Fig. 3. Time course of the effect of a unique (30 mg/kg, intraperitoneal) or cumulative (30 mg/kg × 3, intraperitoneal) dose of magnesium (Mg), administered alone (A ) or in combination with morphine (1.5 mg/kg, subcutaneous) or saline (2 ml/kg, subcutaneous) (B ) on the behavioral scores after the paw injection of formalin (5%; 50 μl). Data are represented as mean ± standard error of the mean. *  P < 0.05;**  P < 0.01;***  P < 0.001 compared with the control saline plus saline group (A ) or saline plus morphine–treated group (B ).