Scientists Study Sea Lamprey's Success At Reconnecting Neurons After Spinal Cord Damage

April 01, 1997

Philadelphia, Pa. -- Young sea lampreys possess a remarkable capability that humans do not: "After a spinal cord injury, the lamprey becomes paralyzed just as humans do, but, within a few weeks, it recovers," says Michael E. Selzer, MD, PhD, a professor of neurology. "Unfortunately, this is something that mammals cannot do, and we would very much like to better understand the basis of the lamprey's regenerative abilities."

Investigations by Selzer and his colleagues of the eel-like fish have shown that lamprey nerve fibers regenerate across the site of injury in a coordinated manner.

"The nerve fibers grow in the correct direction, and when they cross the damaged area they create synapses with the appropriate target nerve cells to restore function. It is not a random process."

Selzer's team is exploring the mechanisms underlying the lamprey's enviable powers. So far, experiments have shown that the tip of the regenerating lamprey nerve cell, known as the growth cone, is tightly packed with structures called neurofilaments. This differs dramatically from what is seen during neural growth in embryonic development -- the only time of life when most mammalian neurons grow. Embryonic neural growth cones lack neurofilament protein and advance with the help of structures known as filopodia, which contain a protein called actin. But filopodia are absent and actin is sparse in the growth cones of regenerating lamprey nerve cells.

"Our hypothesis is that the transport of neurofilament into the growth cone pushes it forward from within, almost as though it was under pressure, as opposed to the embryonic mechanism, whereby the growth cone is pulled by the filopodia," says Selzer.

In current experiments, the scientists are overexpressing the neurofilament protein in lamprey nerve cells to see whether the speed of regeneration can be increased. The lamprey neurofilament protein has mammalian analogs, and Selzer suggests the work might someday lead to new therapies in humans.

"It is pure speculation at this point, but it may be that temporarily expressing lamprey neurofilament in people with central nervous system injuries would cause the nerve fibers to grow and move beyond the barriers to regeneration."

-- Dr. Michael E. Selzer can be reached at (215) 662-3396.

The University of Pennsylvania Medical Center's sponsored research ranks fifth in the United States, based on grant support from the National Institutes of Health, the primary funder of biomedical research in the nation -- $149 million in federal fiscal year 1996. In addition, for the second consecutive year, the institution posted the highest growth rate in its research activity -- 9.1 percent -- of the top ten U.S. academic medical centers during the same period. Penn news releases are available to reporters by direct e-mail, fax, or U.S. mail, upon request. They are also posted electronically to EurekAlert! (http://www.eurekalert.org), an Internet resource sponsored by the American Association for the Advancement of Science, and to the SciNews-MedNews section of the Journalism Forum, a component of CompuServe. Additionally, they are distributed via the electronic news service Quadnet.

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University of Pennsylvania School of Medicine

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