A link between depression and inflammation has been observed in many studies. Aberrant social behaviors, such as aggression, often present with depression and can be indicative of suicidal behavior.
A recent study addressed the association between stress-associated behaviors, such as aggression, and low-level inflammation induced by endotoxin challenge. They found that the addition of endotoxin-induced inflammation exacerbated depression in stress-induced mice but reduced signs of aggression. Specifically, endotoxin caused increases of IL-1β and 5-HT2A mRNA in the brain, increased serum corticosterone and increased TNFα in both the brain and liver. Stress alone did not cause these changes. However, the combination of stress and inflammation resulted in a reduction in the stress-induced changes in 5-HT and IL-1β. These results indicate that low-level inflammation can have significant impact on stress-induced behaviors, specifically reductions in aggression, which can lead to depression.