Development and stability of postional information in Xenopus retinal ganglion cells.

Neuronal specificity in retinal ganglion cells of Xenopus subserves the orderly connections of the optic nerve fibers in the tectum. This specificity derives from positional information acquired by the developing retina at embryonic stages 28-31. Here we report that ganglion cells of embryonic stage 28 eyes can acquire positional information with reference to the major axes of the body not only in the ocular orbit but also at other positions on the side of the body. When returned to the orbit this eye will form appropriate retinotectal connections. Conversely, retinal ganglion cells of stage 31 eyes, which have acquired positional information in the orbit, will retain their original neuronal positional specificities if the formation of retinotectal connections is delayed by grafting the eye to the flank for 30 days before returning it to the orbit. We conclude that neuronal specificity of retinal ganglion cells (a) does not derive from "inducers" unique to the periocular tissues; and (b) persists for some time independently of the establishment of retinotectal connections.