Enlargement of uncrossed retinal projections in the albino rat: additive effects of neonatal eye removal and thalamectomy.

The present study in the albino rat investigates the effects of neonatal unilateral eye removal and/or thalamectomy upon the number of ipsilaterally projecting retinal ganglion cells (IPRGCs), using retrograde fluorescent labelling and electron microscopy. The results show that neonatal unilateral eye removal and thalamectomy result in a significant increase in the number of aberrant IPRGCs as compared to that observed in normal rats, and the effects of the two different neonatal lesions appear to be additive. These findings strongly suggest that there are at least two subpopulations of IPRGCs, which normally do not exist in mature albino rats, but which can be preserved into adulthood by neonatal enucleation or thalamectomy. The data also suggest that about 70% of the entire population of IPRGCs, most of which normally exist only transiently in neonatal retinas, can be retained in rats which receive both unilateral eye removal and thalamectomy at the neonatal stage.