Fig. 5. Cumulative distribution plot of turning angles of retinal growth cones in response to gradients of various axon guidance molecules. On the x axis, turning angles with negative values indicate repulsion and positive values indicate attraction. The y axis gives the percentage of growth cones with turning angles greater than the corresponding angle on the abscissa. Both BDNF (50 µg/ml) and netrin 1 (5 µg/ml) induce repulsive reactions with growth cones turning away from the pipette (avoiding higher concentrations) (not shown here, see Fig. 6) (Mann-Whitney test: P0.012). In an ephrin-A5-Fc gradient, growth cones show substratum-dependent turning responses. On laminin, growth cones turn towards the pipette (attraction) with a mean turning angle of +20°, on fibronectin the turning behaviour is converted to repulsion with a mean turning angle of –25°. Controls consisted of axons growing on laminin or fibronectin without guidance molecules in the pipette. Here growth cones were neither repelled nor attracted. The turning responses are statistically significant (P<0.003, Mann-Whitney test).