Figure 2. Histogram demonstrating the tail-flick test results at zero, 30, 60 and 120 minutes for the forty male rats that were randomly assigned to five groups according to the treatment received: Group I: Control; Group II: Morphine; Group III: Apelin-13; Group IV: Apelin-13+L-NAME; Group V: Apelin-13+Ondansetron. L-NAME: Nw-nitro-L-arginine.