HTR1A and major depressive disorder: Another study demonstrated that the HDACs inhibitor TSA increased hippocampal H3K9, H4K5, and H4K12 acetylation levels, accompanied by a decrease in HDAC1/2/4/5 expression, restoring the transcriptional activity of antidepressant-related genes such as BDNF, and significantly reversing depression-like behaviors induced by the 5-HT1A receptor antagonist in mice (Zhu et al., 2021).