P2RX7 and neurodegenerative disease: With the development of more focused, clinically available PET imaging tracers for the microglia, including those that target the P2X7 (purported to be mainly expressed in microglia and astrocytes; [32]) and CSF1R (purported to be mainly expressed in microglia; [33]), there now exists the opportunity to probe the microglia more exclusively, along with their roles in neurodegenerative disease.