Although female rats are typically described as having a promiscuous mating strategy, if sexually naïve females have their formative sexually rewarding experiences paired with the same male, they will recognize that male and display mate-guarding behavior towards him in the presence of a female competitor. Female rats that display mate guarding behavior also show enhanced activation of oxytocin and vasopressin neurons in the supraoptic and paraventricular hypothalamic nucleus. Here, we examined the potential role that histone demethylation might have in establishing this pair-bonded behavior, and whether the corresponding changes in oxytocin and vasopressin neuronal activation depended on demethylation. To accomplish this, we examined the effect of a lysine-specific demethylase-1 inhibitor to block the action of demethylase enzymes and maintain the methylation state of corresponding genes. Female rats treated with the demethylase inhibitor failed to show any measure of mate guarding, whereas females treated with vehicle displayed mate guarding behavior. Demethylase inhibitor treatment also blocked the ability of familiar male cues to activate oxytocin and vasopressin neurons, whereas vehicle-treated females showed this enhanced activation. These data indicate that histone demethylation is a crucial component in the epigenetic modification of neural circuitry that underlies conditioned mate guarding in female rats. These results are the first to demonstrate the role of histone demethylation underlying changes in mating strategy.
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