Behavioral responses to pups in males with different reproductive experiences are associated with changes in central OT, TH and OTR, D1R, D2R mRNA expression in mandarin voles

• New fathers display more OT-IR and TH-IR neurons.
• New fathers exhibit higher OTR mRNA expression in the Nacc and MeA.
• New fathers have more D1R, D2R mRNA expression in the Nacc.
• New fathers show reduced D1R, D2R mRNA expression in the MeA.
• Transition to fatherhood is associated with altered OT and dopamine systems.

Male rodents behave differently toward pups because of different sexual and/or paternal experiences; however, the mechanisms underlying these responses are not well understood. Using socially monogamous mandarin voles (Microtus mandarinus) we investigated the behavioral responses of males with different reproductive experiences (virgin males, paired males and new fathers) to new born pups. Central levels of neuropeptide oxytocin (OT), tyrosine hydroxylase (TH), as well as oxytocin receptor (OTR), dopamine 1-type receptor (D1R) and dopamine 2-type receptor (D2R) mRNA expression in the nucleus accumbens and medial amygdala were also measured in these males. Our data showed that new fathers exhibited more approaching behavior and contained more OT-immunoreactive and TH-immunoreactive neurons. In addition to increased OTR mRNA expression in the nucleus accumbens and medial amygdala, new fathers had higher D1R and D2R mRNA expression in the nucleus accumbens, and less D1R and D2R mRNA expression in the medial amygdala than paired males. These results demonstrate that males with different reproductive experiences display different behavioral responses to pups and that these differences are associated with altered OT and dopamine, and their receptors in specific brain regions.