Basal ganglia calcification induced by excitotoxicity: an experimental model characterised by electron microscopy and X-ray microanalysis

Activation of glutamate receptors induces an excitotoxic neurodegenerative process characterised in some brain areas by the formation of calcium preci pitates. To examine the pathogenesis of basal ganglia calcification (BGC), an improved procedure of X-ray microanalysis was used to study experimental excitotoxic calcification in the rat. Three weeks after injection of ibote nic acid (IBO) in the rat basal forebrain, calcified inclusions within hype rtrophied astrocytes were characterised. They appeared to form part of a fi lamentous structure localised in the cytoplasm in association with normal m itochondria and other organelles. Larger inclusions were surrounded by reac tive microglia. The main inorganic components in these deposits were Ca and P, frequently accompanied by S, Al, Si and K. The shape and Ca/P molar rat io of the large deposits (> 10 mu m) indicate that they may be biological a patites. Aluminosilicates were detected as small deposits (< 4 mu m) free o f other mineral constituents. To our knowledge this is the first report sho wing that IBO lesion induces brain accumulation of aluminosilicates similar to that described in Alzheimer's or Fahr's patients. Our data indicate tha t precipitation of Ca and Al may reduce their IBO-induced increased concent ration. In conclusion, the experimental model and the improved efficiency o f X-ray analysis described may help us to understand the pathogenesis of BG C.