Invited reviewOverlapping neurobiology of learned helplessness and conditioned defeat: Implications for PTSD and mood disorders
Highlights
► We review two animal models associated with exposure to an acute traumatic event during adulthood. ► We compare and contrast the neural changes that mediate both models. ► We discuss how these animal models provide a better understanding of PTSD and mood disorders.
Section snippets
Animal models
Multiple animal paradigms have been argued to model both PTSD and MDD, which may reflect that these disorders share similar symptoms and/or have a similar biological basis. Animal models of depression have often been evaluated on the basis of several criteria: whether they produce behavioral changes that are similar to those observed in depression, whether these changes can be objectively measured, and whether these changes can be reversed by treatments used to treat depression (McKinney and
Learned helplessness
In humans, trauma requires the experience or witnessing an actual or threatened death, serious injury or threat to the physical integrity of self or others, and the response to this event must involve intense fear, helplessness or horror (APA, 2000). While it is not possible to determine how animals interpret laboratory stressors, behavioral correlates of fear can be assessed, and the controllability of laboratory stressors can be manipulated to produce situations in which animals are made
Conditioned defeat
Social defeat is a robust stressor that, like LH, produces an array of behavioral changes including anxiety- and depression-like behavior (Berton et al., 1998, Heinrichs et al., 1992, Keeney et al., 2006, Krishnan et al., 2007, Rodgers and Cole, 1993). In Syrian hamsters, social defeat leads to a loss of species-typical territorial aggression and increased submissive and defensive behavior in subsequent social encounters with smaller non-aggressive intruders. This phenomenon has been called
New directions
As discussed above, it is likely that the brain regions implicated in LH and conditioned defeat are important targets for current pharmacological approaches in the treatment of MDD and PTSD, and we have previously suggested that changes in the 5-HT response of brain regions like the BNST and DRN mediate the efficacy of some of these treatments (Hammack et al., 2009b, also see Berendsen, 1995, Stahl, 1994, Strome et al., 2005, Yatham et al., 1999). However, the data described above suggest that
Conclusions
The LH and conditioned defeat paradigms produce behavioral changes that may be associated with the symptomatology of trauma-related depression. A consideration of the neural circuitry underlying each of these behavioral paradigms suggests that the DRN, BNST, BLA, and CeA play a critical role in the acquisition and expression of these behavioral changes, although the precise role of these structures may differ depending on the behavioral paradigm studied. Based on these studies, it seems clear
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