Prado Figueroa María, Flores Luis, Sanchez Juvenal, Cesaretti Nora
Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), CONICET/Universidad Nacional del Sur, La Carrindanga km 7, CC 857, FWB8000 Bahía Blanca, Argentina.
Micron. 2008 Oct;39(7):859-67. doi: 10.1016/j.micron.2007.12.005. Epub 2007 Dec 23.
Aluminum and silicon have been observed to be present in the human degenerated brain and normal elderly brains by using a combination of scanning electron microscopy and X-ray spectrometry (EDS-SEM). Al and Si of electric organs were also reported--in electrocytes and cholinergic nerves--from living electric fish (family Rajidae). A biogenically produced crystalline mineral phase (i.e., chalcedony) has also been observed in electric organs by using a mineralogical microscope. Based on this evidence we decided to explore the presence of chalcedony (SiO2) in the human central nervous system (CNS). Sections from aged patients (mean, 81 years) were collected after autopsy and observed using a Leica DMLP mineralogical microscope. Chalcedony was detected in cerebral cortex and cerebellum. In plane-polarized light, chalcedony is rounded in shape, 12-20 microm in size, translucent, with a low refraction index. The crossed-polarizer image shows first order birefringence color (grey-white) and radial extinction. Chalcedony was also detected in the hippocampus in large amounts and sizes (50-60 microm). Chalcedony is a microcrystalline fibrous form of silica. It consists of nanoscale intergrowths of quartz and the optically length-slow fibrous silica polymorph moganite. Chalcedony precipitation occurs at a specific pH (7-8) and oxidation potential (Eh; 0.0 to -0.2) in geological environments. This observation supports the important role played by pH and Eh conditions in silica precipitation in elderly brains, as has also been reported in peripheral cholinergic nerves in electric organ from living electric fish. Carbonic anhydrases (CAs) (silicase) are involved in physiological pH regulation and may also be participating in the polymerization-depolymerization of chalcedony in the human brain. This is the first time a biogenically produced crystalline mineral phase (i.e., chalcedony) has been observed in the human CNS from aged patients.
通过扫描电子显微镜和X射线能谱仪（EDS-SEM）相结合的方法，已观察到铝和硅存在于人类退化大脑和正常老年大脑中。也有报道称，在活电鱼（鳐科）的发电器官中，即电细胞和胆碱能神经中，存在铝和硅。利用矿物显微镜，在发电器官中还观察到一种生物成因产生的结晶矿物相（即玉髓）。基于这些证据，我们决定探索玉髓（SiO₂）在人类中枢神经系统（CNS）中的存在情况。在尸检后收集了老年患者（平均年龄81岁）的切片，并使用徕卡DMLP矿物显微镜进行观察。在大脑皮层和小脑中检测到了玉髓。在平面偏振光下，玉髓呈圆形，大小为12 - 20微米，半透明，折射率低。正交偏光镜图像显示一级双折射颜色（灰白色）和径向消光。在海马体中也检测到了大量且尺寸较大（50 - 60微米）的玉髓。玉髓是二氧化硅的微晶纤维形式。它由石英和光学上长度较慢的纤维状二氧化硅多晶型物莫来石的纳米级共生体组成。在地质环境中，玉髓沉淀发生在特定的pH值（7 - 8）和氧化电位（Eh；0.0至 -0.2）下。这一观察结果支持了pH值和Eh条件在老年大脑二氧化硅沉淀中所起的重要作用，这在活电鱼发电器官的外周胆碱能神经中也有报道。碳酸酐酶（CAs）（硅酶）参与生理pH调节，也可能参与人脑玉髓的聚合 - 解聚过程。这是首次在老年患者的人类中枢神经系统中观察到生物成因产生的结晶矿物相（即玉髓）。
