Investigating the molecular basis of major depressive disorder etiology: a functional convergent genetic approach

microRNA-15b contributes to depression-like behavior in mice by affecting synaptic protein levels and function in the nucleus accumbens

Major depression is a prevalent affective disorder characterized by recurrent low mood. It presumably results from stress-induced deteriorations of molecular networks and synaptic functions in brain reward circuits of genetically-susceptible individuals through epigenetic processes. Epigenetic regulator microRNA-15b inhibits neuronal progenitor proliferation and is up-regulated in the medial prefrontal cortex of mice that demonstrate depression-like behavior, indicating the contribution of microRNA-15 to major depression. Using a mouse model of major depression induced by chronic unpredictable mild stress (CUMS), here we examined the effects of microRNA-15b on synapses and synaptic proteins in the nucleus accumbens of these mice. The application of a microRNA-15b antagomir into the nucleus accumbens significantly reduced the incidence of CUMS-induced depression and reversed the attenuations of excitatory synapse and syntaxin-binding protein 3 (STXBP3A)/vesicle-associated protein 1 (VAMP1) expression. In contrast, the injection of a microRNA-15b analog into the nucleus accumbens induced depression-like behavior as well as attenuated excitatory synapses and STXBP3A/VAMP1 expression similar to the down-regulation of these processes induced by the CUMS. We conclude that microRNA-15b-5p may play a critical role in chronic stress-induced depression by decreasing synaptic proteins, innervations, and activities in the nucleus accumbens. We propose that the treatment of anti-microRNA-15b-5p may convert stress-induced depression into resilience.

Retinal correlates of psychiatric disorders

Diagnosis and monitoring of psychiatric disorders rely heavily on subjective self-reports of clinical symptoms, which are complicated by the varying consistency of accounts reported by patients with an impaired mental state. Hence, more objective and quantifiable measures have been sought to provide clinicians with more robust methods to evaluate symptomology and track progression of disease in response to treatments. Owing to the shared origins of the retina and the brain, it has been suggested that changes in the retina may correlate with structural and functional changes in the brain. Vast improvements in retinal imaging, namely optical coherence tomography (OCT) and electrodiagnostic technology, have made it possible to investigate the eye at a microscopic level, allowing for the investigation of potential biomarkers in vivo. This review provides a summary of retinal biomarkers associated with schizophrenia, bipolar disorder and major depression, demonstrating how retinal biomarkers may be used to complement existing methods and provide structural markers of pathophysiological mechanisms that underpin brain dysfunction in psychiatric disorders.

Evaluation of Serum Glial Cell Line-derived Neurotrophic Factor in Bangladeshi Major Depressive Disorder Patients

Background

Major depressive disorder (MDD) is a global health burden in the 21^st century because of its high rate of prevalence linked with disability, morbidity, and mortality. The actual etiology behind the development of MDD is not understood yet. Various genetic, physiological, biological and environmental factors have been predicted to be involved. As there is currently no sufficient laboratory test for the diagnosis of MDD, it is expected that this investigation can assist in better diagnosis and management of MDD. The present study aimed to evaluate glial cell line-derived neurotrophic factor (GDNF) in MDD patients compared to healthy controls (HCs).

Materials and methods

This case-control study was conducted with 167 participants including 85 MDD patients and 82 age- and sex-matched HCs. A qualified psychiatrist evaluated all the study participants according to the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5). The severity of depression was measured by the Hamilton depression rating scale (Ham-D) and the participants with Ham-D score ≥ 7 were considered as cases. Serum GDNF levels were determined by enzyme-linked immunosorbent assay (ELISA) kits (Boster Bio, Pleasanton, CA, USA).

Results

MDD patients and HCs were similar in terms of their socio-demographic profiles. Serum GDNF was found to have no significant alterations in MDD patients when compared to HCs (p > 0.05). Moreover, no significant positive or negative correlation was found between serum levels of GDNF and Ham-D scores in MDD patients.

Conclusions

It can be predicted from the above findings that there is no significant relation between serum GDNF levels and the pathophysiology of depression. This study should be treated as preliminary and further studies with a more homogeneous and larger study population are required to establish these findings.

microRNA and mRNA profiles in the amygdala are associated with stress-induced depression and resilience in juvenile mice

OBJECTIVES

Major depressive disorder characterized as recurrent negative mood is one of the prevalent psychiatric diseases. Chronic stress plus lack of reward may induce long-term imbalance between reward and penalty circuits in the brain, leading to persistent negative mood. Numerous individuals demonstrate resilience to chronic mild stress. Molecular mechanisms for major depression and resilience in the brain remain unclear.

METHODS

After juvenile mice were treated by the chronic unpredictable mild stress (CUMS) for 4 weeks, they were screened by sucrose preference, Y-maze and forced swimming tests to examine whether their behaviors were depression-like or not. mRNA and miRNA profiles were quantified by high-throughput sequencing in amygdala tissues harvested from control, CUMS-susceptible, and CUMS-resilience mice.

RESULTS

1.5-fold ratio in reads per kilo-base per million reads was set to be the threshold to judge the involvement of mRNAs and miRNAs in the CUMS, major depression, or resilience. In the amygdala from CUMS-susceptible mice, the expression of genes relevant to GABAergic, cholinergic, glutamatergic, dopaminergic, and serotonergic synapses was changed, as well as the expression of genes that encoded signal pathways of PI3K-Akt, calcium, cAMP, MAPK, and drug addiction was imbalanced. The expression of these genes in the amygdala form CUMS-resilience mice was less changed.

CONCLUSIONS

The downregulation of genes relevant to synaptic functions and the imbalance of intra-signaling pathway in the amygdala are associated with major depression. Consistent results through sequencing mRNA and miRNA and using different methods validate our finding and conclusion.

microRNA and mRNA profiles in nucleus accumbens underlying depression versus resilience in response to chronic stress

Major depression in negative mood is presumably induced by chronic stress with lack of reward. However, most individuals who experience chronic stress demonstrate resilience. Molecular mechanisms underlying stress- induced depression versus resilience remain unknown, which are investigated in brain reward circuits. Mice were treated by chronic unpredictable mild stress (CUMS) for 4 weeks. The tests of sucrose preference, Y-maze, and forced swimming were used to identify depression-like emotion behavior or resilience. High-throughput sequencing was used to analyze mRNA and miRNA quantity in the nucleus accumbens (NAc) harvested from the mice in the groups of control, CUMS-induced depression (CUMS-MDD), and CUMS-resistance to identify molecular profiles of CUMS-MDD versus CUMS-resilience. In data analyses and comparison among three groups, 1.5-fold ratio in reads per kilo-base per million reads (RPKM) was set to judge involvements of mRNA and miRNA in CUMS, MDD, or resilience. The downregulations of serotonergic/dopaminergic synapses, MAPK/calcium signaling pathways, and morphine addiction as well as the upregulations of cAMP/PI3K-Akt signaling pathways and amino acid metabolism are associated with CUMS-MDD. The downregulations of chemokine signaling pathway, synaptic vesicle cycle, and nicotine addiction as well as the upregulations of calcium signaling pathway and tyrosine metabolism are associated with CUMS-resilience. The impairments of serotonergic/dopaminergic synapses and PI3K-Akt/MAPK signaling pathways in the NAc are associated with depression. The upregulation of these entities is associated with resilience. Consistent results from analyzing mRNA/miRNA and using different methods validate our finding and conclusion.

Treatment of Major Depressive Disorder in Pediatric Populations

Major depressive disorder (MDD) is a severe illness that afflicts about 16.6% of people over their lifetime. MDD is highly correlated with suicidality, and often first presents in adolescence. Unfortunately, many pediatric patients suffering from MDD go undiagnosed, and current evidence-based treatment options in the U.S. are limited to psychotherapy and two selective serotonin reuptake inhibitors approved by the United States Food and Drug Administration. Molecular mechanisms have been shown to play a role in MDD pathogenesis, progression, and response to medication, yet few studies have explored the role of these pathways in pediatric MDD. In this review, we outline the gravity and importance of MDD in pediatric patients, some challenges in diagnosis and treatment, current treatments available for pediatric patients, and research to investigate differences between pediatric and adult MDD. We hope that this review will provide an outline of the current understanding and treatment of MDD in pediatric patients, and provide thoughtful insights for future work that could advance our understanding of MDD in pediatric populations, and also identify new therapeutic strategies.

GABAergic neurons in nucleus accumbens are correlated to resilience and vulnerability to chronic stress for major depression

Background

Major depression, persistent low mood, is one of common psychiatric diseases. Chronic stressful life is believed to be a major risk factor that leads to dysfunctions of the limbic system. However, a large number of the individuals with experiencing chronic stress do not suffer from major depression, called as resilience. Endogenous mechanisms underlying neuronal invulnerability to chronic stress versus major depression are largely unknown. As GABAergic neurons are vulnerable to chronic stress and their impairments is associated with major depression, we have examined whether the invulnerability of GABAergic neurons in the limbic system is involved in resilience.

Results

GABAergic neurons in the nucleus accumbens from depression-like mice induced by chronic unpredictable mild stress appear the decreases in their GABA release, spiking capability and excitatory input reception, compared with those in resilience mice. The levels of decarboxylase and vesicular GABA transporters decrease in depression-like mice, but not resilience.

Materials and Methods

Mice were treated by chronic unpredictable mild stress for three weeks. Depression-like behaviors or resilience was confirmed by seeing whether their behaviors change significantly in sucrose preference, Y-maze and forced swimming tests. Mice from controls as well as depression and resilience in response to chronic unpredictable mild stress were studied in terms of GABAergic neuron activity in the nucleus accumbens by cell electrophysiology and protein chemistry.

Conclusions

The impairment of GABAergic neurons in the nucleus accumbens is associated with major depression. The invulnerability of GABAergic neurons to chronic stress may be one of cellular mechanisms for the resilience to chronic stress.

Antidepressant-Like Effects of Acupuncture-Insights From DNA Methylation and Histone Modifications of Brain-Derived Neurotrophic Factor

Sensitive and stable biomarkers that facilitate depression detection and monitor the antidepressant efficiency are currently unavailable. Thus, the objective is to investigate the potential of DNA methylation and histone modifications of brain-derived neurotrophic factor (BDNF) in monitoring severity and antidepressive effects of acupuncture. The depression rat model was imitated by social isolation and chronic unpredicted mild stress (CUMS). The expression of serum BDNF was detected by enzyme-linked immunosorbent assay (ELISA), the hippocampal BDNF, acetylation levels in histone H3 lysine 9 (acH3K9), and HDAC2 by Western blot, the hippocampal mRNA of BDNF by RT-polymerase chain reaction (PCR). The DNA methylation patterns of the promoter I of BDNF was detected by MS-PCR. We investigated that the expression of BDNF in serum and hippocampus were significantly downregulated compared with controls. The same trend was found in mRNA of BDNF. Notably, acupuncture reversed the downregulation of BDNF in serum and hippocampus and mRNA of BDNF compared with model group. Acupuncture reversed the CUMS-induced downregulation of hippocampal acH3K9. On the contrary, the CUMS-induced upregulation of hippocampal HDAC2 in model group was significantly reversed by acupuncture. Collectively, the antidepressant effect of acupuncture might be mediated by regulating the DNA methylation and histone modifications of BDNF, which may represent novel biomaker for detection of depression and monitoring severity and antidepressive effects.

Genome-wide transcriptome analysis of hippocampus in rats indicated that TLR/NLR signaling pathway was involved in the pathogenisis of depressive disorder induced by chronic restraint stress

Data from clinical investigations and laboratory fundings have provided preliminary evidence for the effectiveness and safety of acupuncture therapy in depression. However, the mechanisms underlying the antidepressant response of acupuncture are not fully elucidated. To elucidate the potential effects of acupuncture for depression on the hippocampal genome-wide transcriptome at the molecular level, we evaluated the transcriptomic profile of depression rats under treatment of acupuncture, and fluoxetine. We identified a very significant effect of acupucture intervention, with 107 genes differentially expressed in acupuncture vs. model group; while 41 genes between fluoxetine vs. model group. Notably, the 54 differentially expressed genes between acupuncture and fluoxetine showed the significantly different effect between acupuncture and fluoxetine. Through GO (gene ontology) functional term and KEGG (kyoto encyclopedia of genes and genomes) pathway analysis, we identified that the upregulation of gene sets were related to inflammatory response, innate immunity and immune response. We found that toll-like receptor signalling pathway and NOD like receptor signalling pathway were associated with the function of inflammatory response, innate immunity and immune response. Importantly, acupuncture reversed the upregulation of gene sets that were related to inflammatory response, innate immunity and immune response (including toll-like receptor signalling pathway and NOD like receptor signalling pathway), which might be critical for the pathogenesis of depression and provide evidence for the antidepressive effects of acupuncture by regulating inflammatory response, innate immunity and immune response via toll-like receptor signalling pathway and NOD like receptor signalling pathway.

Incoordination among Subcellular Compartments Is Associated with Depression-Like Behavior Induced by Chronic Mild Stress

BACKGROUND

Major depressive disorder is characterized as persistent low mood. A chronically stressful life in genetically susceptible individuals is presumably the major etiology that leads to dysfunctions of monoamine and hypothalamus-pituitary-adrenal axis. These pathogenic factors cause neuron atrophy in the limbic system for major depressive disorder. Cell-specific pathophysiology is unclear, so we investigated prelimbic cortical GABAergic neurons and their interaction with glutamatergic neurons in depression-like mice.

METHODS

Mice were treated with chronic unpredictable mild stress for 3 weeks until they expressed depression-like behaviors confirmed by sucrose preference, Y-maze, and forced swimming tests. The structures and functions of GABAergic and glutamatergic units in prelimbic cortices were studied by cell imaging and electrophysiology in chronic unpredictable mild stress-induced depression mice vs controls.

RESULTS

In depression-like mice, prelimbic cortical GABAergic neurons show incoordination among the subcellular compartments, such as decreased excitability and synaptic outputs as well as increased reception from excitatory inputs. GABAergic synapses on glutamatergic cells demonstrate decreased presynaptic innervation and increased postsynaptic responsiveness.

CONCLUSIONS

Chronic unpredictable mild stress-induced incoordination in prelimbic cortical GABAergic and glutamatergic neurons dysregulates their target neurons, which may be the pathological basis for depressive mood. The rebalance of compatibility among subcellular compartments would be an ideal strategy to treat neural disorders.

Emotional and Behavioral Disorders in 1.5th Generation, 2nd Generation Immigrant Children, and Foreign Adoptees

Existing theories (e.g., acculturative stress theory) cannot adequately explain why mental disorders in immigrants are less prevalent than in non-immigrants. In this paper, the culture-gene co-evolutionary theory of mental disorders was utilized to generate a novel hypothesis that connection to heritage culture reduces the risk for mental disorders in immigrant children. Four groups of children aged 2-17 years were identified from the 2007 United States National Survey of Children's Health: 1.5th generation immigrant children (n = 1378), 2nd generation immigrant children (n = 4194), foreign adoptees (n = 270), and non-immigrant children (n = 54,877). The 1.5th generation immigrant children's connection to their heritage culture is stronger than or similar to the 2nd generation immigrants, while the foreign adoptees have little connection to their birth culture. Controlling for age, sex, family type and SES, the odds for having ADD/ADHD, Conduct Disorder, Anxiety Disorder, and Depression diagnosis were the lowest for the 1.5th generation immigrant children, followed by the 2nd generation immigrant children and the foreign adoptees. The foreign adoptees and non-adopted children were similar in the odds of having these disorders. Connection to heritage culture might be the underlying mechanism that explained recent immigrants' lower rates of mental disorders.

Major depression in China-to-US immigrants and US-born Chinese Americans: testing a hypothesis from culture-gene co-evolutionary theory of mental disorders

BACKGROUND

In this study, the culture-gene co-evolutionary theory of mental disorders was used to test the hypothesis that major depression was less prevalent in China-to-US immigrants who migrated to the US as adults than in US-born adult Chinese Americans.

METHODS

Data from the Collaborative Psychiatric Epidemiology Surveys (CPES) were extracted for secondary data analyses on the rates of major depression disorder (MDD) and major depressive episode (MDE) in the two groups.

RESULTS

Findings showed that for life time MDD, the rates for China-to-US immigrant and US-born Chinese were 5.3% and 7.9% for men and 8.5% and 33.1% for women. For 12-month MDD, the corresponding rates were 2.2% and 3.4% for men, and 4.7% and 12.6% for women. For life time MDE, the corresponding rates were 6.8% and 8.8% for men; for women the rates were 8.5% and 33.1%. For 12-month MDE, the rates were 2.2% and 4.4% for men; the rates were 4.7% and 12.6% for women. Controlling for age, education level, income, BMI, marital status, and income-to-needs ratio, China-to-US immigrant women remained less likely to have life time major depression than US-born Chinese American women.

LIMITATIONS

While the study has the strength of utilizing nationally representative datasets, the approach is limited as the data sources lack the capacity to investigate how the strength of connection with the collectivist culture might be related to major depression in the immigrant group.

Role of orexin in the pathophysiology of depression: potential for pharmacological intervention

Depression is a devastating mental disorder with an increasing impact throughout the world, whereas the efficacy of currently available pharmacological treatment is still limited. Growing evidence from preclinical and clinical studies suggests that orexins (neuropeptides that are also known as hypocretins) and their receptors are involved in the physiopathology of depression. Indeed, the orexinergic system regulates functions that are disturbed in depressive states such as sleep, reward system, feeding behavior, the stress response and monoaminergic neurotransmission. Nevertheless, the precise role of orexins in behavioral and neurophysiological impairments observed in depression is still unclear. Both hypoactivity and hyperactivity of orexin signaling pathways have been found to be associated with depression. These discrepancies in the literature prompted the necessity for additional investigations, as the orexinergic system appears to be a promising target to treat the symptoms of depression. This assumption is underlined by recent data suggesting that pharmacological blockade of orexin receptors induces a robust antidepressant-like effect in an animal model of depression. Further preclinical and clinical studies are needed to progress the overall understanding of the orexinergic alterations in depression, which will eventually translate preliminary observations into real therapeutic potential. The aim of this paper is to provide an overview of human and animal research dedicated to the study of the specific involvement of orexins in depression, and to propose a framework in which disturbances of the orexinergic system are regarded as an integral component of the etiology of depression.

Raphe-Hippocampal Serotonin Neurotransmission In The Sex Related Differences of Adaptation to Stress: Focus on Serotonin-1A Receptor

Stress is the major predisposing and precipitating factor in the onset of depression which is the most significant mental health risk for women. Behavioral studies in animal models show that female sex though less affected by an acute stressor; exposure to repeated stressors induces coping deficits to impair adaptation in them. A decrease in the function of 5-hydroxytryptamine (5-HT; serotonin) in the hippocampus and an increased function of the 5-HT-1A receptor in the raphe nucleus coexist in depression. Pharmacological and neurochemical data are relevant that facilitation of serotonin neurotransmission via hippocampus due to desensitization of somatodendritic 5-HT1A receptors may lead to adaptation to stress. The present article reviews research on sex related differences of raphe-hippocampal serotonin neurotransmission to find a possible answer that may account for the sex differences of adaptation to stress reported in preclinical research and greater incidence of depression in women than men.

Sildenafil, a phosphodiesterase type 5 inhibitor, enhances the antidepressant activity of amitriptyline but not desipramine, in the forced swim test in mice

The cholinergic theory of depression highlights the involvement of muscarinic acetylcholine receptors in the neurobiology of mood disorders. The present study was designed to investigate the effect of sildenafil, a phosphodiesterase type 5 inhibitor which exhibits cholinomimetic properties, alone and in combination with scopolamine in the forced swim test in mice. Moreover, we assessed the ability of sildenafil to modify the antidepressant activity of two tricyclic antidepressants with distinct cholinolytic activity, amitriptyline and desipramine. Swim sessions were conducted by placing mice in glass cylinders filled with water for 6 min and the duration of behavioral immobility during the last 4 min of the test was evaluated. Locomotor activity was measured with photoresistor actimeters. To evaluate the potential pharmacokinetic interaction between amitriptyline and sildenafil, brain and serum concentrations of amitriptyline were determined by HPLC. Sildenafil (1.25-20 mg/kg) as well as scopolamine (0.5 mg/kg) and its combination with sildenafil (1.25 mg/kg) did not affect the total immobility time duration. However, joint administration of scopolamine with sildenafil at doses of 2.5 and 5 mg/kg significantly reduced immobility time as compared to control group. Moreover, co-administration of scopolamine with sildenafil at the highest dose (5 mg/kg) significantly decreased immobility time as compared to scopolamine-treated group. Sildenafil (1.25, 2.5 and 5 mg/kg) significantly enhanced the antidepressant activity of amitriptyline (5 mg/kg). No changes in anti-immobility action of desipramine (20 mg/kg) in combination with sildenafil (5, 10 and 20 mg/kg) were observed. Sildenafil did not affect amitriptyline level in both brain and serum. In conclusion, the present study suggests that sildenafil may enhance the activity of antidepressant drugs which exhibit cholinolytic activity.

Genome-wide linkage scans for major depression in individuals with alcohol dependence

Major depression is more prevalent among individuals with alcoholism than in the general population. Twin studies have found a moderate degree of genetic correlation for alcohol dependence (AD) and major depression (MD), suggesting the existence of loci that confer susceptibility to both disorders. The aim of the present study was to conduct genome-wide linkage analyses to identify loci and to replicate prior evidence for linkage to MD, and to search for linkage regions that may confer risk to the co-occurrence of depression and alcoholism in a sample of sib-pairs affected with AD. A set of 1020 microsatellite markers (average marker spacing of 4cM) were genotyped in 1289 subjects, which consisted of 473 informative families for analysis of depressive traits and 626 sibling pairs for analysis of symptoms of MD and AD. For univariate linkage results for depression, there were six regions (1q, 2p, 4q, 12q, 13q, and 22q) with multipoint LOD scores in excess of 1.00; the highest peak was on chromosome 4q32.3 near marker D4S2952 (LOD=2.17, p=0.0008) for symptoms of MD. Bivariate linkage analysis of symptoms of MD and AD identified only one region at 22q11.21 with LOD>1, which overlapped with the region for symptoms of MD. Several of these regions replicate previously reported linkage results for major depression and emotion-related traits and events, such as neuroticism and suicide attempts. These identified genomic locations, together with results from prior studies, indicate potential regions of interests that may contain susceptibility loci to the risk of depression among individuals with alcohol dependence.

Investigation of an epistastic effect between a set of TAAR6 and HSP-70 genes variations and major mood disorders

Epistasis, the interaction between genes, is a topic of current interest in molecular and quantitative genetics. We have further studied a previously investigated sample of 187 major depressive disorder (MDD) patients, 171 bipolar disorder (BD) patients, and 288 controls, and tried to analyze the interaction between a set of variations of independent genes: the trace amine receptor 6 (rs4305745, rs8192625, rs7452939, rs6903874, and rs6937506) and the heat shock protein 70 (rs562047, rs1061581, rs2227956). The multifactor dimensionality reduction (MDR) method was applied and the covariates associated with diagnosis were also controlled. A significant predictive value of specific interactions between genotypes located in the investigated genes was found. We then report preliminary evidence that the epistasis between trace amine receptor 6 and heat shock protein 70 variations may compose a risk profile for major mood disorders. The level of statistical significance (P < 0.001) and the testing balancing accuracy over 0.62 suggest a cautious optimism toward this result, although the possibility of false positivity warrants further analyses in independent samples.

The effect of depression, BDNF gene val66met polymorphism and gender on serum BDNF levels

OBJECTIVE

To determine the effect of BDNF gene val66met polymorphism on serum BDNF levels in drug-free patients with major depressive disorder (MDD) and healthy subjects, that differ by gender.

METHODS

Sixty-six drug-free patients (19 males+47 females) with non-psychotic MDD and fifty-six healthy controls (18 males+38 females) were recruited. Three-way ANOVA was employed to analyze the effect of mental health status, met-carriage and gender on Hamilton Depression Rating Scale (HDRS) scores and serum BDNF levels, by using the MIXED Procedure (SAS).

RESULTS

Patients had a lower serum BDNF level than healthy subjects (22.47 vs. 27.49; p<0.0001). Met-carrier patients had a higher HDRS score than Val homozygote's (25.99 vs. 22.99, p<0.02). Serum BDNF level for met-carrier subjects (patients+controls) was lower than Val homozygote subjects (23.08 vs. 26.87; p<0.002). However, there were no effects of two-way interactions of met-carriage and mental health status on HDRS scores and serum BDNF levels. There was no gender effect on HDRS scores in the patients. Overall, male subjects (patients+controls) had a higher serum BDNF level than female subjects (26.87 vs. 23.08; p<0.002). However, there were no effects of two-way interactions of gender with mental health status and met-carriage on serum BDNF levels.

CONCLUSIONS

We replicated the previous findings of lower serum BDNF levels during depression and in females. In addition, we found that met-carriage had an effect in reducing serum BDNF levels, regardless of gender and depression. Further animal and human studies with a larger sample size should investigate whether BDNF val66met polymorphism could alter brain and serum BDNF levels.