Journal of Neuroscience, Vol 6, 2479-2488, Copyright © 1986 by Society for Neuroscience
Movement of retinal terminals in goldfish optic tectum predicted by analysis of neuronal proliferation
PA Raymond
Quantitative, computer-assisted autoradiography was used to assess the
relative rate and pattern of growth of retina and tectum in larval and
early juvenile goldfish. 3H-thymidine was used to mark the boundary of
retina and tectum, and the location of this boundary was charted as the eye
and brain grew and added more cells. The pattern of growth is at all times
discordant. The original (larval) retina becomes surrounded by annuli of
new tissue, whereas the larval tectum remains adjacent to the rostral edge
as crescents of new tissue are added to the caudal end. After 2 years of
growth, more than 95% of the total surface area of retina and tectum in
goldfish derives from cells born after larval stages. Computer-aided
reconstructions of 3H-thymidine labeled retina and tecta were used to
predict the direction and magnitude of displacement of the retinotopic map.
It was estimated that retinal terminals can shift 1.5-1.8 mm caudally at a
rate of 5 micron/d during the first 2 years of growth. The terminals that
move the farthest are those from temporal retina that project to rostral
tectum. The magnitude and direction of the predicted movements matches
certain features of HRP-filled retinal axons that others have assumed
represented the history of displacements of the terminal arbors.