OLIG1 and schizophrenia: Furthermore, we investigated whether the density of more premature oligodendrocytes, stained by the oligodendrocyte transcription factors Olig1, or of more mature oligodendrocytes stained by Olig2 respectively, or of parvalbumin-positive interneurons is altered in the posterior part of the hippocampus in the same post-mortem schizophrenia brains as previously investigated by design-based stereology in histologically stained sections (Schmitt et al., 2009; Falkai et al., 2016).