TSPO and Parkinson disease: In addition, noninvasive positron emission tomography (PET) imaging studies using PK-11195, a ligand of the peripheral benzodiazepine receptor (PBR; also known as the mitochondrial 18 kDa translocator protein or TSPO), which is selectively expressed by activated microglia, further confirmed the occurrence of microglial activation in PD [9].