They used pieces of guinea pig spinal cord to test out these effects, although they also say in their article that they are presently working with live guinea pigs. PEG worked regardless of the thickness of the glued axons. Repair with PEG did, however, cause repaired axons to respond slightly more slowly than normal. It's also of interest that the detailed process by which PEG glues together cell membranes isn't yet understood. Figure 2 shows graphs of some of the results with axon membranes found by Borgens and Shi.
Repair often requires regrowth of axons, even in our brain.
Transplants of embryonic neurons and other such external repair methods often need extra chemical support to work out. In their article, Holm and Isacson suggest that Bcl-2 may be one factor helping regrowth, and produced by the neurons themselves. Several scientists have shown that Bcl-2 protects against several factors causing neural cell death, including ischemia, brain injury, or damage from free radicals. It's also interesting that Bcl-2 remains high in peripheral neurons, known to regenerate after injury. All this work suggests that Bcl-2 may play a useful role in brain repair.