Natural variation in paternal behavior is associated with central estrogen receptor alpha and oxytocin levels

In monogamous mammals paternal care plays an important role in the neural and behavioral development of offspring. However, the neuroendocrine mechanisms underlying paternal behavior remain poorly understood. Here, we investigate the association between natural variation in paternal responsiveness and central levels of oxytocin (OT) and estrogen receptor alpha (ER alpha). We used the frequency of licking and grooming behavior to distinguish low paternal responsiveness and high paternal responsiveness in virgin mandarin voles (Microtus mandarinus). Males that engaged in high paternal behavior had elevated levels of OT immunoreactive neurons in the paraventricular nuclei of the hypothalamus and supraoptic nuclei of the hypothalamus compared with males that displayed low paternal behavior. Likewise, males of high paternal responsiveness had more ER alpha immunoreactive neurons in the medial preoptic area, bed nucleus of the stria terminalis, arcuate nucleus of the hypothalamus and medial amygdaloid nucleus compared to low responsive males. The level of ER alpha immunoreactive neurons in the ventromedial hypothalamic nucleus was lower in highly paternal males compared to less paternal males. These results suggest that natural variation in paternal responsiveness may be directly related to variation in central OT and ER alpha.