Regenerating Tissues

The ability to regenerate the tissues of the human central nervous system


(CNS) is one of the greatest projects undertaken by biomedical engineers


today.   With this eventual technology, permanent paralysis and blindness


due to CNS injury will be a thing of the past.   Central nervous system


injuries will   be repairable, an idea that was, until recently, just a


fanciful dream, something out of a science fiction novel.  


In the last few years, however, giant strides have been made to make the


idea of CNS regeneration a reality within the grasp of   engineers and


doctors alike.   This technology has advanced to the point where successful


tests are being performed on lower level adult mammals.   If all continues


to go well,   human implementation may soon follow.


The axons of the central nervous system in adult mammals do not regenerate


spontaneously after injury, mainly because of the presence of


oligodendrocytes that inhibit axonal growth.   These glial cells block the


growth of the axons in the central nervous system, preventing any kind of


regeneration within the CNS.


What was discovered, through experimentation, was that lower non-mammalian


vertebrates could regenerate their central nervous system after injury.


Regeneration of   the optic nerve occurs spontaneously in fish.   This


phenomenon has been correlated to the presence of factors that are toxic


to oligodendrocytes.   This substance is closely related to interleukin-2.  


Lower level mammals, on the other hand, are, like humans, unable to


regenerate their CNS.   The same experiment performed on the fish above


yielded completely different results when done on adult mammals.   Severing


of the optic nerve near the eye is followed by a loss of retinal ganglion


cells combined with a failure of axons to regrow into the brain.


Further...