Cerebral 5-HT2A receptor and serotonin transporter binding in humans are not affected by the val66met BDNF polymorphism status or blood BDNF levels

Genetic contributions to brain serotonin transporter levels in healthy adults

The serotonin transporter (5-HTT) critically shapes serotonin neurotransmission by regulating extracellular brain serotonin levels; it remains unclear to what extent 5-HTT levels in the human brain are genetically determined. Here we applied [11C]DASB positron emission tomography to image brain 5-HTT levels and evaluated associations with five common serotonin-related genetic variants that might indirectly regulate 5-HTT levels (BDNF rs6265, SLC6A4 5-HTTLPR, HTR1A rs6295, HTR2A rs7333412, and MAOA rs1137070) in 140 healthy volunteers. In addition, we explored whether these variants could predict in vivo 5-HTT levels using a five-fold cross-validation random forest framework. MAOA rs1137070 T-carriers showed significantly higher brain 5-HTT levels compared to C-homozygotes (2-11% across caudate, putamen, midbrain, thalamus, hippocampus, amygdala and neocortex). We did not observe significant associations for the HTR1A rs6295 and HTR2A rs7333412 genotypes. Our previously observed lower subcortical 5-HTT availability for rs6265 met-carriers remained in the presence of these additional variants. Despite this significant association, our prediction models showed that genotype moderately improved prediction of 5-HTT in caudate, but effects were not statistically significant after adjustment for multiple comparisons. Our observations provide additional evidence that serotonin-related genetic variants modulate adult human brain serotonin neurotransmission.

The association between brain serotonin transporter binding and impulsivity and aggression in healthy individuals

The serotonin system plays a critical role in the modulation of impulsive aggression. Although serotonin transporters (SERT) are key in modulating synaptic serotonin levels, few studies have investigated the role of SERT levels in human impulsive aggression. The aim of this study was to investigate whether brain SERT levels are associated with trait impulsive aggression. We included 148 healthy individuals (mean age 29.3 ± 13.0, range 18-80 years, 91 females) who had undergone positron emission positron (PET) examinations with the SERT tracer [11C]DASB and filled in self-report questionnaires of trait aggression, trait impulsivity and state aggression. We evaluated the association between cerebral SERT binding (BPND) and trait impulsive aggression in a latent variable model, with one latent variable (LVSERT) modelled from SERT BPND in frontostriatal and frontolimbic networks implicated in impulsive aggression, and another latent variable (LVIA) modelled from various trait measures of impulsivity and aggression. The LVSERT was not significantly associated with the LVIA (p = 0.8). Post-hoc univariate analyses did not reveal any significant associations between regional SERT levels and trait aggression, trait impulsivity or state aggression, but we found that state aggression at the day of PET scan was significantly lower in LA/LA homozygotes vs S-carriers of the 5-HTTLPR gene (p = 0.008). We conclude that brain SERT binding was not related to variations in trait impulsive aggression or state aggression. Our findings do not support that SERT is involved in mediating the serotonergic effects on aggression and impulsivity, at least not in individuals with non-pathological levels of impulsive aggression.

Epistasis of HTR1A and BDNF risk genes alters cortical 5-HT1A receptor binding: PET results link genotype to molecular phenotype in depression

Alterations of the 5-HT_1A receptor and BDNF have consistently been associated with affective disorders. Two functional single nucleotide polymorphisms (SNPs), rs6295 of the serotonin 1A receptor gene (HTR1A) and rs6265 of brain-derived neurotrophic factor gene (BDNF), may impact transcriptional regulation and expression of the 5-HT_1A receptor. Here we investigated interaction effects of rs6295 and rs6265 on 5-HT_1A receptor binding. Forty-six healthy subjects were scanned with PET using the radioligand [carbonyl-¹¹C]WAY-100635. Genotyping was performed for rs6265 and rs6295. Subjects showing a genotype with at least three risk alleles (G of rs6295 or A of rs6265) were compared to control genotypes. Cortical surface binding potential (BP_ND) was computed for 32 cortical regions of interest (ROI). Mixed model was applied to study main and interaction effects of ROI and genotype. ANOVA was used for post hoc analyses. Individuals with the risk genotypes exhibited an increase in 5-HT_1A receptor binding by an average of 17% (mean BP_ND 3.56 ± 0.74 vs. 2.96 ± 0.88). Mixed model produced an interaction effect of ROI and genotype on BP_ND and differences could be demonstrated in 10 ROI post hoc. The combination of disadvantageous allelic expression of rs6295 and rs6265 may result in a 5-HT_1A receptor profile comparable to affective disorders as increased 5-HT_1A receptor binding is a well published phenotype of depression. Thus, epistasis between BDNF and HTR1A may contribute to the multifactorial risk for affective disorders and our results strongly advocate further research on this genetic signature in affective disorders.

BDNF val66met association with serotonin transporter binding in healthy humans

The serotonin transporter (5-HTT) is a key feature of the serotonin system, which is involved in behavior, cognition and personality and implicated in neuropsychiatric illnesses including depression. The brain-derived neurotrophic factor (BDNF) val66met and 5-HTTLPR polymorphisms have predicted differences in 5-HTT levels in humans but with equivocal results, possibly due to limited sample sizes. Within the current study we evaluated these genetic predictors of 5-HTT binding with [¹¹C]DASB positron emission tomography (PET) in a comparatively large cohort of 144 healthy individuals. We used a latent variable model to determine genetic effects on a latent variable (5-HTT_LV), reflecting shared correlation across regional 5-HTT binding (amygdala, caudate, hippocampus, midbrain, neocortex, putamen and thalamus). Our data supported a significant BDNF val66met effect on 5-HTT_LV such that met-carriers showed 2-7% higher subcortical 5-HTT binding compared with val/val individuals (P=0.042). Our data did not support a BDNF val66met effect in neocortex and 5-HTTLPR did not significantly predict 5-HTT_LV. We did not observe evidence for an interaction between genotypes. Our findings indicate that met-carriers have increased subcortical 5-HTT binding. The small difference suggests limited statistical power may explain previously reported null effects. Our finding adds to emerging evidence that BDNF val66met contributes to differences in the human brain serotonin system, informing how variability in the 5-HTT level emerges and may represent an important molecular mediator of BDNF val66met effects on behavior and related risk for neuropsychiatric illness.

Brain-Derived Neurotrophic Factor and Antidepressive Effect of Electroconvulsive Therapy: Systematic Review and Meta-Analyses of the Preclinical and Clinical Literature

Emerging data suggest that Electro-Convulsive Treatment (ECT) may reduce depressive symptoms by increasing the expression of Brain-Derived Neurotrophic Factor (BDNF). Yet, conflicting findings have been reported. For this reason we performed a systematic review and meta-analysis of the preclinical and clinical literature on the association between ECT treatment (ECS in animals) and changes in BDNF concentrations and their effect on behavior. In addition, regional brain expression of BDNF in mouse and human brains were compared using Allen Brain Atlas. ECS, over sham, increased BDNF mRNA and protein in animal brain (effect size [Hedge’s g]: 0.38―0.54; 258 effect-size estimates, N = 4,284) but not in serum (g = 0.06, 95% CI = -0.05―0.17). In humans, plasma but not serum BDNF increased following ECT (g = 0.72 vs. g = 0.14; 23 effect sizes, n = 281). The gradient of the BDNF increment in animal brains corresponded to the gradient of the BDNF gene expression according to the Allen brain atlas. Effect-size estimates were larger following more ECT sessions in animals (r = 0.37, P < .0001) and in humans (r = 0.55; P = 0.05). There were some indications that the increase in BDNF expression was associated with behavioral changes in rodents, but not in humans. We conclude that ECS in rodents and ECT in humans increase BDNF concentrations but this is not consistently associated with changes in behavior.

The Center for Integrated Molecular Brain Imaging (Cimbi) database

We here describe a multimodality neuroimaging containing data from healthy volunteers and patients, acquired within the Lundbeck Foundation Center for Integrated Molecular Brain Imaging (Cimbi) in Copenhagen, Denmark. The data is of particular relevance for neurobiological research questions related to the serotonergic transmitter system with its normative data on the serotonergic subtype receptors 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT4 and the 5-HT transporter (5-HTT), but can easily serve other purposes. The Cimbi database and Cimbi biobank were formally established in 2008 with the purpose to store the wealth of Cimbi-acquired data in a highly structured and standardized manner in accordance with the regulations issued by the Danish Data Protection Agency as well as to provide a quality-controlled resource for future hypothesis-generating and hypothesis-driven studies. The Cimbi database currently comprises a total of 1100 PET and 1000 structural and functional MRI scans and it holds a multitude of additional data, such as genetic and biochemical data, and scores from 17 self-reported questionnaires and from 11 neuropsychological paper/computer tests. The database associated Cimbi biobank currently contains blood and in some instances saliva samples from about 500 healthy volunteers and 300 patients with e.g., major depression, dementia, substance abuse, obesity, and impulsive aggression. Data continue to be added to the Cimbi database and biobank.

BDNF Val66met and 5-HTTLPR polymorphisms predict a human in vivo marker for brain serotonin levels

Brain-derived neurotrophic factor (BDNF) has been implicated in multiple aspects of brain function including regulation of serotonin signaling. The BDNF val66met polymorphism (rs6265) has been linked to aspects of serotonin signaling in humans but its effects are not well understood. To address this, we evaluated whether BDNF val66met was predictive of a putative marker of brain serotonin levels, serotonin 4 receptor (5-HT4 ) binding assessed with [11C]SB207145 positron emission tomography, which has also been associated with the serotonin-transporter-linked polymorphic region (5-HTTLPR) polymorphism. We applied a linear latent variable model (LVM) using regional 5-HT4 binding values (neocortex, amygdala, caudate, hippocampus, and putamen) from 68 healthy humans, allowing us to explicitly model brain-wide and region-specific genotype effects on 5-HT4 binding. Our data supported an LVM wherein BDNF val66met significantly predicted a LV reflecting [11C]SB207145 binding across regions (P = 0.005). BDNF val66met met-carriers showed 2-9% higher binding relative to val/val homozygotes. In contrast, 5-HTTLPR did not predict the LV but S-carriers showed 7% lower neocortical binding relative to LL homozygotes (P = 7.3 × 10(-6)). We observed no evidence for genetic interaction. Our findings indicate that BDNF val66met significantly predicts a common regulator of brain [11C]SB207145 binding, which we hypothesize reflects brain serotonin levels. In contrast, our data indicate that 5-HTTLPR specifically affects 5-HT4 binding in the neocortex. These findings implicate serotonin signaling as an important molecular mediator underlying the effects of BDNF val66met and 5-HTTLPR on behavior and related risk for neuropsychiatric illness in humans.

Exploring the impact of BDNF Val66Met genotype on serotonin transporter and serotonin-1A receptor binding

Background

The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism (rs6265) may impact on the in-vivo binding of important serotonergic structures such as the serotonin transporter (5-HTT) and the serotonin-1A (5-HT_1A) receptor. Previous positron emission tomography (PET) studies on the association between Val66Met and 5-HTT and 5-HT_1A binding potential (BP_ND) have demonstrated equivocal results.

Methods

We conducted an imaging genetics study investigating the effect of Val66Met genotype on 5-HTT or 5-HT_1A BP_ND in 92 subjects. Forty-one subjects (25 healthy subjects and 16 depressive patients) underwent genotyping for Val66Met and PET imaging with the 5-HTT specific radioligand [¹¹C]DASB. Additionally, in 51 healthy subjects Val66Met genotypes and 5-HT_1A binding with the radioligand [carbonyl-¹¹C]WAY-100635 were ascertained. Voxel-wise and region of interest-based analyses of variance were used to examine the influence of Val66Met on 5-HTT and 5-HT_1A BP_ND.

Results

No significant differences of 5-HTT nor 5-HT_1A BP_ND between BDNF Val66Met genotype groups (val/val vs. met-carrier) were detected. There was no interaction between depression and Val66Met genotype status.

Conclusion

In line with previous data, our work confirms an absent effect of BDNF Val66Met on two major serotonergic structures. These results could suggest that altered protein expression associated with genetic variants, might be compensated invivo by several levels of unknown feedback mechanisms. In conclusion, Val66Met genotype status is not associated with changes of in-vivo binding of 5-HTT and 5-HT_1A receptors in human subjects.

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

BACKGROUND/AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

Association of brain serotonin transporter availability and brain-derived neurotrophic factor in models of serotonin transporter genotypes in healthy subjects

The S-allele of functional polymorphisms of the serotonin transporter (SERT) gene has been demonstrated to have lower transcriptional activity compared with the L-allele, which shows low expression of SERT in the brain. However, this finding cannot be consistently replicated in vivo. The aim of this study was to determine the availability of SERT based on SERT genotype. We also examined the relationship between brain-derived neurotrophic factor (BDNF) and the availability of SERT. Sixty-two healthy subjects were recruited. Each subject underwent single-photon emission computed tomography with I-ADAM (I-labeled 2-([2-({dimethylamino}methyl)phenyl]thio)-5-iodophenylamine) for imaging SERT in the brain. The specific uptake ratio was measured, and venous blood was drawn when the subject underwent single-photon emission computed tomography to evaluate BDNF levels and SERT genotype. All subjects expressed SERT genotypes that were consistent with a biallelic model, and 26 subjects had SERT genotypes that were consistent with a triallelic model. No differences in specific uptake ratio were detected in the midbrain, putamen, caudate, and thalamus based on the SERT genotype using the biallelic and triallelic models. Interestingly, The Pearson correlation coefficient revealed a positive correlation between BDNF and SERT availability. In particular, this relationship was observed in homozygous S-allele expression and a genotype with low functional expression (SaSa/SaLg) in the biallelic and triallelic models of SERT genotypes, respectively. This finding might explain why the SS genotype of SERT did not increase the risk of major depressive disorder in Asian populations and implicate an important role of BDNF in the patients, who has the SS genotype of the SERT gene.