Resident-intruder test
Group-reared mice were kept in isolation for 5 days before the test. The test was carried out in a dark phase (0:30 to 2:30) in a chamber that keeps the cage under dim (infrared) light at 25°C. Video recording from two opposite directions was initiated once the intruder mice had been gently placed in a vacant spot in the cage of the resident mice. The behaviors of the resident mouse were recorded for 10 min. The duration and number of times the resident mice spent sniffing, in active contact with, and in pursuit and attack with the intruder mice were measured by observers who were blinded to the genotypes of the mice.