Hippocampal volumes and the brain-derived neurotrophic factor val66met polymorphism in geriatric major depression

Association between the BDNF Val66Met polymorphism and major depressive disorder: a systematic review and meta-analysis

Study objectives

This meta-analysis analytically reviewed recent studies concerning the potential associations between the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism and susceptibility to major depressive disorder (MDD), with subgroup analyses for race and age.

Methods

Relevant case-control studies were systematically searched for in PubMed, Embase, the Web of Science, China National Knowledge Infrastructure (CNKI), Wanfang, and Sinomed databases. A total of 24 studies were finally identified to have reported outcomes including alleles, dominant genes, recessive genes, homozygosity, and heterozygosity. Subgroup meta-analyses were performed based on participant age and ethnicity. Publication bias was represented by funnel plots. All meta-analyses of the randomized controlled trials included for evaluation were performed using RevMan5.3 software.

Results

The findings revealed no significant association between BDNF Val66Met polymorphism and MDD. However, the Met allele was found to be associated with genetic susceptibility to MDD among white populations on subgroup analysis (OR = 1.25, 95% CI: 1.05-1.48, P = 0.01). In the genetic model, dominant (OR = 1.40, 95% CI: 1.18-1.66, P = 0.0001), recessive (OR = 1.70, 95% CI: 1.05-2.78, P = 0.03), and homozygous (OR = 1.77, 95% CI: 1.08-2.88, P = 0.02) genes were all associated with MDD.

Conclusions

Despite the outcome limitations, this meta-analysis confirmed that the BDNF Val66Met polymorphism is a susceptibility factor for MDD in white populations.

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.

The non-linear correlation between the volume of cerebral white matter lesions and incidence of bipolar disorder: A secondary analysis of data from a cross-sectional study

Cerebral white matter lesions (WML) are major risk factors for bipolar disorder (BD). However, studies on the association between cerebral WML volume and BD risk are limited. This study aimed to investigate the relationship between cerebral WML volume and BD incidence. This is a secondary retrospective analysis of patients (N = 146, 72 males, 74 females, mean age = 41.77 years) who have previously undergone magnetic resonance imaging examinations. Information was obtained from the Dryad database. Univariate analysis, piecewise linear regression model, and multivariable logistic regression model were used for statistical analysis. A non-linear relationship was recognized between the cerebral WML volume and BD incidence, in which the inflection point of the WML volume was 6,200 mm³. The effect sizes and confidence intervals on the left and right sides of the emphasis point were 1.0009 (1.0003, 1.0015) and 0.9988 (0.9974, 1.0003), respectively. Subgroup analysis (WML volume < 6,200 mm³) showed that the cerebral WML volume (for 0.1 mm³ increase) was positively related to the BD incidence (OR = 1.11, 95% confidence interval [CI] (1.03, 1.21)). Here we show that the cerebral WML volume is positively and non-linearly correlated to the BD risk. Volumetric analysis of WML provide a better understanding of the association between WML and the BD risk, and thereby the pathophysiological mechanisms of BD.

Graphical abstract

A non-linear relationship between the volume of cerebral white matter lesions (WML) and bipolar disorder (BD) incidence is shown. The cerebral WML volume is positively and non-linearly correlated to the BD risk. The correlation is stronger when the cerebral WML volume was <6,200 mm³.Graphical AbstractA non-linear relationship between the volume of cerebral white matter lesions and bipolar disorder incidence is shown after adjusting for age; sex; lithium, atypical antipsychotic, antiepileptic, and antidepressant drug use; BMI; migraine; smoking; hypertension; diabetes mellitus; substance and alcohol dependency; and anxiety disorder.

Grey matter volume abnormalities in the first depressive episode of medication-naïve adult individuals: a systematic review of voxel based morphometric studies

BACKGROUND

To identify the reliable and consistent grey matter volume (GMV) abnormalities associated with major depressive disorder (MDD), we excluded the influence of confounding clinical characteristics, comorbidities and brain degeneration on brain morphological abnormalities by inclusion of non-comorbid and non-geriatric drug-naïve MDD individuals experiencing first episode depressive.

METHODS

The PubMed, Scopus, Web of Science, Science Direct and Google scholar databases were searched for papers published in English up to April 2020.

RESULTS

A total of 21 voxel based morphometric (VBM) studies comparing 845 individuals in the first depressive episode and medication-naïve with 940 healthy control subjects were included. The results showed a grey matter volumes reductions in the orbitofrontal cortex (OFC), prefrontal cortex (PFC), frontal and temporal gyri, temporal pole, insular lobe, thalamus, basal ganglia, cerebellum, hippocampus, cingulate cortex, and amygdala. In addition, increased grey matter volumes in the postcentral gyrus, superior frontal gyrus, insula, basal ganglia, thalamus, amygdala, cuneus, and precuneus differentiated the first depressive episode in medication-naïve individuals from healthy subjects.

CONCLUSION

The present systematic review provided additional support for the involvement of grey matter structural abnormalities in limbic-cortical circuits as possibly specific structural abnormalities in the early stage of MDD.Key pointsDistinct brain regions in MDD patients might be associated with the early stages of illness, and thus it is critical to study the causal relationship between brain structures and the onset of the disease to improve the evaluation in clinic.Grey matter alterations in the fronto-limbic networks in the first episode, medication-naïve MDD might suggest that these abnormalities may play an important role in the neuropathophysiology of MDD at its onset.First episode, medically naïve depressive patients show grey matter volume alterations in brain regions mainly associated with emotion regulation including parietal-temporal regions, PFC, insular lobe, thalamus, basal ganglia, cerebellum and limbic structures that may be specific changes in early stage of MDD.Genotype-diagnosis interaction effects on brain morphology in the cortico-limbic-striatal circuits, including the PFC, amygdala, hippocampus and striatum that might be implicated in the dysfunctional regulation of emotion in first-episode MDD patients.Future longitudinal and prospective studies should be conducted to identify the core structural brain changes in people at-risk for MDD and explore the association of their brain volumes with symptom onset.

Volumetric brain differences in clinical depression in association with anxiety: a systematic review with meta-analysis

BACKGROUND

Structural differences associated with depression have not been confirmed in brain regions apart from the hippocampus. Comorbid anxiety has been inconsistently assessed, and may explain discrepancies in previous findings. We investigated the link between depression, comorbid anxiety and brain structure.

METHODS

We followed Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines (PROSPERO CRD42018089286). We searched the Cochrane Library, MEDLINE, PsycInfo, PubMed and Scopus, from database inception to Sept. 13, 2018, for MRI case-control studies that reported brain volumes in healthy adults and adults with clinical depression. We summarized mean volumetric differences using meta-analyses, and we assessed demographics, depression factors and segmentation procedure as moderators using meta-regressions.

RESULTS

We included 112 studies in the meta-analyses, assessing 4911 healthy participants and 5934 participants with depression (mean age 49.8 yr, 68.2% female). Volume effects were greater in late-onset depression and in multiple episodes of depression. Adults with depression and no comorbidity showed significantly lower volumes in the putamen, pallidum and thalamus, as well as significantly lower grey matter volume and intracranial volume; the largest effects were in the hippocampus (6.8%, p < 0.001). Adults with depression and comorbid anxiety showed significantly higher volumes in the amygdala (3.6%, p < 0.001). Comorbid anxiety lowered depression effects by 3% on average. Sex moderated reductions in intracranial volume.

LIMITATIONS

High heterogeneity in hippocampus effects could not be accounted for by any moderator. Data on symptom severity and medication were sparse, but other factors likely made significant contributions.

CONCLUSION

Depression-related differences in brain structure were modulated by comorbid anxiety, chronicity of symptoms and onset of illness. Early diagnosis of anxiety symptomatology will prove crucial to ensuring effective, tailored treatments for improving long-term mental health and mitigating cognitive problems, given the effects in the hippocampus.

A precision medicine approach to pharmacological adjuncts to extinction: a call to broaden research

There is a pressing need to improve treatments for anxiety. Although exposure-based therapy is currently the gold-standard treatment, many people either do not respond to this therapy or experience a relapse of symptoms after treatment has ceased. In recent years, there have been many novel pharmacological agents identified in preclinical research that have potential as adjuncts for exposure therapy, yet very few of these are regularly integrated into clinical practice. Unfortunately, the robust effects observed in the laboratory animal often do not translate to a clinical population. In this review, we discuss how age, sex, genetics, stress, medications, diet, alcohol, and the microbiome can vary across a clinical population and yet are rarely considered in drug development. While not an exhaustive list, we have focused on these factors because they have been shown to influence an individual's vulnerability to anxiety and alter the neurotransmitter systems often targeted by pharmacological adjuncts to therapy. We argue that for potential adjuncts to be successfully translated from the lab to the clinic empirical research must be broadened to consider how individual difference factors will influence drug efficacy.

Imaging genetics paradigms in depression research: Systematic review and meta-analysis

Imaging genetics studies involving participants with major depressive disorder (MDD) have expanded. Nevertheless, findings have been inconsistent. Thus, we conducted a systematic review and meta-analysis of imaging genetics studies that enrolled MDD participants across major databases through June 30th, 2017. Sixty-five studies met eligibility criteria (N = 4034 MDD participants and 3293 controls), and there was substantial between-study variability in the methodological quality of included studies. However, few replicated findings emerged from this literature with only 22 studies providing data for meta-analyses (882 participants with MDD and 616 controls). Total hippocampal volumes did not significantly vary in MDD participants or controls carrying either the BDNF Val66Met 'Met' (386 participants with MDD and 376 controls) or the 5-HTTLPR short 'S' (310 participants with MDD and 230 controls) risk alleles compared to non-carriers. Heterogeneity across studies was explored through meta-regression and subgroup analyses. Gender distribution, the use of medications, segmentation methods used to measure the hippocampus, and age emerged as potential sources of heterogeneity across studies that assessed the association of 5-HTTLPR short 'S' alleles and hippocampal volumes. Our data also suggest that the methodological quality of included studies, publication year, and the inclusion of brain volume as a covariate contributed to the heterogeneity of studies that assessed the association of the BDNF Val66Met 'Met' risk allele and hippocampal volumes. In exploratory voxel-wise meta-analyses, MDD participants carrying the 5-HTTLPR short 'S' allele had white matter microstructural abnormalities predominantly in the corpus callosum, while carriers of the BDNF Val66Met 'Met' allele had larger gray matter volumes and hyperactivation of the right middle frontal gyrus compared to non-carriers. In conclusion, few replicated findings emerged from imaging genetics studies that included participants with MDD. Nevertheless, we explored and identified specific sources of heterogeneity across studies, which could provide insights to enhance the reproducibility of this emerging field.

Neuroimaging genomic studies in major depressive disorder: A systematic review

Genetic-neuroimaging studies could identify new potential endophenotypes of major depressive disorder (MDD). Morphological and functional alterations may be attributable to genetic factors that regulate neurogenesis and neurodegeneration. Given that the association between gene polymorphisms and brain morphology or function has varied across studies, this systematic review aims at evaluating and summarizing all available genetic-neuroimaging studies. Twenty-eight gene variants were evaluated in 64 studies by structural or functional magnetic resonance imaging. Significant genetic-neuroimaging associations were found in monoaminergic genes, BDNF genes, glutamatergic genes, HPA axis genes, and the other common genes, which were consistent with common hypotheses of the pathogenesis of MDD.

The Correlations among Depressive Symptoms, Cognitive Performance and Serum BDNF Levels in the Patients with Chronic Kidney Disease

OBJECTIVE

In the current study, we investigated whether there are relations among depressive symptoms, cognitive performance and serum BDNF levels in the patients with chronic kidney disease (CKD).

METHODS

Sixty patients with CKD and 65 healthy controls participated. Depressive symptoms were evaluated with Beck depression inventory (BDI) and Hamilton Depression Rating Scale (HDRS). Mini-Mental State Examination included in the Korean version of the Consortium to Establish a Registry for Alzheimer's disease (MMSE-KC) assessment packet was used for the evaluation of overall cognitive function. To assess memory function, the Korean version of the Hopkins Verbal Learning Test (K-HVLT) was used. BDNF levels were measured using an enzyme-linked immunosorbent assay (ELISA) kit.

RESULTS

The CKD patients showed more depressive symptoms when compared with controls. The depressive symptoms and cognitive function were not associated with serum BDNF levels in the CKD patients.

CONCLUSION

In the current study, CKD patients had more depressive symptoms when compared controls. However, the serum BDNF levels of CKD patients were not associated with depressive symptoms and cognitive functions. These findings suggested that the serum BDNF levels may not be reflect the cognitive function and depressive mood state in the CKD patients.

The antidepressant efficacy of subanesthetic-dose ketamine does not correlate with baseline subcortical volumes in a replication sample with major depressive disorder

BACKGROUND

This study sought to reproduce, in a larger sample, previous findings of a correlation between smaller raw 3-Tesla (3T) hippocampal volumes and improved antidepressant efficacy of ketamine in individuals with major depressive disorder (MDD). A secondary analysis stratified subjects according to functional BDNF rs6265 (val66met) genotype.

METHODS

Unmedicated subjects with treatment-resistant MDD ( n=55) underwent baseline structural 3T MRI. Data processing was conducted with FSL/FIRST and Freesurfer software. The amygdala, hippocampus, and thalamus were selected a priori for analysis. All subjects received a single 0.5mg/kg × 40-minute ketamine infusion. Pearson correlations were performed with subcortical volumes and percent change in MADRS score (from baseline to 230 minutes, 1 day, and 1 week post-infusion).

RESULTS

Raw and corrected subcortical volumes did not correlate with antidepressant response at any timepoint. In val/val subjects ( n=23), corrected left and right thalamic volume positively correlated with antidepressant response to ketamine at 230 minutes post-infusion but did not reach statistical significance. In met carriers ( n=14), corrected left and right thalamic volume negatively correlated with antidepressant response to ketamine.

CONCLUSION

Baseline subcortical volumes implicated in MDD did not correlate with ketamine's antidepressant efficacy. Baseline thalamic volume and BDNF genotype may be a combinatorial rapid antidepressant response biomarker.

TESC gene-regulating genetic variant (rs7294919) affects hippocampal subfield volumes and parahippocampal cingulum white matter integrity in major depressive disorder

Two recent genome-wide association studies have suggested that rs7294919 is associated with changes in hippocampal volume. rs7294919 regulates the transcriptional products of the TESC gene, which is involved in neuronal proliferation and differentiation. We investigated the interactive effect of rs7294919 and major depressive disorder (MDD) on the volume of the hippocampal subfields and the integrity of the parahippocampal cingulum (PHC). We also investigated the correlation of these structural changes with the DNA methylation status of rs7294919. A total of 105 patients with MDD and 85 healthy control subjects underwent T1-weighted structural magnetic resonance imaging and diffusion tensor imaging. The rs7294919 was genotyped and its DNA methylation status was assessed in all the participants. We analyzed the hippocampal subfield volumes and PHC integrity using FreeSurfer and the Tracts Constrained by Underlying Anatomy (TRACULA) respectively. Significant interactive effects of rs7294919 and MDD were observed in the volumes of the dentate gyrus and CA4. The patients with MDD had increased methylation in two of the three CpG loci of rs7294919, and the methylation of CpG3 was significantly correlated with right PHC integrity in the MDD group. Our results provide neurobiological evidence for the association of rs7294919 with brain structural changes in MDD.

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.

Systematic review and meta-analysis of genetic studies of late-life depression

Late-life depression (LLD) is thought to be multifactorial in etiology, including a significant genetic component. While a number of candidate gene studies have been carried out, results remain inconclusive. We undertook a systematic review of all genetic association studies of depression or depressive symptoms in late life published before February 2016, and performed meta-analyses on polymorphisms investigated in three or more independent studies. A total of 46 candidate gene studies examining 56 polymorphisms in 23 genes as well as a genome-wide association study (GWAS) were included. Meta-analyses were conducted for four polymorphisms using random effects models, of which three (APOE, BDNF, SLC6A4) were associated with LLD. These genes are implicated in hippocampal plasticity and stress reactivity, suggesting that dysregulation of these pathways may contribute to LLD. Despite using a large sample, the only GWAS published to date identified only one genome-wide significant locus in the 5q21 region. In the future, larger genetic studies specifically examining LLD, including non-hypothesis-driven GWAS, are required to further identify genetic determinants of LLD.

Shared Genetic Risk Factors for Late-Life Depression and Alzheimer's Disease

BACKGROUND

Considerable evidence has been reported for the comorbidity between late-life depression (LLD) and Alzheimer's disease (AD), both of which are very common in the general elderly population and represent a large burden on the health of the elderly. The pathophysiological mechanisms underlying the link between LLD and AD are poorly understood. Because both LLD and AD can be heritable and are influenced by multiple risk genes, shared genetic risk factors between LLD and AD may exist.

OBJECTIVE

The objective is to review the existing evidence for genetic risk factors that are common to LLD and AD and to outline the biological substrates proposed to mediate this association.

METHODS

A literature review was performed.

RESULTS

Genetic polymorphisms of brain-derived neurotrophic factor, apolipoprotein E, interleukin 1-beta, and methylenetetrahydrofolate reductase have been demonstrated to confer increased risk to both LLD and AD by studies examining either LLD or AD patients. These results contribute to the understanding of pathophysiological mechanisms that are common to both of these disorders, including deficits in nerve growth factors, inflammatory changes, and dysregulation mechanisms involving lipoprotein and folate. Other conflicting results have also been reviewed, and few studies have investigated the effects of the described polymorphisms on both LLD and AD.

CONCLUSION

The findings suggest that common genetic pathways may underlie LLD and AD comorbidity. Studies to evaluate the genetic relationship between LLD and AD may provide insights into the molecular mechanisms that trigger disease progression as the population ages.

Single Nucleotide Polymorphisms in the BDNF, VDR, and DNASE 1 Genes in Dry Eye Disease Patients: A Case-Control Study

PURPOSE

To identify single nucleotide polymorphisms (SNPs) in the brain-derived neurotrophic factor (BDNF), vitamin D receptor (VDR), and DNASE1 genes that may be associated with dry eye disease (DED), and determine whether this association varies by the presence of depression.

METHODS

A case-control study was performed with 64 DED cases and 51 controls. We collected 2 mL of saliva following a routine eye exam. Genotyping was performed using both custom and predesigned TaqMan SNP genotyping assays for 12 hypothesized SNPs. Genotype and allele frequencies of cases and controls were evaluated. Odds ratios were calculated for allele frequencies. Stratified analysis was performed to determine if the association between SNPs and DED varied by depression status.

RESULTS

A total of 18% of cases had the minor allele A of Val66Met (rs6265) SNP in the BDNF gene compared with 9% of the controls (P = 0.05). Odds ratio was 2.22. Two SNPs (Fokl-rs2228570 and Apal-rs7975232) in the VDR genes also varied between DED cases and controls. Cases were 1.72 and 1.66 times more likely to have the minor allele A in rs2228570 and rs7975232, respectively, than controls (P = 0.06 for both). While not statistically significant, among patients with depression, DED cases were 3.93 times more likely to have the minor allele A of the Val66Met SNP compared to controls.

CONCLUSIONS

This pilot study showed that Val66Met in the BDNF gene and two SNPs, Fokl and Apal, in the VDR gene may potentially be associated with DED. Additionally, the association between DED and Val66Met may vary by depression status.

Impact of 5-HTTLPR on hippocampal subregional activation in older adults

Studies have shown that a functional polymorphism of the serotonin transporter gene (5-HTTLPR) impacts performance on memory-related tasks and the hippocampal structures that subserve these tasks. The short (s) allele of 5-HTTLPR has been linked to greater susceptibility for impaired memory and smaller hippocampal volume compared to the long allele (l). However, previous studies have not examined the associations between 5-HTTLPR allele and activation in subregions of the hippocampus. In this study, we used functional magnetic resonance imaging (fMRI) to measure activation in hippocampal and temporal lobe subregions in 36 elderly non-clinical participants performing a face-name encoding and recognition task. Although there were no significant differences in task performance between s allele carriers and l homozygotes, right CA1 and right parahippocampal activation during recognition errors was significantly greater in individuals bearing the s allele. In an exploratory analysis, we determined that these effects were more pronounced in s allele carriers with the apolipoprotein ɛ4 allele. Our results suggest that older individuals with the s allele inefficiently allocate neural resources while making errors in recognizing face-name associations, which could negatively impact memory performance during more challenging tasks.

Relationship between a BDNF gene polymorphism and the brain volume in treatment-naive patients with major depressive disorder: A VBM analysis of brain MRI

The brain-derived neurotrophic factor (BDNF) relates to basic neuronal functions, such as cell survival, axonal outgrowth, and dendritic growth. The Val66Met polymorphism of the BDNF gene may affect genetic susceptibility to major depressive disorder (MDD). We prospectively investigated the relationship between the Val66Met BDNF genotype and voxel-based morphometry (VBM) findings for first episode and drug-naïve MDD patients and healthy subjects (HS). Participants comprised 38 MDD patients and 42 age- and sex-matched HS were divided into groups based on their BDNF genotype. The effects of diagnosis and genotype, as well as the genotype-diagnosis interaction, in relation to brain morphology were evaluated using a voxel-by-voxel statistical analysis of high-resolution magnetic resonance imaging (MRI) findings. Among the Met-carriers, the volume of the left middle frontal gyrus (composition of the prefrontal cortex [PFC]) was significantly smaller for MDD patients than for the HS, i.e., there was a significant genotype-diagnosis interaction effect on brain morphology noted in the left PFC. The BDNF polymorphism was associated with atrophy of the PFC in MDD patients, which suggests that the BDNF Val66Met polymorphism may play an important role in the pathogenesis of early stages of MDD.

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.

Modulatory effects of brain-derived neurotrophic factor Val66Met polymorphism on prefrontal regions in major depressive disorder

BACKGROUND

Brain-derived neurotrophic factor (BDNF) Val66Met polymorphism contributes to the development of depression (major depressive disorder, MDD), but it is unclear whether neural effects observed in healthy individuals are sustained in MDD.

AIMS

To investigate BDNF Val66Met effects on key regions in MDD neurocircuitry: amygdala, anterior cingulate, middle frontal and orbitofrontal regions.

METHOD

Magnetic resonance imaging scans were acquired in 79 persons with MDD (mean age 49 years) and 74 healthy volunteers (mean age 50 years). Effects on surface area and cortical thickness were examined with multiple comparison correction.

RESULTS

People who were Met allele carriers showed reduced caudal middle frontal thickness in both study groups. Significant interaction effects were found in the anterior cingulate and rostral middle frontal regions, in which participants in the MDD group who were Met carriers showed the greatest reduction in surface area.

CONCLUSIONS

Modulatory effects of the BDNF Val66Met polymorphism on distinct subregions in the prefrontal cortex in MDD support the neurotrophin model of depression.

New hypothesis and treatment targets of depression: an integrated view of key findings

Major depressive disorder (MDD) is a common and devastating psychiatric disorder characterized by persistent low mood, cognitive disorder, and impaired social function. Despite its complex mechanisms, increasing evidence has identified the involvement of neurotrophic factors, inflammatory cytokines, the hypothalamus-pituitary-adrenal axis, and glutamate receptors in the pathophysiology of this illness. The present review synthesizes recent research achievements to define the network between different hypotheses of MDD and to understand which part is most pivotal for its pathogenesis. By integrating MDD-related signal pathways, we highlight brain-derived neurotrophic factor (BDNF) dysfunction and increased apoptosis as the final common cascades, and new therapeutic strategies aiming to enhance BDNF function have been shown to exert a rapid and effective antidepressant action.

Structural imaging in late-life depression: association with mood and cognitive responses to antidepressant treatment

OBJECTIVES

Recent positron emission tomography studies of cerebral glucose metabolism have identified the functional neural circuitry associated with mood and cognitive responses to antidepressant treatment in late life depression (LLD). The structural alterations in these networks are not well understood. The present study used magnetic resonance (MR) imaging and voxel-based morphometry to evaluate the association between gray matter volumes and changes in mood symptoms and cognitive function with treatment with the antidepressant citalopram.

DESIGN

Open-label trial with baseline brain MR scan. Mood and cognitive assessments performed at baseline and during citalopram treatment.

SETTING

Outpatient clinics of an academic medical center.

PARTICIPANTS

17 previously unmedicated patients age 55 years or older with a major depressive episode and 17 non-depressed comparison subjects.

INTERVENTION

12-week trial of flexibly dosed citalopram.

MEASUREMENTS

Gray matter volumes, Hamilton Depression Rating Scale, California Verbal Learning Test, Delis-Kaplan Executive Function System.

RESULTS

In LLD, higher gray matter volumes in the cingulate gyrus, superior and middle frontal gyri, middle temporal gyrus, and precuneus was associated with greater mood improvement. Higher gray matter volumes in primarily frontal areas were associated with greater improvement in verbal memory and verbal fluency performance.

CONCLUSIONS

Associations with antidepressant induced improvements in mood and cognition were observed in several brain regions previously correlated with normalization of glucose metabolism after citalopram treatment in LLD. Future studies will investigate molecular mechanisms underlying these associations (e.g., beta-amyloid, inflammation, glutamate).

Hippocampal gene expression in a rat model of depression after electroacupuncture at the Baihui and Yintang acupoints

Preliminary basic research and clinical findings have demonstrated that electroacupuncture therapy exhibits positive effects in ameliorating depression. However, most studies of the underlying mechanism are at the single gene level; there are few reports regarding the mechanism at the whole-genome level. Using a rat genomic gene-chip, we profiled hippocampal gene expression changes in rats after electroacupuncture therapy. Electroacupuncture therapy alleviated depression-related manifestations in the model rats. Using gene-chip analysis, we demonstrated that electroacupuncture at Baihui (DU20) and Yintang (EX-HN3) regulates the expression of 21 genes. Real-time PCR showed that the genes Vgf, Igf2, Tmp32, Loc500373, Hif1a, Folr1, Nmb, and Rtn were upregulated or downregulated in depression and that their expression tended to normalize after electroacupuncture therapy. These results indicate that electroacupuncture at Baihui and Yintang modulates depression by regulating the expression of particular genes.

Molecular pharmacodynamics of new oral drugs used in the treatment of multiple sclerosis

New oral drugs have considerably enriched the therapeutic armamentarium for the treatment of multiple sclerosis. This review focuses on the molecular pharmacodynamics of fingolimod, dimethyl fumarate (BG-12), laquinimod, and teriflunomide. We specifically comment on the action of these drugs at three levels: 1) the regulation of the immune system; 2) the permeability of the blood-brain barrier; and 3) the central nervous system. Fingolimod phosphate (the active metabolite of fingolimod) has a unique mechanism of action and represents the first ligand of G-protein-coupled receptors (sphingosine-1-phosphate receptors) active in the treatment of multiple sclerosis. Dimethyl fumarate activates the nuclear factor (erythroid-derived 2)-related factor 2 pathway of cell defense as a result of an initial depletion of reduced glutathione. We discuss how this mechanism lies on the border between cell protection and toxicity. Laquinimod has multiple (but less defined) mechanisms of action, which make the drug slightly more effective on disability progression than on annualized relapse rate in clinical studies. Teriflunomide acts as a specific inhibitor of the de novo pyrimidine biosynthesis. We also discuss new unexpected mechanisms of these drugs, such as the induction of brain-derived neurotrophic factor by fingolimod and the possibility that laquinimod and teriflunomide regulate the kynurenine pathway of tryptophan metabolism.

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

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

Future perspectives on the treatment of cognitive deficits and negative symptoms in schizophrenia

Drug discovery based on classic models for cognitive impairment and negative symptoms of schizophrenia have met with only modest success. Because cognitive impairment and negative symptoms may result from disruptions in neurodevelopment, more complex developmental models that integrate environmental and genetic risk factors are needed. In addition, it has become clear that biochemical pathways involved in schizophrenia form complex, interconnected networks. Points at which risk factors converge, such as brain-derived neurotrophic factor (BDNF) and protein kinase B (AKT), and from which processes involved in neuroplasticity diverge, are of particular interest for pharmacologic interventions. This paper reviews elements of neurodevelopmental models for cognitive deficits and negative symptoms of schizophrenia with the aim of identifying potential targets for interventions.

Inflammatory cytokines in depression: neurobiological mechanisms and therapeutic implications

Mounting evidence indicates that inflammatory cytokines contribute to the development of depression in both medically ill and medically healthy individuals. Cytokines are important for development and normal brain function, and have the ability to influence neurocircuitry and neurotransmitter systems to produce behavioral alterations. Acutely, inflammatory cytokine administration or activation of the innate immune system produces adaptive behavioral responses that promote conservation of energy to combat infection or recovery from injury. However, chronic exposure to elevated inflammatory cytokines and persistent alterations in neurotransmitter systems can lead to neuropsychiatric disorders and depression. Mechanisms of cytokine behavioral effects involve activation of inflammatory signaling pathways in the brain that results in changes in monoamine, glutamate, and neuropeptide systems, and decreases in growth factors, such as brain-derived neurotrophic factor. Furthermore, inflammatory cytokines may serve as mediators of both environmental (e.g. childhood trauma, obesity, stress, and poor sleep) and genetic (functional gene polymorphisms) factors that contribute to depression's development. This review explores the idea that specific gene polymorphisms and neurotransmitter systems can confer protection from or vulnerability to specific symptom dimensions of cytokine-related depression. Additionally, potential therapeutic strategies that target inflammatory cytokine signaling or the consequences of cytokines on neurotransmitter systems in the brain to prevent or reverse cytokine effects on behavior are discussed.

Brain-derived neurotrophic factor serum levels and genotype: association with depression during interferon-α treatment

Depression has been associated with inflammation, and inflammation may both influence and interact with growth factors such as brain-derived neurotrophic factor (BDNF). Both the functional Val66Met BDNF polymorphism (rs6265) and BDNF levels have been associated with depression. It is thus plausible that decreased BDNF could mediate and/or moderate cytokine-induced depression. We therefore prospectively employed the Beck Depression Inventory-II (BDI-II), the Hospital Anxiety and Depression Scale (HADS), and the Montgomery-Asberg Depression Rating Scale (MADRS) in 124 initially euthymic patients during treatment with interferon-alpha (IFN-α), assessing serum BDNF and rs6265. Using mixed-effect repeated measures, lower pretreatment BDNF was associated with higher depression symptoms during IFN-α treatment (F144,17.2=6.8; P<0.0001). However, although the Met allele was associated with lower BDNF levels (F1,83.0=5.0; P=0.03), it was only associated with increased MADRS scores (F4,8.9=20.3; P<0.001), and not the BDI-II or HADS. An exploratory comparison of individual BDI-II items indicated that the Met allele was associated with suicidal ideation, sadness, and worthlessness, but not neurovegetative symptoms. Conversely, the serotonin transporter promoter polymorphism (5-HTTLPR) short allele was associated with neurovegetative symptoms such as insomnia, poor appetite and fatigue, but not sadness, worthlessness, or suicidal ideation. IFN-α therapy further lowered BDNF serum levels (F4,37.7=5.0; P=0.003), but this decrease occurred regardless of depression development. The findings thus do not support the hypothesis that decreasing BDNF is the primary pathway by which IFN-α worsens depression. Nonetheless, the results support the hypothesis that BDNF levels influence resiliency against developing inflammatory cytokine-associated depression, and specifically to a subset of symptoms distinct from those influenced by 5-HTTLPR.

Involvement of brain-derived neurotrophic factor in late-life depression

Brain-derived neurotrophic factor (BDNF), one of the major neurotrophic factors, plays an important role in the maintenance and survival of neurons, synaptic integrity, and synaptic plasticity. Evidence suggests that BDNF is involved in major depression, such that the level of BDNF is decreased in depressed patients and that antidepressants reverse this decrease. Stress, a major factor in depression, also modulates BDNF expression. These studies have led to the proposal of the neurotrophin hypothesis of depression. Late-life depression is associated with disturbances in structural and neural plasticity as well as impairments in cognitive behavior. Stress and aging also play a crucial role in late-life depression. Many recent studies have suggested that not only expression of BDNF is decreased in the serum/plasma of patients with late-life depression, but structural abnormalities in the brain of these patients may be associated with a polymorphism in the BDNF gene, and that there is a relationship between a BDNF polymorphism and antidepressant remission rates. This review provides a critical review of the involvement of BDNF in major depression, in general, and in late-life depression, in particular.

Val66Met BDNF genotypes in melancholic depression: effects on brain structure and treatment outcome

BACKGROUND

A brain-derived neurotrophic factor (BDNF) prodomain single-nucleotide polymorphism resulting in a valine to methionine substitution (Val66Met) has been associated with depression-related phenotypes and brain alterations involving regions consistently associated with major depressive disorder (MDD). The aim of our study was to evaluate the association of regional gray matter (GM) volume within the hippocampus and other unpredicted regions at the whole-brain level with the BDNF Val66Met polymorphism in MDD patients with melancholic features and their impact on treatment outcome.

METHODS

A sample of 37 MDD inpatients was assessed with three-dimensional magnetic resonance imaging (1.5-T scanner). GM volume was analyzed with voxel-based morphometry (VBM) using Statistical Parametric Mapping (SPM5). The BDNF Val66Met variant was genotyped using SNPlex technology. MDD patients were classified according to genotype distribution under a dominant model of inheritance and thus comparing Val66 homozygotes (n = 22) versus Met66 carriers (n = 15).

RESULTS

A significant GM volume reduction in the left hippocampus was observed in Met66 carriers. Conversely, in the same group, a volume increase in the right orbitofrontal cortex was detected. Moreover, a significant negative correlation between left hippocampal volume and days to remission was found in Val66 homozygotes, whereas right orbitofrontal volume was inversely correlated to days to remission in Met66 carriers.

CONCLUSIONS

Our results suggest that the Val66Met BDNF variant may have a differential impact on the brain structure of melancholic patients with possible treatment outcome implications.

No association of genetic variants in BDNF with major depression: a meta- and gene-based analysis

Major depressive disorder (MDD) is a complex psychiatric condition with strong genetic predisposition. The association of MDD with genetic polymorphisms, such as Val66Met (rs6265), in the brain derived neurotrophic factor (BDNF), have been reported in many studies and the results were conflicting. In this study, we performed a systematic literature search and conducted random-effects meta-analysis to evaluate genetic variants in BDNF with MDD. A gene-based analysis was also conducted to investigate the cumulative effects of genetic polymorphisms in BDNF. A total of 28 studies from 26 published articles were included in our analysis. Meta-analysis yielded an estimated odds ratio (OR) of 0.96 (95% CI: 0.89-1.05; P = 0.402) for Val66Met (rs6265), 0.83 (95% CI: 0.67-1.04; P = 0.103) for 11757C/G, 1.16 (95% CI: 0.74-1.82; P = 0.527) for 270T/C, 1.03 (95% CI: 0.18-5.75; P = 0.974) for 712A/G and 0.98 (95% CI: 0.85-1.14; P = 0.831) for rs988748. The gene-based analysis indicated that BDNF is not associated with MDD (P > 0.21). Our updated meta- and novel gene-based analyses provide no evidence of the association of BDNF with major depression.

Chronic clomipramine treatment restores hippocampal expression of glial cell line-derived neurotrophic factor in a rat model of depression

BACKGROUND

Because there is evidence that certain neurotrophic factors are involved in depression and the mechanism of antidepressant treatment, it is hypothesized that neurotrophic factors may also play a functional role in the etiology of depression and treatment. Glial cell line-derived neurotrophic factor (GDNF) is a member of the transforming growth factor (TGF-β)-super-family. We performed a study to assess the impact of chronic unpredictable stress (CUS) and clomipramine treatment on GDNF expression in the rat hippocampus.

METHOD

Using a rat model of CUS-induced depression, we administered clomipramine, one of the typical antidepressants, every day for 3 weeks starting 2 weeks after the beginning of the experiment. GDNF level in the hippocampus was detected by immunohistochemsitry, Western blot analysis, and reverse transcription-polymerase chain reaction (RT-PCR). Behavioral changes were measured by forced swimming test (FST) and open field test (OFT).

RESULTS

Animals exposed to CUS showed depression-like behavior and exhibited a significant decrease in GDNF expression in the hippocampus. Chronic clomipramine treatment reversed the behavioral deficits and the decrease in GDNF levels induced by CUS.

LIMITATION

The relatively small number of the depression-model rats may cause some bias of behavioral tests.

CONCLUSION

In our study, chronic clomipramine treatment restored GDNF expression in the hippocampus of CUS-induced depression rats, suggesting that GDNF is involved in the behavioral responses to antidepressants. The beneficial effects of clomipramine suggest that GDNF may be a viable target for new antidepressant drug development.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A systematic review and meta-analysis on the association between BDNF val(66)met and hippocampal volume--a genuine effect or a winners curse?

Inconsistenties have been reported with regard to an association between val(66)met, a polymorphism on the BDNF gene, and hippocampal volume. We performed a systematic review and a meta-analysis to determine the magnitude and direction of this putative association and estimated the potential influence of demographic, clinical, and methodological characteristics of studies. Tests of publication bias and time-related trends were performed and statistical power of the included studies was calculated. The literature search for MRI studies on differences in total hippocampal volume as a function of BDNF val(66)met returned 25 records that fulfilled our criteria (total N = 3,620). Meta-analysis showed that carriers of a met allele had lower hippocampal volumes relative to val/val homozygotes (d = 0.13, P = 0.02). Between-study heterogeneity in effect size estimates was substantial (Q = 54.47, P < .001) and this could not be explained by demographic, clinical, and methodological differences across studies. Funnel plot inspection and trim-and-fill estimations suggested evidence for publication bias and effect sizes decreased substantially over the years (Pearson's r = -0.54, P < .01). All included studies were underpowered. This meta-analysis shows that carriers of a met allele have lower total hippocampal volumes relative to val/val homozygotes. However, effect sizes converged closer to null with virtually each attempt at replication and were based on underpowered studies. Altogether, this may call into question whether the observed effect is a genuine biological effect of the met allele or whether it is subject to a winners curse, with large effect sizes found in a few early studies and increasingly smaller effect sizes in later studies.

Alterations in grooming activity and syntax in heterozygous SERT and BDNF knockout mice: the utility of behavior-recognition tools to characterize mutant mouse phenotypes

Serotonin transporter (SERT) and brain-derived neurotrophic factor (BDNF) are key modulators of molecular signaling, cognition and behavior. Although SERT and BDNF mutant mouse phenotypes have been extensively characterized, little is known about their self-grooming behavior. Grooming represents an important behavioral domain sensitive to environmental stimuli and is increasingly used as a model for repetitive behavioral syndromes, such as autism and attention deficit/hyperactivity disorder. The present study used heterozygous ((+/-)) SERT and BDNF male mutant mice on a C57BL/6J background and assessed their spontaneous self-grooming behavior applying both manual and automated techniques. Overall, SERT(+/-) mice displayed a general increase in grooming behavior, as indicated by more grooming bouts and more transitions between specific grooming stages. SERT(+/-) mice also aborted more grooming bouts, but showed generally unaltered activity levels in the observation chamber. In contrast, BDNF(+/-) mice displayed a global reduction in grooming activity, with fewer bouts and transitions between specific grooming stages, altered grooming syntax, as well as hypolocomotion and increased turning behavior. Finally, grooming data collected by manual and automated methods (HomeCageScan) significantly correlated in our experiments, confirming the utility of automated high-throughput quantification of grooming behaviors in various genetic mouse models with increased or decreased grooming phenotypes. Taken together, these findings indicate that mouse self-grooming behavior is a reliable behavioral biomarker of genetic deficits in SERT and BDNF pathways, and can be reliably measured using automated behavior-recognition technology.

Reduced fractional anisotropy in the uncinate fasciculus in patients with major depression carrying the met-allele of the Val66Met brain-derived neurotrophic factor genotype

Experimental studies support a neurotrophic hypothesis of major depressive disorder (MDD). The aim of this study was to determine the effect of Val66Met brain-derived neurotrophic factor (BDNF) polymorphism on the white matter fiber tracts connecting hippocampus and amygdala with the prefrontal lobe in a sample of patients with MDD and healthy controls. Thirty-seven patients with MDD and 42 healthy volunteers were recruited. Diffusion tensor imaging (DTI) data with 61 diffusion directions were obtained with MRI 3 Tesla scanner. Deterministic tractography was applied with ExploreDTI and Val66Met BDNF SNP (rs6265) was genotyped. Fiber tracts connecting the hippocampus and amygdala with the prefrontal lobe, namely uncinate fasciculus (UF), fornix, and cingulum were analyzed. A significant interaction was found in the UF between BDNF alleles and diagnosis. Patients carrying the BDNF met-allele had smaller fractional anisotropy (FA) in the UF compared to those patients homozygous for val-allele and compared to healthy subjects carrying the met-allele. A significant three-way interaction was detected between region of the cingulum (dorsal, rostral, and parahippocampal regions), brain hemisphere and BDNF genotype. Larger FA was detectable in the left rostral cingulum for met-allele carriers when compared to val/val alelle carriers. We provide evidence for the importance of the neurotrophic involvement in limbic and prefrontal connections. The met-allele of the BDNF polymorphism seems to render subjects more vulnerable for dysfunctions associated with the UF, a tract known to be related to negative emotional-cognitive processing bias, declarative memory problems, and autonoetic self awareness.

The brain-derived neurotrophic-factor (BDNF) val66met polymorphism is associated with geriatric depression: a meta-analysis

Depression has been associated with reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus. Genetic association studies of the BDNF Val66Met polymorphism (rs6265) in geriatric depression have produced inconsistent results. A meta-analysis of studies was conducted to compare the frequency of the BDNF Val66Met variant between cases with geriatric depression and age-matched controls. A total of five studies involving 523 cases with geriatric depression and 1,220 psychiatrically healthy controls was included. Met allele carriers had an increased risk for geriatric depression when compared to Val/Val homozygotes (P = 0.004, OR = 1.48, 95% CI = 1.13-1.93). Our findings suggest the BDNF Met allele may confer increased risk for depression as individual age.

Impact of BDNF Val66Met and 5-HTTLPR polymorphism variants on neural substrates related to sadness and executive function

The brain-derived neurotrophic factor (BDNF) Val(66) Met allelic variation is linked to both the occurrence of mood disorders and antidepressant response. These findings are not universally observed, and the mechanism by which this variation results in increased risk for mood disorders is unclear. One possible explanation is an epistatic relationship with other neurotransmitter genes associated with depression risk, such as the serotonin-transporter-linked promotor region (5-HTTLPR). Further, it is unclear how the coexistence of the BDNF Met and 5-HTTLPR S variants affects the function of the affective and cognitive control systems. To address this question, we conducted a functional magnetic resonance imaging (fMRI) study in 38 older adults (20 healthy and 18 remitted from major depressive disorder). Subjects performed an emotional oddball task during the fMRI scan and provided blood samples for genotyping. Our analyses examined the relationship between genotypes and brain activation to sad distractors and attentional targets. We found that 5-HTTLPR S allele carriers exhibited stronger activation in the amygdala in response to sad distractors, whereas BDNF Met carriers exhibited increased activation to sad stimuli but decreased activation to attentional targets in the dorsolateral prefrontal and dorsomedial prefrontal cortices. In addition, subjects with both the S allele and Met allele genes exhibited increased activation to sad stimuli in the subgenual cingulate and posterior cingulate. Our results indicate that the Met allele alone or in combination with 5-HTTLPR S allele may increase reactivity to sad stimuli, which might represent a neural mechanism underlying increased depression vulnerability.

Magnetic resonance imaging studies in unipolar depression: systematic review and meta-regression analyses

Previous meta-analyses of structural MRI studies have shown diffuse cortical and sub-cortical abnormalities in unipolar depression. However, the presence of duplicate publications, recruitment of particular age groups and the selection of specific regions of interest means that there is uncertainty about the balance of current research. Moreover, the lack of systematic exploration of highly significant heterogeneity has prevented the generalisability of finding. A systematic review and random-effects meta-analysis was carried out to estimate effect sizes. Possible publication bias, and the impact of various study design characteristics on the magnitude of the observed effect size were systematically explored. The aim of this study was 1) to include structural MRI studies systematically comparing unipolar depression with bipolar disorder and healthy volunteers; 2) to consider all available structures of interest without specific age limits, avoiding data duplication, and 3) to explore the influence of factors contributing to the measured effect sizes systematically with meta-regression analyses. Unipolar depression was characterised by reduced brain volume in areas involved in emotional processing, including the frontal cortex, orbitofrontal cortex, cingulate cortex, hippocampus and striatum. There was also evidence of pituitary enlargement and an excess of white matter hyperintensity volume in unipolar depression. Factors which influenced the magnitude of the observed effect sizes were differences in methods, clinical variables, pharmacological interventions and sample age.

No effect of 5HTTLPR or BDNF Val66Met polymorphism on hippocampal morphology in major depression

Neuroimaging research implicates the hippocampus in the aetiology of major depressive disorder (MDD). Imaging genetics studies have investigated the influence of the serotonin transporter-linked polymorphic region (5HTTLPR) and brain-derived neurotrophic factor (BDNF) Val66Met polymorphism on the hippocampus in healthy individuals and patients with depression (MDD). However, conflicting results have led to inconclusive evidence about the effect of 5HTTLPR or BDNF on hippocampal volume (HCV). We hypothesized that analysis methods based on three-dimensional (3D) hippocampal shape mapping could offer improved sensitivity to clarify these effects. Magnetic resonance imaging data were collected in parallel samples of 111 healthy individuals and 84 MDD patients. Manual hippocampal segmentation was conducted and the resulting data used to investigate the influence of 5HTTLPR and BDNF Val66Met genotypes on HCV and 3D shape within each sample. Hippocampal volume normalized by intracranial volume (ICV) showed no significant difference between 5HTTLPR S allele carriers and L/L homozygotes or between BDNF Met allele carriers and Val/Val homozygotes in the group of healthy individuals. Moreover, there was no significant difference in normalized HCV between 5HTTLPR diallelic and triallelic classifications or between the BDNF Val66Met genotypes in MDD patients, although there was a relationship between BDNF Val66Met and ICV. Shape analysis detected dispersed between-group differences, but these effects did not survive multiple testing correction. In this study, there was no evidence of a genetic effect for 5HTTLPR or BDNF Val66Met on hippocampal morphology in either healthy individuals or MDD patients despite the relatively large sample sizes and sensitive methodology.

Biomarkers for major depression and its delineation from neurodegenerative disorders

Major depressive disorders (MDD) are among the most debilitating diseases worldwide and occur with a high prevalence in elderly individuals. Neurodegenerative diseases (in particular Alzheimer's disease, AD) do also show a strong age-dependent increase in incidence and prevalence among the elderly population. A high number of geriatric patients with MDD show cognitive deficits and a very high proportion of AD patients present co-morbid MDD, which poses difficult diagnostic and prognostic questions. Especially in prodromal and in very early stages of AD, it is almost impossible to differentiate between pure MDD and MDD with underlying AD. Here, we give a comprehensive review of the literature on the current state of candidate biomarkers for MDD ("positive MDD markers") and briefly refer to established and validated diagnostic AD biomarkers in order to rule out underlying AD pathophysiology in elderly MDD subjects with cognitive impairments ("negative MDD biomarkers"). In summary, to date there is no evidence for positive diagnostic MDD biomarkers and the only way to delineate MDD from AD is to use "negative MDD" biomarkers. Because of this highly unsatisfactory current state of MDD biomarker research, we propose a research strategy targeting to detect and validate positive MDD biomarkers, which is based on a complex (genetic, molecular and neurophysiological) biological model that incorporates current state of the art knowledge on the pathobiology of MDD. This model delineates common pathways and the intersection between AD and MDD. Applying these concepts to MDD gives hope that positive MDD biomarkers can be successfully identified in the near future.