Mice lacking a functional NMDA receptor exhibit social subordination in a group-housed environment.

Social dominance, in which an individual asserts control over others or benefits most after social conflict, has an influence on social behaviour. However, the mechanisms mediating social dominance remain unclear. Social dominance within social groups determines the distribution of rewards such as food and access to mating partners, which can act as reinforcers. In this study, we used the water competition test to determine whether mice were dominant or subordinate. It has been previously reported that mice heterozygous for a missense mutation in Grin1 (Grin1 ) showed altered social behaviour, with increased locomotor activity, novelty seeking and anxiety. However, social dominance in these mice has not been previously investigated. We subjected Grin1 mice to the water competition test using IntelliCage and observed that Grin1 influences competitive dominance. We found that Grin1 mice exhibited social subordination characterised by decreased corner visit frequency and occupancy time at the beginning of the task. However, Grin1 mice retained increased basal activity and exploring behaviour under a group-housed environment. Our findings suggested that Grin1 plays an important role in determining social dominance.