The effects of early prenatal monocular enucleation on the routing of uncrossed retinofugal axons and the cellular environment at the chiasm of mouseembryos

Whereas it has been shown that early monocular enucleations produce a reduc tion in the uncrossed pathway from the surviving eye in rats and ferrets, s imilar evidence for binocular interactions in the development of the uncros sed component in mice is currently open to question. Using retrograde traci ng, we have investigated the time course of changes in the uncrossed retino fugal pathway immediately after the early prenatal monocular enucleation in mouse embryos. Removal of one eye from C57 pigmented mice at embryonic day (E) 13 does not cause a reduction of the earliest uncrossed component from the central retina examined 1 day later at E14. However, a substantial red uction of the uncrossed pathway is seen at E15, the time when the major unc rossed projection first arises from the ventral temporal retina. This reduc tion is greater in E16 one-eyed embryos, indicating that most retinal axons from the ventral temporal retina rely on a binocular interaction for their turning at the chiasm. Further, early removal of one eye at E13 does not p roduce any obvious changes in the cytoarchitecture of RC-2-immunopositive r adial glia at the chiasm, nor of the stage-specific antigen-1 (SSEA-1) -exp ressing neurons. This lack of changes in the cellular organization at the c hiasm indicates that the reduction of the uncrossed pathway is probably pro duced by an elimination of binocular fibre interactions at the chiasm, rath er than through a degenerative change of cellular elements at the chiasm as a consequence of the eye removal procedure.