Document Type

Article

Publication Date

Fall 2010

Abstract

Individuals respond differently to traumatic stress. Social status, which plays a key role in how animals experience and interact with their social environment, may influence how individuals respond to stressors. In this study, we used a conditioned defeat model to investigate whether social status alters susceptibility to the behavioral and neural consequences of traumatic stress. Conditioned defeat is a model in Syrian hamsters in which an acute social defeat encounter results in a long term increase in submissive behavior and a loss of normal territorial aggression. To establish social status, we weight matched and paired Syrian hamsters in daily aggressive encounters for two weeks to create dominant/subordinate relationships. We also included controls which were exposed daily to a clean empty cage for the same 14 day period. Twenty-four hours after the final pairing or empty cage exposure, subjects were divided into defeat and no defeat groups. Individuals in the defeat group received three 5 minute social defeats at 5 minute intervals in the cage of a larger aggressive hamster. Individuals in the no defeat group were exposed to the empty cage of a larger aggressive hamster at the same time intervals. In experiment 1, subjects of both groups were tested for conditioned defeat with a non-aggressive intruder 24 hours after social defeat training. In experiment 2, brains were collected 65 minutes following social defeat training and immunohistochemistry was performed for c-Fos protein, a marker of neural activation. We quantified the number of c-Fos immunopositive cells in brain regions known to be involved in stress and aggression, including the ventral medial prefrontal cortex, medial amygdala, and lateral and ventromedial hypothalamus. We found that subordinate animals showed significantly more conditioned defeat behavior than did dominants or controls, and subordinates showed significantly less c-Fos immunoreactivity than did dominants in all these brain regions. These results suggest that decreased neural activity in these brain regions corresponds to an increased susceptibility to conditioned defeat. In sum, social status plays an important role in how animals respond to social stressors and this corresponds to activity in specific brain areas.

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