HDAC9 and Alzheimer disease: In fear-conditioned AD mouse models, the HDAC inhibitors such as trichostatin A (TSA), VPA, SAHA (vorinostat) or sodium butyrate increase the synapse remodeling and enhance the contextual memory by regulating H3/H4 acetylation of relevant gene promoters to enhance hippocampal long-term potentiation (Fischer et al., 2007, 2010; Francis et al., 2009; Guan et al., 2009; Kilgore et al., 2010; Ricobaraza et al., 2012).