. To translate these results to humans, this randomized, double-blind, placebo-controlled, crossover magnetic resonance imaging (MRI) study assessed ketamine's rapid neuroplastic effects on hippocampal subfield measurements in healthy volunteers. S-Ketamine vs. placebo data were analyzed, and data were also grouped by brain-derived neurotrophic factor (BDNF) genotype. Linear mixed models showed that overall hippocampal subfield volumes were significantly larger (p = 0.009) post ketamine than post placebo (LS means difference=0.008, standard error=0.003). Post-hoc tests did not attribute effects to specific subfields (all p > 0.05). Trend-wise volumetric increases were observed within the left hippocampal CA1 region (p = 0.076), and trend-wise volumetric reductions were obtained in the right hippocampal-amygdaloid transition region (HATA) (p = 0.067). Neither genotype nor a genotype-drug interaction significantly affected the results (all p > 0.7). The study provides evidence that ketamine has short-term effects on hippocampal subfield volumes in humans. The results translate previous findings from animal models of depression showing that ketamine has pro-neuroplastic effects on hippocampal structures and underscore the importance of the hippocampus as a key region in ketamine's mechanism of action.

Brain-derived neurotrophic factor Val66Met variant on brain volumes in infants

The brain-derived neurotrophic factor (BDNF) has many important roles in neurogenesis and neuronal health. BDNF is also involved in learning and memory. Individuals with BDNF-Val66Met variant (Met +) are at higher risk for neuropsychiatric disorders and have smaller hippocampi and amgydalae compared to those without this variant (Met -). Whether these smaller brain volumes are already present at birth is unknown and were evaluated. 66 newborn infants were genotyped for BDNF-rs6265 and had brain MRI scans. The T1-weighted images were automatically parcellated for hippocampus and amygdala, as well as the intracranial volume (ICV), total brain volume, total gray and white matter, using a multi-atlas label fusion method implemented in the MRICloud ( https://braingps.anatomyworks.org ). The segmented brain volumes were normalized to the ICV for group comparisons. The two infant groups were not different in their demographics and birth characteristics. However, compared to Met - infants, the Met + infants had smaller hippocampi (p = 0.013), smaller amygdalae (p = 0.041), and less steep age-related declines in total brain volume and % white matter volume. The smaller relative hippocampal and amygdala volumes in Met + infants suggest that the Met + genotype affected prenatal developmental processes. In addition, the slower age-dependent declines in the relative total brain and white matter volumes of the Met + group in this cross-sectional dataset suggest the BDNF-Val66Met variant might have an ongoing negative influence on the postnatal developmental processes.

Testing influences of APOE and BDNF genes and heart failure on cognitive function

BACKGROUND

Apolipoprotein E (APOE) ε2, ε4 and brain-derived neurotrophic factor (BDNF) Val66Met alleles have been associated with cognition. Associations of these alleles with cognition in heart failure (HF) and influences of HF across the cognitive spectrum (i.e., cognitively normal to Alzheimer's dementia [AD]) remain unexplored.

OBJECTIVES

To investigate influences of APOE ε2, ε4, BDNF Met and HF on cognition among participants across the cognitive spectrum.

METHODS

Genetic association study using national databases (N = 7,166).

RESULTS

APOE ε2 frequencies were similar across the cognitive spectrum among participants with HF. APOE ε4 frequency was lower among participants with HF and AD than non-HF participants with AD. BDNF Met frequencies did not differ across the spectrum. HF was associated with worse attention and language. In the HF subsample, ε4 was associated with worse memory.

CONCLUSION

Associations between APOE and cognition may differ in HF but need to be tested in a larger sample.

The BDNFVal66Met SNP modulates the association between beta-amyloid and hippocampal disconnection in Alzheimer's disease

In Alzheimer's disease (AD), a single-nucleotide polymorphism in the gene encoding brain-derived neurotrophic factor (BDNF_Val66Met) is associated with worse impact of primary AD pathology (beta-amyloid, Aβ) on neurodegeneration and cognitive decline, rendering BDNF_Val66Met an important modulating factor of cognitive impairment in AD. However, the effect of BDNF_Val66Met on functional networks that may underlie cognitive impairment in AD is poorly understood. Using a cross-validation approach, we first explored in subjects with autosomal dominant AD (ADAD) from the Dominantly Inherited Alzheimer Network (DIAN) the effect of BDNF_Val66Met on resting-state fMRI assessed functional networks. In seed-based connectivity analysis of six major large-scale networks, we found a stronger decrease of hippocampus (seed) to medial-frontal connectivity in the BDNF_Val66Met carriers compared to BDNF_Val homozogytes. BDNF_Val66Met was not associated with connectivity in any other networks. Next, we tested whether the finding of more pronounced decrease in hippocampal-medial-frontal connectivity in BDNF_Val66Met could be also found in elderly subjects with sporadically occurring Aβ, including a group with subjective cognitive decline (N = 149, FACEHBI study) and a group ranging from preclinical to AD dementia (N = 114, DELCODE study). In both of these independently recruited groups, BDNF_Val66Met was associated with a stronger effect of more abnormal Aβ-levels (assessed by biofluid-assay or amyloid-PET) on hippocampal-medial-frontal connectivity decreases, controlled for hippocampus volume and other confounds. Lower hippocampal-medial-frontal connectivity was associated with lower global cognitive performance in the DIAN and DELCODE studies. Together these results suggest that BDNF_Val66Met is selectively associated with a higher vulnerability of hippocampus-frontal connectivity to primary AD pathology, resulting in greater AD-related cognitive impairment.

Effect of BDNF Val66Met on hippocampal subfields volumes and compensatory interaction with APOE-ε4 in middle-age cognitively unimpaired individuals from the ALFA study

Background

Current evidence supports the involvement of brain-derived neurotrophic factor (BDNF) Val66Met polymorphism, and the ε4 allele of APOE gene in hippocampal-dependent functions. Previous studies on the association of Val66Met with whole hippocampal volume included patients of a variety of disorders. However, it remains to be elucidated whether there is an impact of BDNF Val66Met polymorphism on the volumes of the hippocampal subfield volumes (HSv) in cognitively unimpaired (CU) individuals, and the interactive effect with the APOE-ε4 status.

Methods

BDNF Val66Met and APOE genotypes were determined in a sample of 430 CU late/middle-aged participants from the ALFA study (ALzheimer and FAmilies). Participants underwent a brain 3D-T1-weighted MRI scan, and volumes of the HSv were determined using Freesurfer (v6.0). The effects of the BDNF Val66Met genotype on the HSv were assessed using general linear models corrected by age, gender, education, number of APOE-ε4 alleles and total intracranial volume. We also investigated whether the association between APOE-ε4 allele and HSv were modified by BDNF Val66Met genotypes.

Results

BDNF Val66Met carriers showed larger bilateral volumes of the subiculum subfield. In addition, HSv reductions associated with APOE-ε4 allele were significantly moderated by BDNF Val66Met status. BDNF Met carriers who were also APOE-ε4 homozygous showed patterns of higher HSv than BDNF Val carriers.

Conclusion

To our knowledge, the present study is the first to show that carrying the BDNF Val66Met polymorphisms partially compensates the decreased on HSv associated with APOE-ε4 in middle-age cognitively unimpaired individuals.

Electronic supplementary material

The online version of this article (10.1007/s00429-020-02125-3) contains supplementary material, which is available to authorized users.

The mouse-equivalent of the human BDNF VAL66MET polymorphism increases dorsal hippocampal volume and does not interact with developmental ethanol exposure

A relatively common polymorphism in the human brain-derived neurotrophic factor (BDNF) gene (Val66Met, which corresponds to Val68Met in mice) has been shown to modulate cognitive function and vulnerability to mental health disorders. This substitution impairs trafficking and activity-dependent release of BDNF. A number of studies with both humans and transgenic mice suggest that carriers of the Met allele have deficits in the structure and/or function of the hippocampal formation. Using a relatively new transgenic mouse model of this polymorphism, we recently demonstrated that it modulates the effects of developmental ethanol exposure in the hippocampus. Here, we further characterized the effect of this polymorphism on hippocampal morphology and its interaction with ethanol vapor exposure during the 2nd and 3rd trimester equivalents of human pregnancy. We found that BDNF^met/met mice have slightly larger hippocampal volumes than BDNF^val/val mice. Ethanol vapor exposure during the 2nd and 3rd trimester equivalents of human pregnancy increased hippocampal volume in a single hippocampal subregion, the CA1 stratum radiatum. Ethanol exposure did not interact with BDNF genotype to affect volume in any hippocampal subregion. These results suggest that the Val66Met polymorphism does not reduce hippocampal size (i.e., it rather increases it slightly) or increase susceptibility to prenatal ethanol exposure-induced structural hippocampal damage during adulthood.

The impact of BDNF Val66Met on cognitive skills in veterans with posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is a trauma-induced disorder characterized with impaired cognitive function. BDNF modulates cognition and is involved in neuroprotection and neurocognitive processing. The BDNF Val66Met polymorphism was found to influence cognitive functions. In PTSD, carriers of the BDNF GG genotype had better spatial processing of navigation performance, and lower hyperarousal and startle reaction than A allele carriers. The hypothesis was that veterans with PTSD, carriers of the BDNF Val66Met A allele, will show reduced cognitive skills. The study included 315 male Caucasian combat veterans, with (N = 199) or without (N = 116) current and chronic PTSD. Cognition was assessed using the Rey-Osterrieth Complex Figure (ROCF) test that determines visual-spatial perception and short and long-term visual memory function. The results revealed that cognitive decline measured with ROCF test was associated with PTSD. Presence of the BDNF Val66Met GG genotype in veterans with PTSD, but not in veterans without PTSD, showed protective association with visual short-term memory and visual object manipulation after few seconds (executive function), assessed with the ROCF immediate recall test, compared to the A carriers with PTSD. In conclusion, this was the first study to confirm the association between BDNF Val66Met and memory and attention performed with ROCF in male veterans with PTSD. The results corroborated that the BDNF Val66Met A allele, compared to GG genotype, is associated with poorer short-term visual memory and attention linked with executive functions, in veterans with PTSD.

Genetic Contributions to Multivariate Data-Driven Brain Networks Constructed via Source-Based Morphometry

Identifying genetic factors underlying neuroanatomical variation has been difficult. Traditional methods have used brain regions from predetermined parcellation schemes as phenotypes for genetic analyses, although these parcellations often do not reflect brain function and/or do not account for covariance between regions. We proposed that network-based phenotypes derived via source-based morphometry (SBM) may provide additional insight into the genetic architecture of neuroanatomy given its data-driven approach and consideration of covariance between voxels. We found that anatomical SBM networks constructed on ~ 20 000 individuals from the UK Biobank were heritable and shared functionally meaningful genetic overlap with each other. We additionally identified 27 unique genetic loci that contributed to one or more SBM networks. Both GWA and genetic correlation results indicated complex patterns of pleiotropy and polygenicity similar to other complex traits. Lastly, we found genetic overlap between a network related to the default mode and schizophrenia, a disorder commonly associated with neuroanatomic alterations.

The BDNF Val66Met Polymorphism Modulates Resilience of Neurological Functioning to Brain Ageing and Dementia: A Narrative Review

Brain-derived neurotropic factor (BDNF) is an abundant and multi-function neurotrophin in the brain. It is released following neuronal activity and is believed to be particularly important in strengthening neural networks. A common variation in the BDNF gene, a valine to methionine substitution at codon 66 (Val66Met), has been linked to differential expression of BDNF associated with experience-dependent plasticity. The Met allele has been associated with reduced production of BDNF following neuronal stimulation, which suggests a potential role of this variation with respect to how the nervous system may respond to challenges, such as brain ageing and related neurodegenerative conditions (e.g., dementia and Alzheimer’s disease). The current review examines the potential of the BDNF Val66Met variation to modulate an individual’s susceptibility and trajectory through cognitive changes associated with ageing and dementia. On balance, research to date indicates that the BDNF Met allele at this codon is potentially associated with a detrimental influence on the level of cognitive functioning in older adults and may also impart increased risk of progression to dementia. Furthermore, recent studies also show that this genetic variation may modulate an individual’s response to interventions targeted at building cognitive resilience to conditions that cause dementia.

The Influence of the Val66Met Polymorphism of Brain-Derived Neurotrophic Factor on Neurological Function after Traumatic Brain Injury

Functional outcomes after traumatic brain injury (TBI) vary widely across patients with apparently similar injuries. This variability hinders prognosis, therapy, and clinical innovation. Recently, single nucleotide polymorphism (SNPs) that influence outcome after TBI have been identified. These discoveries create opportunities to personalize therapy and stratify clinical trials. Both of these changes would propel clinical innovation in the field. This review focuses on one of most well-characterized of these SNPs, the Val66Met SNP in the brain-derived neurotrophic factor (BDNF) gene. This SNP influences neurological function in healthy subjects as well as TBI patients and patients with similar acute insults to the central nervous system. A host of other patient-specific factors including ethnicity, age, gender, injury severity, and post-injury time point modulate this influence. These interactions confound efforts to define a simple relationship between this SNP and TBI outcomes. The opportunities and challenges associated with personalizing TBI therapy around this SNP and other similar SNPs are discussed in light of these results.

Brain-Derived Neurotrophic Factor: A Key Molecule for Memory in the Healthy and the Pathological Brain

Brain Derived Neurotrophic Factor (BDNF) is a key molecule involved in plastic changes related to learning and memory. The expression of BDNF is highly regulated, and can lead to great variability in BDNF levels in healthy subjects. Changes in BDNF expression are associated with both normal and pathological aging and also psychiatric disease, in particular in structures important for memory processes such as the hippocampus and parahippocampal areas. Some interventions like exercise or antidepressant administration enhance the expression of BDNF in normal and pathological conditions. In this review, we will describe studies from rodents and humans to bring together research on how BDNF expression is regulated, how this expression changes in the pathological brain and also exciting work on how interventions known to enhance this neurotrophin could have clinical relevance. We propose that, although BDNF may not be a valid biomarker for neurodegenerative/neuropsychiatric diseases because of its disregulation common to many pathological conditions, it could be thought of as a marker that specifically relates to the occurrence and/or progression of the mnemonic symptoms that are common to many pathological conditions.

The brain-derived neurotrophic factor Val66Met genotype does not influence the grey or white matter structures underlying recognition memory

A single nucleotide polymorphism (SNP) in the gene coding for brain-derived neurotrophic factor (BDNF) has previously been associated with a reduction in recognition memory performance. While previous findings have highlighted that this SNP contributes to recognition memory, little is known about its influence on subprocesses of recognition, familiarity and recollection. Previous research has reported reduced hippocampal volume and decreased fractional anisotropy in carriers of the Met allele across a range of white matter tracts, including those networks that may support recognition memory. Here, in a sample of 61 healthy young adults, we used a source memory task to measure accuracy on each recognition subprocess, in order to determine whether the Val66Met SNP (rs6265) influences these equally. Additionally, we compared grey matter volume between these groups for structures that underpin familiarity and recollection separately. Finally, we used probabilistic tractography to reconstruct tracts that subserve each of these two recognition systems. Behaviourally, we found group differences on the familiarity measure, but not on recollection. However, we did not find any group difference on grey- or white-matter structures. Together, these results suggest a functional influence of the Val66Met SNP that is independent of coarse structural changes, and nuance previous research highlighting the relationship between BDNF, brain structure, and behaviour.

BDNF, endurance activity, and mechanisms underlying the evolution of hominin brains

OBJECTIVES

As a complex, polygenic trait, brain size has likely been influenced by a range of direct and indirect selection pressures for both cognitive and non-cognitive functions and capabilities. It has been hypothesized that hominin brain expansion was, in part, a correlated response to selection acting on aerobic capacity (Raichlen & Polk, 2013). According to this hypothesis, selection for aerobic capacity increased the activity of various signaling molecules, including those involved in brain growth. One key molecule is brain-derived neurotrophic factor (BDNF), a protein that regulates neuronal development, survival, and plasticity in mammals. This review updates, partially tests, and expands Raichlen and Polk's (2013) hypothesis by evaluating evidence for BDNF as a mediator of brain size.

DISCUSSION

We contend that selection for endurance capabilities in a hot climate favored changes to muscle composition, mitochondrial dynamics and increased energy budget through pathways involving regulation of PGC-1α and MEF2 genes, both of which promote BDNF activity. In addition, the evolution of hairlessness and the skin's thermoregulatory response provide other molecular pathways that promote both BDNF activity and neurotransmitter synthesis. We discuss how these pathways contributed to the evolution of brain size and function in human evolution and propose avenues for future research. Our results support Raichlen and Polk's contention that selection for non-cognitive functions has direct mechanistic linkages to the evolution of brain size in hominins.

Interactions of BDNF Val66Met Polymorphism and Menstrual Pain on Brain Complexity

The irregularity and uncertainty of neurophysiologic signals across different time scales can be regarded as neural complexity, which is related to the adaptability of the nervous system and the information processing between neurons. We recently reported general loss of brain complexity, as measured by multiscale sample entropy (MSE), at pain-related regions in females with primary dysmenorrhea (PDM). However, it is unclear whether this loss of brain complexity is associated with inter-subject genetic variations. Brain-derived neurotrophic factor (BDNF) is a widely expressed neurotrophin in the brain and is crucial to neural plasticity. The BDNF Val66Met single-nucleotide polymorphism (SNP) is associated with mood, stress, and pain conditions. Therefore, we aimed to examine the interactions of BDNF Val66Met polymorphism and long-term menstrual pain experience on brain complexity. We genotyped BDNF Val66Met SNP in 80 PDM females (20 Val/Val, 31 Val/Met, 29 Met/Met) and 76 healthy female controls (25 Val/Val, 36 Val/Met, 15 Met/Met). MSE analysis was applied to neural source activity estimated from resting-state magnetoencephalography (MEG) signals during pain-free state. We found that brain complexity alterations were associated with the interactions of BDNF Val66Met polymorphism and menstrual pain experience. In healthy female controls, Met carriers (Val/Met and Met/Met) demonstrated lower brain complexity than Val/Val homozygotes in extensive brain regions, suggesting a possible protective role of Val/Val homozygosity in brain complexity. However, after experiencing long-term menstrual pain, the complexity differences between different genotypes in healthy controls were greatly diminished in PDM females, especially in the limbic system, including the hippocampus and amygdala. Our results suggest that pain experience preponderantly affects the effect of BDNF Val66Met polymorphism on brain complexity. The results of the present study also highlight the potential utilization of resting-state brain complexity for the development of new therapeutic strategies in patients with chronic pain.

Could a blood test for PTSD and depression be on the horizon?

INTRODUCTION

Depression and posttraumatic stress disorder (PTSD) are two complex and debilitating psychiatric disorders that result in poor life and destructive behaviors against self and others. Currently, diagnosis is based on subjective rather than objective determinations leading to misdiagnose and ineffective treatments. Advances in novel neurobiological methods have allowed assessment of promising biomarkers to diagnose depression and PTSD, which offers a new means of appropriately treating patients. Areas covered: Biomarkers discovery in blood represents a fundamental tool to predict, diagnose, and monitor treatment efficacy in depression and PTSD. The potential role of altered HPA axis, epigenetics, NPY, BDNF, neurosteroid biosynthesis, the endocannabinoid system, and their function as biomarkers for mood disorders is discussed. Insofar, we propose the identification of a biomarker axis to univocally identify and discriminate disorders with large comorbidity and symptoms overlap, so as to provide a base of support for development of targeted treatments. We also weigh in on the feasibility of a future blood test for early diagnosis. Expert commentary: Potential biomarkers have already been assessed in patients' blood and need to be further validated through multisite large clinical trial stratification. Another challenge is to assess the relation among several interdependent biomarkers to form an axis that identifies a specific disorder and secures the best-individualized treatment. The future of blood-based tests for PTSD and depression is not only on the horizon but, possibly, already around the corner.

Actions of Brain-Derived Neurotrophin Factor in the Neurogenesis and Neuronal Function, and Its Involvement in the Pathophysiology of Brain Diseases

It is well known that brain-derived neurotrophic factor, BDNF, has an important role in a variety of neuronal aspects, such as differentiation, maturation, and synaptic function in the central nervous system (CNS). BDNF stimulates mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK), phosphoinositide-3kinase (PI3K), and phospholipase C (PLC)-gamma pathways via activation of tropomyosin receptor kinase B (TrkB), a high affinity receptor for BDNF. Evidence has shown significant contributions of these signaling pathways in neurogenesis and synaptic plasticity in in vivo and in vitro experiments. Importantly, it has been demonstrated that dysfunction of the BDNF/TrkB system is involved in the onset of brain diseases, including neurodegenerative and psychiatric disorders. In this review, we discuss actions of BDNF and related signaling molecules on CNS neurons, and their contributions to the pathophysiology of brain diseases.

Impact of brain-derived neurotrophic factor genetic polymorphism on cognition: A systematic review

INTRODUCTION

Brain-derived neurotrophic factor (BDNF) has an important role in the neurogenesis and neuroplasticity of the brain. This systematic review was designed to examine the association between BDNF Val66Met (rs6265) polymorphism and four cognitive domains-attention and concentration, executive function, verbal fluency, and memory, respectively.

METHODOLOGY

Primary literature search was performed using search engines such as PubMed and Scopus. Observational studies that evaluated the neurocognitive performances in relation to BDNF polymorphism within human subjects were included in this review, while animal studies, overlapping studies, and meta-analysis were excluded.

RESULTS

Forty of 82 reviewed studies (48.8%) reported an association between Val66Met polymorphism and neurocognitive domains. The proportion of the studies showing positive findings in cognitive performances between Val/Val homozygotes and Met carriers was comparable, at 30.5% and 18.3%, respectively. The highest percentage of positive association between Val66Met polymorphism and neurocognition was reported under the memory domain, with 26 of 63 studies (41.3%), followed by 18 of 47 studies (38.3%) under the executive function domain and four of 23 studies (17.4%) under the attention and concentration domain. There were no studies showing an association between Val66Met polymorphism and verbal fluency. In particular, Val/Val homozygotes performed better in tasks related to the memory domain, while Met carriers performed better in terms of executive function, in both healthy individuals and clinical populations.

CONCLUSION

While numerous studies report an association between Val66Met polymorphism and neurocognitive changes in executive function and memory domains, the effect of Met allele has not been clearly established.

Critical Issues in BDNF Val66Met Genetic Studies of Neuropsychiatric Disorders

Neurotrophins have been implicated in the pathophysiology of many neuropsychiatric diseases. Brain-derived neurotrophic factor (BDNF) is the most abundant and widely distributed neurotrophin in the brain. Its Val66Met polymorphism (refSNP Cluster Report: rs6265) is a common and functional single-nucleotide polymorphism (SNP) affecting the activity-dependent release of BDNF. BDNF Val66Met transgenic mice have been generated, which may provide further insight into the functional impact of this polymorphism in the brain. Considering the important role of BDNF in brain function, more than 1,100 genetic studies have investigated this polymorphism in the past 15 years. Although these studies have reported some encouraging positive findings initially, most of the findings cannot be replicated in following studies. These inconsistencies in BDNF Val66Met genetic studies may be attributed to many factors such as age, sex, environmental factors, ethnicity, genetic model used for analysis, and gene–gene interaction, which are discussed in this review. We also discuss the results of recent studies that have reported the novel functions of this polymorphism. Because many BDNF polymorphisms and non-genetic factors have been implicated in the complex traits of neuropsychiatric diseases, the conventional genetic association-based method is limited to address these complex interactions. Future studies should apply data mining and machine learning techniques to determine the genetic role of BDNF in neuropsychiatric diseases.

Predicting age from cortical structure across the lifespan

Despite interindividual differences in cortical structure, cross-sectional and longitudinal studies have demonstrated a large degree of population-level consistency in age-related differences in brain morphology. This study assessed how accurately an individual's age could be predicted by estimates of cortical morphology, comparing a variety of structural measures, including thickness, gyrification and fractal dimensionality. Structural measures were calculated across up to seven different parcellation approaches, ranging from one region to 1000 regions. The age prediction framework was trained using morphological measures obtained from T1-weighted MRI volumes collected from multiple sites, yielding a training dataset of 1056 healthy adults, aged 18-97. Age predictions were calculated using a machine-learning approach that incorporated nonlinear differences over the lifespan. In two independent, held-out test samples, age predictions had a median error of 6-7 years. Age predictions were best when using a combination of cortical metrics, both thickness and fractal dimensionality. Overall, the results reveal that age-related differences in brain structure are systematic enough to enable reliable age prediction based on metrics of cortical morphology.

Translational Functional Neuroimaging in the Explanation of Depression

Translation as a notion and procedure is deeply embodied in medical science and education. Translation includes the possibility to translate data across disciplines to improve diagnosis and treatment procedures. The evidence accumulated using translation serves as a vehicle for reification of medical diagnoses. There are promising, established post hoc correlations between the different types of clinical tools (interviews and inventories) and neuroscience. The various measures represent statistical correlations that must now be integrated into diagnostic standards and procedures but this, as a whole, is a step forward towards a better understanding of the mechanisms underlying psychopathology in general and depression in particular. Here, we focus on functional magnetic resonance imaging studies using a trans-disciplinary approach and attempt to establish bridges between the different fields. We will selectively highlight research areas such as imaging genetics, imaging immunology and multimodal imaging, as related to the diagnosis and management of depression.

BDNF genotype is associated with hippocampal volume in mild traumatic brain injury

The negative long-term effects of mild traumatic brain injury (mTBI) have been a growing concern in recent years, with accumulating evidence suggesting that mTBI combined with additional vulnerability factors may induce neurodegenerative-type changes in the brain. However, the factors instantiating risk for neurodegenerative disease following mTBI are unknown. This study examined the link between mTBI and brain-derived neurotrophic factor (BDNF) genotype, which has previously been shown to regulate processes involved in neurodegeneration including synaptic plasticity and facilitation of neural survival through its expression. Specifically, we examined nine BDNF single-nucleotide polymorphisms (SNPs; rs908867, rs11030094, rs6265, rs10501087, rs1157659, rs1491850, rs11030107, rs7127507 and rs12273363) previously associated with brain atrophy or memory deficits in mTBI. Participants were 165 white, non-Hispanic Iraq and Afghanistan war veterans between the ages of 19 and 58, 110 of whom had at least one mTBI in their lifetime. Results showed that the BDNF SNP rs1157659 interacted with mTBI to predict hippocampal volume. Furthermore, exploratory analysis of functional resting state data showed that rs1157659 minor allele homozygotes with a history of mTBI had reduced functional connectivity in the default mode network compared to major allele homozygotes and heterozygotes. Apolipoprotein E (APOE) was not a significant predictor of hippocampal volume or functional connectivity. These results suggest that rs1157659 minor allele homozygotes may be at greater risk for neurodegeneration after exposure to mTBI and provide further evidence for a potential role for BDNF in regulating neural processes following mTBI.

Picture free recall performance linked to the brain's structural connectome

INTRODUCTION

Memory functions are highly variable between healthy humans. The neural correlates of this variability remain largely unknown.

METHODS

Here, we investigated how differences in free recall performance are associated with DTI-based properties of the brain's structural connectome and with grey matter volumes in 664 healthy young individuals tested in the same MR scanner.

RESULTS

Global structural connectivity, but not overall or regional grey matter volumes, positively correlated with recall performance. Moreover, a set of 22 inter-regional connections, including some with no previously reported relation to human memory, such as the connection between the temporal pole and the nucleus accumbens, explained 7.8% of phenotypic variance.

CONCLUSIONS

In conclusion, this large-scale study indicates that individual memory performance is associated with the level of structural brain connectivity.

The BDNF Val66Met polymorphism is associated with structural neuroanatomical differences in young children

The brain-derived neurotrophic factor (BDNF) Val⁶⁶Met single nucleotide polymorphism (SNP) has been associated with individual differences in brain structure and function, and cognition. Research on BDNF's influence on brain and cognition has largely been limited to adults, and little is known about the association of this gene, and specifically the Val⁶⁶Met polymorphism, with developing brain structure and emerging cognitive functions in children. We performed a targeted genetic association analysis on cortical thickness, surface area, and subcortical volume in 78 children (ages 6-10) who were Val homozygotes (homozygous Val/Val carriers) or Met carriers (Val/Met, Met/Met) for the Val⁶⁶Met locus using Atlas-based brain segmentation. We observed greater cortical thickness for Val homozygotes in regions supporting declarative memory systems (anterior temporal pole/entorhinal cortex), consistent with adult findings. Met carriers had greater surface area in the prefrontal and parietal cortices and greater cortical thickness in lateral occipital/parietal cortex in contrast to prior adult findings that may relate to performance on cognitive tasks supported by these regions in Met carriers. Finally, we found larger right hippocampal volume in Met carriers, although inconsistent with adult findings (generally reports larger volumes for Val homozygotes), is consistent with a recent finding in children. Gene expression levels vary across different brain regions and across development and our findings highlight the need to consider this developmental change in explorations of BDNF-brain relationships. The impact of the BDNF Val⁶⁶Met polymorphism on the structure of the developing brain therefore reflects regionally-specific developmental changes in BDNF expression and cortical maturation trajectories.

BDNF Variants May Modulate Long-Term Visual Memory Performance in a Healthy Cohort

Brain-derived neurotrophic factor (BDNF) is involved in numerous cognitive functions including learning and memory. BDNF plays an important role in synaptic plasticity in humans and rats with BDNF shown to be essential for the formation of long-term memories. We previously identified a significant association between the BDNF Val66Met polymorphism (rs6265) and long-term visual memory (p-value = 0.003) in a small cohort (n = 181) comprised of healthy individuals who had been phenotyped for various aspects of memory function. In this study, we have extended the cohort to 597 individuals and examined multiple genetic variants across both the BDNF and BDNF-AS genes for association with visual memory performance as assessed by the Wechsler Memory Scale—Fourth Edition subtests Visual Reproduction I and II (VR I and II). VR I assesses immediate visual memory, whereas VR II assesses long-term visual memory. Genetic association analyses were performed for 34 single nucleotide polymorphisms genotyped on Illumina OmniExpress BeadChip arrays with the immediate and long-term visual memory phenotypes. While none of the BDNF and BDNF-AS variants were shown to be significant for immediate visual memory, we found 10 variants (including the Val66Met polymorphism (p-value = 0.006)) that were nominally associated, and three variants (two variants in BDNF and one variant in the BDNF-AS locus) that were significantly associated with long-term visual memory. Our data therefore suggests a potential role for BDNF, and its anti-sense transcript BDNF-AS, in long-term visual memory performance.

Effect of childhood maltreatment and brain-derived neurotrophic factor on brain morphology

Childhood maltreatment (CM) has been associated with altered brain morphology, which may partly be due to a direct impact on neural growth, e.g. through the brain-derived neurotrophic factor (BDNF) pathway. Findings on CM, BDNF and brain volume are inconsistent and have never accounted for the entire BDNF pathway. We examined the effects of CM, BDNF (genotype, gene expression and protein level) and their interactions on hippocampus, amygdala and anterior cingulate cortex (ACC) morphology. Data were collected from patients with depression and/or an anxiety disorder and healthy subjects within the Netherlands Study of Depression and Anxiety (NESDA) (N = 289). CM was assessed using the Childhood Trauma Interview. BDNF Val66Met genotype, gene expression and serum protein levels were determined in blood and T1 MRI scans were acquired at 3T. Regional brain morphology was assessed using FreeSurfer. Covariate-adjusted linear regression analyses were performed. Amygdala volume was lower in maltreated individuals. This was more pronounced in maltreated met-allele carriers. The expected positive relationship between BDNF gene expression and volume of the amygdala is attenuated in maltreated subjects. Finally, decreased cortical thickness of the ACC was identified in maltreated subjects with the val/val genotype. CM was associated with altered brain morphology, partly in interaction with multiple levels of the BNDF pathway. Our results suggest that CM has different effects on brain morphology in met-carriers and val-homozygotes and that CM may disrupt the neuroprotective effect of BDNF.

Post-traumatic stress disorder risk and brain-derived neurotrophic factor Val66Met

Brain-derived neurotrophic factor (BDNF), which regulates neuronal survival, growth differentiation, and synapse formation, is known to be associated with depression and post-traumatic stress disorder (PTSD). However, the molecular mechanism for those mental disorders remains unknown. Studies have shown that BDNF is associated with PTSD risk and exaggerated startle reaction (a major arousal manifestation of PTSD) in United States military service members who were deployed during the wars in Iraq and Afghanistan. The frequency of the Met/Met in BDNF gene was greater among those with PTSD than those without PTSD. Among individuals who experienced fewer lifetime stressful events, the Met carriers have significantly higher total and startle scores on the PTSD Checklist than the Val/Val carriers. In addition, subjects with PTSD showed higher levels of BDNF in their peripheral blood plasma than the non-probable-PTSD controls. Increased BDNF levels and startle response were observed in both blood plasma and brain hippocampus by inescapable tail shock in rats. In this paper, we reviewed these data to discuss BDNF as a potential biomarker for PTSD risk and its possible roles in the onset of PTSD.

The influence of 5-HTTLPR and Val66Met polymorphisms on cortical thickness and volume in limbic and paralimbic regions in depression: a preliminary study

BACKGROUND

Structural brain abnormalities have been investigated in multi-genetic and complex disorders such as major depressive disorder (MDD). Among the various candidate genes implicated in MDD, the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism and 5-HT transporter gene linked polymorphism (5-HTTLPR) have garnered the most attention due to their putative roles in neural plasticity and antidepressant response. However, relatively few studies have assessed the influence of these polymorphysims on cortical thickness or brain volume in para-limbic and limbic regions in MDD, which was the aim of this study.

METHODS

Forty-three adults with MDD and 15 healthy controls (HC) underwent structural magnetic resonance imaging (MRI). Cortical thickness was assessed in frontal, cingulate and temporal regions. Volumetric measures were carried out in the thalamus, caudate, putamen, pallidum, hippocampus and amygdala. Participants were genotyped to determine their 5-HTTLPR (tri-allelic) and Val66Met polymorphisms.

RESULTS

In the combined sample (MDD + HC), smaller right pallidum volumes were found in LA/S (LA/S & LA/LG) heterozygotes compared to S/S (S/S, LG/S & LG/LG) homozygotes, though the effect was modest. In the MDD group, larger left thalamus and putamen volumes were observed in LA/LA homozygotes. No Val66Met or 5-HTTLPR genotype effects existed on cortical thickness and no main effects of the Val66Met polymorphism were observed.

CONCLUSION

Our preliminary results suggest that the 5-HTTLPR polymorphism is associated with morphometric changes in regions known to play an important role in emotional and reward processing in depression. A larger sample size is required to replicate these findings and to potentially reveal subtle morphometric changes.

Effects of BDNF polymorphism and physical activity on episodic memory in the elderly: a cross sectional study

BACKGROUND

The brain-derived neurotrophic factor (BDNF) concentration is highest in the hippocampus compared with that in other brain structures and affects episodic memory, a cognitive function that is impaired in older adults. According to the neurotrophic hypothesis, BDNF released during physical activity enhances brain plasticity and consequently brain health. However, even if the physical activity level is involved in the secretion of neurotrophin, this protein is also under the control of a specific gene. The aim of the present study was to examine the effect of the interaction between physical activity and BDNF Val66Met (rs6265), a genetic polymorphism, on episodic memory.

METHODS

Two hundred and five volunteers aged 55 and older with a Mini Mental State Examination score ≥ 24 participated in this study. Four groups of participants were established according to their physical activity level and polymorphism BDNF profile (Active Val homozygous, Inactive Val homozygous, Active Met carriers, Inactive Met carriers). Episodic memory was evaluated based on the delayed recall of the Logical Memory test of the MEM III battery.

RESULTS

As expected, the physical activity level interacted with BDNF polymorphism to affect episodic memory performance (p < .05). The active Val homozygous participants significantly outperformed the active Met carriers and inactive Val homozygous participants.

CONCLUSION

This study clearly demonstrates an interaction between physical activity and BDNF Val66Met polymorphism that affects episodic memory in the elderly and confirms that physical activity contributes to the neurotrophic mechanism implicated in cognitive health. The interaction shows that only participants with Val/Val polymorphism benefited from physical activity.

BDNF Val66Met polymorphism and plasma levels in Chinese Han population with obsessive-compulsive disorder and generalized anxiety disorder

BACKGROUND

Anxiety disorders are a category of mental disorders characterized by feelings of anxiety and fear, which include generalized anxiety disorder (GAD). Obsessive-Compulsive Disorder (OCD) used to be categorized as anxiety disorder in DSM-IV. However OCD was no longer included in anxiety disorders and came into its own category titled as Obsessive-Compulsive and Related Disorders (OCRD) in DSM-5. It will be interesting to explore is there any different biological characteristics between OCD and anxiety disorders. Brain-derived neurotrophic factor (BDNF) was a potential candidate gene in both OCD and GAD. The results of genetic association studies between BDNF and OCD have been inconsistent. BDNF plasma/serum levels in OCD have been found lower than those in healthy controls. However the heritable reason of the lowered BDNF levels was not well elucidated. The amount of studies about BDNF and GAD were relatively small. The aims of this study were to determine whether single nucleotide polymorphism Val66Met of BDNF was associated with OCD and GAD, to examine BDNF plasma levels in OCD and GAD, and to explore whether Val66Met variation influences BDNF plasma levels.

METHODS

We genotyped Val66Met variation in 148 OCD patients, 108 GAD patients and 99 healthy controls. Within the same sample, BDNF plasma levels were determined in 113 OCD patients, 102 GAD patients and 63 healthy controls.

RESULTS

Val66Met variation was not associated with OCD or GAD. BDNF plasma levels in OCD and GAD patients were significant lower than those in healthy controls. Val66Met variation had no influence on BDNF plasma levels. No difference was found between OCD and GAD. Results do not change no matter taking OCD and GAD as one group or separated two.

LIMITATIONS

First, the sample size for genotyping was relatively small, which leaded to a low statistical power of the genetic part in this study. Second, we genotyped just one SNP in BDNF gene. Third, parts of the participants did not be assayed for BDNF plasma levels.

CONCLUSIONS

Our findings support the hypothesis that BDNF is involved in the pathophysiology of mental disorders, not only OCD but also GAD. OCD and GAD patients both show lower BDNF plasma levels compared to healthy controls. The BDNF plasma levels are not associated with Val66Met variation.

The brain-derived neurotrophic factor (BDNF) val66met polymorphism differentially affects performance on subscales of the Wechsler Memory Scale - Third Edition (WMS-III)

Single nucleotide polymorphisms in the brain-derived neurotrophic factor (BDNF) gene and the catechol-O-methyltransferase (COMT) gene influence brain structure and function, as well as cognitive abilities. They are most influential in the hippocampus and prefrontal cortex (PFC), respectively. Recall and recognition are forms of memory proposed to have different neural substrates, with recall having a greater dependence on the PFC and hippocampus. This study aimed to determine whether the BDNF val⁶⁶met or COMT val¹⁵⁸met polymorphisms differentially affect recall and recognition, and whether these polymorphisms interact. A sample of 100 healthy adults was assessed on recall and familiarity-based recognition using the Faces and Family Pictures subscales of the Wechsler Memory Scale – Third Edition (WMS-III). COMT genotype did not affect performance on either task. The BDNF polymorphism (i.e., met carriers relative to val homozygotes) was associated with poorer recall ability, while not influencing recognition. Combining subscale scores in memory tests such as the WMS might obscure gene effects. Our results demonstrate the importance of distinguishing between recall and familiarity-based recognition in neurogenetics research.

BDNF Val66Met polymorphism and hippocampal volume in neuropsychiatric disorders: A systematic review and meta-analysis

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a neurotrophin involved in neurogenesis and synaptic plasticity in the central nervous system, especially in the hippocampus, and has been implicated in the pathophysiology of several neuropsychiatric disorders. Its Val66Met polymorphism (refSNP Cluster Report: rs6265) is a functionally relevant single nucleotide polymorphism affecting the secretion of BDNF and is implicated in differences in hippocampal volumes.

METHODS

This is a systematic meta-analytical review of findings from imaging genetic studies on the impact of the rs6265 SNP on hippocampal volumes in neuropsychiatric patients with major depressive disorder, anxiety, bipolar disorder or schizophrenia.

RESULTS

The overall sample size of 18 independent clinical cohorts comprised 1695 patients. Our results indicated no significant association of left (Hedge's g=0.08, p=0.12), right (g=0.07, p=0.22) or bilateral (g=0.07, p=0.16) hippocampal volumes with BDNF rs6265 in neuropsychiatric patients. There was no evidence for a publication bias or any demographic, clinical, or methodological moderating effects. Both Val/Val homozygotes (g=0.32, p=0.004) and Met-carriers (g=0.20, p=0.004) from the patient sample had significantly smaller hippocampal volumes than the healthy control sample with the same allele. The magnitude of these effects did not differ between the two genotypes.

CONCLUSION

This meta-analysis suggests that there is no association between this BDNF polymorphism and hippocampal volumes. For each BDNF genotype, the hippocampal volumes were significantly lower in neuropsychiatric patients than in healthy controls.

Investigating the Role of Hippocampal BDNF in Anxiety Vulnerability Using Classical Eyeblink Conditioning

Dysregulation of brain-derived neurotrophic factor (BDNF), behavioral inhibition temperament (BI), and small hippocampal volume have been linked to anxiety disorders. Individuals with BI show facilitated acquisition of the classically conditioned eyeblink response (CCER) as compared to non-BI individuals, and a similar pattern is seen in an animal model of BI, the Wistar-Kyoto (WKY) rat. The present study examined the role of hippocampal BDNF in the facilitated delay CCER of WKY rats. Consistent with earlier work, acquisition was facilitated in WKY rats compared to the Sprague Dawley (SD) rats. Facilitated acquisition was associated with increased BDNF, TrkB, and Arc mRNA in the dentate gyrus of SD rats, but learning-induced increases in BDNF and Arc mRNA were significantly smaller in WKY rats. To determine whether reduced hippocampal BDNF in WKY rats was a contributing factor for their facilitated CCER, BDNF or saline infusions were given bilaterally into the dentate gyrus region 1 h prior to training. BDNF infusion did not alter the acquisition of SD rats, but significantly dampened the acquisition of CCER in the WKY rats, such that acquisition was similar to SD rats. Together, these results suggest that inherent differences in the BDNF system play a critical role in the facilitated associative learning exhibited by WKY rats, and potentially individuals with BI. Facilitated associative learning may represent a vulnerability factor in the development of anxiety disorders.

The BDNF p.Val66Met polymorphism, childhood trauma, and brain volumes in adolescents with alcohol abuse

BACKGROUND

Previous studies have indicated that early life adversity, genetic factors and alcohol dependence are associated with reduced brain volume in adolescents. However, data on the interactive effects of early life adversity, genetic factors (e.g. p.Met66 allele of BDNF), and alcohol dependence, on brain structure in adolescents is limited. We examined whether the BDNF p.Val66Met polymorphism interacts with childhood trauma to predict alterations in brain volume in adolescents with alcohol use disorders (AUDs).

METHODS

We examined 160 participants (80 adolescents with DSM-IV AUD and 80 age- and gender-matched controls) who were assessed for trauma using the Childhood Trauma Questionnaire (CTQ). Magnetic resonance images were acquired for a subset of the cohort (58 AUD and 58 controls) and volumes of global and regional structures were estimated using voxel-based morphometry (VBM). Samples were genotyped for the p.Val66Met polymorphism using the TaqMan® Assay. Analysis of covariance (ANCOVA) and post-hoc t-tests were conducted using SPM8 VBM.

RESULTS

No significant associations, corrected for multiple comparisons, were found between the BDNF p.Val66Met polymorphism, brain volumes and AUD in adolescents with childhood trauma.

CONCLUSIONS

These preliminary findings suggest that the BDNF p.Met66 allele and childhood trauma may not be associated with reduced structural volumes in AUD. Other genetic contributors should be investigated in future studies.

Interplay between childhood trauma and BDNF val66met variants on blood BDNF mRNA levels and on hippocampus subfields volumes in schizophrenia spectrum and bipolar disorders

OBJECTIVE

Here we investigated a two hit gene environment model in relation to functional genomic factors (BDNF mRNA), and volume of hippocampal subfields in schizophrenia spectrum and bipolar disorders, focusing on both an environmental (childhood trauma) and genetic risk factor (BDNF val66met).

METHOD

A total of 323 patients with a broad DSM-IV schizophrenia spectrum disorder or bipolar disorder were consecutively recruited. A history of childhood trauma was obtained using the Childhood Trauma Questionnaire. BDNF DNA and RNA were analyzed using standardized procedures. A subsample of n = 108 underwent MRI scanning, and the FreeSurfer was used to obtain measures of hippocampal subfield. All MRI data were corrected for age and gender, with post-hoc analysis correcting for ICV.

RESULTS

A history of childhood trauma or being a met carrier of the BDNF val66met was associated with significantly reduced BDNF mRNA level. Additive effects were observed between a history of childhood trauma and BDNF val66met, in the direction of met carriers with high levels of childhood trauma having the lowest BDNF mRNA levels. Lastly, met carriers reporting high levels of childhood trauma (specifically sexual or physical abuse) had significantly reduced hippocampal subfield volumes CA2/3 and CA4 dentate gyrus.

CONCLUSION

The current findings demonstrate that the reduced BDNF mRNA levels found in psychosis may be associated with both a history of childhood trauma and BDNF val66met variants. Further, our study supports a two hit model including a history of childhood trauma as well as genetic vulnerability (met carriers of the BDNF val66met) behind reduced volume of hippocampal subfields in psychosis. This was specifically found for areas important for neurogenesis, the CA2/3 and the CA4 DG.

APOE and BDNF Val66Met polymorphisms combine to influence episodic memory function in older adults

Genetic polymorphisms of apolipoprotein E (APOE) and brain-derived neurotrophic factor (BDNF) have shown inconsistent associations with healthy adult cognitive functions. Recent investigations have suggested that APOE polymorphisms do not contribute to non-pathological cognitive function and that any effect is likely due to prodromal Alzheimer's disease (AD). Similarly, although BDNF Val66Met polymorphisms affect hippocampal morphology and function, associations with learning and/or memory have not always been found. This study sought to determine whether APOE and BDNF polymorphisms were associated, either independently or in combination, with adult cognition. Comprehensive neuropsychological assessments were conducted on 433 older adults, aged 50-79 years (M=62.16, SD=6.81), which yielded measures of episodic memory, working memory, executive function, and language processing. Participants underwent comprehensive neuropsychological assessment to ensure that only cognitively intact individuals comprised the sample. APOE and BDNF polymorphic data were used as predictors in general linear models that assessed composite cognitive domain variables, while covarying for education and age. Although no main effects for APOE or BDNF were found, the analysis identified a significant APOE×BDNF interaction that predicted episodic memory performance (p=.02, η(2)=.02). Post-hoc analyses demonstrated that in BDNF Val homozygotes, the cognitive consequences of APOE polymorphisms were minimal. However, in BDNF Met carriers, the hypothesized beneficial/detrimental effects of APOE polymorphisms were found. Our data show that concurrent consideration of both APOE and BDNF polymorphisms are required in order to witness a cognitive effect in healthy older adults.