Demonstration of ipsilateral retinocollicular projections in the tree shrew (Tupaia glis)

Ipsilateral retinocollicular projections labeled by anterograde transport of wheatgerm agglutinin-horseradish peroxidase (HRP) conjugate in the tree shrew were examined. For those animals in which this pathway was demonstrated (4 of 14) ipsilateral collicular labeling extended across approximately the anterior two-thirds of the colliculus, with the exception of the extreme rostral pole. Labeling was invariably punctuate and spaced at regular intervals in the lower stratum griseum superficiale. The laminar distribution and patchy terminations of ipsilateral projections are discussed in relation to two apparently independent pathways originating in the temporal retina, the crossed and uncrossed collicular pathways.