Smith Marquitta, Piehler Thuvan, Benjamin Richard, Farizatto Karen L, Pait Morgan C, Almeida Michael F, Ghukasyan Vladimir V, Bahr Ben A
Biotechnology Research and Training Center, University of North Carolina-Pembroke, Pembroke, NC 28372, USA.
U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005, USA.
Exp Neurol. 2016 Dec;286:107-115. doi: 10.1016/j.expneurol.2016.10.002. Epub 2016 Oct 5.
Explosives create shockwaves that cause blast-induced neurotrauma, one of the most common types of traumatic brain injury (TBI) linked to military service. Blast-induced TBIs are often associated with reduced cognitive and behavioral functions due to a variety of factors. To study the direct effects of military explosive blasts on brain tissue, we removed systemic factors by utilizing rat hippocampal slice cultures. The long-term slice cultures were briefly sealed air-tight in serum-free medium, lowered into a 37°C water-filled tank, and small 1.7-gram assemblies of cyclotrimethylene trinitramine (RDX) were detonated 15cm outside the tank, creating a distinct shockwave recorded at the culture plate position. Compared to control mock-treated groups of slices that received equal submerge time, 1-3 blast impacts caused a dose-dependent reduction in the AMPA receptor subunit GluR1. While only a small reduction was found in hippocampal slices exposed to a single RDX blast and harvested 1-2days later, slices that received two consecutive RDX blasts 4min apart exhibited a 26-40% reduction in GluR1, and the receptor subunit was further reduced by 64-72% after three consecutive blasts. Such loss correlated with increased levels of HDAC2, a histone deacetylase implicated in stress-induced reduction of glutamatergic transmission. No evidence of synaptic marker recovery was found at 72h post-blast. The presynaptic marker synaptophysin was found to have similar susceptibility as GluR1 to the multiple explosive detonations. In contrast to the synaptic protein reductions, actin levels were unchanged, spectrin breakdown was not detected, and Fluoro-Jade B staining found no indication of degenerating neurons in slices exposed to three RDX blasts, suggesting that small, sub-lethal explosives are capable of producing selective alterations to synaptic integrity. Together, these results indicate that blast waves from military explosive cause signs of synaptic compromise without producing severe neurodegeneration, perhaps explaining the cognitive and behavioral changes in those blast-induced TBI sufferers that have no detectable neuropathology.
爆炸物产生的冲击波会导致爆炸所致神经创伤，这是与军事服役相关的最常见的创伤性脑损伤（TBI）类型之一。由于多种因素，爆炸所致的创伤性脑损伤常与认知和行为功能减退有关。为了研究军事爆炸对脑组织的直接影响，我们利用大鼠海马切片培养物消除了全身因素。将长期切片培养物在无血清培养基中短暂气密密封，放入37℃的水箱中，在水箱外15厘米处引爆1.7克的环三亚甲基三硝胺（RDX）小组件，在培养板位置记录到明显的冲击波。与接受相同浸没时间的对照模拟处理切片组相比，1 - 3次爆炸冲击导致AMPA受体亚基GluR1呈剂量依赖性减少。虽然在单次RDX爆炸后1 - 2天收获的海马切片中仅发现GluR1有小幅减少，但间隔4分钟接受两次连续RDX爆炸的切片中GluR1减少了26 - 40%，连续三次爆炸后该受体亚基进一步减少了64 - 72%。这种减少与HDAC2水平升高相关，HDAC2是一种组蛋白脱乙酰酶，与应激诱导的谷氨酸能传递减少有关。爆炸后72小时未发现突触标记物恢复的证据。发现突触前标记物突触素与GluR1对多次爆炸引爆具有相似的敏感性。与突触蛋白减少形成对比的是，肌动蛋白水平未改变，未检测到血影蛋白分解，并且在接受三次RDX爆炸的切片中，Fluoro - Jade B染色未发现神经元退变迹象，这表明小型、亚致死性爆炸物能够对突触完整性产生选择性改变。总之，这些结果表明军事爆炸产生的冲击波会导致突触受损迹象，但不会造成严重的神经退行性变，这或许可以解释那些爆炸所致创伤性脑损伤患者虽无明显神经病理学改变但出现认知和行为变化的原因。
