Exposure to the stressor environment prevents the temporal dissipation of behavioral depression/learned helplessness

Background: Exposure to uncontrollable stressors such as inescapable shock (IS) produces a set of behavioral changes such as poor escape learning that have been called behavioral depression and learned helplessness. This paradigm has been proposed to be a model of depression and of anxiety-related disorders such as posttraumatic stress disorder (PTSD). However, the behavioral changes persist for only a few days after the stressor, rendering the phenomenon questionable as a model. However, the original traumatic experience is re-experienced in PTSD and rumination occurs in depression. In a series of experiments we therefore sought to determine whether behavioral depression/learned helplessness could be made to endure by periodically “reminding” the subject of the original IS experience. Methods: Rats exposed to IS were tested for escape learning at various times thereafter. In different experiments the subjects were exposed to the environment in which IS had occurred at differing points in the interval between IS and escape testing. Results: Exposure to the environment in which IS had occurred prolonged the duration of behavioral depression/learned helplessness, and repeated exposures prolonged it indefinitely. This effect required exposure to the cues that had been present during IS (i.e., reminding) and was not duplicated by exposure to other stressors or stress environments. Conclusions: Behavioral depression/learned helplessness can be maintained over time by processes that may be similar to those occurring in depression and PTSD, thereby strengthening the possibility that this paradigm is indeed a reasonable model of these disorders.