April 9, 2004

Nerve damage can affect both sides of body

MGH researchers have found evidence of a previously unknown communication between nerves on opposite sides of the body. In the upcoming Annals of Neurology, scientists describe how cutting a major nerve in one paw of a group of rats resulted in a significant decrease in skin nerve endings in the corresponding area of the opposite limb. The study may have major implications for the care of patients with nerve damage and also questions the common practice of using opposite-side tissues as controls in scientific experiments.

"Patients with pain syndromes related to nerve damage sometimes report symptoms on the side opposite their injury, but those reports are usually discounted because there has been no biological framework for the phenomenon," says Anne Louise Oaklander, MD, PhD, director of the MGH Nerve Injury Unit, the report's principal author.

Reports of opposite-side sensory effects of injury date back more than 100 years. No connections are known to exist, however, between nerve cells supplying corresponding areas on the left and right sides. Oaklander and Jennifer Brown studied a group of rats in which the tibial branch of the sciatic nerve was cut in one back paw and in two control groups, one had sham surgery and the other had no procedures. Within one week of injury, rats in the experimental group lost almost all skin nerve endings in the area supplied by the severed tibial nerve and also lost 54 percent of nerve endings in the corresponding area in the opposite paw. No changes were seen in either control group.

"This loss of nerve fibers in the contralateral limb is so precise that the communication is likely to involve nerve cells or the supporting glial cells," says Oaklander. "We need to look into what regulates this communication and how it may be altered to help treat nerve injury and pain patients."