For nearly 100 years neural tissue has been transplanted in animals. Transplantation of neural tissue into humans, however, began only a few years ago (1). It has been found in animals, that fetal brain grafts in damaged adult host brains reduce some of the functional deficits caused by brain lesions. Even though some neurons from the transplanted tissue survive and develop reciprocal connections with host brain tissue, this is not enough to completely replace damaged fibers and support behavioral recovery Usually the grafts will not develop a normal morphological appearance, but some metabolic activity can be found within the transplant. Release and diffusion of trophic substances from the transplant and the damaged host brain may partially restore neuronal and behavioral functions. It is hypothesized that this combination of fetal brain transplants and trophic substances may provide a better opportunity for recovery than either treatment given by itself. While this paper focuses on fetal brain grafts as a means to treat Parkinsonism, research is also being conducted in conjunction with Alzheimer’s Disease, visual, frontal, and motor cortex lesions, hippocampal lesions, and many others (2,3)
There are two current approaches to neural transplantation regarding Parkinson s; adrenal medullary and fetal brain grafts. Both methods suffer from limitations in tissue availability, cellular uniformity, and general applicability. The success of neural transplantation in animal models of Parkinson’s syndrome led to its clinical application in human patients with the syndrome. Each of the two methods mentioned has advantages and disadvantages. Transplantation of adrenal medullary tissue has the advantage of ready availability of human leukocyte antigen (matched cells), but has little potential for future use in diseases involving transmitter systems other than dopamine or other amines. Furthermore, adrenal medullary transplants have proved to be only minimally effective (4).
Fetal brain transplants have been more successful in animal and human studies, but ethical concerns have been raised. An alternative method using genetically engineered fibroblasts has been introduced. Although the fibroblasts may be used as a source of trophic factors or hormones, they lack neuronal properties that may be important in future development of neural transplants. A new technique has been devised to overcome these limitations: transplantation with temperature-sensitive immortalized clonal neural cells (4).
One example of this system was to use primary rat central nervous system cells immortalized with a temperature-sensitive Rous Sarcoma virus, cloned, and previously analyzed for neural and glial characteristics. The cells were not permissive for replication of the avian virus, however, expression of the viral genes did occur. The cells were transformed and immortalized at 34°C but differentiated at 38°C. Along with differentiation came a halt in cell division,...