The Effects of Monocular Enucleation on Ganglion Cell Number and Terminal Distribution in the Ferret's Retinal Pathway

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Abstract
Anterograde and retrograde tracing techniques were used to examine the effects of removing one eye at birth on the remaining uncrossed retinal pathway in adult ferrets. After enucleation, the adult number of labelled ganglion cells projecting ipsilaterally changed from an average of 6068 in normal pigmented ferrets to an average of 7813 (29% increase) in pigmented enucleates. The change in albino ferrets was from 1455 in normals to 2319 in enucleates (59% increase). Labelled cells scattered across nasal retina accounted for over half the increase in the uncrossed population. After neonatal enucleation, the volume of lateral geniculate nucleus occupied by the uncrossed projection increased substantially: five-fold in pigmented animals and 20-fold in albinos. These results suggest that neonatal removal of one eye has a greater effect on the distribution of uncrossed terminals than on the survival of uncrossed ganglion cells. There was also an increase in the total number of axons in the surviving optic nerve of both pigmented and albino ferrets (93,000 in enucleates compared with 79,000 in normal animals), which cannot be simply explained as a disruption of binocular competition.