Mapping the cellular basis of species differences in oxytocin and dopamine receptor expression in the vole nucleus accumbens.

Oxytocin (Oxtr) and dopamine (Drd1, Drd2) receptors provide a canonical example for how differences in neuromodulatory receptors drive individual and species-level behavioral variation. These systems exhibit striking and functionally relevant differences in nucleus accumbens (NAc) expression across monogamous prairie voles (Microtus ochrogaster) and promiscuous meadow voles (Microtus pennsylvanicus). However, their cellular organization remains largely unknown. Using multiplex in situ hybridization, we mapped Oxtr, Drd1, and Drd2 expression in sexually naïve and mate-paired prairie and meadow voles. Prairie voles have more Oxtr+ cells than meadow voles, but Oxtr distribution across dopamine-receptor cell class was similar, indicating a general upregulation rather than cell class bias. Oxtr was enriched in cells that express both dopamine receptors (Drd1+/Drd2+) in prairie voles, suggesting these cells may be particularly sensitive to oxytocin. We found no species or pairing-induced differences in Drd1+ cell counts, suggesting prior reports of expression differences may reflect upregulation in cells already expressing these receptors. Finally, we used single-nucleus sequencing to provide the first comprehensive map of Oxtr and Drd1-5 across molecularly-defined NAc cell types in the prairie vole. These results provide a critical framework for understanding how nonapeptide and catecholamine systems may recruit distinct NAc cell types to shape social behavior.