Age, sex and smoking influence opioid receptor function in the brain

Summary: Age, sex, and gender influence the organization of the brain’s opioid system. Findings shed light on why there are significant differences between the opioid system on an individual level, and why some are more prone to developing opioid-linked pathologies than others.

Source: University of Turku

Opioids regulate the feelings of pleasure and pain in the brain. A study by the national Turku PET Centre in Finland shows that age, sex and smoking influence μ-opioid receptor density in the brain. The results of the study help to better understand the differences between individuals when it comes to neuropsychiatric disorders.

Dysfunctions of the brain’s opioid system are associated with several disorders, such as addiction, and chronic pain problems.

“We noticed in our study that age, sex and smoking have fundamental influence on the organisation of the human brain’s opioid system. This suggests that there are significant differences in the opioid system between individuals, which may explain why some individuals are prone to develop opioid-linked pathological states,” such as psychiatric disorders, explains Tatu Kantonen, Doctor of Medicine.

Brain’s μ-opioid receptors act as important mediators for body’s own opioids in the brain. This study analysed positron emission tomography (PET) brain scans targeting μ-opioid receptors from 204 individuals with no neurologic or psychiatric disorders. This database was compiled with new computational tools developed at the Turku PET Centre.

“When an opioid molecule binds to a dock-like receptor in the brain, it may cause a feeling of reduced pain or increased pleasure. Putting it more simply, opioids are like the body’s own ambassadors of pleasure and relief,” explains Kantonen.

This shows brain scans from the study
Distribution of μ-opioid receptors in the human brain. Warmer colour stands for more receptors, and colder colour for less receptors. The original image has been published in the NeuroImage. Image is credited to Tatu Kantonen, University of Turku.

Older age was associated with increased μ-opioid receptors in the cerebral cortex, whereas in the deeper parts of the brain they were decreased. The increase in receptors was stronger in males. Smoking was associated with decreased μ-opioid receptors in most brain regions.

The researchers also discovered that there are more μ-opioid receptors in the right versus the left hemisphere of the brain. This observation may help to explain the previously reported differences between the two hemispheres in the processing of emotions and pain.

The study is based on the AIVO database hosted by Turku University Hospital and Turku PET Centre. The database contains different in vivo molecular brain scans for extensive analyses: https://aivo.utu.fi/

About this neuroscience research article

Source:
University of Turku
Media Contacts:
Tatu Kantonen – University of Turku
Image Source:
The image is credited to Tatu Kantonen, University of Turku.

Original Research: Open access
“Interindividual variability and lateralization of μ-opioid receptors in the human brain”. byTatu Kantonen et al.
NeuroImage doi:10.1016/j.neuroimage.2020.116922

Abstract

Interindividual variability and lateralization of μ-opioid receptors in the human brain

Alterations in the brain’s μ-opioid receptor (MOR) system have been associated with several neuropsychiatric disorders. Central MOR availability also varies considerably in healthy individuals. Multiple epidemiological factors have been proposed to influence the MOR system, but due to small sample sizes the magnitude of their influence remains inconclusive. We compiled [11C]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 [11C]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 specialization in central emotion and pain processes.

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