Effects of thienorphine on release of dopamine and noradrenalin: An in vivo microdialysis study in rats

Thenorphine is a new potent long-acting partial opioid agonist. In present study, the effect of thienorphine on noradrenalin (NA) in the locus coeruleus (LC) and dopamine (DA) and its metabolites in the nucleus acumbens (NAc) and the striatum were examined in freely moving rats during acute and chronic thienorphine treatment followed by naloxone-precipitated withdrawal using the in vivo microdialysis technique. Acute thienorphine (1.0 mg/kg, s.c.) treatment had no effect on the level of NA in the LC and the level of DA in the NAc and the striatum. Chronic thienorphine (1.0 mg/kg, s.c.) third per day for continued 5 days treatment followed by naloxone-precipitated (5.0 mg/kg, i.p.) had not alter the extracellular NA level in the LC and the extracellular level of DA in the NAc and the striatum, but significantly increased the level of DOPAC in the striatum. These changes are thought to reflect a direct effect of thienorphine on release of NA and DA. Thus thienorphine deserves further study as a new treatment for opioid dependence. (c) 2012 Elsevier Ireland Ltd. All rights reserved.