Aggression-Induced Stress in Mice

This procedure was performed as described by Goto et al. [46 (link)] with minor modifications from 1:00 p.m. to 4:00 p.m. [47 (link)]. Before R-SDS, male ICR mice were screened for their aggressiveness against a novel male B6 mouse for 3 min daily for 3 days. We evaluated the aggressiveness of the ICR mice based on the latency time and the number of attacks during the observation period, and we used only mice whose aggressiveness was stable. Before R-SDS, male B6 mice were individually housed with free access to food and water for one week. White-color partitioning boards were placed between every single cage so that the mice were not affected by the behaviors of neighboring mice. Three days before R-SDS, ICR mice were moved into a compartment of each cage (width × depth × height = 213 mm × 320 mm × 130 mm), which was divided by an acrylic divider containing holes to allow the mice to establish their territories in the cage (Figure 2A). A nine-week-old male B6 mouse, after isolation, was transferred to the territories of a male ICR mouse in the cage for 10 min daily for 10 days. After the physical contact time, a male B6 mouse was placed into another compartment next to the male ICR mouse in the cage until exposure to physical stress the next day so that a B6 mouse was exposed to various emotional stresses, including visual, auditory, and olfactory stimuli, from an ICR mouse for 24 h every day. The pairs of male B6 mice and male ICR mice were randomized daily to minimize variability in the aggressiveness of male ICR mice. Nonstressed control B6 mice were placed into each compartment divided by the divider to keep the mice in pairs in the cage and exchanged the pair every day.