Fig. 6

Metformin attenuated spinal microglial activation in chronic morphine administration. Morphine was injected subcutaneously (10 mg/kg) once a day for 7 days; metformin (200 mg/kg) was administered intraperitoneally daily 15 min before each morphine injection. The lumbar spines (L1–L6) were collected and analyzed 120 min after the last morphine administration. a, b Metformin inhibited up-regulation IBA-1 protein expression induced by chronic morphine treatment in the spinal cord (n = 4). c, d Metformin inhibited expression of IBA-1 induced by chronic morphine (n = 4). Confocal images and immunofluorescence analysis data showed IBA-1 in the dorsal horns (scale bar, 100 μm). Quantification of IBA1 immunofluorescence was represented as mean fluorescence pixels in the superficial dorsal horns (n = 5, 5 images per animal) (*p < 0.05; **p < 0.01; Bonferroni’s post hoc tests)