The Nogo-66 Receptor NgR1 Is Required Only for the Acute Growth Cone-Collapsing But Not the Chronic Growth-Inhibitory Actions of Myelin Inhibitors

MAG- and OMgp-induced growth cone collapse is attenuated in NgR1-null neurons. A, Growth cones of postnatal DRG explants of wild-type (NgR1^+/+) and NgR1 mutant (NgR1^−/−) mice were treated with no inhibitor, AP-Sema3A (10 nm), MAG-Fc (100 nm), or OMgp-Fc (6 nm) for 30 min and stained with rhodamine-conjugated phalloidin. Scale bar, 10 μm. B, Quantification of collapsed growth cones. Results are presented as mean ± SEM from 6–16 independent experiments with NgR1^+/+ (black bars) and NgR1^−/− (gray bars). For MAG-Fc, n = 6 NgR1^+/+ and n = 6 NgR1^−/−; for OMgp-Fc, n = 9 NgR1^+/+ and n = 10 NgR1^−/−; for Sema3A, n = 15 NgR1^+/+ and n = 16 NgR1^−/−; and for no inhibitor, n = 15 NgR1^+/+ and n = 16 NgR1^−/−. The number of growth cones quantified for each condition is indicated in parentheses. *p < 0.001, significant difference between NgR1^+/+ and NgR1^−/− DRG neurons treated with MAG-Fc. **p < 0.001, significant difference between NgR1^+/+ and NgR1^−/− DRG neurons treated with OMgp-Fc [Kruskal–Wallis one-way ANOVA (post hoc Dunn's test)].