Fig. 4From: The effects of serotonin/norepinephrine reuptake inhibitors and serotonin receptor agonist on morphine analgesia and tolerance in ratsEffects of amitriptyline, venlafaxine, and dihydroergotamine on the tolerance morphine analgesia. a Effects of amitriptyline, venlafaxine, and dihydroergotamine in the tail-flick test, and b effects of amitriptyline, venlafaxine, and dihydroergotamine in the hot-plate test. Pretreatment of morphine tolerant animals with amitriptyline and venlafaxine significantly increased % MPE (decrease tolerance to morphine) in both tail-flick (p < 0.01; a) and hot-plate tests (p < 0.01; b) compared to morphine-tolerant animals. However, pretreatment of animals with dihydroergotamine showed no significant increase in % MPE in either tail-flick or hot-plate tests. Each point represents the mean ± SEM of percent of maximal possible effect (% MPE) for 6 rats. *p < 0.01 and **p < 0.05 compared to the morphine-tolerant groupBack to article page