Thursday, 24 January 2013

How Repeated Aggression Triggers Social Aversion in Mice

Jan. 18, 2013 — One of the mechanisms involved in the onset of stress-induced depression has been highlighted in mice by researchers from CNRS, Inserm and UPMC (1). They have determined the role of the corticosterone (stress hormone) receptor, in the long-term behavioral change triggered by chronic stress. In mice subject to repeated aggressions, this receptor participates in the development of social aversion by controlling the release of dopamine (2), a key chemical messenger. If this receptor is blocked, the animals become "resilient": although anxious, they overcome the trauma and no longer avoid contact with their fellow creatures.

This work is published in Science on 18 January 2013.

In vertebrates, stress triggers a rapid release of glucocorticoid hormones, corticosterone in rodents and cortisol in humans. This hormone modifies the expression of numerous genes in such a way that the individual can best respond to the cause of stress. However, chronic or excessive stress can lead to depression, anxiety and social behavioral difficulties. Understanding the mechanisms involved is an important challenge in the treatment of stress-related psychiatric illnesses.

The researchers already suspected that the emergence of depressive symptoms caused by stress brought into play not only the stress hormone but also the dopamine neurons releasing this neurotransmitter, which is vital in controlling mood. To better understand this interdependence, the researchers subjected a group of mice to repeated attacks by stronger, aggressive congeners. After about ten days, the mice showed signs of anxiety and strong social aversion. In fact, when faced with a new congener, the aggressed mice preferred to avoid any contact. This social aversion is considered as a marker of depression.

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