Inhibition of DNA Methylation in the Developing Rat Brain Disrupts Sexually Dimorphic Neurobehavioral Phenotypes in Adulthood

Accumulating evidence indicates a critical implication of DNA methylation in the brain development. We aim to determine whether the disruption of DNA methylation patterns in the developing brain adversely affects neurobehavioral phenotypes later in life in a sex-dependent manner. 5-Aza-2′-deoxycytidine (5-Aza), a DNA methylation inhibitor, was administered in newborn rats from postnatal day 1 to 3. Neurobehavioral outcomes were analyzed at 3 months of age. 5-Aza treatment significantly inhibited DNA methyltransferase activity and decreased global DNA methylation levels in neonatal rat brains, resulting in asymmetric growth restriction with the increased brain to body weight ratio in both male and female rats at 14 days and 3 months of age. Compared with the saline control, 5-Aza treatment significantly improved performance of male rats on the rotarod test, and 5-Aza-treated female rats demonstrated less anxiety, less depression-like behaviors, and enhanced spatial learning performance. Of importance, neonatal 5-Aza treatment eliminated the sexually dimorphic differences in several neurobehavioral tests in adult rats. In addition, 5-Aza treatment decreased promoter methylation of brain-derived neurotrophic factor (BDNF) gene and significantly increased BDNF mRNA and protein abundance in the prefrontal cortex and hippocampus of female rats in a sex-dependent manner. Thus, brain DNA methylation appears to be essential for sexual differentiations of the brain and neurobehavioral functions. Inhibition of DNA methylation in the developing brain of early life induces aberrant neurobehavioral profiles and disrupts sexually dimorphic neurobehavioral phenotypes in adulthood, of which altered BDNF signaling pathway may be an important mediator.