Astrocytic neuroglial cells, oligodendrocytes and microgliacytes in the spinal cord of the toad

Summary

Three types of glial cells corresponding to astrocytes, oligodendrocytes, and microgliacytes were found in the toad spinal cord stained with a modification of the Golgi-Río Hortega technique. Each can be correlated with a characteristic type of nucleus stained with toluidine blue.

Astrocytic neuroglial cells are common near the central canal and have large nuclei with lightly stained nucleoplasm and finely granular chromatin. In silver impregnations, astrocytic neuroglial cells are characterized by many fine, spinose or lamellate excrescences which arise from cell somata and from the long peripherally directed processes that extend to the pia. No cells having the stellate form of mammalian astrocytes were seen, and large end-feet have only been seen near the surface of the brain suggesting that the primary relation of this cell is with the pia rather than with the capillaries.

Oligodendrocytes are common in the white matter and near capillaries, but do not occur as neuronal satellites. Nuclei are characterized by large aggregates of chromatin and deep membrane invaginations. A spectrum of oligodendrocytes has been seen with the Golgi technique similar to the four types described in mammals by del Río Hortega. Small stellate cells of type I and II are most common and are seen in both white and gray matter. Tubular reticulate structures typical of type IV oligodendrocytes are identical to Golgi impregnated Schwann cells of peripheral nerves and are most abundant in the white matter. The absence of an identifiable soma raises the question of whether the reticulum is located on the outer or the inner surface of myelin.

Microgliacytes are most common in areas of dense neuropile and do not form satellites. Nuclei are small, dark, and elongate often with irregular protuberances. In Golgi impregnations two or more long processes arise from a small, irregularly shaped soma. They are covered by spinous or thorn-like processes similar to those of the primitive mammalian pseudopodial variety.