Aggressiveness is a common symptom in patients with psychiatric disorders and developmental disorders. Behavioral assessment of aggressiveness in laboratory animals is essential for the analysis of aggression mechanisms and evaluation of the action of psychotropic drugs. Currently, behavioral research of aggressiveness is often conducted with intraspecific aggression tests using one set of male laboratory animals, such as a resident-intruder test. The intraspecific aggression is not detectable in female animals, except during the nursing period.
We developed a semi-automated apparatus (ARM: Aggression Response Meter) for measurement of aggressive biting behavior (ABB) in male and female 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.
The estrous cycle in normal and aggressive female mice was monitored daily with a vaginal impedance checker and changes in ABB were assessed daily using the ARM. The results indicate that the intensity and incidence rate of ABB were unrelated to estrous cycle. Female mice were isolated for 7 weeks and then re-socialized for 2 weeks. Changes in ABB were assessed during the isolation-reared/re-socialized periods using the ARM weekly. ABB significantly increased during isolation rearing, and then significantly decreased throughout the re-socialization period; both changes were time-dependent, as well as male mice. Additional isolation-reared female mice were tested before and after administration of buspirone, a serotonin 1A receptor agonist. Buspirone significantly inhibited ABB in female mice.
The results suggest that ABB toward inanimate objects is a reliable paradigm that makes it possible to detect aggressiveness in the early stage of psychiatric disorders in female mice as well as male mice. 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, using with both male and female mice.