Development of visual projections in the marsupial, Setonix brachyurus.

Retinal projections to the primary visual centres were studied following injection of tritiated proline into one eye in the Marsupial, Setonix brachyurus between 10 and 100 days postnatal and in adults. Initially, projections from the two eyes overlapped extensively, particularly between 20 and 50 days. There was a gradual refinement thereafter, including a segregation of inputs from the two eyes within both the lateral geniculate nucleus (LGN) and superior colliculus (SC) by 70 days. Such refinement in visual centres is discussed in relation to the concurrent emergence of retinal ganglion cell density gradients, a decrease in ganglion cell numbers, cell death in the ganglion cell layer and loss of optic axonal profiles.