Agonistic behavior and unpredictable chronic mild stress in mice.

A significant proportion of patients suffering from major clinical depression exhibit sudden bursts of anger often described as "panic attacks without anxiety or fear" or "irritability." We investigated aggressive behavior in mice from four different inbred strains subjected to unpredictable chronic mild stress (UCMS). Our results show that UCMS affects self-grooming behavior, as evaluated by the state of an animal's fur, with severity of symptoms differing according to genetic background. Furthermore, UCMS increased aggression both in a resident-intruder test and between cage-mates. UCMS is therefore a valuable model of the problematic aggressive behavior seen in depressive patients.