Basic NeuroscienceA novel semi-automated apparatus for measurement of aggressive biting behavior in mice

•We developed an ARM (Aggression Response Meter) for evaluations of aggressiveness in mice.•Aggressive biting behavior (ABB) toward inanimate objects was used as a paradigm.•ARM can detect aggressiveness in the early stages of psychiatric disorders in mice.•ARM can be used for the evaluation of ABB in both male and female mice.•ARM can measure ABB repeatedly using the same individual over a long period of time.

BackgroundCurrently, behavioral research of aggressiveness is often conducted with intraspecific intermale aggression tests. Intraspecific aggression is not detectable in early stages of psychiatric disorders or in female animals, except during the nursing period.New methodWe developed a semi-automated apparatus (ARM: Aggression Response Meter) for measurement of aggressive biting behavior (ABB) in mice. The apparatus is loaded with computer-controlled sticks that stimulate the mouse through touch, inducing irritation and anger. When the mouse bites the sticks in anger, a load sensor attached to the sticks detects ABB dynamically. Changes in ABB were assessed with isolation-reared/re-socialized mice using the ARM, and additional isolation-reared mice were tested using both the ARM and the resident-intruder test, and then buspirone, a serotonin 1A receptor agonist, was administered.ResultsABB significantly increased during isolation rearing, and then significantly decreased throughout the re-socialization period; both changes were time-dependent. The ARM also detected ABB of female mice after 3 weeks of isolation rearing. Buspirone significantly inhibited aggressive behavior in both tests in a similar manner.Comparison with existing methodThe ARM detects aggressiveness in psychiatric disorders at an earlier stage and in both male and female mice.ConclusionsABB toward inanimate objects is a reliable paradigm that makes it possible to detect aggressiveness in the early stage of psychiatric disorders. The ARM is useful for the quantification of aggressiveness using the same individual repeatedly, and for objective evaluation of the effects of drugs on aggressiveness. The ARM can be used with both male and female mice.