Epistatic interaction of BDNF and COMT on the frontostriatal system

The influence of COMT rs4680 on functional connectivity in healthy adults: A systematic review

The aim of this systematic review was to qualitatively synthesise the available research that investigated the influence of COMT genotype at SNP rs4680 on both task-based and resting-state connectivity in healthy adults. Thirty-five studies were identified that met inclusion criteria. Of the included studies, 20 studies reported resting-state findings and 16 studies reported task-based findings (emotion-processing, memory, working memory, reward-based learning and executive function). Studies were highly heterogeneous but an overall trend towards an association of the Val allele with greater resting-state connectivity and the Met allele with greater task-based connectivity is reported. A possible interpretation of current findings is discussed, whereby the Val allele is associated with improved cognitive flexibility allowing integration of novel relevant stimuli, and the Met allele allows improved sustained attention and targeted neural processing, particularly between limbic regions and prefrontal cortex. The most promising brain regions implicated in a COMT genotype influence on functional connectivity include prefrontal regions, amygdala and hippocampus.

Mice engineered to mimic a common Val66Met polymorphism in the BDNF gene show greater sensitivity to reversal in environmental contingencies

•

A new line of mice,Val68Met, mimic human BDNF Val66Met polymorphism.

•

New knock-in BDNF Met mice reverse more efficiently than Val in two separate tasks.

•

Supports theory that BDNF Met allele confers greater sensitivity to the environment.

•

Reversal performance can be dissociated from go/no-go and extinction performance.

•

Phenotypes differ between newer and older BDNF Val66Met mouse models.

•

A common human polymorphism in the gene that encodes brain derived neurotrophic factor (BDNF), Val66Met, is considered a marker of vulnerability for mental health issues and has been associated with cognitive impairment. An alternate framework has been proposed in which “risk alleles” are reinterpreted as “plasticity alleles” that confer vulnerability in adverse environments and positive effects in neutral or positive environments (Belsky et al., 2009). These frameworks produce divergent predictions for tests of learning and cognitive flexibility. Here, we examined multiple aspects of learning and cognitive flexibility in a relatively new BDNF Val66Met mouse model (BDNF Val68Met, Warnault et al., 2016), including multiple choice discrimination and reversal, go/no-go learning and reversal, and appetitive extinction learning. We found that mice homozygous for the Met allele show more efficient reversal learning in two different paradigms, but learn at rates comparable to Val homozygotes on the multiple choice discrimination task, a go/no-go task, and in appetitive extinction. Our results dissociate reversal performance from go/no-go learning and appetitive extinction and support the plasticity allele framework that suggests BDNF Met carriers are potentially more sensitive to changes in the environment.

Interaction Effects of BDNF and COMT Genes on Resting-State Brain Activity and Working Memory

Catechol-O-methyltransferase (COMT) and brain-derived neurotrophic factor (BDNF) genes have been found to interactively influence working memory (WM) as well as brain activation during WM tasks. However, whether the two genes have interactive effects on resting-state activities of the brain and whether these spontaneous activations correlate with WM are still unknown. This study included behavioral data from WM tasks and genetic data (COMT rs4680 and BDNF Val66Met) from 417 healthy Chinese adults and resting-state fMRI data from 298 of them. Significant interactive effects of BDNF and COMT were found for WM performance as well as for resting-state regional homogeneity (ReHo) in WM-related brain areas, including the left medial frontal gyrus (lMeFG), left superior frontal gyrus (lSFG), right superior and medial frontal gyrus (rSMFG), right medial orbitofrontal gyrus (rMOFG), right middle frontal gyrus (rMFG), precuneus, bilateral superior temporal gyrus, left superior occipital gyrus, right middle occipital gyrus, and right inferior parietal lobule. Simple effects analyses showed that compared to other genotypes, subjects with COMT-VV/BDNF-VV had higher WM and lower ReHo in all five frontal brain areas. The results supported the hypothesis that COMT and BDNF polymorphisms influence WM performance and spontaneous brain activity (i.e., ReHo).

Interaction of COMT rs4680 and BDNF rs6265 polymorphisms on functional connectivity density of the left frontal eye field in healthy young adults

As modulators of dopamine availability and release in the brain, COMT and BDNF polymorphisms have demonstrated interactions on human cognition; however, the underlying neural mechanisms remain largely unknown. In this study, we aimed to investigate the interactions of COMT rs4680 and BDNF rs6265 on global functional connectivity density (gFCD) of the brain in 265 healthy young subjects. We found a significant COMT × BDNF interaction on the gFCD in the left frontal eye field (FEF), showing an inverted U-shape modulation by the presumed dopamine signaling. This finding was consistently repeated in the gFCD analyses using other four connection thresholds. Our findings reveal a COMT × BDNF interaction on the FCD in the left FEF, which may be helpful for understanding the neural mechanisms of the COMT × BDNF interactions on the FEF-related cognitive functions. Hum Brain Mapp 37:2468-2478, 2016. © 2016 Wiley Periodicals, Inc.