Figure 3.

On day five, acute injection of different doses of morphine (0.3–3 mg/kg) in animals that received saline over four days produced a dose-dependent significant antinociceptive response when compared to responses obtained in animals receiving an equivalent volume of its vehicle. The antinociceptive response to morphine was not altered in animals that were treated over four days with MnTE-2-PyP⁵⁺ or MnTnHex-2-PyP⁵⁺ (3 and 0.1 mg/kg/day respectively, n=6) indicating lack of acute interaction between morphine and these compounds. Results are expressed as mean ± s.e.m for six animals. *P<0.001 for the vehicle group when compared to values obtained in the absence of morphine.