Reduced aggressive behaviour in mice with targeted disruption of the oxytocin gene.

Oxytocin (OT) has been reported to mediate aggressive and affiliative behaviours in several species. The behavioural role of OT has been established with physiological manipulations that potentially affected blood pressure, which may have indirectly affected the behaviours under study. To provide converging evidence of the physiological role of OT in aggressive behavior, wild type (WT), heterozygous (OT-/+), and homozygous (OT-/-) mutant mice were tested in two aggression paradigms. In general, there was no significant difference in aggressiveness between WT and OT-/+ mice. However, there were significant reductions in the duration of aggressive behaviors among OT-/- animals, especially in agonistic encounters within neutral arenas. The OT-/- mice did not exhibit any sensorimotor deficits or display any altered general anxiety levels that may have accounted for the observed reduction in aggressive behavior. These data indicate that aggression is mediated in part by OT in mice and that increased aggressiveness is not an obligatory phenotypic result of targeted genetic disruption of any gene.