Section of Physiology, Department of Integrative Medical Biology, Umeå University , Umeå , Sweden.
Department of Physiology, Institute of Neuroscience and Physiology, Sahlgrenska Academy at University of Gothenburg , Gothenburg , Sweden.
Front Neurol. 2014 Jun 20;5:103. doi: 10.3389/fneur.2014.00103. eCollection 2014.
The corticospinal system is a major motor pathway in the control of skilled voluntary movements such as reaching and grasping. It has developed considerably phylogenetically to reach a peak in humans. Because rodents possess advanced forelimb movements that can be used for reaching and grasping food, it is commonly considered that the corticospinal tract (CST) is of major importance for this control also in rodents. A close homology to primate reaching and grasping has been described but with obvious limitations as to independent digit movements, which are lacking in rodents. Nevertheless, it was believed that there are, as in the primate, direct cortico-motoneuronal connections. Later, it was shown that there are no such connections. The fastest excitatory pathway is disynaptic, mediated via cortico-reticulospinal neurons and in the spinal cord the excitation is mainly polysynaptically mediated via segmental interneurons. Earlier behavioral studies have aimed at investigating the role of the CST by using pyramidotomy in the brainstem. However, in addition to interrupting the CST, a pyramidal transection abolishes the input to reticulospinal neurons. It is therefore not possible to conclude if the deficits after pyramidotomy result from interruption of the CST or the input to reticulospinal neurons or both. We have re-investigated the role of the CST by examining the effect of a CST lesion in the C1-C2 spinal segments on the success rate of reaching and grasping. This lesion spares the cortico-reticulospinal pathway. In contrast to investigations using pyramidal transections, the present study did not demonstrate marked deficits in reaching and grasping. We propose that the difference in results can be explained by the intact cortical input to reticulospinal neurons in our study and thus implicate an important role of this pathway in the control of reaching and grasping in the rat.
皮质脊髓系统是控制熟练自主运动（如伸手和抓握）的主要运动通路。它在系统发生上有了相当大的发展，在人类中达到了顶峰。由于啮齿动物具有可以用于伸手和抓握食物的先进前肢运动，因此通常认为皮质脊髓束（CST）在啮齿动物中对此类控制也很重要。已经描述了与灵长类动物伸手和抓握的密切同源性，但由于缺乏独立的手指运动，存在明显的局限性。尽管如此，人们认为存在类似于灵长类动物的皮质-运动神经元直接连接。后来，事实证明没有这样的连接。最快的兴奋性通路是双突触的，通过皮质-网状脊髓神经元介导，在脊髓中，兴奋主要通过节段性中间神经元多突触介导。早期的行为研究旨在通过脑桥中的锥体切开术来研究 CST 的作用。然而，除了中断 CST 之外，锥体切开术还会破坏网状脊髓神经元的输入。因此，无法确定锥体切开术后的缺陷是由于 CST 的中断还是网状脊髓神经元的输入或两者都有。我们通过检查 C1-C2 脊髓段 CST 损伤对伸手和抓握成功率的影响，重新研究了 CST 的作用。该损伤保留了皮质网状脊髓通路。与使用锥体横断术的研究不同，本研究未显示在伸手和抓握方面有明显缺陷。我们提出，结果的差异可以用我们研究中皮质对网状脊髓神经元的完整输入来解释，因此暗示该通路在大鼠伸手和抓握控制中起着重要作用。
