Electron microscopic studies on neuroblast differentiation in the central nervous system of domestic fowl

Summary

Using optic lobe and telencephalon of the domestic fowl, ranging in age from 2 days of incubation to the adult, the fine structure of the nerve cells and the morphologic changes associated with their differentiation were observed with the electron microscope. Data of ³H-thymidine autoradiography were used for orientation as to the distribution of the matrix cells and neuroblasts in the wall of the neural tube.

• 1. The matrix layer, which earlier has been called primitive ependymal layer, is composed of solely one kind of cell, named the matrix cell.

• 2. The characteristics in the fine structure of the matrix cell are abundant free ribosomes and a poorly developed intracellular membrane system. The matrix cell contains a small Golgi complex, but little rough-surfaced endoplasmic reticulum. In the cytoplasm several mitochondria are scattered and the ribosomes form small aggregates throughout the cytoplasm.

• 3. From the earliest stage of differentiation, the neuroblasts differ from the matrix cells as to the development of a rough-surfaced and a smooth endoplasmic reticulum.

• 4. As the neuroblast matures, the endoplasmic reticulum, intracellular vacuoles, and mitochondria gradually develop, and the rough-surfaced endoplasmic reticulum seems eventually to become the structure called Nissl substance.