Figure 1

Time course for mechanical hypersensitivity, thermal hyperalgesia, mechanical hyperalgesia, and spontaneous pain. (A) A 3.2-g von Frey filament was used to evaluate mechanical hypersensitivity. Root constriction (RC) rats (black circles) showed mechanical hypersensitivity from day 3–14 after the nerve root injury compared with sham rats (white triangles) and naïve rats (white squares). (B) The differential score was used to evaluate thermal hyperalgesia. The differential score was significantly higher in the RC rats than in the sham rats and naïve rats from day 3 thereafter. (C) The pin-prick test was used to evaluate mechanical hyperalgesia. RC rats showed significantly higher withdrawal responses than the others from day 3 thereafter. In addition, the injured side in the RC rats (black circles), sham rats, and naïve rats and the noninjured side in the RC rats (white circles) also showed withdrawal responses. Error bars denote the standard error of the mean. *P < 0.05 compared with sham and naïve rats; one-way factorial measures of analysis of variance followed by the Tukey–Kramer test. (D) The numerical scale (see text) at day 14 was used to evaluate the degree of spontaneous pain-related behavior. All RC rats showed abnormal positioning of the lesioned hind paw, whereas all sham rats and naïve rats showed normal positioning of the hind paw. *P < 0.05 (Mann–Whitney U test).