McCann KE, Bicknese CN, Norvelle A, Huhman KL.
Physiol Behav. 2014 Apr 22;129:25-9. doi: 10.1016/j.physbeh.2014.02.039. Epub 2014 Feb 28.
Stress from social situations is the most prevalent type of stressor experienced by humans, and exposure to such stressors can lead to a number of psychiatric disorders, including depression, anxiety, and posttraumatic stress disorder. Improving our understanding of how stress causes changes in the brain will suggest new ways that these disorders can be treated or even prevented. The Huhman laboratory uses Syrian hamsters as an animal model of social stress because these rodents readily produce aggressive behavior towards conspecifics. After losing in an inescapable, brief pairing with a larger, more aggressive opponent, hamsters instead become highly submissive and subsequently abandon all territorial aggression, a response that we have called conditioned defeat.
We had previously explored whether conditioned defeat is produced because the initial pairing is inescapable. We compared the behavioral response of animals tested after our customary, inescapable defeat with that produced by animals tested after a shorter, escapable defeat. We found that animals experiencing both types of defeat exhibited conditioned defeat but that animals in the inescapable defeat group displayed significantly stronger responses. We were unsure if this difference was due to differences in duration of defeat or in the controllability (escapability) of the stressful experience. In order to examine this question, we developed a defeat model in which each animal in the escapable defeat group was paired, or “yoked”, with an animal in the inescapable defeat group, such that their defeat sessions lasted the same amount of time. Thus, the only difference between the two groups was now the way in which the stressful experience ended - animals in the escapable defeat group could control the end of the session by jumping out of the cage, while the researcher ended the defeat session for animals in the inescapable defeat group.
Using this “yoked” design, there were no differences between the two defeat groups, suggesting that having the ability to escape a stressful social situation does not reduce the impact of that stressor. This indicates that social stress, even if very brief and escapable, is capable of producing marked behavioral responses. Our lab is continuing to study how these changes are mediated in the brain and how they might be reversed.