| Summary: | Chronic opioid and alcohol dependence are widespread problems with enormous associated individual and societal costs. The disruption of normal motivational processes is characteristic in addiction and studying the neurobiological mechanisms involved is key to helping develop treatments. This thesis has studied specific mechanisms in two different ways, firstly using neuroimaging and secondly by applying existing understanding to trial a novel treatment approach. The central role played by the mesolimbic dopaminergic system in the motivational system is well established, however compared to other drugs of abuse, it has been studied very little in opioid dependence. Two linked neuroimaging studies were conducted using llC-raclopride positron emission tomography, to better characterise the dopaminergic system. in opioid dependence. There was no detectable increase of striatal dopamine levels in opioid-dependent participants, to either expectation or delivery of a heroin related reward, and there was also no significant difference found in striatal dopamine D2/3 receptor availability compared with healthy controls. The lack of detectable changes contrasts with those seen in abstinent stimulant users. This may have been due to the impact of substitute medication and further research is needed to explore the neurobiological effects of different opioid substitutes.
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