An Ultrastructural Study of the Development of Astrocytes in the Midbrain of the Lizard

Astrocyte development was investigated electron microscopically in the midbrain of the lizard Gallotia galloti from E32 to adult. At E32 only very immature (early) glioblasts were present in the midbrain and similar cells could be found until hatching. From E34 two other types of glioblast could be identified--dark glioblasts which had a slightly greater amount of cytoplasm than early glioblasts and light glioblasts, in which cytoplasmic organelles were more abundant. Both dark and light glioblasts were present in very small numbers in the adults. Astroblasts, which could be identified by the characteristic appearance of their rough endoplasmic reticulum, first appeared at E35, at which stage a few very immature astrocytes containing small quantities of gliofilaments were also present. With increasing age the quantity of gliofilaments in astrocyte cytoplasm increased. Astrocytes in the adult white matter contained very large amounts of gliofilaments whereas those in grey matter contained many fewer gliofilaments and had glycogen granules in their cytoplasm which were rarely present in mature fibrous astrocytes.