A polymorphism of serotonin 2A receptor (5-HT 2A R) influences delay discounting

A Genetic Variation in the Y Chromosome Among Modern Japanese Males Related to Several Physiological and Psychological Characteristics

Previous studies in population genetics have proposed that the Y-chromosomal (Y-DNA) haplogroup D ancestor likely originated from Africa. The haplogroup D branch next started Out-of-Africa migration, rapidly expanded across Eurasia, and later diversified in East Asia. Y-DNA haplogroup D-M55, one of the branches of haplogroup D, is only found in modern Japanese males, suggesting that individuals with Y-DNA haplogroup D migrated from the Eurasian continent. Based on previous observations, Y-DNA haplogroup D is expected to be associated with some male characteristics including personality. Therefore, this study investigated whether the Y-DNA haplogroup D-M55 is associated with several physiological and psychological characteristics, including exploratory motivation and human relationship-related perception. We recruited Japanese young adult males and females and investigated the association between Y-DNA haplogroup D-M55, physiological [body mass index (BMI)], and several psychological parameters [perceived number of close friends, behavioral inhibition system/behavioral activation system (BIS/BAS), perceived happiness, and perceived loneliness]. The results indicated that males with haplogroup D-M55 had a higher BMI and more close friends, compared with non-carrier males. Additional multiple regression analyses, which tested the hypothesis that haplogroup D-M55 predicts BMI and perceived number of close friends, confirmed our hypothesis, even after controlling for the potentially confounding variables of age and sex. We also analyzed the gene-gene interaction between haplogroup D-M55 and an autosomal gene polymorphism associated with BMI and human relationships, such as the dopamine D2 receptor gene (DRD2: rs1800497). Results showed gene-gene interactions between haplogroups D-M55 and DRD2 in BMI. Based on these findings, it is demonstrated that Y-DNA haplogroup D is associated with human personality.

Methylation Patterns of the HTR2A Associate With Relapse-Related Behaviors in Cocaine-Dependent Participants

Relapse during abstinence in cocaine use disorder (CUD) is often hastened by high impulsivity (predisposition toward rapid unplanned reactions to stimuli without regard to negative consequences) and high cue reactivity (e.g., attentional bias towards drug reward stimuli). A deeper understanding of the degree to which individual biological differences predict or promote problematic behaviors may afford opportunities for clinical refinement and optimization of CUD diagnostics and/or therapies. Preclinical evidence implicates serotonin (5-HT) neurotransmission through the 5-HT2A receptor (5-HT2AR) as a driver of individual differences in these relapse-related behaviors. Regulation of 5-HT2AR function occurs through many mechanisms, including DNA methylation of the HTR2A gene, an epigenetic modification linked with the memory of gene-environment interactions. In the present study, we tested the hypothesis that methylation of the HTR2A may associate with relapse-related behavioral vulnerability in cocaine-dependent participants versus healthy controls. Impulsivity was assessed by self-report (Barratt Impulsiveness Scale; BIS-11) and the delay discounting task, while levels of cue reactivity were determined by performance in the cocaine-word Stroop task. Genomic DNA was extracted from lymphocytes and the bisulfite-treated DNA was subjected to pyrosequencing to determine degree of methylation at four cytosine residues of the HTR2A promoter (-1439, -1420, -1224, -253). We found that the percent methylation at site -1224 after correction for age trended towards a positive correlation with total BIS-11 scores in cocaine users, but not healthy controls. Percent methylation at site -1420 negatively correlated with rates of delay discounting in healthy controls, but not cocaine users. Lastly, the percent methylation at site -253 positively correlated with attentional bias toward cocaine-associated cues. DNA methylation at these cytosine residues of the HTR2A promoter may be differentially associated with impulsivity or cocaine-associated environmental cues. Taken together, these data suggest that methylation of the HTR2A may contribute to individual differences in relapse-related behaviors in CUD.

Cultural Similarities and Differences in Social Discounting: The Mediating Role of Harmony-Seeking

One's generosity to others declines as a function of social distance, which is known as social discounting. We examined cultural similarities and differences in social discounting and the mediating roles of the two aspects of interdependence (self-expression and distinctiveness of the self) as well as the two aspects of independence (harmony-seeking and rejection avoidance). Using the same procedure that previous researchers used to test North Americans, Study 1 showed that compared to North Americans, Japanese discount more steeply a partner's outcomes compared to their own future outcomes, whereas the decrease in the subjective value of the partner's outcomes accelerates less as a function of social distance. To examine the cultural similarities and differences in social discounting in more detail, Study 2 tested Japanese and Germans and found that the hyperbolic with exponent model fitted the participants' discounting behaviors better than the other models, except for the loss condition in Germans where the utility of the q-exponential model was indicated. Moreover, although the social discounting rate was higher in Japanese than in Germans, the cultural difference was limited to the gain frame. However, the decline in a person's generosity accelerated less as a function of social distance in Japanese than in Germans. Furthermore, the cultural difference in the social discounting in gains was mediated by the level of harmony-seeking, which was higher in Germans than in Japanese. Implications for individuals' generosity against the backdrop of cultural characteristics are discussed.

Serotonergic gene polymorphisms (5-HTTLPR, 5HTR1A, 5HTR2A), and population differences in aggression: traditional (Hadza and Datoga) and industrial (Russians) populations compared

Background

Current knowledge on genetic basis of aggressive behavior is still contradictory. This may be due to the fact that the majority of studies targeting associations between candidate genes and aggression are conducted on industrial societies and mainly dealing with various types of psychopathology and disorders. Because of that, our study was carried on healthy adult individuals of both sex (n = 853).

Methods

Three populations were examined: two traditional (Hadza and Datoga) and one industrial (Russians), and the association of aggression with the following polymorphisms 5-HTTLPR, rs6295 (5HTR1A gene), and rs6311 (5HTR2A gene) were tested. Aggression was measured as total self-ratings on Buss-Perry Aggression Questionnaire.

Results

Distributions of allelic frequencies of 5-HTTLPR and 5HTR1A polymorphisms were significantly different among the three populations. Consequently, the association analyses for these two candidate genes were carried out separately for each population, while for the 5HTR2A polymorphism, it was conducted on the pooled data that made possible to introduce ethnic factor in the ANOVA model. The traditional biometrical approach revealed no sex differences in total aggression in all three samples. The three-way ANOVA (μ + 5-HTTLPR + 5HTR1A + 5HTR2A +ε) with measures of self-reported total aggression as dependent variable revealed significant effect of the second serotonin receptor gene polymorphism for the Hadza sample. For the Datoga, the interaction effect between 5-HTTLPR and 5HTR1A was significant. No significant effects of the used polymorphisms were obtained for Russians. The results of two-way ANOVA with ethnicity and the 5HTR2A polymorphism as main effects and their interactions revealed the highly significant effect of ethnicity, 5HTR2A polymorphism, and their interaction on total aggression.

Conclusions

Our data provided obvious confirmation for the necessity to consider the population origin, as well as cultural background of tested individuals, while searching for associations between genes and behavior, and demonstrated the role of cultural attitudes towards the use of in-group aggression. Our data partly explained the reasons for disagreement in results of different teams, searching for candidate-gene associations with behavior without considerations of culturally desirable norms. Previous studies suggested that the 5HTR2A gene polymorphism associates with aggression and criminality. Our data extended these findings, demonstrating the role of rs6311 (5HTR2A gene) in aggression in adult healthy men and women from our samples. We found that G-allele carriers were rated higher on total aggression.

Neural and Genetic Correlates of the Social Sharing of Happiness

Happiness is regarded as one of the most fundamental human goals. Given recent reports that positive feelings are contagious (e.g., the presence of a happy person enhances others' happiness) because of the human ability to empathize (i.e., sharing emotions), empathic ability may be a key factor in increasing one's own subjective level of happiness. Based on previous studies indicating that a single nucleotide polymorphism in the serotonin 2A receptor gene [HTR2A rs6311 guanine (G) vs. adenine (A)] is associated with sensitivity to emotional stimuli and several mental disorders such as depression, we predicted that the polymorphism might be associated with the effect of sharing happiness. To elucidate the neural and genetic correlates of the effect of sharing happiness, we first performed functional magnetic resonance imaging (fMRI) during a “happy feelings” evocation task (emotional event imagination task), during which we manipulated the valence of the imagined event (positive, neutral, or negative), as well as the presence of a friend experiencing a positive-valence event (presence or absence). We recruited young adult women for this fMRI study because empathic ability may be higher in women than in men. Participants felt happier (p < 0.01) and the mentalizing/theory-of-mind network, which spans the medial prefrontal cortex, temporoparietal junction, temporal poles, and precuneus, was significantly more active (p < 0.05) in the presence condition than in the absence condition regardless of event valence. Moreover, participants with the GG (p < 0.01) and AG (p < 0.05) genotypes of HTR2A experienced happier feelings as well as greater activation of a part of the mentalizing/theory-of-mind network (p < 0.05) during empathy for happiness (neutral/presence condition) than those with the AA genotype. In a follow-up study with a vignette-based questionnaire conducted in a relatively large sample, male and female participants were presented with the same imagined events wherein their valence and the presence of a friend were manipulated. Results showed genetic differences in happiness-related empathy regardless of sex (p < 0.05). Findings suggest that HTR2A polymorphisms are associated with the effect of sharing happiness by modulating the activity of the mentalizing/theory-of-mind network.