Differentiation of neurons and radial glia in the spinal cord of the teleost Brachydanio rerio (the zebrafish): An immunocytochemical study.

The differentiation of neurons and glial cells in the spinal cord of the zebrafish was studied by means of immunohistochemistry, using antisera against the 68 kD subunit of neurofilament (anti-NFP68) and against glial fibrillary acidic protein (anti-GFAP), both isolated from the bovine brain. Anti-NFP68 and anti-GFAP reactivity appear in the spinal cord at about 60 h after fertilization. At that time the anti-NFP68 reactivity is detectable in the dorsal Rohon-Beard neurons. About 12 h later, NFP68 positive neurons appear in the prospective motor column. In this respect the differentiation of the primary sensory system precedes that of the spinal motor system. During development the configuration of the glial cell processes changes from a horizontal arrangement in embryos to a radial frame work in larvae and in adults. From these observations together with data on the organization of the adult spinal motor column(28) we conclude that the motoneurons of the white and those of the red myotomal muscle fibers may have different origins in the neuroepithelial germinal layer. The anti-NFP68 serum recognizes a 120 and a 94 kD component of fish neurofilaments. Thus the subunit composition of neurofilament in fishes differs from that in mammals.