Researchers Begin to Crack the Code Behind Nerve Regeneration, Healing Paralysis

By discovering how sea lampreys regrow the neurons that link their brains and spinal cords, researchers from the University of Missouri hope to contribute to future efforts designed to promote recovery in victims of spinal cord injuries.

The scientists focused on the regrowth of a group of nerve cells necessary for movement called reticulospinal neurons. Found in the brainstem of all vertebrates, these neurons cause paralysis in any part of the body below them when damaged by a spinal cord injury. However, while humans and other higher vertebrates remain permanently paralyzed, lower vertebrates, including the sea lamprey, are able to regrow these neurons in just a few short weeks, regaining movement.

According to Andrew McClellan, professor of biological sciences in the College of Arts and Science and director of the UM Spinal Cord Injury Research Program (SCIRP), the reason for this is the focus of significant attention.

In their study, McClellan and his fellow researchers isolated and removed injured reticulospinal neurons from a sea lamprey and grew them in cultures, applying chemicals designed to activate a group of molecules called second messengers to see what effect they had on the neurons' ability to grow.

Activation of a molecule responsible for relaying chemical signals inside cells, known as cyclic AMP, triggered the conversion of neurons from a non-growing state, to a growing one, though it had no effect on those that were already growing.

Published in the journal Neuroscience, the discovery could help better explain other studies focused on neural regeneration in humans, according to McClellan.

"In mammals, cyclic AMP does appear to enhance neural regeneration within the central nervous system in an environment that normally inhibits regeneration," he said. "Cyclic AMP seems to be able to overcome some of these inhibitory factors and promotes at least some regeneration. Hopefully our studies with the lamprey can provide a list of conditions that are important for neural regeneration to help guide therapies in higher vertebrates, and possibly in humans."