Ferguson Shane C D, McFarlane Sarah
Genes and Development Research Group, University of Calgary, AB, Canada.
J Neurobiol. 2002 Jun 15;51(4):272-84. doi: 10.1002/neu.10061.
In the developing visual system of Xenopus laevis retinal ganglion cell (RGC) axons extend through the brain towards their major target in the midbrain, the optic tectum. Enroute, the axons are guided along their pathway by cues in the environment. In vitro, neurotransmitters have been shown to act chemotropically to influence the trajectory of extending axons and regulate the outgrowth of developing neurites, suggesting that they may act to guide or modulate the growth of axons in vivo. Previous work by Roberts and colleagues (1987) showed that populations of cells within the developing Xenopus diencephalon and mid-brain express the neurotransmitter gamma amino butyric acid (GABA). Here we show that Xenopus RGC axons in the midoptic tract grow alongside the GABAergic cells and cross their GABA immunopositive nerve processes. Moreover, RGC axons and growth cones express GABA-A and GABA-B receptors, and GABA and the GABA-B receptor agonist baclofen both stimulate RGC neurite outgrowth in culture. Finally, the GABA-B receptor antagonist CGP54626 applied to the developing optic projection in vivo causes a dose-dependent shortening of the optic projection. These data indicate that GABA may act in vivo to stimulate the outgrowth of Xenopus RGC axons along the optic tract.
在非洲爪蟾发育中的视觉系统里，视网膜神经节细胞（RGC）的轴突穿过大脑，朝着中脑的主要靶标视顶盖延伸。在途中，轴突由环境中的线索引导其路径。在体外实验中，神经递质已被证明具有化学趋向性，可影响延伸轴突的轨迹并调节发育中神经突的生长，这表明它们可能在体内引导或调节轴突的生长。罗伯茨及其同事（1987年）之前的研究表明，在发育中的非洲爪蟾间脑和中脑内的细胞群表达神经递质γ-氨基丁酸（GABA）。在此我们表明，视束中部的非洲爪蟾RGC轴突与GABA能细胞一起生长，并穿过它们的GABA免疫阳性神经突起。此外，RGC轴突和生长锥表达GABA-A和GABA-B受体，并且GABA和GABA-B受体激动剂巴氯芬都能刺激培养中的RGC神经突生长。最后，将GABA-B受体拮抗剂CGP54626应用于体内发育中的视投射会导致视投射出现剂量依赖性缩短。这些数据表明，GABA可能在体内发挥作用，刺激非洲爪蟾RGC轴突沿视束生长。
