Behar T N, Dugich-Djordjevic M M, Li Y X, Ma W, Somogyi R, Wen X, Brown E, Scott C, McKay R D, Barker J L
Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Eur J Neurosci. 1997 Dec;9(12):2561-70. doi: 10.1111/j.1460-9568.1997.tb01685.x.
During mammalian cortical development, neuronal precursors proliferate within ventricular regions then migrate to their target destinations in the cortical plate, where they organize into layers. In the rat, most cortical neuronal migration occurs during the final week of gestation (Bayer et al, 1991; Jacobson, 1991). At this time (E15-E21), reverse transcriptase-polymerase chain reaction demonstrated that cortical homogenates contain mRNA encoding brain derived neurotrophic factor (BDNF) and the catalytic form of its high-affinity receptor, TrkB. Immunocytochemistry and in situ hybridization of sections revealed that the catalytic TrkB receptors predominantly localize to regions containing migratory cells. Many TrkB+ cells exhibited the classic morphology of migrating neurons, suggesting that TrkB ligands play a role in cortical neuronal migration. We analysed whether TrkB ligands influence the motility of embryonic cortical cells (from E15-E21) using a quantitative in vitro chemotaxis assay. High-affinity TrkB ligands (BDNF and NT4/5) stimulated chemotaxis (directed migration) of embryonic neurons at concentrations ranging from 1 to 100 ng/ml. NT-3, a low-affinity TrkB ligand, only stimulated significant migration at high concentrations (> or =100 ng/ml). Peak migration to BDNF was observed at gestational day 18 (E18). BDNF-induced chemotaxis was blocked by either tyrosine kinase inhibitor, K252a, or the Ca2+-chelator, BAPTA-AM, suggesting that BDNF-induces motility via autophosphorylation of TrkB receptor proteins and involves Ca2+-dependent mechanisms. BDNF-stimulation of increased cytosolic Ca2+ was confirmed with optical recordings of E18 cortical cells loaded with Ca2+ indicator dye. Thus, signal transduction through the TrkB receptor complex directs neuronal migration, suggesting that, in vivo, BDNF exerts chemotropic effects that are critical to morphogenesis of the cortex.
在哺乳动物皮质发育过程中，神经元前体细胞在脑室区域增殖，然后迁移到皮质板中的目标位置，并在那里分层排列。在大鼠中，大多数皮质神经元迁移发生在妊娠的最后一周（Bayer等人，1991年；Jacobson，1991年）。此时（胚胎第15 - 21天），逆转录聚合酶链反应表明，皮质匀浆中含有编码脑源性神经营养因子（BDNF）及其高亲和力受体TrkB催化形式的mRNA。切片的免疫细胞化学和原位杂交显示，催化性TrkB受体主要定位于含有迁移细胞的区域。许多TrkB阳性细胞呈现出迁移神经元的典型形态，这表明TrkB配体在皮质神经元迁移中发挥作用。我们使用定量体外趋化性分析方法，分析了TrkB配体是否影响胚胎皮质细胞（胚胎第15 - 21天）的运动性。高亲和力TrkB配体（BDNF和NT4/5）在1至100 ng/ml的浓度范围内刺激胚胎神经元的趋化性（定向迁移）。低亲和力TrkB配体NT - 3仅在高浓度（≥100 ng/ml）时刺激显著迁移。在妊娠第18天（E18）观察到对BDNF的迁移峰值。酪氨酸激酶抑制剂K252a或Ca2+螯合剂BAPTA - AM均可阻断BDNF诱导的趋化性，这表明BDNF通过TrkB受体蛋白的自磷酸化诱导运动性，并涉及Ca2+依赖性机制。用装载Ca2+指示剂染料的E18皮质细胞进行光学记录，证实了BDNF刺激导致胞质Ca2+增加。因此，通过TrkB受体复合物的信号转导指导神经元迁移，这表明在体内，BDNF发挥着对皮质形态发生至关重要的化学趋向性作用。
