Effects of paeoniflorin on the formalin-induced nociceptive behaviour in mice

In this study, we attempted to identify the mechanisms of paeoniflorin on antinociceptive effects in mice. Paeoniflorin (48, 96, 240, 480 microg, i.c.v.) showed dose-related antinociception both on the early and late phases of formalin test in mice. Moreover, paeoniflorin (48 microg, i.c.v.) could potentiate the antinociception of morphrine (0.5, 1.0 mg/kg, s.c.) in the formalin test. However, the antinociceptive effects of paeoniflorin were not potentiated by L-arginine (600 mg/kg, i.p.) or antagonized by beta-funaltrexamine (beta-FNA) (10 microg, i.c.v.), ICI-174,864 (1 microg, i.c.v.) and ryanodine (10 ng, i.c.v.) on both the early and late phases of formalin test. L-NAME (75 mg/kg, i.p.) could reverse the effect of paeoniflorin on the late phase of formalin test. Naloxone (1 mg/kg, i.p.) and nor-binaltorphimine (nor-BNI) (1 microg, i.c.v.) could block the paeoniflorin-induced antinociception on the early phase of formalin test. These results suggested that the central antinociceptive effects of paeoniflorin on formalin test in mice were mediated by the activation of kappa-opioid receptor and not related to the increase of intracellular calcium.