Figure 1

Local administration of morphine in the early, but not the late phase, alleviates hypersensitivity to mechanical stimuli. Morphine (3 μg or 10 μg) and/or naloxone (5 μg) were injected into the incisional sites during the early phase (1 h after incision and on PODs 1 and 2) or late phase (PODs 5, 6, and 7). The withdrawal threshold to mechanical stimuli (A), withdrawal latency to thermal stimuli (B), and paw edema (C) were examined in groups, receiving morphine in the early phase. The withdrawal threshold to mechanical stimuli was not altered by morphine administered in the late phase (D). *P < 0.001, Mor 10 μg compared with Veh, **P < 0.001, Mor 10 μg compared with Mor 3 μg, ***P < 0.0001, Mor 10 μg compared with (Mor 10 μg + Nal 5 μg), ^# P < 0.001, Mor 10 μg compared with Nal 5 μg (two-way ANOVA followed by Bonferroni post-hoc testing). Data are mean ± SEM (Figure 1A-C, n = 8 for each group, Figure 1D, n = 5 for each group). Veh; vehicle, Mor; morphine, Nal; naloxone.