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

NgR1 is dispensable for OMgp-mediated inhibition of neurite extension. A, Postnatal day 25 DRG neurons of wild-type (NgR1^+/+; n = 3) and NgR1 mutants (NgR1^−/−; n = 3) were either cultured on control substrate (PDL/laminin) or plates also containing recombinant Nogo-66 or OMgp. Neurons were labeled by TuJ1 immunofluorescence. Scale bar, 100 μm. B, Quantification of neurite lengths of wild-type (black bars) and NgR1^−/− (gray bars) neurons. Compared with control substrate, Nogo-66 and OMgp substrates significantly inhibit growth of DRG neurons from wild-type mice (Nogo-66, p = 0.006; OMgp, p = 0.003) and NgR1^−/− mice (Nogo-66, p = 0.001; OMgp, p = 0.0009). No significant (n.s.) difference in neurite outgrowth between wild-type and NgR1 mutant DRGs was observed. Results are presented as mean ± SEM from three independent experiments, and the number of neurites quantified for each condition is indicated in parentheses. Statistical analyses were done using Student's t test.