Opioid and monoamine systems mediate the discriminative
stimulus of tramadol in rats

Filip M, Wydra K, Yalcin Inan S,
Dziedzicka-Wasylewska M, Przegalinski E.
Department of Pharmacology,
Institute of Pharmacology Polish Academy of Sciences,
31-343 Krakow, 12 Smetna, Poland.
Eur J Pharmacol. 2004 Sep 13;498(1-3):143-51


We analyzed the ability of the mu opioid peptide receptor ligands morphine and naloxone and several antidepressant drugs that are serotonin (fluoxetine), noradrenaline (reboxetine), mixed serotonin and noradrenaline (milnacipram and venlafaxine), dopamine (nomifensine) reuptake inhibitors, as well as roxindole (a nonselective drug) to substitute for, or alter, tramadol discrimination. Male Wistar rats were trained to discriminate tramadol (20 mg/kg) from saline in a two-choice water-reinforced paradigm. Out of the drugs studied, only morphine substituted for tramadol. In combination experiments, naloxone (0.1-1 mg/kg) attenuated the stimulus effects of tramadol (20 mg/kg) and the substitution evoked by morphine (2 mg/kg). Milnacipram (10 mg/kg) or reboxetine (10 mg/kg) enhanced the effects of tramadol (2.5-10 mg/kg); the other antidepressant drugs used failed to modulate tramadol discrimination. Our results indicate that tramadol can be used as a stimulus cue in rats, and that mu opioid peptide mechanisms are involved in its effects, while noradrenergic uptake inhibitors can enhance tramadol discrimination.
Rats like tramadol
Tramadol plus pindolol
Tramadol and analgesia
Tramadol: pharmacology
Tramadol as an antidepressant
Tramadol: risk/benefit analysis
Tramadol versus buprenorphine
Tramadol : morning or evening?
Methadone for tramadol addicts?
Tramadol, morphine and the stomach
Tramadol, noradrenaline and dopamine
Pharmacokinetics and pharmacodynamics
Tramadol, depression and Parkinson's disease
Tramadol and the alpha(2)-adrenergic receptors

and further reading

Future Opioids
BLTC Research
Utopian Surgery?
The Abolitionist Project
The Hedonistic Imperative
The Reproductive Revolution
Critique of Huxley's Brave New World

The Good Drug Guide
The Good Drug Guide

The Responsible Parent's Guide
To Healthy Mood Boosters For All The Family