GFAP and major depressive disorder: Reactive astrogliosis has been detected in depression and PTSD [23], with high expression levels of specific astrocytic proteins such as the cytoskeletal marker glial fibrillary acidic protein (GFAP), S100B, a Ca2+-binding protein that regulates neuronal firing at physiological levels but is neurotoxic when released in excessive amounts [24, 25], and connexin 43 (CX43), a component of the gap junctions responsible for the passage of gliotransmitters and other molecules that enables cell-cell communication [26].