Investigation of glial cells in semithin sections. I. Identification of glial cells in the brain of young rats

Abstract

Abstract The staining of half‐micron thick Epon sections with toluidine blue provides a reliable method for the identification of glial cells. The diagnostic features of these cells observed in the corpus callosum of one‐month‐old rats are as follows: (1) Astrocytes have a very pale nucleus and cytoplasm; the nuclear envelope is sharply outlined by a thin chromatin lining with occasional chromatin beads; (2) Microglia have a small nucleus in which large, dark chromatin masses contrast with the nucleoplasm; the nucleus is round or elongated, and may be somewhat angular. The pericytes, which have a similar but usually crescentic nucleus, may be related to microglia. (3) Oligodendrocytes vary from pale to very dense and may be arbitrarily classified into three subgroups: The light oligodendrocytes are large pale cells with round to ovoid nucleus containing a prominent nucleolus and little or no condensed chromatin; the cytoplasm is extensive and appears pale, although less so than the nucleus. The medium shade oligodendrocytes are smaller cells that have an ovoid nucleus carrying small chromatin clumps and appearing moderately basophilic throughout; the cytoplasm is less extensive and somewhat darker than in the “light” subgroup. The dark oligodendrocytes are usually smaller than medium shade cells and often have an indented or angular nucleus with large chromatin masses; both nucleoplasm and cytoplasm are densely stained; the cytoplasm is often scanty and accumulated on one side of the nucleus. Semithin sections of the cerebral cortex show glia with similar features, with the exception of the astrocytes, which have a smaller but more basophilic cytoplasm than in corpus callosum. The cells of the subependymal layer of the lateral ventricle, when examined in semithin sections in the neighborhood of the corpus callosum, display a patchy, irregular nucleus and a scanty cytoplasm. Similar cells with a more regular nucleus are found outside the layer and in the corpus callosum; they are designated free subependymal cells .