Persistence of reduced aggression in vasopressin 1b receptor knockout mice on a more “wild” background

It has been previously reported that vasopressin 1b receptor knockout (Avpr1b−/−) mice have reduced levels of aggressive behavior compared to wildtype littermates. However, as the background of the mice was always a mixture of 129/SvJ and C57BL/6, we wanted to determine if the phenotype persisted when our laboratory line was crossed with a wild-derived sub-species of house mice. To this end, we crossed our Avpr1b−/− mice with Mus musculus castaneus, one of the few sub-species that will breed with laboratory strains. Subsequent F2 offspring were tested in a resident–intruder behavioral test to assess aggressive behavior. We found that even on this more “wild” background, Avpr1b−/− mice continued to demonstrate longer attack latencies and fewer attacks in a resident–intruder test than wildtype littermates. These findings are consistent with previous reports of reduced aggressive behavior in Avpr1b−/− mice and show that the deficit does persist on a different background strain. Further, these findings confirm the importance of the Avpr1b to normal displays of social forms of aggressive behavior.