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  • Addiction, Drugs
  • Information from Lay-Language Summaries is Embargoed Until the Conclusion of the Scientific Presentation

    541—Mood Disorders: Animal Models II

    Tuesday, November 12, 2013, 8:00 am - 12:00 noon

    541.01: One-time brief vicarious pain is sufficient to enhance fear learning and trigger depression-like behaviors in mice

    Location: Halls B-H

    *W. ITO, A. MOROZOV;
    Virginia Tech. Carilion Res. Inst., Roanoke, VA

    Abstract Body: (Rationale) Psychological stress is a major trigger of mental disorders, but prevalent rodent models of distress involve physical pain or physical discomfort. Here, we characterized a mouse model of vicarious pain from one-time brief exposure to conspecifics receiving electrical footshocks.
    (Experiments and results) Single exposure (duration: 4min) to a distressed cagemate decreased preference to sucrose water measured during the following 12 hours. Moreover, the observers showed enhanced contextual fear and passive avoidance learning, performed 24 hours after the vicarious pain. Despite causing behavioral changes, observing other pain did not increase plasma corticosterone (CORT) more than the control procedure, in which demonstrator did not receive footshocks. A restraint (2hr), however, increased CORT more than the vicarious pain, but did not reduce sucrose preference.
    (Discussion) The finding suggests that (1) vicarious pain, even brief, is sufficient to produce lasting changes in mouse brain circuits underlying fear and reward, and (2) the mechanism does not solely involve raise of plasma CORT, as observed in physical stress.

    Lay Language Summary: Brief psychological traumatic event elicits traits of fear and depression in mice:
    A soldier witnessing his squad’s decimation while perched from a helicopter; a child hearing the violence of domestic abuse behind closed doors; a bystander seeing an innocent man’s mutilation by terrorists in the streets of London. There is mounting evidence that such psychological stress from experiencing vicarious pain can contribute to and even trigger mental disorders.
    While animal models have helped reveal some of the neuronal mechanisms of mental illness, previous experiments have not separated psychological distress from physical distress. This study shows, using a mouse model, that one brief exposure to psychological trauma independent of physical stressors can elicit traits of depression and make the animal more susceptible to aversive events.
    In the study, two mice that grew up together were placed in adjacent chambers separated by a transparent, perforated wall. While one mouse - the observer - remained unharmed, the cage mate was subjected to a series of electrical shocks. Though the observer mouse was physically unharmed, this brief exposure to vicarious pain proved enough to alter both behavior and synaptic connections in the brain.
    In the day following the exposure, the observer mice showed a classic trait of depression. Two separate water bottles were available for them to drink from - one containing tap water and the second filled with sugar water. Just like a person, a mouse will typically enjoy the sweet drink and prefer it to the regular water. After experiencing psychological distress, however, the mice in this study showed no preference, drinking equal amounts of each.
    In addition, the observer mice became more susceptible to further stressors and were affected more by fear-learning activities. For example, all of the mice learned to avoid the compartment where they received electrical foot shocks, or to freeze up in fear if escape was unavailable. But the lessons stuck more for the animals with prior exposure to vicarious pain, who took longer to re-enter the compartment and froze more often when tested 24 hours after the psychological traumatization.
    This study shows that a brief psychological traumatic event alone makes a mouse’s brain susceptible to subsequent stress, leading to symptoms reminiscent of depression and post-traumatic stress disorder. What’s more, the same research group revealed alterations to the neural circuitry connecting the prefrontal cortex and the amygdala, the brain’s centers for cognitive function and emotion, respectively. The changes may be the invisible brain injury caused by the psychological distress and might predict the subsequent mental disorders that the psychological traumatic event can promote.