The functions of cortical networks are progressively established during development by series of events shaping the neuronal connectivity. Synaptic elimination, which consists of removing the supernumerary connections generated during the earlier stages of cortical development, is one of the latest stages in neuronal network maturation. The semaphorin 3F coreceptors neuropilin 2 (Nrp2) and plexin-A3 (PlxnA3) may play an important role in the functional maturation of the cerebral cortex by regulating the excess dendritic spines on cortical excitatory neurons. Yet, the identity of the connections eliminated under the control of Nrp2/PlxnA3 signaling is debated, and the importance of this synaptic refinement for cortical functions remains poorly understood. Here, we show that Nrp2/PlxnA3 controls the spine densities in layer 4 (L4) and on the apical dendrite of L5 neurons of the sensory and motor cortices. Using a combination of neuroanatomical, ex vivo electrophysiology, and in vivo functional imaging techniques in Nrp2 and PlxnA3 KO mice of both sexes, we disprove the hypothesis that Nrp2/PlxnA3 signaling is required to maintain the ectopic thalamocortical connections observed during embryonic development. We also show that the absence of Nrp2/PlxnA3 signaling leads to the hyperexcitability and excessive synchronization of the neuronal activity in L5 and L4 neuronal networks, suggesting that this system could participate in the refinement of the recurrent corticocortical connectivity in those layers. Altogether, our results argue for a role of semaphorin–Nrp2/PlxnA3 signaling in the proper maturation and functional connectivity of the cerebral cortex, likely by controlling the refinement of recurrent corticocortical connections.

SIGNIFICANCE STATEMENT The function of a neuronal circuit is mainly determined by the connections that neurons establish with one another during development. Understanding the mechanisms underlying the establishment of the functional connectivity is fundamental to comprehend how network functions are implemented, and to design treatments aiming at restoring damaged neuronal circuits. Here, we show that the cell surface receptors for the family of semaphorin guidance cues neuropilin 2 (Nrp2) and plexin-A3 (PlxnA3) play an important role in shaping the functional connectivity of the cerebral cortex likely by trimming the recurrent connections in layers 4 and 5. By removing the supernumerary inputs generated during early development, Nrp2/PlxnA3 signaling reduces the neuronal excitability and participates in the maturation of the cortical network functions.

皮质网络的功能在发育过程中通过塑造神经元连接的一系列事件逐渐建立。突触消除包括消除皮质发育早期阶段产生的多余连接，是神经元网络成熟的最新阶段之一。semaphorin 3F 辅助受体神经纤毛蛋白 2 (Nrp2) 和 plexin-A3 (PlxnA3) 可能通过调节皮质兴奋性神经元上多余的树突棘在大脑皮质的功能成熟中发挥重要作用。然而，在 Nrp2/PlxnA3 信号控制下消除的连接的身份存在争议，这种突触细化对皮质功能的重要性仍然知之甚少。这里，我们发现 Nrp2/PlxnA3 控制第 4 层（L4）和感觉和运动皮层 L5 神经元顶端树突的脊柱密度。结合神经解剖学，体外电生理学，以及Nrp2和PlxnA3的体内功能成像技术KO 小鼠，我们反驳了 Nrp2/PlxnA3 信号是维持胚胎发育过程中观察到的异位丘脑皮质连接所必需的假设。我们还表明，缺乏 Nrp2/PlxnA3 信号会导致 L5 和 L4 神经元网络中神经元活动的过度兴奋和过度同步，这表明该系统可以参与这些层中复发性皮质皮质连接的细化。总之，我们的研究结果表明信号素-Nrp2/PlxnA3 信号在大脑皮层的适当成熟和功能连接中的作用，可能是通过控制复发性皮质连接的细化。

重要性声明神经元回路的功能主要由神经元在发育过程中相互建立的连接决定。了解建立功能连接的机制对于理解网络功能的实现方式以及设计旨在恢复受损神经元回路的治疗方法至关重要。在这里，我们表明信号素指导家族的细胞表面受体提示神经纤毛蛋白 2 (Nrp2) 和 plexin-A3 (PlxnA3) 在塑造大脑皮层的功能连接方面可能通过修剪第 4 层中的循环连接发挥重要作用5. 通过去除早期发育过程中产生的多余输入，Nrp2/PlxnA3 信号降低了神经元的兴奋性并参与了皮层网络功能的成熟。