Abstract：
Ultrastructural studies of contusive spinal cord injury (SCI) in mammals have shown that the most prominent acute changes in white matter are periaxonal swelling and separation of myelin away from their axon, axonal swelling, and axonal spheroid formation. However, the underlying cellular and molecular mechanisms that cause periaxonal swelling and the functional consequences are poorly understood. We hypothesized that periaxonal swelling and loss of connectivity between the axo-myelinic interface impedes neurological recovery by disrupting conduction velocity, and glial to axonal trophic support resulting in axonal swelling and spheroid formation. Utilizing in vivo longitudinal imaging of Thy1YFP+ axons and myelin labeled with Nile red, we reveal that periaxonal swelling significantly increases acutely following a contusive SCI (T13, 30 kdyn, IH Impactor) versus baseline recordings (laminectomy only) and often precedes axonal spheroid formation. In addition, using longitudinal imaging to determine the fate of myelinated fibers acutely after SCI, we show that ∼73% of myelinated fibers present with periaxonal swelling at 1 h post SCI and ∼ 51% of those fibers transition to axonal spheroids by 4 h post SCI. Next, we assessed whether cation-chloride cotransporters present within the internode contributed to periaxonal swelling and whether their modulation would increase white matter sparing and improve neurological recovery following a moderate contusive SCI (T9, 50 kdyn). Mechanistically, activation of the cation-chloride cotransporter KCC2 did not improve neurological recovery and acute axonal survival, but did improve chronic tissue sparing. In distinction, the NKKC1 antagonist bumetanide improved neurological recovery, tissue sparing, and axonal survival, in part through preventing periaxonal swelling and disruption of the axo-myelinic interface. Collectively, these data reveal a novel neuroprotective target to prevent periaxonal swelling and improve neurological recovery after SCI.
摘要：
哺乳动物挫伤性脊髓损伤（SCI）的超微结构研究表明，白质中最突出的急性变化是轴突周围肿胀和髓鞘从轴突分离。轴突肿胀,和轴突球状体的形成。然而,导致轴突周围肿胀的潜在细胞和分子机制以及功能后果知之甚少。我们假设轴突周围肿胀和轴髓界面之间的连通性丧失通过破坏传导速度来阻碍神经恢复。和神经胶质到轴突营养支持导致轴突肿胀和球体形成。利用Thy1YFP+轴突和尼罗红标记的髓鞘的体内纵向成像，我们发现，在挫伤性脊髓损伤后，轴突周围肿胀显著增加(T13，30kdyn，IH冲击器）与基线记录（仅椎板切除术）相比，并且通常先于轴突球体形成。此外,使用纵向成像来确定SCI后急性有髓纤维的命运，我们显示，SCI后1小时，有73%的有髓纤维出现轴突周围肿胀，SCI后4小时，这些纤维中有51%过渡到轴突球体。接下来,我们评估了在中度挫伤性SCI(T9,50kdyn)后,节间存在的阳离子-氯化物协同转运蛋白是否导致轴突周围肿胀,以及它们的调节是否会增加白质的保留并改善神经系统恢复.机械上,阳离子-氯化物协同转运蛋白KCC2的激活并不能改善神经恢复和急性轴突存活,但确实改善了慢性组织的保留。在区别上,NKKC1拮抗剂布美他尼改善了神经恢复，组织保留，和轴突存活，部分通过防止轴突周围肿胀和轴突-髓质界面的破坏。总的来说，这些数据揭示了一种新的神经保护靶点,可预防脊髓损伤后轴突周围肿胀并改善神经功能恢复.
