Sex differences in the epigenetic regulation of chronic visceral pain following unpredictable early life stress.

BACKGROUND

We previously reported that early life stress (ELS) dysregulated glucocorticoid receptor (GR) and corticotrophin-releasing hormone (CRH) expression in the central nucleus of the amygdala (CeA). Epigenetic modifications serve as memories of adverse events that occurred during early life. Therefore, we hypothesized that epigenetic mechanisms alter GR and CRH expression in the CeA and underlie chronic visceral pain after ELS.

METHODS

Neonatal rats were exposed to unpredictable, predictable ELS, or odor only (no stress control) from postnatal days 8 to 12. In adulthood, visceral sensitivity was assessed or the CeA was isolated for Western blot or ChiP-qPCR to study histone modifications at the GR and CRH promoters. Female adult rats underwent stereotaxic implantation of indwelling cannulas for microinjections of garcinol (HAT inhibitor) into the CeA. After 7 days of microinjections, visceral sensitivity was assessed or the CeA was isolated for ChIP-qPCR assays.

RESULTS

Unpredictable ELS increased visceral sensitivity in adult female rats, but not in male counterparts. ELS increased histone 3 lysine 9 (H3K9) acetylation in the CeA and H3K9 acetylation levels at the GR promoter in the CeA of adult female rats. After unpredictable ELS, H3K9 acetylation was increased and GR binding was decreased at the CRH promoter. Administration of garcinol in the CeA of adult females, that underwent unpredictable ELS, normalized H3K9 acetylation and restored GR binding at the CRH promoter.

CONCLUSION

Dysregulated histone acetylation and GR binding at the CRH promoter in the CeA are an important mechanism for "memorizing" ELS events mediating visceral pain in adulthood.