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Life Sci. 1998;63(12):PL175-80.

Tramadol induces antidepressant-type effects in mice.

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Department of Neuroscience, Faculty of Medicine, University of Cádiz, Spain.


Tramadol is a clinically-effective, centrally-acting analgesic. This drug is a racemic mixture of two enantiomers, each one displaying different mechanisms: (+)tramadol displays opioid agonist properties and inhibits serotonin reuptake while (-)tramadol inhibit preferentially noradrenaline reuptake. The action of tramadol on the monoaminergic reuptake is similar to that of antidepressant drugs. Therefore, we have examined the effects of (+/-)tramadol, (+)tramadol and (-)tramadol in a test predictive of antidepressant activity, the forced swimming test in mice. Both (+/-)tramadol and its (-) enantiomer displayed a dose-dependent reduction on immobility; while the effect induced by the (+) enantiomer was not significant. Inhibition of noradrenaline synthesis, but not of serotonin synthesis, was capable of blocking the effect of (+/-)tramadol. The alpha-adrenoceptor antagonist phentolamine, as well as the alpha2-adrenergic antagonist yohimbine, and the beta-adrenoceptor blocker propranolol countered the immobility-reducing action of (+/-)tramadol. Moreover, neither the serotoninergic blocker methysergide nor the opioid antagonist naloxone antagonized the effect of (+/-)tramadol. Our results show that (+/-)tramadol and (-)tramadol have antidepressant-like effect in mice, probably mediated by the noradrenergic system rather than the serotoninergic or opioidergic ones.

[Indexed for MEDLINE]

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