JOCHEN WALTER, SIGRID HENKE-FAHLE and FRIEDRICH BONHOEFFER

Membrane carpets consisting of alternating membrane stripes were prepared from plasma membranes of anterior and posterior chick optic tectum. Axons from retinal explants extend neurites on these carpets. Axons of the nasal retina do not distinguish between the stripes. Axons of the temporal retina prefer to extend neurites on anterior tectal membranes. Treatment of the membrane fragments with high temperature interferes with the pattern of neurite outgrowth from temporal axons. When growing on carpets consisting of treated anterior and posterior tectal membranes, temporal retinal axons no longer distinguish between the stripes. Treatment of posterior membranes alone is sufficient to abolish the preference of temporal axons to extend neurites on anterior tectal membranes. Treatment of the anterior membranes alone has no effect. This result is best explained by a repulsive component in the posterior tectal membranes. Temporal, but not nasal, axons specifically recognize and avoid that component, with the result that they do not extend neurites on posterior tectal membrane stripes. Once the repulsive component is destroyed, temporal axons are able to extend neurites on posterior tectal membranes.