The idea of brain repair is not new dating back to the experimental transplantation of brain tissue between dogs and cats by the US biologist, W.G. Thompson, in 1890. It is like rewiring a burnt out fuse in an electric circuit of an appliance rather than replacing the whole appliance. An important consideration for us was finding cells suitable for implantation. Stem cells are remnants of the basic cellular templates from which all others cells then develop. In theory, it can become any kind of cell.
Embryonic neurons are young and flexible enough to grow well in the host brain.
Stem cells may lead to another intermediary stage where they create progenitor cells, which have a more narrow range of potential offsprings. We experimentally induced strokes in rats and transplanted about 300,000 to 500,000 harvested progenitor cells from young rat embryos since these cells are highly flexible in their commitment and behaviour and can easily adapt to any new environment they are put into. When transplanted into brain-damaged rats, the cells developed into mature brain cells to replace those that are missing. A transplanted cell must do the 'right thing' in order to play its part in the cerebral symphony. Each of these 'signals' pushes a cell farther along its destined path of differentiation and to determining its final fate.