Exposure to traumatic events can increase the r
isk for major depressive d
isorder (MDD) as well as posttraumatic stress d
isorder (PTSD), and pharmacological treatments for these d
isorders often involve the modulation of serotonergic (5-HT) systems. Several behavioral paradigms in rodents produce changes in behavior that resemble symptoms of MDD and these behavioral changes are sensitive to antidepressant treatments. Here we review two animal models in which MDD-like behavioral changes are elicited by exposure to an acute traumatic event during adulthood, learned helplessness (LH) and conditioned defeat. In LH, exposure of rats to
inescapable, but not escapable,
tailshock produces a constellation of behavioral changes that include deficits in fight/flight responding and enhanced anxiety-like behavior. In conditioned defeat, exposure of Syrian hamsters to a social defeat by a more aggressive animal leads to a loss of territorial aggression and an increase in subm
issive and defensive behaviors in subsequent encounters with non-aggressive conspecifics. Investigations into the neural substrates that control LH and conditioned defeat revealed that increased 5-HT activity in the dorsal raphe nucleus (DRN)
is critical for both models. Other key brain regions that regulate the acqu
isition and/or expression of behavior in these two paradigms include the basolateral amygdala (BLA), central nucleus of the amygdala (CeA) and bed nucleus of the stria terminal
is (BNST). In th
is review, we compare and contrast the role of each of these neural structures in mediating LH and conditioned defeat, and d
iscuss the relevance of these data in developing a better understanding of the mechan
isms underlying trauma-related depression.
This article is part of a Special Issue entitled ¡®Post-Traumatic Stress Disorder?