Homing behaviour of axons in the embryonic vertebrate brain.
Homing behaviour of axons in the embryonic vertebrate brain.
复制标题
胚胎脊椎动物大脑中轴突的归巢行为。
作者：
Harris,WA
在胚胎神经系统中，生长中的轴突通常必须通过不同的细胞外地形长途跋涉才能到达突触后伙伴。在大多数胚胎中，轴突沿着沿着特定的神经束或神经生长到适当的目标，就好像它们遵循特定路径的指导线索1 -3。例如，在所有脊椎动物中，来自视网膜的轴突总是沿着轮廓分明的视束生长到顶盖4 -6。然而，移植实验表明，即使视网膜轴突在明显离开视神经束的位置进入大脑，它们也会进行顶盖投射7 -11。直到最近，才有可能标记胚胎脊椎动物大脑中谨慎生长的突起12。因此，目前尚不清楚移位的视网膜轴突是直接向顶盖生长，还是通过随机延伸偶然发现顶盖。为了解决这个问题，先锋轴突从正常和移植的眼睛在胚胎Xenopus标记使用短期生存辣根过氧化物酶（HRP）的方法4，并在生长过程中的方向进行了定量评估。异位纤维朝向其远端目标的发现意味着引导信号并不局限于特定的通路，而是分布在整个胚胎大脑中。这一结果的意义进行了讨论方面的视觉通路的个体发育和进化。
In embryonic nervous systems, growing axons must often travel long distances through diverse extracellular terrains to reach their postsynaptic partners. In most embryos, axons grow to their appropriate targets along particular tracts or nerves, as though they were following guidance cues confined to specific pathways1–3. For example, in all vertebrates, axons from the retina invariably grow to the tectum along the well-defined optic tract4–6. Yet, transplant experiments demonstrate that retinal axons make tectal projections even though they enter the brain at locations which are distinctly off the optic tract7–11. Only recently has it become possible to label discreet growing projections in the embryonic vertebrate brain12. Thus, it is not yet known whether displaced retinal axons grow directly towards the tectum or find it accidently, through random extension. To resolve this question, pioneering axons from normal and transplanted eyes in embryonicXenopuswere labelled using a short-survival horseradish peroxidase (HRP) method4, and their orientation during growth was quantitatively assessed. The finding that the ectopic fibres head towards their distant targets implies that guidance cues are not restricted to specific pathways but are distributed throughout the embryonic brain. The significance of this result is discussed with respect to the ontogeny and evolution of the visual pathway.