Evaluation of aggressiveness of female mice using a semi-automated apparatus for measurement of aggressive biting behavior toward an inanimate object

BACKGROUND: Most laboratory research on aggressive behavior has focused on intraspecific intermale aggression tests. The intraspecific confrontation is not available for the evaluation of female aggressiveness, since androgens are critical for maintenance of this behavior, whereas aggressive biting behavior toward inanimate objects (ABI) occurs in both males and females. NEW METHOD: We propose an experimental method for evaluating female aggressiveness. We improved the previously developed semi-automated apparatus (Aggression Response Meter, ARM) to apply it to measurement of female ABI, and measured changes of ABI in stressed mice and drug actions on ABI. RESULTS: ABI assessment was performed daily in sexually mature female mice using ARM. The intensity and number of ABI in one session did not significantly change during an estrous cycle, suggesting that ABI is not influenced by the dynamics of sex hormones. Additional female mice were socially isolated for 7 weeks and then re-socialized for 2 weeks, and ABI was monitored weekly. ABI significantly increased during the isolation period, and then significantly decreased during re-socialization; both were time-dependent. In prolonged-isolated aggressive mice, a serotonin 1A receptor agonist, buspirone, significantly decreased ABI. COMPARISON WITH EXISTING METHOD: There are no experimental methods or apparatus available for evaluating female aggressiveness using one individual repeatedly. We could measure ABI semi-quantitatively using the ARM. CONCLUSIONS: ABI is a useful behavioral paradigm in the evaluation of aggressiveness in female mice, regardless of the estrous cycle, and can also be used for evaluating the actions of drugs on aggressiveness.