The expanded visual projections which develop after unilateral eye removal have been associated in some studies, but not in others, with the survival of more
ganglion cells than normal in the remaining eye. We have addressed this issue using the small wallaby Setonix brachyurus, quokka. Moreover to determine whether more
ganglion cells survive when the eye is removed at a very early stage, we have compared the effect of enucleations at two ages. These were within 3 days of birth, before optic fibres innervate visual centres, and at 35-40 days postnatal, when visual projections are exuberant. At 100 days postnatal, retinal ganglion cells were retrogradely labelled from primary visual centres and tracts with
horseradish peroxidase, allowing 24 h for transport. Numbers of
ganglion cells were similar between animals enucleated as neonates (X = 231,000, n = 3) and at 35-40 days postnatal (X = 218,000, n = 4). These results were comparable to those of controls (X = 227,000, n = 5). Distributions of
ganglion cells were also essentially similar in experimental and control series. However, mean
ganglion cell
soma diameter was significantly greater than normal in both the area centralis and temporal retina after neonatal enucleation. Our results indicate that in enucleated quokkas increased
ganglion cell numbers do not underlie enhanced retinofugal projections.