Liao Chia-Chi, DiCarlo Gabriella E, Gharbawie Omar A, Qi Hui-Xin, Kaas Jon H
Department of Psychology, Vanderbilt University, Nashville, Tennessee, 37240, USA.
J Comp Neurol. 2015 Oct 1;523(14):2138-60. doi: 10.1002/cne.23783. Epub 2015 Jun 2.
Dorsal column lesions at a high cervical level deprive the cuneate nucleus and much of the somatosensory system of its major cutaneous inputs. Over weeks of recovery, much of the hand representations in the contralateral cortex are reactivated. One possibility for such cortical reactivation by hand afferents is that preserved second-order spinal cord neurons reach the cuneate nucleus through pathways that circumvent the dorsal column lesions, contributing to cortical reactivation in an increasingly effective manner over time. To evaluate this possibility, we first injected anatomical tracers into the cuneate nucleus and plotted the distributions of labeled spinal cord neurons and fibers in control monkeys. Large numbers of neurons in the dorsal horn of the cervical spinal cord were labeled, especially ipsilaterally in lamina IV. Labeled fibers were distributed in the cuneate fasciculus and lateral funiculus. In three other squirrel monkeys, unilateral dorsal column lesions were placed at the cervical segment 4 level and tracers were injected into the ipsilateral cuneate nucleus. Two weeks later, a largely unresponsive hand representation in contralateral somatosensory cortex confirmed the effectiveness of the dorsal column lesion. However, tracer injections in the cuneate nucleus labeled only about 5% of the normal number of dorsal horn neurons, mainly in lamina IV, below the level of lesions. Our results revealed a small second-order pathway to the cuneate nucleus that survives high cervical dorsal column lesions by traveling in the lateral funiculus. This could be important for cortical reactivation by hand afferents, and recovery of hand use.
高颈段的背柱损伤使楔束核和大部分体感系统失去了主要的皮肤传入信号。在数周的恢复过程中，对侧皮质中手部的大部分表征会重新激活。手部传入信号引起这种皮质重新激活的一种可能性是，保留的脊髓二级神经元通过绕过背柱损伤的通路到达楔束核，并随着时间的推移以越来越有效的方式促进皮质重新激活。为了评估这种可能性，我们首先将解剖示踪剂注入楔束核，并绘制了对照猴中标记的脊髓神经元和纤维的分布。颈脊髓背角中有大量神经元被标记，尤其是同侧的IV层。标记纤维分布在楔束和外侧索中。在另外三只松鼠猴中，在颈4节段进行单侧背柱损伤，并将示踪剂注入同侧楔束核。两周后，对侧体感皮质中对手部的反应基本消失，证实了背柱损伤的有效性。然而，向楔束核注射示踪剂仅标记了损伤水平以下背角神经元正常数量的约5%，主要在IV层。我们的结果揭示了一条通向楔束核的小二级通路，该通路在高颈段背柱损伤后通过外侧索传导得以保留。这可能对手部传入信号引起的皮质重新激活以及手部功能恢复具有重要意义。
