S100B and major depressive disorder: Furthermore, in agreement with MDD astrocytic pathology, S100β cerebrospinal fluid and serum levels are increased (Grabe et al., 2001, Rothermundt et al., 2001, Schroeter et al., 2002, Schroeter et al., 2008), probably reflecting leakage of S100β from astrocytic cytoplasm into extracellular compartments.