Now, scientists from the University at Buffalo may have found an answer.
In study results presented today (Nov. 10, 2003) at the annual meeting of the Society for Neuroscience in New Orleans, the researchers present the first evidence that the effectiveness of antidepressant drugs such as amitryptyline in treating pain stems from their ability to inhibit the production of the inflammatory protein tumor necrosis factor (TNF) in the brain.
This study, conducted in rats as an animal model, builds on their earlier published research showing a direct link between an increase in pain and an increase in TNF production in the brain. The new results also shed light on how these same antidepressant drugs work to treat depression.
"We've discovered that a primary action of antidepressant drug treatment for depressive behavior and chronic pain symptoms is to decrease levels of TNF in the brain," said Robert N. Spengler, Ph.D., UB associate professor of pathology and anatomical sciences and senior researcher on the project.
Tracey A. Ignatowski, Ph.D., UB assistant research professor of pathology and anatomical sciences, is a co-author on the study. Jessica L. Reynolds, a doctoral student in Spengler's lab, is first author.
The findings showed that the time required for the drug to increase neurotransmitter release in the brain, as well as to eliminate pain, was the same in rats as in humans, suggesting the results may apply directly to humans.
"Our findings should contribute significantly to the development of new strategies to treat chronic pain, which affects more than six million people in the U.S. alone," Spengler said.