Immonen Riikka J, Kharatishvili Irina, Sierra Alejandra, Einula Christine, Pitkänen Asla, Gröhn Olli H J
Department of Neurobiology, University of Kuopio, FIN-70211 Kuopio, Finland.
Neuroimage. 2008 May 1;40(4):1718-30. doi: 10.1016/j.neuroimage.2008.01.042. Epub 2008 Feb 7.
We tested a hypothesis that manganese enhanced magnetic resonance imaging (MEMRI) after systemic injection of MnCl(2) could detect axonal sprouting in the hippocampus following kainate (KA) induced status epilepticus (SE). MEMRI was performed at 3 h, 25 h, 4 days, and 2 months post-SE. To assess the contribution of various cellular alterations that occur in parallel with sprouting to the MEMRI signal, we sacrificed animals for histology at 4 days and 2 months post-SE. Neurodegeneration was assessed from thionin and Fluoro-Jade B stained preparations, astrogliosis from GFAP (glial fibrillary acidic protein) and microgliosis from Ox-42 immunostained preparations. Sprouting of granule cells axons (mossy fibers) in the dentate gyrus was analyzed from Timm stained sections. Occurrence of spontaneous epileptic seizures was analyzed at 2 months post-SE using continuous video-EEG monitoring. Integrity of the blood-brain barrier (BBB) was studied using Gd-enhanced MRI. We found abnormal MEMRI hyperintensity in the CA1 and the dentate gyrus at 2 months post-SE but not at earlier time points. Based on histologic analysis of individual animals with MEMRI hyperintensity, hippocampal MEMRI changes could be attributed to increasing axonal density rather than to neurodegeneration, astrogliosis, or microgliosis. Moreover, MEMRI contrast was not affected by seizure activity, and we could not detect any leakage of the BBB that could have explained the observed MEMRI hyperintensity. Present data show that systemic MEMRI can reveal axonal sprouting, and thus, can potentially serve as a marker for neuroplasticity in preclinical studies.
我们测试了一个假设，即全身注射氯化锰（MnCl₂）后的锰增强磁共振成像（MEMRI）能够检测到在谷氨酸钾（KA）诱导的癫痫持续状态（SE）后海马体中的轴突发芽。在SE后3小时、25小时、4天和2个月进行MEMRI检查。为了评估与发芽同时发生的各种细胞改变对MEMRI信号的贡献，我们在SE后4天和2个月处死动物进行组织学检查。从硫堇和氟玉髓B染色制剂评估神经变性，从胶质纤维酸性蛋白（GFAP）评估星形胶质细胞增生，从抗小鼠巨噬细胞抗体（Ox-42）免疫染色制剂评估小胶质细胞增生。从Timm染色切片分析齿状回中颗粒细胞轴突（苔藓纤维）的发芽情况。在SE后2个月使用连续视频脑电图监测分析自发性癫痫发作的发生情况。使用钆增强MRI研究血脑屏障（BBB）的完整性。我们发现在SE后2个月时CA1和齿状回出现异常的MEMRI高信号，但在早期时间点未出现。基于对具有MEMRI高信号的个体动物的组织学分析，海马体MEMRI变化可归因于轴突密度增加，而非神经变性、星形胶质细胞增生或小胶质细胞增生。此外，MEMRI对比不受癫痫活动影响，并且我们未检测到任何可能解释所观察到的MEMRI高信号的BBB渗漏。目前的数据表明，全身MEMRI能够揭示轴突发芽，因此，在临床前研究中有可能作为神经可塑性的标志物。
