Genetic variations in the serotonin transporter gene-linked polymorphic region influence attraction for a favorite person and the associated interactions between the central nervous and immune systems

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.

Preliminary evidence that sub-chronic citalopram triggers the re-evaluation of value in intimate partnerships

Depression frequently involves disrupted inter-personal relationships, while treatment with serotonergic anti-depressants can interfere with libido and sexual function. However, little is known about how serotonin activity influences appraisals of intimate partnerships. Learning more could help to specify how serotonergic mechanisms mediate social isolation in psychiatric illness. Forty-four healthy heterosexual adults, currently in romantic relationships, received 8 days treatment with the selective serotonin re-uptake inhibitor citalopram (N = 21; 10 male) or placebo (N = 23; 12 male). Participants viewed photographs of unknown, heterosexual couples and made a series of judgements about their relationships. Participants also indicated the importance of relationship features in their own close partnerships, and close partnerships generally. Citalopram reduced the rated quality of couples' physical relationships and the importance attributed to physical and intimate aspects of participants' own relationships. In contrast, citalopram also enhanced the evaluated worth of mutual trust in relationships. Amongst males, citalopram was associated with judgements of reduced turbulence and bickering in others' relationships, and increased male dominance. These data constitute preliminary evidence that enhancing serotonin activity modulates cognitions about sexual activity as part of a re-appraisal of sources of value within close intimate relationships, enhancing the judged importance of longer-term benefits of trust and shared experiences.

A dialogue between the immune system and brain, spoken in the language of serotonin

Neuropsychiatric disorders have long been linked to both immune system activation and alterations in serotonin (5-HT) signaling. In the CNS, the contributions of 5-HT modulate a broad range of targets, most notably, hypothalamic, limbic and cortical circuits linked to the control of mood and mood disorders. In the periphery, many are aware of the production and actions of 5-HT in the gut but are unaware that the molecule and its receptors are also present in the immune system where evidence suggests they contribute to the both innate and adaptive responses. In addition, there is clear evidence that the immune system communicates to the brain via both humoral and neuronal mechanisms, and that CNS 5-HT neurons are a direct or indirect target for these actions. Following a brief primer on the immune system, we describe our current understanding of the synthesis, release, and actions of 5-HT in modulating immune function, including the expression of 5-HT biosynthetic enzymes, receptors, and transporters that are typically studied with respect to the roles in the CNS. We then orient our presentation to recent findings that pro-inflammatory cytokines can modulate CNS 5-HT signaling, leading to a conceptualization that among the many roles of 5-HT in the body is an integrated physiological and behavioral response to inflammatory events and pathogens. From this perspective, altered 5-HT/immune conversations are likely to contribute to risk for neurobehavioral disorders historically linked to compromised 5-HT function or ameliorated by 5-HT targeted medications, including depression and anxiety disorders, obsessive-compulsive disorder (OCD), and autism. Our review raises the question as to whether genetic variation impacting 5-HT signaling genes may contribute to maladaptive behavior as much through perturbed immune system modulation as through altered brain mechanisms. Conversely, targeting the immune system for therapeutic development may provide an important opportunity to treat mental illness.