Humankind has never taken brain transplantation seriously. The changing concepts of death, making brain function the yardstick to determine the existence of life, the intricate relationship between the mind and the brain, and ofcourse the impossibility of technically transferring this complex organ in toto, have precluded the brain in any discussion of transplantation. Brain transplantation actually refers to selective implantation of certain types of tissue into specific areas in the brain with a view to restore neurological function. Though not yet accepted as a regular treatment option, several centers have been carrying out critical trials in selected patients.
The grafted tissue may serve as a biochemical source, may replace lost nerve cells, make a recovery of partly damaged cells, supply growth factors to stimulate function or may simply act as tissue bridge. The idea of bridging suggests that the grafted tissue provides the framework necessary to allow the growth of the host nerve cells. Different mechanisms may act at different times.
Donor
Embryonic brain tissue or chromaffin cells derived from the adult adrenal medulla are good source of catecholamines. Cells in the peripheral nerve, called Schwann cells, rich in Nerve Growth Factor, have been used. The human amniotic membrane from the fetus has also been found to be rich in neurotropic factors. When used as a codonor this helps in sprouting and growth of the host’s nerve cells. Genetically engineered cells programmed to perform specific function have also been tried as co donors. The long term immunologic response to the transplanted tissue is still not clear. Experts are confident that ultimately the potential benefits will outweigh the possible hazards.
The future
Considerable time, effort and funds are being deployed to establish brain implantation as treatment alternative. The specific areas being looked into are neuro–degenerative disorders, particularly Parkinsons and Alzheimer’s disease. Their possible use in acute head and spinal injury and certain type of neuropsychiatric disorders, if established may open a Pandora’s box. The demand for donor tissue will far exceed the legitimate supply. The spectacle of mass scale elective abortions to supply fetal brain tissue looms in the horizon. The very idea is horrendous. Of course in the Brave New World, one may be able to cryopreserve fetal tissue and immortalize cell lines.
As in any new area, several questions have to be answered. Which conditions promote maximum graft survival and function? Who are suitable for brain transplantation therapy? Why do some improve more than others? Is immunosuppression necessary for fetal tissues which supposedly do not elicit an antibody reaction? The key issue for the success of brain transplantation is not surgical technique, but how to increase transplanted brain matter survival, and proper growth of nerve cells in the recipient. The problems no doubt seem insurmountable, but then as John F. Kennedy once remarked, the greatest failure of all failures is the failure to attempt. The sub specialty of Neurotransplantation is not even in its embryonic stage. It has just been conceived. Indications are that it will eventually proceed to term, even, if there are initially a few abortions on the way!
Neurosurgeons of the 21st century will be the ones who deliver the goods! Genetically engineered cells that have been altered to produce dopamine will be implanted into the Substantia Nigra in patients with Parkinsons. The neurosurgeon of the next millennium will perhaps be injecting genetically engineered cells into damaged areas in head injured brains. This would cause the endogenous production or liberation of nerve growth factors which would stimulate dying cells to recover. Recombinant technology will provide new thrombolytic agents that will revolutionize the treatment of stroke. The neurologist of tomorrow will be an interventional neurologist.