Figure 4.

Agonist dose–antinociceptive response curves for paired combinations of CP55,940, dexmedetomidine and morphine (s.c.) in the (a) hot plate and (b) tail flick assays in conscious mice. Responses are expressed as %MPE (see Methods). %MPE values at the time point at which peak antinociceptive responses were observed for each respective agonist (see Figure 3) were used to plot the curves. The total dose for each agonist combination is shown on the x-axis. Combinations were of equal fractions (1.0, 0.5, 0.25, 0.125 or 0.0625) of each paired agonist's respective ED₅₀ value (see Table 1) coadministered in a fixed 1 : 1 ratio of the ED₅₀ of agonist A : ED₅₀ of agonist B. For each curve, total n values in the hot plate and tail flick assays, respectively, were as follows: CP55,940 and dexmedetomidine n=52 and 38; CP55,940 and morphine n=57 and 45; and dexmedetomidine and morphine n=65 and 41. For each agonist dose, n values in the hot plate and tail flick assays, respectively, were as follows: CP55,940 and dexmedetomidine n=7–13 and 7–11; CP55,940 and morphine n=8–13 and 3–12; and dexmedetomidine and morphine n=12–16 and 10–11. Symbols are mean±s.e.m.