Department of Developmental Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
PLoS One. 2011;6(12):e27048. doi: 10.1371/journal.pone.0027048. Epub 2011 Dec 13.
Cortical GABAergic interneurons originate from ganglionic eminences and tangentially migrate into the cortical plate at early developmental stages. To elucidate the characteristics of this migration of GABAergic interneurons in living animals, we established an experimental design specialized for in vivo time-lapse imaging of the neocortex of neonate mice with two-photon laser-scanning microscopy. In vesicular GABA/glycine transporter (VGAT)-Venus transgenic mice from birth (P0) through P3, we observed multidirectional tangential migration of genetically-defined GABAergic interneurons in the neocortical marginal zone. The properties of this migration, such as the motility rate (distance/hr), the direction moved, and the proportion of migrating neurons to stationary neurons, did not change through P0 to P3, although the density of GABAergic neurons at the marginal zone decreased with age. Thus, the characteristics of the tangential motility of individual GABAergic neurons remained constant in development. Pharmacological block of GABA(A) receptors and of the Na⁺-K⁺-Cl⁻ cotransporters, and chelating intracellular Ca²⁺, all significantly reduced the motility rate in vivo. The motility rate and GABA content within the cortex of neonatal VGAT-Venus transgenic mice were significantly greater than those of GAD67-GFP knock-in mice, suggesting that extracellular GABA concentration could facilitate the multidirectional tangential migration. Indeed, diazepam applied to GAD67-GFP mice increased the motility rate substantially. In an in vitro neocortical slice preparation, we confirmed that GABA induced a NKCC sensitive depolarization of GABAergic interneurons in VGAT-Venus mice at P0-P3. Thus, activation of GABA(A)R by ambient GABA depolarizes GABAergic interneurons, leading to an acceleration of their multidirectional motility in vivo.
皮质 GABA 能中间神经元起源于神经节隆起，并在早期发育阶段横向迁移到皮质板。为了阐明这种 GABA 能中间神经元在活体动物中的迁移特征，我们建立了一种专门用于利用双光子激光扫描显微镜对新生小鼠大脑皮层进行活体延时成像的实验设计。在出生后（P0）到 P3 的 VGAT-Venus 转基因小鼠中，我们观察到了基因定义的 GABA 能中间神经元在新皮层边缘区的多向横向迁移。这种迁移的特性，如迁移速度（距离/小时）、迁移方向和迁移神经元与静止神经元的比例，在 P0 到 P3 期间没有变化，尽管边缘区 GABA 能神经元的密度随年龄而降低。因此，个体 GABA 能神经元的横向迁移特性在发育过程中保持不变。GABA(A) 受体和 Na⁺-K⁺-Cl⁻共转运体的药理学阻断以及细胞内 Ca²⁺螯合，都显著降低了体内的迁移速度。新生 VGAT-Venus 转基因小鼠皮层中的迁移速度和 GABA 含量明显大于 GAD67-GFP 敲入小鼠，表明细胞外 GABA 浓度可以促进多向性的横向迁移。事实上，地西泮应用于 GAD67-GFP 小鼠显著增加了迁移速度。在体外大脑皮层切片制备中，我们证实 GABA 在 P0-P3 的 VGAT-Venus 小鼠中诱导了 GABA 能中间神经元的 NKCC 敏感去极化。因此，环境 GABA 激活 GABA(A)R 使 GABA 能中间神经元去极化，导致其在体内多向性迁移加速。
