Positron emission tomography of type 2 cannabinoid receptors for detecting inflammation in the central nervous system

Cannabinoid receptor CB₂ (CB₂R) is upregulated on activated microglia and astrocytes in the brain under inflammatory conditions and plays important roles in many neurological diseases, such as Alzheimer’s disease, amyotrophic lateral sclerosis, and ischemic stroke. The advent of positron emission tomography (PET) using CB₂R radiotracers has enabled the visualization of CB₂R distribution in vivo in animal models of central nervous system inflammation, however translation to humans has been less successful. Several novel CB₂R radiotracers have been developed and evaluated to quantify microglial activation. In this review, we summarize the recent preclinical and clinical imaging results of CB₂R PET tracers and discuss the prospects of CB₂R imaging using PET.