2.5. Resident-intruder test

To assess attack behavior, the resident-intruder (RI) test was given according to previous studies (Chang et al., 2020). To maintain the territory of the resident mice, the home cage bedding of the resident mice was not changed on the first day before the RI test or during the RI test. To trigger stress-induced outbursts of aggression (referred to as impulsive aggression), the resident mice were placed on a foot-shock grid (San Diego Instrument, USA) and received five 0.1 mA, 1 s, foot-shocks at random intervals, 30 min before the RI test. In the RI test, the intruder (a male BABL/c mouse) was placed in the home cage of the resident mice for 15 min. Behavioral videos were recorded with a SONY digital camera and were analyzed by a blinded observer. The observed behaviors referred to the descriptions provided in previous studies (Fish et al., 1999; Koolhaas et al., 2013). Biting behavior included incidences of the resident mice biting the vulnerable parts (belly and paws) and the non-vulnerable parts (back) of the intruder mice. Offensive behaviors comprised mounting, pursuit, boxing, and tail rattling. Non-aggressive behaviors included social sniffing, social grooming, self-grooming, and inactivity.