Maybe, for mice. With the results possibly relevant to us. There is evidence, obtained from both post-mortem human brains and from animal experiments, that persistent depression may involve long term chemical changes in gene-protein complexes called chromatin. Covington et al find that chronic social defeat stress in mice causes a transient decrease, followed by a persistent increase, in levels of acetylated histone H3 (a chromatin protein) in the nucleus accumbens, an important limbic brain region. They then find that infusion into this region of inhibitors of the enzyme that removes acetate groups lessens behavioral symptoms of depression and also reverses the effects of chronic defeat stress on global patterns of gene expression in the nucleus accumbens.