Association of smoking with μ-opioid receptor availability before and during naltrexone blockade in alcohol-dependent subjects

Persons with a history of alcohol dependence are more likely to use tobacco and to meet criteria for nicotine dependence compared with social drinkers or non-drinkers. The high levels of comorbidity of nicotine and alcohol use and dependence are thought to be related to interactions between nicotinic, opioid and dopamine receptors in mesolimbic regions. The current study examined whether individual differences in regional mu-opioid receptor (MOR) availability were associated with tobacco use, nicotine dependence and level of nicotine craving in 25 alcohol-dependent (AD) subjects. AD subjects completed an inpatient protocol, which included medically supervised alcohol withdrawal, monitored alcohol abstinence, transdermal nicotine maintenance (21 mg/day) and Positron Emission Tomography (PET) imaging using the MOR agonist [C-11]-carfentanil (CFN) before (basal scan) and during treatment with 50 mg/day naltrexone (naltrexone scan). Subjects who had higher scores on the Fagerstrom Nicotine Dependence Test had significantly lower basal scan binding potential (BPND) across mesolimbic regions, including the amygdala, cingulate, globus pallidus, thalamus and insula. Likewise, the number of cigarettes per day was negatively associated with basal scan BPND in mesolimbic regions. Higher nicotine craving was significantly associated with lower BPND in amygdala, globus pallidus, putamen, thalamus and ventral striatum. Although blunted during naltrexone treatment, the negative association was maintained for nicotine dependence and cigarettes per day, but not for nicotine craving. These findings suggest that intensity of cigarette smoking and severity of nicotine dependence symptoms are systematically related to reduced BPND across multiple brain regions in AD subjects.