In male Mongolian gerbils, giving testosterone, estradiol, or dihydrotestosterone turned aggressive dads into caring ones. The hormones boosted oxytocin and its receptor in brain areas linked to parenting, suggesting the oxytocin system helps mediate this behavior change.

In the Mongolian gerbil (Meriones unguiculatus), testosterone (T) and its metabolites estradiol (E₂) and dihydrotestosterone (DHT) participate in the regulation of paternal behaviour. E₂ activates the oxytocinergic system, comprised of oxytocin (OT) and its receptor (OTR), in maternal behaviour. However, whether T, E₂ and DHT regulate paternal behaviour through the activation of OT/OTR is unknown. The aim of this study was to determine whether these hormones activate the oxytocinergic system as part of the neuroendocrine mechanism in the regulation of paternal behaviour in the Mongolian gerbil through increases in OT and the OTR in the medial preoptic area (mPOA), bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and olfactory bulb (OB). Fifty males aggressive towards pups were organised into five groups of 10 animals each: bilateral castration + T injection, bilateral castration + E₂ injection, bilateral castration + DHT injection, bilateral castration simulation + vehicle, and bilateral castration. After paternal behaviour tests were performed, blood samples were obtained to quantify T, E₂, and DHT by ELISA. The brains were removed and analysed for immunoreactivity (ir) of OT and OTR. One hundred percent of the males who received T, E₂, and DHT injections stopped being aggressive and became paternal. Compared with castrated and sham-castrated males, males that received T, E₂, and DHT injections presented greater numbers of OT-ir and OTR-ir cells in the mPOA and BNST. These results suggest that the oxytocinergic system could be one of the mechanisms through which T, E₂, and DHT regulate paternal behaviour.