Quantification of CTB-labeled axon profiles after transient NT-3 gene expression. A, The number of axonal profiles crossing the rostral host/graft interface (H/G; 0 μm) and increasing distances (50–1600 μm) beyond the lesion was quantified in one of seven sagittal sections. Compared with animals that received tet-off-NT-3 virus and no doxycycline for 4 weeks (NT-3/−Dox, 4 weeks), a decrease in the number of axons is evident when NT-3 expression is turned on for 4 weeks and then turned off for 6 weeks (NT-3/−Dox, 4 weeks, +Dox, 6 weeks). B, Animals with transient NT-3 expression also exhibit significantly fewer CTB-labeled axons within the graft compared with animals with continuous NT-3 expression for 4 weeks or 10 weeks. C, In contrast, no significant difference is observed in the average maximum distance of axon growth between animals with continuous NT-3 gene expression for 4 weeks and animals with transient NT-3 expression. *p < 0.05, **p < 0.01, ***p < 0.001, NS p > 0.05; ANOVA followed by Fisher's post hoc test.