Microglial activation in healthy adult Japanese subjects: apositron emission tomography study

Background: Accumulating evidence suggests that microglia cells contribute to the normal brain homeostasis in addition to working as immune-competent cells in pathological processes associated with neurodegeneration or neuroinflammation. Microglial activation can be measured in vivo using 11C-(R)-PK11195 and positron emission tomography (PET). The aim of the study was to determine possible relationships between microglial activation and age as well as cognitive functioning in healthy Journal of Brain Science, June 30, 2016,Vol.46 56 subjects. Methods: Fifty-five healthy subjects (male/female = 35/20, age range 18-84 years) underwent a PET measurement with 11C-(R)-PK11195 and T1-weighted magnetic resonance imaging (MRI). A subset of young male subjects (age range 21-40 years) were assessed their intelligence quotient (IQ) using the third edition of Wechsler adult intelligence scale within the same day. The binding potentials of 11C-(R)-PK11195 in selected brain regions were estimated by a modified simplified reference tissue model in each of subjects. Results: Bindings of 11C-(R)-PK11195 in the cerebral cortices and subcortical regions significantly and positively correlated with age of subjects. When each sex was separately analyzed, the significant positive correlation was observed in male, but not female, subjects. In a subset of young male subjects, there was a negative correlation between the IQ scores and regional 11C-(R)-PK11195 bindings in cortical and subcortical regions. Conclusion: Results suggest that microglial activation in the brain might be associated with not only normal aging but also cognitive functioning in the youth.