Serotonin (5-HT) is an important neurotransmitter, which is involved in various physiological functions, such as emotion, cognition, motion, appetite and rhythm. Until now, there are many studies about serotonin system, but systematic researches about the genetic effect of serotonin system related genes on the brain networks are still scarce. So, based on the multi-modal neuroimage data, this dissertation systematically investigates the impact of gene polymorphisms in 5-HT system on the brain networks in a large sample of Han Chinese by using imaging genetics method. This research reveals the neural basis for the effect of 5-HT system on the emotional process and cognitive function, and helps us to understand the association between 5-HT system and neuropsychiatric disorders. The main contents and contributions in the dissertation are as follows: Serotonin-transporter-linked polymorphic region (5-HTTLPR) is a polymorphism in the promoter region of serotonin transporter (5-HTT) gene, which is associated with mood disorders. The studies in Caucasian have shown that the S allele of 5-HTTLPR is associated with higher risk for depression and anxiety. However, the results in Asian are contrary to the findings in Caucasian. We systematically investigated the effect of 5-HTTLPR in Han Chinese by combining behavioral and magnetic resonance imaging (MRI) data. This study found that L allele was associated with higher level of anxiety and reduced amygdala-prefrontal cortex (PFC) functional and structural connectivity in Han Chinese, which is also contrary to the findings in Caucasian. Moreover, the connectivity between amygdala and PFC was correlated with depression or anxiety scores. Therefore, the study demonstrates that the amygdala-PFC connectivity is a useful endophenotype linking gene and mood disorders. Meanwhile, this work suggests that there is the fundamental genetic difference between Asian and Caucasian. So the ethnic background should be considered as an important factor in gene-disorder association analysis and treatment for mood disorders. Previous studies mainly focused on the amygdala-PFC pathway, so we tried to investigate the effect of 5-HTTLPR on the other neural circuit associated with emotion processing and cognitive function. Default mode network (DMN) is an important resting-state network, which reflects the intrinsic activity and organization of brain. We compared the DMN functional connectivity between different genotypes gro...
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