TSPO and schizophrenia: Studies using the first-generation radiotracer [11C] PK11195 suggested higher TSPO expression in schizophrenia (Doorduin et al., 2009; van Berckel et al., 2008) or equivalent binding relative to controls (Di Biase et al., 2017; Holmes et al., 2016; van der Doef et al., 2016).