- In various studies it could be demonstrated that the regulation of iNOS as well as the activation of Microglia at the MSA play an important role. This activation of Microglia in persons can be proved by Positron-emission-tomography (PET) with the Benzodiazepine-Ligands PK11195. PK11195 (1-(2-chlorophenyl)–N-methyl-N-(1-methylpropyl)-3isoquinoline- carboxamide) is a highly specific Ligand for peripheral Benzodiazepine-binding sites (PBBS) (Leong et al., 1996). As in a normal brain only a few binding sites for PK11195 can be verified, a significant increase of the PBBS-Expression by activated microglia after neuronal cell death can be verified (Gerhard et al., 2001).