ELECTRON MICROSCOPIC OBSERVATIONS OF THE CENTRAL NERVOUS SYSTEM

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Abstract
Sections of the brains and spinal cords of mice, rabbits, guinea pigs and rats; and portions of tumors of the human brain were examined by electron microscopy. Identification of neurons was made possible by the distinct and characteristic granular and membranous ergastoplasmic pattern, unlike that of any other cell in the central nervous system. The shape of the neuron is similar to that seen by light microscopy. Synapses are relatively common on the surface. Microglial cells are small, dense, with few processes, and occasionally contain phagocytized material. The oligodendroglial cells are identifiable by their position as perineuronal satellites and in rows in the white matter. They have a round to ovoid nucleus and pale cytoplasm. The processes are few and relatively straight. The predominant cellular type in an oligoden-droglioma was similar. The astrocytes are variable in appearance. Their nuclei are moderately large, irregularly ovoid, and the cytoplasm adjacent to the nucleus is finely granular and scant. In the protoplasmic astrocytes the cytoplasm has a complicated infolded arrangement with reduplication of the plasma membrane, numerous processes extending radially from the cell and rebranching. Fibrous astrocytes, to a certain extent, show a similar folded plasma membrane arrangement but their processes were straighter and filled with numerous fine dense fibrils. The processes of the astrocyte often surrounded axons and other cellular processes; they surrounded some vessels and attached to part of the wall of other vessels. Proliferating cells in experimentally produced gliosis and in astrocytic neoplasms were similar. The ependymal cells and epithelium of the choroid plexus have microvilli as well as varying numbers of cilia on their surfaces.