Exogenous oxytocin microinjection into the nucleus accumbens shell attenuates social dominance in group-housed male mice

The nucleus accumbens (NAc), a part of the brain's limbic system, is involved in a variety of brain functions, including reward motivation and social hierarchy. Here, the study investigated the effect of intra-NAc different subregions microinjections of oxytocin on social hierarchy regulation. The hierarchical ranking of group-housed male mice in laboratory settings was determined through the tube test, and a new reliable and robust behavior assay-the mate competition test-was proposed. The mice were randomly divided into two groups, and the bilateral guide cannula was implanted into the shell and core of the NAc, respectively. After social dominance stabilized, changes in social hierarchy were determined through the tube test, warm spot, and mate competition tests. Intra-NAc shell microinjections of oxytocin (0.5 & mu;g/site), but not the core (0.5 & mu;g/site), significantly reduced the social dominance of mice. In addition, oxytocin microinjection into both the shell and core of the NAc significantly increased locomotor ability without affecting anxious behaviors. These findings are tremen-dously important in understanding the functions of the NAc subregions for social dominance and are more likely to indicate the potential of an oxytocin therapeutic strategy for psychiatric disorders and social impairments.