In humans with PTSD, the only relevant studies are those involving PET scans using the translocator protein (TSPO) and those involving the glucocorticoid (GC) signaling pathway; but because TSPO is expressed by both microglia and astrocytes, and that expression varies according to the time following the event causing a brain reaction, the interpretation of PET studies in humans using TSPO ligands, is difficult (see Ref. Here, TSPO is linked to post-traumatic stress disorder.