Lack of enhanced 5-HT axon regeneration after a complete transection spinal cord injury in NgR1 single-mutant and Nogo/MAG/NgR1 triple-mutant mice. A, B, D, E, Representative sagittal sections immunostained for 5-HT (green) and GFAP (red) along with 4′,6-diamidino-2-phenylindole (DAPI) nuclear staining (blue) in completely transected spinal cord of an NgR1 mutant (B), a Nogo/MAG/NgR1 triple-mutant (E), and respective WT controls (A, D). Open arrow indicates injury site. KO, Knock-out (mutant). Scale bar, 500 μm. C, F, Quantification of 5-HT immunoreactivity caudal to the injury. n = 8 for WT and 8 for NgR1 knock-outs (C); n = 8 for WT and 6 for Nogo/MAG/NgR1 triple knock-outs (TKO). No statistically significant differences, two-way ANOVA.