St. Louis, Oct. 18, 1999 -- Researchers have found that cells in the spinal cord can transmit sensations of pain through a network of cellular receptors not previously associated with pain. This network may be responsible for transmitting chronic pain, and blocking its activity may provide a new strategy for pain management.

Scientists from Washington University School of Medicine in St. Louis and Howard Hughes Medical Institute investigators at Massachusetts General Hospital and Harvard Medical School reported this finding in the November issue of Nature Neuroscience. They say serotonin--a neurotransmitter in the central nervous system (CNS)--and a cell-surface receptor called AMPA can activate silent synapses in the CNS. These synapses--junctions between nerve cells--then transmit pain signals even when no painful stimulus is present.

"Most pain medications target signals carried through a different system of receptors, so they have little or no effect on chronic pain signals transmitted at AMPA receptor sites," said Min Zhuo, Ph.D., the study's principal investigator and an assistant professor of anesthesiology and neurobiology at Washington University School of Medicine in St. Louis.

When we encounter a painful event, receptors on the skin, muscle or internal organs trigger an electrical impulse that travels along a nerve fiber to the dorsal horn of the spinal cord. That fiber connects with a nerve cell that passes the pain signal up the spinal cord to the brain. Because the signals cross junctions--synapses--on their way to the brain, they can be modified en route. For example, opioid drugs prevent signals from crossing synapses, preventing patients from feeling pain.

Silent synapses provide a second network of junctions that normally are not used, but through which pain signals can travel to the brain. Their existence was suggested more than 20 years ago but, until last year, technical limitations prevented detailed studies
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Contact: Jim Dryden
dryden@medicine.wustl.edu
314-286-0110
Washington University School of Medicine
17-Oct-1999