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Study finds nerve damage can affect
opposite side of body
MGH report suggests previously unknown
communication between nerve cells
BOSTON - April 2, 2004 - Researchers from Massachusetts General
Hospital (MGH) have found physical evidence of a previously unknown
communication between nerves on opposite sides of the body. In the
May 2004 issue of Annals of Neurology, the 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, released on the journal's
website, may have major implications for the care of patients with
nerve damage and also calls into question the common practice of
using tissues on the opposite side of the body as controls in scientific
experiments.
"Patients with pain syndromes related to nerve damage sometimes
report symptoms on the side opposite their injury as well, 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. "Our evidence means that these reports can no longer
be ignored and gives us a new direction for research."
It has been known for more than 100 years that, when a nerve is
cut, skin nerve endings in the area supplied by that nerve quickly
disappear. This is because nerve cell bodies are actually located
near the spinal cord, and nerve fibers called axons extend into
the limbs. When axons are severed, downstream nerve endings are
cut off from the cell body and die.
Reports of opposite-side sensory effects of injury date back to
the American Civil War. However, no connections are known to exist
between nerve cells supplying corresponding areas on the left and
right sides. In previous research Oaklander and her colleagues examined
nerve endings in patients with post-herpetic neuralgia - persistent
pain in an area of skin previously affected by shingles, also called
herpes zoster. Along with an almost total loss of nerve endings
at the site of the shingles outbreak, they also found that almost
half the nerve endings on the opposite side skin had been lost,
even though patients did not report pain on that side. But since
shingles is caused by the varicella zoster virus, which also causes
chicken pox, there was a possibility that the damage had been caused
by viral spread through the spinal cord.
In the current study, Oaklander and her co-author Jennifer Brown
describe their experiment in three groups of rats - an experimental
group in which the tibial branch of the sciatic nerve was cut in
one hind paw and two control groups, one which 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 part of the paw supplied by the tibial nerve. Surprisingly,
they also lost 54 percent of nerve endings in the corresponding
area in the opposite paw. No changes were seen in either control
group. The researchers also examined the opposite-limb-area supplied
by the uncut nearby sural branch of the sciatic nerve and found
no change in nerve endings.
"This loss of nerve fibers in the contralateral limb is so
precise - being confined to areas innervated by the matching nerve
- that the communication is likely to involve nerve cells or the
supporting glial cells," says Oaklander, an assistant professor
of Anesthesia and Neurology at Harvard Medical School. "We
need to look into what regulates this communication and how it may
be altered to help treat nerve injury and pain patients."
This study was supported by grants from the National Institutes
of Health and a Paul Beeson Award from the American
Federation for Aging Research.
Massachusetts General Hospital, established in 1811, is the original
and largest teaching hospital of Harvard Medical School. The MGH
conducts the largest hospital-based research program in the United
States, with an annual research budget of more than $400 million
and major research centers in AIDS, cardiovascular research, cancer,
cutaneous biology, medical imaging, neurodegenerative disorders,
transplantation biology and photomedicine. In 1994, MGH and Brigham
and Women's Hospital joined to form Partners HealthCare System,
an integrated health care delivery system comprising the two academic
medical centers, specialty and community hospitals, a network of
physician groups, and nonacute and home health services.
Media Contact: Sue
McGreevey, MGH Public Affairs
Physician Referral Service: 1-800-388-4644
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