BDNF and post-traumatic stress disorder: Takei et al used an SEFL paradigm with an SPS in rats and observed an increased level of acetylation of histone H3 and H4 at the exon I and IV BDNF promoter regions in SPS rats in their hippocampus.43Takei et al demonstrated enhanced hippocampal BDNF/TrkB signaling in response to fear conditioning in this animal model of PTSD.43The reversible nature of epigenetic modifications makes them a therapeutic target.