Hoskins S G, Grobstein P
Nature. 1984;307(5953):730-3. doi: 10.1038/307730a0.
Hormones are important in the development of behaviour and there is now abundant evidence that they also affect the morphological development of the nervous system. In principle, hormones could act by inducing new patterns of connectivity between widely separated structures in the nervous system or by influencing local connectivity. Most available work documents effects of the latter sort. We present here evidence for the former. Our results indicate that thyroxine, the hormone which causes metamorphosis in the frog Xenopus laevis, can induce precociously in a pre-metamorphic tadpole the ipsilateral retinothalamic projection, a retinofugal pathway which normally develops during metamorphosis. Our evidence suggests that the hormone's presence in one eye alone is sufficient to cause axons of some ganglion cells in that eye to grow to targets in the ipsilateral thalamus and to form terminal fields of appropriate morphology. Since the axons of the induced pathway project ipsilaterally, unlike axons in the normal premetamorphic tadpole, virtually all of which project contralaterally, our results are also relevant to questions concerning the control of axonal trajectory in the optic chiasm.
激素在行为发育中起着重要作用，现在有大量证据表明它们也会影响神经系统的形态发育。原则上，激素可以通过诱导神经系统中广泛分离的结构之间形成新的连接模式，或者通过影响局部连接来发挥作用。大多数现有研究记录了后一种作用类型的影响。我们在此展示前一种作用类型的证据。我们的结果表明，甲状腺素这种能使非洲爪蟾发生变态的激素，可以在变态前的蝌蚪中过早诱导同侧视网膜丘脑投射，这是一条通常在变态过程中发育的视网膜传出通路。我们的证据表明，仅一只眼中存在该激素就足以使该眼中一些神经节细胞的轴突生长至同侧丘脑的靶点，并形成形态合适的终末场。由于诱导通路的轴突同侧投射，这与正常变态前蝌蚪中几乎所有轴突都对侧投射不同，所以我们的结果也与有关视交叉中轴突轨迹控制的问题相关。
