Microglia-like cells in the chicken ciliary ganglion

Abstract

Using light and electron microscopy we have identified in the ciliary ganglion of the chick a class of small cells characterized by the electron-dense appearance of both nucleus and cytoplasm, slender cell processes, paucity of mitochondria and microtubules, presence of elongated cisterns of granular endoplasmic reticulum with narrow lumina, free ribosomes, dense bodies of varying size and coated vesicles. The small, elongated electron-dense cells lack a basal lamina and occur within the satellite sheath surrounding ganglionic perikarya as well as in the endoneurial connective tissue. Occasionally, the small electron-dense cells within the ganglion cell capsule contain phagocytized cell debris. The small electron-dense cells of the ciliary ganglion differ substantially from satellite cells and other types of cell in the endoneurial connective tissue, except those of hematic origin. On the other hand, in their fine structure they closely resemble resting microglial cells of the CNS. We suggest that small electron-dense cells in the ganglion and microglial cells in the CNS belong to the same cell category.