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

青春期，人类的年龄跨度大致为12-18岁，啮齿动物的年龄跨度为4-8周，是生命中的关键时期，通常发生成人决策，认知控制和奖励相关行为的轮廓。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和纹状体内的发育过程被认为与持续到青少年晚期/成年早期的渐进性变化有关。有趣的是，中脑多巴胺（DA）的输入在PFC和基底神经节中特别突出，在青春期左右达到高峰。 由于DA神经支配和皮质/纹状体发育之间的平行发展，有人建议，青少年DA可能在与PFC和纹状体相关的行为成熟中发挥作用。然而，目前，很少有人知道中脑DA神经元的黑质/腹侧被盖区（SN/VTA）的活动编排在PFC和纹状体的神经适应的机制。 我们的研究计划的目标是检查是否以及如何DA传输的发展动态平衡影响神经回路的完善，导致特征成人行为。 我们推测，DA调节PFC和皮质-纹状体回路的成熟，通过影响树突棘的发育，突触修剪和分化的PFC和纹状体的神经元。我们将使用一种创新的药物遗传学系统在小鼠中沉默或过度刺激中脑DA神经元可逆地在定义的发展时期，以研究其长期后果。该方法涉及AAV病毒介导的Cre依赖性DREADD（由设计者药物激活的设计者受体）在转基因DA转运蛋白-Cre小鼠的中脑DA神经元中的表达。利用这个系统，本提案的目标是解决问题：（1）是否会在青春期过度DA神经元活动改变运动，认知，社会和奖励相关的行为的小鼠？ (2)过量的多巴胺活动对磁共振成像（MRI）监测的大脑发育轨迹有什么影响？我们还将使用Golgi-Cox染色和免疫染色研究神经元的形态和功能发育。 (3)是什么机制介导的青少年DA操纵的影响？我们将研究在青春期突触修剪中起关键作用的细胞因子和小胶质细胞的水平。 我们还将研究抑制性中间神经元的发育，特别是表达GABA神经元的小白蛋白。 (4)我们想研究是否DA D1或D2样受体介导的长期神经元和行为的变化引起的青少年DA过度活跃。我们希望我们的研究将填补有关神经调质在大脑发育基本过程中作用的知识空白。

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.