ABSTRACT
The human nervous system has the potential to regenerate, although a number of biological restrictions are evident. Healing of lesions must occur via true regeneration, because simple scar formation (i.e., filling of tissue gaps by nonneuronal tissue) will reestablish electrical connectivity neither within the neuronal network nor with target cells, including muscle fibers. Neuronal regeneration is confined to regrowth of severed nerve fibers and proliferation of such accessory cells as myelinating glial cells. With the exception of quantitatively negligible stem cell proliferation, no new neurons can be generated in the adult nervous system. In the broadest sense, the aims of neural tissue engineering are: 1) to restore aspects of the three-dimensional architecture using biological or synthetic scaffolds (e.g., nerve guides in lesion sites); 2) to supplement biological functions, as by the implantation of neurotransmitter-producing cells (e.g., dopamineproducing cells in Parkinson’s disease); or 3) to counteract defective metabolism, inflammation, or cell death using genetic engineering with viral vectors (e.g., apoptosis in amyotrophic lateral sclerosis).
