A common morphological response of astrocytes to various injuries: "dark" astrocytes. A light and electron microscopic analysis.

Our previous studies showed that neurons became argyrophilic following different kinds of brain injuries. In the present study we demonstrated that astrocytes could also become argyrophilic following compressive or concussive head injuries and following intraperitoneal administration of pentylenetetrazole or kainic acid. Furthermore the soma, nucleus and processes of these argyrophilic astrocytes were shown in other preparations to be hyper-basophilic with the light microscope, and hyper-electron dense and shrunken at the ultrastructural level. When the head injuries were inflicted either at the 15th min. of perfusion-fixation or at the 30th min. of transcardial perfusion with chilled physiological saline, several astrocytes also became argyrophilic, hyper-basophilic, shrunken and hyper-electron dense. These data indicate that (i) the intracellular pathological event in these astrocytes is similar to that of "dark" neurons or "dark" cells of non-neural tissues, (ii) the formation of "dark" astrocytes can be independent of the actual state of metabolism, and (iii) the "dark" morphological state of astrocytes might have a role in neuropathological processes.