There is a dynamic nature to the epigenetic alterations we have observed across the lifespan. For example, at exon IV of the Bdnf gene in the medial prefrontal cortex, female rodents with a history of maltreatment had less methylation in adolescence but higher methylation in adulthood (Blaze et al., 2013). However, in the whole prefrontal cortex, Bdnf exon IX methylation was increased 24 hours after the final day of maltreatment exposure (i.e. PD8) and this increase persisted into adulthood. Outcomes of maltreatment are also sex-specific; in the amygdala, adult females have increased methylation of Bdnf exons I and IV while males have reduced methylation at both exons (Roth et al., 2014). This demonstrates that although DNA methylation changes resulting from postnatal stress can be long lasting, they can also change over time and the changes are highly dependent upon sex, gene locus, and brain region. Further work is needed to identify reasons underlying temporal, regional, and sex differences in methylation.
