A banded distribution of retinal afferents within layer 9A of the normal frog optic tectum.

A banded distribution of retinal ganglion cell axons within layer 9A of the superficial tectal neuropil in Rana pipiens was revealed through anterograde labeling with horseradish peroxidase. Layer 9A previously has been demonstrated to mediate binocular vision through a polysynaptic pathway by way of the nucleus isthmi. This nucleus interconnects analogous regions of the two tectal lobes such that isthmic axons retinotopically map the visual world of the ipsilateral eye within tectal layers 9A and 8. Thus, we have found that a pattern of retinal ganglion cell bands occurs in binocular regions of normal frogs. This pattern is similar, but not identical, to the experimentally produced stripes previously observed in the doubly innervated tecta of 3-eyed and single tecta frogs. Qualitative and quantitative comparisons of these two types of afferent segregation patterns have implicated several structural and functional parameters which might be involved in band formation.