POSTNATAL CHANGES IN THE UNCROSSED RETINAL PROJECTION OF PIGMENTED AND ALBINO SYRIAN-HAMSTERS AND THE EFFECTS OF MONOCULAR ENUCLEATION

Anterograde and retrograde tracing techniques have been used to study the uncrossed retinal projection in neonatal pigmented and albino Syri an hamsters. The total number of retinal ganglion cells projecting ips ilaterally peaks at postnatal days 2-4 (P2-P4) and declines to adult v alues by P12. The change in cell numbers has a similar time course in albino and pigmented animals. Although the population of uncrossed cel ls in the temporal retina of albino hamsters is always less than that in pigmented hamsters, no difference between the colour phases was fou nd for the population of uncrossed cells in nasal retina. Differential cell death also contributes to the adult albino decussation pattern i n hamsters: The relative loss of cells from temporal retina in albinos (72%) is greater than that in pigmented animals (56%). The additional loss in albinos does not appear to depend on binocular interactions: The same proportion (30%) of uncrossed cells is ''rescued'' from death by neonatal monocular enucleation in both colour phases. Flat-mount p reparations showing the distribution of uncrossed fibres reveal that a distinct focus of terminals emerges in rostral superior colliculus, w hich is topographically appropriate for a binocular mapping, at the pe ak of uncrossed ganglion cell numbers (P4). Comparison of uncrossed te rminal distributions and ganglion cell death reveals considerable refi nement of the terminals prior to the main phase of cell death. Monocul ar enucleations performed some time after birth have a greater effect on uncrossed terminal distributions than on cell death. These observat ions suggest that independent mechanisms may be involved in the regula tion of terminal distributions and of cell numbers in the developing u ncrossed retinal pathways. (C) 1995 Wiley-Liss, Inc.