One of dopamine's roles is to regulate the nerves that control the body movement, and as these cells die less dopamine is produced, therefore leading to the movement difficulties associated with Parkinson's. (Stem Cells: Scientific Progress and Future Research Directions, 2001, p. 80) .
Over the last 10 years scientists have been experimenting with transplanting neuronal cells from a donor to the Parkinson's infected patient, however this method has had limited success in that obtaining the significant number of cells needed for implantation is extremely difficult and often unlikely. (Chemistry & Industry, No. 5, p. 133) What researchers are hoping to find in stem cells is a renewable source that can operate as dopamine neurons. As of now, laboratory grown cells derived from a stem cell is the best potential source. One way to get these cells to the point of dopamine production is to find the right combination of growth factors and cell-culture conditions where they are actually committed to be dopamine neurons and then injecting them directly into the brain. Another method is to place less committed cells into a damaged brain and rely on "environmental" signals to guide the cell into becoming a dopamine neuron. (Stem Cells: Scientific Progress and Future Research Directions, 2001, p.83) Present research has shown that both human fetal cells and embryonic stem cells can become fully functional dopamine neurons; however whether adult stem cells will have a similar effect is presently unknown.
Researchers of Parkinson's disease are also searching for way to ignite the stem cell repair mechanisms already in a patient's brain to fix the problems the mechanisms couldn't otherwise manage. In a study conducted by James Fallon and colleagues it was discovered that by injecting a protein called transforming growth factor (TGFa) it will trigger the brain's repair process, which is otherwise not triggered by a slowly developing degenerative disease like Parkinson's.
