An interesting new report of animal research published in Biological Psychiatry suggests that common antidepressant medications may impair a form of learning that is important clinically.
Selective serotonin reuptake inhibitors, commonly called SSRIs, are a class of antidepressant widely used to treat depression, as well as a range of anxiety disorders, but the effects of these drugs on learning and memory are poorly understood.
In a previous study, Nesha Burghardt, then a graduate student at New York University, and her colleagues demonstrated that long-term SSRI treatment impairs fear conditioning in rats. As a follow-up, they have now tested the effects of antidepressant treatment on extinction learning in rats using auditory fear conditioning, a model of fear learning that involves the amygdala. The amygdala is a region of the brain vitally important for processing memory and emotion.
They found that long-term, but not short-term, SSRI treatment impairs extinction learning, which is the ability to learn that a conditioned stimulus no longer predicts an aversive event.
"This impairment may have important consequences clinically, since extinction-based exposure therapy is often used to treat anxiety disorders and antidepressants are often administered simultaneously," said Dr. Burghardt. "Based on our work, medication-induced impairments in extinction learning may actually disrupt the beneficial effects of exposure-therapy."
This finding is consistent with the results of several clinical studies showing that combined treatment can impede the benefits of exposure therapy or even natural resilience to the impact of traumatic stress at long-term follow-up.
The authors also suggest a mechanism for this effect on fear learning. They reported that the antidepressants decreased the levels of one of the subunits of the NMDA receptor (NR2B) in the amygdala. The NMDA receptor is critically involved in fear-related learning, so these reductions are believed to contribute to the observed effects.
Dr. John Krystal, Editor of Biological Psychiatry, commented, "We know that antidepressants play important roles in the treatment of depression and anxiety disorders. However, it is important to understand the limitations of these medications so that we can improve the effectiveness of the treatment for these disorders."
The article is "Chronic Antidepressant Treatment Impairs the Acquisition of Fear Extinction" by Nesha S. Burghardt, Torfi Sigurdsson, Jack M. Gorman, Bruce S. McEwen, and Joseph E. LeDoux (doi: 10.1016/j.biopsych.2012.10.012). The article appears in Biological Psychiatry, Volume 73, Issue 11 (June 1, 2013), published by Elsevier.
Notes for Editors
Full text of the article is available to credentialed journalists upon request; contact Rhiannon Bugno at +1 214 648 0880 or Biol.Psych@utsouthwestern.edu. Journalists wishing to interview the authors may contact Nesha S. Burghardt at firstname.lastname@example.org.
The authors' affiliations, and disclosures of financial and conflicts of interests are available in the article.
John H. Krystal, M.D., is Chairman of the Department of Psychiatry at the Yale University School of Medicine and a research psychiatrist at the VA Connecticut Healthcare System. His disclosures of financial and conflicts of interests are available here.
About Biological Psychiatry
Biological Psychiatry is the official journal of the Society of Biological Psychiatry, whose purpose is to promote excellence in scientific research and education in fields that investigate the nature, causes, mechanisms and treatments of disorders of thought, emotion, or behavior. In accord with this mission, this peer-reviewed, rapid-publication, international journal publishes both basic and clinical contributions from all disciplines and research areas relevant to the pathophysiology and treatment of major psychiatric disorders.
The journal publishes novel results of original research which represent an important new lead or significant impact on the field, particularly those addressing genetic and environmental risk factors, neural circuitry and neurochemistry, and important new therapeutic approaches. Reviews and commentaries that focus on topics of current research and interest are also encouraged.
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