Fig. 1

Effect of amitriptyline (AMI) on the morphine analgesia. a Effect of amitriptyline (20 mg/kg) in the tail-flick test, and b effect of amitriptyline in the hot-plate test. Amitriptyline in combination with morphine produce a significant increase in % MPE in both the tail-flick (p < 0.05; a) and hot-plate assays (p < 0.05; b) as compared to the morphine-treated rats. The maximum % MPE is observed at 60 min after administration of morphine by the tail-flick and hot-plate test. Each point represents the mean ± SEM of percent of maximal possible effect (% MPE) for 6 rats. *p < 0.05 compared to the morphine-treated group and **p < 0.01 compared to saline-treated group