The present study aimed to elucidate the distribution of ferric and ferrous iron in the hippocampus after kainate-induced neuronal injury. A modified Perl's or Turnbull's blue histochemical stain was used to demonstrate Fe3+ and Fe2+ respectively. Very light staining for iron was observed in the hippocampus, in normal or saline-injected rats and 1-day post-kainate-injected rats. At 1 week postinjection, a number of Fe3+-positive, but very few Fe2+-positive, cells were present, in the degenerating CA fields. At 1 month postinjection, large numbers of Fe3+-positive glial cells, and some Fe2+-positive blood vessels, were observed. At 2 months postinjection, large numbers of Fe3+- and Fe2+-positive glial cells were present. The labeled cells had light and electron microscopic features of oligodendrocytes, and were double labeled with CNPase, a marker for oligodendrocytes. The observation of an increasing number of Fe3+- and Fe2+-positive cells in the degenerating hippocampus with time is consistent with the results of a nuclear microscopic study, in which an increasing amount of iron was detected in the degenerating hippocampus after kainate injection. In addition, the present study showed a shift in the oxidation state of the accumulated iron, with more cells becoming Fe2+ at a late stage. A possible consequence of the high amounts of Fe2+ in the hippocampus after kainate injection is that it could promote free radical damage in the lesioned areas.
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