Fig. 3

Thermal hyposensitivity induced by intrathecal application of DAMGO was attenuated by pre-treatment with CCL2 in a microglia activation-dependent manner. Acute i.t. application of DAMGO (0.01 µg, n = 5) increased the PWL to thermal stimuli. A single i.t. CCL2 (1.4 µg, n = 5) pre-treatment 30 min before the i.t. application of DAMGO (0.01 µg) prevented the DAMGO-induced increase of the PWL and the PWL remained unchanged throughout the testing period. Single i.p. application of minocycline (45 mg/kg, n = 6) prevented the CCL2-induced effect on the DAMGO-evoked thermal hypoalgesia in all of the tested animals. Statistical differences in each experimental group were identified using RM ANOVA on ranks followed by the Dunnett`s test; ^*P < 0.05, **P < 0.01, ^***P < 0.001 versus Ctrl. Differences between treatments were analyzed using one-way ANOVA followed by the Bonferroni test. ^˄P < 0.05, ^˄˄P < 0.01 versus DAMGO group; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 versus Minocycline + CCL2 + DAMGO group