Parkinson's Disease - caused by destruction of dopamine secreting cells in the substantia nigra which send impulses to the caudate nucleus and putamen. The result is that without these inhibitory impulses, tremor and rigidity occur. Also akinesia occurs, or lack of the ability to perform willful movements. Treatments: 1) use of L-dopa which is converted into dopamine in the brain (eventually the brain resists this); 2) transplanted fetal dopamine cells and genetically engineered dopamine cells; 3) the use of the MAO inhibitor Deprenyl. MAO (mono amine oxidase) is the chemical which breaks down dopamine); growth factors which stimulate recovery or block deterioration of the dopamine cells.