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.
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