Role of dopamine in the maturation of prefrontal cortex and associated behaviors.

成熟的认知、动机和社会行为的完善通常发生在青春期，与前额叶皮质(PFC)的长期发育有关。在PFC的神经输入中，中额叶多巴胺(DA)系统是有趣的，因为当关键的组织事件在PFC发生时，DA能传入达到峰值。多巴胺能信号除了对皮层兴奋性和抑制性神经元兴奋性有急性影响外，还介导突触重构和长期可塑性。虽然有大量关于成人DA系统的作用的文献，但对于早期DA平衡失调对前额叶网络和相关行为发展的长期后果知之甚少。*为了研究DA平衡被破坏的影响，我们正在使用可诱导的DREADD(由设计药物激活的设计者受体)药物遗传学系统来远程沉默或刺激中脑DA神经元长达几个小时，可逆地，并在特定的发育时期。该方法涉及腺相关病毒(AAV)介导的基因工程hM3Dq(用于神经元激活)或hM4Di(用于抑制)在DA转运体(DAT)-cre小鼠中的表达。受体被合成的药物氯氮平-N-氧化物(CNO)刺激。我们使用带有hM3Dq的病毒载体的初步数据显示，青春期中期腹侧被盖区(VTA)神经元的亚慢性激活导致新颖性诱导的运动活动显著增加，并导致与PFC电路活动有关的时序记忆任务中的缺陷。*在拟议的研究计划中，我们希望使用药物遗传系统系统地研究PFC相关行为的青春期后发展轨迹，如运动、PPI、焦虑、社交以及社会和工作记忆。我们以前在评估不同年龄的大鼠和小鼠的行为方面有经验，所需的设备可以在我们的实验室或道格拉斯神经表型鉴定中心获得。我们还将使用结构磁共振成像(MRI)和组织学技术纵向评估PFC中皮质灰质的发育和突触修剪。可能介导DA刺激效应的机制将被研究，例如，不同的DA受体和细胞内信号通路的作用。未来的研究将类似地检验青少年DA抑制对大脑和行为的影响，以及青春期早期和新生儿DA操作的影响。我们相信，这些研究将大大有助于我们理解参与青少年向成人行为转变的调控机制。

The refinement of mature cognitive, motivational and social behaviors typically takes place during adolescence, and is linked to the protracted development of the prefrontal cortex (PFC). Among neural inputs to the PFC, the mesofrontal dopamine (DA) system is interesting as DAergic afferents peak when key organizational events are taking place in the PFC. DAergic signaling, besides its acute effects on cortical excitatory and inhibitory neuron excitability, also mediates synaptic remodeling and long-term plasticity. While a large body of literature exists on the role of adult DA system, very little is known of the long-term consequences of early dysregulated DA homeostasis on the development of prefrontal networks and associated behaviors.****To study the effects of disruption in DA homeostasis, we are using the cre-inducible DREADD (designer receptors activated by designer drugs) pharmacogenetic system in mice to remotely silence or stimulate the mid-brain DA neurons up to several hours, reversibly and at defined developmental periods. The method involves adeno-associated virus (AAV)-mediated expression of genetically engineered hM3Dq (for neuronal activation) or hM4Di (for inhibition) in DA transporter (DAT)-cre mice. The receptors are stimulated by a synthetic (and otherwise physiologically inert) drug clozapine-N-oxide (CNO). Our preliminary data using the viral vector with hM3Dq shows that mid-adolescence sub-chronic activation of ventral tegmental area (VTA) neurons led to a marked increase in novelty-induced locomotor activity and deficits in a task of temporal order memory that is linked to the activity of PFC circuits.****In the proposed research programme, we want to systematically examine post-adolescent developmental trajectory of PFC-linked behaviors such as locomotion, PPI, anxiety, social interaction, and social and working memories in mice with sub-chronic adolescent stimulation of VTA DA neurons using the pharmacogenetic system. We have previous experience with the assessment of behaviors in rats and mice of different ages and required equipment is available in our laboratory or the Douglas Neurophenotyping Centre. We will also longitudinally assess cortical gray matter development and synaptic pruning in the PFC using structural magnetic resonance imaging (MRI) and histological techniques. Possible mechanisms that may mediate the effects of DA stimulation will be studied, e.g., the role of different DA receptors and intracellular signaling pathways. Future studies will similarly examine the effects of adolescent DA inhibition on brain and behavior, as well as the effects of early adolescent and neonatal DA manipulations. We believe that these studies will contribute significantly to our understanding of regulatory mechanisms that participate in the transition from adolescent to adult behavior.****