Brain Research Institute, University of Zurich and Swiss Federal Institute of Technology, ETH,8057 Zurich, Switzerland.
Cereb Cortex. 2012 Jun;22(6):1309-17. doi: 10.1093/cercor/bhr191. Epub 2011 Aug 11.
A large thoracic spinal cord injury disconnects the hindlimb (HL) sensory-motor cortex from its target, the lumbar spinal cord. The fate of the synaptic structures of the axotomized cortical neurons is not well studied. We evaluated the density of spines on axotomized corticospinal neurons at 3, 7, and 21 days after the injury in adult mice expressing yellow fluorescence protein in a subset of layer 5 neurons. Spine density of the dendritic segment proximal to the soma (in layer 5) declined as early as 3 days after injury, far preceding the onset of somatic atrophy. In the distal segment (in layer 2/3), spine loss was slower and less severe than in the proximal segment. Axotomy of corticospinal axons in the brainstem (pyramidotomy) induced a comparable reduction of spine density, demonstrating that the loss is not restricted to the neurons axotomized in the thoracic spinal cord. Surprisingly, in both forms of injury, the spine density of putative non-axotomized layer 5 neurons was reduced as well. The spine loss may reflect fast rearrangements of cortical circuits after axotomy, for example, by a disconnection of HL cortical neurons from synaptic inputs that no longer provide useful information.
大的胸段脊髓损伤使后肢（HL）感觉-运动皮层与其靶标，即腰脊髓相分离。轴突切断的皮质神经元的突触结构的命运尚未得到很好的研究。我们在成年小鼠中评估了在损伤后 3、7 和 21 天表达黄色荧光蛋白的一小部分 5 层神经元中轴突切断的皮质脊髓神经元的棘突密度。早在损伤后 3 天，靠近胞体的树突段（5 层）的棘突密度就开始下降，远早于体萎缩的发生。在远端段（2/3 层），棘突丢失比近端段慢且不严重。脑桥皮质脊髓轴突的轴突切断（锥体切开术）诱导了类似的棘突密度降低，表明这种丢失不仅限于胸段脊髓中被轴突切断的神经元。令人惊讶的是，在这两种形式的损伤中，假定未被轴突切断的 5 层神经元的棘突密度也降低了。棘突丢失可能反映了轴突切断后皮质回路的快速重排，例如，HL 皮质神经元与不再提供有用信息的突触输入的分离。
