Fig. 4. Isobologram for the interaction between WIN 55,212-2 and neostigmine during phase 1 (A ) and phase 2 (B ) in the formalin test. The ED50values for each agent are plotted on the x and y axes, respectively. Horizontal and vertical bars indicate confidence intervals. The straight line connecting each ED50value is the theoretical additive line and the point on this line is the theoretical additive ED50.The experimental ED50point was significantly different from the theoretical ED50point, indicating a synergistic interaction.