Role of dopamine in adolescent maturation of prefrontal cortical circuits and associated behaviors

人类的青春期大约是12-18岁，啮齿类动物的青春期大约是4-8周，是人生的关键时期，成人的决策、认知控制和奖励相关行为通常在这个时期发生。在大脑回路中，前额叶皮层（PFC）及其与纹状体的连接至关重要地支持这些行为。PFC和纹状体的发育过程被认为与持续到青春期晚期/成年早期的渐进式变化有关。有趣的是，中脑多巴胺（DA）输入在前前额叶和基底神经节尤为突出，在青春期前后达到峰值。由于DA神经支配的发育与皮层/纹状体发育的平行性，已经有人提出青春期DA可能在与PFC和纹状体相关的行为成熟中起作用。然而，目前对中脑黑质/腹侧被盖区（SN/VTA） DA神经元的活动如何协调PFC和纹状体的神经适应机制知之甚少。我们的研究计划的目标是检查DA传递的发育稳态是否以及如何影响导致典型成人行为的神经回路的改进。我们假设DA通过影响PFC和纹状体中树突棘的发育、突触修剪和神经元的分化来调节PFC和皮质纹状体回路的成熟。我们将在小鼠身上使用一种创新的药物遗传系统，在特定的发育时期可逆地沉默或过度刺激中脑DA神经元，以研究其长期后果。该方法涉及AAV病毒介导的转基因DA转运体-Cre小鼠中脑DA神经元中Cre依赖的DREADD（由设计药物激活的设计受体）的表达。利用这一系统，本提案的目标是解决以下问题：(1)青春期过量的DA神经元活动是否会改变小鼠的运动、认知、社会和奖励相关行为？(2)过量DA活动对磁共振成像（MRI）监测的脑发育轨迹有何影响？我们还将使用高尔基-考克斯染色和免疫染色研究神经元的形态和功能发育。(3)青少年行为干预的中介机制是什么？我们将研究细胞因子和小胶质细胞在青春期突触修剪中起关键作用的水平。我们还将研究抑制性中间神经元的发育，特别是表达GABA的小白蛋白神经元。(4)我们想要研究DA d1样受体或d2样受体是否介导青少年DA多动症引起的长期神经元和行为改变。我们期望我们的研究将填补关于神经调节剂在大脑发育基本过程中的作用的重要知识空白。

Adolescence, an age span roughly ranging from 12-18 years in humans and 4-8 weeks in rodents, is a critical period in life when contours of adult decision-making, cognitive control and reward-related behaviors typically take place. Among brain circuits, the prefrontal cortex (PFC) and its connectivity with the striatum critically support these behaviors. Developmental processes within the PFC and striatum are believed to be linked to progressive changes lasting till late adolescent/early adult ages. Interestingly, midbrain dopamine (DA) inputs, that are particularly prominent in the PFC and the basal ganglia, peak around adolescence. Due to the parallel between the development of DA innervation and cortical/striatal development, it has been suggested that adolescent DA may play a role in the maturation of behaviors linked to the PFC and striatum. However, at present, very little is known of the mechanisms by which activity of the midbrain DA neurons of the substantia nigra/ventral tegmental area (SN/VTA) orchestrate neuroadaptations in the PFC and striatum. The goal of our research programme is to examine whether and how the developmental homeostasis of DA transmission affects the refinement of neural circuits leading to characteristic adult behaviors. We hypothesize that DA regulates the maturation of PFC and cortico-striatal circuit by affecting the development of dendritic spines, synaptic pruning and differentiation of neurons in the PFC and striatum. We will use an innovative pharmacogenetic system in mice to silence or overstimulate midbrain DA neurons reversibly at defined developmental periods in order to study its long-term consequences. The method involves AAV virus-mediated expression of Cre dependent DREADD (designer receptor activated by designer drug) in the midbrain DA neurons of transgenic DA transporter-Cre mice. Using this system, the goal of the present proposal is to address the questions: (1) Will excess DA neuronal activity during adolescence alter motor, cognitive, social and reward-related behaviors of mice? (2) What is the impact of excess DA activity on the developmental trajectory of the brain monitored by magnetic resonance imaging (MRI)? We will also study the morphological and functional development of neurons using Golgi-Cox staining and immunostaining. (3) What are the mechanisms that mediate the effects of adolescent DA manipulation? We will examine the levels of cytokines and microglia cells that play a critical role in synaptic pruning during adolescence. We will also examine the development of inhibitory interneurons, specifically the parvalbumin expressing GABA neurons. (4) We want to investigate whether DA D1-like or D2-like receptors mediate the long-term neuronal and behavioral changes induced by adolescent DA hyperactivity. We expect that our studies will to fill an important gap in knowledge regarding the role of neuromodulators in fundamental processes of brain development.