By means of a condenser discharge electric shock paradigm, "dark" (compacted) granule neurons were momentarily produced in the hippocampal dentate gyri of rats, which were sacrificed either immediately or following survival periods ranging from 1 h to 30 days. Except for the morphological changes related to the formation, recovery or death of the "dark" neurons, the affected brain areas remained undamaged. Vibratome, frozen, cryostat and paraffin sections were stained with Mayer's hematoxylin, acid fuchsin, or Fluoro-Jade and by three silver methods widely used for the demonstration of damaged neurons; with or without previous removal of nucleic acids, partial digestion of proteins or blockade of the negatively charged side-groups of nucleic acids and proteins. The results allowed the following conclusions: (i) "Dark" neurons acquire argyrophilia and excess basophilia simultaneously with their momentary formation. (ii) Negatively charged protein molecules are responsible for these processes. (iii) From the recovering "dark" neurons, the acquired basophilia and argyrophilia disappear within a few hours post-insult. (iv) From the moribund or dead "dark" neurons, the acquired basophilia disappears in the same period of time while the acquired argyrophilia in a few days. (vi) Freshly-produced or recovering "dark" neurons are slightly acidophilic, whereas the moribund or dead ones display intense acidophilia.
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