Temporal retinal growth cones collapse on contact with nasal retinal axons

The behavior of retinal ganglion cell growth cones was examined as they met retinal ganglion cell axons in culture. All possible pairings of growth cones and axons from the ventral-nasal, ventral-temporal, and dorsal-temporal quadrants of the chick retina were examined. Growth cones grow across axons with little difficulty in all those combinations in which nasal growth cones meet either nasal or temporal axons or temporal growth cones meet temporal axons. However, temporal growth cones generally collapse on contact with nasal axons and thereby experience great difficulty in crossing them. These results are consistent with the hypothesis that nasal axons have associated with them a cue that (i) interferes with temporal growth cone motility, (ii) is absent on temporal axons, and (iii) is not recognized by nasal growth cones. This finding may explain why temporal growth cones prefer to grow on temporal as opposed to nasal axons, while nasal growth cones display no such preference.