Figure 2.

Effects of MOP and NOP receptor antagonists on alfentanil- and Ro 64-6198-induced antinociceptive effects in monkeys. A MOP receptor antagonist (naltrexone, 0.03 mg/kg, s.c.) or a NOP receptor antagonist (J-113397, 0.1 mg/kg, s.c.) was administered s.c. 15 min before redetermination of the dose–response curve of alfentanil and Ro 64-6198. Left panel: antagonist effects of s.c. naltrexone and J-113397 on the dose–response curve of Ro 64-6198-induced antinociception in 50 °C water. Right panel: antagonist effects of s.c. naltrexone and J-113397 on the dose–response curve of alfentanil-induced antinociception in 50 °C water. Each data point represents a mean ± SEM (n = 6). [Reprinted with permission from Neuropsychopharmacology.⁸⁴]