Figure 4.

Turning behavior of growth cones approaching a stripe devoid of permissive (laminin) substrate. Neurites of dissociated adult map1b+/+ (a) and map1b-/- (b) DRG neurons were grown for 2 d on a laminin substrate (gray background), on which nonpermissive stripes were created by scratching off the laminin (dark bands). Neurites are visualized by immunofluorescence staining for tubulin (Tuj-1 antibody). Scale bar, 50 μm. a, typical example of a map1b+/+ growth cone that turns and continues its outgrowth after facing the nonpermissive substrate. The angle between a turning neurite and the nonpermissive band is usually <45°. b, In the same situation, a majority of map1b-/- growth cones is stopped, exhibiting an angle of >45° to the nonpermissive band. c, Both behaviors in higher magnification. d, Quantification of the number of stopped and turning growth cones, in relation to the neuron genotype. The difference between map1b+/+ (n = 137) and map1b-/- neurons (n = 97) is significant (^***p < 0.001; t test).