Retinal ganglion cell death and terminal field retraction in the developing rodent visual system

The anterograde and retrograde transport of HRP has been employed in neonatal rats and adult rats which were unilaterally enucleated at various stages during the first week after birth. In neonatal animals given unilateral thalamic implants of horseradish peroxidase, the number of labelled retinal ganglion cells in the ipsilateral eye declines over the first week. This is considered to be a consequence of cell death. At the same time unilateral intraocular injections of the same tracer reveals that the terminal field of ipsilaterally projecting retinal axons in the dorsal lateral geniculate nucleus is retracting to form the adult pattern. It is proposed that retraction and ganglion cell death are related. In the monocular adult animals it is shown that fewer ipsilaterally projecting ganglion cells are found the later enucleation takes place. But the number of ipsilaterally projecting cells found in the adult animal enucleated at birth is not as great as the number found in the newborn rat. In spite of this the proportion of the dorsal lateral geniculate nucleus occupied by ipsilaterally projecting ganglion cells is similar in neonates of a given age and adults that were enucleated at that age.