Behar T N, Smith S V, Kennedy R T, McKenzie J M, Maric I, Barker J L
Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Cereb Cortex. 2001 Aug;11(8):744-53. doi: 10.1093/cercor/11.8.744.
During development, postmitotic neurons migrate from germinal regions into the cortical plate (cp), where lamination occurs. In rats, GABA is transiently expressed in the cp, near target destinations for migrating neurons. In vitro GABA stimulates neuronal motility, suggesting cp cells release GABA, which acts as a chemoattractant during corticogenesis. Pharmacological studies indicate GABA stimulates migration via GABA(B)-receptor (GABA(B)-R) activation. Using immunohistochemistry, RT-PCR and Western blotting, we examined embryonic cortical cell expression of GABA(B)-Rs in vivo. At E17, GABA(B)-R1(+) cells were identified in the ventricular zone (vz) and cp. RT-PCR and Western blotting demonstrated the presence of GABA(B)-R1a and GABA(B)-R1b mRNA and proteins. Using immuno- cytochemistry, GABA(B)-R expression was examined in vz and cp cell dissociates before and after migration to GABA in an in vitro chemotaxis assay. GABA-induced migration resulted in an increase of GABA(B)-R(+) cells in the migrated population. While <20% of each starting dissociate was GABA(B)-R(+), >70% of migrated cells were immunopositive. We used a microchemotaxis assay to analyze cp cell release of diffusible chemotropic factor(s). In vitro, cp dissociates induced vz cell migration in a cell density-dependent manner that was blocked by micromolar saclofen (a GABA(B)-R antagonist). HPLC demonstrated cp cells release micromolar levels of GABA and taurine in several hours. Micromolar levels of both molecules stimulated cell migration that was blocked by micromolar saclofen. Thus, migratory cortical cells express GABA(B)-Rs, cp cells release GABA and taurine, and both molecules stimulate cortical cell movement. Together these findings suggest GABA and/or taurine act as chemoattractants for neurons during rat cortical histogenesis via mechanisms involving GABA(B)-Rs.
在发育过程中，有丝分裂后的神经元从生发区迁移到皮质板（cp），在此发生分层。在大鼠中，γ-氨基丁酸（GABA）在cp中短暂表达，靠近迁移神经元的目标位置。在体外，GABA刺激神经元运动，提示cp细胞释放GABA，其在皮质发生过程中作为化学引诱剂发挥作用。药理学研究表明，GABA通过激活GABA(B)受体（GABA(B)-R）刺激迁移。我们运用免疫组织化学、逆转录聚合酶链反应（RT-PCR）和蛋白质免疫印迹法，在体内检测胚胎皮质细胞中GABA(B)-R的表达。在胚胎第17天（E17），在脑室区（vz）和cp中鉴定出GABA(B)-R1(+)细胞。RT-PCR和蛋白质免疫印迹法证实存在GABA(B)-R1a和GABA(B)-R1b的信使核糖核酸（mRNA）及蛋白质。运用免疫细胞化学方法，在体外趋化性分析中，检测迁移到GABA之前和之后vz和cp细胞解离物中GABA(B)-R的表达。GABA诱导的迁移导致迁移群体中GABA(B)-R(+)细胞增加。虽然每个起始解离物中<20%为GABA(B)-R(+)，但>70%的迁移细胞免疫呈阳性。我们使用微量趋化性分析来分析cp细胞释放的可扩散化学趋向因子。在体外，cp解离物以细胞密度依赖性方式诱导vz细胞迁移，这种迁移被微摩尔浓度的巴氯芬（一种GABA(B)-R拮抗剂）阻断。高效液相色谱法（HPLC）显示cp细胞在数小时内释放微摩尔水平的GABA和牛磺酸。这两种分子的微摩尔水平刺激细胞迁移，且被微摩尔浓度的巴氯芬阻断。因此，迁移的皮质细胞表达GABA(B)-R，cp细胞释放GABA和牛磺酸，且这两种分子均刺激皮质细胞运动。这些发现共同表明，在大鼠皮质组织发生过程中，GABA和/或牛磺酸通过涉及GABA(B)-R的机制作为神经元的化学引诱剂。
