GUIDANCE OF RETINAL AXONS BY MEMBRANE-COMPONENTS DERIVED FROM THE BARN OWLS OPTIC TECTUM

The mechanisms involved in the formation of the retinotopic map in the optic tectum of barn owls were studied by using an in vitro assay (Wa iter et al. 1987a). Most experiments were performed as cross-species e xperiments with chicken retinal axons growing on membrane components d erived from owl tecta. In addition, the growth patterns of owl retinal axons on tectal membranes derived from chicken and owl were examined. To analyze our data, we developed a new simulation program which allo wed us to judge the selectivity of growing retinal axons. Retinal axon s from both species showed characteristic growth patterns on tectal me mbranes: many axons from the temporal retina grew preferably on anteri or membranes. No specificity was found for nasal axons. The selectivit y of the temporal axons was high on tectal membranes derived from embr yos younger than 18.5 days (stage 37), and was absent on membranes fro m owl embryos older than 25 days (stage 40.5). These data suggest that owls possess similar guidance molecules as chickens, that the express ion of these molecules in the tectum is developmentally regulated, and that the time course of expression is prolonged compared to that in c hickens.