Researchers have long sought treatments that can slow the progression of Parkinson's disease. Current treatments have for decades been only symptomatic in nature, supplying the neurotransmitter dopamine, which the dying nerve cells can no longer produce. Results from a recent clinical study offer hope that future therapies could take advantage of the brain's own protective mechanisms to limit neuronal cell death and restore dopamine production to natural levels. In the first time in humans, researchers have applied a growth factor to the brain with the hope of preserving dopaminergic cells and fibers.