A review of positron emission tomography studies exploring the dopaminergic system in substance use with a focus on tobacco as a co-variate.

With the evolving sensitivity of positron emission tomography (PET) and the emergence of novel radiotracers, greater insight has been gained into the dopaminergic system as it relates to substance use. In this review, we summarize PET investigations from the last ten years that explore the dopaminergic system in tobacco, alcohol, stimulant, opiates, and cannabis addiction. In light of the prevalence of substance co-use, this review will also explore the effect of tobacco and other substance abuse co-morbidity on the dopaminergic system across study samples in the reviewed literature. In non-dependence, increased DA transmission following acute stimulant administration is a robust and consistent observation but is less detectable following acute alcohol and tobacco, where it likely represents a conditioned effect mediating reward expectation. Chronic drug exposure is generally associated with a hypo-functioning pre-synaptic dopamine system and lower D2/D3 receptor availability relative to healthy controls. Emerging evidence also shows that stimulant use disorders in particular may also be associated with greater D3 receptor availability relative to controls. A defined role for the dopaminergic system in cannabis and opiate use is yet to be elucidated. Future work is also needed to delineate the potential interactive effects of acute and chronic tobacco and substance co-use on the dopaminergic system.