Neurogenesis of GABAergic neurons in the neocortex

在发育中的啮齿动物新皮质中，谷氨酸能神经元由大脑皮层脑室带(VZ)的放射状胶质细胞增殖供应，而GABA能神经元则产生于大脑皮层下结构-神经节隆起(GE)，然后通过切向细胞迁移进入新皮质。然而，逆转录病毒的细胞谱系分析通常显示克隆相关的GABA能神经元对紧密位于新皮质内。根据这些报道，我们推测一些GABA能神经元是在啮齿动物的新皮质产生的。在GAD67-GFP敲入小鼠中，我们发现出生时单脉冲(30min)BrdU和GFP或Ki-67和GFP共存于新皮质的脑室下区(SVZ)和中间区(IZ)。SVZ和IZ中1/4的GFP阳性细胞Ki-67阳性。在新皮质中，三分之一的GFP阳性细胞呈Nestin阳性。这些数据表明，部分GAD67阳性细胞是增殖的，提示这些细胞是致力于GABA能神经元的祖细胞。为了评估GABA能神经元的前体细胞是否也来自GE的切向细胞迁移，我们将腺病毒或逆转录病毒(CA启动子-loxP-GFP-loxP)注射到Emx1-Cre敲入小鼠胚胎的脑室：这些病毒揭示了新皮质中Emx1阴性细胞的起源。我们发现新皮质中一些可能的GABA能神经前体细胞呈Emx1阴性表达，起源于大脑皮质下VZ。我们的结论是，啮齿动物新皮质内的GABA能神经元不仅来自GE的有丝分裂后GABA能神经元的迁移，而且其前体细胞从GE迁移到新皮质的增殖也是如此。

In the developing rodent neocortex, the glutamatergic neurons are supplied by proliferation of radial glias in the ventricular zone(VZ) of the pallium, while the GABAergic neurons are produced in the the ganglionic eminence(GE), a subpallial structure, and then come into the neocortex by tangential cell migration. However, cell lineage analyses with a retrovirus have often revealed clonally related GABAergic neuron pairs located closely within the neocortex. Following these reports, we speculated that some of the GABAergic neurons were produced in the rodent neocortex. In GAD67-GFP knock-in mice, we found colocalization of single-pulse (30 min) BrdU and GFP, or Ki-67 and GFP in the subventricular zone(SVZ)and the intermediate zone(IZ) of the neocortex at birth. One forth of GFP-positive cells in the SVZ and the IZ were positive for Ki-67. And one thirds of GFP-positive cells in the neocortex were positive for nestin. These data indicate that a portion of GAD67-positivecells are proliferative, suggesting these cells are the progenitorscommitted to GABAergic neurons. To assess whether the putative progenitors for GABAergic neurons were also supplied by tangential cellmigration from the GE, we injected an adenovirus or retrovirus witha construct (CA promoter-loxP-GFP-loxP) into the ventricle of Emx1-Cre knock-in mouse embryos : These viruses reveal the origin of the Emx1-negative cells in the neocortex. We found some of the putative GABAergic neuron progenitors in the neocortex were in Emx1-negativelineage and derived from the subpallial VZ. We conclude that the GABAergic neurons in the rodent neocortex are supplied not only by migration of postmitotic GABAergic neurons from the GE, but also by proliferation of their progenitors immigrated from the GE to the neocortex.