Neural transplantation: scientific gains and clinical perspectives.

Neural transplantation, once deemed impossible, is being studied in many laboratories. Embryonic CNS from a variety of sites can be grafted into an adult host. The foreign cells differentiate and then produce neurotransmitters or neurohormones. Physical connection can be seen between graft and host. Grafting of fetal tissue may be followed by improved function of animals with experimental forms of neurologic disease or physical injury. Grafted segments of peripheral nerve become innervated by central axons that can conduct physiologic impulses. Grafted glial cells can form myelin within the CNS. Therapeutic grafting into the human nervous system may be feasible, but many scientific and ethical questions remain to be addressed.