Abstract

Buprenorphine (BUP), a mixed opioid agonist-antagonist, is currently used as a treatment for opioid addiction. Previous research has shown that chronic BUP treatment decreases self-administration of drugs such as heroin and cocaine and drug-seeking behaviour in monkeys, rats, and humans. Furthermore, BUP attenuates the increase in nucleus accumbens (NAc) dopamine (DA) levels in response to an acute injection of heroin in naïve rats, whereas BUP potentiates the DA response to acute cocaine. To establish whether the suppression of drug seeking by BUP stems from an effect on motivated behaviour in general, four experiments were conducted to determine the effect of chronic BUP (3.0mg/kg/day) on responding for sucrose pellet reward. Chronic exposure to BUP was achieved with the use of subcutaneous osmotic minipumps. Results from Experiments 1 and 2 showed that rats exposed to chronic BUP took fewer sucrose pellets and reduced their active lever responding on a fixed ratio (FR) 1 schedule of self-administration; however, no such effect of BUP was observed on FR5 or progressive ratio (PR) schedules. In Experiment 3, chronic BUP slightly reduced sucrose seeking during extinction of self-administration and suppressed reinstatement of responding after sucrose priming. In Experiment 4, it was found using in vivo microdialysis that chronic BUP had no effect on the sucrose- or lab chow-induced rise in NAc DA, but did significantly increase basal DA tone. Overall, these results indicate that chronic BUP decreases motivation induced by sucrose reward and suggest that BUP reduces drug seeking and drug taking by blunting motivation in general.