Fig. 2. Threshold change  versus time in 2- (n = 10), 4- (n = 8), and 16- (n = 8) week-old animals for L5–L6 lumbar spinal nerve root ligation (SNL). The left paw in the treated animals was compared with the left paw in the control animals with no surgery. The  vertical solid line above the graph is the median time to return to 80% of control threshold, and the  horizontal solid line is the range. The median time to return to 80% of control values was shorter in the 2-week-old animals than in either the 4- or 16-week-old animals (  P < 0.05). * Significantly different from baseline threshold. All ages had development of a threshold different from baseline.