Abstract: The present invention provides an effective approach to achieve the tightly modulated production of L-DOPA and/or dopamine at a preselected target location in the brain of a mammal by combining gene therapy approaches to supply a key enzyme in the synthesis of L-DOPA, and novel drug delivery modalities to administer a uniform level of a modulator of the activity of such key enzyme. The fine-tuned administration of the modulator establishes continuously uniform levels of modulator which in turn allow the effective modulation of L-DOPA and/or dopamine levels at a preselected target location in the brain of the mammal.