Many people who try to quit smoking are unsuccessful, and tobacco use remains the leading cause of preventable death in the United States. As with other drugs, the addictiveness of cigarettes is due to the response they elicit in the brain’s reward system. While some of the rewarding effects are caused by the direct action of nicotine, additional rewarding effects may be caused by a nicotine-induced increase in endogenous opioids. Endogenous opioids, like the endorphins associated with the “runner’s high,” are molecules that bind to the same mu opioid receptors (MOR) in the brain as morphine or heroin that can lessen feelings of pain and increase feelings of euphoria.
This study used PET scan (positron emission tomography) brain imaging to assess the binding potential of endogenous opioids to MOR in the brains of smokers and nonsmokers while they smoked regular or placebo (nicotine-free) cigarettes. While MOR binding potential did not vary according to smoking history or the nicotine content of the cigarette, it did vary according to the subject’s affective experience (whether they experienced good, bad, or no effect and if they liked the effect). Specifically, in smokers smoking placebo cigarettes, binding of endogenous opioids to MOR (in superior temporal cortex) was positively correlated with dependence on nicotine. Also in smokers, the increase in binding of endogenous opioids to MOR in the frontal cortex caused by smoking regular cigarettes was associated with self-reports of liking and wanting cigarettes. This study provides insight into the neural circuitry connecting the activity of the brain’s opioid system to cigarette addiction, which may help guide future development of effective smoking cessation treatments.
Mu Opioid Receptor Binding Correlates with Nicotine Dependence and Reward in Smokers; Kuwabara H, Heishman SJ, Brasic JR, Contoreggi C, Cascella N, Mackowick KM, Taylor R, Rousset O, Willis W, Huestis MA, Concheiro M, Wand G, Wong DF, Volkow ND. PLoS One. 2014 Dec 10;9(12):e113694. doi: 10.1371/journal.pone.0113694. eCollection 2014. PubMed PMID: 25493427 http://www.ncbi.nlm.nih.gov/pubmed/?term=25493427
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