Many teenagers experience bullying, and adolescent bullying is a severe stressor associated with greater incidence for psychiatric disorders that can persist into adulthood, including depression and substance use disorders. Such disorders are characterized by deficits in executive functioning, which are known to be mediated by medial prefrontal cortex (mPFC) and dopamine (DA) activity.
In order to assess how bullying changes DA in the mPFC after adolescent bullying, MJ Watt and colleagues employed a rodent model of repeated social aggression during adolescence in which peripubertal rats were exposed to an older and aggressive adult male for 10 minutes a day over a 5 day period (PN35-39). Following each “bullying bout”, a wire mesh was placed in the chamber to separate the intruder (i.e. aggressor) from the test rat for 25 minutes, which is a form of chronic psychosocial stress and may serve to model the intimidation many teens may experience with their own aggressors (i.e. school mates, peers, etc). The researchers found that rats experiencing adolescent social defeat show increased mPFC DA activity at PN40 (the day after the last bullying session), which was maintained until PN49- even after the stressor hadn’t been experienced since PN39. However, at PN56 these same animals had decreased mPFC DA activity, which may be due to over-compensation to reduce the elevated activity seen from PN40-49. Furthermore, mPFC DA hypofunction induced by social defeat stress was specific to animals experiencing it during adolescence, as the same manipulation in adults only led to increased mPFC DA activity following exposure to social aggression. Importantly, this manipulation did not change norepinephrine (NE) or serotonin (5-HT) activity in the mPFC, and animals experiencing social defeat stress during adolescence did not become more aggressive later in development. Collectively, these findings suggest that mPFC DA is particularly susceptible to social stressors during adolescence and that social defeat changes not only mPFC DA function, but also behavioral responses to later life social events.
On a side note, I would be interested to see how these animals perform in a go/no-go task or in a rodent model of the Iowa gambling task. Also, how would these animals perform in a self-administration paradigm and how would it be modulated by social context? Also, I really like the idea of framing the social defeat paradigm as a model of bullying instead of depression. Kudos!
Lesson of the day: Be nice to each other, because you never know how your words/actions are affecting the other person.
M.J. Watt, L.C. Miller, J.L Scholl, K.J. Renner, A.M. Novick, G.L. Forster. Trajectory of alterations to cortical dopamine activity in a model of teenage bullying. Program No. 84.03/ZZ23.2013. Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2013. Online.