Laboratory domestication changed the expression patterns of oxytocin and vasopressin in brains of rats and mice.

The process of domestication is recognized to exert significant effects on the social behaviors of various animal species, including defensive and cognitive behaviors that are closely linked to the expression of oxytocin (OT) and vasopressin (AVP) in selected areas of the brain. However, it is still unclear whether the behavioral changes observed under domestication have resulted in differences in the neurochemical systems that regulate them. In this study, we compared the differences in distribution patterns and regional quantities of OT and/or AVP staining in the forebrains of wild and laboratory strains of rats and mice. Our results indicated that, in the anterior hypothalamus (AH), laboratory strains showed significantly higher densities of OT-ir (immunoreactive) and AVP-ir cells than wild strains, while no significant difference in the densities of those cells in the lateral hypothalamus (LH) was detected between wild and laboratory strains. Laboratory strains showed higher densities of OT-ir and AVP-ir cells than wild strains in the medial preoptic area (MPOA), and differed in almost every MPOA subnucleus. Our results suggest that domestication significantly alters the expression of OT and AVP in related brain areas of laboratory rats and mice, an observation that could explain the identified changes in behavioral patterns.