Papers of the Week

Alterations in the brain's μ-opioid receptor (MOR) system have been associated with several neuropsychiatric diseases. Also healthy individuals vary considerably in MOR availability. Multiple epidemiological factors have been proposed to influence MOR system, but due to small sample sizes the magnitude of their influence remains inconclusive. We compiled [C]carfentanil positron emission tomography scans from 204 individuals with no neurologic or psychiatric disorders, and estimated the effects of sex, age, body mass index (BMI) and smoking on [C]carfentanil binding potential using between-subject regression analysis. We also examined hemispheric differences in MOR availability. Older age was associated with increase in MOR availability in frontotemporal areas but decrease in amygdala, thalamus, and nucleus accumbens. The age-dependent increase was stronger in males. MOR availability was globally lowered in smokers but independent of BMI. Finally, MOR availability was higher in the right versus the left hemisphere. The presently observed variation in MOR availability may explain why some individuals are prone to develop MOR-linked pathological states, such as chronic pain or psychiatric disorders. Lateralized MOR system may reflect hemispheric work distribution in central emotion and pain processes.