Figure 3

Tail flick responses and percent of maximal possible effect (%MPE) to logarithmic doses of morphine (1, 10, 100 mg/kg, ip) administered on Day 14 after a 13 days continuous systemic drug administration. Each point represents the mean ± sem for 8 rats. Different morphine doses administered on day 14 demonstrated a significant shift to the right in the dose–response curve and antinociceptive ED₅₀ values in animals treated with morphine + 0 mg/kg donepezil compared with those receiving saline or morphine + donepezil (1.5 mg/kg, ip) or morphine + MK801 (0.1 mg/kg, ip). M = Morphine; DPZ = Donepezil.