National Institute for Physiological Sciences, National Institutes of Natural Sciences, Department of Developmental Physiology, Myodaiji, Okazaki 444-8585, Japan.
J Neurophysiol. 2010 Sep;104(3):1707-16. doi: 10.1152/jn.00968.2009. Epub 2010 Jul 21.
Neonatally hemidecorticated rats show fairly normal reaching and grasping behaviors of the forelimb contralateral to the lesion at the adult stage. Previous experiments using an anterograde tracer showed that the corticospinal fibers originating from the sensorimotor cortex of the intact side projected aberrant collaterals to the spinal gray matter on the ipsilateral side. The present study used electrophysiological methods to investigate whether the aberrant projections of the corticospinal tract mediated the pyramidal excitation to the ipsilateral forelimb motoneurons and, if so, which pathways mediate the effect in the hemidecorticated rats. Electrical stimulation to the intact medullary pyramid elicited bilateral negative field potentials in the dorsal horn of the spinal cord. In intracellular recordings of forelimb motoneurons, oligosynaptic pyramidal excitation was detected on both sides of the spinal cord in the hemidecorticated rats, whereas pyramidal excitation of motoneurons on the side ipsilateral to the stimulation was much smaller in normal rats. By lesioning the dorsal funiculus at the upper cervical level, we clarified that the excitation was transmitted to the ipsilateral motoneurons by at least two pathways: one via the corticospinal tract and spinal interneurons and the other via the cortico-reticulo-spinal pathways. These results suggested that in the neonatally hemidecorticated rats, the forelimb movements on the side contralateral to the lesion were modulated by motor commands through the indirect ipsilateral descending pathways from the sensorimotor cortex of the intact side either via the spinal interneurons or reticulospinal neurons.
新生期半脑切除大鼠在成年期表现出与病变对侧前肢相当正常的伸展和抓握行为。以前使用顺行示踪剂的实验表明，来自完整侧感觉运动皮层的皮质脊髓纤维向同侧脊髓灰质投射异常侧支。本研究使用电生理方法研究皮质脊髓束的异常投射是否介导了对同侧前肢运动神经元的锥体激发，如果是这样，那么在半脑切除大鼠中哪种途径介导了这种效应。对完整延髓锥体进行电刺激，在脊髓背角诱发双侧负场电位。在半脑切除大鼠的前肢运动神经元的细胞内记录中，在脊髓的两侧都检测到了少突触的锥体激发，而在正常大鼠中，同侧刺激侧的运动神经元的锥体激发要小得多。通过在上颈段背侧束损伤，我们明确了兴奋通过至少两种途径传递到同侧运动神经元：一种是通过皮质脊髓束和脊髓中间神经元，另一种是通过皮质网状脊髓束。这些结果表明，在新生期半脑切除大鼠中，病变对侧的前肢运动通过来自完整侧感觉运动皮层的间接同侧下行通路通过脊髓中间神经元或网状脊髓神经元来调制运动指令。
