The effects of fathering experience on paternal behaviors and levels of central expression of oxytocin and dopamine-2 type receptors in mandarin voles.

Mothers' brains change dramatically in response to the release of hormones related to pregnancy and labor; however, fathers' brains are also sensitive to the experience of paternal care. Thus, fathers with differing fathering experience may exhibit different behavioral responses towards pups. Using socially monogamous mandarin voles (Microtus mandarinus), effects of fathering experience on levels of paternal behavior as well as oxytocin (OT) and dopamine-2 type (D2) receptors in the nucleus accumbens (NaCC) and medial nucleus of the amygdala (MeA) were investigated. The obtained results showed that experienced fathers displayed more active paternal behaviors such as licking, retrieval, and nest building than new fathers; however, new fathers spent more time in inactive huddling than experienced fathers. Western blot analysis showed that new fathers had significantly higher levels of OTR, but lower levels of D2R compared to experienced fathers in the NaCC. Levels of OTR and D2R in the NaCC and MeA of new and experienced fathers changed with the age of pups. OTR levels in the NaCC of both new and experienced fathers significantly decreased in response to increasing age of pups. Levels of D2R in the NaCC of new fathers on postnatal day 7 (PND 7) were significantly higher than on PND1 and PND14, and levels of D2R in the NaCC of experienced fathers increased with the age of pups. OTR levels in the MeA of new fathers decreased with the age of pups. In contrast, OTR levels of experienced fathers significantly increased with the age of pups. The D2R level in the MeA of new fathers did not change significantly, while the D2R levels of experienced fathers increased with the age of pups. These data illustrate that fathering experience could increase the active components of parental care and alter the expression levels of OTR and D2R in a region- and time-dependent way.