Characterization of the analgesic properties of nomifensine in rats

The analgesic properties of the catecholamine uptake inhibitor nomifensine were investigated in the tail immersion, hot plate and formalin tests. Syst emic administration of nomifensine produced analgesia only in the formalin test. The analgesia was dose-dependent (0.625-5 mg/kg), and the highest dos e completely abolished nociceptive behaviors induced by 2% formalin. The an algesia was not affected by the opioid antagonist naltrexone (2.5-40 mug sc ) but was dose-dependently reversed by the D2 antagonist eticlopride (181.3 -270 mug/kg ip). Neither naltrexone nor eticlopride affected formalin pain scores. Nomifensine analgesia appears to be dopamine-mediated but independe nt of opioid mechanisms. (C) 2001 Elsevier Science Inc. All rights reserved .