DIFFERENTIAL ACTION OF THE ALBINO MUTATION ON 2 COMPONENTS OF THE RATS UNCROSSED RETINOFUGAL PATHWAY

The development of the uncrossed retinofugal pathways in normally pigm ented and albino rats, aged from embryonic day (E) 14.5 to E18.5, was investigated. DiI was placed into one optic tract and the retinal orig in of the uncrossed component, as well as its course in the optic stal k, was studied. The results show that, as in the mouse, the uncrossed retinal projection has two components. The first component is seen at E15.5 in normally pigmented animals. It develops exclusively in the ce ntral parts of the retina and is normal in albino littermates. The sec ond component, which arises from the peripheral parts of the ventrotem poral retina, is seen two days later at E17.5 in all animals but is si gnificantly smaller in albinos than in their pigmented littermates. St udies of axons in the optic stalk labelled retrogradely with DiI place d in the optic tract indicate that the uncrossed axons have no prefere nce for any position in the stalk except when they approach the chiasm , where they tend to accumulate at the caudal region of the stalk. The uncrossed axons intermingle with the crossed axons along the entire l ength of the stalk. In albino embryos, no obvious difference in the pr echiasmatic course of uncrossed axons was seen at any age examined. It is concluded that the albino mutation in rats affects the late ventro temporal component of the uncrossed pathway selectively. It does not a ct on the early central component. Further, the intermingling of cross ed and uncrossed axons in the stalk and the apparently unaffected prec hiasmatic course of uncrossed axons in albinos indicate that the albin o gene has its primary action in the retina. (C) 1993 Wiley-Liss, Inc.