SEGREGATION OF OPTIC AXONS BASED ON CENTRAL TARGET - THE MEDIAL OPTICTRACT IN RANA-PIPIENS

The retinofugal projection to the nucleus of Bellonci (nB) was examine d in Rana pipiens using both anterograde and retrograde transport of h orseradish peroxidase (HRP). Following HRP injection into the nB, retr ogradely labeled optic axons formed a discrete fascicle that crossed t he lateral margin of the anterior diencephalon. We have designated thi s branch of the retinofugal pathway as the ''medial optic tract.'' HRP -positive, medial optic tract axons projecting to nB occupied the rost ral and most dorsal portion of the optic chiasm. The present findings indicate that within the optic chiasm, retinal axons are sorted accord ing to their final destinations.