Scientists have long dreamed of prompting adult neurons of the central nervous system to regenerate. But these cells have the deck stacked against them in several ways. Molecules from the myelin sheath surrounding their axons actively discourage growth. After injury, nearby astrocytes form a dense scar to block them. Even the signals that once guided axons as they formed during development now seem to prevent regeneration. And most neurons also have lost the internal factors that enabled them to stretch their axons out in the first place – even if allowed to, they wouldn’t grow.
Regeneration seems like a daunting task with all of these circumstances conspiring against it. Still, most researchers in the field believe it will be possible to remove the brakes on growth in the centrall nervous system if they can identify the restraints. An encouraging study in the Oct. 7, 2005 Science from the lab of Zhigang He, Harvard Medical School assistant professor of neurology at Children’s Hospital Boston, uncovers a surprising new player on the side of inhibition – the well-known epidermal growth factor (EGF) receptor. The molecule appears to mediate the inhibitory signals of both myelin and proteoglycans from the glial scar – a convergence of pathways in a field that has become increasingly complex.