Immunohistochemical study of glutamine synthetase expression in early glial development

Early glial development in the brains of rat embryos was immunohistochemically studied using antibodies to two kinds of glial-specific proteins, glutamine synthetase (GS) and glial fibrillary acidic protein (GFAP). The results showed that GS was first expressed in the ependymal lining of the ventral side of the neural tube in the cervical segment on Embryonic Day 14 and then in the radial glia radiating from the neural tube on Embryonic Day 16. Subsequently, GS-positive glia cells increased in number with time. On the other hand, GFAP was first expressed in the fimbria hippocampi and the pial surface on Embryonic Day 18, but no marked evidence of GFAP expression was noted in the GS-positive radial glia. These results suggested that a specific protein is expressed at each stage of early glial development. Since the radial glia was positive for GS, it was thought that GS-mediated neuronal-glial interactions may play an important role in the development of the central nervous system.