A comparison of the initial retinal ganglion cell projection to the contralateral superior colliculus in albino and pigmented rats.

Newborn albino and pigmented rats received localised Fast blue (FB) injections into the most caudal part of the contralateral superior colliculus (SC). A proportion of retinal ganglion cells (RGC's) from the temporal retina which in the adult projects exclusively to the rostral half of the colliculus are labelled by injections to the caudal colliculus in neonatal animals. The majority of these cells die during the period of naturally occurring cell death in the retina, which occurs during the first 10 postnatal days. The object of this experiment was to see whether albino rats, which have well documented abnormalities in axon pathfinding in their visual system, had a larger number of cells in temporal retina which initially project to caudal colliculus than pigmented animals. On postnatal day 2 (P2), the ratio of temporal to nasal RGCs projecting to the caudal SC is greater in albino than pigmented rats (6.2% vs 2.65%). After the wave of naturally occurring cell death, at P14, when many of the neonatal errors have been eliminated, the ratio of temporal to nasal RGC's is reduced to 1.71% for albinos versus 1.53% for pigmented rats.