Immune activity linked to a predisposition to depressive behavior

He's going to be mean to me, isn't he?

NIH

Individuals with major depressive disorder or post-traumatic stress disorder have elevated levels of proteins linked to immune activity and inflammation called cytokines. It hasn’t been clear, however, whether depression increases cytokine levels, or if the cytokines themselves contribute to depression.

Figuring out the cytokine-depression link would be difficult to do in human subjects. However, depression can be induced in lab animals that have been exposed to repeated social stresses. Now, researchers have used this approach to reveal that elevated cytokine levels can be used to predict an animal’s susceptibility to depression.

In this study, researchers subjected mice to repeated social defeats by putting them in a cage with larger, more aggressive mice for short periods over a 10 day span. Each defeat event lasted only 5-10 minutes; however, the mice were also exposed to continued psychological stress by placing the aggressive mouse on the other side of a clear divider 24 hours a day. To make things worse, each day, a new aggressor was chosen. This protocol has previously been demonstrated to induce depression-like social avoidance behaviors in mice.