Differences in social approach in two inbred strains of mice

The present study used trios of two familiar male mice of the same strain and an intruder of a different strain to evaluate the robustness of the protocol in encounters involving strains with different motor activity levels. The results validated the methods and showed subtle inter-strain differences in reactions to the presence of an intruder. The frequency and mean duration of the proximity episodes showed an inter-strain difference in social interactions with the intruder: B6 increased the duration of contacts without changing the frequency, whereas 129S2 increased the frequency of contacts but these were of a shorter duration. The results are discussed in relation to a possible effect of strain differences on anxiety levels or, more generally, the influence of genetic background on the social behaviour of mice.