Departments of Neuroscience, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
J Neurosci. 2010 Feb 10;30(6):2277-88. doi: 10.1523/JNEUROSCI.5286-09.2010.
Development of skilled movements and the corticospinal tract (CST) begin prenatally and continue postnatally. Because the CST is required for skilled movements in maturity, it is accepted that motor skills cannot occur until the CST develops a mature organization. We recently showed that the CST plays an essential role in postnatal development of interneurons comprising the spinal circuits it engages. We proposed that CST signals are more effectively transmitted to ventral motor circuits after interneuron maturation, thereby enabling expression of CST motor functions, suggesting development of a segmental switch promoting transmission. We tested this by recording CST-evoked focal synaptic potentials, extracellularly, in the cervical enlargement of cats before and after interneuron maturation [postnatal week 5 (PW5) to PW7]. We compared monosynaptic CST amplitude input to segmental circuits with oligosynaptic ventral horn responses, as a measure of CST-evoked segmental response transmission from input to output. The M1 primary motor cortex was unilaterally inactivated between PW5 and PW7 to determine activity dependence. CST interneuron contacts were identified using confocal microscopy. CST terminals contact diverse interneuron classes. CST stimulation strongly activated ventral motor circuits at the ages when both interneurons and CST spinal terminations have developed a mature phenotype, supporting development of segmental transmission of CST signals. CST activity blockade impeded development of effective segmental transmission by the inactivated CST and created a novel path for transmission from the ipsilateral, unaffected, CST. Our findings show that development of segmental CST signal transmission regulates nascent CST motor control functions and provide insight into systems-level mechanisms for protracted motor skill development.
运动技能的发展和皮质脊髓束（CST）在产前开始，并在产后继续。由于 CST 是成熟时进行运动技能所必需的，因此人们认为，直到 CST 形成成熟的组织结构，运动技能才能发生。我们最近表明，CST 在参与的脊髓回路中构成的中间神经元的产后发育中起重要作用。我们提出，CST 信号在中间神经元成熟后更有效地传递到腹侧运动回路，从而使 CST 运动功能得以表达，这表明促进了节段性转换的发展。我们通过在猫的颈膨大区（cervical enlargement）中进行记录之前（出生后第 5 周（PW5）至第 7 周（PW7））和之后的 CST 诱发的焦点突触电位的体外记录来测试这一点。我们将 CST 诱发的单突触 CST 幅度输入与少突触腹角反应进行了比较，作为 CST 从输入到输出诱发的节段反应传递的测量。在 PW5 和 PW7 之间，单侧使初级运动皮层（M1）失活，以确定活动依赖性。使用共聚焦显微镜识别 CST 中间神经元接触。CST 末端接触多种中间神经元类。在中间神经元和 CST 脊髓末端均已发育出成熟表型的年龄，CST 刺激强烈激活了腹侧运动回路，支持 CST 信号的节段传递的发展。CST 活动阻断会阻碍失活的 CST 产生有效的节段传递，并为来自对侧未受影响的 CST 的传递创造了新途径。我们的发现表明，节段性 CST 信号传递的发展调节了 CST 运动控制功能的出现，并为深入了解运动技能发育的系统水平机制提供了见识。
