Darkness Reduces BDNF Expression in the Visual Cortex and Induces Repressive Chromatin Remodeling at the BDNF Gene in Both Hippocampus and Visual Cortex

Neuronal activity regulates the expression of brain-derived neurotrophic factor (BDNF) in brain. In darkness, reduced neuronal activity in the visual cortex markedly decreases total BDNF transcription level in adult rats. Epigenetic mechanisms are crucially involved in the regulation of gene expression in response to environmental stimuli. In this study, we examined the effect of 1 week of light deprivation (LD) on the activity-dependent changes in BDNF expression from different promoters in the visual cortex and hippocampus. We analyzed the correlation between the chromatin state of Bdnf promoters, exon-specific transcripts levels, and total protein levels in light-deprived rats and in rats reared under normal light-dark cycle. We found that 1 week of LD significantly reduced Bdnf mRNA and protein in the visual cortex but not in the hippocampus. However, epigenetic analysis revealed that LD increased histone-3 methylation and DNA methylation at the Bdnf promoter IV in both the visual cortex and hippocampus. These data highlight the spatial differences in signaling pathways that lead to the BDNF expression in response to diminished ambient light.