Tramadol increases extracellular levels of serotonin and noradrenaline as measured by in vivo microdialysis in the ventral hippocampus of freely-moving rats

▶ The atypical opioid tramadol dose-dependently increased extracellular serotonin (5-HT) and noradrenaline (NA) levels in the ventral hippocampus of freely moving rats. ▶ The antidepressant drugs duloxetine, venlafaxine and clomipramine increased extracellular 5-HT and NA levels. ▶ Citalopram selectively increased extracellular 5-HT levels. ▶ Reboxetine increased extracellular NA levels and to a minimal degree 5-HT levels.▶ The effects of tramadol on the 5-HT and NA levels resemble those of duloxetine, venlafaxine, and clomipramine, and differ from those of citalopram and reboxetine.