What is a brain graft
The possibility of various kinds of organ transplants of the kidneys, liver, and even heart-has received a great deal of popular attention in recent years. The notion of transplanting brain tissue, also known as brain grafting, probably calls forth images of mad scientists, like Frankenstein, working with sinister-looking equipment in some secluded laboratory. Efforts to graft tissue in the central nervous systems of laboratory animals goes back at least to 1890, although it was generally assumed that neurons in the central nervous system of humans and other mammals could not regenerate after injury and that, consequently, grafts of neuronal tissue were doomed to failure. Only recently have scientists become optimistic about the possibilities of repairing damage in the central nervous system of mammals. Most typically, the research has been carried out with rats, but other species, such as mice and rabbits, have also been used.
A number of transplantation methods have been tried in the effort to graft healthy neurological tissue to damaged areas of the central nervous system. The earliest approach was to insert the graft from one animal directly into a slit near the surface of another animal's cortex. While there was some success with this method in immature rats, it did not work as well in mature animals. A more successful technique is to place the graft into a surgically prepared transplantation cavity. This procedure allows for better control over the placement of the graft and the use of larger tissue pieces (usually from the brain matter of a rat embryo).
Anders Bjorklund and Ulf Stenevi, in their 1984 review of research on intracerebral neural implants, note that the single most important factor for good survival of neural grafts is the developmental stage of the donor tissue and, to a lesser degree, the age of the recipient animal. In rats, at least, there is no strong evidence of rejection of neurological transplants by the body's immune system, leading to the possibility that the brain may be an immunologically privileged site, partly because of its protective blood-brain barrier.
What do neurological transplants do when they are successfully grafted into a damaged area of a rat's brain? One suggestion is that the effect of the implant is to stimulate and promote a regenerative response already present in the recipient's brain as a result of the lesion. Research suggests that the transplant acts as a bridge to guide regenerating axons back to their original sites.
What does all this research with rats have to do with people? Many of the experimentally induced lesions are designed to mimic the kinds of neuropathological changes associated with some diseases. Research on the ability of transplants to offset the effects of these changes may ultimately improve our ability to deal with such diseases in humans. Moreover, efforts have been made to use tissue implants to offset age-related deficits in aging rats. Such research has implications for the treatment of impairments associated with human aging, including the premature senility caused by Alzheimer's disease. Research on this serious problem is beginning to show some hopeful breakthroughs.
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