Collateral sprouting contributes to functional recovery of sensory neurons after peripheral nerve injury. A, Immunostaining for EYFP (green) in lumbar DRGs from Pirt^Cre+;Rosa26^{LSL-ChR2-EYFP} mice. Scale bar, 100 μm. B, Whole mount immunostaining for EYFP (green) on the contralateral and ipsilateral hindpaw plantar hairy skin before and 1 and 8 weeks after SNI in Pirt^Cre+;Rosa26^{LSL-ChR2-EYFP} mice. C, Schematic of mouse paw stimulation using 473 nm blue laser (left) and the frequency of withdrawal from light stimulation of the hindpaw of Pirt^Cre+;Rosa26^{LSL-ChR2-EYFP} and Pirt^Cre-;Rosa26^{LSL-ChR2-EYFP} mice (right). Data are presented as mean ± SEM. Mann-Whitney test. ***p = 0.0002, Cre- versus Cre⁺. D, Time course of 100 ms blue light-induced paw withdrawal frequency in the ipsilateral tibial nerve-stimulated plantar hair skin after SNI (n = 11) and sham (n = 9) surgery in Pirt^Cre+;Rosa26^{LSL-ChR2-EYFP} mice. In panels D, E, and I, circles represent data from individual mice. E, Time course of 10 ms blue light-induced paw withdrawal frequency in the ipsilateral tibial nerve-stimulated plantar hair skin after SNI (n = 11) and sham (n = 9) surgery in Pirt^Cre+;Rosa26^{LSL-ChR2-EYFP} mice. In panels D and E, two-way repeated measures ANOVA with p-value from overall comparison between groups over time shown at top. Results of Bonferroni post hoc correction shown as: *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001, sham versus SNI. All quantified data are presented as mean ± SEM. In panels C,F,G,H, symbols represent individual mice. F, Time course of pinprick (red) or 1.4 g von Frey filament (blue) evoked mechanical sensitivity, after SNI, in the ipsilateral tibial nerve-innervated plantar hairy skin of C57BL6 mice (n = 10). One-way repeated measures ANOVA with p-value for difference between baseline and ipsilateral hindpaw s over time shown at bottom. Results of Bonferroni post hoc correction shown as: *p < 0.05; **p < 0.01; ****p < 0.0001. G, Punctate mechanical sensitivity measured across forces in the ipsilateral tibial nerve-innervated plantar hairy skin of C57BL6 mice at baseline (grey), and 1 (black), 4 (blue), and 8 weeks (red) after SNI (n = 10). Two-way repeated measures ANOVA with p-value from overall comparison between groups over time shown at bottom. Results of Bonferroni post hoc correction shown as: ****p < 0.0001, baseline versus SNI. H, Punctate mechanical sensitivity measured across forces using von Frey filaments in the ipsilateral sural nerve-innervated lateral hindpaw plantar skin at baseline (grey), and 1 (black), 4 (blue), and 8 weeks (red) after SNI (n = 10). Two-way ANOVA with p-value from overall comparison between groups over time shown at bottom. Results of Bonferroni post hoc correction shown as: ****p < 0.0001, baseline versus SNI. I, Time course of hindpaw sensitivity to 0.4 g von Frey filaments, after SNI, in the contralateral and ipsilateral tibial nerve-innervated plantar hairy skin of C57BL6 mice (n = 10). Two-way repeated measures ANOVA with p-value from overall comparison between groups over time shown at top. Results of Bonferroni post hoc correction shown as: *p < 0.05; **p < 0.01; ****p < 0.0001, contra versus ipsi. Full statistical details can be found in Table 1.