(Philadelphia, PA) - Researchers at the University of Pennsylvania School of Medicine have found that the neurotransmitter norepinephrine is essential in retrieving certain types of memories. This represents the first description of a molecule implicated in recalling memories as opposed to laying down new memories. Teasing apart different components of this pathway may help physicians better understand post-traumatic stress disorder (PTSD) and depression -- both of which involve alterations in memory retrieval, says lead author Steven A. Thomas, MD, PhD, Assistant Professor of Pharmacology. The findings of this research appear in the April 2 issue of Cell.

Using mutant mice lacking norepinephrine and rats treated with drugs that block some norepinephrine receptors (beta blockers), the research team found that this neurotransmitter is critical for retrieving intermediate-term contextual and spatial memories, but not for the formation or long-term consolidation of emotional memories, as previously hypothesized by others.

Mice and rats went through learning tasks that employ different brain regions: the hippocampus, which governs spatial and contextual memories; and the amygdala, which is important for emotional learning and memory in general.

The results of their tests ran counter to currently held hypotheses that suggest that stress hormones like norepinephrine are responsible for enhanced memory formation during emotionally arousing times. "Indeed, we set out to test that hypothesis with our norepinephrine-deficient mice," says Thomas. "We expected to see a difference in amygdala-dependent behaviors between the mutants and controls if it were emotional memory, in general, that was being affected by the absence of norepinephrine. But we didn't see that. Instead, we found a specific impairment in hippocampus-dependent contextual memory retrieval."

Using rats given beta blockers and a swimming navigation task in a water maze,
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Contact: Karen Kreeger
karen.kreeger@uphs.upenn.edu
215-349-5658
University of Pennsylvania School of Medicine
1-Apr-2004

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