A Double Hit Stress Rodent Model of Major Depressive Disorder
Social defeat is an ethologically relevant stressor that utilizes the natural establishment of social rank in male rodents and has been shown to be relevant to major depressive disorder (MDD) and post-traumatic stress disorder (PTSD). In the present study, we wished to establish a social defeat stress model in combination with the chronic unpredictable stress model, which is considered a mild stressor to the rodent. In this way, we create a “double hit” model that may more accurately mimic severe stress that is common in both MDD and PTSD. In the present study, residents established dominance over the intruder for 10 consecutive days. In addition, social defeat stress was followed by another stressor given at random times during each day, i.e. chronic unpredictable stress. These unpredictable stressors included 30 min restraint, 1 h shaking/crowding, a cold water swim, a warm water swim or a tipped cage for 24 h. In one cohort of animals, brain tissue was taken 24 h after the last stressor for DNA. In a second cohort, animals were tested on a sucrose preference test in which two bottles containing 0.8% sucrose was placed on their cages for 3 consecutive days (days 8-10 of social defeat stress), and the total amount of sucrose was calculated relative to total volume consumed. Brain tissue analyses revealed significantly elevated DNA oxidation in white matter comparing stressed animals to non-stressed controls, consistent with what has been found in post-mortem white matter from MDD subjects. Further, animals given the social defeat + chronic unpredictable stress demonstrated a deficit in sucrose preference, a natural reward, revealing that these animals were anhedonic as compared to controls. Stressed animals also demonstrated fear of the intruder in a social interaction test performed one day after the social defeat/chronic unpredictable stress was complete. Therefore, it appears that social defeat plus chronic unpredictable stress produces a phenotype relevant to clinical data in humans.
Hernandez, Liza J.; Burgess, Katherine C.; Wherry, J. D.; Szebeni, Attila; Szebeni, Katalin; Ordway, Gregory A.; and Brown, Russell W.. 2016. A Double Hit Stress Rodent Model of Major Depressive Disorder. Poster presentation. Society for Neuroscience Conference, Washington, DC. http://www.abstractsonline.com/pp8/#!/4071/presentation/29671