Dopamine-dependent behavioural stimulation by non-peptide delta opioids BW373U86 and SNC80: 2. Place-preference and brain microdialysis studies in rats

The motivational properties of the non-peptide delta-opioid receptor agonists BW373U86 and SNC 80 were investigated using the place-conditioning paradigm. BW373U86 (0.5 1.0 mg/kg s.c.) and SNC 80 (1.25 5.0 mg/kg s.c.) elicited significant preference for the drug-paired compartment, in a dose-related fashion. Naltrindole (5.0 mg/kg s.c.) pretreatment, while failing to modify preference when given alone, completely prevented place-preference induced by BW373U86 (1.0 mg/kg s.c.) and SNC 80 (1.25 mg/kg s.c.). The dopamine D-1 receptor antagonist SCH23390, given at doses that do not affect place-preference (0.012 mg/kg s.c.), completely prevented the place-preference induced by BW373U86 and SNC 80. At the doses effective in eliciting place-preference, BW373U86 and SNC 80 failed to modify extracellular dopamine in the medial nucleus accumbens, while in the dorso-lateral caudate-putamen BW373U86 (1.0 and 2.5 mg/kg s.c.) reduced extracellular dopamine, and this effect was prevented by naltrindole (5.0 mg/kg s.c.). SNC 80, only at the dose of 5 mg/kg s.c., significantly reduced extracellular DA in the dorso-lateral caudate-putamen. The results indicate that stimulation of delta-opioid receptors has incentive properties that might be related to an indirect amplification of post-synaptic dopamine transmission.