A possible confound and the role of olfaction in mouse aggressive interactions

In investigating the olfactory modulation of aggression in mice, a urine-coating technique frequently has been used. Fighters typically have been tested against castrated animals coated with either urine or water. Then, if the fighters are more aggressive toward urine-coated castrates than toward water-coated castrates, it is concluded that olfaction plays a role in this discriminatory response. However, it is possible that the fighers might react to behavioral differences between these two groups of castrates caused by the different experimental treatment. Three experiments were conducted to study this possible confound and the role of olfaction in the control of agonistic encounters. The results indicated that 1) the confound is not likely to operate; 2) even if the confound is allowed to operate, it is not an effective discriminatory cue; and 3) anosmic fighters do not exhibit differential attacks toward castrates treated with different chemo-signals. Therefore, the emission and perception of olfactory cues do play an important role in mouse agonistic interactions.