I think Fibrinogen has been mentioned before, but here is a new report about how it prevents neurons from regrowing after damage:
Public release date: 3-Jul-2007
Contact: Debra Kain
University of California - San Diego
Blood clotting protein may inhibit spinal cord regeneration
Fibrinogen, a blood-clotting protein found in circulating blood, has been found to inhibit the growth ...