Department of Psychology, Vanderbilt University, Nashville, Tennessee 37240, USA.
J Neurosci. 2011 Sep 21;31(38):13662-75. doi: 10.1523/JNEUROSCI.2366-11.2011.
An incomplete lesion of the ascending afferents from the hand in the dorsal columns of the spinal cord in monkeys is followed after weeks of recovery by a reactivation of much of the territory of the hand representations in primary somatosensory cortex (area 3b). However, the relationship between the extent of the dorsal column lesion and the amount of cortical reactivation has not been clear. Largely, this is due to the uncertainties about axon sparing after spinal cord lesions. Here, we unilaterally sectioned dorsal column afferents in the cervical spinal cord (C4-C6) in adult squirrel monkeys. After weeks of recovery, cholera toxin subunit B (CTB) was injected into the distal phalanges to label normal and surviving afferents to the cuneate nuclei representing the hands. Days later, the responsiveness of neurons in cortical areas 3b and 1 to tactile stimulation on the hand was evaluated in a microelectrode mapping session. The sizes and densities of CTB-labeled patches in the cuneate nuclei of both sides were quantified and compared. The results indicate that extensive reactivations of the hand representations in cortical areas 3b and 1 occur contralateral to the spinal cord lesion, even when <1% of labeled dorsal column terminations in the cuneate nucleus remained. These results raise the possibilities that secondary afferents from innervated neurons in the spinal cord contribute to the reactivation, and that the reactivation of area 1 is not completely dependent on inputs from area 3b.
在猴子的脊髓背柱中，手部上升传入纤维的不完全损伤，在数周的恢复后，初级体感皮层（第 3b 区）中手部代表区的大部分区域重新活跃。然而，背柱损伤的程度与皮质再激活的程度之间的关系尚不清楚。在很大程度上，这是由于脊髓损伤后轴突保留的不确定性。在这里，我们在成年松鼠猴的颈段脊髓（C4-C6）中单侧切断背柱传入纤维。在数周的恢复后，霍乱毒素亚单位 B（CTB）被注入远节指骨，以标记代表手部的楔状核中的正常和存活传入纤维。几天后，在手部触觉刺激下，评估了皮质区域 3b 和 1 中神经元的反应性。对两侧楔状核中 CTB 标记斑块的大小和密度进行了定量比较。结果表明，即使在楔状核中标记的背柱末端只剩下<1%，手部代表区在皮质区域 3b 和 1 中的广泛再激活也会发生在脊髓损伤的对侧。这些结果提出了以下可能性：来自脊髓中受神经支配神经元的次级传入可能有助于再激活，并且 1 区的再激活并不完全依赖于 3b 区的输入。
