Behar T N, Schaffner A E, Colton C A, Somogyi R, Olah Z, Lehel C, Barker J L
Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
J Neurosci. 1994 Jan;14(1):29-38. doi: 10.1523/JNEUROSCI.14-01-00029.1994.
During CNS development, neuroblasts proliferate within germinal zones of the neuroepithelium, and then migrate to their final positions. Although many neurons are thought to migrate along processes of radial glial fibers, increasing evidence suggests environmental factors also influence nerve cell movement. Extracellular matrix molecules are thought to be involved in guiding neuronal migration, and molecules such as NGF and GABA exert trophic effects on immature neurons. The nature of the signals that initiate and direct neuroblast migration, however, is unknown. In vitro, NGF and GABA promote neurite outgrowth from cultured cells, and NGF induces axonal chemotaxis (directed migration along a chemical gradient). At earlier developmental stages, these molecules could influence neuroblast movement. Therefore, we investigated whether these molecules induce embryonic neuronal migration. Using an in vitro microchemotaxis assay, we show that rat embryonic spinal cord neurons migrate toward picomolar NGF and femtomolar GABA beginning at embryonic day 13 (E13). Cells exhibit chemotactic responses to NGF while GABA stimulates chemokinesis (increased random movement). GABA effects are mimicked by muscimol and inhibited by bicuculline and picrotoxin, suggesting GABA motility signals are mediated by GABA receptor proteins. Expression of GABA receptors by embryonic cord cells has been previously reported (Mandler et al., 1990; Walton et al., 1993). We used polymerase chain reaction analysis to demonstrate the presence of NGF and trk mRNA in E13 and E14 cord cells, indicating the cells express message for both NGF and high-affinity NGF receptors. Immunohistochemistry of E13 spinal cord sections indicates that NGF and GABA colocalize in fibers close to the target destinations of migrating neurons, suggesting diffusible gradients of these molecules provide chemoattractant signals to migratory cells. Thus, in vitro, neuroblast migration is induced by specific signaling molecules that are present in the developing spinal cord, and may stimulate migration of embryonic neurons prior to synaptogenesis.
在中枢神经系统发育过程中，神经母细胞在神经上皮的生发区内增殖，然后迁移至其最终位置。尽管许多神经元被认为是沿着放射状胶质纤维的突起迁移，但越来越多的证据表明环境因素也会影响神经细胞的移动。细胞外基质分子被认为参与引导神经元迁移，而诸如神经生长因子（NGF）和γ-氨基丁酸（GABA）等分子对未成熟神经元具有营养作用。然而，启动和指导神经母细胞迁移的信号的本质尚不清楚。在体外，NGF和GABA可促进培养细胞的神经突生长，并且NGF可诱导轴突趋化性（沿化学梯度的定向迁移）。在发育的早期阶段，这些分子可能会影响神经母细胞的移动。因此，我们研究了这些分子是否诱导胚胎神经元迁移。使用体外微趋化性分析，我们发现大鼠胚胎脊髓神经元从胚胎第13天（E13）开始向皮摩尔浓度的NGF和飞摩尔浓度的GABA迁移。细胞对NGF表现出趋化反应，而GABA则刺激趋动性（增加随机移动）。蝇蕈醇可模拟GABA的作用，荷包牡丹碱和印防己毒素可抑制其作用，这表明GABA的运动信号是由GABA受体蛋白介导的。先前已有报道胚胎脊髓细胞表达GABA受体（曼德勒等人，1990年；沃尔顿等人，1993年）。我们使用聚合酶链反应分析来证明E13和E14脊髓细胞中存在NGF和trk mRNA，这表明这些细胞表达NGF和高亲和力NGF受体的信息。E13脊髓切片的免疫组织化学表明，NGF和GABA共定位于靠近迁移神经元目标目的地的纤维中，这表明这些分子的可扩散梯度为迁移细胞提供了化学吸引信号。因此，在体外，神经母细胞迁移是由发育中的脊髓中存在的特定信号分子诱导的，并且可能在突触形成之前刺激胚胎神经元的迁移。
