Unraveling the developmental role of Cajal-Retzius neurons during the establishment of neocortical circuits in mice

Cajal-Retzius神经元（CRN）代表新皮层的层状组织所必需的短暂神经元群体。CRN在出生后第二周结束时被细胞凋亡消除之前填充新皮层的外层。CRN似乎很好地整合到新皮层中：它们显示复杂和长距离的轴突过程，接收GABA能介导的输入，并能够激发动作电位。我最近证明了兴奋性GABAA受体介导的输入是触发细胞死亡所必需的。然而，CRN是否参与到典型的体内活动模式显示的发展皮层网络，以及这种活动是否是必要的感觉皮层电路的建立尚未调查。在这里，我将研究CRN是否显示自发的和感觉诱发的活动在体内，以及它们的电活动，然后是否转化为发育功能。实验将在初级躯体感觉皮层（S1 BF）的桶场进行，该区域显示胡须垫的地形图。如果CRN参与建立躯体感觉刺激的地形表示，我希望它们对感觉输入做出反应。在第一部分的资金，身份的突触前神经元发送到S1 BF CRNs的输入将建立在转基因小鼠的单突触逆行病毒追踪，清除和免疫染色程序相结合，在该项目的第二部分，我计划调查CRNs是否参与自发的，同步活动在体内和评估的作用，胡须刺激在其电活动。为此，将在小鼠幼仔的躯体感觉皮层外层注射钙指示剂。在体内钙成像将在有和没有机械晶须刺激的情况下进行。在该项目的最后一部分，CRNs沉默对发育中的网络的影响将被评估。CRN将被专门沉默在新生小鼠使用设计师受体专门激活的设计师药物（DREADDs），和沉默CRN对S1 BF神经元和S1 BF架构的活动模式的影响将进行评估。总之，在本基金提案中描述的实验将允许描述的自发和感觉诱发的活动模式的S1 BF CRN在体内，以及他们的解剖输入。这些实验将进一步揭示CRN活动与功能性皮层回路建立之间的假定因果关系。

Cajal-Retzius neurons (CRNs) represent a transient population of neurons necessary for the laminar organization of the neocortex. CRNs populate the outer layer of the neocortex before being eliminated by apoptosis by the end of the second post-natal week. CRNs seem well integrated into the neocortex: they display complex and long-range axonal processes, receive GABAergic-mediated inputs and are able to fire action potentials. I have recently demonstrated that excitatory GABAA-receptor mediated inputs are necessary to trigger their cell death. However, whether CRNs participate into the typical in vivo activity patterns displayed by developing cortical networks and whether this activity is necessary for the establishment of sensory cortical circuits has not yet been investigated. Here, I will investigate whether CRNs display spontaneous and sensory-evoked activity in vivo, and whether their electrical activity then translates into a developmental function. Experiments will be performed in the barrel field of the primary somatosensory cortex (S1BF), a region that displays a topographic map of the whisker pad.If CRNs participate in the establishment of the topographic representation of somatosensory stimuli, I expect them to be responsive to sensory inputs. In the first part of the funding, the identity of presynaptic neurons sending inputs into S1BF CRNs will be established by combining monosynaptic retrograde viral tracing, clearing and immunostaining procedures on transgenic mice.In a second part of the project, I plan to investigate whether CRNs participate into the spontaneous, synchronous activity in vivo and assess the role of whisker stimulation in their electrical activity. To this aim, mouse pups will be injected in the outer layer of the somatosensory cortex with a calcium indicator. In vivo calcium imaging will then be performed with and without mechanical whisker stimulation.In the last part of the project, the effect of CRNs silencing on the developing network will be assessed. CRNs will be specifically silenced in newborn mice using Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), and the effect of silencing CRNs on the activity patterns of S1BF neurons and S1BF architecture will be assessed.To conclude, the experiments described in this funding proposal will allow the description of the spontaneous- and sensory-evoked activity patterns of S1BF CRNs in vivo as well as their anatomical inputs. These experiments will further unravel a putative causal relationship between the activity of CRNs and establishment of functional cortical circuits.