Mackenzie R. Mears


Teenage bullying is associated with fear and anxiety disorders characterized by impaired extinction of conditioned fear responses. Medial prefrontal cortex (mPFC) dopamine (DA) is known to be required for fear extinction. Adolescent rats exposed to social defeat, as a model of teenage bullying, exhibit reduced adult mPFC DA activity. We tested whether adolescent social defeat also results in impaired fear extinction. Adolescent rats (postnatal day [P]35) were exposed daily to social defeat for five consecutive days. Age-matched controls experienced no defeat but were exposed daily to novel empty cages. Subjects underwent fear-learning trials in early adulthood (P56). Fear conditioning consisted of presenting an auditory tone (56dB, 5s duration) paired with a mild foot shock (0.7mA, 0.5s duration) 10 times over a 10-minute period. Recall of conditioned fear learning along with fear extinction were assessed by measuring conditioned freezing to tone presentation alone over the subsequent 3 days. Defeated and control rats showed no difference in conditioned freezing in the recall test, and freezing responses declined equally on each subsequent day. Defeated rats did show a trend for greater freezing over time on the last extinction day, suggesting delayed fear extinction, which will be confirmed by future experiments. Establishing this link between adolescent social stress and later deficits in fear learning will allow investigation of underlying neural mechanisms, and pave the way for developing more effective treatments for anxiety disorders exhibited by victims of teenage bullying.