Figure 4.

Isobolograms for morphine in combination with JNJ and MPEP on the hotplate (left) and warm water tail-withdrawal (right) procedures. The effects of JNJ and MPEP are illustrated in each panel of the graph, as comparisons were made to a single morphine curve in the hotplate procedure and a single morphine curve in warm water tail-withdrawal procedure. Horizontal axis: ED₅₀ value (95% C.L.) for morphine expressed in mg/kg. The perpendicular line intersecting the morphine ED₅₀ value represents the theoretical line of additivity. Vertical axis: dose of JNJ or MPEP, expressed in mg/kg, administered in combination with a morphine dose-effect curve. Vertical lines represent the 95% C.L. of the ED₅₀ values for morphine: when the ED₅₀ was to the left of the theoretical line of additivity and the C.L. lines did not overlap the shaded area, the interaction was considered to be supra-additive, whereas when the C.L. lines did overlap with the shaded area, the interaction was considered additive.