The role of serotonin in human brain development: validation studies on the use of peripheral measures of serotonin in children and adults

动物研究表明，5-羟色胺（5-HT）系统在大脑发育中起着重要作用，参与神经元回路的结构和功能塑造。然而，令人惊讶的是，对5-HT在正常人脑发育中的作用知之甚少。这种知识上的差距很大程度上是由于很难研究人类大脑中的5-HT。正电子发射断层扫描（Positron Emission Tomography，PET）是研究人脑5-HT最直接的方法，但它是有创的，不能用于未成年人的研究。本研究计划的长期目标是开发无创测量活体脑5-HT水平的方法，用于研究5-HT在整个生命周期中对人脑功能的作用。我们将研究脑内5-HT的两个潜在指标：外周细胞5-HT系统基因DNA甲基化和听觉诱发电位（IDAEP）的N1/P2分量，第一个候选指标是在我们和其他人的数据基础上选择的，显示外周细胞5-HT系统基因DNA甲基化与体内5-HT PET测量之间的相关性。研究IDAEP EEG信号的基本原理是在动物中证明其与测量5-HT传输相关的证据。该研究计划将重点关注与这两个潜在指标的测量有效性和可靠性相关的重要问题：这些指标随着时间的推移有多稳定？它们与青少年大脑发育有什么关系？这两个指标是否相互关联，并利用类似的大脑和认知过程？我们将在健康个体中进行3项研究，使用DNA甲基化，EEG，PET和fMRI技术。该计划涉及相关性研究以及实验性5-HT耗竭研究，允许调查因果关系。关于甲基化，基于我们的初步数据，我们的主要兴趣是从口腔细胞获得的数据，我们将与从血液获得的结果进行比较。我们将使用焦磷酸测序法，我们已经发现可靠的定量甲基化在特定的基因启动子。我们还将在整个研究计划中研究其他调控元件，如增强子，通常以发育阶段特异性的方式起作用。所提出的计划可以导致脑5-HT，这将是令人难以置信的有用研究人类大脑发育的多个方面。该计划还将为学生提供机会，在一个高度多学科的培训环境中工作，并获得行为神经科学前沿研究方法的经验。对在这种环境下受过培训的学生的需求越来越大。因此，拟议的研究计划在科学和社会经济层面都具有重要意义。

Animal studies have shown that the serotonin (5-HT) system plays a major role in brain development, participating in structural and functional shaping of the neuronal circuit. However, surprisingly little is known about the roles of 5-HT in normal human brain development. This gap in knowledge is largely due to the fact that it is difficult to study brain 5-HT in humans. Positron Emission Tomography (PET) is the most direct way to study human brain 5-HT, but it is invasive and can't be used in research with minors.The long-term goal of this research program is to develop non-invasive methods to measure living brain 5-HT levels that can be used in studies on the roles of 5-HT in the function of the human brain throughout the lifespan. We will study 2 potential indicators of brain 5-HT: DNA methylation of 5-HT system genes in peripheral cells and the electroencephalogram (EEG) N1/P2 component of auditory evoked potential (IDAEP).The first indicator candidate was chosen based on data from us and others, showing correlations between DNA methylation of 5-HT system genes in peripheral cells and in vivo PET measures of 5-HT. The rationale to study the IDAEP EEG signal is evidence in animals demonstrating its relevance for measuring 5-HT transmission. The research program will focus on important questions related to measurement validity and reliability of these potential two indicators: how stable are these measures over time? What is their relevance for youth brain development? Are both indicators interrelated and tapping into similar brain and cognitive processes?We will perform 3 studies in healthy individuals, using DNA methylation, EEG, PET and fMRI techniques. The program involves correlational studies as well as experimental 5-HT depletion studies, allowing investigation of causal relationships. Regarding methylation, based on our pilot data, our primary interest are the data obtained from buccal cells that we will compare with results obtained from blood. We will use pyrosequencing assays that we have found to reliably quantify methylation in specific gene promoters. We will also study other regulatory elements throughout the research program, such as enhancers, that often act in a developmental stage-specific way.The proposed program can lead to the development of non-invasive indicator(s) for brain 5-HT which will be incredibly useful in research on multiple aspects of human brain development.The program will also provide students opportunities to work in a highly multidisciplinary training environment and gain experience in cutting-edge research methods in behavioural neuroscience. There is increasing demand for students who have been trained in such settings. Thus, the proposed research program has important implications at both scientific and socio-economic levels.