¶ … Bridging Spinal Cord Injuries" by James W. Fawcett

This article is basically a review of earlier research into spinal cord injuries, specifically that which was conducted by Stephen Davies and colleagues. The paper focuses, as the title suggests, on one method of repairing damage to the central nervous system (specifically the spinal cord) -- bridging the gap caused by the injury with cells that promote regeneration of CNS tissue. Davies and his team have just come out with more research regarding the types of astrocytes that can be optimally used -- and ones that shouldn't be -- in this process of bridging spinal cord injuries for the purpose of regeneration.

Previous problems with this method of bridging had to do not so much with the response of th CNS -- it is very possible to re-grow CNS tissue -- but with the substance the bridge was made of. Using peripheral nervous tissue didn't work because the growing CNS axons liked the PNS as a growth medium too much -- they wouldn't leave it to connect to the spinal cord. Fawcett compares uses a freeway analogy to describe this, saying the axons have no problem with the onramp (growing onto the PNS bridge), but get stuck at the off-ramp (leaving the PNS tissue). Why axons can't simply get "on" from both sides and meet in the middle is not addressed in this paper; presumably the axons grow only in one direction.

Davies and colleagues created two different types of astrocytes using the same stem-cell derived precursors. One proved to be an effective bridge, the other actually inhibited axon growth but stimulated the growth o pain receptors, increasing pain at the injury site. The fact that the two astrocytes are so closely related is worrisome, as it may lead to complications in large-scale or human applications. Also, there could be problems in obtaining the useful kind of astrocyte. Right now, all work is being conducted on rats in a lab, where the transplant occurs at the time of the injury and the stem cells are in ready supply. Different factors exist for humans in the real world.