Chronic treatment with hormonal contraceptives alters hippocampal BDNF and histone H3 post-translational modifications but not learning and memory in female rats

Hormonal contraceptives prevent ovulation with subsequent reduction in endogenous levels of estradiol, progesterone and its neuroactive metabolite allopregnanolone. These neurosteroids modulate several brain functions, including neuronal plasticity, cognition and memory. We hypothesized that hormonal contraceptives might affect synaptic plasticity, learning and memory, as a consequence of suppressed endogenous hormones levels. Female rats were orally treated with a combination of ethinyl estradiol (EE, 0.020 mg) and levonorgestrel (LNG, 0.060 mg) once daily for four weeks. Decreased hippocampal brain-derived neurotrophic factor (BDNF) levels and altered histone H3 post-translational modifications (PTMs) were observed 14 days after discontinuation from chronic EE-LNG treatment. These effects were not accompanied by alterations in long-term plasticity at glutamatergic synapses, recognition memory in the novel object and novel place location tests, or spatial learning, memory, and behavioral flexibility in the Morris water maze test. Thus, decreased BDNF content does not affect synaptic plasticity and cognitive performance; rather it might be relevant for the occurrence of certain psychiatric symptoms, reported by some women using hormonal contraceptives. These results provide the first evidence of hippocampal epigenetic changes induced by hormonal contraceptives and complement previous studies on the neurobiological actions of hormonal contraceptives; the finding that effects of chronic EE-LNG treatment on BDNF content and histone PTMs are observed 14 days after drug discontinuation warrants further investigation to better understand the implications of such long-term consequences for women's health.