depressive-like behavior. Regimens of chronic stress or repeated administration of

gluccocorticoids increase the amount of time an animal spends immobile, decrease the

latency to immobility, and decrease the amount of time engaged in active swimming

(Molina et al., 1994; Johnson et al., 2006). Antidepressant drugs, on the other hand,

ameliorate these effects. For example, desipramine (a tricyclic antidepressant) and

fluoxetine (a selective serotonin reuptake inhibitor) reduce immobility and increase the

amount of time a stressed animal will struggle to escape the forced swim (Molina et al.,

1994; Lucki et al., 2001).

 Based on the results of investigations using social defeat stress and the Porsolt

swim test, we have begun to further characterize the social defeat model of emotional

stress in rats. We have evaluated the impact of both acute and repeated social defeat

stress on regulation of ACTH and CORT at various times after the stressor. We have

also compared six daily social defeat sessions to one month of stress every third day to

examine the effectiveness of massed and intermittent stress exposure. In addition, we

exposed socially defeated rats to the Porsolt swim test in order to characterize the

enduring behavioral effects of social defeat stress.